Sven Lidin | Searcharxiv

arXiv2015

New kind of dodecagonal quasicrystal

We report a novel kind of dodecagonal quasicrystal that has so far never been observed, nor theoretically predicted. It is composed of axially stacked hexagonal particle layers, with 12-fold rotational symmetry induced by 30 degrees rotation of adjacent layers with respect to each other. The quasicrystal was produced in a molecular-dynamics simulation of a single-component system of particles interacting via a spherically-symmetric potential, as a result of a first-order phase transition from a liquid phase under constant-density cooling. This finding implies that a similarly structured quasicrystal can possibly be produced by the mesogens of the kind that produce smectic-B crystals and in a system of spherically-shaped colloidal particles with appropriately tuned potential.

cond-mat.soft↗

arXiv2009

A Structural Model for Octagonal Quasicrystals Derived from Octagonal Symmetry Elements Arising in $β$-Mn Crystallization of a Simple Monatomic Liquid

While performing molecular dynamics simulations of a simple monatomic liquid, we observed the crystallization of a material displaying octagonal symmetry in its simulated diffraction pattern. Inspection of the atomic arrangements in the crystallization product reveals large grains of the beta-Mn structure aligned along a common 4-fold axis, with 45 degree rotations between neighboring grains. These 45 degree rotations can be traced to the intercession of a second crystalline structure fused epitaxially to the beta-Mn domain surfaces, whose primitive cell has lattice parameters a = b = c = a_{beta-Mn}, alpha = beta = 90 degrees, and gamma = 45 degrees. This secondary phase adopts a structure which appears to have no known counterpart in the experimental literature, but can be simply derived from the Cr_3Si and Al_3Zr_4 structure types. We used these observations as the basis for an atomistic structural model for octagonal quasicrystals, in which the beta-Mn and the secondary phase structure unit cells serve as square and rhombic tiles (in projection), respectively. Its diffraction pattern down the octagonal axis resembles those experimentally measured. The model is unique in being consistent with high-resolution electron microscopy images showing square and rhombic units with edge-lengths equal to that of the beta-Mn unit cell. Energy minimization of this configuration, using the same pair potential as above, results in an alternative octagonal quasiperiodic structure with the same tiling but a different atomic decoration and diffraction pattern.

cond-mat.mtrl-sci↗