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Abstract
Raman scattering and lattice dynamical calculations were performed to discuss the origin of the incommensurate(INC) phase in quartz. A broad low frequency mode was found to exist in a wide temperature range. Its intensity significantly increase in β phase on cooling towards the transition temperature. The lattice dynamical calculation suggests that this mode reflects the increase of the phonon density of TA-mode along the ∑ line. The results are consistent with the new model by Aslanyan et al. (J.Phys.Condens.Matter, 10, 4575(1998).) which claims that the INC modulation would occur first near b/3 rather than close to Γ point and that there exists another commensurate phase just above the α phase. Keywords: Quartz, Incommensurate, Phase transition, Raman scattering, Lattice dynamics
