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A novel lead-free NaNbO3–Bi(Zn0.5Ti0.5)O3 ceramics system for energy storage application with excellent stability
Journal of Alloys and Compounds 815 (2020) 152356
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A novel lead-free NaNbO3eBi(Zn0.5Ti0.5)O3 ceramics system for energy storage application with excellent stability Ruike Shi, Yongping Pu*, Wen Wang, Xu Guo, Jingwei Li, Mengdie Yang, Shiyu Zhou Shaanxi Key Laboratory of Green Preparation and Functionalization for Inorganic Materials, Shaanxi University of Science & Technology, 710021, Xi'an, China
a r t i c l e i n f o
a b s t r a c t
Article history: Received 24 July 2019 Received in revised form 17 September 2019 Accepted 18 September 2019 Available online 19 September 2019
Many researches have been referred to the AFE structure of NaNbO3 in order to develop high power energy storage for NaNbO3-based ceramic. However, the square P-E loops with large Pr was observed in NaNbO3 ceramics due to the coexistence of AFE and the field-induced metastable FE, which suppress the energy storage property of NaNbO3-based ceramics. In the present work, lead-free (1-x)NaNbO3xBi(Zn0.5Ti0.5)O3 (abbreviated as (1-x)NN-xBZT) dielectric ceramics were prepared via the traditional solid-state route. The structures, relaxor behavior and energy storage property of (1-x)NN-xBZT ceramics were investigated with the introduction of BZT. The slim P-E loops were obtained while x ¼ 0.09e0.12 and the maximum discharge energy storage density (Wrec ¼ 2.1 J/cm3) was obtained while x ¼ 0.09, meanwhile a high energy storage efficiency (h ¼ 76%) was achieved. Moreover, the charge-discharge tests show that 0.91NN-0.09BZT ceramics can achieve fast discharge rate (50 ns) and exhibit excellent stabilities of temperature and electric field, which guarantee the application prospect of 0.91NN-0.09BZT ceramics for lead-free plus power system in a wide temperature range. © 2019 Elsevier B.V. All rights reserved.
Keywords: Lead-free NaNbO3 Energy storage Temperature stability Charge-discharge
1. Introduction With the development of new pulse, more requirements for energy storage devices have been raised such as high efficiency, excellent thermal stability, safe and reliable. In this context, ceramic-based dielectric for electrical energy storage become one of the most potential materials which were widely investigated, as it can meet these practical demands and display the fast chargedischarge property [1e3]. Particularly, lead zirconate titanate (Pb(Ti, Zr)O3) based materials, as a well-known anti-ferroelectric in the modern dielectric capacitor family, have been widely studied in the system of dielectric energy storage due to the excellent energy storage performance in the past several decades [4e6]. Nevertheless, the frequent transition between anti-ferroelectricity and ferroelectricity can cause the inevitable electrical failure during the charging-discharging process [7,8]. In addition, the use of Pb gives rise to environmental degradation and impairment of human health, which is the drive force for development of lead-free ceramic-based dielectric materials for energy storage application [9].
* Corresponding author. E-mail address: [email protected] (Y. Pu). https://doi.org/10.1016/j.jallcom.2019.152356 0925-8388/© 2019 Elsevier B.V. All rights reserved.
Sodium niobate (NaNbO3, NN)-based lead-free ceramics have been extensively investigated for several decades in the lead-free dielectric ceramic family since Geifman succeeded in growing single crystal of NaNbO3, as its exceptional piezoelectric property and extremely complicated phase transition in a wide temperature range of 100 to 650 C [10e18]. Although the phase transition is still controversial, it is commonly accepted that NaNbO3 undergo the following seven major phases with the rise of temperature, 100 C
which are outlined as: N ðFEÞ / P 520 C
575 C
640 C
360 C
480 C
ðAFEÞ / R ðAFEÞ /
S ðPEÞ / T1 ðPEÞ / T2 ðPEÞ / U ðPEÞ, where FE, AFE, and PE are abbreviation for freeoelectric, anti-ferroelectric, and paraelectric [19e22]. Many researches have been referred to the AFE structure for development of high power energy storage in NaNbO3-based ceramic [23e25]. Unfortunately, instead of AFE typical double polarization-electric field (P-E) loops, the square P-E loops was observed in NaNbO3 due to the coexistence of the fieldinduced metastable FE, P21ma (Q) and AFE Pbma (P) [26e28], which is related to the weak energy difference between AFE and FE [23]. Frequently, the discharge energy storage density (Wrec), charge energy storage density (Wch) and energy storage efficiency h could be calculated according to the integral of P-E loops [29,30]. These RP RP parameters can be represented as: Wrec ¼ Prm EdP, Wch ¼ 0 m EdP,
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rec and h ¼ W Wch 100%, where E, P, Pm and Pr represent the electric field
strength, polarization, maximum and remnant polarization, respectively. There is no doubt that the synchronization with high electric field endurance, low Pr and large Pm are necessary conditions for dielectric ceramics to obtain high energy storage performance. However, it is difficult to realize excellent energy storage performance for unmodified NN ceramic due to the square P-E loops with large Pr. Therefore, it is the primary goal to reduce Pr and enhance the energy storage performance of NN ceramic, eventually. A careful analysis of the literature regarding dielectric energy storage ceramics reveal that the introduction of PE phase into FE material can break ferroelectric long-range order, which will significantly reduce the remnant polarization and enhance the energy storage performance [31e33]. For instance, Zhang et al. [34] reported the Wrec of Bi0.5Na0.5TiO3 (NBT) ceramics doped with 25 mol% BaSnO3 was enhanced to 1.911 J/cm3 at electric field of 19 kV/mm. Similarly, excellent energy storage property were obtained in NBT and BaTiO3 (BT)-based ceramics when adding different compounds [34,35]. However, the introduction of PE phase can reduce Pr and decrease Pm, which are disadvantageous to obtain high energy storage density. Another approach for reducing Pr is to introduce ions with different radii and valence into A or B site of perovskite structure, which contribute to local component fluctuation and thus create dielectric relaxation behavior. For