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

• The optimized condition for synthesis of Gd0.4Ce0.6PO4 solid solution is investigated.
• Xenotime (GdPO4) to monazite transition occurs during the immobilization of Ce element.
• Monazite-type Gd1-xCexPO4 solid solutions form in the range 0.1 ≤ x ≤ 1.
• Monazite could be considered as a plausible host for minor actinide americium.

Monazites are of considerable interest for immobilization of minor actinides. In this work, the Gd1-xCexPO4 (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 Gd0.4Ce0.6PO4 solid solution is more than 1300 °C. At 1400 °C, the GdPO4 ceramic is essentially monazite with little metastable xenotime phase. The metastable xenotime (GdPO4) to monazite transformation occurs during the immobilizing phase of Ce element. The formation of monazite-type Gd1-xCexPO4 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 Gd1-xCexPO4 compounds.