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, and 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 ${\mathrm{PbTiO}}_3$ 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.

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• Ferroelectric phase transition
• Ferroelectricity
• Lattice thermal conductivity
• Phonons
• Specific heat
• Thermal properties
• Transition temperature