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Page 2 of 11 Zhao et al. Microstructures 2023;3:2023002 https://dx.doi.org/10.20517/microstructures.2022.21

INTRODUCTION
Dielectric capacitors, as fundamental components in high-power energy storage and pulsed power systems,
play an important role in many applications, including hybrid electric vehicles, portable electronics, medical
devices and electromagnetic weapons, due to their high power density, ultrafast charge-discharge rates and
[1-6]
long lifetimes . However, most current commercial polymer dielectric capacitors and multilayer ceramic
-3
capacitors (MLCCs) possess somewhat low energy densities of < 1-2 J cm , which results in them occupying
relatively large volumes and/or weights in devices [7-10] . The development of third-generation semiconductors
and the need for device miniaturization have resulted in an urgent demand for high-energy-density
dielectric capacitors [1,11] .

Under an applied voltage, the dielectric materials in dielectric capacitors polarize to store energy [1,12,13] . Their
energy storage properties can be calculated through polarization-electric field (P-E) loops, namely,
, and η = W /W , where W and W are the charge and discharge energy density,
d
d
c
c
respectively, P and P are the maximum and remnant polarization, respectively, and η is the energy
r
max
efficiency [14-16] . Among all dielectric materials, relaxor ferroelectrics with high P , low P , high breakdown
r
max
strength (E ) and slim P-E loops have been investigated extensively for their excellent energy storage
b
properties [17-22] . The polar nanoregions in relaxor ferroelectrics can switch rapidly under an applied electric
[23-28]
field, which significantly reduces loss and results in high η . In addition, the excellent fatigue and
temperature stability of the pulsed discharge behavior and energy storage properties are highly desirable for
dielectric capacitors operating in harsh environments, i.e., aerospace fields and oil-well drilling [29-32] . Many
strategies have been utilized to enhance the temperature stability of dielectric materials in recent years,
[27]
including multiscale optimization , composite strategy design , unmatched temperature range design
[28]
[33]
[34]
and special sintering methods . However, the temperature stability of pulsed discharge behavior is not
given sufficient attention in current research into dielectric materials.
In this study, we prepare nanograined (1-x)BaTiO -xNaNbO ceramics, which possess relaxor ferroelectric
3
3
characteristics with a good P-E relationship (high P , low P and slim P-E loops) and high E , using a solid-
r
max
b
state reaction method. The 0.60BaTiO -0.40NaNbO ceramics exhibit an optimal W of 3.07 J cm and a
-3
3
d
3
high η of 92.6% under 38.1 MV m at ambient temperature. Stable energy storage properties in terms of
-1
frequency (0.1-100 Hz), fatigue (10 cycles) and temperature (25-120 °C) are also achieved. Moreover, the
6
ceramics possess an ultrafast discharge rate of 39 ns and a high power density of 100 MW cm . The
-3
variation of the power density is less than 15% from 25 to 140 °C. All these results suggest that 0.60BaTiO 3
-0.40NaNbO ceramics are ideal candidates for energy storage applications in pulsed power systems.
3
MATERIALS AND METHODS
(1-x)BaTiO NaNbO ((1-x)BT-xNN) dielectric ceramics with x = 0.35, 0.40, 0.45 and 0.50 were prepared
3-x
3
through a conventional solid-state method. According to the stoichiometric ratio of (1-x)BT-xNN ceramics,
BaCO , TiO , Na CO and Nb O powders with analytical grade, as the raw materials, were weighed and ball
2
2
5
3
2
3
milled with ethanol for 24 h. The mixed powders were then dried at 80 °C and calcined at 950-1030 °C for
5 h in the closed alumina crucibles to avoid the volatilization of Na. Afterward, the calcined (1-x)BT-xNN
powders were ground with a polyvinyl butyraldehyde solution (PVB, 10 wt.%) and uniaxially pressed into
cylinders with a diameter of 8 mm and a thickness of 0.5 mm under a pressure of 2 MPa. The cylinders were
heated at 600 °C for 5 h to remove the PVB binder and then sintered with a two-step sintering method [35,36]
(all samples were heated to 1250-1350 °C for 1-10 min and then cooled down to 1100-1150 °C for 3-5 h).