Composition Design for Growth of Single Crystal by Abnormal Grain

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Composition Design for Growth of Single Crystal by Abnormal Grain Growth in Modified Potassium Sodium Niobate Ceramics Cheol-Woo Ahn, Attaur Rahman, Jungho Ryu, Jong-Jin Choi, Jong-Woo Kim, Woon-Ha Yoon, Joon-Hwan Choi, Dong-Soo Park, and Byung-Dong Hahn Cryst. Growth Des., Just Accepted Manuscript • DOI: 10.1021/acs.cgd.6b01287 • Publication Date (Web): 13 Oct 2016 Downloaded from http://pubs.acs.org on October 18, 2016

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Crystal Growth & Design

Composition Design for Growth of Single Crystal by Abnormal Grain Growth in Modified Potassium Sodium Niobate Ceramics Cheol-Woo Ahn*, Attaur Rahman, Jungho Ryu, Jong-Jin Choi, Jong-Woo Kim, Woon-Ha Yoon, Joon-Hwan Choi, Dong-Soo Park, and Byung-Dong Hahn Functional Ceramics Department, Powder & Ceramics Division, Korea Institute of Materials Science (KIMS), Changwon, Gyeongnam 641-831, Korea KEYWORDS: Abnormal Grain Growth, Single Crystal, Pb-free Ceramics, Piezoelectric Material

In this manuscript, it is reported how the composition can be designed, in order to obtain large crystals (> 2 cm, required for device application) through the abnormal grain growth (AGG) in (K,Na)NbO3 (KNN)-based ceramics. The AGG of KNN-based ceramics can be expedited by considering three factors, such as the stoichiometry of compositions, the large amount of liquid phase, and the donor-doping to enhance the growth rate of a large grain. The composition of (1x)(K0.5Na0.5)NbO3-xBa(Cu1/3Nb2/3)O3 (KNN-xBCuN) was designed to satisfy the three factors. A Ba2+ ion was a donor in KNN and CuO was added to form the large amount of liquid phase. During the sintering process, Cu ions melt into the liquid phase of KNN ceramics and Ba2+ ions

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enter the vacant sites of Na+ ions. Therefore, Ba2+ ions can compensate for the Na+ loss in KNNxBCuN ceramics. The growth rate of large grains was enhanced approximately 1000 times and the single crystal (approximately 3 cm) was successfully obtained. In addition, this single crystal showed an excellent sensor property and Curie temperature which were higher than them of PZT-based single crystals.

Introduction Abnormal grain growth (AGG) is an interesting phenomenon in ceramic materials. During the sintering process, some grains grow much faster than the others in the materials which show AGG. This AGG is observed at the materials which have angular grains and are sintered with the formation of liquid phase.[1-24] Among the materials, several perovskite-based ceramics are well-known to show AGG, such as BaTiO3 (BT), SrTiO3 (ST), and (K0.5Na0.5)NbO3 (KNN).[1-7,17-24] When AGG occurs in the ceramics, the size of grown grains is much larger than that of small grains. In general, nevertheless, the size of grown grains is not larger than 2 cm which is required to be used alone for electronic devices. Recently, we have reported, in order to develop the Pb-free material for sensor application, that a single crystal (>2 cm) was produced by normal sintering process in KNN-based ceramics.[17] However, it has not been reported how the composition was designed to obtain the single crystal, in detail. In this study, it is reported how to maximize AGG in KNN-based ceramics, in order to obtain a giant grain which is a single crystal (>2 cm). In addition, the progress in crystal size is also reported in this manuscript. There are a lot of factors which affect AGG in perovskite-based ceramics, such as the heterogeneity between a grain and liquid phase, the composition and amount of liquid phase, the


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additives for the formation of liquid phase, donors, the stoichiometry of compositions (A/B at ABO3 of perovskite structure).[1-16] Considering these factors, the compositions were designed to maximize AGG in KNN-based ceramics, in this study.

