LATTICE-DYNAMICAL STUDY OF THE ALPHA -BETA PHASE TRANSITION OF QUARTZ : SOFT-MODE BEHAVIOR AND ELASTIC ANOMALIES

The mechanism of the \ensuremath{\alpha}-\ensuremath{\beta} phase transition of quartz is investigated within the framework of a lattice-dynamical model using the pair-wise potential by Tsuneyuki et al. [Phys. Rev. Lett. 61, 869 (1988)]. The model well describes this effect and shows that the related phenomena (the soft-mode behavior and the negative Poisson ratios) can be mainly attributed to the sensitivity of the potential surface to volume extension.