On the greenish-yellow color of natural Brazilian titanite

database, nuove specie, discrediti,
ridefinizioni, classificazioni, ecc.
Avatar utente
Marco E. Ciriotti
Messaggi: 25330
Iscritto il: ven 25 giu, 2004 11:31
Località: via San Pietro, 55 I-10073 Devesi/Cirié TO - Italy

On the greenish-yellow color of natural Brazilian titanite

Messaggio da Marco E. Ciriotti » lun 08 apr, 2019 14:03

▪ Tolentino, E.L., Dias, C.H., Chaves, M.L.S.C., Krambrock, K., Pinheiro, M.V.B. (2019): On the greenish-yellow color of natural Brazilian titanite. Physics and Chemistry of Minerals, 46, 202-213.

Natural greenish-yellow titanites from two localities in Brazil (Bananal/Capelinha, MG and Xambioá, TO) were characterized by electron paramagnetic resonance (EPR) and optical absorption. Along with vanadyl ions (VO2+) substituting Ti4+, two other paramagnetic centers were identified: the Fe3+ and the Mn2+. For the VO2+, the principal values and orientations of the g and A tensors were derived from a careful analysis of the angular dependence of the EPR spectra. The obtained results, although different to previously reported data, still support the model for the VO2+ bonds to the nearest oxygen (O1) in the TiO6-distorted octahedra. In addition, the titanite optical absorption spectra were analyzed, and the yellow color was ascribed to Fe3+ ↔ O2− ligand–metal charge transfer transitions (LMCT) in the near-ultraviolet, extending to the violet and blue spectral ranges. The VO2+ center seen by EPR was in low concentration and had no visible effect on the color. Finally, γ-irradiation up to 200 kGy and thermal treatments in oxidizing/reducing atmospheres up to 600–700 °C also had no big influence on the dominant yellow color.
Marco E. Ciriotti

«Things are interesting only in so far as they relate themselves to other things»


Chi c’è in linea

Visitano il forum: Bing [Bot], Google [Bot] e 2 ospiti