Three approaches for the synthesis of multiferroic BiFeO3

Multiferroics represent a class of new materials having potential applications for design and preparation of multifunctional material due to the possibility of the coupling of their coexisting electric and magnetic orderings. The magnetic polarization can be switched by applying an electric field; and the electric polarization, by applying a magnetic field. We report here our attempts using three approaches for fabricating multiferroic ferrites: autoclave, microemulsion and spin-casting. All three methods are based on a precursor solution prepared by dissolving stoichiometric amount of bismuth(III) nitrate and iron(III) nitrate in ethylene glycol. In the autoclave synthesis, sodium hydroxide and hydrogen peroxide were dissolved in DI water with surfactant (Triton x-100, Tx-100) and then the precursor solution was added. The solution was transferred to an autoclave at either 165 or 185°C for reaction for 24 hours. The two temperatures led to two different bismuth ferrite nanocrystals, Bi₂Fe₄O₉ (165°C) and BiFeO₃ (185°C). For microemulsion synthesis, sodium hydroxide and hydrogen peroxide were dissolved in DI water and added to an oil solution (cyclohexane and n-butanol) with added surfactant, Tx-100, as “Emulsion I”. “Emulsion II” was made by adding precursor in an oil solution (cyclohexane and n-butanol). “Emulsion I” was allowed to react with “emulsion II” at 80°C for 3 hours. A non-crystalline bismuth ferrite with a 1:1 atomic ratio for Bi: Fe was obtained. The spin-casting method produced the BiFeO₃ (BFO) thin film with the desired quality. The quality of the resulting BFO thin film depended strongly on the spinning rates and annealing temperatures. The morphology of all samples was studied by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). X-ray dispersive spectroscopy (EDS) was used- - to confirm the elemental composition in bismuth ferrite samples. X-ray diffraction (XRD) was used for establishing crystalline structures.