Ternary silicides M2Cr 4Si 5 ( M=Ti, Zr, Hf): filled variants of the Ta 4SiTe 4 structure type

Abstract

The isostructural ternary silicides M 2Cr 4Si 5 ( M=Ti, Zr, Hf) were prepared by arc-melting of the elemental components. The single-crystal structure of Zr 2Cr 4Si 5 was determined by X-ray diffraction (Pearson symbol oI44, orthorhombic, space group Ibam, Z=4, a=7.6354(12) Å, b=16.125(3) Å, c=5.0008(8) Å). Zr 2Cr 4Si 5 adopts the Nb 2Cr 4Si 5-type structure, an ordered variant of the V 6Si 5-type structure. It consists of square antiprisms that have Zr and Cr atoms at the corners and Si atoms at the centers; they share opposite faces to form one-dimensional chains ∞ 1[Zr 4/2Cr 4/2Si] surrounded by additional Si atoms and extending along the c direction. In a new interpretation of the structure, additional Cr atoms occupy interstitial octahedral sites between these chains, clarifying the relation between this structure and that of Ta 4SiTe 4. The formation of short Si–Si bonds in Zr 2Cr 4Si 5 is contrasted with the absence of Te–Te bonds in Ta 4SiTe 4. The compounds M 2Cr 4Si 5 ( M=Ti, Zr, Hf) exhibit metallic behavior and essentially temperature-independent paramagnetism. Bonding interactions were analyzed by band structure calculations, which confirm the importance of Si–Si bonding in these metal-rich compounds.