Sintering and microstructure of rare earth phosphate ceramics REPO4 with RE = La, Ce or Y

Sintering of rare earth phosphates REPO4 (RE = La, Ce or Y) was studied using dilatometry. The presence of a secondary rare earth metaphosphate phase RE(PO3)3 as sintering aid was investigated. It proved to accelerate the densification but it activated fast grain growth, which was very detrimental to the microstructural design of processed ceramics. A temperature of 1400–1450 °C was required to sinter pure LaPO4 and CePO4 ceramics with fine grains. Both compounds behave similar while YPO4 did not densify even at 1500 °C. The influence of specific surface area of starting powders, temperature and holding time on the sintering rate and microstructures of dense REPO4 materials is also reported.