Defects in quasicrystals, revisited I-flips, approximants, phason defects

TL;DR

This paper revisits defects in quasicrystals and their approximants, highlighting the role of flips and phason defects, and how approximant defects relate to those in the parent quasicrystal.

Contribution

It clarifies that approximant defects differ from quasicrystals mainly by the density of flips and that flips can split into phason defects, providing a new perspective on defect analysis.

Findings

Approximants differ from quasicrystals by flip density.

Flips can split into phason defects of opposite signs.

Imperfect dislocations are related to phason defects.

Abstract

The recent discovery of metadislocations in some periodic complex metallic alloys and of their 'phason' defects has given a new impetus to the study of QC approximant defects. In this paper we emphasize: 1- that approximants differ from a QC by a suitable density of 'flips' only, one per unit cell in the case of Fibonacci approximants; these flips are not topological defects, 2- a flip can split into two 'phason' defects of opposite signs, thus the approximant defects can be studied in a first step as defects of the parent QC. In a companion paper this analysis of QC defects is extended to dislocations; the difference between perfect and imperfect dislocations is emphasized. Imperfect dislocations are the phason defects alluded to above.