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M: Metallphysik

M 22: Symposium on Structurally Complex Alloy Phases IV (SCAP IV)

M 22.4: Fachvortrag

Donnerstag, 14. März 2002, 16:45–17:00, H16

Interstitial relaxation as a probe to study structurally complex alloy phases — •Hans-Rainer Sinning — Institut für Werkstoffe, TU Braunschweig, Langer Kamp 8, 38106 Braunschweig

As a special application of mechanical spectroscopy, relaxation by interstitial solute atoms - especially hydrogen - can be used as a probe to study local structures and properties in structurally complex solids. We discuss the use of both short-range reorientation and long-range diffusion mechanisms for this purpose. The short-range (Snoek-type) mechanism, directly related to the configuration of the local atomic cages around the jumping H-atoms, represents a direct, selective probe of atomic short-range order. Whereas in general the use of this probe is often prevented by a lack of knowledge of the exact site occupancy, the situation may even be easier in structurally complex phases if they belong to the family of polytetrahedral structures: only tetrahedral sites, sometimes with preferred chemical surroundings (e.g. Zr), have to be considered in that case. First H-induced damping peaks in Zr-Cu-Ni-Al and Ti-Zr-Ni quasicrystals look promising with respect to a distinction between quasicrystalline phases from the viewpoint of short-range order. Concerning long-range H diffusion, the recently discovered intercrystalline Gorsky effect [PRL 85, 3201 (2000)] offers the possibility to detect the elastic anisotropy of the grains in a polycrystal even for a grain size less than 100 nm. As an example, the absence of this effect indicates elastic isotropy not only for quasicrystals but also for the metastable No-dqbig cubeNo-dq (NiTi2-type) phase in the case of CoZr2.