2009 Fiscal Year Final Research Report
Phonon analysis and crystal chemical simulation of dielectrics based on sub-millimeter wave ellipsometry
| Project/Area Number |
19206068
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| Research Category |
Grant-in-Aid for Scientific Research (A)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Inorganic materials/Physical properties
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| Research Institution | Tokyo Institute of Technology |
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Principal Investigator |
TSURUMI Takaaki Tokyo Institute of Technology, 大学院・理工学研究科, 教授 (70188647)
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| Co-Investigator(Kenkyū-buntansha) |
TAKEDA Hiroaki 東京工業大学, 大学院・理工学研究科, 准教授 (00324971)
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| Co-Investigator(Renkei-kenkyūsha) |
HOSHINA Takuya 東京工業大学, 大学院・理工学研究科, 助教 (80509399)
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| Project Period (FY) |
2007 – 2009
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| Keywords | 誘電体 / 結晶化学 / 格子振動 |
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| Research Abstract |
Sub-millimeter wave spectroscopic ellipsometry has been developed to study the size effect of barium titanate and the phase transition behaviors of barium titanate-based relaxors. Ellipsometer is equipment which measures the change of polarizing state of reflected light to determine the complex dielectric permittivity of materials. Accuracy of the ellipsometer developed in this study was verified and the complex permittivity of a barium titanate single crystal was directly determined using it. S for the size effect, the permittivity of barium titanate ceramics increased with decreasing grain size when the grain size was over 1.1μm, while that decreased when the grain size was below 1μm. Most of the domains in BaTiO_3 grains had simple lamellar structures, and 90° domain width decreased with decreasing grain size. Based on wide band dielectric spectroscopy, the domain contribution to the permittivity was investigated. In BaTiO_3 ceramics with grain sizes over 1μm, the dipole and ionic polarizabilities were enhanced by the high domain density. In contrast, for the BaTiO_3 ceramics with grain sizes below 1μm, these polarizabilities were weakened. As for the phase transition of barium titanate-based relaxors, wideband dielectric spectra from kHz to THz were measured for ceramics of BaTiO_3 (BT), Ba_<0.6>Sr_<0.4>TiO_3 (BST-0.6) and BaZr_<0.25>Ti_<0.75>O_3 (BZT-0.25). The behavior in the dipole polarization near the dielectric maximum temperature (T_m) in BST-0.6 and BZT-0.25 could be explained by the behavior in polar nanoregions (PNRs), while the ferroelectric domains contribute to dipole polarization in BT. Relaxation in BT could be interpreted as successive change in polarization behavior from normal ferroelectrics to relaxor ferroelectric via DPT ferroelectrics.
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