Enhanced Thermoelectric Efficiency in P-Type Mg 3 Sb 2 : Role of Monovalent Atoms Codoping at Mg sites

Due to natural abundance, low cost, and compatibility with sustainable green technology, Mg Sb -based Zintl compounds are comprehensively explored as potential thermoelectric materials for near-room temperature applications. The effective use of these materials in thermoelectric devices requires both p and n-type Mg Sb having comparable thermoelectric efficiency. However, p-type Mg Sb has inferior thermoelectric efficiency efficiency compared to its n-type counterpart due to low electrical conductivity . Here, we show that codoping of monovalent atoms (Li-Ag, and Na-Ag) at the Mg site of Mg Sb produces a synergistic effect and boosts the electrical conductivity, which enhances the thermoelectric properties of p-type Mg Sb . While, Ag prefers to occupy the Mg2 site, Li and Na are favorable at the Mg1 site of Mg Sb lattice. Compared to Li-Ag codoping, Na-Ag codoping in Mg Sb is found to be more effective for increasing the charge carrier concentration and significantly augmenting the electrical conductivity. The dominance of the three-phonon scattering mechanism in Li and Li-Ag doped Mg Sb and the four-phonon scattering process for the Na and Na-Ag doped Mg Sb are confirmed. Due to the simultaneous increase in electrical conductivity and decrease in thermal conductivity, the value ∼0.8 at 675 K achieved for Mg Na Ag Sb is the highest value among p-type Mg Sb . Our work shows a constructive approach to enhance the of p-type Mg Sb via monovalent atoms codoping at the Mg sites.