Flux Method\nGrowth and Structural Analysis of Two\nTetravalent Uranium Orthophosphate Single Crystals, Cs<sub>2</sub>U<sup>IV</sup>(PO<sub>4</sub>)<sub>2</sub> and Isostructural Cs<sub>2</sub&

Two novel uranium(IV) orthophosphate framework compounds\nwere obtained\nby the high-temperature flux method in CsCl-CsF eutectic salt. Cs<sub>2</sub>U<sup>IV</sup>(PO<sub>4</sub>)<sub>2</sub> (<b>1</b>) and isostructural Cs<sub>2</sub>(U<sup>IV</sup><sub>0.75</sub>Ce<sup>IV</sup><sub>0.25</sub>)(PO<sub>4</sub>)<sub>2</sub> (<b>2</b>) are tetragonal structures bridged by (U/Ce)<sup>IV</sup>-O octacoordinated\ndodecahedra and PO<sub>4</sub> tetrahedra, with Cs<sup>+</sup> cations\nfilling in the channels. The crystal structures exhibit good structural\nand thermal stability with a potential capacity to immobilize tetravalent\nradionuclides.