Enhancement of energy storage performance in lead-free barium titanate-based relaxor ferroelectrics through a synergistic two-step strategy design

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Highlights

  • Two-step strategy provides a common way for designing high comprehensive ESP ceramic.

  • BST-BZN9VPP ceramic achieved an ultrahigh Wrec of 5.16 J/cm3 under 540 kV/cm.

  • The essential mechanism of high energy storage characteristics is visualized.

Abstract

Dielectric capacitors are widely used because of their advanced performance, including superior power density and high charge–discharge speed. Nevertheless, limitations in energy-storage density (Wrec), efficiency (η) and thermal stability hinder their practical application. Herein, these concerns are addressed using a synergistic two-step strategy of designing the composition of Bi(Zn2/3Nb1/3)O3 and optimizing the preparation for viscous polymer processing (VPP), thus achieving domain engineering, enhanced relaxor behavior, and improved breakdown strength (Eb) in (Ba0.8Sr0.2)TiO3-based ceramics. The broadening of the permittivity peak and highly dynamic polar nanoregions (PNRs) are correlated to expected relaxation characteristics, as indicated by the brightness of atomic position and calculated spontaneous polarization vectors determined through transmission electron microscopy. The relatively small grain size and increased band gap, verified through scanning electron microscopy and ultraviolet − visible spectrophotometry, contribute to the Eb. A prominent Wrec of 5.16 J/cm3 under 540 kV/cm and excellent temperature stability (Wrec = 3.6 J/cm3, η = 92.8%, 20–120 °C) are achieved in 0.91(Ba0.8Sr0.2)TiO3 − 0.09Bi(Zn2/3Nb1/3)O3 ceramics formed by VPP (BZN9VPP). The material possesses an exceptional current density of 647.56 A/cm2, a power density of 113.32 MW/cm3, and a rapid discharge speed of < 60 ns. The comprehensive outstanding performance supports the great potential of this sample for application in pulsed power capacitors.

Introduction

Dielectric capacitors, which possess the advantages of rapid charge − discharge speed and ultrahigh power density, have been utilized extensively in advanced pulsed power capacitor systems (APPCSs) [1], [2], [3]. Nevertheless, the low energy storage density (Wrec), small capacity storage efficiency (η) and poor thermal stability hinder their general applications in APPCSs. Coupled with the trend of miniaturization and integration of capacitors, improvements to their comprehensive performance have become more urgent. Their properties are usually determined based on their polarization–electric field (PE) hysteresis loops and the following formulas [4]:W=0PmEdP,Wrec=PrPmEdP,η=WrecW×100%=WrecWrec+Wloss×100%,

where Pm denotes the maximum polarization and Pr denotes remanent polarization. As estimated, high Wrec and η values demand a high breakdown strength (BDS, Eb) and a large difference (ΔP) between Pm and Pr. Among the five commonly available dielectric types, linear dielectrics (LDs) have ultrahigh η; however, their low Pm limits the acquisition of high Wrec [5], [6], [7]. While normal ferroelectrics (FEs) have a large Pm, their high Pr and Wloss limit E, thus yielding low Wrec [8], [9]. Antiferroelectrics (AFEs) have an ideal large Pm and low Pr, whereas the FE-AFE phase transition occurs under a high electric field accompanied by internal stress concentration and failure, which cause poor fatigue resistance [10], [11], [12]. Relaxor antiferroelectrics (RAFEs) combine the advantages of the mentioned AFEs and the latter relaxor ferroelectrics (RFEs) together, thus realizing a high Wrec and a high η under a high electric field [13]. Meanwhile, RFEs with small Pr, large Pm and low Wloss can undertake high Eb, enabling efficient implementation of a large Wrec. Moreover, the permittivity of RFEs is generally thermally insensitive within a given temperature range owing to the diffusion phase transition, which promotes the temperature stability of RFEs in energy-storage applications.

