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@ARTICLE{Uygur:1016797,
      author       = {Uygur, Selim and Delville, Rémi and Schreinemachers,
                      Christian and Leinders, Gregory and Vanhove, Nico and Van
                      Renterghem, Wouter and Verwerft, Marc and Vleugels, Jozef},
      title        = {{C}ation-heterogeneity in internally gelated
                      {U}$_{1-z}${C}e$_{z}${O}$_{2-x}$, 0.15 ≤ $z$ ≤ 0.3
                      microspheres},
      journal      = {Journal of nuclear materials},
      volume       = {587},
      issn         = {0022-3115},
      address      = {Amsterdam},
      publisher    = {Elsevier Science},
      reportid     = {FZJ-2023-03781},
      pages        = {154749 -},
      year         = {2023},
      abstract     = {Internal gelation of aqueous mixtures of metal (M = Ln, An)
                      nitrate with Uranyl Nitrate is generally assumed to yield
                      cation homogeneity and a fluorite type single phase
                      U1-zMzO2±x solid solution. As-sintered (U,Ce)O2 internally
                      gelated microspheres, manufactured with target z values up
                      to 0.3 using Ce(NO3)3, were observed to exhibit systematic
                      peak broadening and splitting at higher 2θ angles in their
                      X-Ray diffraction (XRD) patterns, correlating with
                      increasing z≥0.15. This was interpreted as an unexpected
                      departure from a single phase material. Thermogravimetry was
                      used to make an initial assessment whether these peak
                      anomalies were caused by an oxygen hypostoichiometry.
                      Results indicated global oxygen stoichiometry for all
                      compositions. The subsequent detailed characterization study
                      via Electron Probe Micro Analysis of cross-sections of the
                      as-sintered microspheres revealed the systematic presence of
                      spherical Ce concentration gradients, as well as µm-sized
                      highly Ce-enriched features. EDS and TEM studies on focused
                      ion beam lamellae extracted from the cross-sections of
                      as-sintered microspheres revealed a hexagonal Ce4.67(SiO4)3O
                      minor phase manifesting as single grain precipitates and
                      clusters uncovering the presence and critical role of
                      Silicon as an unexpected contaminant and Ce-scavenger from
                      surrounding (U,Ce)O2 grains. Characterization at
                      intermediate heat treatment steps revealed that the
                      systematic U/Ce heterogeneity features are already present
                      post-gelation and are independent of the superimposed trace
                      Ce-Si-O phase. This work constitutes the first systematic
                      cation distribution study on cross-sections of (U,Ce)O2±x
                      microspheres, executed on a series of compositions, using a
                      combination of elemental mapping techniques.},
      cin          = {IEK-6},
      ddc          = {620},
      cid          = {I:(DE-Juel1)IEK-6-20101013},
      pnm          = {1411 - Nuclear Waste Disposal (POF4-141)},
      pid          = {G:(DE-HGF)POF4-1411},
      typ          = {PUB:(DE-HGF)16},
      UT           = {WOS:001086750800001},
      doi          = {10.1016/j.jnucmat.2023.154749},
      url          = {https://juser.fz-juelich.de/record/1016797},
}