Combined Tactics for Elevating the Thermoelectric Performance of CaMg2Sb2-Based p-type Materials

p-type CaMg2Sb2 has not been favorably considered a promising thermoelectric material in comparison to other Zintl phases. However, a series of meticulously designed tactics is successfully implemented here to analyze and improve the thermoelectric performance of a CaMg2Sb2-based material. Band structure calculations show that the pristine CaMg2Sb2 has a wide indirect band gap of approximate to 1.11 eV, which results in its less optimal carrier concentration. To improve its consequently inferior thermoelectric performance, Na doping is first deployed to increase the carrier concentration to an optimal level. Subsequently, the ideal bandwidth and enhanced carrier mobility are simultaneously obtained through Zn alloying. Finally, partial Yb substitution for Ca effectively restrains the bipolar effect in this CaMg2Sb2-based material and augments its power factor while suppressing its lattice thermal conductivity to a minimum. As a result, a 20-fold-higher peak figure of merit (zT) of approximate to 0.85 at 773 K and an average zT value of approximate to 0.50 from 298 to 773 K are achieved in Ca0.69Yb0.3Na0.01Mg1.1Zn0.9Sb2, the highest for both values among all [Ca,Mg,Eu,Yb]Mg2Sb2-based materials reported to date. Furthermore, such a combination of rationally designed tactics as proposed here may assist in exploring the improvement of other thermoelectric materials that have long been overlooked.