Remarkable Enhancement in Thermoelectric Performance and Thermal Stability of AgCuTe through Cation Vacancy Regulation

As a phonon-liquid electron-crystal (PLEC), AgCuTe exhibits unique advantages due to its complex crystal structure and inherently low lattice thermal conductivity. However, the high concentration of Ag/Cu cation vacancies in AgCuTe leads to an excessively high carrier concentration, which restricts its thermoelectric performance. In this study, both the phase composition and carrier concentration were tailored by tuning the Ag/Cu content in AgCuTe. As the Ag/Cu content increases, the phase composition evolves from Ag 2 Te and Cu 2 Te secondary phases to a predominant AgCuTe phase. Seebeck coefficient measurements reveal that AgCuTe exhibits a conduction type transition upon tailoring the Ag/Cu content. The Ag/Cu-deficient samples exhibit n-type semiconducting behavior at room temperature. Increasing the Ag/Cu content gradually reduces the Ag 2 Te secondary phase, which in turn decreases electron carriers. Meanwhile, positron annihilation measurements reveal that more cation vacancies are introduced with increasing Ag/Cu content, which afford a high concentration of hole carriers and thus switch samples to p-type conduction. At temperatures higher than 527 K, all the samples exhibit a pure cubic AgCuTe phase and show p-type conduction behavior. The increased Ag/Cu content reduces Hall carrier concentration, leading to enhanced power factor and decreased electronic thermal conductivity. In addition, the increased Ag/Cu content further reduces the lattice thermal conductivity by decreasing the sound velocity and enhancing lattice anharmonicity. Collectively, these factors realize synergistic optimization of thermoelectric performance. The (AgCu) 1.06 Te sample achieves a remarkable zT max value of 1.39 at 737 K, with an average zT ( zT ave ) of 1.29 between 523 and 737 K, which show enhancement of 74 and 94% compared with the pristine AgCuTe, respectively. The Ag/Cu excess samples also demonstrate excellent thermal stability up to 873 K. This work provides a strategy for further optimizing the thermoelectric performance of AgCuTe-based materials.