- Email: [email protected]
Effect of calcium on the piezoelectric and dielectric properties of Sm-modified PbTiO3 ceramics
Sensors and Actuators A 89 (2001) 210±214
Effect of calcium on the piezoelectric and dielectric properties of Sm-modi®ed PbTiO3 ceramics Sheng-Yuan Chu*, Chia-Hsin Chen Department of Electrical Engineering, National Cheng Kung University, 1 University, Tainan, Taiwan, ROC Accepted 6 November 2000
Abstract In this paper, effects of calcium dopants on the piezoelectric and dielectric properties of Sm-modi®ed lead titanate (PbTiO3) ceramics have been investigated. Sm-modi®ed PbTiO3 ceramics with a composition of (Pb0.88ÿxCaxSm0.08)(Ti0.98Mn0.02)O3; x 0:11±0.17 were prepared by conventional mixed-oxide methods with sintering temperature at 12008C. We successfully showed that Ca additive is helpful to obtain much higher thickness electromechanical coupling coef®cient, kt (> 0:57), than that of conventional PbTiO3 based ceramics and still keep small planar electromechanical coupling coef®cient, kp. Microstructural and compositional analyses of these doped ceramics have been carried out using X-ray diffractometer (XRD) and scanning electron microscope (SEM). # 2001 Elsevier Science B.V. All rights reserved. Keywords: Calcium doping; Piezoelectric; Dielectric; Modi®ed PbTiO3
1. Introduction In recent years, lead titanate (PbTiO3) ceramics have been attracted attentions due to its high Curie temperature (Tc) 4908C and low dielectric constant of about 200, which make them attractive for high-temperature and high-frequency transducer applications than that of PZT ceramic system [1,2]. However, pure lead titanate ceramics are very dif®cult to be sintered because of its large lattice anisotropy (c/ a 1:064). On cooling through Tc, the large anisotropy of ceramic material becomes fragile. In addition, it is dif®cult to pole the ceramics with low resistivity (107 ÿ108 O cm). By substitution of isovalent (Ca2, Ba2, Cd2, etc.) or off-valent (Sm3, Gd3,Y3, etc.) ions into the Pb2 sites, the lattice anisotropy is reduced [3±7], and the samples become more dense. These modi®ed PbTiO3 ceramics will result in a relatively large thickness electromechanical coupling coef®cient, kt and a small planar electromechanical coef®cient, kp. In other words, the electromechanical coupling factor for thickness vibration kt will be much larger than that for planar extensional vibration kp (kt @ kp ). The addition of Ca or Sm into PbTiO3 results in a higher kt/kp ratio compared with PZT ceramics. This property makes it
* Corresponding author. Fax: 886-6-234-5482. E-mail address: [email protected] (S.-Y. Chu).
possible that PbTiO3 based ceramics can be used for highfrequency applications such as SAW devices and piezoelectric transformer [8,9]. Many researchers reported that (Pb0.85Sm0.1)(Ti0.98Mn0.02)O3 ceramics shows exceptionally large electromechanical anisotropy [10±12]. In this paper, we prepare (Pb0.88ÿxCaxSm0.08)(Ti0.98Mn0.02)O3 (x 0:11±0.17) system with additional dopants of Ca to investigate the dielectric and piezoelectric properties. 2. Experimental procedure A conventional ceramics preparation procedure was used to prepare the sample. Raw materials were mixed by pure reagent PbO, TiO2, Sm2O3, MnO2, CaCO3 powders (>99.0% purity). The materials (Pb0.88ÿxCaxSm0.02)(Ti0.98Mn0.02)O3, x 0:11±0.17, were synthesized by calcining at 9008C for 2 h, and excess PbO was added to counteract the volatilization of PbO during ®ring, then followed by pulverization. After that, the powders were dried and milled with 8 wt.% of a 5% PVA solution. After that, the samples were pressed into a disk of 12 mm diameter and 1.5 mm thickness at pressure of 25 kg cmÿ2 Specimen were then sintered isothermally with a heating rate of 108C minÿ1 at 12008C for 2 h. A PbO rich atmosphere was maintained with PbTiO3 powder to minimize the lead
0924-4247/01/$ ± see front matter # 2001 Elsevier Science B.V. All rights reserved. PII: S 0 9 2 4 - 4 2 4 7 ( 0 0 ) 0 0 5 3 6 - 7
S.-Y. Chu, C.-H. Chen / Sensors and Actuators A 89 (2001) 210±214
211
Fig. 2. Dependence of the bulk density on the amount of Ca additives.
