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Page 6 of 11 Liu et al. Microstructures 2023;3:2023009 https://dx.doi.org/10.20517/microstructures.2022.29

Figure 2. (A) High-energy synchrotron XRD, and (B) powder neutron diffraction structure refinement patterns of 0.85NN-0.15CZ
Ceramic. (C) Schematic diagram of the large antiferrodistortion in 0.85NN-0.15CZ ceramic.

disappearance of anti-phase tilt modules along b axis. Moreover, the formation of dielectric relaxation
behavior would also destroy the long-range polarization ordering. As a result, a superparaelectric state with
large antiferrodistortion can be detected in 0.85NN-0.15CZ ceramic at room temperature.

TEM is an essential and helpful method to characterize the domain morphology and lattice microstructure
for ferroelectric materials. Figure 3A suggests that 0.85NN-0.15CZ ceramic exhibits apparent 90° and 180°
microdomains. Figure 3B and C display high-resolution TEM lattice fringe images along [100] and [111]
c
c
directions, respectively, demonstrating good sample quality. Figure 3D and E show the SAED image along
[100] and [111] directions, respectively, which once again confirm that 0.85NN-0.15CZ ceramic should be
c
c
pure perovskite structure. It is recognized that the 1/2 types of superlattice diffractions of (ooe)/2 and
(ooo)/2 (o and e are odd and even, respectively) are mainly related to the in-phase and anti-phase oxygen
[32]
octahedron tilt, respectively . Therefore, the 1/2 type superlattice diffraction spots observed in the
accordingly SAED images further prove the existence of oxygen octahedral distortion. It is widely accepted
that normal ferroelectrics with macrodomains exhibit poor energy storage properties ascribed to the large
polarization hysteresis along with irreversible domain switching, which occurs together with polarization
reorientation. However, there is no macroscopic polarization alignment in this superparaelectric sample,
which could be further directly confirmed by the quantitative analysis of the polarization mapping using
HAADF-STEM results, as shown in Figure 4. Therefore, these macrodomains should be ferroelastic
domains constructed by the ordered oxygen octahedron tilt, and the domain switching process has very
little influence on polarization reorientation. According to the polarization mapping, ultrasmall PNRs with
a size of about 2-3 nm can be seen, which is at the same level as other superparaelectrics. Namely, fast
response of PNRs with little polarization hysteresis during charging and discharging processes can also be
expected for this sample, benefiting excellent energy storage properties. Moreover, large antiferrodistortion
would also delay the polarization saturation process, which would also favor the energy storage properties.

Due to the irreversible phase transition from antiferroelectric to ferroelectric under electric fields for pure
NN ceramic, a square P-E loop with poor energy storage properties can be achieved, as shown in
Supplementary Figure 6. With the stabilization of antiferroelectric P phase by adding a small content of
[35]
CZ , even though increased energy storage density can be obtained along with the appearance of