example, Zhao et al. [36] reported the Wrec of BaTiO3 ceramics were enhanced to 0.81 J/cm3 by doping Bi(Zn0.5Ti0.5)O3. Yuan et al. [37] reported high Wrec of 2.46 J/cm3 in BaTiO3 doped by Bi(Zn0.5Zr0.5)O3 system. Recently, Zhou et al. [38] firstly reported excellent energy storage performance in NN-based ceramic by adding Bi2O3. Subsequently, Zhou et al. [39] obtain high Wrec of 2.8 J/cm3 in NaNbO3eBi(Mg2/3Nb1/3)O3 system. In addition, Yang et al. [40] realized a large Wrec of 1.5 J/cm3 in 0.77NaNbO3-0.23BaTiO3 ceramics using Bi2O3 as a sintering aid. These researches indicated the addition of Bi2O3 can effectively promote the energy storage performance of NN-based ceramics whether used as sintering aid or dopant. In the present work, we use Bi(Zn0.5Ti0.5)O3 (BZT) to ameliorate the energy storage performances of NN-based ceramics, mainly for the following considerations: (ⅰ) The addition of Bi2O3 and ZnO can availably reduce the sintering temperature. Hence, the volatilization of Na can be restrained and improve the density of ceramics, which contribute to achieve high breakdown strength. (ⅱ) The substitution of Zn2þ and Ti4þ at B-site causes the fluctuation of local components and then obtain slim P-E loops with low Pr. Meanwhile, a large Pm is guaranteed due to the hybridization between the Bi3þ and O2. As expected, 0.91NN-0.09BZT ceramics demonstrate excellent energy storage performance (Wrec ¼ 2.1 J/cm3, h ¼ 76%) and maintain the outstanding stability of energy storage performance for temperature (20e120 C) and frequency (5e500 Hz). In addition, this work provided a new light for the development of energy storage performance for NN-BiMeO3 family (Me represents the trivalent or average trivalent metallic ions). 2. Experiment A series of (1-x)NN-xBZT (x ¼ 0.03e0.12) ceramics were prepared by traditional solid-state route. The starting powders were consisted of analytical grade Na2CO3, Nb2O5, Bi2O3, ZnO and TiO2 (all with purity 99.9%) which were stoichiometrically weighted, and then mixed uniformly with ZrO2 ball in the alcohol as media by ball-milling. The dried mixed powders were calcined at 850 C for 4 h in an alumina crucible. Subsequently, the calcined powers were re-milling again and compacted uniaxial to form cylindrical pellets with a diameter of 10 mm, and then cold isostatic pressure at 200 MPa was applied to the pellets holding for 3 min. These pellets
were sintered in air over a temperature range of 1180e1250 C for 2 h. The density of pellets after sintering can reach above 95% measured by Archimedes method. With the utilization of X-ray diffractometer (XRD D/max-2200PC, RIGAKU, Japan) and scanning electron microscopy (SEM, S-4800, RIGKU Co, Japan) in the crystal structure and microstructure of sintered ceramics. Prior to measurement of SEM, the sample were polished to obtain smooth surfaces and thermally etching for 20 min below the sintering temperature of 150 C. Then, a silver paste was applied to the parallel faces of polished ceramics and fired at 600 C for 20 min prior to characterize the electrical properties. The permittivity and dielectric loss as functions of frequency (100 Hz-2 MHz) at room temperature using an Agilent 4980A. The temperature-dependent of permittivity and tangent loss from 190 to 150 C were characterized by Agilent 4294A. The unipolar P-E loops were measured at temperature by a ferroelectric analyzer (Aix ACCT Systems GmbH, Germany) and the test of high temperature using TF Analyzer 2000. The commercial energy storage properties were measured by charge-discharge equipment (CFD-003, Gogo Instruments Technology, Shanghai, China). 3. Results and discussion The XRD patterns of (1-x)NN-xBZT (x ¼ 0.03e0.12) ceramics are shown in Fig. 1(a). The XRD result shows that pure perovskite structure is formed for the samples with 0.03 x 0.10, while the secondary phase (Bi2TiO7) form in x ¼ 0.12 sample because the added BZT exceeds the solid solubility limit. Initially, as shown in the enlarged view of Fig. 1(b), the ceramics maintain an orthorhombic Pbcm structure for 0.03 x 0.06 samples. However, the positions of two diffraction characteristic peaks (200) and (002) corresponding to orthorhombic structure close to each other and merge into a single peak at x ¼ 0.09, indicating that the AFE characteristic of NN ceramic is gradually weakened with the introduction of BZT. In addition, the peak of (002) shifts continuously towards lower 2-theta angles with the introduction of BZT due to the differences among ionic radius. For NN, the radius Nb5þ at Bsite is 64 p.m. based on 6-coordination, but in BZT crystal, Zn2þ and Ti4þ occupy B-site together, where the ions radius of Zn2þ is 74 p.m. (CN ¼ 6) and Ti4þ is 61 p.m. (CN ¼ 6) [41]. The smaller ionic radius Nb5þ is substituted by Zn2þ and Ti4þ with a larger average ionic radius at B-site, which contributes to the increase of lattice parameters and the shift of 2-theta to low angle. Fig. 2 (a)-(d) shows the SEM images of ceramics after polishing and thermally etching. The sintered NN-BZT ceramics with all of components are found to possess uniform grain and extremely low porosity, which contributes to achieve high breakdown strength. It is obvious that the grain size sharply increases when x ¼ 0.09, which is related to the liquid phase in NN ceramics. It is well known that ZnO and Bi2O3 as effective sintering additive can promote the densification of ceramics owing to the formation of liquid phase promotes the densification of ceramics [38,42]. Furthermore, the content of liquid phase increase with the introduction of BZT, which accelerates the mass transfer rate between particles and weakens the competition of among the adjacent grains, leading to accelerated grain growth [31,43]. Fig. 3 presents the permittivity and dielectric loss as functions of temperature for the (1-x)NN-xBZT ceramics measured in a range frequency from 0.1 kHz to 1000 kHz during the temperature rising from 200 C to 150 C. For the all composition, an obvious broad permittivity peaks corresponding to FE-PE phase transition appearance in the low temperature region, which indicates that the (1-x)NN-xBZT ceramics are mainly presented PE phase at room temperature. Furthermore, the temperature at the maximum
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Fig. 1. (a) XRD patterns of (1-x)NN-xBZT ceramics; (b) enlarged XRD patterns from 32 to 34 of (1-x)NN-xBZT ceramics.
