Thermoelectric properties of nanostructured Si1−xGex and potential for further improvement

We theoretically investigate the thermoelectric properties of sintered SiGe alloys, compare them with new and previous experimental measurements, and evaluate their potential for further improvement. The theoretical approach is validated by extensive comparison of predicted bulk mobility, thermopower, and thermal conductivity, for varying Ge and doping concentrations, in the 300–1000K temperature range. The effect of grain boundaries is then included for Si0.8Ge0.2 sintered nanopowders and used to predict optimized values of the thermoelectric figure of merit at different grain sizes. Our calculations suggest that further optimization of current state of the art n-type (p-type) material would be feasible, possibly leading to ∼5% (4%) ZT enhancement at 1000 K and 16% (6%) at room temperature. Even larger enhancements should be possible if the phonon scattering probability of the grain boundaries could be increased beyond its present value.