Yosio Hiki

Calculation of the Third- and Fourth-Order Elastic Constants of Alkali Halide Crystals

The evluation of six third-order and eleven fourth-order elastic constants of an alkali halide crystal has been made by calculating higher order strain derivatives of the crystal free energy. The energy adopted was the sum of the long-range Coulomb and the short-range Born-Mayer potentials and the vibrational free energy of the lattice. The evaluation of the higher order elastic constants has been done for LiF, NaCl, and KCl at 0 K and 300 K, and the results were in reasonable agreement with conclusions of other experimental and theoretical studies. The third-order and the fourth-order elastic constants largest in absolute values were respectively negative and positive in their signs, and one and two orders larger in their magnitudes than the second-order elastic constants.

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.

Scattering of Lattice Waves by Static Strain Fields in Crystals

On the basis of nonlinear elasticity theory, the scattering of lattice waves by a static strain field has been treated with special consideration of the elastic anisotropy of wave-propagating medium. A general form for the wave equation in strained medium was derived, and the scattered waves were determined by means of perturbation method by adopting the Born approximation. The Greens function method was conveniently used to determine the displacement of the scattered waves. The general method was applied to the case of scattering of lattice waves incident normally on a screw dislocation in a cubic crystal. The results of the calculation showed that the scattering was very anisotropic with regard to the incident direction and the scattering angle of the waves. It was found that, contrary to the dominance of purely forward scattering in isotropic medium, obliquely forward scattering occurred intensively in crystals.

Low-frequency high-temperature internal friction of bulk metallic glasses

Abstract The internal friction (IF) of Johnson alloy (Zr–Ti–Cu–Ni–Be) glass prepared by a single-roller melt-spinning method was measured using an inverted torsion pendulum with the free decay method. The measurements were performed from room temperature, through the glass transition temperature T g , up to the crystallization temperature T x . The effect of isothermal annealing at a temperature about 20 K below T g was studied. By the annealing the unstable glassy state and the metastable supercooled state were transferred to more stable ones (stabilization). In a well-stabilized state, the background IF was flat at lower temperatures, increased rapidly at higher temperatures, and an IF peak appeared near T x together with another peak at a lower temperature. No IF peak was observed near T g . Qualitative discussions are presented for the experimental results, and possible use of the glass as a high damping material is briefly mentioned.

Effect of Dislocations on Low-Temperature Thermal Conductivity and Specific Heat of Copper-Aluminum Alloy Crystals

Simultaneous measurements of the thermal conductivity and specific heat of copper-aluminum (2, 5, 8, and 12 at.%) alloy crystals have been done by the temperature-wave method at 1.4–7.5 K. Specimens containing dislocations of medium (10 10 cm -2 ) and high (10 12 cm -2 ) densities were used. In the case of crystals of medium dislocation density, the lattice thermal conductivity data were well explained by the mechanism of the strain-field scattering of phonons, and the numerical results agreed with those recently calculated by the authors. The lattice specific heat of the crystals was found to be strongly decreased by the introduction of dislocations, and the results were interpreted by considering the effect of atmosphere of alloying atoms. Anomalous behaviors of the specific heat and thermal conductivity were found in crystals of high dislocation density. The origin was assumed to be quasi-local phonon modes around dislocations, and the analysis of the data along this idea gave reasonable results.

Simulation of Dislocation Configuration in Rare Gas Crystals

A simulation has been made for a screw dislocation in argon and xenon model crystals with various sizes. The number of atom rows in the crystal was 360-1400, and the Lennard-Jones (12-6) interatomic potential truncated at the third neighbors was adopted. The ordinary relaxation method was used to obtain the stable configuration of atoms in the crystal. It was found that the dislocation split into two Shockley partials, and the configuration of the partials depended on the boundary condition of the crystal surface. A method of modified boundary condition was proposed to control the effect of the surface. The split dislocations were able to stably exist when their separation was in a definite range, which was well understood by considering the balance of three forces: the interaction force between partials, the force due to stacking fault, and the image force from the crystal surface. By taking the limiting value of the separation distance for the crystal of infinite size, the stacking fault energy was esti...

Ultrasonic Three-Phonon Process in Copper Crystal

The large angle noncollinear three-phonon interactions have been studied by using longitudinal ( L ) and transverse ( T ) pulsed ultrasonics with megahertz frequencies. Two types of process, T [100]+ T [\bar110]→ L and L [100]+ T [010]→ L , were observed in the (001) interaction plane of a copper single crystal. The incident ultrasonic beams were approved to be cylindrical in shapes and almost non-diverging. The displacement amplitude of the produced sound was found to be proportional to the product of the amplitudes of two incident sounds, to vary wholly as the cosine of the angle between the polarization direction of T incident wave and the interaction plane, being agreed with theoretical predictions. The ratio of the amplitudes of the produced sounds in two types of interaction was disagreed with the theoretical value perhaps due to the difficulty in transmitting the transverse waves into the specimen.

Simultaneous Measurement of Low-Temperature Specific Heat and Thermal Conductivity by Temperature-Wave Method

An experimental procedure is proposed for a simultaneous measurement of thermal conductivity and thermal diffusivity of a specimen by a modified temperature-wave (Angstroms) method. The temperature wave is generated by an AC current in a heater attached to the specimen. The diffusivity can be obtained from the phase difference of the temperature wave between two positions of the specimen, and the conductivity is determined from the static temperature gradient produced by the DC component of input power. The temperatures and their variation at two positions are detected by carbon film resistance thermometers. The specific heat of the specimen is derived from the values of thermal diffusivity and conductivity. An example of experimental results is given for the case of Cu-Al alloy specimen. The reliability of the measured values of conductivity and diffusivity is estimated to be 5~8% in liquid-helium temperature range.

Low-temperature thermal diffusivity measurement by laser-flash method

The pulse heating method has been developed for measuring the thermal diffusivity of solids at low temperatures. The experimental procedures were such that the front surface of a disk-shaped specimen was irradiated by a ruby-laser pulse (pulse width< 1 msec), and the time variation of the temperature at the rear surface was detected by thin-film bolometers (sputtered gold film at higher temperatures and painted carbon film at lower temperatures) and was recorded by a sensitive high-speed electronic apparatus. The measurements were made at temperatures between 300 and 4.2 K, and the specimen used were polyethylene (60% crystallinity). The method to analyze the experimental data was precisely described. It was shown that the finite pulse-time effect could be ignored due to the short duration of the laser pulse, and that the consideration should be made on the heat loss from the specimen to its surroundings through the heat conduction, and also that an adequate choice of the bolometers was important especial...

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.