- Email: [email protected]
Influence of Nb2O5 addition on dielectric properties and diffuse phase transition behavior of BaZr0.2Ti0.8O3 ceramics
Ceramics International ∎ (∎∎∎∎) ∎∎∎–∎∎∎
Contents lists available at ScienceDirect
Ceramics International journal homepage: www.elsevier.com/locate/ceramint
Influence of Nb2O5 addition on dielectric properties and diffuse phase transition behavior of BaZr0.2Ti0.8O3 ceramics Zheng Sun a,b, Lingxia Li a,b,n, Jiangteng Li a,b, Haoran Zheng a,b, Weijia Luo a,b a b
Key Laboratory for Advanced Ceramics and Machining Technology of Ministry of Education, Tianjin University, Tianjin 300072, China School of Electronic and Information Engineering, Tianjin University, Tianjin 300072, China
art ic l e i nf o
a b s t r a c t
Article history: Received 25 February 2016 Received in revised form 25 March 2016 Accepted 28 March 2016
Nb2O5 doped Ba(Zr0.2Ti0.8)O3 (short as BZT20) ceramics were prepared by a mixed-oxide method using a high-energy planetary ball mill and the influence of Nb2O5 addition on microstructure, dielectric properties and diffuse phase transition behavior of BZT20 ceramics were investigated. It was demonstrated that Nb5 þ entered the B-site of BZT20 ceramic and substituted for Ti4 þ , which caused the expansion and distortion of crystal lattice. BZT20 ceramics doped with 0.2 mol% Nb2O5 showed excellent dielectric property and lower diffusivity with εm ¼37,823 and γ ¼ 1.49. We supposed that the increase of dielectric constant and decrease of diffuseness parameter with increasing Nb2O5 content were caused by lattice disorder and unbalancing of cations induced by the substitution of Ti4 þ by Nb5 þ in the B sites of BZT20 ceramics. The Curie temperature decreased with the increase of Nb2O5 content, which can be attributed to enlarged distortion energy of the Nb doped BZT20 structure. Besides, grain size effect on the dielectric property and diffuse phase transition behavior of Nb2O5 doped BZT20 ceramics was also investigated. & 2016 Elsevier Ltd and Techna Group S.r.l. All rights reserved.
Keywords: C. Dielectric properties Ba(Zr0.2Ti0.8)O3 ceramics Diffuse phase transition
1. Introduction Diffuse phase transition (DPT) is one of the most interested characteristic in ferroelectric physics [1]. The typical feature of DPT is the relaxor behavior happened in ferroelectric phase transition, mostly in perovskite structure materials, especially in lead-based compounds (PMN, PSN, PLZT, etc.) with more than one type of ions occupying the equivalent six-coordinated crystallographic sites [2– 5]. However, the intrinsic properties of volatility and toxicity in these lead-based ceramics have restricted their application in environmental friendly devices (such as dielectrics for capacitors, actuators, etc.). In recent years, most researchers focus on developing lead-free ceramics with DPT behavior [6–8]. Lead-free solid solutions of BaTiO3 and BaZrO3 (Ba(ZrxTi1 x)O3, abbreviated as BZT) is one of the most important compositions for dielectrics in multilayer ceramic capacitors which is found to show DPT behavior [9,10]. The permittivity of BZT ceramic is increased more by the addition of zirconium due to the higher chemical stability of Zr ion than Ti ion [11,12]. The DPT of BZT ceramics is caused by a broadening of the permittivity maximum in the temperature range, which is stimulated by the increase of n Corresponding author at: Key Laboratory for Advanced Ceramics and Machining Technology of Ministry of Education, Tianjin University, Tianjin 300072, China. E-mail address: [email protected] (L. Li).
zirconium amount. As the zirconium content increases to 20%, only one phase transition exists. Below this content, the rhombohedral phase is stable; above the content, the cubic phase is stable [13]. As the ratio of Zr is up to 25%, BZT appears strong relaxor property, and the Curie temperature shifts to lower temperature [9]. Nb2O5 doped ceramics, such as Nb2O5 doped PZT [14–16] and BNKT [17], have been investigated by many researchers. Chu et al. reported that Nb2O5 enabled a good sintering process, promoted domain wall motion and enhanced the densification and dielectric properties of Pb1 0.5x(Zr0.52Ti0.48)1 xNbxO3 ceramics[14]. Tănăsoiu et al. found that Nb5 þ in PbZr0.51(Nb3Li)xTi0.49 xO3 ceramics is helpful to improve the dielectric and piezoelectric properties [16]. Kumar et al. investigated the effect of Nb2O5 doping on the properties of Bi0.5(Na0.5K0.5)0.5TiO3 ceramic, the results showed that 0.4 wt% Nb2O5 doping exhibited higher Pr and Rsq values and also showed relaxor behaviors with DPT [17]. However, the effect of Nb2O5 on the DPT behavior and dielectric properties of BZT ceramics has been seldom reported. In this work, Nb2O5 doped BZT20 ceramics were prepared by solid-state method. The influence of Nb2O5 contents ranging from 0.1 to 0.4 mol% on the microstructure and dielectric properties BZT20 ceramics were examined and discussed. Moreover, the relationship between DPT behavior and the contents of Nb2O5 have been investigated.
http://dx.doi.org/10.1016/j.ceramint.2016.03.212 0272-8842/& 2016 Elsevier Ltd and Techna Group S.r.l. All rights reserved.
Please cite this article as: Z. Sun, et al., Influence of Nb2O5 addition on dielectric properties and diffuse phase transition behavior of BaZr0.2Ti0.8O3 ceramics, Ceramics International (2016), http://dx.doi.org/10.1016/j.ceramint.2016.03.212i
Z. Sun et al. / Ceramics International ∎ (∎∎∎∎) ∎∎∎–∎∎∎
2
mixed thoroughly with 0.5 wt% polyvinyl alcohol (PVA) organic binder solution to granulate and compacted into disk samples with a diameter of 10 mm and a thickness of 1.0 mm. After burning out PVA at 600 °C in the electric furnace, pellets of Nb2O5-doped BZT20 were sintered at 1270 °C for 4 h. Then the silver pastes were fired at 800 °C for both sides of these samples as electrodes for electrical measurements. The crystalline structures of the sintered samples were identified by Powder X-ray diffraction (XRD), using a diffractometer (D8Focus; Bruker AXS GmbH, Karlsruhe, German) with Cu Kα radiation over a 2θ angle from 20° to 80°. The morphologies of the sintered samples were performed and analyzed with field emission scanning electron microscopy (FE-SEM, S-4800; Hitachi, Ltd., Tokyo, Japan). The temperature dependence of dielectric permittivity was measured with a capacitance meter (HP4278A; HewlettPackard, SantaClara, California, USA.) in conjunction with a temperature chamber (GZ-ESPEC) over a temperature range of 50 to 145 °C at 1 kHz.
