A Dual Role by Incorporation of Magnesium in YbZn₂Sb₂ Zintl Phase for Enhanced Thermoelectric Performance

1-2-2-type Zintl phase compounds have promising thermoelectric properties because of their complex crystal structures and multiple valence-band structures. In this work, a series of single phase (Yb_0.9Mg_0.1)Mg_xZn_2−xSb₂ (x = 0, 0.2, 0.4, 0.6, 0.8, and 1) compounds are prepared by alloying YbZn₂Sb₂ with 10 at% MgZn₂Sb₂ and different amounts of YbMg₂Sb₂. The incorporation of Mg at the Yb site, as well as at the Zn site, not only leads to an effective orbital alignment confirmed by the dramatically enhanced density of states effective mass and Seebeck coefficients, but also increases the point defect scattering, contributing to a low lattice thermal conductivity ≈0.54 W m⁻¹ K⁻¹ at 773 K. Combined with the optimization of the carrier concentration by Ag doping at the Zn site, a highest ZT value ≈1.5 at 773 K is achieved in (Yb_0.9Mg_0.1)Mg_0.8Zn_1.2Ag_0.002Sb₂, which is higher than that of all the previously reported 1-2-2-type Zintl phase compounds.