- Email: [email protected]
Effects of doping sites on electrical properties of yttrium doped BaTiO3
Materials Letters 174 (2016) 197–200
Contents lists available at ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/matlet
Effects of doping sites on electrical properties of yttrium doped BaTiO3 Pengrong Ren a,n, Qian Wang a, Xin Wang b, Lu Wang a, Jing Wang c, Huiqing Fan d, Gaoyang Zhao a a
School of Materials Science and Engineering, Xi’an University of Technology, Xi’an 710048, China Shaanxi Province Thin Film Technology and Optical Test Open Key Laboratory, Xi’an Technological University, Xi’an 710032, China c Department of Mechanical, Materials and Manufacturing Engineering, University of Nottingham, Nottingham NG7 2RD, UK d State Key Laboratory of Solidification Processing, Northwestern Polytechnical University, Xi’an 710072, China b
art ic l e i nf o
a b s t r a c t
Article history: Received 19 November 2015 Received in revised form 27 February 2016 Accepted 19 March 2016 Available online 23 March 2016
Ba1 xYxTiO3 (BYT), BaTi1 yYyO3 y/2 (BTY) and Ba1 zYzTi1 zYzO3 (BYTY) are prepared by using a solid state reaction method. Their lattice parameters and solubility are determined. And the correlations between doping sites, concentrations and electrical properties are studied. Doping Y3 þ at A-site, which is associated with the electron compensation, leads to high conductivity in BYT, accompanied by giant permittivity and large dielectric loss. However, BTY is relative insulating since its doping mechanism is dominated by the charge compensation of oxide ion. Although BYTY is self-compensated, it behaves more semiconductive, which is probably due to the oxygen loss during the sintering at high temperature. & 2016 Elsevier B.V. All rights reserved.
Keywords: BaTiO3 Dielectrics Electrical properties
1. Introduction Barium titanate (BaTiO3) is one of the most important ferroelectric materials, which can be widely used in multilayer ceramic capacitors (MLCC) [1,2]. The ferroelectric to paraelectric phase transition of pure BaTiO3 occurs at 120–130 °C and is known as the Curie temperature (Tc). Around Tc, the strong temperature dependence of permittivity restricts the applications of BaTiO3 in MLCC. Therefore, BaTiO3 are usually tailored through different dopants. In many cases, doping leads to an adjustment of Tc in BaTiO3, which is rationalized by simple ion-size effects and changes in the tolerance factor [3]. On the other side, doping results in the variance of conduction in BaTiO3. Donor doped BaTiO3 associated with electron compensation usually increases its conductivity properties [4]. The incorporation of acceptors into BaTiO3 has the effect of fixing the charged oxygen vacancies through ionic compensation [5]. Yttrium has a fixed 3 þ oxidation state, and its ionic radius (0.9 Å, CN ¼6; 1.234 Å, CN¼ 12) [6] is between that of Ba2 þ (1.61 Å, CN¼ 12) and Ti4 þ (0.605 Å, CN ¼6) [7]. Thus, Y3 þ might substitute either Ba2 þ or Ti4 þ in the BaTiO3 crystalline lattice, corresponding to different mechanisms of charge compensation. Although the effects of Y3 þ doping on the electrical properties of BaTiO3 based ceramics have been studied [8,9], a contrast of the correlations between doping sites, concentrations and electrical n
Corresponding author. E-mail address: [email protected] (P. Ren).
http://dx.doi.org/10.1016/j.matlet.2016.03.110 0167-577X/& 2016 Elsevier B.V. All rights reserved.
properties has not been reported, as far as we know. Therefore, in the present paper, Ba1 xYxTiO3 (BYT), BaTi1 yYyO3 y/2 (BTY) and Ba1 zYzTi1 zYzO3 (BYTY) are prepared in a compositional range of 0 r x, y, z r0.03. The solubility, dielectric and conductivity properties of BaTiO3 with different doping sites and concentrations of Y3 þ ion are investigated.
