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Diffuse phase transition in (Na,Bi)-doped PbSnxTi1−x O3 ferroelectric ceramics
PERGAMON
Solid State Communications 112 (1999) 219–221 www.elsevier.com/locate/ssc
Diffuse phase transition in (Na,Bi)-doped PbSnxTi12x O3 ferroelectric ceramics F. Caldero´n a,*, J.M. Siqueiros b, J. Portelles a, b, J.L. Heiras b a
b
Facultad de Fı´sica-IMRE, Universidad de La Habana, San La´zaro y L, 10400, Vedado, Cuba Centro de Ciencias de la Materia Condensada, UNAM, Apartado Postal 2681, Ensenada, BC, 22800, Mexico Received 24 May 1999; accepted 21 June 1999 by R.C. Dynes
Abstract The temperature dependence of the dielectric behavior of Pb0.85(Na0.5Bi0.5)0.15SnxTi12x O3 (PSNB) with x 0:40; 0:45; 0:50; 0:55; 0:60 has been investigated. A careful analysis of the dielectric properties reveals a relaxor behavior near Tc where the diffuseness parameter (d ) increases as the content of Sn 41. It is observed that the temperature of the permittivity maximum shifts toward lower temperatures and the permittivity maximum decreases with the increase of Sn content in the PSNB solid solutions. The diffuseness (d ) and deformation structure (g ) parameters were determined for each composition using the results of the dielectric measurements and experimental lattice constant values. q 1999 Elsevier Science Ltd. All rights reserved. Keywords: A. Ferroelectrics; D. Phase transitions
1. Introduction Relaxor ferroelectrics are characterized by a diffuse phase transition (DPT). The complex perovskite PbMg1/3Nb2/3O3 is just one of many relaxors that have been extensively studied [1]. In the early stages of ferroelectric research the BaTiO3 – BaSnO3 (BSN) [2] solid solutions established that the peaks of the dielectric permittivity (e ) notably broadened as the SnO2 concentration increased. Even today, the theory of Smolensky–Isupov remains a good approach for describing the behavior of these materials together with the superparaelectric theory proposed by Cross [1]. The experimental results reported in this study point to a quadratic dependence of the reciprocal dielectric permittivity 1=1 2 1=1m versus temperature (T), although valid only in the region where the DPT exists due to small interacting polarized regions. The normal Curie–Weiss law will hold at higher temperatures [3]. Experimental data have been reported previously for a number of compounds, e.g. PMN, PMN-PT and PLZT [4]. According to the main ideas of Bokov [4] and Zhi [5], in the case of BSN, the ferroactive ion is in the B site (Ti 41) of the unit cell * Corresponding author.
while in PbTiO3 it is in the A site (Pb 21). In the present work, a systematic study of the samples with nominal composition Pb0.85(Na0.5Bi0.5)0.15Ti12x SnxO3 (PSNB) in the x 0:40 to x 0:60 range was carried out following the same line of reasoning, i.e. such cationic substitution would induce a relaxor behavior state in the modified PSN samples.
2. Experimental procedure The samples were prepared using the standard ceramic method. The mixture of constituent powders was ball-milled in ethanol, dried, and calcined at 6008C for 1 h, 7008C for 1 h and 8008C for 2 h, respectively. The dried powder was then granulated with 10 wt% polyvinyl alcohol binder in water media. After passing the mixture through a 100 mesh sieve, 10 mm disks were cold pressed in a steel die at 100 Mpa. All measured samples were sintered at 10008C for 1 h. To control PbO loss from the pellets, a compensating PbZrO3 atmosphere was maintained inside a covered platinum crucible where the sintering process was performed. The weight loss during these preparation stages was carefully monitored.
0038-1098/99/$ - see front matter q 1999 Elsevier Science Ltd. All rights reserved. PII: S0038-109 8(99)00314-2
F. Caldero´n et al. / Solid State Communications 112 (1999) 219–221
220
Table 1 Lattice parameters and crystalline structure of Pb0.85(Na0.5Bi0.5)0.15Ti12x SnxO3
Table 2 Relevant parameters for PSNB for all the compositions studied x
x
˚) a (A
˚) c (A
Structure
c/a
0.40 0.45 0.50 0.55 0.60
3.980 3.989 3.993 4.013 4.020
4.059 4.053 4.046 4.033
Tetragonal Tetragonal Tetragonal Tetragonal 1 rombohedral Rombohedral
1.019 1.016 1.013 1.004
XRD studies of the samples were performed over the 208 , 2u , 608 angular range in 0.028 steps. Samples for dielectric measurements were prepared from the sintered pellets by polishing the major faces. The dielectric permittivity versus temperature was measured using a Tesla model E7-9 LCR meter, at 1 kHz and the transition temperatures Tc were determined from the maximum of these curves.
