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Energy storage performance in BiMnO3-modified AgNbO3 anti-ferroelectric ceramics
Materials Letters 237 (2019) 278–281
Contents lists available at ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/mlblue
Energy storage performance in BiMnO3-modified AgNbO3 anti-ferroelectric ceramics Aizhen Song a, Jianmin Song b,c, Yunkai Lv a, Linlin Liang a, Jing Wang a,⇑, Lei Zhao b,⇑ a
Key Laboratory of Analytical Science and Technology of Hebei Province, College of Chemistry and Environmental Science, Hebei University, Baoding 071002, China Hebei Key Lab of Optic-Electronic Information and Materials, College of Physics Science and Technology, Hebei University, Baoding 071002, China c College of Science, Agriculture University of Hebei, Baoding 071001, China b
a r t i c l e
i n f o
Article history: Received 17 September 2018 Received in revised form 28 October 2018 Accepted 18 November 2018 Available online 19 November 2018 Keywords: Lead-free anti-ferroelectric ceramic AgNbO3 BiMnO3 Energy storage performance
a b s t r a c t AgNbO3-based ceramics are promising lead-free anti-ferroelectric (AFE) materials for high power energy application. Herein, enhanced energy storage performance was obtained in BiMnO3 modified AgNbO3 ceramics. It was found that the introduction of BiMnO3 leads to decreased tolerance factor, which is responsible for the enhanced AFE stability. The enhanced AFE stability causes reduced remnant polarization (Pr) and increased AFE-FE phase transition fields (EF/EA), which is beneficial for the energy storage performance. Better recoverable energy storage density (Wrec) of 2.4 J/cm3 at 175 kV/cm was achieved in AgNbO3-0.6 mol% BiMnO3 ceramics, which is due to the enhanced AFE stability. Ó 2018 Elsevier B.V. All rights reserved.
1. Introduction Energy storage materials are receiving tremendous attention and research interest due to the increasing concerns regarding the sustainable developments of energy, economy, and society. Compared with batteries and supercapacitors, dielectric capacitors possess higher power density, which makes them promising for pulse power applications [1–3]. Among current dielectrics, antiferroelectric (AFE) ceramics with double hysteresis loop are favored for energy storage due to their large polarization (Pmax) in FE phase and small remnant polarization (Pr) in AFE phase. In the past decades, the mainstay AFE ceramics for energy storage applications are mainly focused on the La-doped Pb(Zr,Ti)O3based ceramics, and high recoverable energy densities (Wrec) up to 6.4 J/cm3 has been obtained [4]. However, in recent years, more and more attention has been paid to lead-free dielectric materials due to environmental requirements [5,6]. In 2007, Fu et al. reported the double hysteresis loops of pure AgNbO3 ceramics [7], and it is speculated that they can be used as energy storage materials. The Wrec of AgNbO3 ceramics is 2.0–2.1 J/cm3 [8,9]. The energy density and thermal stability of AgNbO3-based ceramics were further enhanced by adding MnO2 [10], Bi2O3 [11], Ta2O5 [12] or WO3 [13]. It is found that the increased energy density is attributed to the increased dielectric breakdown strength (Eb) ⇑ Corresponding authors. E-mail addresses: [email protected] (J. Wang), [email protected] (L. Zhao). https://doi.org/10.1016/j.matlet.2018.11.105 0167-577X/Ó 2018 Elsevier B.V. All rights reserved.
