α-AlMnSi phase to a bcc structure by XE+ ion-beam irradiation

1996 ◽  
Vol 54 ◽  
pp. 720-721
Author(s):  
Y.X. Guo ◽  
L.M. Wang ◽  
R.C. Ewing
Keyword(s):  
Ion Beam ◽  
Alloy System ◽  
Icosahedral Quasicrystal ◽  
Icosahedral Symmetry ◽  
Structure Unit ◽  
Α Phase ◽  
Bcc Structure ◽  
Icosahedral Quasicrystals ◽  
Mackay Icosahedron ◽  
Important Structure

AlMnSi alloy system has attracted great attentions since the first report on the icosahedral quasicrystal materials in 1984. The rapidly quenched AlMnSi alloy around the stoichiometry of the α-AIMnSi phase (α-phase below) may form icosahedral quasicrystals. And the structure unit of the α-phase is of near icosahedral symmetry. The α-phase has a cubic structure with space group Pm3 (a= 1.268 nm). In each unit cell there are 138 atoms. The most important structure unit in this phase is the so-called MacKay icosahedron. In such a structure unit, 12 Al atoms are decorating the vertices of an icosahedron. Surrounding this icosahedron is another same oriented icosahedron of 12 Mn atoms, which is about twice the diameter of the former. Furthermore, 30 Al atoms define a shell outside the two inner icosahedra with each atom sitting at the midpoint just out of the Mn icosahedron edges. In the structure of α-phase, the icosahedra are slightly distorted and are connected along those of their three fold axes that coincide with the <111> direction of the cubic lattice.

scholarly journals Computational prediction of an icosahedral quasicrystal

2014 ◽  
Vol 70 (a1) ◽  
pp. C890-C890
Author(s):  
Michael Engel ◽  
Pablo Damasceno ◽  
Carolyn Phillips ◽  
Sharon Glotzer
Keyword(s):  
Self Assembly ◽  
Computational Prediction ◽  
Real Space ◽  
Icosahedral Quasicrystal ◽  
Icosahedral Symmetry ◽  
Structure Model ◽  
Colloidal Systems ◽  
Naturally Occurring ◽  
Higher Dimensional ◽  
Icosahedral Quasicrystals

From the first quasicrystal discovered in the laboratory 30 years ago to the only known specimen of naturally occurring quasicrystals, quasicrystals with icosahedral symmetry have received great attention. There are more than one hundred stable icosahedral quasicrystals in metallic alloys; all are identified by their diffraction spectra. Despite this abundance, resolving the positions of the atoms within the solid has been possible only indirectly. Moreover, unlike dodecagonal and other axial quasicrystals, icosahedral quasicrystals have been observed neither in simulations nor in non-atomic (e.g. micellar or colloidal) systems, where real-space information would be available. Here we present an icosahedral quasicrystal discovered in computer simulation via self-assembly from the liquid phase. We provide a structure model by analyzing atomic surfaces and report the presence of phason flips. Our results constitute a direct microscopic confirmation of the higher-dimensional crystallographic description of icosahedral quasicrystals.

Mackay icosahedron explaining orientation relationship of dispersoids in aluminium alloys

2014 ◽  
Vol 70 (5) ◽  
pp. 888-896 ◽  
Author(s):  
Astrid Marie F. Muggerud ◽  
Yanjun Li ◽  
Randi Holmestad ◽  
Sigmund J. Andersen
Keyword(s):  
Alloy System ◽  
Icosahedral Quasicrystal ◽  
High Symmetry ◽  
Low Temperature Annealing ◽  
Orientation Relations ◽  
Transmission Electron ◽  
Fixed Orientation ◽  
Mackay Icosahedron ◽  
Quasi Crystals ◽  
Relationship Of

The orientation relations (ORs) of the cubic icosahedral quasicrystal approximant phase α-Al(Fe,Mn)Si have been studied after low temperature annealing of a 3xxx wrought aluminium alloy by transmission electron microscopy. From diffraction studies it was verified that the most commonly observed OR for the α-Al(Fe,Mn)Si dispersoids is [1\bar 11]α // [1\bar 11]Al, (5\bar 2\bar 7)α // (011)Al. This orientation could be explained by assuming that the internal Mackay icosahedron (MI) in the α-phase has a fixed orientation in relation to Al, similar to that of the icosahedral quasi-crystals existing in this alloy system. It is shown that mirroring of the normal-to-high-symmetry icosahedral directions of the MI explains the alternative orientations, which are therefore likely to be caused by twinning of the fixed MI. Only one exception was found, which was related to the Bergman icosahedron internal to the T-phase of the Al–Mg–Zn system.

