High-pressure infrared absorption in Cs2TCNQ3 crystals grown under magnetic field

Pressure dependence of infrared absorption has been measured in Cs ₂TCNQ ₃ single crystals grown under magnetic field of 5 T (5 T crystals). The behavior of the C CN as well as C H stretching modes suggest that there occurs a phase transition which resembles to the one related to the insulator to metal transition in the crystals grown without magnetic field (0 T crystals). This transition, however, takes place at 4.1 GPa, slightly higher than the case of 0 T crystals. The charge transfer degree of the neutral and radical molecules are found to be ρ = 0.30–0.37 and 0.81–0.85, respectively, which are significantly different from that of 0 T crystals. These differences are suggested to arise from the changes in the relative positions of the TCNQ molecules, as indicated from the behavior of the EMV mode.