Temperature—pressure phase diagrams of double-column organic conductors: (DMET)2BF4, (DMET)2ClO4 and (DIMET)2BF4

The electrical resistivity under hydrostatic pressure was measured for the double-column organic conductors, (DMET)2BF4, (DMET)2ClO4 and (DIMET)2BF4, where DMET and DIMET are dimethyl(ethylenedithio)diselenadithiafulvalene and dimethyl(ethylenedithio)tetrathiafulvalene, respectively. Each of these conducting salts undergoes three phase transitions at and below the metal-to-semiconductor transition temperature of about 30 K at 0 kbar. The temperatures of the metal-to-insulator/semiconductor (M-I) transition and two other ones were determined and the temperature—pressure phase diagrams were constructed. It was found that the second up to 15 kbar and third transition temperatures of (DMET)2BF4 and (DMET)2ClO4 are almost independent of pressure. The characteristics of the phase transitions are discussed by comparing the pressure dependence of the transition temperatures with that of single-column organic conductors.