permittivity moves toward higher temperature as the frequency increases, suggesting a typical dielectric diffuse behavior. Similar phenomenon has been found in other perovskite relaxor ferroelectrics [37e39,44,45]. It is believed that this similar relaxation behavior is related to the ion occupation of the different valence at A and B-site. There are significant differences in ion valences and sizes at both A and B-site in NN-BZT ceramics with the introduction of BZT. The disorder of charge and size at A and B-site contribute to the random electric fields (RFs) and weaken the long-range driving dipoles [36e38,45,46]. Fig. 4 shows the permittivity and dielectric loss of (1-x)NN-xBZT ceramics as functions of frequency, which are measured in a range of frequency from 100 Hz to 2 MHz at room temperature. Although
the permittivity inevitably decreases slightly with increasing frequency due to the contribution of Maxwell-Wagner-Sillars interfacial polarization, it is seen that a relatively excellent frequency stability of permittivity and dielectric loss lower than 0.04 is still maintained for ceramics of all components, which contribute to the wider application in each frequency. In order to characterize the energy storage property, Fig. 5 (a) presents the unipolar P-E loops of (1-x)NN-xBZT ceramics at room temperature. It seems that the P-E loops exhibit the coexistence of FE and weak AFE characteristics for x ¼ 0.06, while P-E loops become slimmer and exhibit the characteristic of relaxor ferroelectric with low Pr for x 0.09 sample, which is consistent with the phase structure transformation detected by XRD. Fig. 5 (b)
Fig. 2. SEM images of thermally etched surface of NN-BZT ceramics: (a) x ¼ 0.03; (b) x ¼ 0.06; (c) x ¼ 0.09; (d) x ¼ 0.12.
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Fig. 3. Temperature dependence of permittivity and dielectric loos of (1-x)NN-xBZT ceramics: (a) x ¼ 0.03; (b) x ¼ 0.06; (c) x ¼ 0.09; (d) x ¼ 0.12 measured from 200 C to 150 C.
Fig. 4. Frequency dependence of permittivity and dielectric loos of (1-x)NN-xBZT ceramics.
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Fig. 5. (a) Unipolar P-E loops of (1-x)NN-xBZT ceramics; (b) Jd and h as a function of BZT concentration; (c) Unipolar P-E loops of 0.91NN-0.09BZT ceramics under different electric fields; (d) Pm, Pr and Jd of 0.91NN-0.09BZT ceramics as a function of electric field.
shows the discharge energy storage density (Wrec) and efficiency (h) for different component. By contrast, the component of x ¼ 0.09 exhibits the maximum Wrec of 2.1 J/cm3, meanwhile a high energy storage efficiency (h ¼ 76%) was achieved at electric field of 200 kV/ cm due to largest Pm (29.36 mC/cm2) and quite low Pr (2.86 mC/cm2). Fig. 5 (c) and (d) shows the unipolar P-E loops under various electric field and corresponding to Pm, Pr and Wrec at a frequency of 10 Hz for x ¼ 0.09 sample. Although both Pm and Pr increase as the electric field intensifies, the acceleration of Pr lags significantly behind that of Pm due to relaxation behavior induced by the co-occupation of Zn2þ and Ti4þ at B-site [37e39]. As a consequence, Wrec enhances from 0.26 to 2.11 J/cm3 when the electric field reaches 200 kV/cm. Eventually, The (1-x)NN-xBZT ceramic obtain a higher Jd value and an appropriate h when x ¼ 0.09. For the application of dielectric energy storage capacitor, thermal and frequency stability are important characteristics. Fig. 6 (a) shows the unipolar P-E loops of 0.91NN-0.09BZT ceramics measured between 20 C and 120 C at 120 kV/cm. It is found that Pm and Pr decreases slightly and P-E loops maintain slim as the temperature increases. The Wrec and h at different temperatures are represented in Fig. 6 (b). Significantly, the value of Wrec exhibits a slight change (8%) from 20 C to 140 C and the h remains above 80% at the same time, indicating it can be used as a dielectric energy storage at wide temperature. Furthermore, the unipolar P-E loops and corresponding Wrec and h of 0.91NN-0.09BZT at different
frequency are represented in Fig. 6 (c) and (d). It's seen that there is only a small decline in Pm and Pr with frequency increasing meanwhile the Wrec and h exhibits a minimal fluctuations, which indicates an excellent frequency-insensitive characteristics. For evaluating the feasibility of ceramics capacitor application, the charge-discharge test of 0.91NN-0.09BZT ceramics was carried out in RLC circuits. Fig. 7 shows the underdamped current waveforms of 0.91NN-0.09BZT and corresponding maximum current (Imax), current density (CD¼Imax/S), and power density (PD ¼ EImax/ 2S) under different electric field (a)-(b) and various temperature (c)-(d) in the process of discharge. It can been seen that the maximum of current augments from 7.2 A to 80.7 A when the electric field increases from 20 kV/cm to 120 kV/cm. In addition, the corresponding CD and PD obtains the maximum of 642.2 A/cm2 and 38.5 MW/cm3 respectively. The discharge parameters at various temperatures show that the Imax, CD and PD maintain a larger value about 75 A, 597.1 A/cm2 and 35.8 MW/cm3 at 120 C, indicating 0.91NN-0.09BZT ceramics exhibits excellent temperature stability and practical prospect in pulse power application. Fig. 8 presents the current curves of 0.91NN-0.09BZT and Jd under different electric field (a)-(b) in the process of overdamped discharge. It is found that the maximum of current increases from 2.1 A to 25.8 A when the electric field increase from 20 kV/cm to 120 kV/cm as shown in inset of Fig. 8 (a). The Jd can be deduced by R the integral: Jd ¼ R iðtÞ2 dt =V where the volume of sample is
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Fig. 6. Unipolar P-E loops of 0.91NN-0.09BZT ceramics at different (a) temperature and (c) frequency at 120 kV/cm; (b) (d) The corresponding Jd and h as a function of temperature and frequency.
