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Bi(Mg0.5Ti0.5)O3 addition induced high recoverable energy-storage density and excellent electrical properties in lead-free Na0.5Bi0.5TiO3-based thick films
Accepted Manuscript Title: Bi(Mg0.5 Ti0.5 )O3 addition induced high recoverable energy-storage density and excellent electrical properties in lead-free Na0.5 Bi0.5 TiO3 -based thick films Authors: Jiaheng Wang, Yong Li, Ningning Sun, Jinhua Du, Qiwei Zhang, Xihong Hao PII: DOI: Reference:
S0955-2219(18)30623-X https://doi.org/10.1016/j.jeurceramsoc.2018.10.008 JECS 12126
To appear in:
Journal of the European Ceramic Society
Received date: Revised date: Accepted date:
25-4-2018 9-10-2018 9-10-2018
Please cite this article as: Wang J, Li Y, Sun N, Du J, Zhang Q, Hao X, Bi(Mg0.5 Ti0.5 )O3 addition induced high recoverable energy-storage density and excellent electrical properties in lead-free Na0.5 Bi0.5 TiO3 -based thick films, Journal of the European Ceramic Society (2018), https://doi.org/10.1016/j.jeurceramsoc.2018.10.008 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Bi(Mg0.5Ti0.5)O3 addition induced high recoverable energy-storage density and excellent electrical properties in lead-free Na0.5Bi0.5TiO3-based thick films Jiaheng Wang, Yong Li, Ningning Sun, Jinhua Du, Qiwei Zhang and Xihong Hao*,
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Inner Mongolia Key Laboratory of Ferroelectric-related New Energy Materials and Devices, School of Materials and Metallurgy, Inner Mongolia University of Science and Technology,
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Baotou 014010, China
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*Corresponding author: [email protected]; Tel: +86-472-5951572
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Abstract: (1-x)Na0.5Bi0.5TiO3-xBi(Mg0.5Ti0.5)O3 (NBT-BMT) thick films were designed for achieving large recoverable energy-storage density (Wrec). A large Wrec of 40.4 J/cm3 was
ED
detected in the thick film for x=0.4, which was more than 4 times larger than that of the pure
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NBT film. The addition of BMT induced slim polarization hysteresis (P-E) loops at room temperature. The slim P-E loops improved the difference between the maximum polarization
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(Pmax) and the remnant polarization (Pr). Besides, a breakdown strength field (BDS) of 2440 kV/cm was also detected in the thick film for x=0.4. The high BDS was caused by the reduced leakage current density. Furthermore, the thick film for x=0.4 possessed superior
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energy-storage stability under different temperature, frequency and electric-field cycling. In addition, 90% of the pulsed discharge energy density could be released in less than 1100 ns by using a pulsed discharge measurement.
Keywords:
NBT-BMT
thick
films;
Dielectric
property;
Sol-gel;
Energy-storage
performances
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1. Introduction
With the growth of the requirement for electronic communication, hybrid electric vehicles,
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health care and electrical weapons, the pulsed power technology has been received
considerable attention [1-5]. Dielectric capacitors are core elements in the electronic circuitry
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of the pulsed power systems. As the important parameter for the dielectric capacitors, high
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recoverable energy-storage density is needed to satisfy the miniaturization, lightening and
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integration of the device [6-10]. Besides, the energy-storage efficiency, fatigue resistance,
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temperature and frequency stability, and discharge properties also have great influence on the stable work of the whole systems. Generally, antiferroelectrics (AFEs), ferroelectrics (FEs),
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and linear dielectrics are the most widely studied energy-storage materials for dielectric capacitor [2]. AFEs exhibit the large energy-storage density because of their large maximum
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polarization (Pmax) and nearly zero remanent polarization (Pr). However, it is very difficult for AFE materials to withstand over several hundred charge-discharge circulations, because they
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are often cracked due to the phase transition during the charge-discharge process [11]. Linear dielectrics show small Wrec because of their smaller Pmax [2]. In contrast, FEs are more likely
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to achieve high Wrec due to their relatively high Pmax [1, 3]. For dielectric capacitors, increasing the difference between the maximum polarization (Pmax) and remnant polarization (Pr) is an effective way to increase the recoverable energy-storage density. Numerous studies have demonstrated that increasing the value of Pmax-Pr can be achieved by controlling the composition to decrease the tolerance factor (t) [6]. The tolerance
factor indicates the stability and distortion of the ABO3 perovskite structure, which is defined as [12]:
t
RA RO 2 ( RB RO )
(1)
where RA, RB, and RO are the ionic radii of the A-site cation, B-site cation, and oxygen anion,
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respectively. Thus, the tolerance factor can be reduced by introducing smaller ions on A site and larger ions on B site. In recent decade, a promising new energy-storage material based on
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Na0.5Bi0.5TiO3 (NBT) has been developed and studied for dielectric capacitors. The stereo-chemically active lone pair electrons of Bi3+ produce high polarization, which benefits for the energy storage [13]. However, pure NBT exhibits strong ferroelectricity at room
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temperature, and its high Pr can be serious limitation for practical applications [14].
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According to the above discussion, composition modifications should be used to suppress the
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Pr in NBT based materials in order to improve the energy-storage performance. Quite a few
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works are carried out to achieve this purpose by introducing oxides, such as BaTiO3, SrTiO3,
solid
solutions
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(K0.5Na0.5)NbO3, (K0.5Bi0.5)TiO3 and Bi(Mg0.5Ti0.5)O3, into NBT to form binary or ternary [15-18].
For
example,
Chen
reported
the
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(1-x)(Na0.5Bi0.5)0.92Ba0.08TiO3-x0.1Bi(Mg0.5Ti0.5)O3 (x=0, 0.02, 0.04, 0.06 and 0.10) ceramics [18]. The ionic radius of Mg2+ (0.83Å) is larger than that of Ti4+ (0.61Å), which induced slim
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P-E loops. The slim P-E loops increase the value of Pmax-Pr. As a result, the Pr/Pmax value of (1-x)(Na0.5Bi0.5)0.92Ba0.08TiO3-xBi(Mg0.5Ti0.5)O3
ceramics
decrease
from
0.8
for
(Na0.5Bi0.5)0.92Ba0.08TiO3 to 0.2 for 0.9(Na0.5Bi0.5)0.92Ba0.08TiO3-0.1Bi(Mg0.5Ti0.5)O3. The Wrec
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of 0.9(Na0.5Bi0.5)0.92Ba0.08TiO3-0.1Bi(Mg0.5Ti0.5)O3 ceramic is improved to 0.78 J/cm3, which is much larger than the Wrec of (Na0.5Bi0.5)0.92Ba0.08TiO3 ceramic of 0.2 J/cm3 at room temperature. Besides, improving the electrical BDS of the materials is another way to increase the recoverable energy density. The reported works on energy-storage NBT-based solutions are
mainly focused on bulk ceramics. Due to the lower BDS, the Wrec of the bulk ceramics is usually very small. Comparatively, film-form dielectrics with high BDS should be suitable for high energy storage. However, pure NBT film-form dielectrics are affected by high leakage current, and a material with a high leakage current has a low BDS that is not conducive to energy storage applications [13]. In order to improve the BDS, appropriate oxygen vacancies
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can be introduced to act as trap sites, thereby, electron trap levels become deeper, and acceptor doping usually introduces oxygen vacancies [19].
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According to the above discussing, in this work, composition modifications by adding
Bi(Mg0.5Ti0.5)O3 (BMT) into Na0.5Bi0.5TiO3 (NBT) are designed to increase the Pmax-Pr value
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and the BDS in NBT-based thick films. On the one hand, the Mg2+ substitution Ti4+ in NBT-based thick film forming the deep trap levels will reduce the leakage current. On the
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other hand, substitution of Mg2+ for Ti4+ in the B-site is expected to induce slim P-E loops,
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according to formula (1), which is because the ionic radius of Mg2+ is larger than that of Ti4+. (1-x)Na0.5Bi0.5TiO3-xBi(Mg0.5Ti0.5)O3 [abbreviated as (1-x)NBT-xBMT, x=0, 0.2, 0.4 and 0.6]
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thick films were selected as a representative example to verify whether high Wrec can be obtained in their thick films. The corresponding energy-storage efficiency, fatigue resistance,
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temperature and frequency stability, discharge properties were also investigated.
2. Experimental procedure (1-x)NBT-xBMT
(x=0,
0.2,
0.4
and
0.6)
thick
films
were
grown
on
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LaNiO3(100)/Pt(111)/TiO2/SiO2/Si substrate by using a polyvinylpyrrolidone (PVP)-modified sol-gel method. Sodium acetate trihydrate (99%), bismuth nitrate (99%), tetrabutyl titanate (98%) and magnesium acetate tetrahydrate (99%) were chosen as the raw materials with glacial acetic acid (99.5%), acetylacetone (99%) and distilled water as the solvents. The solutions of Na0.5Bi0.5TiO3 and Bi(Mg0.5Ti0.5)O3 were prepared separately and then mixed
together. The specific preparation procedure of Na0.5Bi0.5TiO3 precursor solution was as follows. Firstly, sodium acetate trihydrate and bismuth nitrate were dissolved in glacial acetic acid and distilled water at 80 oC. After cooling to room temperature, acetylacetone was added and stirred for 20 min. Finally, tetrabutyl titanate was added and stirred for 20 min until a stable yellow transparent solution was formed. The volume ratio of glacial acetic acid,
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distilled water and acetylacetone is 4:1:1. The preparation procedure of Bi(Mg0.5Ti0.5)O3 precursor solution is the same as that of Na0.5Bi0.5TiO3. Methanamide (99.5%), lactic acid
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(85%) and polyvinylpyrrolidone (PVP) (94.4%) were added into the mixed solution to avoid the appearance of cracks and increase the viscosity of the solution. The mole ratio of the final
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solution, methanamide, lactic acid and polyvinylpyrrolidone was 1:1:1:1. The final concentration of the solution was 0.45 M. NBT-BMT solutions were spin-coated onto
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substrates at 3000 rpm for 30 s. The wet films were firstly dried at 200 oC for 3 min, then
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pyrolysed at 400 oC for 10 min, and finally annealed at 700 oC for 3 min. This spin-coating and heat-treatment process was repeated 7 times to achieve the films with a desired thickness.
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Phase composition of the NBT-BMT thick films was measured by X-ray diffraction (XRD, Bruker D8 Advanced Diffractometer, German). The cross-sectional microstructure and the
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surface of these thick films were observed by field-emission scanning electron microscopy (FE-SEM, ZESIS Supra 55, German), atomic force microscope (AFM) (Dimension Icon,
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Bruker, German), and piezoelectric force microscopy (PFM, Bruker, Icon), respectively. Au top electrodes of 0.2 mm in diameter were sputtered through a mask version to measure the
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dielectric properties and energy-storage performances. Dielectric properties were measured by Agilent E4980A LCR analyzer. The electric field-induced polarization hysteresis (P-E) loops, leakage current density and BDS of the thick films were tested by a Radiant Technology Ferroelectric tester (Radiant Technologies, Inc., Albuquerque, NM). Au top electrodes of 1 mm in diameter were used to test the discharge properties and leakage current density. The
pulsed discharge current was captured by a Rogowski coil (Pearson 6595, Pearson Electronics, Palo Alto, CA) and recorded by an oscilloscope (TBS 1102B-EDU, Tektronix Co. Ltd., China). The energy-storage properties of NBT-BMT thick films were calculated according to P-E loops and pulsed discharge currents.
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3. Results and discussion
The XRD patterns of the LNO substrates and the NBT-BMT thick films with x=0, 0.2, 0.4
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and 0.6 are shown in Fig. 1 (a). It is observed that all of the thick films are polycrystalline and
exhibit random orientation. The thick films with x=0, 0.2, 0.4 show pure perovskite phase,
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indicating that BMT and NBT combine to form a stable solid solution. However, a secondary
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phase (Bi2Ti2O7) is detected in the thick film with x=0.6, which means that BMT exceeds the
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solubility limit, and this unstable component causes the impurity phase. Fig. 1 (b) presents the
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XRD patterns of (100) peaks of these thick films. With the increase of the BMT content, the diffraction peaks of the (100) shift to a lower diffraction angle owing to the relatively larger
expanded cell volumes.
