Ba1.01Sr0.99P2O7: un nouveau site Ba2+révélé par diffraction des rayons X

Abstract

Single crystals of barium strontium diphosphate, Ba1.01Sr0.99P2O7, were prepared by a solid-state reaction. The compound is isostructural with α-Ba2P2O7, α-Sr2P2O7and BaPbP2O7. The structure has only one diphosphate group of the dichromate type that is repeated by symmetry to form sheets. These sheets present mirror planes perpendicular to theaaxis, situated atx= {1 \over 4} and {3 \over 4}. All the cations and three of the five independent O atoms are located on these mirror planes. The Ba2+cations are nine-coordinated by O atoms. The Ba2+and Sr2+cations are distributed on three different sites, in contrast with the isostructural compounds where only two sites are fully occupied. The refined site occupancies sum to a Ba:Sr ratio of 1.0133 (18):0.9867 (13), which leads to the reported deviation from the BaSrP2O7stoichiometry. The Raman spectrum of the compound is also reported and discussed.