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Solid solution Pb1−xSrxTiO3 and its thermal expansion
Journal of Alloys and Compounds 360 (2003) 286–289
L
www.elsevier.com / locate / jallcom
Solid solution Pb 12x Sr x TiO 3 and its thermal expansion Xianran Xing*, Jun Chen, Jinxia Deng, Guirong Liu Department of Physical Chemistry, University of Science & Technology Beijing, Xueyuan Road 30, Beijing 100083, China Received 27 November 2002; received in revised form 28 February 2003; accepted 28 February 2003
Abstract The solid solution limit of Pb 12x Sr x TiO 3 was determined in the composition range of 0#x#1.0 at room temperature (RT). The phases were isolated and indexed in a tetragonal system with x,0.5 and in a cubic one with x$0.5. The cell parameters of Pb 12x Sr x TiO 3 continuously, but nonlinearly, change with solubility x. The intrinsic thermal expansions of the solid solution compounds Pb 12x Srx TiO 3 (x50, 0.15, 0.20, 0.50, 0.90, 1.0) were obtained in the temperature range from RT to 1173 K with high-temperature X-ray powder diffraction. Negative thermal expansion coefficients of Pb 12x Sr x TiO 3 (x50, 0.15, 0.20) were found below the Curie points. The thermal expansions of these titanate ceramics were highly correlated with the solubility in the solid solution Pb 12x Srx TiO 3 . 2003 Elsevier B.V. All rights reserved. Keywords: Lead strontium titanate; Phase transition; Thermal expansion; X-Ray diffraction
1. Introduction
To overcome the thermal shock damage of these materials becomes a substantial problem. One point of interest of solid solutions of ceramics is the possibility to adjust the thermal expansion, reaching better compatibility in ceramic devices [15–17]. Previous work and our recent research revealed that lead titanate exhibited very uncommon thermal expansion coefficients (TECs) [7,18]. Below the Curie point of lead titanate (763 K), the c axis decreases, the a(5b) axis increases, and the cell volume shrinks with increasing temperature. Such a negative thermal expansion (NTE) in lead titanate permits us to make some promising strategies for material designs. For example, one can prepare specific TEC titanate ceramics by doping lead so as to meet the practical usage. In the present study, we determined the solid solution limit of lead strontium titanate by X-ray powder diffraction (XRPD) and investigated the structure of the solid solution compounds as a function of temperature using HTXRPD (high temperature X-ray powder diffraction) so as to obtain the intrinsic thermal expansions and the related phase transitions.
Considerable efforts have been invested in the study of the anomalous positive temperature coefficients of the resistivity (PTCRs) of titanate ceramics such as barium titanate, barium lead titanate, barium strontium titanate and so on [1–3]. Recent studies revealed that strontium lead titanate presented a typical PTCR effect similar to BaTiO 3 [4–6]. It is well known that the Curie points of lead and strontium titanates are 763 and 108 K, respectively [7,8]. Both of them are used as common elements to change the Curie point, shifting it to lower temperatures by substituting strontium and to higher temperatures by substituting lead [9,10]. The work was successfully applied to obtain PTCR effects with Curie points of 633 K for Ba 0.35 Pb 0.65 TiO 3 and 693 K for Ba 0.2 Pb 0.8 TiO 3 [3,11,12]. Similar situations were observed in lead strontium titanate [6,13] and barium strontium titanate [14]. Such solid solutions in ferroelectric ceramics are technologically important because they allow the electric properties to be tailor-made for practical applications. This policy is widely used in functional materials. The ceramics in perovskites are usually prepared at high temperatures and undergo one or more phase transitions.
2. Experimental
*Corresponding author. Tel.: 186-10-6233-4200; fax: 186-10-62333477. E-mail address: [email protected] (X. Xing).
