PbTe and its alloys are considered to be some of the best thermoelectric materials for mid temperature power generation. However, environmental concern about Pb limits its usage in the large scale thermoelectric applications. SnTe and GeTe, having valence band structure similar to PbTe, recently has attracted attention for thermoelectric heat to electricity generation. Pristine SnTe and GeTe are p-type degenerate semiconductor with large carrier density (~1021 cm-3) due to intrinsic Sn and Ge-vacancy, respectively, which resulted in low Seebeck coefficient, thus leading to low thermoelectric figure of merit, zT. Mg (2-10 mol%) alloying in SnTe modulates its electronic band structure by increasing the band gap of SnTe, and results in decrease in the energy separation between its light and heavy hole valence bands. Thus, solid solution alloying with Mg enhances the contribution of heavy hole valence band, leading to significant improvement in the Seebeck coefficient in Mg alloyed SnTe, which in turn results in remarkable enhancement in power factor. Maximum zT of ~1.2 is achieved at 860K in high quality crystalline ingot of p-type Sn0.94Mg0.09Te.1 High zT of ~1.9 at 725 K along with significant cyclable temperature stability was recetly achieved in p-type Ge1-xSbxTe samples through simultaneous enhancement in Seebeck coefficient and reduction of thermal conductivity.2 Sb doping in GeTe decreases the carrier concentration due to the donor dopant nature of Sb and enhances the valence band degeneracy by increasing the cubic nature of the sample, which collectively boost Seebeck coefficient in the temperature range of 300-773 K. Significant thermal conductivity reduction was achieved due to collective phonon scattering from various meso-structured domain variants, twin and inversion boundaries, nano-structured defect layers, and solid solution point defects. The high performance Ge0.9Sb0.1Te sample shows mechanical stability (Vickers microhardness) of ~206 Hv, which is significantly higher compared to other popular thermoelectric materials such as Bi2Te3, PbTe, PbSe, Cu2Se and TAGS. 1. Banik, A.; Shenoy, U. S.; Anand, S.; Waghmare, U. V. and Biswas, K. Chem. Mater. 2015, 27, 581. 2. Perumal, S.; Roychowdhury, S.; Negi, D. S.; Datta, R. and Biswas, K. Chem. Mater. 2015, DOI: 10.1021/acs.chemmater.5b03434.

Efficient thermoelectric energy conversion in SnTe and GeTe

251st National Meeting (2016)

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