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 loc ated just below the Fermi level of the pi band. This compound undergoe s a metal-insulator transition at about 50 K. The nonmetallic state be low 50 K is regarded as the Anderson localization caused by a small am ount of randomly distributed 3d holes (Ni3+). High pressure lifts up t he 3d band and causes the gradual charge transfer from 3d to pi bands, which enhances the randomness of Ni3+ distribution. High-pressure exp eriments of X-ray diffraction, electrical resistivity and thermopower show that high pressure expands this nonmetallic phase to the high-tem perature region in thr P-T phase diagram. This extension is consistent with the enhancement of the randomness of Ni3+ distribution. (C) 1998 Elsevier Science S.A. All rights reserved.