Entropically Stabilized Local Dipole Formation in Lead Chalcogenides

Abstract

A Hot Dipole In a ferroelectric material, there is an alignment of local electric dipole moments that produces a net overall electric polarization. This state is accompanied by a decrease in symmetry, which can be restored by heating above a critical temperature. In contrast, through a combination of theory and experiments, Božin et al. (p. 1660 ) now show that with increasing temperature, rock-salt–structured lead telluride and lead sulfide go through a phase transition from a high symmetry phase to a low symmetry phase with an associated dipole moment. Paradoxically, the dipoles are stabilized in the disordered state at high temperature, even though the undistorted structure has lower internal energy.