Different piezoelectric grain size effects in BaTiO3 ceramics

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Different piezoelectric grain size effect in BaTiO3 ceramics J.C. Wang, P. Zheng, R.Q Yin, L.M. Zheng, J. Du, L. Zheng, J.X. Deng, K.X. Song, H.B. Qin

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Cite this article as: J.C. Wang, P. Zheng, R.Q Yin, L.M. Zheng, J. Du, L. Zheng, J.X. Deng, K.X. Song, H.B. Qin, Different piezoelectric grain size effect in BaTiO3 ceramics, Ceramics International, http://dx.doi.org/10.1016/j.ceramint.2015.07.039 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting galley proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Different piezoelectric grain size effect in BaTiO3 ceramics J.C. Wanga, P. Zhenga*, R.Q Yina, L.M. Zhengb, J. Duc, L. Zhenga, J.X. Denga, K.X. Songa, and H.B. Qina. a

b

College of Electronics and Information, Hangzhou Dianzi University, Hangzhou 310018, China

Condensed Matter Science and Technology Institute, Harbin Institute of Technology, Harbin 150001, China c

School of Materials Sciences and Engineering, Liaocheng University, Liaocheng 252059, China

Abstract

Four groups of barium titanate (BaTiO3) ceramics with high piezoelectric coefficient have been successfully fabricated from different raw materials. Their average grain size (g) dependences of the piezoelectric coefficient d33 were systematically studied. It was found that for two groups of BaTiO3 ceramics, d33 firstly increases and then decreases with the increase of g, with a maximum d33 of 449 pC/N and 501 pC/N respectively at approximately 1 µm grain size, while for the other two groups of BaTiO3 ceramics, d33 keeps increasing with the increase of g. The highest d33 of 401 pC/N and 424 pC/N were obtained when g is larger than 50 µm. The experimental results indicated that piezoelectric grain size effect in BaTiO3 ceramics may be not absolute. Possible mechanisms arising from differences in domain configuration were discussed.

Keywords: Barium titanate; Grain size; Piezoelectric coefficient.

1.

Introduction

Much effort has been paid to develop high performance lead-free ferroelectric ceramics for piezoelectric applications in substitution of Lead Zirconate-Titanate (PZT) based ceramics [1-5]. Among all these lead-free candidates, barium titanate *

Corresponding author. Tel.: +86 571 86878678; E-mail: [email protected] 1

based materials is one important family. But for a long time, it had been reported to show a moderate d33 of 191 pC/N, which is much lower than those of commercial PZT ceramics [6]. However, recent studies have revealed that much higher d33 value (419 pC/N and 519 pC/N, respectively) could be obtained in conventionally sintered BaTiO3 ceramics prepared by solid-state reaction with ordinary BaCO3 and TiO2 raw powders, two-step sintering using hydrothermally synthesized BaTiO3 fine powder, respectively [7-9]. These breakthroughs indicate that BaTiO3-based ceramics have great potential to be used as a lead-free piezoelectric material. In most of the previous reports, it is widely accepted that the microstructure, especially the grain size, is the major factor that affects d33 value in BaTiO3 ceramics [7-16]. However, there still exist some disagreements in the variations of the d33 with the average grain sizes (g) [7,9,10,15]. Generally, it was reported that the d33 of BaTiO3 ceramics increased with the decrease of g and maximized around 1 µm, then it decreased significantly with the further decrease of g [7,9-12]. This phenomenon was referred as the piezoelectric grain size effect in previous studies [7,9], after the well-known dielectric grain size effect [18]. However, a few researchers’ results show that the grain size dependence of d33 in some BaTiO3 ceramics do not follow this trend, relatively high d33 values were obtained in the ceramics with the g larger than 10 µm or even up to several tens of micrometers [8,15,16]. Unfortunately, the results of these studies are scattered and not systematic. Further studies still need to be done to disclose the exact relationship between the grain size and d33 of BaTiO3 ceramics.

2

On the other hand, it should be noted that in these studies, the BaTiO3 ceramics were prepared with different raw materials [7-9,14], which should be probably responsible for the different piezoelectric grain size effect. In this study, four groups of BaTiO3 ceramic with high d33 have been fabricated with different ordinary BaCO3 and TiO2 powders as the raw materials through conventional solid-state reaction route. It was found that the d33 of two groups of BaTiO3 ceramics firstly increase then decrease with the increase of grain sizes, with the maximum d33 value at approximately 1 µm. However, for the other two groups of BaTiO3 ceramics, the d33 keeps increasing with the increase of average grain sizes, with the maximum d33 values obtained at g larger than 50 µm. Possible mechanisms that result in the different piezoelectric grain size effect were discussed.

