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3)O3 solid solution
Ceramics International 43 (2017) 926–929
Contents lists available at ScienceDirect
Ceramics International journal homepage: www.elsevier.com/locate/ceramint
High thermal stability and low dielectric loss of BaTiO3-Bi(Li1/3Zr2/3)O3 solid solution
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⁎
Xiuli Chen , Guisheng Huang, Dandan Ma, Gaofeng Liu, Huanfu Zhou Collaborative Innovation Center for Exploration of Hidden Nonferrous Metal Deposits and Development of New Maaterials in Guangxi, Guangxi MinistryProvince Jointly-Constructed Cultivation Base for State Key Laboratoary of Processing for Non-ferrous Metal and Featured Materials, Guangxi Key Laboratory in Universities of Clean Metallurgy and Comprehensive Utilization for Non-ferrous Metals Resources, School of Materials Science and Engineering, Guilin University of Technology, Guilin 541004, China
A R T I C L E I N F O
A BS T RAC T
Keywords: Dielectric properties BaTiO3 Phase evolution Thermal stability
(1−x)BaTiO3-xBi(Li1/3Zr2/3)O3 [(1−x)BT-xBLZ, 0.02≤x≤0.1] solid solution ceramics were prepared by a conventional solid state reaction technique. The effects of BLZ addition on the phase structure and dielectric properties of ceramics were systematically studied. Raman spectra and XRD analysis confirmed that the ceramics transform from tetragonal to pseudocubic symmetry at 0.04≤x≤0.06. High thermal stability of permittivity and low dielectric loss were obtained with increasing BLZ contents. When x=0.1, the ceramics possessed optimum dielectric performance with good thermal stability of permittivity (Δε/ε25 °C≤ ± 15%) over a broad temperature range from −70 °C to 144 °C and low dielectric loss (≤2%) from −21 °C to 200 °C, suggesting that (1−x)BT-xBLZ ceramics are promising candidates for thermally stable electronic components.
1. Introduction Ceramic capacitors with high and stable permittivity at elevated temperatures are growing demands for electronic components, such as anti-lock brake system, programmed fuel injection, transducers, infrared detectors, and aerospace, etc [1–5]. BaTiO3-based perovskite materials have been extensively researched over the last 50 years owing to their good dielectric properties [6–11]. However, pure BaTiO3 ceramic exhibited three phase transition at about 125 °C, 0 °C, −90 °C, leading to highly and strongly temperature-sensitive dielectric properties and a serious deterioration in permittivity [12], which restricts its further application in the electronic information manufacturing. Therefore, it is very important to develop high-performance BaTiO3based perovskite materials with high and stable permittivity to satisfy the requirement of electronic components [13]. BaTiO3-BiMeO3 perovskite materials have received much attention because BiMeO3 compounds will effectively improve the dielectric properties of ceramics, where Me can be Al3+, Y3+, (Zn1/2Ti1/2)3+, (Mg1/2Zr1/2)3+, etc [14–18]. Besides, the previous reports showed that the substitution of Li for Ti could improve the permittivity of BaTiO3base perovskite materials at high temperature near the Curie point [19,20]. Recently, BaTiO3-Bi(Li1/3Ti2/3)O3 ceramic has been reported to possess good temperature-stable dielectric behavior [21]. Ti4+ and Zr4+ possess identical valence. Moreover, due to the more chemical
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stability and larger ionic size of Zr4+, the substitution of Zr for Ti could restrain the conduction and decrease the leakage current of BaTiO3 systems [22], inducing good thermal stability of ceramics [23–26]. In this work, the effects of Bi(Li1/3Zr2/3)O3 addition on the phase evolution, microstructure and dielectric properties of BaTiO3 ceramics were investigated to obtain a material with low dielectric loss, high relative permittivity and good thermally stable permittivity for ceramic capacitors application. 2. Experimental (1−x)BaTiO3-xBi(Li1/3Zr2/3)O3 [(1−x)BT-xBLZ, 0.02≤x≤0.1] ceramics were prepared by the conventional solid-state reaction method. The starting powders were high-purity (≥99%, Guo-Yao Co. Ltd., Shanghai, China) BaCO3, TiO2, Li2CO3, Bi2O3 and ZrO2. Stoichiometric proportions of BT and BLZ were weighed and milled in alcohol (≥99.7%, Guo-Yao Co. Ltd., Shanghai, China) medium using zirconia balls for 4 h. After drying, the powders were calcined at 1100 °C and 650 °C for 4 h in air, respectively. Then, (1-x)BT-xBLZ (0.02≤x≤0.1) compositions were weighed and milled in alcohol medium using zirconia balls for 4 h. After drying, the powders were mixed with 5% polyvinyl alcohol (PVA) and pressed into pellets with 12 mm in diameter and 1–2 mm in thickness by uniaxial pressing at a pressure of 200 MPa. The pellets were embedded with the same calcined
Corresponding author. E-mail addresses: [email protected] (X. Chen), [email protected] (H. Zhou).