ties were calculated from the resonance measurement method [13]. The phase relations for the sintered body were identi®ed using X-ray diffractometer (XRD) and microstructures were observed using a scanning electron microscope (SEM). 3. Results and discussion
Fig. 1. Flow diagram of the sample preparation procedure.
loss during sintering. The ¯ow diagram of the sample preparation procedure is shown in Fig. 1. Bulk densities of sintered bodies were measured by the Archimedes method. In order to measure the electrical properties, silver paste was coated to form electrodes on both sides of the sample, then subsequently ®red at 8008C for 20 min. The dielectric (measured at 1 kHz) and piezoelectric properties were measured using an impedance analyzer (HP4194A) after poling under 5 kV mmÿ1 bias at 1508C in a silicone oil bath for 15 min. Piezoelectric proper-
Fig. 2 shows the bulk density as a function of the amount of Ca ceramics. The density was decreased slightly with increasing Ca substitutions. This result is reasonable because Ca is lighter than Pb. After sintering, all samples were >95% theoretical density, which is necessary to withstand the high electric ®eld (50 kV cmÿ1) to pole PbTiO3based systems. XRD patterns of (Pb0.88ÿxCaxSm0.08)(Ti0.98Mn0.02)O3 ceramics are shown in Fig. 3. PbTiO3 and Ca-doped PbTiO3 ceramics have major peaks at (1 0 1), and all of them belong to the tetragonal phase. There is no obvious difference of XRD patterns between PbTiO3 and Ca-doped PbTiO3 samples. The peak values of (0 0 2) and (2 0 0) (around 458) move to each other as Ca dopants increase. Thus, the lattice anisotropy, c/a ratio, decreased with increasing the amount of Ca additive, as shown in Fig. 4.
Fig. 3. XRD patterns of (Pb0.88ÿxCaxSm0.08)(Ti0.98Mn0.02)O3 samples.
212
S.-Y. Chu, C.-H. Chen / Sensors and Actuators A 89 (2001) 210±214
Fig. 6. Dependence of the grain size on the amount of Ca additives.
Fig. 4. Dependence of the (a) lattice constant and (b) lattice anisotropy on the amount of Ca additives.
Since CaTiO3 is cubic phase at room temperature, increasing Ca2 concentration causes microstructure of PbTiO3 system change into slightly cubic morphology. The SEM pattern of PbTiO3 and Ca-doped PbTiO3 samples were shown in Fig. 5 reveals uniform microstructures and both of them are very dense. Grain sizes on the order of 1.5±2 mm which is smaller than that of previously published data [14]. Fig. 6 shows the dependence of grain size on the Ca dopant. Ca dopant was found to change grain size little. Fig. 7(a) and (b) display the dielectric constant and loss factor of samples versus the amount of Ca, respectively. It shows that the dielectric constant increase correspondingly with the increase of amount of Ca at room temperature because the Tc of PbTiO3 system decreases as Ca2 concentration increases, while the loss factor changes little. The
Fig. 7. Dependence of the (a) dielectric constant and (b) loss factor on the amount of Ca additives.
dielectric constant is 210 for Ca dopant 11% and is 290 for Ca dopant 17%. The dielectric loss was <1% for all components. The dielectric constant of samples doping with both Ca and Sm
Fig. 5. SEM photographs of (a) (Pb0.85Sm0.1)(Ti0.98Mn0.02)O3 and (b) (Pb0.75Ca0.13Sm0.08)(Ti0.98Mn0.02)O3 samples sintered at 12008C for 2 h (bar 2 mm).
