Determination and evaluation of empirical optical parameters

• Applicant: Professor Dr. Reinhard X. Fischer
• Subject Area: Mineralogy, Petrology and Geochemistry
• Term: from 2013 to 2019
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 233158000

This is a continuation of the project on the determination of empirical electronic polarizabilities for cations and anions based on more than 4000 datsets of refractive indices of minerals and inorganic compounds. A subset of refractive indices determined at lambda = 589.3 nm from about 2500 measurements on 1200 minerals, 675 synthetic compounds, 200 F-containing compounds, 65 Cl-containing compounds, 700 hydroxides was used to obtain mean total polarizabilities. Multi regression analyses using least squares procedures yielded 271 polarizability values for 76 cations in various coordinations and 4 anions. We identified some groups of minerals and compounds systematically deviating from the scheme of polarizabilities. Thus, we intend to investigate the following groups: (1) Compounds containing lone electron pair (LEP) ions to derive polarizabilities for Tl+, Sn2+, Pb2+, As3+, Sb3+,Bi3+, S4+, Se4+, Te4+, Cl5+, Br5+, I5+ weighted by the stereochemical influence of the LEP. (2) Zeolites showing deviations mainly due to inaccurately determined chemical compositions and/or refractive indices which will be redetermined here. (3) Minerals and compounds with hydrogen bonds. The bond length OH...O will be introduced as an additional parameter in the least-squares procedures. (4) Mullite and mullite-type compounds. Accurate optical data do not exist for mullite but they are needed to interpret the influence of the oxygen vacancies on the optical properties. - Additionally, the chemical compositions, crystal structures, and optical properties of several single compounds will be redetermined showing large deviations from the polarizability scheme developed in the first period of this project. Thus, the investigations in the continuation period will provide a significant extension of the set of electronic polarizabilities of ions, classes of compounds deviating from the scheme can be included by introducing additional parameters, and the optical properties of some compounds like the important ceramic material mullite will be determined for the first time.

• DFG Programme: Research Grants
• International Connection: USA
• Cooperation Partners: Dr. Olaf Medenbach; Professor Robert D. Shannon, Ph.D.