Controlled tuning of atomic structure in functional materials by acoustic waves and electric fields

凝聚态物质和纳米技术领域的活跃研究不仅在理解电极化和磁电现象的形成机制方面取得了重大进展，而且还展示了创造基于磁电和压电性能相结合的新型器件的可能性。同时，宏观性质，如多铁性和压电性，与在外部扰动影响下发生的局部结构变化有关。控制这种位移的关键能力需要仔细研究它们与外场参数的关系，这是一项基本任务。由于外界影响引起的原子水平的结构变化很小，因此需要高精度地确定原子位移的方法。最近出现了新的可能性，这要归功于该项目的德国合著者(C.Richter等人，《自然通讯》2018年)开发的新方法，该方法允许使用同步辐射的共振衍射以皮秒精度确定原子位移。在这个项目中，我们计划研究一些压电体和多铁性材料在驻波和电场作用下结构特征的变化。为此，提出了一种新的方法，该方法基于同步辐射的共振X射线衍射的禁忌布拉格反射的出现和干涉效应导致的布拉格反射的放大，期望该结果将更好地揭示在外部物理场的影响下控制功能材料中的原子位移的机制，如LiNbO_3/LiTaO_3，Li_2B_4O_7，Fe_2Mo_3O_8，GaN，ZnO，RbH_2PO_4，BiFeO_3，BaTiO_3，以及SrTiO_3中的MFP相，以及关于局域原子位移与声波的幅度和频率的关系的定量信息。此外，功能材料中结构参数的受控和可逆转换的新方法以及与传统X射线源和同步辐射设施中最先进的光束线兼容的新实验设备将被提供。所得结果可大大拓宽功能材料的应用范围，并可直接用于现代技术应用。

Active research in the field of condensed matter and nanotechnology not only led to significant progress in understanding the mechanisms of formation of electrical polarization and magnetoelectric phenomena, but also showed the possibilities of creating new classes of devices based on a combination of magnetoelectric and piezoelectric properties. Meanwhile, macroscopic properties, such as multiferroism and piezoelectricity, are associated with local structural changes that occur under the influence of external perturbations. The key ability to control such displacements requires careful study of their connection with the parameters of external fields, and is a fundamental task. Since structural changes at the atomic level caused by external influences are very small, methods for determining atomic displacements with high accuracy are required. New possibilities for that emerged recently due to the novel method developed by the German co-authors of this project (C. Richter et al., Nature Communications 2018), which allows to determine atomic displacements with picometer accuracy using resonant diffraction of synchrotron radiation. In this project, it is proposed to study the transformations in the structural characteristics of a number of piezoelectrics and multiferroics excited by standing acoustic waves and electric fields. For this it is proposed to develop a new method based on the appearance of forbidden Bragg reflections using Resonant X-ray Diffraction of synchrotron radiation and their amplification due to interference effects.It is expected that the results will give a better insight into the mechanisms, controlling the atomic displacement in functional materials under influence of external physical fields, as exemplified by a number of materials, such as such as LiNbO3/LiTaO3, Li2B4O7, Fe2Mo3O8, GaN, ZnO, RbH2PO4, BiFeO3, BaTiO3, and the MFP phase in SrTiO3, and quantitative information regarding the dependence of local atomic displacements on the amplitude and frequency of acoustic waves. Further, new methods for controlled and reversible transformation of structural parameters in functional materials and new experimental equipment compatible both with conventional X-ray sources as well as with the state of the art beamlines at synchrotron radiation facilities will be made available. The obtained results can significantly widen the range of functional materials and can be directly used in modern technological applications.