The effect of grain size on the lattice thermal conductivity of an individual polyacrylonitrile-based carbon fiber

The lattice thermal conductivity (λL) of general purpose grade polyacrylonitrile (PAN)-based carbon fibers with a crystallite size (La) of several nanometers was examined. Using a modified 3ω method, the λL of the fibers with different heat-treatment temperatures were detected, and it was found that the λL was linearly dependent on −1/La. Based on phonon scattering theory, this observation can be attributed to the combined effect of boundary scattering and point-defect scattering. The constant for point-defect scattering (A) was evaluated and a formula was derived.