Simultaneously enhanced mechanical and thermoelectric performance of Ag9GaSe6 argyrodites via tailoring chemical compositions

Argyrodite materials with ion diffusion (Ag+, Cu+, and Li+) and inherently low thermal conductivity have attracted significant interest as promising candidates for thermoelectric and solid-state battery applications. Empirically, poor mechanical performance often accompanies such low thermal conductivity, but the mechanical properties of argyrodite compounds have rarely been reported, especially for high-performance argyrodite Ag9GaSe6. In this work, we reveal the inferior hardness and elastic modulus of argyrodite Ag9GaSe6 through experimental measurements and theoretical calculations, primarily attributed to the presence of a large number of weak chemical bonds. To enhance the mechanical properties, Mn atoms were introduced to partially substitute either the rigid Ga sites or the highly diffusive Ag sites, forming composition of Ag9Ga1-xMnxSe6 (0≤x≤0.1) and Ag9-yMnyGaSe6 (0≤y≤0.2). As a result, the doped samples exhibited approximately 38% higher hardness (2.3 GPa) and 44% higher elastic modulus (30.1 GPa) compared to pristine Ag9GaSe6. In addition, the slightly optimized carrier concentration, along with the preservation of low thermal conductivity, contributed to enhanced average zT values as high as 0.9 for Mn-doped Ag9GaSe6. This work demonstrates an effective strategy for simultaneously improving both mechanical and thermoelectric performance in argyrodite materials for thermoelectric applications.