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Crystal chemistry, structural defects and electronic spectroscopy of transition metal-ion-bearing rock-forming silicates

Ziel



This joint research project concerns the crystal chemistry, structures, structural defects, including OH-defects and their role in phase transformations, reaction kinetics, thermodynamics and genesis characteristics of 3dN-ion bearing rock-forming silicate minerals.

Three complementary methodological approaches will be used: spectroscopic methods, indicative predominantly of local structural peculiarities, such as electronic absorption spectroscopy (UV/VIS/NIR), Mössbauer spectroscopy, X-ray spectroscopy (XANES, EXASS), vibrational spectroscopy (STIR); diffraction methods of structural research, integrating over larger structure volumes and TEM; and, on the theoretical side, modelling of potentials and chemical bonding in the materials under study.

Results expected are: clarification of the role of next structural neighbours on the Racah-parameter B; identification of Fe2+- Ti4+ charge-transfer; spectroscopic identification of Cr2+ and Cr5+ in oxygen based structures; an answer to the question whether Ti3+ does really exist in terrestrial minerals; determination of the influence of P and T on the spectroscopic parameters of iron ions in natural spinels and garnets; examination of local compressibility and thermal expansion versus the respective bulk properties; elucidation of expected differences between mean distances of individual (3dNO6)-octahedra; confirmation of current results of the dependence of UV-edge properties on Fe3+- point defect concentration in Fe(II)-olivine; identification and structural interpretation of OH-valence vibrational bands in OH-bearing effects in garnets; possible use of band intensities in quantitative determination of hydrogen traces; theoretically calculated geometry and energetics of such defects; prediction of structures, defects and properties of the mineral structures studied; elucidation of the oxidation rate laws and activation energies for oxidation paths in Fe(II)-olivine; clarification of the role of Fe3+ and OH- in naturally oxidised olivine.

The results will have a bearing in the fields of geosciences and material sciences as well. Favoured 3dN-ions will be those of chromium, iron, manganese, nickel, and titanium. Favoured oxygen-based rock-forming minerals will be those whose structures are based on simple fcc or hc oxygen packings as olivine, spinel, corundum, kyanite, staurolite, chloritoid, sapphirine, pyroxene, amphibole and the densely packed garnet type. Natural minerals as well as their synthetic equivalents will be studied, produced under controlled physico-chemical conditions of Ptot, fugacity (for non-ideality corrected partial pressure) of fluid components, fi, temperature and composition, X, to obtain defined compositions especially with respect to transition metal valencies.

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Koordinator

Technische Universität Berlin
EU-Beitrag
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Adresse
Ernst Reuter-Platz 1
10587 Berlin
Deutschland

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Beteiligte (4)