High-Energy Storage Properties over a Broad Temperature Range in La-Modified BNT-Based Lead-Free Ceramics

Abstract

The development of high-performance energy storage materials is decisive for meeting the miniaturization and integration requirements in advanced pulse power capacitors. In this study, we designed high-performance [(Bi0.5Na0.5)0.94Ba0.06](1–1.5x)La x TiO3 (BNT-BT-xLa) lead-free energy storage ceramics based on their phase diagram. A strategy combining phase adjustment and domain control via doping was proposed to enhance the energy storage performance. The obtained results showed that La3+ ions doped into BNT-BT improved the crystal structure symmetry and induced a strong dielectric relaxation behavior, which destroyed the long-term ferroelectric order and effectively promoted the formation of polar nanoregions. At x = 0.12, a high recoverable energy density (W rec) of ∼5.93 J/cm3 and a relatively large energy storage efficiency (η) of 77.6% were obtained under a high breakdown electric field of 440 kV/cm. By using a two-step sintering approach for the microstructural optimization, the energy storage performance was further improved, yielding much higher W rec (6.69 J/cm3) and η (87.0%). Additionally, both conventionally sintered and two-step-sintered samples showed excellent frequency stability (0.5–500 Hz), thermal endurance (25–180 °C), and fatigue resistance (105 cycles). Regarding the pulse charge–discharge performance, the samples exhibited ultrashort discharge time (t 0.9 ∼ 89 ns for the conventionally sintered sample and ∼75 ns for the two-step-sintered sample) under an electric field of 240 kV/cm. Furthermore, the breakdown process of the material was simulated based on the finite element analysis, and it was shown that high breakdown strength of the material could be ascribed to fine grains, which significantly hindered the crack propagation during the application of the electric field. These results show that the presented materials have great potential as high-energy storage capacitors.

Simultaneous Enhancement of Energy Storage and Hardness Performances in (Na0.5Bi0.5)0.7Sr0.3TiO3-Based Relaxor Ferroelectrics Via Multiscale Regulation

“…The secondary phase is readily detected in BNST-based ceramics owing to the solubility limitation of doped ions and the complicated sintering process . A previous study revealed that the introduction of other elements into BNT ceramics will lead to the appearance of secondary phase Bi 2 Ti 2 O 7 after the element exceeds its solid solution limit . On the basis of the extrapolation method [Figure S1], when we compared the ionic radius at A-sites to that at B-sites, the difference between the ionic radius of Na + (1.39 Å), Bi 3+ (1.45 Å), Sr 2+ (1.44 Å), and doped Li + (1.25 Å) with 12 coordination (CN) is smaller than that of Ti 4+ (0.605 Å, CN = 6)/Li + (0.76 Å, CN = 6).…”

“…As the doping amount of LT is excessive, some Bi 3+ and Ti 4+ may be repelled from the crystal lattice to maintain charge neutrality. Accordingly, the rejected Bi 3+ and Ti 4+ ions thus can form the A 2 B 2 O 7 (Bi 2 Ti 2 O 7 ) pyrochlore phase . In addition, the formation of the pyrochlore phase may also be related to the Na deficiency due to its volatility at high temperatures .…”

“…Accordingly, the rejected Bi 3+ and Ti 4+ ions thus can form the A 2 B 2 O 7 (Bi 2 Ti 2 O 7 ) pyrochlore phase. 22 In addition, the formation of the pyrochlore phase may also be related to the Na deficiency due to its volatility at high temperatures. 23 Similar phenomena are also observed in some Pb-based and Bi-based ceramics.…”

Realizing high energy density and efficiency simultaneously in (Bi0.5Na0.5)0.7Sr0.3TiO3-based ceramics via introducing linear dielectric CaTiO3

“…3(d 2 ). Interestingly, local heterogeneity, corresponding to a large number of weakly polar [red and green regions] and a small number of polar PNRs [blue regions], 30,64 is detected. Unlike the BNST ceramics with large-size domains, the presence of a large number of weakly polar PNRs (or the absence of polar phases) in this work means that it is extremely difficult to obtain long-range dipole orientation under low electric elds, resulting in delayed polarization saturation.…”

“…2(c) provides the W rec and η values of the 0.60BNST-0.40CT ceramics and related lead-free bulk ceramics reported in previous literature. 11,22,28–61 Although a significant amount of work has been done, there are still few studies reporting that an ultrahigh W rec (>6.5 J cm −3 ) and a high η (>85.0%) can be obtained simultaneously in BNST-based or other lead-free bulk ceramics. Achievement of excellent comprehensive energy storage performances in 0.60BNST-0.40CT ceramics demonstrates their significant potential for practical application in pulsed power capacitors.…”