Fuminao Shimizu

New Ferroelectric K2ZnBr4

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.

Time-dependent phase transition in K2CoBr4

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.

AFM Observation of 90° Domains of BaTiO3 Butterfly Crystals

We used atomic force microscopy (AFM) to study the surface morphology of tetragonal barium titanate BaTiO 3 at room temperature. An undulation of the surface was observed around the boundary of 90° domains of the as-grown surface of the so-called butterfly crystals, which can be reasonably explained by the tetragonality of this crystal at room temperature.

Dielectric Properties of Ferroelectric Rb2CoCl4

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.

Atomic Force Microscope Observation of Ferroelectrics: Barium Titanate and Rochelle Salt

We applied atomic force microscopy (AFM) to study the surface morphology of ferroelectric BaTiO3 (barium titanate, BT) and NaKC4H4O64H2O (Rochelle salt, RS). At room temperature, an undulation of the crystal surface was observed around the 90° domain boundary in BT and around the monoclinic domain boundary in RS.

Phase transitions in K2ZnBr4 and K2CoBr4

Abstract The phase transition sequences in K2ZnBr4 and K2 CoBr4 were investigated by means of dielectric constant measurements and DTA (Differential Thermal Analysis).

Experimental Studies on Phase Transitions in Ferroelectric {N(CH3)4}2ZnCl4

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.

Ferroelectricity in A 2 BX 4-type halide compounds

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.

Ferroelectricity in K2ZnI4

Single crystals of K 2 ZnI 4 with monoclinic Sr 2 GeS 4 structure prepared by the Bridgman method were investigated through DTA and dielectric measurements. Ferroelectric activity was found below 270 K, where the b -direction dielectric constant showed a sharp peak. The spontaneous polarization measured by the pyroelectric charge method was 0.32 µ C/cm 2 at 100 K. The dielectric constant also showed a small stepwise anomaly around 190 K.

Temperature Dependent Surface Images of BaTiO3 Observed by Atomic Force Microscopy

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.