Fig. 7. Underdamped discharge current wave of 0.91NN-0.09BZT ceramics under different (a) electric fields and (c) temperature; (b) (d) The corresponding Imax, CD and PD as a function of electric field and temperature.
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Fig. 8. (a) Overdamped discharge current wave of 0.91NN-0.09BZT ceramics at different electric fields. (b) Jc as a function of time for 0.91NN-0.09BZT ceramics at various electric field. (c) Overdamped discharge current wave of 0.91NN-0.09BZT ceramics at different temperature under 120 kV/cm. (d) Jc as a function of time for 0.91NN-0.09BZT ceramics at different temperature.
represented V, and the load resistor is represented R. In addition, the rate of discharge is evaluated as t0.9, which represents the time it takes to release 90% of all energy. The value of t0.9 keep a smaller value of 50 ns with the electric field increasing. Furthermore, the value of Jd amplifies from 0.05 to 0.77 J/cm3 when the electric field increases to 120 kV/cm. The overdamped discharge current curves and Jd at different temperature as shown in Fig. 8 (c)e(d). It is obvious that the value of current peak is almost not fluctuated at various temperature as shown in inset of Fig. 8 (c). Similarly, the Jd also keep a stable value between 0.77 and 0.72 J/cm3 when the temperature rises from 20 C to 120 C. The results show that the change of temperature has insignificant influence on chargedischarge performance of 0.91NN-0.09BZT ceramics, which suggests it is promising in pulsed power application in a wide range of temperature. 4. Conclusions In the present work, a series of lead-free solid solution (1-x)NNxBZT dielectric ceramics were prepared by traditional solid-state route. The dense microstructure and relaxor behavior were observed obviously in all component ceramics. The random electric fields (RFs) and the weakened long-range driving reduce the value of Pr while maintaining a relatively high value of Pm owing to the
differences in ion valences and sizes at both A and B-site in (1-x) NN-xBZT ceramics. By contrast, 0.91NN-0.09BZT ceramics exhibit a high Wrec (2.1 J/cm3) and h (76%) at 200 kV/cm, meanwhile Wrec has a slight change (8%) in a range of temperature from 20 C to 140 C, suggesting that 0.91NN-0.09BZT ceramics were promising candidate materials for high-temperature dielectric capacitors. Moreover, 0.91NN-0.09BZT realizes fast discharge and exhibits outstanding temperature and electric field stability in the process of charge-discharge test in RLC circuits. Significantly, this work provided a basis for the development high energy storage NNBiMeO3 family (Me represents the trivalent or average trivalent metallic ions) relaxor ferroelectric ceramics. Acknowledgements This work was financed by the National Natural Science Foundation of China (51872175), the International Cooperation Projects of Shaanxi Province (2018KW-027). References [1] Y. Cao, P.C. Irwin, K. Younsi, The future of nanodielectrics in the electrical power industry, IEEE Trans. Dielectr. Electr. Insul. 11 (2004). [2] Z. Yang, H. Du, S. Qu, Significantly enhanced recoverable energy storage density in potassiumesodium niobate-based lead free ceramics, J. Mater.
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density ceramics by molten salt synthesis, J. Am. Ceram. Soc. 94 (2011) 4329e4334. H. Shimizu, K. Kobayashi, G.L. Brennecka, Advantages of low partial pressure of oxygen processing of alkali niobate: NaNbO3, J. Am. Ceram. Soc. 97 (2014) 1791e1796. L. Chao, Y. Hou, M. Zhu, Macroscopic ferroelectricity and piezoelectricity in nanostructured NaNbO3 ceramics, Appl. Phys. Lett. 110 (2017) 122901. L. Zhang, Y. Pu, M. Chen, High energy-storage density under low electric fields and improved optical transparency in novel sodium bismuth titanate-based lead-free ceramics, J. Eur. Ceram. Soc. (2020), https://doi.org/10.1016/ j.jeurceramsoc.2019.09.001. W. Huang, Y. Chen, X. Dong, Ultrahigh recoverable energy storage density and efficiency in barium strontium titanate-based lead-free relaxor ferroelectric ceramics, Appl. Phys. Lett. 113 (2018) 203902. Y. Pu, L. Zhang, M. Chen, High energy storage density and optical transparency of microwave sintered homogeneous (Na0.5Bi0.5)(1ex)BaxTi(1ey)SnyO3 Ceramics, ACS Sustain. Chem. Eng. 6 (2018) 6102e6109. L. Zhang, Y. Pu, M. Chen, Influence of BaZrO3 additive on the energy-storage properties of 0.775Na0.5Bi0.5TiO3-0.225BaSnO3 relaxor ferroelectrics, J. Alloy. Comp. 775 (2019) 342e347. L. Jin, F. Li, D.J. Green, Decoding the fingerprint of ferroelectric loops: comprehension of the material properties and structures, J. Am. Ceram. Soc. 97 (2014) 1e27. L. Zhang, X. Pu, Y. Pu, Influence of BaSnO3 additive on the energy storage properties of Na0.5Bi0.5TiO3-based relaxor ferroelectrics, J. Eur. Ceram. Soc. 38 (2018) 2304e2311. F. Li, J. Zhai, H. Zeng, Influence of structural evolution on energy storage properties in Bi0.5Na0.5TiO3-SrTiO3-NaNbO3 lead-free ferroelectric ceramics, J. Appl. Phys. 121 (2017), 054103. X. Zhao, Z. Zhou, X. Dong, High-energy storage performance in lead-free (1-x) BaTiO3-xBi(Zn0.5Ti0.5)O3 relaxor ceramics for temperature stability applications, Ceram. Int. 43 (2017) 9060e9066. Q. Yuan, F. Yao, H. Wang, Relaxor ferroelectric 0.9BaTiO3e0.1Bi(Zn0.5Zr0.5)O3 ceramic capacitors with high energy density and temperature stable energy storage properties, J. Mater. Chem. C 5 (2017) 9552e9558. M. Zhou, R. Liang, X. Dong, Superior energy storage properties and excellent stability of novel NaNbO3-based lead-free ceramics with A-site vacancy obtained via a Bi2O3 substitution strategy, J. Mater. Chem. 6 (2018) 17896e17904. J. Ye, G. Wang, X. Dong, Excellent comprehensive energy storage properties of novel lead-free NaNbO3-based ceramics for dielectric capacitor applications, J. Mater. Chem. C 7 (2019) 5639e5645. Z. Yang, H. Du, Z. Xu, A new family of sodium niobate-based dielectrics for electrical energy storage applications, J. Eur. Ceram. Soc. 39 (2019) 2899e2907. R.D. Shannon, Revised effective ionic-radii and systematic studies of interatomic distances in halides and chalcogenides, Acta Crystallogr. A 32 (1976) 751e767. X. Guo, Y. Pu, W. Wang, High insulation resistivity and ultralow dielectric loss in La-doped SrTiO3 colossal permittivity ceramics through defect chemistry optimization, ACS Sustain. Chem. Eng. 7 (2019) 13041e13052. R. Shi, Y. Pu, W. Wang, Flash sintering of barium titanate, Ceram. Int. 45 (2019) 7085e7089. C. Cui, Y. Pu, R. Shi, High-energy storage performance in lead-free (0.8-x) SrTiO3-0.2Na0.5Bi0.5TiO3-xBaTiO3 relaxor ferroelectric ceramics, J. Alloy. Comp. 740 (2018) 1180e1187. T. Wang, L. Jin, D. Lupascu, Relaxor ferroelectric BaTiO3-Bi(Mg2/3Nb1/3)O3 ceramics for energy storage application, J. Am. Ceram. Soc. 98 (2015) 559e566. L. Jin, F. Li, S. Zhang, Decoding the fingerprint of ferroelectric loops: comprehension of the material properties and structures, J. Am. Ceram. Soc. 97 (2014) 1e27.
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Journal of Alloys and Compounds journal homepage: http://www.elsevier.com/locate/jalcom
A novel lead-free NaNbO3eBi(Zn0.5Ti0.5)O3 ceramics system for energy storage application with excellent stability Ruike Shi, Yongping Pu*, Wen Wang, Xu Guo, Jingwei Li, Mengdie Yang, Shiyu Zhou Shaanxi Key Laboratory of Green Preparation and Functionalization for Inorganic Materials, Shaanxi University of Science & Technology, 710021, Xi'an, China
a r t i c l e i n f o
a b s t r a c t
Article history: Received 24 July 2019 Received in revised form 17 September 2019 Accepted 18 September 2019 Available online 19 September 2019
Many researches have been referred to the AFE structure of NaNbO3 in order to develop high power energy storage for NaNbO3-based ceramic. However, the square P-E loops with large Pr was observed in NaNbO3 ceramics due to the coexistence of AFE and the field-induced metastable FE, which suppress the energy storage property of NaNbO3-based ceramics. In the present work, lead-free (1-x)NaNbO3xBi(Zn0.5Ti0.5)O3 (abbreviated as (1-x)NN-xBZT) dielectric ceramics were prepared via the traditional solid-state route. The structures, relaxor behavior and energy storage property of (1-x)NN-xBZT ceramics were investigated with the introduction of BZT. The slim P-E loops were obtained while x ¼ 0.09e0.12 and the maximum discharge energy storage density (Wrec ¼ 2.1 J/cm3) was obtained while x ¼ 0.09, meanwhile a high energy storage efficiency (h ¼ 76%) was achieved. Moreover, the charge-discharge tests show that 0.91NN-0.09BZT ceramics can achieve fast discharge rate (50 ns) and exhibit excellent stabilities of temperature and electric field, which guarantee the application prospect of 0.91NN-0.09BZT ceramics for lead-free plus power system in a wide temperature range. © 2019 Elsevier B.V. All rights reserved.
Keywords: Lead-free NaNbO3 Energy storage Temperature stability Charge-discharge
1. Introduction With the development of new pulse, more requirements for energy storage devices have been raised such as high efficiency, excellent thermal stability, safe and reliable. In this context, ceramic-based dielectric for electrical energy storage become one of the most potential materials which were widely investigated, as it can meet these practical demands and display the fast chargedischarge property [1e3]. Particularly, lead zirconate titanate (Pb(Ti, Zr)O3) based materials, as a well-known anti-ferroelectric in the modern dielectric capacitor family, have been widely studied in the system of dielectric energy storage due to the excellent energy storage performance in the past several decades [4e6]. Nevertheless, the frequent transition between anti-ferroelectricity and ferroelectricity can cause the inevitable electrical failure during the charging-discharging process [7,8]. In addition, the use of Pb gives rise to environmental degradation and impairment of human health, which is the drive force for development of lead-free ceramic-based dielectric materials for energy storage application [9].
* Corresponding author. E-mail address: [email protected] (Y. Pu). https://doi.org/10.1016/j.jallcom.2019.152356 0925-8388/© 2019 Elsevier B.V. All rights reserved.
