Materials Research Bulletin: Yuwen Liu, Yongping Pu, Zixiong Sun, Qian Jin
Materials Research Bulletin: Yuwen Liu, Yongping Pu, Zixiong Sun, Qian Jin
Materials Research Bulletin: Yuwen Liu, Yongping Pu, Zixiong Sun, Qian Jin
A R T I C L E I N F O A B S T R A C T
Article history: Dense ceramics in the solid solution system, Ba0.9Ca0.1Ti0.9Zr0.1O3–0.06Fe3+ (BCTZ–Fe3+) were prepared
Received 28 November 2014 by hydrothermal method assisted by microwave sintering. And the electrical properties were
Received in revised form 4 March 2015 investigated by the dielectric and impedance spectroscopies. The e–T/tan d–T curve revealed relaxor
Accepted 23 March 2015
behaviors below Curie temperature (TC) and a loss peak’s shifting to higher temperature with increasing
Available online 25 March 2015
frequency. Moreover, the BCTZ–Fe3+ ceramic exhibits only one loss peak which can be analyzed in terms
of the Maxwell–Wagner capacitor model at lower temperature, while the second peak related to the
Keywords:
space charge polarization between the ceramic and electrode appeared above 623 K. The impedance
A. Ceramics
B. Chemical synthesis
complex plane plots of BCTZ–Fe3+ ceramic turned into one semicircular arc at 473 K from a single line at
B. Piezoelectricity 373 K and then to two semicircular arcs at 573 K and 643 K, which were analyzed as four different
D. Dielectric properties equivalent circuits.
ã 2015 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.materresbull.2015.03.054
0025-5408/ ã 2015 Elsevier Ltd. All rights reserved.
196 Y. Liu et al. / Materials Research Bulletin 70 (2015) 195–199
that, the powders were pressed into pellets of 12 mm diameter and Curie temperature (TC) of 326 K is detected due to the
the green bodies were sintered at 1573 K for 10 min under ferroelectric–paraelectric phase transition (Tetragonal–Cubic).
microwaves. Phase structure was examined using an X-ray The inset in Fig. 2(a) indicates a standard relaxor ferroelectric
diffraction (D/max 2200 pc, Rigaku, Tokyo, Japan) with CuKa with dispersion phase transition and dispersion frequency with
radiation and the microstructure morphologies were obtained by DTres = 278 K. And the loss peaks corresponding to TC can also be
scanning electron microscopy (JEOL JSM-6390A JEOL Ltd., Tokyo). observed in the inset of Fig. 2(b), which resulted from the ionic
Dielectric properties and impedance complex plots were measured polarization during the phase transition. To characterize the
by Agilent 4980 A impedance analyzer. relaxor behavior of BCTZ–Fe3+ ceramic, the relationship between
inverse dielectric permittivity and temperature at 10 kHz is plotted
3. Results and discussion in Fig. 3, showing the T0 = 349 K and Tcm = 394 K. And the inset is the
plot of log(1/e–1/em) as a function of log(T–Tm) by fitting the Uchino
Fig. 1 shows the data of XRD pattern, SEM image, as well as equation:
ferroelectric P–E loop of the BCTZ–Fe3+ ceramic collected at an
ambient temperature of 297 K. The phase analysis identified a 1 1 ðT T m Þg
¼ 1<g<2 (1)
monophase of tetragonal structure type with the lattice param- e em C
eters a and c = 3.998 and 4.005 Å, respectively. The Fe3+ (0.785 Å) where em refers to the maximum value of dielectric permittivity,
probably occupied B-site of BCTZ ceramic for the closer ionic e to the dielectric permittivity at temperature T, Tm to the
radius to Ti4+ (0.605 Å) and Zr4+ (0.72 Å) than Ba2+ (1.61 Å) and Ca2+ temperature at the peak of the dielectric permittivity, C to the Curie
(1.34 Å). The no-splitting of (2 0 0)/(0 0 2) peak indicates the constant, and g to the diffuseness degree indicator, taking
coexistence of tetragonal and cubic phase. SEM image shows the value between 1 (for a normal ferroelectric) and 2 (for a
well-sintered ceramics with grain sizes of 500 nm, which is a complete diffuse phase transition) is calculated to be 1.69.
