The Ti environment in natural hibonite: XANES spectroscopy and computer modelling

Abstract

Abstract. The local atomic structure around Ti in Ti-bearing hibonite (CaAl 12 O 19 ) was studied using X-ray absorption near-edge structure (XANES) spectroscopy and computer modelling. Structural models of the direct substitution of Al by Ti 3+ , Al by Ti 4+ charge balanced by the coupled substitution of Mg 2+ for Al, and small Ti clusters were considered. The Ti K-XANES spectra of natural hibonite with different Ti concentration were recorded. Theoretical Ti K-XANES spectra for structural models of hibonite were calculated. It was shown that the theoretical Ti K-XANES spectra for a model with Ti at the five-coordinated M2 site are in agreement with the experimental XANES spectra of hibonite with low concentrations of Ti, while the theoretical spectra for a structural model of clustered Ti are in agreement with the experimental spectra of hibonite with higher Ti contents.