Abstract
Ultrafine 5.5 mol% CeO <sub>2</sub> -2 mol% YO <sub>1.5</sub> -ZrO <sub>2</sub> powders with controllable crystallite size were synthesized by two kinds of coprecipitation methods and subsequent crystallization treatment. The amorphous gel produced by ammonia coprecipitation and hydrothermal treatment at 200°C for 3.5 h results in an ultrafine powder with a surface area of 206 m <sup>2</sup> /g and a crystallite size of 4.8 nm. The powder produced by urea hydrolysis and calcination exhibits a purely tetragonal phase. In addition, the powders crystallized by hydrothermal treatment exhibit high packing density and can be sintered at lower temperature (<1400°C) with nearly 100% tetragonal phase achieved.