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

We have investigated the crystal structure and the ferroelectric properties of BaTiO3 thin films with YBa2Cu3O7-delta as the bottom and Au as the top electrode. Epitaxial heterostructures of YBa2Cu3O7-delta and BaTiO3 were pr epared bg de and rf sputtering, respectively. The crystal structure of the films nias characterised by X-ray diffraction.. The ferroelectric behaviour of the BaTiO3 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 mu C/cm(2). At sub-switching fields the capacitance o f 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 irrever sible domain wall motion to the total dielectric constant.