Hiroshi Kameyama

Phase Diagram of DSP/DLP Mixed Crystal System

The phase diagram of the Ca 2 Pb x Sr 1- x (C 2 H 5 CO 2 ) 6 mixed system is presented on the basis of dielectric and dilatometric anomalies. By the continuity of the phase in the mixed crystal system to those of two end members the space groups of Ca 2 Pb(C 2 H 5 CO 2 ) 6 are identified to be D 4 4 (D 8 4 ) and C 2 4 (C 4 4 ) at high, intermediate and low temperatures, respectively.

Elastic Constants in Cupric Formate Tetrahydrate Single Crystals

Ultrasonic wave velocities in Cu(HCOO) 2 ·4H 2 O single crystals were measured at room temperature and all of thirteen elastic stiffness constants of this monoclinic crystal were obtained. The directions of both the displacement and the energy flow in sound waves were calculated using the data obtained and the relations between the energy flow directions and the wave normals were discussed. The temperature dependences of the ultrasonic wave velocities and the anomalous absorption were also measured with the special care in the vicinity of the transition temperature.

Elastic Constants of Ca2Ba(C2H5CO2)6 Single Crystal

The temperature dependences of the ultrasound velocities and the thermal expansion have been measured with special care in the vicinity of the phase transition temperatures. All of three elastic stiffness constants of Ca 2 Ba(C 2 H 5 CO 2 ) 6 single crystal are found as follows: at room temperature C 11 =7.64±0.05, C 12 =4.50±0.06 and C 44 =2.85±0.06 in the unit of 10 10 dyne/cm 2 . The temperature coefficients, d C i j /d T , of all of the elastic stiffness constants over the range from 110°C to -8.5°C (the upper phase transition temperature) are found to be positive. All the measured modes have shown large jumps at the upper phase transition temperature and clear dips at the lower phase transition temperature.

Pure and Semipure Mode Directions in the Piezoelectric Crystal

The contribution of piezoelectricity was taken into consideration in the elastic wave equation referred to the rotated coordinates, and investigated for all of the pure and semipure mode directions in the crystals of the piezoelectric point groups. In the point groups belonging to cubic, tetragonal I, trigonal I, orthorhombic, monoclinic and triclinic systems, pure and semipure mode directions are determined similarly to the case of neglecting the piezoelectric effect. In the points groups belonging to trigonal II, tetragonal II and hexagonal systems, it is found that the piezoelectric effect shows a remarkable contribution to pure and semipure mode directions. The pure and semipure mode directions can be derived taking account of the crystal symmetry elements.

Anomalous Ultrasonic Attenuation near the Ferroelectric Phase Transition Point of Ca2Sr(C2H5CO2)6

The temperature dependence of the anomalous ultrasonic attenuation in Ca 2 Sr(C 2 H 5 CO 2 ) 6 has been measured in the frequency range 10.3–72.1 MHz above and below the ferroelectric phase transition temperature. Shift of the attenuation peaks towards the lower temperature side with increasing frequency has been observed. It has turned out that the behavior of the anomalies of the ultrasonic attenuation in the vicinity of ferroelectric phase transition point can be well explained by the Levanyuk theory. The elastic relaxation time τ=3.0 ×10 -9 /( T 1 - T ) sec. estimated from the first order (piezoelectric) effect in the sound attenuation is found to be quite close to the dielectric relaxation time at T 1 - T =1°C.

Elastic Properties of Ca2Sr(C2H5CO2)6

All the elastic stiffness constants in the I and II phases of Ca 2 Sr(C 2 H 5 CO 2 ) 6 were determined in an ultrasonic frequency region in the temperature range from -80^° C to 70°C. The anomalies in the velocities of the longitudinal modes show the logarithmic divergence above the I–II phase transition temperature, whereas the velocities of the transverse modes show no anomaly in the I phase. These phenomena can be well explained by the Levanyuk-Dvořak theory of the nonpiezoelectric material.