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ionic radius of Mg2+ (0.83Å) compared with that of Ti4+ (0.61Å), which indicates the
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Fig. 2 (a)-(d) shows the AFM micrographs obtained for the surface of NBT-BMT thick films. Evidently, all samples have a similar morphology, which is dense and low porosity. Fig. 2
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(e)-(h) exhibit distribution of the grain size of the NBT-BMT thick films, which were calculated from 100 grains using a Nano Measurement software. The average grain (avg)
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sizes are 92.6, 97.3, 104 and 93.8 nm for x=0, 0.2, 0.4 and 0.6, respectively. The cross-sectional SEM image and film thickness are shown in the inset of Fig. 2 (i)-(l). Clearly, the multi-layer structure is composed of a Pt(111)/TiO2/SiO2/Si substrate, a LaNiO3 (LNO) bottom electrode and the NBT-BMT thick film. All the thick films display a dense and
uniform microstructure with a thickness of 1000 nm. The thickness of the LNO bottom electrode is about 200 nm. Frequency-dependent dielectric constant and dielectric loss (tanδ) of the NBT-BMT thick films are plotted in Fig. 3, which were measured at room temperature and in the range of 1 kHz-1 MHz. As the frequency increases, the dielectric constant decreases gradually while the
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tanδ increases slightly. Dielectric constant and dielectric loss of the NBT-BMT thick films at 100 kHz are 504.3, 436.1, 392.2, 255.8 and 0.028, 0.033, 0.022, 0.070 for x=0, 0.2, 0.4 and
increase
of
the
BMT
content.
Pharatree
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0.6, respectively. The dielectric constant of the NBT-BMT thick films decreases with the reported
the
similar
result
for
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(1-x)K0.5Bi0.5TiO3-xBi(Mg0.5Ti0.5)O3 (KBT-BMT) ceramics, where the dielectric constant of
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KBT-BMT ceramic decreases when x is above 0.15 [20]. The corresponding
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frequency-dependent dielectric constant and dielectric loss of the pure BMT thick film are
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displayed in the inset of Fig. 3 (a).
Fig. 4 (a)-(d) demonstrates the dielectric constant and dielectric loss of NBT-BMT thick films
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as a function of temperature at 50 kHz, 100 kHz, 500 kHz and 1 MHz. With increasing x, the dielectric maximum temperature (Tm) shifts to high temperature. The Tm for the x=0, 0.2, 0.4
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and 0.6 are 339.1 oC, 356 oC, 383.2 oC and 501.1 oC, respectively, as listed in Table 1. The similar result was reported in Bi(Mg0.5Ti0.5)O3-modified (Na0.5Bi0.5)0.92Ba0.08TiO3 ceramics
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[18]. Furthermore, the addition of BMT decreases the dielectric constant of the thick films for x=0.4 and 0.6. The overall effect of BMT addition is that the temperature stability of the
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dielectric constant is enhanced in a wide temperature range from 30 oC to Tm for the x=0.4 and 0.6 thick films. This phenomenon indicates that the 0.4 and 0.6 thick films could be suitable for high temperature dielectric applications. It is well known that the dielectric constant of a normal ferroelectric material above Curie temperature follows the Curie-Weiss law described by [21]:
1
T T0 (T T0 ) C
(2)
Where T0 is the Curie-Weiss temperature and C is the Curie-Weiss constant. The plots of temperature versus inverse dielectric constant of x=0, 0.2 and 0.4 are fitted to the Curie-Weiss law at 100 kHz, as shown in Fig. 5 (a)-(c). The parameter ∆Tm which is often used to show the
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degree of the deviation from the Curie-Weiss law is defined as [22]:
Tm Tcw Tm
(3)
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Where Tcw denotes the temperature from which the dielectric constant starts to deviate from the Curie-Weiss law and Tm represents the temperature of the dielectric constant maximum. The values of the Tcw and ∆Tm are also listed in Table 1. With the increase of BMT addition,
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the Tm and Tcw increase. The value of ∆Tm increases from 60.4 oC to 116.1 oC. These results
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indicate that the diffuse phase transition (DPT) behavior of NBT-BMT thick film is enhanced
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gradually with the increase of BMT addition. For the ferroelectrics, the reciprocal of the
r
1
m
(T Tm ) C
(4)
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1
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dielectric constant and the temperature obey the Uchino and Nomura function [23].
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Where εm is the maximum value of the dielectric constant, γ is the indicator of the degree of diffuseness. The inset of Fig. 5 (a)-(c) show the plots of ln(1/εr-1/εm) versus ln(T-Tm) for the
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NBT-BMT thick films. The slope of the fitting curves is used to represent the value of γ. With the increase of BMT addition, the value of γ increases from 1.69 to 1.78. The limiting value γ=1 and γ=2 are the character for normal ferroelectric phase transition and for complete
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diffuse phase transition, respectively [24]. This result also demonstrates that the addition of BMT enhanced the DPT behavior of NBT-BMT thick films. As for energy-storage applications, BDS is one of the most important parameters to determine the operative electric field and energy-storage density. The characteristic BDS of the NBT-BMT thick films was analyzed by the Weibull distribution [10, 14, 19]:
X i ln( Ei )
(5)
Yi ln(ln(1 /(1 Pi )))
(6)
Pi i /( n 1)
(7)
where Xi and Yi are two parameters in Weibull distribution function, Ei is the specific breakdown
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electric field of each specimen in the experiments, Pi is the possibility of a dielectric breakdown, n is the sum of specimens of each composition, and i is the rank of specimens. The Ei is arranged in
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ascending order of E1 ≤ E2 ≤ … ≤ Ei ≤ … ≤ En. In this work, we prepared three thick films for each composition. Au top electrodes were sputtered onto the surface of the thick film through a mask version. There were many top electrodes on each thick film, and each top electrode
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corresponded to one specimen. For the three thick films, 8 close data values were chosen as
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the final data to calculate the breakdown strength of each component, so n=8. Due to the
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problems such as the uneven sputtering of the gold electrode, some specimens with
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abnormally low or abnormally high values may be generated, and these specimens should be excluded. According to the above Weibull distribution equation, Xi and Yi have a linear
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relationship. The intersection of the fitted line and the X axis is the value of BDS when Yi=0. As is
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shown in Fig. 6 (a), the BDS values of the NBT-BMT thick films with x=0, 0.2, 0.4 and 0.6 obtained from the intercept on the x-axis are 1613, 1874, 2440 and 1605 kV/cm, respectively.
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Compared to the NBT thick film, the percentages of BDS enhancement are 16.2% and 51.3% for x=0.2 and 0.4, indicating that BMT adding could increase the BDS. The current densities for NBT-BMT thick films are plotted against the applied electric field (J-E) and shown in Fig. 6
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(b). Compared with pure NBT thick film, the enhancement of insulation property is realized in BMT added thick film. The enhancement of insulation property could improve the value of BDS in the thick films. The leakage current density is the lowest when x=0.4, which is consistent with the result in Fig. 6 (a). In order to find out the origin of leakage current reduction in BMT added NBT thick films, the conduction mechanism of the prepared samples
is discussed. Fig. 6 (c)-(f) show the logarithmic plots of J as a function of E for NBT-BMT thick films. Clearly, all curves can be modeled in terms of space-charge-limited current (SCLC). In the low field region, the curves follow Ohmic conduction properties (α~1). With the increasing electric field, the curves follow modified Child’s law conduction (α~2). When the applied field is further increased, a sharp increase in the slope (α>3) in the curves occurs
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because of large leakage current density [25]. According to Lampert’s theory of SCLC
conductions, the transition electric field can be defined as Ec (Ohmic to modified Child’s law)
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and ETFL (modified Child’s law to the large leakage current field), respectively. For the
0.8NBT-0.2BMT thick film, ETEL is not observed. For the 0.6NBT-0.4BMT thick film, Ec is
So, the
ETFL for
each thick
film
is
found out
as
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scope of measurement.
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not observed. The phenomenon may be because the transition electric field is higher than the
ETFL(NBT)
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indicates that doped Mg2+ ions in the thick films mainly act as carrier trap sites. Also, Ec for the 0.8NBT-0.2BMT and 0.6NBT-0.4BMT thick films are much higher than that of the pure
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NBT thick film. This suggests that Mg2+ ions give rise to deeper traps than Ti4+ ions. Thus, it means that deep traps were formed by Mg2+ doping. Moreover, the enhancement of insulation
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property of NBT-BMT thick films is closely related to such deep trap levels formed by ion doping. So, the leakage current density of BMT added NBT thick films in the modified
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Child’s law conduction region have been suppressed compared to the pure NBT thick film [19].
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The P-E loops of the NBT-BMT thick films are shown in Fig. 7, which were measured under 1400 kV/cm, 1 kHz and room temperature. As the BMT content increases, the Pmax decreases, which corresponds to the change trend of the dielectric constant. Moreover, the thick films with BMT addition exhibit slim P-E loops with small Pr value. This behavior will increase the value of Pmax-Pr, which is beneficial for the energy storage. As shown in the inset of Fig. 7,
the value of Pmax-Pr is 25.4, 33.6, 36.1 μC/cm2 for x=0, 0.2, 0.4, respectively. However, the value of Pmax-Pr of the thick film for x=0.6 is only 25.1 μC/cm2. The leakage current of the thick film for x=0.6 increases dramatically, which causes a poor P-E loops with round-shaped feature [26]. This phenomenon results in a small value of the Pmax-Pr. Evidently, the thick film for x=0.4 shows the largest value of Pmax-Pr. It could be predicted that the excellent
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energy-storage performance would be achieved in the NBT-BMT thick film for x=0.4.
Fig. 8 shows the PFM images of NBT-BMT thick films. With the BMT addition increasing,
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the domains become blurry, and the area of polar nanoregions (PNRs) increases. When BMT addition is increased to x=0.4, it is difficult to find uniform and continuous large area domain
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structure. The structural transformation verifies the dielectric results, exhibiting the DPT
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behavior. Moreover, PNRs are beneficial to the switching behavior of the polarization,
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leading to a slim hysteresis loop in Fig. 7.
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The recoverable energy-storage density Wrec of the ferroelectric thick films is usually studied by their P-E loops. The specific formula is as follows [13]: P max
Pr
Edp
ED
Wrec
(8)
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where E is the applied electric field, Pr is the remanent polarization and Pmax is the maximum polarization, illustrated by the green area in Fig. 9 (a). In the practical applications, in addition
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to higher recoverable energy-storage density Wrec, the corresponding higher efficiency η is also required. The η is calculated as the following formula [13]: Wrec Wrec Wloss
(9)
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where Wloss is the closed red area of the P-E hysteresis loops as shown in Fig. 9 (a), which is represented by the unrecovered stored energy owing to the hysteresis loss. Fig. 9 (c) and (d) shows the Wrec and η of the NBT-BMT thick films, which were calculated from the P-E loops, ranging from 200 kV/cm to their BDS. Fig. 9 (b) shows their corresponding P-E loops under
the BDS. Clearly, with the increase of the applied electric field, the Wrec values for all the thick films increase, while η shows the contrary variation tendency. Typically, the maximum Wrec values of the NBT-BMT thick films at their BDS are 10, 18.3, 40.4 and 13.6 J/cm3 for x=0, 0.2, 0.4 and 0.6, and the η values are 19.6%, 31.8%, 54.6% and 31.8%, respectively. The thick film for x=0.4 shows better energy-storage performances than the other thick films
attributed to the large value of Pmax-Pr, high BDS and low dielectric loss.
