High energy storage performance in Ca-doped PbZrO3 antiferroelectric films

Journal Pre-proof High energy storage performance in Ca-doped PbZrO3 antiferroelectric films Yi Zhuo Li, Zhan Jie Wang, Yu Bai, Zhi Dong Zhang

PII:

S0955-2219(19)30808-8

DOI:

https://doi.org/10.1016/j.jeurceramsoc.2019.11.063

Reference:

JECS 12888

To appear in:

Journal of the European Ceramic Society

Received Date:

25 August 2019

Revised Date:

19 November 2019

Accepted Date:

21 November 2019

Please cite this article as: Li YZ, Wang ZJ, Bai Y, Zhang ZD, High energy storage performance in Ca-doped PbZrO3 antiferroelectric films, Journal of the European Ceramic Society (2019), doi: https://doi.org/10.1016/j.jeurceramsoc.2019.11.063

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High energy storage performance in Ca-doped PbZrO3 antiferroelectric films Yi Zhuo Li1, 2, Zhan Jie Wang1, 2, 3,*, Yu Bai3, Zhi Dong Zhang1, 2

1

Shenyang National Laboratory for Materials Science, Institute of Metal Research,

Chinese Academy of Sciences, Shenyang 110016, China 2

School of Materials Science and Engineering, University of Science and Technology of

3

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China, Shenyang 110016, China School of Materials Science and Engineering, Shenyang University of Technology,

Shenyang110870, China

author; E-mail: [email protected] or [email protected]

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†Corresponding

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Abstract

In this work, antiferroelectric Pb1-xCaxZrO3 (PCZ) thin films with different concentrations of

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Ca2+ were prepared by chemical solution deposition, and the effects of Ca2+ concentration on the antiferroelectric properties and energy storage performance were investigated. The results

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show that the optimal Ca2+ concentration in the PCZ thin films is x = 0.12 for electric properties and energy storage performance. The recoverable energy storage density and energy storage efficiency is 50.2 J/cm3 and 83.1% at 2800 kV/cm, which is 261% and 44.8%

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higher than those of the PbZrO3 (PZ) films. These effects are attributed to the enhancement of stability of antiferroelectric phase, diffused degree in the field-induced phase transition and

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electric breakdown strength by Ca2+-doping in the PZ films. Our results demonstrate that doping an appropriate amount of Ca2+ ions in antiferroelectric thin films is an effective way to improve their energy storage performance. Keywords: lead zirconate, Ca2+ doping, electric breakdown strength, diffused phase transition, recoverable energy storage

1

1. INTRODUCTION With the rapid development of sustainable electricity, a great deal of attention has been paid today to the research of energy storage by using dielectric materials because of their very high charging and discharging rates.[1-3] Recently, the energy storage properties of dielectric materials can be gradually improved by improving the polarization intensity and electric breakdown strength and other ways, so that they can be better applied in the field of solid

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state energy storage.[4-6] In particular, antiferroelectric materials, as a typical dielectric material, have been gradually stressed in the field of high-density energy storage because they can possess a higher energy storage density during the antiferroelectric-ferroelectric (AFE-FE)

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phase transition.[7-10]

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As shown in Fig. 1, the recoverable energy storage density (Wrec) of AFE materials is equal to the area between the polarization–electric field (P–E) hysteresis loop and the Y axis

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and could be calculated by the following formula:[11-12]

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(1)

where E is the applied field, Pmax is the maximum polarization, and Pr is the remnant

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polarization. The energy storage efficiency (η) can be calculated by the following equation: (2)

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where Wloss is the energy loss density that can be calculated by the numerical integration of closed area of the P–E hysteresis loop. Based on the above definition, the Wrec and η of the AFE materials can be mainly improved by increasing the maximum polarization (Pmax), the behavior of field-induced phase transition between AFE and FE phases, and the electric breakdown strength (EBDS). PbZrO3 (PZ) as a typical AFE material has been widely studied 2

for high-density energy storage.[13-15] The Wrec of epitaxial PZ films can be increased by controlling the crystal orientation to improve the Pmax.[16] Moreover, the addition of Au nanoparticles into PZ films can improve the Pmax and the diffuse behavior of AFE-FE phase transition,

thereby

double-heterojunction

enhancing

the

Wrec

and

η.[17] By constructing

ferroelectricity–insulator–ferroelectricity

an

configuration

opposite of

the

PZT/Al2O3/PZT thin film, the EBDS can be improved and therefore enhance the energy storage

