Yuji Ike

Broadband inelastic light scattering of a relaxor ferroelectric 0.71Pb(Ni1/3Nb2/3)O3-0.29PbTiO3

Brillouin and Raman scatterings of a 0.71Pb(Ni1∕3Nb2∕3)O3-0.29PbTiO3 single crystal have been measured to investigate broadband inelastic spectra. The two different central peaks related to fast and slow relaxation processes have been observed separately. These two processes are attributed to the thermally activated switching of polarization in polar nanoregions. By the analysis of modified superparaelectric model, the activation energies of fast and slow relaxation processes are determined to be 3.66×103 and 4.31×102K, respectively. The fast process with the lower activation energy probably originated from 180° switching, whereas the slow one with the higher energy from non-180° switching.

Brillouin Scattering Study of Liquid Glass Transition in Lithium Borate Glass

Elastic properties of different compositions of lithium borate glasses xLi2O(1-x)B2O3 (x=0.06–0.28) were investigated in the temperature range from 25 to 600 °C by Brillouin scattering spectroscopy. The composition dependence of the lithium borate glass system shows a stiffening tendency and a higher onset temperature of softening with increasing mole fraction of Li2O. We successfully observed the change in longitudinal elastic modulus in the vicinity of the glass transition temperature (Tg). The elastic moduli show a marked temperature dependence above the glass transition temperature Tg, while they show little change below Tg. These results strongly relate to the structural conversion of cross-linking borate units from triangular BO3 to tetrahedral BO4 units by the addition of Li2O. The increase in lithium oxide enhances the glass network integrity in the composition range of this study. A significant decrease in the elastic modulus above Tg can be attributed to the association of boroxol ring deformation and a change in the coordination number of boron atoms. These elastic properties were discussed in comparison with lithium silicate glass.

Glass Transitions and Elastic Properties of Lithium Borate Glasses over a Wide Composition Range Studied by Micro-Brillouin Scattering

The elastic properties of lithium borate glasses, denoted by the composition formula xLi2O(100 - x)B2O3 where x is the molar concentration in mol %, have been investigated over a wide composition range 6 ≤x ≤52 mol % by micro-Brillouin scattering. From the observed values of the longitudinal and transverse sound velocities, the elastic constants such as longitudinal modulus, shear modulus, Youngs modulus, and Poissons ratio have been determined. The elastic constants have shown a strong composition dependence due to the variation of intermediate structural units. The temperature dependences of the longitudinal sound velocity and absorption coefficient of 44Li2O56B2O3 clearly show the anomalies at the glass transition and crystallization temperatures.

Dynamic Specific Heat, Glass Transition, and Non-Debye Nature of Thermal Relaxation in Lithium Borate Glasses

The physical properties of lithium borate glasses, x Li 2 O·(100- x )B 2 O 3 , vary anomalously with the lithium oxide content, known as “borate anomaly”. In this study, the compositional variations of the dynamic glass transition temperature T g ω and the non-Debye nature (or stretched exponentiality β KWW ) in the vicinity of T g have been investigated over a wide composition range. Since T g ω depends on the frequency of the temperature modulation, a more precise composition dependence can be discussed. The trend of T g ω shows a single broad maximum at about x = 26–28. Moreover, the composition dependence of the non-Debye behavior has been presented. It shows a broad maximum at about x = 40 mol %. It is found that β KWW is systematically controlled using the fraction of each intermediate structural unit, particularly the tetrahedron composed of the 4-coordinated boron atom. Both the composition dependences of T g ω and β KWW can be explained using the structure-superposition model.

Trehalose Bioprotective Effects in Lysozyme Aqueous Solution Studied by Brillouin Scattering and Calorimetric Measurements

The bioprotective effect of trehalose in lysozyme aqueous solutions has been investigated by Brillouin scattering and modulated-temperature differential scanning calorimetry (MDSC). MDSC experiments show that the isothermal kinetics of thermally irreversible denaturation can be described by the Arrhenius equation. By the addition of trehalose, the irreversible denaturation of lysozyme is suppressed, and its activation energy is half that of the denaturation without trehalose. The sound velocity of lysozyme–trehalose–water ternary solutions obviously depends on the trehalose concentration. With increasing trehalose concentration, the sound velocity becomes higher because the hydration of trehalose reduces the hydrogen bonds between water molecules. Moreover, hydration around lysozyme molecules increases the sound velocity further. Trehalose molecules tend to aggregate with lysozyme molecules at high trehalose concentrations. The bioprotective effect of trehalose probably originates from the mechanical suppression of conformational fluctuations of lysozyme molecules.

