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Characteristics and dielectric properties of (Pb0.97−xLa0.02Bax)(Zr0.72Sn0.22Ti0.06)O3 ceramics
Journal of Alloys and Compounds 539 (2012) 280–283
Contents lists available at SciVerse ScienceDirect
Journal of Alloys and Compounds journal homepage: www.elsevier.com/locate/jalcom
Characteristics and dielectric properties of (Pb0.97 xLa0.02Bax)(Zr0.72Sn0.22Ti0.06)O3 ceramics Wang Jinfei, Yang Tongqing ⇑, Chen Shengchen, Li Gang, Yao Xi Functional Materials Research Laboratory, Tongji University, Shanghai 200092, China
a r t i c l e
i n f o
Article history: Received 12 January 2012 Received in revised form 31 May 2012 Accepted 5 June 2012 Available online 13 June 2012 Keywords: Antiferroelectric Ba-doped Dielectric properties Change of temperature
a b s t r a c t (Pb0.97 xLa0.02Bax)(Zr0.72Sn0.22Ti0.06)O3 (PLBZST) ceramics with x in the range of 0.09, 0.11, 0.13, 0.15 were fabricated by conventional solid-state reaction process, and their crystal structure, dielectric and electrocaloric effect were systemically investigated. The results showed that the ceramics with different Ba contents had a perovskite structure. Besides, it was found the ceramics transform gradually from antiferroelectric phase to paraelectric phase and the Curie temperature decreased with the increase of Ba content, when x = 0.15, the Curie temperature of the ceramics decreased to 30 °C near room temperature. The dielectric constant increased to about 12000 with increasing Ba contents. The change of temperature increased from 0.10 K to 0.25 K sharply at 2.2 kV/mm. Ó 2012 Elsevier B.V. All rights reserved.
1. Introduction Ferroelectric (FE) perovskites such as BaTiO3(BT), PbTiO3, and solid solutions of PbZrO3–PbTiO3 [Pb(ZrxTi1 x)O3, PZT] have received great interest because of their potential applications in micro- and nano-electronics as elements of nonvolatile random access memories. PbZrO3 was antiferroelectric ceramic reported for the first time. However it has a high phase transition electricfield of antiferroelectric (AFE) to ferroelectric (FE). Then, Ti4+, Sn4+ and La3+ were modified into B site or A site of PbZrO3 for lowering the phase transition electric-field, and lead lanthanum zirconate stannate titanate antiferroelectric system (PLZST) were developed [1–6]. These materials can be applied in high-energy storage capacitors [7], explosive electrical transducers [8], actuators, pyroelectric detectors [9,10], antiferroelectric cold cathode materials [11], ferroelectric refrigeration [12], and so on. However, the pyroelectric response encountered a problem that the Curie temperature is too high (>120 °C) to be used practically and the range of the antiferroelectric is too narrow. In previous works, researchers reported that, for PZST ceramics, A-site modification with Ba2+ could clearly shift the Curie temperature to low temperature [13–20]. Zhang et al. [21] observed a change in isothermal entropy of more than 55 J/(kg K) and a change in adiabatic temperature of over 12 °C. They also showed that the relaxor ferroelectric polymer of P(VDF-TrFE-chlorofluoroethylene) has a large electrocaloric effect. However, the result was obtained and calculated by DSC or hysteresis loop at adiabatic state. ⇑ Corresponding author. E-mail address: [email protected] (Y. Tongqing). 0925-8388/$ - see front matter Ó 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.jallcom.2012.06.028
In this paper, (Pb0.97 xLa0.02Bax)(Zr0.72Sn0.22Ti0.06)O3 ceramics with x being 0.09, 0.11, 0.13, 0.15 were fabricated respectively, and the dielectric properties and electrocaloric effect of the specimens was investigated by directly measured at room temperature. 2. Experimental procedure Ferroelectric ceramics were fabricated using a solid-state route. Metal oxides of Pb3O4, La2O3, ZrO2, TiO2 and SnO2 (purity of 99.0%) were used to synthesize (Pb0.97 xLa0.02Bax)(Zr0.72Sn0.22Ti0.06)O3 + 2 mol% PbO ceramics with x = 0.09, 0.11, 0.13, 0.15, respectively. The high purity raw materials were weighted, mixed and calcined at 900 °C for 2 h. Then, the calcined powder was remixed in alcohol using a zirconia ball mill in polyethylene pot for 24 h. After drying and granulating with PVA, the well mixed powders were pressed into a disk (U10 mm 2 mm) at 40 MPa and then sintered at 1200 °C1260 °C for 2 h in air. The surfaces silver electrode was sintered and fired at 550 °C for 10 min. The lattice structure and average grain size were determined by using an X-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively. The dielectric properties with different temperature and dc bias field were measured at 1 kHz frequency using a LCR analyzer (Agilent 4284). The electrocaloric effect was determined by a directly method. For this method, the sample in series with a high-voltage power supply was connected to a Keithley 2000 to detect the change rate of temperature when sample was applied the signal of variation of field strength.
