Quasicrystals, which have long-range order but a non-periodic structure, are a unique class of materials that have attracted considerable scientific interest. Determining their atomic structure is challenging due to the lack of periodicity, which makes traditional crystallography techniques difficult to apply.
Neutron scattering is a powerful method for studying the structure of quasicrystals, since neutrons interact with the nuclei of atoms and are sensitive to isotopic composition. The double isotopic substitution (DIS) method allows one to isolate the contribution of individual elements to the structure factor, which significantly simplifies the analysis.
This paper presents a study of the structure of the icosahedral AlCuFe quasicrystal by the neutron scattering method using DIZ. Samples with different isotopic compositions of copper (Cu) and iron (Fe) were prepared. Neutron diffraction measurements were performed on a high-resolution diffractometer.
Using six samples of the quasicrystalline compound AlCuFe, which exhibits 6D face-centered icosahedral symmetry, neutron diffraction data were collected by the double isotope substitution method using two isotopes of iron and copper. Hetero- and homoatomic pair correlation functions were calculated for this structure. Our study reveals the presence of a well-localized site for copper at the center of the six-dimensional solid. This provides a clear, albeit qualitative, insight into the structure in which chemically ordered iron, copper, and aluminum atoms are arranged in successive concentric “layers” on extensive atomic surfaces. These surfaces are centered on two key atomic sites, n1 = [0, 0, 0, 0, 0, 0,] and n2 = [1, 0, 0, 0, 0, 0,], (indexed relative to the primitive unit cell), characteristic of the NaCl-type 6D structure. There is reason to believe that some proportion of aluminium is mixed with iron or is contained in a small volume within the iron surface.
The resulting diffraction spectra were analyzed using the inverse Monte Carlo method. This method allows one to construct a three-dimensional model of the atomic structure that best fits the experimental data.
The results of the study showed that the atomic structure of the AlCuFe quasicrystal is characterized by the presence of icosahedral clusters consisting of Al, Cu and Fe atoms. These clusters are linked together by “linking” atoms, forming a complex three-dimensional network. Analysis of interatomic distances made it possible to establish the preferred positions of Cu and Fe atoms in the quasicrystal structure.
Author: M Cornier-Quiquandon, R Bellissent, Y Calvayrac, JW Cahn, D Gratias, B Mozer
Institute: Materials Science and Engineering Laboratory, National Institute of Standards and Technology, Gaithersburg, MD 20899, USA, Léon Brillouin Laboratory (CEA-CNRS), CE Saclay, F-91191 Gif-sur-Yvette, France, CECM / National Centre for Scientific Research, 15 rue G. Urbain, F-94407 Vitry-le-François, France