Byoung Wan Lee

Pressure Dependence of Acoustic Properties of Liquid Ethanol by using High-pressure Brillouin Spectroscopy

Brillouin spectroscopy has been widely used for the investigation of acoustic properties of condensed matters in the hypersonic region. A high-pressure Brillouin spectrometer was set up by combining a diamond anvil cell and a tandem multi-pass Fabry-Perot interferometer. It was successfully applied to liquid ethanol, and the pressure dependence of the sound velocity, the refractive index and other acoustic properties were derived based on the measurements. The detailed optical setup and experimental procedure are described.

Phase transitions and interrelated instabilities in PbHfO3 single crystals

PbHfO(3) is investigated theoretically and experimentally with respect to possible precursor effects starting in the paraelectric phase far above the cubic to tetragonal phase transition temperature. The theoretical modeling within the polarizability model predicts a giant softness of the system with spatially large polar and antiferrodistortive domain formation which compete with each other. These predictions are substantiated by the experiments, where the softness and the precursor effects are confirmed by birefringence, dielectric permittivity measurements and elastic properties by Brillouin scattering. The intermediate phase is found to have the polar nature confirmed by P-E hysteresis loop measurements, which is another manifestation of the competition between interrelated instabilities, namely a polar one and an antiferroelectric one.

Acoustic anisotropy of oriented polyethylene terephthalate films studied through Brillouin light scattering

The polyethylene terephthalate (PET) substrate is one of the key materials comprising optical films, which are essential components in various optical devices, such as displays. The elastic properties of oriented PET were investigated via Brillouin light scattering spectroscopy. The high-frequency longitudinal and transverse sound velocities in the hypersonic region were determined using a special right-angle scattering geometry, where the information of the refractive index was not included in the calculation. When the propagation direction of the acoustic modes was changed in the plane with respect to the stretching directions, the longitudinal and transverse sound velocities exhibited periodic modulations, clearly revealing the acoustic anisotropy of the film arising from the stretching condition.

Enhanced Polarization Fluctuations in PbZr0.72Sn0.28O3 Compared to PbZrO3 Single Crystals Studied by Brillouin Light Scattering

Acoustic properties of antiferroelectric (AFE) PbZr0.72Sn0.28O3 single crystals were investigated in a wide temperature range by Brillouin light scattering spectroscopy. The Brillouin frequency shift of the longitudinal acoustic (LA) mode exhibited three abrupt changes corresponding to the successive phase transitions between the paraelectric, intermediate, antiferroelectric (AFE2) and antiferroelectric (AFE1) phases upon cooling. The change in the LA mode frequency and the damping maximum of PbZr0.72Sn0.28O3 were much higher than those of pure PbZrO3. This was attributed to enhanced polarization fluctuations caused by increased ferroelectric distortions due to Sn substitution and the proximity to the tricritical point on the phase diagram of PbZr1-xSnxO3.

Phase Transition Behaviors of Lead-Free (Na1/2Bi1/2)TiO3-BaTiO3 Single Crystals Studied by Inelastic Light Scattering Spectroscopy

Acoustic anomalies of (1-x)(Na1/2Bi1/2)TiO3-xBaTiO3 (NBT-xBT) with x = 0.05 were investigated over a wide temperature range of from 900°C to −200°C by using Brillouin light scattering. The sound velocity of the longitudinal acoustic mode propagating along the [100] direction showed a substantial softening, while the acoustic attenuation coefficient of this mode exhibited a large increase in the paraelectric phase. These anomalies were attributed to the formation and growth of noncentrosymmetric polar regions in the paraelectric phase, which was supported by the appearance of the strong polarized central peak. The absence of any sharp or discontinuous changes in the acoustic properties seems to suggest that the polar regions remain short-ranged and do not form macroscopic polar domains at low temperatures, which may be attributed to the inherent A-site disorder induced by random substitutions of Bi, Na and Ba cations.

Boson peak dynamics of glassy glucose studied by integrated terahertz-band spectroscopy

We performed terahertz time-domain spectroscopy, low-frequency Raman scattering, and Brillouin light scattering on vitreous glucose to investigate the boson peak (BP) dynamics. In the spectra of

Acoustic and relaxation behaviors of polydimethylsiloxane studied by using brillouin and dielectric spectroscopies

\ensuremath{\alpha}(\ensuremath{\nu})/{\ensuremath{\nu}}^{2}

Temperature and pressure dependences of acoustic anomalies of PET films studied by using Brillouin spectroscopy

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Pressure and temperature dependences of the acoustic behaviors of biocompatible silk studied by using Brillouin spectroscopy

is the absorption coefficient], the BP is clearly observed around 1.1 THz. Correspondingly, the complex dielectric constant spectra show a universal resonancelike behavior only below the BP frequency. As an analytical scheme, we propose the relative light-vibration coupling coefficient (RCC), which is obtainable from the combination of the far-infrared and Raman spectra. The RCC reveals that the infrared light-vibration coupling coefficient