Temperature-dependent X-ray dynamical diffraction: Darwin theory simulations

Citation
Js. Chung et Sm. Durbin, Temperature-dependent X-ray dynamical diffraction: Darwin theory simulations, ACT CRYST A, 55, 1999, pp. 14-19
Citations number
16
Categorie Soggetti
Physical Chemistry/Chemical Physics
Journal title
ACTA CRYSTALLOGRAPHICA SECTION A
ISSN journal
01087673 → ACNP
Volume
55
Year of publication
1999
Part
1
Pages
14 - 19
Database
ISI
SICI code
0108-7673(199901)55:<14:TXDDDT>2.0.ZU;2-I
Abstract
Thermal vibrations destroy the perfect crystalline periodicity generally as sumed by dynamical diffraction theories. This can lead to some difficulty i n deriving the temperature dependence of X-ray reflectivity from otherwise perfect crystals. This difficulty is overcome here in numerical simulations based on the extended Darwin theory, which does not require periodicity. U sing Si and Ge as model materials, it is shown how to map the lattice vibra tions derived from measured phonon dispersion curves onto a suitable Darwin model. Good agreement is observed with the usual Debye-Waller behavior pre dicted by standard theories, except at high temperatures for high-order ref lections. These deviations are discussed in terms of a possible breakdown o f the ergodic hypothesis for X-ray diffraction.