Lattice dynamics and Debye-Waller factors of some compounds with the sodium chloride structure.

Abstract

The lattice dynamics of 19 compounds with the sodium chloride structure have been investigated using shell models. The models are compared with existing experimentally measured phonon-dispersion curves and refined using a multidimensional downhill simplex method. Debye-Waller factors for these compounds are calculated over the temperature range from 1 to 1000 K where appropriate and the results are fitted analytically using polynomial regression. The results are compared with experimentally measured room-temperature Debye-Waller factors and for most of the compounds the agreement is found to be better than 10%. At lower temperatures, it is expected that these results would be more accurate, since the harmonic approximation, which is crucial to the calculation of the Debye-Waller factors, works better. In choosing the models for particular applications, it is recommended that the model with the smallest standard error sigma is used for fitting the experimentally measured phonon-dispersion curves, or the model that shows best agreement with reliable experimental measurements of more relevant physical quantities, such as Debye-Waller factors in crystallography.