Electronic structure of Zr4Fe2O: Ab initio APW+LO calculations and X-ray spectroscopy studies

First-principles band-structure augmented plane wave +local orbitals (APW+LO) calculations as incorporated in the WIEN2k code as well as X-ray photoelectron spectroscopy (XPS) and X-ray emission spectroscopy (XES) measurements are performed to elucidate the electronic structure of Zr4Fe2O oxide, a very prospective hydrogen-storage material. Total and partial densities of states for Zr4Fe2O are derived from the APW+LO calculations. The XPS valence-band spectrum as well as the XES Zr Lβ2,15, Fe Lα and O Kα bands are measured for Zr4Fe2O0.6 oxide. Our APW+LO calculations show that the O 2p-like states make the major contributions at the bottom of the valence band, whilst the Fe 3d- and Zr 4d-like states are the dominant contributors at the top of the valence band and at the bottom of the conduction band of Zr4Fe2O. Peculiarities of the occupation of the valence band of Zr4Fe2O predicted by the APW+LO calculations are confirmed experimentally by comparison, on the common energy scale, of the XPS valence-band spectrum and the XES bands representing the energy distributions of the Zr 4d-, Fe 3d- and O 2p-like states in the compound under consideration. In addition, the XPS Zr 3d, Fe 2p and O 1s core-level binding energies are derived for Zr4Fe2O0.6 oxide.