S.-Y. Chu, C.-H. Chen / Sensors and Actuators A 89 (2001) 210±214
213
Ca dopants decrease lattice anisotropy and increase dielectric constant linearly. On the other hand, as comparing Figs. 4 and 8, we found that the highest value of kt/kp occurs as Ca 13 mol% at which c/a value did not reach its maximum or minimum value. Therefore, lattice anisotropy (c/a value) is independent of high electromechanical anisotropy (kt/kp) in PbTiO3-based ceramics. We think the key factor that affects kt is doping concentration. We see little relationship between grain size and kt in our investigation. It probably is because that the grain size of our samples did not change a lot. Fig. 9 shows frequency constant versus the amount of Ca. The planar and thickness frequency constant are about 2850 and 2050 kHz mm, respectively. 4. Conclusions Fig. 8. Dependence of the (a) thickness coupling factor and (b) planar coupling on the amount of Ca additives.
are higher than that of samples doping with Ca [7] or Sm [6], either. The results of the thickness (kt) and planar (kp) coupling factors were shown in Fig. 8. As Ca additive increases, kp increases at ®rst and reaches its maximum value of 0.574 as Ca 13 mol%. It is obvious that kp for x 0:13±0.15 is about 0.57, which is higher than previously reported data for Sm-modi®ed lead titanate [14]. The value kp is about 0.04± 0.05 as Ca changes, and the minimum value occurs as Ca 13 mol%. Compared Figs. 4 and 7, we found that
Fig. 9. Dependence of the frequency constant (a) Np and (b) Nt on the amount of Ca additives.
The additives of Ca and Sm simultaneous cannot only reduce the lattice anisotropy (c/a), but also keep good dielectric and anisotropy properties of the Sm- or Ca-modi®ed PbTiO3 ceramics. In general, increasing the Ca doping level decreased the Tc, ranging from 3008C for Ca 0:11% down to 2508C for Ca 0:17% [15]. The highest value of kt/kp occurs as Ca 0:13%, which we think it as the preferred Ca content ratio. The measured coupling coef®cient, kt is 0.57 as Ca 13±15 mol%, which can be used for high-temperature and high-frequency applications.
References [1] S. Ikegami, I. Ueda, T. Nagata, Electromechanical properties of PbTiO3 ceramics containing La and Mn, J. Acoust. Soc. Am. 50 (1971) 1060±1066. [2] T. Takahashi, Lead titanate ceramics with large piezoelectric anisotropy and their application, Ceram. Bull. 69 (1990) 691±695. [3] H. Takeuchi, S. Jyomura, E. Yamamoto, Y. Ito, Electromechanical properties of (Pb, Ln)(Ti, Mn)O3 ceramics, J. Acoust. Soc. Am. 72 (1982) 1114±1120. [4] K. Takeuchi, D. Damjanovic, T.R. Gururaja, S.J. Jang, L.E. Cross, Electromechanical properties of calcium-modified lead titanate ceramics, in: Proceedings of the Sixth ISAF IEEE, 1986, pp. 402± 405. [5] J. Shenglin, Z. Xuli, W. Xiaozhen, W. Xianghong, Investigation on anisotropy in piezoelectric properties of modified PbTiO3 ceramics, Piezoelect. Acoust. 17 (1995) 26±29. [6] I. Ueda, S. Ikegami, Piezoelectric properties of modified PbTiO3 ceramics, Jpn. J. Appl. Phys. 7 (1968) 236±242. [7] Y. Yamashita, K. Yokoyama, H. Honda, T. Takahashi, (Pb, Ca)[(Co1/2W1/2), Ti]O3 piezoelectric ceramics and their applications, Jpn. J. Appl. Phys. 20 (1981) 183±187. [8] O. Ohnishi, H. Kishie, A. Iwamoto, Y. Sasaki, T. Zaitsu, T. Inoue, Piezoelectric ceramic transformer operating in thickness extensional vibration mode for power supply, IEEE Ultrason. Symp. (1992) 483± 488. [9] K.M. Rittenmyer, R.Y. Ting, Piezoelectric and dielectric properties of calcium and samarium modified lead titanate ceramics for hydroacoustic application, Ferroelectrics 110 (1990) 171±182. [10] J.N. Kim, M.I. Haun, S.J. Jang, L.E. Cross, X.R. Xue, Temperature
