Li20Mg6Cu13Al42: a new ordered quaternary superstructure to the icosahedral T-Mg32(Zn,Al)49 phase with fullerene-like Al60 cluster

Abstract

The new quaternary aluminide Li₂₀Mg₆Cu₁₃Al₄₂ was synthesized from the elements in a sealed tantalum crucible. The crystal structure was studied by single crystal and confirmed by X-ray powder diffraction. Li₂₀Mg₆Cu₁₃Al₄₂ {cI162, Im{\overline 3}, a = 13.8451 (2), R[F² > 2σ(F²)] = 0.023} crystallizes as an ordered version of Mg₃₂(Al,Zn)₄₉ and Li-Cu-X (X = Al, Ga, Si) periodic crystals containing icosahedral clusters. The Li₂₀Mg₆Cu₁₃Al₄₂ structure can also be described as three-shell icosahedral clusters of [CuAl₁₂@Li₂₀Cu₁₂@Al₆₀], enclosed inside a distorted triacontahedron. The electronic structure calculations were performed by means of the TB-LMTO-ASA program and confirm the core-shell packing of these clusters. The isostructural compound of Li₂₀Mg₆Cu₁₃Ga₄₂ was found in a Li-Mg-Cu-Ga quaternary system.

Keywords: chemical bonding; core–shell packing; electronic structure calculations; icosahedral clusters; intermetallics; quaternary systems; single-crystal methods; structural relations; triacontahedrons.