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Xu et al. Microstructures 2023;3:2023034 https://dx.doi.org/10.20517/microstructures.2023.19 Page 3 of 13

RESULTS AND DISCUSSION
The X-Ray diffraction analysis (XRD) patterns of the NN-SMZ ceramics are shown in Figure 1A. Enlarging
the characteristic peak clearly shows that with the addition of SMZ, the (200) characteristic peak shifts to a
lower angle, indicating that the sample lattice has expanded [13,14] . After doping with SMZ, Sm (1.24 Å)
3+
2+
+
4+
partially replaces Na (1.39 Å) at the A site, and Mg (0.72 Å) and Zr (0.72 Å) replace the smaller Nb 5+
(0.64 Å) at the B site . The results show that the lattice expansion of the sample was mainly affected by the
[15]
2+
introduction of Mg and Zr at the B site . To explore the reason for this phenomenon, the NN-SMZ
[7]
4+

c o m p o n e n t s a m p l e s w e r e r e f i n e d . T h e r e f i n e d r e s u l t s a r e s h o w n i n Figure 1B-E a n d
Supplementary Figure 1. The NaNbO ceramic exhibited an orthorhombic phase at room temperature; with
3
the increase in SMZ doping, the sample gradually changed from the orthorhombic phase (Pnma) to the
pseudocubic phase (Pm3m). When x = 0.05 and 0.08, the sample exhibited a two-phase coexistence
phenomenon. Supplementary Figure 2 shows the refinement results for the NN-SMZ at 35°-45°. The
refinement result for the sample was good. As the sample gradually changed to the pseudocubic phase, the
intensity of the superlattice diffraction peak gradually decreased.
The Raman spectra of each component sample are shown in Figure 2A. The gradually widened peak width
and gradually decreased peak intensity indicate that the complexity of the sample and the disorder of ions
increased owing to the nonequivalent substitution of ions with different radii at the A and B sites [16,17] . To
study further the effect of adding SMZ to the system, Peakfit software was used to analyze the Raman
spectra of each component sample. The center position, peak intensity, and peak half-width of the vibration
modes v and v fitted by each Raman component are shown in Figure 2B and C. With an increase in the
5
1
SMZ content, the peak intensities of vibration modes v and v gradually decreased, and the half-width and
5
1
height gradually increased, which proved that the complexity of the sample and the disorder of the ions
increased. The vibration mode v moved to a high-wavenumber position, and a blue shift occurred. The red
5
shift of the vibration mode v may be caused by the phase transition of the sample, which corresponds to the
1
XRD refinement results in this study .
[18]
Scanning electron microscopy (SEM) images of the NN-SMZ components under the natural surface and the
average grain size fitted by the Gaussian function are shown in Figure 3A. The surfaces of the NN-SMZ
ceramic component samples were dense and had no obvious defects, and the average grain size generally
increased. The grain sizes of 0.08 SMZ and 0.12 SMZ significantly increased. According to the XRD
refinement results, the appearance of the pseudo-cubic phase is one reason for this phenomenon. According
−1/2
to the formula E ∝G , the grain size (G) is negatively correlated with the breakdown field strength (E ).
b
b
The grain size of each component is smaller than that of pure NaNbO (generally tens of micrometers) [19,20] ,
3
[21]
which helps the samples obtain a higher E . The energy dispersive spectrometry (EDS) mapping of the
b
0.08 SMZ ceramic is shown in Figure 3B. Each element was uniformly distributed without enrichment,
[22]
indicating that the SMZ was uniformly dissolved in the NN lattice . An atomic force microscopy analysis
was performed on the samples after hot corrosion. The test results are shown in Supplementary Figure 3.
The surface of each component sample was dense, without obvious pores or defects. The sintering densities
of the NN-SMZ samples are shown in Supplementary Table 2. The incorporation of the SMZ reduced the
sintering temperature, improved the density of the ceramics, and helped the samples obtain a higher
breakdown field strength.
A Transmission Electron Microscope test can effectively observe the domain morphology and phase
structure of FE materials. The domain morphology of pure NaNbO ceramics is shown in Figure 4A and
3
clearly shows the existence of a 180° domain. The domain morphology of the 0.08 SMZ sample is shown in
Figure 4B, and the larger domain cannot be clearly observed, which is related to the gradual transition of the