Theoretical investigation of the lattice thermal conductivities of II-IV-V2 pnictide semiconductors

TL;DR

This study uses machine learning and phonon transport calculations to accurately predict lattice thermal conductivities of II-IV-V2 pnictide semiconductors, identifying promising thermoelectric materials with reduced thermal conductivity.

Contribution

It introduces a machine-learning approach to efficiently estimate force constants and predict thermal conductivities, improving accuracy over previous theoretical models.

Findings

Zn-based pnictides have higher thermal conductivity than Cd-based ones.

Thermal conductivity anisotropy increases with A-B mass difference.

CdGeAs2 identified as a promising thermoelectric candidate.

Abstract

Ternary pnictides semiconductors with II-IV-V2 stoichiometry hold potential as cost effective thermoelectric materials with suitable electronic transport properties, but their lattice thermal conductivities ($\kappa$) are typically too high. Gaining insight into their vibrational properties is therefore crucial to finding strategies to reduce $\kappa$ and achieve improved thermoelectric performance. We present a theoretical exploration of the lattice thermal conductivities for a set of pnictide semiconductors with ABX2 composition (A = Zn, Cd; B = Si, Ge, Sn; and X = P, As), using machine-learning based regression algorithms to extract force constants from a reduced number of density functional theory simulations, and then solving the Boltzmann transport equation for phonons. Our results align well available experimental data, decreasing the mean absolute error by ~3 Wm-1K-1 with respect to the best previous set of theoretical predictions. Zn-based ternary pnictides have, on average, more than double the thermal conductivity of the Cd-based compounds. Anisotropic behaviour increases with the mass difference between A and B cations, but while the nature of the anion does not affect the structural anisotropy, the thermal conductivity anisotropy is typically higher for arsenides than for phosphides. We identify compounds, like CdGeAs2, for which nanostructuring to an affordable range of particle sizes could lead to values low enough for thermoelectric applications.