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performance.[5] In addition, the energy storage performance of the PZ and PZ-based AFE films can also be improved by controlling the microstructures[13] and by organic-inorganic combination.[14]

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Recent studies have found that the ionic doping is one of the effective and simple

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methods to improve energy storage performance. For example, the Wrec and η could be enhanced through the doping of La3+, Y3+, Eu2+, Ba2+ and Sr2+ at the Pb2+ site, and Ti4+ and

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Sn4+ at the Zr4+ site in the PZ lattice.[18-24] The effect of cation doping on the phase transition

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behavior of ABO3 perovskite in antiferroelectric materials generally conforms to the law of tolerance factor, which can be calculated as follow:[25]

ur

(3)

where rA, rB, and rO represent the radius of A, B, and oxygen ion, respectively. When the

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radius of doped ions is less than that of the original A-site ions or larger than that of the original B-site ions, the AFE phase is stabilized. Conversely, the ferroelectric phase is more stable. For example, because the ion radius of Ba2+ (1.35 Å) is larger, and the ion radius of Sr2+ (1.12 Å) is smaller than that of Pb2+ (1.20 Å),[26] the t value is increased in the Ba-doped PZ film and decreased in the Sr-doped PZ film, respectively. Therefore, the AFE phase is 3

stabilized for (Pb,Sr)ZrO3 and the FE phase is stabilized for (Pb,Ba)ZrO3.[27] Similarly, Sr-doped (Pb,La)(Zr,Sn,Ti)O3 ceramics have better energy storage performance because of the more stable AFE phase.[22] It is well known that Ca, Sr and Ba belong to the same main group elements, and the ionic radius of Ca is smaller than that of the latter two elements. According to the law of tolerance factor, when the tolerance factor t is in the range of 0.75~1, the perovskite structure can remain stable under the condition that the radius of A-site ion is

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greater than 0.9 Å and B-site ion is greater than 0.51 Å. [28] If Ca2+ is doped into the perovskite phase of PZ at a suitable concentration, the range of tolerance factor can satisfy the condition of forming stable perovskite structure because the radii of Ca and Zr ions are 0.99 Å and 0.80

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Å, respectively. Therefore, according to the law of tolerance factor, Ca-doped PZ should have

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more stable AFE phase due to the relatively small ion radius of Ca, so it is possible to obtain greater energy storage performance by adjusting the behavior of field-induced phase

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transition.

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In addition, it is also notable that doping appropriate Sr2+ into the (Pb,La)(Zr,Sn,Ti)O3 antiferroelectric ceramics can effectively enhance the diffused degree of the phase

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transition.[22] The similar phenomenon also exists in Ba-doped PZ films.[19] Generally, the composition fluctuation caused by doping at A or B sites will lead to the diffused phase

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transition, which can effectively improve the energy storage performance. So it is also possible that Ca2+ doping may induce the diffused phase transition caused by the composition fluctuation while stabilizing the antiferroelectric phase. Therefore, energy storage performance of PZ antiferroelectric thin films may be improved by doping moderate Ca2+. In this study, Ca2+-doped PZ antiferroelectric thin films are prepared by chemical 4

solution deposition (CSD), and the effects of Ca2+ concentration on the antiferroelectric properties and the energy storage performance are systematically studied. The experimental results show that the Wrec and η of the 300-nm-thick Pb1-xCaxZrO3 films with x = 0.12 are 50.2 J/cm3 and 83.1% at 2800 kV/cm, which are higher than those of the PZ thin film by 261% and 44.8%, respectively. The large enhancement in energy storage performance can be attributed to the stable AFE phase, the diffuse behavior in the field-induced AFE-FE phase

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transition and the increased EBDS. Our results demonstrate that doping an appropriate amount of the ions with smaller ion radius into antiferroelectric thin films is an effective way to

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improve antiferroelectric properties and energy storage performance.

