Yoshiaki Uesu

Universal phase diagram for high-piezoelectric Perovskite systems

Strong piezoelectricity in perovskite-type PbZn1−xTixO3 (PZT) and Pb(Zn1/3Nb2/3)O3–PbTiO3 (PZN–PT) systems is generally associated with the existence of a morphotropic phase boundary (MPB) separating regions with rhombohedral and tetragonal symmetry. An x-ray study of PZN–9% PT has revealed the presence of an orthorhombic phase at the MPB, and a near-vertical boundary between the rhombohedral and orthorhombic phases, similar to that found for PZT between the rhombohedral and monoclinic phases. We discuss the results in the light of a recent theoretical paper by Vanderbilt and Cohen [Phys. Rev. B 63, 94108 (2001)], which attributes these low-symmetry phases to the high anharmonicity in these oxide systems.

Monoclinic structure of unpoled morphotropic high piezoelectric PMN-PT and PZN-PT compounds

Evidences of a monoclinic phase in unpoled (PbMg1/3Nb2/3O3)1-x-(PbTiO3)x with x=0.35 (PMN-PT 35%) and unpoled (PbZn1/3Nb2/3O3)1-x-(PbTiO3)x with x=0.09 (PZN-PT 9%) are presented from a neutron Rietveld analysis. This monoclinic phase is different from the phase recently evidenced by Noheda and coworkers in PbZr1-xTixO3 with x=0.481 but is identical to the phase observed in poled PZN-PT with x=0.102 by the same authors. The structural resolutions allowed us to compare both structures and to deduce the direction and magnitude of polarization. In PMN-PT 35% and PZN-PT 9% this phase is characterised by a weak value of polarization, a strong deformation of oxygen polyhedra and weak cationic shifts.

Domain inversion in ferroelectric MgO:LiNbO3 by applying electric fields

An antiparallel ferroelectric domain in LiNbO3 doped with 5 mol % MgO (MgO:LN) was inverted at room temperature by applying a step‐like electric field. The lowest electric field was about one fifth of that for undoped LN, but a high field compared to that for BaTiO3 was found to be necessary from the analysis of the switching current. The long switching time (about 102 s under an electric field of 4.45 kV/mm) enabled us to observe the domain growth process in MgO:LN. The needle‐shaped nuclei grew into larger domains by nucleation on the existing domain wall, and the wall of the coalesced domain moved forward slowly. The process was similar to the domain reversal model proposed for BaTiO3 under low electric fields.

Optical second harmonic images of 90° domain structure in BaTiO3 and periodically inverted antiparallel domains in LiTaO3

By using the second harmonic generation (SHG) microscope, which we have recently developed, two‐dimensional images of ferroelectric domain structure were successfully obtained by exploiting the inhomogeneous distribution of the quadratic nonlinear optical constant in specimens. 90° domain structure of BaTiO3 was observed with intensity contrast of the second harmonic wave. A periodically inverted antiparallel domain in LiTaO3 was also observed. This fact indicates that the SHG microscope provides a new method of observing antiparallel ferroelectric domain structure in a nondestructive way, which is especially important for characterizing the quasiphase matched devices for compact blue light lasers.

Application of the second harmonic generation microscope to nondestructive observation of periodically poled ferroelectric domains in quasi-phase-matched wavelength converters

A technique for observation of 180° domains in ferroelectric crystals is demonstrated by the use of the second harmonic generation (SHG) microscope. The phase reversal of the SH wave accompanying inversion of spontaneous polarization is exploited to visualize domains. Interference between SH waves converts the phase information to the SH contrast. The domain mapping is achieved in LiNbO3 and LiTaO3 by nonlinear coefficients d33 and d22 under the microscope, which enables the characterization of a periodically poled structure in quasi-phase-matched wavelength converters in a nondestructive way. The validity of the technique is proved by another characterizing tool of destructive etching.

Electric-field-induced resistance switching universally observed in transition-metal-oxide thin films

We show that polarity-dependent, nonvolatile resistance switching by electric field occurs in the thin film of various transition-metal oxides in almost the same manner. This result indicates that, contrary to the general acceptance, perovskite manganite is by no means a special compound for this phenomenon. It is also suggested that the resistance switching is not dominated by a detailed electronic structure of each sample, but dominated by a more general origin, e.g., crystalline defect.

Anomalous dielectric response in the dimer Mott insulatorκ−(BEDT-TTF)2Cu2(CN)3

We have measured and analyzed the dielectric constant of the dimer Mott insulator

Symmetry of High-Piezoelectric Pb-Based Complex Perovskites at the Morphotropic Phase Boundary: I. Neutron Diffraction Study on Pb(Zn1/3Nb2/3)O3–9%PbTiO3

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Optical Observation of Heterophase and Domain Structures in Relaxor Ferroelectrics Pb(Zn1/3Nb2/3)O3/9%PbTiO3

(BEDT-TTF)

Tem observation of polar domains in relaxor ferroelectric Pb(Mg1/3Nb2/3)O3

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