Rietveld refinement of Ba5(AsO4)3Cl from high-resolution synchrotron data

Abstract

The apatite-type compound Ba5(AsO4)3Cl, pentabarium tris[arsenate(V)] chloride, has been synthesized by ion exchange at high temperature from a synthetic sample of mimetite (Pb5(AsO4)3Cl) with BaCO3 as a by-product. The results of the Rietveld refinement, based on high resolution synchrotron X-ray powder diffraction data, show that the title compound crystallizes in the same structure as other halogenoapatites with general formula A5(YO4)3X (A = divalent cation, Y = pentavalent cation, X = Cl, Br) in space group P63/m. The structure consists of isolated tetrahedral AsO43− anions (m symmetry), separated by two crystallographically independent Ba2+ cations that are located on mirror planes and threefold rotation axes, respectively. The Cl− anions are at the 2b sites (overline{3} symmetry) and are located in the channels of the structure.