mixedoxideoxidesulfide

Mixed oxide–sulfide compounds are solid-state materials that incorporate both oxide (O2−) and sulfide (S2−) anions in a single crystalline phase. They are commonly referred to as oxysulfides or mixed-anion oxide–sulfide materials. This class spans a broad range of compositions and structural types, including transition-metal oxysulfides and rare-earth oxysulfides. Structural motifs frequently feature alternating oxide and sulfide subunits, layered arrangements, or three-dimensional frameworks in which metal cations are coordinated by both O and S.

Synthesis and structure: They are usually prepared by high-temperature solid-state reactions or flux methods under inert or reducing conditions to preserve sulfide components. Some systems are accessible via solvothermal routes or chemical vapor transport. Depending on composition, O and S can be ordered on distinct anion sites or distributed over a single site. Common structural archetypes include layered oxysulfides with alternating oxide and sulfide layers and oxysulfide frameworks that resemble perovskite- or wurtzite-derived motifs.

Properties: The mixed anion composition tunes electronic structure and physical properties. Band gaps can be narrower than those of comparable oxides, enabling visible-light activity in some cases. Materials may display semiconducting or insulating behavior, with transport properties that depend on cation type, anion ordering, and microstructure. They can also show ionic conductivity under certain conditions.

Applications and research: Oxysulfides are explored for photocatalysis, including water splitting and CO2 reduction, and as potential electrode or electrolyte materials for energy storage and conversion. Research emphasizes controlling anion ordering, phase stability, and scalable synthesis, as well as correlating structure with optical and transport properties.

Challenges: Achieving phase-pure materials and long-term stability remains difficult due to competing oxide and sulfide phases. Moisture sensitivity, synthesis reproducibility, and limited composition space pose barriers to practical deployment. Ongoing work aims to expand known chemistries and to develop reliable processing routes.