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) 2 BF 4 , (DMET) 2 ClO 4 and (DIMET) 2 BF 4 , 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) 2 BF 4 and (DMET) 2 ClO 4 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.