Abstract
We calculated the phonon mean free path by a spectral phonon gas model to understand the reduction of lattice thermal conductivities. The effects of anisotropy of bismuth telluride on heat conduction were considered in the model using the anisotropy of elastic stiffness. The phonon mean free paths were assumed to be cut off by nano-sized grains. As a result, the a-axis and c-axis cumulative lattice thermal conductivities of bismuth telluride are similar values in the cutoff phonon free path less than a few 100 nm. The result shows that the lattice thermal conductivity of nanostructured highly anisotropic materials with a-axis and c-axis can be evaluated by the spectral phonon gas model. Furthermore, we apply to design the nanostructured materials lattice thermal conductivities with micro and nano thermoelectric devices.