Samples were prepared by a solid-state reaction at high temperature. The starting materials were Pb(NO 3 ) 2 (A.R., analytical reagent grade), SrCO 3 (A.R.) and TiO 2 (99.9%
0925-8388 / 03 / $ – see front matter 2003 Elsevier B.V. All rights reserved. doi:10.1016 / S0925-8388(03)00345-1
X. Xing et al. / Journal of Alloys and Compounds 360 (2003) 286–289
287
purity). The starting reagents were weighed in the proper molar ratios, mixed, fully ground together, using an agate mortar and pestle. Then they were pressed into small pellets, measuring 13 mm in diameter and 2|3 mm thick. The pellets were calcined in a platinum crucible at 773 K for 24 h and at 1223 K for another 24 h, then quenched in air. After this procedure had been repeated two times, the samples were sintered at a specific temperature (from 1223 to 1523 K) for 24 h and slowly cooled to room temperature in the furnace. The final sintering temperature depended on the content of lead in a sample. Samples with a high content of lead were sintered at lower temperature. Phase identification and structural characterization were conducted using a 21 kW extra-power powder XRD system (Model M21XVHF22, Mac Science Co., Ltd., Yokohama, Japan), with Cu Ka radiation, curved crystal graphite monochromators, and scintillation counter (SC) detectors. Two fully automatic vertical goniometers were allocated on both sides of the self-rotating anode (SRA) target. An attachment for high-temperature measurements was assembled on the left goniometer. Because the sample holder remained in an almost horizon position, the sample could not fall from the sample holder at high temperatures. The scanning speed of the 2u angle was 48 / min, the heating speed was 10 K / min, and the sample was maintained at the specified temperature for 15 min, to reach thermal balance. Air was incorporated into the sample chamber. For measuring the lattice parameters of the compound, pure silicon powder was added to the sample, as an internal standard.
3. Results and discussion The compounds Pb 12x Sr x TiO 3 of nominal composition were synthesized, as described in Section 2 and were isolated as a pure phase. The XRPD patterns of the solid solution compounds at RT were indexed in a tetragonal system for x,0.5 and in a cubic one for x$0.5. We found that the c axis sharply decreases and a(5b) axis slightly increases with solubility for x,0.5, and then a(5b5c) axis slightly decreases with solubility for x$0.5 (see Fig. 1a). The cell volumes also decrease sharply for x,0.5 but only slightly beyond x50.5 (see Fig. 1b). It should be pointed out that the variations of the cell parameters are continuous, but nonlinear with solubility in the range 0%x%1.0. Such tendencies are of great importance to predict the Curie points and the ferroelectric properties of lead strontium titanates. Using HTXRPD, the structures of Pb 12x Sr x TiO 3 (x50, 0.15, 0.20, 0.50, 0.90, 1.00) with temperature were determined. In the temperature range of RT-673 K, the Pb 0.85 Sr 0.15 TiO 3 diffractograms were indexed in a tetragonal system, and beyond the critical point at 673 K in a cubic system. Fig. 2a shows that the a(5b) axis expands and the c axis contracts with temperature. A phase
Fig. 1. (a) Cell parameters of Pb 12x Sr x TiO 3 vs. solubility. (b) Cell volumes of Pb 12x Sr x TiO 3 vs. solubility.
transition occurs at 673 K. Above 673 K, the lattice constant (a5b5c) linearly increases with temperature. However thermal contraction hysteresis was observed after the phase transition. Similar results were obtained in the solution compounds Pb 0.80 Sr 0.20 TiO 3 and PbTiO 3 (see Fig. 3). When x50.5, however, the structure is cubic at all temperature and the lattice constant a(5b5c) linearly increases with temperature (see Fig. 4). For higher x, no phase transition in the compound Pb 12x Sr x TiO 3 was observed in the temperature range RT–1173 K (see Figs. 5 and 6). In general, the bulk TEC can be expressed by following equations: 1 ≠V b 5]?] V0 ≠T or 1 DV ] b 5]?] V0 DT ] where b and b are TEC and average TEC. V and T are the
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X. Xing et al. / Journal of Alloys and Compounds 360 (2003) 286–289
Fig. 4. Cell parameters of Pb 0.5 Sr 0.5 TiO 3 vs. temperature.
Fig. 2. (a) Cell parameters of Pb 0.85 Sr 0.15 TiO 3 vs. temperature. (b) Cell volumes of Pb 0.85 Sr 0.15 TiO 3 vs. temperature.
cell volume and the temperature, respectively. The average bulk TECs of the solid solution compounds Pb 12x Sr x TiO 3 were calculated from the cell volumes (see Fig. 2b) and are listed in Table 1.