Experimental Section The KNN-based systems were synthesized from the oxides of >99% purity by the conventional solid-state route. The powders of K2CO3, Na2CO3, Nb2O5, Li2CO3, BaCO3, and CuO (all obtained from Sigma Aldrich) were mixed for 18 h in a polypropylene jar with zirconia balls. This mixture of powders was dried and calcined at 900oC for 3 h. Calcined powders were milled for 18 h, dried and pressed into disks under the pressure of 100 MPa and sintered in the range of 850-1150oC for 0-10 h. The heating rate was 5oC/min, but the cooling rate was not controlled (that is furnace-cooling). The crystal structure of specimens was examined using Rigaku D/max-RC X-ray diffractometer. The microstructure was observed using a scanning electron microscope (SEM, JSM-5800; JEOL CO., Tokyo, Japan). The samples were poled in silicone oil at 120oC by applying a dc field of 1 kV/mm for 30 min. All of the electrical measurements were conducted after aging the samples for 24 h. The piezoelectric and dielectric properties were determined using a piezo d33 meter (Micro-Epsilon Channel Product DT-3300) and an impedance analyzer (4294A, Agilent Technologies, Santa Clara, CA, USA).

Result and Discussion


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AGG in KNN-based Ceramics The purpose of this study is to maximize the size of grains which are abnormally grown in KNN-based ceramics. Hence, in order to clarify the sintering behavior and AGG in KNNbased ceramics, the variation of microstructure was investigated as a function of sintering temperature in pure KNN ceramics, as shown in Fig. 1. Before sintering the specimens, the random morphology was observed at their particles. This is due to the grinding effect of ballmilling process. The particles were gradually changed to be angular grains when the samples were sintered at the range of ≥850oC. The grain growth and densification occurred and the grains became angular, at the temperature range which is higher than 950oC as seen in Fig. 1. It was interesting that the liquid phase was also observed from 1000oC at which the grain growth and densification took place in the KNN specimens as exhibited in Figs. 1 and 2(a). Namely, the formation of liquid phase might assist the pure KNN to be sintered at the temperature higher than 950oC. In particular, AGG was distinctly observed in the KNN specimen sintered at 1030oC as shown in Fig. 2(b). Therefore, the sintering behavior of pure KNN ceramics could be summarized as the schematic diagram shown in Fig. 3. At the stage I, the liquid phase is formed and the seed for AGG can be grown at stage II. AGG occurs at stage III, owing to the formation of seed and liquid phase. However, the grain, which is abnormally grown at stage III, shows several micro-meters in size, when the specimen is sintered at 1030oC for 2 h, as seen in Figs. 2(b) and 3. Hence, the grains are grown approximately 20 times at 1030oC for 2 h, through AGG. The average size of particles is approximately 0.2~0.3 μm, before grain growth, as shown in Fig. 1. The nucleation still appears at stage III as shown in Fig. 3. Stage IV is the final stage at which


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the grain growth and densification are completed. The grain size of stage IV is dependent on that of stage III. The liquid phase is formed by Na2O volatilization and the composition is observed to be Na-deficient glassy phase. In addition, the ratio of a Na+ ion is quite small (approximately 5~30%) in the liquid phase, compared to that of the matrix in KNN-based ceramics.[17-21] This serious heterogeneity between a grain and liquid phase might become an obstacle for a grain to become huge during the sintering process of KNN-based ceramics. Thus, the Na+ loss was compensated by a Na-rich composition, as shown in Figs. 4 and 5, in this study. As seen in Fig. 4, the perovskite structure was well-formed at the compositions and any secondary phase was not detected in XRD patterns. The Na-rich composition showed the grain size which was larger than that of a pure KNN, although the difference of grain size was not significant. Therefore, the compensation of Na+ loss might assist the large grains in growing more than the others, at the stage III of Fig. 3. Another factor, which is considered in this study, is the amount of liquid phase, in order to dilate the large grains (at stage III in Fig. 3) in KNN-based ceramics. The Na-deficient KNN compositions were prepared to increase the amount of liquid phase as exhibited in Figs. 6 and 7, since the composition of liquid phase was a Na-deficient phase as mentioned above. In (K0.5Na0.47)NbO3 (0.47KNN), the secondary phase of K6Nb10.8O30 was detected as seen in Fig. 6. This phenomenon might be due to the large amount of Na-deficient liquid phase. During the sintering process, the large amount of liquid phase is formed in 0.47KNN, compared to the others. This liquid phase is recrystallized to be KNN and K6Nb10.8O30 phases during the cooling process. The amount of K6Nb10.8O30 might be increased in 0.47KNN, compared to the others, since the amount of liquid phase was larger in 0.47KNN than in the others, as shown in Fig. 7. In


