Polymorphism in A3MF6 (A = Rb, Cs; M = Al, Ga) grown using mixed halide fluxes

Abstract

Single crystals of A₃MF₆ (A = Rb, Cs; M = Al, Ga) were grown from mixed alkali chloride/fluoride fluxes in sealed silver tubes. For Cs₃AlF₆ and Cs₃GaF₆, two polymorphs were observed at room temperature: m-Cs₃MF₆ and o-Cs₃MF₆. For the two Rb containing compositions, only one room temperature polymorph was observed: o-Rb₃AlF₆ and t-Rb₃GaF₆, respectively. Simultaneous TGA/DSC and high temperature SCXRD/PXRD were used to study the high temperature behavior of A₃MF₆. The compounds of all four compositions were found to undergo structure transitions upon heating to the same cubic structure type, c-A₃MF₆.