Tuning the carrier scattering mechanism to improve the thermoelectric performance of p-type Mg3Sb1.5Bi0.5-based material by Ge doping

Abstract

P-type Mg3Sb2-based Zintl compounds remain largely unexplored due to their inferior ZT values compared with n-type counterparts. The intrinsic p-type Mg3Sb1.5Bi0.5 manifests relatively poor thermoelectric performance because of its low electrical conductivity of about 3 × 102 S/m at room temperature. In this work, Ge is doped on the Bi site of Mg3Sb1.5Bi0.5, where the carrier scattering mechanism changes from ionized impurity scattering to mixed ionized impurity and acoustic phonon scattering. A significant improvement in Hall mobility from ∼1.8 to ∼24 cm2 V−1/s is obtained, thus leading to a notably enhanced electrical conductivity of 2.2 × 104 S/m from 2.9 × 102 S/m. A simultaneous reduction in lattice thermal conductivity is also achieved. Collectively, a maximum ZT value of 0.5 is obtained at 723 K in Mg3Sb1.5Bi0.47Ge0.03 with a carrier concentration of 5.02 × 1019/cm3.