Khusnutdinoff R M, Khairullina R R, Suslov A A, Lad'yanov V I, Mokshin A V
Department of Physics, Kazan (Volga Region) Federal University, Kazan 420008, Russia.
Udmurt Federal Research Center, Ural Branch of Russian Academy of Sciences, Izhevsk 426068, Russia.
J Phys Condens Matter. 2022 Jul 7;34(36). doi: 10.1088/1361-648X/ac7cae.
Supercooled transition metals are characterized by the absence of long-range order and the presence of a specific short-range order in the arrangement of atoms. So, the presence of shoulders and broadenings at the second maximum in the experimentally measured quantity-in the static structure factor()-is usually interpreted as a manifestation of the icosahedral (ideal or distorted) short-range order (ISRO-). Icosahedral short-range order is a structure with fivefold symmetry in the arrangement of atoms, which can lead to the possibility of achieving deep supercooling. In this work, we study the local structural features of equilibrium and supercooled nickel melts under various cooling protocols (γ∈1010,1014 K s) in order to clarify the mechanism of formation of the icosahedral short-range order in pure transition metals. Comprehensive studies of the properties of nickel melts were carried out using experiments on x-ray diffraction, large-scale molecular dynamics (MD) simulations with subsequent structural and cluster analysis. A good agreement was found between the results of x-ray diffraction data and the MD simulations results for an equilibrium nickel melt. It was found that the nickel melt is characterized by a short-range order, formed by fragments of icosahedra and distorted icosahedral clusters. It was revealed that the 'liquid-crystal' phase transition in nickel is accompanied by the transformation of distorted icosahedral clusters into clusters with the-symmetry. It is shown that, in contrast to the Voronoi tessellation method, the cluster analysis method based on the (q4,q6) rotational invariants does not allow sufficiently correct identification of the distorted icosahedral short-range order in metal melts.
过冷过渡金属的特征是原子排列中不存在长程有序，而存在特定的短程有序。因此，在实验测量量（静态结构因子）的第二个最大值处出现的肩部和展宽通常被解释为二十面体（理想或扭曲）短程有序（ISRO -）的表现。二十面体短程有序是原子排列具有五重对称性的结构，这可能导致实现深度过冷的可能性。在这项工作中，我们研究了在各种冷却速率（γ∈10¹⁰，10¹⁴ K s⁻¹）下平衡态和过冷镍熔体的局部结构特征，以阐明纯过渡金属中二十面体短程有序的形成机制。使用X射线衍射实验、随后进行结构和团簇分析的大规模分子动力学（MD）模拟对镍熔体的性质进行了综合研究。对于平衡态镍熔体，发现X射线衍射数据结果与MD模拟结果之间有很好的一致性。发现镍熔体的特征是由二十面体片段和扭曲的二十面体团簇形成的短程有序。结果表明，镍中的“液晶”相变伴随着扭曲的二十面体团簇向具有 - 对称性的团簇的转变。结果表明，与Voronoi镶嵌方法不同，基于（q4，q6）旋转不变量的团簇分析方法不能充分正确地识别金属熔体中扭曲的二十面体短程有序。
