Influence of mass contrast in alloy phonon scattering

TL;DR

This study examines how mass contrast affects alloy phonon scattering in Lennard-Jones crystals, revealing the limits of perturbation models and identifying a critical mass contrast impacting thermal conductivity predictions.

Contribution

It introduces a modal analysis method to evaluate the applicability of mass-difference perturbation theory in alloy phonon scattering.

Findings

Critical phonon frequency decreases with increasing mass difference.

Mass-difference perturbation model underestimates thermal conductivity beyond a critical contrast.

The limits of perturbation theory depend on the magnitude, not the sign, of mass difference.

Abstract

We have investigated the effect of mass contrast on alloy phonon scattering in mass-substituted Lennard-Jones crystals. By calculating the mass-difference phonon scattering rate using a modal analysis method based on molecular dynamics, we have identified the applicability and limits of the widely-used mass-difference perturbation model in terms of magnitude and sign of the mass difference. The result of a phonon -mode-dependent analysis reveals that the critical phonon frequency, above which the mass-difference perturbation theory fails, decreases with the magnitude of the mass difference independently of its sign. This gives rise to a critical mass contrast, above which the mass-difference perturbation model noticeably underestimates the lattice thermal conductivity.