Towards the grain boundary phonon scattering problem: an evidence for a low-temperature crossover

TL;DR

This paper investigates phonon scattering at grain boundaries using the wedge disclination dipole model, revealing a low-temperature crossover in thermal conductivity that explains deviations from the expected T^3 behavior in LiF and NaCl.

Contribution

It introduces a WDD-based model to explain low-temperature phonon scattering and thermal conductivity crossover in crystalline materials.

Findings

The model predicts a specific q-dependence of phonon mean free path.

Results explain the deviation from T^3 law below 0.1K in LiF and NaCl.

Provides a theoretical framework for grain boundary phonon scattering.

Abstract

The problem of phonon scattering by grain boundaries is studied within the wedge disclination dipole (WDD) model. It is shown that a specific q-dependence of the phonon mean free path for biaxial WDD results in a low-temperature crossover of the thermal conductivity, $\kappa$. The obtained results allow to explain the experimentally observed deviation of $\kappa$ from a $T^3$ dependence below $0.1K$ in $LiF$ and $NaCl$.