2.

Experimental

BaTiO3 powders were prepared by the conventional solid-state reaction technique, starting from properly choosing the raw materials of commercial BaCO3 powder (BaCO3-Sin, purity≥99.0%, Sinopharm Chemical Reagent Co. Ltd.) and BaCO3 powder (BaCO3-Ala, purity≥99.8%, Aladdin Industrial Corporation), TiO2 powder (TiO2-01, purity≥99.8%, Xiantao Zhongxing Electronic Material Co. Ltd.) and TiO2 powder (TiO2-07, purity≥99.8%, Xiantao Zhongxing Electronic Material Co. Ltd.). The raw materials were weighed according to the stoichiometric ratio and ball-milled in ethanol for 12 h on a planetary ball mill. The milled slurry mixture was dried, crushed in an agate mortar and then pressed into large circular plates at 30MPa. Calcination was performed at 1050oC for 4 h, followed by a second ball-milling in 3

ethanol procedure for 12 h. After the second ball-milling, the BaTiO3 powders was mixed with a 0.5 wt. % polyvinyl alcohol (PVA) binder and pressed into small disks (15 mm in diameter and 1.5 mm in thickness) at 200 MPa. The PVA binder was then burned out at 650oC for 0.5 h. Finally, BaTiO3 ceramics were densified by conventional sintering at different temperatures (from 1150oC to 1450oC) for 2 h. To characterize piezoelectric properties, the ceramic specimens were coated with silver paint on the upper and bottom surfaces and fired at 575oC for 20 min. Poling was accomplished at 80oC in silicon oil under 5.0 kV/mm for 30min. Measurements of the piezoelectric properties were taken out after 24 h. The d33 value was measured by a Berlicourt-type d33 meter (YE 2730A). Crystallographic structure was investigated by X-ray diffraction (XRD; Rigaku Co., Tokyo, Japan). The microstructure and domain configuration of the ceramics were examined by scanning electron microscope (SEM, JEOL JSM6380-LV), based on which the average grain size g and domain width were calculated. To characterize the inner microstructure of the ceramics, the specimens were mirror-polished after grinding off ~0.1 mm of the surface layer with a fine Al2O3 powder and etched thermally under 1000oC for 1 h. While for the domain configuration observation, the polished specimens were chemically etched for 30 s in an aqueous solution of 5% HCl (into which a few drops of HF was added).

3.

Results and Discussion

Fig. 1 presents SEM images of four kinds of starting raw materials powder. The mean particle size was calculated by averaging at least 100 particles sizes. For 4

BaCO3-Ala and BaCO3-Sin, the powders show rod granular structure, with a mean diameter of about 247nm and 341nm respectively. For TiO2-01 and TiO2-07, the powders show globular granular structure, with a mean diameter of about 931nm and 225nm respectively. The XRD profiles of these four raw material powders are shown in Fig.2. It can be found that all the raw materials powders exhibit a pure structure without detectable impurity phase (JCPDS-ICDD file no.05-0378 for BaCO3 and no.21-1276 for TiO2). Fig. 3 presents SEM images of the four groups of BaTiO3 powders after calcination and the second ball-milling. For convenience, BT-Sin-01 is employed to stand for the BaTiO3 powder prepared by BaCO3-Sin and TiO2-01 powders and BT-Sin-07 represents the powder prepared by BaCO3-Sin and TiO2-07 powders, respectively. Similar abbreviations are used for the other two groups of powder as BT-Ala-01 and BT-Ala-07. As shown, the average particle diameters of BT-Sin-01 and BT-Ala-01 powders are larger than those of the BT-Sin-07 and BT-Ala-07 powders, which may be attributed to the larger particle size of TiO2 raw materials used in these samples. The type of BaCO3 raw material has little influence on the microstructures of the powders. Fig. 4 shows the XRD profiles of these four groups of powders. It can be seen that the crystallographic structures of all these powders are of pure tetragonal BaTiO3 symmetry (JCPDS-ICDD file no.05-0626). It indicates that the raw materials used in this experiment have little influences on the crystalline structure of BaTiO3 powders.

