KSbF6 revisited. I—A Raman and infrared study of the tetragonal phase I

Abstract

AbstractThe polarized Raman spectra of single crystals of KSbF6‐I of P42m‐D symmetry are reported. The predicted LO‐TO splittings of the B2 and E modes were not observed and the vibrational spectra do not indicate a non‐centrosymmetric structure. The calculated relative intensities of the Raman bands in the single‐crystal spectra agree very well with the observed values. It is shown that the anions execute fourfold reorientational motions around the S4 axis of the crystals and an activation energy of 3.2 kcal mol−1 (13.4 kJ mol−1) is calculated from the variation of the linewidths of Raman bands with temperature. The barrier is penetrated by the anions and because of the jumping motions of the anions in KSbF6‐I the small distortions from a centrosymmetric structure are averaged out and the Raman and infrared spectra appear to be mutually exclusive.