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Liu et al. Microstructures 2023;3:2023009 https://dx.doi.org/10.20517/microstructures.2022.29 Page 5 of 11

polarization saturation process under a low electric field and reduce the possibility of electromechanical
breakdown generated by the electrostriction effect. These phenomena indicate that 0.85NN-0.15CZ ceramic
shows excellent potential to become a high energy storage material.

Another basic guarantee for realizing high energy storage properties is the uniform and compact
microstructure. As shown in Figure 1D, the surface morphology of 0.85NN-0.15CZ ceramic presents a
dense microstructure with few pores. A uniform grain size distribution can be found in 0.85NN-0.15CZ
ceramic with a smaller average grain size (G ) of ~2.1 μm compared with that of pure NN ceramic shown in
a
Supplementary Figure 2. Moreover, the uniform distribution of elements in Supplementary Figure 3
suggests the achievement of a pure phase structure. It is believed that good sample quality, along with small
grain size and dense structure, is beneficial to strengthening E .
b

Even though a superparaelectric state for the 0.85NN-0.15CZ ceramic can be easily identified by using
dielectric spectra, however, it is widely known that there are several different paraelectric states as well as
(anti)ferroelectric states in NN ceramics at different temperature ranges. To analyze the phase structure of
0.85NN-0.15CZ ceramic, as shown in Figure 2A and B, high-energy SXRD and powder neutron diffraction
data were collected and refined. Together with the EDS images shown in Supplementary Figure 3, the
sample should certainly be a pure perovskite phase. Moreover, apparent non-cubic phase structure can be
identified for 0.85NN-0.15CZ ceramic according to the split main diffraction peaks and superlattice
diffraction peaks. This feature is quite different from the average structure characteristics of traditional
superparaelectrics [15,16] , indicating the existence of lattice distortion. The lattice distortion in
(anti)ferroelectrics mainly includes oxygen octahedron tilt and cation off-centering displacement.
Considering the macro nonpolar feature of superparaelectrics, the lattice distortion in the studied sample
should be attributed to the oxygen octahedron tilt. As the insensitive response of X-ray to the oxygen ions,
powder neutron diffraction was measured. Rietveld refinement using the model with P2 ma space group
1
was taken simultaneously on the SXRD and neutron diffractions, and the satisfying results with low-
reliability factors of weighted patterns (R ) are shown in Figure 2A and B. To convince the best refinement
wp
result, Rietveld refinement of SXRD data using the model with cubic space group of Pm-3m was also carried
out in Supplementary Figure 4. It can be found that the 0.85NN-0.15CZ ceramic should be a ferroelectric Q
phase with P2 ma space group and a b c oxygen octahedron tilt system but small polarization displacement,
- + -
1
- - -
which is different from that of NN ceramic (P phase: a b c /a b c ). According to Glazer notation, the
- + -
superscripts +, -, and 0 represent in-phase tilt, anti-phase tilt, and no tilt of oxygen octahedral along one
[32]
axis, respectively . The tilt degree of oxygen octahedron can be calculated using ω = (180°- B-O-B)/2. As
shown in Supplementary Figure 5, the oxygen octahedron tilt degree for NN ceramics with Pbcm space
group at room temperature is calculated as ~7.9°-13.15°. According to the lattice parameters obtained from
the refinement results of SXRD and powder neutron diffraction, the crystal structure model of 0.85NN-
0.15CZ ceramic was drawn and displayed in Figure 2C. A large oxygen octahedron tilt of ~10.89°-12.20°
can be calculated according to the B-O1-B ~157.55°, B-O2-B ~156.61°, B-O3-B ~155.61°, and B-O4-B
~158.22°, which is much larger than that of traditional relaxor ferroelectrics such as Pb(Mg Nb )O and
1/3
3
2/3
Ba(Ti, Zr)O . That is to say, the relaxor ferroelectric Q phase can be identified in 0.85NN-0.15CZ ceramic,
3
which is quite different from the previously reported results that the addition of CZ would stabilize
antiferroelectric P phase in NN ceramic [33-35] . The decreased tolerance factor after doping CZ into NN
ceramic would increase the oxygen octahedron tilt. However, according to the statistics of recently reported
antiferroelectrics (NN, AgNbO , (Bi Na )TiO -based, BiFeO -based, PbZrO , and PbHfO -based
3
3
3
0.5
3
0.5
3
ceramics), it can be found that the antiferroelectric phase only exists in a narrow tolerance factor range. The
perovskites with ultralow tolerance factor are usually paraelectrics, such as CaZrO and CaHfO . Therefore,
3
3
the polarization ordering would be destroyed when the amount of CZ is over a critical value, leading to the