Voronoi analysis of the structure of Cu–Zr and Ni–Zr metallic glasses T. Fukunaga a, * , K. Itoh a , T. Otomo b , K. Mori a , M. Sugiyama a , H. Kato c , M. Hasegawa c , A. Hirata d , Y. Hirotsu d , A.C. Hannon e a Research Reactor Institute, Kyoto University, Kumatori-cho, Sennan-gun, Osaka 590-0494, Japan b Institute of Material Structure Science, KEK, 1-1 Oho, Tsukuba 305, Japan c Institute for Material Research, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai 980-8577, Japan d The Institute of Scientific and Industrial Research, Osaka University, Ibaraki 567-0047, Japan e ISIS Facility, Rutherford Appleton Laboratory, Chilton, Didcot, Oxon OX11 0QX, UK Available online 20 February 2006 Abstract The structures of Cu–Zr and Ni–Zr metallic glasses have been studied by neutron diffraction and Reverse Monte Carlo (RMC) modeling. A pre- peak at Qw17 nm K1 was observed in the structure factor, S(Q), of Ni–Zr metallic glasses, and this is associated with the Ni–Ni partial structure factor was well reproduced by the RMC modeling. An analysis of Voronoi polyhedra in the RMC simulations was used to characterise the different atomic configurations around Zr, Ni and Cu atoms. The Zr environments are very similar in the two systems, but there are marked differences between the polyhedra around Ni and Cu atoms. The polyhedra around Ni atoms are dominated by trigonal prismatic-like, Archimedian antiprismatic-like, and similar polyhedra, with smaller total coordination numbers less than 10. In contrast, icosahedron-like polyhedra with total coordination numbers in excess of 11 are preferred for Cu. q 2006 Elsevier Ltd. All rights reserved. Keywords: B. Glasses, metallic; C. Rapid solidification processing; E. Simulations, Monte Carlo; F. Diffraction 1. Introduction Metallic glasses have great potential in a variety of applications, and recently various kinds of bulk metallic glasses have been investigated because of the ease of control of the metallurgical morphology through heat treatment near the glass transition temperature. However, whilst the glass transition phenomenon is observed in most bulk metallic glasses, some metallic glasses do not show glass transition. It is of particular interest to note that Cu–Zr metallic glass exhibit a glass transition, but Ni–Zr metallic glass does not show a glass transition [1], and it is of interest to investigate the relation of this difference to the local atomic structure. Previously this has been studied by means of a limited X-ray diffraction study of Cu 30 Zr 70 and Ni 30 Zr 70 [1]. For Cu 30 Zr 70 the total Zr coordination number was reported to be 12.4 which was interpreted as indicating the possibility that an icosahedral configuration is formed around Zr. A lower total Zr coordination number of 10.7 was reported for Ni 30 Zr 70 , and this was ascribed to a tetragonal local atomic configuration. In this work, we used a combination of time-of-flight (T-O-F) neutron diffraction and Reverse Monte Carlo (RMC) modeling to investigate the topology of the atomic configurations over a range of composition in the Ni X Zr 100KX and Cu X Zr 100KX glass forming systems. The diffraction data show a pre-peak at Qw17 nm K1 , similar to the pre-peaks previously observed in Ni–Zr, Ni–Ti and Ni–V metallic glasses which have been associated with Ni–Ni correlations [2–5]. Although the pre-peak has been reported to be associated with the medium-range order, its exact structural origin is not yet understood. By contrast, the pre-peak has not been observed in the structure factor of Cu–Zr metallic glasses, which are considered to have a randomly distributed configuration [6–8]. Time-of-flight (T-O-F) neutron diffraction using neutrons of short-wavelength was employed to make high real-space resolution measurements on the atomic configurations of Ni–Zr and Cu–Zr metallic glasses. Reverse Monte Carlo (RMC) modeling [9] has been recognized to be an excellent method for visualizing the three-dimensional atomic arrange- ment of liquid and amorphous materials, based on the results of diffraction experiments. Therefore, in this study RMC modeling based on the neutron diffraction data was used for Intermetallics 14 (2006) 893–897 www.elsevier.com/locate/intermet 0966-9795/$ - see front matter q 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.intermet.2006.01.006 * Corresponding author. Fax:C81 724 51 2635. E-mail address: tfuku@rri.kyoto-u.ac.jp (T. Fukunaga).