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Silver niobate lead-free antiferroelectric ceramics: enhancing energy storage density by B-site doping Lei Zhao, Jing Gao, Qing Liu, Shujun Zhang, and Jing-Feng Li ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.7b17382 • Publication Date (Web): 15 Dec 2017 Downloaded from http://pubs.acs.org on December 17, 2017
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ACS Applied Materials & Interfaces
Silver niobate lead-free antiferroelectric ceramics: enhancing energy storage density by B-site doping Lei Zhao,a Jing Gao,a Qing Liu,a Shujun Zhang,b and Jing-Feng Li*a a
State Key Laboratory of New Ceramics and Fine Processing, School of Materials Science and Engineering, Tsinghua University, Beijing, 100084, China. b Institute for Superconducting and Electronic Materials, Australian Institute of Innovative Materials, University of Wollongong, NSW, 2500, Australia. KEYWORDS: Silver niobate, lead-free, antiferroelectric, energy storage density, B-site doping
ABSTRACT: Lead-free dielectric ceramics with high recoverable energy density are highly desired to sustainably meet the future energy demand. AgNbO3-based lead-free antiferroelectric ceramics with double ferroelectric hysteresis loops have been proved to be a potential candidate for energy storage applications. Enhanced energy storage performance with recoverable energy density of 3.3J/cm3, and high thermal stability with minimal energy density variation (3.0J/cm3 and >50%, respectively, as demonstrated in Figure 3(d), indicating that the addition of WO3 plays an important role in increasing energy storage density and decreasing energy dissipation. The highest Wrec, up to 3.3J/cm3, is achieved in AgNbO30.1wt%WO3 ceramic, being 100% higher than that of pure counterpart. No further increased energy storage density is obtained in samples with x=0.2-0.3wt% due to the limited solubility of W6+ ions (less than 0.1wt%). This also indicates that the excess WO3 has no impact on the ferroelectric or antiferroelectric behaviours as shown in Figure 3(a). The energy storage densities of recently studied lead-free ceramics are summarized in Table 1. It can be seen that the Wrec of 3.3J/cm3 achieved in AgNbO3-0.1wt%WO3 ceramic is among the top values of lead-free ceramics,11-13,18-27 demonstrating AgNbO3based ceramic a potential candidate for energy storage applications. To confirm the antiferroelectricity in AgNbO3-xwt%WO3 ceramics, the polarization hysteresis and dielectric tunability were measured at 20oC and 100oC under an applied electric field of 100kV/cm, respectively, as shown in Figure 4. The pure AgNbO3 ceramic shows slim and double hysteresis loops at 20oC and 100oC respectively, indicating that the AFE-FE phase transition is triggered by temperature. On the contrary, the room temperature hysteresis loop becomes slimmer after adding 0.1wt%WO3, with no double hysteresis loop observed even at 100oC, demonstrating the addition of WO3 leads to increased forward switching field EF. Together with the decreased Pr as shown in Figure 3, reveals that the WO3 addition stabilizes the antiferroelectricity in AgNbO3. In addition, the dielectric tunability of pure AgNbO3 shows a significant shape change at 20oC and 100oC. At 20oC, the dielectric constant first decreases and then increases with increasing electric field, while different dielectric tunability behaviour is observed at
Figure 3 Hysteresis loops (a), Pr/Pmax (b), EF/EA (c) and Wrec/η (d) of AgNbO3-xwt%WO3 ceramics.
Figure 4 Hysteresis loops and dielectric tunability of AgNbO3 (a, c) and AgNbO3-0.1wt%WO3 (b, d) ceramics at 20oC and 100oC.
