Field-Induced Point Defect Redistribution in Metal Oxides: Mesoscopic Length Scale Phenomena

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NON-TECHNICAL DESCRIPTION: Oxide materials are being used increasingly in electronic and memory devices, and the properties of this class of materials are strongly influenced by the material's stoichiometry and the concomitant defects in the material's crystalline lattice. The redistribution of defects under an applied voltage leads to failure of many capacitive devices, but the redistribution can also lead to unique material functionalities such as resistive switching, which is being explored as a future memory technology. This research program aims to understand fundamental issues of the point defect redistribution process under applied voltage, focusing on the interactions of point defects with higher dimensional lattice defects and the effects of the metallic electrodes. The program utilizes and trains students in a variety of state-of-the-art electron imaging and spectroscopy techniques to study the dynamic evolution of defects under applied bias and the implications for the material electrical properties. TECHNICAL DETAILS: The mobility of charged lattice defects under applied electrical bias can have far reaching ramifications for functional electroceramic devices. For example, the redistribution of point defects during prolonged DC biasing is responsible for leakage current enhancement in oxide-based capacitors. Conversely, electric-field-induced defect migration in oxides can give rise to useful device properties such as resistive switching, which is being explored aggressively for nonvolatile memory. The overall objective of the proposed research is to develop a phenomenological and kinetic understanding of point defect distribution at the mesoscopic length scale. The proposed methodology is to conduct studies on a well-controlled model material system, rutile TiO2, as a function of the initial defect chemistry state, electrode boundary conditions, dislocation concentration, and crystallographic orientation. The experimental approach couples electrical transport measurements with local-stoichiometry and atomic-structure analysis. The advancement of fundamental science in the proposed research is enabling to the development of next-generation functional ceramics, and the program trains both graduate and undergraduate students in state-of-the-art electron microscopy and materials research.