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owing to the higher Wrec and η. The enhanced energy-storage performances are mainly
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For the practical applications, besides higher Wrec and η values a good frequency-dependent stability is needed. The energy-storage density and the corresponding efficiency of the
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0.6NBT-0.4BMT thick film were calculated from the P-E loops measured under an electric
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field of 1200 kV/cm at different frequency. The results are displayed in Fig. 10 (a) and (b). As the frequency increases up to 5 kHz, P-E loops of the thick film change slightly. The Wrec
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fluctuates only between 14.5 and 14.7 J/cm3, while the corresponding η changes from 65.5% to 69.9%. These results indicate that 0.6NBT-0.4BMT thick film shows excellent
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energy-storage frequency-related stability. The good thermal stability is also desired for the practical applications. Fig. 10 (c) presents P-E results of the 0.6NBT-0.4BMT thick film,
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which were tested at 1 kHz, in the range of 25-105 oC. As the temperature is increasing, the Pmax increases gradually and the Pr decreases firstly and then increases slightly. As a result,
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the Wrec and η increase firstly and then decrease. Changes of Wrec are less than 0.5 J/cm3. Furthermore, η also exhibits a relatively high value of 64.7% at 105 oC, as shown in Fig. 10
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(d). This result suggests that the 0.6NBT-0.4BMT thick film possesses good thermal stability in the temperature range of 25-105 oC. In addition to the above, the endurance of the unit in terms of cycles should also be considered in the real capacitor applications. Fig. 10 (e) shows the polarization fatigue behavior of the 0.6NBT-0.4BMT thick film in the P-E loops after 1, 103, 106 and 107 switching cycles at room temperature, 1 kHz, the applied electric field of 600
kV/cm. The Pmax and Pr are almost not change after 103, 106 and 107 cycles of testing. Fig. 10 (f) shows the corresponding energy-storage density and efficiency stability after different fatigue cycles. Clearly, after 107 switches, the Wrec declines slightly while η reduces less than 4%. These results indicate that the 0.6NBT-0.4BMT thick film exhibits high fatigue endurance behavior.
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A comparison of BDS and recoverable energy-storage density of the NBT-based ceramics and films are displayed in Table 2. It could be found from Table 2 that the NBT-based ceramics
BDS
of
the
ceramics
is
often
lower
than
200
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usually exhibit recoverable energy-storage density lower than 2 J/cm3. This is because that the kV/cm.
For
example,
the
density
of
1.2
J/cm3
at
the
BDS
of
155
kV/cm,
and
the
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energy-storage
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0.85Ba0.04Bi0.48Na0.48TiO3-0.15SrZrO3 ceramic (Table 2, ref. 29) shows an recoverable
0.90(0.92Na0.5Bi0.5TiO3-0.08BaTiO3)-0.10Bi(Mg0.5Ti0.5)O3 ceramic (Table 2, ref. 18) shows
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an recoverable energy-storage density of 2 J/cm3 at the BDS of 135 kV/cm. Comparatively, the film form materials show large energy-storage densities. For example, the lead-based
ED
0.4Bi(Ni0.5Zr0.5)O3-0.6PbTiO3 film exhibits an ultra-high recoverable energy-storage density of 39.8 J/cm3 at 2167 kV/cm (Table 2, ref. 34), while the lead-free thick film
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0.6NBT-0.4BMT fabricated in this work exhibits a higher recoverable energy-storage density of 40.4 J/cm3 under an electric field of 2440 kV/cm. However, lead-based materials are
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harmful to the environment and human beings [30]. Thus, the developments of 0.6NBT-0.4BMT thick films as a lead-free material will arouse considerable attention for the
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dielectric capacitors applied in energy-storage fields. Recently, a pulsed discharge method has been utilized more and more extensively to evaluate the practical working performance. The equivalent circuit diagram of the method is displayed in Fig. 11 (a). The detailed measuring process by the pulsed discharge method was reported in the ref [9]. The pulsed discharged energy density Wdis can be calculated as [9, 14]:
Wdis
R i '2 (t )dt
(10)
V
where i’(t), R and V are the current, load resistance and the volume of the thick film capacitors, respectively. The pulsed discharge current of the 0.6NBT-0.4BMT thick film is shown in Fig. 11 (b), which was measured at room temperature under different electric fields.
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Obviously, the pulsed discharge current reaches their peak value quickly and decreases rapidly, and with the increase of the strength of the electric field, the current peak is also
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increasing. Under 700 kV/cm, the current peak is 0.22 A. The electrode area for pulsed
discharge measurement is about 0.00785 cm2. Thus, the current density is 28 A/cm2. This result is as high as that of the Pb0.94La0.04[(Zr0.70Sn0.30)0.86Ti0.14]O3 ceramics [35]. The pulse
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power applications of the dielectric capacitor require a fast discharge speed. Most of the
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stored energy in the thick film is released quickly after starting the test. Thus, a parameter t0.9
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which means the time required for the Wdis to reach 90% of its final value is utilized to
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describe the energy release speed. The time-dependence of the pulsed discharged energy
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density Wdis of 0.6NBT-0.4BMT thick film under different electric fields are shown in Fig. 11 (c), and the inset of Fig. 11 (c) shows the t0.9 of the film. The discharge process lasts about
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2500 ns. The Wdis are 1.34, 2.17, 2.41, 2.74, 3.4 J/cm3 and the t0.9 are 804, 980, 1090, 1076, 820 ns under 300, 400, 500, 600 and 700 kV/cm, respectively. The t0.9 results mean 90% of
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the stored energy can be released in less than 1100 ns under the electric field from 300 kV/cm to 700 kV/cm. Fig. 11 (d) shows the comparison between Wrec and Wdis under different
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electric field. The difference between Wrec and Wdis is quite large, and the similar result has been proved in series of former works [9, 35, 36]. This phenomenon may be because of the different discharge time. The thick films discharge quickly in submicrosecond using the pulsed discharge method. The discharge process is faster than that calculated from the P-E loops.
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4. Conclusion
In summary, (1-x)NBT-xBMT (x=0, 0.2, 0.4 and 0.6) lead-free thick films were fabricated
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using the sol-gel/spin coating technique. The addition of BMT induced slim P-E loops at room temperature. This behavior caused the large value of Pmax-Pr. Meanwhile, Mg2+ substituting Ti4+ at B-site forms the deep trap levels and then decreases the leakage current
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density, leading to a large BDS value. As a result, the maximum Wrec of 40.4 J/cm3 was
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obtained under a high BDS of 2440 kV/cm in the film of x=0.4, which was more than 4 times
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large than that of the pure NBT thick film. A fast discharge speed (t0.9<1100 ns) was also found in this thick film by using a pulsed discharge measurement. Meanwhile, the film
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exhibited superior thermal, frequency and electric-field cycling energy-storage stability. These results indicated that the 0.6NBT-0.4BMT thick film is a promising candidate for the
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dielectric capacitor devices. Acknowledgement
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The authors would like to acknowledge the financial support from the Natural Science Foundation of Inner Mongolia (2015JQ04, 2017BS0503), the Natural Science Foundation of
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China (51702169), the Program for Innovative Research Team in Universities of Inner Mongolia Autonomous Region (NMGIRT-A1605), the Program for Young Talents of Science and Technology in Universities of Inner Mongolia Autonomous Region, the Grassland Talent Plan of Inner Mongolia Autonomous Region, the Innovation Guide Fund of Baotou (CX2017-58) and the Innovation Fund of Inner Mongolia University of Science, Technology
(2014QNGG01, 2016QDL-S01, 2016QDL-B03) and the Innovation Guide Fund for Science
Reference
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and Technology of Inner Mongolia Autonomous Region(KCBJ2018034).
[1] F. Li, J.W. Zhai, B. Shen, X. Liu, K. Yang, Y. Zhang, P. Li, B.H. Liu, H.R. Zeng, of
structural
evolution
on
energy
storage
properties
SC R
Influence
in
Bi0.5Na0.5TiO3-SrTiO3-NaNbO3 lead-free ferroelectric ceramics, J. Appl. Phys. 121 (2017)
U
054103.
N
[2] T.Q. Shao, H.L. Du, H. Ma, S.B. Qu, J. Wang, J.F. Wang, X.Y. Wei, Z. Xu,
A
Potassium-sodium niobate based lead-free ceramics: novel electrical energy storage
M
materials, J. Mater. Chem. A 5 (2017) 554-563.
[3] Q.Y. Hu, T. Wang, L.Y. Zhao, L. Jin, Z. Xu, X.Y. Wei, Dielectric and energy storage
ED
properties of BaTiO3-Bi(Mg1/2Ti1/2)O3 ceramic: Influence of glass addition and biasing electric field, Ceram. Int. 43 (2017) 35-39.
PT
[4] Y.Y. Wu, X.H. Wang, C.F. Zhang, L.T. Li, Effect of Mn doping on microstructure and electrical properties of the (Na0.85K0.15)0.5Bi0.5TiO3 thin films prepared by sol–gel method,
CC E
J. Am. Ceram. Soc. 94 (2011) 3877-3882.
[5] Y. Li, D.W. Wang, W.Q. Cao, B. Li, J. Yuan, D.Q. Zhang, S.J. Zhang, M.S. Cao, Effect of
A
MnO2 addition on relaxor behavior and electrical properties of PMNST ferroelectric ceramics, Ceram. Int. 41 (2015) 9647-9654.
[6] P. Chen, P. Li, J.W. Zhai, B. Shen, F. Li, S.H. Wu, Enhanced dielectric and energy-storage properties in BiFeO3-modified Bi0.5(Na0.8K0.2)0.5TiO3 thin films, Ceram. Int. 43 (2017) 13371-13376.
[7] B.H. Ma, D.K. Kwon, M. Narayanan, U. Balachandran, Dielectric properties of PLZT film-on-foil capacitors, Mater. Lett. 62 (2008) 3573-3575. [8] C.W. Ahn, G. Amarsanaa, S.S. Won, S.A. Chae, D.S. Lee, I.W. Kim, Antiferroelectric thin-film capacitors with high energy-storage densities, low energy losses, and fast discharge time, ACS Appl. Mater. Interfaces 7 (2015) 26381-26386.
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[9] R. Xu, Z. Xu, Y.J. Feng, J.J. Tian, D. Huang, Energy storage and release properties of
Sr-doped (Pb,La)(Zr,Sn,Ti)O3 antiferroelectric ceramics, Ceram. Int. 42 (2016)
SC R
12875-12879.
[10] W.P. Cao, W.L. Li, Y. Feng, T. Bai, Y.L. Qiao, Y.F. Hou, T.D. Zhang, Y. Yu, W.D. Fei,
U
Defect dipole induced large recoverable strain and high energy-storage density in
N
lead-free Na0.5Bi0.5TiO3-based systems, Appl. Phys. Lett. 108 (2016) 202902.
A
[11] J.G. Hao, Z.J. Xu, R.Q. Chu, W. Li, J. Du, P. Fu, Enhanced energy-storage properties of
M
(1-x)[(1-y)(Bi0.5Na0.5)TiO3-y(Bi0.5K0.5)TiO3]-x(K0.5Na0.5)NbO3 lead-free ceramics, Solid State Commun. 204 (2015) 19-22.
ED
[12] L.M. Chen, N.N. Sun, Y. Li, Q.W. Zhang, L.W. Zhang, X.H. Hao, Multifunctional relaxor antiferroelectric multilayer ceramic capacitors with high energy-storage properties
PT
and large field-induced strain, J. Am. Ceram. Soc. DOI: 10.1111/jace.15380. [13] J.H. Wang, N.N. Sun, Y. Li, Q.W. Zhang, X.H. Hao, X.J. Chou, Effects of Mn doping on
CC E
dielectric properties and energy-storage performance of Na0.5Bi0.5TiO3 thick films, Ceram. Int. 43 (2017) 7804-7809.
A
[14] J.H. Wang, Y. Li, N.N. Sun, Q.W. Zhang, L.W. Zhang, X.H. Hao, X.J. Chou, Effects of Fe3+ doping on electrical properties and energy-storage performances of the (Na0.85K0.15)0.5Bi0.5TiO3 thick films prepared by sol-gel method, J. Alloys Compd. 727 (2017) 596-602.
[15] Q. Xu, T.M. Li, H. Hao, S.J. Zhang, Z.J. Wang, M.H. Cao, Z.H. Yao, H.X. Liu, Enhanced energy storage properties of NaNbO3 modified Bi0.5Na0.5TiO3 based ceramics, J. Eur. Ceram. Soc. 35 (2015) 545-553. [16] N.N Sun, Y. Li, Q.W. Zhang, X.H. Hao, Giant energy-storage density and high
nanoregions, J. Mater. Chem. C DOI: 10.1039/c8tc03481h.
