A nonlinear thermodynamic theory is applied to strained ferroelectric superlattices and used to determine the dependence of superlattice permittivity on composition. To that end, spontaneous polarizations and field-induced polarization changes in the ferroelectric layers A and B with thicknesses t(A) and t(B) are calculated as a function of the volume fraction phi(A)=t(A)/(t(A)+ t(B)). The existence of a dielectric anomaly at a specific composition phi(A)* is predicted for the superlattices, where only one of ferroelectric layers has nonzero out-of-plane polarization in the uncoupled state. The theoretical predictions agree with the composition dependence of permittivity displayed by the Pb(Sc1/2Nb1/2)O-3/PbTiO3 superlattices grown on SrRuO3-covered SrTiO3.

From density-functional calculations, we show that large off-center motions (approximate to 1.0 angstrom) of Li impurities in the KTaO3 matrix (studied at 3.7% concentration) create very anisotropic polar clusters oriented along the Li off-center dipole. The polarization induced by Li in the matrix decreases very sharply in the lateral directions so that polar clusters are only approximate to two lattice constants thick (one-dimensional or needlelike clusters). The polarization in such polar regions is mainly constituted by the displacements in the (highly polarizable) matrix rather than by the impurity itself. These results suggest that Li-doped potassium tantalate (3.7% concentration) is not ferroelectric at low temperature and rather behaves as a relaxor. These small polar zones around Li correlate at TB to form larger polar nanoregions, in which the matrix remains however nonpolar. This is confirmed by a low temperature neutron-diffraction analysis showing that the KTaO3 matrix remains paraelectric. Li-doped KTaO3 is an order-disorder system with a very deep local potential felt by the Li impurities (approximate to-200 meV). The energy barrier for Li hopping is estimated at 80-90 meV. An analytic expression for this local potential is provided, as well as a simple model describing the energetics of K1-xLixTaO3.

Dielectric properties of KH(2)PO(4) (KDP) crystals doped with complex organic (Amaranth, Chicago Sky Blue, Xylenol Orange) and inorganic (Potassium PentoChloroRuthenate) molecules were analyzed in the frequency range of 10 mHz-10 MHz. A noticeable dispersion in paraelectric phase at 30-80 degrees C is revealed. In some crystals with dyes the deviation of Cole-Cole diagrams from Debye-type relaxation is shown. Conductivity and activation energy of the conductivity mechanism at high temperature are determined.

LiTaO3(LT)/LiNbO3(LN) super-lattice thin films with different LT/LN ratios are fabricated on (0001) sapphire (-Al2O3) substrates using the pulsed laser deposition method. Well-defined X-ray super-lattice reflections are observed, and the SL period are calculated from these super-lattice positions, which coincide well with design ones estimated from the deposition velocities of LN and LT. X-ray -2 and in-plane phi-scans confirm the epitaxial growth of the films. Photon energy dependence of complex refractive indices n* of these super-lattice thin films are measured by a spectroscopic ellipsometer. The blue shift of n* with increase of LT ratio is observed.

Thin-film transistors (TFTs) with amorphous InGaZnO4 as a channel layer are known to exhibit high field-effect mobility. We studied the characteristic of the accumulated carriers in this TFT by optical spectroscopy and observed Drude absorption and oscillation in the transmittance spectrum of the channel region appearing with an applied gate voltage. The scattering rate of the carriers in the accumulation layers estimated from the optical spectrum is (h) over bar/tau(AL) = 0.19eV. and this small value is the origin of the high mobility of the TFT with amorphous InGaZnO4.

Periodically poled domain structures in stoichiometric LiNbO3 (PPSLN) and LiTaO3 (PPSLT) are observed using an optical second harmonic generation (SHG) interference microscope. Three-dimensional section images can be obtained in PPSLN using d(31) SHG tensor component. In PPSLT, the images of top and bottom surfaces are obtained using d(22) component. The difference in SHG images with and without interference is discussed. (C) 2009 The Japan Society of Applied Physics

Anisotropy of the optical second harmonic generation (SHG) in a multiferroic BiFeO3 single crystal is observed by an SHG microscope. Polarization dependences of SH intensities are measured in several polarization configurations of the incident and SH waves to determine the magnitude and sign of polar i-type SHG tensor components. To obtain proper values of these SHG tensors, the effects of the interference term and wave number mismatch are taken into account in these analyses. d(24) component is 15 times larger than d(32) and this result is essentially different from the thin film case.

By the microspectroscopic imaging of optical reflectivity for the La1-xSrxFeO3-delta thin film with indium-tin-oxide electrodes, we observed that the shape of the conducting area between two electrodes is reversibly varied with applied electric voltage pulses and that causes a repeatable change in the electrical resistance between the electrodes. These results can be explained by the oxygen-ion migration with applied electric field, which induces a variation in the distribution of the Fe4+ ions in the thin film.

Ferroelectric domain structures of BiFeO3 single crystals are observed using second harmonic generation and polarization microscopes. Anisotropy of SHG intensities is measured on (111)c and (110)c plates and analyzed by the Sapriel theory. The observed domains keep the same pattern from room temperature to above T-N of 643 K without essential change.

Optical second harmonic generation (SHG) and birefringence Delta n of ferroelectric LaBGeO5 are measured as a function of temperature. Using the Maker-Fringe method, magnitudes of SHG tensor components and coherence lengths are determined. From the symmetry analysis of d tensor components, the space group of the paraelectric phase is assigned to be non-centrosymmetric P3(1)2. The critical index of the order parameter is determined to be 0.5 from the birefringence measurement in the vicinity of T-C.