High-resolution EM investigation about effect of stress on formation of ω-phase crystals in β-tttanium alloys

1996 ◽  
Vol 54 ◽  
pp. 1006-1007
Author(s):  
E. Sukedai ◽  
M. Shimoda ◽  
A. Fujita ◽  
H. Nishizawa ◽  
H. Hashimoto
Keyword(s):  
High Resolution ◽  
Titanium Alloys ◽  
High Resolution Electron Microscopy ◽  
Dark Field ◽  
Zone Refining ◽  
Ω Phase ◽  
Α Phase ◽  
Nucleation Sites ◽  
Resolution Electron ◽  
Bcc Structure

ω-phase particles formed in β-titanium alloys (bcc structure) act important roles to their mechanical properties such as ductility and hardness. About the ductility, fine ω-phase particles in β–titanium alloys improve the ductility, because ω-phase crystals becomes nucleation sites of α-phase and it is well known that (β+α) duplex alloys have higher ductility. In the present study, the formation sites and the formation mechanism of ω-phase crystals due to external stress and aging are investigated using the conventional and high resolution electron microscopy.A β-titanium alloy (Til5Mo5Zr) was supplied by Kobe Steel Co., and a single crystal was prepared by a zone refining method. Plates with {110} surface were cut from the crystal and were pressured hydrostatically, and stressed by rolling and tensile testing. Specimens for aging with tensile stress were also prepared from Ti20Mo polycrystals. TEM specimens from these specimens were prepared by a twin-jet electron-polishing machine. A JEM 4000EX electron microscope operated at 400k V was used for taking dark field and HREM images.

Formation of F- and P-Type Icosahedral Quasicrystals in the Zn–Mg–Ho Alloy System*

1998 ◽  
Vol 37 (Part 1, No. 10) ◽  
pp. 5691-5696 ◽  
Author(s):  
Takayuki Shimizu ◽  
Tsutomu Ishimasa
Keyword(s):  
Alloy System ◽  
Icosahedral Quasicrystals ◽  
P Type

Formation of icosahedral quasicrystal by crystallization of Zr70(Ni, Cu, Pd)30 amorphous alloys

2001 ◽  
Vol 16 (1) ◽  
pp. 20-23 ◽  
Author(s):  
T. Zhang ◽  
A. Inoue ◽  
M. Matsushita ◽  
J. Saida
Keyword(s):  
Amorphous Alloys ◽  
Volume Fraction ◽  
Alloy System ◽  
Icosahedral Phase ◽  
Icosahedral Quasicrystal ◽  
Maximum Volume Fraction ◽  
Higher Temperature ◽  
Binary Alloy System ◽  
Primary Precipitation ◽  
Precipitation Phase

An icosahedral phase was found to be formed as a primary precipitation phase in the crystallization process of binary Zr70Pd30, ternary Zr70Ni30−xPdx, and Zr70Cu30−xPdx (x = 10 and 20 at.%) and quaternary Zr70Ni10Cu10Pd10 amorphous alloys. The maximum volume fraction of the icosahedral phase was nearly 100% for the 20% Pd alloys and the grain size tended to decrease in the range from 40 to 70 nm with increasing Pd content. No icosahedral phase was formed in the Zr–Ni–Cu alloys without Pd, and hence, the addition of Pd was concluded to be essential for the formation of the icosahedral phase in the Zr-based amorphous alloys. It also was noticed that the icosahedral phase was formed even in the binary Zr70Pd30 amorphous alloy. The icosahedral phase was in a metastable state and changes to equilibrium crystalline phases by annealing in the higher temperature range. The finding of the formation of the icosahedral phase in the binary alloy system allowed us to predict the future appearance of a number of icosahedral base alloys in other alloy systems.