IP T
efficiency achieved in (Bi0.5Na0.5)TiO3-Bi(Ni0.5Zr0.5)O3 thick films with polar
[17] F. Gao, X.L. Dong, C.L. Mao, F. Cao, G.S. Wang, c/a Ratio-dependent energy-storage
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density in (0.9-x)Bi0.5Na0.5TiO3-xBaTiO3-0.1K0.5Na0.5NbO3 ceramics, J. Am. Ceram. Soc. 94 (2011) 4162-4164.
U
[18] P. Chen, B.J. Chu, Improvement of dielectric and energy storage properties in
N
Bi(Mg1/2Ti1/2)O3-modified (Na1/2Bi1/2)0.92Ba0.08TiO3 ceramics, J. Eur. Ceram. Soc. 36
A
(2016) 81-88.
M
[19] Y.L. Zhang, W.L. Li, W.P. Cao, Y. Feng, Y.L. Qiao, T.D. Zhang, W.D. Fei, Mn doping to enhance energy storage performance of lead-free 0.7NBT-0.3ST thin films with weak
ED
oxygen vacancies, Appl. Phys. Lett. 110 (2017) 243901. [20] P. Jaita, P. Jarupoom, Rattikorn. Y, Gobwute. R, D. Cann, Phase transition and tolerance
PT
factor relationship of lead-free (Bi0.5K0.5)TiO3-Bi(Mg0.5Ti0.5)O3 piezoelectric ceramics, Ceram. Int. 42 (2016) 15940-15949.
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[21] Y. Li, D.W. Wang, W.Q. Cao, B. Li, J. Yuan, D.Q. Zhang, S.J. Zhang, M.S. Cao, Effect of MnO2 addition on relaxor behavior and electrical properties of PMNST ferroelectric
A
ceramics, Ceram. Int. 41 (2015) 9647-9654.
[22] X.G. Tang, K.H. Chew, H.L.W. Chan, Diffuse phase transition and dielectric tunability of Ba(ZryTi1-y)O3 relaxor ferroelectric ceramics, Acta Mater. 52 (2004) 5177–5183. [23] K. Uchino, S. Nomura, Critical exponents of the dielectric constants in diffused-phase-transition crystals, Ferroelectrics 44 (1982) 55–61.
[24] J.Q. Zhang, L. Wang, L. Bian, J.B. Xu, A.M. Chang, Structural, dielectric and piezoelectric properties of xBiFeO3-(1-x)BaTi0.9Zr0.1O3 ceramics, Ceram. Int. 40 (2014) 5173–5179. [25] T. Kawae, Y. Terauchi, H. Tsuda, M. Kumeda, A. Morimoto, Improved leakage and ferroelectric properties of Mn and Ti codoped BiFeO3 thin films, Appl. Phys. Lett. 94
IP T
(2009) 112904.
[26] C. Feng, C.H. Yang, H.T. Sui, F.J. Geng, Y.J. Han, Effect of Fe doping on the
SC R
crystallization and electrical properties of Na0.5Bi0.5TiO3 thin film, Ceram. Int. 41 (2015) 4214-4217.
U
[27] Y.L. Zhang, W.L. Li, Y.L. Qiao, Y. Zhao, Z.Y. Wang, Y. Yu, H.T. Xia, Z. Li, W.D. Fei,
N
0.6ST-0.4NBT thin film with low level Mn doping as a lead-free ferroelectric capacitor
A
with high energy storage performance, Appl. Phys. Lett. 112 (2018) 093902.
M
[28] F. Gao, X.L. Dong, C.L. Mao, W. Liu, H.L. Zhang, L.H. Yang, F. Cao, G.S. Wang, Energy-storage properties of 0.89Bi0.5Na0.5TiO3-0.06BaTiO3-0.05K0.5Na0.5NbO3 lead-free
ED
anti-ferroelectric ceramics, J. Am. Ceram. Soc. 94 (2011) 4382-4386. [29] X.X. Zhou, C.L. Yuan, Q.N. Li, Q, Feng, C.R. Zhou, X. Liu, Y. Yang, G.H. Chen, storage
properties
and
electrical
behavior
of
lead-free
PT
Energy
(1-x)Ba0.04Bi0.48Na0.48TiO3-xSrZrO3 ceramics, J. Mater. Sci: Mater. Electron. 27 (2016)
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3948-3956.
[30] Y. Zhao, X.H. Hao, M. Li, Dielectric properties and energy-storage performance of
A
(Na0.5Bi0.5)TiO3 thick films, J. Alloys. Comp. 601 (2014) 112-115.
[31] Y.L. Zhang, W.L. Li, W.P. Cao, T.D. Zhang, T.R.G.L. Bai, Y. Yu, Y.F. Hou, Y. Feng, W.D. Fei, Enhanced energy-storage performance of 0.94NBT-0.06BT thin films induced by a Pb0.8La0.1Ca0.1Ti0.975O3 seed layer, Ceram. Int. 42 (2016) 14788-14792.
[32] Z.S. Xu, X.H. Hao, S.L. An, Dielectric properties and energy-storage performance of (Na0.5Bi0.5)TiO3–SrTiO3 thick films derived from polyvinylpyrrolidone-modified chemical solution, J. Alloy Compd. 639 (2015) 387-392. [33] J.Q. Sun, C.H. Yang, J.H. Song, Y.Y. Zhou, Q. Yao, X.S. Sun, The microstructure, ferroelectric and dielectric behaviors of Na0.5Bi0.5(Ti,Fe)O3 thin films synthesized by
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chemical solution deposition: Effect of precursor solution concentration, Ceram. Int. 43 (2017) 2033-2038.
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[34] Z.K. Xie, Z.X. Yue, G. Ruehl, B. Peng, J. Zhang, Q. Yu, X.H. Zhang, L.T. Li,
Bi(Ni1/2Zr1/2)O3-PbTiO3 relaxor-ferroelectric films for piezoelectric energy harvesting and
U
electrostatic storage, Appl. Phys. Lett. 104 (2014) 243902.
N
[35] R. Xu, Z. Xu, Y.J. Feng, X.Y. Wei, J.J. Tian, D. Huang, Evaluation of discharge energy
A
density of antiferroelectric ceramics for pulse capacitors, Appl. Phys. Lett. 109 (2016)
M
032903.
[36] R. Xu, Z. Xu, Y.J. Feng, H.L. He, J.J. Tian, D. Huang, Temperature dependence of
ED
energy storage in Pb0.90La0.04Ba0.04[(Zr0.7Sn0.3)0.88Ti0.12]O3 antiferroelectric ceramics, J.
A
CC E
PT
Am. Ceram. Soc. 99 (2016) 2984-2988.
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Figure caption
Fig. 1 (a) The XRD patterns of the NBT-BMT thick films. (b) The magnified picture of (100)
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peak of the films.
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Fig. 2 (a)-(d) Surface microstructure of the NBT-BMT thick films with x=0, 0.2, 0.4 and 0.6.
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(e)-(h) Grain size distributions of the films. (i)–(l) Cross-sectional SEM images of the
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films.
Fig. 3 Room-temperature frequency-dependent dielectric constant and dielectric loss of the
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NBT-BMT thick films. The inset shows frequency-dependent dielectric constant and dielectric loss of the pure BMT thick film.
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Fig. 4 (a)-(d) Temperature dependences of dielectric constant and dielectric loss of the NBT-BMT thick films at 50 kHz, 100 kHz, 500 kHz and 1 MHz.
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Fig. 5 (a)-(c) The inverse dielectric constant (1000/εr) as a function of temperature for the NBT-BMT thick films at 100 kHz. The insets show the plots of ln(1/εr-1/εm) as a
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function of ln(T-Tm) for the NBT-BMT thick films.
Fig. 6 (a) The Weibull distribution of BDS for NBT-BMT thick films. (b) Leakage current characteristics of all thick films. (c)-(f) Logarithmic plots of the dependence of J as a function of E of NBT-BMT thick films. Fits of these data are shown to help in determining the leakage mechanism.
Fig. 7 The P-E loops of the NBT-BMT thick films measured under 1400 kV/cm and at room temperature. The inset shows their corresponding Pmax-Pr values. Fig. 8 Room-temperature phase PFM images of the NBT-BMT thick films: (a) x=0; (b) x=0.2; (c) x=0.4. Fig. 9 (a) Schematic diagram of the energy storage properties of ferroelectric thick films. (b)
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The P-E loops of the NBT-BMT thick films measured under their BDS and at room
temperature. (c) The recoverable energy-storage density (Wrec) and (d) efficiency (η) of
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the NBT-BMT thick films measured from 200 kV/cm to their BDS at room temperature.
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Fig. 10 (a) P-E hysteresis loops and (b) recoverable energy-storage density and efficiency as
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functions of the electric field of the 0.6NBT-0.4BMT thick film at different frequency.
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(c) P-E hysteresis loops and (d) recoverable energy-storage density and efficiency as functions of the electric field of the 0.6NBT-0.4BMT thick film at various temperatures
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(25-105 oC). (e) P-E hysteresis loops and (f) recoverable energy-storage density and
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efficiency as functions of the electric field of the 0.6NBT-0.4BMT thick film after various electric field cycling procedures with 600 kV/cm.
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Fig. 11 (a) Experimental platform for measurement of pulsed discharge current. (b) The pulsed discharge current waveform of the 0.6NBT-0.4BMT thick film under different
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electric field. (c) The time-dependence of the Wdis of 0.6NBT-0.4BMT thick film under different electric fields, and the inset shows the t0.9 of the film. (d) Electric field
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dependence of Wrec and Wdis of the 0.6NBT-0.4BMT thick film.
A ED
PT
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A
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A ED
PT
CC E
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U
N
A
M
IP T SC R U N A M ED PT CC E
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Table 1. The temperature of the maximum dielectric constant Tm, temperature of the dielectric constant that follows the Curie-Weiss law Tcw, deviation ΔTm, and the degree of diffuseness γ for the NBT-BMT thick films at 100 kHz.
Compositions
Tm(oC)
Tcw(oC)
∆Tm(oC)
γ
339.1
399.5
60.4
1.69
0.8NBT-0.2BMT
356
434.8
78.8
1.70
0.6NBT-0.4BMT
383.2
499.3
116.1
1.78
0.4NBT-0.6BMT
501.1
-
-
-
A
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PT
ED
M
A
N
U
SC R
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NBT
I N U SC R
Table 2. Wrec and applied electric field of NBT-based ceramics and films.
