Zintl germanides for thermoelectric applications: Insights from DFT and Boltzmann transport theory

• DFT and Boltzmann transport study reveals thermoelectric properties of AeNiGe compounds. • BaNiGe and SrNiGe achieve ∼ 40 µV/K Seebeck and < 1 W/mK thermal conductivity at 450 K. • Ni-d and Ge-p states dominate electronic structure, influenced by Ae element variations. • MgNiGe shows higher thermal conductivity (∼7 W/mK), limiting its thermoelectric potential. • BaNiGe and SrNiGe are promising candidates for energy conversion technologies. We present a comprehensive theoretical investigation of the electronic and thermoelectric properties of Zintl germanides AeNiGe (Ae = Mg, Sr, Ba) using density functional theory (DFT) combined with Boltzmann transport theory. Our calculations reveal that all three compounds exhibit metallic behavior, with notable differences in their electronic band structures and density of states. Analysis of the partial density of states shows that the bands near the Fermi level are primarily composed of Ni- d and Ge- p states, with varying contributions from the alkaline earth metals’ orbitals. The thermoelectric properties, calculated using the BoltzTraP code within the relaxation time approximation, indicate a strong dependence on temperature and chemical potential. Ba- and Sr-based compounds demonstrate superior thermoelectric performance compared to Mg-based counterparts, achieving maximum Seebeck coefficients of approximately 40 µV/K at 450 K under negative chemical potentials (−2.00 eV). Additionally, Ba- and Sr-based materials exhibit significantly lower thermal conductivity (below 1 W/mK at high temperatures) compared to Mg-based materials (up to 7 W/mK). These findings suggest that BaNiGe and SrNiGe are promising candidates for thermoelectric applications, offering an optimal balance of high Seebeck coefficient, moderate electrical conductivity, and low thermal conductivity. Our results provide valuable insights for the design and ptimization of Zintl-based thermoelectric materials for energy conversion applications.