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Journal of Electroceramics (v.13, #1-3)

Editorial by Harry L. Tuller (pp. 13-13).

Recent Developments on MOCVD of Ferroelectric Thin Films by Yohei Otani; Soichiro Okamura; Tadashi Shiosaki (pp. 15-22).
Ferroelectric Pb(Zr, Ti)O3 thin films were fabricated by liquid delivery MOCVD using Pb(DPM)2, Ti(OiPr)2(DPM)2 and Zr(DIBM)4. The deposition rate of 12.3 nm/min was attained on 6-inch Pt/Ti/SiO2/Si wafers at 550C. The average and the deviation of twofold remanent polarization were 45.5 μ C/cm2 and ± 6.4%, respectively, over the 6-inch wafer. Step coverage was improved from 44% to 90% by decreasing deposition temperature from 550 to 400C although the deposition rate decreased by 60%. TiO2 nanoparticles diffused to the surface of platinum bottom electrodes were effective as a seed to obtain 111 preferential oriented PZT thin films at the deposition temperature of 550C. Iridium oxide bottom electrodes were reduced to metal ones by CO and/or H2 gases generated by decomposition of precursors. Oxide materials seem to be not the best as bottom electrodes in liquid delivery MOCVD. A cocktail source consisted of Pb(METHD)2, Ti(MPD)(METHD)2 and Zr(METHD)4 was also examined. PbPtx alloy phase existed in PZT films deposited at 500C was disappeared by post-annealing at 600C and the annealed film showed hysteresis properties with the 2Pr of 56 μ C/cm2 and the 2Ec of 181 kV/cm.

Keywords: liquid delivery; MOCVD; PZT; cocktail source; 6 inch wafer

Substrate Surface Engineering for Functional Ceramic Thin Film Growth by H.-U. Habermeier (pp. 23-27).
A concept is introduced, using oxide substrates for functional ceramic thin film deposition beyond their usual application as chemical inert, lattice-matched support for the films. The substrates are applied as a functional element in order to controllably modify the atom arrangement and the growth mode of cuprate superconductors and colossal magnetoresistance materials. These materials have been chosen as prototypes of the general class of perovskite functional ceramics. One example studied is the use of epitaxial strain to adjust the relative positions of cations and anions in the film and thus modify their physical properties. The other makes use of vicinal cut SrTiO3 which enables the fabrication of regular nanoscale step and terrace structures. In YBa2Cu3O7 − x thin films grown on vicinal cut SrTiO3 single crystals a regular array of antiphase boundaries is generated causing an anisotropic enhancement of flux-line pinning. In the case of La-Ca-Mn-O thin films grown on vicinal cut substrates it could be demonstrated that magnetic in-plane anisotropy is achieved.

Polarization Switching in (100)/(001) Oriented Epitaxial Pb(Zr, Ti)O3 Thin Films by M. Tsukada; H. Yamawaki; M. Kondo; J. S. Cross; K. Kurihara (pp. 29-33).
Thin films made of (100)/(001)-oriented Pb(Zr, Ti)O3 (PZT) were deposited by liquid-delivery metal-organic chemical vapor deposition on Ir/MgAl2O4/SiO2/Si(100) substrates. For comparison, PZT thin films were also deposited on Ir/MgO(100) substrates. The X-ray Φ scan spectra for the (202) reflections revealed that the PZT films have four-fold symmetry. It indicates that the PZT films were epitaxially grown as a cube-on-cube structure on both substrates. The switchable polarization (Qsw) of the PZT capacitors on the silicon substrate was only 23 μ C/cm2 at 1.8 V; however, Qsw of PZT capacitors on MgO was 99 μ C/cm2. In the case of PZT films deposited on silicon, the volume fraction of (001)-oriented domains (which contribute to polarization switching) was 15.1% (calculated from an XRD pattern). This result is due to the lower Qsw of PZT capacitors on silicon. By piezoresponse-force microscopy, switchable and unswitchable domains could be identified by imaging color contrast, namely, (001) and (100) domains, respectively. Consequently, domain distribution of the PZT film on a silicon substrate indicates that the (001) domain exists in the (100) domain matrix.

Keywords: PZT; epitaxial; orientation; polarization; switching; domain; PFM

Influence of the Lead Source Materials on the Microstructure and Ferroelectric Properties of PZT Films Sputter-Deposited Using Lead and Lead Oxide by W. L. Chang; J. L. He (pp. 35-39).
In this investigation, PZT films were sputter-deposited on Si/SiO2/Ti/Pt substrates using a dual-target system. The dual targets Pb/PZT(PbZr0.54Ti0.46O3) and PbO/PZT(PbZr0.54Ti0.46O3) were used to reveal the effects of various lead compensation source materials on the microstructure and ferroelectric properties of the films. The structures of the films were characterized by X-ray diffractometry (XRD) and field emission scanning electron microscopy (FESEM). The chemical binding state was determined using X-ray photoelectron spectrometry (XPS). Ferroelectric polarizability was measured using a Radiant Technology RT66A tester. The influence of deposition temperatures on the microstructure and ferroelectric properties of the films was studied. Perovskite PZT films were successfully deposited using the Pb/PZT and the PbO/PZT dual target sputtering systems at a substrate temperature of between 500 and 580∘C. Structural change was elucidated as a function of deposition temperatures and the lead sources were correlated with the ferroelectric properties of the film. The ferroelectric characteristics of the PZT films deposited using the PbO/PZT dual target were better than those of films deposited using the Pb/PZT dual target, because the former films had a higher bonding energy.

Keywords: PZT film; Pb compensation; microstructure; ferroelectric properties

Effect of Zr/Ti Ratio on Microstructure and Electrical Properties of Lead Zirconate Titanate Thin Films Derived by Pulsed Laser Deposition by Zhanxy Jie Wang; Yuki Aoki; Hiroyuki Kokawa; Masaaki Ichiki; Ryutaro Maeda (pp. 41-45).
PZT films were fabricated using various targets of Pb(ZrxTi1 − x)O3 with Zr/Ti ratios of 70/30, 58/42, 52/48, 45/55 and 30/70, and with excess PbO of 20 wt% on Pt/Ti/SiO2/Si(100) substrates. The rosette structure was observed in the films derived from the target with a Zr/Ti ratio of 70/30 and disappeared with increasing titanium composition. The observations on surface and cross-sectional microstructure were consistent with a higher perovskite nucleation for the higher Ti content films. The PZT films derived from the target with a Zr/Ti ratio of 45/55 had a polycrystalline columnar microstructure extending throughout the thickness of the film and no pyrochlore phase on the surface was observed. The PZT films derived from the target with a Zr/Ti ratio of 45/55 exhibited better electric properties than those derived from the target with a Zr/Ti ratio of 52/48.

Keywords: lead zirconate titanate; thin film; pulsed laser deposition; crystalline phases; microstructure; ferroelectric properties

XPS Studies of PZT Films Deposited by Metallic Lead and Ceramic PZT Dual Target Co-Sputtering by W. L. Chang; J. L. He (pp. 47-50).
The dependence of the chemical states of the constituent elements of a PZT thin film prepared by RF magnetron co-sputtering using ceramic PZT and metallic Pb dual target materials on the Ar+ etching time was studied using XPS. The metallic Pb, lead oxide and Pb in PZT led to the different binding energies of the Pb lines. The intensity of binding energy of metallic Pb relative to that of bulk Pb increased with the depth of the film. The peak position and the line shape of the O1s electron was associated with the different binding energies of oxygen, which interacts with Pb and Ti and Zr atoms to form the metal oxides, and the softening of the O1s bonds by the bonding interaction in Ti–O, Zr–O and Pb–O. The broad Ti2p3/2 line in the PZT film could has been associated with the various charge state of Ti and no spectral changes of Ti2p and Zr3d were observed as the Ar+ ion sputtering time was increased.

Keywords: XPS; PZT; binding energy; RF sputtering; thin film

Ionic Doping Effects in SrBi2Nb2O9 Ferroelectric Ceramics by S. E. Park; J. A. Cho; T. K. Song; M. H. Kim; S. S. Kim; H. -S. Lee (pp. 51-54).
Ionic doping effects of various ions in Bi-layered ferroelectric SrBi2Nb2O9 (SBN) ceramics were studied. Un-doped and doped SBN ceramics with Ba2+, Pb2+, Ca2+, Bi3+, La3+, Ti4+, Mo6+, and W6+ ions were made with solid state reactions. Temperature dependent dielectric constants were measured. Ferroelectric transition temperature (TC) decreased with Ba2+ and Pb2+ ions but increased with Ca2+ ion which substitutes the 12-coordinated Sr2+ site. TC increased with Ti4+, Mo6+, and W6+ ions which substitute the 6-coordinated Nb5+ sites. With trivalent Bi3+ and La3+ ions, TC increased with Bi3+ ion but much decreased with La3+ ion. These results showed that the ion size plays an important role in ferroelectricity of SBN ceramics.

Keywords: SrBi2Nb2O9ionic doping; ion size; ferroelectric phase transition

Platinum (100) Hillock Growth in Pt/Ti Electrode Stack for SrBi2Ta2O9 Ferroelectric Random Access Memory by Won Woong Jung; Si Kyung Choi; Soon Yong Kweon; Seung Jin Yeom (pp. 55-63).
The ferroelectric material SrBi2Ta2O9 (SBT) has been extensively investigated in connection with integrating nonvolatile ferroelectric random-access memory (FeRAM). The SBT layer must be annealed in an oxygen atmosphere after deposition to crystallize the ferroelectric oxide film, which induces Pt hillock formation in a Pt/Ti electrode stack. The Pt hillock in a Pt/Ti electrode stack has been the main concern in SBT FeRAM due to reliability problems, such as capacitor shorts. Reportedly, the compressive stress generated in thin film is widely accepted as being responsible for the occurrence of hillocks in thin film and the main mass transport mechanism for hillock formation is the grain boundary diffusion for thin film with a columnar structure. In this study, three factors are considered in the total compressive stress generated during both deposition and post-annealing in Pt/Ti electrode stack: intrinsic stress, thermal stress, and extrinsic stress. Moreover, we found that an orientation relationship of Pt (100)hillock//Pt (111)thin film existed between the Pt hillock and the thin film. The Pt hillock was a single crystal, having facets with polyatomic steps. From these results, we suggest that the Pt hillock growth mechanism is the layer growth of flat faces, which shapes the hillock into a tetrahedron single crystal.

Keywords: FeRAM; hillock; stress; facet; single crystal

Ferroelectric and Dielectric Properties of Lanthanum-Modified Bismuth Titanate Thin Films Obtained by the Polymeric Precursor Method by A. Z. Simões; A. H. M. Gonzalez; C. S. Riccardi; E. C. Souza; F. Moura; M. A. Zaghete; E. Longo; J. A. Verela (pp. 65-70).
Lanthanum-modified bismuth titanate, Bi4 − xLaxTi3O12 (BLT), thin films with a La concentration of 0.75 was grown on Pt/Ti/SiO2/Si substrates by using the polymeric precursor solution and spin-coating method. The scanning electron microscopy (SEM) showed rounded grains, which is not typical for these system. The BLT films showed well-saturated polarization-electric field curve which 2Pr = 41.4 μC/cm2 and Vc = 0.99 V. The capacitance dependence on the voltage is strongly nonlinear, confirming the ferroelectric properties of the film resulting from the domains switching. These properties make BLT a promising material for FERAM applications.

Keywords: bismuth lanthanum titanate; FERAM; thin film

Phase Formations and Electrical Properties of Various (Bi, La)4Ti3O12 Thin Films by Chemical Solution Deposition by Won-Jae Lee; Guoxia Liu; Byoung-Chul Shin; Geun-Hyoung Lee; Il-Soo Kim; Nam-Yeal Lee; Sang-Ouk Ryu; Woong-Chul Shin; Jae-Man Lee; Jindong Kim (pp. 71-75).
The phase formation and electrical properties of (Bi, La)4Ti3O12 (BLT) thin film and V-, Sm-doped BLT thin films prepared by the chemical solution deposition method on Pt/TiO2/SiO2/Si substrates have been investigated. It was observed that the microstructure and electrical properties of BLT thin films dramatically varied with V- and Sm-doping. The crystallinity and grain size of BLT thin films were definitely increased by V- and Sm-doping into BLT films, which resulted in the enhancement of remanent polarization in doped BLT films. The remanent polarization (Pr) of Sm-doped BLT films annealed for 3 min by an RTA system was about 9 μC/cm2. The V- and Sm-doped BLT films also exhibited good fatigue characteristics under bipolar stressing to 1010 cycles.

Keywords: (Bi, La)4Ti3O12doping; ferroelectrics; remanent polarization; leakage current

Ferroelectric Properties of Bi3.25Nd0.75Ti3O12 Thin Films Prepared by MOD Process by Kibeom Kim; Guneik Jang; Changhoon Kim; Daeho Yoon (pp. 77-81).
Ferroelectric Bi4 − xNdxTi3O12(BNdT) thin films with the composition (x = 0.75) were prepared on Pt/Ti/SiO2/Si(100) substrate by metal-organic deposition. The films were annealed by various temperatures from 550 to 650C and then the electrical and structural characteristics were investigated for the application of FRAM. Electrical properties such as dielectric constant, 2Pr and capacitance were quite dependent on the thermal heat treatment. The measured 2Pr value on the BNdT capacitor annealed at 650C was 56 μ C/cm2 at an applied voltage of 5 V. No fatigue was observed up to 8 × 1010 read/write switching cycles at a frequency of 1 MHz regardless of annealing temperatures.

Keywords: ferroelectric; Bi4 − xNdxTi3O12 thin films; MOD method; dielectric constant; fatigue

Ferroelectric Properties of (Bi, Sm)4Ti3O12 (BST) Thin Films Fabricated by a Metalorganic Solution Deposition Method by S. S. Kim; E. K. Choi; H. J. Kim; M. H. Park; H. S. Lee; W. J. Kim; J. C. Bae; T. K. Song; H. S. Lee; J. Y. Lee (pp. 83-88).
Ferroelectric properties of samarium substituted Bi4Ti3O12 films, Bi3.15Sm0.85Ti3O12 (BST), were evaluated for use as lead-free thin film ferroelectrics for FeRAM applications. The BST films were fabricated on the Pt/Ti/SiO2/Si(100) substrates by a metalorganic solution deposition method. The measured XRD patterns revealed that the BST films showed only a Bi4Ti3O12-type phase with a random orientation. The BST film capacitors showed excellent ferroelectric properties. For the film capacitor annealed at 700C, 2Pr of 64.2 μ C/cm2 and 2Ec of 101.7 kV/cm at applied electric field of 150 kV/cm were observed. The capacitor did not show any significant fatigue up to 1.5 × 108 read/write switching cycles at a frequency of 1 MHz, which suggests that the samarium should be considered for a promising lanthanide elements to make a good thin ferroelectric film for memory applications.

Keywords: ferroelectric; Bi3.15Sm0.85Ti3O12Bi4Ti3O12thin film; remanent polarization

Three Dimensional Domain Structure in Epitaxial Barium Titanate Thin Films by D. J. Towner; T. J. Lansford; B. W. Wessels (pp. 89-93).
The three dimensional domain structure of barium titanate thin films was determined using a serial sectioning technique. The domain structure varied sharply through the film thickness, being primarily a-oriented near the substrate and increasingly c-oriented away from this interface. The variation in domain structure is explained in terms of a strain gradient due to partial relaxation of epitaxial coherency strains. The refractive index also varied through the film thickness. A simple relationship based on areal fraction of each domain type aptly described the changes in refractive index with domain structure. These results indicate the importance of understanding three-dimensional domain structure and its impact on film properties.

Keywords: ferroelectric; domain; thin film

BaTiO3 Films by Low-Temperature Hydrothermal Techniques for Next Generation Packaging Applications by D. Balaraman; P. M. Raj; L. Wan; I. R. Abothu; S. Bhattacharya; S. Dalmia; M. J. Lance; M. Swaminathan; M. D. Sacks; R. R. Tummala (pp. 95-100).
This work reports synthesis, characterization and integration of sub-micron thick nano-grained barium titanate films on organic Printed Wiring Boards (PWB). Barium titanate films were synthesized on titanium foils at 95C. SEM of films revealed 80 nm grains. The films were characterized using XRD, FTIR and Raman spectroscopy. As-synthesized films exhibited high capacitance densities and dielectric loss. The films were treated with oxygen plasma to reduce entrapped hydroxyl groups and this resulted in improved dielectric properties. The plasma treated films exhibited a capacitance density of 1 μ F/cm2 and a dielectric loss of 0.06. The high frequency dielectric properties were extracted from s-parameter measurements on CPW structures on these films and were found to be stable up to 8 GHz.

Keywords: embedded capacitors; decoupling; Raman; FTIR; dielectric constant; PWB; barium titanate; high frequency

Scaling Effect on the Dielectric Constant in Ba(TixZr1−x)O3 Thin Films by C. Hoffer; U. Ellerkamnn; S. Halder; R. Meyer; R. Waser (pp. 101-104).
Recent work on PZT and BST thin films reveal a thickness dependence of the dielectric constant for a film thickness below 100 nm. This effect is commonly attributed to an interfacial layer between the electrode and the dielectric film (dead layer). In this contribution we report on the influence of the film thickness on the dielectric constant of Ba(TixZr1 − x)O3 thin films with different Zr-contents (x = 0–30 at.%). The films were prepared by chemical solution deposition (CSD) with thickness between 30 and 350 nm.The electrical characterization was performed in a temperature range between 25 and 200C. Results were interpreted with respect to the formation of a serial dead layer capacitance.

Keywords: dielectric properties; Ba(TixZr1 −x)O3interface capacitance

Anodizing Properties of High Dielectric Oxide Films Coated on Aluminum by Sol-Gel Method by Sang-Shik Park; Byong-Taek Lee (pp. 111-116).
In order to obtain the high capacitance in aluminum electrolytic capacitor, ZrO2 and Nb2O5 films were coated on aluminum foils by sol-gel method, and then the properties of anodized films were examined. The triple layer of ZrO2/Al-Zr(Nb)Ox/Al2O3 was formed on aluminum substrates after anodizing of ZrO2(Nb2O5)/Al film. The thickness of Al2O3 layer decreased with increasing the annealing temperature due to the densification of ZrO2 film and the capacitance of ZrO2 coated aluminum foil annealed at low temperature was higher than that at high temperature. The increase of capacitance was due to the high capacitance of ZrO2 film annealed at low temperature. The capacitance of ZrO2 and Nb2O5 coated aluminum increased about 3 and 1.7 times compared to that of Al2O3 layer anodized with 400 V, respectively. From these results, the aluminum foils with composite oxide layers are found to be applicable to the aluminum electrolytic capacitor.

Keywords: Al electrolytic capacitor; sol-gel; anodizing; ZrO2Nb2O5

Modelling the Deposition of High-k Dielectric Films by First Principles by Simon D. Elliott; Henry P. Pinto (pp. 117-120).
Considerable interest is focussed on high-k dielectrics as replacements for the gate oxide in future MOSFETs. Atomic Layer Deposition (ALD) is the method of choice to produce conformal thin films for the gate dielectric, but a deeper understanding of this method is needed for process optimisation. For ALD of alumina, we use first principles density functional (DFT) calculations to describe the surface intermediates and pathways of precursor adsorption/decomposition at the atomic scale, yielding quantitative reaction energetics. This reveals the intrinsic limits on ALD growth rate as a function of OH coverage.

