Graduate School of Science, Kumamoto University, Kurokami 2-39-1, Kumamoto 860-8555, Japan.
J Synchrotron Radiat. 2011 Nov;18(Pt 6):885-90. doi: 10.1107/S0909049511036326. Epub 2011 Oct 4.
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 Å; type II, Ti occupies a five-coordinated trigonal bipyramidal or tetragonal pyramidal site with Ti-O distances of 1.92-1.89 Å; type III, Ti occupies a six-coordinated octahedral site with Ti-O distances of 2.00-1.96 Å. Although Ti occupies the TiO(6) 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.
为了提供关于 Ti-O 距离和 Ti 配位数的定量数据，研究了来自六个散布场的玻璃陨石中钛的局部结构，采用 Ti K 边 X 射线吸收近边结构 (XANES) 和扩展 X 射线吸收精细结构 (EXAFS)。玻璃陨石中的钛具有不同的配位环境类型。XANES 光谱模式与高温 TiO(2)-SiO(2) 玻璃和 TiO(2)锐钛矿相似。所有样品均表明 Ti 的价态为 4+。基于 EXAFS 分析确定的 Ti-O 距离、配位数和径向分布函数，将玻璃陨石分为三类：I 型，Ti 占据四配位四面体位，Ti-O 距离为 1.84-1.79 Å；II 型，Ti 占据五配位三角双锥或四方锥位，Ti-O 距离为 1.92-1.89 Å；III 型，Ti 占据六配位八面体位，Ti-O 距离为 2.00-1.96 Å。尽管在环境条件下大多数钛矿物中 Ti 占据 TiO(6) 八面体位，但一些玻璃陨石中 Ti 具有四配位和五配位。本研究表明，Ti 的局部结构可能在撞击事件及随后的阶段发生变化。
