The role of lattice thermal conductivity suppression by dopants from a holistic perspective

TL;DR

This paper introduces a holistic approach to understanding how dopants suppress lattice thermal conductivity by explicitly considering their effects on phonon properties, offering a new perspective beyond traditional defect scattering models.

Contribution

The study proposes a holistic method to analyze dopant effects on thermal conductivity, explicitly accounting for changes in phonon dispersion and interactions, validated with experimental data.

Findings

Holistic approach effectively predicts thermal conductivity reduction.

Light dopants induce avoided-crossing phonon behavior.

Mass and force constant imbalance contribute to phonon scattering.

Abstract

Dopants play an important role in improving electrical and thermal transport. In the traditional perspective, a dopant suppresses lattice thermal conductivity kL by adding point defect (PD) scattering term to the phonon relaxation time, which has been adopted for decades. In this study, we propose an innovative perspective to solve the kL of defective systems-the holistic approach, i.e., treating dopant and matrix as a holism. This approach allows us to handle the influences from defects explicitly by the calculations of defective systems, about their changed phonon dispersion, phonon-phonon and electron-phonon interaction, etc, due to the existence of dopants. The kL reduction between defective MxNb1-xFeSb (M=V, Ti) and NbFeSb is used as an example for the holistic approach, and comparable results with experiments are obtained. It is notable that light elemental dopants also induced the avoided-crossing behavior. It can be further rationalized by a one-dimensional atomic chain model. The mass and force constant imbalance generally generates the avoided-crossing phonons, mathematically in a similar way as the coefficients in traditional PD scattering, but along a different direction in kL reduction. Our work provides another perspective for understanding the mechanism of dopants influence in material's thermal transport.