Sodium niobate (NaNbO3, NN)-based lead-free ceramics have been extensively investigated for several decades in the lead-free dielectric ceramic family since Geifman succeeded in growing single crystal of NaNbO3, as its exceptional piezoelectric property and extremely complicated phase transition in a wide temperature range of 100 to 650 C [10e18]. Although the phase transition is still controversial, it is commonly accepted that NaNbO3 undergo the following seven major phases with the rise of temperature, 100 C
which are outlined as: N ðFEÞ / P 520 C
575 C
640 C
360 C
480 C
ðAFEÞ / R ðAFEÞ /
S ðPEÞ / T1 ðPEÞ / T2 ðPEÞ / U ðPEÞ, where FE, AFE, and PE are abbreviation for freeoelectric, anti-ferroelectric, and paraelectric [19e22]. Many researches have been referred to the AFE structure for development of high power energy storage in NaNbO3-based ceramic [23e25]. Unfortunately, instead of AFE typical double polarization-electric field (P-E) loops, the square P-E loops was observed in NaNbO3 due to the coexistence of the fieldinduced metastable FE, P21ma (Q) and AFE Pbma (P) [26e28], which is related to the weak energy difference between AFE and FE [23]. Frequently, the discharge energy storage density (Wrec), charge energy storage density (Wch) and energy storage efficiency h could be calculated according to the integral of P-E loops [29,30]. These RP RP parameters can be represented as: Wrec ¼ Prm EdP, Wch ¼ 0 m EdP,
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rec and h ¼ W Wch 100%, where E, P, Pm and Pr represent the electric field
strength, polarization, maximum and remnant polarization, respectively. There is no doubt that the synchronization with high electric field endurance, low Pr and large Pm are necessary conditions for dielectric ceramics to obtain high energy storage performance. However, it is difficult to realize excellent energy storage performance for unmodified NN ceramic due to the square P-E loops with large Pr. Therefore, it is the primary goal to reduce Pr and enhance the energy storage performance of NN ceramic, eventually. A careful analysis of the literature regarding dielectric energy storage ceramics reveal that the introduction of PE phase into FE material can break ferroelectric long-range order, which will significantly reduce the remnant polarization and enhance the energy storage performance [31e33]. For instance, Zhang et al. [34] reported the Wrec of Bi0.5Na0.5TiO3 (NBT) ceramics doped with 25 mol% BaSnO3 was enhanced to 1.911 J/cm3 at electric field of 19 kV/mm. Similarly, excellent energy storage property were obtained in NBT and BaTiO3 (BT)-based ceramics when adding different compounds [34,35]. However, the introduction of PE phase can reduce Pr and decrease Pm, which are disadvantageous to obtain high energy storage density. Another approach for reducing Pr is to introduce ions with different radii and valence into A or B site of perovskite structure, which contribute to local component fluctuation and thus create dielectric relaxation behavior. For example, Zhao et al. [36] reported the Wrec of BaTiO3 ceramics were enhanced to 0.81 J/cm3 by doping Bi(Zn0.5Ti0.5)O3. Yuan et al. [37] reported high Wrec of 2.46 J/cm3 in BaTiO3 doped by Bi(Zn0.5Zr0.5)O3 system. Recently, Zhou et al. [38] firstly reported excellent energy storage performance in NN-based ceramic by adding Bi2O3. Subsequently, Zhou et al. [39] obtain high Wrec of 2.8 J/cm3 in NaNbO3eBi(Mg2/3Nb1/3)O3 system. In addition, Yang et al. [40] realized a large Wrec of 1.5 J/cm3 in 0.77NaNbO3-0.23BaTiO3 ceramics using Bi2O3 as a sintering aid. These researches indicated the addition of Bi2O3 can effectively promote the energy storage performance of NN-based ceramics whether used as sintering aid or dopant. In the present work, we use Bi(Zn0.5Ti0.5)O3 (BZT) to ameliorate the energy storage performances of NN-based ceramics, mainly for the following considerations: (ⅰ) The addition of Bi2O3 and ZnO can availably reduce the sintering temperature. Hence, the volatilization of Na can be restrained and improve the density of ceramics, which contribute to achieve high breakdown strength. (ⅱ) The substitution of Zn2þ and Ti4þ at B-site causes the fluctuation of local components and then obtain slim P-E loops with low Pr. Meanwhile, a large Pm is guaranteed due to the hybridization between the Bi3þ and O2. As expected, 0.91NN-0.09BZT ceramics demonstrate excellent energy storage performance (Wrec ¼ 2.1 J/cm3, h ¼ 76%) and maintain the outstanding stability of energy storage performance for temperature (20e120 C) and frequency (5e500 Hz). In addition, this work provided a new light for the development of energy storage performance for NN-BiMeO3 family (Me represents the trivalent or average trivalent metallic ions). 2. Experiment A series of (1-x)NN-xBZT (x ¼ 0.03e0.12) ceramics were prepared by traditional solid-state route. The starting powders were consisted of analytical grade Na2CO3, Nb2O5, Bi2O3, ZnO and TiO2 (all with purity 99.9%) which were stoichiometrically weighted, and then mixed uniformly with ZrO2 ball in the alcohol as media by ball-milling. The dried mixed powders were calcined at 850 C for 4 h in an alumina crucible. Subsequently, the calcined powers were re-milling again and compacted uniaxial to form cylindrical pellets with a diameter of 10 mm, and then cold isostatic pressure at 200 MPa was applied to the pellets holding for 3 min. These pellets
