Dielectric and Ferroelectric Properties of SrTiO3–Bi0.5Na0.5TiO3

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Dielectric and Ferroelectric Properties of SrTiO3−Bi0.5Na0.5TiO3− BaAl0.5Nb0.5O3 Lead-Free Ceramics for High-Energy-Storage Applications Fei Yan, Haibo Yang,* Ying Lin, and Tong Wang School of Materials Science and Engineering, Shaanxi University of Science and Technology, Weiyang District, Xi’an 710021 China ABSTRACT: Pulsed capacitors require high-recoverable energystorage density (Wrec) and high energy-storage efficiency (η), which can be realized through the selection and adjustment of the composition. In this work, (1 − x)SrTiO 3 − x(0.95Bi 0.5 Na 0.5 TiO 3 −0.05BaAl 0.5 Nb 0.5 O 3 ) [(1 − x)ST− x(BNT−BAN)] ceramics were successfully prepared via the pressureless solid-state reaction method. The dielectric constant increases gradually with the introduction of BNT−BAN and obtains a maximum value of 3430 with the composition of 0.4ST−0.6(BNT−BAN) at 100 Hz, which is 10.39 times higher than that of the pure ST sample (∼330). Dispersive relaxor behaviors and ferroelectric performances can be enhanced with the introduction of BNT−BAN. The composition of 0.5ST− 0.5(BNT−BAN) exhibits a high Wrec of 1.89 J/cm3 as well as a high η of 77%. Therefore, the (1 − x)ST−x(BNT−BAN) systems are candidate materials for pulsed capacitor applications.

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INTRODUCTION With the increasing demands of society, energy storage has become a focused topic in today’s society.1,2 Compared with batteries and supercapacitors, dielectric capacitors exhibit many advantages in terms of exceedingly quick charge−discharge rate and durability.3,4 Particularly, ceramic-based dielectrics are essential materials for pulsed power capacitors because of excellent thermal and mechanical properties.5,6 Generally, W, Wrec, and η can be evaluated by eqs 1−3, respectively.7 W=

∫0

Wrec =

Pmax

∫P

E dP

Pmax

(1) Figure 1. Schematic for calculation of the energy-storage properties.6

E dP

(2)

r

η=

Wrec × 100% W

the Wrec value of antiferroelectric materials is higher than those of ferroelectric and linear dielectrics because of high Pmax, low Pr, and moderate BDS.7,10,11 For example, (Pb0.87Ba0.1La0.02)(Zr0.65Sn0.3Ti0.05)O3 ceramics with Y addition could obtain a Wrec value of 2.75 J/cm3, accompanied by an η value of 71.5%.12 For Pb(Tm1/2Nb1/2)O3−Pb(Mg1/3Nb2/3)O3 ceramics, a Wrec value of 3.12 J/cm3 could be achieved.13 However, most of antiferroelectrics are lead-based materials. The toxicity of lead would cause a series of human health hazards and environmental deteriorations. Thus, lead-free materials with excellent Wrec and η need to be developed. SrTiO3 (ST) belongs to linear dielectrics and possesses unique physical properties, such as moderate dielectric constant

(3)

where P, Pmax, Pr, and E are the polarization, maximum polarization, remnant polarization, and applied electric field, respectively. The value of Wrec can be calculated via the green area in Figure 1, and the value of W can be calculated via the yellow and green areas in Figure 1. As shown in Figure 1 and eq 2, the achievement of high Wrec needs the combination of large breakdown strength (BDS), high Pmax, and low Pr. For the practical application, η is also an important indicator of energystorage capacitors.8 Higher η implies that more energy may be converted to heat in the process of discharge, which will degrade the properties or even damage the capacitors.9 Among the various dielectric ceramic materials developed at present, © XXXX American Chemical Society

Received: August 29, 2017

A

DOI: 10.1021/acs.inorgchem.7b02181 Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry

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RESULTS AND DISCUSSION Figure 2 illustrates the XRD results of (1 − x)ST−x(BNT− BAN) ceramics at room temperature. As shown in Figure 2,

(∼290), relatively high BDS (∼200 kV/cm) and low dielectric loss ( 0.6 is due to the introduction of BNT−BAN with large ε′ and high Curie temperature (TC),32−34 leading to TC shifting toward higher temperatures, as shown in Figure 7. Commonly, dielectric materials possess maximum values of ε′ at TC. Meanwhile, all of the samples with different values of x can maintain a low value of tan δ ( 0. It makes clearly strong relaxor behaviors of (1 − x)ST− x(BNT−BAN) samples. Figure 9a illustrates P−E loops of (1 − x)ST−x(BNT− BAN) samples. It is obviously observed that the P−E loops transform from a linear dielectric behavior to a relaxor ferroelectric behavior gradually with the addition of BNT− BAN. That is to say, the ferroelectric properties of ST can be enhanced observably with BNT−BAN addition. Therefore, Pmax and Pr can be enhanced substantially with increasing BNT−BAN content, as shown in Figure 9b. Pmax is improved to 41.81 μC/cm2 for the sample of x = 0.8 at 140 kV/cm, which is 8.90 times high than that of the pure ST sample (4.70 μC/ cm2). As shown in Figure 9b, the significant improvement of Pmax and a slight increase of Pr are conducive to achieving high Wrec. Figure 10 presents P−E loops of (1 − x)ST−x(BNT− BAN) samples. It is evidently observed that the samples possess slim P−E loops, high BDS, and large Pmax. According to eq 2, the (1 − x)ST−x(BNT−BAN) systems are favorable for obtaining high Wrec because of the fact that they simultaneously possess large Pmax, small Pr, and high BDS.

Figure 4. Average grain size of (1 − x)ST−x(BNT−BAN) ceramics.

