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Review Articles

Title: "New phenomena in epitaxial growth: Solid films on quasicrystalline substrates"

Authors: V. Fournée and P.A. Thiel

Contact: P.A. Thiel

Journal: J. Phys. D: Appl. Phys. (2005) 38, R83-R106.

Abstract:
An overview is given of the research conducted in the field of solid film growth on quasiperiodic surfaces. An atomistic description of quasicryst. surfaces is presented and discussed in relation to bulk structural models. The various systems for which thin film growth has been attempted so far are reviewed. Emphasis is placed on the nucleation mechanisms of the solid films, on their growth modes in relation to the nature of the deposited metals, on the possibility of intermixing or alloying at the interface and on the epitaxial relationships at the crystal-quasicrystal interfaces. We also describe situations where the deposited elements adopt a quasiperiodic structure, which opens up the possibility of extending our understanding of the relation between quasiperiodicity and the physical properties of such structurally and chemically complex solids.

Title: "Concluding remarks to quasicrystals 2001"

Author: P.A. Thiel

Contact: P.A. Thiel

Journal: J. Alloys Compd. (2002) 342, 477-479.

Abstract:

Unavailable

Title: "Quasicrystals"

Authors: E. Macia, J.-M. Dubois, and P.A. Thiel

Contact: P.A. Thiel

Ullmann's Encyclopedia of Industrial Chemistry, Wiley-VCH, Verlag GmBH, Weinheim, Germany (2002).

Abstract:

Unavailable

Title: "Electrons in a strange sea"

Authors: P.A. Thiel and J.M. Dubois

Contact: P.A. Thiel

Journal: Nature (2000) 408, 570-571.

Abstract:

Unavailable

Title: "Recent advances in the study of quasicrystals"

Authors: I.R. Fisher, M.J. Kramer, and A.I. Goldman

Contact: A.I. Goldman

Journal: Micron (2000) 31, 469-473.

Abstract:

A review, with 20 references, is given. Some recent advances in the study of quasicrystals at Ames Laboratoy are reviewed. In particular, growth from the melt of large, high-quality, single-grain quasicrystals is described in detail for icosahedral R-Mg-Zn and decagonal Al-Ni-Co. In addition, the magnetic properties of the rare-earth-containing icosahedral R-Mg-Zn quasicrystals are discussed.

Title: "Surface science of quasicrystals"

Authors: P.A. Thiel, A.I. Goldman, and C.J. Jenks

Contact: P.A. Thiel

Journal: Springer Ser. Solid-State Sci. (1999) 126, 327-359.

Abstract:

A review, with many references, is given on Al-rich alloy quasicrystals and their surface properties.

Title: "Quasicrystals: Reaching maturity for technological applications"

Authors: P.A. Thiel and J.M. Dubois

Contact: P.A. Thiel

Journal: Materials Today (1999) 2, 3-7.

Abstract: Unavailable.

Title: "Horizons in Quasicrystal Research"

Authors: A.I. Goldman and P.A. Thiel

Contact: P.A. Thiel

In Quasicrystals: The State of Art, Ed. by P. Steinhardt and D. DiVincenzo, World Scientific, Singapore (1999).

Abstract: Unavailable.

Title: Recent advances in the study of quasicrystals"

Authors: I.R. Fisher, M.J. Kramer and A.I. Goldman

Contact: A.I. Goldman

Journal: Micron (2000) 31(5), 469-473.

Abstract:

A review, with 20 refs., is given. Some recent advances in the study of quasicrystals at Ames Lab. are reviewed. In particular, growth from the melt of large, high-quality, single-grain quasicrystals is described in detail for icosahedral R-Mg-Zn and decagonal Al-Ni-Co. In addn., the magnetic properties of the rare-earth-contg. icosahedral R-Mg-Zn quasicrystals are discussed.

Title: "Quasicrystals: Perspectives and potential applications"

Authors: D.J. Sordelet and J.M. Dubois, Guest Editors

Contact: D.J. Sordelet

Journal: MRS Bulletin (1997) 22(11), 34-37.