http://dx.doi.org/10.1016/j.ceramint.2016.10.099 Received 4 October 2016; Received in revised form 15 October 2016; Accepted 16 October 2016 Available online 17 October 2016 0272-8842/ © 2016 Elsevier Ltd and Techna Group S.r.l. All rights reserved.
Ceramics International 43 (2017) 926–929
X. Chen et al.
Fig. 2. Room temperature Raman spectra of (1−x)BT-xBLZ (0.02≤x≤0.1) ceramics. Fig. 1. (a) X-ray diffraction patterns of (1−x)BT-xBLZ (0.02≤x≤0.1) ceramics, (b) Enlarged XRD patterns of (1−x)BT-xBLZ ceramics in the range of 2θ from 43° to 47°.
170 cm−1 and 270 cm−1 are attributed to phonon vibrations of Ti–O bonds. The peaks of 520 cm−1 and 720 cm−1 are assigned with phonon vibrations of Ba–O bonds [33]. With increasing x values (0.06≤x≤0.1), the one at 170 cm−1 vanishes and a new mode 1 can be observed in its place, demonstrating that the long-range ferroelectric order is destroyed. Mode 1 is related to A-O vibrations, and its emergence suggests that there exist Ba2+ or Bi3+ cation-enriched nano-sized zones (clusters) [34]. Furthermore, an A1 g octahedral breathing mode is observed at 790 cm−1, which is Raman active for complex perovskites and solid solutions with two or more B-site species since the presence of dissimilar ions in the center of the octahedral creates asymmetry in the breathing-like mode [35]. Fig. 3 shows the SEM images of natural surface for (1−x)BT-xBLZ ceramics sintered at their optimized temperatures. The dense microstructures and few pores of (1−x)BT-xBLZ ceramics were obtained in all samples. As the BLZ contents increased, a significant increase in average grain size was observed, which indicates that the addition of BLZ enhances the grain growth of (1−x)BT-xBLZ ceramics. The temperature dependences of the relative permittivity and dielectric loss for the (1-x)BT-xBLZ ceramics measured from −70 °C to 200 °C at various frequencies are plotted in Fig. 4. As BLZ contents increased, there was a reduction in the peak values of εr, from ~6200 (x=0.02, 1 kHz) to ~1500 (x=0.1, 1 kHz), which may be explained by the decrease in polarization with increasing the nonferroelectric phase in grain. This phenomenon was similar to the previous reports [31]. With further increasing x values, the broadening of tetragonal-cubic transition peaks cannot be observed above 130 °C. The thermal stability of permittivity (Δε/ε25 °C), dielectric loss (tan δ) and relative permittivity (εm) as a function of the measured temperature and frequency for (1−x)BT-xBLZ ceramics (x=0.1) are illustrated in Fig. 5. It is clearly observed that the samples possess optimum dielectric performances with small Δε/ε25 °C values ( ± 15%) over a broad temperature range from −70 °C to 144 °C, high relative permittivity (~1500–1800), and low dielectric loss (tan δ≤0.02) from −21 °C to 200 °C. Table 1 lists the values of maximum relative permittivity, dielectric loss and thermal stability of permittivity in the operating temperature range with several dielectric materials. BaTiO3-BiAlO3 [36], BaTiO3Bi(Mg2/3Ta1/3)O3 [27] and BaTiO3-Bi(Mg1/2Zr1/2)O3 [24] systems exhibited good thermal stability of permittivity (Δε/ε25 °C≤ ± 15%) and low dielectric loss (≤2%) in a broader temperature range. By contrast, an evidently high relative permittivity (≥1726), low dielectric loss (≤2%) and good thermal stability of permittivity (Δε/ε25 °C≤ ± 15%) for (1−x)BT-xBLZ (0.08≤x≤0.1) systems were obtained over a wide temperature range, which shows that BLZ addition could significantly improve the dielectric properties of BT ceramics.
