The structures of hexagonal phases in Mg–Zn–RE (RE = Sm and Gd) alloys

Abstract

Abstract The structures of hexagonal μ-MgZnRE phases of Mg28.3Zn65.2Sm6.5 and Mg28.6Zn63.8Gd7.7, were determined by single crystal X-ray structural analysis: μMgZnSm, P63/mmc (No. 194), a = 14.619(1) Å, c = 8.708(1) Å, atoms/cell = 92, F(000) = 2484, μ = 27.44 mm−1, D calc = 5.621 Mg m−3, R = 0.0201 for the observed 1110 reflections with F obs > 4.0σ(F obs) and μ-MgZnGd, P63/mmc (No. 194), a = 14.633(2) Å, c = 8.761(2) Å, atoms/cell = 92, F(000) = 2527, μ = 28.51 mm−1, D calc = 5.707 Mg m−3, R = 0.0210 for the observed 1084 reflections with F obs > 4.0σ(F obs). The structure of μ-MgZnRE is closely related to that of the MgZn2 Laves phase (P63/mmc, a = 5.223 Å, c = 8.566 Å). The introduction of large RE elements increases the distortion of the icosahedral atomic arrangement around Zn and this produces a variety of icosahedral linkages in the μ-MgZnRE structure.