Enhanced electric resistivity and dielectric energy storage by vacancy defect complex

As a promising lead-free ferroelectric, BiFeO3 has a very large intrinsic polarization of ∼100 μC/cm2, enabling its great potential in electronic applications especially in a film format. In this sense, reliable ferroelectric properties are desired; however, pure-phase BiFeO3 films are notorious for their large leakage current, especially of those processed by using the sol–gel methoda facile and industrially scalable method for film preparation. In this study, a protection layer, which can be easily integrated in the sol–gel process, is used to ensure the acquirement of remnant polarization of ∼65 μC/cm2 in ∼200 nm BiFeO3 thin films, whereas O2 annealing can enhance that to ∼120 μC/cm2 in ∼400–700 nm films. Reliable ferroelectricity of BiFeO3 films on Si wafers within a wide thickness range was thus achieved. The obtained ferroelectricity is among the best-achieved properties to date of BiFeO3 films for both thin and intermediate thicknesses, including both chemically and physically derived. These results are helpful to advance potential use of sol–gel-processed BiFeO3 films in electromechanical devices with different desired thicknesses.

Section: Resultssupporting

confidence: 90%

Outstanding Ferroelectricity in Sol–Gel-Derived Polycrystalline BiFeO₃ Films within a Wide Thickness Range

Liu

Liang

et al. 2022

“…For the S1 sample, single peaks in both -Z ″ and M ″ spectroscopic plots belong to the same electroactive component . While for the S3 sample, an obvious difference in the peak positions of -Z ″ and M ″ plots can be observed, indicating that the Sb incorporation induces the electrically inhomogeneous microstructure . The lattice disorder and the existence of local random field may provide a possible explanation for the observed electrical heterogeneity.…”

Section: Resultsmentioning

confidence: 90%

“…36 While for the S3 sample, an obvious difference in the peak positions of -Z″ and M″ plots can be observed, indicating that the Sb incorporation induces the electrically inhomogeneous microstructure. 37 The lattice disorder and the existence of local random field may provide a possible explanation for the observed electrical heterogeneity. Moreover, the leakage current of the SBN-based ceramics is also depicted in Figure 7e, whose evolution agrees with the whole conductivity obtained from Figure 7a.…”

Section: ■ Introductionmentioning

confidence: 99%

Enhancing Comprehensive Energy Storage Properties in Tungsten Bronze Sr_0.53Ba_0.47Nb₂O₆-Based Lead-free Ceramics by B-Site Doping and Relaxor Tuning

Yang

Zhang

Lou

et al. 2022

Dielectric ceramics with relaxor characteristics are promising candidates to meet the demand for capacitors of next-generation pulse devices. Herein, a lead-free Sb-modified (Sr0.515Ba0.47Gd0.01) (Nb1.9‑x Ta0.1Sb x )O6 (SBGNT-based) tungsten bronze ceramic is designed and fabricated for high-density energy storage capacitors. Using a B-site engineering strategy to enhance the relaxor characteristics, Sb incorporation could induce the structural distortion of the polar unit BO6 and order–disorder distribution of B-site cations as well as the modulation of polarization in the SBGNT-based tungsten bronze ceramic. More importantly, benefiting from the effective inhibition of abnormal growth of non-equiaxed grains, Sb introduction into SBGNT-based ceramics could effectively suppress the conductivity and leakage current density, enhancing the breakdown strength, as proved by the electrical impedance spectra. Consequently, a remarkable comprehensive performance via balancing recoverable energy density (∼3.26 J/cm3) and efficiency (91.95%) is realized simultaneously at 380 kV/cm, which surpasses that of the pristine sample without the Sb dopant (2.75 J/cm3 and 80.5%, respectively). The corresponding ceramics display superior stability in terms of fatigue (105 cycles), frequency (1∼200 Hz), and temperature (20∼140 °C). Further charge–discharge analysis indicates that a high power density (89.57 MW/cm3) and an impressive current density (1194.27 A/cm2) at 150 kV/cm are achieved simultaneously. All of the results demonstrate that the tungsten bronze relaxors are indeed gratifying lead-free candidate materials for dielectric energy storage applications.

“…Finally, the energy storage density and efficiency of the F8 film in this work are compared with the corresponding values of representative perovskite film capacitors in the recent 2 years, − as shown in Figure i. It is suggested that the F8 film has a considerable role in perovskite energy storage, especially in the comparison of energy storage density.…”

Section: Results and Discussionmentioning

confidence: 82%

Capturing Carriers and Driving Depolarization by Defect Engineering for Dielectric Energy Storage

Zhao

Yang

Liu

et al. 2022

The inevitable defect carriers in dielectric capacitors are generally considered to depress the polarization and breakdown strength, which decreases energy storage performances. Distinctive from the traditional aims of reducing defects as much as possible, this work designs (FeTi ′ – Vo ••)• and (FeTi ″ – Vo ••) defect dipoles by oxygen vacancy defect engineering in acceptor doped Sr2Bi4Ti(5–x)Fe x O18 layered perovskite films with n-type leakage conductance. It is shown that oxygen vacancies effectively capture electrons (carriers) in n-type dielectrics to enhance the breakdown strength. Meanwhile, defect dipoles provide a driving field for depolarization to engineer the generation energy of domains and the domain wall energy, which effectively lowers the residual polarization P r but not at the expense of the maximum polarization P max as relaxor ferroelectric regulations. Such defect engineering effectively breaks through the limitation, in which the energy storage density suffers from the trade-off relationship between polarization and breakdown strength. The Sr2Bi4Ti4.92Fe0.08O18 film with the proper oxygen vacancy content achieves a high energy density of 110.5 J/cm3 and efficiency of 70.0% at a high breakdown strength of 3915 kV/cm. This work explores an alternative way for breakthroughs possible in the intrinsic trade-off relationship to regulate dielectric energy storage by defect engineering.