powders to avoid elements volatilization and sintered at different temperatures (1260–1360 °C) for 2 h in air, depending on the content of BLZ. X-ray diffraction (XRD) patterns were recorded using an X-ray diffractometer (XRD, Model X’Pert PRO; PANalytical, Almelo, the Netherland) with CuKα radiation (λ=0.15406 nm) operated at 40 kV and 40 mA with a step size of 0.02°. The phase analysis for the XRD data was performed by a PANalytical software (X’Pert Highscore Plus). Raman spectroscopy was carried out on a Thermo Fisher Scientific DXR Raman Microscope using a 10 mW laser with a wave length of 532 nm. The microstructural observation of the sintered samples was performed using a scanning electron microscopy (Model JSM6380-LV SEM, JEOL, Tokyo, Japan). Silver electrodes were coated on both sides of the pellets, and then fired at 650 °C for 30 min. Dielectric properties were measured with an applied voltage of 500 mV over 1 kHz-1 MHz from −70 °C to 200 °C using a precision impedance analyzer (Model 4294A, Hewlett-Packard Co, Palo Alto, CA) at a heating rate of 3 °C/ min. 3. Results and discussion Fig. 1(a) shows the room temperature X-ray diffraction (XRD) patterns of (1-x)BT-xBLZ ceramics. All peaks are indexed and no additional second peaks are observed. When 0.02≤x≤0.04, the X-ray diffraction patterns present a similar structure to tetragonal BaTiO3 (JCPDS: #75-0460) [27,28]. With increasing x values, the main phase of (1-x)BT-xBLZ ceramics is pseudo-cubic and tetragonal phase is absent, which is characterized by the merging of (002)/(200) peaks into a single (200) peak. When 0.04≤x≤0.06, the ceramics exhibit the coexistence of tetragonal and pseudo-cubic phases [29]. The enlarged XRD patterns in the range of 2θ from 43° to 47° are shown in Fig. 1(b). As BLZ content increases, it can be seen that the (200) peak shifts to low angles. This change is mainly related to the increase of lattice parameters, which can be explained by the effect of the incorporation. 2+ The Bi3+(1.03 Å ≤r 3+ Bi ≤1.61 Å) ion is slightly smaller than Ba (1.61 Å + 4+ in 12-fold coordination) in A-site. But Li (0.76 Å) and Zr (0.98 Å) have larger radius than that of Ti4+(0.605 Å in 6-fold coordination) in B-site [16,30]. The substitution of B-site may be the main influence factor to induce the increase of the lattice parameters. Fig. 2 demonstrates the spontaneous Raman spectra of (1-x)BTxBLZ ceramics recorded at room temperature. When 0.02≤x≤0.04, the main spectral features for (1−x)BT-xBLZ ceramics are five distinct bands at 720, 520, 306, 270 and 170 cm−1, which are characteristics of tetragonal BaTiO3 [31,32]. Whereas, rhombohedral and orthorhombic phases are absent in all samples, because there are no signs of a weak band at 478 cm−1 and asymmetric peak at 188 cm−1. The peaks at 927
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Fig. 3. SEM micrographs of (1−x)BT-xBLZ ceramics sintered at their optimized temperatures: (a) x=0.02, 1360 °C, (b) x=0.04, 1340 °C, (c) x=0.08, 1280 °C, and (d) x=0.1, 1260 °C.
bic phase occurred at 0.04≤x≤0.06. All BT-BLZ ceramics featured a dense microstructure. With increasing BLZ content (0.08≤x≤0.1), good thermal stability of permittivity (Δε/ε25 °C≤ ± 15%), high relative permittivity(~1500–2200) and low dielectric loss (2%) were obtained over a broad temperature range at 1 kHz, which indicates that (1−x) BT-xBLZ ceramics could have a potential application for thermally
4. Conclusions (1-x)BT-xBLZ (0.02≤x≤0.1) lead-free ceramics have been successfully synthesized by the solid-state reaction technique. XRD analysis verified that all samples exhibited a single perovskite structure and a systematically structural transformation from tetragonal to pseudocu-
Fig. 4. Temperature dependences of relative permittivity (a) and dielectric loss (b) for (1−x)BT-xBLZ (0.02≤x≤0.1) ceramics measured at 1 kHz, 10 kHz, 100 kHz and 1 MHz.
