Giant permittivity and electrostriction induced by dynamic Jahn-Teller and pseudo Jahn-Teller effects

We revealed specific properties of molecular systems and solids with dynamic Jahn-Teller effect (JTE) or pseudo JTE (PJTE) that enhance permittivity and electrostriction by several orders of magnitude. These effects occur due to the spontaneous symmetry breaking at the JTE or PJTE centers resulting in several equivalent minima of the adiabatic potential energy surface in which the system is dipolar-distorted in different directions. In the absence of external perturbations the distortions resonate between the equivalent orientations via tunneling between the minima, but an external electric field, similar to external strain considered earlier [I. B. Bersuker, Appl. Phys. Lett. 106, 022903 (2015)], makes the minima nonequivalent, trapping all the centers polar-distorted along one direction. This results in an orientational contribution to the polarization and electrostriction of the system which is much stronger than the displacive one. Under this effect, the estimated permittivity and electrostriction of paraelectric BaTiO₃ and similar crystals is enhanced by approximately three orders of magnitude, in agreement with experimental data. A variety of many other systems are expected to possess similar properties.