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

The Raman spectra of stronadelphite, Sr-5(PO4)(3)F, 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 Sr-5(PO4)(3)F continuously decrease. The quantitative analysis of temperature dependences for the Raman active PO4 internal modes indicates that the v(3) and v(1) stretching vibrations have larger absolute temperature coefficients (from -1.18 x 10(-2) to -1.46 x 10(-2)cm(-1) K-1) whereas the v(4) and v(2) bending vibrations show smaller absolute temperature coefficients (from -0.08 x 10(-2) to -0.90 x 10(-2) cm(-1) K-1), which may be attributed to the structural evolution of PO4 tetrahedron in Sr-5(PO4)(3)F at high temperature. The temperature and pressure dependence of the force constant for P-O stretching modes in Sr-5(PO4)(3)F were calculated. The isobaric mode Gruneisen parameters were determined as 0.046-0.365 with an average of 0.252, and the anharmonic mode parameters as -0.28 similar to 1.55 with an average of 0.33. The nonzero anharmonic mode parameters indicate an intrinsic anharmonicity for stronadelphite Sr-5(PO4)(3)F.