Introduction:

For decades scientists have accepted the premise that solid matter can only order in two ways: amorphous (or glassy) like window glass or crystalline with atoms arranged according to translational symmetry. The science of crystallography, now two centuries old, was able to relate in a simple and efficient way all atomic positions within a crystal to a frame of reference in which a single unit cell was defined. Positions within the crystal could all be deduced from the restricted number of positions in the unit cell by translations along vectors formed by a combination of integer numbers of unit vectors of the reference frame. Of course disorder, which is always present in solids, could be understood as some form of disturbance with respect to this rule of construction. Also amorphous solids were naturally referred to as a full breakdown of translational symmetry yet preserving most of the short-range order around atoms. Incommensurate structures, or more simply modulated crystals, could be understood as the overlap of various ordering potentials not necessarily with commensurate periodicities.

For so many years, no exception to the canonical rule of crystallography was discovered. Any crystal could be completely described using one unit cell and its set of three basis vectors. In 1848 the French crystallographer Bravais demonstrated that only 14 different ways of arranging atoms exist in three-dimensional space according to translational symmetry. This led to the well-known cubic, hexagonal, tetragonal, and associated structures. Furthermore, the dihedral angle between pairs of faces of the unit cell cannot assume just any number since an integer number of unit cells must completely fill space around an edge. This is more easily visualized in a two-dimensional plane: rectangles, squares, triangles, and hexagons do tile the plane with no voids or overlaps. Therefore, only two-, four-, three-, and sixfold rotational symmetries are allowed. Fivefold symmetry as well as any h-fold symmetry beyond six were not compatible with this rule and were not observed.

The discovery of quasicrystals, however, has forced crystallographers to reconsider what they originally accepted as obvious: Ordered solid matter cannot show fivefold rotational symmetries. Try, for instance, to tile the floor of your kitchen with pentagonal tiles. To illustrate the point, Figure 1 shows a computer-drawn copy of the first experimental evidence proving the lack of completeness in classical crystallography. The image shows an electron-diffraction pattern from a rapidly solidified Al-Mn alloy. Diffraction is an experiment that preserves the angular relationships between rows of atoms in the specimen. Two conflicting issues are visible in Figure 1. First, we see sharp spots. Therefore the materials must be ordered up to long distances (disorder would broaden them into halos). This fits the description of a crystal. Second, the rotational symmetry around the center of the image is perfectly fivefold. Hence the atoms are arranged along the same orientations. Thus it cannot be a crystal according to the historical definition.

The story of quasicrystals began in 1982 when Dan Shechtman discovered his first specimen. Other examples with 10-fold, 12-fold, and eightfold symmetries were found soon after by Ranganation, Bendersky, Nissen, Kuo, and their collaborators. These alloys were metastable and transformed upon heating into equilibrium mixtures of crystalline phases. Later stable, faceted quasicrystalline materials were pointed out in Al-Li-Cu, Al-Fe-Cu, Al-Ni-Co, Al-Cu-Co, and Al-Pd-Mn alloys. Similar progress occurred more recently with the study of Ti-based icosahedral phases, the discovery of new icosahedral phases in Al-Pd-Re and Y-Mg-Zn alloys, and the observation of precipitates with apparent icosahedral morphology in stainless steels.

After some unavoidable and presumably fruitful initial controversies, the key to understanding these new forbidden symmetries was finally found in a broader generalization of crystallography into dimensions higher than 3. This is a mathematical game required to provide enough degrees of freedomæthe dimensions of the higher spaceæto account accurately for the irrational coordinates of the atoms. This exercise goes far beyond the scope of MRS Bulletin, and the reader can review published textbooks. The materials-science community nevertheless began to accept these odd structures with a greater degree of comfort when it became clear that the formation path of the stable quasicrystals may be depicted according to the usual equilibrium phase diagrams. This concept is discussed by A. P. Tsai on the metallurgy of quasicrystals. Interest beyond academic curiosity has evolved partly because on the one hand the unconventional crystallographic nature of quasicrystal allows a clear distinction of these materials and therefore may be used in patents to substantiate the field where claims are applicable. On the other hand, quasicrystals exhibit fascinating properties compared to common metals. Some of these properties may be useful in technological applications.

