Electrical transport properties of benzene-derived graphite fibers

Detailed measurements of the transverse magnetoresistance of a benzene-derived graphite fiber annealed at 3000^∘{}C have been carried out between temperatures of 1.4 and 249 K and in magnetic fields between 30 and 80 000 G. Using a modification of a simple two-band theory due to Noto and Tsuzuku, we have been able to generate a good fit to the magnetoresistance data over the entire magnetic field range studied. Using this model, we find that the mobility varies from 9.8 ×{} 10³ cm²/V sec at 249 K to 3.2 ×{} 10⁴ cm²/V sec at 1.4 K the total carrier density varies from 9.7 ×{} 10¹⁸/cm³ at 249 K to 3 ×{} 10¹⁸/cm³ at 1.4 K and | (nₑ-nₕ)(nₑ+nₕ) | changes from 0.21 at 249 K to 0.094 at 1.4 K. Various other models have also been employed to estimate carrier densities and mobilities. Using simple theories, we can fit the temperature dependence of the mobility, the carrier density, and the resistivity. We show that changes in the temperature dependence of the resistivity of pyrolytic graphites and benzene-derived graphite fibers annealed at temperatures between ~ 2500 and 3500^∘{}C can be understood simply by changes in the crystallite size which alter the amount of boundary scattering.