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Ferroelectric, piezoelectric and electrostrictive properties of Ba(Ti1−xSnx)O3 ceramics obtained from nanocrystalline powder
Materials Science and Engineering B 172 (2010) 151–155
Contents lists available at ScienceDirect
Materials Science and Engineering B journal homepage: www.elsevier.com/locate/mseb
Ferroelectric, piezoelectric and electrostrictive properties of Ba(Ti1−x Snx )O3 ceramics obtained from nanocrystalline powder A.K. Nath a,∗ , K. Chandramani Singh a , Radhapiyari Laishram b , O.P. Thakur b a b
Department of Physics, Sri Venkateswara College, University of Delhi, New Delhi 110021, India Solid State Physics Laboratory, Lucknow Road, Timarpur, Delhi 110054, India
a r t i c l e
i n f o
Article history: Received 27 February 2010 Received in revised form 22 April 2010 Accepted 28 April 2010 Keywords: Nanocrystalline powder High energy ball mill Sintering Ferroelectric Piezoelectric
a b s t r a c t Ba(Ti1−x Snx )O3 powders with particle size 77.48 nm has been obtained through high energy ball milling. A detailed TEM study confirms the particle size to be 77.48 nm. Electromechanical coupling constant (Kp ), piezoelectric strain constant (d33 ) and density follow decreasing trend with increasing tin concentration. As Sn concentration increases, ferroelectricity decreases with lower values of coercive field and remnant polarization, and this is due to replacement of Ti4+ ion by Sn4+ ion in the ABO3 structure of BaTiO3 . Considerable strain values have been observed with very low value of degree of hysteresis and this implies good applicability of the ceramics. © 2010 Elsevier B.V. All rights reserved.
1. Introduction As increasing demand for environmental protection, studies based on environmental friendly applications have therefore been performed in detail on different lead free ceramics such as BaTiO3 (BT) and its doped species on A and B sites of ABO3 perovskite structure. In recent years all-embracing efforts have been made to develop high quality lead free piezoelectric ceramics to replace toxic lead based materials. Barium titanate is one of the most widely studied lead free ferroelectric ceramics due to its excellent properties, high dielectric constant [1,2] and low loss characteristics [3]. However, the production and application of pure BaTiO3 are limited by poor dielectric temperature stability and high sintering temperature. By adding dopants interesting characteristics for various applications can be obtained [4–6]. Among the modified BaTiO3 compositions, the barium stannate titanate system has attracted considerable attention. Barium stannate titanate is a binary solid solution system composed of ferroelectric barium titanate and nonferroelectric barium stannate and this material system is one of the earliest prototypes of diffused phase transition study [7]. This material system may find applications for various purposes because the Curie temperature or dielectric maximum can be widely shifted by changing the Sn content. Du et al. studied different properties of barium stannate titanate ceramics with varying concentration of Sn [8]. However, piezo-
∗ Corresponding author. Tel.: +91 9899635179; fax: +91 1124118535. E-mail address: [email protected] (A.K. Nath). 0921-5107/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.mseb.2010.04.039
electric, ferroelectric and electrostrictive properties of this type of ceramics have not been studied properly. The works described by this paper includes synthesis of Ba(Ti1−x Snx )O3 nanopowder by solid state reaction followed by high energy ball milling and systemic studies on piezoelectric, ferroelectric and electrostrictive properties of these ceramics with varying concentration of Sn. 2. Experimental The Ba(Ti1−x Snx )O3 nanocrystalline powders were synthesized by solid state reaction followed by high energy ball milling. The raw materials were AR grade BaCO3 (99.9%), TiO2 (99.9) and SnO2 (99.8%). The raw materials were weighed in proportion to the stochiometric ratio and then homogeneously mixed in isopropyl alcohol medium using ball mill with Zirconia balls. The mixture was dried in an oven and calcined at 1050 ◦ C for 4 h to yield Ba(Ti1−x Snx )O3 where x = 0.025, 0.045, 0.065, 0.085 and 0.105. The calcined powders were then ball milled using high energy planetary ball mill (Retsch PM100). The milling was performed at 300 rpm for 8 h to get nanocrystalline powders. The powders were dried and pressed into pellets and densified to ceramics by sintering at temperature of 1350 ◦ C for 4 h. The particle sizes of the milled powders were determined by using TEM (Morgagni 268D). The density of the samples was measured using Archimedean method with an electronic balance. The hysteresis loops were traced by M/s AR Imagetronics, India. Dielectric properties have been studied by impedance analyzer (Agilent 4294A, Precision Impedance Analyzer). In order to study electrostrictive properties the field induced strain was measured using
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Fig. 2. Gaussian fitting of the particle size vs. frequency curve.