Fig. 1. XRD patterns of Nb2O5 doped BZT20 ceramics sintered at 1270 °C.
2. Experimental procedures BZT20 þxmol% Nb2O5 ceramics with x¼ 0.1, 0.15, 0.2, and 0.4 were fabricated by solid-state reaction using a high-energy planetary ball mill. The raw materials of AR grade BaCO3 (99%), TiO2 (99%) and ZrO2 (99%) powders were weighted at appropriate proportion. Powdered oxides in stoichiometry were homogeneously ball milled in deionized water for 6 h using ZrO2 balls as milling media. The homogeneous mixtures were dried and calcined at 1100 °C for 4 h, and then the pre-synthesized BZT20 powders and Nb2O5 (99%) powder were mixed according to the formula and re-milled for 12 h. The powers were subsequently
3. Results and discussion Fig. 1 plots the XRD patterns of BZT20 þ xmol% Nb2O5 ceramics with x ¼0.1, 0.15, 0.2, and 0.4. From the XRD patterns, it can be seen that all samples exhibited pure perovskite phase with no impurity phase, which suggested that the Nb ion can be dissolved in BZT20 to form a homogenous solid solution. Fig. 2 illustrates the SEM micrographs of BZT20 ceramics with different Nb2O5 contents. The grain sizes of specimens doped with 0.1–0.2 mol% Nb2O5 are continually increased with the increasing amount of Nb2O5 addition. However, the SEM micrograph in Fig. 2 (d) shows that further increasing the amount of Nb2O5 to 0.4 mol% gives rise to the decrease of grain size. In Ba(ZrxTi1 x)O3 solid solution, Ba2 þ occupies site A of perovskite structure, while
Fig. 2. SEM patterns of the Nb2O5 doped BZT20 ceramics. (a) x ¼0.1 mol% (b) x¼ 0.15 mol% (c) x ¼0.2 mol% and (d) x¼ 0.40 mol%.
Please cite this article as: Z. Sun, et al., Influence of Nb2O5 addition on dielectric properties and diffuse phase transition behavior of BaZr0.2Ti0.8O3 ceramics, Ceramics International (2016), http://dx.doi.org/10.1016/j.ceramint.2016.03.212i
Z. Sun et al. / Ceramics International ∎ (∎∎∎∎) ∎∎∎–∎∎∎
3
ceramics may also be attributed to the lager grain size which can be confirmed by the SEM in Fig. 2(c). The generation of vacancies and inner stress due to the distortion of lattice in Nb doped BZT20 structure is another factor that can improve the dielectric property [22]. The vacancies in Nb doped BZT20 ceramics can be described through the behavior of ion doped ceramics using Eq. (1)–(3). It is known that the Nb5 þ doped BaTiO3 creates a donor like behavior because the valance size of the Nb ion is larger than the valance size of the Ba and Ti ions. For small Nb5 þ content, compensation of electron can be described by Eq. (1) [23]:
Nb2 O5 → 2Nb 5 +4 + + 4O0 + Ti
1 O 2 + 2e ′ 2
(1)
5þ
Fig. 3. Temperature dependence of the dielectric constant and tangent loss of Nb2O5 doped BZT20 ceramics measured at the frequency of 1 kHz.
″ With the increase of Nb content, A or B site vacancies ( VBa ′ ′′ ) will be produced. These vacancies are created due to the and VTi lattice disordered, and produce inner stress as shown in Eqs. (2) and (3) [24]:
″ Nb2 O5 → 2Nb 5 +2 + + 5O0 + VBa
(2)
2Nb2 O5 → 4Nb 5 +4 + + 10O0 + V Ti′′′
(3)
Ba
Zr4 þ and Ti4 þ occupy site B. Zr4 þ (0.72 Å) is larger and more stable than Ti4 þ (0.605 Å). Generally, it is easier for Nb5 þ (0.69 Å) to enter into the B site of Ba(ZrxTi1 x)O3 structure than A site for electric balance [1]. When Nb5 þ enters into B site of BZT20 ceramics, it tends to substitute the Ti4 þ , which generates oxygen vacancies in BZT20, and these defects accelerate the mass transport process, further improving the grain growth [18]. The decrease of grain size with higher Nb doping may be due to the small particle size of the Nb ion accumulating near the grain boundary which leads to suppress grain growth during the sintering process [19]. Fig. 3 shows the temperature dependence of dielectric constant and tangent loss of BZT20 ceramics doped with Nb2O5 as 0.1 mol%, 0.15 mol%, 0.2 mol% and 0.4 mol% at the frequency of 1 kHz. With the increase of Nb contents, the peak temperature Tm at the maximum dielectric constant is shifted to lower temperature. The variation of Tm with Nb content measured at 1 kHz is recorded in Table 1, indicating a negative correlation between Tm and Nb content in Nb2O5 doped BZT20 ceramics. As mentioned above, Nb5 þ tended to substitute Ti4 þ in BZT20 ceramics. The part substitution will lead to the distortion of lattice and expand the unit cell volume. The enlarged distortion energy of Nb doped BZT20 structure facilitates the vibration of Ti4 þ at relatively low temperature which stabilizes the Ti4 þ in the center of the oxygen octahedral [20]. Thus, the value of Tm decreases with the increase of Nb content. Furthermore, it can be seen from Fig. 3 that the dielectric constants increased with the increase of Nb and reached a maximum value at 0.2 mol% Nb2O5. The values of dielectric constant maximum ɛm corresponding to different Nb content measured at 1 kHz are listed in Table 1. As is well known, the grain size will influence the dielectric constant. Moulson and Herbert et al. have reported that the increasing grain size resulted in the distinct enhancement of the dielectric constant in BaTiO3 materials [21]. The higher dielectric value of 0.2 mol% Nb2O5 doped BZT20 Table 1 Values of Curie point temperature (T0), Tm, Tcw, ΔTm, εm and γ for Nb2O5 doped BZT20 ceramics. Samples 0.1 mol%Nb2O5 0.15 mol% Nb2O5 0.2 mol% Nb2O5 0.4 mol% Nb2O5 Tm(°C) Tcw(°C) T0(°C) ΔTm εm γ
18 80 45 62 10,187 1.86
16 78 9 62 20,176 1.57
1.65 67 5 65.35 37,823 1.49
15 55 17 70 33,373 1.58
Ti
