First-principles calculations of the diffusion of atomic oxygen in nickel: thermal expansion contribution

Abstract

Within the framework of density functional theory using the projector augmented-wave (PAW) method, we present some energetic properties of atomic oxygen interstitials in crystalline Ni, i.e. the insertion and activation energies of the O diffusion. Concerning the activation energy, two pathways for the migration process are studied. The charge transfer process between atomic oxygen and nickel atoms is analysed in the interstitial sites. We find that the interstitial octahedral site (O site) is lower in energy than the tetrahedral site (T site). The most favourable pathway for the migration between two octahedral sites corresponds to an intermediate metastable state located in a tetrahedral site. Concerning the charge transfers we find that the atomic oxygen ionizes as O(-) and that the electron migrates essentially from the Ni nearest neighbours of atomic oxygen. In addition, the thermal expansion contribution through the dilatation of the solid is studied. When the thermal expansion is introduced, we show that the insertion process is stabilized and that the tetrahedral insertion energy becomes nearly equal to the octahedral ones. However, the activation energy decreases with the dilatation. Taking into account the thermal expansion effects, our results are consistent with the more reliable experimental data.

First-principles studies on vacancy-modified interstitial diffusion mechanism of oxygen in nickel, associated with large-scale atomic simulation techniques

“…The energetics of the migration barriers and saddle states predicted using the CI-NEB method for both pathways are shown in Table II, the calculated migration barriers are consistent with the DFT predictions from literature, 14,15 even though there is a small difference of 0.04 $ 0.30 eV. As previously discussed, this difference is primarily due to the different exchange functionals and structural relaxation schemes used in the calculations.…”

“…The DFT calculated solution energies are qualitatively consistent with other DFT calculated values from the literature. 14,15 However, the present results are more negative. This is probably a consequence of the present study employing the LDA exchange functional, while the other studies utilizing the GGA functional, as the former generally overestimates the bonding strength while the latter underestimates.…”

“…The literature reports two possible jump pathways. 14,15,30 One is the direct jump from one octahedral site to an adjacent octahedral site (O-O) The other is the jump between the octahedral sites by passing through an adjacent tetrahedral site (O-T-O), as shown in Figure 2.…”

“…Young et al, 13 Megchiche et al, 14 and Kim et al 15 studied oxygen migration barriers in fcc nickel by using the first-principles calculations, and the predicted values are 0.95 6 0.28, 1.12, and 1.23 eV at ground state, respectively, which are far below the range of experimental data. These first-principles calculations indicate that the oxygen diffusion in fcc nickel is via the interstitial mechanism and the minimum energy pathway corresponds to the jump from octahedral interstitial site to an adjacent octahedral site bypassing a co-neighboring tetrahedral site (O-T-O).…”

First-principles study of interstitial diffusion of oxygen in nickel chromium binary alloy

“…For pure nickel, Garruchet et al 8 evaluated the diffusion of oxygen in nickel by the variable charge molecular dynamics, and Young et al 9 calculated the diffusion coefficient of hydrogen and the activation energy of oxygen of diffusion in nickel by using the first-principles method and also Megchiche et al 10 calculated the diffusion of oxygen in nickel using the first-principles calculation. In addition, the effect of thermal expansion on the diffusion process was studied by varying the lattice expansion that was concerned with varying the lattice constant by Finnis et al 11 and Mishin et al 12 They explored some properties in oxidation of bimetal such as NiAl.…”