2. EXPERIMENTAL PROCEDURE

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Pb1-xCaxZrO3 (PCZ, x = 0, 0.04, 0.08, 0.12, 0.16) thin films with a thickness of about

High-purity

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300 nm were fabricated on Pt/Ti/SiO2/Si substrates by chemical solution deposition (CSD). Pb(CH3COO)2·3H2O,

Ca(NO3)2·4H2O

and

zirconium-n-propoxide

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(Zr(OCH2CH2CH3)4) were used as starting raw materials in the preparation of the PCZ solutions, and 2-methoxyethanol was used as solvent. First, 3.6599, 3.5133, 3.3669, 3.2206

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and 3.0742 grams of Pb(CH3COO)2·3H2O (99.5%) and 0, 0.0573, 0.1147, 0.1720 and 0.2293

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grams of Ca(NO3)2·4H2O (99%) were dissolved in 2-methoxyethanol in proportion at 120°C for 60 min, respectively. A 20% excess of lead was added to the solvent to compensate for lead loss and to prevent the formation of pyrochlore phase in the film during annealing. And then 3.7436 grams of zirconium-n-propoxide (Zr(OCH2CH2CH3)4) was added into the above solution when it cooled down to room temperature. After stirring for 120 min, the concentration of the solution was adjusted to 0.2 mol/L by adding 2-methoxyethanol to 40mL. 5

After 24 hours of aging, the PCZ precursor solutions were coated on Pt/Ti/SiO2/Si substrates via a multiple-spin-coating procedure. Each PCZ layer was spin coated at 3000 rpm for 30 s and pyrolyzed in an electric furnace at 450 °C for 5 min. To obtain the PCZ thin films with the designed thickness, the steps mentioned above were repeated several times. To prevent Pb loss during the final heat treatment, the 0.4 M PbO precursor solution was deposited on the PCZ thin films at 3000 rpm for 30s as a capping layer,[29-30] and then the PCZ thin films were

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annealed by rapid thermal annealing (RTA) at 650°C for 3 min.

The crystalline structure of PCZ films were analyzed by X-ray diffraction (XRD, Rigaku RINT2000, Cu Kα radiation). The microstructures of the PCZ films were studied by

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transmission electron microscopy (TEM, Tecnai G2F20). The surface morphology was

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investigated by scanning electron microscopy (FE-SEM; Supra 55, Ziess, Germany). The temperature-dependent dielectric properties of the PCZ films were measured using a

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computer-controlled Agilent E4980A LCR analyzer. The P–E hysteresis loop was measured at

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1 kHz and room temperature using a standard ferroelectric testing system (TF2000E; Aixacct).

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3. RESULTS AND DISCUSSION

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Fig. 2(a) shows XRD patterns of the PCZ films with different Ca2+ concentrations. All the PCZ films have crystallized into the perovskite phase without any second phase and display a (111)-preferred orientation. When Ca2+ concentration is equal to or greater than 12%, the (111) diffraction peak of PCZ thin films decreases, while (110) diffraction peak increases gradually. This is presumably caused by the different ionic radius between Pb2+ (1.20 Å) and Ca2+ (1.00 Å). The difference in ionic radius results in the change of crystallization energy of 6

the films along (111) orientation, which is similar to the results of the Sr-doped PbZrO3 thin films.[23] As shown in the Fig. 2(b), (111)-diffraction peak moves toward high diffraction angles with the increasing of Ca2+ concentrations, indicating that Ca2+ ions enter the PZ lattices, which results in the decrease of out-of-plane lattice constant of PZ perovskite phase. In the Pb1-xCaxZrO3 films, the tolerance factor for all doping concentrations is ranging from 0.77 to 0.84, which meets the conditions (0.75  t  1) to form the stable perovskite structure.

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According to the law of tolerance factor, the t value decreases with the increase of Ca2+ doping concentration, which may lead to more stable AFE phase, thus improving the energy storage performance of the PCZ films.