2. Experimental procedure Ba1 xYxTiO3 (x ¼0, 0.005, 0.01, 0.015, 0.02, 0.03, labeled as BT, BYT5, BYT10, BYT15, BYT20 and BYT30, respectively), BaTi1 yYyO3 y/2 (y¼ 0.005, 0.01, 0.015, 0.02, 0.03, labeled as BTY5, BTY10, BTY15, BTY20 and BTY30, respectively) and Ba1 zYzTi1 zYzO3 (z ¼0.005, 0.01, 0.015, 0.02, labeled as BYTY5, BYTY10, BYTY15 and BYTY20, respectively) ceramics were prepared by a solid state method. BaCO3 (99.9%), Y2O3 (99.9%) and TiO2 (99.9%), which are purchased from Sinopharm Chemical Reagent Co., Ltd and were used as raw materials. The powders were mixed with ethanol and ball-milled for 12 h. The mixture was dried, calcined at 1150 °C for 6 h, then crushed and ball-milled for 12 h. The dried powders were sieved and then uniaxially pressed into green pellets at room temperature. The pellets were sintered at various temperatures between 1275 and 1325 °C for 3 h, respectively. The present phases were analyzed from X-ray powder diffraction (XRD) using Cu-Kα1 radiation with linear positionsensitive detector. Lattice parameters were determined by least -squares refinement for reflections in the range 20o 2θ o60°, using the software Jade version 6.0 and an external Si standard.
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P. Ren et al. / Materials Letters 174 (2016) 197–200
Microstructural properties were determined using field-emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM). Dielectric properties and impedance spectroscopy were studied by using an Agilent 4284A LCR meter and Agilent 4294A impedance analyzer.
3. Results and discussions XRD patterns show that all compositions are pure except for BYT30, BTY30 and BYTY20 (Fig. S1). Lattice parameters (a and c) and cell volumes (V) as a function of the concentrations of Y3 þ ions (x) are shown in Fig. 1. For BYT, a, c and V decrease linearly with x increasing. This result supports the hypothesis that the Y3 þ ion replaces the Ba2 þ ion in BaTiO3 lattice because the ionic size of Y3 þ ion is smaller than that of Ti4 þ ion. For BTY, a increases with the contents of Y3 þ ions increasing, but c decreases. Additionally V increases in the whole composition region. In regard to BTY, because ionic radius of Ti4 þ ion is smaller than that of Y3 þ ion, substitution of Ti4 þ by Y3 þ leads to the increase of cell volume. For BYTY, a increases but c decreases with the increase of the doping concentration of Y3 þ , and then V increases slightly with the contents of Y3 þ ion increasing, suggesting substitution of Ti4 þ by Y3 þ plays a major role on the lattice distortion in BYTY system. Fig. 2 illustrates SEM images of BT, BYT, BTY and BTYT ceramics sintered at 1275 and 1325 °C, respectively. As shown in Fig. 2(a), BT has a very dense microstructure, and the grain size is about 15– 20 mm. Fig. 2(b)–(d) shows the microstructures of BYT20, BTY20 and BTYT15, respectively. Compared with other two samples, the grain size of BTY is much bigger. As we known, the grain growth of ceramics is mainly dependent on the diffusion during the sintering. The formation of the oxygen vacancies induced by Y3 þ acceptor-doping and their motion can accelerate the diffusion, therefore, leading to the bigger grain size in BTY than BYT and BYTY. The insets of Fig. 2(b)–(d) show the microstructures of BYT30, BTY30 and BTYT20, respectively. As shown in the labeled region, the grains of BYT30 present abnormal shape, and some liquid-like phase appears in the grain boundary of BTY and BYTY. Therefore, it can be confirmed that the solution limitations of Y3 þ ion are dependent on the doping sites in BaTiO3, which are about 0.02, 0.02 and 0.015 in BYT, BTY and BYTY, respectively. Permittivity and loss tangent as a function of the temperature for BYT, BTY and BYTY are shown in Fig. 3. Two obvious phase transitions corresponding to the orthorhombic-tetragonal (TO–T) and