Synthesis, Property And Microstructural Characterizations Of Bismuth Ferrite Multiferroic Solid Solutions And Low-dimensional Nanostructures

Multiferroic xBaTiO3-(1-x)BiFeO3and ymol%Mn-doped0.33BaTiO3-0.67BiFeO3solid solutions were synthesized by conventional solid-state reaction. Their microstructures were investigated by X-ray diffraction (XRD), Raman scattering, transmission electron microscopy (TEM), and selected area electron diffraction (SAED). The dielectric properties were measured by impedance analyzer.The perovskite phase structure of the solid solutions was confirmed by XRD patterns and Raman patterns, and the formation of minor impure phase of Bi2Fe4O9was prevent effectively by BaTiO3-doping. However, the dielectric property of BaTiO3-BiFeO3solid solutions was not good at the low frequency (around1kHz). It was found that Mn-doping between0.1mol%-1.0mol%could improve the dielectric properties of y mol%Mn-doped0.33BaTiO3-0.67BiFeO3solid solutions, and the formation of impurity phase Bi2Fe409was better suppressed. As increased the Mn-doped content to higher concentrations (2mol%-10mol%) in0.33BaTiO3-0.67BiFeO3, the impurity phase was much lesser, whereas the dielectric property was not improved further. As a result, the optimized amount of BaTiO3-doping should be x=0.33, and y≤1mol%for Mn-doping in xBaTiO3-(1-x)BiFeO3solid solutions. The ferroelectric domain structures were also examined by TEM.Spherical perovskite-type BiFeO3nanocrystals with diameters of10-50nm and hexagonal-shaped sillenite-type Bi12Fe0.63O18.945nanocrystals with sizes of18-33nm were synthesized at low temperatures by microwave hydrothermal process. Their structural, optical, and photocatalytic properties were investigated. The single-crystalline nature of the as-synthesized nanocrystals was confirmed by XRD, SAED, and high-resolution transmission electron microscopy (HRTEM). The visible-light photocatalytic activities evaluated by the degradation of rhodamine B (RhB) in aqueous solution show that the both sillenite-type bismuth ferritic nanocrystals and perovskite-type ones exhibit photocatalytic ability, which can be used as novel visible-light-responsive photocatalysts for degradation of organic compounds.Perovskite epitaxial multiferroic BiFeO3nanoislands were also grown on SrTiO3(100) and Nb-doped SrTiO3(100) single crystal substrates by chemical self-assembled method. Their phase structure and morphology were characterized by XRD, scanning electron microscopy (SEM), and atomic force microscopy (AFM), respectively. The results showed that epitaxial multiferroic BiFeO3nanoislands were obtained via post-annealing process in the temperature range of650-800℃, and their lateral sizes were in the range of50-160nm and height of6-12nm. By using piezo-force microscopy (PFM), ferroelectric characteristics of a single epitaxial BiFeO3nanoisland (with lateral size of-50nm and height of12nm) grown on Nb-doped SrTiO3(100) single crystal substrate was characterized. The results demonstrated that fractal ferroelectric domains existed in the single BiFeO3nanoisland, and self-biased polarization was also observed within this multiferroic nanoisland. This phenomenon can be ascribed to the interfacial stress caused by the lattice misfit between the BiFeO3nanoisland and the SrTiO3single crystal substrate.