2, Department of Materials Science and Engineering, Yeonsei University, Seoul, , Korea (the Republic of)
3, Department of Energy Science, Sungkunkwan University, Suwon, , Korea (the Republic of)
Bismuth Antimony Telluride (Bi,Sb)2Te3 alloys are the most widely used thermoelectric bulk materials near room temperature, developed in 1950s. Nevertheless, wide use of applications using (Bi,Sb)2Te3 alloys are yet constrained because of the low thermoelectric conversion efficiency. In order to enhance the thermoelectric conversion efficiency, low total thermal conductivity of the alloy is required, which can maintain the temperature difference across a material. The total thermal conductivity of (Bi,Sb)2Te3 alloys is divided into three components in respect to its physical nature, including electronic, bipolar, and lattice thermal conductivity. Since the electronic thermal conductivity is simply proportional to electrical conductivity under Wiedermann-Franz law, the bipolar and lattice thermal conductivities should be minimized to reduce the total thermal conductivity. Bipolar thermal conductivity can be engineered by controlling band structures, such as carrier concentration or bandgap, and the lattice thermal conductivity can be reduced by introducing various defect structures enhancing phonon scattering. Herein, we analyzed the bipolar and lattice thermal conductivies of (Bi,Sb)2Te3 alloys with defect structures, including point defects (0 dimension, 0D), dislocations (1D), grain boundaries (2D), or nano-sized metal inclusions (3D), by using Debye-Callaway model and a single parabolic band model based on Boltzmann transport. Then, the lattice thermal conductivity depending on the density of each defect was estimated based on the analysis, providing materials design rule for reducing thermal conductivity of (Bi,Sb)2Te3 alloy. Furthermore, the influence of multiple defects on frequency-dependent phonon scattering was evaluated in order to properly design multi-defect structure.