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

Iwami, Shuhei  ,  Ishimasa, Tsutomu

95 ( 4 )  , pp.229 - 236 , 2015-04-04 , Taylor & Francis
A dodecagonal quasicrystal showing 12-fold symmetry forms in Mn-rich quaternary alloys containing 5.5 or 7.5at.% Cr, 5.0at.% Ni and 17.5at.% Si. After annealing at 700 degrees C for 130h, the quasicrystal precipitated in a matrix of beta-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 h(1)h(2)h(2)h(1)h(5)-type reflections with odd h(5) index, and then five-dimensional space group P12(6)/mmc. Indexing of the reflections indicated that the dimension of the common edge in the equilateral triangle-square tiling is 4.560 angstrom, and the periodicity is 4.626 angstrom 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.

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