1988 Fiscal Year Final Research Report Summary
Dynamics of Formation of Discommensuration Lattice
| Project/Area Number |
62540232
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| Research Category |
Grant-in-Aid for General Scientific Research (C)
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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 | Tokyo Institute of Technology |
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Principal Investigator |
HAMANO Katsumi Tokyo Institute of Technology, Faculty of Science, 理学部, 教授 (10017189)
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| Co-Investigator(Kenkyū-buntansha) |
EMA Kenji Tokyo Institute of Technology, Faculty of Science, 理学部, 助教授 (80108183)
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| Project Period (FY) |
1987 – 1988
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| Keywords | Discommensuration lattice / Commensurate-incommensurate phase transition / Dynamics of phase transition / Nucleation and growth / Observation of domain structure / Rubidium tetra-chloro zincate / Potassium tetra-chloro zincate / チオ尿素 |
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| Research Abstract |
The dynamical process of the commensurate(C)-incommensurate(IC) phase transitions in Rb_2ZnCl_4, K_2SeO_4 and thiourea has been investigated experimentally by the measurement of the time evolution of polarization and dielectric constant during the field-induced transition. The process has also been studied theoretically using the free energy of a system which undergoes a first-order C-IC transition. The following picture of the phase transition has been obtained. In the early stage of the C-to-IC transition, the nucleated discommensurations(DC's) are arranged at intervals slightly wider than those in the final equilibrium state. After a complete DC lattice is formed over the crystal, the lattice spacing decreases toward the equilibrium value. In the early stage of the IC-to-C transition, DC's are annihilated successively and the lattice spacing increases.
When the spacing has increased to a certain threshold value, regions of the C phase start to appear, they grow and finally cover the whole crystal.
The nucleation process in the first-order C-IC transition in K_2ZnCl_4 has been studied by the measurement of the time evolution of the dielectric constant and by the observation of domain patterns revealed by etching, powder and replica methods. The experimental results can be explained if we assume the following. The nucleation of stripples consisting of six DC's occurs at some specified positions, probably at some kind of defects, which are nearly equally spaced in the crystal. Each stripple grows to a cluster of six parallel DC's. The next nucleations of stripples occur alongside the outermost DC's of each cluster; thus the clusters expand sidewise at a constant speed. Such a model is reasonable because there is an attractive interaction between DC's in the case of a first-order C-IC transition.
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