Fig. 1. A typical TEM micrograph of the milled powder of Ba(Ti1−x Snx )O3 system.
a SS50 strain measurement system (Sensor Tec Canada) with linear voltage differential transducer (LVDT) as displacement sensor and high voltage power supply (4 kV). The piezoelectric charge coefficient (d33 ) was measured with a piezometer (Take Control, PM 25). 3. Results and discussions 3.1. TEM study of nanocrystalline Ba(Ti1−x Snx )O3 powders As shown in Fig. 1 the TEM micrograph confirms the production of nanocrystalline Ba(Ti1−x Snx )O3 powders. The size of each particle has been calculated using ImageJ. The particle size varies from minimum of 69.64 nm to maximum of 90.43 nm with 78.57 nm size particle mostly occurring. The average particle size calculated using statistical formula has come out to be 78.23 nm. Furthermore in order to get a detailed view, a histogram of particle size versus particle frequency has been plotted with a Gaussian
fitting and is shown in Fig. 2. From the Gaussian fit of the histogram the mean particle size has been determined to be 77.48 nm with standard deviation of 4.93. The statistical average and Gaussian curve fitting thus provide almost the same particle size confirming that nanocrystalline Ba(Ti1−x Snx )O3 powders with average particle size of 77.48 nm have been produced. 3.2. XRD results Fig. 3 shows the X-ray diffraction patterns of Ba(Ti1−x Snx )O3 ceramics with x = 0.025, 0.045, 0.065, 0.085 and 0.105 at room temperature. It is seen that all the compositions are single phase perovskite structure. No trace of any secondary phase is detected. The enlarged XRD patterns of the ceramics in the range of 2 from 44◦ to 47◦ clearly show that the crystal structure of the ceramic possesses tetragonal structure for x = 0.025 and an orthorhombic structure for x = 0.045 and 0.065, with the splitting of the (2 0 0) and (0 0 2) characteristic peaks at a 2 of ∼45.5◦ [9–13]. The crystal has cubic structure for x = 0.085 and 0.105. Moreover, it is noted that the positions of the diffraction peaks of the ceramics shift slightly to lower angles with increasing x. This result is attributed to the
Fig. 3. XRD patters of Ba(Ti1−x Snx )O3 ceramics with (a) x = 0.025, (b) x = 0.045, (c) x = 0.065, (d) x = 0.085 and (e) x = 0.105.
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Fig. 6. Variation of Kp with concentration of Sn of Ba(Ti1−x Snx )O3 ceramics.
Fig. 4. P–E hysteresis curves of Ba(Ti1−x Snx )O3 with (a) x = 0.025, (b) x = 0.045, (c) x = 0.065, (d) x = 0.085 and (e) x = 0.105 measured at 25 ◦ C and 50 Hz. Table 1 Some properties of Ba(Ti1−x Snx )O3 ceramics. Parameter
x = 0.025
x = 0.045
Pr (C/cm2 ) Ec (kV/cm) Kp (%) d33 (pC/N) Relative density (%) Strain (%) Degree of hysteresis (%)
3.1 2.5 33.63 111 92.2 0.07 12
1.8 1.6 27.36 60 90.19 0.06 0.83
x = 0.065 0.3 0.8 19.27 4 86.46 0.023 1
greater ionic radius of Sn4+ (83.0 pm) than that of Ti4+ (74.5 pm), which gives rise to a small enlargement of cell volumes. 3.3. Variation of P–E hysteresis loop with Sn concentration
Fig. 7. Variation of d33 with concentration of Sn of Ba(Ti1−x Snx )O3 ceramics.
