Characteristics of ultrafine (CeO2)0.9(Gd2O3)0.1 powders prepared by the glycine-nitrate process

Ultrafine and polycrystalline (CeO₂)_0.9(Gd ₂O₃)_0.1 powders with specific surface areas of 19~23 m²/g were synthesized by the glycine-nitrate process and then their sintering and electrical characteristics were investigated with the dilatometric and AC impedance measurements. In the dilatometric measurements green bodies from the synthesized powders after milling shrank to about 1470°C in appearance and then expanded thermally with the increase of the heating temperature, whereas those from the synthesized powders before milling continuously shrank to the temperatures of 1600°C. It may be due to the change of the packing density of the synthesized powders by milling. Therefore, the sintered (CeO₂)_0.9(Gd₂O₃)_0.1 bodies from the as-milled powders could be obtained to have near the theoretical density controlling the sintering time at a sintering temperature more than 1470°C in air. In the AC impedance measurements, the electrical resistivity of the (CeO₂)_0.9(Gd₂O₃)_0.1 bodies from the as-milled powders, sintered at 1500°C with the increase of the sintering time, showed a minimum value at the sintering time of 10 h. The minimum total resistivity of the (CeO₂ )_0.9(Gd₂O₃)0.1 bodies sintered at 1500°C for 10 h seems to result from the lowest activation energy for the combination between the activation energies for the resistivities at the grain interior and grain boundary