Electronic Conductivity Upturn of HOPG Contrast to Transport Properties   of Polycrystal Graphite
  The transport properties of highly oriented pyrolitic graphite (HOPG) and polycrystal graphite have been studied. The electric conductivity of HOPG is several times larger than that of the polycrystal graphite. Along with the large magnetoresistances (MR), the polycrystal graphite show the accordant semiconductor-like character in a wide temperature (roughly range from 20K to 120K) under 0, 4, 8, 12 T applied magnetic field, while the magnetic-field-induced metal-semiconductor-like transition was only found in HOPG. The difference of transport properties originates from the Coulomb interaction quasipartical in HOPG graphite layers in contrast with the grain boundary scattering in the polycrystal graphite. 
Zhiming Wang, Feng Xu, Chao Lu, He Zhang, Qingyu Xu, Jinan Zhu   (Institute of Mechanical Engineering, Nanjing University of...