ICT2014 Abstracts

A ZT value as high as ~1.9 was achieved at 773K in GeTe based Pb_0.13Ge_0.87Te upon the introduction of 3mol% Bi₂Te₃. This excellent performance stemmed from a synergetic incorporation of improved thermopower and reduced thermal conductivity, compared with Bi₂Te₃-free GeTe based materials. The involvement of Bi₂Te₃ caused a promoted solubility of PbTe in GeTe matrix, thus greatly strengthened the point defects scattering which leads to a significantly reduced thermal conductivity. Meanwhile, the filling of Ge/Pb in the “neutral” vacancies introduced by Bi₂Te₃ reduced the hole concentration and thereby lifted up the thermopower. Moreover, thermopower was further enhanced in the sense that the solid solutioned Bi₂Te₃ in GeTe facilitated a much higher contribution to electrical conduction from the highly degenerated Σ valence band, as evidenced by Density Functional Theory calculations. These mechanisms above were then discussed in a 3-band (L+Σ valence bands and C conduction band) model, the fairly good agreement of the simulated results under this model with experiments justified the rationality of our previous discussions.