Electronic Structure and Phase Transition in Ferroelectic $\rm \mathbf{Sn_2P_2S_6}$ Crystal

TL;DR

This study uses first-principles calculations to analyze the electronic structure and phase transition mechanisms in the ferroelectric crystal $ m Sn_2P_2S_6$, highlighting the role of lone pair electrons and covalent bonding changes.

Contribution

It provides a detailed electronic structure analysis of $ m Sn_2P_2S_6$ and clarifies the origin of its ferroelectric phase transition based on hybridization and covalence.

Findings

Spontaneous polarization arises from lone pair activity of tin cations.

Valence band changes are linked to increased covalence during phase transition.

Electronic structure analysis explains the ferroelectric behavior.

Abstract

For $\rm Sn_2P_2S_6$ ferroelectrics by first-principles calculations an analysis of the $\rm P_2S_6$ cluster electronic structure and their comparison with crystal valence band in paraelectric and ferroelectric phases has been done and the origin of ferroelectricity has been outlined. It was established that the spontaneous polarization follows from the stereochemical activity of the electron lone pair of tin cations that is determined by hybridization with $\rm P_2S_6$ molecular orbitals. Increase of the chemical bonds covalence and their rearrangement are related to the valence band changes at transition from paraelectric phase to ferroelectric one.