Microstructure of LaCoO3 prepared by freeze-drying of metal–citrate precursors revealed by EPR

Two methods for the preparation of LaCoO3 samples were used: thermal decomposition of La–Co citrate precursors obtained by freeze-drying of the corresponding solutions and by a solid state reaction. Microstructural characterization was made by electron paramagnetic resonance spectroscopy (EPR). For assignment of the EPR signals, La1−xSrxCoO3 samples were used as EPR references. The LaCoO3 oxides prepared from citrates and by a solid state reaction were shown to differ in respect of the mean oxidation state of the cobalt ions, the specific surface area and the particle morphology. EPR spectroscopy reveals for ex-citrate LaCoO3 ferromagnetic Co3+ and Co4+ coupled ions. For LaCoO3 samples obtained by a solid state reaction, EPR permits detecting Co3O4 impurities only.