Diffraction studies of icosahedral phases in the AlFeW system

A variety of diffraction effects has been observed in electron diffraction patterns recorded from the fivefold axis of an icosahedral phase in an Al70Fe20W10 alloy. Both diffuse rings and changes in the shape and position of weak-intensity reflections have been observed. The diffuse rings come from a quenched-in amorphous phase in the rapidly solidified ribbon. The shift in the position of reflections has been analyzed in terms of a phason strain. The measured value lies between the predicted values calculated for the 2/1 and 3/2 rational approximant structures.