Ferroelectric Instability Driven Unusual Thermal Transport and High Thermoelectric Performance

Thermoelectric energy conversion possesses the unique capability of directly transforming waste heat into electricity. A key challenge in optimizing thermoelectric performance lies in effectively reducing lattice thermal conductivity while simultaneously ensuring an uninterrupted pathway for charge carriers. While numerous extrinsic strategies have been proposed to control phonon dynamics, a critical and less-explored avenue lies in understanding the chemical bonding and structural features that underpin intrinsic mechanisms. Engineering ferroelectric instability in crystalline solids has emerged as an efficacious method to control structural disorder through local distortions involving the off-centering of cations. The coupling of soft phonons associated with these instabilities with acoustic phonons suppresses their ability to transport heat while preserving the anionic sublattice and global structural symmetry, which facilitates efficient electronic transport. In this perspective, we discuss the chemical design approaches to tune ferroelectric instability in a few group IV metal chalcogenides such as SnTe, GeSe, and GeTe for achieving high thermoelectric performance. We highlight the intriguing phenomenon of inhomogeneous ferroelectric instability recently demonstrated in doped GeTe to obtain fascinating glassy thermal transport. Finally, we provide an outlook on key experimental and theoretical challenges, potential new research directions, and the integration of advanced techniques aimed at ferroelectric instability-driven low thermal conductivity and high thermoelectric performance.