Electronic structure of face-centred cubic MoO2: A comparative study by the full potential linearized augmented plane wave method, X-ray emission spectroscopy and X-ray photoelectron spectroscopy

X-ray emission spectroscopy (XES) and X-ray photoelectron spectroscopy (XPS) methods were employed in the present paper to investigate the electronic structure of face-centred cubic (fcc) molybdenum dioxide, fcc-MoO2. For the mentioned compound, the XES O Kα and Mo Lβ2,15 bands reflecting the valence O p- and Mo s,d-like states, respectively, were derived and compared on a common energy scale with the XPS valence-band spectrum. For comparison, the similar experimental studies of the electronic structure were made for a usual orthorhombic form of molybdenum trioxide, MoO3. Band-structure calculations of fcc-MoO2 were made using the full potential linearized augmented plane wave (FP-LAPW) method. A rather good agreement of the experimental XES and XPS results and the theoretical FP-LAPW data for the electronic properties of fcc-MoO2 has been achieved in the present paper. A new near-Fermi sub-band was detected on both the XES Mo Lβ2,15 band and the XPS valence-band spectrum when going from orthorhombic MoO3 to fcc-MoO2. The FP-LAPW calculation reveals that the main contributors into the aforementioned sub-band of fcc-MoO2 are the Mo 4d(eg) states. Further, the FP-LAPW data indicate that the O 2p and Mo 4d(t2g) states contribute into both the central part and the bottom of the valence band of fcc-MoO2, while the Mo 4d(eg) states contribute almost exclusively into the bottom of the valence band of the oxide. A significant portion of density of states (mainly Mo 4d(eg) states) detected by the FP-LAPW calculation at the Fermi energy of fcc-MoO2 indicates that the oxide is rather unstable.