Wrec (J/cm3)
E (kV/cm)
Ref
0.95(0.8Bi0.5Na0.5TiO3-0.2SrTiO3)-0.05NaNbO3
0.74
70
1
1.2
100
11
0.90(0.92Na0.5Bi0.5TiO3-0.08BaTiO3)-0.10Bi(Mg0.5Ti0.5)O3
2
135
18
0.89Na0.5Bi0.5TiO3-0.06BaTiO3-0.05(K0.5Na0.5)NbO3
0.59
56
28
0.85Ba0.04Bi0.48Na0.48TiO3-0.15SrZrO3
1.2
155
29
Na0.5Bi0.5Ti0.99Mn0.01O3
30.2
2310
13
Sr0.3(Na0.5Bi0.5)0.7Ti0.99Mn0.01O3
27
1894
19
Sr0.6(Na0.5Bi0.5)0.4Ti0.99Mn0.01O3
33.58
3134
27
Na0.5Bi0.5TiO3
12.4
1200
30
0.94Na0.5Bi0.5TiO3-0.06BaTiO3
17.2
3310
31
0.95Na0.5Bi0.5TiO3-0.5SrTiO3
36.1
1965
32
Na0.5Bi0.5Ti0.98Fe0.02O3
30.15
1000
33
0.4Bi(Ni0.5Zr0.5)O3-0.6PbTiO3
39.8
2167
34
0.6Na0.5Bi0.5TiO3-0.4Bi(Mg0.5Ti0.5)O3
40.4
2440
This work
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Composition
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PT
ED
ceramics
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0.84(Bi0.5Na0.5)TiO3-0.16(K0.5Na0.5)NbO3
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films
S0955-2219(18)30623-X https://doi.org/10.1016/j.jeurceramsoc.2018.10.008 JECS 12126
To appear in:
Journal of the European Ceramic Society
Received date: Revised date: Accepted date:
25-4-2018 9-10-2018 9-10-2018
Please cite this article as: Wang J, Li Y, Sun N, Du J, Zhang Q, Hao X, Bi(Mg0.5 Ti0.5 )O3 addition induced high recoverable energy-storage density and excellent electrical properties in lead-free Na0.5 Bi0.5 TiO3 -based thick films, Journal of the European Ceramic Society (2018), https://doi.org/10.1016/j.jeurceramsoc.2018.10.008 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Bi(Mg0.5Ti0.5)O3 addition induced high recoverable energy-storage density and excellent electrical properties in lead-free Na0.5Bi0.5TiO3-based thick films Jiaheng Wang, Yong Li, Ningning Sun, Jinhua Du, Qiwei Zhang and Xihong Hao*,
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Inner Mongolia Key Laboratory of Ferroelectric-related New Energy Materials and Devices, School of Materials and Metallurgy, Inner Mongolia University of Science and Technology,
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Baotou 014010, China
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*Corresponding author: [email protected]; Tel: +86-472-5951572
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Abstract: (1-x)Na0.5Bi0.5TiO3-xBi(Mg0.5Ti0.5)O3 (NBT-BMT) thick films were designed for achieving large recoverable energy-storage density (Wrec). A large Wrec of 40.4 J/cm3 was
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detected in the thick film for x=0.4, which was more than 4 times larger than that of the pure
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NBT film. The addition of BMT induced slim polarization hysteresis (P-E) loops at room temperature. The slim P-E loops improved the difference between the maximum polarization
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(Pmax) and the remnant polarization (Pr). Besides, a breakdown strength field (BDS) of 2440 kV/cm was also detected in the thick film for x=0.4. The high BDS was caused by the reduced leakage current density. Furthermore, the thick film for x=0.4 possessed superior
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energy-storage stability under different temperature, frequency and electric-field cycling. In addition, 90% of the pulsed discharge energy density could be released in less than 1100 ns by using a pulsed discharge measurement.
Keywords:
NBT-BMT
thick
films;
Dielectric
property;
Sol-gel;
Energy-storage
performances
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1. Introduction
With the growth of the requirement for electronic communication, hybrid electric vehicles,
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health care and electrical weapons, the pulsed power technology has been received
considerable attention [1-5]. Dielectric capacitors are core elements in the electronic circuitry
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of the pulsed power systems. As the important parameter for the dielectric capacitors, high
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recoverable energy-storage density is needed to satisfy the miniaturization, lightening and
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integration of the device [6-10]. Besides, the energy-storage efficiency, fatigue resistance,
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temperature and frequency stability, and discharge properties also have great influence on the stable work of the whole systems. Generally, antiferroelectrics (AFEs), ferroelectrics (FEs),
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and linear dielectrics are the most widely studied energy-storage materials for dielectric capacitor [2]. AFEs exhibit the large energy-storage density because of their large maximum
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polarization (Pmax) and nearly zero remanent polarization (Pr). However, it is very difficult for AFE materials to withstand over several hundred charge-discharge circulations, because they
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are often cracked due to the phase transition during the charge-discharge process [11]. Linear dielectrics show small Wrec because of their smaller Pmax [2]. In contrast, FEs are more likely
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to achieve high Wrec due to their relatively high Pmax [1, 3]. For dielectric capacitors, increasing the difference between the maximum polarization (Pmax) and remnant polarization (Pr) is an effective way to increase the recoverable energy-storage density. Numerous studies have demonstrated that increasing the value of Pmax-Pr can be achieved by controlling the composition to decrease the tolerance factor (t) [6]. The tolerance
factor indicates the stability and distortion of the ABO3 perovskite structure, which is defined as [12]:
t
RA RO 2 ( RB RO )
(1)
where RA, RB, and RO are the ionic radii of the A-site cation, B-site cation, and oxygen anion,
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respectively. Thus, the tolerance factor can be reduced by introducing smaller ions on A site and larger ions on B site. In recent decade, a promising new energy-storage material based on
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Na0.5Bi0.5TiO3 (NBT) has been developed and studied for dielectric capacitors. The stereo-chemically active lone pair electrons of Bi3+ produce high polarization, which benefits for the energy storage [13]. However, pure NBT exhibits strong ferroelectricity at room
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temperature, and its high Pr can be serious limitation for practical applications [14].
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According to the above discussion, composition modifications should be used to suppress the
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Pr in NBT based materials in order to improve the energy-storage performance. Quite a few
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works are carried out to achieve this purpose by introducing oxides, such as BaTiO3, SrTiO3,
solid
solutions
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(K0.5Na0.5)NbO3, (K0.5Bi0.5)TiO3 and Bi(Mg0.5Ti0.5)O3, into NBT to form binary or ternary [15-18].
For
example,
Chen
reported
the
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(1-x)(Na0.5Bi0.5)0.92Ba0.08TiO3-x0.1Bi(Mg0.5Ti0.5)O3 (x=0, 0.02, 0.04, 0.06 and 0.10) ceramics [18]. The ionic radius of Mg2+ (0.83Å) is larger than that of Ti4+ (0.61Å), which induced slim
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P-E loops. The slim P-E loops increase the value of Pmax-Pr. As a result, the Pr/Pmax value of (1-x)(Na0.5Bi0.5)0.92Ba0.08TiO3-xBi(Mg0.5Ti0.5)O3
ceramics
decrease
from
0.8
for
(Na0.5Bi0.5)0.92Ba0.08TiO3 to 0.2 for 0.9(Na0.5Bi0.5)0.92Ba0.08TiO3-0.1Bi(Mg0.5Ti0.5)O3. The Wrec
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of 0.9(Na0.5Bi0.5)0.92Ba0.08TiO3-0.1Bi(Mg0.5Ti0.5)O3 ceramic is improved to 0.78 J/cm3, which is much larger than the Wrec of (Na0.5Bi0.5)0.92Ba0.08TiO3 ceramic of 0.2 J/cm3 at room temperature. Besides, improving the electrical BDS of the materials is another way to increase the recoverable energy density. The reported works on energy-storage NBT-based solutions are
mainly focused on bulk ceramics. Due to the lower BDS, the Wrec of the bulk ceramics is usually very small. Comparatively, film-form dielectrics with high BDS should be suitable for high energy storage. However, pure NBT film-form dielectrics are affected by high leakage current, and a material with a high leakage current has a low BDS that is not conducive to energy storage applications [13]. In order to improve the BDS, appropriate oxygen vacancies
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can be introduced to act as trap sites, thereby, electron trap levels become deeper, and acceptor doping usually introduces oxygen vacancies [19].
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According to the above discussing, in this work, composition modifications by adding
Bi(Mg0.5Ti0.5)O3 (BMT) into Na0.5Bi0.5TiO3 (NBT) are designed to increase the Pmax-Pr value
U
and the BDS in NBT-based thick films. On the one hand, the Mg2+ substitution Ti4+ in NBT-based thick film forming the deep trap levels will reduce the leakage current. On the
N
other hand, substitution of Mg2+ for Ti4+ in the B-site is expected to induce slim P-E loops,
M
A
according to formula (1), which is because the ionic radius of Mg2+ is larger than that of Ti4+. (1-x)Na0.5Bi0.5TiO3-xBi(Mg0.5Ti0.5)O3 [abbreviated as (1-x)NBT-xBMT, x=0, 0.2, 0.4 and 0.6]
ED
thick films were selected as a representative example to verify whether high Wrec can be obtained in their thick films. The corresponding energy-storage efficiency, fatigue resistance,
CC E
PT
temperature and frequency stability, discharge properties were also investigated.
2. Experimental procedure (1-x)NBT-xBMT
(x=0,
0.2,
0.4
and
0.6)
thick
films
were
grown
on
A
LaNiO3(100)/Pt(111)/TiO2/SiO2/Si substrate by using a polyvinylpyrrolidone (PVP)-modified sol-gel method. Sodium acetate trihydrate (99%), bismuth nitrate (99%), tetrabutyl titanate (98%) and magnesium acetate tetrahydrate (99%) were chosen as the raw materials with glacial acetic acid (99.5%), acetylacetone (99%) and distilled water as the solvents. The solutions of Na0.5Bi0.5TiO3 and Bi(Mg0.5Ti0.5)O3 were prepared separately and then mixed
together. The specific preparation procedure of Na0.5Bi0.5TiO3 precursor solution was as follows. Firstly, sodium acetate trihydrate and bismuth nitrate were dissolved in glacial acetic acid and distilled water at 80 oC. After cooling to room temperature, acetylacetone was added and stirred for 20 min. Finally, tetrabutyl titanate was added and stirred for 20 min until a stable yellow transparent solution was formed. The volume ratio of glacial acetic acid,
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distilled water and acetylacetone is 4:1:1. The preparation procedure of Bi(Mg0.5Ti0.5)O3 precursor solution is the same as that of Na0.5Bi0.5TiO3. Methanamide (99.5%), lactic acid
SC R
(85%) and polyvinylpyrrolidone (PVP) (94.4%) were added into the mixed solution to avoid the appearance of cracks and increase the viscosity of the solution. The mole ratio of the final
U
solution, methanamide, lactic acid and polyvinylpyrrolidone was 1:1:1:1. The final concentration of the solution was 0.45 M. NBT-BMT solutions were spin-coated onto
N
substrates at 3000 rpm for 30 s. The wet films were firstly dried at 200 oC for 3 min, then
M
A
pyrolysed at 400 oC for 10 min, and finally annealed at 700 oC for 3 min. This spin-coating and heat-treatment process was repeated 7 times to achieve the films with a desired thickness.
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Phase composition of the NBT-BMT thick films was measured by X-ray diffraction (XRD, Bruker D8 Advanced Diffractometer, German). The cross-sectional microstructure and the
PT
surface of these thick films were observed by field-emission scanning electron microscopy (FE-SEM, ZESIS Supra 55, German), atomic force microscope (AFM) (Dimension Icon,
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Bruker, German), and piezoelectric force microscopy (PFM, Bruker, Icon), respectively. Au top electrodes of 0.2 mm in diameter were sputtered through a mask version to measure the
A
dielectric properties and energy-storage performances. Dielectric properties were measured by Agilent E4980A LCR analyzer. The electric field-induced polarization hysteresis (P-E) loops, leakage current density and BDS of the thick films were tested by a Radiant Technology Ferroelectric tester (Radiant Technologies, Inc., Albuquerque, NM). Au top electrodes of 1 mm in diameter were used to test the discharge properties and leakage current density. The
pulsed discharge current was captured by a Rogowski coil (Pearson 6595, Pearson Electronics, Palo Alto, CA) and recorded by an oscilloscope (TBS 1102B-EDU, Tektronix Co. Ltd., China). The energy-storage properties of NBT-BMT thick films were calculated according to P-E loops and pulsed discharge currents.
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3. Results and discussion
The XRD patterns of the LNO substrates and the NBT-BMT thick films with x=0, 0.2, 0.4
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and 0.6 are shown in Fig. 1 (a). It is observed that all of the thick films are polycrystalline and
exhibit random orientation. The thick films with x=0, 0.2, 0.4 show pure perovskite phase,
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indicating that BMT and NBT combine to form a stable solid solution. However, a secondary
N
phase (Bi2Ti2O7) is detected in the thick film with x=0.6, which means that BMT exceeds the
A
solubility limit, and this unstable component causes the impurity phase. Fig. 1 (b) presents the
M
XRD patterns of (100) peaks of these thick films. With the increase of the BMT content, the diffraction peaks of the (100) shift to a lower diffraction angle owing to the relatively larger
expanded cell volumes.
