破解非晶结构之谜: 连接非晶态和晶态的中程序结构单元

The nature of the glassy state is always one of the most exciting and fundamental issues in condensed matter physics and materials science. Metallic glasses provide ideal models for investigating amorphous physics due to the simple metal bonding and close-packed structure. Studies have found various orders in metallic glasses, among which medium-range order structures play an increasingly critical role in the phase transformation and deformation of amorphous alloys. However, the existing theories or experimental results are challenging to determine whether there is a structural connection between the amorphous state and its corresponding crystalline state in the medium range or more extensive length scale range. Moreover, the existing characterization methods are difficult to accurately analyze its short-range to medium-range order structure, further compounding its issue. Most recently, a unique metastable cubic phase has been found as an essential intermediate state during the heating process before crystallization 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 six-membered tricapped trigonal prism (6M-TTP) cluster. This structure’s short-range clusters are organized as a peculiar chiral structure to form a medium-range building block with about 12.5 Å. The 6M-TTP clusters tend to randomly pack to be long-range disordered structures in the as-cast state and later transform to be an ordered cubic metastable phase at a certain temperature. In order to reveal the nature of the amorphous structure, a new structural model is provided, and a new explanation is proposed for the precipitation kinetics of metastable mesophase in metallic glasses. These findings will help clarify the structural arrangement of metallic glasses in the medium-range and even more extensive length scales. Our findings would shed light on capture and decipher more building blocks of medium-range ordering in amorphous alloys and would help solve the long-standing issue of amorphous structures.