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[6] D. Hennings, A. Schnell, G. Simon, Diffuse ferroelectric phase transitions in Ba(Ti1−yZry)O3 ceramics, J. Am. Ceram. Soc. 65 (1982) 539–544. [7] Q. Zhang, Z.R. Li, F. Li, Z. Xu, Structural and dielectric properties of Bi(Mg1/2Ti1/2) O3-BaTiO3 lead-free ceramics, J. Am. Ceram. Soc. 94 (2011) 4335–4339. [8] J. Chen, X.L. Chen, F. He, Y.L. Wang, H.F. Zhou, L. Fang, Thermally stable BaTiO3Bi(Mg0.75W0.25)O3 solid solutions: sintering characteristics, phase evolution, Raman spectra, and dielectric properties, J. Electron. Mater. 43 (2014) 1112–1118. [9] K. Suzuki, K. Kijima, Phase transformation of BaTiO3 nanoparticles synthesized by RF-plasma CVD, J. Alloy. Compd. 419 (2006) 234–242. [10] H.I. Won, H.H. Nersisyan, C.W. Won, Low temperature solid-phase synthesis of tetragonal BaTiO3 powders and its characterization, Mater. Lett. 61 (2007) 1492–1496. [11] I. Velasco-Davalos, F. Ambriz-Vargas, C. Gómez-Yáñez, R. Thomas, A. 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Zhang, Evolution of phase transformation behavior and dielectric temperature stability of BaTiO3Bi(Zn0.5Zr0.5)O3 ceramics system, J. Alloy. Compd. 551 (2013) 365–369. [27] D.D. Ma, X.L. Chen, G.S. Huang, J. Chen, H.F. Zhou, F. Fang, Temperature stability, structural evolution and dielectric properties of BaTiO3-Bi(Mg2/3Ta1/3)O3 perovskite ceramics, Ceram. Int. 41 (2015) 7157–7161. [28] K. Suzuki, K. Kijima, Size driven phase transition of barium titanate nanoparticles prepared by plasma chemical vapor deposition, J. Mater. Sci. 40 (2005) 1289–1892. [29] T. Li, K. Yang, R.Z. Xue, Y.C. Xue, Z.P. Chen, The effect of CuO doping on the microstructures and dielectric properties of BaTiO3 ceramics, J. Mater. Sci. Mater. Electron. 22 (2011) 838–842. [30] D.I. Woodward, I.M. Reaney, R.E. Eitel, C.A. Randall, Crystal and domain structure of the BiFeO3-PbTiO3 solid solution, J. Appl. Phys. 94 (2003) 3313–3318. [31] J. Pokorny, U.M. Pasha, L. Ben, O.P. Thakur, D.C. Sinclair, I.M. Reaney, Use of raman spectroscopy to determine the site occupancy of dopants in BaTiO3, J. Appl. Phys. 109 (2011) 114110. [32] U.D. Venkateswaran, V.M. Naik, R. Naik, High-pressure raman studies of polycrystalline BaTiO3, Phys. Rev. B 58 (1998) 14256–14260. [33] V.S. Puli, D.K. Pradhan, K. Perez, R.S. Katiyar, Structure, dielectric tunability, thermal stability and diffuse phase transition behavior of lead free BZT-BCT ceramic capacitors, J. Phys. Chem. Solids 74 (2013) 466–475. [34] J. Kreisel, P. Bouvier, M. Maglione, B. Dkhil, A. Simon, High-pressure raman investigation of the Pb-free relaxor BaTi0.65Zr0.35O3, Phys. Rev. B 69 (2004) 092104. [35] H. Yu, Z.G. Ye, Dielectric properties and relaxor behavior of a new (1-x)BaTiO3xBiAlO3 solid solution, J. Appl. Phys. 103 (2008) 034114. [36] M.Y. Liu, H. Hao, Y.C. Zhen, T. Wang, D.D. Zhou, H.X. Liu, M.H. Cao, Z.H. Yao, Temperature stability of dielectric properties for xBiAlO3-(1−x)BaTiO3 ceramic, J. Eur. Ceram. Soc. 35 (2015) 2303–2311.
Fig. 5. (a) Δε/ε25 °C, (b) temperature dependences of relative permittivity and dielectric loss for (1−x)BT-xBLZ (x=0.1) ceramics at 1 kHz, 10 kHz and 100 kHz from −70 °C to 200 °C. Table 1 Comparison of dielectric properties between (1-x)BT-xBLZ (0.08≤x≤0.1) and other works at 1 kHz. System
εr max
Temperaturerange/°C Tan δ≤0.02
Temperature range/°C Δε/εmid ≤15%
Refs.
