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

TL;DR

This paper reports the discovery of a dodecagonal quasicrystal with 12-fold symmetry in Mn-based quaternary alloys, synthesized through standard metallurgical methods, revealing unique structural characteristics and forming after specific heat treatment.

Contribution

First synthesis of a dodecagonal quasicrystal in 3d transition-metal alloys using conventional metallurgical techniques.

Findings

Quasicrystal exhibits 12/mmm diffraction symmetry.

Presence of systematic extinction for certain reflections.

Identified five-dimensional space group P126/mmc.

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 \b{eta}-Mn type crystalline phase. The shape of the quasicrystal is needle-like having a length of several tens of micrometers. Electron diffraction as well as powder X-ray diffraction experiments have revealed the following characteristics of the quasicrystal; diffraction symmetry 12/mmm, 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 {\AA}, and the periodicity is 4.626 {\AA} 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.