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Dynamics of Formation of Discommensuration Lattice

失配晶格形成动力学

基本信息

批准号：
62540232
负责人：
HAMANO Katsumi
金额：
$ 1.28万
依托单位：
Tokyo Institute of Technology
依托单位国家：
日本
项目类别：
Grant-in-Aid for General Scientific Research (C)
财政年份：
1987
资助国家：
日本
起止时间：
1987 至 1988
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-62540232/
关键词：
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 チオ尿素塩化亜塩酸ルビジウムセレン酸カリ

项目摘要

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.

通过测量Rb_2ZnCl_4、K_2SeO_4和硫脲在场致转变过程中极化和介电常数的时间演变，研究了相应(C)-非相应（IC）相变的动力学过程。用一阶C-IC跃迁系统的自由能对这一过程进行了理论研究。得到了下面的相变图。在C-to-IC转变的早期，成核失调（DC’s）的排列间隔比最终平衡态稍宽。在晶体上形成完整的直流晶格后，晶格间距向平衡值减小。在ic - c跃迁初期，直流电被连续湮灭，晶格间距增大。当间距增大到一定阈值时，C相区域开始出现，并逐渐生长，最终覆盖整个晶体。通过测量介电常数的时间演变，以及通过刻蚀法、粉末法和复刻法观察到的畴图，研究了K_2ZnCl_4中一阶C-IC转变的成核过程。如果我们做以下假设，实验结果可以得到解释。由6个直流电组成的条纹的成核发生在某些特定的位置，可能是在晶体中几乎等距的某种缺陷上。每个条纹成长为6个并行直流的集群。条纹的下一个成核发生在每个星团最外层的DC附近；因此星团以恒定的速度向侧面膨胀。这种模型是合理的，因为在一阶C-IC跃迁的情况下，DC之间存在吸引人的相互作用。