Norikazu Ohtori

Raman spectra of K2O–B2O3 glasses and melts

The structures of K2O–B2O3 glasses and melts have been studied by high-temperature Raman spectroscopy. With an increase in the K2O content and with increasing temperature, the boroxol rings, which only consist of BO3 triangular units, were converted into pentaborate groups which consist of BO4 tetrahedral (O=bridging oxygen atom) and BO3 units in the 10 and 20 mol% K2O–B2O3 glasses/melts. In the 30 mol% K2O–B2O3 glass/melt, the Raman spectra indicated a structural change in the borate species from BO4 tetrahedral units to metaborate, BO2O−, triangular units with non-bridging oxygen with increasing temperature. The fraction of four-coordinated boron atoms, N4, obtained from deconvolution of the Raman bands was gradually reduced above the glass transition temperature and converged to a constant value over 1400 K. This phenomenon could be explained by a thermodynamic process.

Liquid Structure of 1-Propanol by Molecular Dynamics Simulations and X-Ray Scattering

Molecular dynamics (MD) simulations and X-ray scattering experiments have been carried out on liquid 1-propanol. The radial distribution functions obtained from these two methods were in good agreement with each other. On the basis of the hydrogen-bond number and the angular correlation functions of the four sequentially hydrogen-bonded O atoms derived from the MD calculation, it was found that the hydrogen-bonded O atoms preferentially form a planar zigzag chain structure, but that the plane undulates like a wave.

Thermal conductivity of molten alkali halides: Temperature and density dependence

The thermal conductivities of a series of molten alkali halides have been evaluated by using molecular dynamics simulation within the framework of Fumi-Tosi potential models. Although the calculated results showed 0%-50% larger values than experimental results depending on system, they are in agreement with each other in showing both negative temperature and ionic mass dependence. In order to clarify the cause of the negative temperature dependence in more detail, the thermal conductivity under constant temperature or constant density was evaluated for all alkali chlorides and all sodium halides. The calculations reveal that the thermal conductivity depends strongly on density but only weakly on temperature. While the integrated value of the autocorrelation function for energy current increases with temperature, this is canceled out by the reciprocal temperature factor in relation to the thermal conductivity. With increasing density the integrated value increases, and this dominates the behavior of the thermal conductivity. By repeating the calculations with different ionic masses, we have concluded that the thermal conductivity is a function of m(-1/2)(N/V)(2/3), where m is the geometric mean of ionic mass between anion and cation and N/V is the number density.

Thermal Conductivity of Molten Alkali Metal Fluorides (LiF, NaF, KF) and Their Mixtures

The thermal conductivities of molten alkali fluorides (LiF, NaF, and KF) and their mixtures (LiF-NaF, LiF-KF, and NaF-KF binaries and LiF-NaF-KF ternary) are predicted using molecular dynamics simulation with the Green-Kubo method. A polarizable ion model is used to describe the interionic interactions. All the systems except LiF-KF and LiF-NaF-KF mixtures follow a scaling law: it is proportionnal to mA (-1/2)(N/V)(2/3), where mA is the arithmetic average of the ionic species masses in a given melt and N is the total number of ions included in the system volume V. In LiF-KF and LiF-NaF-KF mixtures a significant departure from the scaling law is observed. By examining separately the effects of the cation mass and size asymmetry in LiF-KF mixtures, we show that both of them account for half of the deviation. Finally, we observe that the temperature dependence of the thermal conductivity is very small in these molten fluorides.

Measurement of Wave Velocity in Bovine Bone Tissue by Micro-Brillouin Scattering

To evaluate microscopic bone elasticity without contribution from macroscopic structures, a micro-Brillouin scattering technique was used. Our micro-Brillouin scattering system enables the measurement of wave velocities in the GHz range over a minute area (diameter: approximately 10 µm). We have applied this technique to thinly sliced bovine trabecular bone and collagen film. The average wave velocity in one trabecula was approximately 4.8 ×103 m/s, which was much higher than the velocity in the collagen film. The velocity anisotropy near the trabecular nodes was weak but complicated. In addition, these velocities were also higher than velocities in the cortical bone, which were in the MHz range. These investigations show the possibility of using the Brillouin scattering technique to evaluate microscopic bone elasticity, which is closely related to the quality of bone matrix.

Brillouin Scattering Study on the Elastic Properties of Epoxy Adhesive Layer

Wave properties (wave velocity and attenuation) in epoxy adhesive layers during cure were investigated. Longitudinal and shear wave properties in the GHz region were measured by the Brillouin scattering technique using 90°A-scattering geometry. The longitudinal and shear wave properties showed similar changes during cure. Compared with the ultrasonic wave properties in the MHz region, a clear frequency dispersion could be seen during cure, in the glass transition region. It is supposed that this dispersion results from a strong α relaxation. Longitudinal modulus and shear modulus were also obtained from the longitudinal and shear wave velocities. The longitudinal modulus was always proportional to the shear modulus during the entire curing process.

Short-range structure of alkaline-earth borate glasses by pulsed neutron diffraction and molecular dynamics simulation

Abstract The structure of vitreous MO· n B 2 O 3 (M=Ca and Ba; n =2, 3 and 4) has been studied by pulsed neutron diffraction measurement with the help of molecular dynamics (MD) simulation. The first and second peaks assigned to the nearest-neighbor B–O and O–O correlations, respectively, in the obtained total pair distribution functions shifted little with increasing MO content, while the asymmetry of the first peak increased significantly with MO content; these results are different from those for potassium borate glasses. It was inferred that the BO 3 and BO 4 units are better defined in these alkaline-earth borate glasses than those in the potassium borate glasses. Both the full-width at half maximum (FWHM) of the first peak and the average co-ordination number of O around B clearly increased as MO content increased which is the same behavior with alkali borate glasses. The fraction of four-co-ordinated B showed a larger deviation from x /(1− x ) for CaO–B 2 O 3 glasses than that for BaO–B 2 O 3 glasses which shows a different dependence of the deviation on cation size from that in alkali borate glasses, and is in good agreement with the results from MD simulation.

Brillouin Scattering Study on the Opto-Acoustic Properties of Thin Piezoelectric Polymer Films

Reflection-induced ΘA Brillouin scattering (RIΘA) is introduced to investigate the opto-acoustic anisotropy of uniaxially stretched polyvinylidene fluoride (PVDF) films (0.04 mm in thickness). Although the films are not perfectly transparent, their elastic and optical anisotropy could be investigated nondestructively. The optical anisotropy, which is observed as birefringence, showed a clear decrease near the Curie temperature (Tc).

“Two-Pass” Brillouin Scattering Geometry for the Investigation of Opto-Acoustic Properties of Thin Films

A new optical geometry for Brillouin scattering measurement of thin films is proposed. Making use of the two incident laser beams focused on the sample, simultaneous measurements of 90A scattering and back scattering were performed. The strong scattering peaks in the spectra enabled simultaneous measurements of hypersonic wave velocity and refractive index. Actually, the appearance of anisotropy in the polypropylene (PP) film was continuously observed as an increase of birefringence during the ultra-drawing process.

Observation of Induced Shear Acoustic Phonons by Brillouin Scattering

As the first step in realizing the simple and nondestructive measurement of shear waves in the GHz range, a technique involving Brillouin scattering and a ZnO shear wave transducer is proposed. Making use of transmitted shear waves, we have succeeded in observing a strong Stokes Brillouin peak in the quartz sample. This technique can be applied to the measurement of anisotropic layers and small samples.