Use of electron backscatter diffraction patterns to determine the crystal lattice. Part 2. Offset corrections

Abstract

A band width determination using the first derivative of the band profile systematically underestimates the true Bragg angle. Corrections are proposed to compensate for the resulting offset Δa/aof the mean lattice parameters derived from as many Kikuchi band widths as possible. For dynamically simulated Kikuchi patterns, Δa/acan reach up to 8% for phases with a high mean atomic numberZ, whereas for much more common low-Zmaterials the offset decreases linearly. A predicted offset Δa/a=f(Z) is therefore proposed, which also includes the unit-cell volume and thus takes into account the packing density of the scatterers in the material. SinceZis not always available for unknown phases, its substitution byZmax,i.e.the atomic number of the heaviest element in the compound, is still acceptable for an approximate correction. For simulated Kikuchi patterns the offset-corrected lattice parameter deviation is Δa/a< 1.5%. The lattice parameter ratios, and the angles α, β and γ between the basis vectors, are not affected at all.