Keywords: Atomic Layer Deposition; ab initio calculations; oxide surface; alumina; high-k dielectrics

Current Conduction and Dielectric Behavior of High k-Y2O3 Films Integrated with Si Using Chemical Vapor Deposition as a Gate Dielectric for Metal-Oxide-Semiconductor Devices by A. C. Rastogi; S. B. Desu (pp. 121-127).
Integration of Y2O3 high-k thin film over Si as gate dielectric in high performance CMOS and high-density MOS memory storage capacitor devices is described. Y2O3 film growth by low-pressure chemical vapor deposition induces interfacial reactions and complex SiO2 − x layer growth. It has a graded structure, in crystalline-SiO2 form at Y2O3 side and amorphous SiO2 − x form at Si side. MIS devices based on Y2O3/SiO2-SiO2 − x composite dielectric integrated with Si show high frequency C-V behavior indicative of inversion to accumulation changes in capacitance. Observed bi-directional hysterisis in C-V is detrimental to the functioning of storage capacitor in memory function. Detailed investigation of this effect led to understanding of gate bias controlled emission of carriers as responsible mechanism. Observed anomalous increase in inversion capacitance at low frequency is attributed to additional charges transferred from SiO2 − x/Si interface states. Leakage current and injected charge carrier transport across bilayer interface is dominated by Poole-Frankel (PF) process at low fields and by Fowler-Nordhiem (FN) at high fields. This investigation provides a greater understanding of the complex nature of integration of Y2O3 films.

Keywords: Y2O3 films; high k oxides; LPCVD; MOS storage capacitor

Electronic Conductivity and Dielectric Properties of Nanocrystalline CeO2 Films by Jyrki Lappalainen; Harry L. Tuller; Vilho Lantto (pp. 129-133).
The growth of dielectric layers on silicon substrates has attracted a great deal of recent interest given their potential applicability in the fabrication of high quality silicon-on-insulator (SOI) structures, high density capacitor devices, and stable buffer layers between silicon and other materials. In this study, nanocrystalline CeO2 films were deposited on n-type (100) silicon substrates using pulsed laser deposition (PLD) to form a gate dielectric for a Pt/n-Si/CeO2/Pt MOS device. XRD, AFM and FESEM measurements were used to characterize the crystal structure and grain size of the CeO2 films. The electrical properties of the device structure were examined by capacitance-voltage (C-V) and impedance spectroscopy measurements. The CeO2 films exhibited an activated conductivity, characterized by an activation energy Ea = 0.45 eV. An estimated room temperature electron mobility μe of 2.8 × 10− 7 cm2/Vs leads to a corresponding electron concentration n of 5.5 × 1017 cm− 3. In contrast to conventional MOS capacitors, we find an additional capacitive contribution under strong accumulation conditions as a result of space charge effects inside the CeO2 thin film.

Keywords: CeO2nanoparticles; MOS device; space charge effects/

Thin Film Ferroelectrics for Guided Wave Devices by B. W. Wessels (pp. 135-138).
Thin film ferroelectrics are being developed for guided wave optical devices. Of particular interest is BaTiO3 because of its high electro-optic coefficient. Epitaxial thin films have been deposited by metalorganic chemical vapor deposition that are suitable for electro-optic devices. Thin film electro-optic modulators have been fabricated and their optical properties characterized. Factors that determine the ultimate bandwidth of these devices are discussed.

Keywords: ferroelectrics; waveguide; optical properties

Pyroelectric Arrays: Ceramics and Thin Films by Roger W. Whatmore (pp. 139-147).
Pyroelectric infra-red detectors have been of-interest for many years because of their wide wavelength response, good sensitivity and lack of need for cooling. They have achieved a wide market acceptance for such applications as people sensing, IR spectrometry (especially for environmental protection) and flame/fire protection. Arrays of such detectors, comprising a pyroelectric material interfaced to an application specific integrated circuit for signal amplification and read out, provide an attractive solution to the problem of collecting spatial information on the IR distribution in a scene and a range of new applications are appearing for such devices, from thermal imaging to people sensing and counting. The selection of the best material to use for such a device is very important. Because all polar dielectrics are pyroelectric, there is a very wide range of such materials to choose. The performance of a pyroelectric IR sensor array can be derived from the physics of their operation and figures-of-merit (FoM) defined that will describe the performance of a material in a device, in terms of its basic pyroelectric, dielectric and thermal properties. These FoM and their appropriateness for the array application are reviewed. Large arrays of small detectors are best served by the use of pyroelectric materials with permittivities between 200 and 1000, depending upon the element size and the element thermal conductance, and a maximised FoM FD = p{c′ (ε εotan δ)1/2}. Such properties are found in ferroelectric perovskite ceramics and a wide range have been explored for their use in pyroelectric arrays. These include materials based on compositions in the PbZrxTi1 − xO3 (PZT) system, for example close to PbZrO3, with Curie temperatures well above ambient. Examples of the ways in which these materials can be modified by doping to optimise their FoM and other important properties such as electrical resistivity are given and the physics operating behind this discussed. The performances and costs of uncooled pyroelectric arrays are ultimately driven by the materials used. For this reason, continuous improvements in materials technology are important. In the area of bulk ceramics, it is possible to obtain significant improvements in both production costs and performance though the use of tape-cast, functionally-gradient materials. Finally, the use of directly-deposited ferroelectric thin films on silicon ASIC’s is offering considerable potential for low cost high performance pyroelectric arrays. The challenges involved in developing such materials will be discussed, especially from the aspect of low temperature deposition and other fabrication issues, such as patterning. Sol gel deposition provides an excellent technique for thin film growth and Mn-doped PZT films can be grown at 560C with a FoM FD exceeding those of many bulk materials.

Integration of MgO on Si(001) Using SrO and SrTiO3 Buffer Layers by Molecular Beam Epitaxy by F. Niu; A. Meier; B. W. Wessels (pp. 149-154).
Epitaxial MgO was deposited onto Si(001) substrates by molecular beam epitaxy using elemental metallic sources and molecular oxygen at temperatures from 150 to 400C. To facilitate epitaxy through misfit strain relaxation, epitaxial MgO layers were grown on SrO and SrTiO3 buffer layers deposited on Si(001) substrates. The structure of the epitaxial layers was determined by X-ray diffraction, reflection high-energy electron diffraction and transmission electron microscopy. The observed orientation for the MgO/SrO/Si multilayer is cube-on-cube. The X-ray rocking curve full width half maximum of the MgO on SrO buffer layers was 2.2. SrTiO3 buffer layers grown by recrystallization were epitaxial and exhibited improved morphology relative to those grown at a fixed growth temperature. X-ray analysis of a 5.2 nm recrystallized SrTiO3 film indicates a fully relaxed and phase pure film. The observed orientation of MgO using SrTiO3 buffer layers is MgO[100]‖SrTiO3[100]‖Si[110].

Keywords: MgO; SrO; Si; SrTiO3epitaxy

Ca Substituted PbTiO3 Thin Films for Infrared Detectors by Sonalee Chopra; Seema Sharma; T. C. Goel; R. G. Mendiratta (pp. 155-158).
Crack free Ca substituted PT thin films have been deposited on ITO coated 7059 glass substrates by sol gel technique and crystallized at 650∘C. Characterization of these films by X-ray diffraction show that the films exhibit tetragonal structure with perovskite phase. AFM, hysteresis, dielectric relaxation and pyroelectric studies have been carried out. The pyroelectric figures of merit of the films have been calculated. Our investigations show that these films are expected to give high infrared detector performance due to its high pyroelectric coefficient (∼43 nC/cm2K), high voltage responsivity (∼2340 Vcm2/J) and detectivity(∼3 × 10− 5 Pa− 1/2) along with small value of dielectric constant (∼83) and loss tangent (∼0.04).

Keywords: sol gel technique; dielectrics; hysteresis; pyroelectric detector

Effect of Thickness on the Electrical and Optical Properties of Sb Doped SnO2 (ATO) Thin Films by T. R. Giraldi; M. T. Escote; M. I. B. Bernardi; V. Bouquet; E. R. Leite; E. Longo; J. A. Varela (pp. 159-165).
This work reports the preparation and characterization of (SnO2) thin films doped with 7 mol% Sb2O3. The films were prepared by the polymeric precursor method, and deposited by spin-coating, all of them were deposited on amorphous silica substrate. Then, we have studied the thickness effect on the microstrutural, optical and electric properties of these samples. The microstructural characterization was carried out by X-ray diffraction (XRD) and scanning tunneling microscopy (STM). The electrical resistivity measurements were obtained by the van der Pauw four-probe method. UV-visible spectroscopy and ellipsometry were carried out for the optical characterization. The films present nanometric grains in the order of 13 nm, and low roughness. The electrical resistivity decreased with the increase of the film thickness and the smallest measured value was 6.5 × 10− 3Ω cm for the 988 nm thick film. The samples displayed a high transmittance value of 80% in the visible region. The obtained results show that the polymeric precursor method is effective for the TCOs manufacturing.

Keywords: thin film; tin oxide; antimony

Chemical and Structural Factors Governing Transparent Conductivity in Oxides by B. J. Ingram; G. B. Gonzalez; D. R. Kammler; M. I. Bertoni; T. O. Mason (pp. 167-175).
The history, applications, and basic requirements of transparent conducting oxides (TCOs) are reviewed. Four basic families of TCOs are recognized, including n-type oxides with tetrahedrally-coordinated cations (e.g., ZnO), n-type oxides with octahedrally-coordinated cations (e.g., CdO, In2O3, SnO2, and related binary and ternary compounds), p-type oxides with linearly-coordinated cations (e.g., CuAlO2, Cu2SrO2, and related compounds), and n-type oxides with cage structures (e.g., 12CaO⋅ 7Al2O3). TCO behavior is discussed with attention to structural and chemical factors, especially point defect chemistry, governing carrier generation and transport properties.

Keywords: transparent conducting oxide (TCO); electrical conductivity; point defects; transport

The Photoresponse of Iron- and Carbon-Doped TiO2 (Anatase) Photoelectrodes by Cristina S. Enache; Joop Schoonman; Roel Van Krol (pp. 177-182).
Fe-doped and C-doped anatase TiO2 films were made by spray pyrolysis. For Fe:TiO2, a small sub-bandgap photoresponse is observed which is attributed to the presence of additional states located just above the valence band. Although no visible-light photoresponse is observed for carbon-doped TiO2 due to the low carbon content, the photocurrent at hν > Eg is significantly larger than for undoped TiO2. At the same time, the donor density of oxidized C-doped TiO2 is > 1.9× 1019 cm−3, compared to 3.2× 1017 cm−3 for undoped TiO2. Assuming that only light absorbed in the depletion layer contributes to the photocurrent, the photoresponse of C-doped anatase (at 330 nm) is 16 times larger than that predicted for undoped TiO2 under similar conditions. The strong enhancement of the absorption is most likely caused by a change in the electronic structure of the material due to the presence of carbon and/or related defects. Photoluminescence measurements suggest that the defects present in oxidized carbon-doped anatase resemble those present in undoped, reduced TiO2.

Keywords: photocatalyst; titanium dioxide; anion dopants; photoluminescence; defects

Photoluminescence of ZnO:Ga Thin Films Fabricated by Pulsed Laser Deposition Technique by Z. F. Liu; F. K. Shan; J. Y. Sohn; S. C. Kim; G. Y. Kim; Y. X. Li; J. Y. Sohn (pp. 183-187).
Highly c-axis oriented Ga-doped ZnO films (GZO) have been grown on sapphire (0001) substrates by pulsed laser deposition (PLD) method. Photoluminescence (PL) spectra indicate that Ga atoms have a large effect on the luminescent properties of ZnO films. PL spectra of GZO films show near band edge (NBE) emissions and broad orange deep-level emissions. The NBE emission shifts to higher energy region and the intensity decreases with the increase of Ga concentration. The blue shift of NBE emission results from Burstein-Moss effect. The quenching of NBE emission is ascribed to the noradiative recombination. The orange emission is related to the oxygen vacancies.

Keywords: Ga-doped ZnO; thin films; photoluminescence

Studies of ZnO Thin Films On Sapphire (0001) Substrates Deposited by Pulsed Laser Deposition by F. K. Shan; Z. F. Liu; G. X. Liu; W. J. Lee; G. H. Lee; I. S. Kim; B. C. Shin; Y. S. Yu (pp. 189-194).
ZnO thin films are deposited on sapphire (0001) substrates at different temperatures in the pulsed laser deposition (PLD) system. By measurements of X-ray diffraction (XRD), atomic force microscopy (AFM), and Photoluminescence (PL) at room temperature, fabrication temperatures higher than 400∘C is found to be the optimum condition for the structural and optical properties of ZnO thin films. With the increase of the fabrication temperature, the grain size becomes bigger and the thin film becomes more homogeneous. In order to get the high-quality ZnO thin film at low temperature, ZnO thin films are deposited at room temperature and annealed in a rapid thermal annealing (RTA) system. It is found that the optical property of the thin film can be greatly improved by annealing in RTA system.

Keywords: ZnO thin films; pulsed laser deposition; rapid thermal annealing; photoluminescence

Aging and Annealing Effects of ZnO Thin Films on GaAs Substrates Deposited by Pulsed Laser Deposition by F. K. Shan; Z. F. Liu; G. X. Liu; W. J. Lee; G. H. Lee; I. S. Kim; B. C. Shin; Y. S. Yu (pp. 195-200).
Zinc oxide (ZnO) thin films were deposited on GaAs (100) substrates at different temperatures in the pulsed laser deposition (PLD) system. From the measurements of X-ray diffraction (XRD) at room temperature, 300–500°C were found to be good condition for the crystallization of the thin films. From the photoluminescence (PL) measurements, 500°C was found to be the optimized temperature for its optical property. Samples grown at 100, 200, 300, and 400°C showed near band-edge (NBE) emissions and deep-level emissions. The intensity of deep-level emissions decreased as time goes on, which is believed to originate from oxygen vacancies or zinc interstitials in thin films. While for the sample grown at 500°C, bright NBE emissions were observed at room temperature, and no deep-level emissions observed. This means that the high-optical-quality thin film was grown at 500°C. At the same time, annealing process of ZnO thin films grown at room temperature was carried out in PLD chamber. It was found that the annealing temperature of 600°C has strong effects on its PL. Aging and annealing effects in ZnO thin films grown on GaAs substrates by PLD were observed for the first time.

Keywords: ZnO thin films; pulsed laser deposition; aging effect; annealing effect

Formation and Size Control of ZnO Nanowires on Al-Zn-Si-Fe Alloy by Directed Melt Oxidation Process by Geun-Hyoung Lee; Byoung-Chul Shin; Il-Soo Kim; Won-Jae Lee; Myung-Ok Kyun; Hyoung-Do Jeon (pp. 201-207).
Tetrapod like ZnO nanowires were formed by the directive melt oxidation of Al-Zn-Si-Fe alloy at the temperature over 1000°C in air. X-ray diffraction patterns revealed that the ZnO nanowires had wurtzite structure with the c-axis and a-axis lattice constants of 0.520 and 0.325 nm, respectively. The lattice constants are similar with those of ZnO single crystal. The size control of ZnO nanowires was achieved by varying the oxidation temperature and the amount of Zn in alloy. The lower the oxidation temperature was, the smaller was the diameter of the ZnO nanowires. And with decreasing the amount of Zn, it was diminished the diameter of the formed ZnO nanowires. The diameter was as small as 50 nm at the amount of Zn of 5 wt%.

Keywords: ZnO; nanowires; tetrapod shape; directive melt oxidation; size control

Characterization of Hydrothermally Synthesized PLZT for Pyroelectric Applications by S. Kongtaweelert; P. Anuragudom; S. Nualpralaksana; R. B. Heimann; S. Phanichphant (pp. 209-214).
PLZT fine powders have been synthesized by a hydrothermal process using lead acetate, lanthanum acetate, zirconium n-propoxide and titanium isopropoxide as starting materials. The synthesis was performed at 200°C for 8, 12 and 24 h. 4 M KOH was used as a mineralizer to adjust the pH to an optimum value for the mixed precursor solution. After hydrothermal treatment the solid portion was separated out, washed and dried at 100°C for 12 h, where PLZT fine powders were obtained. PLZT powders were characterized using X-ray diffraction (XRD) and scanning electron microscopy (SEM). The PLZT powders were pressed and sintered to obtain high density ceramics, which then were investigated by XRD and SEM. The dielectric properties of the ceramics were investigated by measurements of dielectric constant and dielectric loss as a function of temperature at a fixed frequency.

Keywords: PLZT; hydrothermal; pyroelectric

Polar Ceramics in RF-MEMS and Microwave Reconfigurable Electronics: A Brief Review on Recent Issues by N. Setter; V. Sherman; K. Astafiev; A. K. Tagantsev (pp. 215-222).
Properties and fabrication status of microdevices for microwaves based on polar ceramics are reviewed. We discuss bulk acoustic wave devices with AlN films, rf-MEMS capacitive switches with high permittivity materials, and tunable ferroelectrics. The relevant properties of ferroelectrics for microwave applications are summarized with emphasis on composites and thin films.

Keywords: ferroelectric; tunable; microwave; AlN; BST; piezoelectric; bulk acoustic waves; rf switch; rf-MEMS

Nonlinear Microwave Properties of Ferroelectric Thin Films by R. Wördenweber; R. Ott; P. Lahl (pp. 223-227).
The nonlinear microwave properties of ferroelectric SrTiO3 thin films are characterized via complex analysis of the intermodulation distortion (IMD) signals up to high microwave power. The measurements reveal an unusual dependence of the IMD signals on the input power, which indicates the presence of two different nonlinear properties being responsible for the generation of the intermodulation. IMD measurements on tuned ferroelectric films and simultaneous conductivity measurements reveal the two different properties to be the nonlinear permittivity at low rf power and a finite nonlinear conductivity at high rf power levels, respectively. The IMD signal strength can not be explained in terms of the classical description based on a Taylor expansion of the nonlinear parameter. In contrast, simulations of the frequency spectra using more appropriate descriptions of two nonlinear parameters yield an excellent agreement between theory and experiment, and, thus, demonstrate, that the IMD experiments together with the simulation might provide further insight into the mechanism of nonlinear behavior of these material.

Keywords: ferroelectrics; thin films; nonlinear microwave properties; inter modulation distortion

Annealing Effects on Structural and Dielectric Properties of Tunable BZT Thin Films by Jin Xu; Wolfgang Menesklou; Ellen Ivers-Tiffée (pp. 229-233).
Ba(Zr, Ti)O3 thin films have attracted great attention in recent years for their potential use in DRAMs and MCMs due to their high dielectric constant and relatively low leakage current. However, their tunable dielectric properties were rarely investigated and the corresponding potential for tunable microwave applications was seldom reported. In this paper, we present the tunable dielectric behavior of BZT thin films deposited by RF magnetron sputtering from a Ba(Zr0.3Ti0.7)O3 ceramic target on MgO single crystal substrates. The composition, thickness and crystallinity of the thin films were analyzed by Rutherford backscattering (RBS), scanning electron microscopy (SEM) and X-ray diffraction (XRD), respectively. The dielectric constant and loss tangent were measured as a function of electric field (0–7 kV/mm) and temperature (−140 to +160°C) at frequencies up to 1 MHz, using interdigital capacitors (IDC) with Au electrodes on thin films. By optimizing the preparation process, a tunability {defined as τ = [ε (0) − ε (Emax)]/ε (0)} of 76% at Emax = 7 kV/mm and a low loss tangent of 0.0078 can be achieved. In addition, the influence of annealing temperature on the dielectric properties of the thin films is also discussed.

