- Email: [email protected]
Effect of substitution of Pb on ferroelectric and piezoelectric properties BZT ceramics
Materials Letters 146 (2015) 40–42
Contents lists available at ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/matlet
Effect of substitution of Pb on ferroelectric and piezoelectric properties BZT ceramics Parveen Kumar a,n, Sangeeta Singh b, J.K. Juneja c, Chandra Prakash d, K.K. Raina e a
Department of Physics, DIT University, Dehradun 248009, India Department of Physics, GVM Girls College, Sonepat 131001, India c Department of Physics, Hindu College, Sonepat 131001, India d Solid State Physics Laboratory, Lucknow Road, Delhi 110054, India e DIT University, Dehradun 248009, India b
art ic l e i nf o
a b s t r a c t
Article history: Received 10 December 2014 Accepted 31 January 2015 Available online 11 February 2015
Material series with compositional formula Ba1 xPbxTi0.90Zr0.10O3 was prepared by the conventional solid state reaction method. Pb content varied from 0 to 20 mol% in the steps of 5 mol%. Relative density and coercive field ‘Ec’ increases with increase in Pb content. The variation of Ec and the ratio of remanent to spontaneous polarization ‘Pr/Ps’ with temperature shows a ferroelectric to paraelectric phase transition. Piezoelectric charge coefficient ‘d33’ was found to have significant improvement with increase in Pb content upto 10 mol%, while for higher Pb content it decreases. Thus, the effect of Pb substitution on the physical, ferroelectric and piezoelectric properties of the prepared ceramics is discussed here. & 2015 Elsevier B.V. All rights reserved.
Keywords: Barium titanate BZT Ferroelectrics Piezoelectrics
1. Introduction In the field of electroceramics, barium titanate (BT) based ferroelectric ceramics have an immense contribution due to their special characteristics like high dielectric constant, low loss, high electromechanical coupling factor and obviously its good piezoelectric properties [1,2]. Moreover, different substituents for lattice sites (Ba and Ti) can be used for tailoring its properties. Isovalent ions (like Zr4 þ , Sn4 þ , Mn4 þ for Ti4 þ and Pb2 þ , Sr2 þ , Ca2 þ for Ba2 þ ) and aliovalent ions (like Mn3 þ , Nb5 þ , Fe3 þ for Ti4 þ and Sm3 þ ,La3 þ , Pr3 þ , Gd3 þ for Ba2 þ ) can result in modification of properties making it useful for various applications like MLCC, PTCR, FRAMS, and sensors [3–8]. For the present study, a BT-based composition with formula Ba1 xPbxTi0.90Zr0.10O3 (0 rx r0.20, in steps of 0.05) was selected. We have earlier reported the influence of Pb substitution on the structural and dielectric properties [9]. Effect of Pb substitution on the physical, ferroelectric and piezoelectric properties was studied and discussed here.
2. Experimental Ceramic samples with compositional formula Ba1 xPbxTi0.90 Zr0.10O3 (0rxr0.20, in steps of 0.05) were prepared by the n
Corresponding author. Mobile: þ 91 999 666 0707. E-mail address: [email protected] (P. Kumar).
http://dx.doi.org/10.1016/j.matlet.2015.01.160 0167-577X/& 2015 Elsevier B.V. All rights reserved.
conventional solid state reaction method. The details of the experimentation about synthesis have been discussed in our earlier publication [9]. PE hysteresis loops were recorded at different temperatures. Piezoelectric charge constant d33 was measured by using Piezometer system of Concord Electroceramics Ind., India.