3. Results and discussion The XRD patterns of the calcined samples evidenced the presence of residual PbO in all of the samples. However, the sintered samples were found to be pure perovskite. In Table 1, the lattice parameters and corresponding crystalline structure for the different compositions are presented: the PbTiO3-rich solid solutions have a tetragonal structure with decreasing c/a ratio as the Sn 41 concentration increases. The behavior of the relative dielectric permittivity (e ) versus temperature of the PSNB at 500 kHz, for all compositions, is shown in Fig. 1. The maximum value of the dielectric permittivity decreases with Sn concentration (x). The expression for the diffuseness (d ) can be determined
em d (8C) em d2 × 106 Tc (8C)
0.40
0.45
0.50
0.55
0.60
8891 35 10 256
8423 45 17 226
8865 46 18 199
5259 60 18 167
3200 66 13 154
[6] from the slope of the equation 1 1 T 2 Tc 2 1 1 1m 2d2 1m The parameter d (see Table 2) increases systematically from x 0 to x 60; indicating that the cationic disorder in the perovskite structure increases. The observed increase in the width of dielectric response reflects a gradual increase in the relaxor characteristics as proposed earlier. An example of the dependence of 1=1 2 1=1m versus T 2 Tc 2 is presented in Fig. 2 for the experimental values corresponding to x 0:55 d 608C: The fit is in good agreement with the general approach of Smolensky and Rolov [7]. In Table 2 we summarize the relevant parameters for PSNB for all the studied compositions. It is worth noting the enhancement of the diffuse character of the ceramic with Sn concentration while the maximum permittivity decreases, indicating a reorientation of the cations with respect to the local electric field, rendering lower permittivity values. Fig. 3 shows the dependence of the maximum permittivity temperature with composition. The linear behavior evidences the incorporation of the dopant into the crystal
Fig. 1. Permittivity versus temperature for Pb0.85(Na0.5Bi0.5)0.15SnxTi12x O3 samples with different Sn concentration.
F. Caldero´n et al. / Solid State Communications 112 (1999) 219–221
221
Fig. 2. Inverse of the permittivity versus T 2 Tc 2 for Pb0.85(Na0.5Bi0.5)0.15SnxTi12x O3, x 0:55.
Fig. 3. Curie temperature as a function of composition for the Pb0.85(Na0.5Bi0.5)0.15SnxTi12x O3 system.
structure causing the Curie temperature (Tc) of the system to decrease.
4. Conclusions The analysis of the dielectric properties of the Pb0.85(Na0.5Bi0.5)0.15SnxTi12x O3 samples with x 0:40; 0:45; 0:50; 0:55; 0:60 reveals a relaxor behavior near Tc where the diffuseness parameter d increases as the relative concentration of Sn 41 increases. The temperature of the permittivity maximum was shifted toward lower temperature values and the permittivity maximum decreased with the increase of Sn content in the PSNB solid solutions. These results point to a cationic reorientation with respect to the local electric field producing a reduction in the maximum dielectric-permittivity values. The decrease in the critical temperature as well as the decrease of the c/a ratio with Sn concentration are taken as evidence of the incorporation of the dopant into the crystal structure of the system.
Acknowledgements This work was partially sponsored by CoNaCyT Project no. 26314E and DGAPA Project no. IN115098. J.P. thanks the CoNaCyT, Me´xico for its support.
References [1] L.E. Cross, Ferroelectrics 76 (1987) 241. [2] G. Taylor (Ed.), Ferroelectric and Related Materials, vol. III, Gordon and Breach, London, 1984. [3] S.M. Pilgrim, A.E. Sutherland, S.R. Winzer, J. Am. Ceram. Soc. 73 (1990) 3122. [4] A.A. Bokov, Recent advances in diffuse ferroelectric phase transitions, Ferroelectrics 131 (1992) 49. [5] Y. Zhi, A. Chen, P.M. Vilarinho, P.Q. Mantas, J.L. Baptista, in: J.L. Baptisa, J.A. Labrincha, P.M. Vilarinho (Eds.), Proceedings of Electroceramics V, Book 2, 1996, p. 9. [6] C.A. Randall, A.D. Hilton, D.J. Barber, T.R. Shrout, J. Mater. Res. 8 (1993) 880. [7] K.M. Lee, H.M. Jang, J. Mater. Res. 12 (1997) 1614.
