Structural models for decagonal quasicrystals with pentagonal atom-cluster columns

摘要

Based on high-resolution electron microscopy images and convergent-beam electron diffraction patterns, structural models of decagonal quasicrystals, which have pentagonal atom-cluster columns and belong to the space groups P<(10)over bar>m2 and P10(5)/mmc, have been contructed by the section method. The model for the space group P<(10)over bar>m2 stands for melt-quenched quasicrystals of Al70NixFe30-x (10 less than or equal to x less than or equal to 17), Al70CuxCo30-x (2 less than or equal to X less than or equal to 12), Al65CuxCo35-x (x = 15 and 20), Al73Co27 and Al70Ni3Co27. All the pentagonal cluster columns in these alloys have the same sense of polarity in an inversion domain. The model for the space group P10(5)/mmc stands for melt-quenched quasicrystals of Al70NixFe30-x (17 < x less than or equal to 20) and Al70Ni15Co15, and annealed quasicrystals of Al65Cu20Co15 and Al70Ni15Co15 The pentagonal cluster columns with opposite senses mixed uniformly. This is the first P10(5)/mmc model composed of the pentagonal cluster columns. 10(5) screw axes do not exist at the centre of the cluster column but at the adjoining point of the two cluster columns with opposite senses of polarity.