Topological Frustration and Glass-Forming Ability of Sulfur-containing Metallic Glass-Formers

最近，R. Busch和他的同事开发了一种新的含硫(S)合金元素的金属玻璃。对于这些合金，在大多数情况下，与不含S的类似合金成分相比，玻璃形成能力得到了改善。在某些情况下，S的加入甚至第一次创造了大量玻璃化的可能性。在这种情况下，重要的是要记住，硫具有复杂的配位行为，并且比任何其他元素形成更多的同素异形体，在环境和近环境条件下，s8环是最丰富的晶体同素异形体。在纯硫的熔融状态下，也有大量不同的同素异形体共存，包括s8环，以及每转8个原子的螺旋结构的出现也是已知的。因此，从概念上讲，向金属熔体中添加硫大大增加了拓扑的可变性和复杂性。从形成玻璃的金属液体的结构模型来看，包括早期的关联模型，由于几何挫折，这种情况很容易发生玻璃化。因此，新的含s玻璃成形合金家族为系统分析特定合金元素的影响提供了独特的机会，这种元素在很大程度上提高了液态抗结晶的稳定性。在这个系统的研究中，确定了三组不同的合金，分别是低硫、中硫和高硫。如果考虑各自的无s基合金体系，则观察到以下相关性：高s含量的大块金属玻璃为20 at。%或更多与固溶体形成基合金有关，如Pd-Ni，根本不形成玻璃；培养基s含量低于10 at。要在基合金中形成大块的金属玻璃，就需要%的硫，少量添加几个原子百分比的硫可以增强基合金的玻璃形成能力（GFA），即使不添加硫，基合金也可以形成大块的玻璃。因此，不同组的含s和大块玻璃形成合金允许以独特和前所未有的方式解决金属系统中关于玻璃形成的长期和基本问题。因此，我们提出了一种系统且紧密相连的方法，结合了三个参与研究玻璃形成金属合金的小组的互补和长期专业知识，以解决以下相互关联的问题：-硫作为合金元素如何改变熔体和玻璃中元素物种的粘度和原子迁移率？-含s体系的gfa增强是由于微观迁移率的降低、介观流动行为的改变还是热力学约束的改变？- s的加入如何影响液体和玻璃的中量程顺序？

Very recently, a new family of metallic glasses that contain Sulfur (S) as alloying element has been developed by R. Busch and co-workers. For those alloys, in most cases the glass-forming ability was improved as compared to similar alloy compositions where S was absent. In some cases, the addition of S even served to create the possibility for bulk vitrification for the first time. In that context it is important to recall that Sulfur has a complex coordination behavior and forms more allotropes than any other element, with the S8-ring being the most abundant crystalline allotrope under ambient and near-ambient conditions. In the molten state of pure sulfur, also a large variety of largely different allotropes coexist, including S8-rings, and the occurrence of a helical structure with eight atoms per turn is also known. Thus, conceptually, adding sulfur to a metallic melt increases considerably the topological variability and complexity. In the view of structural models of glass-forming metallic liquids, including early association models, such a situation is prone to vitrification due to geometrical frustration. Thus, the new family of S-containing glass-forming alloys offers the unique opportunity to systematically analyze the impact of a specific alloying element that largely enhances the stability of the liquid state against crystallization. For this systematic study, three distinct groups of alloys with minor -, medium - and high Sulfur content have been identified. If the respective S-free base alloy systems are regarded, the following correlation is observed: bulk metallic glasses with high S-content of 20 at. % or more are related to solid-solution-forming base alloys such as Pd-Ni that do not form glasses at all; medium S-contents below 10 at. % are required to form bulk metallic glasses in base alloys that are marginal glass-formers and minor S additions of the order of a few atomic percent serve to enhance the glass-forming ability (GFA) of base alloys that are already allowing for bulk glass formation even without the addition of sulfur. Thus, the different groups of S-containing and bulk glass-forming alloys allow addressing long-standing and basic issues concerning glass formation in metallic systems in a unique and unprecedented way. We thus propose a systematic and strongly interlinked approach that combines the complementing and long-standing expertise of the three participating groups in research on glass-forming metallic alloys to address the following interconnected questions: - How does sulfur as alloying element modify the viscosity and the atomic mobility of the elemental species in the melt and the glass?- Do the enhanced GFAs of S-containing systems result from a decreased microscopic mobility, from a modified mesoscopic flow behavior or from changed thermodynamic constraints?- How does the S-addition affect the medium-range order of the liquid and the glass?