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고재현,Seiji Kojima 한국물리학회 2005 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.47 No.2
A nonscanning angular-dispersion-type Fabry-Perot interferometer (NSFPI) was built by using a high-resolution charge-coupled-device (CCD) detector and a solid etalon. It was possible to measure Brillouin spectra of condensed matter within a very short time of the order of a few seconds by using the NSFPI. Thanks to the good sensitivity and high resolution of the CCD detector, the real-timeestimation of the elastic-stiffness coefficients of a single crystal, ammonium dihydrogen phosphate, could be obtained. The results were compared with those obtained from a conventional Sandercocktype tandem Fabry-Perot interferometer, resulting in good consistency. The improvement and modification of the NSFPI will make it possible to achieve real-time monitoring of the acoustic properties of condensed matter including single crystals and thin films.
김태현,Seiji Kojima,고재현 한국물리학회 2014 Current Applied Physics Vol.14 No.12
The effect of the electric field on the dielectric and acoustic properties of Pb[(Mg1/3Nb2/3)0.83Ti0.17]O3 single crystals was investigated as functions of temperature and the electric field strength. The dielectric constant and the acoustic mode behaviors exhibited typical relaxor behaviors when there was no bias field. The longitudinal acoustic mode showed splitting under a moderate electric field of 1 kV/cm applied along the [001] direction, indicating coexistence of macroscopic/mesoscopic ferroelectric states and relaxor states. Further increase in the electric field up to 2 kV/cm induced a clear ferroelectric phase transition, which became smeared out due to the proximity of the electric field to the critical point. The electric field-temperature phase diagram of Pb[(Mg1/3Nb2/3)0.83Ti0.17]O3 was suggested based on the observed field-induced changes in the dielectric and the acoustic properties.
고재현,Seiji Kojima 한국물리학회 2003 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.42 No.IV
Brillouin spectra of a relaxor-based ferroelectric Pb[(Zn1=3Nb2=3)0:91Ti0:09]O3 (PZN-9%PT) single crystal have been examined under an electric eld oriented along the pseudocubic [001] direction. One longitudinal and two transverse modes are softened along with the increase of the Brillouin linewidth during the polarization reversal. The eld-induced changes in the frequency shift of the three modes are maximum at the coercive eld of about 2.5 kV/cm, and then they recover their initial values with further increasing the electric eld. In particular, one transverse mode, which corresponds to the (c11 .. c12)=2 elastic stiness coecient, shows the most drastic changes at two electric elds. This seems to indicate the existence of intermediate monoclinic phases during the eld-induced transformation. Our results demonstrate that Brillouin scattering is a powerful tool in investigating elastic properties of ferroelectric relaxors during the polarization reversal.
Angular Dispersion-type Nonscanning Fabry-Perot Interferometer Applied to Ethanol-water Mixture
고재현,Seiji Kojima 한국광학회 2009 Current Optics and Photonics Vol.13 No.2
The angular dispersion-type non-scanning Fabry-Perot was applied to an ethanol-water mixture in order to investigate its acoustic properties such as the sound velocity and the absorption coefficient. The scattered light from the mixture was analyzed by using the charge-coupled-device area detector, which made the measurement time much shorter than that obtained by using the conventional scanning tandem multi-pass Fabry-Perot interferometer. The sound velocity showed a deviation from ultrasonic sound velocities at low temperatures accompanied by the increase in the absorption coefficient, indicating acoustic dispersion due to the coupling between the acoustic waves and some relaxation process. Based on a simplified viscoelastic theory, the temperature dependence of the relaxation time was obtained. The addition of water molecules to ethanol reduced the relaxation time, consistent with dielectric measurements. The present study showed that the angular dispersion- type Fabry-Perot interferometer combined with an area detector could be a very powerful tool in the real-time monitoring of the acoustic properties of condensed matter.
김태현,Seiji Kojima,안창원,김일원,고재현 한국물리학회 2013 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.62 No.7
The Raman and Brillouin spectra of lead-free piezoelectric Bi<SUB>0.5</SUB>(Na<SUB>0.78</SUB>K<SUB>0.22</SUB>)<SUB>0.5-<I>x</I></SUB>TiO<SUB>3</SUB> ceramics with A-site vacancies of <I>x</I>= 0 ~ 0.05 were investigated. The Raman spectra measured at room temperature showed seven broad bands over the range of 50 ??1000 cm<SUP>-1</SUP>, reflecting strong anharmonicity, inherent A-site disorder and the resulting breakdown of the Raman selection rule. The splitting of the A<SUB>1</SUB> mode near 270 cm<SUP>-1</SUP> indicated that the tetragonal symmetry was maintained over the whole <I>x</I> range, consistent with the x-ray diffraction results. The Brillouin spectrum consisted of distributed acoustic modes and central peaks, the former being due to the scattering events at all scattering angles from 0 to 180<SUP>o</SUP> due to multiple reflections and refractions at the grain boundaries. The relaxation time obtained from fitting the broad central peak by using a Debye function exhibited a slowing-down behavior in the paraelectric phase. The formation of the central peak was attributed to the existence of nano-sized polar regions due to anharmonic vibrations and hopping motions of the A-site cations.
Comparison of Acoustic Behaviors Between Ethanol and Partially-Deuterated Ethanol
고재현,Seiji Kojima 한국물리학회 2010 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.56 No.1
The temperature dependence of the Brillouin spectrum of partially-deuterated ethanol (C2H5OD)was investigated over the temperature range covering the liquid and supercooled liquid phases, from which the sound velocity and the hypersonic damping were derived. The results were compared to those of undeuterated ethanol (C2H5OH). The sound velocity showed a linear temperature dependence in the liquid phase, but exhibited a deviation from that, upon further cooling, at about 300K along with increasing hypersonic damping. The relaxation time of the relaxation process coupled to the longitudinal acoustic phonons was obtained by using a single relaxation-time approximation and was compared to that of ethanol. Both undeuterated and deuterated ethanols displayed almost the same temperature dependences, indicating that the deuteration of the hydroxyl group does not have a substantial effect on the relaxation process which is responsible for the acoustic dispersion in the supercooled liquid phase.
Yuji Ike,Seiji Kojima 한국물리학회 2005 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.46 No.1
An angular dispersion-type Fabry-Perot interferometer (ADFPI) was used to measure the Brillouin scattering spectra of nearly stoichiometric composition of lithium niobate single crystals. Ahigh-reectivity and - atness solid etalon and a highly sensitive charge-coupled-device (CCD) detector were employed to obtain high-resolution spectra and to reduce the acquisition time signicantly compared to the conventional scanning-type Brillouin scattering measurement. The temperature dependence of acoustic properties was investigated in a broad temperature range by ADFPI and the longitudinal and transverse sound velocities were determined between 100 and 900 K.
Ghulam Shabbir,Seiji Kojima 한국물리학회 2005 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.46 No.1
High-resolution Brillouin-scattering experiments were performed to investigate the lowtemperature elastic properties of the lanthanum lead zirconate titanate (PLZT) relaxor ferroelectric ceramics of the composition PLZT-10/65/35 and { 7.6/72/28. The Brillouin frequency shift of the longitudinal acoustic (LA) mode showed a clear anomaly at To 46 K for both ceramics with decreasing temperature. This in ection in the relaxor ceramics indicates a glassy nature of the non-ergodic relaxor state below To.