Influence of Chemical Disorder, Magnetic Field and Phason Flipd on the Localization of Electronic States in a Regular Icosahedral Quasicrystal

2000 ◽  
Vol 643 ◽  
Author(s):  
Yu.Kh. Vekilov ◽  
E.I. Isaev ◽  
S.F. Arslanov
Keyword(s):  
Magnetic Field ◽  
Electronic Spectrum ◽  
Long Range ◽  
Electronic States ◽  
Wave Functions ◽  
Icosahedral Quasicrystal ◽  
Long Range Order ◽  
Level Statistic ◽  
Chemical Disorder ◽  
Icosahedral Quasicrystals

AbstractThe influence of substitutional chemical disorder, magenetic field and phasons, on the electronic spectrum and wave functions of icosahedral quasicrystals is investigated by means of tight-biding approximation and level statistic method. The results show that the localization of electronic states in an ideal quasictystal exists due to their coherent interfernce at the Fremi level which is caused by the symmetry and aperiodic long-range order.

scholarly journals Long-range magnetic order in real icosahedral quasicrystals

2021 ◽  
Author(s):  
Ryuji Tamura ◽  
Asuka Ishikawa ◽  
Shintaro Suzuki ◽  
Akihiro Kotajima ◽  
Yujiro Tanaka ◽  
...  
Keyword(s):  
Specific Heat ◽  
Long Range ◽  
Magnetic Order ◽  
Global Symmetry ◽  
Icosahedral Symmetry ◽  
Ferromagnetic Transition ◽  
Range Magnetic Order ◽  
Magnetic Orders ◽  
Icosahedral Quasicrystals ◽  
Long Range Magnetic Order

Abstract Quasicrystals (QCs), first discovered in 1984, generally do not exhibit long-range magnetic order. Here, we report on long-range magnetic order in the real icosahedral quasicrystals (i QCs) Au–Ga–Gd and Au–Ga–Tb. The Au65Ga20Gd15 i QC exhibits a ferromagnetic transition at TC = 23 K, manifested as a sharp anomaly in both magnetic-susceptibility and specific-heat measurements. Quick magnetic saturation to almost the full moment (7μB/Gd3+) is observed under 100 Oe at 2 K. This is the first observation of long-range magnetic order in a real quasicrystal, in contrast to the spin-glass-like behaviours observed for the other magnetic quasicrystals found to date. Moreover, when Gd is replaced by Tb, i.e. for the Au65Ga20Tb15 i QC, a ferromagnetic behaviour is still retained with TC = 16 K. Although the sharp anomaly in the specific heat observed for the Au65Ga20Gd15 i QC is significantly broadened upon Tb substitution, neutron-diffraction experiments clearly show the marked development of magnetic Bragg peaks below TC, indicating long-range magnetic order for the Au65Ga20Tb15 i QC also. Our findings can contribute to the further investigation of exotic magnetic orders formed on real quasiperiodic lattices with unprecedented highest global symmetry, i.e. icosahedral symmetry.

Incommensurate nature of the “decagonal” Phase Al65Cu20Co15 in the Al-Cu-Co ternary system

1990 ◽  
Vol 48 (4) ◽  
pp. 136-137
Author(s):  
Atul S. Ramani ◽  
Shihong Song ◽  
Earle R. Ryba ◽  
Paul R. Howell
Keyword(s):  
Ion Beam ◽  
Argon Atmosphere ◽  
Quasicrystalline Phase ◽  
Nominal Composition ◽  
Icosahedral Symmetry ◽  
Two Dimensional ◽  
Decagonal Phase ◽  
Thin Foils ◽  
Diffraction Patterns ◽  
Argon Ion

The discovery of a phase in Al-14 at% Mn alloys which displays forbidden icosahedral symmetry spurred a massive effort towards synthesis, characterization and theoretical modeling of the so - called “quasicrystalline” phase. Subsequendy, “decagonal” phases in Al-Mn and Al-Fe, having diffraction patterns characteristic of a periodic stacking of two-dimensional “quasicrystalline” structures, have been discovered. The present paper, reports preliminary results of our investigation of the “decagonal” phase first discovered by He et al. in an Al65Cu20Co15 alloy.High purity metals (Al, Cu, Co) were arc-melted in an argon atmosphere into alloy buttons of nominal composition Al65Cu20Co15. Specimens for TEM were prepared by ion-beam milling in a Gatan ionmilling system operated with an argon ion-beam, at an accelerating voltage of 4 kV and at specimen current of 1 μA. The thin foils were examined in a Phillips EM 420T microscope operating at 120 kV. Selected alloy buttons were fractured and prepared for examination on an ISI - SX 40 SEM operated at 25 kV.

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