Asymmetric ferroelectricity and anomalous current conduction in heteroepitaxial BaTiO3 thin films

Asymmetric ferroelectricity and conduction of anomalous leakage current were observed in heteroepitaxial BaTiO3 thin films grown by rf magnetron sputtering at 600 degrees C on three different electrode/substrate combinations: SrRuO3/SrTiO3, Pt/MgO and Nb doped SrTiO3. The voltage shift of hysteresis loops of the capacitance was a linear function of the thickness of the BaTiO3 films and became as large as 10 V in the him with a thickness of 410 nm. The asymmetry did not disappear even after a heat treatment carried out at 800 degrees C in air. On the other hand, a steep increase in the leakage current was observed in the heteroepitaxial films when a positive voltage was applied. The origin of both the asymmetric hysteresis and the anomalous conduction is discussed in terms of asymmetric crystal structure caused by misfit dislocations introduced in heteroepitaxial growth.