A new interpretation of incommensurate phase of quartz

Optical and lattice dynamical studies were performed on the incommensurate( IC) phase in quartz. There are two different regions (fog- and m- zone) nea r the boundary between alpha and IC phase. The birefringence in the fog-zon e was found to be much larger than that expected from the currently accepte d model. The lattice dynamical calculation using the Tsuneyuki potential (P hys. Rev. Lett., 61, 869(1988)), revealed that a stable modulated structure with a short period exists between alpha and beta phases. Both results qua litatively agree with the new model recently proposed by Aslanyan et al. (J . Phys. Condens. Matter, 10, 4575(1998)) which assumes that the softening w ould occur near b/3 rather than close to Gamma point.