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Dielectric properties and substitution preference of yttrium doped barium zirconium titanate ceramics
Solid State Communications 141 (2007) 65–68 www.elsevier.com/locate/ssc
Dielectric properties and substitution preference of yttrium doped barium zirconium titanate ceramics D. Shan a,∗ , Y.F. Qu a , J.J. Song b a Key Laboratory for Advanced Ceramics and Machining Technology of Ministry of Education, Tianjin University, Tianjin 300072, China b Research and Development Group, Tianjin Samsung Electro-Mechanics Company, Tianjin 300072, China
Received 21 September 2006; accepted 27 September 2006 by F. De la Cruz Available online 23 October 2006
Abstract The dielectric properties of Ba(Zr0.25 Ti0.75 )O3 + xY2 O3 ceramics are investigated. We believe that, integrating with the lattice parameters, there is an alternation of substitution preference of yttrium ions for the host cations in perovskite lattice that is responsible for the Curie point. The Tc rises with the increase of Y3+ doping when the doping content is less than 0.05 at%, owing to the replacement of Y3+ ions for Ba2+ ions at the A-site; when the Y3+ content is more than 0.05 at%, Y3+ ions tend to occupy the B-site in perovskite lattice, causing a drop of Tc . Owing to the modifications of Y3+ doping, the loss tangent of BZT ceramics is depressed remarkably, making it a superior candidate to replace widely used lead-contained ceramics. c 2006 Elsevier Ltd. All rights reserved.
PACS: 77.22.-d Keywords: A. Ferroelectrics; C. Yttrium doping; D. Dielectric properties
1. Introduction BaTiO3 -based ceramics are widely used in the manufacture of thermistors and multiplayer ceramic capacitors (MLCC) owing to their high dielectric permittivity. Much effort has been expended to improve the dielectric properties by way of substitution for the host cations in perovskite lattice. Various BaTiO3 -based solid solutions have been developed, such as Ba(TiZr)O3 , [Ba(Bi0.5 Na0.5 )]TiO3 , (BaSr)TiO3 [1–3]. Among these solid solutions, the Ba(Ti1−y Zry )O3 (BZT) material has attracted considerable attention because Zr4+ is chemically more stable than Ti4+ [4–10]. Furthermore, it was reported that BZT ceramics showed a broad dielectric peak near Tm owing to the inhomogeneous distribution of Zr ions on Ti sites and to mechanical stress in the grain [8]. In perovskites, the relaxor behavior occurs mainly in lead-based compositions with more than one type of ion occupying the equivalent six coordinated crystallographic sites [11,12]. Lead-free compositions can be of
∗ Corresponding address: Materials Science and Engineering Department, Tianjin University, Tianjin, 300072, China. Tel.: +86 2228328757; fax: +86 2227404724. E-mail address: song and [email protected] (D. Shan).
c 2006 Elsevier Ltd. All rights reserved. 0038-1098/$ - see front matter doi:10.1016/j.ssc.2006.09.050
great interest for environmentally friendly applications such as actuators, dielectrics for capacitors, etc. Ionic doping is a common method for optimizing the electric properties of ceramics. The influence of rare earth dopant on the dielectric properties of barium titanate has been widely researched. The doping of yttrium in BZT ceramics, however, is rarely found in the literature. In this experiment, we synthesized the BZT + xY2 O3 ceramics (x = 0.025, 0.05, 0.1, 0.2, 0.4, 0.6 at%) in an ambient atmosphere using a conventional ceramics fabrication technique. The lattice parameters were calculated using XRD analysis. The influence of yttrium content on the dielectric properties of BZT ceramics was investigated. 2. Experimental procedure BaZrx Ti1−x O3 ceramics has been widely investigated. In this experiment, we chose BaZr0.25 Ti0.75 O3 as the ground component, which has been reported to have excellent relaxor properties. High purity (at least 99.5%) metal oxide and carbonate powder such as: ZrO2 , TiO2 , BaCO3 and Y2 O3 (Tianjin No. 3 chemical reagent factory), were used as the raw materials. The mixtures were milled in ethanol with nylon balls for 4 h. After drying, the mixed powder was calcined at 1150 ◦ C for 2 h. The yttrium element was added to the BZT precursor
66
D. Shan et al. / Solid State Communications 141 (2007) 65–68 Table 1 Relative density of BZT + xY2 O3 samples x (at%)
Relative density (%)
0 0.025 0.05 0.1 0.2 0.4 0.6
97.8 98.1 97.5 97.1 98.2 97.3 97.6
Fig. 1. X-ray diffraction patterns of BZT + Y2 O3 samples.
