High pressure X-ray study on CPDT-TCNQ anion radical salts

Abstract Isostructural anion radical salts Me 4 X(CPDT-TCNQ) 2 (X=N, P, As) have extremely one-dimensional electronic system. We investigated their high pressure properties from X-ray diffraction measurements. The superlattice reflections were observed at room temperature above 7.9, 12.1 and 9.5 kbar on the Me 4 N, Me 4 P and Me 4 As salts, respectively. They are relevant to the stepwise increase of resistivity under pressure. The origins of the transitions are thought to be the 2 k F CDW for the Me 4 N and Me 4 P salts, and the 4 k F CDW for the Me 4 As salt. In addition, the 4 k F -to-2 k F transition is observed at 10.4 kbar on the Me 4 As salt.