Toshihisa Yamaguchi
Meisei University
Network
Latest external collaboration on country level. Dive into details by clicking on the dots.
Publication
Featured researches published by Toshihisa Yamaguchi.
Journal of the Physical Society of Japan | 1990
Fuminao Shimizu; Toshihisa Yamaguchi; Haruhiko Suzuki; Masaaki Takashige; Shozo Sawada
The phase transition sequence of a K 2 ZnBr 4 crystal was investigated by DTA and dielectric measurements. It was found that the crystal undergoes at least two phase transitions, at -118°C and around 200°C, on heating. Ferroelectricity was observed below the lower transition point.
Journal of the Physical Society of Japan | 1990
Haruhiko Suzuki; Fuminao Shimizu; Masaaki Takashige; Shozo Sawada; Toshihisa Yamaguchi
The phase-sequence of K 2 CoBr 4 was investigated by measuring the time dependence of dielectric constant. It was revealed that the crystal undergoes a phase transition around 200°C and the high-temperature phase can be brought into the low-temperature region. The time-dependent recovering process from this metastable phase to the original low-temperature phase was observed. A ferroelectric-like behavior was detected.
Journal of the Physical Society of Japan | 1991
Hiroyuki Mashiyama; Hironobu Kasano; Toshihisa Yamaguchi
The structural phase transitions of K 2 ZnBr 4 and K 2 CoBr 4 are investigated by means of X-ray scattering. The transition from the room-temperature α phase to the high-temperature β phase takes place at about 200°C. It is found that the β phase is an incommensurate one with the modulation wave vector q =(1/3-δ) c * , which is followed by a normal phase of Pmcn above 288°C (Zn-salt) or 282°C (Co-salt). If the β phase is supercooled to below room temperature, then the crystal is a commensurate phase with q =1/3 c * . With increasing temperature, the commensurate-incommensurate phase transition is observed at 5°C in Zn-salt. The transition sequence of normal, incommensurate and commensurate phases is quite common in A 2 X Y 4 -type incommensurate materials, though the α phase is very different from others.
Journal of the Physical Society of Japan | 1988
Fuminao Shimizu; Haruhiko Suzuki; Toshihisa Yamaguchi; Shozo Sawada
Phase transition temperatures of single crystals of Rb 2 CoCl 4 prepared by the Bridgman method were checked by a DTA technique and a dielectric measurement and it was found that the Curie temperature T C is -74°C and the normal-incommensurate transition point T i is 21°C on heating. The thermal anomaly at the Curie temperature T C was observed by the DTA technique with a Ge–Ag thermocouple. The temperature dependence of the dielectric constants in the b and c directions was measured in a temperature range covering these phase transition points and the temperature dependence of P s and E c was determined from the observed 50 Hz D - E hysteresis loop, respectively. It was determined that the ferroelectric axis of Rb 2 CoCl 4 is the a axis in reality.
Journal of the Physical Society of Japan | 1985
Shozo Sawada; Toshihisa Yamaguchi; Haruhiko Suzuki; Fuminao Shimizu
Thermal, dielectric and dilatational measurements were performed to study the phase transitions in ferroelectric {N(CH 3 ) 4 } 2 ZnCl 4 . The temperature dependence of triple D - E hysteresis loop in ferroelectric Phase III (3.3∼6.0°C, C 2 v 9 - P 2 1 c n ) was observed in detail. The crystal is paraelectric along the b and c directions. A remarkable contraction of the lattice is seen in Phase V (-112∼-92°C, C 2 h 5 - P 12 1 / c 1). Calculated pressure-coefficients of transition temperatures were compared with the measured ones.
Ferroelectrics | 1995
Shozo Sawada; Masaaki Takashige; Fuminao Shimizu; Haruhiko Suzuki; Toshihisa Yamaguchi
Abstract A review was given for our search for halide ferroelectrics with the chemical formula A 2 BX 4-type, having structure of β-K2SO4-type and Sr2GeS4-type.
Japanese Journal of Applied Physics | 1999
Masaaki Takashige; Sin-Ichi Hamazaki; Yoshio Takahashi; Fuminao Shimizu; Toshihisa Yamaguchi
We used an atomic force microscope (AFM) to study the surface morphology of butterfly-like crystals of BaTiO3. Observations were made while varying the temperature from room temperature to 150°C and the annihilation process of the surface structure due to 90° domain boundaries was detected. The relationship between the surface gradient change at the domain boundaries and the tetragonal distortion was discussed.
Journal of the Physical Society of Japan | 1988
Toshihisa Yamaguchi; Fuminao Shimizu; Minoru Morita; Haruhiko Suzuki; Shozo Sawada
Single crystals of K 2 CoCl 4 grown from a melt by the Bridgman method undergo phase transitions at -131°C and 181°C, respectively, and show ferroelectricity along the a -axis in the phases below 181°C.
Journal of the Physical Society of Japan | 1985
Shozo Sawada; Toshihisa Yamaguchi; Haruhiko Suzuki; Fuminao Shimizu
Dielectric properties of ferroelectric {N(CH 3 ) 4 } 2 CoCl 4 were measured in detail, covering its all transition points. The triple D - E hysteresis loop in Phase III (4.6∼7.1°C, C 2 v 9 - P 2 1 c n ) was ascertained. The lattice distortion of this ferroelectric was determined along the three crystallographic axes by a differential-transformer type dilatometer. The pressure-coefficient of transition temperature was discussed.
Journal of the Physical Society of Japan | 1980
Shozo Sawada; Toshihisa Yamaguchi; Naomi Shibayama
Triple 60 Hz hysteresis loops have been observed in (NH 4 ) 2 SO 4 , (NH 4 ) 2 BeF 4 and K 2 SeO 4 crystals of the (NH 4 ) 2 SO 4 family. From these experimental results and other facts already known, these ferroelectrics are concluded to be really ferrielectric.