First-principles characterization of thermal conductivity in LaPO4-based alloys

TL;DR

This study uses first-principles calculations and the Wigner transport equation to understand and predict the thermal conductivity of LaPO4-based alloys, revealing the roles of anharmonicity and disorder.

Contribution

It introduces a first-principles approach combined with the Wigner formulation to accurately model heat transport in disordered alloys, surpassing traditional methods.

Findings

Wigner transport equation accurately describes thermal conductivity in disordered alloys.

Predictions of vibrational properties match experimental Raman spectra.

Insights into optimizing thermal barrier coatings based on fundamental physics.

Abstract

Alloys based on lanthanum phosphate (LaPO$_{4}$) are often employed as thermal barrier coatings, due to their low thermal conductivity and structural stability over a wide temperature range. To enhance the thermal-insulation performance of these alloys, it is essential to comprehensively understand the fundamental physics governing their heat conduction. Here, we employ the Wigner formulation of thermal transport in conjunction with first-principles calculations to elucidate how the interplay between anharmonicity and compositional disorder determines the thermal properties of La$_{1{-}x}$Gd$_{x}$PO$_{4}$ alloys, and discuss the fundamental physics underlying the emergence and coexistence of particle-like and wave-like heat-transport mechanisms. We also show how the Wigner transport equation describes correctly the thermodynamic limit of a compositionally disordered crystal, while the Boltzmann transport equation does not. Our predictions for microscopic vibrational properties (temperature-dependent Raman spectrum) and for macroscopic thermal conductivity are validated against experiments. Finally, we leverage these findings to devise strategies to optimize the performance of thermal barrier coatings.