0.8BT0.2BA 0.6BT0.4BMZ 0.92BT0.08BMT 0.92BT0.08BLZ 0.9BT0.1BLZ
~1238
0–200
−55–145
[36]
~650
55–280
−25–420
[24]
~1534
30–190
30–150
[27]
~2228
13–200
−54–153
~1726
−21–200
−70–144
This work This work
0.8BT-0.2BA, (1−x)BaTiO3-xBiAlO3; 0.6BT-0.4BMZ, (1−x)BaTiO3-xBi(Mg1/2Zr1/2)O3; 0.92BT-0.08BMT, (1−x)BaTiO3-xBi(Mg2/3Ta1/3)O3; 0.92BT-0.08BLZ, (1−x)BaTiO3xBi(L1/3Zr2/3)O3; 0.9BT-0.1BLZ, (1−x)BaTiO3- xBi(L1/3Zr2/3)O3.
stable ceramic capacitors. Acknowledgments This work was supported by Natural Science Foundation of China (Nos. 11664008, 11464009 and 11364012), Natural Science Foundation of Guangxi (Nos. 2015GXNSFDA139033, 2014GXNSFAA118312 and 2014GXNSFAA118326), Research Startup Funds Doctor of Guilin University of Technology (Nos. 002401003281 and 002401003282) and Project of Outstanding Young Teachers ׳Training in Higher Education Institutions of Guangxi. References [1] W. Chen, X. Zhao, J.G. Sun, L.X. Zhang, L.S. Zhong, Effect of the Mn doping concentration and ferroelectric properties of different-routes-fabricated BaTiO3based ceramics, J. Alloy. Compd. 670 (2016) 48–54. [2] Y. Yuan, M. Du, S.R. Zhang, Effects of BiNbO4 on the microstructure and dielectric properties of BaTiO3-based ceramics, J. Mater. Sci. Mater. Electron. 20 (2009) 157–162. [3] S. Wang, S.R. Zhang, X.H. Zhou, B. Li, Z. Chen, Investigation on dielectric properties of BaTiO3 co-doped with Ni and Nb, Mater. Lett. 60 (2006) 909–911. [4] R. Dittmer, W. Jo, D. Damjanovic, J. Rodel, Lead-free high-temperature dielectrics with wide operational range, J. Appl. Phys. 109 (2011) 034107. [5] J.B. Lim, S.J. Zhang, N. Kim, T.R. Shrout, High-temperature dielectrics in the BiScO3-BaTiO3-(K1/2Bi1/2)TiO3 ternary system, J. Am. Ceram. Soc. 92 (2009) 679–682.
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Contents lists available at ScienceDirect
Ceramics International journal homepage: www.elsevier.com/locate/ceramint
High thermal stability and low dielectric loss of BaTiO3-Bi(Li1/3Zr2/3)O3 solid solution
crossmark
⁎
Xiuli Chen , Guisheng Huang, Dandan Ma, Gaofeng Liu, Huanfu Zhou Collaborative Innovation Center for Exploration of Hidden Nonferrous Metal Deposits and Development of New Maaterials in Guangxi, Guangxi MinistryProvince Jointly-Constructed Cultivation Base for State Key Laboratoary of Processing for Non-ferrous Metal and Featured Materials, Guangxi Key Laboratory in Universities of Clean Metallurgy and Comprehensive Utilization for Non-ferrous Metals Resources, School of Materials Science and Engineering, Guilin University of Technology, Guilin 541004, China
A R T I C L E I N F O
A BS T RAC T
Keywords: Dielectric properties BaTiO3 Phase evolution Thermal stability
(1−x)BaTiO3-xBi(Li1/3Zr2/3)O3 [(1−x)BT-xBLZ, 0.02≤x≤0.1] solid solution ceramics were prepared by a conventional solid state reaction technique. The effects of BLZ addition on the phase structure and dielectric properties of ceramics were systematically studied. Raman spectra and XRD analysis confirmed that the ceramics transform from tetragonal to pseudocubic symmetry at 0.04≤x≤0.06. High thermal stability of permittivity and low dielectric loss were obtained with increasing BLZ contents. When x=0.1, the ceramics possessed optimum dielectric performance with good thermal stability of permittivity (Δε/ε25 °C≤ ± 15%) over a broad temperature range from −70 °C to 144 °C and low dielectric loss (≤2%) from −21 °C to 200 °C, suggesting that (1−x)BT-xBLZ ceramics are promising candidates for thermally stable electronic components.