P–E hysteresis loop is an important characteristic of ferroelectrics. Fig. 4 shows the P–E hysteresis loops at room temperature of Ba(Ti1−x Snx )O3 ceramics. Well-saturated hysteresis shape typical of ferroelectric materials is evident for the ceramics with x = 0.025, 0.045 and 0.065. The P–E loops become narrower as the value of x increases and practically no loop is formed for x = 0.085 and 0.105 as these samples fall in paraelectric region, in agreement with the XRD results discussed earlier. The values of remnant polar-
ization (Pr ) and coercive field (Ec ), determined from the loops are summarized in Table 1. It is seen that Pr and Ec values follow a decreasing trend with increasing concentration of Sn. Barium stannate titanate is a binary solid solution composed of ferroelectric BaTiO3 and non-ferroelectric barium stannate [14,15]. The Sn4+ ion replaces the Ti4+ ion in BaTiO3 and consequently decreases the ferroelectric property.
Fig. 5. Frequency dependence of dielectric constant of Ba(Ti, Sn)O3 ceramics with (a) x = 0.025, (b) x = 0.045 and (c) x = 0.065.
Fig. 8. Variation of relative density with concentration of Sn of Ba(Ti1−x Snx )O3 ceramics.
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Fig. 10. Variation of degree of hysteresis with concentration of Sn of Ba(Ti1−x Snx )O3 ceramics.
in Fig. 5. From the measurement of resonant and antiresonant frequencies various piezoelectric constants can be extracted. The first resonance peaks occur at 355.41 kHz for all the concentrations but the first antiresonant peaks occur at 371.42, 366.01 and 360.67 kHz, respectively for x = 0.025, 0.045 and 0.065. Based on these data the electromechanical coupling coefficient Kp can be calculated by using the relation, Kp2 = 2.51 × (fa − fr )/fr where fa and fr are antiresonant and resonant frequencies [16]. The calculated Kp value decreases from 33.63% for x = 0.025 to 19.27% for x = 0.065 as given in Table 1, and the trend is shown graphically in Fig. 6. This observation indicates that the piezoelectric efficiency of the ceramic samples decreases with increasing Sn concentration. It has been found that the piezoelectric charge coefficient (d33 ) of Ba(Ti1−x Snx )O3 ceramics also follows the same trend as that of Kp as given in Table 1. The largest value is 111 pC/N obtained for x = 0.025. The variation of d33 with concentration is shown graphically in Fig. 7. The decreasing trend of d33 can be explained on the basis of decreasing density of the ceramics with increasing Sn concentration (shown in Fig. 8). We have thus observed that Kp , d33 and density follow the same decreasing trend with increasing concentration of Sn. 3.5. Electrostrictive strain properties
Fig. 9. (a) Strain vs. electric field variation curve of Ba(Ti1−x Snx )O3 ceramic with x = 0.025; (b) strain vs. electric field variation curve of Ba(Ti1−x Snx )O3 ceramic with x = 0.045; (c) strain vs. electric field variation curve of Ba(Ti1−x Snx )O3 ceramic with x = 0.065.
3.4. Variation of dielectric constant with frequency and piezoelectric constants The frequency dependence of the dielectric constant of the Ba(Ti1−x Snx )O3 ceramics with x = 0.025, 0.045 and 0.065 are shown
The bipolar strain (S) versus electric field (E) butterfly loops for Ba(Ti1−x Snx )O3 ceramics are shown in Fig. 9(a)–(c). It is seen that in the same manner as those of other properties, strain also decreases with increasing concentration of Sn. The maximum strain determined is 0.07% for x = 0.025 as given in Table 1. The reasonably high values of strain observed show the potential for piezoelectric applications of the ceramics. Moreover, the degree of hysteresis, which is the ratio of the strain deviation during the rise and fall with the field to the maximum strain at highest field, is also significantly less. The variation of degree of hysteresis with concentration is shown in Fig. 10. From Fig. 10, it is observed that degree of hysteresis decreases at first with increasing Sn and becomes minimum of 0.83% at x = 0.045. But on further increase of Sn, it increases and becomes 1% for x = 0.065. It suggests the existence of an optimum composition for tin doped barium titanate ceramics at which degree of hysteresis becomes minimum. This peculiar behavior may be related with not only the amount of tin content but with also the grain size of the ceramics. However, more work is required to be done to establish the actual reason behind this observation. From the point of view of applicability in positioning actuators, the ceramic sample with x = 0.045 has a promising
A.K. Nath et al. / Materials Science and Engineering B 172 (2010) 151–155
role as it has reasonably high value of strain and very less degree of hysteresis.
155
fully acknowledged. We also acknowledge the Director, Solid State Physics Laboratory and AIIMS Research Section, Delhi, for providing facilities for some measurements.
