Evidence for clustering in Fe3+-doped CaO

Electron spin resonance spectra of iron-doped calcium oxide have been studied at 77 K for Fe concentrations between 0.01 and 1.00 mol%. The linewidth and intensity of the line associated with the 1/2↔−1/2 transition have a maximum between 0.20 and 0.40 mol%. The results suggest that the solid solution of Fe in CaO is not random, but exhibits significant clustering effects.