Weakening the spin–orbital coupling for band convergence

Band convergence is a favorable strategy that is utilized to improve the thermoelectric performance in experiment, whereas a theoretical guidance for this purposive design is rare. With high-level first-principles treatment of electronic and transport properties in the emerging ABX (A = Ca, Sr, Ba; B = Cu, Ag; X = P, As, Sb) Zintl systems, a principled scheme via weakening the spin–orbital coupling is proposed based on symmetry and orbital analysis to promote the band convergence. This given rule is numerically confirmed in BaAgX alloys. Despite the intensified intervalley electron–phonon scattering, the alloying of BaAgP in BaAgSb prominently triggers the band convergence and contributes to much larger density of state effective mass, which eventually results in a ∼40% improvement in zT values. This work offers an applicable principle for designing band convergence, which also broads the compositions of thermoelectrics to light and earth-abundant elements.