Icosahedral quasicrystals in Zn–T–Sc (T = Mn, Fe, Co or Ni) alloys

Abstract

Starting from the Zn 17 Sc 3 cubic approximant, new quasicrystal alloys were searched by replacement of Zn with transition elements, T. In the cases of T=Mn, Fe, Co and Ni, new icosahedral quasicrystals are formed in as-cast alloys as major phases at the alloy compositions of Zn 75 T 10 Sc 15 . All these quasicrystals belong to a primitive type, and have 6-dimensional lattice parameters, a 6D , ranging from 7.044 to 7.107 Å. They have the valence electron concentrations, e/a, ranging from 2.01 to 2.14, and almost the same ratios between the edge-length of the Penrose tile, a R , and the averaged atomic diameter d: a R /d~1.75. Moreover other Zn-and Cd-based quasicrystals including the same type of atomic cluster, Tsai-type cluster, also have the same values of e/a~2.1 and a R /d~1.75. The equality in e/a indicates that the Hume-Rothery mechanism plays an important role for the formation of these quasicrystals.

Icosahedral clusters, icosaheral order and stability of quasicrystals—a view of metallurgy∗

“…Assigning negative valencies for TM elements in Al-TM alloys has been controversial, but the important point is that the use of these values led to the discovery of a number of stable iQcs. Recently, these values were estimated to be positive in some complex Zn-TM and Al-V alloys [64] and Zn-TM-Sc iQcs [31]. However, to date, there are still no available values for Fe and Mn in Al-TM alloys.…”

“…In the core of each cluster, there is a tetrahedron created by four positionally disordered Cd atoms, as shown in figure 3(c), which breaks the icosahedral symmetry. The iQcs and approximants having identical cluster structures have been found in several alloys [11,30,31]. The iQcs and approximants of the Cd-Yb class have been found in a large number of alloys and constitute the largest of the three classes of iQcs.…”

Atomic structure of the binary icosahedral Yb–Cd quasicrystal

“…Therefore, the atomic order in i-QCs remains a challenging and outstanding question. The recent discovery of the first stable binary icosahedral YbCd 5.7 QCs 9,10 has been a breakthrough and led to discoveries of a whole series of related ternary i-QCs 11 . This i-QC offers a unique opportunity for the structural analysis of i-QCs.…”

Formation of Icosahedral Quasicrystal and Its 1/1 Crystal Approximant in Al-Pd-Sc System

“…Using the atomic radius values in Ref. 24 16 . The e/a values of them are all 2.10, assuming that the valences for Al, Pd, Cu and Sc are +3, +0, +1 and +3, respectively.…”

“…Many Al-based i-phases including Al-CuFe 6) and Al-Pd-Mn 7) belong to the Mackay-type whereas Al-Li-Cu, 8) Zn-Mg-Ga 9) and Zn-Mg-RE (RE: rare earth metals) 10) belong to the Bergman-type. The i-phases of the Tsai-type include Cd-based, 11,12) Ag-In based, 13) Znbased [14][15][16] and Cu-based 17,18) systems. It is experimentally established that the following factors are important in the formation of i-phases.…”