Relaxor/ferroelectric super lattice films Pb(Sc1/2Nb1/2)O-3/PbTiO3 (PSN/PT) with different PT ratios are synthesized on the lattice cell scale by the pulsed laser deposition method. X-ray diffraction analyses reveal that fabricated and designed super-lattice (SL) periods coincide well within 6% error, and are uniform over thin film thickness of 100 nm. The lattice constant of PT in SL films shows an abrupt increase at a specific PT ratio of around 30%, which indicates the change in the a-axis to the c-axis domain configuration. The dielectric constant shows also the maximum at this PT ratio probably due to the dielectric anisotropy of PT, and it does not depend on the SL period.

The temperature dependence of the heat capacity of thin epitaxial films BaTiO(3)/MgO is studied by the dynamic 3 omega method in the thickness range 50-500 nm. It is revealed that the heat capacity exhibits diffuse anomalies due to phase transitions. The temperature of the ferroelectric phase transition T (C) increases with decreasing film thickness. The reasons for the strong diffuseness of the transition and the nonlinear dependence of the transition temperature on the film thickness are discussed.

The necessary conditions for nondestructive and three-dimensional (3D) observations of inverted polar domain structures using the second-harmonic generation interference microscope (SHGIM) are examined experimentally and theoretically using MgO doped congruent LiNbO3 and periodically poled (PP) MgO doped near stoichiometrical LiNbO3. The results can be explained well by the Boyd and Kleinman theory of strongly focused optical systems. To obtain clear 3D images of domain structures by SHGIM, the sign of the wave number Delta k offset of the fundamental and SH waves should be negative and the SHG tensor components d(31) should be used for both samples when they are observed with a wavelength of 1064 nm at room temperature. Under these conditions, 3D PP domain structures are clearly revealed by SHGIM. General conditions for the 3D visualization of polar domain structures are discussed for the cases of sum-frequency and difference-frequency generations. (C) 2008 American Institute of Physics.

Relaxor/ferroelectric superlattice (SL) films Pb(Sc(1/2)Nb(1/2))O(3)(PSN)/PbTiO(3)(PT) with nine different PT concentrations x are fabricated by a pulsed laser deposition method, which keeps the total film thickness at 100 nm. The structure of the SL films is examined by out-of-plane and in-plane x-ray diffractions. All films are epitaxial and their SL structures are coherent over the whole sample. SL reflections up to the fourth order are observed. Lattice constants of the PT and PSN layers in the SL are determined, and the PT lattice constant exhibits a marked increase at x(m)=32%. At this PT concentration, this phenomenon is due to a polarization reorientation from the a-axis oriented to the c-axis oriented domain. The complex dielectric constants of all samples are measured in the frequency region from 1 to 10(6) Hz, and the intrinsic dielectric constant epsilon of the SL is derived by an analysis using the equivalent electric circuit model. epsilon takes the maximum at x(m). The possible origin of this peculiar phenomenon is discussed. (C) 2008 American Institute of Physics.

Temperature evolution of the lattice parameters of relaxor PbSc1/2Nb1/2O3 (PSN) thin films have been measured and compared to the evolution of bulk PSN. In PSN films, a room temperature tetragonal polar phase transforms at higher temperature into a nonpolar tetragonal phase. Critical and Burns temperatures, associated, respectively, to the onset of the ferroelectric phase and to the nucleation of polar nanoregions have been assigned from strong anomalies in the temperature evolution of the film. These complex behaviors are explained by a quantitative study of the strains lying in the film. (C) 2008 American Institute of Physics.

Temperature dependences of the optical second harmonic generation in Li-doped KTaO3 (KLT) with different Li concentrations x are measured to determine the coefficients in the Landau-Devonshire free energy function. The result specifies the tri-critical Li concentration xc. Temperature dependences of the dielectric constant of KLT with Li concentrations nearly located at xc are also measured under dc bias fields and the result suggests that these compounds lie in close vicinity of the line of critical end points. The tertiary phase diagram (T, x, E) of KLT is disclosed from the experiments. ©2008 The Physical Society of Japan.

Optical second harmonic (SH) intensities and dielectric constants of Li doped KTaO3 are measured under an external electric field. Applying the Landau-Devonshire phenomenological theory to the temperature dependence of SH intensities, we find that the order of ferroelectric phase transition changes from 2nd to 1st with the increase of Li concentration. The dielectric measurement reveals that a critical behaviour similar to Pb(Mg1/3Nb2/3)O3-PbTiO3 is observed. Additionally, we find that the critical electric field depends on the frequency of electric field and the effect becomes conspicuous in lower frequencies in Li doped KTaO3.

A novel nonlinear optical interference microscope which enables us to take 3D images of ferroelectric domain structures is developed. This microscope is of a transmission type equipped with the confocal optical system, and exploits, as a probe, second harmonic waves generated in a sample by an incident laser beam. We apply the microscope to the observation of periodically poled domain structure in a LiTaO3 quasi-phase matching device.

A novel confocal second harmonic generation (SHG) interference microscope with a transmission optical system is devised. This microscope is a kind of SHG tomography which provides us 3-dimensional images of heterogeneous structures in polar materials in non-destructive way. We apply successfully this microscope to observations of periodically poled domain structures in quasi-phase matching devices.

Optical second harmonic (SH) intensities and dielectric constants of Li doped KTaO3 are measured under an external electric field. Applying the Landau-Devonshire phenomenological theory to the temperature dependence of SH intensities, we find that the order of ferroelectric phase transition changes from 2nd to 1st with the increase of Li concentration. The dielectric measurement reveals that a critical behaviour similar to Pb(Mg 1/3Nb2/3)O3-PbTiO3 is observed. Additionally, we find that the critical electric field depends on the frequency of electric field and the effect becomes conspicuous in lower frequencies in Li doped KTaO3.

