234 D14. Recent Advances in Mineralogy/Crystallography

Wednesday, 25 September 2019
8:00 AM - 12:00 PM
Room 125AB, North Building

OXIDATION AND ANION LATTICE DEFECT SIGNATURES OF HYPOSTOICHIOMETRIC DOPED UO2

Paper number: 234-14
Program: Technical Sessions
Time: 11:15 AM – 11:30 AM

Authors

Abstract

A series of sintered UO2 pellets doped with lanthanide elements (Ce, Nd, Yb), Th and Zr were investigated using powder X-ray diffraction, Raman spectroscopy, thermogravimetric analyses and differential scanning calorimetry. A combination of electron microprobe analyses and thermogravimetric analysis, for oxygen content, enabled precise determination of the hypostoichiometry for doped samples at 1 and 5 atom percent. Two Raman laser wavelengths (785 and 455 nm) have afforded greater sensitivity to spectroscopic signatures of the oxidation of (U1-yMy)O2-x and the anion defects introduced by dopant element substitution. Oxygen hypostoichiometry forces a reduction in the average coordination number surrounding (U,M) sites, which is compensated by a decrease in U-O bond length, and concomitantly the lattice parameter, consistent with the obtained Raman spectra. The evolution of O/M ratio up to (U1-yMy)O2 after oxidation was also examined using Raman spectroscopy, which revealed that the relative area of the LO Raman band at ~540 cm-1, attributed to oxygen vacancies, increased relative to the T2g band with increasing dopant concentration, and decreased upon oxidation. The chosen dopants inhibited oxidation to U3O8, most prominently for Yb 5 at%, having been delayed by ~180° C. Many of the doped samples exhibit an early oxidation feature that may be related to influx of O to satisfy hypostoichiometry up to (U1-yMy)O2, and subsequently stabilizing a U4O9 or U3O7 intermediate, delaying oxidation to U3O8.

Geological Society of America Abstracts with Programs. Vol. 51, No. 5

doi: 10.1130/abs/2019AM-340107

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