Electric and Thermosalient Properties of a Charge-Transfer Complex Exhibiting a Minor Valence Instability Transition

The charge-transfer (CT) complex 3,3′,5,5′-tetramethylbendizine-7,7,8,8-tetracyanoquinodimethane was found to display the thermosalient effect, in which crystals exhibit mechanical responses due to temperature changes. Such responses are rarely observed with CT complexes. Furthermore, while this crystalline complex was known to have an interesting phase transition in which the charge distribution changes at low temperatures, some of the physical properties of single crystals of the material were unknown, because the crystal is broken during the thermosalient event. In this study, we used a polymer-coating method to prevent cracking of the crystal, allowing us to observe drastic changes in resistivity and ferroelectric-like dielectric response accompanied by the phase transition at low temperature. This result suggests that organic solids with mechanical response and electric and magnetic functions can be produced, since CT complexes exhibit various electric and magnetic functions and physical properties.