Enhanced Thermoelectric Performance in n-Type SrTiO3/SiGe Composite.

Silicon germanium (SiGe) alloys hold promise for thermoelectric power generation at high temperatures and have been applied in deep-space missions. However, enhancement of the dimensionless thermoelectric figure-of-merit (ZT) is still needed for practical civil applications of SiGe. In this work, we report high-performance oxide/SiGe bulk composites that were obtained via hot-press sintering of mixed powders composed of phosphorus (P)-doped SiGe prepared via mechanical alloying, using a ball-milling technique and La-Nb-doped SrTiO3 (La-Nb-STO). The La-Nb-STO powder was obtained from ball milling of a bulk La-Nb-STO sample that was sintered via hot pressing of hydrothermally synthesized La-Nb-STO powder. Controlling the amount of La-Nb-STO nanoparticles added to SiGe matrix increased the power factor by optimizing the electron concentration and mobility in the composite. In addition, compared with single-phase P-doped SiGe, the second phase decreased the thermal conductivity because of additional phonon scattering at the interface. As a result, a high ZT of 0.91 was realized in the n-type oxide/SiGe bulk composite at 1000 K, which was 18% larger than that for the typical materials used in space flight missions and 5% higher than the single-phase SiGe alloys obtained in the present study. The strategy used in this study could also be viable to further enhance the ZT of nanostructured n-type SiGe and SrTiO3-based oxide materials.