Fig. 3. Cell parameters of Pb 0.80 Sr 0.2 TiO 3 vs. temperature.
Fig. 5. Cell parameters of Pb 0.1 Sr 0.9 TiO 3 vs. temperature.
The TECs of the compounds Pb 12x Sr x TiO 3 have quite novel features. Below the Curie point, the TEC of a given compound is negative and decreases with solubility for x#0.2, but this behavior probably extends to higher
Fig. 6. Cell parameters of SrTiO 3 vs. temperature.
X. Xing et al. / Journal of Alloys and Compounds 360 (2003) 286–289
289
Table 1 The average bulk TECs of Pb 12x Sr x TiO 3 Compound
PbTiO 3 Pb 0.85 Sr 0.15 TiO 3 Pb 0.80 Sr 0.20 TiO 3 Pb 0.50 Sr 0.50 TiO 3 Pb 0.10 Sr 0.90 TiO 3 SrTiO 3
TEC (310 25 / K) T phase
Temperature (K)
C phase
Temperature (K)
21.62 21.11 20.52
RT|763 RT|673 RT|623
3.55 3.81 4.27 3.70 3.42 3.42
763|1223 673|1173 623|1173 RT|1173 RT|1173 RT|1173
contents of strontium. Above the Curie point, the TEC presents a semi-parabolic curve with a maxim in the composition range of 0%x%1.00. Table 1 clearly demonstrates that neither the bulk thermal expansion coefficient nor the Curie point of the solid solution compound are the mean value of those of the two end compounds in the solid solution series Pb 12x Sr x TiO 3 . A similar conclusion was drawn for the solid solution system Ba 12x Pb x TiO 3 [18]. As discussed in our previous study, some authors simply described the permittivity and Curie point as being linearly correlated with the solubility in solid solution Ba 12x Pb x TiO 3 [11]. This result might be quite wrong and could give rise to substantial errors when predicting the ferroelectric properties. For example in Ref. [11], the Curie point of Ba 0.8 Pb 0.2 TiO 3 was determined to be 443 K (on set) from measurements of the specific heat, but the value predicted was beyond 473 K. The Roberts equation can be expressed as: 1 1 da ]5b 2]?] C 3a dT where C is the Curie–Weiss constant, and a is the atomic polarizability. Usually the second term on the right side of the above equation is small. Therefore we can conclude that the ferroelectric properties are highly correlated with the thermal expansion of ceramics.
4. Conclusions 1. The solid solution limit of Pb 12x Sr x TiO 3 was determined and Pb can be completely replaced by Sr in the composition range of 0#x%1.0. The solid solution compounds were indexed in a tetragonal system for x%0.5 and in a cubic one for x^0.5. The cell parameters of Pb 12x Sr x TiO 3 continuously change, but the changing tendency is nonlinear. 2. Using HTXRPD, the bulk thermal expansion coefficients of Pb 12x Sr x TiO 3 (x50, 0.15, 0.20, 0.50, 0.90, 1.00) were determined in the temperature range RT| 1173 K. Possibly Curie points were detected. The TECs of Pb 12x Sr x TiO 3 with x%0.2 are negative, and those above the Curie points vary semi-parabolic with x for 0%x%1.0.
Curie point (K) 763 [18] 673 623 Below RT Below RT 108 [10]
3. The ferroelectric properties are probably highly correlated with the thermal expansion of the titanate ceramics. Both ferroelectric properties and thermal expansion are also nonlinearly correlated with the solubility in the solid solution Pb 12x Srx TiO 3 (0%x% 1.0).
Acknowledgements This work was financially supported by National Natural Science Foundation of China (No. 20171006), and Funds of Ministry of Education of China for Training Ph.D. Candidates (No. 2001008005).
