Synthesis of perovskite LaCoO_3 by thermal decomposition of oxalates: Phase evolution and kinetics of the thermal transformation of the precursor

摘要

LaCoO_3 precursor was synthesized by solid-state reaction at low temperatures using La(NO_3)_3 - 6H_2O, CoSO_4 - 7H_2O, and Na_2C_2O_4 as raw materials. LaCoO_3 was obtained by calcining a precursor, 0.97/2La_2(C_2O_4)_3-CoC_2O_4-5.3H_2O, at 1123 K in air. The precursor and its calcined products were characterized by thermogravimetry and differential scanning calorimetry, Fourier transform infrared spectroscopy, X-ray powder diffraction, and scanning electron microscopy. A high-crystallized LaCoO_3 with a rhombohedral structure was obtained when the precursor was calcined at 1123 K in air for 2 h. The thermal transfonnation of the precursor from ambient temperature to 1150 K in air presented six steps. The values of the activation energies associated with the thermal transformation of 0.97/2La_2(C_2O_4)_3-CoC_2O_4 - 5.3H_2O were determined based on the Starink equation.