Thermal conductivity and Raman spectra of carbon fibers

The thermal conductivity between 12 and 300 K is reported for graphite fibers carbonized from a variety of precursors, including spun polyacrylonitrile, petroleum pitch, or grown by chemical vapor deposition of methane. The fibers were studied as grown as well as heat treated to temperatures up to 3000 °C. First-order Raman spectra of the same fibers were taken with use of a microprobe, and the intensity ratio $I_{1360}$/$I_{1580}$ between the disorder-induced line at 1360 ${\mathrm{cm}}^{\mathrm{-}1}$ and the Raman-allowed line at 1580 ${\mathrm{cm}}^{\mathrm{-}1}$ correlates well with the amplitude of the low-temperature thermal-conductivity data. Using the Kelly model for the phonon-dominated thermal conductivity, we deduce the defect-limited phonon mean free path $L_{\phi }$ from our data below 100 K. We find $L_{\phi }$ approximately equal to $L_a$, the x-ray in-plane correlation length which had been related by Tuinstra and Koenig to the Raman intensity ratio $I_{1360}$/$I_{1580}$. We show further correlations between $L_{\phi }$ and the electrical resistivity ρ, the interplane distance (1/2)$c_0$, and the c-axis correlation length $L_c$.