Increasing energy storage capabilities of space-charge dominated ferroelectric thin films using interlayer coupling

Abstract In our previous work (W. Zhang et al., Space-charge dominated epitaxial BaTiO 3 heterostructures, Acta Mater. 85 (2015) 207–215), it was demonstrated that a space charge dominated BaTiO 3 thin film can have much improved energy storage characteristics when compared with a regular insulating film of ferroelectric BaTiO 3 . However, the improved recoverable electric energy density (discharged energy per unit volume), W re , is still constrained by the maximum/saturated polarization ( P s ) of the BaTiO 3 thin film. Here we propose a novel method to further improve W re in ferroelectric thin film heterostructures by using interlayer coupling in an epitaxial ferroelectric bilayer. In our model structure, a ferroelectric BiFeO 3 layer with a large remnant polarization ( P r ∼70 μC/cm 2 ) was deposited in-situ on top of a BaTiO 3 /SrRuO 3 heterostructure which shows a small remnant polarization ( P r ∼ 3 μC/cm 2 ). The resulted bilayer structure showed a slim P - E hysteresis loop characterized by a small remnant polarization and a large saturated one ( P s ≫ P r ), which can be well explained by a competition between the effect of space charges (dominant at low field) and that of the interlayer charge coupling (dominant at high field). The large difference, i.e. P s − P r , increases the recoverable electric energy density by about 85% (from ∼28 J/cm 3 to ∼51 J/cm 3 ).