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

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 (PuO2). The considered variation ranges of the concentration of interstitial H (theta: H to Pu ratio), the concentration of oxygen vacancy (OV) (n(ov) : OV to O ratio), and the temperature were1/32 similar to 14/32,0 similar to 8/64, and 300 similar to 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 PuO2. In the OU PuO2 the O atoms will transport due to the presence of large concentration of H. The octahedral interstitial site in the OS PuO2 and the OV in the OU PuO2 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 PuO2 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. (C) 2020 Elsevier B.V. All rights reserved.