Multiferroic Properties Of BiFeO₃Thin Films Prepared By Sol-gel Method

Bismuth ferrite, BiFeO3(BFO), is one kind of typical Single-phase multielectric material with a rhombohedrally distorted perovskite structure included the R3c space group. BFO is almost the only material that simultaneously exhibits antiferromagnetic ordering with a Neel temperature (TN)of370℃and ferroelectric ordering with a Curie temperature (Tc)of850℃at room temperature.Although BFO, theoretically, has a large saturation polarization (about100μC/cm2),the Experimental value of BFO ceramic’s saturation polarization is as low as a fewμC per cm2.the reason that causes the large difference between the theoretical value and the experimental value is the Fe3+ion in BFO easily truns into the Fe2+ion and oxygen vacation infroms, witch decreases insulating quality of BFO materials. In order to solve this problem, the preparation method is improved and the preparation of BFO thin films or one-dimensional nanofibers becomes the focus.In this paper,the BFO film was prepared via a simple sol-gel process using bismuth nitrate [Bi (NO3)3-5H2O] and iron nitrate [Fe (NO3)3-9H2O] as starting materials on Pt/SiO2/Si subtrates. Different experimental parameters of Ferroelectric thin films such as the volume of ethanol and annealing temperature were considered. X-ray diffraction pattern showed that the more suitable volume of ethanol is0.05ml and the sample is BFO phase annealed at500℃and there are hardly an impurity phases in sample annealed at550℃. Remnant polarization of10.12μC/cm2and saturation polarization of14.62μC/cm2were identified by the measuring of P-E loops at room temperature for the samples annealed at500℃.The film sample shows a stable dielectric constant and dissipation between1KHz and1MHz. In addition, ferromagnetic properties were showed by the measuring of M-H loops for the samples at room temperature.In theory, there is terrific change in the properties of the materials at the nanometer scale.The electrical and magnetic properties of one-dimensional structure of the BFO is more Improved than the thin film, so people started to pay attention to the BFO with one-dimensional nanostructures.Pure BFO fibers were prepared via sol-gel method and electrospinning technique. Through the analysis of the experiment results, we get a better preparation of BFO fibers. The better voltage was25kv and the better solution is the mix of PVP ethanol solution (Concentration of0.6g/mL) and BFO precursor solution with the same volume. By this preparation,the BFO fibers were smooth, continual, uniform without beans and intercross network structure.The diameter of BFO fibers is1.2±0.5μm before annealing and the diameter of BFO became420±40nm annealed at550℃.