4. Conclusion References In this work we synthesize nanosize Ba(Ti1−x Snx )O3 powders with particle size of 77.48 nm. From this nanocrystalline powders ceramic samples have been prepared with varying concentration of Sn. The change in ferroelectric, piezoelectric and electrostrictive properties of Ba(Ti1−x Snx )O3 ceramics has been studied with varying x. The electromechanical coupling constant (Kp ) and piezoelectric strain constant (d33 ) values are found to decrease with higher values of Sn content. These results reveal that x = 0.025 corresponds to the best concentration for good dielectric and piezoelectric properties. The strain value is also maximum for x = 0.025, and with increasing x it decreases. The ceramic with x = 0.045 possessing the minimum degree of hysteresis (0.83%) and high strain (0.06%) has a potential for actuator applications where high strain as well as low degree of hysteresis is desirable. Acknowledgements The financial support from UGC of India in form of Major Research Project Scheme vide No. F. 33-25/2007 (SR) is grate-
[1] Z. Yu, R. Guo, A.S. Bhalla, J. Appl. Phys. 88 (2000) 410–415. [2] J. Zhao, L. Li, Y. Wang, Z. Gui, Mater. Sci. Eng. B 99 (2003) 207–210. [3] B.D. Stojanovic, C.R. Foschini, V.B. Pavlovic, V.M. Pavlovic, V. Pejovic, J.A. Varela, Ceram. Int. 28 (2002) 293–298. [4] B. Cui, P. Yu, J. Tian, H. Guo, Z. Chang, Mater. Sci. Eng. A 454–455 (2007) 667–672. [5] D. Voltzhe, H.P. Abicht, Solid State Sci. 2 (2000) 149–159. [6] B. Cui, P. Yui, J. Tian, Z. Chang, Mater. Sci. Eng. B 133 (2006) 205–208. [7] G.A. Smolensky, J. Phys. Soc. Jpn. 28 (1970) 26–37. [8] F. Du, B. Cui, H. Cheng, R. Niu, Z. Chang, Mater. Res. Bull. 44 (2009) 1930–1934. [9] D. Lin, K.W. Kwok, K.H. Lam, H.L.W. Chan, J. Appl. Phys. 101 (2007) 07411(1)–07411(6). [10] M. Matsubara, T. Yamaguchi, W. Sakamoto, K. Kikuta, T. Yogo, S. Hirano, J. Am. Ceram. Soc. 88 (2005) 1190–1196. [11] M. Matsubara, T. Yamaguchi, K. Kikuta, S. Hirano, Jpn. J. Appl. Phys. 44 (2005) 6136–6142. [12] M.N. Hagh, B. Jadidian, A. Safari, J. Electroceram. 18 (2007) 339–346. [13] G. Jiao, H. Fan, L. Liu, W. Wang, Mater. Lett. 61 (2007) 4185–4187. [14] X. Wei, X. Yao, Mater. Sci. Eng. B 137 (2007) 184–188. [15] S.G. Lu, Z.K. Xu, H. Chen, Appl. Phys. Lett. 85 (2004) 5319–5321. [16] T.F. Hueter, D.P. Neuhaus, J. Kolb, J. Acous. Soc. Am. 26 (1954) 696–703.
Contents lists available at ScienceDirect
Materials Science and Engineering B journal homepage: www.elsevier.com/locate/mseb
Ferroelectric, piezoelectric and electrostrictive properties of Ba(Ti1−x Snx )O3 ceramics obtained from nanocrystalline powder A.K. Nath a,∗ , K. Chandramani Singh a , Radhapiyari Laishram b , O.P. Thakur b a b
Department of Physics, Sri Venkateswara College, University of Delhi, New Delhi 110021, India Solid State Physics Laboratory, Lucknow Road, Timarpur, Delhi 110054, India
a r t i c l e
i n f o
Article history: Received 27 February 2010 Received in revised form 22 April 2010 Accepted 28 April 2010 Keywords: Nanocrystalline powder High energy ball mill Sintering Ferroelectric Piezoelectric
a b s t r a c t Ba(Ti1−x Snx )O3 powders with particle size 77.48 nm has been obtained through high energy ball milling. A detailed TEM study confirms the particle size to be 77.48 nm. Electromechanical coupling constant (Kp ), piezoelectric strain constant (d33 ) and density follow decreasing trend with increasing tin concentration. As Sn concentration increases, ferroelectricity decreases with lower values of coercive field and remnant polarization, and this is due to replacement of Ti4+ ion by Sn4+ ion in the ABO3 structure of BaTiO3 . Considerable strain values have been observed with very low value of degree of hysteresis and this implies good applicability of the ceramics. © 2010 Elsevier B.V. All rights reserved.