and enhanced anti-ferroelectricity. The increased Eb is caused by the decreased grain size, and the enhanced anti-ferroelectric stability (i.e., reduced Pr, and increased AFE-FE phase transition fields, EF/ p EA,) is related to decreased tolerance factor t (t = (RA + RO)/ 2 (RB + RO), where RA, RB, and RO are the radii of A-site ions, B-site ions, and oxygen ion, respectively) or reduced polarizability of Bsite cations. In MnO2 and Bi2O3 doped AgNbO3 ceramics, the decreased t is responsible to the enhanced anti-ferroelectric stability [10,11]. In Ta2O5 and WO3 doped AgNbO3 ceramics, the enhanced anti-ferroelectric stability is due to the reduced polarizability of B-site cations [12,13]. Generally, the phase stability of perovskite structure can be evaluated based on the t. FE phase is stabilized at t > 1, AFE phase is favored at t < 1 [14]. The ionic radius of Bi3+ (1.17 Å, CN = 8) ion is smaller than that of Ag+ (1.28 Å, CN = 8) ion, but the ionic radii of Mn3+ (0.645 Å, CN = 6) ion and Nb5+ (0.64 Å, CN = 6) ion are nearly the same [15]. The introduction of BiMnO3 into AgNbO3 will lead to decreased t, which would enhance the anti-ferroelectric stability and benefit the energy storage performance. In this work, BiMnO3 was introduced into AgNbO3 ceramics. As expected, an enhanced anti-ferroelectric stability was achieved, leading to reduced Pr and increased EF/EA. All of these changes favor an enhanced Wrec. 2. Experimental AgNbO3-xBiMnO3 (ANBM) (x = 0, 0.3, 0.6 and 0.8 mol%) ceramics were prepared by conventional solid state reaction method by using Ag2O (99.7%), Nb2O5 (99.99%), Bi2O3 (99.99%) and MnO2
A. Song et al. / Materials Letters 237 (2019) 278–281
(97%) as raw materials. More details can be found in the Supplementary material. 3. Results and discussion Fig. 1 shows the SEM images (a, b), grain size and relative density (c), and XRD patterns (d) of ANBM ceramics. All of the ceramics have dense microstructure with relative density over 95%. In addition, the introduction of BiMnO3 leads to decreased grain size from 7.9 mm to 2.7 mm. All of the ceramics are of a single perovskite structure as shown in Fig. 1(d). The relative intensity of (0 2 0) and (1 1 4) peaks is different for pure and BiMnO3-doped AgNbO3, which may be caused by the orientation since the XRD patterns of BiMnO3 bulk and AN powder match well with PDF#70-4738 card as shown in Fig. S1. No difference was observed in the XRD
279
patterns of ANBM bulk and powder, indicating that the addition of BiMnO3 suppresses the orientation. With increasing BiMnO3, both (0 2 0) and (2 2 0) diffraction peaks shift to high angles, while (1 1 4) and (0 0 8) diffraction peaks shift to low angles, indicating that Mn3+ and Bi3+ ions are diffused into the AgNbO3 crystal lattice to form a solid solution, and result in complicated lattice changes. According to the ionic radius of Bi3+ (1.17 Å, CN = 8) and Ag+ (1.28 Å, CN = 8), Mn3+ (0.645 Å, CN = 6) and Nb5+ (0.64 Å, CN = 6) ions [15], the complicated lattice changes may be caused by the different ionic radius of Bi3+ and Ag+ ions since the ionic radius of Mn3+ (0.645 Å, CN = 6) and Nb5+ (0.64 Å, CN = 6) ions are nearly the same. Fig. 2(a)-(b) shows the dielectric properties of ANBM ceramics as a function of temperature. The introduction of BiMnO3 has little effect on the dielectric constant. This may be attributed the low
Fig. 1. SEM images (a, b), grain size and relative density (c), and XRD patterns (d) of ANBM ceramics.
Fig. 2. Temperature dependences of dielectric constants (a), dielectric loss (b) and phase diagrams (c) of ANBM ceramics.
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Fig. 3. P-E loops and I-E loops of AgNbO3 (a) and AgNbO3-0.6 mol% BiMnO3 (b) ceramics from 100 to 175 kV/cm.
