Search

• The general trends of stability of stoichiometric and non-stoichiometric Pu oxides are firstly reported. • A rigorous quantum definition of oxidation state is used to determine the atomic ratio of Pu3+/Pu4+ in Pu oxides. • The proposed ladder-like Pu oxide layer structure might be more reasonable than the sandwich-like structure. The oxide layer structure over Pu is the central issue of Pu corrosion science; however, the widely discussed sandwich-like structure (Pu//Pu 2 O 3 //PuO 2) might be just a phenomenological description. Here we perform first-principles calculations with the method verification on Ce oxides, the ideal analogues of Pu oxides, to establish a universal picture of Pu oxide layer structure. The results show that homogeneous Pu n O 2 n -2 between PuO 2 and Pu 2 O 3 are energetically more favorable than PuO 2- x with ordered arrays of oxygen vacancies. Thus, a ladder-like oxide layer structure is proposed to improve a simple sandwich-like model of the Pu oxide layers. [ABSTRACT FROM AUTHOR]

First-principles density functional theory–generalized gradient approximation methods are used to calculate the energetics of Ga in Ga-stabilized δ phase Pu, Pu 2 O 3 and PuO 2 , in order to elucidate the relative stability of Ga in the Pu oxide layers. The Hubbard parameter U is used to describe the strongly correlated electron behavior of Pu 5 f electrons. Three incorporation sites for Ga, i.e., interstitial site, Pu and O vacancies, are considered. The results indicate that the energetics of Ga significantly depend on the inherent properties of the host materials and the incorporation sites in them. Ga incorporation into interstitial sites and O vacancies of both Pu 2 O 3 and PuO 2 are energetically unfavorable. Ga incorporation into Pu vacancy of PuO 2 is the most energetically favorable, followed by Ga incorporation into Pu vacancies of Pu 2 O 3 and Pu. However, this does not mean that there would be the highest concentration of Ga in PuO 2 among these three Ga-stabilized Pu substances because it is most difficult for Pu vacancy formation in PuO 2 . The distribution of Ga in the Pu oxide layers is proposed to be strongly dependent on the distribution and the concentration of Pu vacancy, as a result, Ga concentration likely decrease with the transitions of Pu → Pu 2 O 3 → PuO 2 . [ABSTRACT FROM AUTHOR]

The structural, electronic, mechanical, optical, thermodynamic properties of plutonium monoxide monohydride (PuOH) are studied by density-functional calculations within the framework of LDA/GGA and LDA/GGA+U. From the total energy calculation, the lowest-energy crystal structure of PuOH is predicted to have space group F 4 ¯ 3 m (No. 216). Within the LDA+U framework, the calculated lattice parameter of F 4 ¯ 3 m -PuOH is in good agreement with the experimental value and the corresponding ground state is predicted to be an antiferromagnetic charge-transfer insulator. Furthermore, we investigate the bonding character of PuOH by analyzing the electron structure and find that there are a stronger Pu-O bond and a weaker Pu-H bond. The mechanical properties including the elastic constants, elastic moduli and Debye's temperature, and the optical properties including the reflectivity and absorption coefficient are also calculated. We then compute the phonon spectrum which verified the dynamical stability of F 4 ¯ 3 m -PuOH. Some thermodynamic quantities such as the specific heat are evaluated. Finally we calculate the formation energy of PuOH, and the reaction energies for the oxidation of PuOH and PuOH-coated Pu, which are in reasonable agreement with the experimental values. [ABSTRACT FROM AUTHOR]

• The microscopic mechanisms of inhibit plutonium hydriding with different oxide overlayers were revealed. • The PuO 2 inhibits plutonium hydriding mainly due to the formation of hydroxyl groups. • The α-Pu 2 O 3 could inhibit plutonium hydriding at low hydrogen concentration conditions. • Plutonium hydriding could not be effectively resisted with α-Pu 2 O 3 when hydrogen concentration is high. The hydriding corrosion of metallic plutonium (Pu) is a crucial issue for its actual applications. The current work performs systematic ab initio molecular dynamics calculations to reveal the microscopic mechanism of Pu oxides over metallic Pu in resisting hydriding reaction. The results show that Pu hydriding is inhibited by PuO 2 because hydrogen atoms are captured by lattice oxygen to form hydroxyl groups. In α-Pu 2 O 3 the hydrogen attack could be prevented when hydrogen concentration is low because oxygen vacancy acts as a trap for hydrogen migration. Whereas, when the hydrogen concentration is high enough the hydriding corrosion could not be effectively resisted. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]