The Silicides YT_2Si_2 (T =Co, Ni, Cu, Ru, Rh, Pd): A Systematic Study by ~(89)Y Solid-state NMR Spectroscopy

摘要

The ThCr_2Si_2-type silicides YT_2Si_2 (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 YRu_2Si_2 which has by far the smallest c/a ratio along with elongated Y- Si distances. Systematic ~(89)Y 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 YRu_2Si_2 manifests itself in a sizeable magnetic shielding anisotropy. Electronic structure calculations for YRu_2Si_2 and YRh_2Si_2 reveal similar projected density of states (PDOS) shapes with an energy upshift of the Fermi level in YRh_2Si_2 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 T_2Si_2 layers, YRh_2Si_2 exhibits significantly stronger Y-Si bonding.