核壳CFO@PMN-PT多铁复合材料的界面设计与制备

In CoFe2O4/PbMg1/3Nb2/3-PbTiO3 (CFO/PMN-PT) composites, the multiferroic magneto -electric (ME) effect is generated as a strain-mediated product property of a magnetostrictive and piezoelectric substance. However, due to leakage current problem, which limits the realization of large ME coupling response in multiferroic composites. In our experimental laboratory, CFO/PMN-PT composite thin films with (111) and (100) textures were prepared utilizing the sol-gel method. The maximal in-plane ME coupling coefficient of the composite thin films reaches up to about 65.2 mV/cmoOe when the thickness of CFO layer is 400 nm. By appling the dc bias magnetic fiele Hdc=6000 Oe, the magnetically induced voltages for (111) and (100) textured CZFO/PMN-PT composite thin films with Zn-doping in the CFO layer of 300 nm thick are found to be 27.42 and 43.91 μV, respectively. The ME coupling properties of composite thin films were improved through the Zn substitute in the CFO layer. In the application core/shell nanostructures were design. CFO/PMN-PT core/ shell-type building blocks with very strong interactions could act as ideal strain transfer mediums to construct high-order multiferroic ceramic composites. Since the dielectric layer could decrease the conductivity of the composites significantly and overcome the leakage problem effectively, a further enhanced ME coupling is expected by employing fast sintering ceramic techniques（SPS）and rapid annealing thin film to remain the core/shell feature of the nanostructures. The novel structure also gives a new way to investigate the complex interfacial charge-spin interactions, which might provide another perspective to understand the physical mechanism of the ME effect.

CoFe2O4/PbMg1/3Nb2/3-PbTiO3 (简称CFO/PMN-PT)体系中，PMN-PT具有优异的电致伸缩和压电性能，CFO在铁氧体中具有大的磁致伸缩系数，但二者组成的复合多铁材料体系中激发出的电荷被界面损耗，进而显著降低了磁电耦合效应。本课题组生长的CFO/PMN-PT双层磁电复合薄膜面内磁电耦合系数为65.2mV/cmoOe。本申请中通过设计有效的纳米结构核壳CFO/PMN-PT界面，使其在该复合材料和薄膜中担当理想的应力传递介质，因此介电层可以显著降低复合材料的导电性并有效地克服漏电。通过探寻可靠的保持纳米结构核壳特征的快速陶瓷材料烧结技术(SPS) 和薄膜快速热处理技术，更进一步增强磁电耦合效应，此外该材料界面设计的实现也为深入理解磁电耦合效应中界面电荷与自旋感应的作用提供依据。

本文以0.68Pb(Mg1/3Nb2/3)O3–0.32PbTiO3(PMN–PT)和CoFe2O4(CFO)为研究对象，为了调控CFO/PMN-PT界面结合程度，提高磁电耦合性能，采用溶胶-凝胶法和脉冲激光沉积制备了CFO/PMN-PT复合薄膜，结果表明层层复合时6C6P结构复合薄膜的正磁电系数最大；两相的溶胶混合制备复合薄膜时，CFO与PMN-PT摩尔比为3:1时获得最大正磁电系数，为2.7mV/cm Oe。.制备CFO/PMN-PT复合陶瓷时，分别采用三种方式制备复合粉体：第一种是固相法即将两相颗粒混合制备复合粉体；第二种是将两相的干凝胶粉体混合合成复合粉体；第三种是将两相的溶胶混合制备复合粉体。探索烧结工艺得到的最佳的包埋方式是PbZrO3粉体包埋，烧结温度为1150℃时的复合陶瓷电学性能最好；组织结构观察表明将两相溶胶混合合成复合粉体制备的复合陶瓷中两相颗粒分布最为均匀，对比三种复合方式制备的复合陶瓷的磁电耦合性能可知，总体上第三种方法制备的复合陶瓷磁电耦合效应较强；第一种方法制备的复合陶瓷磁电效应较弱；其中CFO摩尔含量x=0.1时，磁电电压系数最大的是溶液法的陶瓷αE31=85.7μV/(cm•Oe)；x=0.2时，固相前驱体混合法的复合陶瓷磁电系数最大αE31=138μV/(cm•Oe)；x=0.3时，溶液法的陶瓷磁电系数最大αE31=253μV/ (cm•Oe)。.此外，采用直接包覆法即将水热法制备的CFO粉体均匀分散到PMN-PT溶胶中，制备CFO@PMN-PT复合粉体和复合陶瓷。发现1100℃烧结的CFO@PMN-PT复合陶瓷致密度最高，磁电耦合性能较强，x=0.5时αE31最大为491μV/(cm•Oe)。