Rietveld refinement of AgCa10(PO4)7 from X-ray powder data

Abstract

Polycrystalline silver(I) decacalcium heptakis(orthophosphate), AgCa 10(PO4)7, was obtained by solid-state reaction. It is isotopic with members of the series MCa10(PO4) 7 (M = Li, Na, K and Cs), and is closely related to the structure of β-Ca3(PO4)2. The crystal structure of the title compound is built up from a framework of [CaO9] and two [CaO8] polyhedra, one [CaO6] octahedron (site symmetry 3.) and three PO4 tetrahedra (one with site symmetry 3.). The Ag + cation is likewise located on a threefold rotation axis and resides in the cavities of the rigid [Ca10(PO4)7] - framework. It is surrounded by three O atoms in an almost regular triangular environment.