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Doped CeO2-(CeO2)0.9(Gd2O3)0.1pellets were prepared using the glycine-nitrate process with various sintering times and sintering temperatures. Compositional and structural characterizations were carried out using X-ray diffraction (XRD) with CuK? radiation, a scanning electron microscope (SEM) and a Transmission electron microscope (TEM). Sintering and electrical characteristics were investigated using dilatometer measurement and the AC impedance analyser. Powder characteristics were also investigated by the BET method. Polycrystalline (CeO2)0.9(Gd2O3)0.1powders with specific surface areas of 19-23 m2/ g were obtained. Green bodies from the synthesized powders after milling shrunk up to about 1470° C, above which they expanded with heating temperature, whereas those before milling shrank continuously up to a temperature of 1600° C. This difference might be attributed to the change of the packing density of the synthesized powders upon milling: from 25% without milling to about 40% after milling. Therefore the sintered (CeO2)0.9(Gd2O3)0.1bodies having a theoretical density of 7.25 g/cm3were considered to be obtained from the as-milled powders by controlling the sintering time at a sintering temperature higher than 1470° C in air. In the AC impedance measurements, the electrical resistivity of the (CeO2)0.9-(Gd2O3)0.1bodies, produced from as-milled powders, and sintered at 1500° C with increasing sintering time, showed the minimum total value at the sintering time of 10 h. The minimum total resistivity of the (CeO2)0.9(Gd2O3)0.1bodies sintered at 1500° C for 10 h seems to be obtained when the sum of the activation energy for the resistivities in the grain and at the grain boundary.

Ultrafine crystalline TiO2powders were prepared by just heating and stirring aqueous TiOCl2solution with a Ti+4concentration of 0.5 mol/lat room temperature to 100°C under one atmosphere. The crystallinity, the phase transformation and the particle shape of ultrafine TiO2powders obtained by this simple precipitation method were analyzed using an X-ray diffractometer (XRD), transmission electron microscopy (TEM), differential thermal analyzer (DTA), and scanning electron microscopy (SEM). TiO2crystalline precipitates with a pure rutile phase were formed below 65°C, then TiO2crystalline precipitates with an anatase phase started forming at temperatures higher than 65°C, which ends with the pure anatase phase at 100°C. The direct formation of TiO2crystalline precipitates from an aqueous TiOCl2solution is due to the existence of the OH-ions in distilled water which cause the crystallization of TiOCl2to TiO2without hydrolyzation to Ti(OH)4. Conventionally, rutile-phase TiO2is obtained at much higher temperatures. However, in this study a stable rutile-phase TiO2was obtained by a simple method at close to room temperature.