Dynamical structure analyses of phase transitions and physical properties in minerals

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In this study, X-ray diffraction data obtained in accurate structure analyses of some common minerals such as quartz and its related materials were interpreted in conjunction with lattice dynamical calculations of phonon frequencies. The chief results are summarized below.1. Anisotropic Debye-Waller factors of atoms in quartz obtained in normal structure analyses were reproduced in lattice dynamical calculations with sufficient agreement. This agreement strongly supports that the alpha-beta phase transition is rather displacive.2. The cusp-shape anomaly of the Debye-Waller factors of atoms in quartz, which were previously found around the alpha-beta transition, was found to be caused not only by the optic soft mode, but also by the low frequency acoustic mode in the 00xi direction.3. The alpha-beta transition in AlPO_4, which has the quartz-type structure, is also displacive.4. Diffraction data such as anisotropic temperature factors of atoms can be a useful candidate in analyzing dynamics of structures, in conjunction with lattice dynamical calculations.