Enhanced electrical transport properties via Pb vacancies in single crystalline PbTe prepared by Te-flux method

In PbTe system, Pb vacancies (VPb) are preferentially formed compared with other intrinsic point defects (anti-sites TePb and interstitials Tei) under the Te-rich condition. In order to explore the effect of VPb on electrical transport properties of PbTe thermoelectric material, the electronic structures of PbTe with VPb are determined by the first principle calculations. Theoretical calculations reveal that the VPb can modify the band structure near the Fermi level, which can increase the number of carrier pockets thus increase the carrier concentration. Based on the calculated results, single crystalline PbTe samples with VPb have been prepared by Te-flux method according to the stoichiometric ratio of PbTe1+x (x = 2.0, 2.5, 3.0 and 3.5). The experimental results show that carrier concentration is optimized significantly by tuning Te-flux content, and it varies from 2.94 × 1018 to 8.01 × 1018 cm−3. The highest electrical conductivity reaches 3.1 × 104 S m−1 at 300 K for x = 3.5. A large Seebeck coefficient of 562 μV/K is obtained at 480 K for x = 2.0. Due to the synergistic effect of the Seebeck coefficient and the electrical conductivity, the highest power factor of 3.17 × 10−3 W m−1 K−2 is achieved at 450 K for x = 3.0.