Orthophosphates of Tetravalent Ce, Th, U, Np, and Pu with the Monazite Structure

The problem of development of a ceramic phosphate matrix for solidification of the lanthanideactinide fraction of radioactive wastes is tackled from the crystal-chemical viewpoint. New double orthophosphates of tetravalent f elements (Ce, Th, U, Np, Pu) with alkaline-earth elements and cadmium of the formulas B0.5M2(PO4)3 and B1.5M1.5(PO4)3 (B = Mg, Ca, Sr, Ba, Cd; M = Ce, Th, U, Np, Pu) were prepared. The compounds were characterized by X-ray diffraction (including high-temperature measurements) and IR spectroscopy. They crystallize in the monazite structural type (space group P21/n). The thermal behavior of the compounds was studied. The unit cell parameters of the phases synthesized were determined. The influence of the cationic composition on the structure formation is analyzed.