Defect Chemistry for N-Type Doping of Mg₃Sb₂-Based Thermoelectric Materials

Abstract

N-Type Mg3Sb2-based Zintl compounds have recently been discovered to be a promising class of thermoelectric materials. Effective n-type dopants are crucial for realizing high thermoelectric performance. Here, using first-principles defect calculations, we investigate that Tm and Ce are effective n-type dopants in Mg3Sb2 and explain why n-type conduction can be successfully achieved by a simple doping without extra Mg. Under Mg-rich conditions, the maximal achievable free carrier concentrations for Tm and Ce substitution on Mg sites at 750 K exceed 1020 cm–3, approaching the optimal carriers of ∼1020 cm–3. Under Mg-poor conditions, the miraculous n-type conduction achieved by a simple extrinsic n-type doping can be explained by the sufficiently low defect formation energy for the substitutional donor defect.