tetragonal-cubic (TC) are observed, and both TO–T and TC peaks are broadened for BaTiO3 with lower doping level of Y3 þ ion (BYT5, BYT10 and BYTY5). In addition, the samples behave abnormally high permittivity, accompanied by large dielectric loss when BaTiO3 is substituted by less concentrations of Y3 þ ions (BYT5, BYT10, BTY5, BYTY5 and BYTY10, for example), The permittivity of BYT5 has reached 6.5 104 at room temperature. These broadened peaks and high permittivity might be due to the high conductivities, which are discussed in details in the following. Fig. 4 illustrates impedance spectra of BYT, BTY and BYTY at 300 °C in the air. At 300 °C BT is rather insulating. The complex impedance spectra consist of two arcs, which are generally believed to be associated with two main resistances from the contribution of grain and grain boundary, respectively [10]. When Y3 þ exclusively substitutes Ba2 þ (BYT), the resistances significant decrease, and the complex impedance is only dominated by the contribution of the grain. However, the resistances increase and both the grain and grain boundary contributes on the complex impedance when Y3 þ exclusively substitutes Ti4 þ (BTY). Additionally, when Ba2 þ and Ti4 þ are co-substituted by Y3 þ (BYTY), the resistances increase at the beginning, and then decrease with the concentrations of Y3 þ increasing. The high conductivities in
Fig. 1. Lattice parameters a (a), c (b) and cell volumes V (c) as a function of the doping concentrations of Y3 þ ion in BYT, BTY and BYTY.
BYT are associated with the doping mechanisms of electron compensation, as shown in Eq. (1):
Y2O3 → 2Y •Ba + 2e′ + 3O×O
(1)
However, BTY is rather insulating since its doping mechanism is dominated by the charge compensation of oxide ion, as shown in Eq. (2): × Y2O3 → 2Y′Ti + V •• O + 3OO
(2)
Although BYTY is self-compensated, as shown in Eq. (3): • ′ + 3OO× Y2O3 → 2Y Ba + 2YTi
(3)
it behaves more semiconductive, which is probably due to the oxygen loss during the sintering at high temperature.
4. Conclusions The solubility limitations are determined to be x ¼0.02, y¼0.02 and z¼ 0.015 in BYT, BTY and BYTY, respectively. Compared to BT, doping Y3 þ ions leads to the expansion of cell volumes in BTY and BYTY, yet contraction of cell volume in BYT. In addition, doping Y3 þ at A-site, which is associated with the electron compensation, leads to high conductivity in BYT, accompanied by giant permittivity and large dielectric loss. However, BTY is rather insulating since its doping mechanism is dominated by the oxide ion compensation. Although BYTY is self-compensated, it behaves more semiconductive, which is probably due to the oxygen loss during the high temperature sintering. Therefore, this study will be beneficial to the doping modification of BaTiO3-based MLCC
P. Ren et al. / Materials Letters 174 (2016) 197–200
199
Fig. 2. SEM images of the surfaces: (a) BT, (b) BYT20, (c) BTY20 and (d) BYTY15. The insets in (b–d) show the microstructures of BYT30, BTY30 and BYTY20, respectively.
Fig. 3. Temperature dependence of permittivity (ε′) and loss tangent (tan δ) at 10 kHz over 100 to 300 °C of BYT, BTY and BYTY.
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P. Ren et al. / Materials Letters 174 (2016) 197–200
Fig. 4. Impedance spectra of BYT, BTY and BYTY at 300 °C.
materials. [2]
Acknowledgements [3]
The authors would like to thank the support from the National Natural Science Foundation (No. 51402234), Natural Science Basic Research Plan in Shaanxi Province of China (No. 2015JQ5198, 2015JQ5142), the Doctoral Starting Fund (No. 101-211408) and New-Star of Science and Technology (101-256101511) of Xi'an University of Technology.
[4]
[5]
[6]
Appendix A. Supplementary material Supplementary data associated with this article can be found in the online version at http://dx.doi.org/10.1016/j.matlet.2016.03. 110.
