Deciphering Silver Diffusion Pathway and Local Structure of Thermoelectric Ag₈SnSe₆

Argyrodite compounds have garnered significant attention for their exceptional thermoelectric (TE) properties, with Ag₈SnSe₆ standing out as a prominent high-performance material, particularly at elevated temperatures. Ag₈SnSe₆ undergoes an order–disorder phase transition, which leads to the formation of a 3D percolation network of Ag ion transport in the disordered high-temperature phase. Despite significant interest in the TE properties of Ag₈SnSe₆, systematic experimental studies on its crystal structures, particularly the local structure in the disordered and ordered states and Ag ion migration pathways, remained largely unexplored. This study focuses on the structural evolution during phase transition and Ag ion diffusion at elevated temperatures. Synchrotron X-ray total scattering is utilized to systematically study the crystal structure and local atomic environment, especially across the phase transition. Additionally, synchrotron single-crystal X-ray diffraction is combined with the maximum entropy method (MEM) to provide a detailed analysis of the Ag ion migration pathways. The findings clarify the specific Ag diffusion channels connecting different Ag ions in Ag₈SnSe₆, offering valuable structural insights that serve as a benchmark for understanding the TE properties.