1. Introduction Ceramic capacitors with high and stable permittivity at elevated temperatures are growing demands for electronic components, such as anti-lock brake system, programmed fuel injection, transducers, infrared detectors, and aerospace, etc [1–5]. BaTiO3-based perovskite materials have been extensively researched over the last 50 years owing to their good dielectric properties [6–11]. However, pure BaTiO3 ceramic exhibited three phase transition at about 125 °C, 0 °C, −90 °C, leading to highly and strongly temperature-sensitive dielectric properties and a serious deterioration in permittivity [12], which restricts its further application in the electronic information manufacturing. Therefore, it is very important to develop high-performance BaTiO3based perovskite materials with high and stable permittivity to satisfy the requirement of electronic components [13]. BaTiO3-BiMeO3 perovskite materials have received much attention because BiMeO3 compounds will effectively improve the dielectric properties of ceramics, where Me can be Al3+, Y3+, (Zn1/2Ti1/2)3+, (Mg1/2Zr1/2)3+, etc [14–18]. Besides, the previous reports showed that the substitution of Li for Ti could improve the permittivity of BaTiO3base perovskite materials at high temperature near the Curie point [19,20]. Recently, BaTiO3-Bi(Li1/3Ti2/3)O3 ceramic has been reported to possess good temperature-stable dielectric behavior [21]. Ti4+ and Zr4+ possess identical valence. Moreover, due to the more chemical
⁎
stability and larger ionic size of Zr4+, the substitution of Zr for Ti could restrain the conduction and decrease the leakage current of BaTiO3 systems [22], inducing good thermal stability of ceramics [23–26]. In this work, the effects of Bi(Li1/3Zr2/3)O3 addition on the phase evolution, microstructure and dielectric properties of BaTiO3 ceramics were investigated to obtain a material with low dielectric loss, high relative permittivity and good thermally stable permittivity for ceramic capacitors application. 2. Experimental (1−x)BaTiO3-xBi(Li1/3Zr2/3)O3 [(1−x)BT-xBLZ, 0.02≤x≤0.1] ceramics were prepared by the conventional solid-state reaction method. The starting powders were high-purity (≥99%, Guo-Yao Co. Ltd., Shanghai, China) BaCO3, TiO2, Li2CO3, Bi2O3 and ZrO2. Stoichiometric proportions of BT and BLZ were weighed and milled in alcohol (≥99.7%, Guo-Yao Co. Ltd., Shanghai, China) medium using zirconia balls for 4 h. After drying, the powders were calcined at 1100 °C and 650 °C for 4 h in air, respectively. Then, (1-x)BT-xBLZ (0.02≤x≤0.1) compositions were weighed and milled in alcohol medium using zirconia balls for 4 h. After drying, the powders were mixed with 5% polyvinyl alcohol (PVA) and pressed into pellets with 12 mm in diameter and 1–2 mm in thickness by uniaxial pressing at a pressure of 200 MPa. The pellets were embedded with the same calcined
Corresponding author. E-mail addresses: [email protected] (X. Chen), [email protected] (H. Zhou).
http://dx.doi.org/10.1016/j.ceramint.2016.10.099 Received 4 October 2016; Received in revised form 15 October 2016; Accepted 16 October 2016 Available online 17 October 2016 0272-8842/ © 2016 Elsevier Ltd and Techna Group S.r.l. All rights reserved.
Ceramics International 43 (2017) 926–929
X. Chen et al.
Fig. 2. Room temperature Raman spectra of (1−x)BT-xBLZ (0.02≤x≤0.1) ceramics. Fig. 1. (a) X-ray diffraction patterns of (1−x)BT-xBLZ (0.02≤x≤0.1) ceramics, (b) Enlarged XRD patterns of (1−x)BT-xBLZ ceramics in the range of 2θ from 43° to 47°.
170 cm−1 and 270 cm−1 are attributed to phonon vibrations of Ti–O bonds. The peaks of 520 cm−1 and 720 cm−1 are assigned with phonon vibrations of Ba–O bonds [33]. With increasing x values (0.06≤x≤0.1), the one at 170 cm−1 vanishes and a new mode 1 can be observed in its place, demonstrating that the long-range ferroelectric order is destroyed. Mode 1 is related to A-O vibrations, and its emergence suggests that there exist Ba2+ or Bi3+ cation-enriched nano-sized zones (clusters) [34]. Furthermore, an A1 g octahedral breathing mode is observed at 790 cm−1, which is Raman active for complex perovskites and solid solutions with two or more B-site species since the presence of dissimilar ions in the center of the octahedral creates asymmetry in the breathing-like mode [35]. Fig. 3 shows the SEM images of natural surface for (1−x)BT-xBLZ ceramics sintered at their optimized temperatures. The dense microstructures and few pores of (1−x)BT-xBLZ ceramics were obtained in all samples. As the BLZ contents increased, a significant increase in average grain size was observed, which indicates that the addition of BLZ enhances the grain growth of (1−x)BT-xBLZ ceramics. The temperature dependences of the relative permittivity and dielectric loss for