were sintered in air over a temperature range of 1180e1250 C for 2 h. The density of pellets after sintering can reach above 95% measured by Archimedes method. With the utilization of X-ray diffractometer (XRD D/max-2200PC, RIGAKU, Japan) and scanning electron microscopy (SEM, S-4800, RIGKU Co, Japan) in the crystal structure and microstructure of sintered ceramics. Prior to measurement of SEM, the sample were polished to obtain smooth surfaces and thermally etching for 20 min below the sintering temperature of 150 C. Then, a silver paste was applied to the parallel faces of polished ceramics and fired at 600 C for 20 min prior to characterize the electrical properties. The permittivity and dielectric loss as functions of frequency (100 Hz-2 MHz) at room temperature using an Agilent 4980A. The temperature-dependent of permittivity and tangent loss from 190 to 150 C were characterized by Agilent 4294A. The unipolar P-E loops were measured at temperature by a ferroelectric analyzer (Aix ACCT Systems GmbH, Germany) and the test of high temperature using TF Analyzer 2000. The commercial energy storage properties were measured by charge-discharge equipment (CFD-003, Gogo Instruments Technology, Shanghai, China). 3. Results and discussion The XRD patterns of (1-x)NN-xBZT (x ¼ 0.03e0.12) ceramics are shown in Fig. 1(a). The XRD result shows that pure perovskite structure is formed for the samples with 0.03 x 0.10, while the secondary phase (Bi2TiO7) form in x ¼ 0.12 sample because the added BZT exceeds the solid solubility limit. Initially, as shown in the enlarged view of Fig. 1(b), the ceramics maintain an orthorhombic Pbcm structure for 0.03 x 0.06 samples. However, the positions of two diffraction characteristic peaks (200) and (002) corresponding to orthorhombic structure close to each other and merge into a single peak at x ¼ 0.09, indicating that the AFE characteristic of NN ceramic is gradually weakened with the introduction of BZT. In addition, the peak of (002) shifts continuously towards lower 2-theta angles with the introduction of BZT due to the differences among ionic radius. For NN, the radius Nb5þ at Bsite is 64 p.m. based on 6-coordination, but in BZT crystal, Zn2þ and Ti4þ occupy B-site together, where the ions radius of Zn2þ is 74 p.m. (CN ¼ 6) and Ti4þ is 61 p.m. (CN ¼ 6) [41]. The smaller ionic radius Nb5þ is substituted by Zn2þ and Ti4þ with a larger average ionic radius at B-site, which contributes to the increase of lattice parameters and the shift of 2-theta to low angle. Fig. 2 (a)-(d) shows the SEM images of ceramics after polishing and thermally etching. The sintered NN-BZT ceramics with all of components are found to possess uniform grain and extremely low porosity, which contributes to achieve high breakdown strength. It is obvious that the grain size sharply increases when x ¼ 0.09, which is related to the liquid phase in NN ceramics. It is well known that ZnO and Bi2O3 as effective sintering additive can promote the densification of ceramics owing to the formation of liquid phase promotes the densification of ceramics [38,42]. Furthermore, the content of liquid phase increase with the introduction of BZT, which accelerates the mass transfer rate between particles and weakens the competition of among the adjacent grains, leading to accelerated grain growth [31,43]. Fig. 3 presents the permittivity and dielectric loss as functions of temperature for the (1-x)NN-xBZT ceramics measured in a range frequency from 0.1 kHz to 1000 kHz during the temperature rising from 200 C to 150 C. For the all composition, an obvious broad permittivity peaks corresponding to FE-PE phase transition appearance in the low temperature region, which indicates that the (1-x)NN-xBZT ceramics are mainly presented PE phase at room temperature. Furthermore, the temperature at the maximum
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Fig. 1. (a) XRD patterns of (1-x)NN-xBZT ceramics; (b) enlarged XRD patterns from 32 to 34 of (1-x)NN-xBZT ceramics.
permittivity moves toward higher temperature as the frequency increases, suggesting a typical dielectric diffuse behavior. Similar phenomenon has been found in other perovskite relaxor ferroelectrics [37e39,44,45]. It is believed that this similar relaxation behavior is related to the ion occupation of the different valence at A and B-site. There are significant differences in ion valences and sizes at both A and B-site in NN-BZT ceramics with the introduction of BZT. The disorder of charge and size at A and B-site contribute to the random electric fields (RFs) and weaken the long-range driving dipoles [36e38,45,46]. Fig. 4 shows the permittivity and dielectric loss of (1-x)NN-xBZT ceramics as functions of frequency, which are measured in a range of frequency from 100 Hz to 2 MHz at room temperature. Although
the permittivity inevitably decreases slightly with increasing frequency due to the contribution of Maxwell-Wagner-Sillars interfacial polarization, it is seen that a relatively excellent frequency stability of permittivity and dielectric loss lower than 0.04 is still maintained for ceramics of all components, which contribute to the wider application in each frequency. In order to characterize the energy storage property, Fig. 5 (a) presents the unipolar P-E loops of (1-x)NN-xBZT ceramics at room temperature. It seems that the P-E loops exhibit the coexistence of FE and weak AFE characteristics for x ¼ 0.06, while P-E loops become slimmer and exhibit the characteristic of relaxor ferroelectric with low Pr for x 0.09 sample, which is consistent with the phase structure transformation detected by XRD. Fig. 5 (b)
Fig. 2. SEM images of thermally etched surface of NN-BZT ceramics: (a) x ¼ 0.03; (b) x ¼ 0.06; (c) x ¼ 0.09; (d) x ¼ 0.12.
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Fig. 3. Temperature dependence of permittivity and dielectric loos of (1-x)NN-xBZT ceramics: (a) x ¼ 0.03; (b) x ¼ 0.06; (c) x ¼ 0.09; (d) x ¼ 0.12 measured from 200 C to 150 C.
Fig. 4. Frequency dependence of permittivity and dielectric loos of (1-x)NN-xBZT ceramics.
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Fig. 5. (a) Unipolar P-E loops of (1-x)NN-xBZT ceramics; (b) Jd and h as a function of BZT concentration; (c) Unipolar P-E loops of 0.91NN-0.09BZT ceramics under different electric fields; (d) Pm, Pr and Jd of 0.91NN-0.09BZT ceramics as a function of electric field.
