Abstract

Previously reported experimental methods for X-ray phase determination are analyzed using the plane-wave dynamical theory of X-ray diffraction. The relation between the dispersion surface and the phases are considered as well as the influence of the crystal rotation relative to the Ewald sphere on the diffraction line profile. It is shown that the phase information obtained from the intensity of three-beam Borrmann diffraction may get lost due to crystal thickness effects. Three-beam Bragg reflections, either Umweg or Aufhellung, give optimal conditions to reveal the phases, provided that the relative rotation of the additional reciprocal-lattice point entering or leaving the Ewald sphere is known. With the exception of special situations, N-beam cases with N > 3 are found not to be suitable for phase determination, since they involve high-order phase products and thus complicate the experimental determination of the phases.