Enhancement of the thermoelectric properties of Zintl phase SrMg2Bi2 by Na-doping

Abstract

Due to their low lattice thermal conductivity and manipulable electronic properties, AB₂X₂ Zintl phases have been widely studied for thermoelectric applications. This has motivated numerous efforts to focus on the exploration of novel AB₂X₂ Zintl thermoelectrics. In this study, SrMg₂Bi₂ was systematically investigated to reveal its potential for thermoelectric application. Pristine SrMg₂Bi₂ exhibits an intrinsic p-type semiconducting behavior. The Hall carrier concentration (n_H) was efficiently increased to ∼9 × 10¹⁹ cm⁻³ by Na-substitution at the Sr site. The increased n_H leads to enhanced electrical conductivity, but reduced Seebeck coefficient. Moreover, Na doping effectively decreased the thermal conductivity because of the intensified scattering from defects and lattice distortion. Thus, the zT of the Na-doped SrMg₂Bi₂ can reach 0.44 and be extremely higher than that of the pristine one. The well-known single parabolic band (SPB) model estimated that the increase in N_v and m* through doping boosts the electrical conductivity. This work sheds light on the discovery of new prospective thermoelectric materials and demonstrates that Bi-based p-type AB₂X₂ Zintl phases can achieve high thermoelectric performance.