Studies of fluorite and related divalent fluoride systems at high pressure by Raman spectroscopy

Raman spectra of CaF2, BaF2, CdF2, and PbF2 have been measured at pressures as high as 35 kbar at room and liquid-nitrogen temperatures. The mode Grüneisen constants for the Raman-active modes of the fluorite phases of the Ca, Ba, and Cd salts are 1.8, 2.0, and 1.4, respectively. BaF2 (at 23 kbar) and PbF2 (at 4 kbar) undergo phase transformations to Vh16 (α-PbCl2-like) structures. Raman spectra of the high-pressure phases have been obtained. The spectra of these high-pressure phases have been assigned by comparison with the recently assigned spectrum of the corresponding phase of BaBr2. These observations are compared with predictions derived from relatively simple models of the lattice dynamics of ionic materials.