# Strong anharmonicity and high thermoelectric efficiency in high temperature SnS from first-principles

## TL;DR

This study uses first-principles calculations to demonstrate that high-temperature SnS exhibits strong anharmonic vibrational properties similar to SnSe, indicating its potential as an efficient thermoelectric material.

## Contribution

The paper reveals that SnS has high thermoelectric efficiency at high temperatures due to its anharmonic vibrational properties, comparable to SnSe, supported by first-principles calculations.

## Key findings

- SnS and SnSe have similar electronic and vibrational properties in the high-temperature phase.
- SnS exhibits strong anharmonic effects affecting phonon spectra and thermal conductivity.
- Non-perturbative anharmonic effects are crucial for accurate thermal conductivity calculations.

## Abstract

SnS and SnSe are isoelectronic materials with a common phase diagram. Recently, SnSe was found to be the most efficient intrinsic thermoelectric material in its high-temperature Cmcm phase above 800 K. Making use of first-principles calculations, here we show that the electronic and vibrational properties of both materials are very similar in this phase and, consequently, SnS is also expected to have a high thermoelectric figure of merit at high temperature in its Cmcm phase. In fact, the electronic power factor and lattice thermal conductivity are comparable for both materials, which ensures a similar figure of merit. As in the case of SnSe, the vibrational properties of SnS in the Cmcm phase are far from trivial and are dominated by huge anharmonic effects. Its phonon spectra are strongly renormalized by anharmonicity and the spectral functions of some particular in-plane modes depict anomalous non-lorentzian profiles. Finally, we show that non-perturbative anharmonic effects in the third-order force-constants are crucial in the calculation of the lattice thermal conductivity. Our results motivate new experiments in the high temperature regime to measure the figure of merit of SnS.