The vibrational spectra of potassium hexafluorosilicate, K2SiF6

Potassium hexafluorosilicate, K2SIF6, exists in cubic and hexagonal modifications. The vibrational spectra of both phases are reported in this study, those of the hexagonal phase for the first time. The internal infrared and Raman bands of the SiF6=-ions do not vary very much in these two phases reflecting the very small differences in the structures of these ions. The far-infrared spectra of the two phases differ significantly and those of the hexagonal phase can be interpreted in terms of the space group P6(3)mc-C-6v(4), with Z=2. There are indications in the far-infrared spectrum of cubic K2SiF6 that the structure might be lower than the average one of Fm3m-O-h(5) space group symmetry obtained from single-crystal X-ray measurements.