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Femtosecond Time-Resolved Spectroscopic Study of the Slow Dynamics
Toshirou Yagi,June Kano,Keith A. Nelson,Takeo Watanuki,Yuhji Tsujimi 한국물리학회 2003 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.42 No.IV
The femtosecond time-resolved spectroscopy has been applied for the study of the B2 soft mode in the phase transition of the hydrogen-bonded ferroelectric KDP. An extremely early stage of the excitation of the B2 soft mode in KDP reveals newly existence of the mechanical forming process of the soft modes over the limit of the Debye model. The method shows its high resolution on the wave vector in the study of the A1 phonon-polariton dispersion relation of LiNbO3.
Light Scattering Study of the Phase Transition in Quantum Paraelectric Strontium Titanate
Toshirou Yagi,H Taniguchi,M Itoh,M Takesada 한국물리학회 2007 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.51 No.2I
New features of the ferroelectric phase transition are found by using light scattering studies on quantum paraelectric SrTi16O3 (STO16) and its oxygen-isotope exchanged compound SrTi18O3 (STO18). The ferroelectric Eu mode observed by using high-resolution spectroscopy with interferometry shows a perfect softening at the phase transition point of the ferroelectric STO18-95, where 95 % of the oxygen atoms are replaced by the oxygen isotope 18O. The phase transition is concluded to be an ideal displacive-type transition accompanied with the complete freezing of the Slater-type polar mode. The role of the substituted 18O atoms is elucidated in more detail by using low-frequency Raman scattering below 1 K with a triple monochromator. The dynamical inhomogeneity enhanced by the inhomogeneous distribution of 18O atoms plays an essential role in quantum paraelectric STO18 where the concentration of 18O is less than the critical value of 33 %. Both the decrease in the frequency of the polar modes as a mass effect and the enhancement of the dynamical inhomogeneity take place cooperatively in the quantum paraelectric-ferroelectric phase transition in STO18.
Raman Scattering Study of Rb3DxH1-x(SO4)2
Masaru Kasahara,Toshirou Yagi 한국물리학회 2003 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.42 No.IV
The temperature dependences of 2 mode frequencies of sulfate ions were measured in Rb3DxH1..x(SO4)2 with x = 0.98, 0.90, 0.70 and 0.50. A single 2 line observed in the paraelectric phase split into three lines in the antiferroelectric phase. It was revealed from the x dependence of line intensities that spectrum consists of SO2.. 4 , HSO..4 and DSO..4 lines. Frequency shifts of these lines increased with decreasing temperature and saturated around 20 K. The saturated frequency shift of HSO..4 depends on x, while that of DSO..4 reaches much the same value for all x. These results imply that the length of H-hydrogen bonds depends on x whereas that of D-hydrogen bonds does not.
Broad Doublet Spectra in SrTiO3
Mingqiu Tan,Yuhji Tsujimi,Toshirou Yagi 한국물리학회 2005 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.46 No.1
Broad doublet (BD) spectra have been investigated in quantum paraelectric SrTiO3 by a 180 Brillouin-scattering experiment. Spectral analyses suggest that the second-sound scenario seems to be unfavorable for explaining the physical origin of BD. We nd that the integrated intensity of BD shows quite strong anisotropy; the BD exists clearly around 27 K in the direction = 0.4deviated from [001]c to [110]c, whereas the BD is almost absent in the direction = 21. We also nd that the integrated intensity of the longitudinal acoustic mode decreases as increases, while that of the pure transverse acoustic mode increases. All these anisotropies can be explained by the conventional formula with Pockel's tensor, signifying that the concept of antiphase-domain walls is not needed for such explanation.
Hiroki Taniguchi,Masaki Takesada,Mitsuru Itoh,Toshirou Yagi 한국물리학회 2005 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.46 No.1
The oxygen-isotope exchange eect on the ferroelectric micro-regions (FMR) in SrTiO3 is investigated by Raman scattering in the low-temperature region near 1 K by using a 3He cryostat. With decreasing temperature, the intensity of the FMR spectra decreases and a sharp peak newly appears with increasing intensity. The sharp peak is assigned to be the polar Eu mode activated by local symmetry breaking induced by the growth of FMR.
Hyper-Raman scattering of SrTi18O3
Yusuke Minaki,Yuhji Tsujimi,Makoto Nakanishi,Mika Kobayashi,Mitsuru Itoh,Ruiping Wang,Toshirou Yagi 한국물리학회 2003 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.42 No.IV
Hyper-Raman scattering experiment has been performed in the SrTi(18Ox 16O1..x)3 single crystal plate with x = 0:87. Raman inactive ferroelectric Eu Slater mode is directly detected in the tetragonal phase. The mode clearly shows a softening behavior and seems to cause the ferroelectric transition at Tc = 26 1 K.
Soft Modes in SrTi18O3 Studied by Light Scattering and Dielectric Measurements
Yohei Nakata,Mika Kobayashi,Mitsuru Itoh,Ruiping Wang,Toshirou Yagi,Yuhji Tsujimi 한국물리학회 2005 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.46 No.1
Light-scattering and dielectric easurements have been carried out, mainly in SrTi18O3, to clarify the physical origin of the two modes (Eu1 and Eu2) which were supposed to originate from a doubly degenerated ferroelectric Eu soft mode. The combined results of both measurements strongly suggest that the Eu1 and Eu2 modes correspond to the polarization uctuation parallel to the spontaneous polarization Ps (the mode of A1 symmetry) and to that perpendicular to Ps (the mode of B2 symmetry), respectively.