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 (nH) was efficiently increased to ∼9 × 1019 cm-3 by Na-substitution at the Sr site. The increased nH 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 Nv 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.