The overall goal of this project is to understand the thermodynamic driving forces for the chemical and structural changes involved in the synthesis, processing, and degradation of complex materials. Order-disorder on different length and time scales is critically important in these processes and in the stabilization and/or persistence of intermediates, some of which have distinct and potentially useful properties, leading to potential uses in energy storage, water splitting, catalysis, separations, nuclear energy, and waste containment and environmental remediation. A number of distinct oxide systems will be studied by high temperature reaction calorimetry to determine their enthalpies of formation and transformation as a function of structural state determined by diffraction, spectroscopy and electron microscopy. The interplay of positional disorder (one dimensional point defects and their clusters) with two- and three-dimensional defects (layering, shear planes, block structures) will be studied. Shear phases, are now of interest for fast-charging battery applications. Systems with shear structures include Nb2O5-TiO2, TiO2-Cr2O3 and many others. These ordering and phase change phenomena involve a competition of enthalpy and entropy terms, with disorder on cation sites providing entropy stabilization to compensate for loss of entropy by defect ordering of anions and vacancies. Order-disorder induced by preparation conditions in fluorite related materials will be studied by a combination of thermodynamic and neutron diffraction techniques, the latter in collaboration with Maik Lang at the University of Tennessee. In collaboration with Lang and Tomislav Fricic at McGill University, synthesis, transformation and energetic differences induced by mechanochemistry will be examined. Structural and thermodynamic changes resulting from grinding and radiation damage will be compared. Perovskites and layered structures especially in halide and hybrid organic-inorganic perovskites will be investigated. Understanding thermodynamic stability is crucial to successful synthesis of materials and to predicting their persistence in solar cell operating environments. A number of newly proposed new battery cathode materials in both lithium and sodium systems will be studied by calorimetry. The combined synthetic, structural, and thermodynamic studies will elucidate the competition between order and disorder on different length scales in stabilizing both final products and intermediate states in a variety of distinct but related complex oxide materials. This deeper understanding will enable the control of synthesis to produce materials with desired properties. Equally importantly, the thermochemical data will enable prediction of materials stability, compatibility, and degradation when used under a variety of conditions.
|Effective start/end date||7/1/21 → 6/30/24|
- DOE: Office of Science (OS): $666,000.00
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