3. Results and discussion Fig. 1 shows the XRD patterns of PLBZST ceramics with various Ba contents. For each sample with x from the 0.09 to 0.15, a clear single-perovskite phase is observed, all samples showed no second phase appeared from XRD results, which indicates PLBZST ceramics with different Ba content are basically soluted in the lattice of PLBZST. When x = 0.15, (2 0 0)(0 0 2), (3 0 1)(1 0 3) disappear gradually, the double peaks transit into the single peak, which is
W. Jinfei et al. / Journal of Alloys and Compounds 539 (2012) 280–283
Fig. 1. X-ray diffraction patterns of (Pb0.97 xLa0.02Bax)(Zr0.72Sn0.22Ti0.06)O3 ceramics sintered in air at 1240 °C for 2 h.
attributed that the antiferroelectric phase transform to paraelectric phase with increasing Ba content. Fig. 2 shows the SEM micrographs of the as-sintered surface of (Pb0.97 xLa0.02Bax)(Zr0.72Sn0.22Ti0.06)O3ceramics sintered in air in 1240 °C for 2 h. From the figure, it is can be seen that the grains of the samples become more uniform and the grain size of the samples increases up to x = 0.13, the average grain size of the ceramics is about 3–4 lm (Fig. 2(a–c)). The addition of Ba promotes the grain-growth of the PLBZST samples, and the grains were found to be uniformly distributed throughout the surface and tightly bound with homogeneous microstructure supporting the dopants diffusion uniformly. However, when x increases to 0.15, small grain begins to appear at grain boundaries, which may need higher sintering temperature. The dielectric properties at 10 kHz as a function of temperature for the (Pb0.97 xLa0.02Bax)(Zr0.72Sn0.22Ti0.06)O3 ceramics sintered in air at 1240 °C for 2 h are illustrated in Fig. 3. The curve of dielectric constant (e) shows a peak, and the peak is up to >11,000. With the increase of Ba2+ contents, the peak moved from 100 to 30 °C. As well known, the peak position of e-temperature curve was corre-
281
Fig. 3. Temperature dependence of permittivity of (Pb0.97 xLa0.02Bax)(Zr0.72Sn0.22Ti0.06)O3 ceramics sintered in air at 1240 °C for 2 h.
