Zintl compounds (Mg3Sb2-based) are explored as potential thermoelectric materials for near-room temperature applications, due to their natural abundance, low cost, and compatibility with sustainable green technology. The effective use of these materials in thermoelectric devices requires both p and n-type Mg3Sb2 having comparable thermoelectric efficiency. However, p-type Mg3Sb2 has lower thermoelectric efficiency than its n-type counterpart due to low electrical conductivity (~ 103 Sm-1). In this talk, I will present the successful realization of p-type Mg3Sb2 via doping the suitable elements at the Mg sites, achieved using a combined approach involving theoretical calculations and experimental realizations. We show that codoping of monovalent atoms (Li−Ag, Na−Ag, and Cu-Ag) at the Mg site of Mg3Sb2 produces a synergistic effect that not only boosts the electrical conductivity but also enhances the thermoelectric properties of p-type Mg3Sb2 [1]. The enhancement of the figure-of-merit (zT) comes from a drastic reduction of the lattice thermal conductivity aided by the rattling of co-doped atoms. The dominance of the three-phonon scattering mechanism in Li and Li−Ag doped Mg3Sb2 and the four-phonon scattering process for the Na and Na−Ag doped Mg3Sb2 are confirmed. Due to the simultaneous increase in electrical conductivity and decrease in thermal conductivity, a zT value ∼0.8 at 675 K is achieved for Na-Ag co-doped sample and is the highest value reported to date for p-type Mg3Sb2 [2]. Apart from thermoelectric properties, we also investigated the phonon anharmonicity in polycrystalline Mg3Sb2 using temperature-dependent Raman spectroscopy and heat-capacity measurements [3].

[1] Minati Tiadi, et al., ACS Appl. Mater. Interfaces, 15, 20175 (2023).
https://doi.org/10.1021/acsami.3c02151

[2] Minati Tiadi, et al., Sustainable Energy Fuels, 5, 4104 (2021).
https://doi.org/10.1039/D1SE00656H

[3] Minati Tiadi, et al., Physical Review Materials, 7, 015401, (2023).
https://doi.org/10.1103/PhysRevMaterials.7.015401