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Local Phenomena in meta-mict Titanite

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Bismayer U., Paulmann C., Groat L., Zhang M.

issue 1

74-77

Pure titanite is a mineral with chemical composition CaTiSiO_{5}. Its structure consists of corner linked TiO_{6}-octahedra, SiO_{4}-tetrahedra and sevenfold coordinated Ca positions. In nature various impurities like U and Th can be incorporated in the structure showing alpha and beta radiation. On meta-mictization, a process which occurs in nature when a mineral is exposed to radioactive irradiation, strong modifications of the structure are observed. Recoil processes due to alpha radiation change over geological time scales the originally periodically structured material into a quasi-amorphous state with persisting short-range order but destroyed long-range order. We report IR and Raman spectra as well as X-ray diffraction data of meta-mict and heat treated titanite from the Cardiff mine, Canada. IR as well as the Raman modes are strongly broadened in the meta-mict material and sharpen on annealing. The OH-stretching mode at 3486 cm^{-1} indicates strong changes in the local environment of OH in meta-mict titanite. The appearance of the Raman excitations between 620 and 750 cm^{-1} in meta-mict titanite, which in IR spectra are due to Ti-O stretching from TiO_{6} octahedra, indicates the breakdown of the Raman selection rules. This points to the breaking of the octahedral symmetry of TiO_{6} polyhedra.

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1 Acta Physica Polonica A

1 2010

1 Bismayer U.

1 Groat L.

1 Paulmann C.

1 Zhang M.

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Local Phenomena in meta-mict Titanite