The use of strain and grain boundaries to tailor phonon transport properties: A first principles study of 2H-phase $CuAlO_{2}$ (Part II)

TL;DR

This study uses first-principles calculations to explore how strain and grain boundaries influence phonon transport in 2H-phase CuAlO2, aiming to optimize its thermoelectric properties for practical applications.

Contribution

It provides the first detailed analysis of strain effects on lattice thermal conductivity in 2H CuAlO2 using phonon Boltzmann transport equations derived from first-principles.

Findings

Thermal conductivity drops significantly with smaller grain sizes.

Strain can both increase and decrease thermal conductivity.

Grain size plays a dominant role in thermal transport properties.

Abstract

Transparent oxide materials, such as $CuAlO_{2}$, a p-type transparent conducting oxide (TCO), have recently been studied for high temperature thermoelectric power generators and coolers for waste heat. TCO materials are generally low cost and non-toxic. The potential to engineer them through strain and nano-structuring are two promising avenues toward continuously tuning the electronic and thermal properties to achieve high zT values and low cost/kW-hr devices. In this work, the strain-dependent lattice thermal conductivity of 2H $CuAlO_{2}$ is computed by solving the phonon Boltzmann transport equation with interatomic force constants extracted from first-principles calculations. While the average bulk thermal conductivity is around 32 W/(K-m) at room temperature, it drops to between 5-15 W/(K-m) for typical experimental grain sizes from 3nm to 30nm at room temperature. We find that strain can offer both an increase as well as a decrease in the thermal conductivity as expected, however the overall inclusion of small grain sizes dictates the potential for low thermal conductivity in this material.