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

The structures of hexagonal μ-MgZnRE phases of Mg_28.3Zn_65.2Sm_6.5 and Mg_28.6Zn_63.8Gd_7.7, were determined by single crystal X-ray structural analysis: μ-MgZnSm, 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_0bS > 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.