Hidehiro Ohwa

Dielectric Properties and Phase Transitions of Ba(Ti1-xSnx)O3 Solid Solution

In Ba(Ti1-x Snx )O3 solid solution, for Sn concentration x≤0.1, the permittivity follows the Curie-Weiss law above the Curie point T c. The increase in the peak value of the permittivity at T c is due to the change in ferroelectric transition from first order to second order with increasing x. For x>0.1, some deviations from the Curie-Weiss law are observed in a narrow temperature region above T c. The diffuse phase transition was observed. For x>0.2, the Curie-Weiss law does not hold over a wide temperature range. The dielectric dispersion was observed in the radio-frequency range (10 kHz–10 MHz). With increasing Sn concentration, the change in the phase transition from a normal ferroelectric transition to relaxor through the diffuse phase transition was observed.

Raman Scattering in (1-x)Pb(Mg1/3Nb2/3)O3–xPbTiO3

Single crystals and ceramics of (1- x )PMN– x PT were synthesized in the whole concentration range from x =0 to x =1, and the temperature-concentration phase diagram of the system was determined fr...

Crystal Growth and Dielectric Properties of Solid Solutions of Pb(Yb1/2Nb1/2)O3?PbTiO3 with a High Curie Temperature near a Morphotropic Phase Boundary

The Pb(Yb1/2Nb1/2)O3–PbTiO3 (PYN–PT) binary system single crystal near the morphotropic phase boundary (MPB) composition with (100) planes of 1–2 mm length on one side was successfully grown by the flux method using PbO–PbF2–B2O3 flux. The PYN–PT (47/53) single crystal was found, by simultaneous microdifferential thermal analysis and thermogravimetric analysis, to show a peritectic melting point at 1205°C with a decomposition of the perovskite crystals into a pyrochlore phase and a liquidus point at 1253°C. The structure of the PYN–PT (47/53) single crystal was determined by X-ray diffraction study to be tetragonal with a=4.05±0.01 A and c=4.14±0.01 A at room temperature. The PYN–PT single crystal shows the maximum value of the relative permittivity er of 16000 at 1 kHz at a Curie temperature Tc of 404°C, which is as high as that in the Pb(Zr, Ti)O3 system near the MPB and the value of the remanent polarization Pr of about 26 µC/cm2 at 140°C.

Domain Observation in Pb(Zn1/3Nb2/3)O3–PbTiO3 Mixed Crystals

Domain-wall structures in the vicinity of the morphotropic phase boundary (MPB) in (1-x)Pb(Zn1/3Nb2/3)O3–xPbTiO3 (PZN–xPT) mixed crystals (x=5% and 8%) were investigated by means of a polarizing microscope. It was found that the apparent jump of the indicatrix rotation as a function of temperature appears in the MPB region (x=8%) without the poling process, indicating the occurrence of a phase transition between the tetragonal and rhombohedral phases, despite the fact that this transition is known to be observed only in a poled sample in the case of dielectric constant measurements. We concluded that the sharp phase transition between the tetragonal and rhombohedral phases in the PZN–PT crystal can be observed in the small region of 50 µm order even without the poling process. It was also found that the principal axis of the indicatrix slightly rotates in the MPB region, implying the appearance of the lower symmetry phase such as a monoclinic structure.

The Temperature and Pressure Dependence of the Dielectric Properties of Disordered and Ordered Pb(In1/2Nb1/2)O3 Single Crystals.

Dielectric properties of the disordered and ordered Pb(In 1/2 Nb 1/2 )O 3 (abbreviated as PIN) single crystals were investigated in the range of temperature T from -70 to 200°C and of hydrostatic pressures p up to 0.7 GPa. For the disordered PIN, a typical dielectric dispersion which obeys the empirical Vogel-Fulcher relation was observed. Such dielectric dispersion strength was weakened with an increase in the degree of chemical ordering (S) at the B-site cations in the perovskite ABO 3 , and then relaxor behavior disappears. The relaxor behavior was also weakened with increasing pressure up to 0.7 GPa for the quenched disordered PIN with S=0.2, whereas for the disordered PIN with S=0.4, the relaxor behavior was weakened with increasing pressure and then the antiferroelectric phase transition was induced by the application of pressure above 0.4 GPa. For the ordered PIN, the phase below the transition temperature was confirmed to be antiferroelectric by observation of P - E double hysteresis loops. The st...

