Ordering Principles in Decagonal Al-Co-Ni Quasicrystals

Abstract

The discovery of quasicrystals has extended the traditional concept that crystalline matter is a periodic arrangement of identical units such as atoms or molecules. The typical quasicrystal is an intermetallic compound in which the building blocks are arranged in a non-periodic but highly ordered way. Of particular interest is the study of these ordering principles as a function of chemical composition and temperature in decagonal quasicrystals where periodic and aperiodic ordering even coexists in the same crystal structure. Structural information from diffraction experiments is the key for revealing these ordering principles and the prerequisite for a comprehensive study of the structure–property relationships. We present here the first all-inclusive in-situ high-temperature X-ray diffraction study of decagonal Al70Co12Ni18, a stable quasicrystal with a wealth of diffraction phenomena.

In situstudy of icosahedral Zn–Mg–Dy and Co-rich decagonal Al–Co–Ni at high pressures and high temperatures

“…Reconstructive phase transitions, which would be expected for the transformation from a quasiperiodic to a periodic crystal, need activation energy and may therefore be kinetically hindered at ambient temperature. Phase transitions in quasicrystals are sometimes accompanied by only small changes in the diffraction images, as shown for example in a high-temperature study of d-Al-Co-Ni [4]. Therefore single-crystal investigations at high pressures and high temperatures are of special interest.…”

A single-crystal high-pressure x-ray diffraction study of decagonal Al–Co–Cu up to 19.1 GPa

“…Decagonal Al-Co-Ni, for example, shows a phase transition at about 800 • C that goes along with the disappearance of weak superstructure reflections and a change in the shape of the diffuse scattering. Both features can only be observed with in situ high-temperature single-crystal diffraction [2].…”