Super abundant vacancies (SAVs) have been suggested to form in the fcc phase of plutonium, δ-Pu, under a low-pressure hydrogen environment. Under these conditions, the vacancy concentration is proposed to reach 10⁻³ at% due to H trapping in vacancies lowering the effective vacancy formation energy. Previous density functional theory (DFT) results suggest that seven H atoms can be trapped in a single vacancy when a collinear special quasirandom magnetic structure is used to stabilize the δ phase, suggesting SAVs are a possible source of H stored in plutonium. In this report, we present DFT results for δ-Pu in the noncollinear 3Q magnetic state to study the formation of SAVs in mechanically stable δ-Pu. Together with these new simulations, we use publicly available computational and experimental data to provide further constraints on the physical conditions needed to thermodynamically stabilize SAVs in δ-Pu. Using several thermodynamic models, we estimate the vacancy concentrations in δ-Pu and discuss the limits of hydrogen driven formation of vacancies in δ-Pu. We find that, when hydrogen in the lattice is equilibrated with gaseous H₂, the formation of SAVs in δ-Pu is unlikely and any excess vacancy concentration beyond thermal vacancies would need to occur by a different mechanism.

中文翻译：

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δ-Pu超丰富空位前景的电子结构和热力学方法

研究表明，在低压氢气环境下，钚 δ-Pu 的面心立方相中会形成超丰富的空位 (SAV)。在这些条件下，由于空位中的H捕获降低了有效空位形成能，空位浓度预计达到10 ^-3 at%。先前的密度泛函理论（DFT）结果表明，当使用共线特殊准随机磁结构来稳定δ相时，七个H原子可以被捕获在单个空位中，这表明SAVs是存储在钚中的H的可能来源。在本报告中，我们提出了非共线 3Q 磁态下 δ-Pu 的 DFT 结果，以研究机械稳定的 δ-Pu 中 SAV 的形成。与这些新的模拟一起，我们使用公开的计算和实验数据来进一步限制热力学稳定 δ-Pu 中的 SAV 所需的物理条件。使用几种热力学模型，我们估计了 δ-Pu 中的空位浓度，并讨论了氢驱动的 δ-Pu 中空位形成的极限。我们发现，当晶格中的氢与气态H ₂平衡时，δ-Pu 中不太可能形成SAV，并且任何超出热空位的过量空位浓度都需要通过不同的机制发生。