3. Results and discussion Fig. 1 represents the variation relative density and volume of the lattice cell with x. Although the unit cell volume increases with increase in x, relative density also increases because of high density of PbO. Tetragonality (c/a) was also found to increase with increase in Pb [9]. Well saturated PE loops for all x are shown in Fig. 2. Increasing width of loop with x indicates that Pb2 þ is acting as hardener for the selected BZT system, i.e., coercive field increases. The increase in coercive field indicates the formation of 901 domains in the material with Pb substitution. The variation of coercive field (Ec), remanent polarization (Pr) and remanent to spontaneous polarization (Pr/Ps) with x is shown in Fig. 2. The increase–decrease in Pr and Pr/Ps may be due to transition in phase of the material from rhombohedral to tetragonal and other intrinsic factors like dipole moment and grain size etc. [9,10]. Fig. 3(a and b) shows the variation of Ec and Pr/Ps with temperature for all x. However, a decreasing trend in Ec could be noticed for x ¼0, which indicates that the dipoles are becoming less stable with increase in temperature. While, for further values of x this
P. Kumar et al. / Materials Letters 146 (2015) 40–42
decrease is prominent only at higher temperatures (as T approaches Tc). This may be due to presence of 901 domains, which can be perturbed only at higher temperatures. Thus all the prepared materials soften after heating. The increase in Pr/Ps is mainly due to increase in internal energy caused by thermal
64.9 64.8
86
64.7
84
64.6
82 64.5
80
64.4
78 0.00
0.05
0.10
0.15
0.20
x Fig. 1. Relative density and unit cell volume vs x.
x=0
15
x = 0.05
15
10
10
5
5
2
P (µC/cm )
0 -5
0 -5
-10
-10
-15
-15
-20
-20 -30
-20
-10
0
10
20
-30
30
-20
-10
15
15
10
10 P (µC/cm )
5
2
2
P (µC/cm )
x = 0.10
0 -5
20
30
x = 0.15
5 0 -5
-10
-10
-15
-15
-20
-20 -30
-20
-10
0
10
20
30
-30
-20
-10
E (kV/cm)
0
10
20
30
E (kV/cm)
20
0.48
10
x = 0.20
Pr /Ps 2
Ec (kV/cm), Pr (µC/cm )
10 2
10
20
20
15
0 E (kV/cm)
E (kV/cm)
5 0 -5 -10 -15
8
0.46
Pr
0.44
6
0.42 0.40
4 Ec
0.38
2
-20
0.36 -30
-20
-10
0 E (kV/cm)
10
20
30
0.00
0.05
0.10 x
Fig. 2. P–E loops at 30 1C for all x and variation of Ec, Pr and Pr/Ps with x.
0.15
0.20
Pr /Ps
2
P (µC/cm )
excitation leading to greater dipole alignment [11]. Thus the value of Ec and Pr/Ps falls with increase in temperature and indicates that the phase is changing from ferroelectric to paraelectric. Piezoelectric charge coefficient ‘d33’ and planar electromechanical coupling factor ‘kp’ was found to vary with x as given in Fig. 4. Improvement in d33 was observed with increase in x. However, kp values remain smaller and changes in an irregular way. The charge coefficient ‘d33’ increases sharply as x increases to 0.05, while above x¼ 0.05 there is a very small increase. Since the piezoelectric properties are strongly depend on microstructure. The sharp increase in ‘d33’ can be related to density variation. Relative density increases sharply up to x¼ 0.05 and then for further values it increases in small amount. In general there are two kinds of factors, intrinsic (related to lattice cell deformations) and extrinsic factors (domain wall motion, grain boundary, etc.) affect the piezoelectric properties [12–14]. However with increase in tetragonality the internal stresses increases and favors the dipole formation. Also the ceramic samples are sintered at 1300 1C. Thus, the small increase in relative density and d33 above x¼ 0.05 can be related to the increasing amount of Pb, which causes increase in density of Pb vacancies at the grain boundaries in comparison to grain body. The increase in
20
20
P (µC/cm )
Relative density (%)
88
-24 Unit cell volume (x10 cm3 )
90
41
42
P. Kumar et al. / Materials Letters 146 (2015) 40–42
0.6
10 x=0 0.05 0.10 0.15 0.20
6
0.5 0.4 Pr/Ps
Ec (kV/cm)
8
0.3
4 x=0 0.05 0.10 0.15 0.20
0.2 2
0.1 40
60
80
100
120
140
160
40
60
80
100
120
140
160
o
T ( C)
o
T ( C) Fig. 3. (a) Variation of Ec and, (b) Pr/Ps with T for all x.
with temperature. Phase transition could be noticed by variation of Ec and Pr/Ps ratio with temperature. Piezoelectric charge coefficient ‘d33’ improves with Pb content.
