| Project/Area Number |
14340094
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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 |
固体物性Ⅰ(光物性・半導体・誘電体)
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| Research Institution | Shimane University |
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Principal Investigator |
SHIGEMATSU Hirotake (2003-2004) Shimane Univ., Faculty of Education, Associate Prof., 教育学部, 助教授 (40281068)
秋重 幸邦 (2002) 島根大学, 教育学部, 教授 (50159331)
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| Co-Investigator(Kenkyū-buntansha) |
AKISHIGE Yukikuni Shimane Univ., Faculty of Education, Prof., 教育学部, 教授 (50159331)
KAWAGUCHI Takaaki Shimane Univ., Faculty of Education, Associate Prof., 教育学部, 助教授 (10273913)
MATSUMOTO Ichiro Shimane Univ., Faculty of Education, Associate Prof., 教育学部, 助教授 (30335541)
MIYOSHI Kiyotaka Shimane Univ., Interdisciplinary Faculty of Science and Engineering, Associate Prof., 総合理工学部, 助教授 (10294365)
重松 宏武 島根大学, 教育学部, 助教授 (40281068)
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| Project Period (FY) |
2002 – 2004
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| Project Status |
Completed (Fiscal Year 2004)
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| Budget Amount *help |
¥10,400,000 (Direct Cost: ¥10,400,000)
Fiscal Year 2004: ¥1,100,000 (Direct Cost: ¥1,100,000)
Fiscal Year 2003: ¥900,000 (Direct Cost: ¥900,000)
Fiscal Year 2002: ¥8,400,000 (Direct Cost: ¥8,400,000)
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| Keywords | Lead Free / Ferroelectrics / Relaxor / Perovskite / Oxides / Dielectric Constant / Structural Phase Transition / Single Crystals / 強誘電性 / チタン酸バリウム / 層状ペロブスカイト / 圧電性 / 酸素欠損 |
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| Research Abstract |
Development of new relaxor ferroelectric materials with lead-free compositions is an urgent problem in an environmental aspect. We have performed a research project to search for lead-free relaxor ferroelectric materials. (1)In the system of Ba-Ti oxides, we found a new ferroelectric material of BaTi_2O_5, that has a high Curie temperature Tc of 700-750 K and has a spontaneous polarization Ps of 7 μCcm^<-2> at room temperature (the crystal system is monoclinic, space group C_2). The crystal, prepared in air, has a sharp dielectric anomaly reaching ε'_b=30,000 at the ferroelectric Curie temperature of Tc=752 K and has a low dielectric loss even at high temperatures : tanδ<0.1 at 800 K. By contrast, the crystal prepared in a reducing atmosphere shows a diffuse phase transition near Tc=703 K. Thus the crystal is very desirable for high temperature application. Furthermore, we carried out X-ray diffraction measurement and Raman scattering measurement. XRD patterns of the pulverized single
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crystals were measured in the temperature range of 300-1000 K ; the thermal expansion coefficients of lattice-parameters were estimated. Tiny jumps were observed in the lattice constants vs.T curves around Tc by Δa/a=0.10%, Δb/b=-0.11% and Δc/c=0.13%. X-ray diffraction measurements for the single crystal were carried out at room temperature and at 773 K using a spherical sample. The result revealed atomic displacements responsible for the ferroelectricity of BaTi_2O_5. Up to now, no soft optic mode was observed by the Raman scattering measurements. Thus, we consider the mechanism of the ferroelectric phase transition of BaTi_2O_5 as the order-disorder type. (2)In the system of (Sr_<1-x>Ba_x)_2Nb_2O_7, we found a new ferroelectric phase at temperatures below 465 K for x=0.32. (3)In the system of K-Nb oxides, we found a new material K_5Nb_9O_<25>, which shows ferroelectric activity at temperatures below ca.100K. These new ferroelectric materials without lead ions, especially BaTi_2O_5, are promising for a variety of application such as condenser, electro-optic switch and FeRAM. Less
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