Search

Recently, dielectrics for energy storage have been attracting increasing attention due to their ultrahigh power density. However, the widespread application of dielectrics remains limited by their low energy density. In this work, lead-free single-phase relaxor (1 − x)Ba0.55Sr0.45TiO3-xBiMg2/3Nb1/3O3 [(1 − x)BST-xBMN] (x = 0, 0.05, 0.07, and 0.10) bulk ceramics were prepared by a conventional solid-state reaction process. The dielectric properties, the relaxor behavior, and the energy storage properties were explored in detail. With increasing BMN content, the observed increase in activation energy (Ea) and the decrease in freezing temperature (Tf) indicate that the coupling between polar nano-regions (PNRs) gradually weakened, leading to the decrease in remanent polarization (Pr) and the increase in energy storage efficiency (η). For the composition x = 0.07, the breakdown strength (BDS) significantly increased from 240 kV cm of pure BST to 450 kV cm. Finally, large Wrec (4.55 J cm3) and high η (81.8%) were achieved in 0.93BST-0.07BMN ceramics. The results demonstrate that the (1 − x)BST-xBMN ceramics have superior potential for use in advanced pulsed power capacitors. [ABSTRACT FROM AUTHOR]

It has been reported that grain size has significant influence on the dielectric properties of barium strontium titanate (BST) thin films. In this paper we have proposed a multilayer structure in which BST layers are separated by thin MgO layers which are expected to function as barrier to atomic diffusion so that the grain size of BST could be confined. By simulation we have found that for a device with a coplanar/composite film/substrate configuration, the introduction of MgO can effectively change the dielectric constant of the composite while the tunability is not significantly affected, provided the amount of MgO is smaller than 25%. A prototype device was prepared to demonstrate the feasibility of this idea. By X-ray diffraction measurements it is revealed that BST and MgO coexist in the composite. The dielectric property of the composite film was determined and it was found that the film has a tunability of up to ~7% at 500 MHz and under an electric field of 13.3 kV/mm. [ABSTRACT FROM AUTHOR]

Barium Strontium Titanate (Ba 1-x Sr x TiO 3 , BST) possesses the advantages of high permittivity, low remnant polarization and dielectric loss, suggesting great potential in the application of power capacitors. However, the low maximum polarization severely restricts the achievement of outstanding energy storage properties (ESP). Herein, we design a lead-free bulk ceramic: (1-x)Ba 0. 55 Sr 0 · 45 TiO 3 -xBi 0.5 Na 0. 5 TiO 3 [(1-x)BST-xBNT] (x = 0.1–0.4), prepared by two-step solid-state reaction method. The introduction of BNT contributes to (1) the boost of maximum polarization (from 21 μC/cm2 up to 32.6 μC/cm2) due to Bi3+ lone pair covalent effect (2) strong relaxor behavior (1.71≪ γ 1.84) derived from weakly coupled nanopolar regions, which can be verified by high activation energy E a = 0.341 eV at x = 0.3, improves the ESP and thermal stability of the ceramics. According to the above strategies, high W rec = 1.73 J/cm3 and η = 84.4% are achieved in the 0.7BST-0.3BNT ceramics at 206 kV/cm, which is preferable to the previous results regarding BST-based bulk ceramics. The excellent thermal stability (20–120 °C), frequency stability (1–500 Hz), as well as anti-fatigue characteristic (cycling number: 105) were obtained in the 0.7BST-0.3BNT. Furthermore, 0.7BST-0.3BNT ceramics exhibit high-power density (P D = 44.9 MW/cm3) and rapid discharge rate (t 0.9 = 99.2 ns) from 20 °C to 120 °C. This work provides a feasible way to achieve good energy storage and charge-discharge properties for pulse power energy storage systems. [ABSTRACT FROM AUTHOR]

Abstract: Grain size effect on phase transition, dielectric and pyroelectric properties of BST ceramics under DC bias field was reported for the first time. With the grain size increased by one order of magnitude, phase transition diffuseness parameters δ and γ decreased from 282 to 63 and 1.64–1.33, respectively. This resulted in the dielectric constant maximum increased by 65%, the pyroelectric coefficient maximum and corresponding figure of merit were quadrupled and tripled, respectively. The physical essence of the great size effect can be attributed to a combination of surface effect, mechanical stress effect and extrinsic effect of grain boundary. A well understanding of the grain size effect and its mechanism will be useful for the BaTiO3-based ceramics and other ferroelectrics. [Copyright &y& Elsevier]