Exploratory Synthesis with Molten Aluminum as a Solvent and Routes to Multinary Aluminum Silicides. Sm2Ni(NixSi1-x)Al4Si6(x= 0.18−0.27): A New Silicide with a Ferromagnetic Transition at 17.5 K

A new quaternary silicide, Sm 2 Ni(Ni x Si 1 - x )Al 4 Si 6 ( x = 0.18−0.27), has been synthesized from Sm 2 O 3, NiO, and Si or Sm, Ni, and Si in Al metal flux at 800 °C. The structure, determined by single-crystal X-ray diffraction, is tetragonal, space group P 4/ nmm (No. 129) with Z = 2, and lattice parameters a = b = 5.8060(3) Å, c = 14.845(1) Å. Refinement based upon F 2 [ I > 2σ( I )] yielded R 1 = 0.0252 and wR 2 = 0.0634. The compound exhibits a new structure type containing two different alternating layers which are linked together through Si/Ni−Si bonds to form a three-dimensional framework. One layer is formed by edge-shared (the edges parallel to c ) NiAl 8 cubes. The other layer is a Si-based net which consists of six-member, five-member, and square planar rings. The structure of this compound cannot be rationalized on the basis of the Zintl−Klemm concept. Extended Hückel, tight binding calculations were carried out for different hypothetical stoichiometries, besides the observed one, of the compound Sm 2 Ni(Ni x Si 1 - x )Al 4 Si 6 . Five models were investigated with x = 0, 0.25, 0.5, 0.75, and 1. The compounds with x = 0 and 0.25 are predicted to be more stable than the others. Electrical conductivity and thermopower data indicate that the compound is p-type metallic. The temperature-dependent magnetic susceptibility exhibits an antiferromagnetic ordering near 60 K and a weak ferromagnetic (WF) transition near 17 K. High temperature (150−300 K) magnetic susceptibility data suggest that Sm is in the 3+ oxidation state.