Abstract
The atomic structures of four Ca 40+XMg 25Cu 35-X (X 0, 5, 10, and 20 at.%) ternary metallic glasses have been determined using a synergistic combination of neutron diffraction, ab initio molecular dynamics (MD) simulation, and constrained reverse Monte Carlo modeling. It is described as close-packing of efficiently packed Cu-centered clusters that have Ca, Mg, and Cu atoms in the first coordination shell. The close-packed arrangement of the clusters provides a characteristic medium range order in these alloys. An average coordination number (CN) of 10 (with about 5-7 Ca, 2-3 Mg, and 1-2 Cu atoms) is most common for the Cu-centered clusters. The average coordination numbers around Mg and Ca are 12-13 (∼6-8 Ca, 3 Mg, and 1-4 Cu) and 13-15 (7-9 Ca, 3-4 Mg, and 2-5 Cu), respectively, and they are composition dependent. Strong interaction of Cu with Mg and Ca results in pair bond shortening. Icosahedral short range order does not dominate in these amorphous alloys, although polytetrahedral packing and five-fold bond configurations resulting in pentagonal bi-pyramids have been found to be the most common nearest atom configurations.
Original language | English |
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Article number | 123515 |
Journal | Journal of Applied Physics |
Volume | 111 |
Issue number | 12 |
DOIs | |
State | Published - Jun 15 2012 |
Funding
Extensive discussions with E. Ma, A. Kolesnikov, and W. Dmowski and technical support from J. M. Scott in conducting neutron experiments are recognized. The neutron experiments at the ISIS Pulsed Neutron and Muon Source were supported by a beamtime allocation (RB 820097) from the Science and Technology Facilities Council. Work at the Air Force Research Laboratory was supported through the Air Force Office of Scientific Research (M. Berman, Program Manager, Grant Number 10RX14COR) and the Air Force under on-site contract No. FA8650-10-D-5226 conducted through UES, Inc., Dayton, Ohio. Work at John Hopkins University was supported through the National Science Foundation under Contract No. NSF-DMR 0904188. Work at Oak Ridge National Laboratory was supported by the Scientific User Facilities Division, Office of Basic Energy Sciences, US Department of Energy.