Substitution Mechanism of Mn and Fe Ions in Bi₄Ti₃O₁₂

Single-phased polycrystalline Mn-and Fe-doped Bi₄Ti₃O₁₂ were fabricated using a solid-state reaction technique, doping with various concentrations of Mn and Fe ions. Substitution mechanism of Mn and Fe ions in Bi₄Ti₃O₁₂ were investigated with X-ray absorption near-edge structure (XANES) measurements and first-principles calculations. The valence states of the Mn and Fe ions are 4+ and 3+, respectively, inferred from the L_2,3-edge XANES profiles. From the K-edge XANES analysis, it is determined that Mn and Fe ions are substituted at one of the Ti sites, i.e., Ti(2a) or Ti(4e) sites. Our first-principles total electronic energy calculations suggest that Mn ions are likely to substitute at Ti(2a) sites rather than at Ti(4e) sites, whereas the opposite is true for Fe substitution. Taken together, these results give a clear description of the locations and charge states of the Mn and Fe dopants in Bi₄Ti₃O₁₂.