Rietveld refinement, morphological, vibrational, Raman, optical and electrical properties of Ca/Mn co-doped BiFeO3

Abstract

Ca and Mn co-substituted Bi1-xCaxFe1-xMnxO3 (x = 0 and 0.10) polycrystalline ceramic samples were prepared using conventional solid state reaction method. The structural, morphological, vibrational, Raman, optical and electrical properties of co-doped and pristine compounds were carried out. The formation of the compounds was analyzed using RT (room temperature) X-ray diffraction patterns. These diffraction patterns were further refined using Rietveld refinement via FULLPROF software and were found to fit in rhombohedral crystalline structure with space group R3c. The observed and calculated diffraction patterns are in good agreement with each other. The average crystallite size has been calculated using Scherrer formula. The same has also been calculated using W–H plot along with the strain developed in the lattice due to substitution. The average crystallite size has further been used to calculate the dislocation density and number of crystallites in a given pellet of area 38.56 mm2 and 63.92 mm2 for Bi1-xCaxFe1-xMnxO3 with x = 0 and 0.10 respectively. The 2D and 3D surface morphology of prepared samples were analyzed using Atomic Force Microscopy (AFM). The average roughness and average crystallite size was also calculated using SPIP software. FTIR spectra in transmittance mode give a brief idea of Vibrational modes around Fe–O–Fe stretching bonds. The appearance of active modes in Raman spectroscopy at RT also confirmed the rhombohedral structure with R3c space group. The Optical property of the materials has been studied using UV-VIS-NIR spectroscopy. The optical energy band gap of the pristine compound was found to be 2.04eV which is comparable to that of the literature value but the co-doping of Ca and Mn in pristine compound lowered (1.86eV) the optical band gap. The dc conductivity was analyzed and the activation energies were calculated using Arrhenius relation. The Current-Voltage (I–V) characteristic as a function of temperature was also analyzed which shows the semiconducting behaviour of the compounds. The results are discussed in detail.