Abstract
In this work, the thermal, microstructural, magnetic, and optical studies for both La0.7Ca0.3CoO3 (LCCO) and La0.7Pb0.3CoO3 (LPCO) cobaltite perovskites synthesized by sol-gel route were investigated. The TGA study reveals the completion of the crystallization route and the immediate formation of LCCO and LPCO samples. The X-ray diffractograms with Rietveld refinement confirmed the development of the rhombohedral structure with R (3) over barc space group. The lattice constants, the average grain size, and the bond length are higher for LPCO sample than LCCO sample. However, the relative coordinate (x(O)) of oxygen anion decreases with substitution of Ca by Pb which leads to the decrease of the bond angle (theta(Co-O-Co)). The grain size variation was also confirmed by SEM analysis. The spontaneous magnetization, coercivity, and remanence increase by substituting Ca by Pb. From the FTIR spectra, the characteristics vibrational modes corresponding to the LaCoO3 perovskite were observed. From the ultraviolet-visible optical absorbance, it was apparent that the LCCO sample displayed remarkable visible light absorption than LPCO sample. The estimated direct band gap energies were found as E-gd = 1.492 eV (for LCCO) and E-gd = 1.640 eV (for LPCO). The obtained Urbach energy values demonstrate that there is a disorder in the prepared samples and reflects the higher density of localized states in their structures.