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addition, the grain size was also increased in 0.47KNN, owing to the large amount of liquid phase as indicated in the insets of Fig. 7. However, the difference of grain size was not significant. In order to enhance the amount of liquid phase more than 0.47KNN, Li-added KNN (0.95KNN-0.05LiNbO3, KNLN) and CuO-added KNN (KNN + 0.2 wt.% CuO, CuO-KNN) were prepared and their microstructures were shown in Figs. 8 and 10. As shown in Fig. 8, the grain size was large in KNLN and CuO-KNN, compared to KNN. It is well-known that the large amount of liquid phase is observed in KNLN and CuO-KNN systems.[18-19,21-24] Hence, the large grain size of KNLN and CuO-KNN might be due to the large amount of liquid phase as seen in the inset of Figs. 8(b)-(c). Because of this large amount of liquid phase, the rapid grain growth was observed in KNLN, compared to KNN as shown in Fig. 9-10. Although the sintering time was 0 min, AGG occurred in KNLN, as exhibited in Fig. 10. Therefore, the large amount of liquid phase is also an important factor in order to expedite AGG in KNN-based ceramics. In particular, CuO is the additive which enhances the amount of liquid phase and reduces the sintering temperature in KNN-based ceramics.[22-24] When CuO is added to KNN-based ceramics, the liquid phase is formed from 925oC. Moreover, the large amount of liquid phase and grain growth are observed at the temperature range of ≥925oC. However, as indicated in Fig. 8, the enhancement of grain size was not significant in CuO-KNN as well as KNLN, compared to KNN. At XRD patterns, while KNLN showed the peaks for a secondary phase which was due to the large amount of liquid phase, any secondary phase was not detected in CuO-KNN as shown in Fig. 11. Hence, we have chosen the CuO-addition to enhance the amount of liquid phase in KNN-based ceramics, for the next step.


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Consequently, another factor must be considered in order to significantly expedite AGG in KNN-based ceramics, since the giant grain (> 2 cm) is not obtained by the stoichiometry of compositions (the compensation of Na+ loss) or the large amount of liquid phase, in KNN-based ceramics. Composition Design for AGG Maximized in KNN-based Ceramics Donor-doped KNN ceramics were chosen to enhance the size of large grains which were formed by AGG during the sintering process, since AGG was frequently expedited by the donordoping in ST and BT ceramics. It has been reported that the ionic vacancies, which were formed by the addition of a donor, could be responsible for the AGG in perovskite-based ceramics.[5,7-8] A Ba2+ ion is the donor in KNN, since it can enter a K+ or Na+ site in KNN. In addition, as explained above, the stoichiometry of compositions (the compensation of Na+ loss) and the large amount of liquid phase should be also considered to maximize AGG in KNN-based ceramics. Therefore, the composition (designed in this study) is (1-x)(K0.5Na0.5)NbO3-xBa(Cu1/3Nb2/3)O3 [KNN-xBCuN]

(1)

As shown in Fig. 12(a), a Ba2+ ion was selected for the donor in KNN and CuO was added to form the large amount of liquid phase. Ba(Cu1/3Nb2/3)O3 was designed due to the stoichiometry of compositions. In addition, Cu ions can melt into the liquid phase of KNN-based ceramics and Ba2+ ions can enter the vacant sites of Na+ ions. Hence, the addition of a Ba2+ ion can compensate for the Na+ loss, which appears due to the Na2O volatilization, in KNN-based ceramics.


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Figure 12 indicates the sintering process which is designed in order to obtain the giant grain in KNN-xBCuN ceramics, in this study. It was achieved by the three ways, such as the compensation of Na+ loss, the large amount of liquid phase, and the donor-doping to enhance the growth rate of a large grain. The dissolution of Cu ion might not occur, simultaneously, at all of the places in the specimens. It might show the time difference and the grain growth could be much faster at the area where Cu ions melted into the liquid phase as shown in Fig. 12(b). The dissolution of Cu ion means that Ba2+ ions enter the vacant Na+ sites [Fig. 12(a)]. Thus, in the left figure of Fig. 12(b), the growth rate of the yellow grain (which showed Cu dissolution) might be much faster than that of the others. The large grain [a yellow grain in Fig. 12(a) and the center figure of Fig. 12(b)] could be a seed for AGG. The growth rate of this seed might be much faster than that of normal KNN-based ceramics (approximately 1000 times, as mentioned below), since the donor (Ba2+) was doped in this composition. Because of this rapid growth, the giant grain (> 2 cm) could be obtained through the normal sintering process as indicated in Fig. 12. Figure 13 shows the microstructures of KNN-xBCuN ceramics, sintered at 1080oC for 2 h. As seen in Fig. 13, the significant AGG was observed at the range of 0.01≤x≤0.0175 and the largest grain was found in KNN-0.015BCuN. The grain size of KNN-0.015BCuN was larger than 1 mm. The growth of this huge grain might be due to the effect of a donor on the acceleration of AGG in KNN ceramics. Cu ions melted into the liquid phase as shown in Fig. 14(f). In addition to this dissolution of Cu ions, Ba2+ ions could enter the vacant Na+ sites as indicated in Fig. 12(a). This donor effect might be responsible for the formation of giant grains in KNN-0.015BCuN. The giant grain was a single crystal as shown in the insets of Fig. 13(b) and Fig. 15. As exhibited in Fig. 15, while KNN was poly-crystalline, KNN-0.015BCuN showed the


