Atomic Structure of Ca40+xMg25Cu35-x Metallic Glasses (Preprint)

The atomic structures of four Ca40+XMg25Cu35-X (X = 0, 5, 10, and 20 at.%) ternary metallic glasses have been determined using a synergistic combination of neutron diffraction, quantum molecular dynamic (QMD) simulation and constrained reverse Monte Carlo modeling. The amorphous structure of these alloys can be described as close-packing of efficiently packed Cu-centered clusters that have Ca, Mg and Cu atoms in the first coordination shells. Experimental evidence is given for the presence of Cu atoms in inter-cluster sites for the two most Cu-rich glasses. The close-packed arrangement of clusters is present only within length scale a length scale of approximately 10 A providing a characteristic medium range order prepeak at Q approximately 1.2 A in the total scattering structure factors of these alloys. An average coordination number 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 (approximately 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. Journal article submitted to Physical Review B. Prepared in collaboration with the Department of Materials Science and Engineering, John Hopkins University, Baltimore, MD and ISIS Facility, Rutherford Appleton Laboratory, Chilton, Didcot, United Kingdom.