STRUCTURE MODEL FOR THE PHASE ALMFE DERIVED FROM 3-DIMENSIONAL ELECTRON-DIFFRACTION INTENSITY DATA COLLECTED BY A PRECESSION TECHNIQUE - COMPARISON WITH CONVERGENT-BEAM DIFFRACTION

Three-dimensional electron diffraction intensity data have been collec ted for the metastable alloy phase AlmFe by a precession technique. Th e structure model has been derived by Patterson and Fourier calculatio ns and by the direct method using either maximum entropy and likelihoo d or the tangent formula; both were based on the kinematical scatterin g approximation. Energy-filtered convergent-beam profiles for reflecti ons along two systematic rows h00 and hh0 were used to determine the c orresponding structure factors; these were introduced in a dynamical s cattering correction procedure for all hk0 structure factors. The tetr agonal AlmFe structure (a = 8.84, c = 21.6 Angstrom, space group <I(4) over bar 2m>) with 90 Al and 20 Fe atoms can be described by ten-coord inated Fe or by a distorted CsCl-type network with vacancies.