The in-depth understanding of hydrogen permeation through plutonium-oxide overlayers is the prerequisite to evaluate the complex hydriding induction period of Pu. In this work, the incorporation, diffusion and dissolution of hydrogen in $\alpha$-Pu$_{ 2}$O$_{ 3}$ are investigated by the first-principles calculations and $\textit{ ab initio}$ thermodynamic method based on DFT+U and DFT-D3 schemes. Our study reveals that the hydrogen incorporation is endothermic and the separated H atoms prefer to recombine as H$_{ 2}$ molecules rather than reacting with $\alpha$-Pu$_{ 2}$O$_{ 3}$. The H and H$_{ 2}$ diffusion are both feasible, generally, H will recombine first as H$_{ 2}$ and then migrate. Both pressure P$_{ H2}$ and temperature can promote the hydrogen dissolution in $\alpha$-Pu$_{ 2}$O$_{ 3}$. The single H$_{ 2}$ molecule incorporation and (H+H$_{ 2}$) mixed dissolution will successively appear when increasing P$_{ H2}$. Compared to PuO$_{ 2}$, this work indicates that Pu sesquioxide is hardly reduced by hydrogen, but the porous $\alpha$-Pu$_{ 2}$O$_{ 3}$ facilitates hydrogen transport in Pu oxide layers. We presents the microscopic picture of hydrogen behaviors in the defect-free $\alpha$-Pu$_{ 2}$O$_{ 3}$, which could shed some light on the study of the hydriding induction period of Pu.
Categories: cond-mat.mtrl-sci