Bergman-type medium-range order in rapidly quenched Ag0.74Ge0.26 eutectic alloy studied by ab initio molecular dynamics simulation

Abstract

The structure of liquid and rapid quenched amorphous Ag 0.74 Ge 0.26 alloy at the eutectic composition was studied by ab initio molecular dynamics (MD) simulations. The local structural properties from the liquid at 1123 K to amorphous solid at 300 K were systematically investigated. The pair-correlation function at 1123 K from the MD simulations agrees well with the experimental data. The local structures were also analyzed using Honeycutt-Andersen (HA) indices, Voronoi tessellation, and atomic cluster alignment (ACA) method. The HA indices analysis reveals that pentagonal bipyramid structure has high population which become more predominant upon solidification. Voronoi tessellation analysis indicates strong icosahedral short-range orders (SRO) in the liquid and amorphous samples generated by the MD simulations. Using the ACA, the development of icosahedral SRO upon cooling is further confirmed and a Bergman medium-range order is also observed. The analysis of structural properties and chemical short-range order suggests that Ag atoms trend to have a Bergman-like packing, while the dispersed Ge atoms prevent the alloy from forming a long-range order upon cooling. The Bergman medium-range order is also confirmed by the constrained Reversed Monte Carlo results.

Temperature-dependent structure evolution in liquid gallium

“…This method has been applied to directly visualize the average local short-range order and medium range order [83][84][85]. Thus, the cluster alignment method is applied to further elucidate the short-range order difference between high-and low-temperature regions in 9 liquid Ga. 2000 clusters are randomly selected from the AIMD simulation trajectories at four selected temperatures of 600, 1000, 1200 and 1600 K. Each cluster consists of 16 atoms.…”

Bergman-type medium range order in amorphous Zr77Rh23 alloy studied by ab initio molecular dynamics simulations

“…A Bergman-type cluster is one of the MROs in MGs, and is an icosahedral-based cluster which, moving outward from the center atom, forms an icosahedron, dodecahedron, and a larger icosahedron [19,20]. The Bergman-type MRO seems to be related to splitting in the second peak of the PDF in a Cu-Zr system [18,21] and an Ag0.74Ge0.26 alloy [22]. The positions of the two sub-peaks formed by the splitting of the second peak are the same as the maxima of the corresponding distribution of the second and third shells of the Bergman-type cluster.…”

Optical Properties and Local Structure Evolution during Crystallization of Ga16Sb84 Alloy

“…The 7 atom template represents the short-range order, and the template with 19 atoms represents the medium-range order. Unlike some metallic glasses 42 where icos is the dominating local motif, the amount of icos, bcc, fcc, hcp and zb in Ga 16 Sb 84 is not detectable with the temperature change. The fraction of rhombohedral clusters for 7 and 19 atom templates for different centered clusters are illustrated in Fig.…”