An electron diffraction and lattice‐dynamical study of the diffuse scattering in β‐cristobalite, SiO2

摘要

Strong diffuse scattering has been observed on electron diffraction photographs ofβ‐cristobalite. This is observed to be in the form of diffuse planes normal to the six (110) directions. A simple Born–von Karman force model including nearest‐neighbour Si–O, O–O and Si–Si interactions has been used to calculate lattice‐dynamical properties forβ‐cristobalite assuming the structure to be the simple Wyckoff Z. Kristallogr.(1925),62, 189–200C9 structure. The force‐model parameters used were obtained by fitting to the infrared and Raman frequencies ofα‐cristobalite and are very similar to those obtained by Barron, HuangPasternak J. Phys. C(1976),9, 3925–3940 for quartz. Calculated thermal diffuse scattering patterns obtained are in good agreement with the observed patterns, and may be interpreted in terms of low‐lying relatively dispersionless branches of the phonon dispersion curve diagrams. These branches correspond to motions of the structure involving coupled rotations of the tetrahedra in columns along the (110) directions, the motion in neighbouring colum