| Project/Area Number |
12640322
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| Research Category |
Grant-in-Aid for Scientific Research (C)
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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 | Iwaki Meisei University |
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Principal Investigator |
SHIMIZU Fuminao Iwaki Meisei University, Dept. Electronics and Computer Science, Associate Professor, 理工学部, 講師 (20206212)
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| Co-Investigator(Kenkyū-buntansha) |
HAMAZAKI Sin-ichi Iwaki Meisei University, Dept. Electronics and Computer Science, Research Assistant, 理工学部, 助手 (20306096)
TAKASHIGE Masaaki Iwaki Meisei University, Dept. Electronics and Computer Science, Professor, 理工学部, 教授 (70114527)
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| Project Period (FY) |
2000 – 2001
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| Project Status |
Completed (Fiscal Year 2001)
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| Budget Amount *help |
¥3,600,000 (Direct Cost: ¥3,600,000)
Fiscal Year 2001: ¥700,000 (Direct Cost: ¥700,000)
Fiscal Year 2000: ¥2,900,000 (Direct Cost: ¥2,900,000)
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| Keywords | Ferroelectrics / Phase Transition / Pyroelectric Charge / Orthorhombic / β-K_2SO_4 Structure / Monocolinic / Sr_2GeS_4 Structure / Ferroelectricity / 単結晶 |
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| Research Abstract |
We reexamined dielectric properties of typical ferroelectric Rb_2CdI_4 using the samples with evaporated gold electrode instead of silver paste. The stable results of the temperature dependence of the dielectric constant and pyroelectric charge are obtained. The experimental data established that ferroelectric Curie point T_C is 211 K and spontaneous polarization P_s is about 0.4μC/cm^2 around 4K.
Crystal of Tl_2CoCl_4 having orthorhombic β-K_2S0_4 structure is obtained by Bridgman method. We found a sharp peak at 73 K, a broad maximum at around 120 K and a bending curve at 165 K in the temperature dependence of dielectric constant. We could observe ferroelectric activity below 73 K in the α-direction. The spontaneous polarization P_s estimated from D-E hysteresis loop is about 4.5 nC/cm^2 around 65K.
The end member Rb_2CdI_4 is a typical A_2BX_4-type ferroelectric and another member Cs_2CdI_4 has no phase transition at low temperatures. In concentration of χ = 0.6 and χ 0.7, three dielectric anomalies are observed. We temporarily call T_<C'>, T_<s1> and T_<s2> in order of decreasing temperature. It seems that T_<s1> and T_<C'> are unified one peak and it becomes finally the ferroelectric Curie point T_c, whereas T_<s2> corresponds to the shoulder-type anomaly T_s for χ > 0.7.
There are two groups of halide ferroelectrics with general formula A_2BX_4-type. One is called Rb_2ZnCl_4 group ferroelectrics which are found by Sawada et al. in the late 1970's having orthorhombic β-K_2SO_4 structure. Another is a group of crystals having monoclinic Sr_2GeS_4 structure. First one this group is Tl_2ZnI_4 found by Gesi. Afterward, we have been searching for new ferroelectrics of this group. To date, it has been known that six ferroelectrics in this group. We call this group of ferroelectrics "Tl_2ZnI_4 group ferroelectrics".
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