Keywords: Ba(Zr, Ti)O3thin films; tunable dielectric properties; RF sputtering

Ceramics Materials Based on (Ba, Sr)TiO3 Solid Solutions for Tunable Microwave Devices by E. A. Nenasheva; A. D. Kanareykin; N. F. Kartenko; A. I. Dedyk; S. F. Karmanenko (pp. 235-238).
Structure and electrical properties at radio frequencies as well as within the 3.5–35 GHz frequency range have been investigated for ceramic samples of the (1−y)(BaxSr1 − x)TiO3 · yMgO (BSM) system where x = 0.4–0.6; y = 0.15–0.30. For the compositions studied the bulk ferroelectrics were synthesized with the dielectric constant of 400–600 and high tunability coefficient. We indicated that the quality factor of the samples was in the range of 100–1000 within the frequency band of 3.5–35 GHz. The phase correlations and unit cell constants of the perovskite phase of the BSM samples were studied. The low loss factor and high tunability of the bulk material allowed us using the BSM ferroelectric ceramic layer for tunable accelerating structures of the Argonne Dielectric Wakefield Accelerator and for high power switches design and development for the future linear colliders.

Keywords: ferroelectric; BSTO; magnesium oxide additives; tunability; dielectric loss factor

Frequency and Voltage Dependent Dielectric Properties of Ni-doped Ba0.6Sr0.4TiO3 Thin Films by Mi-Hwa Lim; Hyun-Suk Kim; Nan-Young Kim; Ho-Gi Kim; Il-Doo Kim; Seung Eon Moon; Min-Hwan Kwak; Han-Cheol Ryu; Su-Jae Lee (pp. 239-243).
Highly (100) preferred undoped and 1–5% Ni-doped Ba1−xSrxTiO3 (BST) thin films were deposited onto MgO (100) single crystal substrate at 750°C using pulsed laser deposition. BST thin film-based interdigital capacitors (IDC) were prepared by standard photolithography process. The microwave properties of BST films were measured at 10 GHz. Ni-doped BST films showed better dielectric properties by exhibiting improved dielectric Q while retaining an appropriate capacitance tuning compared to undoped BST films. 1% Ni-doped BST film showed the maximum figure of merit of 2896.1. It is suggested that 1 mol% Ni doped BST film is an effective candidate for high performance tunable device applications.

Keywords: BST; Ni doping; microwave; interdigital capacitor

Coplanar Waveguide Using Ferroelectric Thin Oxide Film: Dielectric Constant by W. J. Kim; S. S. Kim; T. K. Song; S. E. Moon; E. K. Kim; S. J. Lee; S. K. Han; M. H. Kwak; H. Y. Kim; Y. T. Kim; H. C. Ryu; C. S. Kim; K. Y. Hang (pp. 245-249).
Coplanar waveguide (CPW) transmission lines were fabricated on thin ferroelectric Ba1 − xSrxTiO3 films for tunable microwave applications. The growth of the ferroelectric oxide films was accomplished by a pulsed laser deposition with a partial oxygen background. Microwave properties of the CPW phase shifter were measured using a HP 8510C vector network analyzer from 0.045–20 GHz with −40–40 V of dc bias. A large phase shift angle of ∼ 120 at 10 GHz was observed from the CPW (gap = 4μm, length = 3 mm) with a 40 V of dc bias change. The dielectric constant of the thin ferroelectric film was extracted from the dimension of the CPW (gap, width, length) and the measured S-parameter by a modified conformal mapping. However, the dielectric constant of the ferroelectric thin film exhibits a gap dependency; dielectric constant (990–830) decreases with increasing gap size (4–19 μm, respectively). By adjusting the filling factors of the film, a ‘constant’ dielectric constant of BST film is found to be 810 ± 5.

Keywords: (Ba, Sr)TiO3thin film; ferroelectric; conformal mapping; phase shifter; microwave

Microwave Dielectric Properties of Ferroelectric BaTiO3 Thin Film by Y. W. Cho; T. S. Hyun; S. K. Choi (pp. 251-255).
The dielectric properties of c-axis epitaxial BaTiO3 thin film on LaAlO3 are investigated at frequencies of 0.5–30 GHz. For the measurements, interdigital capacitors with the Au/Ti electrode configurations of five fingers pairs that are 15 μm wide and spaced 2 μm apart are prepared by photolithography and lift-off patterning. Finger length varies from 20 to 80 μm. The capacitance of epitaxial BaTiO3 films exhibited no frequency dependence up to 10 GHz with the exception of slightly upward tendency of capacitance in BaTiO3 film with a finger length of 80 μm due to the self resonant frequency at 20 GHz. The Q-factors of the capacitors, defined as Q = 1/ωCR, are decreased up to 10 GHz with increased frequency. At 10 GHz, the BaTiO3 film has a tunability [defined as k(V) = [C(0)−C(V)]C(0)] of 1.5% at 15 V, a loss tangent of ≤ 0.2 at room temperature. The small tunability can be interpreted as a result of in-plane compressive stress of BaTiO3 film exhibiting large dielectric anisotropy. For the improvement of tunability and dielectric loss in the interdigital BaTiO3 capacitor, the tetragonality (c/a) of epitaxial BaTiO3 film and design of interdigital capacitor should be modified.

Keywords: microwave; dielectric; epitaxial; BaTiO3polar phase

Measurement of Microwave Dielectric Properties of Pb(Zr1−xTrx)O3 Thin Films by Seung Eon Moon; Eun-Kyoung Kim; Su-Jae Lee; Min-Hwan Kwak; Young-Tae Kim; Han-Cheol Ryu; Won-Jeong Kim; Tae-Kwun Song (pp. 257-260).
Ferroelectric Pb(Zr1−xTix)O3 (PZT) thin films were prepared by sol-gel deposition method. The structural and surface morphologies were investigated using X-ray diffractometer and atomic force microscope. Microwave dielectric properties were obtained using co-circle electrode patterns, which were made by photolithography and etching process. The dielectric constant of PZT films was about 450 from 0.05–1 GHz range.

Study of Microwave Dielectric Properties of Perovskite Thin Films by Near-Field Microscopy by Yi-Chun Chen; Yun-Shuo Hsieh; Hsiu-Fung Cheng; I-Nan Lin (pp. 261-265).
Perovskite thin film materials possess good dielectric properties, which vary with applied voltage, and have thus been thoroughly investigated for applications as thin film tunable microwave devices. However, the tunability of the thin film materials derived from the frequency response of the thin film devices suffers from ambiguity in extracting the true dielectric response of the thin film materials in microwave frequency regime. To circumvent such a difficulty, we investigated the dielectric properties of perovskite thin films by using a novel scanning evanescent microwave microscopy (SEMM). To extract the dielectric parameters from original microwave frequency response signal of SEMM probe, we perform a 3-dimensional (3D) finite element simulation to model the frequency behavior of the SEMM microwave probe. Dielectric images of the thin films with submicron resolution can be obtained by using such a near-field technique, which correlates very well with the morphology of the films examined by atomic force microscopy. Moreover, the dielectric images of dielectric thin films were compared to those of ferroelectric thin films in order to discuss the related dielectric mechanism of the materials.

Keywords: scanning evanescent microwave microscopy; perovskite; tunable thin films

Fabrication of PZT Composite Thick Films for High Frequency Membrane Resonators by F. F. C. Duval; R. A. Dorey; R. W. Wright; Z. Huang; R. W. Whatmore (pp. 267-270).
High frequency, thickness mode resonators were fabricated using a 7 μm PZT thick film which was produced using a modified composite ceramic sol-gel process. Initial studies dealt with the integration of the PZT thick film onto the substrate. Two different diffusion barrier layers were tested, titanium oxide and zirconium oxide, in conjunction with the use of 2 types of silicon substrate (differing in the etch stop layer employed, either silicon nitride or silicon oxide). Zirconium oxide gave good results in conjunction with silicon oxide. Using these conditions, devices were produced and the acoustic properties measured for different electrode sizes ranging from 45*45 to 250*250 μm2. The best electrode size, which maximised the acoustic response and minimised the insertion loss, was found to have an area of 110*110 μm2. This device showed a resonant frequency of about 200 MHz, an effective electro-mechanical coupling coefficient of 0.29 and a Q factor of 22.

Keywords: PZT; thick film; resonator

Correlation of Microwave Dielectric Properties and Normal Vibration Modes of Ba(Mg1/3Ta2/3)O3-Series Materials by Yi-Chun Chen; Hsiu-Fung Cheng; Chia-Chi Lee; Chih-Ta Chia; Hsiang-Lin Liu; I-Nan Liu (pp. 271-275).
Microwave dielectric properties of Ba(Mg1/3Ta2/3)O3-series materials were investigated using Fourier transform infrared spectroscopy (FTIR) and Raman spectroscopy. The normal vibration modes of these spectra were assigned, and the origin of dielectric response of the materials was deduced. Among the prominent normal vibration modes in the FTIR spectra, those which correlated with O-layers and Ba-layers change with Sr-ratio most significantly, whereas in micro-Raman measurements, the A1g(O) phonon of oxygen-octahedron stretch mode changes with Sr-ratio most profoundly. These results reveal clearly the close relationship between the characteristics of FTIR and Raman spectra of the BMT-series materials and their microwave dielectric properties.

Keywords: microwave dielectrics; Raman spectroscopy; FTIR spectroscopy

Al2O3-MgO-ReOx (Re: Rare Earth)-Based LTCC and its Application to Multilayer Non-Shrinkage Substrate for Microwave Devices by Hiroshi Kagata; Ryuichi Saito; Hidenori Katsumura (pp. 277-280).
We studied the dielectric properties of Al2O3-MgO-ReOx (Re: rare earth) systems in the microwave region and found that the magnetoplumbite phases in the MgO-poor regions of MgReAl11O19 (Re: La ∼ Tb) compositions had positive TCF (temperature coefficient of resonance frequency) values in spite of having low dielectric constants of under 20. By mixing a lead-free glass with the above system, a novel LTCC (which we term an AMSG) was obtained that was characterized by a low dielectric constant (< 10), a near zero TCF, and high bending strength. When firing these AMSG green sheets inserted between HTCC alumina or magnesia green sheets that cannot be sintered at the AMSG sintering temperature, the AMSG sheets were seen to shrink not in the x-y directions but in the z direction due to the constraining effects of the HTCC layers. The obtained non-shrinkage substrate had precise dimensions and a high degree of flatness. The AMSG and the non-shrinking techniques have potential for application to integrated RF modules in mobile communications equipment.

Keywords: LTCC; microwave device; dielectric property; green sheet

Microwave Dielectric Mechanism Studied by Microwave Near-Field Microscopy and Raman Spectroscopy by Yi-Chun Chen; Yeong-Der Yao; Yun-Shuo Hsieh; Hsiu-Fung Cheng; Chih-Ta Chia; I-Nan Lin (pp. 281-286).
Microwave dielectric ceramics such as Ba(Mg1/3Ta2/3)O3 and Ba2Ti9O20 possess high dielectric constant and low dielectric loss in microwave frequency regime and have tremendous potential for device applications. In these materials, the presence of extrinsic defects, such as secondary phases, usually altered the microwave dielectric properties of the materials markedly, but the correlation of the microwave dielectric response of the materials with their microstructure has not been fully understood due to the lack of dielectric response in the local area. In this article, microwave near-field microscopy and Raman spectroscopy were used to investigate the microwave dielectric mechanism, viz. we measured the microwave dielectric properties of the materials in micron region by using a evanescent microwave probe (EMP) and, at the same time, examined the lattice vibration characteristics of the region by using a micro-Raman spectrum. How the presence of the secondary phase affects the microwave dielectric properties of the materials is thus systematically investigated. The causes of intrinsic or extrinsic dielectric loss were explored by comparing the dielectric images in SEMP at microwave frequencies and the corresponding Raman Spectra.

Keywords: Evanescent microwave microscopy; microwave dielectrics; Raman spectroscopy

The Importance of Distributed Loading and Cantilever Angle in Piezo-Force Microscopy by Bryan D. Huey; Chandra Ramanujan; Musuvathi Bobji; John Blendell; Grady White; Robert Szoszkiewicz; Andrzej Kulik (pp. 287-291).
Piezo-force microscopy (PFM) is a variation of atomic force microscopy that is widely applied to investigate piezoelectric thin films at the nanometer scale. Curiously, PFM experiments are found to be remarkably sensitive to the position along the cantilever at which deflection is detected, complicating attempts to use this technique to quantify surface actuation and thereby measure the converse piezoelectric coefficient. A straightforward analytical theory is proposed that accounts for this observation by combining standard PFM analyses with subtleties of the typical AFM detection mechanism as well as the concept of distributed loading. Corresponding simulations of PFM measurements indicate that these experimental artifacts can even lead to an apparent inversion of the detected domain orientation. To better understand the importance of these effects, simulations are used to qualitatively map the theoretical PFM response for a wide range of typical experimental parameters, as well as the relative difference between these measurements and true piezoactuation.

Keywords: PFM; cantilever; piezoelectric; ferroelectric; AFM

Pyroelectric Electron Emission Behaviors of Congruent and Stoichiometric Lithium Niobate Single Crystals by El Mostafa Bourim; Dong-Wook Kim; Vadim Sidor Kin; Chang-Wook Moon; In Kyeong Yoo (pp. 293-297).
Pyroelectric electron emission current measurements and current distribution collecting were performed on congruent and stoichiometric lithium niobate single crystals. Electron emission behaviors were found to be gap distance (crystal-detector) dependent. For small gaps, in both crystal compositions, emission was accompanied by a partial superficial domain inversion, triggered by surface plasma ignition. For large gaps (> 2 mm) in congruent single crystals the emission was activated by a true pyroelectric effect.

Keywords: pyroelectric; electron emission; plasma; lithium niobate

Raman Scattering Study of the Pb(HfxTi1−x)O3 Ceramics by J. Frantti; Y. Fujioka; S. Eriksson; V. Lantto; M. Kakihana (pp. 299-303).
Raman spectroscopy was used to study the long wavelength vibrations of tetragonal perovskite (space group P4mm) Pb(HfxTi1−x)O3 (PHT) (0.10 ≤ x ≤ 0.50) samples at room temperature and at ≈ 20 K. For x ≤ 0.40, Raman spectra collected from the PHT samples were very similar to the previous spectra collected from the PZT samples with the same value of x, except the mode at around 190 cm−1, whose frequency was decreasing with increasing x in PHT ceramics. Correspondingly, the latter feature was taken as a sign of the ‘mass effect’ (Hf versus Zr) while the similarity of the remaining parts of the Raman spectra was assumed to be due to the almost identical ionic radii difference between Ti4+ and Zr4+ and between Ti4+ and Hf4+ ionic radii. The behaviour of the mode at around 280 cm−1 revealed that a phase transition occurred once x was changing from 0.40 to 0.50.

Keywords: Raman spectroscopy; peak split; tetragonal; perovskite; lead hafnate titanate

Electrical Properties of 6H-BaTi0.95M0.05O3−δ Ceramics where M = Mn, Fe, Co and Ni by Gillian M. Keith; Kumaravinothan Sarma; Neil McN. Alford; Derek C. Sinclair (pp. 305-309).
Hexagonal BaTiO3 materials have been stabilised at room temperature according to the formula BaTi0.95M0.05 O3−δ where M = Mn, Fe, Co and Ni. Dense ceramics (> 96% of the theoretical X-ray density) were sintered at 1450C in flowing O2 gas from calcined powders prepared by the mixed oxide route at 1300C. All samples were single-phase and the bulk conductivity, σb, measured by Impedance Spectroscopy and Q.f measured by microwave dielectric resonance methods showed a strong dependence on the type of dopant. σb at 300C was 10−7, 10−5.5, 10−5.5 and 10−4 Scm−1 for M = Mn, Fe, Ni and Co, respectively and Q.f at ∼ 5 GHz was 7790, 6670, 2442 and 1291 GHz, for M = Mn, Fe, Ni and Co, respectively. The correlation between σb and Q.f is attributed to the presence of oxygen vacancies and/or mixed valency of the dopant ions.

Keywords: BaTiO3perovskites; microwave dielectric resonators; impedance spectroscopy

Structural Transformation and Pressure-Induced Phase Transitions in PZT by P. Papet; J. Rouquette; V. Bornand; J. Haines; M. Pintard; P. Armand (pp. 311-314).
Angle-dispersive X-ray diffraction, Raman scattering and dielectric spectroscopy measurements versus hydrostatic pressure were carried out to follow the crystalline-to-crystalline transformation occurring in PbZr1 − xTixO3 ceramic powders. Different PZT compositions under hydrostatic pressure up to 20 GPa were studied. Dielectric measurements versus pressure up to 2 GPa are discussed to bring new insights on the Pressure-composition (P-x) phase diagram. Based on these results, an updated version of the PZT (P-x) phase diagram is proposed.

Keywords: PZT; lead zirconate titanate; phase transition; high pressure; X-ray diffraction; Raman spectroscopy; dielectric properties

Atomic Mixing Behavior of Co/Al(001) vs. Al/fcc-Co(001): Molecular Dynamics Simulation by Sang-Pil Kim; Seung-Cheol Lee; Kwang-Ryeol Lee; Yong-Chae Chung (pp. 315-320).
Using molecular dynamics simulations, we investigated the interface structures and the growth behaviors of nano-scale Al/Co/Al multilayers. For Co on Al(001), interface mixing occurred irrespective of the incident energy (Ki). Interestingly, increasing the incident energy increased the thickness of the mixing layers and decreased the roughness of the Co surface. In the case of Al on Co(001), in contrast to the case of Co/Al, interface mixing could not be found, especially for low incident energy. From these investigations, an optimized deposition technique is proposed that improves the quality of the interface/surface of the deposited thin film by controlling the incident adatom energies.

Keywords: Al/Co/Al; magnetic nano thin films; interface structure; molecular dynamics simulation

Characterization of Crystalline Carbon Nitride Films Deposited on Si and Si3N4/Si Substrate by RF Magnetron Sputtering System with DC Bias by J. G. Lee; S. P. Lee (pp. 321-326).
Crystalline carbon nitride films were deposited on Si and Si3N4/Si substrate by reactive RF magnetron sputtering system with chamber heating and DC bias. The deposited films showed α -C3N4, β -C3N4 and lonsdaleite phase by XRD, XPS and FTIR. The crystalline morphology was found to gave a hexagonal structure, which has theoretical unit cell of carbon nitride observed in SEM photographs. When nitrogen gas ratio is 70%, RF power is 300 W and DC bias is –80 V, the growth rate of carbon nitride film on Si3N4 substrate is 2.2 μm/hr, which is a relatively high growth rate compared with those in previously reported papers. The deposited films have thermally stable properties in the range of 650_∘C to 1,400_∘C.

Keywords: carbon nitride; RF magnetron sputter; crystalline morphology; growth rate/

Ab initio Study of the Si Adsorption on Mo(110) by Yoon-Suk Kim; In-Yong Kang; Hanchul Kim; Yong-Chae Chung (pp. 327-330).
The energetics and the electronic structure of the Si/Mo(110) surface have been investigated using density functional theory calculations based on the generalized gradient approximation. The calculated potential energy surface for a single Si adatom reveals that a hollow site is favored for the adsorption of Si on Mo(110). The energy barrier for hopping between the hollow sites is located at the bridge site and is found to be 0.64 eV. The electron density plot indicates that four Mo-Si covalent bonds were formed around the Si atom at the hollow site. According to the surface formation energy for different Si coverage, 1 ML Si/Mo(110)−p(1× 1) is energetically favorable for a Si-rich environment. For the Si-poor case, the clean Mo(110) surface is the most stable structure.

