Structural and electronic properties of transition-metal/BaTiO3(001) interfaces

Electronic and structural properties of transition-metal/BaTiO3(001) interfaces are studied by first-principles local-density full-potential linearized augmented plane-wave calculations with slab models. Equilibrium inter layer separations between metal overlayers (for the 5d metals Ta, W, Ir, and Pt) and the BaTiO3 substrate are calculated by total-energy determinations. It is found that the preferred adsorption:site for metal atoms on the BaTiO3 surface is above the O site and the metal-oxygen distance increases from Ta to Pt while the binding energy decreases. Significant hybridization is found between metal d states and the O 2p-Ti 3d states. The Fermi levels of the metals lie in the gap of BaTiO3 and metal-induced gap states, as suggested by Heine's theory [Proc. Phys. Sec. London 81, 300 (1962); Surf. Sci. 2, 1 (1964); Phys. Rev. 138, A1689 (1965)], are observed. The Schottky barrier in the interfaces is calculated by the position of E-F in the gap and the dependence of the barrier height on the metal work function is different from either Schottky and Mott's or Bardeen's [Phys. Rev. 71, 717 (1947)] speculation.