Al–Cu–Fe quasicrystals are a unique class of materials that combine the properties of crystalline and amorphous substances. Unlike ordinary crystals, quasicrystals have long-range order but lack translational symmetry. This results in unusual physical properties such as high hardness, low thermal conductivity, and unique electronic characteristics.
Large single crystal grains, obtained both by cooling from the liquid state and by annealing followed by a decrease in temperature to ≈825°, were transformed into near-spherical particles with a size of about 0.2 mm. These crystalline samples were then studied at NSLS, where integrated intensity values were collected for more than 1300 nonequivalent reflections at Q values⊥, exceeding 1.7 Å−1 (in Q|| units).
The key point of the study was the detailed assessment of the quality of the crystal structure. In particular, the radial (φ−2λ) Bragg scans show a nearly perfect Gaussian curve, while the omega scans (ω) are characterized by an almost pure Lorentzian shape. The width at half maximum (FWHM) of the Q-scans increases with increasing Q|| in the range from 1 to 11 Å−1. The full width at half maximum ω is typically within 0.065° with an average deviation of ≈0.001°, while the line shape is apparently due to the true mosaic distribution, since it does not depend significantly on the angle, Q⊥or Qλ.
The depth measurements show that the Lorentz profile is significantly enhanced by mechanical grinding, although even the untreated crystal fragment exhibits Lorentz “wings”. TEM analysis of untreated samples from both sources shows clear diffraction patterns with perfect icosahedral symmetry and images indicating the presence of an icosahedral phase rather than an aggregation of approximating domains. The study of the structure of Al–Cu–Fe quasicrystals is an important task in materials science. Determining the exact atomic structure allows us to understand the relationship between structure and properties, as well as to develop new materials with desired characteristics.
X-ray diffraction and high-resolution electron microscopy were used to study the structure of a single Al–Cu–Fe quasicrystal in detail. X-ray diffraction allowed us to determine the lattice parameters and reveal the presence of icosahedral symmetry, which is typical of quasicrystals. High-resolution electron microscopy made it possible to visualize the atomic structure and establish the presence of defects and domain boundaries.
Author:X.BKana, JL Robertson, SC Moss, J Kulik, T Ishimasa, M Mori, A Quivy, D Gratias, V Elser, P Zschach
Institute: Department of Physics, University of Houston, Houston, TX 77204-5506, USA, Division of Reactor Radiation Safety, NIST, Gaithersburg, MD 20899, USA, Texas Superconductivity Center, University of Houston, Houston, Texas 77004-5932, USA, College of General Education, Nagoya University, Nagoya 464-01, Japan, CECM/CNRS, 94400 Vitry-sur-Seine, France, Department of Physics, Cornell University, Ithaca, NY 14853, USA, ORAU/NSLS, Brookhaven National Laboratory, Upton, New York 11973, USA