NSF-Europe: Multiple Length Scale Experimentation and Modeling of Grain Boundary Segregation in Ionic Materials

晶界和界面偏析对功能陶瓷有着深远的影响，影响着微观结构的演变和电输运性能。 拟议的研究计划旨在阐明原子到介观尺度方面的界面偏析的金属氧化物的补充实验和理论研究。该方法是采用几种实验和理论工具，以提供一个自洽的理解模型金属氧化物，TiO 2的晶界偏析现象。 实验研究将采用扫描透射电子显微镜（STEM）成像和光谱技术，以近原子长度尺度量化局部化学和晶界结构。使用实验得出的晶界模型，密度泛函理论（DFT）计算将被用来计算在散装材料和在晶界的各个站点的缺陷形成能。 这些数据将被用作热力学分离计算的输入参数。 这项工作的部分成果将是对晶界点缺陷能量学的进一步了解，我们预计将收集新的信息，使我们能够改进现有的介观偏析模型。该研究计划的最终目标是开发离子空间电荷分离的定量预测模型。 功能金属氧化物陶瓷在从化学传感器到电容器的技术应用中发挥着关键作用。 这些材料的物理特性（例如电气、机械等）受到杂质和掺杂剂原子偏析到材料中的内部缺陷的强烈影响。 该研究计划旨在通过对模型金属氧化物（即二氧化钛）的补充实验和理论研究，对掺杂剂偏析到内部晶界的基本预测性理解。这项研究的更广泛影响包括基础科学的发展，这将使下一代功能陶瓷的发展成为可能。此外，该计划将对未来科学家的教育产生重大影响，因为研究生和本科生都将积极参与研究计划的各个层面。材料研究部（陶瓷和固态化学）和国际办公室（西欧）作为NSF和欧洲之间材料研究的合作活动（NSF 02 - 135）。这个与宾夕法尼亚州立大学和佛罗里达大学合作的项目正在与贝尔法斯特的女王大学合作进行。

Grain boundary and interfacial segregation have far-reaching ramifications for functional ceramics, affecting both microstructural evolution and electrical transport properties. The proposed research program aims to elucidate atomic- to meso-scale aspects of interfacial segregation in metal-oxides by complementary experimental and theoretical studies. The methodology is to employ several experimental and theoretical tools to provide a self-consistent understanding of grain boundary segregation phenomena in a model metal-oxide, TiO2. The experimental studies will employ scanning transmission electron microscopy (STEM) imaging and spectroscopy techniques for quantifying local chemistry and grain boundary structure at the near-atomic length scale. Using experimentally derived grain boundary models, density functional theory (DFT) calculations will be used to calculate defect formation energies in the bulk material and at various sites in the grain boundary. These data will be used as input parameters in thermodynamic segregation calculations. Part of the outcomes of this effort will be an increased understanding of point defect energetics at grain boundaries, and we anticipate gleaning new information that will allow us to improve existing mesoscopic segregation models. The ultimate goal of the research program is to develop quantitative, predictive models for ionic space charge segregation. Functional metal-oxide ceramics play a critical role in technological applications ranging from chemical sensors to capacitors. The physical properties of these materials (e.g. electrical, mechanical, etc.) are strongly influenced by impurity and dopant atom segregation to internal defects in the material. This research program aims to develop a fundamental, predictive understanding of dopant segregation to internal grain boundaries through complementary experimental and theoretical studies of a model metal-oxide, namely titanium dioxide. The broader impacts of this research include the development of fundamental science that will enable the development of next-generation functional ceramics. Furthermore, the program will have a major impact on the education of future scientists, as both graduate and undergraduate students will be actively involved in all levels of the research program.This NSF project is co-funded by the Office of Multidisciplinary Activities, the Division of Materials Research (Ceramics and Solid-State Chemistry) and the International Office (Western Europe) as a Cooperative Activity in Materials Research between the NSF and Europe (NSF 02-135). This project with PA State University and the University of Florida is being carried out in collaboration with Queen's University in Belfast.