Accurate determination of low-symmetry Bravais unit cells by EBSD.

Unit cells lack of symmetry are difficult to determine accurately, compared to high-symmetry unit cells with many constraints. The electron backscatter diffraction (EBSD) technique in scanning electron microscopy (SEM) was considered inadequate for this task because of the highly defective band detections. We develop a new method for the Kikuchi-band detections, which can improve the accuracy of the EBSD technique in determining the lattice constants of totally unknown Bravais unit cells with low symmetry. The results show that, under ideal conditions (i.e., low-noise EBSD patterns and known projection center), the relative error of the unit-cell constants (a, b, c) is less than 0.3%, and that of the axial ratios (a/b, b/c, c/a) is less than 0.5%. The absolute errors of the inter-axial angles (α, β, γ) and crystal orientations are about 0.1°. Our method is perhaps not as accurate as the classical techniques such as X-ray diffraction, but is demonstrated as a practical tool for crystallographic characterization especially on low-fraction phases, and could be easily incorporated into an SEM to make the most of the SEM in the area of microanalysis.