Local structure orders and glass forming ability of Ni-Nb liquids

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2018-05-04
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Wen, T. Q.
Zhang, Y.
Wang, Cai-Zhuang
Wang, N.
Ho, Kai-Ming
Kramer, Matthew
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Ames National Laboratory

Ames National Laboratory is a government-owned, contractor-operated national laboratory of the U.S. Department of Energy (DOE), operated by and located on the campus of Iowa State University in Ames, Iowa.

For more than 70 years, the Ames National Laboratory has successfully partnered with Iowa State University, and is unique among the 17 DOE laboratories in that it is physically located on the campus of a major research university. Many of the scientists and administrators at the Laboratory also hold faculty positions at the University and the Laboratory has access to both undergraduate and graduate student talent.

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Physics and astronomy are basic natural sciences which attempt to describe and provide an understanding of both our world and our universe. Physics serves as the underpinning of many different disciplines including the other natural sciences and technological areas.
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Ab initio molecular dynamics simulations were performed to study the atomistic structures of Ni48Nb52, Ni59.5Nb40.5 and Ni75Nb25 liquids near their melting temperatures. It is found that the total coordination number only changes slightly across the compositions. However, there is significant difference in the chemical ordering. The Cluster Alignment method was used to identify the dominant local structure motifs. It is found that distorted and perfect icosahedral clusters are the most popular motifs around Ni atoms, while Z14, Z15, and Z16 Frank-Kasper polyhedra are dominant around Nb atoms. Among the three compositions, the eutectic composition (Ni59.5Nb40.5) has the largest population of these dominant motifs and the highest degree of five-fold local symmetry. Chemical order in the distorted icosahedral motif is studied and the occupation probability of Nb in the distorted region is found to be much different from other sites. The network formed by distorted and perfect icosahedral clusters and that by the interconnection of the perfect icosahedra, Z14, Z15, and Z16 motifs are the strongest at the eutectic composition. The high percentage of perfect and distorted icosahedral clusters and their strong network structures in this system (especially around the eutectic composition) correlate well with the excellent glass forming ability in this system.

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