BETA-AL4.5FESI - A COMBINED SYNCHROTRON POWDER DIFFRACTION, ELECTRON-DIFFRACTION, HIGH-RESOLUTION ELECTRON-MICROSCOPY AND SINGLE-CRYSTAL X-RAY-DIFFRACTION STUDY OF A FAULTED STRUCTURE

A previous single-crystal X-ray and electron diffraction structure stu dy [Romming et al. (1994). Acta Cryst. B50, 307-312] of the heavily fa ulted alloy phase beta-Al4.5FeSi has been extended by synchrotron powd er data and further electron microscopy and diffraction observations. Reflections that were omitted in the single-crystal work could be incl uded in the powder refinement, which resulted in some adjustment of ce ll parameters and atom coordinates. The double c axis reported by some authors is explained by periodic faults in the structure, which is de scribed in terms of a tetragonal sub-unit. Apparent discrepancies betw een refinement from single-crystal and powder data are discussed brief ly.