Principal Electrical Conductivities in the Organic Conductors TEA.(TCNQ)₂ and TTF.TCNQ: The Microwave Approach

Abstract

We describe a microwave technique to measure the directions and magnitude of the principal electrical conductivities and permittivities of organic conductors. The method is applied to single crystals of triethylammonium-bis 7,7,8,8-tetracyano-p-quinodimethane (TEA.(TCNQ)₂) and of tetrathiafulvalenium-7,7,8,8-tetracyano-p-quinodimethane (TTF.TCNQ). For the former, the apriori set of principal axes (a*, (a*∧c), c) is confirmed with principal conductivities of 430, 5.3 and 0.41–0.77 Ω⁻¹m⁻¹ respectively. The room temperature permittivities have been measured for the first time (ε*_α ∼ 5.4–5.5, ε*_α∧c ∼ 7.5). For the latter it is clearly shown that the principal electrical axes are (a, b, c*) and, in contrary to earlier d.c data, we observe σ_c· < σ<a which is more consistent with the anisotropy of interchain interactions in this compound. The observed transverse and longitudinal anisotropies (∼3.3 10² and 2.8 10⁴ respectively) are larger than believed up to now.

Keywords:

• microwave
• electrical conductivity
• permittivity
• anisotropy
• organic conductors
• TEA. (TCNQ)₂
• TTF.TCNQ