Enhanced Average Thermoelectric Figure of Merit of p-Type Zintl Phase Mg2ZnSb2 via Zn Vacancy Tuning and Hole Doping.

Abstract

Isoelectronic Zn substitution at the Mg site has been proved to be effective in regulating the carrier concentration of p-type Mg3Sb2 Zintl phase. However, the reported thermoelectric performance is still unsatisfactory compared with that of n-type Mg3Sb2 due to the poor electrical transport properties. Here, we report an enhanced average ZT through improving low-temperature ZTs by introducing Zn vacancy followed suppressing the bipolar effect by doping. First, the Zn vacancy simultaneously increases the power factor and decreases the thermal conductivity, leading to a peak ZT value of ∼0.52 at 773 K in Mg2Zn0.98Sb2. Additionally, doping Li or Ag at the Mg site is identified as a high-efficiency strategy for further increasing the carrier concentration and hence suppressing the bipolar effect. Finally, a peak ZT of ∼0.73 at 773 K and an average ZT of ∼0.46 between 300 and 773 K were obtained in Mg1.98Li0.02Zn0.98Sb2.