Structural diversity of rare earth and transition metal thiophosphates

Abstract

Technological interest in the design of solid state materials has stimulated recent research into the development of mild molten polychalcophosphate salt fluxes for the synthesis of complex, multinary rare earth and transition metal thiophosphate compounds. The reaction pathways from elemental or metal sulfide sources can be influenced by a variety of often interdependent factors of which counter cation sizes and charges, basicity, and temperature are of paramount importance. In rare earth and transition metal containing thiophosphates the dominating structural building units are tetrahedral [PS₄]³⁻ or ethane-like [P₂S₆]⁴⁻ anions. Hierarchical topological relations between individual members of structural families of the type A_mM_nP_yS_z (A = alkali metal, M = rare earth or transition metal) can be established that provide a detailed insight into probable mechanisms of formation. The findings enable the development of guidelines for the employment of suitable counter cations in controlling the condensation of small species into chains, layers or frameworks.