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ionic radius of Mg2+ (0.83Å) compared with that of Ti4+ (0.61Å), which indicates the
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Fig. 2 (a)-(d) shows the AFM micrographs obtained for the surface of NBT-BMT thick films. Evidently, all samples have a similar morphology, which is dense and low porosity. Fig. 2
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(e)-(h) exhibit distribution of the grain size of the NBT-BMT thick films, which were calculated from 100 grains using a Nano Measurement software. The average grain (avg)
A
sizes are 92.6, 97.3, 104 and 93.8 nm for x=0, 0.2, 0.4 and 0.6, respectively. The cross-sectional SEM image and film thickness are shown in the inset of Fig. 2 (i)-(l). Clearly, the multi-layer structure is composed of a Pt(111)/TiO2/SiO2/Si substrate, a LaNiO3 (LNO) bottom electrode and the NBT-BMT thick film. All the thick films display a dense and
uniform microstructure with a thickness of 1000 nm. The thickness of the LNO bottom electrode is about 200 nm. Frequency-dependent dielectric constant and dielectric loss (tanδ) of the NBT-BMT thick films are plotted in Fig. 3, which were measured at room temperature and in the range of 1 kHz-1 MHz. As the frequency increases, the dielectric constant decreases gradually while the
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tanδ increases slightly. Dielectric constant and dielectric loss of the NBT-BMT thick films at 100 kHz are 504.3, 436.1, 392.2, 255.8 and 0.028, 0.033, 0.022, 0.070 for x=0, 0.2, 0.4 and
increase
of
the
BMT
content.
Pharatree
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0.6, respectively. The dielectric constant of the NBT-BMT thick films decreases with the reported
the
similar
result
for
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(1-x)K0.5Bi0.5TiO3-xBi(Mg0.5Ti0.5)O3 (KBT-BMT) ceramics, where the dielectric constant of
N
KBT-BMT ceramic decreases when x is above 0.15 [20]. The corresponding
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frequency-dependent dielectric constant and dielectric loss of the pure BMT thick film are
M
displayed in the inset of Fig. 3 (a).
Fig. 4 (a)-(d) demonstrates the dielectric constant and dielectric loss of NBT-BMT thick films
ED
as a function of temperature at 50 kHz, 100 kHz, 500 kHz and 1 MHz. With increasing x, the dielectric maximum temperature (Tm) shifts to high temperature. The Tm for the x=0, 0.2, 0.4
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and 0.6 are 339.1 oC, 356 oC, 383.2 oC and 501.1 oC, respectively, as listed in Table 1. The similar result was reported in Bi(Mg0.5Ti0.5)O3-modified (Na0.5Bi0.5)0.92Ba0.08TiO3 ceramics
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[18]. Furthermore, the addition of BMT decreases the dielectric constant of the thick films for x=0.4 and 0.6. The overall effect of BMT addition is that the temperature stability of the
A
dielectric constant is enhanced in a wide temperature range from 30 oC to Tm for the x=0.4 and 0.6 thick films. This phenomenon indicates that the 0.4 and 0.6 thick films could be suitable for high temperature dielectric applications. It is well known that the dielectric constant of a normal ferroelectric material above Curie temperature follows the Curie-Weiss law described by [21]:
1
T T0 (T T0 ) C
(2)
Where T0 is the Curie-Weiss temperature and C is the Curie-Weiss constant. The plots of temperature versus inverse dielectric constant of x=0, 0.2 and 0.4 are fitted to the Curie-Weiss law at 100 kHz, as shown in Fig. 5 (a)-(c). The parameter ∆Tm which is often used to show the
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degree of the deviation from the Curie-Weiss law is defined as [22]:
Tm Tcw Tm
(3)
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Where Tcw denotes the temperature from which the dielectric constant starts to deviate from the Curie-Weiss law and Tm represents the temperature of the dielectric constant maximum. The values of the Tcw and ∆Tm are also listed in Table 1. With the increase of BMT addition,
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the Tm and Tcw increase. The value of ∆Tm increases from 60.4 oC to 116.1 oC. These results
N
indicate that the diffuse phase transition (DPT) behavior of NBT-BMT thick film is enhanced
A
gradually with the increase of BMT addition. For the ferroelectrics, the reciprocal of the
r
1
m
(T Tm ) C
(4)
ED
1
M
dielectric constant and the temperature obey the Uchino and Nomura function [23].
PT
Where εm is the maximum value of the dielectric constant, γ is the indicator of the degree of diffuseness. The inset of Fig. 5 (a)-(c) show the plots of ln(1/εr-1/εm) versus ln(T-Tm) for the
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NBT-BMT thick films. The slope of the fitting curves is used to represent the value of γ. With the increase of BMT addition, the value of γ increases from 1.69 to 1.78. The limiting value γ=1 and γ=2 are the character for normal ferroelectric phase transition and for complete
A
diffuse phase transition, respectively [24]. This result also demonstrates that the addition of BMT enhanced the DPT behavior of NBT-BMT thick films. As for energy-storage applications, BDS is one of the most important parameters to determine the operative electric field and energy-storage density. The characteristic BDS of the NBT-BMT thick films was analyzed by the Weibull distribution [10, 14, 19]:
X i ln( Ei )
(5)
Yi ln(ln(1 /(1 Pi )))
(6)
Pi i /( n 1)
(7)
where Xi and Yi are two parameters in Weibull distribution function, Ei is the specific breakdown
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electric field of each specimen in the experiments, Pi is the possibility of a dielectric breakdown, n is the sum of specimens of each composition, and i is the rank of specimens. The Ei is arranged in
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ascending order of E1 ≤ E2 ≤ … ≤ Ei ≤ … ≤ En. In this work, we prepared three thick films for each composition. Au top electrodes were sputtered onto the surface of the thick film through a mask version. There were many top electrodes on each thick film, and each top electrode
U
corresponded to one specimen. For the three thick films, 8 close data values were chosen as
N
the final data to calculate the breakdown strength of each component, so n=8. Due to the
A
problems such as the uneven sputtering of the gold electrode, some specimens with
M
abnormally low or abnormally high values may be generated, and these specimens should be excluded. According to the above Weibull distribution equation, Xi and Yi have a linear
ED
relationship. The intersection of the fitted line and the X axis is the value of BDS when Yi=0. As is
PT
shown in Fig. 6 (a), the BDS values of the NBT-BMT thick films with x=0, 0.2, 0.4 and 0.6 obtained from the intercept on the x-axis are 1613, 1874, 2440 and 1605 kV/cm, respectively.
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Compared to the NBT thick film, the percentages of BDS enhancement are 16.2% and 51.3% for x=0.2 and 0.4, indicating that BMT adding could increase the BDS. The current densities for NBT-BMT thick films are plotted against the applied electric field (J-E) and shown in Fig. 6
A
(b). Compared with pure NBT thick film, the enhancement of insulation property is realized in BMT added thick film. The enhancement of insulation property could improve the value of BDS in the thick films. The leakage current density is the lowest when x=0.4, which is consistent with the result in Fig. 6 (a). In order to find out the origin of leakage current reduction in BMT added NBT thick films, the conduction mechanism of the prepared samples
is discussed. Fig. 6 (c)-(f) show the logarithmic plots of J as a function of E for NBT-BMT thick films. Clearly, all curves can be modeled in terms of space-charge-limited current (SCLC). In the low field region, the curves follow Ohmic conduction properties (α~1). With the increasing electric field, the curves follow modified Child’s law conduction (α~2). When the applied field is further increased, a sharp increase in the slope (α>3) in the curves occurs
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because of large leakage current density [25]. According to Lampert’s theory of SCLC
conductions, the transition electric field can be defined as Ec (Ohmic to modified Child’s law)
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and ETFL (modified Child’s law to the large leakage current field), respectively. For the
0.8NBT-0.2BMT thick film, ETEL is not observed. For the 0.6NBT-0.4BMT thick film, Ec is
So, the
ETFL for
each thick
film
is
found out
as
N
scope of measurement.
U
not observed. The phenomenon may be because the transition electric field is higher than the
ETFL(NBT)
M
A
indicates that doped Mg2+ ions in the thick films mainly act as carrier trap sites. Also, Ec for the 0.8NBT-0.2BMT and 0.6NBT-0.4BMT thick films are much higher than that of the pure
ED
NBT thick film. This suggests that Mg2+ ions give rise to deeper traps than Ti4+ ions. Thus, it means that deep traps were formed by Mg2+ doping. Moreover, the enhancement of insulation
PT
property of NBT-BMT thick films is closely related to such deep trap levels formed by ion doping. So, the leakage current density of BMT added NBT thick films in the modified
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Child’s law conduction region have been suppressed compared to the pure NBT thick film [19].
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The P-E loops of the NBT-BMT thick films are shown in Fig. 7, which were measured under 1400 kV/cm, 1 kHz and room temperature. As the BMT content increases, the Pmax decreases, which corresponds to the change trend of the dielectric constant. Moreover, the thick films with BMT addition exhibit slim P-E loops with small Pr value. This behavior will increase the value of Pmax-Pr, which is beneficial for the energy storage. As shown in the inset of Fig. 7,
the value of Pmax-Pr is 25.4, 33.6, 36.1 μC/cm2 for x=0, 0.2, 0.4, respectively. However, the value of Pmax-Pr of the thick film for x=0.6 is only 25.1 μC/cm2. The leakage current of the thick film for x=0.6 increases dramatically, which causes a poor P-E loops with round-shaped feature [26]. This phenomenon results in a small value of the Pmax-Pr. Evidently, the thick film for x=0.4 shows the largest value of Pmax-Pr. It could be predicted that the excellent
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energy-storage performance would be achieved in the NBT-BMT thick film for x=0.4.
Fig. 8 shows the PFM images of NBT-BMT thick films. With the BMT addition increasing,
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the domains become blurry, and the area of polar nanoregions (PNRs) increases. When BMT addition is increased to x=0.4, it is difficult to find uniform and continuous large area domain
U
structure. The structural transformation verifies the dielectric results, exhibiting the DPT
N
behavior. Moreover, PNRs are beneficial to the switching behavior of the polarization,
A
leading to a slim hysteresis loop in Fig. 7.
M
The recoverable energy-storage density Wrec of the ferroelectric thick films is usually studied by their P-E loops. The specific formula is as follows [13]: P max
Pr
Edp
ED
Wrec
(8)
PT
where E is the applied electric field, Pr is the remanent polarization and Pmax is the maximum polarization, illustrated by the green area in Fig. 9 (a). In the practical applications, in addition
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to higher recoverable energy-storage density Wrec, the corresponding higher efficiency η is also required. The η is calculated as the following formula [13]: Wrec Wrec Wloss
(9)
A
where Wloss is the closed red area of the P-E hysteresis loops as shown in Fig. 9 (a), which is represented by the unrecovered stored energy owing to the hysteresis loss. Fig. 9 (c) and (d) shows the Wrec and η of the NBT-BMT thick films, which were calculated from the P-E loops, ranging from 200 kV/cm to their BDS. Fig. 9 (b) shows their corresponding P-E loops under
the BDS. Clearly, with the increase of the applied electric field, the Wrec values for all the thick films increase, while η shows the contrary variation tendency. Typically, the maximum Wrec values of the NBT-BMT thick films at their BDS are 10, 18.3, 40.4 and 13.6 J/cm3 for x=0, 0.2, 0.4 and 0.6, and the η values are 19.6%, 31.8%, 54.6% and 31.8%, respectively. The thick film for x=0.4 shows better energy-storage performances than the other thick films
attributed to the large value of Pmax-Pr, high BDS and low dielectric loss.