214
S.-Y. Chu, C.-H. Chen / Sensors and Actuators A 89 (2001) 210±214
behavior of dielectric and piezoelectric properties of samariumdoped lead titanate ceramics, IEEE Trans. Ultrason. Ferroelect. Freq. Contr. 36 (1989) 389±392. [11] D. Damjanovic, T.R. Gururaja, L.E. Cross, Anisotropy in the piezoelectric properties of modified lead titanate ceramics, Am. Ceram. Soc. Bull. 66 (1987) 699±703. [12] W.R. Xue, J.N. Kim, S.J. Jang, L.E. Cross, R.E. Newnham, Temperature behavior of dielectric and electromechanical coupling properties of samarium-doped lead titanate ceramics, Jpn. J. Appl. Phys. 24 (1985) 718±720.
[13] IRE standards on piezoelectric crystals: measurements of piezoelectric ceramics 1961, in: Proceedings of the Symposium on IRE, Vol. 49, 1961, pp. 1161±1169. [14] T. Suwannasiri, A. Safari, Effect of rare-earth additives on electromechanical properties of modified lead titanate ceramics, J. Am. Ceram. Soc. 76 (1993) 3155±3158. [15] W.R. Xue, P.W. Lu, W. Huebner, Effect of Calcia additions on the electromechanical properties of Samarium-modified lead titanate ceramics, in: Proceedings of the 1995 IEEE ISAF, 1995, pp. 101± 104.
Effect of calcium on the piezoelectric and dielectric properties of Sm-modi®ed PbTiO3 ceramics Sheng-Yuan Chu*, Chia-Hsin Chen Department of Electrical Engineering, National Cheng Kung University, 1 University, Tainan, Taiwan, ROC Accepted 6 November 2000
Abstract In this paper, effects of calcium dopants on the piezoelectric and dielectric properties of Sm-modi®ed lead titanate (PbTiO3) ceramics have been investigated. Sm-modi®ed PbTiO3 ceramics with a composition of (Pb0.88ÿxCaxSm0.08)(Ti0.98Mn0.02)O3; x 0:11±0.17 were prepared by conventional mixed-oxide methods with sintering temperature at 12008C. We successfully showed that Ca additive is helpful to obtain much higher thickness electromechanical coupling coef®cient, kt (> 0:57), than that of conventional PbTiO3 based ceramics and still keep small planar electromechanical coupling coef®cient, kp. Microstructural and compositional analyses of these doped ceramics have been carried out using X-ray diffractometer (XRD) and scanning electron microscope (SEM). # 2001 Elsevier Science B.V. All rights reserved. Keywords: Calcium doping; Piezoelectric; Dielectric; Modi®ed PbTiO3
1. Introduction In recent years, lead titanate (PbTiO3) ceramics have been attracted attentions due to its high Curie temperature (Tc) 4908C and low dielectric constant of about 200, which make them attractive for high-temperature and high-frequency transducer applications than that of PZT ceramic system [1,2]. However, pure lead titanate ceramics are very dif®cult to be sintered because of its large lattice anisotropy (c/ a 1:064). On cooling through Tc, the large anisotropy of ceramic material becomes fragile. In addition, it is dif®cult to pole the ceramics with low resistivity (107 ÿ108 O cm). By substitution of isovalent (Ca2, Ba2, Cd2, etc.) or off-valent (Sm3, Gd3,Y3, etc.) ions into the Pb2 sites, the lattice anisotropy is reduced [3±7], and the samples become more dense. These modi®ed PbTiO3 ceramics will result in a relatively large thickness electromechanical coupling coef®cient, kt and a small planar electromechanical coef®cient, kp. In other words, the electromechanical coupling factor for thickness vibration kt will be much larger than that for planar extensional vibration kp (kt @ kp ). The addition of Ca or Sm into PbTiO3 results in a higher kt/kp ratio compared with PZT ceramics. This property makes it
* Corresponding author. Fax: 886-6-234-5482. E-mail address: [email protected] (S.-Y. Chu).
