Aliovalent-driven lattice vacancy design for enhancing the thermoelectric performance of SrAgSb Zintl phase

The 1-1-1 type Zintl phase SrAgSb exhibits high carrier mobility due to the honeycomb structure of the anionic groups formed by Ag-Sb. However, the high electrical conductivity and fully occupied lattice sites result in relatively high thermal conductivity, which limits its overall thermoelectric potential. Herein, the substitution of trivalent lanthanides in Sr_0.95X_0.05Ag_0.95Sb (X = La, Ce, Pr, and Nd) is employed to introduce charge-compensating Ag-site vacancies into SrAgSb, and the effect of Ce-content modulation on the thermoelectric properties is systematically investigated. The introduction of Ce increases the density-of-states effective mass, while vacancies within the anionic framework act as scattering centers, thereby reducing the mobility. Besides, lattice vacancies lead to phonon softening, and the combined phonon scattering from Sr-site substitutional defects and Ag-site vacancies significantly suppresses the lattice thermal conductivity. Consequently, Sr_0.9Ce_0.1Ag_0.9Sb achieves a maximum zT of 0.80 at 873 K, demonstrating the effectiveness of lattice-vacancy engineering in suppressing thermal transport in Zintl phases.