Electronic Structure and Bonding in the Ternary Silicide YNiSi₃

Abstract

An analysis of the electronic structure and bonding in the ternary silicide YNiSi 3 is made, using extended Huckel tight-binding calculations. The YNiSi 3 structure consists of Ni-capped Si 2 dimer layers and Si zigzag chains. Significant bonding interactions are present between the silicon atoms in the structure. The oxidation state formalism of (Y 3+ )(Ni 0 )(Si3) 3- for YNiSi3 constitutes a good starting point to describe its electronic structure. Si atoms receive electrons from the most electropositive Y in YNiSi 3, and Ni 3d and Si 3p states dominate below the Fermi level. There is an interesting electron balance between the two Si and Ni sublattices. Since the π * orbitals in the Si chain and the Ni d and s block levels are almost completely occupied, the charge balance for YNiSi3 can be rewritten as (Y 3+ )(Ni 2- )(Si 2- )(Si-Si) + , making the Si 2 layers oxidized. These results suggest that the Si zigzag chain contains single bonds and the Si 2 double layer possesses single bonds within a dimer with a partial double bond character. Strong Si-Si and Ni-Si bonding interactions are important for giving stability to the structure, while essentially no metal-metal bonding exists at all. The 2D metallic behavior of this compound is due to the Si-Si interaction leading to dispersion of the several Si 2 π bands crossing the Fermi level in the plane perpendicular to the crystallographic b axis.