Electron Transport and Magnetic Properties of New Highly Conducting TCNQ Complexes

Single crystals of the 1:1 complexes tetrathiafulvalinium tetracyanoquinodimethane (TTF‐TCNQ) and tetrathianaphthacinium tetracyanoquinodimethane (TTN‐TCNQ) have been synthesized and the electron transport properties and magnetic susceptibility have been measured from 2°K to room temperature. For TTN‐TCNQ, σ at room temperature is 1Ω−1 cm−1. For TTF‐TCNQ, σ at room temperature along the long axis (σ∥) is in the range 192–652Ω−1 cm−1 depending on sample whereas perpendicular to the long axis σ⊥ is 1Ω−1 cm−1. The conductivity remains metallic down to 66°K in both directions whereupon a continuous metal to insulator transition occurs. The activation energy in the insulating state is 0.0062 ev. The transition is associated with a small hysteresis between the heating and cooling curves suggesting a possible structural change. In the metallic region, ρ∥ follows a T2 dependence whereas ρ⊥ follows a T+1 behavior. The magnetic susceptibility is diamagnetic below 20°K becoming increasingly more paramagnetic with increasing T even in the metallic region. It is suggested that spin disorder scattering may account for the anomalous temperature dependence of ρ⊥.