the (1-x)BT-xBLZ ceramics measured from −70 °C to 200 °C at various frequencies are plotted in Fig. 4. As BLZ contents increased, there was a reduction in the peak values of εr, from ~6200 (x=0.02, 1 kHz) to ~1500 (x=0.1, 1 kHz), which may be explained by the decrease in polarization with increasing the nonferroelectric phase in grain. This phenomenon was similar to the previous reports [31]. With further increasing x values, the broadening of tetragonal-cubic transition peaks cannot be observed above 130 °C. The thermal stability of permittivity (Δε/ε25 °C), dielectric loss (tan δ) and relative permittivity (εm) as a function of the measured temperature and frequency for (1−x)BT-xBLZ ceramics (x=0.1) are illustrated in Fig. 5. It is clearly observed that the samples possess optimum dielectric performances with small Δε/ε25 °C values ( ± 15%) over a broad temperature range from −70 °C to 144 °C, high relative permittivity (~1500–1800), and low dielectric loss (tan δ≤0.02) from −21 °C to 200 °C. Table 1 lists the values of maximum relative permittivity, dielectric loss and thermal stability of permittivity in the operating temperature range with several dielectric materials. BaTiO3-BiAlO3 [36], BaTiO3Bi(Mg2/3Ta1/3)O3 [27] and BaTiO3-Bi(Mg1/2Zr1/2)O3 [24] systems exhibited good thermal stability of permittivity (Δε/ε25 °C≤ ± 15%) and low dielectric loss (≤2%) in a broader temperature range. By contrast, an evidently high relative permittivity (≥1726), low dielectric loss (≤2%) and good thermal stability of permittivity (Δε/ε25 °C≤ ± 15%) for (1−x)BT-xBLZ (0.08≤x≤0.1) systems were obtained over a wide temperature range, which shows that BLZ addition could significantly improve the dielectric properties of BT ceramics.
powders to avoid elements volatilization and sintered at different temperatures (1260–1360 °C) for 2 h in air, depending on the content of BLZ. X-ray diffraction (XRD) patterns were recorded using an X-ray diffractometer (XRD, Model X’Pert PRO; PANalytical, Almelo, the Netherland) with CuKα radiation (λ=0.15406 nm) operated at 40 kV and 40 mA with a step size of 0.02°. The phase analysis for the XRD data was performed by a PANalytical software (X’Pert Highscore Plus). Raman spectroscopy was carried out on a Thermo Fisher Scientific DXR Raman Microscope using a 10 mW laser with a wave length of 532 nm. The microstructural observation of the sintered samples was performed using a scanning electron microscopy (Model JSM6380-LV SEM, JEOL, Tokyo, Japan). Silver electrodes were coated on both sides of the pellets, and then fired at 650 °C for 30 min. Dielectric properties were measured with an applied voltage of 500 mV over 1 kHz-1 MHz from −70 °C to 200 °C using a precision impedance analyzer (Model 4294A, Hewlett-Packard Co, Palo Alto, CA) at a heating rate of 3 °C/ min. 3. Results and discussion Fig. 1(a) shows the room temperature X-ray diffraction (XRD) patterns of (1-x)BT-xBLZ ceramics. All peaks are indexed and no additional second peaks are observed. When 0.02≤x≤0.04, the X-ray diffraction patterns present a similar structure to tetragonal BaTiO3 (JCPDS: #75-0460) [27,28]. With increasing x values, the main phase of (1-x)BT-xBLZ ceramics is pseudo-cubic and tetragonal phase is absent, which is characterized by the merging of (002)/(200) peaks into a single (200) peak. When 0.04≤x≤0.06, the ceramics exhibit the coexistence of tetragonal and pseudo-cubic phases [29]. The enlarged XRD patterns in the range of 2θ from 43° to 47° are shown in Fig. 1(b). As BLZ content increases, it can be seen that the (200) peak shifts to low angles. This change is mainly related to the increase of lattice parameters, which can be explained by the effect of the incorporation. 2+ The Bi3+(1.03 Å ≤r 3+ Bi ≤1.61 Å) ion is slightly smaller than Ba (1.61 Å + 4+ in 12-fold coordination) in A-site. But Li (0.76 Å) and Zr (0.98 Å) have larger radius than that of Ti4+(0.605 Å in 6-fold coordination) in B-site [16,30]. The substitution of B-site may be the main influence factor to induce the increase of the lattice parameters. Fig. 2 demonstrates the spontaneous Raman spectra of (1-x)BTxBLZ ceramics recorded at room temperature. When 0.02≤x≤0.04, the main spectral features for (1−x)BT-xBLZ ceramics are five distinct bands at 720, 520, 306, 270 and 170 cm−1, which are characteristics of tetragonal BaTiO3 [31,32]. Whereas, rhombohedral and orthorhombic phases are absent in all samples, because there are no signs of a weak band at 478 cm−1 and asymmetric peak at 188 cm−1. The peaks at 927
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Fig. 3. SEM micrographs of (1−x)BT-xBLZ ceramics sintered at their optimized temperatures: (a) x=0.02, 1360 °C, (b) x=0.04, 1340 °C, (c) x=0.08, 1280 °C, and (d) x=0.1, 1260 °C.
