Two-dimensional transition metal chalcogenides with hexagonal and orthorhombic structures: candidates for auxetics and photocatalysts

TL;DR

This study theoretically investigates two-dimensional transition metal chalcogenides with different lattice structures, revealing their potential as auxetics due to giant negative Poisson's ratios and as efficient photocatalysts for water splitting.

Contribution

It provides a comprehensive analysis of the physical properties of various 2D transition metal chalcogenides, highlighting their anisotropic behaviors and photocatalytic capabilities based on their structural phases.

Findings

Orthorhombic MX$_{2}$ and M$_{2}$X$_{3}$ exhibit highly anisotropic properties.

Orthorhombic MX$_{2}$ have giant negative in-plane Poisson's ratios.

Certain phases are highly efficient water splitting photocatalysts.

Abstract

In this paper, we perform theoretical study on the physical properties of two-dimensional transition metal chalcogenides MX$_{2}$ and M$_{2}$X$_{3}$ (M= Ni, Pd; X= S, Se, Te). These studied materials are classified in three stable phases according to their lattice structures: hexagonal MX$_{2}$, orthorhombic MX$_{2}$ and orthorhombic M$_{2}$X$_{3}$. They have either isotropic or anisotropic in-plane properties depending on their symmetries. In particular, the orthorhombic MX$_{2}$ and M$_{2}$X$_{3}$ have low lattice symmetry and present highly anisotropic properties. The orthorhombic MX$_{2}$ possess giant negative in-plane Poisson's ratios, different from the other two phases. Moreover, by joint analysis of band gap, band edge and optical absorption, the orthorhombic MX$_{2}$ and M$_{2}$X$_{3}$ are found to be highly efficient as water splitting photocatalysts within the visible and ultraviolet sunlight regions.