Page 28 - Read Online

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

The ambient-temperature X-ray diffraction profiles of the (1-x)BT-xNN ceramics were obtained using a
Rigaku 2500 X-ray diffractometer (Rigaku, Tokyo, Japan) with Cu Kα radiation and λ = 1.5418 Å. The
surface microstructures of the ceramics after thermally etching at 1050 °C for 0.5 h were characterized using
scanning electron microscopy (SEM, MERLIN VP Compact, Zeiss Ltd., Germany) at 15 kV. To measure the
ferroelectric properties and pulsed discharge behaviors, the compact ceramics were polished down to
180-200 µm in thickness and then gold electrodes with a radius of 1.5 mm were sputtered on both surfaces.
The P-E loops were measured using a TF ANALYZER 2000E ferroelectric measurement system (aixACCT
Systems GmbH, Aachen, Germany) under different frequencies (0.1-100 Hz) and various temperatures
(25-140 °C). The dielectric properties were measured under a frequency range of 1 kHz to 1 MHz and a
temperature range of -150 to 300 °C using an impedance analyzer (E4980A, Agilent Technologies, USA).
The overdamped and underdamped pulsed discharge behavior was measured using a charge-discharge
platform (CFD-001, Gogo Instruments Technology, Shanghai, China) with a resistor-capacitance load
circuit. More details regarding the resistor-capacitance circuit measurement system are given in
Supplementary Figure 1.

RESULTS AND DISCUSSION
The ambient-temperature X-ray diffraction profiles of the (1-x)BT-xNN ceramics are displayed in Figure 1.
All samples exhibit typical perovskite structures with traces of a Ba Ti Nb O secondary phase
7
6
9
42
(PDF#47-0522). The approximate amounts of Ba Ti Nb O phases are displayed in Supplementary Table 1
9
42
6
7
and are less than 5% in all (1-x)BT-xNN ceramics. The (200) peaks between 45° and 46° without splitting
suggest that all samples are mainly pseudocubic phases at room temperature. The cell parameters of
(1-x)BT-xNN ceramics decrease with increasing NN content [Supplementary Table 2], which is mainly
2+
+
because the radius of Na (1.39 Å) is smaller than that of Ba (1.61 Å). The SEM images of the surface and
cross-section microstructures of the (1-x)BT-xNN ceramics are displayed in Figure 2 and Supplementary
Figure 2. There are no obvious pores in the (1-x)BT-xNN ceramics, suggesting that all samples possess high
relative density. The grain size distributions [Supplementary Figure 3] are counted by the Feret diameters of
more than 250 grains from the SEM images, and they show that all the ceramics possess nanograins with
average grain sizes of 180-280 nm. The grain size tends to increase with NN content and the distribution
moves toward larger sizes. Generally, fine grains are conducive to achieving high E and η. The elemental
b
distribution results of the 0.60BT-0.40NN ceramics are shown in Supplementary Figure 4, where it can be
seen that all the elements are uniformly distributed in the ceramics.
The temperature-dependent (150-300 °C) dielectric properties of the (1-x)BT-xNN ceramics were measured
at various frequencies [Figure 3] and indicated prototypical relaxor ferroelectric characteristics. The
dielectric constants of all the (1-x)BT-xNN ceramics at room temperature are ~1000-1200 and the
Ba Ti Nb O phases are considered to have paraelectric characteristics. Hence, the Ba Ti Nb O phases may
9
42
6
7
9
42
7
6
not significantly affect the dielectric characteristics of the ceramics. It can be found that the dielectric
constant and the Curie temperature increase with increasing NN content. All the (1-x)BT-xNN ceramics
exhibit low dielectric loss of less than 0.012 between -100 and 200 °C. Generally, the modified Curie-Weiss
law, 1/ε – 1/ε = (T - T ) /C, is utilized to describe the dielectric characteristics of relaxor ferroelectrics,
γ
m
m
where ε and ε are the dielectric constant and maximum value of ε, respectively, T and T are the
m
m
corresponding temperatures, C is the Curie constant and γ is used to describe the degree of diffuseness. The
γ value varies from one for typical ferroelectrics to two for ideal relaxor ferroelectrics [24,37] . The fitted γ values
of all the ceramics are shown in Figure 4 and are between 1.686 and 1.766 at 1 MHz, thereby manifesting
strong relaxation behavior. This strong relaxation behavior causes the (1-x)BT-xNN ceramics to respond
rapidly under an applied electric field, resulting in high η.