16 140 14
120
d33
12
80
kp (%)
100
10 60 8
40 0.00
0.05
0.10
0.15
0.20
x Fig. 4. Variation of d33 and kp with x.
density of vacant sites at grain boundaries may also be responsible for increase–decrease in kp. Thus we can say that extrinsic factors dominate for higher values of x. 4. Conclusion Pb substituted BZT ceramics shows relative density with increase in Pb content. Coercive field increases with Pb content and decreases
References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14]
Uchino K. Ferroelectric devices. New York: Marcel Dekker; 2000. Haertling GH. J Am Ceram Soc 1999;82:797–818. Chou X, Zhai J, Sun J, Yao X. Ferroelectrics 2007;356:13–8. Hennings D, Schnell A, Simon G. J Am Ceram Soc 1982;65:539–44. Wang Y, Li L, Qi J, Gui Z. Ceram Int 2002;28:657–61. Kishi H, Kohzu N, Sugino J, Ohsato H, Iguchi Y, Okuda T. J Eur Ceram Soc 1999;19:1043–6. Shirasaki S, Tshukioka M, Yamamura H, Oshima H. Solid State Commun 1976;19:721–4. Chen XM, Wang T, Li J. Mater Sci Eng B 2004;113:117–20. Kumar Parveen, Singh Sangeeta, Juneja JK, Chandra Prakash, Raina KK. Bull Mat Sci 2011;34:1401–5. Kamel TM, de With G. J Eur Ceram Soc 2008;28:851–61. Carl K. Ferroelectrics 1975;9:23–32. Cao W, Randall CA. J Phys Chem Solids 1996;57:1499–505. Zhang QM, Wang H, Kim N, Cross LE. J Appl Phys 1994;75:454–9. Zhang XL, Chen ZX, Cross LE, Schulze WA. J Mater Sci 1983;18:968–71.
Contents lists available at ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/matlet
Effect of substitution of Pb on ferroelectric and piezoelectric properties BZT ceramics Parveen Kumar a,n, Sangeeta Singh b, J.K. Juneja c, Chandra Prakash d, K.K. Raina e a
Department of Physics, DIT University, Dehradun 248009, India Department of Physics, GVM Girls College, Sonepat 131001, India c Department of Physics, Hindu College, Sonepat 131001, India d Solid State Physics Laboratory, Lucknow Road, Delhi 110054, India e DIT University, Dehradun 248009, India b
art ic l e i nf o
a b s t r a c t
Article history: Received 10 December 2014 Accepted 31 January 2015 Available online 11 February 2015
Material series with compositional formula Ba1 xPbxTi0.90Zr0.10O3 was prepared by the conventional solid state reaction method. Pb content varied from 0 to 20 mol% in the steps of 5 mol%. Relative density and coercive field ‘Ec’ increases with increase in Pb content. The variation of Ec and the ratio of remanent to spontaneous polarization ‘Pr/Ps’ with temperature shows a ferroelectric to paraelectric phase transition. Piezoelectric charge coefficient ‘d33’ was found to have significant improvement with increase in Pb content upto 10 mol%, while for higher Pb content it decreases. Thus, the effect of Pb substitution on the physical, ferroelectric and piezoelectric properties of the prepared ceramics is discussed here. & 2015 Elsevier B.V. All rights reserved.
