Anharmonicity of zone-centre optical phonons: Raman spectra of the isomorphous ?-quartz, berlinite and gallium phosphate in the temperature range 8-300 K

Abstract

The temperature dependence of the optical-phonon wavenumbers and bandwidths in the isomorphous α-quartz, berlinite (AlPO4) and gallium phosphate (GaPO4) was investigated by Raman scattering experiments in the temperature range 8–300 K. Combining these data with those from high-pressure Raman scattering experiments (up to 20 GPa), we estimated the implicit (thermal volume expansion) and explicit (pure self-anharmonic) temperature contribution to the temperature wavenumber shifts observed in isobaric experiments. In the framework of the Grüneisen approximation, the mode-Grüneisen parameters of the A1 modes in GaPO4 are given. As expected, these results are similar to those previously reported for quartz and berlinite. In the temperature range 8–300 K, which is less than the α–β temperature of transition (Tα → β ≈ 850 K) of quartz and berlinite, the phonon population decay processes appear to be the main cause of phonon damping in the three materials. Copyright © 2000 John Wiley & Sons, Ltd.