IP T
owing to the higher Wrec and η. The enhanced energy-storage performances are mainly
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For the practical applications, besides higher Wrec and η values a good frequency-dependent stability is needed. The energy-storage density and the corresponding efficiency of the
U
0.6NBT-0.4BMT thick film were calculated from the P-E loops measured under an electric
N
field of 1200 kV/cm at different frequency. The results are displayed in Fig. 10 (a) and (b). As the frequency increases up to 5 kHz, P-E loops of the thick film change slightly. The Wrec
M
A
fluctuates only between 14.5 and 14.7 J/cm3, while the corresponding η changes from 65.5% to 69.9%. These results indicate that 0.6NBT-0.4BMT thick film shows excellent
ED
energy-storage frequency-related stability. The good thermal stability is also desired for the practical applications. Fig. 10 (c) presents P-E results of the 0.6NBT-0.4BMT thick film,
PT
which were tested at 1 kHz, in the range of 25-105 oC. As the temperature is increasing, the Pmax increases gradually and the Pr decreases firstly and then increases slightly. As a result,
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the Wrec and η increase firstly and then decrease. Changes of Wrec are less than 0.5 J/cm3. Furthermore, η also exhibits a relatively high value of 64.7% at 105 oC, as shown in Fig. 10
A
(d). This result suggests that the 0.6NBT-0.4BMT thick film possesses good thermal stability in the temperature range of 25-105 oC. In addition to the above, the endurance of the unit in terms of cycles should also be considered in the real capacitor applications. Fig. 10 (e) shows the polarization fatigue behavior of the 0.6NBT-0.4BMT thick film in the P-E loops after 1, 103, 106 and 107 switching cycles at room temperature, 1 kHz, the applied electric field of 600
kV/cm. The Pmax and Pr are almost not change after 103, 106 and 107 cycles of testing. Fig. 10 (f) shows the corresponding energy-storage density and efficiency stability after different fatigue cycles. Clearly, after 107 switches, the Wrec declines slightly while η reduces less than 4%. These results indicate that the 0.6NBT-0.4BMT thick film exhibits high fatigue endurance behavior.
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A comparison of BDS and recoverable energy-storage density of the NBT-based ceramics and films are displayed in Table 2. It could be found from Table 2 that the NBT-based ceramics
BDS
of
the
ceramics
is
often
lower
than
200
SC R
usually exhibit recoverable energy-storage density lower than 2 J/cm3. This is because that the kV/cm.
For
example,
the
density
of
1.2
J/cm3
at
the
BDS
of
155
kV/cm,
and
the
N
energy-storage
U
0.85Ba0.04Bi0.48Na0.48TiO3-0.15SrZrO3 ceramic (Table 2, ref. 29) shows an recoverable
0.90(0.92Na0.5Bi0.5TiO3-0.08BaTiO3)-0.10Bi(Mg0.5Ti0.5)O3 ceramic (Table 2, ref. 18) shows
M
A
an recoverable energy-storage density of 2 J/cm3 at the BDS of 135 kV/cm. Comparatively, the film form materials show large energy-storage densities. For example, the lead-based
ED
0.4Bi(Ni0.5Zr0.5)O3-0.6PbTiO3 film exhibits an ultra-high recoverable energy-storage density of 39.8 J/cm3 at 2167 kV/cm (Table 2, ref. 34), while the lead-free thick film
PT
0.6NBT-0.4BMT fabricated in this work exhibits a higher recoverable energy-storage density of 40.4 J/cm3 under an electric field of 2440 kV/cm. However, lead-based materials are
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harmful to the environment and human beings [30]. Thus, the developments of 0.6NBT-0.4BMT thick films as a lead-free material will arouse considerable attention for the
A
dielectric capacitors applied in energy-storage fields. Recently, a pulsed discharge method has been utilized more and more extensively to evaluate the practical working performance. The equivalent circuit diagram of the method is displayed in Fig. 11 (a). The detailed measuring process by the pulsed discharge method was reported in the ref [9]. The pulsed discharged energy density Wdis can be calculated as [9, 14]:
Wdis
R i '2 (t )dt
(10)
V
where i’(t), R and V are the current, load resistance and the volume of the thick film capacitors, respectively. The pulsed discharge current of the 0.6NBT-0.4BMT thick film is shown in Fig. 11 (b), which was measured at room temperature under different electric fields.
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Obviously, the pulsed discharge current reaches their peak value quickly and decreases rapidly, and with the increase of the strength of the electric field, the current peak is also
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increasing. Under 700 kV/cm, the current peak is 0.22 A. The electrode area for pulsed
discharge measurement is about 0.00785 cm2. Thus, the current density is 28 A/cm2. This result is as high as that of the Pb0.94La0.04[(Zr0.70Sn0.30)0.86Ti0.14]O3 ceramics [35]. The pulse
U
power applications of the dielectric capacitor require a fast discharge speed. Most of the
N
stored energy in the thick film is released quickly after starting the test. Thus, a parameter t0.9
A
which means the time required for the Wdis to reach 90% of its final value is utilized to
M
describe the energy release speed. The time-dependence of the pulsed discharged energy
ED
density Wdis of 0.6NBT-0.4BMT thick film under different electric fields are shown in Fig. 11 (c), and the inset of Fig. 11 (c) shows the t0.9 of the film. The discharge process lasts about
PT
2500 ns. The Wdis are 1.34, 2.17, 2.41, 2.74, 3.4 J/cm3 and the t0.9 are 804, 980, 1090, 1076, 820 ns under 300, 400, 500, 600 and 700 kV/cm, respectively. The t0.9 results mean 90% of
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the stored energy can be released in less than 1100 ns under the electric field from 300 kV/cm to 700 kV/cm. Fig. 11 (d) shows the comparison between Wrec and Wdis under different
A
electric field. The difference between Wrec and Wdis is quite large, and the similar result has been proved in series of former works [9, 35, 36]. This phenomenon may be because of the different discharge time. The thick films discharge quickly in submicrosecond using the pulsed discharge method. The discharge process is faster than that calculated from the P-E loops.
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4. Conclusion
In summary, (1-x)NBT-xBMT (x=0, 0.2, 0.4 and 0.6) lead-free thick films were fabricated
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using the sol-gel/spin coating technique. The addition of BMT induced slim P-E loops at room temperature. This behavior caused the large value of Pmax-Pr. Meanwhile, Mg2+ substituting Ti4+ at B-site forms the deep trap levels and then decreases the leakage current
N
U
density, leading to a large BDS value. As a result, the maximum Wrec of 40.4 J/cm3 was
A
obtained under a high BDS of 2440 kV/cm in the film of x=0.4, which was more than 4 times
M
large than that of the pure NBT thick film. A fast discharge speed (t0.9<1100 ns) was also found in this thick film by using a pulsed discharge measurement. Meanwhile, the film
ED
exhibited superior thermal, frequency and electric-field cycling energy-storage stability. These results indicated that the 0.6NBT-0.4BMT thick film is a promising candidate for the
PT
dielectric capacitor devices. Acknowledgement
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The authors would like to acknowledge the financial support from the Natural Science Foundation of Inner Mongolia (2015JQ04, 2017BS0503), the Natural Science Foundation of
A
China (51702169), the Program for Innovative Research Team in Universities of Inner Mongolia Autonomous Region (NMGIRT-A1605), the Program for Young Talents of Science and Technology in Universities of Inner Mongolia Autonomous Region, the Grassland Talent Plan of Inner Mongolia Autonomous Region, the Innovation Guide Fund of Baotou (CX2017-58) and the Innovation Fund of Inner Mongolia University of Science, Technology
(2014QNGG01, 2016QDL-S01, 2016QDL-B03) and the Innovation Guide Fund for Science
Reference
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and Technology of Inner Mongolia Autonomous Region(KCBJ2018034).
[1] F. Li, J.W. Zhai, B. Shen, X. Liu, K. Yang, Y. Zhang, P. Li, B.H. Liu, H.R. Zeng, of
structural
evolution
on
energy
storage
properties
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Influence
in
Bi0.5Na0.5TiO3-SrTiO3-NaNbO3 lead-free ferroelectric ceramics, J. Appl. Phys. 121 (2017)
U
054103.
N
[2] T.Q. Shao, H.L. Du, H. Ma, S.B. Qu, J. Wang, J.F. Wang, X.Y. Wei, Z. Xu,
A
Potassium-sodium niobate based lead-free ceramics: novel electrical energy storage
M
materials, J. Mater. Chem. A 5 (2017) 554-563.
[3] Q.Y. Hu, T. Wang, L.Y. Zhao, L. Jin, Z. Xu, X.Y. Wei, Dielectric and energy storage
ED
properties of BaTiO3-Bi(Mg1/2Ti1/2)O3 ceramic: Influence of glass addition and biasing electric field, Ceram. Int. 43 (2017) 35-39.
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[4] Y.Y. Wu, X.H. Wang, C.F. Zhang, L.T. Li, Effect of Mn doping on microstructure and electrical properties of the (Na0.85K0.15)0.5Bi0.5TiO3 thin films prepared by sol–gel method,
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J. Am. Ceram. Soc. 94 (2011) 3877-3882.
[5] Y. Li, D.W. Wang, W.Q. Cao, B. Li, J. Yuan, D.Q. Zhang, S.J. Zhang, M.S. Cao, Effect of
A
MnO2 addition on relaxor behavior and electrical properties of PMNST ferroelectric ceramics, Ceram. Int. 41 (2015) 9647-9654.
[6] P. Chen, P. Li, J.W. Zhai, B. Shen, F. Li, S.H. Wu, Enhanced dielectric and energy-storage properties in BiFeO3-modified Bi0.5(Na0.8K0.2)0.5TiO3 thin films, Ceram. Int. 43 (2017) 13371-13376.
[7] B.H. Ma, D.K. Kwon, M. Narayanan, U. Balachandran, Dielectric properties of PLZT film-on-foil capacitors, Mater. Lett. 62 (2008) 3573-3575. [8] C.W. Ahn, G. Amarsanaa, S.S. Won, S.A. Chae, D.S. Lee, I.W. Kim, Antiferroelectric thin-film capacitors with high energy-storage densities, low energy losses, and fast discharge time, ACS Appl. Mater. Interfaces 7 (2015) 26381-26386.
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[9] R. Xu, Z. Xu, Y.J. Feng, J.J. Tian, D. Huang, Energy storage and release properties of
Sr-doped (Pb,La)(Zr,Sn,Ti)O3 antiferroelectric ceramics, Ceram. Int. 42 (2016)
SC R
12875-12879.
[10] W.P. Cao, W.L. Li, Y. Feng, T. Bai, Y.L. Qiao, Y.F. Hou, T.D. Zhang, Y. Yu, W.D. Fei,
U
Defect dipole induced large recoverable strain and high energy-storage density in
N
lead-free Na0.5Bi0.5TiO3-based systems, Appl. Phys. Lett. 108 (2016) 202902.
A
[11] J.G. Hao, Z.J. Xu, R.Q. Chu, W. Li, J. Du, P. Fu, Enhanced energy-storage properties of
M
(1-x)[(1-y)(Bi0.5Na0.5)TiO3-y(Bi0.5K0.5)TiO3]-x(K0.5Na0.5)NbO3 lead-free ceramics, Solid State Commun. 204 (2015) 19-22.
ED
[12] L.M. Chen, N.N. Sun, Y. Li, Q.W. Zhang, L.W. Zhang, X.H. Hao, Multifunctional relaxor antiferroelectric multilayer ceramic capacitors with high energy-storage properties
PT
and large field-induced strain, J. Am. Ceram. Soc. DOI: 10.1111/jace.15380. [13] J.H. Wang, N.N. Sun, Y. Li, Q.W. Zhang, X.H. Hao, X.J. Chou, Effects of Mn doping on
CC E
dielectric properties and energy-storage performance of Na0.5Bi0.5TiO3 thick films, Ceram. Int. 43 (2017) 7804-7809.
A
[14] J.H. Wang, Y. Li, N.N. Sun, Q.W. Zhang, L.W. Zhang, X.H. Hao, X.J. Chou, Effects of Fe3+ doping on electrical properties and energy-storage performances of the (Na0.85K0.15)0.5Bi0.5TiO3 thick films prepared by sol-gel method, J. Alloys Compd. 727 (2017) 596-602.
[15] Q. Xu, T.M. Li, H. Hao, S.J. Zhang, Z.J. Wang, M.H. Cao, Z.H. Yao, H.X. Liu, Enhanced energy storage properties of NaNbO3 modified Bi0.5Na0.5TiO3 based ceramics, J. Eur. Ceram. Soc. 35 (2015) 545-553. [16] N.N Sun, Y. Li, Q.W. Zhang, X.H. Hao, Giant energy-storage density and high
nanoregions, J. Mater. Chem. C DOI: 10.1039/c8tc03481h.
