Synthesis and characterization of bismuth ferrite nanoparticles with sillenite phase via sol gel auto combustion route

Bismuth ferrite BiFeO3 (BFO) is one of the multiferroic materials that has high ferroelectric behavior and weak magnetic orders. The intrinsic coupling between the electric polarization and magnetic moments makes BFO potential material for advanced technological applications in different fields. The crystal structure plays very crucial role towards electric and magnetic properties of the nanoparticles. Determination and synthesis of the nanoparticles with specific phase is very important for specific applications. Substitution or doping of ferrites with other metal ions allows variations in their electric and magnetic properties which can be optimized for particular applications. Therefore, this research focuses on the synthesis and characterization of BFO nanoparticles with sillenite phase by sol gel auto combustion route. BFO is doped with cobalt, nickel, and magnesium to explore the role of dopants, concentration of dopants and annealing temperature especially for structural (phase) and electro-magnetic characteristics. Three different doping elements i.e. cobalt, nickel, and magnesium are used to study the role of dopants inside the BFO Bi1-xCoxFeO3, Bi1-xNixFeO3, and Bi1-xMgxFeO3 for five different concentrations 5%, 10%, 15%, 20% and 25% in context of structural and electro-magnetic characteristics. Structural and electro-magnetic characteristics of synthesized doped BFO nanoparticles are investigated using X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), vibrating sample magnetometer (VSM) and energy dispersive X-ray (EDX). Results show that, the annealing temperature plays a crucial role towards the phase formation and crystallinity of BFO. At lower annealing temperature 400°C, all BFO nanoparticles possessed R3c rhombohedral phase with poor crystal structure. However, as the annealing temperature is increased, significant increase in the growth of sillenite phase is observed. Dopants such as Co, Mg, and Ni significantly improve the crystal structure, particle size and electro-magnetic characteristics of BFO. Cobalt-doped BFO nanoparticles have shown good ferromagnetic behaviour with high remnant magnetization and coercivity. Ni and Mgdoped BFO possess, super paramagnetic structure with low remnant magnetization and coercivity. Dopants significantly reduce the particle size of the host BFO. The increase in dopant concentration in BFO nanoparticle considerably promotes the formation of sillenite phase. Highly crystalline sillenite phase for BFO nanoparticle is obtained for 25% dopant concentration