织构化BiFeO3基固溶体的强磁场下制备及其压电和多铁性能调控研究

Currently room-temperature single-phase multiferroic material BiFeO3 is difficult to obtain theoretical good ferroelectric properties due to the existence of secondary phases and oxygen vacancies, as well as its anti-ferromagnetic nature at room temperature, which is a large obstacle for the application prospect. Wheareas, the formation of solid solution with other ABO3 ferroelectrics introducing morphotropic phase boundary can not only improve their piezoelectric and ferroelectric properties, but also enhance the magnetic properties. In this.proposal, Textured ceramics and (111)-oriented thin films of (1-x)BiFeO3-xBi0.5K0.5TiO3 solid solution would be prepared through the strong magnetic field for the purpose of enhancing the piezoelectric, ferroelectric and magnetic properties of solid solution. Characterization of the properties of multiferroic and magnetoelectric coupling under a strong magnetic field (20T superconducting magnetic field, variable temperature magnetic force and scanning tunneling microscope) would study the evolution of morphotropic phase boundary, magnetism, dielectric constant and ferroelectric polarization with the strong magnetic field. It is proposed to set up the correlation between magnetic field, microstructure, piezoelectric coefficient and order parameters of multiferroic materials and shed light on the tunability rule and mechanism of the magnitude and direction of high magnetic field on the order parameters of multiferroic materials for the purpose of realization of giant magnetoelectric effect and set-up of the microscopic mechanisms. The proposal aims to explore BiFeO3-based multifunctional solid solution with multiferroicity and piezoelectric properties, and thus provide the experimental basis for the development of magnetoelectrical functional devices.

目前室温单相多铁性材料BiFeO3由于在制备过程中易于产生杂相和氧空位，难以获得理论上较好的铁电性能，以及其室温反铁磁的本质，严重阻碍其潜在的应用。而与其他ABO3型铁电体固溶引入准同型相界不仅可以提高其压电和铁电性，还可增强磁性。本项目拟采用强磁场制备织构化的(l-x)BiFeO3-xBi0.5K0.5TiO3固溶体块体和(111)择优取向薄膜，达到增强体系的磁性和铁电性能的目的；通过强磁场下多铁性能和磁电耦合效应（20T 超导强磁场、变温磁力与扫描隧道组合显微镜）的表征研究强磁场测试条件下材料的准同型相界、磁性、介电常数以及铁电极化随强磁场大小变化的演变过程。建立体系在外加强磁场下微结构的变化和压电及多铁体序参量变化之间的关联，揭示其对压电和多铁体序参量的调控规建和作用机理，实现较大的磁电效应并建立微观物理机制。为开发基于BiFeO3基固溶体的新型磁电子器件奠定实验基础。

由于在高温烧结时，BiFeO3陶瓷样品中Bi的挥发、Fe离子的变价、非化学计比、存在杂相等原因，导致样品具有很大的漏电流，实际测试BiFeO3陶瓷的电滞回线一般都难以饱和且电极化强度较弱。为了实现其固有的优异的性能，本项目通过BiFeO3与其他钙钛矿结构铁电体形成固溶体，引入准同型相界的方式以期提高体系的磁性和铁电性能。基于此，本项目按计划系统地开展了BiFeO3基固溶体块体的结构、磁性、铁电性以及介电性能研究工作，通过加入不同的助烧结剂和改变含量优化体系的铁电和压电性能；在此基础上开展了BiFeO3基固溶体薄膜的研究工作，探索发现发现处于菱方R3C与贋立方相PC相界的附近的样品，其压电系数高达542 pm/V，优于当前的BiFeO3基材料。通过对BiFeO3基固溶体块体和薄膜的研究工作，获得了具有较优铁电和压电性能的体系，理解了BiFeO3基固溶体中准同型相界对体系的铁电和压电性能的作用机制。

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