Critical Effect of Film-Electrode Interface on Enhanced Energy Storage Performance of BaTiO₃-BiScO₃Ferroelectric Thin Films

Although lead (Pb)-based ferroelectric thin films are widely used in many electronic devices, alternative Pb-free materials have been widely investigated in recent years to address concerns about Pb toxicity. In this regard, past research has primarily focused on the design of solid solutions of different Pb-free perovskite oxides to obtain optimum properties. However, the effect of a film-electrode interface on the functional properties of thin films of the recently developed Pb-free ferroelectrics has been largely ignored. This is surprising since the quality of the film-electrode's interface is known to inherently affect the crystallinity and growth direction of the overlying film microstructure. Here, we have addressed this important issue for the ferroelectric thin film of BaTiO₃-BiScO₃ (BSBT), which is attractive for high-temperature capacitor applications. Using high-resolution transmission electron microscopy (TEM) imaging and energy-dispersive X-ray spectroscopy, we show that controlled diffusion of cations and oxygen ions across the film-electrode interface and elimination of a detrimental amorphous layer promotes semiepitaxial growth of the 110-textured BaTiO₃-BiScO₃ (BSBT) films on a Pt-electrode. The changes at the film-electrode interface prove to be crucial in enhancing the energy density of the BSBT/Pt film heterostructure to a maximum of ~30 J cm^-3 and the overall energy efficiency to an impressive 90%. The current results highlight the significance of interfacial diffusion on the functional properties of Pb-free ferroelectric thin films.