From the description above, it can be suggested that the vacancies and inner stress produced in Nb doped BZT20 ceramics have effects on the dielectric properties and give rise to the increase of dielectric constant. For tan δ results with temperatures as shown in Fig. 3, it can be seen that tan δ values tended to increase with the increasing Nb2O5 content, which can be clearly seen for the sample of x ¼0.2 mol%. This may be due to the formation of numerous Ti vacancies by substituted Ti4 þ with high valence Nb5 þ . From Fig. 3, it could be also observed that the Nb2O5 doped BZT20 ceramics gradually show a broad dielectric permittivity– temperature curve in the vicinity of transition temperature, which is referred as diffuse phase transition (DPT). A diffuse phase transition is generally characterized by: (a) broadening in dielectric constant versus temperature curve; (b) a relatively large separation (in temperature) between the maximum of dielectric constant and dielectric loss of the dielectric spectrum; (c) a deviation from Curie–Weiss law in the vicinity of Tm; (d) frequency dispersion of both ε and tan δ (dielectric loss) in transition region thereby implying a frequency dependency of Tm [25]. The dielectric peak at Tm becomes broader with the increase of Nb content as is clearly seen for sample of x¼0.2 and 0.4 mol%. The diffusivity of phase transition can be described through the dielectric behavior of ceramics. It is known that the dielectric permittivity of a normal ferroelectric above the Curie temperature follows the Curie–Weiss law described by
ϵ = C /( T − T0 )
( When
T > Tc )
(4)
where T0 is the Curie–Weiss temperature and C is the Curie–Weiss constant. When the ferroelectric–paraelectric phase transition diffuses, the permittivity would deviate from the Curie–Weiss law. Fig. 4(a–d) shows the plot of inverse dielectric permittivity versus temperature at 1 kHz for the Nb2O5 doped BZT20 ceramics. It is shown that the dielectric curves of all the samples deviate from the Curie–Weiss law at a temperature above the Curie temperature. The parameter ΔTm, which reflects the degree of the deviation from the Curie–Weiss law, is defined as
ΔTm = Tcw − Tm
(5)
where Tcw denotes the temperature from which the permittivity
Please cite this article as: Z. Sun, et al., Influence of Nb2O5 addition on dielectric properties and diffuse phase transition behavior of BaZr0.2Ti0.8O3 ceramics, Ceramics International (2016), http://dx.doi.org/10.1016/j.ceramint.2016.03.212i
Z. Sun et al. / Ceramics International ∎ (∎∎∎∎) ∎∎∎–∎∎∎
4
Fig. 4. Temperature dependence of the inverse dielectric constant at 1 kHz for Nb2O5 doped BZT20 ceramics: (a) x ¼0.1 mol% (b) x ¼0.15 mol% (c) x ¼ 0.2 mol% (d) x¼ 0.40 mol% and the plots of ln (1/ε 1/εm) as a function of ln (T–Tm) for Nb2O5 doped BZT20 ceramics (e).
starts to deviate from the Curie–Weiss law and Tm represents the corresponding temperature of dielectric constant maximum. The Curie temperature is determined from the graph by extrapolation of the reciprocal of dielectric constant. The parameters obtained from the fitting plots at 1 kHz are listed in the Table 1. As can be seen from the table, the values of ΔTm increased with the increase of Nb2O5 content, indicating gradual deviation from the normal Curie–Weiss law and Nb2O5 induced diffuse phase transition in Nb2O5 doped BZT20 samples. A modified Curie–Weiss law was proposed by Uchino et al. to describe the diffusivity of the phase transition [26]: γ
1/ϵ − 1/ϵ m = ( T − Tm ) /C1
(6)
where γ and C1 are assumed to be constant. The parameter γ determines the degree of diffuse phase transition: for γ ¼1, a normal
Curie–Weiss law is obtained, for γ ¼2, it reduces to the quadratic dependency which describes a complete diffuse phase transition [27]. Fig. 4(e) shows the plots of ln (1/ε 1/εm) as a function of ln (T–Tm) at 1 kHz for the four different Nb2O5 compositions. Liner relationships are observed for all the samples. The slopes of the fitting curve are used to determine the parameter γ values. In the studied compositions the values of γ are found to be 1.86, 1.57, 1.49 and 1.58 at 1 kHz for x ¼0.1 mol%, 0.15 mol%, 0.2 mol% and 0.4 mol%, respectively. The value of γ decrease to a minimum at x¼ 0.2 mol% and then increase again at x¼ 0.4 mol% (Table 1), which indicate the Nb2O5 addition have significant influence on the diffusivity of BZT20 ceramics. The broadened dielectric maximum (Fig. 3) and its deviation from Curie–Weiss law are the main characteristics of DPT behavior in Nb2O5 doped BZT20 ceramics. The observed DPT behavior may be due to the increasing
Please cite this article as: Z. Sun, et al., Influence of Nb2O5 addition on dielectric properties and diffuse phase transition behavior of BaZr0.2Ti0.8O3 ceramics, Ceramics International (2016), http://dx.doi.org/10.1016/j.ceramint.2016.03.212i
Z. Sun et al. / Ceramics International ∎ (∎∎∎∎) ∎∎∎–∎∎∎
lattices disorder and unbalancing of cations induced by the substitution of Ti4 þ by Nb5 þ in the sublattice, which produces heterogeneities in the structure and is significant for the DPT behavior [28]. Ti4 þ at B site results in local polar regions while Nb5 þ at B site leads to local non-polar regions, which is responsible for the change of diffusivity in Nb2O5 doped BZT20 samples. Except for the lattices disorder and unbalancing of cations, the effect of grain boundary is another factor that can influence the DPT behavior. This point has been discussed in detail by Zhao [29]. The grain boundary is nonferroelectric phase and has no ferroelectric–paraelectric phase transition. The volume fraction of grain boundary increases with the decrease of grain size. Therefore, the proportion of tetragonal phase and ferroelectricity is lower in smaller-grained ceramics. The result is that phase transition became more diffused.
4. Conclusions Nb2O5 doped Ba(Zr0.2Ti0.8)O3 ceramics with doping addition at 0.1, 0.15, 0.2 and 0.4 mol% had been prepared through solid state reaction route and sintered at 1270 °C. The room temperature XRD study suggested that all the samples had pure perovskite structure. The effect of grain size on the dielectric and diffuse phase transition behavior of Nb2O5 doped BZT20 ceramics was studied. The results revealed that lager grain size improved the dielectric properties. Phase transition became more diffused due to the smaller-grained BZT20 ceramics. Except for the grain size effect, the generation of vacancies and inner stress due to the Nb ions substituted Ti ions in B-site of the Ba(Zr0.2Ti0.8)O3 ceramics leaded to a significant increase in dielectric constant. Moreover, the Curie temperature of Ba(Zr0.2Ti0.8)O3 ceramics decreased with the increase of Nb2O5 addition.
