Quasicrystals in rapidly solidified alloys of AlPt group metals — I. An overview of quasicrystals in aluminium-transition metal alloys

Crystal structure of orthorhombic ε-Al4Cr

The crystal structure of the orthorhombic ε-Al4Cr phase in the Al–Cr system was determined by single crystal X-ray structure analysis: space group Cmcm (No. 63), a = 12.521(1)Å, b = 34.705(2) Å, c = 20.223(1) Å, V = 8787.7(9) Å, Pearson symbol oC58420.48, Z = 8, Mr = 2256, composition Al56.23Cr14.21, D x = 3.41 g/cm3; F(000) = 8576, λ (MoKα ) = 0.71069 Å, μ = 4.510 mm−1, room temperature, R = 0.068 for 2839 reflections, goodness of fit S = 1.084. There are 55 (13Cr + 42 Al) independent atoms in the unit cell, in which 12 Cr atoms and 28 Al atoms have icosahedral coordination. Interatomic distances cover the ranges of 2.570 Å ∼ 2.646 Å, 2.421 Å ∼ 2.978 Å, and 2.480 Å ∼ 2.983 Å, for Cr–Cr, Cr–Al and Al–Al atomic pairs, respectively. The crystalline phase appears obviously as a layered structure perpendicular to the a-axis. A typical aggregation of the icosahedral clusters in the structure of the ε-Al4Cr phase has been pointed out.