Phonon Focusing and Anisotropy of the Lattice Thermal Conductivity of Potassium Crystals at Low Temperatures

Abstract

This work studies the influence of the anisotropy of elastic energy on the lattice thermal conductivity of potassium crystals. Our results have shown that, at sufficiently low temperatures, when diffuse scattering at the boundaries is the dominant mechanism of phonon relaxation, focusing leads to anisotropy of the phonon density of states (PDS) and lattice thermal conductivity. Crystallographic directions providing the maximum and minimum values of the lattice thermal conductivity have been determined. The phonon relaxation mechanisms are analyzed, and conditions under which Knudsen phonon gas flow can be realized in potassium crystals are determined. The role of the relaxation of quasi-longitudinal and quasi-transverse phonons on electrons in the thermal resistance of potassium crystals at low temperatures is studied.