Transition pathways connecting crystals and quasicrystals

Due to structural incommensurability, the emergence of a quasicrystal from a crystalline phase represents a challenge to computational physics. Here, the nucleation of quasicrystals is investigated by using an efficient computational method applied to a Landau free-energy functional. Specifically, transition pathways connecting different local minima of the Lifshitz–Petrich model are obtained by using the high-index saddle dynamics. Saddle points on these paths are identified as the critical nuclei of the 6-fold crystals and 12-fold quasicrystals. The results reveal that phase transitions between the crystalline and quasicrystalline phases could follow two possible pathways, corresponding to a one-stage phase transition and a two-stage phase transition involving a metastable lamellar quasicrystalline state, respectively.

Geometric State Sum Models from Quasicrystals

In light of the self-simulation hypothesis, a simple form of implementation of the principle of efficient language is discussed in a self-referential geometric quasicrystalline state sum model in three dimensions. Emergence is discussed in the context of geometric state sum models.

Geometric State Sum Models from Quasicrystals

In light of the self-simulation hypothesis, a simple form implementation of the principle of efficient language is discussed in a self-referential geometric quasicrystalline state sum model in three dimensions. Emergence is discussed in context of geometric state sum models.

Mechanical Spectroscopy of Quasicrystals

The use of mechanical spectroscopy to characterize the quasicrystalline state of solid matter is reviewed. After a general, chronological survey of existing mechanical spectroscopy studies, which include elastic properties as well as various relaxation phenomena between lowtemperature tunneling processes and high-temperature background damping, three subjects are considered in more detail: (i) the nature of intrinsic relaxation phenomena, including relaxation peaks in Al-Pd-Mn single quasicrystals, (ii) hydrogen-induced loss peaks in Zr/Ti-based quasicrystals and their use as a probe, and (iii) the study of nano-quasicrystalline structures and amorphousquasicrystalline transitions. It is shown that by combined studies of different elastic and anelastic phenomena, mechanical spectroscopy can be a valuable tool to obtain information about the nature and motion of defects, about the type of local atomic order, and about phase transformations and different processes leading to the formation of quasicrystalline order.

Investigation of the Quasicrystalline State of the D-Al67.5Cu17.5Rh15 and I-Al70Cu12Ru18 alloys

In the present study we report on the formation, characterization and magnetic susceptibility of two conventionally solidified quasicrystalline alloys with the nominal composition Al 67.5 Cu 17.5 Rh 15 (decagonal phase) and Al 70 Cu 12 Ru 18 (icosahedral phase). The characterization of the quasicrystalline state was examined by X-ray diffractometry (XRD), differential thermal analysis (DTA), transmission electron microscopy (TEM), scanning electron microscopy (SEM) and energy-dispersive X-ray microanalysis (EDXA). Magnetic susceptibility results in the temperature range from 5 to 300 K utilizing SQUID magnetometry under constant magnetic field H=1 kOe are presented.

CLUSTER STRUCTURE OF THE SURFACE OF Al65Cu20Fe15 ALLOY IN THE QUASICRYSTALLINE AND LIQUID STATE

The atomic structure of an alloy is mainly affected by its electronic structure. The studies of the electronic structure of Al65Cu20Fe15 in both the liquid and quasicrystalline state show that the surface of the sample contains clusters with strong hybridized bonds between atoms which are similar in the liquid and quasicrystalline state. This fact confirms qualitatively the concept of cluster structure of quasicrystals.

Quasicrystallinity Studies on Conventionally Solidified Aluminum-Technetium and Aluminum-Uranium Based Alloys

We present quasicrystallinity investigations on conventionally solidified binary Al-Tc, ternary Al-Tc-M (M = Mn, Ni, Cu, Ru, Rh, Pd, Re, Ir, Pt), Al-Cu-U, as well as quaternary Al-Cu-Ru-U alloys. By conventional cooling (dT/dt≈103 to 102 Ksec -1) crystalline phases were formed in all the systems, except for Al-Tc-Ir system, where only icosahedral quasicrystalline phases were found. A new large (1–1.5 mm in size) icosahedral (F-type structure) quasicrystal with a pentaprismatic growth morphology was obtained in the sample with the nominal composition Al77.6Tc10Ir12.4 . The characterization of the quasicrystalline state was examined by X-ray diffractometry, scanning electron microscopy (SEM) and energy-dispersive X-ray microanalysis (EDXA).