Nanostructure model of thermal conductivity for high thermoelectric performance

The effective medium theory of thermal conductivity of two-phase composites studied by Nan et al. has been extended to investigate concentrated nanocomposites. Due to the presence of inter-particle phonon scattering processes in concentrated nanocomposites, the effective lattice thermal conductivity keff varies more rapidly with the volume fraction of second-phase inclusions in the composite. Applying the new keff expressions to monolithic material systems, the results are found to capture the experimental trend of monolithic nanostructured materials. In particular, it is noted that the dimensionless figure of merit, ZT, is nearly doubled by only reducing the lattice thermal conductivity. Two-phase nanocomposites have also been evaluated, demonstrating that these latter systems are very suited for high thermoelectric performance. Present study leads to several strategies for obtaining ZT ∼ 2 or higher in nanocomposites.