TEMPERATURE DEPENDENCE OF RAMAN LINEWIDTH AND SHIFT IN ALPHA-QUARTZ

The linewidth and frequency of the 128-cm-1 and the 466-cm-1 optical lattice vibrations in quartz have been measured between 5 and 300°K by means of high-resolution Raman spectroscopy. The 128-cm-1 mode, which is both Raman- and infrared-active, is the lowest-lying optical vibration in quartz and shows a marked increase in lifetime at low temperatures. Utilizing available phonon dispersion spectra obtained from neutron scattering, the linewidth and shift are calculated in terms of three-phonon interactions. A simple model for the cubic anharmonicity, which includes relaxation broadening of the thermal phonons, is applied satisfactorily to the residual damping at low temperatures. The 128-cm-1 LO-TO splitting, which is extremely small, is not resolved directly, but manifests itself as an observed broadening at helium temperatures. © 1969 The American Physical Society.