Characterization and thermoelectric performance of mechanochemically synthesized Cu-Ag-Se sample series

The Cu_2-x Ag _x Se potential thermoelectrics series (x = 0.4-1.8) is prepared in a planetary ball mill by high-energy milling of Cu, Ag, and Se powders. After only 7 min of mechanochemical synthesis, the products are analyzed by X-ray diffraction, particle size distribution, specific surface area, X-ray fluorescence analysis, scanning electron microscopy, and thermal analysis. Unlike conventional high-temperature or multi-step syntheses, this rapid mechanochemical method yields phase-pure CuAgSe along with controlled excess metal selenides, thereby enabling a direct correlation among composition, reversible nanoscale ionic rearrangements, and charge-transport behaviour. XRD shows the same multiphase composition in powders and densified pellets, indicating no significant changes during sintering. The BET and PSD values remain similar across all compositions, while SEM reveals two distinct phases whose identities are verified by EDX. DTA shows composition-dependent phase transitions that govern the complex thermal behavior of Cu_2-x Ag _x Se. Tuning the Cu : Ag ratio induces p-to n-type inversion and mixed carrier transport. By systematically mapping how Cu-Ag substitution tunes dual phase transitions, carrier-type inversion (p → n), and mixed electron-hole transport, this work provides fundamentally new mechanistic insight into the interplay between superionic mobility and thermoelectric performance. Remarkably, high ZT values up to 1.47 are achieved without annealing or microstructural engineering, demonstrating that rapid, green mechanochemical synthesis can produce high-performance Cu-Ag-Se thermoelectrics comparable to state-of-the-art methods. The highest ZT of 1.47@574 K is reached for p-type Cu_1.6Ag_0.4Se, and for n-type Cu_0.6Ag_1.4Se, 0.73@570 K after the phase transition.