It is shown that the information about thermophysical parameters of the nanostructured ferroelectrics is a useful supplement to the traditional x-ray and dielectric data. The results of the study of the temperature dependence of heat capacity of BaTiO3/MgO epitaxial thin films by dynamical 3 method for the thickness range 50-450 nm are presented. The blurred specific heat anomalies corresponding to the phase transitions were observed, and the temperature of the transitions increases with decreasing of film thickness compared with Tc in a bulk sample. The causes of the severe smearing of specific heat anomalies as well as pronounced nonlinearity of the dependence of the transition temperature on the film thickness are discussed. Specific heat data for ferroelectric superlattices (BaTiO3)n/(Sr TiO3)m/Sr TiO3 were obtained for the first time for the films with the average thicknesses near 100 nm.

Second harmonic generation interference tomography which enables us to obtain three-dimensional images of ferroelectric antiparallel domain structures is devised. Periodically poled domains (PPDs) inside a LiTaO3 quasiphase matching crystal (QPM) are observed by this microscope. Section images perpendicular to the polar z axis show that the PPD structure is maintained throughout the top quarter of the sample but it starts to lose the periodic nature in the bottom half of the sample. Corresponding degradation of the QPM performance is observed along the z direction of the sample. (c) 2007 American Institute of Physics.

The quantum paraelectric KTaO3 doped with 3 % Li is investigated by using a second harmonic-generation microscope. A slow kinetics of the order parameter is observed under an electric field. At low temperatures below 30 K, the SH intensity doesn't grow in the laboratory time while around 40 K, the SH intensity increases steeply within 10 minutes, followed by a slow increase toward the equilibrium value. The phenomenon is related to three types of domains with different speeds of domain growth. The applicability of the theory proposed by Alberici-Kious et al. is also discussed.

To elucidate the origin of the colossal dielectric response (CDR) of CaCu3Ti4O12 (CCTO), multilayer thin films of CCTO interposed in insulating CaTiO3 (CTO) were synthesized using a pulsed laser deposition technique. The capacitance C of CTO/CCTO/CTO films with different layer thicknesses is measured. After removing the capacitance of CTO by extrapolating C to zero CTO thickness, the real part of dielectric constant of CCTO is estimated to be 329-435, which is much smaller than the reported value for CCTO thin films. This fact indicates that the CDR of CCTO is extrinsic and originates from an internal barrier layer capacitor. (c) 2007 American Institute of Physics.

Superlattice (SL) thin films with different periods and composition ratios of Pb(Sc1/2Nb1/2)O-3 and PbTiO3 (PT), inside and outside the morphotropic phase boundary, are synthesized by a pulsed laser deposition method. High order SL reflections are observed by x-ray diffraction, from which the SL period and correlation length are determined. The coherency of the SL structure is found to extend over the whole film in the thinner films. A maximum dielectric constant of 1800 with a dielectric loss of 0.05 is obtained in the frequency range of 1-10(4) Hz for a SL with average composition of 25% of PT. (c) 2007 American Institute of Physics.

Optical second-harmonic generation (SHG) observations and precise x-ray diffraction experiments have been performed on quantum paraelectrics KTa O3 (KTO) and relaxors K(1-x) Lix Ta O3 with x=3% (KLT-3) and 7% (KLT-7). It is found in KLT-3 and KLT-7 that a pretransitional region exists between two characteristic temperatures TB and Tp (&lt
TB). The average symmetry of the region is tetragonal with a weak lattice deformation, but it is nonpolar on average. The temperature interval between TB and Tp is consistent with the interval in which neutron diffuse scatterings have been previously reported. TB is also found to align with the deviation temperature of the Curie-Weiss behavior of dielectric constant. These facts strongly suggest that polar nanoregions (PNRs) nucleate around TB and grow toward Tp. Below Tp, a larger deformation and a field-induced SH intensity start to develop, while no significant SHG appears in the zero-field-cooling (ZFC) process because of macroscopic inversion symmetry of the polydomain structure. The field-cooling (FC) process breaks the macroscopic inversion symmetry and the temperature dependence of SH intensity in field heating after FC coincides well with that of the tetragonality determined by x-ray diffraction experiments. The Landau-Devonshire phenomenological approach suggests that the ferroelectric phase transition at Tp is of first order and that it approaches the second-order transition with a decrease in the Li concentration. A marked increase of neutron-diffraction intensities below Tp, together with the disappearance of SHG intensity in a ZFC run, indicates that PNRs are transformed to ferroelectric microdomains at Tp. The microdomains become macroscopic below Tp in the FC process. In the lower-temperature region, nonergodic behavior was observed: The ZFC state cannot approach the thermodynamically equilibrium state under the electric field within finite time. © 2007 The American Physical Society.

Dielectric constants of complex perovskite oxide (Ba1-xLax) (Ti1-xCrx)O-3 (BLTC) ceramics with 0.4 <= x <= 0.7 are measured, and a remarkable colossal dielectric relaxation which is quite similar to that of CaCu3Ti4O12 (CCTO) is found in higher temperature region above the ferroelectric phase transition. This kind of dielectric relaxation is successfully explained by an equivalent circuit model of a series of two R - C parallel circuits with temperature-dependent electrical conductivity and temperature-independent intrinsic dielectric constant. It is also found that the dc bias effect on the sample can distinguish this hetero-structure model and the proper Debye relaxation model of a homogeneous phase.

In order to elucidate the origin of the characteristic dielectric response of CaCu3Ti4O12 (CCTO), we synthesize c-axis oriented multilayer thin films composed of alternative layers of CCTO and an insulator CaTiO3 (CTO) using the Pulsed Laser Deposition (PLD) method and measure the capacitance of CTO/CCTO/CTO multilayer thin films with different thicknesses of CTO and CCTO layers. After removing the extrinsic electrode/CCTO boundary effect and the CCTO/CTO interface effect, the inherent dielectric constant of CCTO is determined.

