Experimental and ab initio structural studies of liquid Zr2Ni

TitleExperimental and ab initio structural studies of liquid Zr2Ni
Publication TypeJournal Article
Year of Publication2009
AuthorsHao SG, Kramer MJ, Wang CZ, Ho KM, Nandi S, Kreyssig A, Goldman AI, Wessels V, Sahu KK, Kelton KF, Hyers RW, Canepari SM, Rogers JR
Journal TitlePhysical Review B
Date Published03/01
ISBN Number1098-0121
Accession NumberISI:000264768600049
Keywordsab initio calculations, liquid alloys, liquid structure, liquid theory, local at, molecular dynamics method, nickel alloys, nucleation, rapid solidification, short-range order, supercooling, undercooling, vitrification, x-ray diffraction, zirconium alloys

High-energy x-ray diffraction and ab initio molecular-dynamics simulations demonstrate that the short-range order in the deeply undercooled Zr2Ni liquid is quite nuanced. The second diffuse scattering peak in the total structure factory sharpens with supercooling, revealing a shoulder on the high-Q side that is often taken to be a hallmark of increasing icosahedral order. However, a Voronoi tessellation indicates that only approximately 3.5% of all the atoms are in an icosahedral or icosahedral-like environment. In contrast, a Honeycutt-Andersen analysis indicates that a much higher fraction of the atoms is in icosahedral (15%-18%) or distorted icosahedral (25%-28%) bond-pair environments. These results indicate that the liquid contains a large population of fragmented clusters with pentagonal and distorted pentagonal faces, but the fully developed icosahedral fragments are rare. Interestingly, in both cases, the ordering changes little over the 500 K of cooling. All metrics show that the nearest-neighbor atomic configurations of the most deeply supercooled simulated liquid (1173 K) differ topologically and chemically from those in the stable C16 compound, even though the partial pair distributions are similar. The most significant structural change upon decreasing the temperature from 1673 to 1173 K is an increase in the population of Zr in Ni-centered clusters. The structural differences between the liquid and the C16 increase the nucleation barrier, explaining glass formation in the rapidly quenched alloys.

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