Time-Resolved In Situ Neutron Diffraction Study Of Cu22fe8ge4s32 Germanite: A Guide For The Synthesis Of Complex Chalcogenides

Solid-state synthesis in a sealed silica tube is one of the most popular methods for the production of inorganic materials. Nevertheless, the determination of the best synthesis conditions is a trial-and-error process that generally requires many experiments, varying temperature and duration time. In the present work, the synthesis of a polycrystalline sulfide by solid-liquid-gas reaction in a sealed silica tube is, for the first time, monitored in situ by time-resolved neutron powder diffraction (NPD). All successive crystallization/decomposition sequences and intermediate products were analyzed in detail. These results were combined with ex situ X-ray powder diffraction and thermal analyses on crystallized samples. Our results revealed that sealed tube synthesis is highly dynamic, with reaction times shorter than expected. Importantly, the experiments revealed the primordial role of the cooling conditions on the secondary phase formation and stability. Beyond new data on the complex crystal chemistry of germanite Cu22Fe8Ge4S32, our study demonstrates the compelling benefits of time-resolved in situ NPD in the optimization of the synthesis process for a wide range of complex chalcogenide materials.