Journal of Electroceramics (v.29, #2)

Influence of Al2O3 additive on the dielectric behavior and energy density of Ba0.5Sr0.5TiO3 ceramics by Di Yi; Jiancong Yuan; Haiyang Liu; Yang Shen; Yuan-Hua Lin; Ce-Wen Nan; Xiao Xi; Jinliang He (95-98).
High dense Ba0.5Sr0.5TiO3 ceramics with Al2O3 additives have been prepared by a method combined the sol–gel process and the solid state reaction. Phase compositions, microstructure and dielectric behaviors are investigated systematically. Our experiment results reveal that the Al2O3 additives reduce the dielectric constant slightly and increase the breakdown strength greatly due to the refined microstructure and the formation of the second phases. The estimated energy density of Ba0.5Sr0.5TiO3 ceramics with optimized Al2O3 additives is improved by 1.5 times as compared with that of pure Ba0.5Sr0.5TiO3 ceramics.
Keywords: Dielectric behavior; Breakdown strength; Ba0.5Sr0.5TiO3 ; Energy density

A new double perovskite oxide holmium cadmium zirconate Ho2CdZrO6 (HCZ) is synthesized by solid state reaction technique. The crystal structure has been determined by powder X-ray diffraction (XRD) which shows monoclinic phase at room temperature. The frequency dependent electrical data are analyzed in the framework of conductivity and electric modulus formalisms. The scaling behavior of imaginary electric modulus suggests that the relaxation describe the same mechanism at various temperatures. Nyquist plots are drawn to identify an equivalent circuit and to know the bulk and interface contributions. The conduction mechanism is explained by Mott’s theory. At the high temperature range, conductivity data satisfy the variable range hopping (VRH) model. In this regime, the conductivity of sample obeys Mott’s T 1/4 law indicating 3D charge transport in HCZ compound. High temperature data indicates the formation of thermally activated small polarons.
Keywords: Chemical synthesis; Double perovskite; Electrical properties

This work presents a simple synthetic route to produce WO3 nanofibers functionalized by catalytic Pt and IrO2 nanoparticles and their superior acetone and H2S sensing characteristics, demonstrating the potential use of Pt and IrO2 nanoparticles in applications as sensors of biomarkers of diabetes and halitosis, respectively, in exhaled breath. The individual WO3 fiber, calcined at 500 °C, was composed of small nanoparticles with a size distribution in the range of 30–100 nm. Networks of WO3 fibers exhibited a high surface-to-volume ratio and unique morphologies, thus facilitating efficient gas transport into the entire fiber layers. Pt (4–7 nm) and Ir (4–8 nm) nanoparticles were synthesized by polyol methods and were used as additives to decorate the surface of the WO3 fibers. After a heat treatment, those catalyst particles were partially or fully oxidized to Pt/PtOx and IrO2, respectively. To investigate the advantages of Pt-decorated WO3 fibers (Pt-WO3) and IrO2-decorated WO3 (IrO2-WO3) fibers as acetone (CH3COCH3) and H2S sensing materials, respectively, we carried out gas-sensing measurements in a highly humid atmosphere (RH 75 %) similar to that of an oral cavity. The Pt-WO3 fibers showed a high acetone response (Rair/Rgas = 8.7 at 5 ppm) at 350 °C and a superior H2S response (Rair/Rgas = 166.8 at 5 ppm) at 350 °C. Interestingly, IrO2-WO3 fibers showed no response to acetone, while the gas response to H2S exhibited temperature-insensitivity, which has never been reported in any other work. Thus, the highly selective cross-response between H2S and acetone was successfully achieved via the combination of IrO2 particles on WO3 fibers. This work demonstrates that accurate diagnosis of diabetes and halitosis by sensing exhaled breath can be realized through the use of electrospun WO3 fibers decorated with Pt and IrO2 catalysts.
Keywords: Electrospinning; Nanofibers; Exhaled breath sensors; WO3 ; Pt; IrO2 ; Diabetes; Halitosis