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pattern for an oriented structure, which was the characteristic of a single crystal. In addition, the insets of Fig. 15 show the Laue images of a huge grain. Figure 16 shows the variation of the crystal size as a function of sintering temperature in KNN-0.015BCuN. The sintering time is 2 h. As seen in the figures, the largest crystal was obtained at 1125oC. In order to enhance the crystal size, as shown in Fig. 17, large specimens were used to be sintered at 1125oC 2 and 10 h. The grain size was enhanced to be approximately 1.4 cm when the specimen was sintered at 1125oC for 2 h. It is interesting that the growth rate of this huge grain is much faster approximately 1000 times than that of normal KNN ceramics as seen in Figs. 8 and 17. In order to obtain the single crystal which was larger than 2 cm (the size required for device application), the specimen was sintered at 1125oC for 10 h using large specimens. As shown in Fig. 17, the size of a crystal was approximately 3 cm, which was large enough to be used for device application. Therefore, the three conditions must be satisfied to obtain the single crystal which is large enough to be used for device application, in KNN-based ceramics, as indicated in Fig. 18. The crystals were not transparent as shown in Figs. 16-17. It could be explained by the formation of pores, which was due to the fast growth rate of crystals, as exhibited in the inset of Fig. 13(b). Nevertheless, the relative density of a huge grain was higher than 98%. The crystals were easily separated from the sintered specimens owing to the weak bonding between the crystals and gray areas (small grains). Moreover, as seen in Fig. 17, the cracks were observed at the boundaries between the crystals and gray areas or among the crystals. During the cooling process, the cracks might occur due to the stress difference between the interior and the boundary of crystals. In particular, the recrystallization might appear in the gray areas, which had the liquid


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phase and the small grains of KNN-0.015BCuN, during the cooling process. This recrystallization could also cause the stress between crystals and small grains. The single crystal of KNN-0.015BCuN showed an excellent sensor property (g33, piezoelectric voltage coefficient) as shown in Fig. 19. Compared to the other materials, it showed higher g33 and Curie temperature (TC) as seen in Fig. 19. However, the piezoelectric constants (d33, approximately 200 pC/N) of KNN-0.015BCuN crystals were lower than them of Pb(Zr,Ti)O3 [PZT]-based crystals (higher than 1000 pC/N). Moreover, their dielectric constants (ε3T/ε0, approximately 200, lower than them of PZT-based crystals, >1000) were also low. The piezoelectric and dielectric constants are dependent on the phase transition temperature (TO-T, from orthorhombic to tetragonal phase) in KNN-based materials.[18] Therefore, the next composition design is under study to control TO-T in KNN-based single crystals. It will be our next report.

Conclusion The composition was designed to obtain the single crystal (> 2 cm, required for device application) through AGG in KNN-based ceramics. In order to expedite AGG in KNN-based ceramics, three factors were considered, such as the compensation of Na+ loss, the large amount of liquid phase, and the donor-doping to enhance the growth rate of a large grain. The composition, which was designed in this study, was KNN-xBCuN. A Ba2+ ion was chosen for the donor in KNN and CuO was the additive to form the large amount of liquid phase. Moreover, in order to maintain the stoichiometry of compositions, the complex perovskite structure of Ba(Cu1/3Nb2/3)O3 was designed. In this composition of KNN-xBCuN, Cu ions melt into the