Brillouin Scattering Study of Cluster Structure in Lower Alcohol Water Mixtures

The concentration dependences of sound velocity in lower alcohols [ethanol, 1-propanol, ethylene glycol (EG)] water mixtures were determined by Brillouin scattering. The cluster structures of the alcohol water mixtures were analyzed using the nonlinear coupling equation. The number of nearest neighboring water molecules for an alcohol molecule and the coupling constant between sound velocity and clusters were determined accurately. These parameters show the correlation between the size of an alkyl group and the number of hydroxyl groups of an alcohol molecule.

Broadband Inelastic Light Scattering Study on Relaxor Ferroelectrics

Dielectric and light scattering studies on a Pb(Ni1/3Nb2/3)O3–0.29PbTiO3 single crystal have been conducted in a wide temperature range to clarify the relaxational properties of polar nanoregions (PNRs). The temperature dependences of the relaxation time observed in light scattering spectra show two characteristic temperatures: associated with enhancement of the correlation length in the PNRs T* and related to a temperature-induced macroscopic structural phase transition Tf. These results are closely related to the behavior of the PNRs. We suggest that two relaxation processes are attributed to the central peak and that the origins of the observed relaxation processes are two types of switching processes of dipole moments in the PNRs. In addition, the activation energy at 0 K has been evaluated as H0B=2.11×103 K.

Diffuse Phase Transition of 0.8Pb(Ni1/3Nb2/3)O3-0.2PbTiO3 Single Crystals Studied by Micro-Brillouin Scattering

Brillouin scattering in the relaxor ferroelectric 0.8 Pb(Ni 1/3 Nb 2/3 )O 3 -0.2 PbTiO 3 has been studied in the temperature range from −150°C to 500°C. The anomalies of the frequency shift and full width at half maximum of Brillouin component at the structural phase transition from the paraelectric to ferroelectric phases have been successively detected. The origins of the anomalies of them are discussed from the phenomenological point of view. The central peak caused by the fluctuation of polarization has been also observed in the VV and VH scattering geometries with the large free spectral range of 150 GHz. It is found the difference of central peak intensity obtained in VV and VH scattering geometries.

High-resolution Brillouin spectroscopy with angular dispersion-type Fabry-Perot interferometer and its application to a quartz crystal

Although the multichannel Brillouin spectroscopy with an angular dispersion-type Fabry-Perot interferometer (ADFPI) becomes a powerful tool for quick measurements, its resolution and contrast are not enough for the study of single crystals. A highly sensitive multichannel detector enables the ADFPI to use a solid etalon with high reflectivity (99.5%); hence, the high resolution and the high contrast of a spectrum are achieved. The finesse, the inverse of the resolution, reaches 100 with a 10 mm diameter of aperture size. The highest finesse of 140 is obtained by using a smaller diameter of 2 mm. The accuracy is examined by the measurement of a quartz crystal. The improvement in the resolution and contrast enables investigations of weak attenuation in a quartz crystal. The elastic anomaly of the alpha-beta transition of a quartz crystal is clearly observed both in sound velocity and attenuation. From the elastic constant c(11), the critical parameter K=0.76 is determined.

Complex Heat Capacity of Lithium Borate Glasses Studied by Modulated DSC

Complex heat capacity, Cp* = Cp′ − iCp″, of lithium borate glasses Li2O⋅(1−x)B2O3 (x = 0.00 – 0.33) has been investigated by Modulated DSC (MDSC). We have successfully observed the frequency dependent Cp* by MDSC in the frequency range 0.01 to 0.1 Hz, and the average relaxation time of glass transition has been determined as a function of temperature. Moreover, the composition dependence of the thermal properties has been investigated. The calorimetric glass transition temperatures become higher with the increase of concentration of Li2O and show the board maximum around x = 0.26–0.28. The width of glass transition region becomes narrower as Li2O increases. These results relate to the change of the fragility of the system. It has been proven that the complex heat capacity spectroscopy by MDSC is a powerful tool to investigate the glass transition phenomena.