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  • Title: A combination method of charge density measurement in hard materials using accurate, quantitative electron and X-ray diffraction: the alpha-Al2O3 case.
    Author: Streltsov VA, Nakashima PN, Johnson AW.
    Journal: Microsc Microanal; 2003 Oct; 9(5):419-27. PubMed ID: 19771698.
    Abstract:
    Current X-ray diffraction techniques intended for "ideally imperfect" specimens provide structure factors only on a relative scale and ever-present multiple scattering in strong low-angle Bragg reflections is difficult to correct. Multiple scattering is implicit in the quantitative convergent beam electron diffraction (QCBED) method, which provides absolutely scaled structure factors. Conventional single crystal X-ray diffraction has proved adequate in softer materials where crystal perfection is limited. In hard materials, the highly perfect nature of the crystals is often a difficulty, due to the inadequacy of the conventional corrections for multiple scattering (extinction corrections). The present study on alpha-Al2O3 exploits the complementarity of synchrotron X-ray measurements for weak and medium intensities and QCBED measurement of the strong low-angle reflections. Two-dimensional near zone axis QCBED data from different crystals at various accelerating voltages, thicknesses, and orientations have been matched using Bloch-wave and multislice methods. The reproducibility of QCBED data is better than 0.5%. The low-angle strong QCBED structure factors were combined with middle and high-angle extinction-free data from synchrotron X-ray diffraction measurements. Static deformation charge density maps for alpha-Al2O3 have been calculated from a multipole expansion model refined using the combined QCBED and X-ray data.
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