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Theory of ZT enhancement in nanocomposite materials

The effect of interface scattering on the performance of disordered, nanocomposite thermoelectric materials is studied theoretically using effective medium theory and direct numerics. The interfacial electronic and phonon scattering properties which lead to an enhancement of the thermoelectric figure of merit $ZT$ are described. Generally, $ZT$ enhancement requires the interfacial electrical conductance to be within a range of values, and the thermal phonon conductance to be below a critical value. For the systems considered, these requirements on interface scattering for $ZT$ enhancement are expressed in terms of the bulk properties of the high-$ZT$ material, and the ratio of the constituent bulk $Z$ values.