The concept of the approximants of quasicrystals

Journal Article · Sat Jul 15 00:00:00 EDT 1995 · Scripta Metallurgica et Materialia

DOI:https://doi.org/10.1016/0956-716X(95)00149-P· OSTI ID:99261

Dong, C ^[1]

---

1. Beijing Lab. of Electron Microscopy, Beijing (China)

The study of quasicrystals has always been associated with the research of related crystalline phases. Quasicrystalline alloys are rarely single phase and the secondary phases are usually crystalline. For example, in melt-spun ribbons of Ti{sub 2}Fe alloys, the following phases are observed: an icosahedral phase, Ti{sub 2}Fe (Ti{sub 2}Ni type), {alpha}-Ti{sub 2}Fe ({alpha}-AlMnSi type), TiFe (CsCl type, or B2 structure) and {beta}-Ti (W type, or A3 structure). Similar phases were also observed in Ti-Ni alloys. In Al-Cu-Fe quasicrystalline alloys, one finds {lambda}-Al{sub 13}Fe{sub 4}, a cubic phase (a B2 superstructure), {omega}-Al{sub 7}Cu{sub 2}Fe, {phi}-Al{sub 10}Cu{sub 10}Fe, {theta}-Al{sub 2}Cu, etc. Valence electron concentration has been proposed as a new criterion to define the approximants to quasicrystals: these should satisfy two basic requirements: (1) they possess approximately the same valence electron concentration as that of the corresponding quasicrystal; (2) they arise from the projection of a hyper crystal along rational directions. The first criterion indicates that the approximants are Hume-Rothery phases existing in an e/a-constant band in the phase diagrams; the second implies that their atomic structures are related to those of quasicrystals. According to their positions in the phase diagrams, they can be classified into two groups: the phases to the left of quasicrystal composition are complex approximants retaining some local quasi-periodic structure; those to the right include B2 and its superstructures.

• OSTI ID: 99261
• Journal Information: Scripta Metallurgica et Materialia, Vol. 33, Issue 2; Other Information: PBD: 15 Jul 1995
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
ALLOY SYSTEMS
CRYSTAL STRUCTURE
TITANIUM ALLOYS
IRON ALLOYS
NICKEL ALLOYS
ALUMINIUM ALLOYS
COPPER ALLOYS
MANGANESE ALLOYS
SILICON ALLOYS
INTERMETALLIC COMPOUNDS
PHASE STUDIES
CRYSTALLOGRAPHY
ORIENTATION
CRYSTAL MODELS
CRYSTAL LATTICES
BRILLOUIN ZONES
PHASE TRANSFORMATIONS
VACANCIES
ELECTRONS
VALENCE
PHASE DIAGRAMS