Keywords: Barium titanate BZT Ferroelectrics Piezoelectrics
1. Introduction In the field of electroceramics, barium titanate (BT) based ferroelectric ceramics have an immense contribution due to their special characteristics like high dielectric constant, low loss, high electromechanical coupling factor and obviously its good piezoelectric properties [1,2]. Moreover, different substituents for lattice sites (Ba and Ti) can be used for tailoring its properties. Isovalent ions (like Zr4 þ , Sn4 þ , Mn4 þ for Ti4 þ and Pb2 þ , Sr2 þ , Ca2 þ for Ba2 þ ) and aliovalent ions (like Mn3 þ , Nb5 þ , Fe3 þ for Ti4 þ and Sm3 þ ,La3 þ , Pr3 þ , Gd3 þ for Ba2 þ ) can result in modification of properties making it useful for various applications like MLCC, PTCR, FRAMS, and sensors [3–8]. For the present study, a BT-based composition with formula Ba1 xPbxTi0.90Zr0.10O3 (0 rx r0.20, in steps of 0.05) was selected. We have earlier reported the influence of Pb substitution on the structural and dielectric properties [9]. Effect of Pb substitution on the physical, ferroelectric and piezoelectric properties was studied and discussed here.
2. Experimental Ceramic samples with compositional formula Ba1 xPbxTi0.90 Zr0.10O3 (0rxr0.20, in steps of 0.05) were prepared by the n
Corresponding author. Mobile: þ 91 999 666 0707. E-mail address: [email protected] (P. Kumar).
http://dx.doi.org/10.1016/j.matlet.2015.01.160 0167-577X/& 2015 Elsevier B.V. All rights reserved.
conventional solid state reaction method. The details of the experimentation about synthesis have been discussed in our earlier publication [9]. PE hysteresis loops were recorded at different temperatures. Piezoelectric charge constant d33 was measured by using Piezometer system of Concord Electroceramics Ind., India.
3. Results and discussion Fig. 1 represents the variation relative density and volume of the lattice cell with x. Although the unit cell volume increases with increase in x, relative density also increases because of high density of PbO. Tetragonality (c/a) was also found to increase with increase in Pb [9]. Well saturated PE loops for all x are shown in Fig. 2. Increasing width of loop with x indicates that Pb2 þ is acting as hardener for the selected BZT system, i.e., coercive field increases. The increase in coercive field indicates the formation of 901 domains in the material with Pb substitution. The variation of coercive field (Ec), remanent polarization (Pr) and remanent to spontaneous polarization (Pr/Ps) with x is shown in Fig. 2. The increase–decrease in Pr and Pr/Ps may be due to transition in phase of the material from rhombohedral to tetragonal and other intrinsic factors like dipole moment and grain size etc. [9,10]. Fig. 3(a and b) shows the variation of Ec and Pr/Ps with temperature for all x. However, a decreasing trend in Ec could be noticed for x ¼0, which indicates that the dipoles are becoming less stable with increase in temperature. While, for further values of x this
P. Kumar et al. / Materials Letters 146 (2015) 40–42
decrease is prominent only at higher temperatures (as T approaches Tc). This may be due to presence of 901 domains, which can be perturbed only at higher temperatures. Thus all the prepared materials soften after heating. The increase in Pr/Ps is mainly due to increase in internal energy caused by thermal
64.9 64.8
86
64.7
84
64.6
82 64.5
80
64.4
78 0.00
0.05
0.10
0.15
0.20
x Fig. 1. Relative density and unit cell volume vs x.
x=0
15
x = 0.05
15
10
10
5
5
2
P (µC/cm )
0 -5
0 -5
-10
-10
-15
-15
-20
-20 -30
-20
-10
0
10
20
-30
30
-20
-10
15
15
10
10 P (µC/cm )
5
2
2
P (µC/cm )
x = 0.10
0 -5
20
30
x = 0.15
5 0 -5
-10
-10
-15
-15
-20
-20 -30
-20
-10
0
10
20
30
-30
-20
-10
E (kV/cm)
0
10
20
30
E (kV/cm)
20
0.48
10
x = 0.20
Pr /Ps 2
Ec (kV/cm), Pr (µC/cm )
10 2
10
20
20
15
0 E (kV/cm)
E (kV/cm)
5 0 -5 -10 -15
8
0.46
Pr
0.44
6
0.42 0.40
4 Ec
0.38
2
-20
0.36 -30
-20
-10
0 E (kV/cm)
10
20
30
0.00
0.05
0.10 x
Fig. 2. P–E loops at 30 1C for all x and variation of Ec, Pr and Pr/Ps with x.
