Dielectric capacitors with high energy storage density (Wrec) and efficiency (η) are in great demand for high/pulsed power electronic systems, but the state-of-the-art lead-free dielectric materials are facing the challenge of increasing one parameter at the cost of the other. Herein, we report that high Wrec of 6.3 J cm-3 with η of 90% can be simultaneously achieved by constructing a room temperature M2–M3 phase boundary in (1-x)AgNbO3-xAgTaO3 solid solution system. The designed material exhibits high energy storage stability over a wide temperature range of 20–150 °C and excellent cycling reliability up to 106 cycles. All these merits achieved in the studied solid solution are attributed to the unique relaxor antiferroelectric features relevant to the local structure heterogeneity and antiferroelectric ordering, being confirmed by scanning transmission electron microscopy and synchrotron X-ray diffraction. This work provides a good paradigm for developing new lead-free dielectrics for high-power energy storage applications.
Nanobubbles have many potential applications depending on their types. The long-term stability of different gas nanobubbles is necessary to be studied considering their applications. In the present study, five kinds of nanobubbles (N2, O2, Ar + 8%H2, air and CO2) in deionized water and a salt aqueous solution were prepared by the hydrodynamic cavitation method. The mean size and zeta potential of the nanobubbles were measured by a light scattering system, while the pH and Eh of the nanobubble suspensions were measured as a function of time. The nanobubble stability was predicted and discussed by the total potential energies between two bubbles by the extended Derjaguin–Landau–Verwey–Overbeek (DLVO) theory. The nanobubbles, except CO2, in deionized water showed a long-term stability for 60 days, while they were not stable in the 1 mM (milli mol/L) salt aqueous solution. During the 60 days, the bubble size gradually increased and decreased in deionized water. This size change was discussed by the Ostwald ripening effect coupled with the bubble interaction evaluated by the extended DLVO theory. On the other hand, CO2 nanobubbles in deionized water were not stable and disappeared after 5 days, while the CO2 nanobubbles in 1 mM of NaCl and CaCl2 aqueous solution became stable for 2 weeks. The floating and disappearing phenomena of nanobubbles were estimated and discussed by calculating the relationship between the terminal velocity of the floating bubble and bubble size.
Environmentally friendly lead-free
dielectric ceramics have attracted
wide attention because of their outstanding power density, rapid charge/dischargerate,
and superior stability. Nevertheless, as a hot material in dielectric
ceramic capacitors, the energy storage performance of Na0.5Bi0.5TiO3-based ceramics has been not satisfactory
because of their higher remnant polarization value and low dielectric
breakdown strength, which is a problem that must be urgently overcome.
In this work, the (1 – x) (0.6Na0.5Bi0.5TiO3 – 0.4Sr0.7Bi0.2TiO3) – xBa(Mg1/3Ta2/3)O3 (BNST-xBMT) systems
were designed based on a dual optimization strategy of domain and
bandgap to solve the above problems. As a result, a record-breaking
ultrahigh energy density and excellent efficiency (W
rec = 8.58 J/cm3, η = 93.5%) were obtained
simultaneously under 565 kV/cm for the BNST-0.08BMT ceramic. The introduction
of Sr0.7Bi0.2TiO3 induces the formation
of nanodomains in BNT-based ceramics, leading to slim P-E curves, and the further modification of Mg/Ta
reduces the grain sizes and increases the bandgap width, resulting
in significant enhancement of the dielectric breakdown strength. Moreover,
excellent stability and superior discharge performance (W
d = 4.7 J/cm3, E = 320 kV/cm)
in the BNST-0.08BMT ceramic were also achieved. The results suggest
that the BNST-0.08BMT ceramic shows potential applicability for dielectric
energy storage ceramics. Simultaneously, the composition-design concept
in the system provides a good reference for the further development
of ceramic dielectric capacitors.
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