Synthesis and structural study of the partially disordered complex hexagonal phase δ-MnZn.

A detailed structural analysis of the Zn-rich δ-MnZn phase using single-crystal X-ray diffraction is presented. The δ phase has been synthesized by the high-temperature synthetic route. The structure crystallizes in space group P6/mmc (Pearson symbol hP556) with unit-cell parameters: a = b = 12.9051 (2) Å and c = 57.640 (1) Å. The 556 atoms are distributed over 52 Wyckoff positions in the hexagonal unit cell: seven ordered Mn sites, 37 ordered Zn sites and eight positionally disordered Zn sites. The structure predominantly consists of Frank-Kasper polyhedra (endohedral icosahedra Zn and icosioctahedron Zn) and four distinct types of glue Zn atoms. The structure comprises a 127-atom supercluster (MnZn), a 38-atom extended Pearce cluster (MnZn), a 46-atom L-tetrahedron (MnZn), a Friauf polyhedron (Zn), a disordered icosahedral cluster (MnZn) and four glue Zn atoms. Positionally disordered Zn sites around an Mn site can be visualized as the superimposition of three differently oriented Zn icosahedra.