One of the most intriguing phenomena under radiation is the self-organization of defects, such as the void superlattices, which have been observed in a list of bcc and fcc metals and alloys when the irradiation conditions fall into certain windows defined by temperature and dose rate. A superlattice features a lattice parameter and a crystal structure. Previously, it has been shown that the superlattice parameter is given by the wavelength of vacancy concentration waves that develop when the uniform concentration field becomes unstable. This instability is driven thermodynamically by vacancy concentration supersaturation and affected by the irradiation condition. However, a theory that predicts the superlattice symmetry, i.e., the selection of superlattice structure, has remained missing decades after the first report of superlattices. By analyzing the nonlinear recombination between vacancies and self-interstitial-atoms (SIAs) in the discrete lattice space, this work establishes the physical connection between symmetry breaking and anisotropic SIA diffusion, allowing for predictions of void ordering during defect self-organization. The results suggest that while the instability is driven thermodynamically by vacancy supersaturation, the symmetry development is kinetically rather than thermodynamically driven. The significance of SIA diffusion anisotropy in affecting superlattice formation under irradiation is also indicated. Various superlattice structures can be predicted based on different SIA diffusion modes, and the predictions are in good agreement with atomistic simulations and previous experimental observations.

中文翻译：

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辐照下缺陷自组织过程中的对称破坏

辐射下最引人入胜的现象之一是缺陷的自组织，例如空隙超晶格，当辐射条件落入由温度和剂量率定义的某些窗口时，这些缺陷已在一系列的bcc和fcc金属及合金中观察到。超晶格具有晶格参数和晶体结构。先前已经表明，超晶格参数由当均匀浓度场变得不稳定时产生的空位浓度波的波长给出。这种不稳定性是由空位浓度过饱和热力学驱动的，并受辐照条件的影响。但是，预测超晶格对称性的理论（即，选择超晶格结构）在首次报道超晶格后数十年仍然缺失。通过分析离散晶格空间中空位和自填隙原子（SIA）之间的非线性复合，这项工作建立了对称破坏与各向异性SIA扩散之间的物理联系，从而可以预测缺陷自组织过程中的空隙有序性。结果表明，尽管不稳定性是由空位过饱和热力学驱动的，但对称性的发展是动力学而非热力学驱动的。还指出了SIA扩散各向异性在辐射下影响超晶格形成的重要性。可以基于不同的SIA扩散模式来预测各种超晶格结构，并且这些预测与原子模拟和先前的实验观察非常吻合。