Relaxor-ferroelectric superlattices: high energy density capacitors

We report the breakdown electric field and energy density of laser ablated BaTiO3/Ba(1−x)SrxTiO3 (x = 0.7) (BT/BST) relaxor-ferroelectric superlattices (SLs) grown on (100) MgO single crystal substrates. The dielectric constant shows a frequency dispersion below the dielectric maximum temperature (Tm) with a merger above Tm behaving similarly to relaxors. It also follows the basic criteria of relaxor ferroelectrics such as low dielectric loss over wide temperature and frequency, and 50 K shift in Tm with change in probe frequency; the loss peaks follow a similar trend to the dielectric constant except that they increase with increase in frequency (∼40 kHz), and satisfy the nonlinear Vogel–Fulcher relation. Well-saturated ferroelectric hysteresis and 50–80% dielectric saturation are observed under high electric field (∼1.65 MV cm−1). The superlattices demonstrate an ‘in-built’ field in as grown samples at low probe frequency ( 1 kHz) which rules out the effect of any space charge and interfacial polarization. The P–E loops show around 12.24 J cm−3 energy density within the experimental limit, but extrapolation of this data suggests that the potential energy density could reach 46 J cm−3. The current density versus applied electric field indicates an exceptionally high breakdown field (5.8–6.0 MV cm−1) and low current density (∼10–25 mA cm−2) near the breakdown voltage. The current–voltage characteristics reveal that the space charge limited conduction mechanism prevails at very high voltage.