The neutral-to-ionic phase transition in the mixed-stack charge-transfer complex tetrathiafulvalene-p-chloranil (TTF-CA) has been studied by pressure-dependent infrared spectroscopy up to p = 11 kbar and down to low temperatures, T = 10 K. By tracking the C=O antisymmetric stretching mode of CA molecules, we accurately determine the ionicity of TTF-CA in the pressure-temperature phase diagram. At any point, the TTF-CA crystal bears only a single ionicity; there is no coexistence region or an exotic high-pressure phase. Our findings shed new light on the role of electron-phonon interaction in the neutral-ionic transition.
Evolution of ferroelectricity in tetrathiafulvalene-p-chloranil as a function of pressure and temperature
Armin Dengl, Rebecca Beyer, Tobias Peterseim, Tomislav Ivek, Gabriele Untereiner, Martin Dressel; Evolution of ferroelectricity in tetrathiafulvalene-p-chloranil as a function of pressure and temperature. J. Chem. Phys. 28 June 2014; 140 (24): 244511. https://doi.org/10.1063/1.4884964
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