Fig. 3. Temperature dependence of relative permittivity of Y3+ doped BZT ceramics. Fig. 2. x dependences of relative permittivity and loss tangent of BZT+xY2 O3 samples.
by means of Y2 O3 . The content of dopant was designed to be 0 to 0.6 at%. The powder was then ground by ball mill in ethanol, for a further 6 h. The dried powder was uniaxially pressed into discs at 1000 kg/cm2 . The samples were sintered at 1300–1310 ◦ C for 2 h. The microstructures of the well-sintered samples were observed with ESEM (Philip XL 30 ESEM). The XRD pattern, as shown in Fig. 1, was obtained with X-ray diffraction-meter (Rigaku D/Max 2500V/PL). The XRD results indicated that as-fired compacts consist of a single phase with a cubic or pseudocubic perovskite structure. The relative density of the sintered compacts was measured by Archimedes’ method, with water as the liquid medium. After supersonic cleaning, firedon silver paste was used as the electrodes for purposes of measuring dielectric properties with an Automatic LCR Meter (Automatic LCR Meter 4425, Tianjin) at 1 kHz. Temperature dependences of permittivity and loss tangent were drawn with an automated dielectric system at 1 kHz, which consisted of the Automatic LCR Meter and a temperature-control unit. 3. Results The variation of dielectric properties with x in BZT + xY2 O3 samples is plotted in Fig. 2. Table 1 shows the relative density respectively. With the increase of x, the loss tangent is lowered greatly from 1.22% for a nil Y3+ doped sample to 0.25% for a 0.05 at% Y3+ doped one; meanwhile, the relative
Table 2 x (at%)
Tc (◦ C)
0 0.03 0.05 0.1 0.2 0.4 0.6
−16 −12 −7 −11 −14 −19 −22
permittivity does not fall greatly. Then, when the content of Y3+ continues to increase, the loss tangent rises and the relative permittivity continues to fall. Therefore, the trace amount of Y3+ doping could improve the dielectric properties remarkably, with permittivity falling little. The temperature dependence of the relative permittivity for Y3+ doped BZT ceramics sintered at 1310 ◦ C is illustrated in Fig. 3. With the increase of yttrium content, Tc rises slightly from −16 ◦ C for the nil yttrium sample to −6 ◦ C for the 0.05 at% yttrium doped one. For x > 0.05 at% samples, Tc shifts towards a low temperature with x increasing. The variation of lattice parameters obtained from XRD analysis is plotted in Fig. 4. We can see that the lattice constant (a) decreases with the increase of x at the beginning, and when the content of yttrium is beyond 0.05 at%, (a) rises with the increase of x. Interestingly, samples with 0.05 at% Y3+ have the highest Tc and lowest loss tangent among those Y3+ -doped BZT ceramics (as shown in Table 2 and Fig. 2), and we do not believe this to be coincidental.
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D. Shan et al. / Solid State Communications 141 (2007) 65–68
Fig. 4. Y3+ content dependence of lattice parameters of BZT ceramics.
