Haruyuki Takahashi

Viscosity measurement of organic glasses below and above glass transition temperature

Abstract The viscosity of organic glasses, polystyrene (PS), poly (methylmethacrylate) (PMMA), and polycarbonate (PC) was measured, and the results were compared with those of inorganic glasses previously studied. The measurement was carried out in the pure shear deformation mode using a sandwich method from room temperature (RT) to the glass transition temperature Tg. Two relaxations of thermal activation type appeared in the lower and higher temperature regions (double relaxation). The temperature dependence of the viscosity was found to be sensitive to the mechanical and thermal treatments the specimen received. The compensation effect, a linear relation between the logarithm of the preexponential factor and the activation energy, was observed for the two viscosity relaxations. The shear viscosity measurement was also carried out above Tg using a rotation disk viscometer. The viscosity was in the hydrodynamic regime above Tg and was in the hopping regime below Tg; a crossover occurred near Tg. The overall characteristics of the viscosity of the organic glasses were quite similar to those of inorganic glasses such as metaphosphate glass.

Study on the shear viscosity of several inorganic glasses

The viscosities of metaphosphate, pyrophosphate, molybdate, and fluorophosphate glasses were measured under the shear deformation mode using a sandwich method from room temperature up to the glass transition temperature Tg. An optical method was used to measure the deformation under constant load as a function of time, and the results were analyzed using a mechanical model of anelasticity plus viscosity. In glasses containing long molecular chains, two relaxations appeared at lower and higher temperatures, while only one relaxation existed at higher temperatures in glasses without the chain. Both these relaxations were of the thermal activation type. A correlation between the frequency factor and the activation energy was found for the high temperature relaxation, and the values of the frequency factor were very large. Another apparatus, a rotation disk viscometer, was also used to measure the shear viscosity above Tg. The data obtained by the two experimental methods related to each other well, and the v...

Characteristic features of ionic conduction in AgI–Ag2O–V2O5 glasses

Abstract The glass forming region for AgI, Ag 2 O and V 2 O 5 ternary system was determined. On the basis of the glass forming region, the glass transition temperature, density, ionic conductivity and Raman scattering experiments were performed for n AgI–3Ag 2 O–2V 2 O 5 ( n =0–10) glasses. The glass transition temperature and the density varies linearly with AgI concentration. On the other hand, the activation energy for ionic conductivity and the electric modulus indicate different composition dependence at about 40 mol.% of AgI. It is verified that the network structure is essentially the same below and above this composition by Raman scattering experiment. The formation of AgI partial structure in higher AgI-doped glasses and its relation to the cluster model is discussed in terms of both the present experimental results and previous diffraction experiments.

AN EXPERIMENTAL STUDY ON THE SHEAR VISCOSITY OF SOLIDS

Viscoelastic solids with high viscosity were experimentally studied with the intention of having them deformed under uniform shear stress. A kind of sandwich method was developed for applying a constant shear stress to a specimen, and its deformation was observed optically using heterodyne interferometry with a sensitivity of 10 nm in displacement measurement. Time‐dependent deformation data were analyzed on the basis of a mechanical model of anelasticity plus viscosity. Viscosity in the range of 108–1014 Pa⋅s could be determined at temperatures of 20–200 °C. Through a simulation using the finite element method together with an experiment visualizing the deformation, the specimen deformation was shown to be of an almost uniform shear mode. Experiments were performed to determine the temperature dependence of viscosity for several kinds of glasses near their glass transition Tg, and the determined viscosity values were about 107 Pa⋅s at Tg. The viscosity values measured by a rotation disk viscometer were i...

Electron Density Distribution in AgBr

The electron density distribution in AgBr was investigated on the basis of X-ray intensity data collected by single crystal diffractometry. It was verified from difference Fourier map that the charge tends to accumulate in the intermediate region between the neighbouring unlike atoms. The origin of the extra charge on the difference Fourier map is investigated in terms of the radial distribution of the valence electrons.It is pointed out that the estimated value of the diamagnetic susceptibility of AgBr based on the present result agrees consistently with the observed one.

Electron distribution in silver halides

Abstract Solid fast ion conductors such as silver halides and silver chalcogenides have been recently drawing attention, because of their unusually high ionic conductivity in the high-temperature phase at about 200°C. This peculiar property is of particular importance for both research field of codensed matter physics and practical application as solid state sensors. The information of the bonding nature relevant to the electron distribution is desirable, in order to obtain insights into their characteristic property of solid fast ion conductors. An attempt will be made in this paper to review the current information of the bonding nature of silver halides in terms of the electron density distribution. Thus, this paper is primarily concerned with some physical properties of silver halides including the characteristic features of the crystal structure and the phase diagram. The data of alkali halides are also described for comparison. The experimental results of the magnetic susceptibilities of silver halides are summarized from the phenomenological point of view. The magnetic susceptibilities of silver halides were found to be sensitive to the change of temperature and crystal structure. It implies that the valence electrons of silver halides are loosely bound by the ion core. The electron density distribution in Agl and AgBr is also discussed using the results by single crystal X-ray diffractometry and the following points are suggested; in AgBr, the deformation of the charge distribution in bromine ion is much larger than that of silver ion and the radial distribution of valence electrons in bromine ion is enlarged in comparison with that of free ion state. In Agl, charge accumulation is feasible only on the c -directed bond and the difference Fourier map on the (1 1 0) plane indicates the deficiency of electrons around the silver site.

Structure of Molten AgI

Neutron diffraction measurement has been carried out in order to investigate the structure of molten silver iodide. The observed total structure factor and the pair distribution function of molten ...

The Existence of New Phases in CuBrTe, CuITe and CuITe2

The present study is to investigate the existence of a new phase for the first time by a specific heat measurement

An improved transient hot‐wire method for studying thermal transport in condensed matter

The transient hot‐wire method for simultaneously measuring the thermal conductivity and thermal diffusivity of materials has been modified to improve the accuracy of the measurements. In this new experimental method, called the multicurrent method, several constant current values are used for heating the hot wire in order to determine accurately the thermal transport quantities. The details of the multicurrent method are precisely described, and examples of experiments using the method with pure water, electrolytic solution, and ionic conducting glasses are given. It is shown that this method can be used both for liquid and solid materials; a relatively small amount of the specimen material is sufficient for each experiment; the material can be insulating as well as highly ionic‐conductive; the accuracies of the determined thermal conductivity and the thermal diffusivity values are, respectively, around ±1% and ±5%.

The structure of AgI-Ag2O-V2O5 glasses

Abstract Structures of 10AgI-3Ag 2 O-2V 2 O 5 , 3AgI-3Ag 2 O2V 2 O 5 and 2AgI2Ag 2 O-V 2 O 5 glasses have been investigated by neutron diffraction experiments. The characteristic features of observed structure factors S ( Q ) in 10AgI-3Ag 2 O-2V 2 O 5 glass is similar to those of other superionic conducting glasses and molten AgI. From the standpoint of the pair distribution functions, it is clarified that the Ag-I and I-I correlation strength and AgAg correlation length increase with increasing AgI concentration. Observed results suggest that the local AgI structure accompanied by the re-arrangement of silver ions is formed with highly doped iodide ions.