Strong Intra- and Interchain Orbital Coupling Leads To Multiband and High Thermoelectric Performance In Na2AuX (X = P, As, Sb, and Bi).

The coupling among electrical conductivity ( σ $\sigma$ ), Seebeck coefficient ( S $S$ ), and lattice thermal conductivity ( κ L $\kappa _{\mathrm{L}}$ ) fundamentally limits thermoelectric performance. Increasing band degeneracy can effectively balance σ $\sigma$ and S $S$ to achieve a high-power factor (PF, S 2 σ $S^{2}\sigma$ ), yet highly degenerate electronic structures are uncommon, particularly in low-symmetry materials. In this work, we propose an unconventional strategy to enhance band degeneracy in zig-zag-chain Na 2 Au ${\rm Na}_2{\rm Au}$ X $X$ ( X = $X =$ P, As, Sb, and Bi) compounds. Strong intra-chain hybridization between Au d z 2 ${\rm Au}_{d_{z^2}}$ and X p z $X_{p_z}$ orbitals, together with unexpectedly strong inter-chain coupling of X p x $X_{p_x}$ states, generates a highly dispersive multivalley valence band that supports large PF. Concurrently, the quasi-one-dimensional framework's inherently weak inter-chain interactions, together with the softened Au- X $X$ and Au-Au bonds within the chains due to the antibonding p $p$ - d ∗ $d^{*}$ states, lead to a substantial reduction in κ L $\kappa _{\mathrm{L}}$ . First-principles calculations, integrated with Boltzmann transport theory, confirm that these unique structural and electronic attributes enable p $p$ -type Na 2 AuBi ${\rm Na}_2{\rm AuBi}$ to exhibit high thermoelectric performance. This work establishes a new design paradigm for high-efficiency thermoelectric materials by harnessing substantial orbital overlap within weakly bonded, quasi-one-dimensional systems. The findings open promising avenues for discovering and engineering high-performance thermoelectric materials.