Keywords: density functional theory; Si adsorption; Mo(110); EUV lithography

SrTiO3 Based Side Gate Field Effect Transistor Realized by Submicron Scale AFM Induced Local Chemical Reactions by L. Pellegrino; E. Bellingeri; I. Pallecchi; A. S. Siri; D. Marré; A. Chincarini (pp. 331-337).
In this work we will show how it is possible to apply the so called nano-oxidation technique to pattern electrical circuits on oxygen deficient SrTiO3 (STO) thin films. We will focus on two aspects: the chemical reactions which are triggered at the surface of oxygen deficient STO thin films by the voltage biased tip of an atomic force microscope (AFM) and the exploitation of this phenomenology to pattern insulating regions on oxygen deficient STO thin films in the submicron regime. Due to the insulating nature of the AFM modified regions and to the possibility to remove selectively the modified parts, planar electrical circuits entirely designed over STO thin films can be fabricated. A prototype of planar side gate field effect thin film transistor in which STO acts both as active channel and as gate electrode is presented and discussed.

Keywords: atomic force microscope patterning; strontium titanate; field effect; side gate

Preparation and Properties of Bi4 − xNdxTi3O12 Thin Films by Chemical Solution Deposition by Wataru Sakamoto; Mio Yamada; Naoya Iizawa; Yu-Ki Mizutani; Daichi Togawa; Koichi Kikuta; Toshinobu Yogo; Takashi Hayashi; Shin-Ichi Hirano (pp. 339-343).
Neodymium-modified Bi4Ti3O12, (Bi, Nd)4Ti3O12 (BNT) ferroelectric thin films have been prepared on Pt/TiOx/SiO2/Si substrates using metal-organic precursor solutions by the chemical solution deposition method. The BNT precursor films crystallized into the Bi layered perovskite Bi4Ti3O12 (BIT) as a single-phase above 600C. The synthesized BNT films revealed a random orientation having a strong 117 reflection, whereas non-substituted BIT thin films exhibited a random orientation with strong 00l diffractions. Among Bi4 − xNdxTi3O12 [x = 0.0, 0.5, 0.75, 1.0] thin films, Bi3.25Nd0.75Ti3O12 thin films showed a well-saturated P-E hysteresis loop with the highest Pr (22 μ C/cm2) and a low Ec (69 kV/cm) at an applied voltage of 5 V. The Nd-substitution with the optimum amount for the Bi site in the BIT structure was effective not only for promoting the 117 preferred orientation but also for improving the microstructure and ferroelectric properties of the resultant films.

Keywords: Bi4Ti3O12thin film; chemical solution deposition; Nd substitution; surface morphology; ferroelectric properties

Effect of Strain Gradation on Luminescence and Electronic Properties of Pulsed Laser Deposited Zinc Oxide Thin Films by A. C. Rastogi; S. B. Desu; P. Bhattacharya; R. S. Katiyar (pp. 345-352).
ZnO thin films were grown by ablation of a ZnO ceramic target using pulsed excimer laser (KrF) under 1 mTorr oxygen partial pressure over (0001) α -Al2O3 substrates held at 750_∘C. Highly c-axis oriented (0002) ZnO films with visible range optical transparency over 80% were obtained. Inhomogeneous distribution of strain in the film growth direction was studied by line shape analysis of X-ray diffraction and broad luminescence features centered on near band edge transition at 3.3 eV. Strain in the film adversely affects optical gain and excitonic threshold of UV emission. Post-growth oxygen annealing of films at 850°C for 1 h reduces strain and associated defects at ZnO film interface with (0001) Al2O3 substrate. FWHM of X-ray rocking curves show corresponding lowering from 12.5 arc min to 9.0 arc min signifying improved ZnO crystal quality. ω -rocking curves show line features with two superimposed peaks belonging to interfacial layer and bulk ZnO film. Graded strain in ZnO film is related to differently oriented interfacial layer formed at inception stage of film growth. Decrease in conductivity of annealed ZnO films show that O2-vacancies are primary defects. Formation of strain free (0002) oriented optical quality ZnO films based on combined process of growth in low O2 pressure and post growth anneal at high O2 pressure is proposed for UV-optoelectronic applications.

Keywords: epitaxial ZnO films; pulsed laser deposition; ultraviolet light emission; luminescence; wide band gap

Effect of Thermal Treatment Temperature on the Crystallinity and Morphology of LiTaO3 Thin Films Prepared from Polymeric Precursor Method by A. H. M. González; A. Z. Simões; M. A. Zaghete; E. Longo; J. A. Varela (pp. 353-359).
Lithium tantalate thin films (LiTaO3) with (50:50) stoichiometry were prepared by spin coating method using a polymeric organic solution. The films were deposited on silicon (100) substrates with 4 layers. The substrates were previously cleaned and then the solution of lithium tantalate was deposited by adjusting the speed at 5000 rpm. The thin films deposited were thermally treated from 350 to 600C for 3 hours in order to study the influence of the thermal treatment temperature on the crystallinity, microstructure, grain size and roughness of the final film. X-ray diffraction (XRD) results showed that the films are polycrystalline and secondary phases free. The thickness of films was observed by scanning electron microscopy (SEM). The atomic force microscopy (AFM) studies showed that the grain size and roughness are strongly influenced by thermal treatment.

Keywords: lithium tantalate; thin films; polymeric precursor; crystallinity; morphology

Optimization of Non-Fluorine Sol-Gel Derived YBCO Thin Films by Nick Long; Lily Campbell; Tim Kemmitt; V. John Kennedy; Andreas Markwitz; Andrea Bubendorfer (pp. 361-365).
Sol-gel deposition of thin film YBa2Cu3O7−δ (YBCO) is widely seen as the most cost effective means to manufacture long length HTS wires (A.P. Malozemoff, D.T. Verebelyi, S. Fleshler, D. Aized, and D. Yu, “HTS Wire: Status and Prospects,” Physica C, 386, 424 (2003)). We present a sol-gel technique for YBCO deposition using low cost starting materials and forming only benign by-products during processing. Optimization has concentrated on producing the correct stoichiometry in the final films. RBS measurements show that copper diffuses into the substrate due to its high mobility at the temperatures required to form the YBCO phase. Therefore a starting stoichiometry of 1:2:3 can produce a film highly copper deficient. In order to compensate for this we have made films with different excesses of copper in the precursor solution. The surface morphologies of these films have been examined by SEM and AFM, and the stoichiometry and cation depth profiles characterized by ion beam analysis. The effect of the varying copper stoichiometry is correlated with the superconducting properties and the surface morphology for films on lanthanum aluminate (LAO) and magnesium oxide (MgO) substrates. The residual carbon concentration in the films is measured by nuclear reaction analysis.

Keywords: YBCO films; stoichiometry; sol-gel deposition

Synthesis of Pb(Zr, Ti)O3 Nanopowders by Milling Coprecipitation Method by Myong-Ho Kim; A. Golovchanski; Soon Il Lee; Tae-Gone Park; Tae Kwon Song (pp. 367-371).
Nano-size powders of lead zirconate titanate (PZT) were fabricated by a new milling coprecipitation method (MCP) improved from the conventional wet ball milling and precipitation. This method consists of slurry preparation from nanoparticles of TiO2 with aqueous solution of ZrO(NO3)2 and Pb(NO3)2 with zirconia ball mill media, followed by precipitation with NH4OH as precipitant. Milling media (1mm and 3mm balls) improves the precipitation homogeneity during processing. Single-phase perovskite structure of PZT was formed at a calcination temperature of 500C and powders of 50 nm particle size were obtained. Powders were characterized using TG-DTA, SEM and XRD methods. Sintering ability of powders and piezoelectric properties of the ceramics were also investigated.

Keywords: PZT; piezoelectric; nano-size; coprecipitation; mechano-chemistry

Preparation of Perovskite Pb(B0.5Nb0.5)O3 (B = Rare-Earth Elements) by Takafumi Taniguchi; Yoshio Yoshikawa (pp. 373-377).
Pb(B0.5Nb0.5)O3 (B = Sc, Y, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu) powders were prepared from mixed nitrate solutions by a chemical coprecipitation method. This method produced very small particles (∼30 nm) with good compositional homogeneity. These powders were highly reactive upon calcination. The powders of the systems (B = Sc, Tm, Yb and Lu) yielded ∼100% perovskite phase after calcination between 800C and 1000C for 1 h. For the system with B = Er, 93% perovskite phase was formed at 900C for 1 h. For the other systems of the elements (B = Y, Nd, Sm, Eu, Gd, Tb, Dy and Ho) with a larger ionic size, perovskite compounds were not formed up to 1100C. The stability and the possible formation of the compounds with a perovskite structure for the Pb(B0.5Nb0.5)O3 series were discussed.

Keywords: perovskite; chemical preparation; powder; niobium compound; relaxor

Hydrothermal Preparation and Characterization of Ultra-Fine BaTiO3 Powders from Amorphous Peroxo-Hydroxide Precursor by Byeong Woo Lee; Seung-Beom Cho (pp. 379-384).
Ultra-fine BaTiO3 powders were hydrothermally prepared by using Ba⋅ Ti-peroxo-hydroxide precursor. Amorphous Ba⋅ Ti-peroxo-hydroxide precursor were prepared by coprecipitation of Ba(NO3)2 and TiCl4 aqueous solution adding in NH4OH aqueous solution. The phase-pure BaTiO3 powders with a cubic perovskite structure were synthesized at temperature as low as 110_∘C and in the pH range of 10–12. This processing method provides a simple low temperature route for producing BaTiO3 nanoparticles. Under a TEM image and a SAD pattern analysis, it is evident that BaTiO3 powders had spherical shape and single crystal nature. The BaTiO3 ceramic sintered at 1200_∘C for 1 h had 97% of theoretical density and a relatively high dielectric constant (ε r = 3500).

Keywords: barium titanate; BaTiO3hydrothermal synthesis; coprecipitation; peroxo-hydroxide

Lead Free Piezoelectric Materials by M. Demartin Maeder; D. Damjanovic; N. Setter (pp. 385-392).
Lead oxide based ferroelectrics, represented by lead zirconate titanate (Pb(Zr, Ti)O3) or PZT) are the most widely used materials for piezoelectric actuators, sensors and transducers due to their excellent piezoelectric properties. Considering lead toxicity, there is interest in developing piezoelectric materials that are biocompatible and environmentally friendlier. The low density of non-lead based materials can also be an advantage in transducers for underwater and medical imaging due to expected lower acoustical impedance. Another impetus for seeking alternative to lead based compositions is the need for piezoelectric materials for operation at high temperatures. Several classes of materials are now being reconsidered as potentially attractive alternatives to PZT for special applications. The potassium niobate family, KNbO3, exhibits low dielectric constants, large thickness coupling coefficient along certain non-polar directions, and low density, all of which have advantages for high frequency transducer applications. Several compositions belonging to bismuth titanate family, Bi4Ti3O12, such as SrTi4Bi4O15, are promising candidates for high temperature applications. Lead free materials alone (eg. (Na0.5Bi0.5)TiO3) or in solution with PT (BiScO3 – PbTiO3) are also potentially interesting as they combine high piezoelectric activity and, in some cases, relatively high Tc. For these families of piezoelectric materials, the processing and piezoelectric response under different conditions of pressure, frequency, and temperature are presently much less understood than for the classical lead containing systems. In this presentation we review and discuss piezoelectric properties of selected lead free compositions (principally for members of the potassium niobate family and bismuth titanate layered compounds) in relation to structural and microstructural features as well as extrinsic contributions (domain walls displacement, conductivity) to their electromechanical properties. It is shown that it is possible to obtain remarkably stable piezoelectric response in some compositions, while others exhibit strong dependence of piezoelectric properties on driving field and frequency. Origins of these different behaviours are discussed.

Keywords: lead free; piezoelectric; potassium niobate; bismuth titanate

Micro Piezoelectric Ultrasonic Motors by K. Uchino; S. Cagatay; B. Koc; S. Dong; P. Bouchilloux; M. Strauss (pp. 393-401).
This paper reviews recent developments of micro ultrasonic rotary motors using piezoelectric resonant vibrations. Following the historical background, four ultrasonic motors recently developed at Penn State University are introduced; windmill, PZT tube, metal tube, and shear-type motors. Driving principles and motor characteristics are described in comparison with the conventional ultrasonic motors. Motors with 1.5 mm in diameter and 0.8 mN⋅m in torque have been actually developed.

Keywords: ultrasonic motor; piezoelectric actuator; standing wave motor

Materials for High Performance Cymbal Transducers by Aydin Dogan; Erman Uzgur; Douglas C. Markley; Richard J. Meyer Jr.; Anne C. Hladky-Hennion; Robert E. Newnham (pp. 403-407).
The effects of materials on the performance of the cymbal-type flextensional transducers were investigated under in-air and water-loaded conditions by finite element analysis (FEA) methods. At the initial stage, FEA and experimental studies were conducted in parallel to gain experience with the FEA models. Later, all calculations were carried out by computational methods: resonance frequencies, projector TVR, receiver FFVS, effective coupling coefficient (keff), and mechanical quality factor (Qm) were calculated. Ceramic and endcap materials have strong effects on the TVR/FFVS performance of cymbal transducers. It is possible to tailor a wide range of flexural resonance frequencies by optimizing the ceramics used as the driver and the metals used as the endcaps.

Keywords: cymbal transducer; projectors/receivers; finite element modeling; piezoelectrics

Solid Freeform Fabrication of Piezoelectric Actuators by a Micro-Casting Method by B. Bos; H. Gorter; L. J. M. G. Dortmans (pp. 409-412).
In recent years, there has been much interest in the manufacturing of piezoceramic actuators by Solid Freeform Fabrication (SFF) methods, following developments in polymer and metal shaping. With these methods, actuator shapes can be realized that are impossible or very difficult to obtain by traditional ceramic shaping techniques. At TNO, research is currently performed on the development of technology to use SFF methods to develop multi-material components, i.e. combining polymers, ceramics and metals in one production process. One SFF-technique, which is investigated in this study, is micro-casting. In this process, a highly loaded ceramic suspension is deposited by a nozzle, attached to a computer-controlled positioning system. With this process, it is possible to make 3D components directly from CAD files, or to fill volumes using wider nozzles. As a case study, such a casting process was used to produce a piezo-electric bender and an ultrasonic transducer element.

Keywords: SFF; actuator; multi-material; PZT; casting

Preparation of Functionally Graded PZT Ceramics Using Tape Casting by A. Navarro; R. W. Whatmore; J. R. Alcock (pp. 413-415).
Functionally graded ferroelectric ceramics (FGM) have been fabricated for pyroelectric applications by an aqueous tape casting technology. The FGM produced in this study consisted of a porous Lead Zirconate Titanate (PZT) tape-cast ceramic, which was made by starch inclusions; sandwiched between two dense PZT layers by stacking and lamination. This paper investigates the effect of porosity on the microstructure and electrical properties of the PZT FGM samples produced. The microstructure of the porous and laminated sintered structures was studied using Scanning Electron Microscopy (SEM). The grain size of the porous layer tended to decrease with increasing corn-starch content. The dielectric constant and pyroelectric coefficient of the FGM both showed decreasing behaviour with increasing porosity.

Keywords: ceramics; PZT; FGM; tape casting; aqueous

Fundamental Limits of Organic Packages and Boards and the Need for Novel Ceramic Boards for Next Generation Electronic Packaging by Rao R. Tummala; P. Markondeya Raj; Steve Atmur; Shubhra Bansal; Sounak Banerji; Fuhan Liu; Swapan Bhattacharya; Venky Sundaram; Ken-ichi Shinotani; George White (pp. 417-422).
The system-on-a-package (SOP) paradigm proposes a package level integration of digital, RF/analog and opto-electronic functions to address future convergent microsystems. Two major components of SOP fabrication are sequential build-up of multiple layers (4–8) of conducting copper patterns with interlayer dielectrics on a board and multiple ICs flip-chip bonded on the top layer. A wide range of passives, wave-guides and other RF and opto-electronic components buried within the dielectric layers provide the multiple functions on a single microminiaturized platform.The routing of future nanoscale ICs with 10,000+ I/Os require multiple build-up layers of ultra fine board feature sizes of 10 μm lines/space widths and 40 μm pad diameters. Current FR4 boards cannot achieve this build-up technology because of dimensional instability during processing. These boards also undergo high warpage during the sequential build-up process which limits the fine-line lithography and also causes misalignment between the vias and their corresponding landing pads. In addition, the CTE mismatch between the silicon die and the board leads to IC-package interconnect reliability concerns, particularly in future fine-pitch assemblies where underfilling becomes complicated and expensive.This work reports experimental and analytical work comparing the performance of organic and novel ceramic boards for SOP requirements. The property requirements as deduced from these results indicate that a high stiffness and tailorable CTE from 2–4 ppm/C is required to enable SOP microminiaturized board fabrication and assembly without underfill. A novel ceramic board technology is proposed to address these requirements.

Keywords: FR4; electronic packaging; high density packaging; System-On-Package; Printed Wiring Board; SiC; flip chip; reliability; high density wiring

Development of Spin Coated Mesoporous Oxide Films for MEMS Structures by Jong-Ah Paik; Shih-Kang Fan; Hsin Chang; Chang-Jin Kim; Ming C. Wu; Bruce Dunn (pp. 423-428).
Mesoporous materials offer several unique properties when incorporated in microelectromechanical systems (MEMS) including low density, thermal insulation and the ability to carry out rapid etching. This paper describes the development of two mesoporous thin film materials for MEMS structures, an organically modified silicate and crystalline TiO2. The morphologies of the mesoporous thin films are similar in that they have approximately 50% volume porosity, an average pore diameter of ∼5 nm, and a narrow pore size distribution. However, the chemistries of the two materials are very different as are their properties for MEMS applications. The organically modified silicate film is designed to have controlled hydrophobicity. CH3 groups which are present in the sol precursor are retained in the final material despite the 400C calcination temperature used for producing the porous mesostructure. Contact angles as high as 80 degrees have been achieved. The mesoporous TiO2 is designed to have resistance to HF etching. Heat treatments of the mesoporous material are carefully controlled enabling the TiO2 pore walls to crystallize without collapsing the pore network structure. A combination of anatase and rutile phases are produced in the solid phase and exhibit excellent resistance to HF.

Keywords: mesoporous oxide films; spin coating; MEMS; surface micromachining

Design and Properties of Piezoelectric Vibrator with Generating Function by FEM Analysis by Kee-Joe Lim; Seong-Hwa Kang; Jong-Sub Lee (pp. 429-432).
Bimorph type piezoelectric vibrator with generating function is designed using Finite Element Method (FEM) and fabricated. Design of piezoelectric vibrator by FEM is focused at its length and the weight of added mass. Also, the vibration and charging properties of the fabricated piezoelectric vibrator are investigated. As the FEM analysis results, when the piezoelectric vibrator is the length of 18 mm and the additive weight of 0.3 g, its resonance frequency decrease to 150 Hz. Also, when input voltage of 20 V is applied, output voltage is 10.285 V in generating element. As the properties of piezoelectric vibrator fabricated, when input voltage is 20 Vrms, the acceleration of piezoelectric vibrator and output voltage are about 1.1 G and 10.18 Vrms, respectively. When gold capacitor of 0.0066 [F] is used as the load, the output voltage is about 3 [VDC] after 3600 [sec] driving time.

