The Silicides YT2Si2 (T = Co, Ni, Cu, Ru, Rh, Pd): A Systematic Study by 89Y Solid-state NMR Spectroscopy

The ThCr₂Si₂-type silicides YT₂Si₂ (T = Co, Ni, Cu, Ru, Rh, Pd) were synthesized from the elements by arc-melting. They were characterized by powder X-ray diffraction, and the structures were refined on the basis of single-crystal X-ray diffractometer data. The course of the lattice parameters shows a distinct anomaly for YRu₂Si₂ which has by far the smallest c/a ratio along with elongated Y–Si distances. Systematic ⁸⁹Y solid-state NMR spectra show large Knight shifts arising from unpaired conduction electron spin density near the Fermi edge. The Knight shift decreases with increasing valence electron count (VEC), reflecting the sensitivity of this parameter to electronic properties. The particularly strong structural distortion observed in YRu₂Si₂ manifests itself in a sizeable magnetic shielding anisotropy. Electronic structure calculations for YRu₂Si₂ and YRh₂Si₂ reveal similar projected density of states (PDOS) shapes with an energy upshift of the Fermi level in YRh₂Si₂ due to the extra electron brought in by Rh. As a consequence, the PDOS at the Fermi energy is twice as large in the Ru compound as in the Rh compound. While both compounds show the major bonding interaction within the T₂Si₂ layers, YRh₂Si₂ exhibits significantly stronger Y–Si bonding.