Preparation of High‐Density Ceria‐Yttria Ceramics

Abstract

Fine Ce‐Y oxide powders were prepared by coprecipitation of the carbonate, followed by calcination at 620°C. Hydrolysis of trichloroacetic acid was used to precipitate most of the material from a homogeneous solution; addition of ammonium bicarbonate and ripening of the precipitate were used to increase the yield to 68 to 70%. The precipitate apparently consisted of more than one phase and had an overall composition which suggested that it was a possible mixture of hydrated carbonate, hydroxycarbonate, and hydroxide. The calcined oxide powder was used to prepare an yttria‐doped ceria ceramic by hot‐pressing. The ceramic had the fluorite structure phase with a lattice constant of 0.541088 nm and a composition of Ce0.914Y0.086O1.957. The bulk density of the material was 6.96 g/cm3, or 99.4% of theoretical density. The ceramic had equiaxed grains, with an average dimension of 1 to 4 μm and with residual porosity mainly along the grain boundaries. Ac impedance properties of the chemically prepared oxide are compared with those of mechanically mixed and fired Y‐doped CeOZ.