XRD and Raman spectroscopy study of Fe solubility in cerium oxide

The solubility of Fe in CeO2 was investigated for 3-50 mol% Fe. Powders were synthesized by the Pechini method in air. Raman spectroscopy and lattice parameter analysis revealed that the solubility limit of Fe in CeO2 is less than 3 mol% for the present preparation conditions. The low solubility limit was rationalized in terms of the much smaller ionic radius of Fe versus Ce. As a consequence, an approach to increase the Fe radii size through annealing in reducing conditions (humidified H-2 at 1100 degrees C) was attempted. In this case, the more stable CeFeO3 phase was observed by XRD, thereby indicating difficulty in obtaining Fe doped CeO2 under reducing conditions, as well.