2005 Fiscal Year Final Research Report Summary
Study of Phase Transitions in A_2BX_4- Type Halide Substances
| Project/Area Number |
16540293
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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 |
Condensed matter physics I
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| Research Institution | Iwaki Meisei University |
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Principal Investigator |
SHIMIZU Fuminao Iwaki Meisei University, College of Science and Engineering, Associate Professor, 科学技術学部, 助教授 (20206212)
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| Project Period (FY) |
2004 – 2005
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| Keywords | Rb2ZnCl4 group ferroelectrics / Tl2ZnI4 group ferroelectrics / α-β phase transition / β-K2SO4 structure / Sr2GeS4 structure / Tl2ZnCl4 / (Rb1-xCsx)2ZnI4 / K2ZnCl4 |
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| Research Abstract |
Study of the Mixed System of (Rb_<1-x>Cs_x)_2ZnI_4
This mixed system of (Rb_<1-x>Cs_x)_2ZnI_4 were prepared over full range of x by Bridgman method and the phase transitional properties was investigated. The melting point Tm, α-β phase transition point T_<α-β> and dielectric peak temperature Tc of original Rb_2ZnI_4 and Cs_2ZnI_4 were traced as the function of x. Phase transitions of Rb_2ZnI_4 having Sr_2GeS_4 structure is traceable only for x<0.5 whereas those of Cs_2ZnI_4 having β-K_SO_4 structure only for x>0.5. We proposed supercooling model for disappearance of T_<α-β> line, but in order to prove this, further experiments like observation of time dependence of the dielectric constant after rapid cooling for the sample with x 【approximately equal】 0.5 is necessary.
2)Study of Possible Existence of α-β Phase Transition in Tl_2ZnCl_4
The stable state of Tl_2ZnCl_4 at room temperature is α-phase(monoclinic Sr_2GeS_4 structure), and Tl_2ZnCl_4 has an α-β phase transition point around 340K
… More
. It is found that the β-phase (orthorhombic β-K_2SO_4 structure) can be brought to the liquid-nitrogen temperature range and that at room temperature, the β-phase recovers to the original stable α-phase for about one night as well as in both K_2ZnBr_4 and K_2CoBr_4. So far as authors know, Tl_2ZnCl_4 is the crystal having the lowest α-β phase transition point in Tl_2ZnI_4 group substances.
3)Study of Possible α-β phase transition in Ferroelectric K_2ZnCl_4
It is well known that K_2ZnCl_4 crystal has orthorhombic β-K_2SO_4 structure with space group Pmcn at room temperature. But some specimens show a specific phase-transitional behavior deviated from standard behavior of β-K_2SO_4-type crystals. To investigate this point, we have made DTA(Differential Thermal Analysis) and dielectric constant measurements for K_2ZnCl_4 crystals grown by aqueous solution method. As the result, it is found that evidence of coexistence of the phases with Sr_2GeS_4-type structure and original orthorhombic β-K_2SO_4 structure, at least in a small volume specimen less than about 5mm^3. Less
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Research Products
(6 results)
