Molecular-dynamics study of the high-temperature elasticity of quartz above the α-β phase transition

We have presented the molecular-dynamics (MD) results for the temperature dependence of the adiabatic elastic constants Cᵢⱼ of α and β quartz, using a statistical fluctuation formula. It is noteworthy that the calculated Cᵢⱼ values are in a good agreement with the experimental values in the entire temperature range of 300--1100 K, including the α-β phase-transition region. We have confirmed that the net increase of bulk Cᵢⱼ's in the β 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 β quartz at high temperatures, and its influence on the macroscopic elastic properties, in contrast to the ordered β-quartz structure model.