[7]
[8]
[9]
References [1] T. Wang, H. Hao, M.Y. Liu, D.D. Zhou, Z.H. Yao, M.H. Cao, et al., X9R BaTiO3-
[10]
based dielectric ceramics with multilayer core–shell structure produced by polymer-network gel coating method, J. Am. Ceram. Soc. 98 (2015) 690–693. R.L. Brutchey, G.S. Cheng, Q. Gu, D.E. Morse, Positive temperature coefficient of resistivity in donor-doped BaTiO3 ceramics derived from nanocrystals synthesized at low temperature, Adv. Mater. 20 (2008) 1029–1033. L.B. Ben, D.C. Sinclair, Anomalous Curie temperature behavior of A-site Gddoped BaTiO3 ceramics: the influence of strain, Appl. Phys. Lett. 98 (2011) 092907. Q.B. Yuan, Y.P. Pu, B.T. Cao, Effects of different bismuth-based compounds additives on the positive temperature coefficient effect of BaTiO3 ceramics, Mater. Lett. 86 (2012) 115–118. S.-H. Yoon, C.A. Randall, K.-H. Hur, Difference between resistance degradation of fixed valence acceptor Mg and variable valence acceptor Mn-doped BaTiO3 ceramics, J. Appl. Phys. 108 (2010) 064101. K.J. Park, C.H. Kim, Y.J. Yoon, S.M. Song, Y.T. Kim, K.H. Hur, Doping behaviors of dysprosium, yttrium and holmium in BaTiO3 ceramics, J. Eur. Ceram. Soc. 29 (2009) 1735–1741. R.D. Shannon, Revised effective ionic radii and systematic studies of interatomic distances in halides and chalcogenides, Acta Cryst. Sect. A 32 (1976) 751–767. W. Li, J.G. Hao, W.F. Bai, Z.J. Xu, R.Q. Chu, J.W. Zhai, Enhancement of the temperature stabilities in yttrium doped (Ba0.99Ca0.01)(Ti0.98Zr0.02)O3 ceramics, J. Alloy. Compd. 531 (2012) 46–49. P.K. Patel, K.L. Yadav, Effect of yttrium on microstructure, dielectric, ferroelectric and optical properties of BaZr0.10Ti0.90O3 nanoceramics, Physica B 442 (2014) 39–43. J.T.S. Irvine, D.C. Sinclair, A.R. West, Electroceramics: characterization by impedance spectroscopy, Adv. Mater. 2 (1990) 132–138.
Contents lists available at ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/matlet
Effects of doping sites on electrical properties of yttrium doped BaTiO3 Pengrong Ren a,n, Qian Wang a, Xin Wang b, Lu Wang a, Jing Wang c, Huiqing Fan d, Gaoyang Zhao a a
School of Materials Science and Engineering, Xi’an University of Technology, Xi’an 710048, China Shaanxi Province Thin Film Technology and Optical Test Open Key Laboratory, Xi’an Technological University, Xi’an 710032, China c Department of Mechanical, Materials and Manufacturing Engineering, University of Nottingham, Nottingham NG7 2RD, UK d State Key Laboratory of Solidification Processing, Northwestern Polytechnical University, Xi’an 710072, China b
art ic l e i nf o
a b s t r a c t
Article history: Received 19 November 2015 Received in revised form 27 February 2016 Accepted 19 March 2016 Available online 23 March 2016
Ba1 xYxTiO3 (BYT), BaTi1 yYyO3 y/2 (BTY) and Ba1 zYzTi1 zYzO3 (BYTY) are prepared by using a solid state reaction method. Their lattice parameters and solubility are determined. And the correlations between doping sites, concentrations and electrical properties are studied. Doping Y3 þ at A-site, which is associated with the electron compensation, leads to high conductivity in BYT, accompanied by giant permittivity and large dielectric loss. However, BTY is relative insulating since its doping mechanism is dominated by the charge compensation of oxide ion. Although BYTY is self-compensated, it behaves more semiconductive, which is probably due to the oxygen loss during the sintering at high temperature. & 2016 Elsevier B.V. All rights reserved.
