We present a model describing the carrier conductivity and Seebeck coefficient of thermoelectric nanocomposite materials consisting of granular regions. The model is successfully applied to explain relevant experimental data for PbTe nanocomposites. A key factor is the grain potential boundary scattering mechanism. Other mechanisms, such as carrier-acoustic phonon, carrier-nonpolar optical phonon, and carrier-ionized impurities scattering are also included. Our calculations reveal that by changing the physical characteristics of the grains, such as potential barrier height, width, and distance between the grains, one can increase the mean energy per carrier in order to obtain an optimum power factor for improved thermoelectric performance. The model can be applied to other nanocomposites by incorporating the appropriate electronic structure parameters.

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Interfacing an organic semiconductor C 60 with a non-magnetic metallic thin film (Cu or Pt) has created a novel heterostructure that is ferromagnetic at ambient temperature, while its interface with a magnetic metal (Fe or Co) can tune the anisotropic magnetic surface property of the material. Here, we demonstrate that sandwiching C 60 in between a magnetic insulator (Y 3 Fe 5 O 12 : YIG) and a non-magnetic, strong spin-orbit metal (Pt) promotes highly efficient spin current transport via the thermally driven spin Seebeck effect (SSE). Experiments and first principles calculations consistently show that the presence of C 60 reduces significantly the conductivity mismatch between YIG and Pt and the surface perpendicular magnetic anisotropy of YIG, giving rise to enhanced spin mixing conductance across YIG/C 60 /Pt interfaces. As a result, a 600% increase in the SSE voltage (V LSSE ) has been realized in YIG/C 60 /Pt relative to YIG/Pt. Temperature-dependent SSE voltage measurements on YIG/C 60 /Pt with varying C 60 layer thicknesses also show an exponential increase in V LSSE at low temperatures below 200 K, resembling the temperature evolution of spin diffusion length of C 60 . Our study emphasizes the important roles of the magnetic anisotropy and the spin diffusion length of the intermediate layer in