Synthesis of nano-sized YSZ powders from glycine-nitrate process and optimization of their properties

Nano-sized 8 mol% yttria-stabilized zirconia (YSZ) powders were synthesized using the glycine-nitrate process (GNP). Comparison studies were used to evaluate the effects of different molar ratio of metal ion to glycine (M/G) and heat-treatment conditions on synthesis, sintering and properties of nano-sized YSZ powders. The optimal condition of YSZ electrolyte was determined, in which a high sintered density and a high conductivity could be obtained. The results showed that the products obtained were in non-crystalline state when the M/G ratio was 1:1. The amorphous products were transformed into YSZ of cubic phase at 634 °C, and the maximum sintered density of the nano-sized YSZ powders could be achieved by sintering at 1450 °C for 6 h. Nano-sized YSZ powders could be directly synthesized by means of GNP when the M/G ratio was 1:2, and the maximum sintered density could be achieved by sintering at 1400 °C for 6 h. Impedance spectroscopy results showed that, for the conductivity of the samples obtained from different M/G ratios and heat-treatment conditions, the contributions of the grain and grain boundary inside the samples were different. In this study, it was found that the optimal electrical property of YSZ electrolyte could be obtained after pre-sintering at 1000 °C for 6 h and finally sintering at 1450 °C for 6 h when a M/G ratio of 1:2 was adopted, and the conductivity attained a value of 0.037 S cm−1 at 850 °C.