Fig. 3
From: Wetting and adhesion properties of quasicrystals and complex metallic alloys
The Al-Cr-Fe(-Cu) system is rich in approximant compounds, depending on the respective concentrations of the transition metals. The figure illustrates three different examples, using selected electron diffraction patterns taken along the pseudo fivefold direction of the crystal. The compound shown left contains several thousands at/uc, the one in the middle, few hundreds and the one right, only few tens. The complexity of such structures may be indexed according to a so-called complexity index, which is equal to the natural logarithm of the number of atoms per unit cell, or βC = Ln(number of at/uc). The filling of reciprocal space, which is directly visualized in the figure, also reflects that complexity