2 - Ferroelectric charge-transfer complexes

Abstract

Charge-transfer (CT) complexes and CT salts, i.e., the multicomponent organic molecular compounds comprising the electron donor (D), acceptor (A), and/or counter ions, have yielded an exotic class of π-molecular organic ferroelectrics. Many of these crystals undergo the symmetry-breaking lattice distortion caused by some structural instabilities specific to the quasi-one-dimensional electronic system, e.g., the dimeric distortions in the DA alternating stack for CT complexes. A variety of materials have been developed with their intriguing properties and electronic mechanisms of ferroelectricity, which are related to the correlated interplay of charge, spin, and lattice degrees of freedom. The huge dielectric response near the transition point is attributed to electronically driven ferroelectricity, caused by the valence instability responsible for the neutral-ionic (NI) transition of the CT complexes and the charge ordering (CO) transition of CT salts.