Enhanced thermoelectric properties of polycrystalline BiCuSeO via dual-doping in Bi sites

Abstract

The effect of Pb and La substitution on the thermoelectric properties of BiCuSeO oxyselenide has been studied. It is revealed that Pb doping can significantly improve the electrical conductivity due to the increased carrier concentration, which results in a large power factor in the range of 700 to 800 μW m⁻¹ K⁻² at 873 K. In particular, the electrical transport properties can be further improved obviously over the entire measured temperature range after replacing some Bi³⁺ ions with La³⁺ ions in Bi_0.94Pb_0.06CuSeO. The electrical conductivity has increased from 408 S cm⁻¹ for Bi_0.94Pb_0.06CuSeO to 594 S cm⁻¹ for Bi_0.93Pb_0.06La_0.01CuSeO at 327 K due to the increased carrier mobility. Combining with the moderate Seebeck coefficient which is over 124 μV K⁻¹, the power factor has been significantly improved. An optimal value of 1059 μW m⁻¹ K⁻² at around room temperature is achieved for Bi_0.93Pb_0.06La_0.01CuSeO and is much higher than most reported values. Additionally, the increased total thermal conductivity for the Pb-doped sample compared with the pristine sample has been suppressed after further doping the La element in Bi_0.94Pb_0.06CuSeO. Therefore, a maximum ZT value of nearly 0.90 at 873 K for the sample Bi_0.92La_0.02Pb_0.06CuSeO has been finally obtained, which is ∼36% and ∼16% higher as compared with those of the La-free sample Bi_0.94Pb_0.06CuSeO and the reported Pb-free sample Bi_0.92La_0.08CuSeO.