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Fig. 3(a)–(e) shows the difference in surface morphologies of the PCZ films with

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different Ca2+ concentrations. Polygonal grains of the perovskite phase can be observed clearly. The insets in Fig. 3(a)–(e) exhibit the distribution of grain size of the perovskite phase

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in the corresponding PCZ film, which were calculated from 50 grains using Nano

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Measurement software. Fig. 3(f) shows that the average grain sizes of Pb1-xCaxZrO3 films are 129.4, 110.3, 113.3, 122.4 and 110.5 nm for x = 0, 0.04, 0.08, 0.12 and 0.16, respectively.

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Although the average grain size does not change very much, the distribution of grain size becomes more concentrated with the increase of Ca2+ doping concentration. In addition, the

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densification of the films has been significantly improved with the increasing of Ca2+ concentration, as shown in Fig. 3(a)–(e), which is consistent with the results of Ca-doped La0.46Sm0.21Sr0.33-xCaxMnO3 ceramics.[31] The increase in the densification of the PCZ films may improve the EBDS and consequently the energy storage performance of the PCZ films. Moreover, the cross-sectional images of the PCZ films with different Ca2+ concentrations are 7

shown in Fig. 3(g)-(k). It can be seen that all the films show a columnar grain structure with the same thickness of about 300 nm. Fig. 4(a) shows the planar view of TEM for the Pb0.84Ca0.16ZrO3 film. The grain distribution is uniform and dense in the film. Fig. 4(b) shows the EDS results for t

Year;

he

elemental distribution of Pb, Ca, Zr and O in the selected area shown in Fig. 4(a). The Ca2+ is uniformly distributed in the film, and there is no segregation at the grain boundary. Fig. 4(c)

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shows a high-resolution TEM image of the area marked with a box in Fig. 4(a). Fig. 4(d) shows the Fast Fourier Transform (FFT) patterns transformed from the HRTEM image marked with a box in Fig. 4(c). It can be confirmed that the Pb0.84Ca0.16ZrO3 film crystallized

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into the perovskite phase and the d-spacing of (110) planes is 2.926 Å, which is consistent

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with the XRD result of 2.923 Å. It is noteworthy that the grain boundary is clear and there is no second phase or void. The results show that when the doping concentration reaches 16%,

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affected significantly.

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the preferred orientation of the films changes to some extent, but the crystal quality is not

Fig. 5(a) shows P-E hysteresis loops of the PCZ films with different Ca2+ concentrations

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measured at 10 kHz and room temperature. All the PCZ films display a well developed double hysteresis loop. The remanent polarization of all PCZ films is roughly the same and

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relatively small, which means that the crystalline quality of the PCZ film is relatively high. The maximum polarization (Pmax) decreases evidently with increasing Ca2+ concentration. This variation trend of the Pmax with Ca2+ doping concentration can be observed more intuitively in the inset of Fig. 5(a). Generally, under zero electric field, the polar direction of the antiparallel dipoles is along the [110] direction of the original tetragonal cell. When the 8

electric field is high enough to switch the AFE phase into the FE phase, the original tetragonal cell becomes rhombohedral with the polar directions along the [111] direction.[16, 32] Therefore, the saturation polarization of films decreases with the increase of Ca2+ concentration, because the degree of (111)-preferred orientation decreases with the increase of Ca2+ concentration (as shown in Fig. 2(a)). Moreover, as shown in Fig. 5(a), the maximum voltage that can be loaded on the film gradually increases with the increase of Ca2+ concentration during the test, which

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means that the electric breakdown strength (EBDS) of the PCZ films enhances with the increase of Ca2+ concentration. The EBDS is one of the important factors to obtain high energy storage performance. The characteristic of EBDS can be analyzed by the Weibull distribution

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re

-p

function,[19, 33] as shown in Fig. 5(b). The values of EBDS can be described by

(4) (5) (6)

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where, n is the sum of samples, Ei is the EBDS of each sample, which is arranged in ascending order (E1≤E2≤E3... ≤En). Pi is the probability of dielectric breakdown. According to the

