This article reports a significant advance in materials chemistry by demonstrating, for the first time, the reversible removal and reinsertion of sulfur atoms in a layered oxychalcogenide compound, La₂O₂S₂, using a topochemical approach. This process, known as topochemical (de)intercalation, allows chemists to selectively extract or reinsert sulfur atoms into the crystal structure at low temperatures without destroying the overall layered framework. By reacting La₂O₂S₂ with certain alkali or transition metals, it is possible to remove sulfur atoms to create new, previously unknown metastable phases: La₂O₂S₁.₅ and oA-La₂O₂S. These phases were predicted by advanced structure prediction algorithms and confirmed by electron microscopy and X-ray diffraction. Importantly, the process is fully reversible: sulfur can be reinserted at low temperature to regenerate the original La₂O₂S₂ compound, demonstrating a rare example of reversible anion mobility in a solid-state material.
This discovery opens a new avenue in the topochemistry of chalcogenide compounds, similar to what has already been achieved with oxides. It could have important implications for future battery technologies based on mobile sulfur ions and the design of new electronic or optical materials. The work also highlights how the choice of reducing agent and reaction conditions determines whether sulfur is removed or other elements are intercalated, offering chemists fine control over the composition and properties of these layered materials.
The members of the FZÚ team performed structure analysis of the newly prepared phases by 3D electron diffraction, which revealed the crystal structures of the new phases and validated the success of the whole approach.
