Papers by Keyword: Polycrystalline Material

Abstract: The compound-anion polycrystalline material Yb³⁺:Na₅Bi (WO₄)₂(MoO₄)₂ was synthesized by flux method. Many characterization of XRD, DSC-TG, absorption spectrum and emission spectrum were studied. The result is shown that the new crystal belongs to Tetragonal, and space group is I4₁/a (88). Its melting point is 619 °C and the absorption band, emission band, center emission wavelength are about 83 nm, 50 nm, 1006 nm respectively.

Abstract: Among the various products originating from fission events, the noble gas elements Xe and, in a lesser extent, Kr present important fission yields. The accumulated gas inventory in its various states (e.g. atomically dissolved, precipitated in cavities or released from the fuel) has a strong impact on the performance of LWR fuel and is presently one of the limiting factors for fuel burnup extension. A more fundamental understanding of fission gas behaviour at the atomic scale would enable to improve the modelling of the various mechanisms ultimately leading to fission gas release and to refine conservative safety margins. Lots of efforts have already been undertaken using atomistic computer simulations, ab initio calculations and Empirical Potential Molecular Dynamics (EP-MD) techniques, that relate to the bulk behaviour. This article will discuss EP-MD investigations in nanosized polycrystalline UO₂, constructed from Voronoi cells in a 3-D periodic environment. This study has focused on Xe diffusion at and close to grain boundaries.

Abstract: In this paper, examples of some of the most challenging features of GB diffusion are considered covering selected problems, strongly related to the research activity at our Laboratories and to the scientific interest of Boris Bokstein too. The following problems (and still open questions related to them) are addressed: i) Diffusion in a random network of grain boundaries with different structures and diffusion coefficients in polycrystalline materials; ii) Segregation effects; iii) Stress effects and iv) Effect of the presence of moving and/or non-equilibrium grain boundaries.

Abstract: The implementation of 3-Dimensional X-Ray Diffraction (3DXRD) Microscopy at the Advanced Photon Source is described. The technique enables the non-destructive structural characterization of polycrystalline bulk materials and is therefore suitable for in situ studies during thermo-mechanical processing. High energy synchrotron radiation and area detectors are employed. First, a forward modeling approach for the reconstruction of grain boundaries from high resolution diffraction images is described. Second, a high resolution reciprocal space mapping technique of individual grains is presented.