4. Discussion It has been reported that aliovalent cations incorporated in perovskite lattice served as donors or acceptors, which could affect the electrical characteristics greatly, even though the solubility remained at trace level [13]. Watanabe reported that there were mainly three stages of substitution of rare earth elements in BaTiO3 . In the first two stages, doping ions replaced the original ions located in the lattice on the A or B site, respectively. The third stage was over limit of substitution and a secondary phase appeared [14]. The ionic radii of Ba2+ in 12 coordinates and Ti4+ or Zr4+ in 6 coordinates are 0.161 nm, 0.0605 nm and 0.072 nm, respectively. The ionic radii of Y3+ in 12 and in 6 coordinates are 0.106 nm and 0.086 nm [15]. Therefore, in terms of size, Y3+ can occupy either the A or B site in BZT solid solution. Lattice parameter (a) drops and the a/c ratio rises with Y3+ doping in BZT at the beginning, as shown in Fig. 4. According to Watanabe’s results, we infer that Ba2+ ions are replaced by Y3+ ions in the first stage, which has a smaller ionic radius, and consequently, lattice constant (a) decreases. Moreover, aliovalent substitutions cause a distortion of lattice; therefore,
the tetragonality (c/a ratio) is enhanced, as shown in Fig. 4. Consequently, the interactions between B-site ions and O2− become stronger, resulting in the rise of Tc in the first stage; Whereafter with the increase of x, Y3+ tends to occupy Bsites rather than A-sites. Because of the larger radius, the replacement of Y3+ for Ti4+ /Zr4+ in B-sites may depress the oriented displacement of B-site ions in the oxygen octahedrons, which are responsible for the spontaneous polarization. And the tetragonality (c/a ratio) is restrained. Therefore, the interactions between B-site ions and O2− become weaker and the depression effect results in the drop of Tc . As aforementioned, Ti4+ is chemically less stable. Therefore it is reasonable to assume that traces of TiO2 are lost in the sintering process leaving titanium and oxygen vacancies as shown by Eq. (1): 0000
TiTi + 2O → VTi + 2V•• O + TiO2 ↑ .
(1)
From Fig. 2 we can see that a trace of Y3+ -doping can restrain the loss tangent of BZT ceramics significantly. This is probably a consequence of some Y3+ ions entering titanium vacancies in the first stage, as shown by Eq. (2): 0000
0
Y••• + VTi → YTi .
(2)
In most perovskites, vacancies and holes are major mobile carriers. The occupation of Y3+ ions in titanium vacancies can reduce the quality of mobile carriers; therefore, the loss tangent is lowered effectively. In the second stage, Y3+ tends to substitute B-site ions (Ti4+ and Zr4+ ) and more oxygen vacancies are created, as shown in Eq. (3): 0
Y2 O3 → 2YB + 3OO + V•• O
(B—Zr/Ti).
(3)
This can explain why the loss tangent begins to increase when the content of Y3+ is beyond 0.05 at%, as shown in Fig. 2. Fig. 5 shows the micrographs of BZT+xY2 O3 ceramics. The grain size of BZT samples without yttrium doping was between 0.5 and 1 µm; however, the grain size of the BZT sample with
Fig. 5. SEM micrographs of BZT + xY2 O3 ceramics sintered at 1300–1310 ◦ C. (a) x = 0 (b) x = 0.025 at% (c) x = 0.2 at% (d) x = 0.6 at%.
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D. Shan et al. / Solid State Communications 141 (2007) 65–68
a trace amount of yttrium (0.025 at%) increased significantly to about 5–10 µm. The results indicate that yttrium doping leads to an increase in grain size; and this change might be associated with the large predominance of dielectric properties, which accord with traditional relaxor ferroelectrics [16–18]. With the increase in yttrium content, there is no obvious change in the figure and size of crystal grains, as shown in Fig. 5(c) and (d). 5. Conclusions The dielectric properties of 0–0.6 at% yttrium doping BZT ceramics were investigated. With a trace amount of Y3+ doping, the dielectric properties of BZT ceramics are enhanced remarkably; loss tangent decreases from 1.22% for a nil Y3+ doped sample to 0.25% for a 0.05 at% Y3+ doped one, which might result from stuffing of Y3+ ions in Ti vacancies. Integrating with the lattice parameters, obtained via XRD analysis, we conclude that there is an alternation of substitution preference of yttrium ions for the host cations in perovskite lattice, and this alternation affects the lattice parameters and Tc of BZT ceramics. Thanks to the modifications of Y3+ doping, the dielectric properties (especially the loss tangent) of BZT ceramics are improved remarkably, making it a superior candidate to replace the widely used lead-contained ceramics. Acknowledgements The author would like to acknowledge the support of Key
