Showing papers by "Yoshihiro Ishibashi published in 2011"

Phase Front Near the Critical End Point as the Boundary of the Polar Nanoregions in Relaxor Ferroelectrics

Abstract: The static modulation structure of the phase front at the field-induced first-order transition point near the critical end point (CEP) was discussed on the basis of the Landau-type free-energy function. It was confirmed that the field E dependence of the thickness of the phase front is proportional to ( E CEP - E ) -1/2 , diverging at CEP ( E = E CEP ). It is pointed out that, in relaxor ferroelectrics, the boundary between the polar nanoregion (PNR) and the paraelectric matrix may be considered as a phase front, and that the contribution to the dielectric response of the phase front cannot be ignored.

Hierarchical Domain Structures in Relaxor 24Pb(In$_{1/2}$Nb$_{1/2}$)O$_{3}$–46Pb(Mg$_{1/3}$Nb$_{2/3}$)O$_{3}$–30PbTiO$_{3}$ near a Morphotropic Phase Boundary Composition Grown by Bridgman Method

Abstract: The domain structures of the lead-based relaxor ferroelectric solid solution single crystal, 24Pb(In1/2Nb1/2)O3 (PIN)–46Pb(Mg1/3Nb2/3)O3 (PMN)–30PbTiO3 (PT), near a morphotropic phase boundary (MPB) composition grown by the Bridgeman method were studied by polarized light microscopy (PLM), piezoresponse force microscopy (PFM) and scanning electron microscopy (SEM). The change in domain structures with poling from rhombohedral spindlelike domains of 3–5 µm width to orthorhombic domains of ~20 µm width with rectangular cells with a size of 3–5 µm, characterized with an antiferroelectic double hysteresis loop in the electric field-induced strain behavior, was found. Such domain structures were microscopically identified from SEM images as small circular tetragonal defects, planar monoclinic defects such as edge and screw dislocations with Burgers vector b along cub and/or cub directions and their agglomerate rectangular orthorhombic defects, also characterized by PFM. Hierarchical domain structures are discussed from the viewpoints of domain structures due to defects such as edge and screw dislocations originating in the chemical order region (COR) and the piezoelectric responses and dielectric properties.

Field-induced transition and behavior of the phase front in Pb(Zn1/3Nb2/3)O3–8%PbTiO3

Abstract: Field-induced phase transition in Pb(Zn1/3Nb2/3)O3–8%PbTiO3 was investigated by measuring temperature dependence of the dielectric constant under the DC biasing field. It was revealed that a critical end point (CEP) exists at 170 ± 2°C and 1.5 ± 0.2 kV cm−1. The boundary between the ferroelectric and the paraelectric phases near CEP was discussed on the basis of the Landau-type free energy. It is confirmed that the wall width is proportional to (E ce − E)−1/2, and diverges at CEP (E = E ce), where E is the electric field and E ce is E at CEP.

Piezoelectric Response of Relaxor Solid Solution Na0.5Bi0.5TiO3-BaTiO3 Single Crystal Grown by Bridgman Method

Abstract: While macroscopic observation reveals non-switching of domain in Na0.5Bi0.5TiO3 (NBT)-BaTiO3 (Ba;0.33%) rhombohedral (001) plate, microscopic observation, using the piezoresponse force microscopy (PFM), reveals two kinds of piezoresponse images, one with domain switching and the other without one. Such microscopic remarkable difference of domain switching depends on the coercive field caused by localized nucleation of domains with reversed polarization. Such coercive fields was discussed from the viewpoint of the relaxor states resulting from random fields based on lattice defects due to Bi ions and oxygen vacancies.

The Critical End Point in Pb(Zn1/3Nb2/3)O3–8%PbTiO3

Abstract: Temperature dependence of the dielectric constant under the DC biasing field was measured in Pb(Zn1/3Nb2/3)O3–8%PbTiO3. The temperature-field phase diagram was clarified in the field range below 2.5 kV. The existence of the critical end point at 172 ± 3°C and 1.75 ± 0.25 kV/cm was confirmed.

The Eight-Pseudospin Model of KH2PO4-Type Crystals

Abstract: The eight-pseudospin model of KH 2 PO 4 -type crystals is proposed, where eight pseudo-spins represent protons on the hydrogen bonds connecting four PO 4 radicals in a unit cell. Among the eight eigenstates, one corresponds to the orthorhombic ferroelectric state of KH 2 PO 4 , two correspond to the orthorhombic antiferroelectric state of NH 4 H 2 PO 4 , and two correspond to the monoclinic ferroelectric state, with three others violating the ice condition. The relative stability of three admissible phases is governed by three independent parameters of interactions between the pseudo-spins.

Phase Diagram in Bi4-xGdxTi3O12

Abstract: The temperature dependences of the dielectric constants of Bi4-xGdxTi3O12 (BGT-x) single crystals (x≤04) were measured It was found that the paraelectric–ferroelectric phase transition temperature near 680 °C remains almost unchanged in the concentration range of 0≤x ≤04 Below the transition point at about 680 °C, another dielectric anomaly showing the phase transition was observed in BGT-x, where the transition temperature depends on the concentration x We confirmed that the triggered transition from the tetragonal phase to the monoclinic phase, observed in Bi4Ti3O12, splits into two phase transitions with the addition of Gd cations, ie, from the tetragonal phase to the orthorhombic phase and eventually to the monoclinic phase The temperature-concentration phase diagram in BGT-x was clarified

Field induced effect near MPB in Pb(Zn1/3Nb2/3)O3-9%PbTiO3

Abstract: Temperature dependences of the dielectric constants under the DC biasing fields along the [001]- and [111]-directions in the cubic coordinate were measured in Pb(Zn1/3Nb2/3)O3-9%PbTiO3. The temperature-field phase diagrams were clarified in the field range below 3.5 kV/cm. The existence of the critical end point at 185°C and 1.7 kV/cm was confirmed. The aspect of the temperature-field phase diagram depending on the direction of the field was discussed.

Eight-Pseudospin Model of KH2PO4-Type Crystals: II. Phase Transitions and Dielectric Susceptibilities

Abstract: The phase transitions in ferroelectric KH 2 PO 4 (KDP) and antiferroelectric NH 4 H 2 PO 4 (ADP) crystals are discussed on the basis of the eight-pseudospin model of KH 2 PO 4 -type crystals previously proposed, where eight pseudospins represent protons on hydrogen bonds connecting PO 4 radicals in a unit cell. The dielectric susceptibilities along the c -axis, which is the unique ferroelectric axis, and a ( b )-axis, which is perpendicular to the unique axis, are calculated.

Phase Diagram in Bi$_{4-x}$Gd$_{x}$Ti$_{3}$O$_{12}$

Abstract: The temperature dependences of the dielectric constants of Bi4-xGdxTi3O12 (BGT-x) single crystals (x≤0.4) were measured. It was found that the paraelectric–ferroelectric phase transition temperature near 680 °C remains almost unchanged in the concentration range of 0≤x ≤0.4. Below the transition point at about 680 °C, another dielectric anomaly showing the phase transition was observed in BGT-x, where the transition temperature depends on the concentration x. We confirmed that the triggered transition from the tetragonal phase to the monoclinic phase, observed in Bi4Ti3O12, splits into two phase transitions with the addition of Gd cations, i.e., from the tetragonal phase to the orthorhombic phase and eventually to the monoclinic phase. The temperature-concentration phase diagram in BGT-x was clarified.