# Competing bonding and anharmonicity control piezoelectricity and thermal transport in janus BrSbX monolayers

## TL;DR

This paper explores how bonding strength and lattice anharmonicity affect piezoelectricity and thermal transport in Janus BrSbX monolayers.

## Contribution

The study introduces a practical design rule linking Sb–X covalency to electromechanical coupling and thermal conductivity in 2D Janus materials.

## Key findings

- Piezoelectric strain coefficients d11 decrease from BrSbS to BrSbTe due to reduced Sb–X covalency.
- Thermal conductivity increases with chalcogen from S to Te due to reduced anharmonicity.
- All BrSbX monolayers are mechanically and dynamically stable.

## Abstract

We show how competing bonding strength and lattice anharmonicity govern piezoelectricity and thermal transport in Janus 1T-BrSbX monolayers (X = S, Se, Te). Using density-functional theory and density-functional perturbation theory, combined with machine-learning-accelerated third-order force constants and Boltzmann transport calculations, we map composition property relationships within a single symmetry family. A bonding analysis (COHP) reveals a monotonic reduction in Sb–X covalency from S → Te, which tracks the piezoelectric stress response e11 and yields in-plane strain coefficients d11 = 41.0, 22.1, 6.3 pm V−1 for BrSbS, BrSbSe, and BrSbTe, respectively. In thermal transport, longitudinal-acoustic group velocities decrease from ∼3.41 to <2.78 km s−1 (S → Te), but mode-averaged Grüneisen parameters diminish more strongly, so phonon lifetimes dominate the trend: κL(300 K) = 5.94, 9.39, 12.32 W m−1 K−1 for S, Se, and Te, respectively. All monolayers are mechanically and dynamically stable. Together, these results establish a practical design rule: strengthening directional Sb–X covalency enhances d11, while reduced anharmonicity raises κL; the chalcogen thus provides a clean chemical knob to balance electromechanical coupling against heat transport in 2D Janus pnictogen chalcogenides.

We show how competing bonding strength and lattice anharmonicity govern piezoelectricity and thermal transport in Janus 1T-BrSbX monolayers (X = S, Se, Te).