# Thermoelectric properties of M2BS2 (M = Ti, Zr, Hf) monolayers: An Ab initio study

## TL;DR

This study uses computer simulations to explore the thermoelectric properties of two-dimensional M2BS2 materials, finding that Hf2BS2 performs best for thermoelectric devices.

## Contribution

The paper presents new ab initio insights into the thermoelectric performance of M2BS2 monolayers, particularly highlighting Hf2BS2's high efficiency.

## Key findings

- Hf2BS2 achieves a peak thermoelectric figure of merit of 1.74 in n-type configuration.
- Thermal conductivity decreases in the order Ti2BS2 > Hf2BS2 > Zr2BS2 at room temperature.
- Phonon dispersion analysis reveals distinct vibrational contributions from B, M, and S atoms.

## Abstract

The thermoelectric properties of two-dimensional M2BS2 (M = Ti, Zr, Hf) materials were investigated in this study by using first-principles calculations. The phonon dispersion indicate that the high-frequency branches are dominated by B vibrations, while the mid- and low-frequency branches are primarily influenced by M and S atoms. All three compounds are confirmed to be dynamically stable. The lattice thermal conductivity is primarily contributed by acoustic and low-frequency optical phonons, with its overall magnitude determined by relaxation times, group velocities, and Grüneisen parameters. The resulting thermal conductivities follow the sequence kl(Ti2BS2) > kl(Hf2BS2) > kl(Zr2BS2), reaching 2.35 W·m-1·K-1, 2.14 W·m-1·K-1, and 2.05 W·m-1·K-1 at room temperature, respectively. Monolayer Hf2BS2 maintains relatively high Seebeck coefficients and power factors under either doping polarity, achieving a peak thermoelectric figure of merit of 1.74 in the n-type configuration. These findings provide a strong theoretical foundation for designing novel, high-performance thermoelectric device materials.