Tolborg Kasper, Jørgensen Mads R V, Christensen Sebastian, Kasai Hidetaka, Becker Jacob, Walter Peter, Dippel Ann Christin, Als-Nielsen Jens, Iversen Bo B
Center for Materials Crystallography, Department of Chemistry and iNANO, Aarhus University, Langelandsgade 140, DK-8000 Aarhus C, Denmark.
PETRA III, Deutsches Elektronen-Synchrotron DESY, Notkestrasse 85, D-22607 Hamburg, Germany.
Acta Crystallogr B Struct Sci Cryst Eng Mater. 2017 Aug 1;73(Pt 4):521-530. doi: 10.1107/S2052520617006357. Epub 2017 Jul 27.
In recent years powder X-ray diffraction has proven to be a valuable alternative to single-crystal X-ray diffraction for determining electron-density distributions in high-symmetry inorganic materials, including subtle deformation in the core electron density. This was made possible by performing diffraction measurements in vacuum using high-energy X-rays at a synchrotron-radiation facility. Here we present a new version of our custom-built in-vacuum powder diffractometer with the sample-to-detector distance increased by a factor of four. In practice this is found to give a reduction in instrumental peak broadening by approximately a factor of three and a large improvement in signal-to-background ratio compared to the previous instrument. Structure factors of silicon at room temperature are extracted using a combined multipole-Rietveld procedure and compared with ab initio calculations and the results from the previous diffractometer. Despite some remaining issues regarding peak asymmetry, the new diffractometer yields structure factors of comparable accuracy to the previous diffractometer at low angles and improved accuracy at high angles. The high quality of the structure factors is further assessed by modelling of core electron deformation with results in good agreement with previous investigations.
近年来，粉末X射线衍射已被证明是一种用于确定高对称性无机材料中电子密度分布（包括核心电子密度的细微变形）的有价值的替代方法，可替代单晶X射线衍射。这是通过在同步辐射设施中使用高能X射线在真空中进行衍射测量来实现的。在此，我们展示了我们定制的真空粉末衍射仪的新版本，其样品到探测器的距离增加了四倍。实际上，与之前的仪器相比，这使得仪器峰展宽减少了约三倍，信噪比有了很大提高。使用多极-里特韦尔德联合程序提取了室温下硅的结构因子，并与从头计算结果以及之前衍射仪的结果进行了比较。尽管在峰不对称性方面仍存在一些问题，但新的衍射仪在低角度下产生的结构因子精度与之前的衍射仪相当，在高角度下精度有所提高。通过对核心电子变形进行建模进一步评估了结构因子的高质量，结果与之前的研究吻合良好。
