Quantification of the Ti oxidation state in BaTi1−xNbxO3 compounds

The Ti oxidation state of a series mixed-valence BaTi1−xNbxO3 compound (where x=0.002, 0.004, 0.02, 0.10, 0.20 and 0.50) is investigated using high resolution electron energy loss spectroscopy (EELS). The energy loss near edge structure (ELNES) of the Ti-L2,3 and O-K edges was recorded with high energy resolution. The fraction of Ti4+ and Ti3+ components is determined in each compound by linear profile fitting with Ti4+ and Ti3+ standard spectra obtained from reference compounds within the series. The fitting results indicate an increase in the fraction of the Ti3+ component as the Nb content increases. A deviation from the expected Ti3+ valence fraction based on the charge balance across the series was detected and discussed. By considering all detailed features on the spectra obtained with high energy resolution, this linear fitting method can be used to determine the oxidation state of transition metal oxides, especially for the early transition metals where conventional methods based on the L2,3 edge ratio have shown to fail. The potential of this method to provide insight to mixed valence systems, vacancies and properties of oxides is discussed.