The Structure of the Y-Phase in the Mg—Ni—Sn System.

Abstract The structure of the Y-phase in the Mg–Ni–Sn system with Mg 74.5 Ni 14.5 Sn 11 composition was solved by applying the direct methods refined by a standard least square procedure. The space group is N° 101 (P4 2  cm) and the magnitude of the cell parameters are a = b =9.851(2) A and c =6.868(2) A. The final reliability factor is R =0.04 for 1575 independent reflections. The structure can be described in terms of an ideal structure containing two chains of cubes of Mg aligned along the c -direction. In each chain, Sn (resp. Ni) atoms occupy different opposite faces for adjacent cubes forming a stacking of tetrahedra along the c -direction. An alternative description in terms of two distorted polyhedral units is also given and the structure is compared with related inter-metallic compounds.