Crystal Growth and Some Properties of Lead Indium Niobate-Lead Titanate Single Crystals Produced by Solution Bridgman Method

A single crystal about 15 mm in diameter and 10 mm in length of the lead indium niobate-lead titanate, (1-x)Pb(In1/2Nb1/2)O3–xPbTiO3[PIN–PT(1-x/x)] solid solution system near a morphotropic phase boundary was obtained by the solution Bridgman method using PbO–B2O3 flux. X-ray diffraction study reveals that the ingot cut perpendicularly to the cylindrical as-grown PIN–PT(63/37)(the starting composition) single crystal length exhibits the (110) plane of the perovskite phase, and the wafers cut 2 mm and 10 mm from the bottom of the cylindrical PIN–PT single crystal exhibit the rhombohedral phase and tetragonal one at room temperature, respectively. The crystal growth was almost along the [110] direction. The Ti contents x of these wafers cut at 2 mm and at 10 mm were determined by Inductive Charge Plasma (ICP) chemical analysis to be 0.31 and 0.35, respectively. The Ti content of the as-grown PIN–PT(63/37)(the starting composition) single crystal was found to increase with growth away from the nucleation point. For x=0.31, the relative permittivity er has a peak (37000 at 10 kHz) at the Curie temperature Tc, 300°C and then a shoulder at the ferroelectric rhombohedral to tetragonal phase transition temperature, 120°C with cooling. For x=0.35, the er has a peak (25000 at 10 kHz) at Tc, 313°C.

Pressure-induced dielectric change from relaxor to antiferroelectric behavior in disordered Pb(In1/2Nb1/2)O3

The dielectric properties of Pb(In 1/2 Nb 1/2 )O 3 (abbreviated as PIN) single crystal were investigated under hydrostatic pressures up to 0.7 GPa. The ordered PIN was confirmed to be antiferroelectric by observation of clear P - E double hysteresis loops below the transition temperature. There is a striking pressure effect in the disordered PIN. The relaxor behavior becomes less notable with increasing pressure and disappears at 0.4 GPa. At pressures above 0.4 GPa, the normal phase transition without dielectric dispersion in the low frequency range takes place and with increasing pressure, the temperature T m , indicating the maximum of the dielectric constant, e rm ′ , increases at a rate of 150 K/GPa and the e rm ′ decreases. Such dielectric phenomena with pressure are similar to those observed in antiferroelectric PbZrO 3 .

RAMAN SCATTERING IN RELAXOR PB(ZN1/3NB2/3)O3

The Raman spectra of relaxor ferroelectrics in the single crystal Pb(Zn1/3Nb2/3)O3 (PZN) have been measured with the 90°scattering geometry over a wide temperature range between 100 K and 773 K and over a frequency range up to 1000 cm-1. The Raman-active modes exist well above the diffuse transition temperature of about 413 K (the cubic phase) implying that the space group of the cubic phase in PZN is not Pm3m. It is found that far above room temperature, the Raman spectra in the X(ZZ)Y and X(ZX)Y geometries are different, whereas below room temperature they are almost the same.

Brillouin and dielectric studies of the phase transition in the relaxor ferroelectric Pb(Ni1/3Nb2/3)O3

Brillouin scattering has been performed on the relaxor ferroelectric Pb(Ni1/3Nb2/3)O3 (PNN) from 80 to 450 K across its Curie temperature. A diffuse phase transition from the paraelectric to ferroelectric phase, associated with a broad phonon frequency dip and a damping maximum, is observed around 200 K. A relaxation mode in the form of a broad Rayleigh wing, whose frequency is strongly temperature dependent above 190 K, is observed and analyzed based on a modified superparaelectric model. Dielectric studies of PNN have also been carried out at several measurement frequencies. The relation between the measurement frequency and the dielectric maximum temperature was analyzed on a modified Vogel–Fulcher model.

Observation of the Distribution of the Transition Temperature in PbIn1/2Nb1/2O3.

PbIn 1/2 Nb 1/2 O 3 (PIN) single crystal plates obtained by different thermal treatment were investigated by means of polarizing microscopic observations. It was found that, in an as-grown PIN (cal...