Well-crystallized epitaxial FeTiO3+δ films were prepared on the sapphire substrate by reactive sputtering technique. A wide range of oxygen nonstoichiometry from FeTiO3 to FeTiO3.5 was successfully controlled by controlling the sputtering conditions. All films had uniform structure without phase separation even for the highly oxidized FeTiO3.5 film. Structures, magnetic and electronic properties of the FeTiO3+δ films were seriously influenced by the oxygen nonstoichiometry. The nearly stoichiometric FeTiO3 films had a R structure, while the nonstoichiometric FeTiO3.5 had a R c structure. With increasing the oxygen nonstoichiometry, the valence states of Fe ions in FeTiO3+δ were examined to be changed from Fe2+ to Fe3+ by means of both Mössbauer and XPS spectroscopy. The Ti 2p core-level XPS spectra clearly confirmed the valence states of Ti4+ ions in nonstoichiometric FeTiO3.5. However the Ti ions in stoichiometric FeTiO3 suggested the abundant electron density than the conventional Ti4+ ions due to the Fe2+ to Ti 4+ intervalence charge transfer.
ASJC Scopus subject areas
- Physics and Astronomy(all)