High-Density Arrangement of Nanoscale Regions with Tellurium Interstitial Atoms and Silver/Copper Vacancies in AgCuTe Thermoelectric Materials

The rigid crystalline sublattice of Te ions in AgCuTe provides an effective electrical transport channel, enabling AgCuTe to exhibit good electrical properties. However, the appearance of vacancies or interstitial atoms within the Te^2– rigid anionic framework poses significant challenges both theoretically and experimentally. Here, we are the first to discover the existence of localized Te_i, V_Cu, and V_Ag multiple defects in the AgCuTe phase, as well as a highly ordered arrangement of V_Cu in the Cu₂Te phase of AgCuTe_1–z samples, by only fine-tuning the Te stoichiometric ratio. The formation of these localized defects arises from the excess precipitation of Ag and Cu during the process, which enhances phonon scattering and reduces thermal conductivity. Simultaneously, the total cation content in AgCuTe_1–z samples increases relative to the anion, thereby optimizing total intrinsic vacancies and carrier concentration. As a result, there is a 311% increase in the power factor and a 44% decrease in the lattice thermal conductivity at room temperature, leading to a 54% net increase in ZT compared to that of pristine AgCuTe. This approach is expected to be a universal modification strategy for enhancing the thermoelectric properties of other Te-based anionic framework superionic conductor materials.