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

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 ν3 asymmetric and ν1 symmetric stretching vibrations are with the larger pressure coefficients (from 3.44 to 4.59 cm−1 GPa−1) and that the ν4 bending and ν2 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 Grüneisen parameters of β-Ca3(PO4)2 were calculated. The splitting of the PO4 symmetric stretching ν1 vibrations changes during compression and disappears around 15.4 GPa, which may be attributed to the evolution of PO4 tetrahedra under high pressure.