Hence, eco-friendly lead-free RFEs are considered as promising candidates for use in energy-storage capacitors. BaTiO3 (BT)-based RFEs account for a significant portion of candidate RFEs [14], [15]. Although the derived Ba1−xSrxTiO3 (BST) matrix can improve some characteristics of BT, some deficiencies remain to be solved: (1) BST possesses a relatively high Pm of approximately 27 μC/cm2, mainly owing to the long-range ferroelectric ordered Ti-O coupling at the B-site; however, this ordering is likely to be broken by the new coupling of B-site dopants, thus reducing Pm and Wrec. (2) BST is a normal FE material with regular FE domains accompanied by a large Pr and coercive field (Ec), leading to a high Wloss and low η. (3) While the Curie temperature (TC) of BT can be easily moved to approximately 66 °C by increasing the Sr2+ ion concentration, the TC peak remains high and sharp, which is not conducive to good energy storage performance (ESP) over a wide temperature range. Because an RFE state can be induced by substituting ions into a normal FE material at sufficiently high concentrations, Bi-containing compounds (BiMeO3, where Me denotes different cations) are typically used to dope BT to activate the FE-to-RFE phase transition and optimize the ESP [16]. For instance, Wang et al. synthetized BT-Bi(Mg2/3Nb1/3)O3 samples and obtained a Wrec approximately 1.13 J/cm3 [17]. Jiang et al. achieved an enhanced Wrec of 1.25 J/cm3 with a high η of 95% at 185 kV/cm in BT-Bi(Mg0.5Zr0.5)O3 systems [18]. Hu et al. recorded an ultrahigh Wrec of 4.49 J/cm3 with an η of 93% in BT-Bi(Mg1/2Ti1/2)O3 ceramics at room temperature via polarization mismatch [19].

Herein, we present a synergistic two-step strategy for enhancing the comprehensive ESP of Ba0.8Sr0.2TiO3-based RFEs, achieving outstanding Wrec, η, and thermal stability. As depicted in the left half of Fig. 1, the high Pm and Pr, as well as low Eb, are maintained in BST, in which the ferroelectric-to-paraelectric phase transition occurs at roughly 66 °C. In the first step, we chose Bi-containing Bi(Zn2/3Nb1/3)O3 (BZN) to broaden the Tm peak and disturb the long-range FE order of BST simultaneously, resulting in typical relaxor behaviors and the conversion from macrodomains to polar nanoregions (PNRs), which improves Pm, reduces Pr, and broadens the temperature range of stable permittivity. (1) For the A-site doping of BZN, Bi3+ has an ionic radius (117 pm) comparable to that of Ba2+ (135 pm) and a valence electron configuration (6s26p0) similar to that of Pb2+, where the Bi 6p and O 2p orbitals can be hybridized to yield a larger Pm [20]. (2) The insertion of B-site composite ions can improve the symmetry of eccentric crystals, disrupt the long-range FE order, and create PNRs. The emergence of PNRs facilitates domain switching after removing the electric field, which suppresses energy loss during charge and discharge, thus creating a negligible Pr. (3) The substitution of BZN reduces the Tm of BST to 16 °C and widens the TCC2 °C value that characterizes the temperature stability of permittivity in the range of − 44.9 °C to 88.1 °C, indicating that a corresponding stable polarization occurs in this temperature platform; the dominant paraelectric state above Tm is accompanied by an ultrahigh η. Accordingly, the large Pm, small Pr, and wide TCC2 °C contribute to an intermediate Wrec, and high-temperature stability is attained in BST–BZN ceramics [see Fig. 1(b)]. However, the Eb obtained from this one-step process is not significantly improved, and the overall improvement of the ESP is limited. As shown in the right half of Fig. 1, by reducing the pore concentration, Eb can be efficiently increased. Hence, the second step is to optimize the preparation process using viscous polymer processing (VPP), a simple ceramic production approach that is reasonably inexpensive with minimal equipment requirements [18], [21], [22]. After sintering, ceramics with dense structures and ultralow porosity can be produced by continuously rolling and diluting ceramic micelles to improve the green density. This significantly increases Eb and ameliorates Wrec simultaneously, realizing a satisfactory ESP in BST–BZNVPP ceramics [see Fig. 1(c)].