Measurements of complex refractive indices n* = n - i kappa are performed on pure KTaO3 and K0.93Li0.07TaO3 single crystals by using a spectroscopic ellipsometer in temperature range from room temperature to 10 K. At room temperature, experimentally obtained complex dielectric constants epsilon* = epsilon(1) - i epsilon(2) of both crystals are analyzed by the classical Drude model. Temperature dependence of the imaginary pal-t epsilon 2 of K0.93Li0.07TaO3 shows a small but distinct change around 70 K. The origin of the anomalous behavior is discussed.

The 2D crystallites of polar organic dye molecules on an aqueous subphase exhibit a thermochromic phase transition. The visible absorption band of the crystallites depends on the temperature and the composition of the subphase. In-situ observations of the phase transition were carried out by a grazing incidence X-ray diffraction method. A shift and a split of the diffraction peaks were observed between the different phases, indicating a change in the molecular arrangement of the crystallites in their chromic transition.

Epitaxial Pb(Sc1/2Nb1/2)O-3 (PSN) and PbTiO3 (PT) superlattice thin films are processed on single-stepped SrTiO3 (001) substrates by the pulsed laser deposition (PLD) technique. SrRuO3 is deposited on the substrate as a bottom electrode layer for dielectric measurements. The orientation and structure of the films are determined by X-ray diffraction (XRD) method. Clear superlattice reflections are observed by XRD and the period of superlattice is calculated from difference of 2 theta of superlattice reflection. Real part of dielectric constant is about 350 at room temperature in the frequency range of 10(2)-10(5) Hz.

The experimental data on the thermal properties of the nanostructured perovskite ferroelectrics are presented and analysed. The ability of the modified 3 omega method for specific heat measurements is discussed and illustrated by the thermal properties of the thin polycrystalline (BaTiO(3) on fused SiO(2), 50-1100 nm) and epitaxial (BaTiO(3) on MgO, 50-500 nm) films. The sharp decrease of the transition temperature, surplus entropy and spontaneous polarization were obtained for the polycrystalline films. The critical thickness and crystallite size are estimated for this case from the variation of both crystallite sizes at constant thickness and film thickness at constant crystallite size. The similarity of specific heat, phase transition excess entropy evolution in polycrystalline films and nanograined ceramics is revealed. The data on the specific heat of epitaxial films show the extremely diffused anomaly near 400 K, the phase transition has the weak tendency of shifting to higher temperatures with the decreasing of the film thickness. No anomalies were detected for the thinnest (50 nm) film up to 480 K.

Li-doped KTaO3, K(1-x)LixTaO3 (KTL) has been reported to be a relaxor with an isovalent substitution of Li+ for K+. For confirming the idea, we performed second-harmonic generation microscopic observations, X-ray diffraction experiments and dielectric measurements of KTL with the critical concentration of Li (x = 3%). These reveal that an intermediate phase exists between 2 characteristic temperatures, T-d and T-p. The former corresponds to an elastic change accompanying small deformation and the latter to a dipolar change of the crystal. It is highly probable that the polar-nano regions appear below Td and transformed into ferroelectric domains at T-p. The present experiments support that KTL is a real relaxor.

We have developed LiIO3/laponite nanocomposite thin films to form waveguides with quadratic nonlinear optical properties. The films are dip-coated and annealed to induce LiIO3 crystallisation within the laponite matrix. LilO(3) nanocrystal orientation can be controlled using an electric field during the annealing process. In this article we perform the characterisations of the nanocomposite films through m-line spectroscopy and second harmonic generation microscopy (SHGM). Both refractive indexes deduced from m-line spectra and the SHG signal are shown to depend on the nanocrystal orientation distribution, and a relationship between the optical properties and microscopic structure of the films is developed.

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. (c) 2006 American Institute of Physics.

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. (c) 2006 American Institute of Physics.

The thermochromism of the merocyanine J-aggregates was investigated using the binary counterion subphase containing Mg2+ and Sr2+ (Mg2+/Sr2+ subphase). The behaviors of the thermochromic transition on the Mg2+/Sr2+ subphase and that on the subphase containing Mg2+ and Cd2+ were compared, and the difference was discussed from the viewpoint of the hydrated ionic radii of the counterions.

Incipient ferroelectric KTaO3 with off-center Li impurity of the critical concentration of 2.8 mol % was investigated in order to clarify the dipole state under electric field. Using optical second-harmonic generation (SHG) microscope, we observed a marked history dependence of SHG intensity through zero-field cooling (ZFC), zero-field heating (ZFH), field heating after ZFC (FH/ZFC), and FH after field cooling (FH/FC). These show different paths with respect to temperature: In the ZFC/ZFH process, weak SHG was observed at low temperature, while in the FH/ZFC process, relatively high SHG appears in a limited temperature range below T-F depending on the field strength, and in the FC and FH/FC processes, the SHG exhibits ferroelectriclike temperature dependence: it appears at the freezing temperature of 50 K, increases with decreasing temperature, and has a tendency of saturation. These experimental results strongly suggest that dipole glass state or polar nanoclusters which gradually freezes with decreasing temperature is transformed into a semimacroscopic polar state under the electric field. However at sufficiently low temperature, the freezing is so strong that the electric field cannot enlarge the polar clusters. These experimental results show that the polar nanocluster model similar to relaxors would be more relevant in KTaO3 doped with the critical concentration of Li. Further experiments on the anisotropy of SHG determine that the average symmetry of the field-induced polar phase is tetragonal 4 mm or 4. The tetragonality is also confirmed by the x-ray diffraction measurement.

Complex dielectric constants of SrTiO3 ceramics and single crystals were measured in the temperature range of 303 K to 673 K and the frequency range of 100 mHz to 100 kHz. It was found that the ceramic sample exhibits a steplike colossal dielectric relaxation similar to the distorted perovskite CaCu3Ti4O12, while the single crystal exhibits a relaxor-like relaxation. Both features can be explained with a heterogeneous structure model.