The purpose of this MRS Bulletin issue is to introduce some specific aspects of the preparation and properties of quasicrystals. This selection, which is somewhat selective owing to the limited space available, focuses on a small number of points that in our opinion reflect the leading perspectives for potential technological applications. Moe materials appears elsewhere. In this article, we shall summarize the salient features of current quasicrystal knowledge.

Title: "Quasicrystal research: The next generation"

Authors: Alan I. Goldman, James W. Anderegg, Matthew F. Besser, Tamara E. Bloomer, Sheng-Liang Chang, Drew W. Delaney, Cynthia J. Jenks, Matthew J. Kramer, Thomas A. Lograsso, Diana Lutz, David W. Lynch, R. William McCallum, Jeffrey W. Shield, Daniel J. Sordelet and Patricia A. Thiel

Contact: A.I. Goldman

Journal: American Scientist (1996) 84, 230-241.

Introduction.

Quasicrystals, a class of materials discovered in 1984, are rather like oobleck, a form of precipitation invented by Dr. Seuss. Both the quasicrystals and the oobleck are new and unlike anything seen before. Since the discovery of a new class of materials is only slightly more likely than the occurrence of a new form of precipitation, quasicrystals, like oobleck, suffered at first from a credibility problem. Many scientists thought it possible that instead of being new materials, they were actually anomalous forms of familiar materials, either crystals or glasses.

Among the doubters was the celebrated chemist Linus Pauling, who maintained that quasicrystals were really crystals that weren’t yet understood. Pauling’s skepticism was aroused by the claim that the diffraction pattern obtained from a quasicrystalline alloy could not be mapped to any known crystal structure. As Pauling knew, if the structural building block is carefully chosen, it is possible to come arbitrarily close to matching any diffraction pattern. Indeed, Pauling eventually suggested several complex crystalline models that very nearly described the diffraction patterns obtained from quasicrystalline alloys.

Even those who acknowledged the existence of quasicrystals had trouble absorbing their novelty. Although the diffraction patterns from quasicrystals were reasonably sharp, which is a sign of an orderly structure, many scientists found it hard to believe that quasicrystals are as well ordered as crystals. After a century of modern crystallography the notion of order was so tightly bound up with the notion of periodicity, the prejudice was that the aperiodic quasicrystals must somehow be less ordered than the periodic crystals.

These debates were settled and the structure and properties of quasicrystals clarified over the past 10 years by the techniques of materials science, a discipline that is a silent partner in many scientific endeavors. Figuring out the structure of a novel material is like identifying a geometrical solid sealed in a wooden box. By rotating or moving the box in various ways, one might ascertain that it contained, for example, a prism with a pentagonal cross section. Similarly, by bombarding a material with x rays, electrons or neutrons, or otherwise “shaking” or “rattling” it, scientists can determine its atomic structure and, by extension, its properties as a material.

The picture of quasicrystalline structures that has emerged from this research is not very different from that given five years ago by Paul Steinhardt of the University of Pennsylvania (American Scientist, November/December 1986), and this article focuses instead on the materials science of quasicrystals. Particular emphasis is given to research done at the Ames Laboratory, a Department of Energy Laboratory located in Ames, Iowa, but it is important to point out that many groups in the United States and throughout the world (most notably in France, Germany, Japan, China, India, Canada and Mexico) have active programs in quasicrystal research.

Over the past decade these groups have collectively demonstrated that quasicrystals are indeed a new class of materials, both well ordered and different from other classes. The insights into the properties of the quasicrystals provided by this work has provided are now guiding efforts to put them to practical use.


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