Mechanochemical Formation Mechanism of Alloyed AgBi-Elpasolites

Mechanochemical ball mill synthesis is an emerging method for producing complex materials, including alloyed halide elpasolite semiconductors. This solvent-free method offers precise control over chemical composition, enabling fine-tuning of the optical and mechanical properties. However, the formation mechanism of alloyed elpasolites remains unclear. In this work, we elucidate the crystallization kinetics of mechanochemical formation of Cs₂AgBi_0.5M_0.5Br₆ [M = Sb³⁺, In³⁺, or Fe³⁺] using in situ synchrotron X-ray diffraction experiments. We identify the reaction intermediates for the parent composition Cs₂AgBiBr₆, and we find that -Bi_0.5Sb_0.5- forms via a similar reaction pathway. Alloying with In³⁺ or Fe³⁺, on the other hand, occurs via an additional cation-exchange step. These insights into the mechanochemical formation mechanisms of alloyed AgBi-elpasolites provide guidelines toward rational compositional engineering of complex materials.