The molecular alignment of a merocyanine (MC) J-aggregate monolayer at the air-water interface was determined by a grazing incidence x-ray diffraction method. The obtained molecular arrangement apparently shows that the conventional formula, which accounts only for the transition dipole interaction, is not sufficient to figure out the exciton band wavelength, suggesting the importance of the electric dipole (ED) interaction. We derived a simple formula for the ED interaction energy under an extended dipole approximation and clarified the ED contribution in the MC J aggregate.

The molecular alignment of a merocyanine (MC) J-aggregate monolayer at the air-water interface was determined by a grazing incidence x-ray diffraction method. The obtained molecular arrangement apparently shows that the conventional formula, which accounts only for the transition dipole interaction, is not sufficient to figure out the exciton band wavelength, suggesting the importance of the electric dipole (ED) interaction. We derived a simple formula for the ED interaction energy under an extended dipole approximation and clarified the ED contribution in the MC J aggregate.

We demonstrate a nonvolatile, reversible change of infrared reflectance from the thin film of perovskite manganite (Pr1-xCaxMnO3) by applying electric pulse. The result provides a possibility to use the electric-pulse-induced phenomena of this compound in optical devices. (C) 2004 American Institute of Physics.

The oxygen isotope exchange of O-16 by O-18 in SrTiO3 causes a drastic change from paraelectric to ferroelectric, due to the suppression of quantum fluctuation. The phase transition and origin of the huge domain wall response were evaluated by dielectric, magnetic (NMR), and optical measurements (SHG, light scattering). The results obtained corroborate (1) smeared ferroelectric transition at T-c due to quenched random field, (2) a quite large dielectric contribution from domain walls, (3) incomplete softening of the transverse optic mode, and (4) a large contribution from the relaxational mode to the phase transition. Quantitative explanations, given to individual results, may give hints to grasp the mechanism for the evolution of ferroelectricity, in which quantum fluctuation and random fields are dominant perturbations. Finally, some of the news studies on the SrTiO3 were also introduced. (C) 2004 Elsevier Ltd. All rights reserved.

Optical second-harmonic generation (SHG) in (SrTiO3)-O-16 (STO16) and (SrTiO3)-O-18 (STO18) was investigated using the SHG microscope. While no biased STO16 exhibits weak and almost temperature-independent SHG signals, a marked SHG is observed under the electric field in the quantum paraelectric region. In STO18, strong SHG signals appear spontaneously below 36 K. However, neutron and X-ray diffraction analyses indicate that no structural change appears at low temperature in STO18, or STO16 under the electric field. By taking into account the fact that the SHG is sensitive to the local polar order, the combined studies reveal that the long-range order of the polar phase does not develop on either crystal and is frozen in local regions.

Cadmium fluoride doped with Ga and Y is shown to be a suitable medium for backward-wave four-wave mixing with a grating decay time of a few seconds at room temperature. A 3-mm-thick sample ensures amplified phase-conjugate reflectivity and can therefore be used for building a coherent oscillator with a conventional mirror.

A novel method of 3D visualization of 180-degree domain structures in ferroelectrics is proposed using the second harmonic generation (SHG) microscope. The essential part of the idea is to use 2D images with 4 phase differences, i.e., 0, pi/2, -pi/2 and pi, between SH waves generated in a sample and a homogeneous SHG plate. Inverted domain structures in MgO:LiNbO3 were successfully obtained: they grow in a wedgelike form both along the axial (y) and the lateral (z) directions of the sample under successive applications of pulsed electric field of 6 kV/mm.

Cadmium fluoride codoped with Ga and Y is characterized as a medium for phase grating recording. The dependence of the three-dimensional grating diffraction efficiency on the intensity of the recording light, on the polarization of the recording light, on the fringe contrast, and on the spatial frequency of the fringe was measured together with the dynamic characteristics (grating decay time and grating buildup time). The crystal behaved as a chi((3)) medium with its refractive-index change depending on linear intensity and with nearly exponential buildup-decay temporal characteristics for moderate intensities of the green recording light at room temperature. (C) 2003 Optical Society of America.

A new instrument for measuring piezoelectric coefficients has been developed. The principle of this instrument is simple, namely, applying a uniaxial stress to a sample and measuring the induced charge. The stress applied to the sample is measured as an electric signal. The main part of the instrument is shaped like a small probe with an electrode at the tip for measuring the charge, and piezoelectric coefficients can be measured easily and quickly by pressing the probe on samples by hand. The piezoelectric coefficient $d_{33}$ of ferroelectric Ba1-xLaxTi1-xCrxO3 ceramics were measured using the probe, and it is revealed that the compound shows a maximum $d_{33}$ of 70 pC/N when $x$ is approximately 0.014–0.018.

The grazing incidence X-ray diffraction from the 2D polar crystallites of organic dye molecules on an aqueous subphase was measured. The structure of the 2D crystallites shows a dependence on the subphase composition, and this dependence corresponds well to the results obtained from Langmuir-Blodgett films, which consist of the multilayer of the 2D crystallites deposited on the solid planar supports.

Marked field-induced second harmonic generation was observed in (SrTiO3)-O-16 at liquid. He temperature. The intensity decreased towards 35 K with the increase of temperature but it still remained significantly above 35 K and gradually diminished and vanished around 100 K. This indicates that ferroelectric nano-regions exist in higher temperature region and grow under electric field. On the other hand, O-18-replaced SrTiO3 ((SrTiO3)-O-18) exhibited SHG below 30 K without electric field and the intensity decreased steeply above the temperature. This corresponds to the appearance of ferroelectric phase. The point group of field-induced phase of (SrTiO3)-O-16 and ferroelectric phase of (SrTiO3)-O-18 is orthorhombic mm(2) with polar axis along the cubic {110} direction.

