Ce3Ce4

Ce3Ce4 is a term used in materials chemistry to describe a mixed-valence cerium oxide system, rather than a well-defined, single compound. It is not an established chemical formula with a fixed crystal structure; instead, it signals a system in which cerium exists in two oxidation states, Ce3+ and Ce4+, in a specific ratio. The notation is primarily descriptive, used to discuss redox behavior and defect chemistry in cerium-based oxides.

In practice, such systems arise when cerium oxide (CeO2) is reduced, creating oxygen vacancies and allowing cerium to cycle between Ce4+ and Ce3+. The resulting material often adopts a fluorite-like lattice with nonstoichiometry referred to as CeO2−δ, where δ reflects the amount of oxygen vacancy. The hypothetical Ce3Ce4 composition implies seven cerium atoms per unit with a Ce3+/Ce4+ distribution that requires compensating defects, typically oxygen vacancies, to maintain overall charge balance. The exact structure and stoichiometry depend on synthesis conditions, including temperature, atmosphere, and duration.

Properties of Ce3Ce4-type systems are dominated by redox flexibility and defect chemistry. The Ce3+/Ce4+ couple enables oxygen storage and release, which is valuable in catalysis and environmental remediation. Vacancy-mediated electron hopping can enhance ionic and electronic conductivity, influencing catalytic performance and sensor sensitivity. Synthesis methods include controlled reduction of CeO2 in hydrogen or carbon monoxide atmospheres and solid-state redox treatments, which tune the Ce3+/Ce4+ ratio.

Applications associated with mixed-valence cerium oxides include automotive catalytic converters, solid oxide fuel cells, and gas sensors. The term Ce3Ce4 is more common in pedagogical or speculative discussions and is not a standard designation for a single, discrete compound; researchers instead use CeO2−δ or explicit Ce3+/Ce4+ content when reporting results.