Figure 5. Frequency dependence of the dielectric properties for (1 − x)ST−x(BNT−BAN) ceramics.

ceramics. It can be observed that εm′ (the maximum value of ε′) increases and TC shifts toward higher temperatures gradually with the increasing addition of BNT−BAN, which are summarized in Figure 7. In addition, εm′ moves to higher temperatures gradually with an enhancement in the frequencies. It is known as relaxor behavior and is consistent with that previously reported.35−37 In this study, A- and B-site substitution by Bi3+, Na+ and Ba2+, Nb5+ and Al3+, respectively, C

DOI: 10.1021/acs.inorgchem.7b02181 Inorg. Chem. XXXX, XXX, XXX−XXX

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Inorganic Chemistry

Figure 6. Temperature dependence of the dielectric properties for (1 − x)ST−x(BNT−BAN) ceramics.

high η and low Wloss in practical applications. The values of η and Wloss for (1 − x)ST−x(BNT−BAN) ceramics are exhibited in Figure 11b. One can see that Wloss shows an incremental trend and η shows a decremental trend with increasing addition of BNT−BAN, and η is more than 70% for all of the samples. Figure 12a shows unipolar P−E loops of the 0.5ST− 0.5(BNT−BAN) ceramic with varied electric fields. The value of Pmax increases from 6.38 to 30.56 μC/cm2 with enhancement of the electric field from 20 to 190 kV/cm, indicating that much higher Wrec can be obtained by increasing the value of BDS for 0.5ST−0.5(BNT−BAN) ceramic. The energy-storage properties of the 0.5ST−0.5(BNT−BAN) ceramic are presented in Figure 12b,c. One can see that the values of W and Wrec are enhanced from 0.07 and 0.06 J/cm3 to 2.46 and 1.89 J/cm3, respectively, with increasing electric field from 20 to 190 kV/ cm. However, the value of η decreases with increasing electric field, which is attributed to the fact that Wloss increases with increasing electric field.27 (1 − x)ST−x(BNT−BAN) ceramics exhibit the highest W (2.46 J/cm3) and Wrec (1.89 J/cm3), together with a high η value of 77% at 190 kV/cm. Figure 13

Figure 7. Variation of εm′ and TC for (1 − x)ST−x(BNT−BAN) ceramics.

Figure 11a illustrates the calculated W and Wrec of (1 − x)ST−x(BNT−BAN) ceramics. One can see that both W and Wrec first increase and then decrease with the addition of BNT−BAN, reaching maximum values (W and Wrec are 2.46 and 1.89 J/cm3, respectively) with the composition of 0.5ST− 0.5(BNT−BAN). In addition, it is very important to obtain

Figure 8. Plots of ln(1/ε′ − 1/εm′) versus ln(T − Tm) of (1 − x)ST−x(BNT−BAN) ceramics. D

DOI: 10.1021/acs.inorgchem.7b02181 Inorg. Chem. XXXX, XXX, XXX−XXX

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Figure 9. (a) P−E loops and (b) Pr and Pmax for (1 − x)ST−x(BNT−BAN) ceramics under 140 kV/cm.

Figure 10. P−E loops at critical electric fields of the (1 − x)ST− x(BNT−BAN) ceramics.

Figure 12. (a) Unipolar P−E loops of the 0.5ST−0.5(BNT−BAN) ceramic with different electric fields. (b) Calculated W and Wrec from part a. (c) Calculated Wloss and η from part a.

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Figure 11. (a) Calculated W and Wrec with different values of x. (b) Calculated Wloss and η with different values of x.

CONCLUSIONS (1 − x)ST−x(BNT−BAN) ceramics were successfully prepared via the pressureless solid-state reaction method. The dielectric constant can be enhanced to 3430 with the composition of 0.4ST−0.6(BNT−BAN), which is 10.39 times higher than that of the pure ST sample (∼330). All of the samples possess dense microstructures and strong relaxor behaviors with the composition of x > 0. Pmax can be improved to 41.81 μC/cm2 for the sample with x = 0.8 at 140 kV/cm, which is 8.90 times higher than that of the pure ST sample

summarizes Wrec between (1 − x)ST−x(BNT−BAN) ceramics and other lead-free ceramics in recent literature.2,4,21,26,30,36,37,41−45 It can be found that the ceramics in this study have a relatively high Wrec value of 1.89 J/cm3, which is better than those of other lead-free ceramics and promising candidate lead-free ceramics for pulsed power applications. E

DOI: 10.1021/acs.inorgchem.7b02181 Inorg. Chem. XXXX, XXX, XXX−XXX

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Figure 13. Energy-storage properties of recently reported lead-free ceramics.

(4.70 μC/cm2). Optimum energy-storage properties (W of 2.46 J/cm3, Wrec of 1.89 J/cm3, and η of 77%) can be obtained with the composition of 0.5ST−0.5(BNT−BAN). Compared with the recently reported lead-free ceramics, (1 − x)ST−x(BNT− BAN) ceramics possess a high Wrec value simultaneously with a high η value, which indicates that (1 − x)ST−x(BNT−BAN) ceramics are conducive to applications in pulsed power capacitors.

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. ORCID

Haibo Yang: 0000-0003-1828-3750 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work is supported by the Chinese Postdoctoral Science Foundation (Grant 2016M590916), the National Natural Science Foundation of China (Grant 51572159), the Industrialization Foundation of Education Department of Shaanxi Provincial Government (Grant 16JF002), and the Science and Technology Foundation of Weiyang District of Xi’an City (Grant 201605).

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DOI: 10.1021/acs.inorgchem.7b02181 Inorg. Chem. XXXX, XXX, XXX−XXX

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DOI: 10.1021/acs.inorgchem.7b02181 Inorg. Chem. XXXX, XXX, XXX−XXX