Ferroelectricity and structure of BaTiO3 grown on YBa2Cu3O7-δ thin films

We have investigated the crystal structure and the ferroelectric properties of BaTiO 3 thin films with YBa 2 Cu 3 O 7-δ as the bottom and Au as the top electrode. Epitaxial heterostructures of YBa 2 Cu 3 O 7-δ and BaTiO 3 were prepared by dc and rf sputtering, respectively. The crystal structure of the films was characterised by X-ray diffraction. The ferroelectric behaviour of the BaTiO 3 films was confirmed by hysteresis loop measurements using a Sawyer Tower circuit. We obtain a coercive field of 30 kV/cm and a remanent polarisation of 1.25 μC/cm 2 . At sub-switching fields the capacitance of the films obeys a relation analogous to the Rayleigh law. This behaviour indicates an interaction of domain walls with randomly distributed pinning centres. At a field of 5 MV/m we calculate a 3% contribution of the irreversible domain wall motion to the total dielectric constant.