Chemical bonding and electronic structure ofPd2Si

The chemical bonding and electronic properties of ${\mathrm{Pd}}_2$Si have been investigated by measuring ultraviolet photoemission spectroscopy and Auger electron spectroscopy transitions involving both core and valence electrons for Pd, Si, and ${\mathrm{Pd}}_2$Si. The spectra have been interpreted based on partial state densities calculated for Pd-Si compounds. In the silicide, the $d$ states of the Pd interact strongly with the $p$ states of the Si. The resulting $p-d$ hybrid complex is composed of Pd $d$ states lying almost entirely below $E_F$ with the central peak at - 2.75 eV and two groups of Si states separated by ∼5 eV. The lower-lying group of Si states forms the Si $3p$-Pd $4d$ bonding levels, while the higher-lying group near $E_F$ forms the corresponding antibonding states. The compound stoichiometry can change the position of the $d$ peak as well as the occupation of the antibonding states, thus affecting the phase stability of the compound. Such stoichiometry variations are consistent with filling of the $d-p$ complex in an almost rigid-band-like manner. The results obtained in this study can be used to account for the transport properties of ${\mathrm{Pd}}_2$Si.