| It is well known that doped zirconia has a wide range of applications as solid electrolytes in solid oxide fuel cells(SOFCs), oxygen pumps, and oxygen sensors. Doped zirconia with better performances requires high conductivity, thermal shock-resistance, electrical stability, and good mechanical properties. However, the current available YSZ electrolytes have some disadvantages, such as low conductivity, aging at high temperatures, low temperature degradation and high cost, which impede the commercial progress of SOFCs.The preparation of (CaO/Y2O3)-ZrO2 powders, conductivity improvement of Y2O3 doped tetragonal zirconia and its aging at high temperature, the sinterability of (CaO/Y2C>3)-ZrO2 powders studied by impedance spectroscopy, and properties of grain boundary conduction (extrinsic and intrinsic) in Y2O3-ZrO2 samples with grain boundary conduction models are investigated in depth in this dissertation.12mol%CaO-Zr02(12CSZ) and (ZrO2)1-x-y(Y2O3)x(CaO)y(x=0.06, 0.04, 0.02; y=0.03, 0.06, 0.09, abbreviated as 3CYZ, 6CYZ, 9CYZ, respectively.) ultrafine powders are prepared with polymeric complex method. Effects of the molar ratios of critic acid and ethylene glycol to metal ions and calcining temperature of intermediate on crystal structure, grain size and morphology of zirconia have been investigated. When critic acid: metal ions is 4:1 and ethylene glycol: critic acid is 1:5, weakly aggregated cubic 12CSZ and 6CYZ powders are obtained by calcining at 800℃. The grain size of 12CSZ and 6CYZ powders are around 100nm. The 6CYZ powder has a good sinterability. 96.3% TD can be obtained when the powders are sintered at 1550℃ for 4 hours. The empirical formula for calculating lattice parameters of yttria/calcia or yttria doped zirconia is adopted. The lattice parameters of CYZs calculated from this formula are identical with those determined by XRD results. The relationship between lattice parameters and content of zirconia is in good agreement with Vegard rule.Ultrafine 8mol% yttria-stabilized zirconia (8YSZ) is prepared by nonlinearly heating a mixed oxalate precursor. Effects of molar ratio of metal ions to H2C2O4, R and heating treatment methods of precursor on the crystal structure, specific area, grain size and morphology of 8YSZ have been studied. Optimum fabrication parameters are suggested according to the above results, i.e., R equals to 1.2, calcining temperature is in the range of 600-700℃, and nonlinear heating mode is the best method of heat-treatment. The kinetic for grain growth in the calcining process has been investigated. The results indicate that grain growth is controlled by grain boundary or lattice diffusion with higher activation energy (192.92 kJ/mol) when temperature is above 700℃, or controlled by surface diffusion with low activation energy (87.38kJ/mol) when temperature is below 700℃. The powders calcined at 600-700℃ with nonlinear heating mode are weakly aggregated and equiaxial, with a narrow grain size distribution of 70-90nm and good sinterability. The sintering bodies have 96.3% theoretical density after being calcined at 1550℃ for 4 hours. The preparation method is simple and practical without water washing process, which is expected to be employed in industrial production.The electrical properties and aging at high temperature of 3 mol% Y2O3-doped tetragonal zirconia (3 YTZ) have been studied. The effects of addition of alumina and precursor scavenging methods on the electrical properties have been studied for comparison, respectively. Addition of alumina can increase the density of sintered bodies and decrease grain boundary resistance significantly. However, alumina enters the lattice of zirconia from grain boundary, and aluminum ions complex with oxygen vacancies, which results in the increases of grain resistance and the lower concentration of the effective oxygen vacancies. The precursor scavenging method has the same beneficial effects on the grain boundary resistances, but no detrimental effects on grain resistance. Aging experiment...
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