1. Introduction As increasing demand for environmental protection, studies based on environmental friendly applications have therefore been performed in detail on different lead free ceramics such as BaTiO3 (BT) and its doped species on A and B sites of ABO3 perovskite structure. In recent years all-embracing efforts have been made to develop high quality lead free piezoelectric ceramics to replace toxic lead based materials. Barium titanate is one of the most widely studied lead free ferroelectric ceramics due to its excellent properties, high dielectric constant [1,2] and low loss characteristics [3]. However, the production and application of pure BaTiO3 are limited by poor dielectric temperature stability and high sintering temperature. By adding dopants interesting characteristics for various applications can be obtained [4–6]. Among the modified BaTiO3 compositions, the barium stannate titanate system has attracted considerable attention. Barium stannate titanate is a binary solid solution system composed of ferroelectric barium titanate and nonferroelectric barium stannate and this material system is one of the earliest prototypes of diffused phase transition study [7]. This material system may find applications for various purposes because the Curie temperature or dielectric maximum can be widely shifted by changing the Sn content. Du et al. studied different properties of barium stannate titanate ceramics with varying concentration of Sn [8]. However, piezo-
∗ Corresponding author. Tel.: +91 9899635179; fax: +91 1124118535. E-mail address: [email protected] (A.K. Nath). 0921-5107/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.mseb.2010.04.039
electric, ferroelectric and electrostrictive properties of this type of ceramics have not been studied properly. The works described by this paper includes synthesis of Ba(Ti1−x Snx )O3 nanopowder by solid state reaction followed by high energy ball milling and systemic studies on piezoelectric, ferroelectric and electrostrictive properties of these ceramics with varying concentration of Sn. 2. Experimental The Ba(Ti1−x Snx )O3 nanocrystalline powders were synthesized by solid state reaction followed by high energy ball milling. The raw materials were AR grade BaCO3 (99.9%), TiO2 (99.9) and SnO2 (99.8%). The raw materials were weighed in proportion to the stochiometric ratio and then homogeneously mixed in isopropyl alcohol medium using ball mill with Zirconia balls. The mixture was dried in an oven and calcined at 1050 ◦ C for 4 h to yield Ba(Ti1−x Snx )O3 where x = 0.025, 0.045, 0.065, 0.085 and 0.105. The calcined powders were then ball milled using high energy planetary ball mill (Retsch PM100). The milling was performed at 300 rpm for 8 h to get nanocrystalline powders. The powders were dried and pressed into pellets and densified to ceramics by sintering at temperature of 1350 ◦ C for 4 h. The particle sizes of the milled powders were determined by using TEM (Morgagni 268D). The density of the samples was measured using Archimedean method with an electronic balance. The hysteresis loops were traced by M/s AR Imagetronics, India. Dielectric properties have been studied by impedance analyzer (Agilent 4294A, Precision Impedance Analyzer). In order to study electrostrictive properties the field induced strain was measured using
152
A.K. Nath et al. / Materials Science and Engineering B 172 (2010) 151–155
Fig. 2. Gaussian fitting of the particle size vs. frequency curve.
Fig. 1. A typical TEM micrograph of the milled powder of Ba(Ti1−x Snx )O3 system.
