1993 Fiscal Year Final Research Report Summary
Design and Development of Bismuth Layr-structured Compounds with Large Electrical Anisotropies
| Project/Area Number |
04453064
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| Research Category |
Grant-in-Aid for General Scientific Research (B)
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| Allocation Type | Single-year Grants |
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| Research Field |
無機工業化学・無機材料工学
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| Research Institution | The University of Tokyo |
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Principal Investigator |
MIYAYAMA Masaru Univ.of Tokyo, RCAST,Associate Professor, 先端科学技術研究センター, 助教授 (20134497)
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| Co-Investigator(Kenkyū-buntansha) |
NAKAMURA Yoshinobu Univ.of Tokyo, Fac.Eng., Research Associate, 工学部, 助手 (30198254)
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| Project Period (FY) |
1992 – 1993
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| Keywords | Bismuth layr-structured compounds / Single crystal / ferroelectrics / anisotropy / dielectric permittivity / conductivity |
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| Research Abstract |
The bismuth layr-structured compounds have the crystal structure in which bismuth layrs and quasiperovskite blocks are stacked along the c-axis direction. The objective in this study is to design and develop the inorganic materials with large electrical anisotropies, that is, different electrical properties depending on the crystallographic directions. Dielectric permittivity and DC conductivity in bismuth titanate (Bi_4Ti_3O_<12>) and barium bismuth titanate (BaBi_4Ti_4O_<15>), which have the bismuth layr-structures, were measured on single crystals prepared by a flux method or a melt-solidification method. The anisotropies were compared with those of polycrystalline samples without crystallographic orientation. In the single crystals, dielectric permittivity (epsilon) and DC conductivity (sigma) were larger in the a(b)-axis direction (parallel to the Bi layr) than those in the c-axis direction (perpendicular to the Bi layr) both in bismuth titanate and barium bismuth titanate. Anisotropies were 10 for epsilon at 676ﾟC(Curie Temp.) and 10^3 for sigma at 150ﾟC in bismuth titanate, and 58 for epsilon at 420ﾟC (Curie Temp.) and 10 for sigma at 150ﾟC in barium bismuth titanate. The properties of polycrystalline samples showed an intermediate behavior of those of single crystals in the two directions. Complex impedance measurements also showed the anisotropy in the dielectric and conducting properties even in the paraelectric phase above the Curie temperature. The bismuth layr was thought to act as a layr with insulating and paraelectric properties in the bismuth layr-structured compounds. Those results world be very valuable to control electrical properties in layr-structured compounds and to design the functional devises utilizing crystallographic anisotropy of materials.
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