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We have presented the molecular-dynamics (MD) results for the temperature dependence of the adiabatic elastic constants C₈₉ of and quartz, using a statistical fluctuation formula. It is noteworthy that the calculated C₈₉ values are in a good agreement with the experimental values in the entire temperature range of 300--1100 K, including the - phase-transition region. We have confirmed that the net increase of bulk C₈₉'s in the phase can be attributed to the internal relaxations, which arise from the cooperative motions of corner-linked SiO₄ tetrahedra. Our MD simulations have revealed the existence of dynamical disorder in quartz at high temperatures, and its influence on the macroscopic elastic properties, in contrast to the ordered -quartz structure model.
Kimizuka et al. (Thu,) studied this question.