Flexible Lead-Free Ba0.5Sr0.5TiO3/0.4BiFeO3-0.6SrTiO3 Dielectric Film Capacitor with High Energy Storage Performance

Ferroelectric thin film capacitors have triggered great interest in pulsed power systems because of their high-power density and ultrafast charge–discharge speed, but less attention has been paid to the realization of flexible capacitors for wearable electronics and power systems. In this work, a flexible Ba0.5Sr0.5TiO3/0.4BiFeO3-0.6SrTiO3 thin film capacitor is synthesized on mica substrate. It possesses an energy storage density of Wrec ~ 62 J cm−3, combined with an efficiency of η ~ 74% due to the moderate breakdown strength (3000 kV cm−1) and the strong relaxor behavior. The energy storage performances for the film capacitor are also very stable over a broad temperature range (−50–200 °C) and frequency range (500 Hz–20 kHz). Moreover, the Wrec and η are stabilized after 108 fatigue cycles. Additionally, the superior energy storage capability can be well maintained under a small bending radius (r = 2 mm), or after 104 mechanical bending cycles. These results reveal that the Ba0.5Sr0.5TiO3/0.4BiFeO3-0.6SrTiO3 film capacitors in this work have great potential for use in flexible microenergy storage systems.

Effects of Oxygen Vacancies on Dielectric Properties and Relaxor Behavior of Ba(ZrxTi1-x)O3 Ceramics

By comparing the structure, dielectric and electrical conduction properties of sintered Ba(Zr0.15Ti0.85)O3 ceramics (short as BZT15) annealed in air and oxygen atmosphere was conducted to explore the impact of oxygen vacancies (OVs) on them. The dielectric properties of the samples were studied as changing with temperature (260–400K) in the scope of frequency from 100 Hz to 100 kHz. A typical relaxor behavior was observed in BZT15 and the relaxor behavior was enhanced after oxygen annealing treatment, which confirmed that the relaxation process was connected with the OVs inside ceramics. The value of activation energy was calculated to be 1.76 eV, 1.79eV, and 1.85 eV for as-prepared, air and oxygen annealed samples, respectively. Besides, the dielectric relaxor behavior was found to be associated with the conductivity originated from the dipolar conduction and long-distance movement of doubly ionized OVs. More interestingly, compared with other ferroelectric materials, the higher activation energy of BZT15 ceramics revealed a weaker concentration of OVs for such dielectric materials.

Investigation of the coupling effect of flexoelectricity and ferroelasticity on energy storage efficiency of relaxor ferroelectrics

The Ginzburg–Landau theory and dipole defect model have been employed to investigate the flexoelectric and ferroelastic effects on the ferroelectric and energy storage properties of relaxor ferroelectrics (RFs). The results obtained show that due to the existence of polar nanoregions (PNRs) in RFs, the elastic field of the material, which is induced by both the flexoelectric and ferroelastic effects, leads to the increase of the domain switching energy and coercive field and the decrease of the energy storage efficiency. In contrast, the short-range electric field induced by the dipole defects enhances the energy storage efficiency of the material by enhancing the material’s relaxor behavior. Hence, the energy storage efficiency of RFs can be effectively functionalized by modulating the composition ratio and the electric field of the RF materials.

Realizing Enhanced Energy Storage and Hardness Performances in 0.90NaNbO3-0.10Bi(Zn0.5Sn0.5)O3 Lead-Free Ceramics

Relaxor behavior has been demonstrated responsible for excellent energy storage characteristics in dielectric materials owing to the fast polarization response, and an ultrahigh energy storage density can also be induced in NaNbO3 (NN)-based ceramics via combining antiferroelectric and relaxor features. Most of the existing reports lead-free dielectric ceramics, nevertheless, are still lacking of the relevant research among domain evolution and relaxor behavior. Herein, a novel lead-free solid solution, (1-x)NaNbO3-xBi(Zn0.5Sn0.5)O3 [xBZS, x = 0.05, 0.10, 0.15, and 0.20] ceramics are designed to further illustrate the above issues. Domain evolutions in xBZS ceramics confirm the contribution of relaxor behavior to the excellent energy storage characteristics, owning to fast polarization rotation based on the low energy barrier of polar nanoregions (PNRs). Consequently, a high energy storage density of 3.14 J/cm3 and energy efficiency of 83.30% are simultaneously available at 0.10BZS ceramics, together with the stabilities of energy storage properties in large temperature range (20-100 °C) and wide frequency range (1-200 Hz). Additionally, for practical applications, the 0.10BZS ceramics display a great discharge energy storage density (Wdis ~1.05 J/cm3), fast discharge rate (t0.9 ~60.60 ns), and high hardness (H ~5.49 GPa). These results indicate that this study may provide a considerable new light on the mechanism of high performance lead-free dielectric energy storage materials.