Effect Of Dopant On The Ferroelectric And Ferromagnetic Properties Of BifeO₃Ceramics

With the development of information technology, multi-functional informationstorages are needed. BiFeO3is one of the typical multiferroics owning to acombination of its ferroelectric and ferromagnetic properties at room temperatureand has attracted great interest recently. However, research work has been hinderedessentially by the formation of a second phase and the low resistivity of the samples,as BiFeO3is stable within a narrow temperature. Great efforts have been made toavoid these obstacles by ion doping. In this work, the bulk A-site (La element)and/or B-site (Ru/Mg element) doped ceramics were prepared using a solid statereaction process and a systematic investigation of multiferroic properties wasperformed.Multiferroic ceramics Bi0.9La0.1FeO3are synthesized by solid-state reactions andsintered at various temperatures firstly in our work. The rhombohedral structure withthe space group R3c is confirmed by means of x-ray diffraction, and their multiferroicproperties are investigated. Bi0.9La0.1FeO3ceramics sintered at880℃are found tohave the lowest leakage current density and the largest saturated polarizationcompared with the others. Besides, it shows ferroelectric resistive switching behavioras a result of the formation of a p-n junction due to nonhomogeneously distributedoxygen vacancies. Then, a typical “butterfly” shaped strain-versus-voltage curve isshown with a maximum strain of0.09%at7kV. At last, room temperaturemagnetization exhibits a hysteresis loop, indicating that the modulation of the spinstructure of BiFeO3has been suppressed.Based on the La doped results, the1%～3%B-site (Ru/Mg element) dopedsamples were further fabricated and measured. The results showed that the structuretends to transform from rhombohedral to psedocubic structure with the increased Rudopant. The structural model of samples doped with1%Ru is the morphotropic phaseboundary. The dielectric property is improved for1%Ru-doped sample as thedielectric property keeps stable in the whole frequency range investigated. On theother hand, the number of oxygen vancancies is sharply decreased in the1%Ru–doped sample through XPS results. The enhancement of magnetization is attributedto the increased Fe3+ions and the formation of a local ‘ferrimagnetic’ structure in theRu-doped samples. As is found, Mg dopant also leads to the structural transformation. The multiferroic properties are highly related to the structure and oxygen vancancies.It is our conclusion that the influence of B-site dopant on the samples mainly dependson the effect of the structural type and the number of oxygen vacancies existed in thesamples.