a SS50 strain measurement system (Sensor Tec Canada) with linear voltage differential transducer (LVDT) as displacement sensor and high voltage power supply (4 kV). The piezoelectric charge coefficient (d33 ) was measured with a piezometer (Take Control, PM 25). 3. Results and discussions 3.1. TEM study of nanocrystalline Ba(Ti1−x Snx )O3 powders As shown in Fig. 1 the TEM micrograph confirms the production of nanocrystalline Ba(Ti1−x Snx )O3 powders. The size of each particle has been calculated using ImageJ. The particle size varies from minimum of 69.64 nm to maximum of 90.43 nm with 78.57 nm size particle mostly occurring. The average particle size calculated using statistical formula has come out to be 78.23 nm. Furthermore in order to get a detailed view, a histogram of particle size versus particle frequency has been plotted with a Gaussian
fitting and is shown in Fig. 2. From the Gaussian fit of the histogram the mean particle size has been determined to be 77.48 nm with standard deviation of 4.93. The statistical average and Gaussian curve fitting thus provide almost the same particle size confirming that nanocrystalline Ba(Ti1−x Snx )O3 powders with average particle size of 77.48 nm have been produced. 3.2. XRD results Fig. 3 shows the X-ray diffraction patterns of Ba(Ti1−x Snx )O3 ceramics with x = 0.025, 0.045, 0.065, 0.085 and 0.105 at room temperature. It is seen that all the compositions are single phase perovskite structure. No trace of any secondary phase is detected. The enlarged XRD patterns of the ceramics in the range of 2 from 44◦ to 47◦ clearly show that the crystal structure of the ceramic possesses tetragonal structure for x = 0.025 and an orthorhombic structure for x = 0.045 and 0.065, with the splitting of the (2 0 0) and (0 0 2) characteristic peaks at a 2 of ∼45.5◦ [9–13]. The crystal has cubic structure for x = 0.085 and 0.105. Moreover, it is noted that the positions of the diffraction peaks of the ceramics shift slightly to lower angles with increasing x. This result is attributed to the
Fig. 3. XRD patters of Ba(Ti1−x Snx )O3 ceramics with (a) x = 0.025, (b) x = 0.045, (c) x = 0.065, (d) x = 0.085 and (e) x = 0.105.
A.K. Nath et al. / Materials Science and Engineering B 172 (2010) 151–155
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Fig. 6. Variation of Kp with concentration of Sn of Ba(Ti1−x Snx )O3 ceramics.
Fig. 4. P–E hysteresis curves of Ba(Ti1−x Snx )O3 with (a) x = 0.025, (b) x = 0.045, (c) x = 0.065, (d) x = 0.085 and (e) x = 0.105 measured at 25 ◦ C and 50 Hz. Table 1 Some properties of Ba(Ti1−x Snx )O3 ceramics. Parameter
x = 0.025
x = 0.045
Pr (C/cm2 ) Ec (kV/cm) Kp (%) d33 (pC/N) Relative density (%) Strain (%) Degree of hysteresis (%)
3.1 2.5 33.63 111 92.2 0.07 12
1.8 1.6 27.36 60 90.19 0.06 0.83
x = 0.065 0.3 0.8 19.27 4 86.46 0.023 1
greater ionic radius of Sn4+ (83.0 pm) than that of Ti4+ (74.5 pm), which gives rise to a small enlargement of cell volumes. 3.3. Variation of P–E hysteresis loop with Sn concentration
Fig. 7. Variation of d33 with concentration of Sn of Ba(Ti1−x Snx )O3 ceramics.
P–E hysteresis loop is an important characteristic of ferroelectrics. Fig. 4 shows the P–E hysteresis loops at room temperature of Ba(Ti1−x Snx )O3 ceramics. Well-saturated hysteresis shape typical of ferroelectric materials is evident for the ceramics with x = 0.025, 0.045 and 0.065. The P–E loops become narrower as the value of x increases and practically no loop is formed for x = 0.085 and 0.105 as these samples fall in paraelectric region, in agreement with the XRD results discussed earlier. The values of remnant polar-
ization (Pr ) and coercive field (Ec ), determined from the loops are summarized in Table 1. It is seen that Pr and Ec values follow a decreasing trend with increasing concentration of Sn. Barium stannate titanate is a binary solid solution composed of ferroelectric BaTiO3 and non-ferroelectric barium stannate [14,15]. The Sn4+ ion replaces the Ti4+ ion in BaTiO3 and consequently decreases the ferroelectric property.
Fig. 5. Frequency dependence of dielectric constant of Ba(Ti, Sn)O3 ceramics with (a) x = 0.025, (b) x = 0.045 and (c) x = 0.065.
Fig. 8. Variation of relative density with concentration of Sn of Ba(Ti1−x Snx )O3 ceramics.
