Dynamical mechanism orihe ferreclectric transition caused by isotope exchange

同位素交换引起铁电转变的动力学机制

基本信息

批准号：
14340086
负责人：
TSUJIMI Yuhji
金额：
$ 4.8万
依托单位：
Hokkaido University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (B)
财政年份：
2002
资助国家：
日本
起止时间：
2002 至 2003
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/en/grant/KAKENHI-PROJECT-14340086/
关键词：
quantum paraelectrics isotope exchange light scattering experiment acoustic phonon optical phonon SrTi^<18>O_3 soft mode

项目摘要

The purpose of this study is to clarify the dynamical mechanism of the appearance of ferroelectricity in SrTi ^<18>O_3(STO18) below T_c=22 K. The Brillouin-Raman scattering, the electric field induced Raman scattering, the hyper Raman scattering, the impulsive stimulated Raman scattering (time-domain measurement), and the dielectric measurement have been performed for this purpose. We finally arrived at the following conclusions. The appearance of ferroelectricity in STO18 comes from the ferroelectric phase transition. The transition is caused basically by the freezing of the ferroelectric E_u soft mode of Slater type. The electric diple-diple interaction in STO18 is almost the same as that in SrTi^<16>O_3 (STO16). Since the E_u soft mode of STO18 has a bigger reduced mass than that of STO16, the quantum fluctuation (zero-point vibration) is suppressed much strongly in STO18 than in STO16. As a consequence, the E_u soft mode can freeze in the case of STO18 and the ferroelectric phase with C_<2v> symmetry appears. The transition is a displacive one, but it is not ideal one (soft mode frequency is not 0 but about 200cm^<-1> at the phase transition temperature T_c). Below T_c, the E_u soft mode splits into two modes ; E_u1 (polarization fluctuation parallel to the spontaneous polarization P_s) and E_u2 (polarization fluctuation perpendicular to P_s).

这项研究的目的是阐明在t_c = 22 K下srti ^<18> o_3（sto18）中铁电性外观的动力学机制。布里素 - 拉曼散射，电场引起的拉曼散射，超拉曼散射，超级拉曼散射，脉冲刺激的拉曼散射（时间为时间），以实现时间 - 时间 - 时间量表，并表现出了dielctric the the dielctric and dielctric and dielctric and dielect are deectric and dielctric and dielect are deectric and dielect are deectric。我们终于得出了以下结论。 STO18中铁电性的出现来自铁电相的转变。过渡基本上是由Slater类型的铁电E_U软模式的冻结引起的。 STO18中的电二幅相互作用几乎与Srti^<16> O_3（Sto16）中的电动二重相互作用相同。由于STO18的E_U软模式的质量比STO16的质量更大，因此在STO18中，量子波动（零点振动）的抑制作用要比在Sto16中受到很大的抑制。结果，在Sto18的情况下，E_U软模式可以冻结，并且出现具有C_ <2v>对称性的铁电相。过渡是一个位移的，但它不是理想的（软模式频率不是0，而是在相变温度t_c处约200cm^<-1>）。在T_C以下，E_U软模式分为两种模式； E_U1（平行于自发极化P_S的极化波动）和E_U2（垂直于P_S的极化波动）。