Role of Ferrons in the Heat Capacity and Thermal Transport of Displacive Ferroelectrics

TL;DR

This paper investigates how ferrons, amplitude modes of polarization in displacive ferroelectrics, influence heat capacity and thermal transport, especially near phase transitions, using a microscopic theory and case study of PbTiO3.

Contribution

It introduces a self-consistent microscopic theory highlighting the significant role of ferrons in thermal properties of displacive ferroelectrics near phase transitions.

Findings

Ferrons soften dramatically near the transition, affecting thermal properties.

Including ferrons improves agreement with experimental heat capacity data.

Ferrons are essential for understanding thermal behavior in ferroelectric materials.

Abstract

The collective amplitude mode of the order parameter in displacive ferroelectrics, termed the ferron, represents the amplitude fluctuations of long-range ordered polarization. At temperatures well below phase transition temperature $T_c$, the energy of ferron excitation is significantly gapped in the long-wavelength limit. As $T_c$ is approached, this gap softens dramatically to minimal or gapless values, thereby should lead to a substantial contribution to thermal properties. In this context, we explore the role of ferrons in heat capacity and thermal transport by incorporating a microscopic self-consistent phase-transition theory for displacive ferroelectricity in contrast to the conventional treatment of attributing thermal properties solely to acoustic phonons. Using ferroelectric $\rm{PbTiO}_{3}$ as a case study, we show that the softening of ferrons near the phase transition is essential to accurately capturing the experimental temperature and electric-field dependencies of thermal properties.