High pressure properties of extremely one-dimensional electronic conductors Me4X(CPDT-TCNQ)2 (X=N, P and As)

High pressure properties of isostructural anion radical salts Me4X(CPDT-TCNQ)2 (X=N, P and As) having extremely one-dimensional electronic structures have been investigated by resistivity and X-ray diffraction measurements. The metal–insulator transition temperature shifted to higher temperature with increasing pressure up to around 9 kbar. The abrupt increases in the resistivity at 9.4 and 7.0 kbar correspond to the appearance of superlattice reflections at room temperature for the Me4P and Me4As salts, respectively. The superlattice reflections were also observed above 7.9 kbar on the Me4N salt. The origins of these transitions are thought to be the 2kF CDW for the Me4N and Me4P salts, and the 4kF CDW for the Me4As salt. In addition, the 4kF to 2kF CDW transition is observed at 10.4 kbar for the Me4As salt.