Sinterability and ionic conductivity of coprecipitated Ce _0.8Gd_0.2O_2-δ powders treated via a high-energy ball-milling process

Ceria-based solid solutions are promising electrolytes for intermediate-temperature, solid oxide fuel cells. The effect of a dry, high-energy, ball-milling process on the sintering and densification behaviour of coprecipitated ceria-based powders is investigated by means of X-ray diffraction, Brunauer-Emmett-Teller (BET) surface-area measurements, density measurements, and electron microscopy. The dry ball-milling process leads to (i) a larger specific surface-area with weak agglomeration; (ii) rearrangement of grains into dense granules; (iii) a higher green density. These effects significantly reduce sintering temperatures and promote densification of ceria-based ceramics. Moreover, a comparison is made of the sintering behaviour and ionic conductivity of the milled samples with and without cobalt oxide doping. Cobalt oxide is a very effective sintering aid, but usually results in an enlarged grain-boundary effect for Si-containing samples. Thus, since SiO₂ is a ubiquitous background impurity in both raw materials and ceramic processing, the dry ball-milling process is a more feasible method for improving the sinterability of coprecipitated ceria-based powders.