sponding to the Tc. The results indicate that Tc of (Pb0.97 xLa0.02Bax)(Zr0.72Sn0.22Ti0.06)O3 ceramics move from 100 to 30 °C, when x increases from 0.09 to 0.15, which is attributed that the Ba2+ enters into A-site and Tc decreased with Ba incorporation [22]. Fig. 4 shows several typical Polarization–electric field hysteresis loops (P-E hysteresis loops) of (Pb0.97 xLa0.02Bax)(Zr0.72Sn0.22Ti0.06)O3 ceramics with different Ba contents. As shown in Fig. 4 (a–c), classic double-hysteresis loops characteristic of AFE phase are observed. At the same measurement condition, the largest field applied to the sample is 45 kV/cm and the maximum polarization value is 18 lC/cm2. And hysteresis loop demonstrate that the PLBZST antiferroelectric samples are slim P-E loops, which are suitable for application in high-energy-storage capacitors. Besides, it is showed that the AFE phase change to paraelectric phase with increasing Ba contents. Obviously, the antiferroelectric phase transform to paraelectric phase with increasing Ba content gradually. The directly measured DT for (Pb0.97 xLa0.02Bax)(Zr0.72Sn0.22Ti0.06)O3 ceramics versus electric field with different Ba content is
Fig. 2. SEM micrographs of the as-sintered surface of (Pb0.97 xLa0.02Bax)(Zr0.72Sn0.22Ti0.06)O3 ceramics (a) x = 0.09; (b) x = 0.11; (c) x = 0.13; (d) x = 0.15.
282
W. Jinfei et al. / Journal of Alloys and Compounds 539 (2012) 280–283
Fig. 4. P-E hysteresis loop of (Pb0.97 xLa0.02Bax)(Zr0.72Sn0.22Ti0.06)O3 ceramics with different x contents: (a) x = 0.09; (b) x = 0.11; (c) x = 0.13; (d) x = 0.15.
shown in Fig. 5. In the direct measurement of DT. Due to the ceramic breakdown, the chosen maximum field in the measurement is 2.2 kV/mm. The applied field is 2.2 kV/cm, the DT increased from 0.1 K to 0.25 K when x change from 0.11 to 0.15. The measurement temperature is near Tc, when x=0.15, because the change of temperature was maximum near Tc [21]. According to the directly measured data in Fig. 5, it is noted that DT increases with the increasing of the applied electric field. The DT dependence of electric field of (Pb0.97-0.15La0.02Ba0.15)(Zr0.72 Sn0.22Ti0.06)O3 ceramics is shown in Fig. 6. If we extend the applied field to about 300 kV/mm, which is similar to field strength applied in thin film [21], the DT will also be more than 10 K, which is adapted to practical application. 4. Conclusion
Fig. 5. Temperature dependences of the directly measured DT with different Ba content.
In summary, (Pb0.97 xLa0.02Bax)(Zr0.72Sn0.22Ti0.06)O3 ceramics with perovskite structure were prepared. It is concluded that with increasing Ba contents, the Curie temperature of the ceramics decrease and the antiferroelectric phase transform to paraelectric phase. The dielectric constant (e) is up to >11000. The ceramics exhibit a DT 0.25 K at room temperature by directly measured and DT will be improved with increasing the electric field. Acknowledgements This work was supported by the Nature Science Associate Foundation (NSAF) of China (Grant No. 10874130). The Key Project of Chinese Ministry of Education(No. 108055), Shanghai Pujiang Program and the State Key Laboratory of Electronic Thin Films and Integrated Devices (UESTC). References
Fig. 6. DT dependence of electric field(E) of (Pb0.97 xLa0.02Bax)(Zr0.72Sn0.22Ti0.06)O3 ceramics.
[1] D. Berlincourt, IEEE Trans. Sonics Ultrason. 13 (1966) 116. [2] W.Y. Pan, C.Q. Dam, Q.M. Zhang, L.E. Cross, J. Appl. Phys. 66 (1989) 6014. [3] K. Ramam, A.J. Bell, C.R. Bowen, K. Chandramouli, J. Alloys Compd. 473 (2009) 330. [4] K. Ramam, M. Lopez, J. Alloys Compd. 466 (2008) 398. [5] W. Chan, Z. Xu, Y. Zhang, T. Hung, H. Chen, J. Appl. Phys. 94 (2003) 4563. [6] X. Chen, H. Li, D. Li, F. Cao, X. Dong, Chin. Phys. Soc. 57 (2008) 7298. [7] A.Q. Jiang, T.A. Tang, S. Corkovic, Q. Zhang, Appl. Phys. Lett. 93 (21) (2008) 212908.
