Interfacial Segregation in Oxide Ceramics: Atomic-Scale Experimental and Theoretical Studies

9976851 Dickey Grain boundary and interfacial segregation have far reaching ramifications for many ceramic materials. The proposed research aims to elucidate atomic-scale aspects of interfacial segregation in ionic materials by complementary experimental and theoretical studies. The ultimate goal of the research program is to develop predictive principles from which interfacial chemistry can be designed to tailor interface physical properties. Such predictive principles will require an understanding of segregation on the interrelated aspects of interface atomic structure, point defect chemistry and chemical bonding. The initial material system to be explored will be alpha-alumina since this ceramic is well understood and characterized. Moreover, it has been widely demonstrated that segregants, particularly rare earth elements, have profound effects on physical properties of alumina such as creep and grain boundary transport. Most of the experimental analyses will be based on electron imaging, diffraction and spectroscopy techniques since crystallography, atomic structure and chemistry can be studied simultaneously and therefore correlated. Segregation studies on polycrystalline materials will be carried out with the aim of exploring the complete multidimensional thermodynamic phase space. For special boundaries, those conducive to atomic-scale structure analysis, we will investigate site-specific segregation and changes in grain boundary atomic structure and space charge upon doping. Atomic structures will be quantified by high-resolution electron microscopy and Z-Contrast imaging. Electron energy loss spectroscopy will be performed on a column-by-column basis to obtain site-specific chemical and electronic structure information. Special symmetric tilt boundaries will be studied in parallel by ab initio electronic structure calculations and Monte Carlo simulations using semi-empirical potentials. Transport mechanisms will be modeled using transition state theory combined with ab initio calculations, ab initio molecular dynamics simulations, and semi-empirical molecular dynamics simulations. %%% By performing this systematic series of experiments, fundamental knowledge will be gained about interfacial segregation in ceramics and the effects on grain boundary diffusion and adhesion. This information can have a large impact on the design of both structural ceramics, such as those used in aircraft engines, as well as on functional ceramics, such as those used in cell phones and computers.