bic phase occurred at 0.04≤x≤0.06. All BT-BLZ ceramics featured a dense microstructure. With increasing BLZ content (0.08≤x≤0.1), good thermal stability of permittivity (Δε/ε25 °C≤ ± 15%), high relative permittivity(~1500–2200) and low dielectric loss (2%) were obtained over a broad temperature range at 1 kHz, which indicates that (1−x) BT-xBLZ ceramics could have a potential application for thermally
4. Conclusions (1-x)BT-xBLZ (0.02≤x≤0.1) lead-free ceramics have been successfully synthesized by the solid-state reaction technique. XRD analysis verified that all samples exhibited a single perovskite structure and a systematically structural transformation from tetragonal to pseudocu-
Fig. 4. Temperature dependences of relative permittivity (a) and dielectric loss (b) for (1−x)BT-xBLZ (0.02≤x≤0.1) ceramics measured at 1 kHz, 10 kHz, 100 kHz and 1 MHz.
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Fig. 5. (a) Δε/ε25 °C, (b) temperature dependences of relative permittivity and dielectric loss for (1−x)BT-xBLZ (x=0.1) ceramics at 1 kHz, 10 kHz and 100 kHz from −70 °C to 200 °C. Table 1 Comparison of dielectric properties between (1-x)BT-xBLZ (0.08≤x≤0.1) and other works at 1 kHz. System
εr max
Temperaturerange/°C Tan δ≤0.02
Temperature range/°C Δε/εmid ≤15%
Refs.
0.8BT0.2BA 0.6BT0.4BMZ 0.92BT0.08BMT 0.92BT0.08BLZ 0.9BT0.1BLZ
~1238
0–200
−55–145
[36]
~650
55–280
−25–420
[24]
~1534
30–190
30–150
[27]
~2228
13–200
−54–153
~1726
−21–200
−70–144
This work This work
0.8BT-0.2BA, (1−x)BaTiO3-xBiAlO3; 0.6BT-0.4BMZ, (1−x)BaTiO3-xBi(Mg1/2Zr1/2)O3; 0.92BT-0.08BMT, (1−x)BaTiO3-xBi(Mg2/3Ta1/3)O3; 0.92BT-0.08BLZ, (1−x)BaTiO3xBi(L1/3Zr2/3)O3; 0.9BT-0.1BLZ, (1−x)BaTiO3- xBi(L1/3Zr2/3)O3.
stable ceramic capacitors. Acknowledgments This work was supported by Natural Science Foundation of China (Nos. 11664008, 11464009 and 11364012), Natural Science Foundation of Guangxi (Nos. 2015GXNSFDA139033, 2014GXNSFAA118312 and 2014GXNSFAA118326), Research Startup Funds Doctor of Guilin University of Technology (Nos. 002401003281 and 002401003282) and Project of Outstanding Young Teachers ׳Training in Higher Education Institutions of Guangxi. References [1] W. Chen, X. Zhao, J.G. Sun, L.X. Zhang, L.S. Zhong, Effect of the Mn doping concentration and ferroelectric properties of different-routes-fabricated BaTiO3based ceramics, J. Alloy. Compd. 670 (2016) 48–54. [2] Y. Yuan, M. Du, S.R. Zhang, Effects of BiNbO4 on the microstructure and dielectric properties of BaTiO3-based ceramics, J. Mater. Sci. Mater. Electron. 20 (2009) 157–162. [3] S. Wang, S.R. Zhang, X.H. Zhou, B. Li, Z. Chen, Investigation on dielectric properties of BaTiO3 co-doped with Ni and Nb, Mater. Lett. 60 (2006) 909–911. [4] R. Dittmer, W. Jo, D. Damjanovic, J. Rodel, Lead-free high-temperature dielectrics with wide operational range, J. Appl. Phys. 109 (2011) 034107. [5] J.B. Lim, S.J. Zhang, N. Kim, T.R. Shrout, High-temperature dielectrics in the BiScO3-BaTiO3-(K1/2Bi1/2)TiO3 ternary system, J. Am. Ceram. Soc. 92 (2009) 679–682.
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