Keywords: vibration alarm; piezoelectric vibrator; generating function; FEM

Design and Performance of Miniaturized Piezoelectric Step-Down Transformer by Kee-Joe Lim; Seong-Hwa Kang; Hyun-Hoo Kim; Jong-Sub Lee; Su-Hyun Jeong (pp. 433-442).
Piezoelectric transformers are expected to be small, thin and highly efficient, and which are attractive as a transformer with high power density for step down voltage. For these reasons, we have attempted to develop a step-down piezoelectric transformer for the miniaturized adaptor. we propose a piezoelectric transformer, operating in thickness extensional vibration mode for step-down voltage. This transformer consists of a multi-layered construction in the thickness direction. In order to develop the step-down piezoelectric transformers of 10 W class and turn ratio of 0.1 with high efficiency and miniaturization, the piezoelectric ceramics and piezoelectric transformer designs are estimated with a variety of characteristics. The basic composition of piezoelectric ceramics consists of ternary yPb(ZrxTi1 − x)O3−(1−y)Pb(Mn1/3Nb1/3Sb1/3)O3. In the piezoelectric characteristics evaluations, at y = 0.95 and x = 0.505, the electromechanical coupling factor(kp) is 58%, piezoelectric strain constant (d33) is 270 pC/N, mechanical quality factor(Qm) is 1520, permittivity (ε 33T0) is 1500, and Curie temperature is 350C. At y = 0.90 and x = 0.500, kp is 56%, d33 is 250 pC/N, Qm is 1820, ε33T0 is 1120, and Curie temperature is 290C. It shows the excellent properties at morphotropic phase boundary regions. PZT-PMNS ceramic may be available for high power piezoelectric devices such as piezoelectric transformers. The design of step-down piezoelectric transformers for adaptor proposes a multi-layer structure to overcome some structural defects of conventional piezoelectric transformers. In order to design piezoelectric transformers and analyze their performances, the finite element analysis and equivalent circuit analysis method are applied. The maximum peak of gain G as a first mode for thickness extensional vibration occurs near 0.85 MHz at load resistance of 10 Ω. The peak of second mode at 1.7 MHz is 0.12 and the efficiency is 92%.

Keywords: piezoelectric transformer; PZT-PMNS; adaptor

Hydrostatic Piezoelectric Coefficient dh of PZT Ceramics and PZN-PT and PYN-PT Single Crystals by L. Burianova; P. Hana; S. Panos; E. Furman; S. Zhang; T. R. Shrout (pp. 443-448).
The hydrostatic piezoelectric coefficient dh of Pb(ZrxTi1 − x)O3 ceramics (PZT), and of Pb(Zn1/3Nb2/ 3)O3-PbTiO3 and Pb(Yb1/2Nb1/2)O3-PbTiO3 (PZN-PT, PYN-PT, respectively) single crystals with compositions near to the morphotropic phase boundary (MPB) have been measured using a dynamic hydrostatic method. The effects of DC electric field and static component of hydrostatic stress on dh of PZT ceramics, PZN-PT and PYN-PT single crystals were studied. Changes of the piezoelectric hydrostatic coefficients dh caused by an electric field (DC bias) were observed along with pressure and temperature dependencies. The measurement of the hydrostatic piezoelectric coefficient dh seems to be promising for investigation of intrinsic (single domain) and extrinsic (domain-walls) contributions to piezoelectric behavior of single crystals and ceramic materials.

Keywords: PZT ceramics; PZN-PT and PYN-PT relaxors; morphotropic phase boundary; hydrostatic piezoelectric coefficients

Piezoelectric and Dielectric Properties of Pb(ZrxTi1 − x)O3-Pb(Ni1/3Sb1/3Nb1/3)O3 Piezoelectric Ceramics by Kee-Joe Lim; Si-Yong Lee; Jong-Sub Lee; Mun-Ju Lee; Seong-Hwa Kang (pp. 449-452).
In this paper, piezoelectric and dielectric properties of 0.9PbZrxTi1−xO3-0.1PbNi1/3Sb1/3Nb1/3O3 were studied as a function of Zr/Ti mole ratio(x) for application to piezoelectric actuator. Also, microstructure and crystalline phase are investigated by using SEM and XRD, respectively. As a results, the substitution of Sb5+ to B-site increases the piezoelectric and dielectric properties, and when Zr/Ti mole ratio is 49/51 and ternary mole ration is 0.1(0.9PbZr0.49Ti0.51O3-0.1PbNi1/3Sb1/3Nb1/3O3), the corresponding composition were found belonging to the Morphotropic Phase Boundary region with electromechanical coupling coefficient(kp), mechanical quality factor (Qm), permittivity(εr) and piezoelectric strain constant(d33) equaled to 63%, 360, 2000 and 470 pC/N, respectively. Sintering temperature was about 1150_∘C and Curie temperature was determined around 290_∘C.

Keywords: piezoelectric actuator; MPB; PZT-PNSN; Piezoelectric strain constant

Pb((Mg0.7Zn0.3)1/3Nb2/3)O3 Relaxor Ferroelectric Ceramics by a Reaction-Sintering Process by Yi-Cheng Liou (pp. 453-456).
Pb((Mg1/3Nb2/3)0.7(Zn1/3Nb2/3)0.3)O3 (PMZN) relaxor ferroelectric ceramics produced by a reaction-sintering process were investigated. Without any calcination, the mixture of PbO, Mg(NO3)2, Zn(NO3)2 and Nb2O5 was pressed into pellets and sintered directly. PMZN ceramics of 100% perovskite phase were obtained. Density of 8.11 g/cm3 (> 98% of theoretical value) was obtained after sintered at 1200C for 2 h. 3–9 μm grain size was obtained in PMZN ceramics sintered at 1180C–1250C for two hours by reaction-sintering process.Dielectric constant at room temperature under 1 kHz reaches 18200 after sintered at 1200C for 2 h.

Keywords: relaxor ferroelectrics; PMN-PZN; reaction-sintering process

PZN-PFW and PFN-PFW Relaxor Ferroelectric Ceramics by a Reaction-Sintering Process by Yi-Cheng Liou; Yi-Che Shih; Cheng-Jung Chuang (pp. 457-461).
Pb((Zn1/3Nb2/3)0.6(Fe2/3W1/3)0.4)O3 and Pb((Fe1/2Nb1/2)0.7(Fe2/3W1/3)0.3)O3 (PZNFW and PFNW) perovskite ceramics prepared by a reaction-sintering process were investigated. Without any calcination, the mixture of PbO, Zn(NO3)2, Fe(NO3)3, Nb2O5 and WO3 for stoichiometric PZNFW and PFNW was pressed and sintered directly. Pyrochlore phase more than 25% were formed in PZNFW ceramics after 2 h sintering at 930–980C. PFNW ceramics of 100% perovskite phase were obtained after 4 h sintering at 930–1080C. A density of 8.13 g/cm3 (93.4% of theoretical value) was obtained after sintered at 1080C for 4 h. Dielectric constant at room temperature under 1 kHz reaches 32000 after sintered at 1080C for 4 h.

Keywords: relaxor ferroelectrics; PZN-PFW; PFN-PFW; reaction-sintering process

Improved Electromechanical Response in Rhombohedral BaTiO3 by Y. Avrahami; H. L. Tuller (pp. 463-469).
Zr-, Hf-, and KNb-doped BaTiO3 materials were prepared in a composition range that stabilizes the rhombohedral phase above room temperature. These materials were prepared as bulk polycrystalline material using standard solid-state reaction methods. X-ray diffraction was used to confirm the existence of a stable rhombohedral phase while dielectric constant measurements confirmed the expected phase transition temperatures. A piezoelectric coefficient of d33 = 290–470 pC/N was obtained for Zr- and Hf-doped BaTiO3, compared with d33 = 75 pC/N for pure BaTiO3. An electrostrictive coefficient of Q33 = 0.37 m4/C2 was obtained for the KNb-doped material, compared with Q33 = 0.11 m4/C2 for pure BaTiO3. The maximum strain measured for the doped samples was 5–10 times higher than that of pure BaTiO3.

Keywords: piezoelectric; barium-titanate; dielectric; high strain

Crystal Growth and High Temperature Piezoelectricity of La3Ta0.5Ga5.5 − xAlxO14 Crystals by Il Hyoung Jung; Tsuguo Fukuda; Keun Ho Auh (pp. 471-478).
For the application of high temperature piezoelectric devices, Al3 + substituted La3Ta0.5Ga5.5O14 (LTG) crystals with chemical formula of La3Ta0.5Ga5.5 − xAlxO14 (LTGA) were synthesized and grown by μ-PD (Micro-pulling-down) and Czochralski technique. LTGA compound has been shown to exhibit congruent melting in a wide compositional range without destabilization of the melt during growth, while distribution coefficient of the substituted Al3 + ion was close to unity. LTGA crystals have shown preferable effects for temperature stability on piezoelectric properties in the range from R.T (room temperature) to 500_∘C.

Keywords: La3Ta0.5Ga5.5 −xAlxO14 (LTGA); crystal growth; micro-pulling-down; Czochralski; piezoelectric

Synthesis of Sr0.5Ba0.5Nb2O6 by Coprecipitation Method—Dielectric and Microstructural Characteristics by P. K. Patro; R. D. Deshmukh; A. R. Kulkarni; C. S. Harendranath (pp. 479-485).
Sr0.5Ba0.5Nb2O6 (SBN50) has been synthesized by coprecipitation method using Sr(NO3)2, Ba(NO3)2 and Nb-oxalate as precursors and ammonium hydroxide as precipitant. Calcination at 1150C resulted in pure SBN50 phase (XRD) and nano powder with size varying between 100–250 nm (TEM). The average grain size (SEM) in the sintered pellets ranged from 2.5 to 5 μm as the sintering temperature varied from 1250 to 1350C. The maximum sintered density was observed to be 93% of ρth. The plot of dielectric constant vs. temperature clearly showed a shift of dielectric maxima (εmax) with frequency, indicating the relaxor nature of SBN50. The room temperature dielectric constant (εRT > 2300) observed for all these samples is higher compared to the earlier reported values (εRT ∼ 1500). The Tc (for 1 KHz) varied from 47–60C depending on the sintering conditions. The hystersis loops were recorded at various temperatures. The maximum saturation polarization for the unpoled pellets was found to be 2.3 μ C/cm2 when sintered at 1350C. The improvement in dielectric and ferroelectric behavior is attributed to the enhanced homogeneity attained by the coprecipitation synthesis route used in the present study. Correlations between microstructure (sintering conditions) and dielectric behavior is explored.

Keywords: SBN; ferroelectric; relaxor; microstructure; coprecipitation; strontium barium niobate

Partial Discharge Signal Detection by Piezoelectric Ceramic Sensor and The Signal Processing by Kee-Joe Lim; Seong-Hwa Kang; Kang-Won Lee; Sung-Hee Park; Jong-Sub Lee (pp. 487-492).
Partial discharge (PD) in an insulator or on surface of defective conductor emits acoustic wave transmitting through an air or an insulator. The acoustic wave between 20 kHz and several hundred of kHz can be detected by piezoelectric ceramic sensor that converts the acoustic wave into an electrical signal. Piezoelectric ceramic sensor has either the wide resonant band or the local resonant band depending on the ceramic material or the various combinations of each different component in the manufacturing process. This paper presents the piezoelectric ceramic sensor with 0.95 PZT–0.05 PMNS that yields the piezoelectric properties of high kp, high Qm. It has the frequency characteristics of local resonant band, such that it can be applied to PD detection. We have demonstrated the properties of the proposed piezoelectric ceramic sensor by comparing with the conventional electrical PD detector. Quantitative analysis is accomplished by comparing the ψ -qmax from a PD detector and the ψ -vmax from the proposed sensor while ψ -n distributions are the same for both the conventional phase-resolved PD analysis method and the proposed one.

Keywords: partial discharge; piezoelectric sensor; PZT

Diffuse Dielectric Anomaly in Ferroelectric Materials by S. K. Choi; B. S. Kang; Y. W. Cho; Y. M. Vysochanskii (pp. 493-502).
It has not been clear whether the diffuse dielectric anomaly by Debye-type dielectric relaxation is extrinsic or intrinsic in origin although it has been frequently found in ferroelectric materials regardless of their structures and ferroelectric properties. We experimentally investigated the extrinsic nature of the diffuse dielectric anomaly in ferroelectric oxides and sulfide such as BaTiO3, Pb0.9La0.1TiO3, and SnP2S6. The advanced fitting method using the modified Debye relaxation equation was introduced in order to explain the temperature dependent behavior of the diffuse dielectric anomaly. It was confirmed that the diffuse dielectric anomaly was a competitive phenomenon between the dielectric relaxation and the electrical conduction of the relaxing species. It was also proved that the activation energy of the dielectric relaxation should be always higher than the conductivity activation energy of the relaxing species in the diffuse dielectric anomaly.

Keywords: dielectric relaxation; ferroelectric; Debye relaxation; electrical conductivity

Processing and Dielectric Properties of Sol-Gel Derived PMN-PT (68:32) Thin Films by T. C. Goel; Pawan Kumar; A. R. James; Chandra Prakash (pp. 503-507).
PMN-PT thin films near MPB were prepared using sol-gel technique. A transparent solution of the ceramic was prepared by using lead acetate trihydrate, magnesium ethoxide, niobium ethoxide and titanium isopropoxide as precursors along with 2methoxyethanol as solvent and acetic acid as catalyst. Thin films of the ceramic were prepared on Pt/Si and on ITO coated glass substrates. X-ray diffraction (XRD) studies show the formation of perovskite phase of the films with less than (5%) pyrochlore phase. Scanning electron microscopy (SEM) study of the films on different substrates show well developed grains of sub-micron size. Dielectric constant measurement at different temperature was carried out. Room temperature value of dielectric constant and dielectric loss at 1 kHz of the ceramic thin films on ITO coated glass and Pt/Si substrates were found to be 500, 0.03 and 415, 0.01 respectively. Dielectric measurements for different thicknesses of the films have also been carried out. P-E loop and I-V studies of the films were also carried out.

Keywords: PMN-PT; sol-gel; ferroelectric films; relaxors; MPB

Water-Immersible Micromachined Pb(Zr, Ti)O3 Thin Film Actuators by Yongbae Jeon; Chee Wei Wong; Sang-Gook Kim (pp. 509-513).
We demonstrate a water-immersible thin film lead zirconate titanate, Pb(Zr, Ti)O3, [PZT] actuator, without special passivation layer, towards in-vivo or in-vitro scanning probe microscope (SPM) measurements of living cells in water or biological fluids. In order to be water-immersible, the electrodes need to be electrically insulated and the piezoelectric layer needs to be protected against direct water contact. This paper describes our design solution with a simple fabrication process for a water-immersible piezoelectric device, which separates the bottom electrode from the top electrode by having a narrow ditch covered with PZT film. The PZT film is then encapsulated with the top metal electrode without insulation layer. In this structure, the PZT is sandwiched between the top and bottom metal electrodes to prevent water permeation. The device is fabricated using lift-off processing for the bottom and top electrodes, sol-gel spinning for the PZT thin film and wet etching for the PZT patterning. The piezoelectric constant, d31, is about −100 pC/N. The dielectric polarization and fatigue properties of the devices were measured in air and water. The spontaneous polarization, remnant polarization, coercive field and dielectric constant are 54 μ C/cm2, 15 μ C/cm2, 60 kV/cm and 1200, respectively. The polarization property of the device was unchanged in either air or water up to 1 × 109 continuous cycles.

Keywords: piezoelectric; actuator; thin film; water-immersible; MEMS

Dielectric and Piezoelectric Properties of Nonstoichiometric SrBi2Ta2O9 and SrBi2Nb2O9 Ceramics by J. A. Cho; S. E. Park; T. K. Song; M. H. Kim; H. S. Lee; S. S. Kim (pp. 515-518).
Nonstoichiometric SrBi2Ta2O9 (SBT) and SrBi2Nb2O9 (SBN) ceramics were prepared by a solid state reaction method. X-ray diffraction analysis showed that single-phase of Bi-layered perovskite was obtained. With different Sr/Bi content ratios of SBT and SBN, Curie temperature (TC), electromechanical factor (Kp) and mechanical quality factor (Qm) were measured. TC of SBN (SBT) rose from 414C (314C) to 494C (426C) when Sr/Bi content ratio was increased from 0.55/2.3 to 1.2/1.8. In the most Sr-deficient/Bi-excess ratio of 0.55/2.3, the maximum values of Qm were obtained approximately 1013 and 3325 for SBT and SBN, respectively.

Keywords: Bi-layered perovskite; Curie temperature; electromechanical factor; mechanical quality factor

Microstructural Control of BaTiO3 Thick Film Fabricated by Utilizing Slide-Off Transfer Printing by Takeo Hyodo; Katsuhiko Maeda; Takahiro Ito; Kazuhiro Sasahara; Yasuhiro Shimizu; Makoto Egashira (pp. 519-524).
Effects of fabrication conditions on the microstructure of thick BaTiO3 films have been investigated by employing slide-off transfer printing technique. Formation of dense films with good adhesive properties was difficult when screen-printing was employed in preparing the slide-off transfer sheets (BaTiO3 green films), irrespective of the kind of solvents used for the slurries. On the other hand, relatively dense films could be fabricated from the slide-off transfer sheet prepared by spin-coating of the slurries consisting of fine BaTiO3 powder (particle size: ca. 0.1 μm), printing oil, and 2-propanol, though cracks formed obviously. Co-addition of large BaTiO3 particles (particle size: ca. 0.5 μm) was very effective for reducing the formation of cracks, and homogenous and dense films could be fabricated by controlling the additive amount of the large particles.

Keywords: barium titanate; thick film; slide-off transfer printing; spin-coating; screen-printing

Piezoelectricity in Poled Silica Films with Tetravalent Metal Dopants by Satoru Noge; Makoto Shiroishi; Takehiko Uno (pp. 525-529).
Piezoelectricity was produced in silica films with tetravalent metal dopants by poling. Poling treatment in germanium-doped silica (Ge:SiO2) glass films raises their of optical non-linearity and produces, among other things, the Pockels effect. We generated piezoelectricity in poled Ge:SiO2 glass thin films. Tetravalent-metal-doped SiO2 (M4 +:SiO2) films were prepared on Si substrates by RF magnetron sputtering. We used germanium, titanium, and tin as doping materials. The piezoelectricity of the films was compared with the piezoelectricity of quartz. Piezoelectricity of the same order of magnitude as that in quartz was observed in the M4 +:SiO2 films. However, less than a week later, the piezoelectricity disappeared almost completely in all the samples. To prevent the piezoelectricity from disappearing, we tried to pin the doping ions. We developed a pinning technique based on the structure of a Ge:SiO2-Ti:SiO2-Sn:SiO2-super-lattice. This super-lattice structure was very effective in preventing the piezoelectricity from disappearing.

Keywords: Ge-doped silica; silica; germanosilicate; piezoelectricity; piezoelectric materials; poling; super-lattice structure

Preparation of Bulk Pb(Zr, Ti)O3 with Crystallographic Texture by Templated Grain Growth Method by Hiroki Muramatsu; Toshio Kimura (pp. 531-535).
Polycrystalline Pb(Zr, Ti)O3 (PZT) ceramics with 〈111〉-texture were prepared by the templated grain growth (TGG) method using the platelike Ba6Ti17O40 (B6T17) particles as templates. Textured PZT was obtained by sintering of green compacts containing matrix PZT, aligned B6T17, and excess PbO. Excess PbO formed a liquid phase and promoted the dissolution of PZT grains and the precipitation on B6T17 grains. A similarity of the arrangement of ions on (001) of B6T17 and (111) of PZT gave 〈111〉-texture to matrix PZT.

