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 α-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
α-Al2O3 have been calculated from a multipole
expansion model refined using the combined QCBED and X-ray data.