much smaller grain size compared with other researches [3,7,9,11] The loss peak’s shifting toward higher temperature with the
due to the synthesizing method of hydrothermal and fast increase in frequency emerged in Fig. 2(b) at high temperature as
microwave sintering. The ferroelectric test exhibits well-saturated well as the strong increasing of permittivity in Fig. 2(a) is
P–E loop with a Pr = 10.05 mC/cm2 EC = 4.88 kV/cm and weak switch apparently a correlation of relaxation. What is more interesting, a
current density (<0.8 mA/cm2) at a frequency of 2 Hz. The second loss peak is observed only in 1 kHz at 750 K. These
piezoelectric d33 value measured with the quasi-static method phenomenons can more conveniently be studied from the
equals 350 pC/N with the electromechanical coupling factor frequency response of permittivity formalism measured at
kp = 0.38. different temperatures in Fig. 4, where the ferro-para transition
Fig. 2 shows the dielectric permittivity and dielectric loss (tan d) is excluded. The inset of Fig. 4(b) shows the Maxwell–Wagner and
of the BCTZ–Fe3+ ceramic as a function of temperature measured at Debye relaxation model. The permittivity exhibits an obvious drop
frequencies of 1, 10, 100 and 1000 kHz, respectively. A peak with at low frequencies and seems temperature-independent at
Fig. 1. XRD pattern (a), SEM image (b), ferroelectric P–E loop (c) of the Ba0.9Ca0.1Ti0.9Zr0.1O3–0.06Fe3+ ceramic at room temperature.
Y. Liu et al. / Materials Research Bulletin 70 (2015) 195–199 197
f > 105 Hz. Seen from Fig. 4(b), a common loss peak at higher
frequencies is observed at all the temperatures corresponding to
the step decrease in permittivity in Fig. 4(a), and the second peak in
lower frequencies emerged at higher temperatures [8–13]. To
investigated the relaxation mechanisms of first peak, the thermally
activated parameters during relaxation process were calculated
using Arrhenius law:
E
t ¼ t 0 exp (2)
KBT
where t 0 is the pre exponential factor (or the relaxation time at
infinite temperature), E denotes the activation energy of the
relaxation process, T is the absolute temperature, and KB is the
Fig. 4. Frequency dependence of the dielectric permittivity and dielectric loss tan d
Fig. 3. Relaxor parameters of Ba0.9Ca0.1Ti0.9Zr0.1O3–0.06Fe3+ ceramic. for the Ba0.9Ca0.1Ti0.9Zr0.1O3–0.06Fe3+ ceramic measured at various temperatures.
198 Y. Liu et al. / Materials Research Bulletin 70 (2015) 195–199
Fig. 6. Complex impedance plots for the Ba0.9Ca0.1Ti0.9Zr0.1O3–0.06Fe3+ ceramic measured at different temperatures.
Y. Liu et al. / Materials Research Bulletin 70 (2015) 195–199 199
of electrode increases strongly with temperature. Thus, the two Talents Program of Chinese Education Ministry (NCET-11-1042),
parallel RC elements connected in serial at 400 C in Fig. 6(d) can be the Key Program of Innovative Research Team of Shaanxi
calculated as follows [14,15]: Province (2014KCT-06) and the International Science and
Technology Cooperation Project Funding of Shaanxi Province
1 1
Z ¼ þ ¼ Z 0 iZ 00 (7) (2012KW-06).
R1
g þ ivC g R1
e þ ivC e
References
Rg Re [1] Q. Lin, M. Jiang, D.M. Lin, Q.J. Zheng, X.C. Wu, X.M. Fan, Effects of
Z0 ¼ 2 þ (8) La-doping on microstructure, dielectric and piezoelectric properties of
1 þ vRg C g 1 þ ðvRe C e Þ2
Ba0.85Ca0.15Ti0.90Zr0.10O3 lead-free ceramics, J. Mater. Sci. 24 (2013)
734–739.
[2] Y. Liu, W.C. Wang, J.Q. Huang, F. Tang, C. Zhu, Y.G. Cao, Dielectric properties
" # " # of giant permittivity NaCu3Ti3NbO12 ceramics, Cream. Int. 39 (2013)
Rg Re
Z 00 ¼ Rg 2 þ Re (9) 9201–9206.
1 þ vRg C g 1 þ ðvRe C e Þ2 [3] T. Takenaka, H. Nagata, Current status and prospects of lead-free piezoelectric
ceramics, J. Eur. Ceram. Soc. 25 (2005) 2693–2700.
where (Rg, Re) and (Cg, Ce) are the resistance and capacitance of [4] S. Su, R.Z. Zuo, S.B. Lu, Z.K. Xu, X.H. Wang, L.T. Li, Poling dependence and
stability of piezoelectric properties of Ba(Zr0.2Ti0.8)O3–(Ba0.7Ca0.3)TiO3
grain and electrode, respectively. Based on Eqs. (8) and (9) the ceramics with huge piezoelectric coefficients, Curr. Appl. Phys. 11 (2011)
responses from the grains and grain boundaries are located at S120–S123.
