Pressure-dependent Raman spectra of β-Ca3(PO4)2 whitlockite

Abstract

The pressure dependence of Raman spectra for whitlockite β-Ca3(PO4)2 was investigated up to 18.0 GPa using a diamond-anvil cell at room temperature. The Raman frequencies of all observed bands for β-Ca3(PO4)2 continuously increase with increasing pressure. The quantitative analysis of pressure dependence of Raman bands for the sample shows that the ν 3 asymmetric and ν 1 symmetric stretching vibrations are with the larger pressure coefficients (from 3.44 to 4.59 cm−1 GPa−1) and that the ν 4 bending and ν 2 deforming vibrations are with the smaller pressure coefficients (from 1.46 to 3.12 cm−1 GPa−1). Combined with previous result, the isothermal mode Gruneisen parameters of β-Ca3(PO4)2 were calculated. The splitting of the PO4 symmetric stretching ν 1 vibrations changes during compression and disappears around 15.4 GPa, which may be attributed to the evolution of PO4 tetrahedra under high pressure.