Soft Mode in cubic PbTiO3 by Hyper-Raman Scattering

TL;DR

This study uses hyper-Raman scattering to analyze the soft phonon mode in cubic PbTiO3, revealing its critical role in the ferroelectric phase transition and dielectric behavior.

Contribution

It provides detailed experimental evidence of the soft mode behavior in PbTiO3 across a wide temperature range, confirming its soft mode-driven ferroelectric nature.

Findings

The lowest F1u-symmetry mode softens to 17 cm-1 near Tc.

The mode's spectrum fits a damped harmonic oscillator model.

PbTiO3 is confirmed as a soft mode-driven ferroelectric.

Abstract

Hyper-Raman scattering experiments allowed collecting the spectra of the lowest F1u-symmetry mode of PbTiO3 crystal in the paraelectric phase up to 930K as well as down to about 1K above the phase transition. It is realized that this mode is fully responsible for the Curie-Weiss behavior of its dielectric permittivity above Tc. Near the phase transition, this phonon frequency softens down to 17 cm-1 and its spectrum can be well modeled as a response of a single damped harmonic oscillator. It is concluded that PbTiO3 constitutes a clean example of a soft mode-driven ferroelectric system.