IP T
efficiency achieved in (Bi0.5Na0.5)TiO3-Bi(Ni0.5Zr0.5)O3 thick films with polar
[17] F. Gao, X.L. Dong, C.L. Mao, F. Cao, G.S. Wang, c/a Ratio-dependent energy-storage
SC R
density in (0.9-x)Bi0.5Na0.5TiO3-xBaTiO3-0.1K0.5Na0.5NbO3 ceramics, J. Am. Ceram. Soc. 94 (2011) 4162-4164.
U
[18] P. Chen, B.J. Chu, Improvement of dielectric and energy storage properties in
N
Bi(Mg1/2Ti1/2)O3-modified (Na1/2Bi1/2)0.92Ba0.08TiO3 ceramics, J. Eur. Ceram. Soc. 36
A
(2016) 81-88.
M
[19] Y.L. Zhang, W.L. Li, W.P. Cao, Y. Feng, Y.L. Qiao, T.D. Zhang, W.D. Fei, Mn doping to enhance energy storage performance of lead-free 0.7NBT-0.3ST thin films with weak
ED
oxygen vacancies, Appl. Phys. Lett. 110 (2017) 243901. [20] P. Jaita, P. Jarupoom, Rattikorn. Y, Gobwute. R, D. Cann, Phase transition and tolerance
PT
factor relationship of lead-free (Bi0.5K0.5)TiO3-Bi(Mg0.5Ti0.5)O3 piezoelectric ceramics, Ceram. Int. 42 (2016) 15940-15949.
CC E
[21] Y. Li, D.W. Wang, W.Q. Cao, B. Li, J. Yuan, D.Q. Zhang, S.J. Zhang, M.S. Cao, Effect of MnO2 addition on relaxor behavior and electrical properties of PMNST ferroelectric
A
ceramics, Ceram. Int. 41 (2015) 9647-9654.
[22] X.G. Tang, K.H. Chew, H.L.W. Chan, Diffuse phase transition and dielectric tunability of Ba(ZryTi1-y)O3 relaxor ferroelectric ceramics, Acta Mater. 52 (2004) 5177–5183. [23] K. Uchino, S. Nomura, Critical exponents of the dielectric constants in diffused-phase-transition crystals, Ferroelectrics 44 (1982) 55–61.
[24] J.Q. Zhang, L. Wang, L. Bian, J.B. Xu, A.M. Chang, Structural, dielectric and piezoelectric properties of xBiFeO3-(1-x)BaTi0.9Zr0.1O3 ceramics, Ceram. Int. 40 (2014) 5173–5179. [25] T. Kawae, Y. Terauchi, H. Tsuda, M. Kumeda, A. Morimoto, Improved leakage and ferroelectric properties of Mn and Ti codoped BiFeO3 thin films, Appl. Phys. Lett. 94
IP T
(2009) 112904.
[26] C. Feng, C.H. Yang, H.T. Sui, F.J. Geng, Y.J. Han, Effect of Fe doping on the
SC R
crystallization and electrical properties of Na0.5Bi0.5TiO3 thin film, Ceram. Int. 41 (2015) 4214-4217.
U
[27] Y.L. Zhang, W.L. Li, Y.L. Qiao, Y. Zhao, Z.Y. Wang, Y. Yu, H.T. Xia, Z. Li, W.D. Fei,
N
0.6ST-0.4NBT thin film with low level Mn doping as a lead-free ferroelectric capacitor
A
with high energy storage performance, Appl. Phys. Lett. 112 (2018) 093902.
M
[28] F. Gao, X.L. Dong, C.L. Mao, W. Liu, H.L. Zhang, L.H. Yang, F. Cao, G.S. Wang, Energy-storage properties of 0.89Bi0.5Na0.5TiO3-0.06BaTiO3-0.05K0.5Na0.5NbO3 lead-free
ED
anti-ferroelectric ceramics, J. Am. Ceram. Soc. 94 (2011) 4382-4386. [29] X.X. Zhou, C.L. Yuan, Q.N. Li, Q, Feng, C.R. Zhou, X. Liu, Y. Yang, G.H. Chen, storage
properties
and
electrical
behavior
of
lead-free
PT
Energy
(1-x)Ba0.04Bi0.48Na0.48TiO3-xSrZrO3 ceramics, J. Mater. Sci: Mater. Electron. 27 (2016)
CC E
3948-3956.
[30] Y. Zhao, X.H. Hao, M. Li, Dielectric properties and energy-storage performance of
A
(Na0.5Bi0.5)TiO3 thick films, J. Alloys. Comp. 601 (2014) 112-115.
[31] Y.L. Zhang, W.L. Li, W.P. Cao, T.D. Zhang, T.R.G.L. Bai, Y. Yu, Y.F. Hou, Y. Feng, W.D. Fei, Enhanced energy-storage performance of 0.94NBT-0.06BT thin films induced by a Pb0.8La0.1Ca0.1Ti0.975O3 seed layer, Ceram. Int. 42 (2016) 14788-14792.
[32] Z.S. Xu, X.H. Hao, S.L. An, Dielectric properties and energy-storage performance of (Na0.5Bi0.5)TiO3–SrTiO3 thick films derived from polyvinylpyrrolidone-modified chemical solution, J. Alloy Compd. 639 (2015) 387-392. [33] J.Q. Sun, C.H. Yang, J.H. Song, Y.Y. Zhou, Q. Yao, X.S. Sun, The microstructure, ferroelectric and dielectric behaviors of Na0.5Bi0.5(Ti,Fe)O3 thin films synthesized by
IP T
chemical solution deposition: Effect of precursor solution concentration, Ceram. Int. 43 (2017) 2033-2038.
SC R
[34] Z.K. Xie, Z.X. Yue, G. Ruehl, B. Peng, J. Zhang, Q. Yu, X.H. Zhang, L.T. Li,
Bi(Ni1/2Zr1/2)O3-PbTiO3 relaxor-ferroelectric films for piezoelectric energy harvesting and
U
electrostatic storage, Appl. Phys. Lett. 104 (2014) 243902.
N
[35] R. Xu, Z. Xu, Y.J. Feng, X.Y. Wei, J.J. Tian, D. Huang, Evaluation of discharge energy
A
density of antiferroelectric ceramics for pulse capacitors, Appl. Phys. Lett. 109 (2016)
M
032903.
[36] R. Xu, Z. Xu, Y.J. Feng, H.L. He, J.J. Tian, D. Huang, Temperature dependence of
ED
energy storage in Pb0.90La0.04Ba0.04[(Zr0.7Sn0.3)0.88Ti0.12]O3 antiferroelectric ceramics, J.
A
CC E
PT
Am. Ceram. Soc. 99 (2016) 2984-2988.
IP T SC R
Figure caption
Fig. 1 (a) The XRD patterns of the NBT-BMT thick films. (b) The magnified picture of (100)
U
peak of the films.
N
Fig. 2 (a)-(d) Surface microstructure of the NBT-BMT thick films with x=0, 0.2, 0.4 and 0.6.
A
(e)-(h) Grain size distributions of the films. (i)–(l) Cross-sectional SEM images of the
M
films.
Fig. 3 Room-temperature frequency-dependent dielectric constant and dielectric loss of the
ED
NBT-BMT thick films. The inset shows frequency-dependent dielectric constant and dielectric loss of the pure BMT thick film.
PT
Fig. 4 (a)-(d) Temperature dependences of dielectric constant and dielectric loss of the NBT-BMT thick films at 50 kHz, 100 kHz, 500 kHz and 1 MHz.
CC E
Fig. 5 (a)-(c) The inverse dielectric constant (1000/εr) as a function of temperature for the NBT-BMT thick films at 100 kHz. The insets show the plots of ln(1/εr-1/εm) as a
A
function of ln(T-Tm) for the NBT-BMT thick films.
Fig. 6 (a) The Weibull distribution of BDS for NBT-BMT thick films. (b) Leakage current characteristics of all thick films. (c)-(f) Logarithmic plots of the dependence of J as a function of E of NBT-BMT thick films. Fits of these data are shown to help in determining the leakage mechanism.
Fig. 7 The P-E loops of the NBT-BMT thick films measured under 1400 kV/cm and at room temperature. The inset shows their corresponding Pmax-Pr values. Fig. 8 Room-temperature phase PFM images of the NBT-BMT thick films: (a) x=0; (b) x=0.2; (c) x=0.4. Fig. 9 (a) Schematic diagram of the energy storage properties of ferroelectric thick films. (b)
IP T
The P-E loops of the NBT-BMT thick films measured under their BDS and at room
temperature. (c) The recoverable energy-storage density (Wrec) and (d) efficiency (η) of
SC R
the NBT-BMT thick films measured from 200 kV/cm to their BDS at room temperature.
U
Fig. 10 (a) P-E hysteresis loops and (b) recoverable energy-storage density and efficiency as
N
functions of the electric field of the 0.6NBT-0.4BMT thick film at different frequency.
A
(c) P-E hysteresis loops and (d) recoverable energy-storage density and efficiency as functions of the electric field of the 0.6NBT-0.4BMT thick film at various temperatures
M
(25-105 oC). (e) P-E hysteresis loops and (f) recoverable energy-storage density and
ED
efficiency as functions of the electric field of the 0.6NBT-0.4BMT thick film after various electric field cycling procedures with 600 kV/cm.
PT
Fig. 11 (a) Experimental platform for measurement of pulsed discharge current. (b) The pulsed discharge current waveform of the 0.6NBT-0.4BMT thick film under different
CC E
electric field. (c) The time-dependence of the Wdis of 0.6NBT-0.4BMT thick film under different electric fields, and the inset shows the t0.9 of the film. (d) Electric field
A
dependence of Wrec and Wdis of the 0.6NBT-0.4BMT thick film.
A ED
PT
CC E
IP T
SC R
U
N
A
M
A ED
PT
CC E
IP T
SC R
U
N
A
M
IP T SC R U N A M ED PT CC E
A
Table 1. The temperature of the maximum dielectric constant Tm, temperature of the dielectric constant that follows the Curie-Weiss law Tcw, deviation ΔTm, and the degree of diffuseness γ for the NBT-BMT thick films at 100 kHz.
Compositions
Tm(oC)
Tcw(oC)
∆Tm(oC)
γ
339.1
399.5
60.4
1.69
0.8NBT-0.2BMT
356
434.8
78.8
1.70
0.6NBT-0.4BMT
383.2
499.3
116.1
1.78
0.4NBT-0.6BMT
501.1
-
-
-
A
CC E
PT
ED
M
A
N
U
SC R
IP T
NBT
I N U SC R
Table 2. Wrec and applied electric field of NBT-based ceramics and films.
Wrec (J/cm3)
E (kV/cm)
Ref
0.95(0.8Bi0.5Na0.5TiO3-0.2SrTiO3)-0.05NaNbO3
0.74
70
1
1.2
100
11
0.90(0.92Na0.5Bi0.5TiO3-0.08BaTiO3)-0.10Bi(Mg0.5Ti0.5)O3
2
135
18
0.89Na0.5Bi0.5TiO3-0.06BaTiO3-0.05(K0.5Na0.5)NbO3
0.59
56
28
0.85Ba0.04Bi0.48Na0.48TiO3-0.15SrZrO3
1.2
155
29
Na0.5Bi0.5Ti0.99Mn0.01O3
30.2
2310
13
Sr0.3(Na0.5Bi0.5)0.7Ti0.99Mn0.01O3
27
1894
19
Sr0.6(Na0.5Bi0.5)0.4Ti0.99Mn0.01O3
33.58
3134
27
Na0.5Bi0.5TiO3
12.4
1200
30
0.94Na0.5Bi0.5TiO3-0.06BaTiO3
17.2
3310
31
0.95Na0.5Bi0.5TiO3-0.5SrTiO3
36.1
1965
32
Na0.5Bi0.5Ti0.98Fe0.02O3
30.15
1000
33
0.4Bi(Ni0.5Zr0.5)O3-0.6PbTiO3
39.8
2167
34
0.6Na0.5Bi0.5TiO3-0.4Bi(Mg0.5Ti0.5)O3
40.4
2440
This work
A
Composition
CC E
PT
ED
ceramics
M
0.84(Bi0.5Na0.5)TiO3-0.16(K0.5Na0.5)NbO3
A
films