柔性多铁异质结构的挠曲电效应及多场调控研究

The multiferroic heterostructures prepared on the flexible substrates can present the ductility like flexible electronics and the multifunctional performances like multiferroic materials with avoiding the clamping of rigid substrate. This makes the flexible multiferroic heterostructures better realize the intermodulation among mechanics, electric and magnetic fields, and therefore have potential applications in biomedical therapy, energy, information and national defense. The flexoelectric effect induced by the large strain gradient for the flexible multiferroic heterostructures at the nanoscale should be considered. In the present project, the theoretical method for studying the phase transition and effective physical properties of multiferroic heterostructures on flexible substrates was established by using the nonlinear Landau-Ginsburg-Devonshire thermodynamic theory and the mechanics of continua. The flexoelectric effect of flexible multiferroic heterostructures was analyzed by the combination of theoretical and experimental research. The flexoelectric effect was regulated by the external magnetic field or mechanical field and the polarization was controlled by the changed strain gradient of flexible multiferroic heterostructures. A new extensible multiferroic heterostructure with wave configuration was designed and the effect of magnetic field on the deformation and ferroelectric properties of multiferroic ribbons with wave configuration was discussed. A new mechanism of strain-gradient modulated flexoelectric effect and multi-field coupling in the flexible multiferroic heterostructures was acquired based on the theoretical analysis, numerical simulation and experimental measurement, which provided academic and experimental guidance for the design of multifunctional flexible devices.

柔性多铁异质结构既能发挥柔性电子的可延展性与多铁性材料的多功能性，又能有效避免刚性基底的夹持作用，更好地实现力场、电场、磁场间的相互调控，在生物医疗、能源、信息、国防等领域具有广泛应用前景。纳米尺度的柔性多铁异质结构中大的应变梯度引起的挠曲电效应不容忽视。采用非线性Landau-Ginsburg-Devonshire热力学理论和连续介质力学建立柔性多铁异质结构的相变及有效物理性能的理论研究方法，结合实验研究分析柔性多铁异质结构中的挠曲电效应。通过外加磁场或机械场实现外场调控挠曲电效应，通过改变柔性多铁异质结构的应变梯度调控电极化。设计一种可延展的波形多铁异质结构，研究磁场对波形多铁条带的变形及铁电性能的影响规律。根据理论、数值模拟和实验研究的结果，获得柔性多铁异质结构中应变梯度调节的挠曲电效应及多场耦合特性的新机制，为多功能柔性器件的设计提供理论和实验指导。

柔性多铁异质结构既能发挥柔性电子的可延展性与多铁性材料的多功能性，又能有效避免刚性基底的夹持作用，更好地实现力场、电场、磁场间的相互调控，在生物医疗、能源、信息、国防等领域具有广泛应用前景。纳米尺度的柔性铁电及多铁异质结构中大的应变梯度引起的挠曲电效应将不容忽视。本项目采用非线性的热力学理论建立考虑挠曲电效应的柔性基底/多铁异质结构的有效自由能表达式，结合连续介质力学研究并得到了外场作用下挠曲电效应对柔性多铁异质结构的铁电性能、介电性能、铁磁性能等有效物理性能的影响规律及力场、电场、磁场间的相互调控机理。研究结果表明，结合柔性结构可提供大的应变梯度及挠曲电效应，外加机械载荷可有效调节柔性器件的电极化、压电、电热、磁电耦合性能，为多功能柔性器件的设计提供理论和实验指导。此外，本课题还提出了利用铁电/石墨烯功能材料的力-光-化学多场耦合效应有效提高光催化性能及利用机械载荷有效调控多级柔性器件润湿性的有效方法，有望进一步拓展柔性电子器件的应用领域。