# First-principles study of LaOPbBiS$_3$ and its analogous compounds as thermoelectric materials

## TL;DR

This study uses first-principles calculations to explore and identify potential high-performance thermoelectric materials among LaOBiPbS$_3$ analogs, revealing compounds with significantly improved power factors.

## Contribution

It systematically investigates 24 variations of LaOBiPbS$_3$ compounds, predicting new materials with enhanced thermoelectric properties based on electronic structure analysis.

## Key findings

- LaOSbPbSe$_3$ has a power factor five times higher than LaOBiPbS$_3$.
- The choice of pnictogen atom influences thermoelectric performance through electronic structure effects.
- Hybridization effects are crucial for gap opening and high thermoelectric efficiency.

## Abstract

LaOBiPbS$_3$ is a kind of pnictogen-dichalcogenide layered compounds, which have recently been experimentally investigated as thermoelectric materials owing to their low thermal conductivity and high controllability of constituent elements. However, thermoelectric performance of LaOBiPbS$_3$ is at present not very high and that of its analogous compounds remains to be unknown. In this study, we theoretically investigate thermoelectric properties of 24 possible variations of the constituent elements in LaOBiPbS$_3$ from the viewpoint of the electronic structure. We find that some compounds can have much better thermoelectric performance than LaOBiPbS$_3$; in particular, LaOSbPbSe$_3$ is predicted to have a power factor five times as large as that of LaOBiPbS$_3$. Here, the choice of the pnictogen atom (As, Sb, and Bi), of which the low-energy conduction bands mainly consist, correlates with the calculated power factor and the dimensionless figure of merit, $ZT$. Such correlation comes from the fact that the low-dimensionality of the electronic structure, which enhances the density of states near the band edge, strongly depends on the pnictogen atom through, e.g., the strength of the spin-orbit coupling. Moreover, hybridization of the wave functions in the pnictogen-dichalcogenide layer and those in the rock-salt layer plays a key role in gap opening, and thus is important for achieving high thermoelectric performance. In LaOSbPbSe$_3$, such hybridization also pushes up the conduction band bottom, which enhances the density of states near the band edge and thus the power factor.