Electrical Conductivity of Single Crystals of N-Methylphenazinium–TCNQ and Rb–TCNQ

Abstract
Temperature and pressure dependence of the electrical conductivity of NMP(I)–, NMP(II)–, Rb(I)– and Rb(II)–TCNQ single crystals was studied. NMP(I)–TCNQ showing diffuse streaks was found to have a semiconductive behavior at atmospheric pressure and no conductive maximum appeared at low temperatures. Moreover the metallic behavior was not shown even at 100 kbar. The crystal structure of NMP(II)–TCNQ is not similar to that of NMP(I)–TCNQ. The difference of physical properties of two phases is discussed. The anomalous electrical behavior in the pressure range from 1 bar to 40 kbar was observed for Rb(I)–TCNQ. The resistivity of Rb(II)–TCNQ decreased monotonously with increasing pressure. The magnitude of their activation energies was 0.15 eV for Rb(I) salt and 0.11 eV for Rb(II) salt at 100 kbar. The insulator to metal transition could not be observed at least up to 100 kbar.