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• The doping of SSN increased the band gap width and decreased the grain size. • The ceramic possesses an energy density of 4.42 J/cm3 and an efficiency of 60%. • The transmittance of the ceramic is 76.7% and 84.5% at 780 and 1378 nm, respectively. • 0.825KNN-0.175SSN ceramic exhibited a small strain effect of 0.022%. Lead-free transparent ferroelectric ceramics with superior energy storage properties are highly desirable for pulsed power technologies and the increased optical transparency demand. However, the transparency and energy storage density of lead-free bulk ceramics cannot meet the requirements of their wide applications due to the coarse microstructure and relatively low breakdown strength. In this study, a design strategy is proposed to optimize the energy storage characteristics and transparency of ceramics by introducing nanodomains, increasing the band gap energy and reducing the grain size. The results showed that submicron grain (0.21 μm) and large band gap energy (E g = 3.21 eV) were achieved through the introduction of the second component Sr(Sc 0.5 Nb 0.5)O 3 (SSN). An excellent transparency of up to 84.5% in the near-infrared region (1378 nm), a high energy density (W) of ~4.42 J·cm−3 and an extremely small strain of ~0.022% were simultaneously achieved in the 0.825(K 0.5 Na 0.5)NbO 3 -0.175Sr(Sc 0.5 Nb 0.5)O 3 (0.825KNN-0.175SSN) ceramics. These results revealed the potential applications of (K 0.5 Na 0.5)NbO 3 -based ceramics for energy storage and provide a feasible approach of domain engineering to develop new lead-free energy storage transparency materials. [ABSTRACT FROM AUTHOR]

• An ultrahigh W rec of 5.4 J/cm3 and a relatively high η of 66% were achieved. • Wide E g and suppression of oxygen vacancy result in an improved E b. • Good thermal stability with W rec and η over a wide temperature range. Lead-free silver niobate (AgNbO 3 , AN)-based dielectric ceramics have attracted intense attention for high-power energy storage applications since 2016 due to their electric-field-assisted antiferroelectric-ferroelectric phase transition. In this work, chemical compositions of 0.2 wt.% Mn-doped (1- x)AgNbO 3 - x Ca(Hf 0.2 Ti 0.8)O 3 (AN-CHT x , x = 0.00–0.08) were designed and their ceramic samples were prepared in flowing oxygen via solid-state route. Our results show that the CHT modification not only enhance the antiferroelectricity stability but also the breakdown field (E b). Further investigation reveals that the wider band gap (E g) and suppression of oxygen vacancy play more important role in increasing E b of AN-CHT x ceramics. Consequently, an ultrahigh recoverable energy density (W rec) of 5.4 J/cm3 together with a relatively high energy conversion efficiency (η) of 66% is achieved under an electric field of 300 kV/cm in AN-CHT0.06 ceramics. Meanwhile, this ceramic also exhibits a good thermal stability with W rec (4.5 J/cm3) and η (69%) over a wide temperature range (25–120 °C) under external electric field of 280 kV/cm. The finding in present work indicates that modulating the band structure and oxygen vacancy of AN-based ceramics may lead to the discovery of new antiferroelectric materials with pronounced energy storage properties. [ABSTRACT FROM AUTHOR]

• BMN modified BCZT exhibits higher polarization and breakdown strength. • 0.925BCZT-0.025BMN ceramic possesses a high energy density and efficiency. • Excellent temperature and frequency stability of energy density have been achieved. • Domain engineering on the nanoscale was designed and observed in the ceramics. The improvement of energy density and efficiency is currently the main challenge in the application of lead-free dielectric energy-storage materials. Relaxor ferroelectric ceramics are the most commonly selected materials for pulsed power capacitors because of their inherent advantages, such as ultra-high power density, fast charging/discharging, and long lifetime. In this study, BiMg 2/3 Nb 1/3 O 3 (BMN) was doped to enhance energy density and efficiency in the (1− x)Ba 0.85 Ca 0.15 Zr 0.1 Ti 0.9 O 3 - x BiMg 2/3 Nb 1/3 O 3 systems based on the adjusted breakdown strength and polarization. As a result, a giant recoverable energy density of 3.81 J/cm3 and a high energy efficiency of 90.5% were simultaneously achieved in the 0.925BCZT-0.075BMN ceramic, which the energy density is 26 times as large as that of BCZT ceramic. Excellent temperature (−25 to 100 °C) and frequency (1–100 Hz) stability of recoverable energy density and energy efficiency were confirmed with the fluctuations below 4.5%. Domain engineering on the nanoscale was designed in relaxor ferroelectrics, which effectively improved the energy storage performance. Our study provides a feasible guideline to develop lead-free ceramics for electrical energy storage applications. [ABSTRACT FROM AUTHOR]