Short-Range Order and Atomic Dynamics in Zr-Ni and Zr-Cu Melts

Kurzfassung

A novel electrostatic levitation furnace for neutron scattering experiments on melts has been developed [1]. This containerless technique allows to process even chemically reactive melts at high temperatures. Moreover, the containerless process under high vacuum conditions gives access to the metastable regime of an undercooled liquid below the melting temperature. The avoidance of crucible materials in the vicinity of the freely suspended sample results to an excellent signal to background ratio in scattering experiments. First experiments using the electrostatic levitator allowed us to investigate the structure and the atomic dynamics of different stable and undercooled Zr-based melts by elastic- and quasielastic neutron scattering. The Ni self-diffusion coefficient in Zr64Ni36 was measured by quasielastic neutron scattering. At an undercooling of 167 K below the melting point deviations from an Arrhenius-type temperature dependence as observed in bulk metallic glass forming alloys become evident. By isotopic substitution and elastic neutron scattering partial structure factors have been determined for Ni64Zr36 melts. These are indicative of an icosahedral short-range order, while preceding studies on the Zr-rich side (Zr64Ni36) suggest a different type of short-range order. The structure factors measured for Zr50Cu50, Zr7Cu10 and Zr2Cu revealed large nearest neighbor coordination numbers of ZNN > 13. We find no indications for a dominant icosahedral short-range order in liquid Zr-Cu that has recently been discussed for Zr-Cu metallic glasses. References [1] T. Kordel, D. Holland-Moritz, F. Yang, J. Peters, T. Unruh, T. Hansen, and A. Meyer, Phys. Rev. B (accepted 2011). [2] D. Holland-Moritz, S. Stüber, H. Hartmann, T. Unruh, T. Hansen, and A. Meyer, Phys. Rev. B 79, 064204 (2009).