laboratory for advanced ceramics and machining technology of Ministry of Education. References [1] J.W. Zhai, X. Yao, B. Shen, L.Y. Zhang, H. chen, J. Electroceram. 11 (2003) 157. [2] Y.F. Qu, D. Shan, J.J. Song, Mater. Sci. Eng. B 121 (2005) 148. [3] Y. Skabe, Y. Takeshima, K. Tanaka, J. Electroceram. 3 (1999) 115. [4] Y. Zhi, A. Chen, R.Y. Gu, A.S. Bhalla, Appl. Phys. Lett. 81 (2002) 1285. [5] Y. Zhi, R.Y. Gu, A.S. Bhalla, Appl. Phys. Lett. 77 (2000) 1535. [6] J. Ravez, C. Broustera, A. Simon, J. Mater. Chem. 9 (1999) 1609. [7] X.G. Tang, H.L. Chan, A.L. Ding, Thin Solid Films 460 (2004) 227. [8] U. Weber, G. Greuel, U. Boettger, S. Weber, D. Hennings, R. Waser, J. Amer. Ceram. Soc. 84 (2001) 759. [9] Ph. Sciau, G. Calvarin, J. Ravez, J. Solid State Commun. 113 (2000) 77. [10] X.G. Tang, K.H. Chew, H.L.W. Chan, Acta. Mater. 52 (2004) 5177. [11] C. Lei, K.P. Chen, X.W. Zhang, J. Wang, Solid State Commun. 123 (2002) 445. [12] W. Dmowski, M.K. Akbas, T. Egami, P.K. Davies, J. Phys. Chem. Solids 63 (2002) 15. [13] M.T. Buscaglia, V. Buscaglia, M. Viviani, P. Nanni, M. Hanuskova, J. Eur. Ceram. Soc. 20 (2000) 1997. [14] K. Watanabe, H. Ohsato, H. Kishi, Y. Okino, N. Kohzu, Y. Iguchi, T. Okuda, Solid State Ion. 108 (1998) 129. [15] J.A. Dean, Lange’s Handbook of Chemistry (J.F. Wei, Trans.), Science Press, Beijing, China, 2003, p. 4.31. [16] N.X. Zhang, Z.L. Gui, L.T. Li, Mater. Lett. 56 (2002) 244. [17] P. Pookmanee, G. Rujijanagul, S. Ananta, R.B. Heimann, S. Phanichphant, J. Eur. Ceram. Soc. 24 (2004) 517. [18] S.B. Cho, J.S. Noh, M.M. Lencka, R.E. Riman, J. Eur. Ceram. Soc. 23 (2003) 2323.
Dielectric properties and substitution preference of yttrium doped barium zirconium titanate ceramics D. Shan a,∗ , Y.F. Qu a , J.J. Song b a Key Laboratory for Advanced Ceramics and Machining Technology of Ministry of Education, Tianjin University, Tianjin 300072, China b Research and Development Group, Tianjin Samsung Electro-Mechanics Company, Tianjin 300072, China
Received 21 September 2006; accepted 27 September 2006 by F. De la Cruz Available online 23 October 2006
Abstract The dielectric properties of Ba(Zr0.25 Ti0.75 )O3 + xY2 O3 ceramics are investigated. We believe that, integrating with the lattice parameters, there is an alternation of substitution preference of yttrium ions for the host cations in perovskite lattice that is responsible for the Curie point. The Tc rises with the increase of Y3+ doping when the doping content is less than 0.05 at%, owing to the replacement of Y3+ ions for Ba2+ ions at the A-site; when the Y3+ content is more than 0.05 at%, Y3+ ions tend to occupy the B-site in perovskite lattice, causing a drop of Tc . Owing to the modifications of Y3+ doping, the loss tangent of BZT ceramics is depressed remarkably, making it a superior candidate to replace widely used lead-contained ceramics. c 2006 Elsevier Ltd. All rights reserved.
PACS: 77.22.-d Keywords: A. Ferroelectrics; C. Yttrium doping; D. Dielectric properties
1. Introduction BaTiO3 -based ceramics are widely used in the manufacture of thermistors and multiplayer ceramic capacitors (MLCC) owing to their high dielectric permittivity. Much effort has been expended to improve the dielectric properties by way of substitution for the host cations in perovskite lattice. Various BaTiO3 -based solid solutions have been developed, such as Ba(TiZr)O3 , [Ba(Bi0.5 Na0.5 )]TiO3 , (BaSr)TiO3 [1–3]. Among these solid solutions, the Ba(Ti1−y Zry )O3 (BZT) material has attracted considerable attention because Zr4+ is chemically more stable than Ti4+ [4–10]. Furthermore, it was reported that BZT ceramics showed a broad dielectric peak near Tm owing to the inhomogeneous distribution of Zr ions on Ti sites and to mechanical stress in the grain [8]. In perovskites, the relaxor behavior occurs mainly in lead-based compositions with more than one type of ion occupying the equivalent six coordinated crystallographic sites [11,12]. Lead-free compositions can be of
∗ Corresponding address: Materials Science and Engineering Department, Tianjin University, Tianjin, 300072, China. Tel.: +86 2228328757; fax: +86 2227404724. E-mail address: song and [email protected] (D. Shan).
