Electrical conductivity of tetrathiafulvalenium-tetracyanoquinodimethanide (TTF-TCNQ)

Abstract

New measurements of electrical conductivity along the b axis of tetrathiafulvalenium-tetracyanoquinodimethanide (TTF-TCNQ) are combined with published results to provide a comprehensive summary including approximately 600 samples studied at 18 different laboratories. The magnitudes of these measured conductivities do not necessitate the assumption of superconducting fluctuations or any other collective state in which the conductivity exceeds the limitations of single-particle scattering. Since an adequate theory of the limitations of single-particle scattering for TTF-TCNQ does not exist at present, experiment alone does not rule out the possibility that collective effects may somewhat enhance or suppress the conductivity.The dc electrical conductivity of tetrathiafulvaienium -tetracyanotiuinodimethanide (TTF-TCNQ) was first reported by Ferraris, Cowan, Walatka, and Perlstein' in 1972. Since that time a number of workers have carefully studied the conductivity in this organic charge-transfer salt. Although the results are not in complete agreement and measurements are continuing in some groups, we would like to summarize the substantial body of work that has been completed. The observed magnitude of the conductivity appears to be com-parable to that in common metals and thus, from the limited point of view of an effective mean free path, consistent with a possible contribution to the transport properties from single-particle electron scattering.The original results of Ferraris etal. indicated that TTF-TCNQ was the most highly conducting organic compound known. Its dc conductivity rose with decreasing temperature like a metal and was highly anisotropic. The observed anisotropy was consistent with the crystal structure of other 13 5105

Electrodynamics of Bechgaard Salts: Optical Properties of One-Dimensional Metals

“…This discrepancy between the high dc conductivity and the low far-infrared conductivity seems to be a generic feature found in all one-dimensional conductors. Although the dc conductivity increases by more than an order of magnitude by cooling from room temperatures down to T = 60 K [20][21][22], the infrared conductivity remains low (Figure 2(b)). When the temperature is reduced below the T CDW ≈ 53 K, the low-frequency reflectivity drops because an energy gap opens at the Fermi level.…”

The Ground State Energy of Small Polaron Gas

“…The susceptibility is strongly pressure dependent [Z], a pressure of 5 kbar reducing it by a factor of 2 a t 300 K. At lower temperatures, the pressure dependence becomes much weaker. At 300 K, the transport mean free path 1 is close to the lattice constant b [3,4], and is also very strongly pressure dependent. Thus, the very strong pressure dependence of is associated with I becoming close to b.…”

Solution-Processable Molecular and Polymer Semiconductors for Thermoelectrics

“…The electronic properties are highly anisotropic, and both the conductivity and thermopower vary widely along differing crystal directions (Table 2.2). [69][70][71][72] Other charge transfer salts also exhibit n-type thermoelectric behavior, in particular a wide variety of compounds based on TTF; some examples have been provided in Table 2.2. Modifying the carrier concentration of these compounds is difficult due to the generally fixed stoichiometry of co-crystals.…”