In this work, BST-based ceramics exhibit significant improvements in energy storage density, efficiency, and temperature stability through our synergistic design strategy including the introduction of BZN in the first step and the use of VPP technology in the second step. Accordingly, we report an exceptional room-temperature ESP (Wrec = 5.16 J/cm3, η = 82.3%) in BZN9VPP ceramics. The Wrec fluctuates within 3% (Wrec = 3.6 J/cm3) and the η varies within 2% (η = 92.8%) from 20 to 120 °C, indicating good temperature stability of the ESP. These results demonstrate the efficacy of our synergistic design strategy and the competitiveness of BZN9VPP ceramics in pulsed power capacitor applications.

Section snippets

Fabrications of samples

The conventional solid-state process was adapted for the synthesis of (1 − x)(Ba0.8Sr0.2)TiO3-x Bi(Zn2/3Nb1/3)O3 (BZNx, x  = 0, 0.05, 0.09, 0.12, 0.15, 0.20) ceramic samples. Thereafter, 0.91(Ba0.8Sr0.2)TiO3–0.09Bi(Zn2/3Nb1/3)O3 ceramics were optimized by the VPP technique and denoted as BZN9VPP ceramics. High-purity (AR-grade) SrCO3, BaCO3, TiO2, Bi2O3, ZnO, and Nb2O5 as raw materials were weighed in stoichiometric amounts depending on the above nominal formulas. The raw powders were ground in

Results and discussion

Fig. 2(a) depicts the XRD patterns of the BZNx ceramic powders. All specimens have single perovskite structures with no heterophases, implying that Bi3+, Zn2+, and Nb5+ are completely diffused into the main BST lattice. Fig. 2(b) reveals that as the BZN content increases, the diffraction peaks shift to lower angles, indicating increased cell volume, because Zn2+ (74 pm) and Nb5+ (68 pm) have larger radii than Ti4+ (60.5 pm). Fig. 2(c) and (d) show the Rietveld refinement of the XRD data, error

Conclusions

In summary, the BZN9VPP ceramics synthesized using the synergistic design strategy exhibited improved ESP. In the first step of BZN doping, the temperature range of stability and enhanced relaxor behavior can be attributed to the broadening of the permittivity peak and the generation of highly dynamic PNRs. In the second step of the VPP process, the increased Eb benefits from the relatively small grain size and increased band gap. Consequently, the designed BZN9VPP ceramic acquires the

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgments

This work was supported by the National Natural Science Foundation of China (Grant Nos. 52172127, 51772239 and 51761145024) and the Fundamental Research Funds for the Central Universities (XJTU). The SEM work was done at International Center for Dielectric Research (ICDR), Xi'an Jiaotong University, Xi'an, China. The authors also thank Shiyanjia Lab (www.shiyanjia.com) for the TEM analysis.

References (73)

  • G. Liu et al.

    Energy storage properties of bismuth ferrite based ternary relaxor ferroelectric ceramics through a viscous polymer process

    Chem. Eng. J.

    (2021)
  • Y. Li et al.

    Energy storage performance of BaTiO3-based relaxor ferroelectric ceramics prepared through a two-step process

    Chem. Eng. J.

    (2021)
  • J. Lv et al.

    Significantly improved energy storage performance of NBT-BT based ceramics through domain control and preparation optimization

    Chem. Eng. J.

    (2021)
  • B. Guo et al.

    Energy storage performance of Na0.5Bi0.5TiO3 based lead-free ferroelectric ceramics prepared via non-uniform phase structure modification and rolling process

    Chem. Eng. J.

    (2021)
  • X. Lu et al.

    Structure evolution and exceptionally ultra-low hysteresis unipolar electric field-induced strain in (1–x)NaNbO3-xBaTiO3 lead-free ferroelectrics

    Ceram. Int.

    (2018)
  • L. Jin et al.

    A strategy for obtaining high electrostrictive properties and its application in barium stannate titanate lead-free ferroelectrics

    Ceram. Int.

    (2018)
  • H. Trabelsi et al.

