Evidence for clustering in Cu2+-doped CeO2

Electron spin resonance spectra of Cu2+ in diluted solid solutions of Cu in CeO2 have been studied at room temperature for Cu concentrations between 0.20 and 0.80 mol%. Isolated Cu2+ ions were observed, as well as Cu2+ ions coupled by the exchange interaction. The linewidth and intensity of the line associated with isolated copper ions have a maximum between 0.60 and 0.80 mol%. The results suggest that the solid solution of Cu in CeO2 exhibits clustering effects, as was also observed in Mn:CeO2 solid solutions. A theoretical calculation based on this model yields an effective range of the exchange interaction between Cu2+ ions of 0.38 nm, smaller than that of Mn2+ ions in the same host lattice.