Phase evolution and microstructural studies of Gd1 − xYbxPO4 (0 ≤ x ≤ 1) ceramics for radioactive waste storage

Rare-earth phosphates (REPO 4 ) represent one candidate to contain minor actinides separated from used nuclear fuel. In this work, the Gd 1   −   x Yb x PO 4 (0   ≤   x   ≤ 1) series is synthesized via conventional solid-state reaction using Gd as the surrogate for trivalent actinides (Am, Cm), with microstructure/phase structure characterized by XRD , XPS, HRTEM and SEM as well. Solid solutions of monazite- and xenotime-type compounds are observed in the system. The structural boundary between two phases is based on the experimental temperature. The monazite   →   xenotime transformation is most likely to occur on a (2   0   0) monazite plane along the [0   2   0] zone. The pure xenotime-type crystalline phase with Gd 0.9 Yb 0.1 PO 4 composition is obtained at 1600   °C.