doping level of BiMnO3 (less than 1 mol%). Taking the decreased t into consideration, it seems that the t is more sensitive to the BiMnO3 doping level than that of dielectric constants. Four dielec-
tric peaks corresponding to M1-M2 (TM1-M2), M2-M3 (TM2-M3), M3-O (TM3-O) and O-T (TO-T) phase transitions from room temperature to 500 °C were observed in Fig. 2(a). But no anomaly corresponding to
A. Song et al. / Materials Letters 237 (2019) 278–281
phase transitions was observed in dielectric loss in Fig. 2(b). The dielectric loss of ANBM ceramics is maintained at 0.02 when the temperature is lower than 400 °C, and decreased as the temperature is higher than 400 °C after adding BiMnO3. Based on the dielectric peaks, the phase diagram of ANBM system was plotted as shown in Fig. 2(c). With increasing BiMnO3, TM1-M2 and TO-T gradually decreased, TM2-M3 and TM3-O remained unchanged. According to this phase diagram, samples with x = 0.3–0.8 mol% remains M1 phase at room temperature, which might be mixed ferroelectric and anti-ferroelectric phases because they are close to M1-M2 phase boundary [16]. The appearance of M2 antiferroelectric phases will benefit the enhanced anti-ferroelectric stability. Fig. 3 shows the electric field dependence of P-E hysteresis loops and current-field (I-E) loops for AgNbO3 (a) and AgNbO30.6 mol%BiMnO3 (b) ceramics from 100 kV/cm to 175 kV/cm. The pure AgNbO3 ceramic exhibits a slim hysteresis loop when the electric field (E) is 100 kV/cm. As E increases to 125 kV/cm, a double hysteresis loop occurs, indicating the AFE to FE phase transition. Meanwhile, four peaks were observed in I-E loops, which are due to possible reversible electric field-induced phase transitions [17].When E is high than 150 kV/cm, both the double hysteresis loops and phase transition peaks in I-E loops become more obvious, and the AFE to FE phase transition is more complete. On the contrary, the hysteresis loop becomes slimmer after adding 0.6 mol%BiMnO3 at 100 kV/cm with no double hysteresis loop and peaks in I-E loops observed even at 125 kV/cm, demonstrating that the addition of BiMnO3 leads to increased EA and EF. In addition, the decreased Pr reveals that the BiMnO3 addition stabilizes the anti-ferroelectricity in AgNbO3, which is caused by the decreased t. Meanwhile, the appearance of AFE M2 phase may be also responsible for the enhanced anti-ferroelectric stability. As further increasing E over 150 kV/cm, the double hysteresis loops and phase transition peaks in I-E loops were observed in AgNbO30.6 mol%BiMnO3 ceramics. On the other hand, the addition of BiMnO3 caused reduced Pmax, which is adverse to the energy storage performance and can be compensated by the increased E, as shown in Fig. 3(b). Due to the decreased Pr and increased EA, AgNbO3-0.6 mol%BiMnO3 ceramics show better energy storage performance with Wrec = 2.4 J/cm3 and g = 54% compared to that of pure AgNbO3 ceramics (Wrec = 1.5 J/cm3, g = 33%) at 175 kV/cm.
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4. Conclusions In summary, ANBM ceramics were prepared by solid state reaction process. The introduction of BiMnO3 leads to enhanced antiferroelectric stability, which is account for the decreased Pr and increase EF/EA. Benefiting from the decreased Pr and increase EA, 0.6 mol% BiMnO3-doped AgNbO3 ceramics show better energy storage performance with Wrec = 2.4 J/cm3 and g = 54%, indicating that BiMnO3-doped AgNbO3 lead-free ceramics are promising candidates for high power energy application. Acknowledgements This project is supported by the National Natural Science Foundation of China (Grant No. 51302061 and No. 51802068), Natural Science Foundation of Hebei province, China (Grant No. E2014201076), the Foundation of Agriculture University of Hebei (ZD201614), and the State Key Laboratory of New Ceramic and Fine Processing Tsinghua University (Grant No. KF201812). Appendix A. Supplementary data Supplementary data to this article can be found online at https://doi.org/10.1016/j.matlet.2018.11.105. References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17]
B. Chu, X. Zhou, et al., Science 313 (2006) 334–336. Q. Li, L. Chen, et al., Nature 523 (2015) 576–579. Z. Yao, Z. Song, et al., Adv Mater. 29 (2017) 1601727. G.Z. Zhang, D.Y. Zhu, et al., J. Am. Ceram. Soc. 98 (2015) 1175–1181. H. Ni, L. Luo, et al., J. Alloy. Compd. 509 (2011) 3958–3962. J. Wu, A. Mahajan, et al., Nano Energy 50 (2018) 723–732. D. Fu, M. Endo, et al., Appl. Phys. Lett. 90 (2007) 252907. J. Gao, L. Zhao, et al., J. Am. Ceram. Soc. 101 (2018) 5443–5450. Y. Tian, L. Jin, et al., J. Mater. Chem. A 4 (2016) 17279–17287. L. Zhao, Q. Liu, et al., J. Mater. Chem. C 4 (2016) 8380–8384. Y. Tian, L. Jin, et al., J. Mater. Chem. A 5 (2017) 17525–17531. L. Zhao, Q. Liu, et al., Adv. Mater. 29 (2017) 1701824. L. Zhao, J. Gao, et al., ACS Appl. Mater. Inter. 10 (2018) 819–826. J. Fabry, Z. Zikmund, et al., Acta Crystallogr. Sect. C 56 (2000) 916–918. R.D. Shannon, Acta Crystallogr. Sect. A 32 (1976) 751–767. L. Li, M. Spreitzer, et al., J. Eur. Ceram. Soc. 36 (2016) 3347–3354. G. Viola, T. Saunders, et al., J. Adv. Dielectr. 3 (2013) 1350007–13500011.
