Understanding oxygen adsorption on 9.375 at. % Ga-stabilized δ-Pu (111) surface: A DFT study

Hernandez, Sarah C.; Wilkerson, Marianne P.; Huda, Muhammad N.

doi:10.1016/j.jallcom.2015.08.246

Cited by 7 publications

(5 citation statements)

References 34 publications

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“…Extended X-ray fine structure studies have shown the formation of Ga oxide structures within the Pu oxide, leading to possible disruption of the PuO 2 structure . Recent density functional theory (DFT) studies indicate that Ga will slow down the adsorption of oxygen (O) on Pu–Ga alloy surfaces, leading to possible changes in oxide formation kinetics. , Other recent experimental studies exploring the growth of the native oxide on δ-Pu metal have shown formation of an amorphous oxide structure . What effects impurities might have in the observed amorphous growth remain undetermined.…”

Section: Introductionmentioning

confidence: 99%

DFT+U Study of Chemical Impurities in PuO₂

Hernandez

Holby

2016

J. Phys. Chem. C

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We employ density functional theory to explore the effects of impurities in the fluorite crystal structure of PuO2. The impurities that were considered are known impurities that exist in metallic δ-phase Pu, including H, C, Fe, and Ga. These impurities were placed at various high-symmetry sites within the PuO2 structure including an octahedral interstitial site, an interstitial site with coordination to two neighboring O atoms, an O substitutional site, and a Pu substitutional site. Incorporation energies were calculated to be energetically unfavorable for all sites except the Pu substitutional site. When impurities were placed in a Pu substitutional site, complexes incorporating the impurities and O formed within the PuO2 structure. The observed defect-oxygen structures were OH, CO3, FeO5, and GaO3. The presence of these defects led to distortion of the surrounding O atoms within the structure, producing long-range disorder of O atoms. In contrast, perturbations of Pu atoms had a relatively short-range effect on the relaxed structures. These effects are demonstrated via radial distribution functions for O and Pu vacancies. Calculated electronic structure revealed hybridization of the impurity atom with the O valence states and a relative decrease in the Pu 5f states. Minor differences in band gaps were observed for the defected PuO2 structures containing H, C, and Ga. Fe-containing structures, however, were calculated to have a significantly decreased band gap, where the implementation of a Hubbard U parameter on the Fe 3d orbitals will maintain the calculated PuO2 band gap.

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Section: Introductionmentioning

confidence: 99%

DFT+U Study of Chemical Impurities in PuO₂

Hernandez

Holby

2016

J. Phys. Chem. C

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“…The WIEN2k parameters are kept consistent with previous adsorption studies on a pure δ-Pu and δ-Pu–Ga surface. ,,− The WIEN2k parameters are muffin tin radii (RMT) of 1.127, 1.032, and 0.318 Å for Pu, Ga, and H, respectively, and a plane-wave kinetic energy cutoff of K max 2 = 212 eV for the expansion of the wave function within the interstitial region. Because of previous theoretical studies ,, and a k-point convergence test on the surface, a k-point mesh of 2 × 4 × 1 and a temperature broadening parameter of k B T = 0.068 eV are chosen. The convergence criteria for the total energy and charge are 1.36 × 10 –4 eV and 1 × 10 –3 e – , respectively.…”

Section: Methodsmentioning

confidence: 99%

“…% Ga). The stability of these surfaces is discussed in refs and and concludes that increasing Ga content in the surface increases surface stability of δ-Pu.…”

Section: Methodsmentioning

confidence: 99%

“…27,28,50−53 The WIEN2k parameters are muffin tin radii (RMT) of 1.127, 1.032, and 0.318 Å for Pu, Ga, and H, respectively, and a plane-wave kinetic energy cutoff of K max 2 = 212 eV for the expansion of the wave function within the interstitial region. Because of previous theoretical studies 27,28,37 and a k-point convergence test on the surface, a k-point mesh of 2 × 4 × 1 and a temperature broadening parameter of k B T = 0.068 eV are chosen. The convergence criteria for the total energy and charge are 1.36 × 10 −4 eV and 1 × 10 −3 e − , respectively.…”

Section: ■ Computational Methodsmentioning

confidence: 99%

“…To better understand the catalytic behavior of hydriding, Balasubramanian et al calculated that H 2 will partially dissociate on PuH 2 as a barrierless process and that the Pu atom site is the active site for further catalysis of H 2 . The Ga in the alloy surface has not been included in previous theoretical attempts, even though oxidation/corrosion experimental studies have shown Ga to exist at the surface in some form. , We recently have calculated the effects of atomic oxygen (O) adsorption on a Pu–Ga alloyed surface , and concluded that increasing the Ga in the surface will influence O reactivity. In this paper, we examine the effects of Ga on the reactivity of atomic H with Ga-stabilized δ-Pu (111) surfaces by using a first-principles approach and the influence of Ga on the heat of solution of H in unalloyed and Ga alloyed δ-Pu coupons.…”

Section: Introductionmentioning

confidence: 99%

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Influence of Ga on H Reactivity with Ga-Stabilized δ-Pu Alloys

et al. 2017

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The influence of Ga on the adsorption and solubility of H on Ga-stabilized δ-Pu alloys is investigated using density functional theory and experimentally via a Sieverts' apparatus. Allelectron DFT calculations, with spin−orbit coupling and full relaxations of the surface, are implemented to calculate H adsorption on δ-Pu−Ga alloy (111) surfaces. Chemisorption energies indicate that H prefers a 3-fold hollow site that binds strongly to a Pu-rich environment regardless of Ga concentration of the surface. Sites that include a Ga−H bond yield an increase in chemisorption energies as opposed to chemisorption energies when the H is only bonded to Pu atoms. Also, solution energies for interstitial sites are less exothermic than surface adsorption energies. Experimentally, H-vacancy binding is more exothermic than interstitial binding, and since vacancy binding is the analogue of surface binding, the DFT results are in agreement. Both DFT and experimental results show that with increasing Ga content to 7 at. % Ga there is an increase in H solution energies, thus reducing H solubility. The maximal reduction of H solubility is between 4 and 5 at. % Ga stabilized δ-Pu. The bonding nature of H on the Pu−Ga surface, via analysis of the partial density of states, shows weak hybridizations between the Pu 6d and H 1s states, with a slight decrease of the Pu 5f states near the Fermi level. Overall, Ga will affect the surface adsorption and solubility of H in δ-Pu−Ga alloys.

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