Pressure-Induced Neutral–Ionic Phase Transition of a Tetrathiafulvalene–Iodanil Crystal

Abstract
The pressure dependence of IR spectra measured for a mixed-stack neutral charge-transfer (CT) crystal, tetrathiafulvalene–iodanil (TTF–IA), showed an occurrence of a neutral–ionic (N–I) transition at 1.9 GPa. The N-I transition is accompanied by gradual dimerization of the crystal lattice and a small ionicity jump, in contrast to the case of TTF–chloranil (TTF–CA). Such a quasi-continuous N–I transition is attributable to stronger electron–lattice interaction in TTF–IA than that in TTF–CA.