Contents lists available at ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/mlblue
Energy storage performance in BiMnO3-modified AgNbO3 anti-ferroelectric ceramics Aizhen Song a, Jianmin Song b,c, Yunkai Lv a, Linlin Liang a, Jing Wang a,⇑, Lei Zhao b,⇑ a
Key Laboratory of Analytical Science and Technology of Hebei Province, College of Chemistry and Environmental Science, Hebei University, Baoding 071002, China Hebei Key Lab of Optic-Electronic Information and Materials, College of Physics Science and Technology, Hebei University, Baoding 071002, China c College of Science, Agriculture University of Hebei, Baoding 071001, China b
a r t i c l e
i n f o
Article history: Received 17 September 2018 Received in revised form 28 October 2018 Accepted 18 November 2018 Available online 19 November 2018 Keywords: Lead-free anti-ferroelectric ceramic AgNbO3 BiMnO3 Energy storage performance
a b s t r a c t AgNbO3-based ceramics are promising lead-free anti-ferroelectric (AFE) materials for high power energy application. Herein, enhanced energy storage performance was obtained in BiMnO3 modified AgNbO3 ceramics. It was found that the introduction of BiMnO3 leads to decreased tolerance factor, which is responsible for the enhanced AFE stability. The enhanced AFE stability causes reduced remnant polarization (Pr) and increased AFE-FE phase transition fields (EF/EA), which is beneficial for the energy storage performance. Better recoverable energy storage density (Wrec) of 2.4 J/cm3 at 175 kV/cm was achieved in AgNbO3-0.6 mol% BiMnO3 ceramics, which is due to the enhanced AFE stability. Ó 2018 Elsevier B.V. All rights reserved.
1. Introduction Energy storage materials are receiving tremendous attention and research interest due to the increasing concerns regarding the sustainable developments of energy, economy, and society. Compared with batteries and supercapacitors, dielectric capacitors possess higher power density, which makes them promising for pulse power applications [1–3]. Among current dielectrics, antiferroelectric (AFE) ceramics with double hysteresis loop are favored for energy storage due to their large polarization (Pmax) in FE phase and small remnant polarization (Pr) in AFE phase. In the past decades, the mainstay AFE ceramics for energy storage applications are mainly focused on the La-doped Pb(Zr,Ti)O3based ceramics, and high recoverable energy densities (Wrec) up to 6.4 J/cm3 has been obtained [4]. However, in recent years, more and more attention has been paid to lead-free dielectric materials due to environmental requirements [5,6]. In 2007, Fu et al. reported the double hysteresis loops of pure AgNbO3 ceramics [7], and it is speculated that they can be used as energy storage materials. The Wrec of AgNbO3 ceramics is 2.0–2.1 J/cm3 [8,9]. The energy density and thermal stability of AgNbO3-based ceramics were further enhanced by adding MnO2 [10], Bi2O3 [11], Ta2O5 [12] or WO3 [13]. It is found that the increased energy density is attributed to the increased dielectric breakdown strength (Eb) ⇑ Corresponding authors. E-mail addresses: [email protected] (J. Wang), [email protected] (L. Zhao). https://doi.org/10.1016/j.matlet.2018.11.105 0167-577X/Ó 2018 Elsevier B.V. All rights reserved.
