Electronic properties of kish graphite crystals with low values of residual resistivity ratio Original Research Article

Electronic properties, such as in-plane electrical resistivity ρ, transverse magnetoresistance Δρ/ρ0, Hall coefficient RH and absolute thermoelectric power S, were investigated for kish graphite (KG) specimens with residual resistivity ratio RRR lower than 10. Measurements of mass magnetization were also carried out. A linear dependence of Δρ/ρ0 on magnetic field in fields above about 2 T and an anomalous positive RH were observed at 77 K. S was entirely positive, although phonon drag effects were clearly observed in the temperature dependence. The shifts of RH and S toward the positive side are attributed to excess holes. On the other hand, no anomalous behaviors were found on ρ and a- and c-axes mass susceptibilities. Annealing effect on Δρ/ρ0 and RH for one of the KG specimens by heat-treatments up to 2950°C was also examined. After annealing at 2950°C, Δρ/ρ0 increased and exhibited an usual field dependence similar to that for KG with RRR>10, while RH remained positive. The origin of the excess holes in KG with RRR<10 is assumed to be the presence of a slight amount of iron impurities.