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Interfaces in complex oxide heterostructures provide a new platform for creating novel functionalities. Up to now, the investigation on manipulating vertical interface in vertically aligned nanocomposite films is very limited. By manipulating vertical interface, a significantly reduction of leakage current and Ohmic conduction behavior were achieved in BaTiO 3 :Sm 2 O 3 films, which may enable the design of advanced nanostructures with emergent functionalities. • Ohmic conduction behavior was realized up to 1000 kV/cm. • Leakage current of BaTiO 3 is reduced by the formation of sharp vertical interface. • Enhanced ferroelectric polarization in BaTiO 3. Interface in complex oxide heterostructures provides a new platform for uncovering emergent physical phenomena and engineering novel functionalities. Compared to the control of lateral interface in bilayer or multilayer complex oxide films, the investigation on manipulating the vertical interface in vertically aligned nanocomposite films is rarely studied so far. Here, the vertical interface effect on the leakage behavior of vertically aligned nanocomposite BaTiO 3 :Sm 2 O 3 films grown on (1 1 1) Nb-SrTiO 3 (Nb-STO) substrates is reported. We found that the vertical interface without visible misfit dislocations is formed between BaTiO 3 and Sm 2 O 3. Consequently, the leakage mechanism is determined to be Ohmic conduction up to an electric field of 1000 kV/cm. Also, the leakage current is reduced to be around 3 × 10−7 A/cm2, which is almost two and three orders of magnitude lower than that of BaTiO 3 :Sm 2 O 3 /(0 0 1) Nb-STO and pure BaTiO 3 /(1 1 1) Nb-STO films, respectively. This work demonstrates the ability to realize Ohmic conductive mechanism at high electric field and further provides a new pathway to reduce leakage current and improve ferroelectric polarization of ferroelectric oxide films by manipulating the vertical interface, which opens the door to the design of advanced nanostructures with the emergent functionalities. [ABSTRACT FROM AUTHOR]