5

The relative density (ρ0) of the four groups of BaTiO3 ceramics sintered under the different temperature conditions are listed in Table 1. The density of the specimens are calculated by averaging the density of three samples obtained by measuring the mass and the dimensions, and the ρ0 is calculated according to the theoretical density of 6.017 g/cm3 for the pure BaTiO3 ceramics. As shown in Table 1, for all the four groups of specimens, ρ0 increases with increasing sintering temperature, and could reach nearly 98% at high sintering temperature. However, the densification temperatures are different for each group specimens. The relative density of BT-Sin-01 specimens is less than 94% at a low sintering temperature below 1170oC. Similarly, the relative density of BT-Sin-07 fabricated below 1190oC is less than the 94%. While for BT-Ala-01 and BT-Ala-07 specimens, the sintering temperatures have to be increased to 1230oC to get specimens with relative density higher than 94%. The relationship between sintering temperature and d33 are also shown in Table 1. For the BT-Sin-01 and the BT-Sin-07 specimens, the d33 values increase significantly with increasing sintering temperature, reaching maximum values of 449 pC/N and 501 pC/N at 1190oC and 1210oC, respectively, and then gradually decrease with increasing sintering temperature. However, for the BT-Ala-01and the BT-Ala-07 specimens, the d33 value keeps increasing with increasing sintering temperature and reaches maximum values of 401 pC/N and 424 pC/N at 1450oC. As can be seen, high d33 value (>400 pC/N) can be obtained in all the four groups of BaTiO3, despite of the different sintering temperature. In addition, it should be noted that the maximum d33 value of 501 pC/N obtained in BT-Sin-07 BaTiO3 ceramics is the highest values so far 6

obtained in BaTiO3 ceramics prepared by conventional sintering method, which is close to that (519 pC/N) obtained by two-step sintering method using hydrothermally synthesized fine BaTiO3 powders [9], and higher than the reported value of the 486 pC/N obtained by hot-pressed BaTiO3 ceramics from hydrothermally synthesized fine BaTiO3 powders [8]. This result indicates that the high performance BaTiO3 ceramics could be achieved even by conventional sintering technique from ordinary BaTiO3 powders prepared by solid state reaction method. The piezoelectric properties are considered to be closely related to the microstructure of piezoelectric ceramics. Fig. 5 presents SEM images of four kinds of various BaTiO3 ceramics sintered under different temperatures. As shown, for all the four groups of BaTiO3 ceramics, the grain size increases with the increase of sintering temperature. However, their microstructure exhibits great differences. All the BT-Sin-01 and BT- Sin-07 specimens sintered at different temperatures exhibit uniform grain size distributions below 1450oC. While for BT-Ala-01 and BT-Ala-07 samples, the microstructure are not uniform when sintered at lower temperatures. For the BT-Ala-01 sample sintered at 1250oC, the largest grain size reaches about 26.8 µm in diameter whereas small grains are only about 647 nm. In the BT-Ala-07 sample sintered at 1250oC, the largest grain size reaches about 29.8 µm in diameter whereas small grains are only about 543 nm. However, further increasing the sintered temperature leads to rapid growth of the small grains and the uniform microstructure can be observed. Furthermore, it should be noted that the average grain size of BT-Ala-01 and BT-Ala-07 samples are larger than that of BT-Sin-01 and BT-Sin-07 samples at the same sintering temperature, which may be ascribed to the different 7

purity level of BaCO3 starting powders. Fig. 6 shows d33 value as a function of average grain size g for all the BaTiO3 ceramics. The g values were measured by the line-intercept method based on the SEM micrographs. For BT-Ala-01 and BT-Ala-07 samples sintered at lower temperatures (<1300oC), data are not shown as their bimodal grain sizes distribution. As shown, the BT-Sin-01 and BT-Sin-07 exhibit a trend that the values of d33 increase significantly with decreasing grain-size, reaching maximum at g = 1.32 µm and 1.13 µm respectively, and then decrease rapidly with further decreasing grain-size. This phenomenon agrees well with the piezoelectric grain size effect reported in previous study [7,9]. However, the BT-Ala-01 and BT-Ala-07 samples display entirely different piezoelectric grain size dependence behaviors: d33 increases gradually with the increase of grain size and the highest d33 values are observed at g = 56.3 µm and 59.2 µm respectively. The experimental results reveal us that the previously reported high piezoelectric constant d33 obtained in samples with large grain sizes in not occasional. The mechanism for the grain size effect on in BaTiO3 ceramics may not be absolute. The two entirely different trends of d33 with g are very confusing. The XRD patterns of the BaTiO3 ceramics with the highest d33 values of each group are shown in Fig.7. As can be seen, all the ceramics are of pure tetragonal BaTiO3 symmetry (JCPDS-ICDD file no.05-0626). It indicates that the purity of BaTiO3 ceramic may be not the major reason for the two entirely different trends of d33 with g. As known, the contributions to the piezoelectric properties of the piezoceramics could be attributed to intrinsic and extrinsic parts. The intrinsic contribution is attributed to the relative 8