    Evaluation of the relationship between the magnetism and the optical properties in SrTiO3-δ defective systems: Experimental and theoretical studies

    J. Magn. Magn. Mater.

    (2019)
  • Z. Yang et al.

    A new family of sodium niobate-based dielectrics for electrical energy storage applications

    J. Eur. Ceram. Soc.

    (2019)
  • Q. Yuan et al.

    Simultaneously achieved temperature-insensitive high energy density and efficiency in domain engineered BaTiO3-Bi(Mg0.5Zr0.5)O3 lead-free relaxor ferroelectrics

    Nano Energy

    (2018)
  • X. Dong et al.

    Effective strategy to realise excellent energy storage performances in lead-free barium titanate-based relaxor ferroelectric

    Ceram. Int.

    (2021)
  • X. Dong et al.

    Simultaneous enhancement of polarization and breakdown strength in lead-free BaTiO3-based ceramics

    Chem. Eng. J.

    (2021)
  • F. Si et al.

    Enhanced energy storage and fast charge-discharge properties of (1–x)BaTiO3-xBi(Ni1/2Sn1/2)O3 relaxor ferroelectric ceramics

    Ceram. Int.

    (2019)
  • L. Zhang et al.

    Extreme high energy storage efficiency in perovskite structured (1–x)(Ba0.8Sr0.2)TiO3-xBi(Zn2/3Nb1/3)O3 (0.04 ≤ x ≤ 0.16) ceramics

    J. Eur. Ceram. Soc.

    (2020)
  • G. Liu et al.

    Dielectric, ferroelectric and energy storage properties of lead-free (1–x)Ba0.9Sr0.1TiO3-xBi(Zn0.5Zr0.5)O3 ferroelectric ceramics sintered at lower temperature

    Ceram. Int.

    (2019)
  • G. Liu et al.

    An investigation of the dielectric energy storage performance of Bi(Mg2/3Nb1/3)O3-modifed BaTiO3 Pb-free bulk ceramics with improved temperature frequency stability

    Ceram. Int.

    (2019)
  • X. Chen et al.

    Simultaneously achieving ultrahigh energy storage density and energy efficiency in barium titanate based ceramics

    Ceram. Int.

    (2020)
  • M. Zhou et al.

    Combining high energy efficiency and fast charge-discharge capability in novel BaTiO3-based relaxor ferroelectric ceramic for energy-storage

    Ceram. Int.

    (2019)
  • K. Han et al.

    Structure and energy storage performance of Ba-modified AgNbO3 lead-free antiferroelectric ceramics

    Ceram. Int.

    (2019)
  • A. Song et al.

    Energy storage performance in BiMnO3-modified AgNbO3 anti-ferroelectric ceramics

    Mater. Lett.

    (2019)
  • W. Wang et al.

    Enhanced energy storage properties of lead-free (Ca0.5Sr0.5)1–1.5xLaxTiO3 linear dielectric ceramics within a wide temperature range

    Ceram. Int.

    (2019)
  • W. Wang et al.

    Enhanced energy storage density and high efficiency of lead-free Ca1-xSrxTi1-yZryO3 linear dielectric ceramics

    J. Eur. Ceram. Soc.

    (2019)
  • W. Wang et al.

    Enhanced energy storage and fast charge-discharge capability in Ca0.5Sr0.5TiO3-based linear dielectric ceramic

    J. Alloys Compd.

    (2020)
  • W. Wang et al.

    Combining high energy efficiency and fast charge-discharge capability in calcium strontium titanate-based linear dielectric ceramic for energy-storage

    Ceram. Int.

    (2020)
  • J. Wu et al.

    Perovskite Srx(Bi1-xNa0.97-xLi0.03)0.5TiO3 ceramics with polar nano regions for high power energy storage

    Nano energy

    (2018)
  • X. Ren et al.

    Regulation of energy density and efficiency in transparent ceramics by grain refinement

    Chem. Eng. J.

    (2020)
  • X. Li et al.

    Novel lead-free ceramic capacitors with high energy density and fast discharge performance

    Ceram. Int.

    (2020)
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