possible that PbTiO3 based ceramics can be used for highfrequency applications such as SAW devices and piezoelectric transformer [8,9]. Many researchers reported that (Pb0.85Sm0.1)(Ti0.98Mn0.02)O3 ceramics shows exceptionally large electromechanical anisotropy [10±12]. In this paper, we prepare (Pb0.88ÿxCaxSm0.08)(Ti0.98Mn0.02)O3 (x 0:11±0.17) system with additional dopants of Ca to investigate the dielectric and piezoelectric properties. 2. Experimental procedure A conventional ceramics preparation procedure was used to prepare the sample. Raw materials were mixed by pure reagent PbO, TiO2, Sm2O3, MnO2, CaCO3 powders (>99.0% purity). The materials (Pb0.88ÿxCaxSm0.02)(Ti0.98Mn0.02)O3, x 0:11±0.17, were synthesized by calcining at 9008C for 2 h, and excess PbO was added to counteract the volatilization of PbO during ®ring, then followed by pulverization. After that, the powders were dried and milled with 8 wt.% of a 5% PVA solution. After that, the samples were pressed into a disk of 12 mm diameter and 1.5 mm thickness at pressure of 25 kg cmÿ2 Specimen were then sintered isothermally with a heating rate of 108C minÿ1 at 12008C for 2 h. A PbO rich atmosphere was maintained with PbTiO3 powder to minimize the lead
0924-4247/01/$ ± see front matter # 2001 Elsevier Science B.V. All rights reserved. PII: S 0 9 2 4 - 4 2 4 7 ( 0 0 ) 0 0 5 3 6 - 7
S.-Y. Chu, C.-H. Chen / Sensors and Actuators A 89 (2001) 210±214
211
Fig. 2. Dependence of the bulk density on the amount of Ca additives.
ties were calculated from the resonance measurement method [13]. The phase relations for the sintered body were identi®ed using X-ray diffractometer (XRD) and microstructures were observed using a scanning electron microscope (SEM). 3. Results and discussion
Fig. 1. Flow diagram of the sample preparation procedure.
loss during sintering. The ¯ow diagram of the sample preparation procedure is shown in Fig. 1. Bulk densities of sintered bodies were measured by the Archimedes method. In order to measure the electrical properties, silver paste was coated to form electrodes on both sides of the sample, then subsequently ®red at 8008C for 20 min. The dielectric (measured at 1 kHz) and piezoelectric properties were measured using an impedance analyzer (HP4194A) after poling under 5 kV mmÿ1 bias at 1508C in a silicone oil bath for 15 min. Piezoelectric proper-
Fig. 2 shows the bulk density as a function of the amount of Ca ceramics. The density was decreased slightly with increasing Ca substitutions. This result is reasonable because Ca is lighter than Pb. After sintering, all samples were >95% theoretical density, which is necessary to withstand the high electric ®eld (50 kV cmÿ1) to pole PbTiO3based systems. XRD patterns of (Pb0.88ÿxCaxSm0.08)(Ti0.98Mn0.02)O3 ceramics are shown in Fig. 3. PbTiO3 and Ca-doped PbTiO3 ceramics have major peaks at (1 0 1), and all of them belong to the tetragonal phase. There is no obvious difference of XRD patterns between PbTiO3 and Ca-doped PbTiO3 samples. The peak values of (0 0 2) and (2 0 0) (around 458) move to each other as Ca dopants increase. Thus, the lattice anisotropy, c/a ratio, decreased with increasing the amount of Ca additive, as shown in Fig. 4.
