Structural Studies on Ba2SrMg4F14 and Ba2MM´Mg4F14 (M= Ca, Sr, Ba)

Abstract

The new barium strontium magnesium fluoride Ba2SrMg4F14 has been prepared as an almost single-phase colorless powder by precipitating amorphous precursors and heating them at 650 °C. The compound crystallizes in the space group P42/mnm (no. 136) with a = 12.45514(4), c = 7.46092(3) Å, V = 1157.42(1) Å3 and Z = 4. It is isostructural with the previously known Ca analog, Ba2.2Ca0.8Mg4F14. The structure is built up from a channel-forming network of tetrahedral (MgF6)4 units linked by bridging fluorine atoms. The channels contain the Ba2+ ions (CN = 11) and Sr2+ ions (CN = 8, CaF2 type-related environment). Solid solutions with composition Ba2(Sr1−xCax)Mg4F14 with x = 0.13(1), 0.36(1) and 0.51(1) as well as Ba2(Sr0.83(1)Ba0.17(1))Mg4F14 were synthesized and characterized by powder X-ray diffraction.