Manganese doping induced record-high medium-temperature AgCuTe thermoelectrics

AgCuTe, a superionic conductor with high carrier mobility, ultra-low lattice thermal conductivity, unique crystal structure, and strong tunability of electron and phonon transport, is considered one of the most promising candidates for medium-temperature thermoelectric applications. However, its practical deployment has been hindered by insufficient optimization strategies, resulting in limited thermoelectric performance. In this study, we achieved a high dimensionless figure of merit (ZT) of ∼1.88 at 773 K in p-type manganese-doped polycrystalline AgCuTe, which is one of the highest reported values for AgCuTe-based materials and is comparable to other state-of-the-art medium-temperature thermoelectrics. This enhancement stems from band convergence and valence band flattening without compromising the intrinsically low thermal conductivity. Manganese doping effectively optimizes the electronic band structure to improve the power factor and simultaneously reduces lattice thermal conductivity through intensified lattice defects. These combined effects yield superior thermoelectric performance and higher average ZT values than previously reported p-type AgCuTe materials. Furthermore, a single-leg segmented thermoelectric module incorporating this material and commercial p-type (Bi, Sb)₂Te₃ achieved a high energy conversion efficiency of ∼13.3% under a temperature difference of ∼462 K. This work highlights the effectiveness of electronic band structure engineering in enhancing the thermoelectric performance of superionic conductors.