Keywords: BaTiO3 Dielectrics Electrical properties
1. Introduction Barium titanate (BaTiO3) is one of the most important ferroelectric materials, which can be widely used in multilayer ceramic capacitors (MLCC) [1,2]. The ferroelectric to paraelectric phase transition of pure BaTiO3 occurs at 120–130 °C and is known as the Curie temperature (Tc). Around Tc, the strong temperature dependence of permittivity restricts the applications of BaTiO3 in MLCC. Therefore, BaTiO3 are usually tailored through different dopants. In many cases, doping leads to an adjustment of Tc in BaTiO3, which is rationalized by simple ion-size effects and changes in the tolerance factor [3]. On the other side, doping results in the variance of conduction in BaTiO3. Donor doped BaTiO3 associated with electron compensation usually increases its conductivity properties [4]. The incorporation of acceptors into BaTiO3 has the effect of fixing the charged oxygen vacancies through ionic compensation [5]. Yttrium has a fixed 3 þ oxidation state, and its ionic radius (0.9 Å, CN ¼6; 1.234 Å, CN¼ 12) [6] is between that of Ba2 þ (1.61 Å, CN¼ 12) and Ti4 þ (0.605 Å, CN ¼6) [7]. Thus, Y3 þ might substitute either Ba2 þ or Ti4 þ in the BaTiO3 crystalline lattice, corresponding to different mechanisms of charge compensation. Although the effects of Y3 þ doping on the electrical properties of BaTiO3 based ceramics have been studied [8,9], a contrast of the correlations between doping sites, concentrations and electrical n
Corresponding author. E-mail address: [email protected] (P. Ren).
http://dx.doi.org/10.1016/j.matlet.2016.03.110 0167-577X/& 2016 Elsevier B.V. All rights reserved.
properties has not been reported, as far as we know. Therefore, in the present paper, Ba1 xYxTiO3 (BYT), BaTi1 yYyO3 y/2 (BTY) and Ba1 zYzTi1 zYzO3 (BYTY) are prepared in a compositional range of 0 r x, y, z r0.03. The solubility, dielectric and conductivity properties of BaTiO3 with different doping sites and concentrations of Y3 þ ion are investigated.
2. Experimental procedure Ba1 xYxTiO3 (x ¼0, 0.005, 0.01, 0.015, 0.02, 0.03, labeled as BT, BYT5, BYT10, BYT15, BYT20 and BYT30, respectively), BaTi1 yYyO3 y/2 (y¼ 0.005, 0.01, 0.015, 0.02, 0.03, labeled as BTY5, BTY10, BTY15, BTY20 and BTY30, respectively) and Ba1 zYzTi1 zYzO3 (z ¼0.005, 0.01, 0.015, 0.02, labeled as BYTY5, BYTY10, BYTY15 and BYTY20, respectively) ceramics were prepared by a solid state method. BaCO3 (99.9%), Y2O3 (99.9%) and TiO2 (99.9%), which are purchased from Sinopharm Chemical Reagent Co., Ltd and were used as raw materials. The powders were mixed with ethanol and ball-milled for 12 h. The mixture was dried, calcined at 1150 °C for 6 h, then crushed and ball-milled for 12 h. The dried powders were sieved and then uniaxially pressed into green pellets at room temperature. The pellets were sintered at various temperatures between 1275 and 1325 °C for 3 h, respectively. The present phases were analyzed from X-ray powder diffraction (XRD) using Cu-Kα1 radiation with linear positionsensitive detector. Lattice parameters were determined by least -squares refinement for reflections in the range 20o 2θ o60°, using the software Jade version 6.0 and an external Si standard.
198
P. Ren et al. / Materials Letters 174 (2016) 197–200
Microstructural properties were determined using field-emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM). Dielectric properties and impedance spectroscopy were studied by using an Agilent 4284A LCR meter and Agilent 4294A impedance analyzer.
