Hydride ion formation in stoichiometric UO₂

Abstract

We investigated atomic hydrogen solubility in UO2 using DFT. We predict that hydrogen energetically prefers to exist as a hydride ion rather than form a hydroxyl group by 0.27 eV, and that on diffusion hydrogen's charge state will change. The activation energy for conversion of hydride to hydroxyl is 0.94 eV.

Electronic structure of interstitial hydrogen in lutetium oxide fromDFT+Ucalculations and comparison study withμSRspectroscopy

“…The DFT+U approach is computationally as efficient as conventional DFT, well suited for defect studies which require a large number of atoms and has also proved reliable in recent studies of defects in f -electron solids [25][26][27][28][29]. Our choice is also guided by our goal to examine the full configurational space of hydrogen in lutetium oxide and identify all localenergy minimum configurations which can be probed by the μSR technique.…”

Impact of Hydrogen on the Intermediate Oxygen Clusters and Diffusion in Fluorite Structured UO2+x

“…All interstitial hydrogen was added as neutral defects, this allows for the preferred electronic distribution to occur. Addition of hydrogen, not in the presence of excess oxygen results in a H -/U 5+ or H + /U 3+ defect pair depending on the distance between hydrogen and a lattice oxygen [18][19][20] . In the presence of excess oxygen an OH -/U 5+ defect pair forms, where the hydrogen reduces one of the two U 5+ formed by the excess oxygen 17 .…”

“…Monkhorst-Pack k-point grid was used, in line with previous work 17,18,30,36 . The different sized simulating cells results in a consistent shift to the absolute energies of the defects but the relative energies remain the same, even with the inclusion of spin orbit-coupling 18 . In line with we use the 96 atom unit cell for all our simulations 6, 11-12, 17, 19 .…”

“…All calculations implemented collinear 1k antiferromagnetic ordering, which is considered an appropriate approximation for the experimentally observed 3k noncollinear antiferromagnetic ordering 37,38 , and is line with the literature 4,23,30,36 . The effect of spin orbit coupling has not been included as discussed in the literature 18,[39][40][41] . In line with previous DFT studies the zero point energy (ZPE) was not included in the energy terms 6,19,31,38,42 .…”

“…In fluorite structured materials this is relatively unclear, and so there is a compelling argument to map the interaction of hydrogen with the different components of the lattice. Detecting hydrogen experimentally is somewhat complex so modelling has become a routine way to analyse the details at the nanoscale [17][18][19][20][21][22] . Our research focusses on mapping the interaction between hydrogen and oxygen; the diffusion of hydrogen may indeed be affected by the diffusion of oxygen.…”