References [1] W.Q. Cao, J.W. Xiong, J.P. Sun, Dielectric behavior of Nb-doped Ba(ZrxTi1 x)O3, Mater. Chem. Phys. 106 (2007) 338–342. [2] X.G. Tang, K.H. Chew, H.L.W. Chan, Diffuse phase transition and dielectric tunability of Ba(ZryTi1 y)O3 relaxor ferroelectric ceramics, Acta. Mater. 52 (2004) 5177–5183. [3] L.E. Cross, Ferroelectrics 151 (1994) 305–320. [4] V.S. Puli, R. Martínez, A. Kumar, J.F. Scott, S. Katiyar, A quaternary lead based perovskite structured materials with diffuse phase transition behavior, Mater. Res. Bull. 46 (2011) 2527–2530. [5] J. Wang, X.G. Tang, H.L.W. Chan, C.L. Choy, Dielectric relaxation and electrical properties of 0.94Pb(Fe1/2Nb1/2)O3 0.06PbTiO3 single crystals, Appl. Phys. Lett. 86 (2005) 152907. [6] Y. Tanaka, T. Harigai, M. Ueda, H. Adachi, E. Fujii, Structural modification and large piezoelectricity of strained (Na, Bi) TiO3–BaTiO3 epitaxial thin films, J.
5
Am. Ceram. Soc. 95 (2012) 3547–3553. [7] Z. Yu, R. Guo, A.S. Bhalla, Orientation dependence of the ferroelectric and piezoelectric behavior of Ba(Ti1 xZrx)O3 single crystals, Appl. Phys. Lett. 77 (2000) 1535–1537. [8] Z. Yu, C. Ang, R. Guo, A.S. Bhalla, Piezoelectric and strain properties of Ba (Ti1 xZrx)O3 ceramics, J. Appl. Phys. 92 (2002) 1489–1493. [9] D. Hennings, A. Schnell, G. Simon, Diffuse ferroelectric phase transitions in Ba(Ti1 yZry)O3 ceramics, J. Am. Ceram. Soc. 65 (1982) 539–544. [10] N. Kumar, A. Ionin, T. Ansell, S. Kwon, W. Hackenberger, D. Cann, Multilayer ceramic capacitors based on relaxor BaTiO3-Bi(Zn1/2Ti1/2)O3 for temperature stable and high energy density capacitor applications, Appl. Phys. Lett. 106 (2015) 252901. [11] S. Hoffmann, R. Waser, Control of the morphology of CSD-prepared (Ba,Sr)TiO3 thin films, J. Eur. Ceram. Soc. 19 (1999) 1339–1343. [12] T. Tsurumi, Y. Yamamoto, H. Kakemoto, S. Wada, H. Chazono, H. Kishi, Dielectric properties of BaTiO3-BaZrO3 ceramics under a high electric field, J. Mater. Res. 17 (2002) 755–759. [13] U. Weber, G. Greuel, U. Boettger, S. Weber, D. Hennings, R. Waser, Dielectric properties of Ba(Zr,Ti)O3-based ferroelectrics for capacitor applications, J. Am. Ceram. Soc. 84 (2001) 759–766. [14] S.Y. Chu, T.Y. Chen, I.T. Tsai, W. Water, Doping effects of Nb additives on the piezoelectric and dielectric properties of PZT ceramics and its application on SAW device, Sens. Actuators A 113 (2004) 198–203. [15] M. Pereira, A.G. Peixoto, M.J.M. Gomes, Effect of Nb doping on the microstructural and electrical properties of the PZT ceramics, J. Eur. Ceram. Soc. 21 (2001) 1353–1356. [16] C. Tănăsoiu, E. Dimitriu, C. Miclea, Effect of Nb, Li doping on structure and piezoelectric properties of PZT type ceramics, J. Eur. Ceram. Soc. 19 (1999) 1187–1190. [17] K. Kumar, B. Kumar, Effect of Nb-doping on dielectric, ferroelectric and conduction behaviour of lead free Bi0.5(Na0.5K0.5)0.5TiO3 ceramic, Ceram. Int. 38 (2012) 1157–1165. [18] C. Chen, H. Zhuang, X. Zhu, K. Zhou, D. Zhang, Enhancement of relaxor properties by Nb doping in Ba0.8Sr0.12Ca0.08TiO3 lead-free ferroelectric ceramics, Ceram. Int. 41 (2015) 9893–9898. [19] P. Parjansri, U. Intatha, S. Eitssayeam, Dielectric, ferroelectric and piezoelectric properties of Nb5 þ doped BCZT ceramics, Mater. Res. Bull. 65 (2015) 61–67. [20] C. Chen, H. Zhuang, X. Zhu, K. Zhou, D. Zhang, Enhancement of relaxor properties by Nb doping in Ba0.8Sr0.12Ca0.08TiO3 lead-free ferroelectric ceramics, Ceram. Int. 41 (2015) 9893–9898. [21] A.J. Moulson, J.M. Herbert, Electroceramics: Materials, Properties, Application, Chapman and Hall, London, 1990. [22] P. Parjansri, U. Intatha, S. Eitssayeam, Dielectric, ferroelectric and piezoelectric properties of Nb5 þ doped BCZT ceramics, Mater. Res. Bull. 65 (2015) 61–67. [23] H. Chan, M.P. Harmer, D. Smyth, Compensating defects in highly donor-doped BaTiO3, J. Am. Ceram. Soc. 69 (1986) 507–510. [24] W. Li, J. Qi, Y. Wang, L. Li, Z. Gui, Doping behaviors of Nb2O5 and Co2O3 in temperature stable BaTiO3-based ceramics, Mater. Lett. 57 (2002) 1–5. [25] S.K. Rout, E. Sinha, S. Panigrahi, Dielectric properties and diffuse phase transition in Ba1 xMgxTi0.6Zr0.4O3 solid solutions, Mater. Chem. Phys. 101 (2007) 428–432. [26] K. Uchino, S. Nomura, Critical exponents of the dielectric constants in diffused-phase-transition crystals, Ferroelectrics. 44 (1982) 55–61. [27] C. Ciomaga, M. Viviani, M.T. Buscaglia, V. Buscaglia, L. Mitoseriu, A. Stancu, P. Nanni, Preparation and characterisation of the Ba(Zr,Ti)O3 ceramics with relaxor properties, J. Eur. Ceram. Soc. 27 (2007) 4061–4064. [28] X. Qin, D. Shihua, S. Tianxiu, W. Hongni, Diffuse phase transition of Ba0.92Ca0.08(Ti0.82Zr0.18)O3 based ceramics, Ferroelectrics 426 (2012) 282–289. [29] Z. Zhao, V. Buscaglia, M. Viviani, M.T. Buscaglia, L. Mitoseriu, A. Testino, M. Nygren, M. Johnsson, P. Nanni, Grain-size effects on the ferroelectric behavior of dense nanocrystalline BaTiO3 ceramics, Phys. Rev. B 70 (2004) 024107.
