Synthesis And Microstructural Characterizations Of Bismuth Ferrite Multiferroic Low-dimensional Nanostructures

BiFeO3 multiferroic nanocrystals were synthesized by molten-salt method, and their microstructures were examined by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), High-resolution transmission electron microscopy (HRTEM) and X-ray energy dispersive spectroscopy (EDS). The molten salts used in these experiments were eutectics of NaCl-KCl and NaCl-Na2SO4, and the results show that the main products gradually transformed from BiFeO3 to Bi2Fe4O9 as increasing the annealing temperatures. The BiFeO3 powders with high purity were obtained at 750℃. Meanwhile, the morphology regularity of crystalline particles was enhanced with increasing temperature, and the cubic BiFeO3 nanopowders were obtained at 800℃. In the NaCl-Na2SO4 salt systems, it was found that low NP-9 (nonyl-phenyl ether, NP-9) surfactant content (0-5 mL) led to the formation of almost pure phase BiFeO3 powders, whereas high NP-9 surfactant content (e.g.,20 mL) resulted in pure phase Bi2Fe4O9 powders.Multiferroic BiFeO3 nanotubes and nanorings were also fabricated by using nanoporous alumina membranes (average pore size of 200 or 100 nm) as templates via sol-gel spin coating, negative-pressure, bath immersion methods. The results demonstrated that the fabricated methods played an important role in the morphology and growth length of the BFO nanotubes. In comparison with the above three methods it was found that the the bath immersion method was the best method to fabricate BFO nanotubes, then the sol-gel spin coating method, followed by negative-pressure method. The phase structures and microstructures of the BiFeO3 nanotubes were investigated by XRD, SEM, TEM and EDS, and the formation mechanism of the BiFeO3 nanotubes were discussed. In addition, the BiFeO3 nanorings with a diameter of 170 nm and thickness of 20 nm were also revealed by scanning transmission electron microscopy (STEM)Finally, two filling methods (hyperacoustic immersion method and negative pressure method) along with two kinds of solvent of BFO sol-gel (ethylene glycol monomethylether and ethylene glycol) were used in order to finding the best way to fabricate Bi2Fe4O9 nanotubes. Four different experimental conditions:(a) ethylene glycol monomethylether as solvent, and hyperacoustic immersion method as filling method; (b) ethylene glycol as solvent, and hyperacoustic immersion method as filling method; (c) ethylene glycol monomethylether as solvent, and negative pressure method as filling method; and (d) ethylene glycol as solvent, and negative pressure method as filling method, were used in this work. The phase structures and microstructures of the Bi2Fe4O9 nanotubes were investigated by XRD, SEM, TEM and EDS. The results demonstrate that using ethylene glycol as solvent and negative pressure method as filling method is the best method to fabricate Bi2Fe4O9 nanotubes.