c 2006 Elsevier Ltd. All rights reserved. 0038-1098/$ - see front matter doi:10.1016/j.ssc.2006.09.050
great interest for environmentally friendly applications such as actuators, dielectrics for capacitors, etc. Ionic doping is a common method for optimizing the electric properties of ceramics. The influence of rare earth dopant on the dielectric properties of barium titanate has been widely researched. The doping of yttrium in BZT ceramics, however, is rarely found in the literature. In this experiment, we synthesized the BZT + xY2 O3 ceramics (x = 0.025, 0.05, 0.1, 0.2, 0.4, 0.6 at%) in an ambient atmosphere using a conventional ceramics fabrication technique. The lattice parameters were calculated using XRD analysis. The influence of yttrium content on the dielectric properties of BZT ceramics was investigated. 2. Experimental procedure BaZrx Ti1−x O3 ceramics has been widely investigated. In this experiment, we chose BaZr0.25 Ti0.75 O3 as the ground component, which has been reported to have excellent relaxor properties. High purity (at least 99.5%) metal oxide and carbonate powder such as: ZrO2 , TiO2 , BaCO3 and Y2 O3 (Tianjin No. 3 chemical reagent factory), were used as the raw materials. The mixtures were milled in ethanol with nylon balls for 4 h. After drying, the mixed powder was calcined at 1150 ◦ C for 2 h. The yttrium element was added to the BZT precursor
66
D. Shan et al. / Solid State Communications 141 (2007) 65–68 Table 1 Relative density of BZT + xY2 O3 samples x (at%)
Relative density (%)
0 0.025 0.05 0.1 0.2 0.4 0.6
97.8 98.1 97.5 97.1 98.2 97.3 97.6
Fig. 1. X-ray diffraction patterns of BZT + Y2 O3 samples.
Fig. 3. Temperature dependence of relative permittivity of Y3+ doped BZT ceramics. Fig. 2. x dependences of relative permittivity and loss tangent of BZT+xY2 O3 samples.
by means of Y2 O3 . The content of dopant was designed to be 0 to 0.6 at%. The powder was then ground by ball mill in ethanol, for a further 6 h. The dried powder was uniaxially pressed into discs at 1000 kg/cm2 . The samples were sintered at 1300–1310 ◦ C for 2 h. The microstructures of the well-sintered samples were observed with ESEM (Philip XL 30 ESEM). The XRD pattern, as shown in Fig. 1, was obtained with X-ray diffraction-meter (Rigaku D/Max 2500V/PL). The XRD results indicated that as-fired compacts consist of a single phase with a cubic or pseudocubic perovskite structure. The relative density of the sintered compacts was measured by Archimedes’ method, with water as the liquid medium. After supersonic cleaning, firedon silver paste was used as the electrodes for purposes of measuring dielectric properties with an Automatic LCR Meter (Automatic LCR Meter 4425, Tianjin) at 1 kHz. Temperature dependences of permittivity and loss tangent were drawn with an automated dielectric system at 1 kHz, which consisted of the Automatic LCR Meter and a temperature-control unit. 3. Results The variation of dielectric properties with x in BZT + xY2 O3 samples is plotted in Fig. 2. Table 1 shows the relative density respectively. With the increase of x, the loss tangent is lowered greatly from 1.22% for a nil Y3+ doped sample to 0.25% for a 0.05 at% Y3+ doped one; meanwhile, the relative
Table 2 x (at%)
Tc (◦ C)
0 0.03 0.05 0.1 0.2 0.4 0.6
−16 −12 −7 −11 −14 −19 −22
permittivity does not fall greatly. Then, when the content of Y3+ continues to increase, the loss tangent rises and the relative permittivity continues to fall. Therefore, the trace amount of Y3+ doping could improve the dielectric properties remarkably, with permittivity falling little. The temperature dependence of the relative permittivity for Y3+ doped BZT ceramics sintered at 1310 ◦ C is illustrated in Fig. 3. With the increase of yttrium content, Tc rises slightly from −16 ◦ C for the nil yttrium sample to −6 ◦ C for the 0.05 at% yttrium doped one. For x > 0.05 at% samples, Tc shifts towards a low temperature with x increasing. The variation of lattice parameters obtained from XRD analysis is plotted in Fig. 4. We can see that the lattice constant (a) decreases with the increase of x at the beginning, and when the content of yttrium is beyond 0.05 at%, (a) rises with the increase of x. Interestingly, samples with 0.05 at% Y3+ have the highest Tc and lowest loss tangent among those Y3+ -doped BZT ceramics (as shown in Table 2 and Fig. 2), and we do not believe this to be coincidental.