Please cite this article as: Z. Sun, et al., Influence of Nb2O5 addition on dielectric properties and diffuse phase transition behavior of BaZr0.2Ti0.8O3 ceramics, Ceramics International (2016), http://dx.doi.org/10.1016/j.ceramint.2016.03.212i
Contents lists available at ScienceDirect
Ceramics International journal homepage: www.elsevier.com/locate/ceramint
Influence of Nb2O5 addition on dielectric properties and diffuse phase transition behavior of BaZr0.2Ti0.8O3 ceramics Zheng Sun a,b, Lingxia Li a,b,n, Jiangteng Li a,b, Haoran Zheng a,b, Weijia Luo a,b a b
Key Laboratory for Advanced Ceramics and Machining Technology of Ministry of Education, Tianjin University, Tianjin 300072, China School of Electronic and Information Engineering, Tianjin University, Tianjin 300072, China
art ic l e i nf o
a b s t r a c t
Article history: Received 25 February 2016 Received in revised form 25 March 2016 Accepted 28 March 2016
Nb2O5 doped Ba(Zr0.2Ti0.8)O3 (short as BZT20) ceramics were prepared by a mixed-oxide method using a high-energy planetary ball mill and the influence of Nb2O5 addition on microstructure, dielectric properties and diffuse phase transition behavior of BZT20 ceramics were investigated. It was demonstrated that Nb5 þ entered the B-site of BZT20 ceramic and substituted for Ti4 þ , which caused the expansion and distortion of crystal lattice. BZT20 ceramics doped with 0.2 mol% Nb2O5 showed excellent dielectric property and lower diffusivity with εm ¼37,823 and γ ¼ 1.49. We supposed that the increase of dielectric constant and decrease of diffuseness parameter with increasing Nb2O5 content were caused by lattice disorder and unbalancing of cations induced by the substitution of Ti4 þ by Nb5 þ in the B sites of BZT20 ceramics. The Curie temperature decreased with the increase of Nb2O5 content, which can be attributed to enlarged distortion energy of the Nb doped BZT20 structure. Besides, grain size effect on the dielectric property and diffuse phase transition behavior of Nb2O5 doped BZT20 ceramics was also investigated. & 2016 Elsevier Ltd and Techna Group S.r.l. All rights reserved.
Keywords: C. Dielectric properties Ba(Zr0.2Ti0.8)O3 ceramics Diffuse phase transition
1. Introduction Diffuse phase transition (DPT) is one of the most interested characteristic in ferroelectric physics [1]. The typical feature of DPT is the relaxor behavior happened in ferroelectric phase transition, mostly in perovskite structure materials, especially in lead-based compounds (PMN, PSN, PLZT, etc.) with more than one type of ions occupying the equivalent six-coordinated crystallographic sites [2– 5]. However, the intrinsic properties of volatility and toxicity in these lead-based ceramics have restricted their application in environmental friendly devices (such as dielectrics for capacitors, actuators, etc.). In recent years, most researchers focus on developing lead-free ceramics with DPT behavior [6–8]. Lead-free solid solutions of BaTiO3 and BaZrO3 (Ba(ZrxTi1 x)O3, abbreviated as BZT) is one of the most important compositions for dielectrics in multilayer ceramic capacitors which is found to show DPT behavior [9,10]. The permittivity of BZT ceramic is increased more by the addition of zirconium due to the higher chemical stability of Zr ion than Ti ion [11,12]. The DPT of BZT ceramics is caused by a broadening of the permittivity maximum in the temperature range, which is stimulated by the increase of n Corresponding author at: Key Laboratory for Advanced Ceramics and Machining Technology of Ministry of Education, Tianjin University, Tianjin 300072, China. E-mail address: [email protected] (L. Li).
zirconium amount. As the zirconium content increases to 20%, only one phase transition exists. Below this content, the rhombohedral phase is stable; above the content, the cubic phase is stable [13]. As the ratio of Zr is up to 25%, BZT appears strong relaxor property, and the Curie temperature shifts to lower temperature [9]. Nb2O5 doped ceramics, such as Nb2O5 doped PZT [14–16] and BNKT [17], have been investigated by many researchers. Chu et al. reported that Nb2O5 enabled a good sintering process, promoted domain wall motion and enhanced the densification and dielectric properties of Pb1 0.5x(Zr0.52Ti0.48)1 xNbxO3 ceramics[14]. Tănăsoiu et al. found that Nb5 þ in PbZr0.51(Nb3Li)xTi0.49 xO3 ceramics is helpful to improve the dielectric and piezoelectric properties [16]. Kumar et al. investigated the effect of Nb2O5 doping on the properties of Bi0.5(Na0.5K0.5)0.5TiO3 ceramic, the results showed that 0.4 wt% Nb2O5 doping exhibited higher Pr and Rsq values and also showed relaxor behaviors with DPT [17]. However, the effect of Nb2O5 on the DPT behavior and dielectric properties of BZT ceramics has been seldom reported. In this work, Nb2O5 doped BZT20 ceramics were prepared by solid-state method. The influence of Nb2O5 contents ranging from 0.1 to 0.4 mol% on the microstructure and dielectric properties BZT20 ceramics were examined and discussed. Moreover, the relationship between DPT behavior and the contents of Nb2O5 have been investigated.
http://dx.doi.org/10.1016/j.ceramint.2016.03.212 0272-8842/& 2016 Elsevier Ltd and Techna Group S.r.l. All rights reserved.
Please cite this article as: Z. Sun, et al., Influence of Nb2O5 addition on dielectric properties and diffuse phase transition behavior of BaZr0.2Ti0.8O3 ceramics, Ceramics International (2016), http://dx.doi.org/10.1016/j.ceramint.2016.03.212i
Z. Sun et al. / Ceramics International ∎ (∎∎∎∎) ∎∎∎–∎∎∎
2
mixed thoroughly with 0.5 wt% polyvinyl alcohol (PVA) organic binder solution to granulate and compacted into disk samples with a diameter of 10 mm and a thickness of 1.0 mm. After burning out PVA at 600 °C in the electric furnace, pellets of Nb2O5-doped BZT20 were sintered at 1270 °C for 4 h. Then the silver pastes were fired at 800 °C for both sides of these samples as electrodes for electrical measurements. The crystalline structures of the sintered samples were identified by Powder X-ray diffraction (XRD), using a diffractometer (D8Focus; Bruker AXS GmbH, Karlsruhe, German) with Cu Kα radiation over a 2θ angle from 20° to 80°. The morphologies of the sintered samples were performed and analyzed with field emission scanning electron microscopy (FE-SEM, S-4800; Hitachi, Ltd., Tokyo, Japan). The temperature dependence of dielectric permittivity was measured with a capacitance meter (HP4278A; HewlettPackard, SantaClara, California, USA.) in conjunction with a temperature chamber (GZ-ESPEC) over a temperature range of 50 to 145 °C at 1 kHz.
