Temperature-dependent anisotropy in the bond lengths of UOas a result of phonon-induced atomic correlations.

Previous experiments on cubic UOhave suggested that the temperature dependences of the nearest-neighbour U-O and U-U distances are. We have acquired total-scattering neutron diffraction patterns out to = 23.5 Åfor50 View Article and Find Full Text PDF

Characterization of Oxygen Defect Clusters in UO Using Neutron Scattering and PDF Analysis.

In hyper-stoichiometric uranium oxide, both neutron diffraction work and, more recently, theoretical analyses report the existence of clusters such as the 2:2:2 cluster, comprising two anion vacancies and two types of anion interstitials. However, little is known about whether there exists a region of low deviation-from-stoichiometry in which defects remain isolated, or indeed whether at high deviation-from-stoichiometry defect clusters prevail that contain more excess oxygen atoms than the di-interstitial cluster. In this study, we report pair distribution function (PDF) analyses of UO and UO ( x ≈ 0.

What Is the Actual Local Crystalline Structure of Uranium Dioxide, UO? A New Perspective for the Most Used Nuclear Fuel.

Up to now, uranium dioxide, the most used nuclear fuel, was said to have a Fm3̅m crystalline structure from 30 to 3000 K, and its behavior was modeled under this assumption. However, recently X-ray diffraction experiments provided atomic pair-distribution functions of UO, in which UO distance was shorter than the expected value for the Fm3̅m space group. Here we show neutron diffraction results that confirm this shorter UO bond, and we also modeled the corresponding pair-distribution function showing that UO has a local Pa3̅ symmetry.

Structural Changes in the Local Environment of Uranium Atoms in the Three Phases of U4O9.

The crystal structure of U4O9 remains an enigma because of its differences with U(4+) and U(5+) coordination polyhedral mixtures, as shown in the XANES experimental results. To better understand this crystal structure, its diffraction pattern was measured at seven different temperatures using neutron diffraction before being independently refined by Rietveld's method and pair distribution function analysis. The O cuboctahedron-a structural element consisting of 13 oxygen atoms-is a specific feature of the U4O9 crystal structure.