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• Quasicrystals with an 8-fold Symmetry (Octagonal Quasicrystals)

images/stories/qc-2.jpg


The Nobel Prize in Chemistry 2011 was awarded to Dan Shechtman "for the discovery of quasicrystals"

 

See more: The Nobel Prize in Chemistry 2011


Our octagonal quasicrystal has been cited in Scientific Background of the Nobel Prize in Chemistry 2011.


See the citation # (12) * N. Wang, H. Chen, K.H. Kuo (1987) --"Two-dimensional quasicrystal with eightfold rotational symmetry", Phys. Rev. Lett. 59, pp 1010-1013.


In the physics and materials science communities, "quasicrystal" refers to a new class of ordered metallic alloys.

This new class of materials was first discovered in Al-Mn alloy in 1984 (the 5-fold symmetry by D. S. Schechtman in the National Bureau of Standards (NBS) (now the National Institute of Standards and Technology), USA). Quasicrystals have well-ordered structures (aperiodic crystals) which fall outside the realm of classical crystallography. Their uniqueness stems from the fact that they exhibit rotational symmetries which are not consistent with periodic structures. The discretely diffracting aperiodic crystals have led to much interdisciplinary activity involving mainly materials science, physics, mathematics, and crystallography. It led to a new understanding of how atoms can arrange themselves, the role of periodicity in nature, and led to the study of crystallography in N-dimensional space (N > 3).

Quasicrystals are promising candidates for applications as coatings, metal matrix components, hydrogen storage materials, thermal barriers, infrared sensors, etc. Some applications are already on the market--high-strength Al alloys cookware, surgical tools, and electric shavers. Since 1984, scientists have discovered/proved the following “forbidden” symmetries in solid materials, 5-fold, 8-fold, 10-fold and 12-fold symmetries in solid materials (forbidden symmetries are also found in liquid crystals recently). Quasicrystals with an 8-fold symmetry was discovered by Dr. N. Wang et al. in rapidly solidified Cr-Ni-Si alloy in 1986 (Phys. Rev. Lett. 59 (1987) 1010). Dr. Wang has demonstrated that the Octagonal quasicrystal is a different quasicrysdtal. It is not a twining structure. This kind of symmetry was later confirmed to exit in many other alloy systems. After this discovery, no other “forbidden” symmetries have been observed experimentally in rapidlty solidfied alloys. Because of his discovery of the Octagonal quasicrystal, Dr. N. Wang received the Chien-Shiung WU* Physics Award (* Madam Chien-Shiung WU (吴健雄)as the great female physicist of 20th century because of her glorious achievements, e.g. parity symmetry breaking).


By improving the rapid quenching technique, N. Wang and colleagues fabricated the octagonal quasicrystal first in Cr-Ni-Si and Mn-Si-Al alloys and has pioneered in proving and studying the symmetries, atomic structure, defects and phase transformation associated with the octagonal quasicrystals. These studies have led to a new understanding of how atoms can arrange themselves under 8-fold symmetry scheme in 2-dimensions, the role of periodicity and aperiodicity in nature, and have analyzed the growth of the octagonal crystal in 5 dimensions. This remarkable work has stimulated extensive investigations on understanding the unique structure and the new phenomenon of octagonal quasicrystal growth and their interesting properties, for example, the vibration properties, the anomalous diffusion in octagonal quasicrystals, as well as the band gap and wave guiding effect in octagonal quasiperiodic photonic crystals. His work on octagonal quasicrystals have been quoted in many books (e.g. “Physical Metallurgy” ed. R.W. Cahn and P. Haasen, 1996, Elsevier Science B.V, p382; “Springer Series in Solid-State Science – Physical Properties of Quasicrystals”, Ed. Z.M. Stadnik, Springer, 1998, p17; ). Current, our octagonal quasicrystal research has been cited in the Scientific Background of the Nobel Prize in Chemistry 2011.


images/stories/qc-1.jpgimages/stories/qc-3.jpg images/stories/qc-8hrtem-1.jpg

Figures: Electron diffraction, 8-fold symmetry and 2D quasiperiod structure and HRTEM image of the octagonal quasicrystal.

See details...images/stories/linkmore.gif “Two-dimensional quasicrystal with eightfold rotational symmetry”, N. Wang, H. Chen & K. H. Kuo, Phys. Rev. Lett. 59 (1987) 1010.


Quasicrystals that have been discovered in rapidly qunched alloys. (已经被发现的四种准晶对称性(在急速冷却合金中):

•  Icosahedral quasicrystals with 5-fold synmmetry (D. Shechtman, et al., 1984, USA)

• Decagonal quasicrystals with local 10-fold symmetry (L. Bendersky et al., 1985, USA)

• Dodecagonal quasicrystals with local 12-fold symmetry  (T. Ishimasa, et al., 1985, Switzerland )

• Octagonal quasicrystals with local 8-fold symmetry ( N. Wang et al., 1987, China)

 


Quasicrystal Alloys (有准晶体存在的部分合金系统):

Icosahedral QC:   Al-Mn, Al-Mn-Si, Al-Li-Cu, Al-Pd-Mn, Al-Cu-Fe, Al-Mg-Zn, Zn-Mg-RE (RE=La,Ce,Nd,Sm,Gd,Dy,Y)  
Ti-TM (TM=Fe, Mn, Co, Ni), Nb-Fe, V-Ni-Si, Pd-U-Si 

Octagonal QC:  V-Ni-Si, Cr-Ni-Si, Mn-Si, Mn-Si-Al, Mn-Fe-Si, 

                           Mo-Cr-Ni


Decagonal QC:   Al-TM (TM=Ir,Pd,Pt,Os,Ru,Rh,Mn,Fe,Co,Ni,Cr)  
Al-Ni-Co, Al-Cu-Mn, Al-Cu-Fe, Al-Cu-Ni, Al-Cu-Co, Al-Cu-Co-Si, Al-Mn-Pd, V-Ni-Si, Cr-Ni

Dodecagonal QC:   Cr-Ni, V-Ni, V-Ni-Si,

 

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