Comparative study of lanthanum based perovskites synthesized by different methods

Abstract

A series of lanthanum perovskites LaMO3 (M = Cr, Mn, Fe, Co, Ni and Cu) have been synthesized by different methods: heating a mixture of precursor salts at 800 °C, hydrothermal activation and microwave combustion methods. The hydrothermal synthesis was carried out at 160 °C under autogenous pressure while microwave combustion was done at 80% microwave power. However, pure phase of perovskites were formed only after heating the products of the above synthesis. The precursor salt mixtures and products of hydrothermal activation were heated at 800 °C for 7 h. The microwave combustion products required sintering at 200 °C for minimum of 6 h to yield pure phase products. The formation of products were assured from the Fourier transform infrared (FTIR) analysis of the samples. The band centered at 550 ± 50 cm-1 in the FT-IR spectra corresponds to the metal oxygen bond indicating formation of products. Phase purity of the samples were confirmed from the X-ray diffraction (XRD) analysis. The phases were identified by comparing the results with the standard Joint Committee on Powder Diffraction Standards (JCPDS) data. The products of simple heating and hydrothermal activation are of LaMO3 type except lanthanum copper oxide (La2CuO4). In case of microwave combustion, copper and nickel exhibits La2 MO4 type phase while cobalt shows mixed phase. The micrographs reveal the presence of rod like morphology of the products obtained by hydrothermal synthesis, while, samples obtained after simple heating and microwave combustion synthesis yielded nanoparticles with irregular shape and a size distribution of 16–50 nm.