Screening transition metal-based polar pentagonal monolayers with large piezoelectricity and shift current

Yaguang Guo,Qian Wang,Yanyan Chen,Jian Zhou,Huanhuan Xie

doi:10.1038/s41524-022-00728-4

Yaguang Guo, Qian Wang + Show 3 more

Open Access

https://doi.org/10.1038/s41524-022-00728-4

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Abstract

Two-dimensional (2D) materials entirely composed of pentagon motifs are of interest for their wide applications. Here, we demonstrate that in-plane polar symmetry can exist in ternary pentagonal monolayers, where the induced electric polarization is not associated with specific conditions, such as ferroelectric phase transition, strain gradient, and layer stacking, but is an intrinsic structural property coming from the orderly arranged polar bonds. Based on the high-throughput screening method and first-principles calculations, we find eight stable 2D polar transition metal compounds with a number of intriguing properties. In particular, their piezoelectric coefficients are three orders of magnitude larger than those of 2D elemental and binary pentagonal structures, and their bulk photovaltaic shift current can reach up to 300 μA V−2, superior to that of 2D conventional ferroelectric materials such as GeS. Our identified pentagonal monolayers not only expand the family of 2D pyroelectric materials, but also hold potential for energy conversions.

Highlights

Polar materials with electric polarization exhibit emergent effects and functionalities, which have been found to be crucial for many applications such as sensors, nanogenerators, and energy collectors
Spontaneous polarization is fundamentally determined by the polar symmetry of a crystalline structure
Monolayer group IV monochalcogenides (SnSe, SnS, GeSe, and GeS) are the prominent examples, in which phase transition from a square unit cell to a rectangular one occurs at a critical temperature (TC)[7], creating the ferroelectricity[8]. Such symmetry breaking is associated with the emergence of many interesting properties, including large piezoelectric[9], pyroelectric[10], and bulk photovoltaic effects (BPVE)[11], which are superior to those of 2D non-polar materials[12,13]

Summary

Introduction

Polar materials with electric polarization exhibit emergent effects and functionalities, which have been found to be crucial for many applications such as sensors, nanogenerators, and energy collectors. Spontaneous polarization is fundamentally determined by the polar symmetry of a crystalline structure This can be commonly observed in paraelectric-to-ferroelectric phase transition, where ionic displacement reduces the lattice symmetry from centrosymmetric to polar. Monolayer group IV monochalcogenides (SnSe, SnS, GeSe, and GeS) are the prominent examples, in which phase transition from a square unit cell to a rectangular one occurs at a critical temperature (TC)[7], creating the ferroelectricity[8]. Such symmetry breaking is associated with the emergence of many interesting properties, including large piezoelectric[9], pyroelectric[10], and bulk photovoltaic effects (BPVE)[11], which are superior to those of 2D non-polar materials[12,13]. A recent experimental study showed that the inplane polarization can be formed at the interface of 2D WSe2/BP heterojunction, where the emergence of a strong BPVE is observed[15]

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