Relaxor ferroelectric behavior of “A” site deficient Bismuth doped Barium Titanate ceramic by T. Badapanda; V. Senthil; D. K. Rana; S. Panigrahi; S. Anwar (117-124).
A site deficient Bi doped BaTiO3 ceramic with general formula Ba1-xBi2x/3TiO3 (x = 0.00, 0.01, 0.025) is prepared by solid state reaction route. The phase formation and structural property of all compositions are studied by X-Ray Diffraction pattern. The pattern reports single phase tetragonal crystal system with space group of P4mm. The XRD study also reveals that bismuth (Bi) replaces “A” site (Ba) of the BaTiO3 pervoskite. The surface morphology of the sintered pellets is studied by scanning electron microscopy which shows a decrease in grain size with an increase in Bi concentration. The temperature and frequency dependent dielectric behaviors of the compositions are studied to show the effect of Bi ion on the “A” (Ba) site of BaTiO3 perovskite. The dielectric constant decreases and transition temperature increases with increase in Bi concentration. Substitution of Bi ion induces diffuse ferroelectric behavior and the degree of diffuseness increases with increase in doping concentration. The ferroelectric behavior is also confirmed by the P-E loop study.
Keywords: X-Ray diffraction; Relaxor ferroelectrics; Diffuse phase transition; P-E loop

Varistor behavior of Mn doped ZnO ceramics prepared from nanosized precursors by M. Ebrahimizadeh Abrishami; A. Kompany; S. M. Hosseini (125-132).
Polycrystalline ZnO doped with MnO, from 2 to 15 mol%, was prepared from nanosized precursors. The effect of Mn doping and sintering temperature on phase evolution, microstructure and V-I characteristics were investigated. SEM images showed that the great merit of using nanoparticles is that the samples with high microstructural uniformity and lower grain size can be achieved. Varistor behavior was observed in all specimens, even in the undoped ceramics due to the oxidation process of zinc interstitial defects at grain boundaries. The electric field versus current density (E-J) curves indicated that the breakdown field Eb increased and the nonlinear coefficient α decreased with the increase in doping level. 2 mol% Mn doped ceramic sintered at 1100 °C exhibited the highest nonlinear coefficient, α = 40. The stability test under DC stress was performed for the undoped ZnO ceramics. ZnO varistor sintered at 1300 °C showed not only high nonlinearity, but also high stability under DC stress.
Keywords: Varistor; ZnO; Mn doping; Nanopowders; Barrier layer model

Effect of Sr content in lead zirconate titanate PZT ceramic system on performance of piezoelectric transformer application were studied. Our experiments provide consistent evaluation of doping strontium amount on piezoelctric coefficients values and final voltage gain and efficiency of piezoelectric transformer. Extreme values of these parameters are preferred for MEMS device effective driving. Modification of ferroelectric materials with isovalent ions, however with the bigger radii than the original atoms, significantly affects their properties. Particularly the electromechanical coefficients of (Pb1-xSrx)(Zr0,70Ti0,30)O3, for mole %’s as x = 0.05, 0.10 and 0.15 ceramics exhibit marked increase, if the PSZT material stoichiometry is near the ferroelectric/relaxor phase boundary. To determine the piezoelectric coefficients, the resonance-antiresonance method was implemented. The results indicated that addition of Sr2+ ions in the amount of 5 mol% in the ceramic structure maximally increased the values of piezoelectric parameter to d31 = 8.2 pC/N and mechanical quality factor Qm = 2902. Finally we demonstrated that in spite of the high piezoelectric coefficients for certain material only the practical examination must be applied in order to draw decisive application conclusions due to the complexity of the double energy conversion in such a specific device as the piezoelectric transformer.
Keywords: MEMS; Piezoelectric Transformer; PSZT; Piezoelectric coefficients

Solid state crystal growth of BiScO3-Pb(Mg1/3Nb2/3)O3-PbTiO3 by Jong Bong Lim; Shujun Zhang; Ho-Yong Lee; Thomas R. Shrout (139-143).
Single crystals 0.26BiScO3-0.25Pb(Mg1/3Nb2/3)O3-0.49PbTiO3 [BSPMNT] have been grown for the first time by the solid-state crystal growth (SSCG) method. A <110> oriented Ba(Zr,Ti)O3 crystal seed was embedded in a matrix of BSPMNT compact which was annealed at high temperatures to induce the single crystal growth. Various fluxes, including Bi2O3, LiBiO2, PbO/LiBiO2, and PbO/Bi2O3, were used and their effects on the microstructure of the annealed compacts and the single crystal growth behavior were investigated. In the annealed samples with PbO/Bi2O3 flux, a considerable single crystal growth occurred at 1050 °C (with thickness on the order of 500–1000 μm), without the formation of abnormally large grains in the matrix. The results were explained in terms of the effect of various fluxes, based on the grain growth theory.
Keywords: Interface; Grain growth; Single crystal

