Phonon Scattering and Velocity Considerations in the Minimum Phonon Thermal Conductivity of Layered Solids above the Plateau

The minimum thermal conductivity of amorphous solids is investigated by implementing Einstein's original assumption of scattering at every lattice point within the framework of nonlocalized coupled oscillators. By separating the phase velocity and group velocity, thermal conductivity predictions agree well with experimental results indicating that it is necessary to account for both energy transport via hopping of localized modes (fractons) as well propagation of nonlocalized modes (phonons). The further reduction of thermal conductivity in layered structures is then examined by considering the scattering rates by atoms with a different binding force within the context of these minimum conductivity models.