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|Single-crystal elastic properties of geomaterials|
|Haupttitel||Single-crystal elastic properties of geomaterials|
|Titelvariante||Elastische Einkristall-Eigenschaften von Geomaterialien|
|Gutachter||Prof. Frank R. Schilling|
|weitere Gutachter||Prof. Susan Schorr|
|Freie Schlagwörter||Elastische Eigenschaften, Brillouin Spektroskopie, Spin Übergang|
|Zusammenfassung||The major part of this experimental work is dedicated to the pressure-, temperature-, and compositional-dependence of the elasticity of single-crystal (Mg,Fe)O ferropericlase, the second most abundant mineral of Earth’s lower mantle. The elastic tensor of (Mg0.9Fe0.1)O was determined up to a pressure of 81 GPa by using Brillouin spectroscopy and synchrotron based x-ray diffraction. Based on the experimental data, I report the effect of the pressure-induced spin transition of iron on the elastic properties of ferropericlase and discuss the implications for the interpretation of both one-dimensional and three-dimensional seismic models. The spin-transition lowers compressional wave velocities, but does not affect shear velocities. This leads to significant perturbations of the velocity ratios and their dependence on pressure, temperature, and iron content with important implications for the interpretation of seismological observables.
I also discuss the significance of (Mg,Fe)O for the interpretation of seismic anisotropy observations in the lowermost mantle. Here, the main conclusion is that (Mg,Fe)O likely dominates seismic anisotropy in the lower mantle, even though it composes only
~20 Vol.% of this region. This implies that seismic anisotropy could also be present above the D’’ discontinuity, where seismologists depict it, in regions where deformation is dominated by dislocation creep at very high strain levels.
Furthermore, the effect of chemical substitution on the elastic tensor of both synthetic and natural garnet solid solution series are discussed. Silicate garnets are major components in Earth’s crust and upper mantle, especially in the transition zone. Moreover, members of the garnet group are important compounds in materials science, because they are well suited for a variety of technological applications, such as solid state lasers.
The data, which were derived both experimentally with Brillouin spectroscopy and by computational methods, show that the substitution of yttrium by the smaller and heavier ytterbium in the garnet solid solution series Y3Al5O12-Yb3Al5O12 makes the material stiffer (the bulk modulus increases), but does not affect its elastic shear properties. These results can help to better understand elasticity-composition systematics in isostructural natural garnet solid-solution series and, furthermore, to elucidate the potentials and limitations of computational approaches. I also discuss the elastic properties of natural garnets and relates them to the systematics observed for the synthetic solid solution series. The main outcome is that cation substitution in the studied natural garnet solid solution series produces effects that are comparable to the observations for the synthetic one, where the incompressibility varies, but the shear properties remain unchanged.
Dataobject from FUDISS_thesis_000000010849
|Anmerkungen des Autors||Kapitel 6.1.-6.3 sind aufgrund von Originalzeitschriftenartikel in Online-Version nicht enthalten|
|Tag der Disputation||02.07.2009|
|Erstellt am||01.07.2009 - 11:40:05|
|Letzte Änderung||19.02.2010 - 14:45:45|