W. Jinfei et al. / Journal of Alloys and Compounds 539 (2012) 280–283 [8] O. Essig, P. Wang, M. Hartweg, P. Janker, H. Nafe, F. Aldinger, J. Eur. Ceram. Soc. 19 (1999) 1223–1228. [9] T.Q. Yang, P. Liu, Z. Xu, L. Zhang, X. Yao, Ferroelectrics 230 (1999) 181–186. [10] Z. Sheng, Y. Feng, Z. Xu, X. Sun, X. Huang, J. Xi’an Jiaotong Univ. 42 (8) (2008) 977. [11] P.D. Thacher, J. Appl. Phys. 39 (1968) 1996. [12] B.P. Pokharel, D. Pandey, J. Appl. Phys. 88 (2000) 5364. [13] S.E. Park, K. Markowski, S. Yoshikawa, L. Eric Cross, J. Am. Ceram. Soc. 80 (1997) 407. [14] X. Dai, A. DiGiovanni, D. Viehland, J. Appl. Phys. 74 (1993) 3399.
[15] [16] [17] [18] [19] [20] [21] [22]
283
N.W. Thomas, J. Phys. Chem. Solids 51 (1990) 1419. R. Rai, S. Mishra, N.K. Singh, J. Alloys Compd. 487 (2009) 494. C.C. Tsai, C.S. Hong, C.C. Shih, S.Y. Chu, J. Alloys Compd. 511 (2012) 54. J.H. Zhang, S.J. Mo, H.Y. Wang, S.X. Zhen, H.W. Chen, C.R. Yang, J. Alloys Compd. 509 (2011) 2838. L.B. Kong, J. Ma, R.F. Zhang, T.S. Zhang, J. Alloys Compd. 339 (2002) 167. S. Dutta, R.N.P. Choudhary, P.K. Sinha, J. Alloys Compd. 426 (2006) 345. B. Neese, B. Chu, S.G. Lu, Y. Wang, E. Furman, Q.M. Zhang, Science 321 (2008) 821. Y. Luo, X. Liu, X. Li, G. Liu, Solid State Ionics 177 (2006) 1543.
Contents lists available at SciVerse ScienceDirect
Journal of Alloys and Compounds journal homepage: www.elsevier.com/locate/jalcom
Characteristics and dielectric properties of (Pb0.97 xLa0.02Bax)(Zr0.72Sn0.22Ti0.06)O3 ceramics Wang Jinfei, Yang Tongqing ⇑, Chen Shengchen, Li Gang, Yao Xi Functional Materials Research Laboratory, Tongji University, Shanghai 200092, China
a r t i c l e
i n f o
Article history: Received 12 January 2012 Received in revised form 31 May 2012 Accepted 5 June 2012 Available online 13 June 2012 Keywords: Antiferroelectric Ba-doped Dielectric properties Change of temperature
a b s t r a c t (Pb0.97 xLa0.02Bax)(Zr0.72Sn0.22Ti0.06)O3 (PLBZST) ceramics with x in the range of 0.09, 0.11, 0.13, 0.15 were fabricated by conventional solid-state reaction process, and their crystal structure, dielectric and electrocaloric effect were systemically investigated. The results showed that the ceramics with different Ba contents had a perovskite structure. Besides, it was found the ceramics transform gradually from antiferroelectric phase to paraelectric phase and the Curie temperature decreased with the increase of Ba content, when x = 0.15, the Curie temperature of the ceramics decreased to 30 °C near room temperature. The dielectric constant increased to about 12000 with increasing Ba contents. The change of temperature increased from 0.10 K to 0.25 K sharply at 2.2 kV/mm. Ó 2012 Elsevier B.V. All rights reserved.