Solid State Communications 112 (1999) 219–221 www.elsevier.com/locate/ssc
Diffuse phase transition in (Na,Bi)-doped PbSnxTi12x O3 ferroelectric ceramics F. Caldero´n a,*, J.M. Siqueiros b, J. Portelles a, b, J.L. Heiras b a
b
Facultad de Fı´sica-IMRE, Universidad de La Habana, San La´zaro y L, 10400, Vedado, Cuba Centro de Ciencias de la Materia Condensada, UNAM, Apartado Postal 2681, Ensenada, BC, 22800, Mexico Received 24 May 1999; accepted 21 June 1999 by R.C. Dynes
Abstract The temperature dependence of the dielectric behavior of Pb0.85(Na0.5Bi0.5)0.15SnxTi12x O3 (PSNB) with x 0:40; 0:45; 0:50; 0:55; 0:60 has been investigated. A careful analysis of the dielectric properties reveals a relaxor behavior near Tc where the diffuseness parameter (d ) increases as the content of Sn 41. It is observed that the temperature of the permittivity maximum shifts toward lower temperatures and the permittivity maximum decreases with the increase of Sn content in the PSNB solid solutions. The diffuseness (d ) and deformation structure (g ) parameters were determined for each composition using the results of the dielectric measurements and experimental lattice constant values. q 1999 Elsevier Science Ltd. All rights reserved. Keywords: A. Ferroelectrics; D. Phase transitions
1. Introduction Relaxor ferroelectrics are characterized by a diffuse phase transition (DPT). The complex perovskite PbMg1/3Nb2/3O3 is just one of many relaxors that have been extensively studied [1]. In the early stages of ferroelectric research the BaTiO3 – BaSnO3 (BSN) [2] solid solutions established that the peaks of the dielectric permittivity (e ) notably broadened as the SnO2 concentration increased. Even today, the theory of Smolensky–Isupov remains a good approach for describing the behavior of these materials together with the superparaelectric theory proposed by Cross [1]. The experimental results reported in this study point to a quadratic dependence of the reciprocal dielectric permittivity 1=1 2 1=1m versus temperature (T), although valid only in the region where the DPT exists due to small interacting polarized regions. The normal Curie–Weiss law will hold at higher temperatures [3]. Experimental data have been reported previously for a number of compounds, e.g. PMN, PMN-PT and PLZT [4]. According to the main ideas of Bokov [4] and Zhi [5], in the case of BSN, the ferroactive ion is in the B site (Ti 41) of the unit cell * Corresponding author.
while in PbTiO3 it is in the A site (Pb 21). In the present work, a systematic study of the samples with nominal composition Pb0.85(Na0.5Bi0.5)0.15Ti12x SnxO3 (PSNB) in the x 0:40 to x 0:60 range was carried out following the same line of reasoning, i.e. such cationic substitution would induce a relaxor behavior state in the modified PSN samples.
2. Experimental procedure The samples were prepared using the standard ceramic method. The mixture of constituent powders was ball-milled in ethanol, dried, and calcined at 6008C for 1 h, 7008C for 1 h and 8008C for 2 h, respectively. The dried powder was then granulated with 10 wt% polyvinyl alcohol binder in water media. After passing the mixture through a 100 mesh sieve, 10 mm disks were cold pressed in a steel die at 100 Mpa. All measured samples were sintered at 10008C for 1 h. To control PbO loss from the pellets, a compensating PbZrO3 atmosphere was maintained inside a covered platinum crucible where the sintering process was performed. The weight loss during these preparation stages was carefully monitored.
0038-1098/99/$ - see front matter q 1999 Elsevier Science Ltd. All rights reserved. PII: S0038-109 8(99)00314-2
F. Caldero´n et al. / Solid State Communications 112 (1999) 219–221
220
Table 1 Lattice parameters and crystalline structure of Pb0.85(Na0.5Bi0.5)0.15Ti12x SnxO3
Table 2 Relevant parameters for PSNB for all the compositions studied x
x
˚) a (A
˚) c (A
Structure
c/a
0.40 0.45 0.50 0.55 0.60
3.980 3.989 3.993 4.013 4.020
4.059 4.053 4.046 4.033
Tetragonal Tetragonal Tetragonal Tetragonal 1 rombohedral Rombohedral
1.019 1.016 1.013 1.004
XRD studies of the samples were performed over the 208 , 2u , 608 angular range in 0.028 steps. Samples for dielectric measurements were prepared from the sintered pellets by polishing the major faces. The dielectric permittivity versus temperature was measured using a Tesla model E7-9 LCR meter, at 1 kHz and the transition temperatures Tc were determined from the maximum of these curves.
