MODELING OF MEDIUM-RANGE ORDER IN METALLIC GLASSES - CALCULATION OF X-RAY-SCATTERING IN A TI61CU16NI23 GLASS

Fluctuations in the magnitude of the basic icosahedron are shown to influence the calculated X-ray scattering picture. It is possible to determine the dimensions of the icosahedron and to estimate the magnitude of the effective scattering volume approximately 10(3) angstrom3. The X-ray scattering curve for this metallic glass can be simulated by a set of icosahedral clusters which are described by two breathing parameters, P (contraction in the plane of pentagons and perpendicular to the icosahedral axis) and Q (contraction parallel with the icosahedral axis). A model is presented which is based on ordering of icosahedral clusters consisting of 49 atoms and which explains the high-temperature behaviour of the prepeak in the X-ray scattering intensity.