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A.K. Nath et al. / Materials Science and Engineering B 172 (2010) 151–155
Fig. 10. Variation of degree of hysteresis with concentration of Sn of Ba(Ti1−x Snx )O3 ceramics.
in Fig. 5. From the measurement of resonant and antiresonant frequencies various piezoelectric constants can be extracted. The first resonance peaks occur at 355.41 kHz for all the concentrations but the first antiresonant peaks occur at 371.42, 366.01 and 360.67 kHz, respectively for x = 0.025, 0.045 and 0.065. Based on these data the electromechanical coupling coefficient Kp can be calculated by using the relation, Kp2 = 2.51 × (fa − fr )/fr where fa and fr are antiresonant and resonant frequencies [16]. The calculated Kp value decreases from 33.63% for x = 0.025 to 19.27% for x = 0.065 as given in Table 1, and the trend is shown graphically in Fig. 6. This observation indicates that the piezoelectric efficiency of the ceramic samples decreases with increasing Sn concentration. It has been found that the piezoelectric charge coefficient (d33 ) of Ba(Ti1−x Snx )O3 ceramics also follows the same trend as that of Kp as given in Table 1. The largest value is 111 pC/N obtained for x = 0.025. The variation of d33 with concentration is shown graphically in Fig. 7. The decreasing trend of d33 can be explained on the basis of decreasing density of the ceramics with increasing Sn concentration (shown in Fig. 8). We have thus observed that Kp , d33 and density follow the same decreasing trend with increasing concentration of Sn. 3.5. Electrostrictive strain properties
Fig. 9. (a) Strain vs. electric field variation curve of Ba(Ti1−x Snx )O3 ceramic with x = 0.025; (b) strain vs. electric field variation curve of Ba(Ti1−x Snx )O3 ceramic with x = 0.045; (c) strain vs. electric field variation curve of Ba(Ti1−x Snx )O3 ceramic with x = 0.065.
3.4. Variation of dielectric constant with frequency and piezoelectric constants The frequency dependence of the dielectric constant of the Ba(Ti1−x Snx )O3 ceramics with x = 0.025, 0.045 and 0.065 are shown
The bipolar strain (S) versus electric field (E) butterfly loops for Ba(Ti1−x Snx )O3 ceramics are shown in Fig. 9(a)–(c). It is seen that in the same manner as those of other properties, strain also decreases with increasing concentration of Sn. The maximum strain determined is 0.07% for x = 0.025 as given in Table 1. The reasonably high values of strain observed show the potential for piezoelectric applications of the ceramics. Moreover, the degree of hysteresis, which is the ratio of the strain deviation during the rise and fall with the field to the maximum strain at highest field, is also significantly less. The variation of degree of hysteresis with concentration is shown in Fig. 10. From Fig. 10, it is observed that degree of hysteresis decreases at first with increasing Sn and becomes minimum of 0.83% at x = 0.045. But on further increase of Sn, it increases and becomes 1% for x = 0.065. It suggests the existence of an optimum composition for tin doped barium titanate ceramics at which degree of hysteresis becomes minimum. This peculiar behavior may be related with not only the amount of tin content but with also the grain size of the ceramics. However, more work is required to be done to establish the actual reason behind this observation. From the point of view of applicability in positioning actuators, the ceramic sample with x = 0.045 has a promising
A.K. Nath et al. / Materials Science and Engineering B 172 (2010) 151–155
role as it has reasonably high value of strain and very less degree of hysteresis.
155
fully acknowledged. We also acknowledge the Director, Solid State Physics Laboratory and AIIMS Research Section, Delhi, for providing facilities for some measurements.
4. Conclusion References In this work we synthesize nanosize Ba(Ti1−x Snx )O3 powders with particle size of 77.48 nm. From this nanocrystalline powders ceramic samples have been prepared with varying concentration of Sn. The change in ferroelectric, piezoelectric and electrostrictive properties of Ba(Ti1−x Snx )O3 ceramics has been studied with varying x. The electromechanical coupling constant (Kp ) and piezoelectric strain constant (d33 ) values are found to decrease with higher values of Sn content. These results reveal that x = 0.025 corresponds to the best concentration for good dielectric and piezoelectric properties. The strain value is also maximum for x = 0.025, and with increasing x it decreases. The ceramic with x = 0.045 possessing the minimum degree of hysteresis (0.83%) and high strain (0.06%) has a potential for actuator applications where high strain as well as low degree of hysteresis is desirable. Acknowledgements The financial support from UGC of India in form of Major Research Project Scheme vide No. F. 33-25/2007 (SR) is grate-
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