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D. Shan et al. / Solid State Communications 141 (2007) 65–68
Fig. 4. Y3+ content dependence of lattice parameters of BZT ceramics.
4. Discussion It has been reported that aliovalent cations incorporated in perovskite lattice served as donors or acceptors, which could affect the electrical characteristics greatly, even though the solubility remained at trace level [13]. Watanabe reported that there were mainly three stages of substitution of rare earth elements in BaTiO3 . In the first two stages, doping ions replaced the original ions located in the lattice on the A or B site, respectively. The third stage was over limit of substitution and a secondary phase appeared [14]. The ionic radii of Ba2+ in 12 coordinates and Ti4+ or Zr4+ in 6 coordinates are 0.161 nm, 0.0605 nm and 0.072 nm, respectively. The ionic radii of Y3+ in 12 and in 6 coordinates are 0.106 nm and 0.086 nm [15]. Therefore, in terms of size, Y3+ can occupy either the A or B site in BZT solid solution. Lattice parameter (a) drops and the a/c ratio rises with Y3+ doping in BZT at the beginning, as shown in Fig. 4. According to Watanabe’s results, we infer that Ba2+ ions are replaced by Y3+ ions in the first stage, which has a smaller ionic radius, and consequently, lattice constant (a) decreases. Moreover, aliovalent substitutions cause a distortion of lattice; therefore,
the tetragonality (c/a ratio) is enhanced, as shown in Fig. 4. Consequently, the interactions between B-site ions and O2− become stronger, resulting in the rise of Tc in the first stage; Whereafter with the increase of x, Y3+ tends to occupy Bsites rather than A-sites. Because of the larger radius, the replacement of Y3+ for Ti4+ /Zr4+ in B-sites may depress the oriented displacement of B-site ions in the oxygen octahedrons, which are responsible for the spontaneous polarization. And the tetragonality (c/a ratio) is restrained. Therefore, the interactions between B-site ions and O2− become weaker and the depression effect results in the drop of Tc . As aforementioned, Ti4+ is chemically less stable. Therefore it is reasonable to assume that traces of TiO2 are lost in the sintering process leaving titanium and oxygen vacancies as shown by Eq. (1): 0000
TiTi + 2O → VTi + 2V•• O + TiO2 ↑ .
(1)
From Fig. 2 we can see that a trace of Y3+ -doping can restrain the loss tangent of BZT ceramics significantly. This is probably a consequence of some Y3+ ions entering titanium vacancies in the first stage, as shown by Eq. (2): 0000
0
Y••• + VTi → YTi .
(2)
In most perovskites, vacancies and holes are major mobile carriers. The occupation of Y3+ ions in titanium vacancies can reduce the quality of mobile carriers; therefore, the loss tangent is lowered effectively. In the second stage, Y3+ tends to substitute B-site ions (Ti4+ and Zr4+ ) and more oxygen vacancies are created, as shown in Eq. (3): 0
Y2 O3 → 2YB + 3OO + V•• O
(B—Zr/Ti).