References [1] H.F. Cheng, T.F. Lin, C.T. Hu, J. Am. Ceram. Soc. 76 (1993) 827–830. [2] P.W. Haayman, R.W. Dam, H.A. Klasens, German Pat. No. 929,350 (1955). [3] M. Kuwabara, S. Suemura, M. Kawahara, Am. Ceram. Soc. Bull. 64 (1985) 1394–1398. [4] M. Hamada, H. Taguchi, H. Masumura, Jpn. Pat. No. 63-280401 (1988). [5] Y. Somiya, A.S. Bhalla, L. Eric Cross, Int. J. Inorg. Mater. 3 (2001) 709–714. [6] J. Zhao, L. Li, Z. Gui, J. Eur. Ceram. Soc. 22 (2002) 1171–1175; J. Zhao, L. Li, Z. Gui, Mater. Sci. Eng. B 94 (2002) 202–206. [7] J. Kobayashi, R. Ueda, Phys. Rev. 99 (1955) 1900–1901. [8] B. Alefeld, Z. Phys. 222 (1969) 155–164. [9] A. von Hippel (Ed.), Dielectric Materials and Applications, Technology Press–Wiley, Cambridge, MA–New York, 1954. [10] L. Lenchand, D.B. Dove, Physics of Electric Ceramics, Marcel Dekker, New York, 1971. [11] S. Nomura, S. Sawada, J. Phys. Soc. Jpn. 6 (1951) 36–39. [12] Y.N. Venevtsov, V.S. Bondarenko, G.S. Zhdanov, V.V. Chkalova, N.G. Stember, Kristallografiya 6 (1961) 375–380, in Russian. [13] C.K. Lee, I.N. Lin, C.T. Hu, J. Am. Ceram. Soc. 77 (1994) 1340–1344. [14] H. Cheng, T. Lin, C. Hu, I. Lin, J. Am. Ceram. Soc. 76 (1993) 827–832. [15] D. Taylor, J. Thermal Expansion Data 84 (1985) 181–188. [16] T.A. Mary, J.S.O. Evans, T. Vogt, A.W. Sleight, Science 272 (1996) 90–92. [17] X. Xing, Z. Zhu, X. Qiu, G. Liu, Rare Metals 20 (2001) 1–4. [18] X. Xing, J. Deng, Z. Zhu, G. Liu, J. Alloys Comp. 353 (2003) 1–4.
L
www.elsevier.com / locate / jallcom
Solid solution Pb 12x Sr x TiO 3 and its thermal expansion Xianran Xing*, Jun Chen, Jinxia Deng, Guirong Liu Department of Physical Chemistry, University of Science & Technology Beijing, Xueyuan Road 30, Beijing 100083, China Received 27 November 2002; received in revised form 28 February 2003; accepted 28 February 2003
Abstract The solid solution limit of Pb 12x Sr x TiO 3 was determined in the composition range of 0#x#1.0 at room temperature (RT). The phases were isolated and indexed in a tetragonal system with x,0.5 and in a cubic one with x$0.5. The cell parameters of Pb 12x Sr x TiO 3 continuously, but nonlinearly, change with solubility x. The intrinsic thermal expansions of the solid solution compounds Pb 12x Srx TiO 3 (x50, 0.15, 0.20, 0.50, 0.90, 1.0) were obtained in the temperature range from RT to 1173 K with high-temperature X-ray powder diffraction. Negative thermal expansion coefficients of Pb 12x Sr x TiO 3 (x50, 0.15, 0.20) were found below the Curie points. The thermal expansions of these titanate ceramics were highly correlated with the solubility in the solid solution Pb 12x Srx TiO 3 . 2003 Elsevier B.V. All rights reserved. Keywords: Lead strontium titanate; Phase transition; Thermal expansion; X-Ray diffraction
1. Introduction
To overcome the thermal shock damage of these materials becomes a substantial problem. One point of interest of solid solutions of ceramics is the possibility to adjust the thermal expansion, reaching better compatibility in ceramic devices [15–17]. Previous work and our recent research revealed that lead titanate exhibited very uncommon thermal expansion coefficients (TECs) [7,18]. Below the Curie point of lead titanate (763 K), the c axis decreases, the a(5b) axis increases, and the cell volume shrinks with increasing temperature. Such a negative thermal expansion (NTE) in lead titanate permits us to make some promising strategies for material designs. For example, one can prepare specific TEC titanate ceramics by doping lead so as to meet the practical usage. In the present study, we determined the solid solution limit of lead strontium titanate by X-ray powder diffraction (XRPD) and investigated the structure of the solid solution compounds as a function of temperature using HTXRPD (high temperature X-ray powder diffraction) so as to obtain the intrinsic thermal expansions and the related phase transitions.
