High-temperature synthesis and electronic bonding analysis of Ca-doped LaMnO3 rare-earth manganites

Abstract

Doped lanthanum manganites La1−x Ca x MnO3 with five different concentrations of Ca (x = 0.1, 0.2, 0.3, 0.4 and 0.5) were synthesized by high-temperature solid-state reaction method and characterized. The prepared samples were experimentally analyzed by X-ray diffraction (XRD), ultraviolet-visible spectroscopy (UV-Vis), scanning electron microscopy/energy dispersive spectroscopy (SEM/EDS) and vibrating sample magnetometer (VSM) measurements. Orthorhombic structure is confirmed for this compound from powder X-ray diffraction data. The XRD data confirm the shrinkage in the unit cell of synthesized samples for increasing calcium concentration. The UV–Visible analysis for the estimation of optical band gap (E g) reveals that the band gap decreases with the incorporation of Ca. The synthesized samples were investigated for charge density distribution using maximum entropy method, utilizing the XRD data sets. From the charge density analysis, it is found that the bond lengths for La–O and Mn–O bonds decrease with the addition of Ca. The ionic nature between La and O atoms and covalent nature between Mn and O atoms are enhanced for 40% of calcium-doping. For 50% of Ca-doped sample, ionic nature between La and O atoms and covalent nature between Mn and O atoms decrease. All the prepared samples exhibit ferromagnetism at 20 K and paramagnetism at 300 K.