Strong phonon localization in PbTe with dislocations and large deviation to Matthiessen\u2019s rule

Yandong Sun,Ming Hu,Jian Han,Yanguang Zhou,Cewen Nan,Wei Liu,Yuanhua Lin,Ben Xu

doi:10.1038/s41524-019-0232-x

Abstract

Dislocations can greatly enhance the figure of merit of thermoelectric materials by prominently reducing thermal conductivity. However, the evolution of phonon modes with different energies when they propagate through a single dislocation is unknown. Here we perform non-equilibrium molecular dynamics simulation to study phonon transport in PbTe crystal with dislocations by excluding boundary scattering and strain coupling effect. The frequency-dependent heat flux, phonon mode analysis, and frequency-dependent phonon mean free paths (MFPs) are presented. The thermal conductivity of PbTe with dislocation density on the order of 1015 m−2 is decreased by 62%. We provide solid evidence of strong localization of phonon modes in dislocation sample. Moreover, by comparing the frequency-dependent phonon MFPs between atomistic modeling and traditional theory, it is found that the conventional theories are inadequate to describe the phonon behavior throughout the full phonon spectrum, and large deviation to the well-known semi-classical Matthiessen’s rule is observed. These results provide insightful guidance for the development of PbTe based thermoelectrics and shed light on new routes for enhancing the performance of existing thermoelectrics by incorporating dislocations.

Highlights

Thermoelectric devices directly convert waste heat into reusable electricity[1] and have a promising future, even though their efficiency is low
As phonons carry most of the heat in thermoelectric materials, phonondislocation scattering is apparent; it is still an open question how the phonons of different energies interact with the local distortions induced by dislocation
Callaway assumed that the phonon scattering process can be investigated by frequency-dependent relaxation times and proposed a model based on the Debye approximation to calculate the κ

Summary

INTRODUCTION

Thermoelectric devices directly convert waste heat into reusable electricity[1] and have a promising future, even though their efficiency is low. An effective approach to enhance the power factor is to design materials that consist of defects such as substitutional impurities, vacancies, and micro-nanostructural precipitations, which hinder the propagation of phonons while preserving the electronic transport ability.[2,3] Recently, the introduction of dislocations into thermoelectric materials to reduce the thermal conductivity (κ) to an extremely low level is found to be suitable to increase the efficiency.[4,5,6,7] As phonons carry most of the heat in thermoelectric materials, phonondislocation scattering is apparent; it is still an open question how the phonons of different energies interact with the local distortions induced by dislocation. Once the frequency-dependent heat flux q(ω) are determined, the

AND DISCUSSION

METHODS

Findings

CODE AVAILABILITY