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

In recent years, Multiferroic materials, which show simultaneously ferroelectricity,ferromagnetism and/or even ferroelasticity, and the magnetoelectric coupling between theferroic order parameters, have been in the forefront of materials research due to theirinteresting fundamental physics and potential applications in sensors, spintronics andinformation storage, etc. BiFeO₃is the only one that exhibits both ferroelectricity andG-type antiferromagnetism at room temperature, with a high Curie temperature（TC） of¹103K and Néel temperature （TN） of⁶43K. But measurement of ferroelectricproperties in bismuth ferrite has been limited by leakage problems, due to low resistivity,defect, and non-stoichiometry issues in its bulk form. In addition, the weak magnetic alsoseverely limits the actual application.This dissertation focuses on ions-doping modification and making composite withferromagnetic material to enhance the multiferroic properties and the magnetoelectriccoupling of BiFeO₃ceramic at room temperature and studying the physical mechanismsunderlying in the enhancement. The main research work is listed as follows:1. The Bi1-xBaxFeO₃（x=0,0.05,0.1,0.15,0.2,0.25） nanoparticles were prepared by amodified sol-gel method followed by a rapid quenching process we report the synthesisand study of crystal structure, electric and magnetic properties of nanocrystallinemultiferroic system. When x=0.15, the BBFO ceramic showed a pure phase ofpolycrystalline perovskite structure and exhibited the best ferroelectric property with thelargest remanent polarization. with the increasing of doping content, the magneticcharacteristics of the doped ceramics was improved.2. The Bi_1-xBa_xFeO₃（x=0,0.1,0.15,0.2,0.25） ceramics was prepared by mechanicalball-milling followed by a rapid quenching process. We study the effect of differentdoping content on the crystal Structures Phase，microstructure，magnetic and electricalproperties of BBFO, The possible reasons for this properties were analyzed. 3. Fe₃O₄ferrofluid were prepared by the aqueous co-precipitation method. Theresults revealed that the magnetic nanoparticles were small and dispersive, with narrowsize distribution and average diameter of10nm. And also have superparamagnetic atroom temperature.4. We used the Bi_0.9Ba_0.1FeO₃which was made by sol-gel and Fe₃O₄which was madeby co-precipitation above to make different quality percentage BBFO-FO（BBFO:FO=2:1、1:1、1:2）composites. The effects of different materials and differentcontents on the structure, electrical and magnetic properties of BBFO-FO composites werestudied. When BBFO: FO=1:1, the composite showed the best electrical and magneticproperties among all the composites.