Bestimmung und Evaluierung empirischer optischer Parameter
Zusammenfassung der Projektergebnisse
This work covered the determination of electronic polarizabilities of cations and anions, and the evaluation of systematic deviations between polarizabilities calculated from chemical compositions (αcalc) and polarizabilities derived from refractive indices (αobs). In addition to the set of polarizabilities derived in the first funding period, we have determined the electronic polarizability of 4-coordinated Ti4+ from ABW-type CsMTiO4 (M = Al, Fe, and Ga) and ANA-type CsTi1.10Si1.90O6.50 yielding α([4]Ti4+) = 5.15(5) Å3. The crystal structures of these compounds were redetermined in this project. It could be shown, that five-coordinated Ti4+ and V5+ in vanadyl bonds do not follow the normal trend of relationship between electronic polarizability and coordination number. Whereas the electronic polarizabilities of most cations, such as Na+, Ca2+, Fe2+, Fe3+, and Zr4+, show a monotonic decrease as the cation coordination increases, the polarizabilities of the ions [5]Ti4+, [5]V5+, and [6]V5+ show strong deviations from a regular decrease. The reduced polarizability of [5]Ti4+, [5]V5+, and [6]V5+ ions is probably caused by short Ti–O and V=O bonds. We demonstrated that ion conductivity in minerals and compounds is associated with continuous migration paths and leads to negative total electronic polarizability deviations [Δ = (αobs − αcalc)/αobs)] up to 13%. It could be shown, that electronic polarizabilities derived from refractive indices of hydrous compounds can be used to determine the H2O content of single crystals with high accuracy based on the evaluation of 157 zeolite-type compounds and 770 non-zeolitic hydrous compounds. On average, refractive indices of minerals and inorganic compounds can be predicted with a higher accuracy than with the Gladstone-Dale approach as demonstrated on more than 2,500 refractive indices compiled from literature and complemented by own measurements.
Projektbezogene Publikationen (Auswahl)
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POLARIO, a computer program for calculating refractive indices from chemical compositions. American Mineralogist, 103 (2018) 1345- 1348
Fischer, R.X., Burianek, M., Shannon, R.D.
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Determination of the H2O content in minerals, especially zeolites, from their refractive indices based on mean electronic polarizabilities of cations. European Journal of Mineralogy 32 (2020) 27-40
Fischer, R.X., Burianek, M., Shannon, R.D.
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Synthesis, revised crystal structures, and refractive indices of ABW-type CsMTiO4 (M = Al, Fe, Ga) and ANA-type CsTi1.10Si1.90O6.50, and the determination of the electronic polarizability of 4-coordinated Ti4+. Zeitschrift für Kristallographie 235 (2020) 533-551
Groeneveld, J.D., Burianek, M., Birkenstock, J., Fischer, L.A., Shannon, R.D., Fischer, R.X.
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Empirical electronic polarizabilities for use in refractive index measurements. III. Structures with short [5]Ti-O and vanadyl bonds. Canadian Mineralogist
Shannon, R.D., Fischer, R.X.
