Structure Model for the Phase Al_mFe Derived from Three-Dimensional Electron Diffraction Intensity Data Collected by a Precession Technique. Comparison with Convergent-Beam Diffraction

Three-dimensional electron diffraction intensity data have been collected for the metastable alloy phase Al_mFe by a precession technique. The structure model has been derived by Patterson and Fourier calculations and by the direct method using either maximum entropy and likelihood or the tangent formula; both were based on the kinematical scattering approximation. Energy-filtered convergent-beam profiles for reflections along two systematic rows h00 and hh0 were used to determine the corresponding structure factors; these were introduced in a dynamical scattering correction procedure for all hk0 structure factors. The tetragonal Al_mFe structure (,  Å, space group I42m) with 90 Al and 20 Fe atoms can be described by ten-coordinated Fe or by a distorted CsCl-type network with vacancies.