Studies of Defects, Disorder and Phase Transitions in Alloy Crystals via Diffuse Scattering

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This project is addressed to use synchrotron X-ray and neutron scattering to elucidate the detailed structure of disordered alloys and defective crystals. It contains both an experimental component (the measurement of atomic correlations and displacements in disordered alloys) and a theoretical component (the relation of these quantities to the underlying electronic structure). Novel alloys will be studied such as the null matrix Nio.52Pto.48 whose average scattering is zero as the 62Ni has a negative neutron scattering length and Cu62Ni where magnetic effects become very interesting, especially the displacements originating in the spins. Extended Fermi surface traces in the scattering and their origin in alloy theory will also be explored. Finally, the explanation of the two-length scale phenomenon is V2H, where surface defects induce a continuous phase transition while the bulk shows a first-order transition, will be completed.In this project a variety of scattering methods are applied to elucidate the underlying physical (electronic) origin of a number of interesting and important structures in metals and alloys. These scattering techniques take advantage of the most sophisticated national laboratories such as the Advanced Photon Source at the Argonne National Laboratory, the National Synchrotron Light Source at the Brookhaven National Laboratory, new NSF-supported neutron instrumentation at the National Institute for Standards and Technology, Research Reactor Division, and the High Flux Isotope Reactor at the Oak Ridge National Laboratory. Collaboration with the Max Planck Institute for Metals Research (Stuttgart) is well underway and has been quite productive. The basic aim is the understanding of both simple and complex alloys at the atomic level in order to relate their structure to their function.