1/(2pRgCg) and 1/(2pReCe), respectively. The semicircular arc [5] R.Z. Zuo, X.S. Fang, C. Ye, Phase structures and electrical properties of new lead
free (Na0.5K0.5)NbO3–(Bi0.5Na0.5)TiO3 ceramics, Appl. Phys. Lett. 90 (2007)
decreases with increasing temperature for the contact area 092904.
between grain and electrode makes more contributions to [6] W.F. Liu, X.B. Ren, Large piezoelectric effect in Pb-free ceramics, Phys. Rev. Lett.
increasing the permittivity and decreasing the resistance at higher 103 (2009) 257602 4pp.
[7] X.G. Tang, H.L.W. Chan, Effect of grain size on the electrical properties of
measuring temperature.
(Ba, Ca)(Zr,Ti)O3 relaxor ferroelectric ceramics, J. Appl. Phys. 97 (2005)
034109.
4. Conclusions [8] Z.X. Sun, Y.P. Pu, Z.J. Dong, Y. Hu, X.Y. Liu, P.K. Wang, M. Ge, Dielectric and
piezoelectric properties and PTC behavior of Ba0.9Ca0.1Ti0.9Zr0.1O3xLa
ceramics prepared by hydrothermal method, Mater. Lett. 118 (2014) 1–4.
Lead-free Ba0.9Ca0.1Ti0.9Zr0.1O3–0.06Fe3+ ceramic with average [9] J. Wu, D. Xiao, W. Wu, Q. Chen, J. Zhu, Z. Yang, J. Wang, Role of room-
grain size 500 nm have been prepared by hydrothermal method temperature phase transition in the electrical properties of (Ba, Ca)(Ti, Zr)O3
and was well-sintered by microwave sintering. The sample showed ceramics, Scripta. Mater. 65 (2011) 771–774.
[10] Y.C. Lee, Y.Y. Yeh, P.R. Tsai, Effect of microwave sintering on the microstructure
a relaxor ferroelectric with the coexistence of tetragonal and cubic and electric properties of (Zn, Mg)TiO3-based multilayer ceramic capacitors, J.
phase at room temperature. The first loss peaks in tan d–f curve at Eur. Ceram. Soc. 32 (2012) 1725–1732.
higher frequencies resulted from VO can be analyzed in terms of [11] C.Y. Tsay, K.S. Liu, I.N. Lin, Microwave sintering of (Bi0.75Ca1.2Y1.05)(V0.6Fe4.4)O12
microwave magnetic materials, J. Eur. Ceram. Soc. 24 (2004) 1057–1061.
the Maxwell–Wagner capacitor model. While the second peak at [12] T. Chen, T. Zhang, G. Wang, J. Zhou, J. Zhang, Y. Liu, Effect of CuO on the
lower frequencies was due to the space charge polarization microstructure and electrical properties of Ba0.85Ca0.15Ti0.90Zr0.10O3
between the material and electrode, which is appeared at higher piezoceramics, J. Mater. Sci. 47 (2008) 4612–4619.
[13] P. Wang, Y.X. Li, Y.Q. Lu, Enhanced piezoelectric properties of (Ba0.85Ca0.15)
temperatures. Four different equivalent circuits were established (Ti0.9Zr0.1)O3 lead-free ceramics by optimizing calcination and sintering
to analyze the complex impedance spectra of BCTZ–Fe3+ measured temperature, J. Eur. Ceram. Soc. 31 (2011) 2005–2012.
at 373–673 K and the resistance of grain decreases with increasing [14] J. Tao, Z.G. Yi, Y. Liu, M.X. Zhang, J.W. Zhai, Dielectric tunability dielectric
relaxation, and impedance spectroscopic studies on (Ba0.85Ca0.15)(Ti0.9Zr0.1)O3
temperature.
lead-free ceramics, J. Am. Ceram. Soc. 96 (2013) 1847–1851.
[15] N. Xu, Y.P. Pu, Z. Wang, Large dielectric constant and maxwell-wagner effects in
Acknowledgments BaTiO3/Cu composites, J. Am. Ceram. Soc. 95 (2012) 999–1003.
[16] Z. Wang, X.M. Chen, L. Ni, Y.Y. Liu, X.Q. Liu, Dielectric relaxations in
B(Fe1/2Ta1/2)O3 giant dielectric constant ceramics, Appl. Phys. Lett. 90
This research was supported by the National Natural Science (2007) 102905.
Foundation of China (51372144), the New Century Excellent