Ba1.31Sr3.69(BO3)3Cl: A new structure type in the M5(BO3)3Cl (M = bivalent cation) system

Abstract

A new chloride borate, Ba1.31Sr3.69(BO3)3Cl, was obtained when exploring potential phosphor materials. It belongs to orthorhombic system, Pnma space group, with cell parameters of a = 6.965(1) Å, b = 16.546(3) Å, c = 9.557(1) Å and Z = 4. Ba5-xSrx(BO3)3Cl (x = 0, 0.5, …to 5) was synthesized and the cell volumes of the solid solutions were obtained by Rietveld refinement. Detailed structure description of Ba1.31Sr3.69(BO3)3Cl was conducted and the structure comparison between Ba1.31Sr3.69(BO3)3Cl and M5(BO3)X (M = Ba or Sr, X = Cl or F) was illustrated. In Ba1.31Sr3.69(BO3)3Cl, there are hexagonal tunnels extending along a-axis, which is the main feature of apatite family compounds. The density functional theory calculation suggested that in Ba1.31Sr3.69(BO3)3Cl space group Pnma is more energy favourable than C2221. DSC-TG showed that Ba1.31Sr3.69(BO3)3Cl is stable up to 950 °C and Raman and Infrared spectroscopy demonstrate the existence of planar (BO3)3- in the structure.