Structural and Electronic Properties of (TMTTF)2X Salts with Tetrahedral Anions

Abstract

Comprehensive measurements of the pressure-and temperature-dependent dc-transport are combined with dielectric spectroscopy and structural considerations in order to elucidate the charge and anion orderings in the quasi-one-dimensional charge-transfer salts (TMTTF) 2 X with non-centrosymmetric anions X = BF 4 , ClO 4 and ReO 4. Upon applying hydrostatic pressure, the charge-order transition is suppressed in all three compounds, whereas the influence on the anion order clearly depends on the particular compound. A review of the structural properties paves the way for understanding the effect of the anions in their methyl cavities on the ordering. By determining the complex dielectric constantˆ (ω, T) in different directions we obtain valuable information on the contribution of the anions to the dielectric properties. For (TMTTF) 2 ClO 4 and (TMTTF) 2 ReO 4 , b exhibits an activated behavior of the relaxation time with activation energies similar to the gap measured in transport, indicating that the relaxation dynamics are determined by free charge carriers.

Double Layer Conducting Salts: (CNB-EDT-TTF)4X, X = ClO4−, ReO4−, and SbF6−; Electrical Transport and Infrared Properties

“…the donor molecules become non-equal. However, the effect is much smaller when compared to typical charge-order transitions, as observed in Fabre salts (TMTTF)2X [21][22][23]. We notice indications of these features already at higher temperatures due to charge fluctuations frequently observed in comparable compounds [24].…”

Donor–anion interactions in quarter-filled low-dimensional organic conductors

“…The only exception is (TMTTF) 2 ClO 4 where in contrast with the ReO 4 and BF 4 salts incorporating also tetrahedral anions, the CO/ferroelectric transition is not observed. [157][158] The reason for the absence of CO effects is not clear. A possible explanation could be that the AO transition first occurs in this salt (red segment in Fig.…”

Deuteration Effects on the Transport Properties of (TMTTF)2X Salts

“…For that reason, the coupling via the methyl groups is crucial. A zoomed-in view of the resistivity curves around this transition is presented in The hysteresis is well known from salts with non-centrosymmetric anions [7][8][9] and is an indicator of the first order nature of the AO phase transition. The broader hysteresis implies a stronger interaction of the anions with the caging methyl groups.…”

“…Salts containing tetrahedral anions, such as ClO 4 , ReO 4 and BF 4 , also exhibit some ordering of the anions; for that reason, they are not included in Figure 1. This structural phase transition normally occurs at temperatures T AO well below the charge-ordering temperature [7][8][9]. In (TMTTF) 2 ClO 4 , however, no charge ordering is observed at all; but the anion transition T AO occurs below T ρ .…”