Raman spectroscopic study of stronadelphite Sr5(PO4)3F at various temperatures

The Raman spectra of stronadelphite, Sr5(PO4)3F, were investigated in the temperature range of 80-1023 K at ambient pressure. No phase transition was observed though some vibrations merge or disappear during heating in this study. With increasing temperature the Raman shifts of all observed bands for Sr5(PO4)3F continuously decrease. The quantitative analysis of temperature dependences for the Raman active PO4 internal modes indicates that the ν3 and ν1 stretching vibrations have larger absolute temperature coefficients (from −1.18 × 10−2 to −1.46 × 10−2 cm−1 K−1) whereas the ν4 and ν2 bending vibrations show smaller absolute temperature coefficients (from −0.08 × 10−2 to −0.90 × 10−2 cm−1 K−1), which may be attributed to the structural evolution of PO4 tetrahedron in Sr5(PO4)3F at high temperature. The temperature and pressure dependence of the force constant for PO stretching modes in Sr5(PO4)3F were calculated. The isobaric mode Grüneisen parameters were determined as 0.046-0.365 with an average of 0.252, and the anharmonic mode parameters as −0.28 ∼ 1.55 with an average of 0.33. The nonzero anharmonic mode parameters indicate an intrinsic anharmonicity for stronadelphite Sr5(PO4)3F.