Dielectric ceramic capacitors, with the advantages of high power density, fast charge-discharge capability, excellent fatigue endurance, and good high temperature stability, have been acknowledged to be promising candidates for solid-state pulse power systems. This review investigates the energy storage performances of linear dielectric, relaxor ferroelectric, and antiferroelectric from the viewpoint of chemical modification, macro/microstructural design, and electrical property optimization. Research progress of ceramic bulks and films for Pb-based and/or Pb-free systems is summarized. Finally, we propose the perspectives on the development of energy storage ceramics for pulse power capacitors in the future.

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Progress and perspectives in dielectric energy storage ceramics

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)FexO18 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 Pr but not at the expense of the maximum polarization Pmax 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.

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

BiFeO3-BaTiO3 is a promising high-temperature lead-free piezo-ceramics due to its high Curie temperature (TC > 500 °C) and excellent piezoelectric properties. However, a high leakage current was often detected in this system, which severely affects its applications. In this work, the 0.7BiFe(1−x)GaxO3-0.3BaTiO3 (BFGax-BT, 0.00 ≤ x ≤ 0.10) system was designed to reveal the reason of leakage-current density decreased by their leakage mechanism. Because of the suppression of generation of Fe2+ and oxygen vacancy ( VO∙∙), the leakage mechanism from space charge limited conduction mechanism found in Ga-free BF-BT ceramics turns into Ohmic conduction and Schottky emission mechanism as Fe3+ was replaced with Ga3+. A good combination of piezoelectric properties (d33 = 174 pC N−1 and kp = 29%) and high Curie temperature (TC = 497 °C) was achieved in the BFGa0.06-BT ceramic owning the lowest leakage-current density. This work will provide the clues for preparing the high insulation and high piezoelectric performance BF-BT-based ceramics by suppressing the valence change of Fe3+ and VO∙∙ appearance.

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High Curie temperature BiFeO3-BaTiO3 lead-free piezoelectric ceramics: Ga3+ doping and enhanced insulation properties

We have conducted a careful study of current-voltage (I-V) characteristics in fully integrated commercial PbZr0.4Ti0.6O3 thin-film capacitors with Pt bottom and Ir/IrO2 top electrodes. Highly reproducible steady-state I-V were obtained at various temperatures over two decades in voltage from current-time data and analyzed in terms of several common transport models including space charge limited conduction, Schottky thermionic emission under full and partial depletion, and Poole-Frenkel conduction, showing that the latter is the most plausible leakage mechanism in these high-quality films. In addition, ferroelectric hysteresis loops and capacitance-voltage data were obtained over a large range of temperatures and discussed in terms of a modified Landau-Ginzburg-Devonshire theory accounting for space charge effects

Electrical characteristics of PbZr(0.4)Ti(0.6)O3 capacitors

Lead-free Bi 0.5 Na 0.5 TiO 3 piezoelectric ceramics were successfully prepared by reactive flash sintering of Bi 2 O 3 -NaCO 3 -TiO 2 mixed powders, where phase transformation and densification occurred simultaneously. The influence of electric field strength, current density and holding time at constant current state on the phase transformation and densification were investigated. The current density had a significant influence on the extent of phase transformation and densification. The holding time had no influence on the phase transformation, but had an important effect on crystallinity of sample. The sintered bulks exhibited the maximum polarization P m of 16.8 μC/cm 2 , remanent polarization P r of 9.6 μC/cm 2 , coercive field E c of 29 kV/cmm, maximum electric-field-induced strain of 0.053 %, and piezoelectric coefficient d 33 of 85 pC/N. The reactive flash sintering can prepare the dense and single-phase ceramics from multiphase precursor powders in one step of flash, providing a new way for rapid production of ceramic materials. 

Biaolin Peng

Papers

Simultaneously achieved high-energy storage density and efficiency in (K,Na)NbO3-based lead-free ferroelectric films