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liquid phase of KNN ceramics and Ba2+ ions enter the vacant sites of Na+ ions during the sintering process. Thus, the addition of a Ba2+ ion can compensate for the Na+ loss in KNNxBCuN ceramics. In particular, this donor of a Ba2+ ion might significantly enhance the growth rate of large grains. The growth rate of KNN-0.015BCuN is approximately 1000 times faster than that of normal KNN-based ceramics. Through this composition design, the single crystal (approximately 3 cm) was obtained at the specimen of KNN-0.015BCuN sintered at 1125oC for 10 h. Therefore, it can be suggested that the three conditions must be satisfied to obtain the single crystal which is large enough to be used for device application, in KNN-based ceramics. This single crystal of KNN-0.015BCuN showed an excellent sensor property and Curie temperature which were higher than them of the other piezoelectric materials. Most of all, this single crystal can be produced by the normal ceramic process which is the cheapest one among the various ceramic processes. In addition, it is very interesting that the sintering time is short enough to be used for commercialization and any addition of a seed is not required to obtain the large single crystal.

AUTHOR INFORMATION Corresponding Author 797 Changwondaero, Changwon, Gyeongnam 642-831, South Korea Tel: +82-55-280-3406 Fax: +82-55-280-3289 Email: [email protected] Notes The authors declare no competing financial interests.


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ACKNOWLEDGMENT This study was financially supported by Fundamental Research Program of the Korean Institute of Materials Science (KIMS). REFERENCES (1) Matsuo, Y.; Sasaki, H. J. Am. Ceram. Soc. 1971, 54, 471-479. (2) Schmelz, H.; Meyer, A. Ceram. Forum Int. 1982, 59, 436-440. (3) Schmelz, H. Ceram. Forum Int. 1984, 61, 199-204. (4) Hennings, D. F. K.; Janssen, R.; Reynen, P. J. L. J. Am. Ceram. Soc. 1987, 70, 23-27. (5) Shimanskij. A. F.; Drofenik, M.; Dolar, D. J. Mater. Sci. 1994, 29, 6301-6305. (6) Lee, H. Y.; Kim, J. S.; Kim, D. Y J. Am. Ceram. Soc. 2002, 85, 977-980. (7) Peng, C. J.; Chiang, Y. M. J. Mater. Res. 1990, 5, 1237-1245. (8) Chung, S. Y.; Yoon, D. Y.; Kang, S. J. Acta Mater. 2002, 50, 3361-3371. (9) Carpay, F. M. A.; Stuijts, A. L. Sci. Ceram. 1975, 8, 23-28. (10) Chen, C. J.; Wu, J. M. J. Mater. Sci.1987, 24, 2871-2878. (11) Song. H. S.; Coble, R. L. J. Am. Ceram. Soc. 1990, 73, 2086-2090. (12) Lee, S. H.; Hwang, N. M.; Kim D. Y. J. Eur. Ceram. Soc. 2002, 22, 317-321. (13) Hillert, M. Acta Metall. 1965, 13, 227-238. (14) Rios, P. R. Acta Metall. Mater. 1994, 42, 839-843. (15) Shin, S. D.; Sone, C. S.; Han, D. Y.; Kim, D. Y. J. Am. Ceram. Soc. 1996, 79, 565-567. (16) Kang, M. K.; Kim, D. Y.; Hwang, N. M. . J. Eur. Ceram. Soc. 2002, 22, 603-612. (17) Ahn, C. W.; Lee, H. Y.; Han, G.; Zhang, S.; Choi, S. Y.; Choi, J. J.; Kim, J. W.; Yoon, W. H.; Choi, J. H.; Park, D. S.; Hahn B. D.; Ryu, J.; Sci. Rep. 2015, 5, 17656.


