Synthesis of Ternary, Quaternary, Quinary, and Senary Monazite Phosphate Single Crystals via High-Temperature Flux Crystal Growth and of Bulk Samples via a Low-Temperature Microwave-Assisted Hydrothermal Route.

The safe management of high-level radioactive waste requires durable waste forms that ensure long-term isolation. Monazite-based (LnPO4) materials are known to be excellent waste form materials. We demonstrated that complex monazite compositions can be synthesized via a facile low-temperature method that can potentially facilitate the sequestration of existing nuclear waste. We investigated flux crystal growth and low-temperature syntheses of complex monazite compositions, including ternary, quaternary, quinary, and senary systems. Single crystals, including AmPO4, were obtained via high-temperature molten flux growth, and their structures were determined. Bulk samples were prepared using a microwave-assisted hydrothermal reaction, and their structures were confirmed via Rietveld refinement.