Understanding the Prospects of the Thermoelectric Performance of the YbMg₂(Bi,Sb)₂ Zintl Phase

AM2X2 Zintl compounds, crystallizing in layered structures, have recently garnered attention due to their promising thermoelectric properties. In this study, we explore the chemical bonding and elastic and thermoelectric properties evolution across the full YbMg2Bi2–xSbx solid solution. The transition from YbMg2Bi2 to YbMg2Sb2 leads to a continuous linear chemical-bond shortening and thus a significant enhancement in elastic moduli and sound velocity, resulting in overall significant lattice stiffening. Simultaneously, the shift toward more ionic chemical bonding leads to significant changes in the band structure, particularly an increase in effective mass and a decrease in both carrier concentration and mobility, which in turn reduces the power factor for Sb-rich samples. However, a rapid increase in point-defect scattering causes the lattice thermal conductivity to drop from ≈3 to almost 1 Wm–1–K–1 at 300 K for the intermediate compositions, thus opening new room for further optimization of the Sb-rich representatives of the YbMg2Bi2–xSbx. Therefore, in this work, we have demonstrated that despite the seemingly intrinsically higher thermoelectric performance in the Bi-rich region of the YbMg2Bi2–xSbx solid solution, the Sb-rich representatives may in fact be even more promising due to better mechanical and thermal stability and greater room for further charge carrier concentration optimization.