(3)
This can explain why the loss tangent begins to increase when the content of Y3+ is beyond 0.05 at%, as shown in Fig. 2. Fig. 5 shows the micrographs of BZT+xY2 O3 ceramics. The grain size of BZT samples without yttrium doping was between 0.5 and 1 µm; however, the grain size of the BZT sample with
Fig. 5. SEM micrographs of BZT + xY2 O3 ceramics sintered at 1300–1310 ◦ C. (a) x = 0 (b) x = 0.025 at% (c) x = 0.2 at% (d) x = 0.6 at%.
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D. Shan et al. / Solid State Communications 141 (2007) 65–68
a trace amount of yttrium (0.025 at%) increased significantly to about 5–10 µm. The results indicate that yttrium doping leads to an increase in grain size; and this change might be associated with the large predominance of dielectric properties, which accord with traditional relaxor ferroelectrics [16–18]. With the increase in yttrium content, there is no obvious change in the figure and size of crystal grains, as shown in Fig. 5(c) and (d). 5. Conclusions The dielectric properties of 0–0.6 at% yttrium doping BZT ceramics were investigated. With a trace amount of Y3+ doping, the dielectric properties of BZT ceramics are enhanced remarkably; loss tangent decreases from 1.22% for a nil Y3+ doped sample to 0.25% for a 0.05 at% Y3+ doped one, which might result from stuffing of Y3+ ions in Ti vacancies. Integrating with the lattice parameters, obtained via XRD analysis, we conclude that there is an alternation of substitution preference of yttrium ions for the host cations in perovskite lattice, and this alternation affects the lattice parameters and Tc of BZT ceramics. Thanks to the modifications of Y3+ doping, the dielectric properties (especially the loss tangent) of BZT ceramics are improved remarkably, making it a superior candidate to replace the widely used lead-contained ceramics. Acknowledgements The author would like to acknowledge the support of Key
laboratory for advanced ceramics and machining technology of Ministry of Education. References [1] J.W. Zhai, X. Yao, B. Shen, L.Y. Zhang, H. chen, J. Electroceram. 11 (2003) 157. [2] Y.F. Qu, D. Shan, J.J. Song, Mater. Sci. Eng. B 121 (2005) 148. [3] Y. Skabe, Y. Takeshima, K. Tanaka, J. Electroceram. 3 (1999) 115. [4] Y. Zhi, A. Chen, R.Y. Gu, A.S. Bhalla, Appl. Phys. Lett. 81 (2002) 1285. [5] Y. Zhi, R.Y. Gu, A.S. Bhalla, Appl. Phys. Lett. 77 (2000) 1535. [6] J. Ravez, C. Broustera, A. Simon, J. Mater. Chem. 9 (1999) 1609. [7] X.G. Tang, H.L. Chan, A.L. Ding, Thin Solid Films 460 (2004) 227. [8] U. Weber, G. Greuel, U. Boettger, S. Weber, D. Hennings, R. Waser, J. Amer. Ceram. Soc. 84 (2001) 759. [9] Ph. Sciau, G. Calvarin, J. Ravez, J. Solid State Commun. 113 (2000) 77. [10] X.G. Tang, K.H. Chew, H.L.W. Chan, Acta. Mater. 52 (2004) 5177. [11] C. Lei, K.P. Chen, X.W. Zhang, J. Wang, Solid State Commun. 123 (2002) 445. [12] W. Dmowski, M.K. Akbas, T. Egami, P.K. Davies, J. Phys. Chem. Solids 63 (2002) 15. [13] M.T. Buscaglia, V. Buscaglia, M. Viviani, P. Nanni, M. Hanuskova, J. Eur. Ceram. Soc. 20 (2000) 1997. [14] K. Watanabe, H. Ohsato, H. Kishi, Y. Okino, N. Kohzu, Y. Iguchi, T. Okuda, Solid State Ion. 108 (1998) 129. [15] J.A. Dean, Lange’s Handbook of Chemistry (J.F. Wei, Trans.), Science Press, Beijing, China, 2003, p. 4.31. [16] N.X. Zhang, Z.L. Gui, L.T. Li, Mater. Lett. 56 (2002) 244. [17] P. Pookmanee, G. Rujijanagul, S. Ananta, R.B. Heimann, S. Phanichphant, J. Eur. Ceram. Soc. 24 (2004) 517. [18] S.B. Cho, J.S. Noh, M.M. Lencka, R.E. Riman, J. Eur. Ceram. Soc. 23 (2003) 2323.