EFFECT OF SOLID-SOLUTION ADDITIVES ON THE SINTERING OF ULTRA-FINE CEO2 POWDERS

Ultra-fine CeO2 powders (particle size approximate to 10-15 nm) containing up to 20 at% of various divalent and trivalent cations (Mg2+, Ca2+, SC3+, Y3+ and Nd3+) were prepared by chemical precipitation under hydrothermal conditions. The effects of the cation concentration size and valency on the densification and grain growth of the compacted powders were examined during sintering at a constant heating rate of 10 degrees C/min. Compared to undoped CeO2, all of the additive cations caused a shift in the densification curve to higher temperatures. However, the density and grain size achieved after sintering depended significantly on the elemental composition of the additive. When the radii of the additive cations were larger than that of the host Ce4+ cation, (i.e. Ca2+, Y3+ and Nd-3), nearly full density and ultrafine grain size were achieved. Under identical sintering conditions lower density (approximate to 93-95% of the theoretical) and larger grain size were achieved when the radii of the additive cations were smaller than that of the host, (i.e. Mg2+ and SC3+). Powders doped simultaneously with two cations, (e.g. Ca2+ and Mg2+) showed sintering and grain growth characteristics which were intermediate between those for the powders doped with single cations at the equivalent concentration.