and enhanced anti-ferroelectricity. The increased Eb is caused by the decreased grain size, and the enhanced anti-ferroelectric stability (i.e., reduced Pr, and increased AFE-FE phase transition fields, EF/ p EA,) is related to decreased tolerance factor t (t = (RA + RO)/ 2 (RB + RO), where RA, RB, and RO are the radii of A-site ions, B-site ions, and oxygen ion, respectively) or reduced polarizability of Bsite cations. In MnO2 and Bi2O3 doped AgNbO3 ceramics, the decreased t is responsible to the enhanced anti-ferroelectric stability [10,11]. In Ta2O5 and WO3 doped AgNbO3 ceramics, the enhanced anti-ferroelectric stability is due to the reduced polarizability of B-site cations [12,13]. Generally, the phase stability of perovskite structure can be evaluated based on the t. FE phase is stabilized at t > 1, AFE phase is favored at t < 1 [14]. The ionic radius of Bi3+ (1.17 Å, CN = 8) ion is smaller than that of Ag+ (1.28 Å, CN = 8) ion, but the ionic radii of Mn3+ (0.645 Å, CN = 6) ion and Nb5+ (0.64 Å, CN = 6) ion are nearly the same [15]. The introduction of BiMnO3 into AgNbO3 will lead to decreased t, which would enhance the anti-ferroelectric stability and benefit the energy storage performance. In this work, BiMnO3 was introduced into AgNbO3 ceramics. As expected, an enhanced anti-ferroelectric stability was achieved, leading to reduced Pr and increased EF/EA. All of these changes favor an enhanced Wrec. 2. Experimental AgNbO3-xBiMnO3 (ANBM) (x = 0, 0.3, 0.6 and 0.8 mol%) ceramics were prepared by conventional solid state reaction method by using Ag2O (99.7%), Nb2O5 (99.99%), Bi2O3 (99.99%) and MnO2
A. Song et al. / Materials Letters 237 (2019) 278–281
(97%) as raw materials. More details can be found in the Supplementary material. 3. Results and discussion Fig. 1 shows the SEM images (a, b), grain size and relative density (c), and XRD patterns (d) of ANBM ceramics. All of the ceramics have dense microstructure with relative density over 95%. In addition, the introduction of BiMnO3 leads to decreased grain size from 7.9 mm to 2.7 mm. All of the ceramics are of a single perovskite structure as shown in Fig. 1(d). The relative intensity of (0 2 0) and (1 1 4) peaks is different for pure and BiMnO3-doped AgNbO3, which may be caused by the orientation since the XRD patterns of BiMnO3 bulk and AN powder match well with PDF#70-4738 card as shown in Fig. S1. No difference was observed in the XRD
279
patterns of ANBM bulk and powder, indicating that the addition of BiMnO3 suppresses the orientation. With increasing BiMnO3, both (0 2 0) and (2 2 0) diffraction peaks shift to high angles, while (1 1 4) and (0 0 8) diffraction peaks shift to low angles, indicating that Mn3+ and Bi3+ ions are diffused into the AgNbO3 crystal lattice to form a solid solution, and result in complicated lattice changes. According to the ionic radius of Bi3+ (1.17 Å, CN = 8) and Ag+ (1.28 Å, CN = 8), Mn3+ (0.645 Å, CN = 6) and Nb5+ (0.64 Å, CN = 6) ions [15], the complicated lattice changes may be caused by the different ionic radius of Bi3+ and Ag+ ions since the ionic radius of Mn3+ (0.645 Å, CN = 6) and Nb5+ (0.64 Å, CN = 6) ions are nearly the same. Fig. 2(a)-(b) shows the dielectric properties of ANBM ceramics as a function of temperature. The introduction of BiMnO3 has little effect on the dielectric constant. This may be attributed the low
Fig. 1. SEM images (a, b), grain size and relative density (c), and XRD patterns (d) of ANBM ceramics.
Fig. 2. Temperature dependences of dielectric constants (a), dielectric loss (b) and phase diagrams (c) of ANBM ceramics.
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Fig. 3. P-E loops and I-E loops of AgNbO3 (a) and AgNbO3-0.6 mol% BiMnO3 (b) ceramics from 100 to 175 kV/cm.
doping level of BiMnO3 (less than 1 mol%). Taking the decreased t into consideration, it seems that the t is more sensitive to the BiMnO3 doping level than that of dielectric constants. Four dielec-
tric peaks corresponding to M1-M2 (TM1-M2), M2-M3 (TM2-M3), M3-O (TM3-O) and O-T (TO-T) phase transitions from room temperature to 500 °C were observed in Fig. 2(a). But no anomaly corresponding to
A. Song et al. / Materials Letters 237 (2019) 278–281
