Influence of Ba–Cr substitution on structural, optical and magnetic properties of nanocrystalline BiFeO3

Abstract

Bi1−xBaxFe1−yCryO3 (BBFCO: x = 0, y = 0; x = 0.05, y = 0; x = 0, y = 0.05; x = 0.05, y = 0.05; x = 0.1, y = 0; x = 0, y = 0.1; x = 0.1, y = 0.1; x = 0.2, y = 0) nanoparticles were prepared by a simple cost effective ethylene glycol-based sol–gel technique. The calcination temperature was set at 600 °C for 120 min with a heating rate of 10 °C/min. Effects of Ba, Cr dopant on structural, optical and magnetic properties of BiFeO3 (BFO) nanoparticles have been studied. Perovskite structure was confirmed by the metal-oxide absorption bands appeared at 559 cm−1 and 438 cm−1 in Fourier-transform infrared spectroscopy spectra, which are the characteristic bands of FeO6 octahedral groups in perovskite structure. X-ray diffraction patterns confirmed that Barium (Ba) is an effective dopant to suppress the impurity phases in Cr-doped BFO. Phase transitions from rhombohedral to orthorhombic phase in all doped samples were verified by Rietveld refinement and Raman analysis. Rhombohedral, orthorhombic and tetragonal phases coexist in Bi0.9Ba0.1FeO3 and Bi0.8Ba0.2FeO3, which can be ascribed to the serious lattice distortion due to high-level Ba doping. Well-crystalline BBFCO nanoparticles were observed and the particle size distribution of all samples was calculated from transmission electron microscope images. Ba–Cr co-doping resulted in a dramatic reduction in the particle size. Optical absorption spectra indicated that the optical bandgaps of the doped samples are about 2.20 eV. Clear hysteresis loops were observed in all doped BFO, which indicate their ferromagnetic order at room temperature. Gradually enhanced ferromagnetic property was realized in Ba-doped BFO. The magnetization (at 20 kOe) of BFO, BFO-5Ba, BFO-10Ba and BFO-20Ba are 0.24, 0.33, 1.00 and 1.25 emu/g, respectively. The remanent magnetization of them are near zero, 0.08, 0.44 and 0.53 emu/g, respectively. Particular shape of wasp-waist hysteresis loops observed in BFO-5Ba, BFO-5Cr and BFO-5BaCr can be ascribed to the coexistence of different magnetic phases, and the mixture of single domain and superparamagnetic particles.