0.15
0.20
Pr /Ps
2
P (µC/cm )
excitation leading to greater dipole alignment [11]. Thus the value of Ec and Pr/Ps falls with increase in temperature and indicates that the phase is changing from ferroelectric to paraelectric. Piezoelectric charge coefficient ‘d33’ and planar electromechanical coupling factor ‘kp’ was found to vary with x as given in Fig. 4. Improvement in d33 was observed with increase in x. However, kp values remain smaller and changes in an irregular way. The charge coefficient ‘d33’ increases sharply as x increases to 0.05, while above x¼ 0.05 there is a very small increase. Since the piezoelectric properties are strongly depend on microstructure. The sharp increase in ‘d33’ can be related to density variation. Relative density increases sharply up to x¼ 0.05 and then for further values it increases in small amount. In general there are two kinds of factors, intrinsic (related to lattice cell deformations) and extrinsic factors (domain wall motion, grain boundary, etc.) affect the piezoelectric properties [12–14]. However with increase in tetragonality the internal stresses increases and favors the dipole formation. Also the ceramic samples are sintered at 1300 1C. Thus, the small increase in relative density and d33 above x¼ 0.05 can be related to the increasing amount of Pb, which causes increase in density of Pb vacancies at the grain boundaries in comparison to grain body. The increase in
20
20
P (µC/cm )
Relative density (%)
88
-24 Unit cell volume (x10 cm3 )
90
41
42
P. Kumar et al. / Materials Letters 146 (2015) 40–42
0.6
10 x=0 0.05 0.10 0.15 0.20
6
0.5 0.4 Pr/Ps
Ec (kV/cm)
8
0.3
4 x=0 0.05 0.10 0.15 0.20
0.2 2
0.1 40
60
80
100
120
140
160
40
60
80
100
120
140
160
o
T ( C)
o
T ( C) Fig. 3. (a) Variation of Ec and, (b) Pr/Ps with T for all x.
with temperature. Phase transition could be noticed by variation of Ec and Pr/Ps ratio with temperature. Piezoelectric charge coefficient ‘d33’ improves with Pb content.
16 140 14
120
d33
12
80
kp (%)
100
10 60 8
40 0.00
0.05
0.10
0.15
0.20
x Fig. 4. Variation of d33 and kp with x.
density of vacant sites at grain boundaries may also be responsible for increase–decrease in kp. Thus we can say that extrinsic factors dominate for higher values of x. 4. Conclusion Pb substituted BZT ceramics shows relative density with increase in Pb content. Coercive field increases with Pb content and decreases
References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14]
Uchino K. Ferroelectric devices. New York: Marcel Dekker; 2000. Haertling GH. J Am Ceram Soc 1999;82:797–818. Chou X, Zhai J, Sun J, Yao X. Ferroelectrics 2007;356:13–8. Hennings D, Schnell A, Simon G. J Am Ceram Soc 1982;65:539–44. Wang Y, Li L, Qi J, Gui Z. Ceram Int 2002;28:657–61. Kishi H, Kohzu N, Sugino J, Ohsato H, Iguchi Y, Okuda T. J Eur Ceram Soc 1999;19:1043–6. Shirasaki S, Tshukioka M, Yamamura H, Oshima H. Solid State Commun 1976;19:721–4. Chen XM, Wang T, Li J. Mater Sci Eng B 2004;113:117–20. Kumar Parveen, Singh Sangeeta, Juneja JK, Chandra Prakash, Raina KK. Bull Mat Sci 2011;34:1401–5. Kamel TM, de With G. J Eur Ceram Soc 2008;28:851–61. Carl K. Ferroelectrics 1975;9:23–32. Cao W, Randall CA. J Phys Chem Solids 1996;57:1499–505. Zhang QM, Wang H, Kim N, Cross LE. J Appl Phys 1994;75:454–9. Zhang XL, Chen ZX, Cross LE, Schulze WA. J Mater Sci 1983;18:968–71.