phase transitions was observed in dielectric loss in Fig. 2(b). The dielectric loss of ANBM ceramics is maintained at 0.02 when the temperature is lower than 400 °C, and decreased as the temperature is higher than 400 °C after adding BiMnO3. Based on the dielectric peaks, the phase diagram of ANBM system was plotted as shown in Fig. 2(c). With increasing BiMnO3, TM1-M2 and TO-T gradually decreased, TM2-M3 and TM3-O remained unchanged. According to this phase diagram, samples with x = 0.3–0.8 mol% remains M1 phase at room temperature, which might be mixed ferroelectric and anti-ferroelectric phases because they are close to M1-M2 phase boundary [16]. The appearance of M2 antiferroelectric phases will benefit the enhanced anti-ferroelectric stability. Fig. 3 shows the electric field dependence of P-E hysteresis loops and current-field (I-E) loops for AgNbO3 (a) and AgNbO30.6 mol%BiMnO3 (b) ceramics from 100 kV/cm to 175 kV/cm. The pure AgNbO3 ceramic exhibits a slim hysteresis loop when the electric field (E) is 100 kV/cm. As E increases to 125 kV/cm, a double hysteresis loop occurs, indicating the AFE to FE phase transition. Meanwhile, four peaks were observed in I-E loops, which are due to possible reversible electric field-induced phase transitions [17].When E is high than 150 kV/cm, both the double hysteresis loops and phase transition peaks in I-E loops become more obvious, and the AFE to FE phase transition is more complete. On the contrary, the hysteresis loop becomes slimmer after adding 0.6 mol%BiMnO3 at 100 kV/cm with no double hysteresis loop and peaks in I-E loops observed even at 125 kV/cm, demonstrating that the addition of BiMnO3 leads to increased EA and EF. In addition, the decreased Pr reveals that the BiMnO3 addition stabilizes the anti-ferroelectricity in AgNbO3, which is caused by the decreased t. Meanwhile, the appearance of AFE M2 phase may be also responsible for the enhanced anti-ferroelectric stability. As further increasing E over 150 kV/cm, the double hysteresis loops and phase transition peaks in I-E loops were observed in AgNbO30.6 mol%BiMnO3 ceramics. On the other hand, the addition of BiMnO3 caused reduced Pmax, which is adverse to the energy storage performance and can be compensated by the increased E, as shown in Fig. 3(b). Due to the decreased Pr and increased EA, AgNbO3-0.6 mol%BiMnO3 ceramics show better energy storage performance with Wrec = 2.4 J/cm3 and g = 54% compared to that of pure AgNbO3 ceramics (Wrec = 1.5 J/cm3, g = 33%) at 175 kV/cm.
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4. Conclusions In summary, ANBM ceramics were prepared by solid state reaction process. The introduction of BiMnO3 leads to enhanced antiferroelectric stability, which is account for the decreased Pr and increase EF/EA. Benefiting from the decreased Pr and increase EA, 0.6 mol% BiMnO3-doped AgNbO3 ceramics show better energy storage performance with Wrec = 2.4 J/cm3 and g = 54%, indicating that BiMnO3-doped AgNbO3 lead-free ceramics are promising candidates for high power energy application. Acknowledgements This project is supported by the National Natural Science Foundation of China (Grant No. 51302061 and No. 51802068), Natural Science Foundation of Hebei province, China (Grant No. E2014201076), the Foundation of Agriculture University of Hebei (ZD201614), and the State Key Laboratory of New Ceramic and Fine Processing Tsinghua University (Grant No. KF201812). Appendix A. Supplementary data Supplementary data to this article can be found online at https://doi.org/10.1016/j.matlet.2018.11.105. References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17]
B. Chu, X. Zhou, et al., Science 313 (2006) 334–336. Q. Li, L. Chen, et al., Nature 523 (2015) 576–579. Z. Yao, Z. Song, et al., Adv Mater. 29 (2017) 1601727. G.Z. Zhang, D.Y. Zhu, et al., J. Am. Ceram. Soc. 98 (2015) 1175–1181. H. Ni, L. Luo, et al., J. Alloy. Compd. 509 (2011) 3958–3962. J. Wu, A. Mahajan, et al., Nano Energy 50 (2018) 723–732. D. Fu, M. Endo, et al., Appl. Phys. Lett. 90 (2007) 252907. J. Gao, L. Zhao, et al., J. Am. Ceram. Soc. 101 (2018) 5443–5450. Y. Tian, L. Jin, et al., J. Mater. Chem. A 4 (2016) 17279–17287. L. Zhao, Q. Liu, et al., J. Mater. Chem. C 4 (2016) 8380–8384. Y. Tian, L. Jin, et al., J. Mater. Chem. A 5 (2017) 17525–17531. L. Zhao, Q. Liu, et al., Adv. Mater. 29 (2017) 1701824. L. Zhao, J. Gao, et al., ACS Appl. Mater. Inter. 10 (2018) 819–826. J. Fabry, Z. Zikmund, et al., Acta Crystallogr. Sect. C 56 (2000) 916–918. R.D. Shannon, Acta Crystallogr. Sect. A 32 (1976) 751–767. L. Li, M. Spreitzer, et al., J. Eur. Ceram. Soc. 36 (2016) 3347–3354. G. Viola, T. Saunders, et al., J. Adv. Dielectr. 3 (2013) 1350007–13500011.