破解非晶结构之谜：连接非晶态和晶态的中程序结构单元

非晶态结构本质一直是凝聚态物理和材料科学中最有趣和最基本的问题之一。非晶合金因其简单的金属键结合及密堆积结构而成为研究非晶物理的理想材料模型。研究发现,非晶中存在着不同尺度的局域有序结构,其中5~20 埃米尺度范围对应中程序。近来研究揭示其在非晶合金的相变和形变过程中发挥了越来越关键的作用。现有的理论或者实验结果难以确定非晶态材料与其对应的晶态材料间是否存在中程或更大尺度范围的结构联系,同时现有的表征手段难以精确解析其短程到中程尺度有序结构,导致中程序结构解析问题十分复杂。最近在经典大块非晶合金体系钯-镍-磷中通过对一种独特的亚稳立方中间相进行解析,发现了一种桥接非晶态与晶态的手性中程序结构基元六元三帽三棱柱(6M-TTP)。该结构的短程序团簇以一种奇特的手性结构构成约12.5埃米的中程序结构基元,其在铸态为长程无序堆积,而在一定温度可以转变成有序堆积的亚稳立方相。中程序结构的捕获和解析为揭示非晶态结构本质提供了新的结构模型,并且对非晶合金亚稳态中间相的析出动力学规律提出了新的解释。这些发现将有助于阐明非晶合金在中程序以及更大尺度上的结构排列,为解析非晶态的结构本质提供新的思路。

Solving the structural mystery of glass: A medium-range structure motif linkingamorphous and crystalline states

 The nature of the glassy state is always one of the most exciting and fundamental issues in condensed matter physicsand materials science. Metallic glasses provide ideal models for investigating amorphous physics due to the simple metal bondingand close-packed structure. Studies have found various orders in metallic glasses, among which medium-range order structuresplay an increasingly critical role in the phase transformation and deformation of amorphous alloys. However, the existing theoriesor experimental results are challenging to determine whether there is a structural connection between the amorphous state and itscorresponding crystalline state in the medium range or more extensive length scale range. Moreover, the existing characterizationmethods are difficult to accurately analyze its short-range to medium-range order structure, further compounding its issue. Mostrecently, a unique metastable cubic phase has been found as an essential intermediate state during the heating process beforecrystallization in a classic bulk metallic glass Pd-Ni-P, and a hidden chiral medium-range structure bridging the amorphous state,and the crystalline state was captured and deciphered from the metastable cube phase. The medium-range structure is named the sixmembered tricapped trigonal prism (6M-TTP) cluster. This structure’s short-range clusters are organized as a peculiar chiral structureto form a medium-range building block with about 12.5 Å. The 6M-TTP clusters tend to randomly pack to be long-range disorderedstructures in the as-cast state and later transform to be an ordered cubic metastable phase at a certain temperature. In order to revealthe nature of the amorphous structure, a new structural model is provided, and a new explanation is proposed for the precipitationkinetics of metastable mesophase in metallic glasses. These findings will help clarify the structural arrangement of metallic glasses inthe medium-range and even more extensive length scales. Our findings would shed light on capture and decipher more building blocksof medium-range ordering in amorphous alloys and would help solve the long-standing issue of amorphous structures.