High-pressure Raman spectra of tuite, γ-Ca3(PO4)2

The Raman spectra of a synthetic tuite,. -Ca3(PO4) 2, have been measured up to 23.6 GPa using a diamond-anvil cell at room temperature. The data were collected during compression and decompression. No pressure-induced phase transformation was observed in this pressure range. The behaviors of the phosphate modes and the external modes under high pressures were analyzed. The Raman wavenumbers of all modes increased linearly and continuously with pressure. The pressure coefficients of the phosphate modes range from 0.0034 to 0.0049 GPa(-1) for nu(3), 0.0044 GPa(-1) for nu(3), from 0.0020 to 0.0033 GPa(-1) for nu(4), and 0.0037 GPa(-1) for nu(2), whereas the pressure coefficients of the external modes range from 0.0120 to 0.0138 GPa-1. The corresponding Gruneisen parameters are 0.341-0.491, 0.441, 0.200-0.331 and 0.371 for the phosphate modes nu 3, nu 1, nu 4 and nu 2, respectively, and from 1.20 to 1.38 for the externalmodes. Copyright (C) 2009 John Wiley & Sons, Ltd.