抄録
Offer Organization: Japan Society for the Promotion of Science, System Name: Grants-in-Aid for Scientific Research, Category: Grant-in-Aid for Scientific Research (C), Fund Type: -, Overall Grant Amount: - (direct: 3700000, indirect: -)
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.