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two-parameter Weibull distribution function, Xi and Yi have a linear relationship. The mean EBDS can be extracted from the point where the fitting line intersects with the horizontal axis

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at Yi = 0. According to the Weibull analysis, it can be seen that the EBDS value of Pb0.88Ca0.12ZrO3 (x = 0.12) is the largest among these Pb1-xCaxZrO3 samples, reaching 2787 kV/cm, which is 2.2 times larger than that the pure PbZrO3 (867 kV/cm). This is because with the increase of Ca2+ doping concentration, the densification of the PCZ film is obviously improved, as shown in Fig. 3. Especially, when the doping concentration is x = 0.12, the 9

perovskite grains look more compact. The densification of microstructure plays an important role in improving the EBDS of materials.[34-35] In addition, it can be seen in Fig. 5(a) that the P-E loops of PZ and PCZ thin films are quite different, which may be due to the influence of Ca doping on the field-induced phase transition of AFE-FE and FE-AFE. To confirm the effect of Ca2+ doping on the field-induced phase transition, the P-E loops of PZ and PCZ thin films were measured at the same 867

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kV/cm, as shown in Fig.5(c). The phase transition fields of EAFE-FE and EFE-AFE increase gradually with the increase of Ca2+ doping concentration. The tendency can be seen more clearly in Fig. 5(d). The increase of EAFE-FE means that the phase transition from AFE phase to

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FE phase becomes difficult, that is, Ca2+ doping increases the stability of AFE phase. This can

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be explained by tolerance factor mentioned in the introduction. The radius of Ca2+ is smaller than that of Pb2+, so adding Ca can reduce the tolerance factor and stabilize the

lP

antiferroelectric order. Sr doping has a similar effect on antiferroelectric films or

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ceramics,[22-23] but the radius of Ca2 + is smaller than that of Sr2+, so in this study, Ca2+ doping has a better effect on stabilizing the antiferroelectric order in PZ films.

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Furthermore, it can also be seen from Fig. 5(c) that the hysteresis loop of PCZ thin film becomes slimmer and more inclined with increasing the Ca2+ doping concentration. The slim

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degree of hysteresis loop can be quantitatively expressed as ΔE = EAFE – EFE. The ΔE decreases with the increase of Ca2+ doping concentration (Fig. 5(d)). This means that the energy storage efficiency can increase with the increase of Ca2+ concentration due to that the smaller the ΔE is, the smaller the energy loss is. The inclination of hysteresis loop that is closely related to energy storage density may be caused by diffused phase transition. 10

To clarify whether there is a diffused phase transition and the degree of the diffuse behavior of phase transition, the temperature dependence of relative permittivity of the PCZ films with different Ca2+ doping concentrations was investigated, and the results are shown in Fig. 6(a)-(e). The relative permittivity and dielectric loss was measured at 100 kHz in a temperature range from room temperature to required temperature at 0.1 volts. The relative permittivity first increases and then decreases with increasing temperature. The temperature

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corresponding to the dielectric peak is Curie temperature (TC) that is the transition temperature from the AFE phase to the paraelectric (PE) phase. It can be seen from Fig. 6 that the dielectric peak become rounded gradually with the increasing Ca2+ doping concentration,

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demonstrating that the AFE–PE phase transition of the PCZ films show the characteristic of

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diffused phase transition with the increasing Ca2+ doping concentration. The similar results have been reported in the Sr-doped (Pb,La)(Zr,Sn,Ti)O3 antiferroelectric ceramics.[20] The

lP

degree of diffuse behavior of phase transition can be described by the Lorentz-type

(7)

TC) and εA are the parameters defining the temperature of the dielectric peak,

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where, TA (TA

na

relation:[36].

respectively, and εA is the value of ε at T = TA. The parameter δA is frequency independent at

