Abstract
Sapphire, an inorganic gem-material in a variety of corundum, mainly consists of alpha-alumina (α-Al2O3) structure. The geological origins of sapphire are related to either basaltic or metamorphic rocks. The causes of the color on sapphire are some trace elements such as Cr, Fe, and Ti. It could be mentioned that Ti atoms have cooperated with Fe atoms for creating the blue color. In this study, X-ray absorption spectroscopy (XAS) technique focused on the x-ray absorption near edge structure (XANES) and the extended x-ray absorption fine structure (EXAFS) is employed to identify the oxidation state of Ti atoms and Ti-O bond length on sapphire samples. The Ti K-edge XANES and EXAFS spectra of natural sapphires were carried out using the 13-channel array germanium detector in fluorescence mode. The XANES spectra showed that the oxidation state of Ti was Ti4+ regardless of Fe content. Moreover, the Ti-O bond length on a-Al2O3 was equal to the Ti-O bond length on rutile (TiO2) analyzed from the EXAFS spectra. From these results, it could be concluded that the oxidation state of Ti atoms on natural sapphires was Ti4+ which substitutes Al3+ on the sapphire structure.
Published Version
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