Magnetic and optical studies of chromium oxides. Part 3.—Calcination of coprecipitated chromium and aluminium hydroxide gels

Magnetic and optical studies were performed on coprecipitated chromium and aluminium hydroxide gels after calcination in air at temperatures between 50 and 1150°C. The results show that magnetic dilution was not achieved and that surface clusters of chromium oxide were formed. The magnetism, e.s.r. and optical spectra of oxidised samples are discussed in terms of a mixed-valency phase of partially-oxidised chromium containing Cr3+ and Cr6+ species. This new model of γ-phase chromium is shown to be consistent and an acceptable part of the extensive mixed-valency chemistry of chromium.