Dislocations and dislocation reactions in decagonal Al-Ni-Co quasicrystals

Abstract

were studied by means of diffraction-contrast imaging and defocus convergent beam electron diffraction techniques in the transmission electron microscope. In addition to dislocations with Burgers vectors parallel to the periodic and quasiperiodic directions as first reported by Zhang and Urban ͓Z. Zhang and K. Urban, Philos. Mag. Lett. 60, 97 ͑1989͔͒, a type of dislocation was found possessing a Burgers vector with components in the periodic as well as the quasiperiodic direction. The parallel-space component of this Burgers vector has a length of 2.5 Å. The quasiperiodic Burgers vectors were found to have parallel-space lengths of 2.9 and 4.7 Å. The Burgers vectors determined are correlated with interatomic vectors of the structure of decagonal Al-Ni-Co. In addition, dislocation reactions were identified by the determination of Burgers vectors of dislocations in triple-node arrangements. A model for the dislocation reaction is proposed which is in accordance with the results of the microstructural studies.

Dislocations in basic-nickel decagonal Al–Ni–Co single quasicrystals

“…The two types of quasiperiodic dislocations are-together with dislocations possessing a periodic Burgers vector-the only types of dislocations that we observed in the nickel-rich decagonal phase. The line directions of the quasiperiodic dislocations are inclined to the periodic axis, in contrast to the quasiperiodic dislocations that we observed in the decagonal phases Al 70 Ni 15 Co 15 and Al 73 Ni 10 Co 17 (Schall et al 2004), possessing a line direction strictly parallel to the periodic axis. The observation of the weak-extinction condition confirms the theoretical considerations of Wittmann (1995) who discussed the extinction conditions of dislocations in two-dimensional quasicrystals.…”

“…Dislocations in decagonal quasicrystals were observed with Burgers vectors parallel to the periodic or the quasiperiodic directions (Zhang and Urban 1989, Yan et al 1992, 1994, Yan and Wang 1993a as well as exhibiting components in both directions (Schall et al 2004). The extinction conditions originally discussed for icosahedral quasicrystals should also hold for dislocations with quasiperiodic Burgers vectors in these two-dimensional quasicrystals as discussed by Wittmann (1995).…”

Modeling of decagonal quasicrystal lattice

“…[1,2,16,18,21]), four indices being related to a plain quasilattice and the fifth one being referred to the direction of periodicity. Six-indices labeling of the diffraction reflections of the decagonal quasicrystals was used by [15,22]. In this case, five indices are referred to a plain quasilattice.…”

Dislocations in icosahedral quasicrystals

“…This would exceed the scope of the present paper and hence we limit this review to dislocations in icosahedral structures and for the decagonal case refer to existing comprehensive treatments in the literature. 7,8 Defects in quasicrystals Defects in QCs were firstly discussed by Levine et al 3 The authors treated the hydrodynamics of 2-and 3-dimensional icosahedral lattices in a density wave-approach and identified dislocations as stable structural defects in QCs. Indexing of a dislocation Burgers vector, unlike the case in ordinary crystals, was found to require more indices than real-space dimensions.…”