Nonohmic electrical conductivity and giant dielectric constant in methyltriphenylarsonium ditetracyanoquinodimethane

Abstract

Quite large, well-formed single crystals of m$\phi$3As(TCNQ)2 crystals have been grown. The largest of these crystals are probably the largest TCNQ salt crystals ever grown; they may also be the most perfect. It has been shown that m$\phi$3As(TCNQ)2 has a large, highly anistropic dielectric constant and a nonohmic conductivity. Nonohmic conductivity and a large dielectric constant have been observed in a number of quasi-one-dimensional conductors and semiconductors. A number of models have been proposed to explain both phenomena. None of the published models adequately explains the nonohmic conductivity observed in m$\phi$3As(TCNQ)2. A model based upon charged imperfections in the conducting (TCNQ) strands is developed; it explaines the data quite well. The charged imperfections act as barriers in the conducting strands. Rice and Bernasconi explain the large anisotropic dielectric constant observed in quasi-one-dimensional conductors in terms of a model based upon barriers in the conducting strands. Their model, with minor modifications, explains our dielectric constant measurements quite well. The concentration of charged imperfections was assumed to be equal to the concentration of paramagnetic impurities, which were measured using magnetic resonance techniques. Approximate agreement between the measured imperfection level, the nonohmic behavior, and the dielectric constant were found. A rather wide range of experimental techniques (conductivity and dielectric constant measurements, nuclear and electron spin resonance) all yield data which are in agreement with the proposed model.