Study of Transformation of Ferroeletric Phase Transition Mechanism by Farーinfrared Fourier Spectroscopy

远红外傅立叶光谱研究铁电相变机理

基本信息

批准号：
01540268
负责人：
WADA Mitsuo
金额：
$ 1.09万
依托单位：
Shinshu University
依托单位国家：
日本
项目类别：
Grant-in-Aid for General Scientific Research (C)
财政年份：
1989
资助国家：
日本
起止时间：
1989 至 1990
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-01540268/
关键词：
Infrared Fourier Spectroscopy Far-Infrared Ferroelectrics Structural Phase Transition Transformation of Phase Transition Mechanism Soft Mode Raman Scattering 赤外フ-リェ分光

项目摘要

The ferroelectrics Li_2Ge_7O_<15> undergoes peculiarly interesting phase transition, where both the dielectric critical slowing-down characteristics of the order-disorder type and the soft phonon mode characteristic in the disp laciveone. In this kind of phase transiton it could be considered the following two cases : (i) The soft phonon becomes overdampened and transforms to the relaxational mode.(ii) There exists a relaxational mode with an independent degree of freedom as well as the soft phonon mode and the character of softening transfers from the phonon to the relaxational mode. This is an important problem to understand the dynamics of structural phase transition.In the present study we attempt to measure both the soft phonon and the relaxational mode simultaneously by an infrared Fourier spectrometer particularly designed and to observe the transformation of the phase transition mechanism. In the first year a cryostat for optical measurements was purchased by means of the present Grant-in-Aid. The temperature dependence of the far-infrared transmission spectra have been measured with the cryostat and a handーmade furnace. In the paraelectric phase B phonon with the lowest frequency has been confirmed to show softening as the transition temperature was approached from above. This result shows good agreement with that of Raman scattering measurment.In the second year, to observe both phonon and relaxational mode in the lowerwave number region the improvement of the interferometer has been performed.By means of the interferometer with a high sensitive Si : GA bolometer, the spectra in the frequency region to 4cm^<-1> can be measured. The study is now in progress.

铁电体Li_2Ge_7O_<15>经历了特别有趣的相变，其中有序-无序类型的介电临界减速特性和位移体中的软声子模式特性可以被认为是以下相变。两种情况：（i）软声子变得过阻尼并转变为弛豫模式。（ii）也存在具有独立自由度的弛豫模式随着软声子模式和软化特性从声子转移到弛豫模式，这是理解结构相变动力学的一个重要问题。在本研究中，我们尝试同时测量软声子和弛豫模式。在第一年，通过专门设计的红外傅里叶光谱仪观察相变机制的转变，通过目前的援助购买了用于光学测量的低温恒温器。用低温恒温器和手工炉测量了远红外透射光谱，已证实在顺电相 B 声子中，当从上方接近转变温度时，该结果与拉曼的结果非常吻合。第二年，为了观测低波数区域的声子和弛豫模，对干涉仪进行了改进。采用高灵敏度的Si:GA干涉仪测辐射热计，可以测量频率范围至4cm^<-1>的光谱。目前该研究正在进行中。