Permittivity of BaTiO3 epitaxial films grown on the YBa2Cu3O7−δ(001) surface

The epitaxial heterostructures YBa2Cu3O7−δ and YBa2Cu3O7−δ/(5 nm)SrTiO3/BaTiO3/(5 nm)SrTiO3/YBa2Cu3O7−δ are grown by the laser evaporation method on an LaAlO3(100) substrate. The permittivity of a BaTiO3 layer is approximately doubled (T=300 K) when a SrTiO3 thin layer is inserted between a ferroelectric layer and superconducting cuprate electrodes. A maximum in the temperature dependence of the permittivity for a barium titanate layer in the YBa2Cu3O7−δ/(5 nm)SrTiO3/BaTiO3/(5 nm)SrTiO3/YBa2Cu3O7−δ heterostructure is shifted by 70–80 K toward the low-temperature range with respect to its location in the corresponding dependence for the BaTiO3 bulk single crystal. The bias voltage dependence of the permittivity for the BaTiO3 grown layers exhibits a clearly pronounced hysteresis (T=300 K). The superconducting transition temperature for the lower YBa2Cu3O7−δ electrode in a superconductor/ferroelectric/superconductor heterostructure considerably depends on the rate of its cooling after the completion of the formation process.