1. Introduction Ferroelectric (FE) perovskites such as BaTiO3(BT), PbTiO3, and solid solutions of PbZrO3–PbTiO3 [Pb(ZrxTi1 x)O3, PZT] have received great interest because of their potential applications in micro- and nano-electronics as elements of nonvolatile random access memories. PbZrO3 was antiferroelectric ceramic reported for the first time. However it has a high phase transition electricfield of antiferroelectric (AFE) to ferroelectric (FE). Then, Ti4+, Sn4+ and La3+ were modified into B site or A site of PbZrO3 for lowering the phase transition electric-field, and lead lanthanum zirconate stannate titanate antiferroelectric system (PLZST) were developed [1–6]. These materials can be applied in high-energy storage capacitors [7], explosive electrical transducers [8], actuators, pyroelectric detectors [9,10], antiferroelectric cold cathode materials [11], ferroelectric refrigeration [12], and so on. However, the pyroelectric response encountered a problem that the Curie temperature is too high (>120 °C) to be used practically and the range of the antiferroelectric is too narrow. In previous works, researchers reported that, for PZST ceramics, A-site modification with Ba2+ could clearly shift the Curie temperature to low temperature [13–20]. Zhang et al. [21] observed a change in isothermal entropy of more than 55 J/(kg K) and a change in adiabatic temperature of over 12 °C. They also showed that the relaxor ferroelectric polymer of P(VDF-TrFE-chlorofluoroethylene) has a large electrocaloric effect. However, the result was obtained and calculated by DSC or hysteresis loop at adiabatic state. ⇑ Corresponding author. E-mail address: [email protected] (Y. Tongqing). 0925-8388/$ - see front matter Ó 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.jallcom.2012.06.028
In this paper, (Pb0.97 xLa0.02Bax)(Zr0.72Sn0.22Ti0.06)O3 ceramics with x being 0.09, 0.11, 0.13, 0.15 were fabricated respectively, and the dielectric properties and electrocaloric effect of the specimens was investigated by directly measured at room temperature. 2. Experimental procedure Ferroelectric ceramics were fabricated using a solid-state route. Metal oxides of Pb3O4, La2O3, ZrO2, TiO2 and SnO2 (purity of 99.0%) were used to synthesize (Pb0.97 xLa0.02Bax)(Zr0.72Sn0.22Ti0.06)O3 + 2 mol% PbO ceramics with x = 0.09, 0.11, 0.13, 0.15, respectively. The high purity raw materials were weighted, mixed and calcined at 900 °C for 2 h. Then, the calcined powder was remixed in alcohol using a zirconia ball mill in polyethylene pot for 24 h. After drying and granulating with PVA, the well mixed powders were pressed into a disk (U10 mm 2 mm) at 40 MPa and then sintered at 1200 °C1260 °C for 2 h in air. The surfaces silver electrode was sintered and fired at 550 °C for 10 min. The lattice structure and average grain size were determined by using an X-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively. The dielectric properties with different temperature and dc bias field were measured at 1 kHz frequency using a LCR analyzer (Agilent 4284). The electrocaloric effect was determined by a directly method. For this method, the sample in series with a high-voltage power supply was connected to a Keithley 2000 to detect the change rate of temperature when sample was applied the signal of variation of field strength.
3. Results and discussion Fig. 1 shows the XRD patterns of PLBZST ceramics with various Ba contents. For each sample with x from the 0.09 to 0.15, a clear single-perovskite phase is observed, all samples showed no second phase appeared from XRD results, which indicates PLBZST ceramics with different Ba content are basically soluted in the lattice of PLBZST. When x = 0.15, (2 0 0)(0 0 2), (3 0 1)(1 0 3) disappear gradually, the double peaks transit into the single peak, which is
W. Jinfei et al. / Journal of Alloys and Compounds 539 (2012) 280–283
Fig. 1. X-ray diffraction patterns of (Pb0.97 xLa0.02Bax)(Zr0.72Sn0.22Ti0.06)O3 ceramics sintered in air at 1240 °C for 2 h.