Fig. 1. XRD patterns of Nb2O5 doped BZT20 ceramics sintered at 1270 °C.
2. Experimental procedures BZT20 þxmol% Nb2O5 ceramics with x¼ 0.1, 0.15, 0.2, and 0.4 were fabricated by solid-state reaction using a high-energy planetary ball mill. The raw materials of AR grade BaCO3 (99%), TiO2 (99%) and ZrO2 (99%) powders were weighted at appropriate proportion. Powdered oxides in stoichiometry were homogeneously ball milled in deionized water for 6 h using ZrO2 balls as milling media. The homogeneous mixtures were dried and calcined at 1100 °C for 4 h, and then the pre-synthesized BZT20 powders and Nb2O5 (99%) powder were mixed according to the formula and re-milled for 12 h. The powers were subsequently
3. Results and discussion Fig. 1 plots the XRD patterns of BZT20 þ xmol% Nb2O5 ceramics with x ¼0.1, 0.15, 0.2, and 0.4. From the XRD patterns, it can be seen that all samples exhibited pure perovskite phase with no impurity phase, which suggested that the Nb ion can be dissolved in BZT20 to form a homogenous solid solution. Fig. 2 illustrates the SEM micrographs of BZT20 ceramics with different Nb2O5 contents. The grain sizes of specimens doped with 0.1–0.2 mol% Nb2O5 are continually increased with the increasing amount of Nb2O5 addition. However, the SEM micrograph in Fig. 2 (d) shows that further increasing the amount of Nb2O5 to 0.4 mol% gives rise to the decrease of grain size. In Ba(ZrxTi1 x)O3 solid solution, Ba2 þ occupies site A of perovskite structure, while
Fig. 2. SEM patterns of the Nb2O5 doped BZT20 ceramics. (a) x ¼0.1 mol% (b) x¼ 0.15 mol% (c) x ¼0.2 mol% and (d) x¼ 0.40 mol%.
Please cite this article as: Z. Sun, et al., Influence of Nb2O5 addition on dielectric properties and diffuse phase transition behavior of BaZr0.2Ti0.8O3 ceramics, Ceramics International (2016), http://dx.doi.org/10.1016/j.ceramint.2016.03.212i
Z. Sun et al. / Ceramics International ∎ (∎∎∎∎) ∎∎∎–∎∎∎
3
ceramics may also be attributed to the lager grain size which can be confirmed by the SEM in Fig. 2(c). The generation of vacancies and inner stress due to the distortion of lattice in Nb doped BZT20 structure is another factor that can improve the dielectric property [22]. The vacancies in Nb doped BZT20 ceramics can be described through the behavior of ion doped ceramics using Eq. (1)–(3). It is known that the Nb5 þ doped BaTiO3 creates a donor like behavior because the valance size of the Nb ion is larger than the valance size of the Ba and Ti ions. For small Nb5 þ content, compensation of electron can be described by Eq. (1) [23]:
Nb2 O5 → 2Nb 5 +4 + + 4O0 + Ti
1 O 2 + 2e ′ 2
(1)
5þ
Fig. 3. Temperature dependence of the dielectric constant and tangent loss of Nb2O5 doped BZT20 ceramics measured at the frequency of 1 kHz.
″ With the increase of Nb content, A or B site vacancies ( VBa ′ ′′ ) will be produced. These vacancies are created due to the and VTi lattice disordered, and produce inner stress as shown in Eqs. (2) and (3) [24]:
″ Nb2 O5 → 2Nb 5 +2 + + 5O0 + VBa
(2)
2Nb2 O5 → 4Nb 5 +4 + + 10O0 + V Ti′′′
(3)
Ba
Zr4 þ and Ti4 þ occupy site B. Zr4 þ (0.72 Å) is larger and more stable than Ti4 þ (0.605 Å). Generally, it is easier for Nb5 þ (0.69 Å) to enter into the B site of Ba(ZrxTi1 x)O3 structure than A site for electric balance [1]. When Nb5 þ enters into B site of BZT20 ceramics, it tends to substitute the Ti4 þ , which generates oxygen vacancies in BZT20, and these defects accelerate the mass transport process, further improving the grain growth [18]. The decrease of grain size with higher Nb doping may be due to the small particle size of the Nb ion accumulating near the grain boundary which leads to suppress grain growth during the sintering process [19]. Fig. 3 shows the temperature dependence of dielectric constant and tangent loss of BZT20 ceramics doped with Nb2O5 as 0.1 mol%, 0.15 mol%, 0.2 mol% and 0.4 mol% at the frequency of 1 kHz. With the increase of Nb contents, the peak temperature Tm at the maximum dielectric constant is shifted to lower temperature. The variation of Tm with Nb content measured at 1 kHz is recorded in Table 1, indicating a negative correlation between Tm and Nb content in Nb2O5 doped BZT20 ceramics. As mentioned above, Nb5 þ tended to substitute Ti4 þ in BZT20 ceramics. The part substitution will lead to the distortion of lattice and expand the unit cell volume. The enlarged distortion energy of Nb doped BZT20 structure facilitates the vibration of Ti4 þ at relatively low temperature which stabilizes the Ti4 þ in the center of the oxygen octahedral [20]. Thus, the value of Tm decreases with the increase of Nb content. Furthermore, it can be seen from Fig. 3 that the dielectric constants increased with the increase of Nb and reached a maximum value at 0.2 mol% Nb2O5. The values of dielectric constant maximum ɛm corresponding to different Nb content measured at 1 kHz are listed in Table 1. As is well known, the grain size will influence the dielectric constant. Moulson and Herbert et al. have reported that the increasing grain size resulted in the distinct enhancement of the dielectric constant in BaTiO3 materials [21]. The higher dielectric value of 0.2 mol% Nb2O5 doped BZT20 Table 1 Values of Curie point temperature (T0), Tm, Tcw, ΔTm, εm and γ for Nb2O5 doped BZT20 ceramics. Samples 0.1 mol%Nb2O5 0.15 mol% Nb2O5 0.2 mol% Nb2O5 0.4 mol% Nb2O5 Tm(°C) Tcw(°C) T0(°C) ΔTm εm γ
18 80 45 62 10,187 1.86
16 78 9 62 20,176 1.57
1.65 67 5 65.35 37,823 1.49
15 55 17 70 33,373 1.58
Ti
