Synthesis of Ca1-xCexZrTi2-2xAl2xO7 zirconolite ceramics for plutonium disposition

Highlights: • A series of zirconolite ceramics of Ca1-xCexZrTi2-2xAl2xO7 were prepared. • All the solid solution (x = 0–0.35) adopted zirconolite-2M (C2/c) structure. • XANES data revealed that Ce was partially reduced to the Ce3+ oxidation state. • The most favourable phase assemblage was found for composition with x = 0.20. A series of zirconolite ceramics with stoichiometry Ca_1-xCe_xZrTi_2-2xAl_2xO₇ (x = 0–0.35), considered as a host phase for the immobilisation of separated plutonium, were prepared from a mixture of oxide precursors by sintering in air at 1450 ^°C. Ce was utilised as a structural surrogate for Pu, with Al added to provide charge compensation. XRD and electron diffraction analyses indicated crystallisation of the zirconolite-2M polytype for all compositions, accompanied by various secondary phases contingent on the doping level, consistent with microstructure observation. The relative yield of zirconolite phases remained above 94 wt.% for 0.05 < x < 0.20. It was determined that Ce was partially reduced to the Ce³⁺ oxidation state and Al occupied mainly octahedral Ti sites. The incorporation rate of CeO₂ was calculated to be 9.27 wt.% in Ca_0.80Ce_0.20ZrTi_1.60Al_0.40O₇ with a comparatively high yield of 94.7 wt.%, which is representative of a PuO₂ incorporation rate of 14.86 wt.%.