Chloride-Activated Addition Reactions for Sulfidation and Oxidation

The solid-state reaction is a fundamental strategy for synthesizing advanced ceramics, intermetallic compounds, and functional inorganic materials due to its simplicity, scalability, and suitability for high-temperature-stable phases. However, sluggish solid–solid mass transfer limits the fabrication of complex compounds. Here, we use a molten chloride salt-mediated synthesis strategy for producing highly pure metal oxysulfides and complex oxides via addition reactions using stoichiometric mixtures of oxide or sulfide precursors. Through in situ characterization, the dynamic evolution within the flux was directly observed, combining with ex situ characterizations and basicity measurements, revealing that the chloride ions activate the metal oxide precursor, forming metastable oxychloride intermediates and releasing free O 2– species that accelerates ionic diffusion while simultaneously enhancing flux basicity and enabling rapid synthesis (10–30 times faster than the solid-state reaction using the same precursors without chloride salt) of 48 phase-pure functional materials under milder reaction conditions, including promising semiconductors of metal oxysulfides (Bi 2 O 2 Se, Bi 2 O 2 Te, La 2 O 2 S, Sm 2 O 2 S, GdSmO 2 S, etc.), high-transition-temperature superconductor La 3 Ni 2 O 7, interstitial oxygen conductor La 4 Mn 5 Si 4 O 22, oxosulfates (La 2 O 2 SO 4, Sm 2 O 2 SO 4 ), and other complex oxides (LaSrGa 3 O 7, Ba 7 Nd 4 MoO 20, ZnTeMoO 6, etc.). This work provides deeper insight into the mechanism of chloride-flush-mediated synthesis, establishing a versatile and scalable pathway for the fabrication of complex, high-performance materials.