3. Results and discussion The XRD patterns of the calcined samples evidenced the presence of residual PbO in all of the samples. However, the sintered samples were found to be pure perovskite. In Table 1, the lattice parameters and corresponding crystalline structure for the different compositions are presented: the PbTiO3-rich solid solutions have a tetragonal structure with decreasing c/a ratio as the Sn 41 concentration increases. The behavior of the relative dielectric permittivity (e ) versus temperature of the PSNB at 500 kHz, for all compositions, is shown in Fig. 1. The maximum value of the dielectric permittivity decreases with Sn concentration (x). The expression for the diffuseness (d ) can be determined
em d (8C) em d2 × 106 Tc (8C)
0.40
0.45
0.50
0.55
0.60
8891 35 10 256
8423 45 17 226
8865 46 18 199
5259 60 18 167
3200 66 13 154
[6] from the slope of the equation 1 1 T 2 Tc 2 1 1 1m 2d2 1m The parameter d (see Table 2) increases systematically from x 0 to x 60; indicating that the cationic disorder in the perovskite structure increases. The observed increase in the width of dielectric response reflects a gradual increase in the relaxor characteristics as proposed earlier. An example of the dependence of 1=1 2 1=1m versus T 2 Tc 2 is presented in Fig. 2 for the experimental values corresponding to x 0:55 d 608C: The fit is in good agreement with the general approach of Smolensky and Rolov [7]. In Table 2 we summarize the relevant parameters for PSNB for all the studied compositions. It is worth noting the enhancement of the diffuse character of the ceramic with Sn concentration while the maximum permittivity decreases, indicating a reorientation of the cations with respect to the local electric field, rendering lower permittivity values. Fig. 3 shows the dependence of the maximum permittivity temperature with composition. The linear behavior evidences the incorporation of the dopant into the crystal
Fig. 1. Permittivity versus temperature for Pb0.85(Na0.5Bi0.5)0.15SnxTi12x O3 samples with different Sn concentration.
F. Caldero´n et al. / Solid State Communications 112 (1999) 219–221
221
Fig. 2. Inverse of the permittivity versus T 2 Tc 2 for Pb0.85(Na0.5Bi0.5)0.15SnxTi12x O3, x 0:55.
Fig. 3. Curie temperature as a function of composition for the Pb0.85(Na0.5Bi0.5)0.15SnxTi12x O3 system.
structure causing the Curie temperature (Tc) of the system to decrease.
4. Conclusions The analysis of the dielectric properties of the Pb0.85(Na0.5Bi0.5)0.15SnxTi12x O3 samples with x 0:40; 0:45; 0:50; 0:55; 0:60 reveals a relaxor behavior near Tc where the diffuseness parameter d increases as the relative concentration of Sn 41 increases. The temperature of the permittivity maximum was shifted toward lower temperature values and the permittivity maximum decreased with the increase of Sn content in the PSNB solid solutions. These results point to a cationic reorientation with respect to the local electric field producing a reduction in the maximum dielectric-permittivity values. The decrease in the critical temperature as well as the decrease of the c/a ratio with Sn concentration are taken as evidence of the incorporation of the dopant into the crystal structure of the system.
Acknowledgements This work was partially sponsored by CoNaCyT Project no. 26314E and DGAPA Project no. IN115098. J.P. thanks the CoNaCyT, Me´xico for its support.
References [1] L.E. Cross, Ferroelectrics 76 (1987) 241. [2] G. Taylor (Ed.), Ferroelectric and Related Materials, vol. III, Gordon and Breach, London, 1984. [3] S.M. Pilgrim, A.E. Sutherland, S.R. Winzer, J. Am. Ceram. Soc. 73 (1990) 3122. [4] A.A. Bokov, Recent advances in diffuse ferroelectric phase transitions, Ferroelectrics 131 (1992) 49. [5] Y. Zhi, A. Chen, P.M. Vilarinho, P.Q. Mantas, J.L. Baptista, in: J.L. Baptisa, J.A. Labrincha, P.M. Vilarinho (Eds.), Proceedings of Electroceramics V, Book 2, 1996, p. 9. [6] C.A. Randall, A.D. Hilton, D.J. Barber, T.R. Shrout, J. Mater. Res. 8 (1993) 880. [7] K.M. Lee, H.M. Jang, J. Mater. Res. 12 (1997) 1614.