Phonon dispersion relations in RbCl and RbF at 80 K

Abstract

Phonon dispersion relations have been obtained in the Delta , Sigma and Lambda symmetry directions using inelastic scattering of thermal neutrons. The results are used to calculate effective charges and effective compressibilities from the relations derived by Szigeti (1949 and 1950). Elastic constants are calculated from the slopes of the dispersion curves for small wave vectors and compared to those obtained in ultrasonic work. The dispersion curves are compared with calculations by Karo using the deformed-dipole-next-nearest- neighbours model. The Lyddane-Sachs-Teller (1941) relation is found to be satisfied in all instances except in RbCl at 80 K. Results from earlier work on NaCl and KCl are included for comparison.