Diffusion behavior of hydrogen in oxygen saturated and unsaturated plutonium dioxide: An ab initio molecular dynamics study

Abstract

As the plutonium (Pu) oxides are the crucial issue of the Pu surface and corrosion science and some impurities like hydrogen (H) are virtually impossible to exclude from them in realistic environments, understanding the dynamical behaviors of hydrogen (H) in Pu oxides is essential for the protections and applications of Pu. Here we perform systematic ab initio molecular dynamics (AIMD) calculations to reveal the diffusion behaviors of impurity H in the oxygen saturated (OS) and oxygen unsaturated (OU) Pu dioxide (PuO 2 ). The considered variation ranges of the concentration of interstitial H (θ: H to Pu ratio), the concentration of oxygen vacancy (OV) (n ov : OV to O ratio), and the temperature were 1 32 ∼ 14 32 , 0 ∼ 8 64 , and 300 ∼ 800 K, respectively. The root mean square displacements, radial distribution functions, Bader charge, electronic density of states, and the three-dimensional diffusion coefficients were extracted and analyzed in detail. Results indicate that the H diffusion is inhibited mainly due to the formation of hydroxyl with the host O both in the OS and OU PuO 2 . In the OU PuO 2 the O atoms will transport due to the presence of large concentration of H. The octahedral interstitial site in the OS PuO 2 and the OV in the OU PuO 2 provide a metastable and favorable capturing effect to the interstitial H, respectively. The diffusion coefficient in the OU PuO 2 is smaller than that of in the OS PuO 2 and decreases with n ov essentially as the OV plays the role of a trap for H diffusion. Our conclusions may provide potential guidance for Pu surface and corrosion science. • The mechanisms of inhibit hydrogen diffusion in different plutonium dioxides were confirmed. • Two different capturing effects to hydrogen in saturated and unsaturated PuO 2 were found. • The diffusion coefficients of hydrogen in different plutonium dioxides were obtained. • The variation tendencies of the hydrogen diffusion coefficients were discussed.