Keywords: crystallographic texture; templated grain growth; lead zirconate titanate; texture engineering

Mechanisms of Texture Development in Bismuth Layer-Structured Ferroelectrics Prepared by Templated Grain Growth by Yoshiyuki Sakuma; Toshio Kimura (pp. 537-541).
The mechanism for texture development in bismuth layer-structured ferroelectrics prepared by the templated grain growth method was examined using template and matrix grains with different chemical compositions. The template particles used were platelike Bi4Ti3O12 and Ba6Ti17O40 for SrBi4Ti4O15-matrix composites and platelike Ba6Ti17O40 and Sr3Ti2O7 for BaBi4Ti4O15-matrix. The 〈001〉-texture developed in all composites examined. The origins of texture development were the growth of matrix grains to be platelike and the formation of face-to-face contact between the template and matrix grains and also between matrix grains.

Keywords: bismuth layer-structured ferroelectrics; crystallographic texture; templated grain growth method; texture engineering

Electrical Properties of Bismuth Titanate Based Ceramics with Secondary Phases by M. Villegas; T. Jardiel; A. C. Caballero; J. F. Fernández (pp. 543-548).
Bi4Ti3O12 (BIT) based ceramics were prepared by hydroxide coprecipitation method and subsequent treatment at 650C for 1 h. Calcined BIT was doped with different amounts of WO3 by surface doping using W(C2H5O)6. The amount of dopant modified the sintering behaviour of BIT-based ceramics through a liquid-phase assisted sintering mechanism in the case of low dopant concentration and Zenner effect when high concentration of dopant was used. Consequently, the microstructure and the electrical properties were strongly dependent on the dopant concentration. Doped BIT-based ceramics showed a microstructure composed of very small platelet-like grains and the electrical conductivity was markedly decreased. The high electrical resistivity makes possible the polarization of doped ceramics and relatively good piezoelectric parameters were measured.

Keywords: bismuth titanate; microstructure; piezoelectric properties

Electrical Properties of Acceptor Doped BaTiO3 by Jaill Jeong; Young Ho Han (pp. 549-553).
Electrical properties of acceptor (Mn, Mg or Mn+Mg)-doped BaTiO3 ceramic have been studied in terms of oxygen vacancy concentration, various doping levels and electrical degradation behaviors. The solubility limit of Mn on Ti sites was confirmed to be close to or less than 1.0 mol%. Oxygen vacancy concentration of Ba(Ti0.995 −xMg0.005Mnx)O2.995 −y (x = 0, 0.005, 0.01) was estimated to be ∼ 50 times greater than that of the un-doped BaTiO3. The leakage current of 0.5 mol% Mn-doped BaTiO3 was stable with time, which was much lower than that of the un-doped BaTiO3. The BaTiO3 specimen co-doped with 0.5 mol% Mg and 1.0 mol% Mn showed the lowest leakage current below 10− 10A. It was confirmed that leakage currents of Mg-doped and un-doped BaTiO3 under dc field are effectively suppressed by Mn co-doping as long as the Mn doping level is greater than Mg contents.

Keywords: Mg; Mn; BaTiO3MLCC; degradation

Ferroelectric Property and Crystal Structure of KNbO3 Based Ceramics by Izumi Masuda; Ken-Ichi Kakimoto; Hitoshi Ohsato (pp. 555-559).
Rietveld refinement analysis was carried out to obtain the knowledge on the solid solution structure of the La and Fe co-doped KNbO3 ceramics. The diffraction data was well fitted with tetragonal space group P4mm, and showed that La and Fe located at K and Nb sites in KNbO3 perovskite, respectively. The sum of both occupancy ratios agreed almost well with the doping content. Furthermore, the effects of MnO2 addition on the ferroelectric properties and crystal structure of the La and Fe co-doped KNbO3 ceramics were investigated. MnO2 addition strongly affected the ferroelectric and piezoelectric properties, because the valence of Mn ions changed from Mn4 + to some extents of Mn3 + and Mn2+, which were suggested by XAFS analysis.

Keywords: KNbO3LaFeO3piezoelectrics; Rietveld analysis; XANES analysis

Crystal Growth and Dielectric Properties of New Ferroelectric Barium Titanate: BaTi2O5 by Yukikuni Akishige; Katsuhiro Fukano; Hirotake Shigematsu (pp. 561-565).
Single crystals of the ferroelectric BaTi2O5 and BaTiO3 were prepared from a solution of 33-mol% BaO and 67-mol% TiO2 by a rapid cooling method. The dielectric constant (ε′) and dielectric loss tangent (tanδ) were measured in a wide temperature range of 10–860 K and in a frequency range of 0.1–3,000 kHz. The ε′ along the b-axis of the BaTi2O5 crystal, prepared in air, shows a sharp dielectric anomaly reaching 30,000 at the ferroelectric Curie temperature of TC = 752 K. By contrast, the crystal prepared in a reducing atmosphere shows a diffuse phase transition near TC = 703 K. The values of ε′ and tanδ are compared between these three crystals consisting of two kinds of BaTi2O5 and one BaTiO3.

Keywords: BaTi2O5BaTiO3ferroelectrics; high Curie temperature; high dielectric constant

Microstructure of X7R Type Base-Metal-Electroded BaTiO3 Capacitor Materials Co-Doped with MgO/Y2O3 Additives by Cheng-Sao Chen; Chen-Chia Chou; I-Nan Lin (pp. 567-571).
Detailed microstructure of MgO/Y2O3 co-doped BaTiO3 materials were examined using transmission electron microscopy (TEM). For the 1250_∘C-sintered BaTiO3 samples possessing flat K-T characteristics, which meet the X7R specification, the granular structure is complicated. Most of the grains are very small (∼ 150 nm) and are highly strained. The small grains contain large proportion of Y2O3 species and are paraelectric, whereas the large grains contain Y2O3 species unevenly distributed and are of core-shell structure. In contrast, for the 1300C-sintered BaTiO3 samples, which have K-T properties slightly off the X7R specification, the grains grew larger to around 300 nm. The core-shell structured grains are seldom observed. Apparently, it is the existence of such a non-equilibrium core-shell microstructure, which renders the dielectric properties of the BaTiO3 materials extremely sensitive to the processing parameters.

Keywords: transmission electron microscopy; base-metal-electroded capacitor; BaTiO3X7R

Microwave Sintering of Base-Metal-Electroded BaTiO3 Capacitor Materials Co-Doped with MgO/Y2O3 Additives by Cheng-Sao Chen; Chen-Chia Chou; Wei-Chun Yang; I-Nan Lin (pp. 573-577).
In this paper, we systematically investigated the effect of microwave sintering parameters on the characteristics of BaTiO3 capacitor materials co-doped with Y2O3/MgO species. It is observed that the granular structure of the materials is relatively insensitive to the sintering temperature and soaking time such that the BaTiO3 capacitor materials possessing X7R dielectric constant-temperature (K-T) characteristics can be obtained in a wide range of sintering conditions. TEM examinations reveal that the detailed microstructure of these materials is extremely complicated. The unique K-T properties of these materials are ascribed to the duplex structure of the samples, viz. fine grains of paraelectric phase and large grains of ferroelectric phase.

Keywords: microwave sintering; base-metal-electroded capacitor; X7R-type capacitor

Single-Crystalline KNbO3Thin Film Grown by Liquid Phase Epitaxy by Ken-Ichi Kakimoto; Izumi Masuda; Tomohiko Hibino; Hitoshi Ohsato (pp. 579-583).
The effects of melt composition on the transmittance of single-crystalline KNbO3 films grown on SrTiO3 substrates by liquid phase epitaxy (LPE) technique were investigated. The growth morphology and transmittance of the KNbO3 films strongly depended on the extra K2CO3 self-flux content in K2CO3 (K2O)-Nb2O5 system. With increasing K2CO3 content close to the eutectic composition (≈66 mol%) in the phase diagram, the transmittance of KNbO3 film/SrTiO3 substrate increased up to 70% in the visible wavelength range. Atomic force microscopy (AFM) clearly showed that the parallel flat steps formed toward the dipping direction and their interval decreased with increasing the K2CO3 content.

Keywords: liquid phase epitaxy (LPE); KNbO3SrTiO3single-crystalline film; transmittance

Development of a New MnZn-Ferrite Soft Magnetic Material for High Temperature Power Applications by V. Zaspalis; V. Tsakaloudi; E. Papazoglou; M. Kolenbrander; R. Guenther; P. van der Valk (pp. 585-591).
At power electronic applications (e.g. in automotive, lighting, electrical equipment etc.) the inductive components that consist the heart of the power transformers are made of ceramic ferromagnetic materials of the type (MnxZnyFe2 +1 − xy)Fe3 +2O4. Usually they are designed in such a way in order to exhibit optimum magnetic performance and electromagnetic power loss minimum at 80–100C, which is the steady state operation temperature region for most devices. However, the continuous miniaturization of electric and electronic equipment associated with a continuous increase in the density of electronic components has as unavoidable consequence the gradual shift of the steady state operation temperature to higher levels. The need is therefore becoming obvious for the development of new power soft magnetic materials optimized to operate at higher temperatures than those at which current existing materials operate. In the present work the development is described of such a new soft ferrite material having the chemical composition (Mn0.76Zn0.17Fe2 +0.07)Fe3 +2O4, initial magnetic permeability of 1800 (measured at a frequency f = 10 kHz, an induction level B < 0.1 mT and a temperature T = 25C), Curie temperature of 225C and electromagnetic power losses < 350 mW/cm3 measured at a temperature of 140C, frequency of 100 kHz and a magnetic field strength of 200 mT. The material has been successfully introduced to production and is now commercially available. The largest application is offered by the automotive industry in particular for tackling high temperature operating problems arising when control is being done near the engine (near the engine electronics).

Keywords: electromagnetic ceramics; soft-ferrites; MnZn-ferrites

Nano-Ionics: More Than Just a Fashionable Slogan by Joachim Maier (pp. 593-598).
The paper considers and investigates the dependence of the ionic conductivity on the spacing of interfaces. Not only does a narrow spacing lead to an increased proportion of interfacial conductivity, it may also cause local size effects to occur. The present status as well as the perspective of this field are discussed and shown to justify the term “nano-ionics”.

Keywords: ion conductivity; transport; interfaces; nano-size

Nanocrystalline Alkaline Earth Titanates and Their Conductivity Characteristics Under Changing Oxygen Ambients by Christian Ohly; Susanne Hoffmann-Eifert; Rainer Waser (pp. 599-603).
This work presents the first systematic study of conductivity characteristics of alkaline earth titanates in the form of polycrystalline and heteroepitaxial thin films as well as nanocrystalline ceramics as a function of temperature (between 600_∘C and 1000_∘C) and continuously adjustable oxygen partial pressures ranging from 10− 20 bar to 1 bar. Compared to the well-known log,σ-log, pO2 profiles of single crystals, the conductivity behavior of CSD-prepared, polycrystalline SrTiO3 thin films with a feature size of about 50 nm differs radically. The most prominent characteristics are a sharp drop under reducing conditions followed by a broad plateau region. Tailored investigations on heteroepitaxial as well as polycrystalline thin films grown by PLD and especially by studies on nanocrystalline BaTiO3 ceramics with a mean grain size of ≤100 nm allowed an unambiguous assignment of the described effects to the nanocrystalline morphology of the samples.

Keywords: titanates; electrical conductivity; thin films; nanocrystalline ceramics; grain boundary density

Room Temperature Phase Transition in CeO2 Nanocrystalline Films by Anna Kossoy; Jaya P. Nair; Ellen Wachtel; Igor Lubomirsky; Juergen Fleig; Joachim Maier (pp. 605-608).
The temporal evolution of the lattice parameter of oxygen deficient nanocrystalline cerium oxide films was monitored by X-ray diffraction. It was found that films with lattice parameter of ≈ 5.47 {Å} upon deposition undergo large spontaneous expansion, in which the size of the unit cell increases by ≈ 0.7% during the course of days. The films with as-deposited lattice parameter larger or smaller than ≈ 5.47 Å do not show significant changes. This behavior is consistent with the previously suggested hypothesis of an order-disorder transition of oxygen vacancies and can be viewed as its direct experimental confirmation.

Keywords: nanocrystalline ceramics; mechanical stress; diffusion; cerium oxide

Electrical Conductivity of CeO2 Prepared from Nanosized Powders by E. N. S. Muccillo; R. A. Rocha; S. K. Tadokoro; J. F. Q. Rey; R. Muccillo; M. C. Steil (pp. 609-612).
Nanosized powders of cerium dioxide with controlled physical properties were prepared by the precipitation technique using ammonium hydroxide or oxalic acid as precipitating agent. The calcined precursors were studied by nitrogen adsorption to determine the specific surface area, X-ray diffraction for phase characterization and crystallite size determination, and by laser scattering for particle size distribution. The morphology of powder particles was observed by scanning electron microscopy. It is shown that both precipitating materials may be used for the preparation of nanocrystalline powders (< 10 nm) with high values of specific surface area (> 90 m2 ⋅ g− 1). The observed differences between powders prepared from hydroxides or oxalates rely on the distribution of particle sizes and in the morphology of the agglomerated particles. Impedance spectroscopy experiments were carried out in the 5 Hz–13 MHz frequency range under controlled partial pressure of oxygen from 10 ppm to 1 atm. The analysis of these results allowed for the determination of the charge carriers responsible for the electrical transport in the ceria sintered pellets.

Keywords: ceria; nanocrystalline powders; characterization techniques; electrical conductivity

Oxygen Permeation Properties of Ceria-Ferrite-Based Composites by H. Takamura; K. Okumura; Y. Koshino; A. Kamegawa; M. Okada (pp. 613-618).
The oxygen flux density of Ce0.8Gd0.2O1.9x vol% MnFe2O4 (CGO-xMFO) composite-type ceramics membranes has been investigated. The samples and reforming catalysts were prepared by the Pechini process. For the CGO-xMFO composites, oxygen permeation was observed even at x = 3 vol%, presumably due to the presence of grain boundary phases. For CGO-15MFO, the n-type electronic conductivity was found to be dominant at 900C or higher. The thickness dependence of jO2 revealed that surface exchange kinetics was significantly involved in the case of the membrane thickness of L < 0.5 mm. The highest oxygen flux density of 10 μ mol⋅cm−2⋅s−1 was achieved for CGO-15MFO with the 10 mass% Ni-Pr:CeO2 catalyst (L = 0.25 mm) at 1000C and a flow rate of 270 sccm.

Keywords: oxygen permeable membranes; composites; doped ceria; spinel-type ferrite; partial oxidation of methane

Solid Electrolyte Materials, Devices, and Applications by Ashok V. Joshi; James J. Steppan; Dale M. Taylor; S. Elangovan (pp. 619-625).
This paper outlines the development status, issues, and applications of several solid electrolyte electrochemical devices currently being developed by Ceramatec and its partners. Ceramatec and its commercial partner Air Products and Chemicals, Inc., (APCI) have successfully developed and demonstrated an electrochemical device that utilizes a ceria-based, solid electrolyte to separate oxygen from air [1, 2]. Other oxygen separator projects utilize ion transport membrane(s) (ITM) composed of mixed ionic and electronic conductors to transport oxygen ions across the membrane by means of a pressure differential driving force to generate high purity oxygen or a chemical reaction driving force to produce synthesis gas from methane (ITM Syngas).Ceramatec, in partnership with SOFCo, demonstrated kilowatt class solid oxide fuel cell (SOFC) stacks operating on a variety of fuels such as pipeline natural gas and reformed diesel. Ceramatec is presently working with Cummins and SOFCo to develop low cost modular fuel cells under the Department of Energy’s Solid-state Energy Conversion Alliance (SECA) initiative. Some of Ceramatec’s other programs are focused on development of gallate electrolyte based fuel cells [3] and metallic bipolar plates [4] for lower temperature operation.

Keywords: fuel cells; ion transport membranes; oxygen separators; solid state ionic devices

Properties of CaTi1 − xFexO3 − δ Ceramic Membranes by F. M. Figueiredo; M. R. Soares; V. V. Kharton; E. N. Naumovich; J. C. Waerenborgh; J. R. Frade (pp. 627-636).
CaCO3, TiO2 and Fe2O3 were mixed in the appropriate stoichiometric quantities and calcined at 1100C for 10 h. These powder mixtures were uniaxially pressed and sintered at temperatures ranging from 1350 to 1500_∘C for 2 h in order to obtain dense disk-shaped samples with nominal CaTi1 − xFexO3−δ (x = 0.05, 0.15, 0.20, 0.40 and 0.60) compositions. Dilatometry and in situ high temperature powder X-ray diffraction analysis showed a good agreement on the thermal expansion behaviour of these materials between room temperature and 1000_∘C. The estimated linear thermal expansion coefficient is close to 13× 10− 6 K− 1 and is little affected by composition. No evidence for surface carbonation was detected in the infrared spectra collected on samples previously annealed in CO2 atmospheres. The oxygen permeability measured at temperatures ranging from 750 to 1000_∘C goes through a sharp maximum for x = 0.20. This result is interpreted by structural differences related to change from disordered to ordered oxygen vacancies. The overall performance of CaTi0.80Fe0.20O3−δ is compared to other mixed conducting materials.

Keywords: Calcium titanate; stability; thermal expansion; oxygen permeability

Impedance Spectroscopy on Solids: The Limits of Serial Equivalent Circuit Models by J. Fleig (pp. 637-644).
Impedance spectroscopic data obtained on solids are often interpreted in terms of serial equivalent circuit models. In these models each relaxation process in a spectrum is usually related to exactly one transport or reaction process, i.e. to one sample region (e.g. bulk, grain boundary, electrode) or reaction step. These quasi-one-dimensional, serial models implicitly assume frequency-independent current lines. In this contribution it is shown by finite element calculations that in real systems current lines are often frequency-dependent and that the current passes different sample regions at different frequencies. Several effects such as additional semicircles in the complex impedance plane or non-ideal impedance arcs result from frequency-dependent current lines and cannot be understood in terms of serial (quasi-one-dimensional) equivalent circuit models. In particular, it is discussed that (a) one and the same transport process can be reflected in two or even more impedance arcs and (b) that an arc in the impedance plane can depend on more than one transport process (e.g. charge transport in the bulk and across grain boundaries) even if the dielectric relaxation times of the corresponding sample regions (e.g. bulk and grain boundary) are distinctly different.

Keywords: impedance spectroscopy; grain boundary; electrode; relaxation process

Kinetics of Oxygen Incorporation into SrTiO3 Investigated by Frequency-Domain Analysis by S. F. Wagner; W. Menesklou; Th. Schneider; E. Ivers-Tiffée (pp. 645-651).
The kinetics of oxygen incorporation are of fundamental importance for an application of acceptor doped strontium titanate as a resistive-type oxygen sensor. The electrical conductance of the sample depends on the ambient oxygen partial pressure pO2 due to oxygen exchange between gas phase and solid state which leads to a flow of charge carriers. The kinetics of the incorporation process can be separated into two steps: the oxygen surface transfer and the subsequent bulk diffusion of oxygen vacancies. The rate of the slower step determines the kinetics of the overall incorporation process and thus the sensor’s response behavior.A method for the investigation of the kinetic behavior is presented which is based on a frequency-domain analysis. In the underlying model, a SrTiO3 single crystal is exposed to a harmonically modulated pO2. This leads to a modulation of the sample’s electrical conductance. By way of calculation, it is shown that the shape of the frequency response clearly allows to distinguish whether the kinetics of oxygen incorporation are determined either by bulk diffusion or by surface transfer.The experimental validation of this model is demonstrated by investigations performed on slightly acceptor doped SrTiO3 single crystals of various thicknesses in a kinetic measurement setup at different temperatures.