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Figure Captions Figure 1. Variation of microstructure in KNN sintered at various temperatures for 2 h: The grain growth and densification are observed and the grains became angular, at the temperature range which is higher than 950oC. Figure 2. Formation of liquid phase and AGG in KNN sintered at (a) 1000oC and (b) 1030oC for 2 h: The liquid phase is formed at the sintering temperature of ≥1000oC. AGG, which is wellobserved in KNN, is due to the formation of liquid phase and angular grains. Figure 3. Sintering behavior of KNN: The angular grains and the formation of liquid phase cause AGG in KNN. The grain size of stage IV is dependent on the size of large grains at stage III. Figure 4. XRD patterns of (K0.5Nax)NbO3 ceramics (x=0.50 and 0.51; cal: calcined powder, sin: sintered specimen): The variations of phases are not detected in (K0.5Nax)NbO3 ceramics. After sintering the specimens, the peaks become narrow due to the grain growth which appears during the sintering process. Figure 5. SEM images of (K0.5Nax)NbO3 ceramics [(a) x=0.50 and (b) x=0.51] sintered at 1125oC for 2 h: The grain size is larger in (K0.5Na0.51)NbO3 [Na-rich KNN] than (K0.5Na0.50)NbO3 [KNN]. That is due to the compensation of Na+ loss which happens due to the Na2O volatilization during the sintering process. Figure 6. XRD patterns of (K0.5Nax)NbO3 ceramics (x=0.50, 0.49, and 0.47; cal: calcined powder, sin: sintered specimen): The secondary phase is observed in (K0.5Na0.47)NbO3 ceramics which show the large amount of liquid phase.


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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 7. SEM images of (K0.5Nax)NbO3 ceramics [(a) x=0.50, (b) x=0.49, and (c) x=0.47]: The grain size is larger in (K0.5Na0.47)NbO3 than the others. That is due to the relatively large amount of liquid phase. Figure 8. SEM images of (a) KNN, (b) KNLN, and (c) CuO-KNN ceramics sintered at 1060oC for 2 h: KNLN and CuO-KNN show the large amount of liquid phase and large grains, compared to KNN. Figure 9. Variation of microstructure in KNN sintered at various temperatures for 0 h: The grain growth is not observed. Figure 10. Variation of microstructure in KNLN sintered at various temperatures for 0 h: The grain growth is observed. Figure 11. XRD patterns of KNN, KNLN, and CuO-KNN ceramics: The secondary phase is observed in KNLN ceramics. Any secondary phase is not detected in CuO-KNN. Figure 12. Design of (a) composition and (b) AGG in (1-x)(K0.5Na0.5)NbO3-xBa(Cu1/3Nb2/3)O3 [KNN-xBCuN]: CuO is added to enhance the amount of liquid phase in KNN-based ceramics. When Cu ions melt into liquid phase, Ba2+ ions enter the vacant Na+ sites. This donor-doping can enhance the growth rate of large grains in AGG of KNN-xBCuN ceramics. Figure 13. SEM images of KNN-xBCuN sintered at 1080oC for 2 h: The huge grains are grown in 0.01≤x≤0.0175. The largest grain is observed in KNN-0.015BCuN.


15


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Page 16 of 37

Figure 14. SEM images of KNN-xBCuN sintered at 1060oC for 2 h: Cu is not detected in the huge grains. Cu ions melt into the liquid phase which is existed in the matrix of KNN0.015BCuN. Figure 15. XRD patterns of KNN and KNN-0.015BCuN ceramics: KNN shows the peaks for normal perovskite ceramics. The peaks for an oriented perovskite structure are detected in KNN0.015BCuN.[17] Figure 16. Variation of crystal size with sintering temperature in KNN-0.015BCuN ceramics: Sintering time is 2 h. The crystal size is enhanced when the sintering temperature becomes high. Figure 17. Enhancement of crystal size by controlling specimen size and sintering time in KNN0.015BCuN ceramics: The crystal size can be enhanced by the usage of a large specimen and the increase of sintering time. The large crystal of 3 cm is obtained at the specimen sintered at 1125oC for 10 h, in KNN-0.015BCuN ceramics. Figure 18. Variation of AGG with main factors in sintering behavior of KNN-based ceramics: In order to obtain the giant grains in KNN-based ceramics, the three factors must be considered, such as the compensation of Na+ loss, the large amount of liquid phase, and the donor-doing to enhance the growth rate of large grains. Figure 19. Piezoelectric voltage coefficient (g33) and Curie temperature (Tc) of various piezoelectric materials [BT: BaTiO3-based materials, BNT: (Bi,Na)TiO3-based materials, PZT: Pb(Zr,Ti)O3-based materials, and BF: BiFeO3-based materials, Td: depolarization temperature in BNT-based ceramics]: The single crystal of KNN-0.015BCuN shows higher g33 and Curie temperature (Tc), compared to them of the others.[17-29]


16

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“For Table of Contents Use Only” Composition Design for Growth of Single Crystal by Abnormal Grain Growth in Modified Potassium Sodium Niobate Ceramics Cheol-Woo Ahn*, Attaur Rahman, Jungho Ryu, Jong-Jin Choi, Jong-Woo Kim, Woon-Ha Yoon, Joon-Hwan Choi, Dong-Soo Park, and Byung-Dong Hahn Functional Ceramics Department, Powder & Ceramics Division, Korea Institute of Materials Science (KIMS), Changwon, Gyeongnam 641-831, Korea

Synopsis The rule of composition design is reported to obtain the large crystal through the abnormal grain growth (AGG) in KNN-based ceramics. The AGG of KNN-based ceramics can be expedited by considering three factors, such as the stoichiometry of compositions, the large amount of liquid phase, and the donor-doping to enhance the growth rate of a large grain.


