G. B. M. Vaughan, P. A. Heiney, J. P. McCauley, Jr., and A. B. Smith, III, Phys. Rev. B46, 2787-2791 (1992).
We have measured the DC conductivity and lattice parameters of hexahexylthiotriphenylene (HHTT) saturation-doped by exposure to iodine vapor, using a 4-probe resistivity technique and powder x-ray diffraction. The compound was further characterized by differential scanning calorimetry, thermogravimetric analysis, and polarizing microscopy. Pure HHTT is an insulator, and displays monoclinic crystal (K), incommensurate helical (H), columnar liquid crystal (Dhd), and isotropic liquid (I) phases. The iodine-doped compound retains the K, Dhd, and I phases, but the H phase is suppressed. In addition, the conductivity rises 4-5 orders of magnitude after doping, so that the iodine-HHTT complex has a powder conductivity characteristic of a semiconducting radical-ion salt.
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