Enhanced thermoelectric performance of Mg and Se co-doped Bi2Te3 nanostructures

Bi2Te3-based thermoelectric materials are good candidates for near low and room temperatures. Here, Se and Mg co-doped Bi2Te3 nanostructures were prepared by the solvothermal method. They have rhombohedral crystal structures with space group R-3m as examined by XRD. The nanoplate-like morphology was observed by FESEM. The porosity of the samples was confirmed by FESEM and density measurement. XPS was used to study the valence states and binding energy of the samples. The vibrational modes A1u1, Eg2 and A1g2 are shifted to lower wavenumber with doping, as obtained by Raman spectroscopy. The Hall effect was employed to obtain the carrier concentration and mobility. The band gap energy was obtained in the range of 0.27–0.31 eV by Tauc plotting. In Bi1.94Mg0.06Te2.9Se0.1, the power factor increases to 8.8 × 10−4 Wm−1K−2 at 330 K due to increase in carrier concentration. An ultralow lattice thermal conductivity of ∼0.12 W/m/K was obtained in Bi1.94Mg0.06Te2.9Se0.1 sample, due to the strong phonon scattering at grain boundary and interfaces. The maximum ZT of ∼0.63 was obtained at 300 K for Bi1.97Mg0.03Te2.9Se0.1. The ZT value is about 85 % greater than ZT of pure Bi2Te3 (∼0.34 at 300 K).