Origin of Incommensurate Phase Transition and the New Viewpoint on the Phase Fluctuation

不通约相变的起源及相涨落的新观点

• 批准号: 11640311
• 负责人: SHIGENARI Takeshi
• 金额: $ 2.37万
• 依托单位: The University of Electro-Communications
• 依托单位国家: 日本
• 项目类别: Grant-in-Aid for Scientific Research (C)
• 财政年份: 1999
• 资助国家: 日本
• 起止时间: 1999 至 2001
• 项目状态: 已结题
• 来源: https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-11640311/
• 关键词: PHASE TRANSITION; INCOMMENSURATE PHASE; PHASE FLUCTUATION; RAMAN SCATTERING; MOLECULAR DYNAMICS; QUARTZ; Debye-Waller FACTOR; SiO2; 水晶(SiO_2); ラマンスペクトル; 位相ゆらぎ; SiO_2; フォノン

The aim of this project is to show that the effect of phase fluctuation plays the crucial role in appearance of incommensurate structure in crystals. We propose a new model to explain the origin of the incommensurate phase transition in quartz. In this model, the intensity of the satellite intensity observed in diffraction experiments is strongly attenuated due to the decrease of Debye-Waller factor, which is attributed to the phase fluctuation. In this research we have proved this model from the following method.(1) From the detailed investigation of low frequency Raman spectrum in the high symmetry beta phase, the temperature dependence of the integrated intensity was found not to exactly follow the Curie-Weiss law ,but deviates from 30K above the incommensurate phase transition temperature. This is consistent with our model.(2) The MD calculation was performed using Tsuneyuki potential. The result shows that the short period modulation is more likely to appear than long wave modulation in contrast to the currently accepted model.(3) The characteristics of incommensurate structure in' dielectric crystals are explained by the rotational degree of freedom of certain group of atoms. The elastically hinged molecule (EHM) model was proposed. The dynamics of the transition is investigated by the computer simulation using the EHM model. The negative poison ratio and several non-linear soliton-like behavior of lattice were also investigated by this and similar models.

本项目的目的是表明相位涨落的影响在晶体中不对称结构的出现中起着至关重要的作用。我们提出了一个新的模型来解释石英中不相称相变的起源。在该模型中，由于相位波动导致Debye-Waller因子的减小，衍射实验中观测到的卫星强度发生了强烈的衰减。在本研究中，我们通过以下方法证明了该模型。(1)通过对高对称β相低频拉曼谱的详细研究，发现积分强度的温度依赖关系并不完全遵循居里-魏斯定律，而是偏离了不相称相变温度以上30K。这与我们的模型一致。(2) MD计算采用恒之势。结果表明，与目前公认的模型相比，短周期调制比长波调制更容易出现。(3)用某些原子群的转动自由度来解释介电晶体中不相称结构的特征。提出了弹性铰分子（EHM）模型。利用EHM模型对过渡过程进行了计算机模拟。利用该模型和类似模型研究了晶格的负毒比和几种非线性类孤子行为。

项目成果

重成 武: "SiO2(水晶)の謎を解く:不整合相の起源"固体物理. 35. 659-670 (2000)

Takeshi Shigenari：“解开 SiO2（晶体）之谜：不相容相的起源”固体物理 35. 659-670 (2000)。

S.V. Dmitriev, Y.S. Kivshar and T. shigenari: "Fractal Structures and multiparticle effects in soliton scattering"Phys. Rev. E. 64. 056613-056616 (2001)

S.V.

S.V.Dmitriev, T.Miyauchi, K.Abe, T.Shigenari: "Kink-breather solution in the weakly discrete Frenkel-Kontrova model"Phys. Rev. E. 61. 5880-5885 (2000)

S.V.Dmitriev、T.Miyauchi、K.Abe、T.Shigenari：“弱离散 Frenkel-Kontrova 模型中的 Kink-breather 解决方案”Phys。

S.V.Dmitriev, M.Yajima, Y.Makita, K.Abe, T.Shigenari: "Simulation of Pressure Induced Phase Transition and Modulated Structure of Ouartz"Progr. Theor. Phys. Japan. 138. 243-244 (2000)

S.V.Dmitriev、M.Yajima、Y.Makita、K.Abe、T.Shigenari：“压力诱导相变和 Ouartz 调制结构的模拟”Progr。

S.V. Dmitriev, T. Miyauchi, K. Abe and T. Shigenari: "Kink-breather solution in the weakly discrete Frenkel-Kontrova model"Phys. Rev. E. 61. 5880-5885 (2000)

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