3. Results and discussions XRD patterns show that all compositions are pure except for BYT30, BTY30 and BYTY20 (Fig. S1). Lattice parameters (a and c) and cell volumes (V) as a function of the concentrations of Y3 þ ions (x) are shown in Fig. 1. For BYT, a, c and V decrease linearly with x increasing. This result supports the hypothesis that the Y3 þ ion replaces the Ba2 þ ion in BaTiO3 lattice because the ionic size of Y3 þ ion is smaller than that of Ti4 þ ion. For BTY, a increases with the contents of Y3 þ ions increasing, but c decreases. Additionally V increases in the whole composition region. In regard to BTY, because ionic radius of Ti4 þ ion is smaller than that of Y3 þ ion, substitution of Ti4 þ by Y3 þ leads to the increase of cell volume. For BYTY, a increases but c decreases with the increase of the doping concentration of Y3 þ , and then V increases slightly with the contents of Y3 þ ion increasing, suggesting substitution of Ti4 þ by Y3 þ plays a major role on the lattice distortion in BYTY system. Fig. 2 illustrates SEM images of BT, BYT, BTY and BTYT ceramics sintered at 1275 and 1325 °C, respectively. As shown in Fig. 2(a), BT has a very dense microstructure, and the grain size is about 15– 20 mm. Fig. 2(b)–(d) shows the microstructures of BYT20, BTY20 and BTYT15, respectively. Compared with other two samples, the grain size of BTY is much bigger. As we known, the grain growth of ceramics is mainly dependent on the diffusion during the sintering. The formation of the oxygen vacancies induced by Y3 þ acceptor-doping and their motion can accelerate the diffusion, therefore, leading to the bigger grain size in BTY than BYT and BYTY. The insets of Fig. 2(b)–(d) show the microstructures of BYT30, BTY30 and BTYT20, respectively. As shown in the labeled region, the grains of BYT30 present abnormal shape, and some liquid-like phase appears in the grain boundary of BTY and BYTY. Therefore, it can be confirmed that the solution limitations of Y3 þ ion are dependent on the doping sites in BaTiO3, which are about 0.02, 0.02 and 0.015 in BYT, BTY and BYTY, respectively. Permittivity and loss tangent as a function of the temperature for BYT, BTY and BYTY are shown in Fig. 3. Two obvious phase transitions corresponding to the orthorhombic-tetragonal (TO–T) and tetragonal-cubic (TC) are observed, and both TO–T and TC peaks are broadened for BaTiO3 with lower doping level of Y3 þ ion (BYT5, BYT10 and BYTY5). In addition, the samples behave abnormally high permittivity, accompanied by large dielectric loss when BaTiO3 is substituted by less concentrations of Y3 þ ions (BYT5, BYT10, BTY5, BYTY5 and BYTY10, for example), The permittivity of BYT5 has reached 6.5 104 at room temperature. These broadened peaks and high permittivity might be due to the high conductivities, which are discussed in details in the following. Fig. 4 illustrates impedance spectra of BYT, BTY and BYTY at 300 °C in the air. At 300 °C BT is rather insulating. The complex impedance spectra consist of two arcs, which are generally believed to be associated with two main resistances from the contribution of grain and grain boundary, respectively [10]. When Y3 þ exclusively substitutes Ba2 þ (BYT), the resistances significant decrease, and the complex impedance is only dominated by the contribution of the grain. However, the resistances increase and both the grain and grain boundary contributes on the complex impedance when Y3 þ exclusively substitutes Ti4 þ (BTY). Additionally, when Ba2 þ and Ti4 þ are co-substituted by Y3 þ (BYTY), the resistances increase at the beginning, and then decrease with the concentrations of Y3 þ increasing. The high conductivities in
Fig. 1. Lattice parameters a (a), c (b) and cell volumes V (c) as a function of the doping concentrations of Y3 þ ion in BYT, BTY and BYTY.
BYT are associated with the doping mechanisms of electron compensation, as shown in Eq. (1):
Y2O3 → 2Y •Ba + 2e′ + 3O×O
(1)
However, BTY is rather insulating since its doping mechanism is dominated by the charge compensation of oxide ion, as shown in Eq. (2): × Y2O3 → 2Y′Ti + V •• O + 3OO
(2)
Although BYTY is self-compensated, as shown in Eq. (3): • ′ + 3OO× Y2O3 → 2Y Ba + 2YTi
(3)
it behaves more semiconductive, which is probably due to the oxygen loss during the sintering at high temperature.
