Nonlinear dynamics of ferroelectrics with three-well local potential

TL;DR

This paper models the nonlinear dynamics of Sn2P2S6 ferroelectrics using a three-well local potential, linking lattice instability to low energy optic modes and comparing theoretical spectra with Raman data.

Contribution

It introduces an anharmonic quantum oscillator model with a three-well potential to describe phase transition behavior under pressure in ferroelectrics.

Findings

Spectrum of pseudospin fluctuations calculated and compared with Raman spectroscopy data.

Ferroelectric lattice instability associated with several low energy optic modes.

Model successfully describes the continuous phase transition and pressure effects.

Abstract

For Sn$_2$P$_2$S$_6$ ferroelectrics, the appearance of spontaneous polarization is related to stereoactivity of tin cations and valence fluctuations of phosphorous cations. Here, the continuous phase transition and its behavior under pressure is determined by thee-well local potential and can be described in an anharmonic quantum oscillator model. For such a model, the spectrum of pseudospin fluctuations at different temperatures and pressures has been calculated and compared with the data of Raman spectroscopy. It was revealed that the ferroelectric lattice instability is related to several low energy optic modes.