High-Density Arrangement\nof Nanoscale Regions with\nTellurium Interstitial Atoms and Silver/Copper Vacancies in AgCuTe\nThermoelectric Materials

The rigid crystalline sublattice of Te ions in AgCuTe\nprovides\nan effective electrical transport channel, enabling AgCuTe to exhibit\ngood electrical properties. However, the appearance of vacancies or\ninterstitial atoms within the Te<sup>2–</sup> rigid anionic\nframework poses significant challenges both theoretically and experimentally.\nHere, we are the first to discover the existence of localized Te<sub>i</sub>, V<sub>Cu</sub>, and V<sub>Ag</sub> multiple defects in the\nAgCuTe phase, as well as a highly ordered arrangement of V<sub>Cu</sub> in the Cu<sub>2</sub>Te phase of AgCuTe<sub>1–<i>z</i></sub> samples, by only fine-tuning the Te stoichiometric ratio.\nThe formation of these localized defects arises from the excess precipitation\nof Ag and Cu during the process, which enhances phonon scattering\nand reduces thermal conductivity. Simultaneously, the total cation\ncontent in AgCuTe<sub>1–<i>z</i></sub> samples increases\nrelative to the anion, thereby optimizing total intrinsic vacancies\nand carrier concentration. As a result, there is a 311% increase in\nthe power factor and a 44% decrease in the lattice thermal conductivity\nat room temperature, leading to a 54% net increase in <i>ZT</i> compared to that of pristine AgCuTe. This approach is expected to\nbe a universal modification strategy for enhancing the thermoelectric\nproperties of other Te-based anionic framework superionic conductor\nmaterials.