Electron microscopy study of enantiomorphic ordered structures

Abstract Taking into account the symmetry properties of enantiomorphic crystals, we have deduced from the Howie–Whelan equations the following new results about the relative intensities of the diffracted beams of electrons: (i) In the two-beam and systematic reflection cases, the deviation from Friedel's law may be observed only if g belongs to a non-centric star. In the two-beam case this possible deviation is related to the phase change between the Fourier coefficients of crystal absorption potentials. (ii) Extinction conditions of inversion boundaries have been established in the case of systematic reflection in relation to the location (with respect to the elements of symmetry of the structure) of inversion centres. The absolute determination of LiFe5O8 ordered enantiomorphic structures is performed by comparison between observed and calculated electron diffraction intensities. In particular the exact operating diffraction conditions are carefully examined.