From the description above, it can be suggested that the vacancies and inner stress produced in Nb doped BZT20 ceramics have effects on the dielectric properties and give rise to the increase of dielectric constant. For tan δ results with temperatures as shown in Fig. 3, it can be seen that tan δ values tended to increase with the increasing Nb2O5 content, which can be clearly seen for the sample of x ¼0.2 mol%. This may be due to the formation of numerous Ti vacancies by substituted Ti4 þ with high valence Nb5 þ . From Fig. 3, it could be also observed that the Nb2O5 doped BZT20 ceramics gradually show a broad dielectric permittivity– temperature curve in the vicinity of transition temperature, which is referred as diffuse phase transition (DPT). A diffuse phase transition is generally characterized by: (a) broadening in dielectric constant versus temperature curve; (b) a relatively large separation (in temperature) between the maximum of dielectric constant and dielectric loss of the dielectric spectrum; (c) a deviation from Curie–Weiss law in the vicinity of Tm; (d) frequency dispersion of both ε and tan δ (dielectric loss) in transition region thereby implying a frequency dependency of Tm [25]. The dielectric peak at Tm becomes broader with the increase of Nb content as is clearly seen for sample of x¼0.2 and 0.4 mol%. The diffusivity of phase transition can be described through the dielectric behavior of ceramics. It is known that the dielectric permittivity of a normal ferroelectric above the Curie temperature follows the Curie–Weiss law described by
ϵ = C /( T − T0 )
( When
T > Tc )
(4)
where T0 is the Curie–Weiss temperature and C is the Curie–Weiss constant. When the ferroelectric–paraelectric phase transition diffuses, the permittivity would deviate from the Curie–Weiss law. Fig. 4(a–d) shows the plot of inverse dielectric permittivity versus temperature at 1 kHz for the Nb2O5 doped BZT20 ceramics. It is shown that the dielectric curves of all the samples deviate from the Curie–Weiss law at a temperature above the Curie temperature. The parameter ΔTm, which reflects the degree of the deviation from the Curie–Weiss law, is defined as
ΔTm = Tcw − Tm
(5)
where Tcw denotes the temperature from which the permittivity
Please cite this article as: Z. Sun, et al., Influence of Nb2O5 addition on dielectric properties and diffuse phase transition behavior of BaZr0.2Ti0.8O3 ceramics, Ceramics International (2016), http://dx.doi.org/10.1016/j.ceramint.2016.03.212i
Z. Sun et al. / Ceramics International ∎ (∎∎∎∎) ∎∎∎–∎∎∎
4
Fig. 4. Temperature dependence of the inverse dielectric constant at 1 kHz for Nb2O5 doped BZT20 ceramics: (a) x ¼0.1 mol% (b) x ¼0.15 mol% (c) x ¼ 0.2 mol% (d) x¼ 0.40 mol% and the plots of ln (1/ε 1/εm) as a function of ln (T–Tm) for Nb2O5 doped BZT20 ceramics (e).
starts to deviate from the Curie–Weiss law and Tm represents the corresponding temperature of dielectric constant maximum. The Curie temperature is determined from the graph by extrapolation of the reciprocal of dielectric constant. The parameters obtained from the fitting plots at 1 kHz are listed in the Table 1. As can be seen from the table, the values of ΔTm increased with the increase of Nb2O5 content, indicating gradual deviation from the normal Curie–Weiss law and Nb2O5 induced diffuse phase transition in Nb2O5 doped BZT20 samples. A modified Curie–Weiss law was proposed by Uchino et al. to describe the diffusivity of the phase transition [26]: γ
1/ϵ − 1/ϵ m = ( T − Tm ) /C1
(6)
where γ and C1 are assumed to be constant. The parameter γ determines the degree of diffuse phase transition: for γ ¼1, a normal
Curie–Weiss law is obtained, for γ ¼2, it reduces to the quadratic dependency which describes a complete diffuse phase transition [27]. Fig. 4(e) shows the plots of ln (1/ε 1/εm) as a function of ln (T–Tm) at 1 kHz for the four different Nb2O5 compositions. Liner relationships are observed for all the samples. The slopes of the fitting curve are used to determine the parameter γ values. In the studied compositions the values of γ are found to be 1.86, 1.57, 1.49 and 1.58 at 1 kHz for x ¼0.1 mol%, 0.15 mol%, 0.2 mol% and 0.4 mol%, respectively. The value of γ decrease to a minimum at x¼ 0.2 mol% and then increase again at x¼ 0.4 mol% (Table 1), which indicate the Nb2O5 addition have significant influence on the diffusivity of BZT20 ceramics. The broadened dielectric maximum (Fig. 3) and its deviation from Curie–Weiss law are the main characteristics of DPT behavior in Nb2O5 doped BZT20 ceramics. The observed DPT behavior may be due to the increasing
Please cite this article as: Z. Sun, et al., Influence of Nb2O5 addition on dielectric properties and diffuse phase transition behavior of BaZr0.2Ti0.8O3 ceramics, Ceramics International (2016), http://dx.doi.org/10.1016/j.ceramint.2016.03.212i
Z. Sun et al. / Ceramics International ∎ (∎∎∎∎) ∎∎∎–∎∎∎
lattices disorder and unbalancing of cations induced by the substitution of Ti4 þ by Nb5 þ in the sublattice, which produces heterogeneities in the structure and is significant for the DPT behavior [28]. Ti4 þ at B site results in local polar regions while Nb5 þ at B site leads to local non-polar regions, which is responsible for the change of diffusivity in Nb2O5 doped BZT20 samples. Except for the lattices disorder and unbalancing of cations, the effect of grain boundary is another factor that can influence the DPT behavior. This point has been discussed in detail by Zhao [29]. The grain boundary is nonferroelectric phase and has no ferroelectric–paraelectric phase transition. The volume fraction of grain boundary increases with the decrease of grain size. Therefore, the proportion of tetragonal phase and ferroelectricity is lower in smaller-grained ceramics. The result is that phase transition became more diffused.
4. Conclusions Nb2O5 doped Ba(Zr0.2Ti0.8)O3 ceramics with doping addition at 0.1, 0.15, 0.2 and 0.4 mol% had been prepared through solid state reaction route and sintered at 1270 °C. The room temperature XRD study suggested that all the samples had pure perovskite structure. The effect of grain size on the dielectric and diffuse phase transition behavior of Nb2O5 doped BZT20 ceramics was studied. The results revealed that lager grain size improved the dielectric properties. Phase transition became more diffused due to the smaller-grained BZT20 ceramics. Except for the grain size effect, the generation of vacancies and inner stress due to the Nb ions substituted Ti ions in B-site of the Ba(Zr0.2Ti0.8)O3 ceramics leaded to a significant increase in dielectric constant. Moreover, the Curie temperature of Ba(Zr0.2Ti0.8)O3 ceramics decreased with the increase of Nb2O5 addition.
