Preparation and characterization of cerium-gadolinium monazites as ceramics for the conditioning of minor actinides

Monazites are of considerable interest for immobilization of minor actinides . In this work, the Gd 1-x Ce x PO 4 (0 ≤ x ≤ 1) series is synthesized via conventional solid–state reaction using Ce as the surrogate for minor actinide americium (Am), with microstructure/phase structure characterized by XRD , HRTEM, μ-Raman, and SEM as well. The optimized temperature for preparation of monazite-type Gd 0.4 Ce 0.6 PO 4 solid solution is more than 1300 °C. At 1400 °C, the GdPO 4 ceramic is essentially monazite with little metastable xenotime phase. The metastable xenotime (GdPO 4 ) to monazite transformation occurs during the immobilizing phase of Ce element. The formation of monazite-type Gd 1-x Ce x PO 4 solid solutions in the range 0.1 ≤ x ≤ 1 is confirmed by the Rietveld refinement and Raman spectra . The change of Ce content has no significant influence on the morphology of the monazite-type Gd 1-x Ce x PO 4 compounds.