Gd doping enabling a record zT value of 1.65 at 823 K in Zintl-phase BaCu2Te2

Abstract

BaCu2Te2, a promising Zintl-phase thermoelectric material, exhibits moderate electrical transport properties coupled with intrinsically low thermal conductivity. However, the presence of Cu vacancies in the lattice results in excessively high hole concentrations, which detrimentally affects the thermoelectric figure of merit (zT). To address this issue, a dual strategy is employed involving process optimization for Cu vacancy suppression and carrier concentration regulation for power factor enhancement. Comparative analysis reveals that spark plasma sintered samples demonstrate lower electrical and thermal conductivity compared to their hot-pressed counterparts, attributable to short sintering time to prevent Cu precipitation. Furthermore, Gd substitution at the Ba site is implemented to fine-tune the hole concentration, leading to a significant improvement in the power factor. The doping level of 0.02 Gd yields a peak power factor of 9.56 μW cm⁻¹ K⁻², representing a 63.67% enhancement relative to undoped samples. In addition, Gd doping induces lattice distortion and enhances point defect scattering, thereby effectively suppressing lattice thermal conductivity. At a doping concentration of 0.04 Gd, the lattice thermal conductivity reaches a remarkably low value of 0.12 W m⁻¹ K⁻¹ at 823 K, while the total thermal conductivity attains a minimum of 0.42 W m⁻¹ K⁻¹. Through synergistic optimization of the power factor and thermal conductivity, a maximum zT value of 1.65 is achieved at 823 K for Ba0.96Gd0.04Cu2Te2, a record value for Zintl-phase p-type thermoelectrics. Our findings demonstrate the potential of Zintl-phase BaCu2Te2 as an efficient mid-temperature thermoelectric material.