Heat transfer by mobile low-frequency phonons and "localized" modes in cryocrystal solutions

TL;DR

This paper investigates heat transfer mechanisms in solid Kr-Xe solutions, highlighting the roles of mobile low-frequency phonons and localized modes, and how these contributions vary with temperature and impurity levels.

Contribution

It introduces a model combining phonon and localized mode contributions to explain thermal conductivity in cryocrystal solutions, including the determination of the phonon mobility edge.

Findings

Localized modes significantly contribute to heat transfer above 100 K.

Heat transfer by localized modes increases with temperature and impurity concentration.

The phonon mobility edge is determined by scattering and wavelength constraints.

Abstract

The temperature and volume dependences of the thermal conductivity of solid Kr(1-x)Xe(x)solution are analyzed within the model in which heat is transferred by mobile low-frequency phonons; above the phonon mobility edge this is done by "localized" modes migrating randomly from site to site. The phonon mobility edge (w0)is determined from the condition that the phonon mean -free path restricted by Umklapp processes and point defects scattering cannot be smaller than one-half the phonon wavelength. The Bridgman coefficient is the weighted - mean over these modes whose volume dependences differ widely. It is shown that the amount of heat transferred by the "localized" modes above 100 K is quite large even in pure Kr and it increases with rising temperature and impurity concentration.