Study of multi-doping effect on the structure and multiferroic properties of Bismuth ferrite (BiFeO3)

Abstract

In this study an attempt was taken to experiment and compare conventional co-doping and novel compositionally-complex ceramics (CCCs) concept in multiferroic bismuth ferrite (BiFeO3). Both co-doped BiFeO3(BBFMO; 〖Bi〗_0.8 〖Ba〗_0.2 〖Fe〗_(1-x) 〖Mo〗_x O_3;where,x=0,0.5,0.10 and 0.15) and compositionally complex BiFeO3 (CCBFO; BiFe1-5xMoxTixZrxNixCexO3; where, x=0.01, 0.02, 0.03) samples were prepared by conventional solid-state synthesis method. Reitveld refinement revealed notable distortion in all structures, but Fe-O-Fe bond angle reduced to more extent in CCBFO samples, as low as 100.2° from the ideal value of 180°. Despite structure remained unchanged in the complex samples, while a transition from tetragonal P4mm to rhombohedral R3c phase was observed with doping in BBFMO ones. Presence of Mo-based impurities i.e. BaMoO4and Bi12Mo4O30were found and the influence of those impurities were evaluated in details. SEM images evidenced a gyroid like mesoporous morphology in CCBFO, whereas more compact, round shaped but irregular type morphology in the other type. A very slight increase in particle size from 0.52 µm to 0.58 µm with doping was observed for CCBFO. In contrast, a lofty upraise from 0.361µm to 0.61 µm was found for BBFMO samples. Substantial reduction in bandgap was observed for both types of samples, but a steeper fall from 2.88 eV to 2.14 eV was recorded with the increase of doping from 5% to 15% for the CCBFO ceramics. Although, ferromagnetism was found in both types of samples, it is more prominent in co-doped ones, as high as 2.35 emu/gm of saturation magnetization for BBFMO-10compared to only 0.45 emu/gm for CCBFO-15.Paramagnetic secondary phases found to have a negative influence in the magnetic properties of the later ones. Dielectric constant showed an increasing trend with co-doping, the highest of 1200 at 0.1 kHz for BBFMO-15.These changes in functionalities are in good agreement with the measured structural and morphological parameters. The obtained results suggest that along with the conventional co-doping strategy, CCCs concept can be effectively used to tune the properties of multifunctional ceramic oxides and careful selection of cations might improve the functionalities even to a new extent.

Keywords: Bismuth ferrite, Co-doping, Compositionally-complex ceramics, Structural distortion, Bandgap, Ferromagnetism.