Y. Kajihara

Dielectric relaxation of water and heavy water in the whole fluid phase

Recently we developed a new microwave spectroscopy technique in the frequency range up to 40 GHz, and measured the static dielectric constant and the dielectric relaxation time for supercritical water. In the present work we report the dielectric properties of heavy water at temperatures and pressures up to 770 K and 59 MPa, respectively. The static dielectric constant of D2O as well as H2O are well described by the Uematsu–Franck formula when the number density instead of the mass density is used as the input parameter. The dielectric relaxation time decreases rapidly with increasing temperature in liquid H2O and D2O and jumps to a large value at the liquid–gas transition. The relaxation time of D2O is longer than that of H2O in the liquid state, and the difference becomes smaller with decreasing density in the gaseous state. For both H2O and D2O the most relevant parameter determining the relaxation time is the temperature at high densities or at low temperatures, and it is the density at low densities ...

Transverse excitations in liquid Sn

Transverse acoustic (TA) excitation modes were observed in inelastic x-ray scattering (IXS) spectra of liquid Sn. The excitation energies and widths of the TA modes are in good agreement with results of an ab initio molecular dynamics simulation. By comparing current correlation spectra between the experimental and theoretical results quantitatively, we have concluded that the TA modes can be detected experimentally through the quasi-TA branches in the longitudinal current correlation spectra. The lifetime and propagation length of the TA modes were determined to be ~0.7 ps and 0.8-1.0 nm, respectively, corresponding to the size of cages formed instantaneously in liquid Sn.

Dielectric relaxation measurements on methanol up to the supercritical region

The static permittivity e(0) and the dielectric relaxation time τD have been obtained for methanol over a wide range of temperature and pressure up to 600 K and 21 MPa. The dielectric relaxation time τD decreases with increasing temperature and has little pressure dependence in the liquid state. In the gaseous state, however, τD increases with decreasing density. Since these behaviours are qualitatively the same as those for water, we have successfully applied our model for the dielectric relaxation in water to that in methanol with some appropriate modifications.

Transverse excitations in liquid Fe, Cu and Zn

Transverse acoustic (TA) excitation modes were observed in inelastic x-ray scattering spectra of liquid Fe, Cu and Zn. From the analysis of current correlation functions, we concluded that TA excitation modes can experimentally be detected through the quasi-TA branches in the longitudinal current correlation spectra in these liquid metals. The microscopic elastic constants are estimated and a characteristic difference from macroscopic polycrystalline value was found in Poissons ratio of liquid Fe, which shows an extremely softer value of ∼0.38 compared with the macroscopic value of ∼0.275. The lifetime of the TA modes were determined to be ∼0.45 ps for liquid Fe and Cu and ∼0.55 ps for liquid Zn, reflecting different interatomic correlations between liquid transition metals and non-transition metals. The propagation length of the TA modes are ∼0.85 nm in all of liquid metals, corresponding to the size of icosahedral or similar size of cages formed instantaneously in these liquid metals.

Sound attenuation in supercritical fluid mercury

Abstract The sound attenuation coefficient, α , of fluid mercury has been measured at 20 MHz in the temperature and pressure range to 1600°C and to 200 MPa. Beside the critical attenuation of sound propagation, we have observed a secondary maximum in the density dependence of the sound attenuation coefficient due to the metal–non-metal (M–NM) transition around 9 g/cm 3 . The shape of this maximum depends mainly on density but not on temperature unlike the critical attenuation. On assumption that structural change takes place in the M–NM transition range, we have estimated the time scale of the structural relaxation to be the order of nano seconds. We concluded that in expanded liquid Hg slow dynamics are generated by the sound pressure in the M–NM transition range.

Anomalous sound attenuation in liquid Te50Se50 mixture under high pressure

The sound velocity, v, and the sound attenuation coefficient, ?, have been measured for liquid Te50Se50 mixture at 20, 32 and 43?MHz in the temperature and pressure range up to 1000??C and 150?MPa. Near the melting point ? decreases with increasing temperature, as is expected from the temperature variation of shear viscosity. In addition to the normal behaviour, we have found two peaks of ? in the temperature range where the semiconductor-to-metal transition is observed. One is the high temperature peak, which appears around 850??C irrespective of the frequency, and the other is the low temperature peak, whose position depends strongly on the frequency. The peaks become more prominent with increasing pressure, indicating the importance of the inter-chain couplings. Assuming a Debye-type relaxation for the frequency-dependent adiabatic compressibility, we have estimated the relaxation time to be about 7 ns from the high temperature peak.

Structural study of expanded fluid cesium

We have performed x-ray diffraction and small-angle x-ray scattering measurements for expanded fluid cesium from the triple point up to supercritical regions. The experimental results show that the nearest neighbor distance starts to decrease and the density fluctuation increases below the density around 1.3 g cm−3. These structural features suggest that clustering occurs in the metallic fluid accompanying spatial atomic-density fluctuations. The density range where such inhomogeneity of the atomic arrangement appears corresponds to the region where the compressibility of the interacting electron gas has been predicted to become negative, which suggests that the observed structural changes are those induced by the instability of the electron gas.

Slow dynamics due to the metal–non-metal transition in liquid mercury

Abstract The sound absorption coefficient, α , of expanded liquid mercury has been measured at 20, 32 and 44 MHz in the temperature and pressure range up to 1600 °C and 210 MPa. Besides the critical attenuation, we have observed an anomalous increase of α due to the relaxation process in the metal–non-metal (M–NM) transition range. Assuming a Debye-type relaxation, we show that the relaxation time, τ , is about 2 ns and the relaxation strength has a broad maximum in the M–NM transition range. Introducing a simple model in which the ionization equilibrium is considered, we conclude that the anomalous dynamics should be closely related to the promotion of the 6s electron to the 6p states.

Ellipsometric study of the prewetting transition at the mercury-sapphire interface

Optical reflectivity measurements were carried out on fluid mercury against an optically transparent sapphire window at high temperatures and pressures up to and 180 MPa. In order to make quantitative analyses, we performed not only normal-reflection measurements but also ellipsometric measurements with -reflection geometry, and the occurrence of the prewetting transition was confirmed clearly.

Transverse excitations in liquid metals

The transverse acoustic excitation modes were detected by inelastic x-ray scattering in liquid Ga, Cu and Fe in the Q range around 10 nm−1 using a third-generation synchrotron radiation facility, SPring-8, although these liquid metals are mostly described by a simple hard-sphere liquid. Ab initio molecular dynamics simulations clearly support this finding for liquid Ga. From the detailed analyses for the S(Q,ω) spectra with good statistic qualities, the lifetime of less than 1 ps and the propagating length of less than 1 nm can be estimated for the transverse acoustic phonon modes, which correspond to the lifetime and size of cages formed instantaneously in these liquid metals. The microscopic Poisson’s ratio estimated from the dynamic velocities of sound is 0.42 for liquid Ga and about −0.2 for liquid transition metals, indicating a rubber-like soft and extremely hard elastic properties of the cage clusters, respectively. The origin of these microscopic elastic properties is discussed in detail.