Considerable efforts have been invested in the study of the anomalous positive temperature coefficients of the resistivity (PTCRs) of titanate ceramics such as barium titanate, barium lead titanate, barium strontium titanate and so on [1–3]. Recent studies revealed that strontium lead titanate presented a typical PTCR effect similar to BaTiO 3 [4–6]. It is well known that the Curie points of lead and strontium titanates are 763 and 108 K, respectively [7,8]. Both of them are used as common elements to change the Curie point, shifting it to lower temperatures by substituting strontium and to higher temperatures by substituting lead [9,10]. The work was successfully applied to obtain PTCR effects with Curie points of 633 K for Ba 0.35 Pb 0.65 TiO 3 and 693 K for Ba 0.2 Pb 0.8 TiO 3 [3,11,12]. Similar situations were observed in lead strontium titanate [6,13] and barium strontium titanate [14]. Such solid solutions in ferroelectric ceramics are technologically important because they allow the electric properties to be tailor-made for practical applications. This policy is widely used in functional materials. The ceramics in perovskites are usually prepared at high temperatures and undergo one or more phase transitions.
2. Experimental
*Corresponding author. Tel.: 186-10-6233-4200; fax: 186-10-62333477. E-mail address: [email protected] (X. Xing).
Samples were prepared by a solid-state reaction at high temperature. The starting materials were Pb(NO 3 ) 2 (A.R., analytical reagent grade), SrCO 3 (A.R.) and TiO 2 (99.9%
0925-8388 / 03 / $ – see front matter 2003 Elsevier B.V. All rights reserved. doi:10.1016 / S0925-8388(03)00345-1
X. Xing et al. / Journal of Alloys and Compounds 360 (2003) 286–289
287
purity). The starting reagents were weighed in the proper molar ratios, mixed, fully ground together, using an agate mortar and pestle. Then they were pressed into small pellets, measuring 13 mm in diameter and 2|3 mm thick. The pellets were calcined in a platinum crucible at 773 K for 24 h and at 1223 K for another 24 h, then quenched in air. After this procedure had been repeated two times, the samples were sintered at a specific temperature (from 1223 to 1523 K) for 24 h and slowly cooled to room temperature in the furnace. The final sintering temperature depended on the content of lead in a sample. Samples with a high content of lead were sintered at lower temperature. Phase identification and structural characterization were conducted using a 21 kW extra-power powder XRD system (Model M21XVHF22, Mac Science Co., Ltd., Yokohama, Japan), with Cu Ka radiation, curved crystal graphite monochromators, and scintillation counter (SC) detectors. Two fully automatic vertical goniometers were allocated on both sides of the self-rotating anode (SRA) target. An attachment for high-temperature measurements was assembled on the left goniometer. Because the sample holder remained in an almost horizon position, the sample could not fall from the sample holder at high temperatures. The scanning speed of the 2u angle was 48 / min, the heating speed was 10 K / min, and the sample was maintained at the specified temperature for 15 min, to reach thermal balance. Air was incorporated into the sample chamber. For measuring the lattice parameters of the compound, pure silicon powder was added to the sample, as an internal standard.