ion shift that preserves the ferroelectric crystal structure, whereas the extrinsic contribution is usually ascribed to the domain wall movement [18-21]. Obviously, both the two piezoelectric grain sizes effect are closely related to the extrinsic contributions. For the piezoelectric grain size effect that maximum d33 at around g = 1 µm, a mechanism from the viewpoint of domain wall motions is widely accepted [7,9]. When g is above 1 µm, the 90° domain width diminishes with decreasing g, inducing higher activity of the 90◦ domain walls and enhanced piezoelectric properties [19,20]. Subsequently, d33 rapidly drops with a further decrease in g owing to the reduced domain density [7,9]. Apparently, this mechanism is insufficient to explain the piezoelectric grain-size effect that d33 increase with the g observed in this study, unless the larger grains exhibit smaller 90◦ domain width and higher 90◦ domain walls density than the smaller grains in BT-Ala-01 and BT-Ala-07 samples. Systematic studies of the domain structures are needed. Fig. 8 displays the domain structures of BT-Ala-01 and BT-Ala-07 ceramics with different grain size. As shown, stripes and herringbone patterns are recognizable inside the grains. These have been reported to be typical features of the domain configuration of BaTiO3 ceramics in the tetragonal phase [6-9,17]. The stripes are taken to correspond to the 90o domain patterns. The herringbone patterns are the consequence of the combination of two sets of alternating 90o domains [7]. For the BT-Ala-01 BaTiO3 ceramics, the average domain width after poling are 467, 638 and 777 nm for the samples with typical g values of 19.7, 43.6 and 56.3 µm. Similarly, the 9

average domain width are 343, 635 and 753 nm for BT-Ala-07 BaTiO3 ceramics with typical g of 24.5, 42.4 and 59.2 µm. Obviously, the domain density decreases with increasing g for both groups of BaTiO3 ceramics, which is similar to the ceramics with piezoelectric grain size effect that have maximum d33 at around g = 1 µm [7,9,17]. Therefore, the domain density cannot be the major reason for the d33 increase with increasing g for the BT-Ala-01 and BT-Ala-07 BaTiO3 ceramics. Nevertheless, by carefully analyzing the domain configuration in Fig.8, it can be found that the number of herringbone domain patterns decrease with the increase of the grain size in BT-Ala-01and BT-Ala-07 BaTiO3 ceramics. This phenomenon is obviously different from that reported in the previous studies, in which more herringbone domain patterns appear in the larger grains [7].As known, the motion of a 90o domain wall might be inhibited by the interactions from the neighboring domain walls that are included in the complex and conjoined herringbone domain patterns [7]. In such a case, it might be more proper to consider the motion of domain walls as the joint behavior, which will increase the effective inertia mass for an individual domain wall. This will reduce the domain walls’ response to the external electrical or stress signal, reduce the extrinsic contribution of domain wall motion to piezoelectric activities and lead to the lower d33 value [7,22,23]. Therefore, the decrease of the number of herringbone domain walls may be an important reason for the increase of the d33 in BT-Ala-01 and BT-Ala-07 BaTiO3 ceramics with larger grain. Furthermore, it should be noted the experiment result do not exclude the effect of domain density on the piezoelectric properties. As mentioned above, the d33 values of BT-Ala-07 samples are higher than that of BT-Ala-01 samples at same grain size (as 10

shown in Fig. 7). This may be ascribed to the higher domain density of the BT-Ala-07 samples than that of BT-Ala-01 samples at surrounding grain size. The reason that the d33 values of BT-Sin-07 samples are higher than that of BT-Sin-01 samples at g < 14 µm may be also ascribed to the domain density [7,9]. But in the larger grains, the herringbone domain patterns are considered to be the more important factor that influences the piezoelectric activities. Furthermore, the effect of raw materials on the microstructures and domain configurations is still not clear now. It is speculated that the different purity level of raw material may be an important factor, which will introduce different level of defect during sintering that influence the grain growth.

