Retention of a Paramagnetic Ground State at Low Temperatures in a Family of Structurally Related UIV Phosphates.

A new uranium fluoride phosphate, UFPO4, was synthesized via a mild hydrothermal route and characterized optically, thermally, and magnetically. Two thermal transformation products, U2O(PO4)2 and UIVUVIO2(PO4)2, were discovered to be structurally related, and were subsequently synthesized for bulk property measurements. All three materials failed to follow Curie-Weiss behavior at low temperatures, attributed to the nearly ubiquitous singlet ground state of U(IV), transitioning into a Curie-Weiss paramagnetic regime at high temperatures. Neutron diffraction experiments were performed on UFPO4 and UIVUVIO2(PO4)2 in order to characterize this unusual magnetic behavior.