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通过补充的实验和理论研究来阐明金属氧化物中界面偏析的原子到介观尺度的方面。其方法是使用几种实验和理论工具来提供对模型金属氧化物二氧化钛中晶界偏析现象的自洽理解。实验研究将使用扫描电子显微镜(STEM)成像和光谱技术，在近原子长度尺度上量化局部化学和晶界结构。使用实验得到的晶界模型，密度泛函理论(DFT)计算将被用来计算块体材料和晶界中不同位置的缺陷形成能。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增加对晶界上的点缺陷能量学的理解，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。功能性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。这些材料的物理属性(例如，电气、机械等)受杂质和掺杂原子偏析到材料内部缺陷的强烈影响。这项研究计划旨在通过对一种模型金属氧化物，即二氧化钛的补充实验和理论研究，对掺杂到内部晶界的偏析有一个基本的、预测性的理解。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开发成为可能。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到所有级别的研究计划中。该NSF项目由多学科活动办公室、材料研究(陶瓷和固体化学)和国际办公室(西欧)共同资助，作为NSF和欧洲之间在材料研究方面的合作活动(NSF 02-135)。这项与宾夕法尼亚州立大学和佛罗里达大学合作的项目是与贝尔法斯特的女王大学合作进行的。

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.