100oC, where a dielectric constant drop occurs at 100oC due to the AFE-FE phase transition.17,28 Generally, the dielectric constant of FE materials decreases with increasing electric field, being saturated at higher applied electric field.17,29 For AFE materials, however, the dielectric constant first increases linearly with increasing electric field, behaves nonlinearly at elevated electric field prior to AFE-FE phase transition.28, 29 Thus, AgNbO3 ceramic exhibits both FE-like and AFE-like behaviour in dielectric tunability, being associated with the ferrielectric (FIE) M1 phase. On the other hand, a weakened FE-like behaviour with stronger AFE-like behaviour is observed for AgNbO3-0.1wt%WO3 ceramic at 20oC, further confirms the enhanced antiferroelectricity. The dielectric constant drop occurred at 100oC for the doped ceramic reveals the AFE-FE phase transition, without showing a clear double hysteresis loop. The results indicate that the dielectric tunability is more sensitive than hysteresis loop for determining the polar order in AgNbO3-based ceramics.30 Based on the above analyses, it can be confirmed that an enhanced antiferroelectricity has been achieved in W-doped AgNbO3 ceramics, which leads to the reduced Pr and increased EF/EA, together with the increased Pmax, favouring a higher value of Wrec. The underlying mechanism for the enhanced
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Table 1. Energy storage performance of recently reported lead-free ceramics Wrec (J/cm3)
Materials
Wloss (J/cm3)
η (%)
E (kV/cm)
Ref.
Linear/FE ceramics 0.85(K0.5Na0.5)NbO3-0.15SrTiO3 0.61BiFeO3-0.33BaTiO3-0.06Ba(Mg1/3Nb2/3)O3
4.03 1.56
3.72 0.52
52 75
400 125
20 21
0.85BaTiO3-0.15Bi(Mg2/3Nb1/3)O3
1.13
0.05
90
140
22
0.94Bi0.47Na0.47Ba0.06TiO3-0.06KNbO3
0.89
0.25
78
100
23
Ba0.4Sr0.6TiO3-5vol%(BaO-SiO2-B2O3)
0.89
0.26
76
175
24
0.97(0.65BiFeO3-0.35BaTiO3)-0.02Nb2O5
0.71
0.52
58
90
25
0.92(0.92Bi0.5Na0.5TiO3-0.08BaTiO3)-0.1NaNbO3
0.71
0.37
66
70
26
(Ba0.4Sr0.6)TiO3
1.15
0.25
82
180
27
AFE ceramics 0.84(Bi0.5Na0.5)TiO3-0.16(K0.5Na0.5)NbO3 0.89(Bi0.5Na0.5)TiO3-0.06BaTiO3-0.05(K0.5Na0.5)NbO3
1.20 0.59
0.10 0.18
92 77
100 56
18 19
AgNbO3
1.60
2.40
40
150
12
AgNbO3
2.10
3.15
40
175
11
AgNbO3-0.1wt%MnO2
2.50
2.30
52
150
12
(Ag0.97Bi0.01)NbO3
3.00
2.45
55
175
13
Ag(Nb0.85Ta0.15)O3
4.20
1.90
69
230
5
AgNbO3-0.1wt%WO3
3.30
3.30
50
200
This work
antiferroelectricity in W-doped AgNbO3 ceramics was investigated by phase structure, tolerance factor and polarizability. Figure 5 shows the temperature dependence of dielectric constant and dielectric loss of AgNbO3-xwt%WO3 ceramics. It is observed that the phase transitions for M1-M2 (TM1-M2), M2M3 (TM2-M3) and M3-O (TM3-O) occur approximately at 75oC, 262oC and 355oC, respectively. The pure AgNbO3 ceramics is FIE M1 phase at room temperature. The phase transition temperatures of TM3-O, TM2-M3 and TM1-M2 are found to increase with addition of 0.1wt%WO3, as shown in the inset of Figure 5. The 0.1wt%W-doped AgNbO3 ceramic is still in FIE M1 phase at room temperature, analogous to its pure counterpart. In addition, the dielectric loss decreases after adding WO3, which will benefit the dielectric breakdown strength. Generally, the phase stability of perovskite structure (ABO3) can be evaluated based on the tolerance factor (t), where FE phase is stabilized at t >1 while AFE phase is favoured at t
