Quasicrystal approximants with novel compositions and structures

Abstract

We identify several new quasicrystal approximants in alloy systems in which quasicrystals have not been previously reported. Some occur in alloys with large size contrast between the constituent elements, either containing small Boron atoms, or large Ca/Eu atoms, leading to quasicrystal structures quite different from currently known systems where the size contrast is smaller. Another group of the approximants are layered Frank-Kasper structures, demonstrating competition between decagonal and dodecagonal ordering within this family of structures.

Bulk electronic structure of Zn-Mg-Y and Zn-Mg-Dy icosahedral quasicrystals

“…20 Density functional theoretical (DFT) calculations have been performed by using the VASP code 21 considering 1/1 approximant (which has a local structure that is very similar to quasicrystals but is periodic with a large unit cell) consisting of 160 atoms in a cubic cell (96 Zn, 50 Mg and 14 Y/Dy atoms). 22 The valence 4f states of Dy are shifted to the core states because of the problem of DFT with correct description of f -electrons.…”

On the tetragonality of martensites in ferrous shape memory alloy Fe3Pt: A first-principles study

“…Nevertheless, one should also note that the L1 2 phase is not the 0 K ground state of Fe 3 Pt. Barabash [42] and previous theoretical values (GGA (DTU) [43] and GGA (CMU) [44]). Results computed with the 2 Â 2 Â 2 and 3 Â 3 Â 3 supercells (SC) are given by squares and triangles, respectively.…”

Stability of aperiodic crystals

“…The phase transitions where aperiodic phases are involved may also be studied with simple semi-microscopic models, or, more realistically, ab initio calculations [12]. The latter, however, are restricted to relatively small unit cells, and this provides a legitimacy for the former.…”

“…Experimental determination of the damping of phasons and the elastic constants as function of temperature seems to be in agreement with the prediction of the random tiling model, but a similar prediction for an energetically stable model does not exist, as far as I know. This question could be attacked by more realistic calculations of the stability of the quasicrystalline state, along the lines already followed by Mihalkovič and Widom [12].…”