ICOSAHEDRAL TWINS CAN BE PRODUCED BY SIMPLE MODULATIONS

Crystalline aggregates with icosahedral symmetry exist in the AlMnFeSi and AlCuFe systems. They are built of grains of, respectively, cubic and rhombohedral phases with relative orientations induced by the icosahedral group. We argue that such relative orientations are natural and expected since the two lattices can be related by specially simple displacive transformations, namely periodic modulation fields with one or two Fourier generators. Moreover-this is a feature specific to such orientations-two icosahedral twins of a cubic or a rhombohedral phase provide two different packings of a single common (nonconventional) unit cell. © 1990 IOP Publishing Ltd.