4.

Conclusions

Two different piezoelectric grain-sizes effects were obtained in four groups of BaTiO3 ceramic with high d33 values (>400 pC/N). It was found that two groups of BaTiO3 ceramics exhibited a trend similar to the traditional piezoelectric grain size effect, with the maximum d33 value at average grain size approximately 1 µm. The other two groups of BaTiO3 ceramics displayed an entirely different piezoelectric grain size effect, relatively high d33 values were observed at g values larger than 50 µm. The experimental results revealed that the piezoelectric grain size effect for BaTiO3 ceramics may be not absolute. The decreased number of the herringbone domain walls might be an important reason for the increase of d33 in BT-Ala-01 and BT-Ala-07 BaTiO3 ceramics with larger grains.

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Acknowledgements Financial supports from the National Natural Science Foundation of China (Grant No. 51302056, 51202051, 51102062 and 51302124 and the Nonprofit technology Research program of Zhejiang Province (Grant No. 2013C31064) are gratefully acknowledged.

References [1] L. E. Cross, Materials science: Lead-free at last, Nature, 432, (2004) 24-25. [2] Y. Saito, H. Takato, T. Tani, T. Nonoyama, K. Takatori,T. Homma, T. Nagaya and M. Nakamura, Lead-free piezoceramics, Nature, 432, (2004) 84-87. [3] Limei Zheng, Xiaoqing Huo, Rui Wang, Junjun Wang, Wenhua Jiang and Wenwu Cao, Large size lead-free (Na,K)(Nb,Ta)O3 piezoelectric single crystal: growth and full tensor properties, Chem. Soc. Rev., 15, (2013) 7718–7722. [4] Limei Zheng, Shiyang Li, Shijing Sang, Junjun Wang, Xiaoqing Huo, Rui Wang, Zhongyuan Yuan, and Wenwu Cao, Complete set of material constants of single domain (K, Na)(Nb, Ta)O3 single crystal and their orientation dependence, Appl. Phys. Let., 105, (2014) 212902. [5] T. R. Shrout and S. J. Zhang, Lead-free piezoelectric ceramics: Alternatives for PZT? J. Electroceram., 19, (2007) 111-124. [6] B. Jaffe, W. R. Cook, and H. Jaffe, Piezoelectric ceramics, Academic, London, 1971. 12

[7] P. Zheng, J. L. Zhang, Y. Q. Tan, and C. L. Wang, Grain-size effects on dielectric and piezoelectric properties of poled BaTiO3 ceramics, Acta Mater., 60, (2012) 5022–30. [8] J. L. Zhang, P. F. Ji, Y. Q. Wu, X. Zhao, Y. Q. Tan, and C. L. Wang, Strong piezoelectricity exhibited by large-grained BaTiO3 ceramics, Appl. Phys. Let., 104, (2014) 222909. [9] Yu Huan, Xiaohui Wang, Jian Fang, and Longtu Li, Grain size effects on piezoelectric properties and domain structure of BaTiO3 ceramics prepared by two-step sintering, J. Am. Ceram. Soc., 96 (2013) 3369–3371. [10] H. Takahashi, Y. Numamoto, J. Tani, K. Matsuta, J. Qiu, and S. Tsurekawa, Lead-free barium titanate ceramics with large piezoelectric constant fabricated by microwave sintering, Jpn. J. Appl. Phys., Part 245, (2006) L30. [11] T. Karaki, K. Yan, and M. Adachi, Barium titanate piezoelectric ceramics manufactured by two-step sintering, Jpn. J. Appl. Phys., 46 (2007) 7035–8. [12] K. Kinoshita and A. Yamaji, Grain-size effects on dielectric properties in barium titanate ceramics, J. Appl. Phys., 47, (1976) 371. [13] T. Karaki, K. Yan, and M. Adachi, Subgrain microstructure in high-performance BaTiO3 piezoelectric ceramics, Appl. Phys. Express, 1, (2008) 111402, 3pp. [14] T. Hoshina, Size effect of barium titanate: fine particles and ceramics, J. Ceram. Soc. Jpn., 121, (2013) 156. [15] Z. Y. Shen and J. F. Li, Enhancement of piezoelectric constant d33 in BaTiO3 13

