Nanocrystalline LaMnO3 preparation and kinetics of crystallization process

Precursor of nanocrystalline LaMnO3 was synthesized by solid-state reaction at low heat using La(NO3)3·6H2O, MnSO4·H2O, and Na2CO3·10H2O as raw materials. XRD analysis showed that precursor was a mixture containing orthorhombic La2(CO3)3·8H2O and rhombohedral MnCO3. When the precursor was calcined at 800 °C for 2 h, pure phase LaMnO3 with rhombohedral structure was obtained. Magnetic characterization indicated that rhombohedral LaMnO3 behaved weak magnetic properties. The thermal process of the precursor experienced four steps, which involved the dehydration of crystallization water at first, and then decomposition of manganese carbonate into MnO2, and decomposition of La2(CO3)3 and MnO2 together into La2O2CO3 and Mn2O3, and lastly reaction of monoclinic La2O2CO3 with Mn2O3 and formation of rhombohedral LaMnO3. Based on the Kissinger equation, the value of the activation energy associated with the formation of rhombohedral LaMnO3 was determined to be 260 kJ mol−1. The value of the Avrami exponent, n, was equal to 1.68, which suggested that crystallization process of LaMnO3 was the random nucleation and growth of nuclei reaction.