3. Results and discussion The compounds Pb 12x Sr x TiO 3 of nominal composition were synthesized, as described in Section 2 and were isolated as a pure phase. The XRPD patterns of the solid solution compounds at RT were indexed in a tetragonal system for x,0.5 and in a cubic one for x$0.5. We found that the c axis sharply decreases and a(5b) axis slightly increases with solubility for x,0.5, and then a(5b5c) axis slightly decreases with solubility for x$0.5 (see Fig. 1a). The cell volumes also decrease sharply for x,0.5 but only slightly beyond x50.5 (see Fig. 1b). It should be pointed out that the variations of the cell parameters are continuous, but nonlinear with solubility in the range 0%x%1.0. Such tendencies are of great importance to predict the Curie points and the ferroelectric properties of lead strontium titanates. Using HTXRPD, the structures of Pb 12x Sr x TiO 3 (x50, 0.15, 0.20, 0.50, 0.90, 1.00) with temperature were determined. In the temperature range of RT-673 K, the Pb 0.85 Sr 0.15 TiO 3 diffractograms were indexed in a tetragonal system, and beyond the critical point at 673 K in a cubic system. Fig. 2a shows that the a(5b) axis expands and the c axis contracts with temperature. A phase
Fig. 1. (a) Cell parameters of Pb 12x Sr x TiO 3 vs. solubility. (b) Cell volumes of Pb 12x Sr x TiO 3 vs. solubility.
transition occurs at 673 K. Above 673 K, the lattice constant (a5b5c) linearly increases with temperature. However thermal contraction hysteresis was observed after the phase transition. Similar results were obtained in the solution compounds Pb 0.80 Sr 0.20 TiO 3 and PbTiO 3 (see Fig. 3). When x50.5, however, the structure is cubic at all temperature and the lattice constant a(5b5c) linearly increases with temperature (see Fig. 4). For higher x, no phase transition in the compound Pb 12x Sr x TiO 3 was observed in the temperature range RT–1173 K (see Figs. 5 and 6). In general, the bulk TEC can be expressed by following equations: 1 ≠V b 5]?] V0 ≠T or 1 DV ] b 5]?] V0 DT ] where b and b are TEC and average TEC. V and T are the
288
X. Xing et al. / Journal of Alloys and Compounds 360 (2003) 286–289
Fig. 4. Cell parameters of Pb 0.5 Sr 0.5 TiO 3 vs. temperature.
Fig. 2. (a) Cell parameters of Pb 0.85 Sr 0.15 TiO 3 vs. temperature. (b) Cell volumes of Pb 0.85 Sr 0.15 TiO 3 vs. temperature.
cell volume and the temperature, respectively. The average bulk TECs of the solid solution compounds Pb 12x Sr x TiO 3 were calculated from the cell volumes (see Fig. 2b) and are listed in Table 1.
Fig. 3. Cell parameters of Pb 0.80 Sr 0.2 TiO 3 vs. temperature.
Fig. 5. Cell parameters of Pb 0.1 Sr 0.9 TiO 3 vs. temperature.
The TECs of the compounds Pb 12x Sr x TiO 3 have quite novel features. Below the Curie point, the TEC of a given compound is negative and decreases with solubility for x#0.2, but this behavior probably extends to higher
Fig. 6. Cell parameters of SrTiO 3 vs. temperature.
X. Xing et al. / Journal of Alloys and Compounds 360 (2003) 286–289
289
Table 1 The average bulk TECs of Pb 12x Sr x TiO 3 Compound
PbTiO 3 Pb 0.85 Sr 0.15 TiO 3 Pb 0.80 Sr 0.20 TiO 3 Pb 0.50 Sr 0.50 TiO 3 Pb 0.10 Sr 0.90 TiO 3 SrTiO 3
TEC (310 25 / K) T phase
Temperature (K)
C phase
Temperature (K)
21.62 21.11 20.52
RT|763 RT|673 RT|623
3.55 3.81 4.27 3.70 3.42 3.42
763|1223 673|1173 623|1173 RT|1173 RT|1173 RT|1173
contents of strontium. Above the Curie point, the TEC presents a semi-parabolic curve with a maxim in the composition range of 0%x%1.00. Table 1 clearly demonstrates that neither the bulk thermal expansion coefficient nor the Curie point of the solid solution compound are the mean value of those of the two end compounds in the solid solution series Pb 12x Sr x TiO 3 . A similar conclusion was drawn for the solid solution system Ba 12x Pb x TiO 3 [18]. As discussed in our previous study, some authors simply described the permittivity and Curie point as being linearly correlated with the solubility in solid solution Ba 12x Pb x TiO 3 [11]. This result might be quite wrong and could give rise to substantial errors when predicting the ferroelectric properties. For example in Ref. [11], the Curie point of Ba 0.8 Pb 0.2 TiO 3 was determined to be 443 K (on set) from measurements of the specific heat, but the value predicted was beyond 473 K. The Roberts equation can be expressed as: 1 1 da ]5b 2]?] C 3a dT where C is the Curie–Weiss constant, and a is the atomic polarizability. Usually the second term on the right side of the above equation is small. Therefore we can conclude that the ferroelectric properties are highly correlated with the thermal expansion of ceramics.
