High-pressure study of one-dimensional phthalocyanine conductor, NiPc(AsF6)0.5

NiPc(AsF6)0.5 is a two-band system, in which a narrow 3d band is located just below the Fermi level of the π band. This compound undergoes a metal-insulator transition at about 50 K. The nonmetallic state below 50 K is regarded as the Anderson localization caused by a small amount of randomly distributed 3d holes (Ni3+). High pressure lifts up the 3d band and causes the gradual charge transfer from 3d to π bands, which enhances the randomness of Ni3+ distribution. High-pressure experiments of X-ray diffraction, electrical resistivity and thermopower show that high pressure expands this nonmetallic phase to the high-temperature region in the P-T phase diagram. This extension is consistent with the enhancement of the randomness of Ni3+ distribution.