Structural phase transitions from and to the quasicrystalline state

Abstract

Phase transitions from and to the quasicrystalline state show a typical signature due to some structural peculiarities. Both quasicrystals and most of their translationally periodic transformation products, the approximants, consist of the same basic structural units ('clusters'). This is the cause of low-energy interfaces between the newly forming phase and the parent phase. It is also the origin of the rather high stability of the frequently resulting orientationally twinned nanodomain structures. Owing to topological incompatibilities between quasiperiodic and periodic structures, purely displacive phase transitions are impossible. Diffusion of a significant fraction of atoms, at least on the scale of the cluster diameters, always has to take place. Locally similar icosahedral structural ordering between parent phase and nucleating phase is also responsible for the frequently occurring formation of icosahedral quasicrystals from undercooled liquid alloys or during devitrification of metallic glasses. The different types of experimentally observed phase transitions are discussed, from amorphous to quasicrystalline, quasicrystalline to ordered/disordered quasicrystalline and quasicrystalline to crystalline as a function of temperature, pressure, irradiation and high-energy ball milling, respectively.

Bulk Glassy and Quasicrystalline (Zr<SUB>65</SUB>Al<SUB>7.5</SUB>Cu<SUB>27.5</SUB>)<SUB>100&minus;<I>x</I></SUB>Ti<I><SUB>x</SUB></I> Alloys and Their Mechanical Properties

“…I-phases have strict structures and a limit compositional stability as well. 8,12) BMG formation is also compositional sensitive. 4) Thus in a given system, it is worthwhile to systematically examine the alloy effect on their formations.…”

“…7) On the other hand, icosahedral atomic clusters are the building blocks of icosahedral quasicrystals (I-phase). 8) ISRO would find the chance to extend orderly in the liquid under favorable compositional and kinetic conditions. In this case I-phase appears to compete with glass formation.…”

Fascinating quasicrystals

“…The absence of one-to-one mapping for structures with non-crystallographic symmetry results from the fact that the point-group symmetry of the periodic average structure is lower than that of the quasicrystal structure. Vice versa, it can be adequate to describe an incommensurately modulated structure as a quasicrystal structure if it shows scaling symmetry or results from a phase transformation of a quasicrystal (Steurer, 2005).…”

Stability of the decagonal quasicrystal in the Lennard–Jones–Gauss system

“…Note that each approximant can appear in different orientations according to the symmetry of the quasicrystal. Indeed, experimental observations reveal that the ground state for many systems is a twinned approximant [6]. However it is not known, whether quasicrystals can be stable down to 0 K. If the phase transition occurs at low-temperatures, the flips will be frozen in.…”

“…A more efficient transformation mechanism is the formation of a twinned nanodomain structure [6]. The twinning corresponds to a folding of the de Bruijn surface into piecewise straight segments, while leaving invariant the average orientation of the surface.…”