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high enough frequencies (100 kHz) and reflects the diffused degree of the phase transition. The insets in Fig. 6(a)–(e) show the plots of T-TA versus (2εA/ε-2)1/2 for the PCZ films. The slope of the fitting curves is used to represent the value of δA. With the increase of Ca2+ concentration, the value of δA increases from 37.9 to 127.1, as shown in Fig. 6(f). The large value of δA obtained in this study is comparable to that (103.6) of the typical relaxor 11

Pb(Mg1/3Nb2/3)O3 ceramics.[36] This result indicates that the doping of Ca2+ can enhance the degree of diffuse behavior of phase transition of the PCZ films. In addition, it can be seen from Fig. 6(f) that the TC of pure PZ films is about 232 °C, which is consistent with the reported values in literature.[37] However, the TC of the PCZ films is lower than that of the PZ films, and decreases gradually with the increase of Ca2+ doping concentration. The TC for the Pb1-xCaxZrO3 films with x = 0.04, 0.08, 0.12 and 0.16 Ca2+ doping concentration is 228, 204,

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190, and 156 °C, respectively. It also conforms to the change rule of diffused phase transition caused by doping.[22, 38] The dielectric loss increases slightly with the increase of temperature, which is similar to the results of the PZ and Pb0.8Ba0.2ZrO3 thin films.[19, 39]

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The recoverable energy storage density (Wrec) of the PCZ films can be calculated by

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Equation (1) according to the P–E hysteresis loops (Fig. 5(a)). Fig. 7(a) shows the Wrec as a function of the applied field. For these films, the Wrec increases with increasing the applied

lP

electric field, and the maximum values of 13.9, 24.6, 37.1, 50.2 and 41.8J/cm3 have been

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achieved at the maximum applied electric field for the Pb1-xCaxZrO3 films at x = 0, 0.04, 0.08, 0.12 and 0.16, respectively. The variation trend of Wrec with Ca2+ concentration is shown in

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the inset. Compared with pure the PZ film, the Wrec value of Pb88Ca12ZrO3 thin film increased by 261%. Fig. 7(b) shows the energy storage efficiency as a function of the applied field. The

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η increases with increasing Ca2+ doping concentration, and the maximum values of 57.4%, 72.9%, 80.1%, 83.1% and 82.6% have been achieved at the maximum applied electric field for the Pb1-xCaxZrO3 films at x = 0, 0.04, 0.08, 0.12 and 0.16, respectively. The variation trend of η with Ca2+ concentration is also shown in the inset. The η value of Pb88Ca12ZrO3 thin film increased by 44.8% compared with the PZ film. As mentioned in the introduction, the main 12

factors affecting the Wrec of AFE materials are the Pmax, the behavior of field-induced phase transition and the EBDS. As can be seen from Fig. 5, for the PCZ films, with the increase of Ca2+ doping concentration, although the Pmax decreases gradually, the stability of AFE phase in the field-induced phase transition, the diffused degree in the phase transition process and the EBDS are improved significantly. Therefore, the Wrec and η of the PCZ films are increased obviously. When the Ca2+ doping concentration is more than x = 0.12, the stability of AFE

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phase and the diffuse behavior of phase transition continuously increase, but the Pmax and EBDS decrease evidently. Therefore, the highest Wrec and η obtained in the Pb88Ca12ZrO3 thin films.

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Fig. 8 shows a summary of recently reported data on energy storage density and

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efficiency of antiferroelectric films including lead-based and lead-free antiferroelectric films. It can be seen that the Pb0.97Y0.02[(Zr0.6Sn0.4)0.925Ti0.075]O3 films possesses ultrahigh η (90%)

lP

induced by changing the behavior of phase transition and enhancing the Pmax,[15] but the Wrec

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value is just 32.7 J/cm3 obtained at breakdown strength of 1800 kV/cm. On the other hand, the energy storage performance of (η = 33%, Wrec = 61 J/cm3) has been obtained for the

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Pb0.96La0.04Zr0.98Ti0.02O3 thin films, which exhibits a higher Wrec but a lower η.[40] Therefore, it is difficult to obtain high Wrec and η simultaneously[13,

15, 18-19, 23-24, 38, 40-56]

(The material

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selection and modified way, Wrec and η recorded in relevant literatures can be seen in supporting materials). However, the PCZ films obtained in this study possess an excellent energy storage performance, which not only have excellent energy storage density (50.2 J/cm3), but also has good energy storage efficiency (83.1 %). This is attributed to the fact that Ca2+ doping can improve simultaneously the stability of AFE phase, the diffused degree in the 13

field-induced phase transition process and the electric breakdown strength EBDS.

