Vanadium valency and hybridization in V-doped hafnia investigated by electron energy loss spectroscopy

The valency of vanadium, and thus indirectly the oxygen stoichiometry, of V -doped hafnia synthesized under different atmospheres have been investigate d on a nanometor scale by means of electron energy loss spectroscopy (EELS) . The EELS V L-2,L-3 spectra are compared with the results of crystal field multiplet calculations and experiments oil reference vanadium oxides. The EELS spectra indicate that V-doped hafnia prepared under reducing (H-2) and neutral (Ar) atmosphere are unambiguously substituted with trivalent vanad ium atoms leading to the creation of oxygen vacancies in the structure. On the contrary, stoichiometric (Hf, V)O-2 compound (i.c. V4+) is more likely to be stabilized under oxidative (air) atmospheres. We also show that the a mount of hybridization alters for the different compounds studied but may i n part be analyzed by high spatially resolved EELS. The crystal field multi plet calculations particularly indicate that a simple reduction of the Slat er integrals gives a good account of the spectral modification induced by h ybridization for the case of tetravalent vanadium atoms.