4. Conclusions 1. The solid solution limit of Pb 12x Sr x TiO 3 was determined and Pb can be completely replaced by Sr in the composition range of 0#x%1.0. The solid solution compounds were indexed in a tetragonal system for x%0.5 and in a cubic one for x^0.5. The cell parameters of Pb 12x Sr x TiO 3 continuously change, but the changing tendency is nonlinear. 2. Using HTXRPD, the bulk thermal expansion coefficients of Pb 12x Sr x TiO 3 (x50, 0.15, 0.20, 0.50, 0.90, 1.00) were determined in the temperature range RT| 1173 K. Possibly Curie points were detected. The TECs of Pb 12x Sr x TiO 3 with x%0.2 are negative, and those above the Curie points vary semi-parabolic with x for 0%x%1.0.
Curie point (K) 763 [18] 673 623 Below RT Below RT 108 [10]
3. The ferroelectric properties are probably highly correlated with the thermal expansion of the titanate ceramics. Both ferroelectric properties and thermal expansion are also nonlinearly correlated with the solubility in the solid solution Pb 12x Srx TiO 3 (0%x% 1.0).
Acknowledgements This work was financially supported by National Natural Science Foundation of China (No. 20171006), and Funds of Ministry of Education of China for Training Ph.D. Candidates (No. 2001008005).
References [1] H.F. Cheng, T.F. Lin, C.T. Hu, J. Am. Ceram. Soc. 76 (1993) 827–830. [2] P.W. Haayman, R.W. Dam, H.A. Klasens, German Pat. No. 929,350 (1955). [3] M. Kuwabara, S. Suemura, M. Kawahara, Am. Ceram. Soc. Bull. 64 (1985) 1394–1398. [4] M. Hamada, H. Taguchi, H. Masumura, Jpn. Pat. No. 63-280401 (1988). [5] Y. Somiya, A.S. Bhalla, L. Eric Cross, Int. J. Inorg. Mater. 3 (2001) 709–714. [6] J. Zhao, L. Li, Z. Gui, J. Eur. Ceram. Soc. 22 (2002) 1171–1175; J. Zhao, L. Li, Z. Gui, Mater. Sci. Eng. B 94 (2002) 202–206. [7] J. Kobayashi, R. Ueda, Phys. Rev. 99 (1955) 1900–1901. [8] B. Alefeld, Z. Phys. 222 (1969) 155–164. [9] A. von Hippel (Ed.), Dielectric Materials and Applications, Technology Press–Wiley, Cambridge, MA–New York, 1954. [10] L. Lenchand, D.B. Dove, Physics of Electric Ceramics, Marcel Dekker, New York, 1971. [11] S. Nomura, S. Sawada, J. Phys. Soc. Jpn. 6 (1951) 36–39. [12] Y.N. Venevtsov, V.S. Bondarenko, G.S. Zhdanov, V.V. Chkalova, N.G. Stember, Kristallografiya 6 (1961) 375–380, in Russian. [13] C.K. Lee, I.N. Lin, C.T. Hu, J. Am. Ceram. Soc. 77 (1994) 1340–1344. [14] H. Cheng, T. Lin, C. Hu, I. Lin, J. Am. Ceram. Soc. 76 (1993) 827–832. [15] D. Taylor, J. Thermal Expansion Data 84 (1985) 181–188. [16] T.A. Mary, J.S.O. Evans, T. Vogt, A.W. Sleight, Science 272 (1996) 90–92. [17] X. Xing, Z. Zhu, X. Qiu, G. Liu, Rare Metals 20 (2001) 1–4. [18] X. Xing, J. Deng, Z. Zhu, G. Liu, J. Alloys Comp. 353 (2003) 1–4.