TY - JOUR
T1 - Density functional theory calculations of defective UO2 at U3O7 stoichiometry
AU - Brincat, Nicholas A.
AU - Molinari, M.
AU - Allen, Geoffrey C.
AU - Storr, Mark T.
AU - Parker, Stephen C.
PY - 2015/12/1
Y1 - 2015/12/1
N2 - UO2 is particularly susceptible to oxidation. The oxidation processes and the phases formed as a result are widely studied. In the oxidised phases defect clusters form, although their structure and properties are unclear. Thus, we examine fluorite based U3O7 phases to identify the types of defect present in a 36 atom unit cell. We predict that at this stoichiometry, defective structures form oxygen clusters and that split quad-interstitial clusters are the most thermodynamically stable defects. These are associated with a volume contraction compared to UO2, in line with experimental measurements. Incorporation of oxygen is always associated with oxidation of uranium atoms to U5+, although a single calculation leads to a U6+ ion as well. As this system is relatively unstable, it is proposed that U4+ and U5+ are the preferred oxidation states at U3O7 stoichiometry.
AB - UO2 is particularly susceptible to oxidation. The oxidation processes and the phases formed as a result are widely studied. In the oxidised phases defect clusters form, although their structure and properties are unclear. Thus, we examine fluorite based U3O7 phases to identify the types of defect present in a 36 atom unit cell. We predict that at this stoichiometry, defective structures form oxygen clusters and that split quad-interstitial clusters are the most thermodynamically stable defects. These are associated with a volume contraction compared to UO2, in line with experimental measurements. Incorporation of oxygen is always associated with oxidation of uranium atoms to U5+, although a single calculation leads to a U6+ ion as well. As this system is relatively unstable, it is proposed that U4+ and U5+ are the preferred oxidation states at U3O7 stoichiometry.
KW - Cuboctahedral cluster
KW - DFT
KW - Split di-interstitial cluster
KW - Split quad-interstitial cluster
KW - Split tri-interstitial cluster
KW - Willis cluster
UR - http://www.scopus.com/inward/record.url?scp=84946595526&partnerID=8YFLogxK
U2 - 10.1016/j.jnucmat.2015.10.006
DO - 10.1016/j.jnucmat.2015.10.006
M3 - Article
AN - SCOPUS:84946595526
VL - 467
SP - 724
EP - 729
JO - Journal of Nuclear Materials
JF - Journal of Nuclear Materials
SN - 0022-3115
IS - Part 2
ER -