应力诱导多铁性陶瓷相变的界面构建、铁性行为及本征缺陷研究

The complex multiferroic oxide ceramics have a lot of phase-transition phenomena and attracted great interest to study them. Because the stress plays the fundamental role in such multiferroic ceramics, we can take the stress as a medium to induce the phase transitions. We will construct three types of interfaces (morphotropic phase boundary, core-shell boundary and 0-2 type boundary) and control the ferroic behavior with the aid of the suitable fabrication technology by using the stress as a tool. There are four fundamental questions to be investigated. First, we intend to study the physical and chemical properties of three kinds of interfaces, and find out the relationship between the basic multiferroic properties and the physical and chemical properties of interfaces. Second, we will study the microstructures of crystal boundaries, ferroelectric domains, magnetic domains, revealing the mechanism of the phase transitions induced by stress at three types of interfaces. Third, we aim to investigate the controlling mechanisms of the ferroic orders interacted by each other's at interfaces under the external fields (electric field and stress field), and hope to discover the new phenomena of multiferroic physics. Fourth, we will study the relationship between intrinsic defects and multiferroic properties and ferroic behavior at the interfaces. Based on the investigations on such fundamental questions, it can be expected to provide some technology supports for the design of the electronic functional devices fabricated by the use of multiferroic ceramics, and extend the multiferroic knowledge in the field of electronic ceramics.

多铁性氧化物陶瓷中存在复杂而有趣的相变现象，拟通过在多铁性陶瓷中扮演着重要角色的应力为调控手段诱导其产生相变，借助于合理的制备工艺构建准同型晶相界面、核壳结构界面及0-2型界面等三种类型的界面控制多铁性陶瓷的不同铁性行为，展开以下几个基本问题的研究。第一，分析两相界面的物理、化学性质，研究组成相的宏观铁电铁磁等基本铁性性能与界面物理化学性质的关联；第二，通过对多铁性陶瓷微观组织、铁电畴及铁磁畴等微观结构的研究，搞清楚不同界面结构下应力诱导多铁性陶瓷产生相变的机理；第三，外场（主要指电场、应力场）作用下铁性序通过界面实现相互调控的机制，探索不同界面结构下新的铁性物理现象；第四，研究多铁性陶瓷中本征缺陷对各项铁性性能和界面铁性行为的影响规律。基于对这几个基本问题的研究，期望为基于多铁性陶瓷的电子功能器件设计做一些基础性的技术铺垫，并丰富多铁性这一基本概念在电子陶瓷中的认知。

针对多铁性氧化物陶瓷中存在复杂而有趣的相变现象，采用精细溶胶-凝胶工艺制备出稀土掺杂BiFeO3 (BFO)、铁磁相/铁（顺）电相化合物及Bim+1Fem-3Ti3O3m+3 单相多铁性材料等多种陶瓷体系。. 在稀土Er/Nd掺杂BFO中构建了“准同型晶相界面(MPB)”。根据稀土元素化学性质相近而离子半径相差较大的特点，利用不同离子半径导致的化学压差异调控BFO相变速度，实现人为可控的相界面构成。研究发现MPB中存在的反铁电中间相为极化翻转提供了更多路径并大幅提升BFO的铁电性能。Nd掺杂MPB结构实现铁电、铁磁性能同时达到最优；掺杂量为15 mol.%时，铁电性能最大，Pr=29μC/cm2，磁致介电变化率为1.5%，实现了小电场对磁畴的有效调控。微观分析表明BiFeO3陶瓷中应变钉扎电畴，畴壁发生弯曲；大应变诱导BiFeO3陶瓷晶粒内部产生变形的71o畴界。. 在1350oC烧结的SrTiO3/NiFe2O4体系与1100oC烧结Na0.5Bi0.5TiO3/CoFe2O4体系中实现了优化的“镶嵌结构界面”。均匀分布磁性相产生应力，并诱导顺电相SrTiO3发生铁电相变；Na0.5Bi0.5TiO3/CoFe2O4铁电性能大大增加，Pr=56μC/cm2。. 在具有“0-2型界面”的单相Bim+1Fem-3Ti3O3m+3陶瓷体系，探究了层状钙钛矿结构中层数m对性能的影响。并利用Co/Ni掺杂Bim+1Fem-3Ti3O3m+3陶瓷，使其在室温和低温下呈现铁磁性，具有较高的磁化率，铁电性能增大。. CoFe2O4/Bi3.15Nd0.85Ti3O12复相陶瓷体系中构建出了镶嵌式“核壳结构界面”，两相沿(200)BNdT与(130)CFO晶面呈类共格相界面。这一特殊界面造成Bi3.15Nd0.85Ti3O1局部对称性破缺，有利于提高复合陶瓷的铁电性能。实现了复合陶瓷在较低温度的致密化并对烧结过程进行了微观机理研究。. 利用气氛调控烧结等手段辅以价电子能量分析和微观电导机制分析等手段深入研究了上述材料体系中本征缺陷及铁性行为间的关系。以上研究拓展了对应变诱导相变及铁性行为影响因素等微观机制的深入理解。.