Keywords: strontium titanate; resistive-type oxygen sensor; kinetics; surface transfer; bulk diffusion

Cathodic Polarization Study on Doped Lanthanum Gallate Electrolyte Using Impedance Spectroscopy by Wenquan Gong; Srikanth Gopalan; Uday B. Pal (pp. 653-661).
The perovskite electrolyte La1 − xSrxGa1 − yMgyO3 (LSGM) has received a lot of interest in recent years after it was first reported to have significantly higher oxygen-ion conductivity than conventional YSZ. A very large fraction of the total polarization losses in SOFC is known to occur at the electrode-electrolyte interfaces manifesting itself as the kinetic barrier to charge-transfer reactions. AC complex impedance spectroscopy studies were conducted on symmetrical cells of the type [air, electrode/LSGM electrolyte/electrode, air] to measure the charge-transfer polarization at the cathode-electrolyte interfaces. The electrode materials were slurry-coated on both sides of the LSGM electrolyte support. The cathode materials investigated in this study include La1 − xSrxMnO3(LSM), LSCF (La1 − xSrxCoyFe1 − yO3) and a two-phase particulate composite consisting of LSM +doped-lanthanum gallate (LSGM). Symmetrical cell studies were also performed on SOFC anode materials. The principal anode material investigated in this study is a porous composite of Ni-gadolinium doped ceria (GDC). It is well known that Ni reacts with the state-of-the-art LSGM anode material. Thus our approach is to use a barrier layer of GDC between the Ni-GDC anode and the LSGM electrolyte. This paper will focus on the influence of microstructure, electrode composition, electrode thickness, interfacial compatibility and electrode processing conditions on cathode and anode polarization.

Keywords: solid oxide fuel cell; cathode; anode; polarization; lanthanum gallate; perovskite; electrolyte

Electrochemical Characterization of Thin Films for a Micro-Solid Oxide Fuel Cell by J. L. Hertz; H. L. Tuller (pp. 663-668).
One of the first technological benchmarks towards the realization of a micro solid oxide fuel cell is the production of thin film structures with adequate electrochemical properties. This paper describes the deposition of thin film yttria-stabilized zirconia electrolytes and lithographically patterned platinum and gold electrodes. By using conventional, ultraviolet lithography, electrode patterns were produced with features sizes as fine as 15 μm, enabling a more direct investigation into the role of the triple phase boundary. Impedance spectroscopy measurements show three arcs, ascribed to the grain, grain boundary and electrode processes, and an offset on the real axis due to the leads. The high frequency arc, ascribed to the ohmic resistance of the YSZ electrolyte, exhibited an activation energy of 1.0 eV, while the intermediate frequency arc, attributed to blocking grain boundaries, exhibited an activation energy of 0.69 eV. The low frequency, non-ohmic arc was found to be highly dependent upon the electrode material and exhibited activation energies of 0.91 eV for gold electrodes and 0.77 eV for platinum electrodes. The electrode impedances for different sample geometries were similar when normalized to the triple phase boundary length.

Keywords: solid oxide fuel cell; impedance spectroscopy; microfabrication

Multi-Fuel Capability of Solid Oxide Fuel Cells by K. Sasaki; K. Watanabe; K. Shiosaki; K. Susuki; Y. Teraoka (pp. 669-675).
One of the most attractive features of solid oxide fuel cells is their flexibility for fuels so that internal reforming and/or simple external reforming may be possible. In this study, equilibria in various possible fuel gases are considered, and C–H–O diagrams are constructed. Power generation characteristics for these fuels are measured and compared with those for simulated reformed gas in equilibrium compositions. We have succeeded to demonstrate direct-alcohol SOFCs for e.g. methanol, ethanol, and propanol. Mixtures of CH4 and CO2 are used as simulated biogas, and iso-octane (C8H18) and n-dodecane (C12H26) are highlighted as simulated gasoline and kerosene, respectively. Influence of fuel impurities on power generation characteristics is also discussed.

Keywords: SOFC; anode; fuel gas compositions; alcohols; higher hydrocarbons; biogas

Interaction between Water and Ceria-Zirconia-Yttria Solid Solutions by N. Sakai; K. Yamaji; Y. P. Xiong; H. Kishimoto; T. Horita; H. Yokokawa (pp. 677-682).
We have investigated the water solubility, oxygen isotope diffusivity, and oxygen surface exchange coefficient in a humid atmosphere of the system {(CeO2)x(ZrO2)1−x}0.8(YO1.5)0.2 (x = 0–1) by using isotope exchange and secondary ion mass spectrometry (SIMS). The deuterium ion (2D) was detected from the {(CeO2)x(ZrO2)1−x}0.8(YO1.5)0.2 polycrystals which were annealed in D2O containing atmosphere. The solubility of deuterium in the polycrystals increased with the cerium content (x). The oxygen exchange rate constant (α) in air at T = 973 K shows a maximum at x = 0.2–0.3, which can be correlated to the compositional dependence of electronic conductivity of {(CeO2)x(ZrO2)1−x}0.8(YO1.5)0.2. The effect of water on the surface exchange rate constant was more significantly observed for the samples with higher content of cerium x > 0.6.

Keywords: ceria; zirconia; diffusion; water vapor; surface reaction

Characterization of Pr- and Sm-Doped Ce0.8Gd0.2O2 − δ by R. Torrens; N. M. Sammes; G. Tompsett (pp. 683-689).
Ce0.8Gd0.2 − yPryO2 − δ (y = 0–0.05) and Ce0.8Gd0.2 − ySmyO2 − δ (y = 0–0.05) SOFC electrolyte materials were prepared using a reverse-strike co-precipitation method. The resulting powders were characterized using X-ray diffraction, Raman spectroscopy and electrochemical methods. XRD confirmed a single fluorite phase for all compositions. Increased Pr and Sm dopant level was found to cause a shift in the peak positions to slightly higher d-spacings with respect to pure CeO2. The experimental lattice parameter was calculated using the peak positions determined from the XRD patterns. Raman spectra, for all dopant levels, showed two distinctive band features, namely a band at ca. 460 cm− 1 and a broader, weaker band at ca. 570 cm− 1. As the proportion of praseodymia dopant is increased, the oxygen vacancy band shifts to a slightly lower wavenumber and decreases in relative intensity to the F2g band. However, an anomaly occurs at the 1% dopant level; the oxygen vacancy band having a very low relative intensity. The conductivity was determined using AC—impedance spectroscopy, and it was found that for praseodymia, a maximum is observed at y = 0.015, while for samaria the maximum is observed at y = 0.01. It is also observed that the ionic conductivity for the samaria doped samples are lower than those of the praseodymia doped samples.

Keywords: Ce0.8Gd0.2−yPryO2−δCe0.8Gd0.2−ySmyO2−δ electrolytes; X-ray diffraction; Raman spectroscopy; AC impedance

Microstructural Features of RF-sputtered SOFC Anode and Electrolyte Materials by Gerardo Jose La O; Joshua Hertz; Harry Tuller; Yang Shao-Horn (pp. 691-695).
Thin-film samples of yttria-stabilized zirconia (YSZ), nickel oxide (NiO)-YSZ, and YSZ/nickel (Ni)-YSZ bilayer were fabricated by RF-sputtering. The single YSZ layer and YSZ/Ni-YSZ bilayer samples were annealed while the NiO-YSZ layer remained as-deposited. Cross-section transmission electron microscopy (TEM) samples of these thin-films were then prepared, which allowed detailed chemical and structural characterization of these thin-films on the nanometer-scale. Both YSZ and NiO-YSZ layers were fully dense and exhibiting equiaxed grain morphologies. Selected area electron diffraction (SAED) showed the YSZ crystal structure to be predominantly cubic in the annealed samples and amorphous in the as-deposited NiO-YSZ sample. It was found that YSZ film was 70 nm thick and dense, with equiaxed grains ranging from 12–20 nm. Surface roughness of the YSZ in the bilayer fell in the range of 5–20 nm. The Ni-YSZ film in the bilayer was 230 nm thick and porous, which consisted of columnar grains 13–75 nm in length and 9–22 nm in width. The bilayer sample showed no delamination or cracking along the YSZ/Ni-YSZ interface. It is believed that the nano-sized grains, minimal surface roughness and thin layers found in these films are desirable microstructural features for the anode and electrolyte in micro-solid oxide fuel cells (SOFCs). Correlation between microstructural features and electrochemical performance will be reported in a separate study.

Keywords: SOFC; microstructure; transmission electron microscopy; thin-film; sputtering

On the Relationship Between the Grain Size and Gas-Sensitivity of Chemo-Resistive Metal-Oxide Gas Sensors with Nanosized Grains by Avner Rothschild; Yigal Komem (pp. 697-701).
In this work we elaborate the effect of grain size on the sensitivity of chemo-resistive metal-oxide gas sensors with nanosized grains. The effective carrier concentration in nanocrystalline SnO2 sensors with various grain sizes is calculated as a function of the surface state density. This involves numerical computation of the charge balance equation (i.e., the electroneutrality condition) using approximated analytical solutions of Poisson’s equation for small spherical crystallites. The calculations demonstrate a sharp decrease in the carrier concentration when the surface state density reaches a critical value that corresponds to a condition of fully depleted grains, namely when nearly all the electrons are trapped at the surface. Assuming that the variations in the surface state density are induced by surface interactions with the gas phase, these calculations enable to simulate the response curves of nanocrystalline SnO2 gas sensors. The simulations show that the conductivity increases linearly with decreasing trapped charge densities, and that the sensitivity to the gas-induced variations in the trapped charge density is proportional to 1/D, where D is the average grain size.

Keywords: gas sensors; metal-oxides; grain size; nanocrystalline; SnO2

Development of Resistive Oxygen Sensors Based on Cerium Oxide Thick Film by Noriya Izu; Woosuck Shin; Ichiro Matsubara; Norimitsu Murayama (pp. 703-706).
It is important to shorten the response time of resistive oxygen sensor in order to reduce harmful emission of automobiles. The diffusion and surface reaction theory tells us that reducing particle size leads to shortening the response time. The fine ceria powder was prepared a by new precipitation method and the oxygen sensors having ceria thick film with the particle size of 120 nm were fabricated using fine ceria (cerium oxide) powder. The thick film exhibited good adhesion to alumina substrate. The value of n in RP(O2)1/n at 1073 and 1173 K were 6.2 and 6.4 in the oxygen partial pressures range from 10− 13 to 105 Pa, respectively. The response time for the sensor was 22 and 12 ms at 1073 and 1173 K, respectively. The sensor fabricated in this study showed fast response.

Keywords: oxygen gas sensor; ceria; fast response; precipitation method; carbon powder

Selective Gas Detection of SnO2-TiO2 Gas Sensors by Won Jae Moon; Ji Haeng Yu; Gyeong Man Choi (pp. 707-713).
The composite, consisting of two materials with different sensing temperatures, may show the selectivity for a particular gas. In this study, the microstructural and compositional effects on the electrical conductivity and the CO and the H2 gas sensing properties of SnO2-TiO2 composites were examined. SnO2-TiO2 composites in entire (0–100 mol%) composition range were fabricated in the form of porous pellet by sintering at 800C for 3 h. The effects of CuO-coating (or doping) on the electrical conductivity and the sensing properties to 200 ppm CO and H2 gases were examined.With CuO-coating, SnO2-TiO2 composites showed the increased sensitivity to CO gas and a large difference in the sensing temperatures between CO and H2 gases. As a result, CuO-coated SnO2-TiO2 composites showed the selectivity for CO gas between 100C and 190C and the selectivity for H2 gas between 280C and 380C.

Keywords: SnO2TiO2CuO; composite; sensitivity; selectivity

High Temperature Schottky Barrier on n-Type SrTiO3 and Its Sensitivity to Ambient Gases by T. Kawada; T. Ichikawa; L. Q. Han; K. Yashiro; H. Matsumoto; J. Mizusaki (pp. 715-719).
Metal or oxide electrodes (Pt, Au, Ag, (La, Sr)CoO3) were deposited on single crystals of 0.02 mol% Nb doped SrTiO3 by pulsed laser deposition. Current-voltage and capacitance-voltage responses were measured using three-terminal electrode configuration. Under high oxygen partial pressures, clear rectification behaviors were observed. Diffusion model well explained the current vs. voltage relationship with ideality factors close to unity. The barrier height varied reversibly with oxygen partial pressure, and was almost independent of the electrode materials, which suggested that the Fermi level at the interface was pinned by the surface states. The origin of the surface states was discussed in terms of oxygen adsorption or oxidative formation of metal vacancies around the surface. Chemical interaction between the surface and oxygen and resulting cation rearrangement was concluded to play an important role from the long stabilization time on oxygen partial pressure change. The water vapor pressure dependence of the barrier height was also explained by competitive adsorption of oxygen and water.

Keywords: SrTiO3Schottky barrier; high temperature; water; interface

Gas Sensing with Perovskite-like Oxides Having ABO3 and BO3 Structures by V. Lantto; S. Saukko; N. N. Toan; L. F. Reyes; C. G. Granqvist (pp. 721-726).
WO3 and LaFeO3 are considered as example oxides in gas sensing, respectively of perovskitelike BO3 and ABO3 oxide groups, the structural chemistry of which is based on corner-sharing octahedral oxygen networks where transition metal cations B occupy the octahedral cages of oxygen anioins. WO3 is an n-type semiconductor and many magnetic perovskites like LaFeO3 are p-type semiconductors. There is a great flexibility inherent in the structure of both oxide groups which gives a lot of possibilities for structure engineering of the oxides for gas-sensing applications, e.g., by a temperature treatment or by modifying with impurity atoms. We have used here a high-temperature process, advanced reactive gas deposition, to produce nanoparticle thick films of WO3 with the metastable tetragonal crystal structure at low temperatures up to 300–400C, and sol-gel citrate method to produce nanocrystalline LaFeO3 powder as pure and modified with Sr and Mg, respectively.

Keywords: gas sensor; WO3LaFeO3nanocrystalline; reactive gas deposition; sol-gel

Electrochemical Removal of NOx by Scandium Doped Zirconia Membrane Reactor with Ceria Buffer Layer by Hae Jin Hwang; Ji-woong Moon; Masanobu Awano (pp. 727-732).
We developed a multi-layered LSCF/GDC/ScSZ/GDC/LSCF membrane reactor for NO decomposition, and its electrochemical properties and NO decomposition behaviors were investigated. A GDC buffer layer was able to prevent the harmful interfacial reaction between LSCF and ScSZ, mainly, strontium zirconate, which was observed in LSCF/ScSZ/LSCF membrane reactor. As a result, the electrode polarization resistance of the membrane reactor was significantly decreased in the multi-layered membrane reactor with the GDC buffer layer between the ScSZ electrolyte and LSCF electrode. From SEM observations, it was found that the GDC buffer layer deposited by a pulsed-laser deposition (PLD) process, was dense and showed homogeneous microstructure. Constructing the multi-layered membrane reactor could considerably reduce the consuming electrical power for NO decomposition.

Keywords: NO decomposition; LSCF; GDC; electrolyte; buffer layer; pulsed laser deposition; membrane reactor

Poisoning of Temperature Independent Resistive Oxygen Sensors by Sulfur Dioxide by Frank Rettig; Ralf Moos; Carsten Plog (pp. 733-738).
Sulfur dioxide strongly affects temperature independent resistive oxygen sensors of SrTi1-xFexO3-δ. Time dependent sensor deterioration was investigated for lanthanum doped SrTi0.65Fe0.35O3-δ (STF35). Parameters were sulfur dioxide concentration, oxygen partial pressure, temperature, and sensor morphology. The sensor poisoning consists of two steps. At lower temperatures sulfur dioxide adsorption and sulfate ion formation at the grain surface is suggested. At higher temperatures the material decomposes into SrSO4, iron depleted STF35, and Fe2TiO5.

Keywords: exhaust gas sensor; resistive oxygen sensor; sulfur poisoning; titanates; perovskites

Microvaristors: Functional Fillers for Novel Electroceramic Composites by F. Greuter; M. Siegrist; P. Kluge-Weiss; R. Kessler; L. Donzel; R. Loitzl; H. J. Gramespacher (pp. 739-744).
Microvaristors are tiny electroceramic particles, which have highly nonlinear, voltage controlled electrical transport properties and can be used as active fillers in a variety of insulating matrix materials for functional composites. Due to the internal grain boundary structure, each individual microvaristor particle shows an IV-characteristics similar to the one known from bulk ceramics, except for the scaled down switching voltage. By controlling the material formulation, the particle morphology and the sintering conditions the switching characteristics of microvaristors can be tailored for specific applications.In the present paper the basic properties of ZnO microvaristors are described and it is shown how they impart their nonlinearity to the composite. A single microvaristor can withstand surprisingly high current loadings, without major changes in their electrical properties. Combined with the high manufacturing flexibility known from polymer processing, the varistor composites can be used for new solutions in overvoltage protection or control of electrical fields.

Keywords: microvaristor; nonlinear resistor; functional composite; overvoltage protection

Mechanical Activation of Spinel and Pyrochlore Phases in ZnO Based Varistors by C. Gómez-Yáñez; J. Velázquez-Morales; E. G. Palacios (pp. 745-750).
Mixtures of ZnO, Sb2O3 and Bi2O3 powders corresponding to the stoichiometric compositions of Zn7Sb2O12 (spinel) and Zn2Bi3Sb3O14 (pyrochlore) were milled in a shaker mill (SPEX) up to 180 minutes. The influence of the mechanical activation of the powders, as a result of the milling, was determined by Differential Thermal Analysis, Thermogravimetric Analysis and X-ray Diffraction. Additionally, in order to compare to commercial recipes the mixture ZnO + 2.7 wt% Sb2O3 + 4.5 wt% Bi2O3 was milled in a shaker mill up to 180 minutes. Varistor devices were fabricated with both milled and unmilled mixtures. The devices were characterized by I-V studies, Scanning Electron Microscopy and X-ray Diffraction. Mechanical activation on the system ZnO-Bi2O3-Sb2O3 produced a chemical reaction and amorphization in the powder mixture. The weight loss due to volatilization of Bi2O3 and Sb2O3 that occurrs in both ZnO-Sb2O3 and ZnO-Sb2O3-Bi2O3 systems at temperatures below 1200C is reduced by milling the powder mixtures.

Keywords: mechanical activation; varistors; ZnO; electroceramics

The Microstructure and Electrical Behavior of TiO2 Varistors Processed by Magnetized Water by Jianying Li; Mohammad A. Alim; Shaohua Luo; Weihua Yao; Zilong Tang; Zhongtai Zhang (pp. 751-757).
A comparative study of the microstructures of two kinds of TiO2 based varistor materials processed from the slurry using magnetized water and regular deionized water is conducted. The additives in the form of oxides of Nb, Ce, Ca, and Si were used in the recipe. The electrical behavior reveals that the water magnetized at 0.2 T yielded lower varistor voltage while the water magnetized at 0.3 T yielded higher varistor voltage compared to the regular deionized water. A second phase comprising of Ce, Si, and Ti was found in each of these samples. The distribution of second phase was found strongly dependent on the type of water used. Thus, the magnetized water shows influence on the TiO2 varistor microstructures. It apprehended that the application of magnetized water in the general arena of advanced electronic ceramics may bring novel experimental results as demonstrated in the present work.

Keywords: TiO2 ceramics; magnetized water; microstructure; varistors

Bulk Grain Resistivity of ZnO-Based Varistors by A. C. Caballero; D. Fernández Hevia; J. de Frutos; M. Peiteado; J. F. Fernández (pp. 759-763).
We study the temperature dependence of grain resistivity in ZnO ceramic varistors (300–430 K), finding a positive temperature coefficient (PTC). We devise a high-frequency procedure that allow us to obtain the concentration and energy position of the shallow donor. The observed behavior is consistent with a shallow donor approaching complete ionization, and with an electron mobility mainly controlled by lattice (both optical and acoustical) scattering. The impact of this behavior on varistor performance under high-current pulse loads is discussed.