In this study, to develop the optimal composition of ceramics for low loss piezoelectric actuator and ultrasonic motor applications, (K0.5Na0.5)(Nb0.97Sb0.03)O3 + 0.009 K5.4Cu1.3Ta10O29 + 0.1wt%Li2CO3 + xwt%Bi2O3(x = 0 ~ 0.9) lead-free piezoelectric ceramics with a fixed quantity of 0.009 K5.4Cu1.3Ta10O29 (abbreviated as KCT) were manufactured using the conventional solid-state solution processes. The effects of Bi2O3 addition on the dielectric and piezoelectric properties were then investigated. From the X-ray diffraction analysis result the specimens demonstrated orthorhombic symmetry when Bi2O3 was less 0.6 wt%, a pseudo-cubic phase appeared when Bi2O3 was 0.9 wt%. SEM images indicate that a small amount of Bi2O3 addition affect the microstructure. The piezoelectric properties of (K0.5Na0.5)(Nb0.97Sb0.03)O3 ceramics were greatly improved by a certain amount of Bi2O3 addition. Excellent properties of density = 4.54 g/cm3, relative densities = 98.5 %, k p = 0.468, Q m = 1,715 and d 33 = 183 pC/N were obtained with a composition of 0.3 wt% Bi2O3
Keywords: Piezoelectric; Bi2O3 ; KNN; Electromechanical coupling coefficient (k p); Mechanical quality factor (Q m).

This paper describes a simple approach to prepare manganese dioxide/poly(3,4-ethylenedioxythiophene) (MnO2/PEDOT) core/sheath nanowires with a controlled sheath thickness in the range of 2–10 nm. The PEDOT coating on a MnO2 nanowire was performed by immersing the nanowires in an acidic solution containing 3,4-ethylenedioxythiophene (EDOT) monomers. Analysis of open-circuit potential of the MnO2 nanowire electrode in the solution indicates that a galvanic displacement reaction between MnO2 and EDOT is responsible for the synthesis of the MnO2/PEDOT core/sheath nanowire.
Keywords: MnO2 ; PEDOT; Core/sheath; Galvanic displacement; Open-circuit potential

Controlling of crystal size and optical band gap of CdO nanopowder semiconductors by low and high Fe contents by C. Aydın; Omar A. Al-Hartomy; A. A. Al-Ghamdi; F. Al-Hazmi; I. S. Yahia; F. El-Tantawy; F. Yakuphanoglu (155-162).
The CdO:Fe nanopowder semiconductors were synthesized by the sol–gel calcination for the first time. The structural properties of Fe doped CdO samples were analyzed by AFM and XRD measurements. XRD patterns of the pure and Fe-doped CdO samples reveal that the pure and Fe doped CdO nanopowders are polycrystalline of cubic CdO structure. The crystallite size of undoped and Fe-doped CdO samples is changed unsystematically with a regular increase of Fe content. The optical band gaps of Fe doped CdO samples were determined for the first time by diffused reflectance measurements. The optical band gap of the samples is increased with the increase of Fe dopant inside the host matrix (CdO) up to 15 % followed by a decrease in its value. It is evaluated that Fe doped CdO nanopowder semiconductors can be producted by sol–gel calcination for advanced technological applications
Keywords: CdO:Fe; Nanopowders; Sol gel; Optical properties; Diffused reflectance

LaF3 and MgF2 were introduced for the surface modification of an Li[Ni0.5Co0.2Mn0.3]O2 electrode. The rate capability, cyclic performance, phase stability at a high voltage range, and thermal stability of pristine and coated electrodes were characterized. Surface modification with both coating materials, LaF3 and MgF2, enhanced the rate capability and cyclic performance. The LaF3 and MgF2 coatings also suppressed the structural instability during cycling in the high voltage range (4.8–3.0 V). This implies that both fluoride coating layers successfully protected the Li[Ni0.5Co0.2Mn0.3]O2 electrode from the acidic electrolyte. However, the MgF2 coating improved the thermal stability of the Li[Ni0.5Co0.2Mn0.3]O2 electrode more effectively than the LaF3 coating.
Keywords: Surface coating; Electrochemical properties; Cathode; Lithium battery