ceramics due to nano-domain structure, J. Ceram. Soc. Jpn., 118, (2010) 940. [16] N. Ma, B. P. Zhang, W. G. Yang, and D. Guo, Phase structure and nano-domain in high performance of BaTiO3 piezoelectric ceramics, J. Eur. Ceram., Soc., 32, (2012) 1059. [17] Arlt G, Hennings D, With de G. Dielectric properties of fine-grained barium titanate ceramics, J. Appl. Phys., 58, (1985) 1619–25 [18] D. Ghosh, A. Sakata, J. Carter, P. A. Thomas, H. Han, J. C. Nino, and J. L. Jones, Domain wall displacement is the origin of superior permittivity and piezoelectricity in BaTiO3 at intermediate grain sizes, Adv. Funct. Mater., 24, (2014) 885. [19] Q. M. Zhang, H. Wang, N. Kim, and L. E. Cross, Direct evaluation of domain-wall and intrinsic contributions to the dielectric and piezoelectric response and their temperature dependence on lead zirconate-titanate ceramics, J. Appl. Phys., 75, (1994) 454. [20] M. Demartin and D. Damjanovic, Dependence of the direct piezoelectric effect in coarse and fine grain barium titanate ceramics on dynamic and static pressure, Appl. Phys. Lett., 68, (1996) 3046. [21] Limei Zheng, Junjun Wang, Xiaoqing Huo, Rui Wang, Shijing Sang, Shiyang Li, Peng Zheng, and Wenwu Cao, Temperature dependence of dielectric and electromechanical

properties

of

(K,Na)(Nb,Ta)O3

single

crystal

corresponding domain structure evolution, J. Appl. Phys., 116, (2014) 044105. 14

and

[22] Yongqiang Tan, Jialiang Zhang, Yanqing Wu, Chunlei Wang, Vladimir Koval, Baogui Shi, Haitao Ye, Ruth McKinnon, Giuseppe Viola & Haixue Yan, Unfolding grain size effects in barium titanate ferroelectric ceramics, Sci.Rep.,5, (2015) 9953. [23] P. Zheng, J. L. Zhang, S. F. Shao, Y. Q. Tan and C. L. Wang, Piezoelectric properties and stabilities of CuO-modified Ba(Ti,Zr)O3 ceramics, Appl. Phys. Lett., 94 (2009) 032902.

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Table 1. Room Temperature Physical Properties Of Four Kinds Of BaTiO3 Ceramics Prepared Under Different Sintering Temperatures.

Sintering temperature

BT-Sin-01

BT-Sin-07

ρ0 (%)

d33 (pC/N)

ρ0 (%)

d33 (pC/N)

1150oC

92.7

207

88.6

207

1170oC

94.2

244

92.4

236

1190oC

97.6

449

95.4

275

o

97.6

402

97.9

501

o

97.6

389

98.0

o

97.9

392

o

97.9

o

1300 C 1350oC

BT-Ala-01

BT-Ala-07

ρ0 (%)

d33 (pC/N)

ρ0 (%)

d33 (pC/N)

485

95.4

144

94.1

139

97.9

465

95.9

195

95.6

183

385

97.6

346

96.7

300

96.6

244

97.7

370

97.5

318

96.9

303

97.6

318

97.8

371

97.6

307

97.7

331

97.7

410

o

97.9

374

97.7

292

97.7

380

97.7

419

o

97.7

367

97.8

303

97.9

401

97.9

424

1210 C 1230 C 1250 C 1270 C

1400 C 1450 C

16

Fig. 1. SEM images of four kinds of starting raw materials powder.

Fig. 2. XRD profiles of four kinds of starting raw materials powder, which were taken at room temperature.

1

Fig. 3. SEM images of four kinds of four groups of powders after calcination and second

ball-milling.

Fig. 4. XRD profiles of four kinds of fine BaTiO3 powder after calcination.

2

Fig. 5. SEM images of four kinds of various BaTiO3 ceramics sintered under different temperature conditions.

3

Fig. 6. Grain-size dependence of d33 observed at room temperature in poled BaTiO3 ceramics.

Fig. 7. XRD profiles of some of the sintered BaTiO3 ceramic samples powers which have the highest

。

values of d33 values of each group

4

Fig. 8. Domain structure of BT-Ala-01and BT-Ala-01 BaTiO3 ceramics with different grain size

5