The Sr1-xLaxTi1-xCrxO3 (0 less than or equal to x less than or equal to 1) system was synthesized at 1500degreesC for about 60 h. Their structures were analyzed by the use of powder X-ray diffraction data and Rietveld analysis software GSAS (General Structure Analysis System). Three solid solutions are found: cubic solid solution Sr1-xLaxTi1-xCrxO3 (0 less than or equal to x less than or equal to 0.168, space group Pm (3) over barm), rhombohedral solid solution Sr1-xLaxTi1-xCrxO3 (0.23 less than or equal to x less than or equal to 0.67, space group R (3) over barc) and orthorhombic solid solution Sr1-xLaxTi1-xCrxO3 (0.92 less than or equal to x less than or equal to 1, space group Pnma). The conductivities of this series were measured mainly from 25 to 450degreesC. It was found that this series changed from dielectric material SrTiO3 to semiconductor LaCrO3 continuously. The highest conductive sample was found to be Sr1-xLaxTi1-xCrxO3 with x = 0.92, whose conductivity at room temperature was about 5 X 10(-3) Omega(-1) cm(-1). (C) 2002 Elsevier Science (USA).

The structural characteristics of the perovskite-based ferroelectric Pb(Zn1/3Nb2/3)(1-x)TixO3 at the morphotropic phase boundary (MPB) region (x similar or equal to 0.09) have been analyzed. The analysis is based on the symmetry adapted free energy functions under the assumption that the total polarization and the unit cell volume are conserved during the transformations between various morphotropic phases. Overall features of the relationships between the observed lattice constants at various conditions have been consistently explained. The origin of the anomalous physical properties at MPB is discussed.

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 co-workers in PhZr1-xTixO3 with x=0.48 [B. Noheda et al., Phys. Rev. B. 61, 8687 (2000)] but is identical to the phase observed in poled PZN-PT with x=0.08 [B. Noheda et al.. Phys. Rev. Lett. 86, 3891 (2001)] 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 characterized by a weak value of polarization, a strong deformation of oxygen polyhedra, and weak cationic shifts.

The series Ba1-xLaxTi1-xCrxO3 (0 less than or equal to x less than or equal to 1) was synthesized at 1400degreesC for about 60 h. Their structure was carefully analyzed by the use of powder X-ray diffraction and Rietveld analysis software GSAS (General Structure Analysis System). Four solid solutions are found in this series: tetragonal solid solution Ba1-xLaxTi1-xCrxO3 (0 less than or equal to x less than or equal to 0.029), cubic solid solution Ba1-xLaxTi1-xCrxO3 (0.0365 less than or equal to x less than or equal to 0.600), rhombohedral solid solution Ba1-xLaxTi1-xCrxO3 (0.700 less than or equal to x less than or equal to 0.873), and orthorhombic solid solution Ba1-xLaxTi1-xCrxO3 (0.956 less than or equal to x less than or equal to 1). There are corresponding two-phase regions between the adjacent two solid solutions. The detailed lattice parameters are presented. The relationship between the lattice parameters and the composition of the solid solutions is developed. (C) 2002 Elsevier Science (USA).

Revolutionary development has been recently found in piezoelectric materials. These are Pb-based complex perovskite oxides. In particular, the morphotropic boundary of relaxor and PbTiO₃ complex exhibits huge piezoelectric response. The origin of the phenomenon is ascribed by the symmetry lowering which induces smooth polarization rotation. This report summarizes the experimental results and ab initio and phenomenological approaches to this problem.

Some materials exhibit a huge response to an applied field, the phenomenon being closely related to the mesoscopic hetero-phase fluctuation in materials. It has been revealed that the phenomenon is ubiquitous and is found in variety of materials such as martensitic alloys, dielectric relaxors, colossal magneto-resistance materials and so on. The response characteristics may be termed"super-susceptibility". Examples of the phenomenon and the computer simulation using the time-dependent Ginzburg-Landau theory are reviewed.

The colossal dielectric properties of relaxors are related to the appearance of polar nanoregions in cubic nonpolar matrix. In this hetero-phase structure, the long-range order is locally clamped and the average symmetry of the specimen remains to be cubic down to the low temperature. However, the application of the electric field yields the evolution of longrange order and the ferroelectric state prevails on the specimen. However, it develops with quite long incubation time. We report here this peculiar phenomenon which was observed by optical, X-ray and TEM techniques, and discuss the origin.

This paper describes studies of relaxer ferroelectric Na1/2Bi1/2TiO3 (NBT) by inelastic incoherent neutron scattering at temperatures from 50 to 300 K. Experimental time-of-flight spectra were recalculated into the generalized vibrational density of states (VDOS) function in terms of one-particle incoherent approximation and compared with the behavior of Raman spectra. It is shown that the VDOS of NET in the ferroelectric phase has nontrivial temperature dependence. The relation between the temperature dependence of VDOS and the instability of the NET crystalline lattice below room temperature is discussed. (C) 2000 Published by Elsevier Science Ltd.

The ferroelastic phase transition in K2Cd1.6Mn0.4(SO4)(3) Solid solution was investigated by optical microscopy method. The existence of the permissible domain structure in those compounds in whole temperature region below 23F222 second order phase transition was found. it was shown that in the crystals which belong to the isolated point, the domain walls are permissible due to enantiomorphic twinning. The determined orientation of domain walls is {110}. The investigation of the topography of the optical activity shows the change of optical rotary power in some regions in 23 phase of K2Cd0.4Mn1.6(SO4)(3) crystals. Obtained results are discussed on the base of thermodynamic potential and prototype phase with point group symmetry (4) over bar 3m.

Multi-purpose nonlinear optical microscope is an optical microscope which images 2D distribution of the optical second harmonic (SH) waves from a specimen. Image contrast can be obtained either by inhomogeneous distribution of nonlinear optical tensor components or by the interference between SH waves from a specimen and a standard plate. This microscope also functions as a fluorescence (FL) microscope, and SH and FL images can be obtained from the same part of a specimen. Absorption and FL spectra from a specific part of a specimen are measured through an optical fiber which connects an ocular with a polychromator. These functions are especially useful for investigation of the J-aggregate state of polar dye molecules. Several photographs taken by the microscope revealed the structure of merocyanine dye/arachidic acid mixed monolayer and the role of bridge ions in the subphase. © 1999 American Institute of Physics.

