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

Polycrystalline silver(I) deca­calcium heptakis(orthophos­phate), AgCa₁₀(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.