Fig. 3. XRD patterns of (Pb0.88ÿxCaxSm0.08)(Ti0.98Mn0.02)O3 samples.
212
S.-Y. Chu, C.-H. Chen / Sensors and Actuators A 89 (2001) 210±214
Fig. 6. Dependence of the grain size on the amount of Ca additives.
Fig. 4. Dependence of the (a) lattice constant and (b) lattice anisotropy on the amount of Ca additives.
Since CaTiO3 is cubic phase at room temperature, increasing Ca2 concentration causes microstructure of PbTiO3 system change into slightly cubic morphology. The SEM pattern of PbTiO3 and Ca-doped PbTiO3 samples were shown in Fig. 5 reveals uniform microstructures and both of them are very dense. Grain sizes on the order of 1.5±2 mm which is smaller than that of previously published data [14]. Fig. 6 shows the dependence of grain size on the Ca dopant. Ca dopant was found to change grain size little. Fig. 7(a) and (b) display the dielectric constant and loss factor of samples versus the amount of Ca, respectively. It shows that the dielectric constant increase correspondingly with the increase of amount of Ca at room temperature because the Tc of PbTiO3 system decreases as Ca2 concentration increases, while the loss factor changes little. The
Fig. 7. Dependence of the (a) dielectric constant and (b) loss factor on the amount of Ca additives.
dielectric constant is 210 for Ca dopant 11% and is 290 for Ca dopant 17%. The dielectric loss was <1% for all components. The dielectric constant of samples doping with both Ca and Sm
Fig. 5. SEM photographs of (a) (Pb0.85Sm0.1)(Ti0.98Mn0.02)O3 and (b) (Pb0.75Ca0.13Sm0.08)(Ti0.98Mn0.02)O3 samples sintered at 12008C for 2 h (bar 2 mm).
S.-Y. Chu, C.-H. Chen / Sensors and Actuators A 89 (2001) 210±214
213
Ca dopants decrease lattice anisotropy and increase dielectric constant linearly. On the other hand, as comparing Figs. 4 and 8, we found that the highest value of kt/kp occurs as Ca 13 mol% at which c/a value did not reach its maximum or minimum value. Therefore, lattice anisotropy (c/a value) is independent of high electromechanical anisotropy (kt/kp) in PbTiO3-based ceramics. We think the key factor that affects kt is doping concentration. We see little relationship between grain size and kt in our investigation. It probably is because that the grain size of our samples did not change a lot. Fig. 9 shows frequency constant versus the amount of Ca. The planar and thickness frequency constant are about 2850 and 2050 kHz mm, respectively. 4. Conclusions Fig. 8. Dependence of the (a) thickness coupling factor and (b) planar coupling on the amount of Ca additives.
are higher than that of samples doping with Ca [7] or Sm [6], either. The results of the thickness (kt) and planar (kp) coupling factors were shown in Fig. 8. As Ca additive increases, kp increases at ®rst and reaches its maximum value of 0.574 as Ca 13 mol%. It is obvious that kp for x 0:13±0.15 is about 0.57, which is higher than previously reported data for Sm-modi®ed lead titanate [14]. The value kp is about 0.04± 0.05 as Ca changes, and the minimum value occurs as Ca 13 mol%. Compared Figs. 4 and 7, we found that
Fig. 9. Dependence of the frequency constant (a) Np and (b) Nt on the amount of Ca additives.
