The high-temperature behaviour of PuPO4 monazite and some other related compounds

Thermal behaviour and lattice parameters of monazites MPO4 (M3+ = Ce3+, Nd3+ and Pu3+) and cheralite CaTh(PO4)2 were studied using high-temperature X-ray diffraction. Heat treatment under inert atmosphere caused the decomposition of PuPO4 and CaTh(PO4)2 into the corresponding oxides above 1473 K. The influence of the cation type within the crystallographic structure on the thermal expansion coefficient and the possible cation substitutions are discussed in the frame of nuclear waste management.