STRUCTURAL MODEL OF THE AL-PD DECAGONAL QUASI-CRYSTAL

A structural model of a Al-Pd decagonal quasicrystal has been derived from the structure of the orthorhombic Al3Pd phase according to the fa ct that the transformation from the Al-Pd decagonal quasicrystal to th e Al3Pd phase occurs during heat treatment. The structure of the Al3Pd phase can be described as a periodic packing of subunits of a crown s hape, in which each subunit is composed of four decagonal atomic colum ns. Two other subunits with flattened hexagonal and star shapes have a lso been deduced, which are composed of three and five decagonal atomi c columns respectively. The structure of the Al-Pd decagonal quasicrys tal is described by the three kinds of subunit; the structure observed experimentally is a random packing of the three subunits; the ideal s tructure is a quasiperiodic packing of the three subunits.