Determination of lattice defects in carbon fibers by means of thermal-conductivity measurements

The temperature variation of the thermal conductivity of six samples of pitch-derived carbon fibers has been measured in the temperature range 3T300 K. The lattice thermal conductivity has been fitted, with boundary and point-defect scattering for the phonons taken into consideration. It is shown that the in-plane coherence lengths determined by x-ray diffraction are almost equal to the phonon mean free paths for boundary scattering. It is thus suggested that thermal-conductivity measurements can be used to determine quantitatively in-plane coherence lengths in the range where x-ray techniques are inadequate. The analysis also allows one to compare shear moduli (C₄₄) and yields information on point defects.