Al13−x (Co1−y Ni y )4, a new approximant of the decagonal quasicrystal in the Al–Co–Ni system

Abstract

Abstract The structure of Al13−x (Co1−y Niy)4, with x = 0.9 and y = 0.12, a new monoclinic approximant of the decagonal phase in the system Al–Co–Ni, was determined by means of single-crystal X-ray diffractometry: space group C2/m (No. 12), a = 17.071(2) Å, b = 4.0993(6) Å, c = 7.4910(9) Å, β = 116.17(1)°, V = 470.5(1) Å3, Pearson symbol mC34-1.8, Dx = 3.96 Mg/m3 MoKα , F (000) = 530.6, Mr = 140.5, μ = 7.97 mm−1, Z = 2, wR = 0.034 and goodness of fit S = 1.15 for 963 reflections and 58 refined parameters. Typical interatomic distances are: d Al−Co,Ni = 2.323 Å–2.733 Å, d Al−Al = 2.688 Å–2.956 Å, d Co,Ni∓Co, Ni = 2.891 Å, respectively. Co atoms are coordinated by nine to eleven atoms, Al atoms are surrounded by ten, twelve or 13 neighbors. The relationships to the structurally related quasicrystal approximants with compositions Al13TM4(TM = Co, Fe, Os, Rh, Ru) as well as to the Al–Co–Ni(Cu) decagonal phases are discussed.