Journal
PHYSICAL REVIEW B
Volume 79, Issue 10, Pages -Publisher
AMER PHYSICAL SOC
DOI: 10.1103/PhysRevB.79.104206
Keywords
ab initio calculations; liquid alloys; liquid structure; liquid theory; molecular dynamics method; nickel alloys; nucleation; rapid solidification; supercooling; undercooling; vitrification; X-ray diffraction; zirconium alloys
Funding
- U. S. Department of Energy [DE-AC02-07CH11358]
- Director for Energy Research, Office of Basic Energy Sciences
- Office of Science, Basic Energy Sciences, U. S. Department of Energy [DE-AC02-06CH11357]
- National Science Foundation [DMR-0606065]
- NASA [NNM04AA016]
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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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