The optical second harmonic generation can be applied to the observation of ferroic domains. In particular, ferroelectric 180° domain structures were successfully observed using a nonlinear microscope termed SHG microscope. The principle utilizes the phase difference of the second harmonic waves produced in domains with opposite polarizations and the interference effect was utilized to make the intensity contrast. Other applications to the J-aagre-gate in monomolecular films and antiferromagnetic domain structure are also possible using the SHG microscope.

A microstructure causing the memory effect in the incommensurate phase of barium sodium niobate was investigated by means of a transmission electron microscope. A type of microdomain structure, which is constituted of a complicated array of microscopic ferroelastic domains with a modulation along the [100] direction, is found. Because this microdomain structure appears reversibly during the heating and cooling processes, the microdomain structure is directly related to the memory effect. © 1995 The American Physical Society.

生物の筋肉は階層構造をもつ。筋肉は直径100μmの筋繊維の束からなり、この筋繊維は直径1μmの筋原線維が集合したものである。さらに１本の筋原線維は、サルコメアと呼ばれている単位が線維軸方向に約２μmの周期で規則正しく並んでいる。サルコメアはミオシンフィラメント、アクチンフィラメント、タイタン、などから構成され、極性をもつバンドと極性を持たない部位からなっている。この構造はすでに米国や日本のグループによって光第2高調波（SHG)顕微鏡で観察されている。興味深いことはサルコメアはその構造から、M線と呼ばれる中央線を挟んで極性が反対向きの構造をとるといわれている。しかしながら今まで実験で直接にこの極性構造を観察して例はなかった。本研究は、上江洲研究室で１０年に渡り開発してきたSHG干渉顕微鏡を用いて、世界に先駆けてこの反転分極構造を観測した。成果をまとめると次のようになる。（１）筋繊維は期待していた以上の大きなSHGがある。強度を単純に比較すると、よく用いられる非線形光学結晶ニオブ酸リチウムのd22成分の1/700に達する。（２）周期反転分極をもつということは、筋原線維を一種の反強誘電体とみなすことができる。（３）筋原線維の周期性反転分極構造は、位相を同じにして束ねられて筋繊維となる。SHG強度が大きい理由もこのコヒーレントな構造に由来する。（４）もし軸方向に光を通すと、筋繊維は一種の擬似位相素子となる。周期性が2μmであることから、紫外光への波長変換素子として魅力がある。生体の中でこの現象を利用すれば、拒否反応なく埋め込んだ波長可変の光源ともなるであろう。

高温でのSrTiO3の複素誘電率を詳しく測定し、この結果がCaCu4Ti3O12と非常に類似していること、またMaxwell-Wagner型の不均一２相モデルで定量的に説明できることを示した。巨大な誘電率は見かけのもので、厚い相の電気伝導率がアレニウス型の温度依存性をすることによりもたらされる。(JJAP, 44,No.9B,2005).リラクサーPb(Sc1/2Nb1/2)O3（PSN）薄膜、およびPSNと強誘電体PbTiO3(PT)のモルフォトロピック相境界（MPB）組成薄膜をパルスレーザー成膜（PLD）法で作成し、その構造の評価を行った。その結果、室温ではPSNは擬立方晶、MPB組成をもつPSN/PTは単斜晶であることを明らかにした。これは薄膜についての初めての報告である。（Jpn.J.Appl.Phys.:45, No.1,L42-L45, 2006）温度に対してフラットで巨大な誘電率をもつが誘電損の大きなCaCu3Ti4O12(CCTO)をCaTiO3で挟んだ薄膜を作成し、誘電損を格段に減少させることに成功した。（2006年度春の物理学会誘電体分科会発表予定）Liを添加した量子常誘電体KTaO3の構造相転移をSHG顕微鏡、X線回折、中性子散乱、誘電測定を駆使して測定し、電場のもとで著しい経歴依存性を示すこと、低温では秩序変数は非エルゴード的な挙動示すこと、極性ナノ領域の発生に対応する中間相があることを見出した。これらの事実はこの系がリラクサーであることを示している。(Phys.Rev.B72, 144103(2005))

パルスレーザーデポジション成膜（ＰＬＤ）装置を用いて、次に示すペロブスカイト複合酸化物薄膜の作成を行い。またその構造と物性を評価した。（１）モルフォトロピック相境界組成をもつリラクサーPb(Sc1/2Nb1/2)O3(PSN）と強誘電体PbTiO3(PT)との混晶系PSN/43%PTのセラミックスおよび薄膜を作成した。まずバルク結晶について、その相図を詳細に決定した。とくにＭＰＢの構造は、Tiの組成比に依存して、非常に複雑な様相―ある場合にはナノスケールのchemically disordered状態―を示すことを見出した。一方、薄膜の場合には、ＭＰＢでは単斜晶Pmとなること、しかし基板と薄膜の厚さに依存して、複雑な分域が観測された。また高温では非極性正方晶となることを見出し、バルク結晶とは異なり、950Kまで立方晶にはならなかった。（２）量子常誘電体SrTiO3のエピタキシャル薄膜を厚さを変えて作成した。この結果、室温ではバルク結晶と殆ど変わらない誘電率は、低温とともに増加したが、１０Ｋ付近でゆるやかな極大をとったあと減少した、厚さを増すと誘電率の大きさは増加し、ピーク温度は高温側にシフトした。またいずれの場合も著しい周波数分散が観測された。現在、Ginzburg-Landau理論で解析を行っている。（３）巨大誘電緩和特性を示すCaCu3Ti4O12(CCTO)とCaTiO3からなる多層膜の作成および電荷整列ペロブスカイト型マンガン酸化物薄膜Pr0.7Ca0.3MnO3(PCMO)膜をエピタキシャルに成長させた。特にPCMOにパルス電場をかけると、光学反射率が同様に不揮発かつ可逆的に変化する現象を発見した。これは新しいタイプの光スイッチ、光メモリーとなりうるものである。

