Accurate lattice parameter measurements of stoichiometric uranium dioxide

Abstract

The paper presents and discusses lattice parameter analyses of pure, stoichiometric UO2. Attention was paid to prepare stoichiometric samples and to maintain stoichiometry throughout the analyses. The lattice parameter of UO2.000 ± 0.001 was evaluated as being 547.127 ± 0.008 pm at 20 °C, which is substantially higher than many published values for the UO2 lattice constant and has an improved precision by about one order of magnitude. The higher value of the lattice constant is mainly attributed to the avoidance of hyperstoichiometry in the present study and to a minor extent to the use of the currently accepted CuK X-ray wavelength value. Many of the early studies used CuK wavelength values that differ from the currently accepted value, which also contributed to an underestimation of the true lattice parameter.

The lattice stiffening transition in UO2single crystals

“…Single crystal x-ray diffraction (XRD) measurements yield a lattice constant of 5.4703 ± 0.0006 Å for crystals produced under these growth conditions indicating a stoichiometry of UO 2.003 [15,25]. X-ray fluorescence (XRF) analysis indicated the crystal was of high purity (see supplementary materials (stacks.iop.org/JPhysCM/29/035005/mmedia)).…”

Analysis of oxygen shell splitting in hydrothermally grown single crystal ThO2(200)

“…The analysis was successful in avoiding false minima in the fitting space and eliminated researcher bias in parameter selection. While both XRD and EXAFS confirmed that the ThO 2 is in the fluorite structure, the EXAFS data confirmed the existence of local order distortions, particularly O atoms not on a traditional 1 , , unit cell site.…”

“…1 Introduction UO 2 compounds oxidize readily to form hyper-stoichiometric UO 2+x structures, as previous studies on the U-O system attest [1][2][3][4]. The tendency of these compounds to form defect centers is due to the multiple valence states available to the U atoms, with the 5f electron activity stabilizing interstitial O atoms.…”

Lattice contraction and lattice deformation of UO 2 and ThO 2 doped with Gd 2 O 3

“…For accurate analysis of UO 2 -based systems, it is necessary to avoid stoichiometry variations resulting from air exposure. It was shown by Leinders et al that samples without open porosity remain stable over several weeks [15]. Most of the ThO 2 eGd 2 O 3 specimens reached more than 95% T.D.…”