Unusual electric polarization behavior in elemental quasi-2D allotropes of selenium

TL;DR

This study explores the tunable electric polarization and electronic properties of quasi-2D selenium allotropes, revealing various polarization types and how chain rotation influences their polarization and band gap characteristics.

Contribution

It uncovers the diverse polarization behaviors in quasi-2D selenium allotropes and demonstrates control via chain rotation, a novel approach in 2D material engineering.

Findings

Different allotropes exhibit ferroelectric, ferrielectric, and anti-ferroelectric polarization.

Chain rotation can switch polarization direction and type.

Band gap can be tuned from indirect to direct through chain rotation.

Abstract

We investigate tunable electric polarization and electronic structure of quasi-two-dimensional (quasi-2D) allotropes of selenium, which are formed from their constituent one-dimensional (1D) structures through an inter-chain interaction facilitated by the multi-valence nature of Se. Our em ab initio calculations reveal that different quasi-2D Se allotropes display different types of electric polarization, including ferroelectric (FE) polarization normal to the chain direction in alpha and delta allotropes, non-collinear ferrielectric (FiE) polarization along the chain axis in tau-Se, and anti-ferroelectric (AFE) polarization in eta-Se. The magnitude and direction of the polarization can be changed by a previously unexplored rotation of the constituent chains. In that case, an in-plane polarization direction may change to out-of-plane in alpha-Se and delta-Se, flip its direction, and even disappear in tau-Se. Also, the band gap may be reduced and changed from indirect to direct by rotating the constituent chains about their axes in these quasi-2D Se allotropes.