Enhancing thermoelectric performance of BaMg₂-based compounds by forming solid solutions and biaxial strain

Abstract

Two strategies were proposed to optimize the thermoelectric performance of BaMg 2 (Bi,Sb) through a solid solution method and to tune the crystal field splitting energy of orbital by using first principles calculation and Boltzmann transport theory. The increase in Sb content leads to decreased weight carrier mobility due to the changes in the electronic structure. The lattice thermal conductivity for BaMg 2 SbBi can be as low as 0.45 W m −1 K −1 , which is lower than those of other compounds. The highest ZT of ∼0.88 for BaMg 2 SbBi has been obtained at 750 K with n-type doping carrier concentration of −8.28 × 10 18 cm −3 , indicating that reaching the optimal Sb content (i.e. BaMg 2 SbBi) can make a significant contribution to the maximization of the ZT of n-type BaMg 2 (Bi,Sb) solid solutions. Adjusting the crystal field splitting energy increases the effective mass of density of states, which causes the change in power factor (PF) value and achieves a maximum PF value. When the tensile strain for BaMg 2 Bi 2 , BaMg 2 SbBi, and BaMg 2 Sb 2 is 2%, 2%, and 6%, the ZT value is significantly improved, respectively. Therefore, minimizing crystal field splitting energy is also effective in the optimization of the ZT value.