Electronic structure of SrNb8O14 and Mg3Nb6O11 studied by spectroscopic methods

Although there are many studies about oxides containing Nb6O12 cluster, the electronic structure has not been elucidated experimentally. Therefore, th ose around the Fermi level (E-F) for SrNb8O14 and Mg3Nb6O11, which contain 14 valence electrons per cluster, were evaluated using electronic spectrosc opies. Photoemission spectra showed that the occupied states were roughly s plit into two bands, and the shallower band was primarily composed of Nb 4d orbital. On the other hand, the bottom of the unoccupied state was attribu ted to 4d orbitals of Nb-6 cluster mainly on the basis of information obtai ned by inverse photoemission and Nb L-3-edge X-ray absorption near-edge str ucture spectra, showing that the electronic structure around E-F of these o xides were dominated by the nature of Nb-6 cluster. The optical transition in the region 0.1-4 eV was interpreted as Nb4d-4d intratomic electronic tra nsitions, compared with those of niobium oxides. This indicates that these materials were semimetals or semiconductors with a considerable narrow band gap.