Keywords: varistors; electrical properties; bulk conductivity

Fabrication of SnO2 Particle-Layers using the Electrospray Method and Gas Sensing Properties for H2 by Yuta Matsushima; Tsutomu Yamazaki; Kazuyuki Maeda; Takeyuki Suzuki (pp. 765-770).
The particle layers of SnO2 were prepared using the electrospray pyrolysis method from SnCl2 ethanol solution on the glass substrates heated at 773 K. Pyrex and quartz glass were used for the substrates. The effects of the concentration and the conductivity of the precursor solutions on the morphology and gas sensitivity of the SnO2 layers were investigated. The sensitivity measurements were carried out for 0.5% H2 in synthetic air at the operating temperature of 573 K and that was defined by the resistance ratio of the specimen under synthesized dry-air (Rair) and 0.5% H2 (Rgas), Rair/Rgas. Among the examined concentrations of 1× 10−4, 1× 10−3 and 1× 10−2 mol ⋅ dm−3, the layer prepared at 1× 10−3 mol ⋅ dm−3 exhibited the maximum sensitivity of 20. The particle sizes were 110(30), 160(40), and 150(35) nm in diameter at 1× 10−4, 1× 10−3, and 1× 10−2 mol ⋅ dm−3, respectively. The values in the parentheses indicate the standard deviation of the measured data. On the other hand, the conductivity of the solution exerted no significant influence on the sensitivity, which was adjusted by the addition of dilute hydrochloric acid. The particle size decreased with the conductivity and became 134(30), 105(20) and 87(20) nm in diameter at 7.8, 27.0 and 86.6 μ S ⋅ cm−1, respectively. Under all the conditions the layers had the dendrite-like structure, indicating the in-flight particle formation. The crystallite size was evaluated to be 6 nm from XRD using the Scherrer’s equation. These particles of 87–160 nm was thought to consist of smaller primary particles (crystallites). The Pd doping by 1 wt% to SnO2 enhanced the gas sensitivity by a factor of 4.

Keywords: tin dioxide; gas sensor; electrospray; particle layer; palladium

Praseodymium-Cerium Oxide as a Surface-Effect Gas Sensor by Todd S. Stefanik; Harry L. Tuller (pp. 771-774).
The gas sensing behavior of praseodymium doped cerium oxide (PrxCe1 − xO2 or PCO) has been examined for 0–1000 ppm CO or H2 in a 10% O2 atmosphere at temperatures ranging from 250–350_∘C. Total conductivity as a function of temperature suggests that oxygen diffusion kinetics are slow below approximately 350_∘C. Devices with x = 0.05 and 0.10 show stable, n-type gas sensing response, while those with x = 0.20 exhibit significant drift in sensor output, presumably due to bulk oxygen migration. The response to CO is significantly stronger than that to H2 at 300_∘C, and at 350_∘C the response to H2 is nearly zero, resulting in a CO-selective gas sensing element. Suggestions for the source of selectivity in PCO are presented.

Keywords: selectivity; sensitivity; CO sensing

Thin Film Praseodymium-Cerium Oxide Langasite-Based Microbalance Gas Sensor by Huankiat Seh; Harry L. Tuller; Holger Fritze (pp. 775-778).
Langasite (La3Ga5SiO14) has proven to be a viable piezoelectric material for use in high temperature bulk acoustic wave gas sensors. To detect changes in pO2 under oxidizing conditions, we utilized a PLD deposited Pr0.15Ce0.85O2 − δ film as the gas sensitive layer given its ready reduction under these conditions. The sensor was operated at 600C and showed strong sensitivity to changes in oxygen partial pressure, saturating at a frequency shift of −360 Hz below 1%O2/Ar (pO2 = 103 Pa). The frequency shift was calculated to be too large to be solely accounted for by the corresponding change of mass in the PCO film. Stress induced by dilation of the PCO lattice upon reduction is viewed as being a likely source of sensor sensitivity.

Keywords: langasite; gas sensor; microbalance

Defect Chemical Modeling of (La, Sr)(Co, Fe)O3 − δ by Edith Bucher; Werner Sitte (pp. 779-784).
Different defect chemical models for calculation of ionic and electronic defect concentrations are discussed regarding their applicability to transition metal perovskite-type oxides (ABO3 − δ) with large ranges of oxygen non-stoichiometry. A point defect model, which allows simultaneous consideration of three different B-site species concentrations as a function of the oxygen partial pressure is compared to a simple point defect model, considering only two different B-site species. Additionally, a model assuming electrons/holes as negative resp. positive electronic charge carriers is presented. Further, models involving association of point defects in different complexes are discussed. Examples are given for fits of experimental data of La1 − xSrxBO3 − δ (x = 0.6, B = Fe, Co) to selected models in the temperature range 700–900_∘C and oxygen partial pressures 10− 5 < pO2/atm < 1.

Keywords: perovskite-type oxides; oxygen non-stoichiometry; defect chemical modeling

Co-Doping Effect of Mn and Y on Charge and Mass Transport Properties of BaTiO3 by Chung-Eun Lee; Sun-Ho Kang; Dong-Sook Sinn; Han-Ill Yoo (pp. 785-791).
BaTiO3-based multilayer-ceramic capacitors (MLCC) using base metal (Ni) electrodes normally contains Mn and Y each approximately on the order of 0.5 mol%. It is only empirically known that the co-doping of Y and Mn facilitates sintering with the base-metal electrodes as well as improves the device performance and life time. In order to understand the effect of the co-doping, we have measured the electrical conductivity and chemical diffusivity on polycrystalline BaTiO3 that is co-doped with Y and Mn each by 0.5 mol% against oxygen partial pressure at elevated temperatures. It is found that while the n-type conductivity in reducing atmospheres (e.g., Po2 < 10− 6 atm at 1000C) remains similar to that of undoped or acceptor-doped BaTiO3, its p-type conductivity in oxidizing atmospheres (e.g., Po2 > 10− 6at 1000C) is remarkably suppressed compared to the latter. The chemical diffusivity is also similar to that of the latter in magnitude (e.g., 10− 2−10− 5 cm2/s at 1000C), but its trend of variation with oxygen partial pressure is rather opposite. These variations of the conductivity and chemical diffusivity are mainly attributed to Mn ions changing their valence from +2 to +3 to +4 with increasing oxygen partial pressure. It is explained from a defect-chemical view why the codoping of fixed-valent donor (Y) and variable-valent acceptor (Mn) has been practiced in MLCC processing.

Keywords: MLCC; BaTiO3acceptor-donor codoping; defect structure; chemical diffusivity

Investigation of Semiconducting Barium Titanate Ceramics by Oxygen Coulometry by Hans Theo Langhammer; Miha Drofenik; Karl-Heinz Felgner; Hans-Peter Abicht (pp. 793-797).
Donor-doped BaTiO3 ceramics (0–0.6 mol% Nb) were investigated during the sintering process at an oxygen partial pressure of 2.4 Pa and at a maximum temperature of 1430C. The occurring oxygen exchange with the ambient atmosphere was monitored quantitatively by oxygen coulometry. The coincidence between the grain growth behavior and the occurrence of distinct oxygen release peaks during the anomalous grain growth reveals that significant amounts of the donor are incorporated and charge-compensated by electrons only under the conditions of the anomalous grain growth. Quantitative analysis of the coulometric data shows that at a doping level of 0.2 mol% nearly all donors are charge-compensated by electrons. With increasing Nb concentration also Ti vacancies gradually begin to serve for compensation. At 0.5 mol% Nb their influence reaches 70 % of the electronic compensation.

Keywords: barium titanate; donor-doped; defect chemistry; sintering; oxygen coulometry

Nonstoichiometry and Defect Chemistry in Praseodymium-Cerium Oxide by Todd S. Stefanik; Harry L. Tuller (pp. 799-803).
Praseodymium cerium oxide (PrxCe1 − xO2 − δ) is a mixed ionic-electronic conductor with high levels of nonstoichiometry under oxidizing conditions resulting from reduction of Pr4 + to Pr3 +. Coulometric titration measurements performed on (PrxCe1 − xO2 − δ) with x = 0.2 are generally consistent with those derived from electrical conductivity measurements. Nevertheless, a somewhat larger degree of nonstoichiometry measured via coulometric titration implies that non-charged defect species may be significant in the system.

Keywords: electrical conductivity; coulometric titration; defect modeling

Defect Chemistry of Y Doped BaTiO3 by Ji Hun Jeong; Myung Gyu Park; Young Ho Han (pp. 805-809).
Defect chemistry of Y doped BaTiO3 was investigated as a function of the Ba/Ti ratio. When the Ba/Ti ratio was greater than unity, Y3 + was substituted for the normal Ti site and the equilibrium conductivity showed a strong evidence of acceptor-doped behavior. With the Ba/Ti ratio < 1, Y3 + was substituted for the Ba site and the equilibrium conductivity showed donor-doped behavior. In the case excess Y2O3 was added to the stoichiometric BaTiO3(Ba/Ti = 1), the conductivity profile showed a donor-doped behavior at low concentrations (< 1.0 mol%), whereas, at higher donor levels (> 2.0 mol%), the equilibrium conductivity minimum shifted toward lower Po2, indicating acceptor doped behavior.

Keywords: BaTiO3Y2O3conductivity; nonstoichiometry; solubility

A/B-Ratio and Transport Properties of (La0.85Sr0.15)sCoO3−δ Perovskites by Martin Sòaard; Peter V. Hendriksen; Finn W. Poulsen; Mogens Mogensen (pp. 811-816).
The perovskites (La0.85Sr0.15)0.98CoO3 − δ and (La0.85Sr0.15)1.00CoO3 − δ have been investigated using x-ray diffraction (XRD), scanning electron microscopy (SEM) and electrical conductivity relaxation (ECR). This system was chosen in order to investigate the influence of cation vacancies on the transport properties in the materials. From ECR-measurements it is concluded that no difference in the chemical diffusion coefficient for oxide ions between the two samples can be found. The activation energy for the chemical diffusion coefficient has been found to be 107 ± 5 kJ mol− 1. However, the surface exchange coefficient differs between the two samples. The Co-rich sample has a significantly higher surface exchange coefficient than the A/B-stoichiometric sample. For both samples the surface exchange coefficient was almost independent of the temperature. At all temperatures the Co-rich sample had a significantly higher electrical conductivity. The difference in electrical conductivity between the two samples diminished when going to higher temperatures. Both materials can be assigned to a single phase hexagonal perovskite. An annealed sample of (La0.85Sr0.15)0.98CoO3 − δ did however contain an unidentified secondary phase on the surface.

Keywords: A/B-ratio; oxide ion conductivity; electrical conductivity relaxation; cation vacancies; perovskites; lanthanum strontium cobaltites

Preparation and Electrical Properties of Dense Ceramics with NASICON Composition Sintered at Reduced Temperatures by O. Schäf; A. Weibel; P. L. Llewellyn; P. Knauth; N. Kaabbuathong; M. L. Di Vona; S. Licoccia; E. Traversa (pp. 817-823).
A reduced temperature route is explored for the preparation of ceramics with NASICON composition. The procedure includes sol-gel synthesis, Sample Controlled Thermal Analysis of the precursor powders and hot-pressing the powders under 0.3 GPa and at temperatures between 600 and 900C. It is shown that ceramics with densities around 90% can be obtained by this route. Electrical conductivity values and activation energies are determined and discussed.

Keywords: ionic conductors; hot-pressing; thermal analysis; electrical conductivity

Direct Oxidation of an Alloy Precursor Complete Oxidation of Bismuth and Zinc Powder by Renaud Metz; Celine Machado; Mehrdad Hassanzadeh; Ramon Puyane (pp. 825-827).
This work reports on a process (DOPA: Direct Oxidation of a Precursory Alloy) of preparation of ceramics used as varistors for the electric protection against power surges. This new route has been applied for the production of ZnO varistors doped with Bi2O3, Sb2O3 and other oxides. One important stage of this process is the total conversion of an alloy into the corresponding mixed oxide. We have reported here the studies of the full conversions metal-ceramic powders of the main components of these varistors: zinc and bismuth.

Keywords: zinc; bismuth; oxidation; ceramic-metal conversion

Effect of B2O3 Nano-Coating on the Sintering Behaviors and Electrical Microwave Properties of Ba(Nd2 − xSmx)Ti4O12 Ceramics by Li-Chun Chang; Bi-Shiou Chiou (pp. 829-837).
Ba(Nd0.8Sm0.2)2Ti4O12 ceramics prepared by conventional solid-state sintering have a dielectric constant of about 80 and a nearly zero temperature coefficient of resonant frequency; however, the sintering temperature is above 1350_∘C. Doping with B2O3 (up to 5 wt%) promotes the densification and dielectric properties of BNST ceramics. It is found that coating BNST powder with thin B2O3 layer of about 180 nm reduces the sintering temperature to below 1020_∘C. The effects of B2O3 nano-coating on the dielectric microwave properties and the microstructures of BNST ceramics are investigated. Ninety-six percent of theoretical densities is obtained for specimens coated with 2 wt% B2O3 sintered at 960_∘C and the samples exhibit significant (002) preferred orientation and columnar structure.

Keywords: oxide; microwave dielectric properties; ceramics; liquid phase sintering

Influence of Growth Temperature on Surface Morphologies of GaN Crystals Grown on Dot-Patterned Substrate by Hydride Vapor Phase Epitaxy by Hai-Ping Liu; In-Gann Chen; Jenq-Dar Tsay; Wen-Yueh Liu; Yih-Der Guo; Jung-Tsung Hsu (pp. 839-846).
This paper studies the influence of growth temperatures in the range 825 to 1050_∘C on the surface morphologies of GaN crystals grown on a SiO2 dot-patterned substrate using Epitaxy Lateral Overgrowth (ELO) and Hydride Vapor Phase Epitaxy (HVPE) techniques. A lower growth temperature of 850_∘C prompts the formation of GaN hexagonal pyramidal crystals with a higher fraction of {1 ${ar 1}$ 01}}(0001) facet areas than those grown at high temperatures (>1000∘C). In a subsequent coalescent (or lateral growth) process, a high temperature of 1050∘C is applied to the original GaN hexagonal pyramidal crystals, and the morphologies of the GaN layers are inspected. It is established that the original {1 ${ar 1}$ 01} faceted morphology of the hexagonal pyramids changes to an irregularly-shaped surface comprising {1 ${ar 1}$ 01}, {11 ${overline 2}$ 2} and high index facets, and that the nature of the surface morphology is influenced by the growth time and the application (or not) of Ga precursor support. Hence, the results show that the coalescence and planarization of the GaN layer can be controlled through an appropriate specification of the process parameters. At low temperatures in the region of 850∘C, high index facets are observed on the tops of a small percentage of the hexagonal GaN columnar crystals. It is proposed that this phenomenon is caused by a reduction in the surface diffusion length of the precursors, e.g. NH3 and GaCl, at lower temperature, which in turn, reduces the probability of desorption and increases the lifetime.

Keywords: GaN; HVPE; ELO; hexagonal column

Phase Stability of Tungsten-Bronze-Structured KLN Ceramics: Effect of Excess Nb2O5 by Chul-Young Jang; Joon-Hyung Lee; Jeong-Joo Kim; Sang-Hee Cho; Hee Young Lee (pp. 847-850).
The effect of excess Nb2O5 on the phase stability of tungsten-bronze-structured K3Li2Nb5O15 (KLN) ceramics was studied. Stoichiometric KLN ceramics are not obtained as a single phase and second phases of KNbO3 and Li3NbO4 were observed. Additionally, stoichiometric KLN is difficult to sinter. In Nb-rich compositions, the second phase disappeared and a single KLN phase was obtained. This phase development behavior, that is, the phase stability of the KLN, was analyzed from the viewpoint of the electrostatic potentials of ions. The calculated Madelung energy of the completely filled stoichiometric KLN was unstable, while Nb-rich compositions showed much reduced Madelung energy, indicating that the ions were stabilized electrostatically. Enhanced sinterability in Nb-rich compositions is also discussed.

Keywords: tungsten bronze structure; KLN; Madelung energy; phase stability

Phase Transformation Behavior of Nanocrystalline ITO Powders during Heat-Treatment: Oxygen Partial Pressure Effect by Youn-Gon Park; Kyung-Han Seo; Joon-Hyung Lee; Jeong-Joo Kim; Sang-Hee Cho; CHARLES J. O’Conner; Jai-Sung Lee (pp. 851-855).
Nanocrystalline indium tin oxide (ITO) powders with different tin contents ranging from 0 to 8 at% were prepared by a coprecipitation process. A mixture of rhombohedral and cubic structured nanocrystalline ITO powders was obtained, and the amount of the rhombohedral ITO increased as the content of Sn increased. During heat-treatment the rhombohedral ITO was transformed to cubic around 900C. The phase transformation behavior of the powders was examined as a function of oxygen partial pressure. When the rhombohedral ITO powder was heat-treated in a low oxygen partial pressure (nitrogen gas) atmosphere the phase transformation was accelerated and this acceleration can be attributed to the formation of oxygen vacancies that accelerate atomic transport in the rhombohedral ITO.

Keywords: phase transformation; nanocrystalline powder; ITO; oxygen partial pressure

Effect of Nano-Scale Additions on the Enhancement of Superconductivity in Y-Ba-Cu-O Materials by Shih-Yun Chen; In-Gann Chen; Ping-Chi Hsieh; Maw-Kuen Wu (pp. 857-863).
The coherence length of Y-Ba-Cu-O superconductor is in the nano-meter range, therefore, nano-scale additions can be used to increase the number of effective pinning centers in top-seed melt-growth (TSMG) Y-Ba-Cu-O single grain materials. Different kinds of nano-scale additions: Y2O3, and Y2BaCuO5 (Y211) were mixed with precursor powders (YBa2Cu3O7 + Y2BaCuO) followed by TSMG process in air. SEM and TEM were used to investigate the size and morphology of the 211-particles as well as the distribution of defects (e.g. dislocations) in the matrix. It was found that the size of 211-particles was slightly reduced in nm Y2O3 doped samples, and sub-micro 211-particles were observed in nmY211 doped samples. In addition, the critical temperature, Tc, for all samples was similar and independent of the type of addition, while the enhancement of critical current density, Jc(H, T), varied with the types of nano-scale addition. Accordingly, the reactions between the superconductive matrix and different nano-scale additions resulted in different pinning properties. These samples with different nano-scale additions were studied using scaling rule analysis to differentiate their pinning mechanisms. For comparison, the results of SmBCO samples with nano-scale additions are also discussed in this study.

Keywords: superconductivity; nano-scale; additions; pinning mechanism

High Selective deNOx Electrochemical Cell with Self-Assembled Electro-Catalytic Electrode by Takuya Hiramatsu; Sergei I. Bredikhin; Shingo Katayama; Osamu Shiono; Koichi Hamamoto; Yoshinobu Fujishiro; Masanobu Awano (pp. 865-870).
A new family of electrochemical cells for decomposition of NO gas in the presence of excess O2, in which the cathode was covered with mixed oxide layer of NiO and YSZ (electro-catalytic electrode) were designed and investigated. The deNOx properties were increased by microstructural and compositional control of the electro-catalytic electrode. Nano-size Ni grains were self-assembled at NiO/YSZ interfaces by oxidation-reduction reaction of the NiO during the cell operation. In order to use the reduced Ni for NO decomposition reaction effectively, the authors investigated multilayering of the electro-catalytic electrode. Through this process, the adsorption of coexisting O2 was prevented and the deNOx properties of the electrochemical cell were improved.

Keywords: electrochemical cell; NO decomposition; NiO-YSZ ceramics; NiO/YSZ interface; self-assembly

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