Structure Model for the Phase AI[subm]Fe 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 ahoy phase Al[subm]Fe 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 hbo 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[subm]Fe structure (a = 8.84, c = 21.6 Å, space group 142m) with Al Al and 20 Fe atoms can be described by ten-coordinated Fe or by a distorted CsCltype network with vacancies. [ABSTRACT FROM AUTHOR]