- Email: [email protected]
The discovery of quasicrystals through rapid quenching of metallic alloys
Materials Science and Engineering, 99 (1988) 321
321
The Discovery of Quasicrystals through Rapid Quenching of Metallic Alloys* JOHN W. CAHN
Institute for Materials Science and Engineering, National Bureau of Standards, Gaithersburg, MD 20899 (U.S.A.)
Abstract
A completely unexpected structure was discovered at the National Bureau of Standards by Dan Shechtman working with rapidly solidified Al-Mn alloys. Transmission electron microscopy studies showed dendritic crystals with an icosahedral diffraction pattern of sharp spots. The symmetry of the pattern implies that the structure cannot be periodic; the sharp spots indicated a translational order that approximates what mathematicians call quasiperiodicity. The structures have become known as quasicrystals. Since the initial discovery a large number of systems have yielded quasicrystals by a variety of processing methods. There is even one ternary system AI-Li-Cu in which the quasicrystal is a stable, rather than a metastable phase. At least one other symmetry (decagonal) has been observed and there are indications that there may be more than one crystal structure with icosahedral symmetry.
*Abstract of a paper presented. 0025-5416/88/$3.50
© Elsevier Sequoia/Printed in The Netherlands
321
The Discovery of Quasicrystals through Rapid Quenching of Metallic Alloys* JOHN W. CAHN
Institute for Materials Science and Engineering, National Bureau of Standards, Gaithersburg, MD 20899 (U.S.A.)
Abstract
A completely unexpected structure was discovered at the National Bureau of Standards by Dan Shechtman working with rapidly solidified Al-Mn alloys. Transmission electron microscopy studies showed dendritic crystals with an icosahedral diffraction pattern of sharp spots. The symmetry of the pattern implies that the structure cannot be periodic; the sharp spots indicated a translational order that approximates what mathematicians call quasiperiodicity. The structures have become known as quasicrystals. Since the initial discovery a large number of systems have yielded quasicrystals by a variety of processing methods. There is even one ternary system AI-Li-Cu in which the quasicrystal is a stable, rather than a metastable phase. At least one other symmetry (decagonal) has been observed and there are indications that there may be more than one crystal structure with icosahedral symmetry.
*Abstract of a paper presented. 0025-5416/88/$3.50
© Elsevier Sequoia/Printed in The Netherlands