Studies On The Fabrication And Multiferroic Property Of BiFeO₃-based Ceramic

Multiferroics, which combine the properties of (anti)ferromagnetism, (anti)ferroelectricity or (anti)ferroelasticity, become an original family of materials. Due to their physical mechanism and potential application for designing multifunctional, for example, information storage, spintronics and sensors,multiferroics is worth of study. Among all the multiferroic materials studied so far, perovskite-type BiFeO3 which exhibits the coexistences of ferroelectric with a Curie temperature of 1100K and antiferromagnetic orders with a Neel temperature of 640K has been attracted more and more attention by scientists.However, due to its space-modulated spin structure on a long wavelength of 62nm, even weak ferromagnetism is not observed in BiFeO3 and hence no linear magnetoelectric effect. And it is difficult to fabricate pure product and hence poor ferroelectricity property in BiFeO3 ceramic. So this prevents the large-scale production of it. It show that introducing new fabrication technology, A site rare-earth element-B site high valent state positive ion and ABO3 solid solution are three ways to improve the multiferroic properties in BiFeO3 ceramicBase on the above ideas, there are two experiments in this paper. The first one:fine BiFeO3 nanoparticles, ceramic and A site Dy3+-doped rare-earth elements of the Bi1-xDyxFeO3(x=0.05,0.1.0.15和0.2) powders has been prepared by citrate auto-combustion method using Bi (NO3)3·5H2O, Fe (NO3)3·9H2O and Dy (NO3)3·6H2O as precursors, citrate acid as complexing agent and fuel. The second one:based on the Bi0.9Dy0.1FeO3 has been fabricated by citrate auto-combustion method successfully, then a series of ceramic like Bi0.gDyo.iMnxFe1-xO3 (x=0.05,0.1,0.15,0.2) and xBi0.9Dy0.1Fe03-(1-x) BaTiO3(x=0.2,0.4,0.5,0.6,0.8) will be produced through the solid-state reaction using Bi2O3,BaCO3 and TiO2 as precursors. This paper aims to demonstrate the crystal structure,microstructure,ferroelectric and and ferromagnetic properties of the samples through the following equipment such as TG-DSC,X-ray diffraction, Environment Scanning Electronic Microscope, Ferroelectricity parameter reflectoscope reflector, Vibration Sample Magnetometer. It also make a systematic research on the relation between fabrication,structure,doping effect,and property, which lays the technical and theoretical foundation for the using of BiFeO3-based ceramic.The main research in this paper is as follows:1.The paper discusses the technical conditions for the preparation of BiFeO3 powder and ceramic through the citrate auto-combustion method. Various and optimal processing constants of citrate auto-combustion method for BiFeO3 have been confirmed by researching the influence of PH, the mol proportion between total metal positive ions and citrate acid,the better annealing temperature of BiFeO3 powders and the calcinating temperature of BiFeO3 ceramic on the crystal structures phase, microstructure, magnetic and electrical properties of BiFeO32.Doping Dy3+ can improve the the magnetic property of BiFeO3 powders greatly. When the x equals 0.1,the smallest size of the sample is 126nm and the composite powder saturation magnetization can reach 2.2emu/g. The strength of magnetic property mainly comes from size effect and lattice distortion.3.We discuss the mechanism of enhanced magnetic property by the doping of A and B site rare elements and predict that the largest composite powder saturation magnetization will be achieved by the A site rare element doped BiFeO3 among all the other BiFeO3 samples doped by other rare elements. The improvement of magnetic property is due to the fact that Dy3+has the largest mRe-5.92 among all other rare elements and its lattice distortion. Dy3+,Mn4+ co-doping ceramic's magnetic property magnetism has continued enhancing. The Bio.9Dy0.1Mn0.15Fe0.85O5 ceramics's lattice distortion is biggest (a=5.57, c=6.85,c/a=1.229), and the satuated magnetization value reach the maximum one in all samples corresponding to 5.4emu/g,.That may be due to crystal structure's distortion and Fe+-Mn+-O-Mn4+-Fe+ super exchange interaction.4. A-site doped with Dy3+ will reduce Bi volatility and lead to the distortion of FeO6 octahedron while Mn4+ ion substitutes for Fe3+ in B-site will reduce the oxygen flaw quantity, enhance the compactness and the electronic resistivity. That will cause Dy3+ and Dy3+,Mn4+ co-doping ceramic's ferroelectric property have the greater improvement than pure BiFeO3.5. Using 0.5Bi0.9Dy0.1Fe03-0.5BaTiO3 as the research objective and analysing the crystal structure, we can get the better annealing temperature and the calcinating temperature of this system; This paper makes a careful research on the structure transformation of xBi0.9Dy0.iFeO3-(1-x) BaTiO3 powders and ceramic, and the changes in its ferroelectric property and magnetic property. The MPB of samples is between 0.5 and 0.8.All of the ceramics we make exhibit certain ferroelectricity. When x is 0.4, the largest ceramic polarization saturation is 16.4μC/cm2, the residual polarization saturation 15.2μC/cm2.And the magnetic property will enhance when x increase.