Transport behavior and thermoelectric properties of AMg₂Sb₂-based Zintl phases: The first-principles study

Antimony (Sb)-based Zintl compounds are proved to be a kind of promising thermoelectric materials with the intrinsic "electric-crystal, phonon-glass" nature. Their unique crystal structure results in low lattice thermal conductivities at high temperature. This work investigates the electronic structure, the electronic and phonon transport properties of AMg(2)Sb(2)-based Zintl compounds (A = Ca, Sr, Ba) using the density functional theory and the Boltzmann transport equation. We also analyze the thermal properties including the phonon spectrum and thermal conductivity. The contribution of optical and acoustic branches to the phonon velocity and relaxation time is analyzed. A-site atoms contribute to the low-frequency optical branch, and the frequency decreases from Ca to Ba gradually with the increase of atomic number. The minimum lattice thermal conductivity of the three compounds is calculated as 0.581 W/mK, 0.542 W/mK, and 0.498 W/mK, respectively, which is considerably small in the thermoelectric systems. The maximum zT value of n-type CaMg2Sb2 is calculated to reach 1.2 over the optimal carrier concentration range at 700 K, similar to 71% higher than the value of 0.69 for the p-type, which is expected for potential thermoelectric materials.