First-principles study of defect chemistry and thermoelectric performance of CaMg₂Sb₂

The success of high-performance n-type Mg₃Sb₂ has sparked interest in n-type thermoelectric transport of other AM₂X₂ compounds. However, only a few such compounds have realized n-type transport so far, and their zT values remain low. Therefore, there is an urgent need to systematically understand the factors limiting their n-type thermoelectric performance. Here, using first-principles calculations, this work systematically investigates the defect chemistry, electronic structure, and thermoelectric properties of three-dimensional (3D) bulk CaMg₂Sb₂. Calculated results show that the n-type system shows a much higher power factor than the p-type counterpart, reaching 59 µW cm^-1 K^-1 at 300 K and 39 µW cm^-1 K^-1 at 725 K, and exhibits a maximum zT of ∼1.52 at 725 K. Defect analysis reveals that Sb-rich conditions favor the formation of Ca vacancies, while Mg-rich and Ca-rich conditions favor the formation of Mg and Ca interstitials, yielding n-type conduction with an electron concentration of 3 × 10¹⁶ cm^-3 at 725 K. These findings suggest that establishing Mg-rich and Ca-rich growth conditions is one of the key factors for achieving high-performance n-type thermoelectric transport. This study is expected to provide theoretical guidance for achieving high-performance n-type CaMg₂Sb₂ thermoelectric materials.