Dodecagonal quasicrystal in Mn-based quaternary alloys containing Cr, Ni and Si

Abstract

A dodecagonal quasicrystal showing 12-fold symmetry forms in Mn-rich quaternary alloys containing 5.5 or 7.5 at.% Cr, 5.0 at.% Ni and 17.5 at.% Si. After annealing at 700 °C for 130 h, the quasicrystal precipitated in a matrix of β-Mn-type crystalline phase. The shape of the quasicrystal is needle-like having a length of several tens of micrometres. Electron diffraction as well as powder X-ray diffraction experiments has revealed the following characteristics of the quasicrystal: diffraction symmetry 12/mmm, the presence of systematic extinction for h₁h₂h₂h₁h₅-type reflections with odd h₅ index, and then five-dimensional space group P12₆/mmc. Indexing of the reflections indicated that the dimension of the common edge in the equilateral triangle–square tiling is 4.560 Å, and the periodicity is 4.626 Å along the 12-fold axis. This is the first example of the dodecagonal quasicrystal synthesized by ordinary metallurgical method in 3-d transition-metal alloys.

Keywords:

• quasicrystal
• dodecagonal
• triangle–square tiling
• Mn-based alloy

Acknowledgements

The authors thank Marek Mihalkovič for valuable discussions and advice in the manuscript preparation, and Hayato Iga and Yuya Tanaka for their contributions to this research project. They also thank Nobuyuki Miyazaki for his help in the use of JXA-8530 electron probe microanalyzer.

Disclosure statement

No potential conflict of interest was reported by the authors.