Abstract
The temperature dependence of the infrared reflectivity spectra ( and -type vibrational modes) of quartz is reported in the and phases with emphasis on the vicinity of the phase transition. Spectra have been fitted with a four-parameter dispersion model based on the factorized form of the dielectric function that allows the temperature dependence of the TO and LO frequencies and damping to be determined. Two and three modes (among the six modes studied here) are forbidden in the phase, and they critically lose their polar character at the approach of the phase transition. The frequencies of a number of modes critically soften or harden in the phase, in the vicinity of K. A comparison with thermal lattice expansion indicates that this critical behavior might be understood in term of pure volume effect. In the phase, mode dampings diverge in the vicinity of the transition whereas in the range 300-700 K and in the phase, phonon lifetimes appear limited by anharmonic three-phonon coupling.
- Received 7 December 1974
DOI:https://doi.org/10.1103/PhysRevB.11.3944
©1975 American Physical Society