1998 Fiscal Year Final Research Report Summary
Study in a new fabrication method of BaTiO_3 single crystal
| Project/Area Number |
08455406
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| Research Category |
Grant-in-Aid for Scientific Research (B)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
無機工業化学
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| Research Institution | Nagaoka University of Technology |
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Principal Investigator |
TAKATA Masasuke Nagaoka Univ.of Tech., Faculty of Eng., Professor, 工学部, 教授 (20107551)
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| Co-Investigator(Kenkyū-buntansha) |
NOGUCHI Yuji Univ.of Tokyo, Department of Civil Eng., Research Associate, 大学院・工学系研究科, 助手 (60293255)
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| Project Period (FY) |
1996 – 1998
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| Keywords | BaTiO_3 / TiO_2 / Polycrystalline Body / Single Crystal / Grain Growth / Secondary Recrystallization / Liquid Phase / Solution-reprecipitation |
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| Research Abstract |
We investigated the conditions in which no secondary recrystallization occurred in TiO_2 added BaTiO_3 ceramics for a new fabrication method of BaTiO_3 single crystal. These conditions were confirmed when the specimens were sintered above the eutectic point, The effect of TiO_2 as a secondary recrystallization inhibitor worked on these conditions remarkably by using a low reactive BaTiO_3 powder that have a comparatively large average grain size. In these conditions, the increase of added TiO_2 gave rise to the increase of amount of generated liquid phase. The secondary recrystallization depended on the amount of generated liquid phase and the sintering temperature. Owing to little amount of diffusion of BaTiO_3 in the liquid phase existing between grains, the rapid grain growth, namely, the secondary recrystallization was restrained.
The amount of liquid phase was estimated as the degree of change in electrical conductivity around the eutectic point. The electrical conductivity changed
… More
gradually in the undoped specimen. On the other hand, a striking change of electrical conductivity occurred around the eutectic point in TiO_2 added specimens, proportionally increasing with the amount of added TiO_1, namely, the generated liquid phase. Accordingly, it was found that the measurement of electrical conductivity around the eutectic point was an effective way to determine the amount of liquid phase during heat treatment.
A polycrystalline body that contained a seed crystal was heat-treated to make the seed crystal grow using the above conditions in which no secondary recrystallization occurred. The seed crystal grew in all directions without containing the secondary recrystallized grain. The solution-reprecipitation process was the dominant growth mechanism in this fabrication method. The growth of single crystal was caused by a difference of solubility between the seed crystal and the grains of polycrystalline body. The growth rate of seed crystal embedded in the polycrystalline body increased with decreasing the amount of generated liquid phase and increasing of heat-treating temperature. Pores in the porous polycrystalline area were incorporated into the grown single crystal. However, the growth part of single crystal exhibited similar properties, such as the temperature dependence of relative dielectric constant and the lattice constant. Therefore, a high qualitative BaTiO_3 single crystal might be fabricated by removing pores from the porous polycrystalline body. Less
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