attributed that the antiferroelectric phase transform to paraelectric phase with increasing Ba content. Fig. 2 shows the SEM micrographs of the as-sintered surface of (Pb0.97 xLa0.02Bax)(Zr0.72Sn0.22Ti0.06)O3ceramics sintered in air in 1240 °C for 2 h. From the figure, it is can be seen that the grains of the samples become more uniform and the grain size of the samples increases up to x = 0.13, the average grain size of the ceramics is about 3–4 lm (Fig. 2(a–c)). The addition of Ba promotes the grain-growth of the PLBZST samples, and the grains were found to be uniformly distributed throughout the surface and tightly bound with homogeneous microstructure supporting the dopants diffusion uniformly. However, when x increases to 0.15, small grain begins to appear at grain boundaries, which may need higher sintering temperature. The dielectric properties at 10 kHz as a function of temperature for the (Pb0.97 xLa0.02Bax)(Zr0.72Sn0.22Ti0.06)O3 ceramics sintered in air at 1240 °C for 2 h are illustrated in Fig. 3. The curve of dielectric constant (e) shows a peak, and the peak is up to >11,000. With the increase of Ba2+ contents, the peak moved from 100 to 30 °C. As well known, the peak position of e-temperature curve was corre-
281
Fig. 3. Temperature dependence of permittivity of (Pb0.97 xLa0.02Bax)(Zr0.72Sn0.22Ti0.06)O3 ceramics sintered in air at 1240 °C for 2 h.
sponding to the Tc. The results indicate that Tc of (Pb0.97 xLa0.02Bax)(Zr0.72Sn0.22Ti0.06)O3 ceramics move from 100 to 30 °C, when x increases from 0.09 to 0.15, which is attributed that the Ba2+ enters into A-site and Tc decreased with Ba incorporation [22]. Fig. 4 shows several typical Polarization–electric field hysteresis loops (P-E hysteresis loops) of (Pb0.97 xLa0.02Bax)(Zr0.72Sn0.22Ti0.06)O3 ceramics with different Ba contents. As shown in Fig. 4 (a–c), classic double-hysteresis loops characteristic of AFE phase are observed. At the same measurement condition, the largest field applied to the sample is 45 kV/cm and the maximum polarization value is 18 lC/cm2. And hysteresis loop demonstrate that the PLBZST antiferroelectric samples are slim P-E loops, which are suitable for application in high-energy-storage capacitors. Besides, it is showed that the AFE phase change to paraelectric phase with increasing Ba contents. Obviously, the antiferroelectric phase transform to paraelectric phase with increasing Ba content gradually. The directly measured DT for (Pb0.97 xLa0.02Bax)(Zr0.72Sn0.22Ti0.06)O3 ceramics versus electric field with different Ba content is
Fig. 2. SEM micrographs of the as-sintered surface of (Pb0.97 xLa0.02Bax)(Zr0.72Sn0.22Ti0.06)O3 ceramics (a) x = 0.09; (b) x = 0.11; (c) x = 0.13; (d) x = 0.15.
282
W. Jinfei et al. / Journal of Alloys and Compounds 539 (2012) 280–283
Fig. 4. P-E hysteresis loop of (Pb0.97 xLa0.02Bax)(Zr0.72Sn0.22Ti0.06)O3 ceramics with different x contents: (a) x = 0.09; (b) x = 0.11; (c) x = 0.13; (d) x = 0.15.
shown in Fig. 5. In the direct measurement of DT. Due to the ceramic breakdown, the chosen maximum field in the measurement is 2.2 kV/mm. The applied field is 2.2 kV/cm, the DT increased from 0.1 K to 0.25 K when x change from 0.11 to 0.15. The measurement temperature is near Tc, when x=0.15, because the change of temperature was maximum near Tc [21]. According to the directly measured data in Fig. 5, it is noted that DT increases with the increasing of the applied electric field. The DT dependence of electric field of (Pb0.97-0.15La0.02Ba0.15)(Zr0.72 Sn0.22Ti0.06)O3 ceramics is shown in Fig. 6. If we extend the applied field to about 300 kV/mm, which is similar to field strength applied in thin film [21], the DT will also be more than 10 K, which is adapted to practical application. 4. Conclusion
Fig. 5. Temperature dependences of the directly measured DT with different Ba content.
