Valence states of copper in copper ferrite spinels CuxFe3−xO4 (0 < x ≤ 1) fine powders: Evidence of copper insertion

Abstract The oxidation in cation deficient spinels of copper iron spinels Cu x Fe 3− x O 4 (0 x ≤ 1) synthesized by soft chemistry with a grain size x per mole of ferrite, three oxidation phenomena corresponding to Cu + at B-sites (130°C), Fe 2+ at B-sites (180°C) and Cu + at A-sites (240°C) have been found in close relation with the cation-oxygen distance of each oxidizable cation. For nonstoichiometric synthesized spinels Cu x Fe 3− x O 4+ δ with δ x , the presence of additional interstitial Cu + ions has been envisaged. The oxidation temperature of these interstitial ions (> 300°C) is higher than that for Cu + ions at Asites suggesting that interstitial copper ions also essentially resid…