Effect of Plastic Deformation on the Thermal Conductivity of Calcium Fluoride and Lithium Fluoride

Publisher Website
Google Scholar
Abstract
Measurements of the thermal conductivity of plastically deformed CaF2 and LiF between 1.3° and 80°K indicate the presence of a phonon scattering mechanism which does not display the frequency dependence normally associated with dislocations. Instead of a reciprocal relaxation time τ−1∝ω, which is characteristic of scattering due to individual dislocations, it is found that a stronger frequency dependence is indicated. Furthermore, a large anisotropy in the conductivity of CaF2 is evident from the results obtained when the temperature gradient is parallel to the strongly oriented edge dislocations, as contrasted to when the gradient is perpendicular to them. It is suggested that dislocation dipoles, composed of pairs of edge dislocations of opposite sign and of dipole spacing comparable to the dominant phonon wavelength, are the cause of the observed effects. There is strong evidence for cross‐glide in these materials, and an examination of the etched surface of deformed CaF2 reveals many etch pits which are sufficiently close together to indicate that, as a mode of dislocation multiplication, cross‐glide produces dipoles which could be responsible for the observed departure from normal dislocation scattering.