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

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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.