Neutral and Charged Oxygen Vacancies Induce Two-Dimensional Electron Gas Near SiO2/BaTiO3 Interfaces

J. Phys. Chem. Lett., 2013, 4 (2), pp 333–337

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An atomistic model of the SiO₂/BaTiO₃ interface was constructed using ab initio molecular dynamics. Analysis of its structure and electronic properties reveals that (i) the band gap at the stoichiometric SiO₂/BaTiO₃ interface is significantly smaller than those of the bulk BaTiO₃ and SiO₂, and (ii) the interface contains 5.5 nm^–2 oxygen vacancies (V²⁺) in the outermost TiO₂ plane of the BaTiO₃ and 11 nm^–2 Si–O–Ti bonds resulting from breaking Si–O–Si and Ti–O–Ti bonds and subsequent rearrangement of the atoms. This structure gives rise to the interface polar region with positive and negative charges localized in the BaTiO₃ and SiO₂ parts of the interface, respectively. We propose that high dielectric response, observed experimentally in the SiO₂-coated nanoparticles of BaTiO₃, is due to the electron gas formed in oxygen-deficient BaTiO₃ and localized in the vicinity of the polar interface.