Electronic structure of ZrCuSiAs and ZrCuSiP by X-ray photoelectron and absorption spectroscopy

The electronic structures of quaternary pnictides ZrCuSiPn (Pn=P, As) were analyzed by X-ray photoelectron spectroscopy (XPS) and X-ray absorption near-edge spectroscopy (XANES). Shifts in the core-line XPS and the XANES spectra indicate that the Zr and Cu atoms are cationic, whereas the Si and Pn atoms are anionic, consistent with expectations from simple bonding models. The Cu 2p XPS and Cu L-edge XANES spectra support the presence of Cu1+. The small magnitudes of the energy shifts in the XPS spectra suggest significant covalent character in the Zr–Si, Zr–Pn, and Cu–Pn bonds. On progressing from ZrCuSiP to ZrCuSiAs, the Si atoms remain largely unaffected, as indicated by the absence of shifts in the Si 2p3/2 binding energy and the Si L-edge absorption energy, while the charge transfer from metal to Pn atoms becomes less pronounced, as indicated by shifts in the Cu K-edge and Zr K, L-edge absorption energies. The transition from two-dimensional character in LaNiAsO to three-dimensional character in ZrCuSiAs proceeds through the development of Si–Si bonds within the [ZrSi] layer and Zr–As bonds between the [ZrSi] and [CuAs] layers.