| 概 要 |
We will report on dielectric permittivity measurements performed on the 2D salts, alpha-(BEDT-TTF)2I3 and theta-(BEDT-TTF)2RbZn(SCN)4, on which CO has been detected by NMR.
The behavior is relatively similar for both salts: a smooth monotonic increase of the dielectric permittivity, epsilon', from room temperature with a more sharp growth near TCO = 190K for theta-(BEDT-TTF)2RbZn(SCN)4 (with a noticeable hysteresis due to the first order character of the CO phase transition) and TCO = 135K for theta-(BEDT-TTF)2I3, a jump-like of epsilon' just below TCO down to a small magnitude below the accuracy of the experimental set-up.
These results are at variance with those in (TMTTF)2AsF6 for which epsilon’shows a divergence in a narrow temperature range near TCO well described by a Curie law with a slope at T<TCO twice larger than at T>TCO, a typical feature of a second-order phase transition characteristic of a ferroelectric state.
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