The solubility of Mn in CeO2 was investigated for 3-50 mol% Mn. Powders were synthesized by the Pechini method in air. Raman spectroscopy and lattice parameter analysis revealed that the solubility limit of Mn 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 Mn versus Ce. As a consequence, an approach to increase the Mn radii size through annealing in reducing conditions (humidified H2 at 1100 °C) was attempted. In this case, the MnO phase was observed by XRD, thereby indicating difficulty in obtaining Mn doped CeO2 under reducing conditions, as well.
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