Electron spin resonance of diluted solid solutions of Gd2O3 in CeO2

Electron spin resonance spectra of Gd3+ in diluted solid solutions of Gd2O3 in CeO2 have been studied at room temperature for Gd concentrations between 0.01 and 1.00 mol%. While in the case of Mn2+:CeO2 samples, both the linewidth and the line intensity go through a maximum between 0.2 and 0.4% Mn and then start to decrease, in the case of Gd3+:CeO2 samples the linewidth and the line intensity increase monotonically with the dopant concentration. This as taken as evidence that in Gd2O3–CeO2 diluted solid solutions there are no clustering effects similar to the ones observed in Mn:CeO2 solid solutions. It is not clear why clustering effects are present in Mn:CeO2 solid solutions and not in Gd:CeO2 solid solutions; however, it seems reasonable to assume that this is due to the fact that the ionic radius of Mn2+ (81 pm) is about 25% smaller that that of Gd3+ (107.8 pm). In any case, the fact that Gd:CeO2 solid solutions do not exhibit clustering effects means that ESR linewidth data can be used to estimate the concentration of Gd in CeO2 samples, as it is possible to do in several solid solutions of paramagnetic ions in ceramic materials. The results also suggest that the range of the exchange interaction between Gd3+ ions in CeO2 is about 0.89 nm.