Atomic oxygen adsorption on 3.125 at.% Ga stabilized δ-Pu (1 1 1) surface

Abstract

a b s t r a c tAll-electron density functional theory was used to investigate atomic oxygen adsorption on a gallium stabilized d-plutonium (1 1 1) surface. High symmetry on-surface and interstitial adsorption sites, along with local environment (as determined by the absence or presence of gallium) were explored. The calculations comprised full structural relaxations. Spin-orbit-coupling was also taken into account to assess the complexity of absorbate-substrate interactions. We observed that O adsorbate prefers to bind strongly to a gallium deficient environment, with the most stable site being the threefold hollow fcc site and associated chemisorption energy of À5.06 eV. The binding energies were least favored when gallium is a nearest neighbor to the O adsorbate, suggesting that the presence of gallium in a plutonium matrix tends to slow down the oxide layer growth. Although the oxygen coordination is the highest in the interstitial sites, the adsorption energy is less favored compared to on-surface adsorption, implying that the diffusion of oxygen from the surface layer into the subsurface layers is an activated process. The adsorption process induced non-trivial deformations of the surface. Additionally, some delocalization of the plutonium 5f and 6d partial electron density of states (PDOS) at the Fermi energy was observed. Further analysis in the PDOS indicated that gallium tends to suppress hybridization between the plutonium 5f and oxygen 2p orbitals, while the 6d orbitals hybridized with oxygen 2p orbitals.Published by Elsevier B.V.

First-principles DFT +U calculations on the energetics of Ga in Pu, Pu2O3 and PuO2

“…Additionally, the hydrogen atom prefers to interact much more strongly to the Pu atom than the Ga atom in the hydrogenvacancy complex [31]. The latter calculation results suggested that the presence of Ga in a Pu matrix could slow down the growth of Pu oxide layers [11], judged from the energetics of O atom at different sites (i.e., top of Ga, bridge between Pu and Ga, hollow sites, and interstitial site. ).…”

“…The total energy of a free O atom is calculated by using a periodic cubic cell with a lattice constant of 15 Å and only one k point C in the framework of spin-polarized DFT. Moreover, pure spin-polarized DFT method is used to calculate the total energy of a-Ga crystallized in orthorhombic structure to obtain the energy of a Ga atom [11].…”

“…Knowledge from oxidation behavior of Pu shows that the oxidation rate of Pu-Ga alloy can be generally slower than that of unalloyed Pu. Nevertheless, some experimental results showed that Ga impurity can either enhance or hinder the oxidation rate of d-Pu when compared to unalloyed Pu [10,11]; this is mainly because the initial stages of oxidation are inherently a surface phenomenon, thus the external environment, the chemical states and the occupied sites of Ga can be the influence factors in oxidation rate. Up till now, the underlying reasons for the rate change resulted from Ga have not been well understood.…”

“…Some available theoretical attempts on Pu 2 O 3 have focused only on the ground-state electronic structure of its bulk and surface, and on the reaction energy between PuO 2 and Pu 2 O 3 [15,[27][28][29][30]. Recently, Hernandez et al calculated the formation energy of hydrogen-vacancy complex in Pu-Ga alloy and the atomic oxygen adsorption on Ga stabilized d-Pu (1 1 1) surface by means of an all-electron DFT method [11,31]. The former calculation results showed that hydrogen could stabilize Pu vacancy and drive the formation of superabundant vacancies (SAV) which is very common phenomenon in metal-hydrogen systems [32,33].…”

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

“…We have reported the adsorption of O on a 3.125 at. % Ga stabilized δ-Pu (111) [23], which showed that O preferred to be threefold coordinated in a Pu-environment and Ga does influence the electronic structure of the nearest 5 neighboring Pu atoms. In this paper we selected a higher concentration of Ga within a δ-Pu (111) matrix.…”