Regensburg 2013 – wissenschaftliches Programm
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TT: Fachverband Tiefe Temperaturen
TT 40: Poster Session Correlated Electrons
TT 40.49: Poster
Mittwoch, 13. März 2013, 15:00–19:00, Poster D
Exploring the full phase diagram of TTF-CA under pressure — •Armin Dengl1, Tobias Knoblauch1, Rebecca Beyer1, Tomislav Ivek1,2, Gabriele Untereiner1, and Martin Dressel1 — 11. Physikalisches Institut, University of Stuttgart, Germany — 2Institut za fiziku, P.O. Box 304, HR-10001 Zagreb, Croatia
Tetrathiafulvalene-p-chloranil (TTF-CA) is a 1D organic charge-transfer complex exhibiting a neutral-to-ionic phase transition (NIT), which can be induced both by temperature and pressure. At ambient pressure the phase transition occurs at the critical temperature TNIT=81 K. It is a first order transition with a jump in ionicity from CA−0.3 to CA−0.6. For a long time the pressure induced NIT was assumed to be continuous, but subsequent studies were able to show a small jump in ionicity. Above a pressure of about 8 kbar, a second sort of CA with a slightly different ionization evolves, an effect which is not yet well investigated.
Most studies on this compound were done either with a dependance on temperature or pressure. We performed vibrational reflectance IR-spectroscopy under hydrostatic pressure up to 11 kbar for a temperature range from 10 to 300 K. To determine the average ionicity per CA molecule we took advantage of the b1u C=O stretching vibration which has a strong dependence of resonance frequency on ionicity. By applying pressure, the NIT shifts to higher temperatures by (25.2 ± 1) K/kbar and the transition becomes broader. For the first time we show the ionicity of CA as a function of both temperature and pressure throughout the whole phase diagram.