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

Single crystals of A 3 MF 6 (A = Rb, Cs; M = Al, Ga) were grown from mixed alkali chloride/fluoride fluxes in sealed silver tubes. For Cs 3 AlF 6 and Cs 3 GaF 6 , two polymorphs were observed at room temperature: m -Cs 3 MF 6 and o -Cs 3 MF 6 . For the two Rb containing compositions, only one room temperature polymorph was observed: o -Rb 3 AlF 6 and t -Rb 3 GaF 6 , respectively. Simultaneous TGA/DSC and high temperature SCXRD/PXRD were used to study the high temperature behavior of A 3 MF 6 . The compounds of all four compositions were found to undergo structure transitions upon heating to the same cubic structure type, c -A 3 MF 6 . Single crystals of A 3 MF 6 (A = Rb, Cs; M = Al, Ga) were grown from mixed alkali chloride/fluoride fluxes. The polymorphism of each compound was studied via TGA/DSC and high temperature X-ray diffraction.