Metamictization and recrystallization of titanite: An infrared spectroscopic study

Abstract

Radiation damage and the recrystallization of natural titanite (CaTiSiO5) were studied using infrared spectroscopy in the spectral range from 50 to 7500 cm−1. The results show that radiation damage leads to systematic changes in spectral features: decreasing absorption and reflectivity, line broadening, and loss of orientational dependence. Strongly damaged titanite shows hydroxylate bands between 2200 and 3500 cm−1. The band most affected by radiation damage is the Ti-O stretching band near 670 cm−1. It shifts to 710 cm−1 in the most damaged samples, possibly indicating the presence of TiO5 complexes in metamict titanite. Titanite glasses (quenched melts of CaTiSiO5) show spectral features different from those of radiation-damaged titanite, especially in the Ti-O and Si-O stretching regions. Annealing radiation-damaged titanites at high temperatures results in the recovery of damaged crystalline regions. Recrystallization near 900 K is characterized by an increase in reflectivity, integrated absorbance, and line sharpening. Different infrared bands show recovery at different temperatures. The restoration of the Ti-O stretching band near 670 cm−1 and an infrared band near 285 cm−1 took place at temperatures of 1200–1400 K. Temperature-induced changes of the OH-absorption bands could be responsible for the previously reported differences in the temperature evolution of infrared spectra of OH species between in situ and quench experiments.