本研究室では光第２高調波（SH波）を用いた非線形光学干渉顕微鏡を開発し、それを用いて従来観測不可能とされてきた１８０度強誘電分域構造を非破壊で観測することに成功した。本研究は、この方法をさらに改良し、深さ方向の分域構造をも観察できるようにした。すなわち１８０度強誘電分域の３次元観察を初めて可能にしたものである。　原理は試料が発生するSH波と、標準結晶板が発生するSH波を干渉させ、分域構造に対応したコントラストを生じさせるというものである。３次元観察のためには、従来やってきたような２つのSH波の位相が０だけでは知見は得られない。この他に、９０度、－９０度、および１８０度の４つの位相を用いて、干渉像を撮影し、それからｈ関数と名付ける２つのコントラスト関数（ｈ１、ｈ２）を計算する。この（ｈ１、ｈ２）平面の位相が、分域の深さに対応する。これより、結晶の厚さがコヒーレンス長と呼ばれる特性長さの２倍以下のとき、ユニークに３次元分域構造を明らかにすることができるというものである。　この原理を使用して、応用上重要な強誘電体LiNbO3の電場反転を観察することに成功した。パルス電場印加のもとで、分極が逆向きの分域が横および縦方向に楔形に成長することが、明快に観測できた。　この結果は、２００１年９月に米国Providennceで開催された、圧電セラミックス日米セミナーでPlenary talkとして招待された。講演後、Prof.Crossなど米国の何人かの教授がこの研究に高い関心をもっていることを知り、うれしく思った。

　（１）リラクサーPb(Mg1/3Nb2/3)O3/xPbTiO3について，長距離秩序が大きな経歴依存性を示すこと，また電場を加えると非常に長い緩和時間（一日近くを要することもある）を伴って，長距離秩序度が発達することを見出した。（上江洲）（２）relaxor現象に対して最も核心となると思われる２相共存の問題について、中性子小角散乱実験、及びギンツブルグ－ランダウ理論に基く理論計算を行った。実験についてはrelaxorそのものは小角散乱に寄与しないので、同様の緩和現象を示すMn酸化物系の磁気的２相共存について研究し、この物質中で確かに平均サイズ３０nm程度の強磁性クラスターが、反強磁性母相の中に分布していることを確かめた。（山田）（３）電荷秩序型強誘電体YFe2O4で構造相転移での対称性の低下に伴う誘電分散の消失を見出した。（近）（４）強誘電体LuMn2O5では自発分極の出現等の変化に伴って，らせん磁気秩序の伝播ベクトルが変化することを見出した。（近）（５）BaTiO3およびSrTiO3をベースとした，複合ペロブスカイト酸化物セラミックスを作成し，その構造と誘電応答特性を測定した。特にBa1-XLaXTi1-XCrXO(x=0.028) は，室温で３０００を越える大きな誘電率と比較的フラットな温度特性、また2%以下の小さな誘電損失をもつことを見出した。これがリラクサーであることは今後さらに評価していかなくてはならないが，開発目標にしていた室温で誘電特性が大きくかつ損失の少ない鉛を含有しない化合物を開発することに成功した。（上江洲、近）（６）Pd及びPtをベースにした3d遷移金属との無秩序合金で、不純物の種類によって原因の異なる、原子やスピンの配列に関する非整合な変調波の短距離秩序を中性子散乱で見つけた。この変調波の波長は不純物の濃度と共に連続的に変化し、母体のフェルミ面の形状の反映と考えられる。（角田）

　光屈折効果はレーザー光自身が媒質の屈折率を変化させる現象であり、光伝送、画像処理、波面修復、高密度記録などの先端技術サイドから注目を集めている。一方、この効果が示す、低い注入エネルギーで発現するさまざまな光学非線形性のため、基礎科学においても重要な分野となっている。このような背景にたって、１９８７年より5回の国際会議が２年ごとに米国、欧州で交互に開催され，1997年で第６回を迎える。年々参加者、参加国数が増加しており、この分野の研究の重要性が認識されてきている。そこで１９９５年にアメリカで開かれた会議に引き続き、この分野の日本の活動の中心の一つである早稲田大学が主催し、早稲田大学における基礎・応用分野の研究者が協力して、アジアでの最初の会議を開催する。アメリカで開催された第5回会議の国際諮問委員会の席上、上江洲はこの会議を早稲田大学で開催することを提案した。その後の国内の議論により、早稲田大学ではこの分野で世界的に活躍している著名な研究者に十分時間をかけて、基礎から最先端の仕事を講演してもらうInvitational Symposiumにすることが決定され、また国際諮問委員会でも承認された。この結果、アメリカのカルフォルニア工科大学のAmnon Yariv教授を含めた１４名の招待講演者を決定した。国別にはアメリカ７名、フランス１名、英国１名、ドイツ１名、ウクライナ１名、中国１名、台湾１名、日本１名である。この会議の準備のため、上記国際諮問委員会、組織委員会（委員長、大頭仁早大教授）、プログラム委員会（委員長黒田和男、東大教授）、実行委員会（委員長、上江洲由晃早大教授）を発足させ開催の準備を行ってきた。またウクライナで行なわれた第４回会議の主催者であるProf.S.Odoulvを日本に招聘して意見を聞いた。会議は１９９７年６月９日と１０日の両日、早稲田大学井深大記念ホールで行なわれる。１５ケ国から約２００名の参加が見込まれる。