X-ray Photoelectron and Absorption Spectroscopy of Metal-Rich Phosphides <i>M</i>₂P and <i>M</i>₃P (<i>M</i> = Cr−Ni)

Abstract

The electronic structures of metal-rich binary phosphides M 2 P and M 3 P ( M = Cr−Ni) have been examined by means of X-ray photoelectron and absorption spectroscopy and compared with those of the monophosphides M P. The P 2p 3/2 binding and P K-edge absorption energies decrease with greater ionic character of the M −P bonding and indicate the presence of anionic phosphorus, contrary to previous theoretical assertions but consistent with our previous results. Interatomic effects play a more important role in affecting the energy shifts in these metal-rich phosphides than in the monophosphides, becoming more pronounced with higher metal concentration. Although the M 2p 3/2 XPS spectra show no discernible shifts in binding energies, they reveal satellite features whose intensity can be related to metal charge in the Co- and Ni-containing phosphides. In these cases, the metal charge becomes less positive with higher metal concentration. For Ni 2 P and Ni 3 P, this trend was confirmed from an analysis of the Ni L-edge and M-edge XANES spectra.