The additives of Ca and Sm simultaneous cannot only reduce the lattice anisotropy (c/a), but also keep good dielectric and anisotropy properties of the Sm- or Ca-modi®ed PbTiO3 ceramics. In general, increasing the Ca doping level decreased the Tc, ranging from 3008C for Ca 0:11% down to 2508C for Ca 0:17% [15]. The highest value of kt/kp occurs as Ca 0:13%, which we think it as the preferred Ca content ratio. The measured coupling coef®cient, kt is 0.57 as Ca 13±15 mol%, which can be used for high-temperature and high-frequency applications.
References [1] S. Ikegami, I. Ueda, T. Nagata, Electromechanical properties of PbTiO3 ceramics containing La and Mn, J. Acoust. Soc. Am. 50 (1971) 1060±1066. [2] T. Takahashi, Lead titanate ceramics with large piezoelectric anisotropy and their application, Ceram. Bull. 69 (1990) 691±695. [3] H. Takeuchi, S. Jyomura, E. Yamamoto, Y. Ito, Electromechanical properties of (Pb, Ln)(Ti, Mn)O3 ceramics, J. Acoust. Soc. Am. 72 (1982) 1114±1120. [4] K. Takeuchi, D. Damjanovic, T.R. Gururaja, S.J. Jang, L.E. Cross, Electromechanical properties of calcium-modified lead titanate ceramics, in: Proceedings of the Sixth ISAF IEEE, 1986, pp. 402± 405. [5] J. Shenglin, Z. Xuli, W. Xiaozhen, W. Xianghong, Investigation on anisotropy in piezoelectric properties of modified PbTiO3 ceramics, Piezoelect. Acoust. 17 (1995) 26±29. [6] I. Ueda, S. Ikegami, Piezoelectric properties of modified PbTiO3 ceramics, Jpn. J. Appl. Phys. 7 (1968) 236±242. [7] Y. Yamashita, K. Yokoyama, H. Honda, T. Takahashi, (Pb, Ca)[(Co1/2W1/2), Ti]O3 piezoelectric ceramics and their applications, Jpn. J. Appl. Phys. 20 (1981) 183±187. [8] O. Ohnishi, H. Kishie, A. Iwamoto, Y. Sasaki, T. Zaitsu, T. Inoue, Piezoelectric ceramic transformer operating in thickness extensional vibration mode for power supply, IEEE Ultrason. Symp. (1992) 483± 488. [9] K.M. Rittenmyer, R.Y. Ting, Piezoelectric and dielectric properties of calcium and samarium modified lead titanate ceramics for hydroacoustic application, Ferroelectrics 110 (1990) 171±182. [10] J.N. Kim, M.I. Haun, S.J. Jang, L.E. Cross, X.R. Xue, Temperature
214
S.-Y. Chu, C.-H. Chen / Sensors and Actuators A 89 (2001) 210±214
behavior of dielectric and piezoelectric properties of samariumdoped lead titanate ceramics, IEEE Trans. Ultrason. Ferroelect. Freq. Contr. 36 (1989) 389±392. [11] D. Damjanovic, T.R. Gururaja, L.E. Cross, Anisotropy in the piezoelectric properties of modified lead titanate ceramics, Am. Ceram. Soc. Bull. 66 (1987) 699±703. [12] W.R. Xue, J.N. Kim, S.J. Jang, L.E. Cross, R.E. Newnham, Temperature behavior of dielectric and electromechanical coupling properties of samarium-doped lead titanate ceramics, Jpn. J. Appl. Phys. 24 (1985) 718±720.
[13] IRE standards on piezoelectric crystals: measurements of piezoelectric ceramics 1961, in: Proceedings of the Symposium on IRE, Vol. 49, 1961, pp. 1161±1169. [14] T. Suwannasiri, A. Safari, Effect of rare-earth additives on electromechanical properties of modified lead titanate ceramics, J. Am. Ceram. Soc. 76 (1993) 3155±3158. [15] W.R. Xue, P.W. Lu, W. Huebner, Effect of Calcia additions on the electromechanical properties of Samarium-modified lead titanate ceramics, in: Proceedings of the 1995 IEEE ISAF, 1995, pp. 101± 104.