Enhancement on thermoelectric performance by Ti doping and vacancies

Due to the exceptionally low lattice thermal conductivity, AgSbTe2 has emerged as a promising thermoelectric material. However, unlike other IV-VI compounds, most reported AgSbTe2 samples exhibit relatively poor electrical performance due to low carrier concentration. Herein, an unusually strategy of introducing dopants and vacancies on the same site of Sb is adopted, which significantly improves the electrical performance of AgSbTe2. It is found that Ti doping on Sb site can increase the carrier concentration and promote band convergence, based on which the introduction of Sb vacancy further enlarges the carrier concentration to approach the optimal value without affecting the carrier mobility. Consequently, an excellent average power factor of 1.4 mW m-1K-2 is achieved in AgSb0.94 Ti0.05Te2 from 323 K to 623 K. Combining with reduced thermal conductivity due to strengthened phonon scattering induced by the abundant lattice defects, a peak zT of 1.8 and a high average zT of 1.3 are attained. These results provide some new insights for improving the thermoelectric performance of AgSbTe2 based compounds.