In summary, (Pb0.97 xLa0.02Bax)(Zr0.72Sn0.22Ti0.06)O3 ceramics with perovskite structure were prepared. It is concluded that with increasing Ba contents, the Curie temperature of the ceramics decrease and the antiferroelectric phase transform to paraelectric phase. The dielectric constant (e) is up to >11000. The ceramics exhibit a DT 0.25 K at room temperature by directly measured and DT will be improved with increasing the electric field. Acknowledgements This work was supported by the Nature Science Associate Foundation (NSAF) of China (Grant No. 10874130). The Key Project of Chinese Ministry of Education(No. 108055), Shanghai Pujiang Program and the State Key Laboratory of Electronic Thin Films and Integrated Devices (UESTC). References
Fig. 6. DT dependence of electric field(E) of (Pb0.97 xLa0.02Bax)(Zr0.72Sn0.22Ti0.06)O3 ceramics.
[1] D. Berlincourt, IEEE Trans. Sonics Ultrason. 13 (1966) 116. [2] W.Y. Pan, C.Q. Dam, Q.M. Zhang, L.E. Cross, J. Appl. Phys. 66 (1989) 6014. [3] K. Ramam, A.J. Bell, C.R. Bowen, K. Chandramouli, J. Alloys Compd. 473 (2009) 330. [4] K. Ramam, M. Lopez, J. Alloys Compd. 466 (2008) 398. [5] W. Chan, Z. Xu, Y. Zhang, T. Hung, H. Chen, J. Appl. Phys. 94 (2003) 4563. [6] X. Chen, H. Li, D. Li, F. Cao, X. Dong, Chin. Phys. Soc. 57 (2008) 7298. [7] A.Q. Jiang, T.A. Tang, S. Corkovic, Q. Zhang, Appl. Phys. Lett. 93 (21) (2008) 212908.
W. Jinfei et al. / Journal of Alloys and Compounds 539 (2012) 280–283 [8] O. Essig, P. Wang, M. Hartweg, P. Janker, H. Nafe, F. Aldinger, J. Eur. Ceram. Soc. 19 (1999) 1223–1228. [9] T.Q. Yang, P. Liu, Z. Xu, L. Zhang, X. Yao, Ferroelectrics 230 (1999) 181–186. [10] Z. Sheng, Y. Feng, Z. Xu, X. Sun, X. Huang, J. Xi’an Jiaotong Univ. 42 (8) (2008) 977. [11] P.D. Thacher, J. Appl. Phys. 39 (1968) 1996. [12] B.P. Pokharel, D. Pandey, J. Appl. Phys. 88 (2000) 5364. [13] S.E. Park, K. Markowski, S. Yoshikawa, L. Eric Cross, J. Am. Ceram. Soc. 80 (1997) 407. [14] X. Dai, A. DiGiovanni, D. Viehland, J. Appl. Phys. 74 (1993) 3399.
[15] [16] [17] [18] [19] [20] [21] [22]
283
N.W. Thomas, J. Phys. Chem. Solids 51 (1990) 1419. R. Rai, S. Mishra, N.K. Singh, J. Alloys Compd. 487 (2009) 494. C.C. Tsai, C.S. Hong, C.C. Shih, S.Y. Chu, J. Alloys Compd. 511 (2012) 54. J.H. Zhang, S.J. Mo, H.Y. Wang, S.X. Zhen, H.W. Chen, C.R. Yang, J. Alloys Compd. 509 (2011) 2838. L.B. Kong, J. Ma, R.F. Zhang, T.S. Zhang, J. Alloys Compd. 339 (2002) 167. S. Dutta, R.N.P. Choudhary, P.K. Sinha, J. Alloys Compd. 426 (2006) 345. B. Neese, B. Chu, S.G. Lu, Y. Wang, E. Furman, Q.M. Zhang, Science 321 (2008) 821. Y. Luo, X. Liu, X. Li, G. Liu, Solid State Ionics 177 (2006) 1543.