Enhanced Thermoelectric Performance of p-Type Mg3Sb2 for Reliable and Low-Cost all-Mg3Sb2-Based Thermoelectric Low-Grade Heat Recovery

Bi2Te3-based devices have long dominated the commercial market for thermoelectric cooling applications, but their narrow operating temperature range and high cost have limited their possible applications for conversion of low-grade heat into electric power. The recently developed n-type Mg3Sb2-based compounds exhibit excellent transport properties across a wide temperature range, have low material costs, and are nontoxic, so it would be possible to substitute the conventional Bi2Te3 module with a reliable and low-cost all-Mg3Sb2-based thermoelectric device if a good p-type Mg3Sb2 material can be obtained to match its n-type counterpart. In this study, by comprehensively regulating the carrier concentration, carrier mobility, and lattice thermal conductivity, the thermoelectric performance of p-type Mg3Sb2 is significantly improved through Na and Yb doping in Mg1.8Zn1.2Sb2. Moreover, p- and n-type Mg3Sb2 are similar in terms of their coefficients of thermal expansion and their good performance stability, thus allowing the construction of a reliable all-Mg3Sb2-based unicouple. The decent conversion efficiency (approximate to 5.5% at the hot-side temperature of 573 K), good performance stability, and low cost of this unicouple effectively promote the practical application of Mg3Sb2-based thermoelectric generators for low-grade heat recovery.