High-pressure structures and vibrational spectra of barium fluoride: Results obtained under nearly hydrostatic conditions

Powder x-ray diffraction and Raman spectroscopy experiments, together with first-principles calculations, have been carried out to corroborate and clarify the pressure-dependent structural evolution of barium fluoride. X-ray diffraction experiments were performed both with and without a pressure-transmitting medium. The latter serve to reproduce past experimental results, while the former show a marked difference. Specifically, the experiments employing helium as a pressure-transmitting medium yield observed relative intensities and volume compression consistent with the proposed Ni2In structure of barium fluoride at pressures greater than 14 GPa. The Raman spectroscopy measurements corroborate the proposed Ni2In structure, as the spectra exhibit the two modes expected for the high-pressure phase. The experiments also demonstrate that barium fluoride remains an insulator up to at least 77 GPa, and the results of first-principles calculations suggest that a subsequent insulator-metal transition may not be expected well into the megabar regime.Peer reviewed: YesNRC publication: Ye