Effect of independent and coupled vibrations of dislocations on low-temperature thermal conductivity in alkali halides

Abstract

Recent experimental evidence has established that the scattering of phonons by dislocations at low temperatures in [110] LiF rods is primarily a dynamic rather than a static process, but calculations of the effects of vibrating dislocations have failed to provide quantitative agreement with experimental observations of the magnitudes and temperature dependence of the effect. We have performed a calculation which includes many factors previously neglected and show that the effects of resonance angle scattering, phonon focusing, and the resolved shear stress factor have an important influence on the effect of vibrating dislocations on thermal conductivity. However, the detailed calculation shows that in the case of [110] LiF rods the inclusion of these previously neglected factors still does not resolve the discrepancies observed and it is concluded that independently vibrating dislocations are not the important phonon scatterers above 0.1 K in LiF. It is shown, however, that the experimental data may be fit by assuming reasonable densities and distributions of "optically" vibrating dislocation dipoles.