Local Atomic Structure of Nearly-periodic Solids

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9628134 Egami The local atomic structure of some technologically important new materials, mostly crystalline oxides, will be determined by non-crystallographic diffraction techniques including the atomic pair-distribution analysis. The materials studied include superconducting cuprates, manganates with colossal magnetoresistance, CeO2/ZrO2 mixture for automotive catalyst support, and metallic glasses. Many of these materials have a periodic crystalline structure in average, but show significant local structural deviations from perfect periodicity that can be critically important in determining their properties. Experiments will be carried out using pulsed neutrons and synchrotron x-rays available at national facilities. Results will be analyzed by computer modeling methods developed in our group. To facilitate understanding of the results, theoretical studies will be carried out in collaboration with other theory groups. %%% The properties of a material ultimately depend on the atomic structure. Recent research has shown that the local atomic structure, that is, the structure within a few atomic diameters of an atom, may not be the average structure of the material. In many cases, such local variations do not have significant consequences, but in many cases the properties of a material are critically dependent on the local structure rather than the average structure. The purpose of this project is to determine the local atomic structure of these materials using non-crystallographic scattering techniques. Three materials systems will be examined, all of which are of technological importance. ***