Raman spectroscopy of titanomagnetites: Calibration of the intensity of Raman peaks as a sensitive indicator for their Ti content

摘要

A systematic study of the Raman spectra of the titanomagnetite solid-solution series (Fe_(3-x)Ti_xO_4) for x = ?0.0, 0.2, 0.4, and 0.6 has been conducted. The samples showed combinations of five previously predicted Raman peaks at ?190, 310, 460, 540, and 670 cm~(-1) that correspond to vibrational modes with T_(2g)(1), E_g, T_(2g)(3), T_(2g)(2), and A_(1g), respectively. The calibration of Raman spectra for titanomag-netite with known values of Ti concentrations reveals a strong dependence of relative intensity for the T_(2g)(2) and T_(2g)(3) modes on Ti concentration. The most prominent feature is the appearance and increase in the relative intensity of a T_(2g)(3) peak above x = ?0.2. On the other hand, the Raman peak for the T_(2g)(2) mode gradually diminishes as Ti increases and nearly disappears at x = ?0.6. Combining the two relative intensities potentially provides a sensitive indicator of Ti content. The technique was applied to study titanomagnetite in grains from Hana Volcanics and melatroctolite from Rhode Island. Keywords: Titanomagnetites, Raman spectroscopy, Fe-Ti oxides, spinel.