Papers by Author: He Ping Zhou

Abstract: GdSrCoO3-δ and Gd1-XSrXCoO3-δ (x=0.1~0.5) were synthesized using glycine-nitrate process (GNP). The formation process of perovskite phase and microstructure of powders were characterized using TG-DTA and XRD. All the powders with different doping amounts of Sr2+ on A-site were single-phase solid solutions, and the stable perovskite phase was formed completely after calcination at 1100°C. The crystal structures of the solid solutions transfer to a higher symmetrical perovskite.

Abstract: A citrate gel method was applied to synthesize Ce0.8Sm0.2O1.9 powders by using cerium and samarium nitrates as raw materials and citric acid as complexing agent. It was shown that Ce0.8Sm0.2O1.9 phase was formed when the decomposition of the dried gel completed at 500 °C. The crystallite size of the synthesized powders calcined at 500 °C for 2 h is 5-10 nm. The powders can be easily sintered in air to yield over 97 % relative density at 1250 °C, which is significantly lower than sintering temperature of over 1500°C required by the doped ceria powders prepared via conventional ceramic techniques.

Abstract: The cordierite powders have been synthesized by low temperature combustion technique using urea as fuel, nitrates as oxidizer and silicic acid as silica source. The sintering behavior and crystallization process were investigated. The results showed that the powders could be sintered at a temperature lower than 1000 °C. The μ-cordierite crystallized from glass at first, and then transformed into α-cordierite at higher temperature. The obtained cordierite based glass ceramics at different temperatures have low dielectric constant (4.16 ~ 5.02 at 1 MHz) and low dielectric dissipation factor (≈ 0.003 at 1 MHz) as well as low temperature sintering behavior, which is compatible for electronic packaging.

Abstract: Ba0.5Sr0.5TiO3 (BSTO) ceramics were synthesized by spark plasma sintering (SPS) technique. The phase compositions, microstructure and dielectric properties of BSTO ceramics were investigated. The results indicated that SPS was an alternative sintering technology to synthesize dense BSTO ferroelectric ceramics at low temperature and in a short period.

Abstract: The spark plasma sintering technique was used to fabricate ceramics from Pb(Mg1/3Nb2/3)O3– PbTiO3 ceramic layers which were prepared by tape casting and TGG method used BaTiO3 templates as seeds. During heat treatment, epitaxial grain growth occurred on the BaTiO3 surfaces and formed <001> textured lead magnesium niobate-lead titanate, Pb(Mg1/3Nb2/3)O3-0.325PbTiO3 (PMN-32.5PT) ceramics. The phase compositions and microstructure were investigated. The results indicated that this method was an alternative sintering technology to synthesize dense lead-based relaxor ferroelectric ceramics.

Abstract: <001> textured 0.675Pb(Mg1/3Nb2/3)O3-0.325PbTiO3 (PMN-32.5PT) ceramics were prepared by templated grain growth with micron scale BaTiO3 platelet templates. 0%~7% excess PbO was added to form liquid phase. The influence of liquid phase concentration on the growth of matrix and templated grains was investigated. The growth process was controlled by a dissolution-precipitation mechanism. The templated grain growth was accelerated by the formed liquid phase and resulted in highly textured PMN-32.5PT ceramics.

Abstract: Nanosized Ce0.8Gd0.05Y0.15O1.9 powders were synthesized using glycine nitrate process for use as the electrolyte of intermediate temperature solid oxide fuel cells. The powders were characterized by simultaneous thermogravimetry analysis (TGA) and differential thermal analysis (DTA), X-ray powder diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The XRD pattern indicated that the powders exhibited a single phase with cubic fluorite structure. The TEM studies showed that the calcined powders exhibited an almost spherical morphology and the mean size of the particles was 30nm, which is in agreement with the calculated result of XRD.

Abstract: The effects of Li+ addition on the sintering and microstructural evolution of cordierite were analyzed. As nucleating agent, the Li+ additive decreased the expansion coefficient and dielectric constant. The doping of Li+ was found to block the phase transition from μ-cordierite to α-cordierite and increase sintering temperatures. The effect of Li+ on the activation of cordierite can be attributed to the nucleation of cordierite. Too much Li+ will inhibit the cordierite crystallization and encourage amblygonite crystallization. Cordierite powders were prepared by sol-gel processing.

Abstract: Ceria electrolytes co-doped with Gd3+ and Y3+ (Ce0.8Gd0.2-xYxO1.9) were synthesized by GNP. The crystal structures, lattice parameters and crystallite sizes were determined by XRD. The morphology of the powders was observed by TEM. Sintered at 1250oC for 4 h, all die-pressed ceria pellets achieved densities higher than 95% of theoretical values. The ionic conductivities were measured using AC impedance technique and Ce0.8Gd0.05Y0.15O1.9 showed a higher ionic conductivity than those of other compositions at 500-750oC, indicating that it is an attractive electrolyte material for IT-SOFC.