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Crystal chemistry of Th in fluorapatite

机译：氟磷灰石中Th的晶体化学

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Through the complementary use of single-crystal X-ray diffraction and X-ray absorption spectroscopy, we present in this paper the first direct results on the site occupancy of thorium in the fluorapatite structure and the structural distortion created by its substitution. Structure refinements based on single-crystal X-ray diffraction data from synthetic Th-doped fluorapatite indicates that Th substitutes almost exclusively in the M2 site. A single-crystal X-ray study of natural fluorapatite from Mineville, New York, also indicated that substituting heavy scatterers (including Th) are concentrated in the apatite M2 site, but definitive site assignments of specific elements were not possible. Extended X-ray absorption fine-structure spectroscopy (EXAFS) was used to probe the local structure of Th in the synthetic fluorapatite (single-crystal form) with a Th concentration of roughly 20 000 ppm, as well as Th in the natural Mineville fluorapatite (powder form) with a Th concentration of ?2000 ppm. The EXAFS fitting results also indicate that Th partitions into the M2 site and yield a ?0.05-0.08 A° decrease of average M2-O bond distances associated with local structure distortions that are not obtainable from single-crystal X-ray diffraction studies.
机译：通过单晶X射线衍射和X射线吸收光谱的互补使用，我们在本文中给出了direct在氟磷灰石结构中的位置占有率以及由其取代产生的结构变形的第一个直接结果。基于来自合成的Th掺杂的氟磷灰石的单晶X射线衍射数据的结构优化表明，Th几乎仅在M2位置取代。来自纽约Mineville的天然氟磷灰石的单晶X射线研究还表明，代替重散射体（包括Th）集中在磷灰石M2部位，但是特定元素的确定部位分配是不可能的。使用扩展的X射线吸收精细结构光谱（EXAFS）来探测Th浓度约为20000 ppm的合成氟磷灰石（单晶形式）中的Th以及天然Mineville萤石磷灰石中的Th的局部结构。 （粉末形式）的Th浓度为〜2000ppm。 EXAFS拟合结果还表明，Th进入M2位点，与单晶X射线衍射研究无法获得的局部结构变形相关的平均M2-O键距降低了0.05-0.08 A°。

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