References [1] W.Q. Cao, J.W. Xiong, J.P. Sun, Dielectric behavior of Nb-doped Ba(ZrxTi1 x)O3, Mater. Chem. Phys. 106 (2007) 338–342. [2] X.G. Tang, K.H. Chew, H.L.W. Chan, Diffuse phase transition and dielectric tunability of Ba(ZryTi1 y)O3 relaxor ferroelectric ceramics, Acta. Mater. 52 (2004) 5177–5183. [3] L.E. Cross, Ferroelectrics 151 (1994) 305–320. [4] V.S. Puli, R. Martínez, A. Kumar, J.F. Scott, S. Katiyar, A quaternary lead based perovskite structured materials with diffuse phase transition behavior, Mater. Res. Bull. 46 (2011) 2527–2530. [5] J. Wang, X.G. Tang, H.L.W. Chan, C.L. Choy, Dielectric relaxation and electrical properties of 0.94Pb(Fe1/2Nb1/2)O3 0.06PbTiO3 single crystals, Appl. Phys. Lett. 86 (2005) 152907. [6] Y. Tanaka, T. Harigai, M. Ueda, H. Adachi, E. Fujii, Structural modification and large piezoelectricity of strained (Na, Bi) TiO3–BaTiO3 epitaxial thin films, J.
5
Am. Ceram. Soc. 95 (2012) 3547–3553. [7] Z. Yu, R. Guo, A.S. Bhalla, Orientation dependence of the ferroelectric and piezoelectric behavior of Ba(Ti1 xZrx)O3 single crystals, Appl. Phys. Lett. 77 (2000) 1535–1537. [8] Z. Yu, C. Ang, R. Guo, A.S. Bhalla, Piezoelectric and strain properties of Ba (Ti1 xZrx)O3 ceramics, J. Appl. Phys. 92 (2002) 1489–1493. [9] D. Hennings, A. Schnell, G. Simon, Diffuse ferroelectric phase transitions in Ba(Ti1 yZry)O3 ceramics, J. Am. Ceram. Soc. 65 (1982) 539–544. [10] N. Kumar, A. Ionin, T. Ansell, S. Kwon, W. Hackenberger, D. Cann, Multilayer ceramic capacitors based on relaxor BaTiO3-Bi(Zn1/2Ti1/2)O3 for temperature stable and high energy density capacitor applications, Appl. Phys. Lett. 106 (2015) 252901. [11] S. Hoffmann, R. Waser, Control of the morphology of CSD-prepared (Ba,Sr)TiO3 thin films, J. Eur. Ceram. Soc. 19 (1999) 1339–1343. [12] T. Tsurumi, Y. Yamamoto, H. Kakemoto, S. Wada, H. Chazono, H. Kishi, Dielectric properties of BaTiO3-BaZrO3 ceramics under a high electric field, J. Mater. Res. 17 (2002) 755–759. [13] U. Weber, G. Greuel, U. Boettger, S. Weber, D. Hennings, R. Waser, Dielectric properties of Ba(Zr,Ti)O3-based ferroelectrics for capacitor applications, J. Am. Ceram. Soc. 84 (2001) 759–766. [14] S.Y. Chu, T.Y. Chen, I.T. Tsai, W. Water, Doping effects of Nb additives on the piezoelectric and dielectric properties of PZT ceramics and its application on SAW device, Sens. Actuators A 113 (2004) 198–203. [15] M. Pereira, A.G. Peixoto, M.J.M. Gomes, Effect of Nb doping on the microstructural and electrical properties of the PZT ceramics, J. Eur. Ceram. Soc. 21 (2001) 1353–1356. [16] C. Tănăsoiu, E. Dimitriu, C. Miclea, Effect of Nb, Li doping on structure and piezoelectric properties of PZT type ceramics, J. Eur. Ceram. Soc. 19 (1999) 1187–1190. [17] K. Kumar, B. Kumar, Effect of Nb-doping on dielectric, ferroelectric and conduction behaviour of lead free Bi0.5(Na0.5K0.5)0.5TiO3 ceramic, Ceram. Int. 38 (2012) 1157–1165. [18] C. Chen, H. Zhuang, X. Zhu, K. Zhou, D. Zhang, Enhancement of relaxor properties by Nb doping in Ba0.8Sr0.12Ca0.08TiO3 lead-free ferroelectric ceramics, Ceram. Int. 41 (2015) 9893–9898. [19] P. Parjansri, U. Intatha, S. Eitssayeam, Dielectric, ferroelectric and piezoelectric properties of Nb5 þ doped BCZT ceramics, Mater. Res. Bull. 65 (2015) 61–67. [20] C. Chen, H. Zhuang, X. Zhu, K. Zhou, D. Zhang, Enhancement of relaxor properties by Nb doping in Ba0.8Sr0.12Ca0.08TiO3 lead-free ferroelectric ceramics, Ceram. Int. 41 (2015) 9893–9898. [21] A.J. Moulson, J.M. Herbert, Electroceramics: Materials, Properties, Application, Chapman and Hall, London, 1990. [22] P. Parjansri, U. Intatha, S. Eitssayeam, Dielectric, ferroelectric and piezoelectric properties of Nb5 þ doped BCZT ceramics, Mater. Res. Bull. 65 (2015) 61–67. [23] H. Chan, M.P. Harmer, D. Smyth, Compensating defects in highly donor-doped BaTiO3, J. Am. Ceram. Soc. 69 (1986) 507–510. [24] W. Li, J. Qi, Y. Wang, L. Li, Z. Gui, Doping behaviors of Nb2O5 and Co2O3 in temperature stable BaTiO3-based ceramics, Mater. Lett. 57 (2002) 1–5. [25] S.K. Rout, E. Sinha, S. Panigrahi, Dielectric properties and diffuse phase transition in Ba1 xMgxTi0.6Zr0.4O3 solid solutions, Mater. Chem. Phys. 101 (2007) 428–432. [26] K. Uchino, S. Nomura, Critical exponents of the dielectric constants in diffused-phase-transition crystals, Ferroelectrics. 44 (1982) 55–61. [27] C. Ciomaga, M. Viviani, M.T. Buscaglia, V. Buscaglia, L. Mitoseriu, A. Stancu, P. Nanni, Preparation and characterisation of the Ba(Zr,Ti)O3 ceramics with relaxor properties, J. Eur. Ceram. Soc. 27 (2007) 4061–4064. [28] X. Qin, D. Shihua, S. Tianxiu, W. Hongni, Diffuse phase transition of Ba0.92Ca0.08(Ti0.82Zr0.18)O3 based ceramics, Ferroelectrics 426 (2012) 282–289. [29] Z. Zhao, V. Buscaglia, M. Viviani, M.T. Buscaglia, L. Mitoseriu, A. Testino, M. Nygren, M. Johnsson, P. Nanni, Grain-size effects on the ferroelectric behavior of dense nanocrystalline BaTiO3 ceramics, Phys. Rev. B 70 (2004) 024107.
Please cite this article as: Z. Sun, et al., Influence of Nb2O5 addition on dielectric properties and diffuse phase transition behavior of BaZr0.2Ti0.8O3 ceramics, Ceramics International (2016), http://dx.doi.org/10.1016/j.ceramint.2016.03.212i