17

Fig. 1 Before Sintering 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42

1 μm

950 oC

1 μm

1040 oC

1 μm


Page 18 of 37

Sintering time: 120 min

850 oC

1 μm

1000 oC

1 μm

1050 oC

ACS Paragon Plus Environment1

μm

900 oC

1 μm

1030 oC

1 μm

1060 oC

1 μm

Fig. 2 Page 19 of 37

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42

a)


1000 oC b)

100 nm


1030 oC

1 µm

Fig. 3 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42


Stage I Liquid Phase

Liquid Phase Formation

Stage II

Page 20 of 37

Stage III

Stage IV

Nucleus (Seed)

Nucleation

Abnormal Grain Growth & Nucleation


Grain Growth


(211)C

(200)C

(100)C

(111)C

(210)C

(110)C

(K0.5Nax)NbO3

Intensity (Arb.Units)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42


x=0.51, sin x=0.50, sin x=0.51, cal x=0.50, cal

20

30

40

2


50

60

Fig. 5 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42

a)


x=0.50 b)

10 µm


Page 22 of 37

x=0.51

10 µm


(K0.5Nax)NbO3

*

*

(211)C

(200)C

(111)C

*

(210)C

* : K6Nb10.8O30

(110)C (100)C


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42


x=0.47, sin x=0.49, sin x=0.50, sin

* * **

x=0.47, cal x=0.49, cal x=0.50, cal

20

30

40

2


50

60

Fig. 7 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42



Page 24 of 37


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42

a)


KNN b)

10 µm

KNLN c)

Filled with Liquid Phase

10 µm


CuO-KNN

Filled with Liquid Phase

10 µm

Fig. 9 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42


Page 26 of 37

KNN, sintering time: 0 min

1050oC

1070oC

1 µm

1080oC

1 µm

1100oC

1 µm ACS Paragon Plus Environment

1 µm


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42


KNLN, sintering time: 0 min

1050oC

1070oC

2 µm

1080oC

2 µm

1100oC

2 µm ACS Paragon Plus Environment

2 µm

Fig. 11

Page 28 of 37

(211)C

(210)C

(200)C

(111)C

(100)C

(110)C

*: K6Li4Nb10O30


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42


CuO-KNN

*

* *

KNLN KNN

20

30

40

2


50

60


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42


Designed Composition: (1-x)(K0.5Na0.5)NbO3-xBa(Cu1/3Nb2/3)O3

(a) ACS Paragon Plus Environment

Fig. 12 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42


(b) ACS Paragon Plus Environment

Page 30 of 37


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42


a)

x=0.01

b)

1 mm

x=0.015

etched surface

1 mm

d)

c)

x=0.0175

pores

500 µm

x=0.02


2 µm

Fig. 14 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42

a)


Page 32 of 37

K c)

b)

Grown Grain

Na

Matrix 200 μm

d)

Nb e)

200 μm

200 μm

Ba f)

Cu

Cu

Cu2+ (melt into liquid phase) 200 μm

200 μm


200 μm


(100)C

(1-x)KNN-xBCuN

(211)C

(110)C

(210)C

(200)C


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42


x=0.015 x=0.000

20

30

40

2 ACS Paragon Plus Environment

50

60

Fig. 16 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42


1060oC

4 mm

1080oC

Page 34 of 37

1100oC

4 mm


4 mm

1125oC

4 mm


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42


Specimen Size

Specimen Size + Sintering Time


Fig. 18 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42


Page 36 of 37

10 µm Compensation of Na+ loss

10 µm Grain Growth

Large Amount of Liquid Phase

10 µm Grain Growth


Donor + Compensation + Liquid Phase

1 cm Crystal Growth


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42


This Study


Composition Design for Growth of Single Crystal by Abnormal Grain

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