shows the discharge energy storage density (Wrec) and efficiency (h) for different component. By contrast, the component of x ¼ 0.09 exhibits the maximum Wrec of 2.1 J/cm3, meanwhile a high energy storage efficiency (h ¼ 76%) was achieved at electric field of 200 kV/ cm due to largest Pm (29.36 mC/cm2) and quite low Pr (2.86 mC/cm2). Fig. 5 (c) and (d) shows the unipolar P-E loops under various electric field and corresponding to Pm, Pr and Wrec at a frequency of 10 Hz for x ¼ 0.09 sample. Although both Pm and Pr increase as the electric field intensifies, the acceleration of Pr lags significantly behind that of Pm due to relaxation behavior induced by the co-occupation of Zn2þ and Ti4þ at B-site [37e39]. As a consequence, Wrec enhances from 0.26 to 2.11 J/cm3 when the electric field reaches 200 kV/cm. Eventually, The (1-x)NN-xBZT ceramic obtain a higher Jd value and an appropriate h when x ¼ 0.09. For the application of dielectric energy storage capacitor, thermal and frequency stability are important characteristics. Fig. 6 (a) shows the unipolar P-E loops of 0.91NN-0.09BZT ceramics measured between 20 C and 120 C at 120 kV/cm. It is found that Pm and Pr decreases slightly and P-E loops maintain slim as the temperature increases. The Wrec and h at different temperatures are represented in Fig. 6 (b). Significantly, the value of Wrec exhibits a slight change (8%) from 20 C to 140 C and the h remains above 80% at the same time, indicating it can be used as a dielectric energy storage at wide temperature. Furthermore, the unipolar P-E loops and corresponding Wrec and h of 0.91NN-0.09BZT at different
frequency are represented in Fig. 6 (c) and (d). It's seen that there is only a small decline in Pm and Pr with frequency increasing meanwhile the Wrec and h exhibits a minimal fluctuations, which indicates an excellent frequency-insensitive characteristics. For evaluating the feasibility of ceramics capacitor application, the charge-discharge test of 0.91NN-0.09BZT ceramics was carried out in RLC circuits. Fig. 7 shows the underdamped current waveforms of 0.91NN-0.09BZT and corresponding maximum current (Imax), current density (CD¼Imax/S), and power density (PD ¼ EImax/ 2S) under different electric field (a)-(b) and various temperature (c)-(d) in the process of discharge. It can been seen that the maximum of current augments from 7.2 A to 80.7 A when the electric field increases from 20 kV/cm to 120 kV/cm. In addition, the corresponding CD and PD obtains the maximum of 642.2 A/cm2 and 38.5 MW/cm3 respectively. The discharge parameters at various temperatures show that the Imax, CD and PD maintain a larger value about 75 A, 597.1 A/cm2 and 35.8 MW/cm3 at 120 C, indicating 0.91NN-0.09BZT ceramics exhibits excellent temperature stability and practical prospect in pulse power application. Fig. 8 presents the current curves of 0.91NN-0.09BZT and Jd under different electric field (a)-(b) in the process of overdamped discharge. It is found that the maximum of current increases from 2.1 A to 25.8 A when the electric field increase from 20 kV/cm to 120 kV/cm as shown in inset of Fig. 8 (a). The Jd can be deduced by R the integral: Jd ¼ R iðtÞ2 dt =V where the volume of sample is
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Fig. 6. Unipolar P-E loops of 0.91NN-0.09BZT ceramics at different (a) temperature and (c) frequency at 120 kV/cm; (b) (d) The corresponding Jd and h as a function of temperature and frequency.
Fig. 7. Underdamped discharge current wave of 0.91NN-0.09BZT ceramics under different (a) electric fields and (c) temperature; (b) (d) The corresponding Imax, CD and PD as a function of electric field and temperature.
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Fig. 8. (a) Overdamped discharge current wave of 0.91NN-0.09BZT ceramics at different electric fields. (b) Jc as a function of time for 0.91NN-0.09BZT ceramics at various electric field. (c) Overdamped discharge current wave of 0.91NN-0.09BZT ceramics at different temperature under 120 kV/cm. (d) Jc as a function of time for 0.91NN-0.09BZT ceramics at different temperature.
represented V, and the load resistor is represented R. In addition, the rate of discharge is evaluated as t0.9, which represents the time it takes to release 90% of all energy. The value of t0.9 keep a smaller value of 50 ns with the electric field increasing. Furthermore, the value of Jd amplifies from 0.05 to 0.77 J/cm3 when the electric field increases to 120 kV/cm. The overdamped discharge current curves and Jd at different temperature as shown in Fig. 8 (c)e(d). It is obvious that the value of current peak is almost not fluctuated at various temperature as shown in inset of Fig. 8 (c). Similarly, the Jd also keep a stable value between 0.77 and 0.72 J/cm3 when the temperature rises from 20 C to 120 C. The results show that the change of temperature has insignificant influence on chargedischarge performance of 0.91NN-0.09BZT ceramics, which suggests it is promising in pulsed power application in a wide range of temperature. 4. Conclusions In the present work, a series of lead-free solid solution (1-x)NNxBZT dielectric ceramics were prepared by traditional solid-state route. The dense microstructure and relaxor behavior were observed obviously in all component ceramics. The random electric fields (RFs) and the weakened long-range driving reduce the value of Pr while maintaining a relatively high value of Pm owing to the
differences in ion valences and sizes at both A and B-site in (1-x) NN-xBZT ceramics. By contrast, 0.91NN-0.09BZT ceramics exhibit a high Wrec (2.1 J/cm3) and h (76%) at 200 kV/cm, meanwhile Wrec has a slight change (8%) in a range of temperature from 20 C to 140 C, suggesting that 0.91NN-0.09BZT ceramics were promising candidate materials for high-temperature dielectric capacitors. Moreover, 0.91NN-0.09BZT realizes fast discharge and exhibits outstanding temperature and electric field stability in the process of charge-discharge test in RLC circuits. Significantly, this work provided a basis for the development high energy storage NNBiMeO3 family (Me represents the trivalent or average trivalent metallic ions) relaxor ferroelectric ceramics. Acknowledgements This work was financed by the National Natural Science Foundation of China (51872175), the International Cooperation Projects of Shaanxi Province (2018KW-027). References [1] Y. Cao, P.C. Irwin, K. Younsi, The future of nanodielectrics in the electrical power industry, IEEE Trans. Dielectr. Electr. Insul. 11 (2004). [2] Z. Yang, H. Du, S. Qu, Significantly enhanced recoverable energy storage density in potassiumesodium niobate-based lead free ceramics, J. Mater.
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