4. CONCLUSION In this study, Ca-doped PbZrO3 antiferroelectric thin films were prepared successfully by chemical solution deposition. The experimental results showed that the optimal Ca2+ doping concentration in the Pb1-xCaxZrO3 films is x = 0.12 for the recoverable energy density and

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energy storage efficiency. In the Pb0.88Ca0.12ZrO3 films, the recoverable energy density and energy storage efficiency are 50.2 J/cm3 and 83.1% at 2800 kV/cm, respectively, which are 261% and 44.8% higher than those of pure PbZrO3 films. These results demonstrate that

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storage properties of antiferroelectric thin films.

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doping moderate amount of Ca2+ is an effective and simple method to improve the energy

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Conflicts of interest

There are no conflicts to declare.

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Acknowledgements

This work has been supported by the basic research and common key technology

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innovation projects of Shenyang National Laboratory for Materials Science (No. 2017RP15),

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the key research and development plan of Liaoning Province (No. 2017104002), the basic scientific research projects of colleges and universities of Liaoning Province of China (No. LZGD2017005), the major project of Industrial Technology Research Institute of Liaoning Colleges and Universities (No. 201824010) and the National Basic Research Program (No.2017YFA0206302) of China.

14

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Fig. 1. A schematic diagram for the energy storage of AFE materials.

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The amplification of (111) diffraction peaks of the films.

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Fig. 2. (a) The XRD patterns of the PCZ film with different Ca2+ doping concentrations. (b)

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Fig. 3. The surface SEM images of the PCZ films with different Ca2+ doping concentrations,

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(a) x = 0, (b) x = 0.04, (c) x = 0.08, (d) x = 0.12 and (e) x = 0.16. (f) The average grain size of

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the PCZ film with different Ca2+ doping concentrations. The cross-sectional SEM images of the PCZ films with different Ca2+ doping concentrations, (g) x = 0, (h) x = 0.04, (i) x = 0.08,

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(j) x = 0.12 and (k) x = 0.16.

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Fig. 4. (a) Planar view of TEM for the Pb0.84Ca0.16ZrO3 film, (b) EDS elemental maps gained from the box in (a), (c) High-resolution surface TEM image gained from the box in (a), and (d)

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the Fast Fourier transform (FFT) patterns transformed from the HRTEM image.

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Fig. 5. (a) P‐ E hysteresis loops of the PCZ films with different Ca2+ doping concentrations. Inset: the maximum polarization of the PCZ films as a function of the Ca2+ doping

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concentrations, (b) Weibull plot of the electric breakdown strength and the EBDS values of the samples with different Ca2+ doping concentrations, (c) P‐ E hysteresis loops of the PCZ films

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with different Ca2+ doping concentrations measured at the same 867 kV/cm, (d) Ca2+ doping

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concentration dependence of EAFE-FE, EFE-AFE and ΔE.

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Fig. 6. Temperature dependence of relative permittivity and dielectric loss of the PCZ films with different Ca2+ doping concentrations, (a) x = 0, (b) x = 0.04, (c) x = 0.08, (d) x = 0.12

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and (e) x = 0.16, and the insets show the plots of T-TA as a function of (2εA/ε-2)1/2 of the PCZ

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films with different Ca2+ doping concentrations. (f) The δA and Curie temperature of the PCZ film with different Ca2+ doping concentrations.

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Fig. 7. The energy storage performances of the PCZ films with different Ca2+ doping

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concentrations. a) the recoverable energy storage density Wrec, b) the energy storage efficiency

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η measured at different electric fields.

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Fig. 8. A summary of recently reported data on energy storage density and efficiency of

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antiferroelectric films including lead-based and lead-free antiferroelectric films.

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