Enhancement of the Thermoelectric Properties of BiCuSeO via In Doping and Powder Size Controlling

BiCuSeO is regarded as one of the most promising oxygenated thermoelectric materials because of its special natural superlattice structure and corresponding ultra-low thermal conductivity. In order to improve the thermoelectric performance, we should pay attention to both composition adjustment and structure adjustment. In this paper, we report a study which combines the two ways to improve the electrical transporting performance and suppress the thermal transporting performance, and we have effectively improved the thermoelectric performance. Firstly, by adjusting the composition with In doping at the Bi site, the band gap widens, the energy offset between heavy band and light band increases, and the mobility and electrical transporting performance improves correspondingly. The maximum ZT value is increased to 0.61. Based on this, the thermoelectric properties are further improved in the whole temperature range by increasing the mechanical alloying strength to refine the powders and adjusting the proportion of fine powder and coarse powder. Grain refinement increases the Cu vacancies and corresponding electrical properties. In addition, Grain refinement contributes to enhancing phonon scattering and effectively reduces the lattice thermal conductivity. The thermal conductivity decreases significantly in the whole temperature range because grain refinement can significantly enhance phonon scattering and reduce the lattice thermal conductivity. The appropriate proportion of coarse powder and fine powder can make full use of the fine grains to enhance phonon scattering while enlarging the frequency range of scattered phonons, thus further reducing the thermal conductivity. Finally, the ZT value increased to 1.08.