Atomic mobility in nanoglasses

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Nanoglasses are a relatively new class of amorphous materials, consisting of two distinct amorphous regions with different atomic arrangements with characteristic dimensions of a few nanometer. It has been found that the atomic structure of metallic nanoglasses is distinctly different from that of the well-known metallic glasses prepared by quenching from the melt. Compositional fluctuations (segregation), free volume differences and increased medium range order, but without crystallization, seem to be the major structural differences between the nanoglasses and the rapidly quenched metallic glasses. The structural differences in the two regions result in drastic changes of the mechanical and the functional properties compared to rapidly quenched metallic glasses. Diffusion can be used as a tool to identify structural differences in materials, for example, diffusion along interfaces and in the bulk are typically very different. In the current project, atomic mobility will be studied in nanoglasses and in the rapidly quenched reference structure to identify more details of the drastic structural differences between nanoglasses and the conventionally prepared metallic glasses. Studies of diffusion processes require detailed knowledge of the atomic structure, and, consequently, structural characterization of the metallic nanoglasses will be performed to identify the microstructure of the nanoglasses and the atomic structure of the interfacial regions. Nanoglass samples in three materials systems, i.e. Fe90Sc10, Cu50Zr50 and Pd80Si20, will be prepared by inert gas condensation using thermal evaporation and magnetron sputtering. Standard sample characterization will be performed using XRD, SEM and TEM, and for selected samples also SAXS, EXAFS, radial distribution functions and Mössbauer spectroscopy to characterize the morphology, microstructure and atomic structure of the different amorphous phases. In a complementary research approach the two research groups at Karlsruhe Institute of Technology and at University Münster will study the self diffusion, the impurity diffusion and the interdiffusion in the three selected nanoglass systems and the rapidly quenched reference samples.