A(Fe,Ti)O3型钙钛矿单相多铁材料中多重准同型相界及其磁电耦合特性研究

Multiferroics show an increasing potential applications on multifunctional and energy-saving electronic devices due to the coexistence of ferroelectric and magnetic orderings and the coupling between them. However, the very weak magnetoelectric couplings in single-phase multiferroics especially in the first-type multiferroics strongly restrict their practical application. Note, the morphotropic phase boundary (MPB) in ferroelectrics and ferromagnets can significantly enhance the mechaniclelectric and magnetostrictive coupling respectively, and consequently is of great valua on engineering application. More significantly, our recent studies confirm the coexisting and overlapping of ferroelectric MPB and magnetic MPB, i.e., multiple MPB in the A(Fe,Ti)O3 perovskite type magnetoelectrics, which could point out a promising novel approach to large room-temperature magnetoelectric response in single-phase multiferroics. Therefore, in this research, the micro-structures and the macro-ferroic properties, including the crystal structure, domain structures, magnetic structures, ferroelectricity, magnetic properties, coupling effect, etc., will be studied in detail in order to establish the intrinsic relations between the MPBs of different ferroic sub-systems. Also, the influence of multiple-MPB on the coupling effects of ferroic sub-systems will be investigated and the corresponding physical model between the micro-structures and ferroic properties will be proposed. Finally, the “Multiple-MPB Engineering” will be used to design the new single-phase multiferroic material systems with enhanced magnetoelectric coupling, which could lay a solid foundation for the practical application of single-phase magnetoelectrics.

多铁性磁电材料由于其铁电有序和磁有序的共存及两者间的耦合效应，在新型多功能低功耗电子器件上显示出巨大的应用前景。然而，在单相磁电体尤其是第一类多铁体中，磁电耦合往往很弱，成为限制其实用化的最大瓶颈之一。注意到，准同型相界(MPB)在铁电体和铁磁体中的存在，分别对材料的机电、磁弹耦合性能有着显著的增强效应，具有极大的工程价值并得到广泛使用。本项目前期研究证实，A(Fe,Ti)O3型钙钛矿磁电材料中同时存在铁电MPB和磁性MPB，即磁电多重MPB，预示着一条极具潜力的增强单相多铁体中磁电耦合的新途径。本项目拟通过系统分析多重MPB处微观结构和各宏观铁性性能及其耦合，阐明各铁性子体系中MPB的微观起源及联系，揭示多重MPB对各铁性间耦合性能的影响机制，建立描述其微观结构与多铁耦合特性的物理模型，最终利用“MPB工程”来指导磁电材料的设计，获得具有增强磁电耦合的单相多铁体，为其走向实用化奠定基础。

多铁性磁电材料由于其铁电有序和磁有序的共存及两者间的耦合效应，在新型多功能低功耗电子器件上显示出巨大的应用前景。然而，在单相磁电体尤其是第一类多铁体中，磁电耦合往往很弱，成为限制其实用化的最大瓶颈之一。注意到，准同型相界(MPB)在铁电体和铁磁体中的存在，分别对材料的机电、磁弹耦合性能有着显著的增强效应，具有极大的工程应用价值并得到广泛使用。前期预研究证实，A(Fe,Ti)O3型钙钛矿磁电材料中同时存在铁电MPB和磁性MPB，即磁电多重MPB，预示着一条极具潜力的增强单相多铁体中磁电耦合性能的新途径。本项目在系统的优化工艺获得高质量的目标体系陶瓷和单晶材料基础上，对其微观结构和宏观铁性性能进行系统的表征，得到了三元体系磁电综合相图，获得了多铁性MPB，确定了MPB处材料畴结构，铁电极化态，磁有序态等铁性有序态的演变规律；通过系统表征分析多重MPB处微观结构特征和各宏观铁性性能及其耦合，阐明各铁性子体系中MPB的微观起源及联系；采用高温溶液法技术生长单晶体，得到了合适的工艺条件，成功生长出了xBiFeO3-(1-x)PbTiO3系列组分的单晶体，克服了目前国际上报道的BFPT单晶生长过程中普遍存在的组分分凝的难题，确定了其复杂的多尺度畴结构；针对BFPT单晶中矫顽场高，漏导改善依旧不足导致电学性能差，加上其铁磁分量缺失等问题，成功生长出了Dy改性的0.4BiFeO3-0.6PbTiO3组分单晶体，实现了显著改善的铁电性能；通过改进工艺条件，显著改善了陶瓷材料的杂相及缺陷态，获得了质量较高的陶瓷材料，在改进型传统工艺制备的陶瓷样品中获得了大的可翻转铁电极化，最高剩余极化强度超过50μC/cm2，最高压电系数d33超过100pC/N，这一数值可比拟采用高成本的热压工艺制备的类似体系陶瓷样品，解决了这一类材料中漏导大铁电极化及压电性能极差这一普遍性的重大挑战，为最终利用“MPB工程”手段获得具有增强磁电耦合性能的单相多铁体打下了坚实的基础。