Characterizing new materials or unknown polycrystalline solids is a long-standing challenge for chemists. By analyzing basic crystalline building units, we hope to reduce the characterization problem of low-symmetry systems down to fundamental units. We present an analysis of coordination geometries of over 3,500 uranium oxide and uranium fluoride structures. These structures have been generated using a combination of the structure prediction package Universal Structure Predictor: Evolutionary Xtallography(USPEX), which uses genetic algorithms to search for stable phases, and density functional theory (DFT) as implemented in the Vienna ab initio Simulation Package (VASP) to evaluate the energetics of each predicted structure. This generates a database of structures and energies that is biased toward experimentally favorable compositions (e.g., UO2, UO3) but still searches previously unreported compositions. We have employed the Coordination Environments module in pymatgen to analyze the coordination geometries of all cation sites (i.e., uranium sites) in the database and correlate these geometries with the DFT energies calculated by VASP. The database contains 56 of the 65 IUPAC–approved crystal polyhedra, with cubic, octahedral, and square-face capped trigonal prism being the most common coordination geometries. We present our progress toward correlating vibrational properties, such as phonon modes, with the fundamental coordination environments, with the aim of facilitating interpretation of experimental analytical data including infrared, Raman, and neutron scattering spectroscopies to characterize complex uranium oxide phases.

Exploiting crystal structure–property relationships to characterize uranium materials

2019 Spring National Meeting

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