Synchrotronstrahlungs-Experimente zu Skalierungseffekten und ungewöhnlichen Phasen epitaktischer perowskitischer Schichten

钙钛矿型铁电薄膜在基础研究和技术应用方面具有重要的意义，例如非易失性随机存储器和微电子机械系统。由于降维铁电材料的性质可能与块体材料的性质有很大的不同，因此需要协调的实验和理论努力来阐明这些材料中结构和电学性质的关系。在这个项目中，理论计算和最新的实验技术结合在一起，使用同步辐射和扫描探针技术，深入比较了强、中等和早期铁电薄膜，例如Pb(Zr0.52Ti0.48)03，BaTiO3和SrTiO3。在选定的衬底上沉积限定厚度的单晶外延薄膜将允许精确控制薄膜的应变状态。该项目的目的是：(A)通过在相关温度和应变下的原位X射线散射来研究薄膜中预测的新型铁电相的存在(包括在SrTiO_3中的应变感生铁电性)。用SrRuO_3电极同时测量样品的电学和结构性质，可以对铁电状态进行全面的电学表征。(B)铁电电容器中的极化转换过程，通过同时进行电学和X射线测量以及相应的磁畴动态形核和生长的理论模拟来研究。

Thin films of perovskite ferroelectrics are of great interest for basic research as well as for technological applications, as exemplified by nonvolatile random access memories and microelectromechanical systems. Since the properties of ferroelectric materials in reduced dimensions can differ strongly from those of bulk materials, coordinated experimental and theoretical efforts are required to shed light an the relationship of structure and electrical properties in these materials. In this project, theoretical calculations and state-of-the-art experiments using synchrotron radiation and Scanning probe techniques, are brought together for an in-depth comparison of strong, moderate and incipient ferroelectric thin films, exemplified by Pb(ZrO.52Ti0.48)03, BaTiO3 and SrTiO3. The deposition of single-crystalline, epitaxial films of defined thickness on selected substrates will allow a precise control of the strain state of the films. The project aims at: (a) the investigation of the existence of predicted novel ferroelectric phases in thin films (including strain-induced ferroelectricity in SrTiO3) by in-situ x-ray scattering at the relevant temperatures and strains. The simultaneous measurements of electrical and structural properties on samples with SrRuO3 electrodes will allow a full electrical characterization of the ferroelectric state. (b) the polarization switching process in ferroelectric capacitors, studied by simultaneous electrical and x-ray measurements and corresponding theoretical simulations of the dynamic nucleation and growth of domains.