Structures and electric properties of pitch-based carbon fibers heat-treated at various temperatures

Four kinds of pitch precursor fibers possessing different mean sizes of mesophase domains in their transverse sections, but having the same chemical constituents, were prepared by controlling only the spinning conditions. The fibers were thermoset and heat-treated at various temperatures from 600°C to 3300 °C. L_c (002) or d₀₀₂ vs T_HT curves showed that pitch precursor fibers with finer transverse microstructures have a lower degree of graphitizability. Further, these four kinds of fibers exhibited systematically different d₀₀₂ vs L_c (002) curves. The resistivity at room temperature is dependent on d₀₀₂, being independent of the mean size of the mesophase domains in the transverse section of the pitch precursor fiber. The transverse magnetoresistance at 77 K and 10 kG, (Δ_ρ/ρ)_t, also showed a universal dependence on d₀₀₂ if (Δ_ρ/ρ)_t was positive. However, the (Δ_ρ/ρ)_t vs d₀₀₂ curves seemed to be slightly split in the negative region of (Δ_ρ/ρ)_t for each of the four kinds of fibers.