Studies On Preparation And Properties Of Bismuth Ferrite Based Multiferroic Materials

Magnetic materials and electronic materials are extensively utilized in many fields of modern technology.The increased social informatization and the development trend of miniaturization and multi-functional devices makes researchers to pay much attention on the multi-functional materials possessing both magnetic and electric properties.Multiferroic materials are such a kind of multi-functional material and they have a variety of ferroic ordering.Moreover,the polarization and magnetization can be closely linked through the coupling of ferroic orderings,such as magnetoelectric effect(i.e.the manipulation of polarization and magnetization in the magnetic fields and electric fields,respectively).The introduction of additional control of the degrees of freedom is favorable to develop the next-generation memory devices.From the point of view of the condensed matter physics,the multiferroic phenomenon is also one of the most important problems in the field of quantum control.BiFeO3 exhibits multiferroicity at room temperature.Therefore it has been widely and systematically studied since 2003,and has become the most important material system to promote the current research of multiferroic materials.In the preparation process of the BiFeO3 bulk,it is very difficult to obtain single phase due to volatilization of Bi,the valence change in Fe ions,and oxygen vacancies.The existences of serious leakage current makes it difficult to obtain good ferroelectric properties.Moreover,BiFeO3 exhibits spin spiral structure and the G type antiferromagnetic ordering at room temperature,which is an obstacle to the potential applications.Therefore,it is necessary to optimize the preparation method and doping modification to improve the electrical and magnetic properties of BiFeO3 ceramics.We proposed to improve the multiferroic properties of the BiFeO3-based materials by means of the optimization of preparation method,doping,and the introduction of solid solutions.The main results of this thesis are as follows:(1)We prepared and investigated the structural,magnetic,dielectric and micromorphology complex impedance of 0.67BiFeO3-0.33BaTiO3 solid solutions.The ferroelectricity of 0.67BiFeO3-0.33BaTiO3 solid solutions can be greatly enhanced by water quenching due to the reduced leakage.(2)We synthesized 2BiFeO3-Bi4Ti3O12 samples and the Ni-doping Aurivillius compounds.The structural,magnetic,and dielectric properties were systematically investigated.We found that the Ni-doping can reduce the leakage current and generate the coexistence of ferroelectricity and ferromagnetism at room temperature.(3)We tried to prepare Bi6Fe2Ti3O18 thin film by electrophoretic deposition method and explored the preparation processing.The microstructure and ferroelectric properties are investigated.We cannot obtain a good hysteresis loop due to a serious leakage current arising from the non-compactness of thin film.We proposed some feasible improvement methods to optimize the preparation processing.