An optical transform and Monte Carlo study of the disorder in β-cristobalite SiO2

摘要: A previously reported lattice-dynamical model of β-cristobalite [Hua, Welberry, Withers & Thompson (1988). J. Appl. Cryst. 21, 458–465], which assumed the Wyckoff C9 structure but gave a satisfactory qualitative description observed diffuse intensity in electron diffraction patterns, is shown to give atomic displacements are much too small be consistent with 147° Si—O—Si angle other forms silica. Monte Carlo simulations modified this constrained close have been carried out and optical patterns obtained from resulting lattice realisations. The very similar appearance those calculated for simple model, now both expected geometry also mean-square derived X-ray powder studies. In simulation oxygen atoms distributed uniformly around an annulus encircles 16(c) sites Fd3m structure. hypothesis Wright Leadbetter [Philos. Mag. (1975). 31, 1391–1401], that preferentially occupy six 96(h) occur annulus, has tested it concluded if such ordering exists not pronounced.