4. Conclusions The solubility limitations are determined to be x ¼0.02, y¼0.02 and z¼ 0.015 in BYT, BTY and BYTY, respectively. Compared to BT, doping Y3 þ ions leads to the expansion of cell volumes in BTY and BYTY, yet contraction of cell volume in BYT. In addition, doping Y3 þ at A-site, which is associated with the electron compensation, leads to high conductivity in BYT, accompanied by giant permittivity and large dielectric loss. However, BTY is rather insulating since its doping mechanism is dominated by the oxide ion compensation. Although BYTY is self-compensated, it behaves more semiconductive, which is probably due to the oxygen loss during the high temperature sintering. Therefore, this study will be beneficial to the doping modification of BaTiO3-based MLCC
P. Ren et al. / Materials Letters 174 (2016) 197–200
199
Fig. 2. SEM images of the surfaces: (a) BT, (b) BYT20, (c) BTY20 and (d) BYTY15. The insets in (b–d) show the microstructures of BYT30, BTY30 and BYTY20, respectively.
Fig. 3. Temperature dependence of permittivity (ε′) and loss tangent (tan δ) at 10 kHz over 100 to 300 °C of BYT, BTY and BYTY.
200
P. Ren et al. / Materials Letters 174 (2016) 197–200
Fig. 4. Impedance spectra of BYT, BTY and BYTY at 300 °C.
materials. [2]
Acknowledgements [3]
The authors would like to thank the support from the National Natural Science Foundation (No. 51402234), Natural Science Basic Research Plan in Shaanxi Province of China (No. 2015JQ5198, 2015JQ5142), the Doctoral Starting Fund (No. 101-211408) and New-Star of Science and Technology (101-256101511) of Xi'an University of Technology.
[4]
[5]
[6]
Appendix A. Supplementary material Supplementary data associated with this article can be found in the online version at http://dx.doi.org/10.1016/j.matlet.2016.03. 110.
[7]
[8]
[9]
References [1] T. Wang, H. Hao, M.Y. Liu, D.D. Zhou, Z.H. Yao, M.H. Cao, et al., X9R BaTiO3-
[10]
based dielectric ceramics with multilayer core–shell structure produced by polymer-network gel coating method, J. Am. Ceram. Soc. 98 (2015) 690–693. R.L. Brutchey, G.S. Cheng, Q. Gu, D.E. Morse, Positive temperature coefficient of resistivity in donor-doped BaTiO3 ceramics derived from nanocrystals synthesized at low temperature, Adv. Mater. 20 (2008) 1029–1033. L.B. Ben, D.C. Sinclair, Anomalous Curie temperature behavior of A-site Gddoped BaTiO3 ceramics: the influence of strain, Appl. Phys. Lett. 98 (2011) 092907. Q.B. Yuan, Y.P. Pu, B.T. Cao, Effects of different bismuth-based compounds additives on the positive temperature coefficient effect of BaTiO3 ceramics, Mater. Lett. 86 (2012) 115–118. S.-H. Yoon, C.A. Randall, K.-H. Hur, Difference between resistance degradation of fixed valence acceptor Mg and variable valence acceptor Mn-doped BaTiO3 ceramics, J. Appl. Phys. 108 (2010) 064101. K.J. Park, C.H. Kim, Y.J. Yoon, S.M. Song, Y.T. Kim, K.H. Hur, Doping behaviors of dysprosium, yttrium and holmium in BaTiO3 ceramics, J. Eur. Ceram. Soc. 29 (2009) 1735–1741. R.D. Shannon, Revised effective ionic radii and systematic studies of interatomic distances in halides and chalcogenides, Acta Cryst. Sect. A 32 (1976) 751–767. W. Li, J.G. Hao, W.F. Bai, Z.J. Xu, R.Q. Chu, J.W. Zhai, Enhancement of the temperature stabilities in yttrium doped (Ba0.99Ca0.01)(Ti0.98Zr0.02)O3 ceramics, J. Alloy. Compd. 531 (2012) 46–49. P.K. Patel, K.L. Yadav, Effect of yttrium on microstructure, dielectric, ferroelectric and optical properties of BaZr0.10Ti0.90O3 nanoceramics, Physica B 442 (2014) 39–43. J.T.S. Irvine, D.C. Sinclair, A.R. West, Electroceramics: characterization by impedance spectroscopy, Adv. Mater. 2 (1990) 132–138.