Enhanced Thermoelectric Efficiency in P-Type Mg<sub>3</sub>Sb<sub>2</sub>: Role of Monovalent Atoms Codoping at Mg sites
Minati Tiadi, Vikrant Trivedi, Santosh Kumar, Prashant K. Jain, Satyesh Kumar Yadav, R. Gopalan, Dillip K. Satapathy, Manjusha Battabyal
Abstract
Due to natural abundance, low cost, and compatibility with sustainable green technology, Mg 3 Sb 2 -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 3 Sb 2 having comparable thermoelectric efficiency. However, p-type Mg 3 Sb 2 has inferior thermoelectric efficiency efficiency compared to its n-type counterpart due to low electrical conductivity ( ∼ 10 3 S m − 1 ) . Here, we show that codoping of monovalent atoms (Li–Ag, and Na–Ag) at the Mg site of Mg 3 Sb 2 produces a synergistic effect and boosts the electrical conductivity, which enhances the thermoelectric properties of p-type Mg 3 Sb 2 . While, Ag prefers to occupy the Mg2 site, Li and Na are favorable at the Mg1 site of Mg 3 Sb 2 lattice. Compared to Li–Ag codoping, Na–Ag codoping in Mg 3 Sb 2 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 3 Sb 2 and the four-phonon scattering process for the Na and Na–Ag doped Mg 3 Sb 2 are confirmed. Due to the simultaneous increase in electrical conductivity and decrease in thermal conductivity, the zT value ∼0.8 at 675 K achieved for Mg 2.975 Na 0.02 Ag 0.005 Sb 2 is the highest value among p-type Mg 3 Sb 2 . Our work shows a constructive approach to enhance the zT of p-type Mg 3 Sb 2 via monovalent atoms codoping at the Mg sites.