Phase Transformations in Crystalline Ceramic Oxides

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This grant is a renewal award for DMR-8521834, which was highly productive: development of new analytical techniques to study the fundamental phase transformations and chemical reactions between two different oxide ceramics at near atomic resolution, development of the use of Rutherford backscattering spectroscopy to determine the kinetics of reactions in these systems, and confirmation that topotaxial and epitaxial growth in these materials occurs in layers of several unit cells at a time rather than one atomic layer at a time, as previously believed. The emphasis of this work is to use these new analytical techniques to understand the effect of the structure and chemistry at the phase boundary upon the movement of the interface between two oxides of different crystal structure. Analytical techniques being used include: all aspects of transmission electron microscopy will be used (e.g., chemical analysis, atomic lattice imaging. converging beam electron diffraction), electron microprobe, visible light microscopy, Rutherford backscattering spectroscopy, and x-ray diffraction. Materials if interest include: nickel-aluminum oxide spinels, magnesium-aluminum oxide spinels, magnesium-chromium-aluminum oxide speinels, and iron-aluminum oxide spinels. The research has two main objectives: geometry of the interface, and to understand how the morphology and the chemistry of the interface affect the kinetics with which the interface develops.