Raman Spectra of the High-Temperature Phase of Polycrystalline NaBF4

Abstract

Raman spectral studies on polycrystalline NaBF4 at temperatures a few degrees above and below its phase transition at 245°C show abrupt changes in the splitting of the degenerate ν2 (e) and ν4 (f 2) vibrational modes. The spectrum of the high‐temperature solid phase indicates the presence of a highly symmetric effective field about the BF 4 − ion similar to that previously observed in melt spectra. A complete disordering of the fluoride ion positions must be assumed for the spectral results to be consistent with recent x‐ray data on crystalline NaBF4powders at 265°C which have been indexed in the hexagonal system.