Titanium local structure in tektite probed by X-ray absorption fine structure spectroscopy

摘要

The local structure of titanium in tektites from six strewn fields was studied by Ti K-edge X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) in order to provide quantitative data on Ti-O distance and Ti coordination number. The titanium in tektites possessed different coordination environment types. XANES spectra patterns revealed resemblance to high-temperature TiO_2-SiO_2 glass and TiO_2 anatase. All samples showed that the valence of Ti is 4+. Based on the Ti-O distances, coordination numbers and radial distribution function determined by EXAFS analyses, the tektites were classified into three types: type I, Ti occupies a four-coordinated tetrahedral site with Ti-O distances of 1.84-1.79 ?; type II, Ti occupies a five-coordinated trigonal bipyramidal or tetragonal pyramidal site with Ti-O distances of 1.92-1.89 ?; type III, Ti occupies a six-coordinated octahedral site with Ti-O distances of 2.00-1.96 ?. Although Ti occupies the TiO6 octahedral site in most titanium minerals under ambient conditions, some tektites have four-and five-coordinated Ti. This study indicated that the local structure of Ti might change in impact events and the following stages.