1989 Fiscal Year Final Research Report Summary
Syntheses and Properties of Organic Ferroelectrics Based on Strong Electron-Lattice Interaction
| Project/Area Number |
63460030
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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 |
固体物性
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| Research Institution | University of Tokyo |
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Principal Investigator |
TOKURA Yoshinori University of Tokyo, Department of Physics, Assistant Professor, 理学部, 助教授 (30143382)
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| Co-Investigator(Kenkyū-buntansha) |
KOSHIHARA Shin-ya University of Tokyo, Department of Physics, Research Associate, 理学部, 助手 (10192056)
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| Project Period (FY) |
1988 – 1989
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| Keywords | low-dimensional ferroelectricity / Organic pi-molecule / Charge-transfer compounds / hydrogen bonded solids / Spin-lattice interaction / domain-walls / Soliton / photo-electric |
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| Research Abstract |
In this study, we have proposed new ideas for organic pi-molecular solids with low-dimensional ferroelectricity. The key to get the molecular ferroelectrics is to utilize the strong pi-electron-lattice interaction characteristic of the one-dimensional(lD) system which can promote the phase transition to the polar structure below finite temperature (T_c). Here, the "lattice" means , for example, the molecular stack in the charge-transfer(CT) compounds with s=1/2 spins, the molecular moiety showing the planar-nonplanar transition and the hydrogen-bonding chains between pi-molecules. We have studied two typical examples which show such a 1D ferroelectricity with dynamical domain-walls; (1) ionic donor(D)-acceptor(A) charge-transfer compounds with the bond-ordered-wave (BOW) type stack dimerization and (2) hydrogen bonded solids consisting of enol-form -molecules with the -C=O and =C-OH groups.
In the former systems, the spin-lattice interaction causes the polar BOW states (D^+A^-D^+A^-D^+A^- or A^-D^+A^-D^+A^-D^+), which show the 3D ordering below T^c. On the other hand, in the hydrogen bonded pi- molecular solids the bond alternation pattern within the molecule is governed by the position of proton in-between the neighboring molecules (O=C-C=C-OH..O=C-C=C-OH..O=C-C=C-OH.. or HO-C=C-C=O..HO-C=C-C=O..HO-C=C-C=OH..). It was shown in both cases, the mobile kink-type domain-walls (or solitons) do exist between the two degenerate structures with opposite pi-electron polarization. We have obtained experimental results indicating such charge- and/or spin-carrying domain-walls play a crucial role in dielectric and photo-electric properties in those new dielectrics.
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