New thorium and uranium monophosphates in the KTh2(PO4)3 family: structure and cationic non-stoichiometry

Abstract

A new uranium monophosphate KU ₂ (PO ₄ ) ₃ has been synthesized. The structure of this phase, isotypic with KTh ₂ (PO ₄ ) ₃ , has been determined using a single crystal. The analysis of this structure leads to a new description, in which the [U ₂ (PO ₄ ) ₃ ] _∞ framework, built up of edge- and corner-sharing PO ₄ tetrahedra and UO ₉ polyhedra, forms eight-sided tunnels. New non-stoichiometric phosphates, A _0.5 Th ₂ (PO ₄ ) ₃ with A = Ba, Sr, Pb, Ca, Cd and K _1–2x Ba _x Th ₂ (PO ₄ ) ₃ , have been synthesized, showing the great flexibility of this structure.