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Domain boundaries in ferroic materials are found to have various physical properties not presenting in the surrounding domains. Such differences can be enhanced and bring promising functionalities when centrosymmetric non-polar materials encounter polar domain boundaries. Here, a tunable polar domain boundary is discovered in an antiferroelectric single crystal. Under a small stress or electric field, the density, volume, and polarity of the boundaries are successfully controlled. This article is protected by copyright. All rights reserved.

Ferroelastic $\mathrm{La}\mathrm{Al}{\mathrm{O}}_{3}$ (space group $R\overline{3}c$) exists with two different microstructures: twins and tweed. Both microstructures contain electrical dipole moments. Polarity inside ferroelastic twin walls has been shown using two complementary experimental techniques and identical samples. PFM reveals a weak piezoelectric effect at the loci of the domain walls. In tweed samples, the PFM signal is finite but variable in the entire sample. PFM shows that same characteristic tweed microstructure as observed optically. The piezoelectric effect is of a similar magnitude inside twin walls and, space averaged, in the tweed microstructure (and approximately one order of magnitude smaller than in $c$-oriented $\mathrm{Pb}\mathrm{Ti}{\mathrm{O}}_{3}$ single crystals). Resonance piezoelectric spectroscopy proves that domain walls vibrate under the application of an external driving electric field. The resonance frequency is very close to stress induced vibrations. This is evidence for weak but finite coupling between the local dipole moments in the domain walls and the external electric field. The same coupling and the piezoelectric response are much stronger in the tweed sample. Symmetry breaking by dipolar vectors in a $\mathrm{La}\mathrm{Al}{\mathrm{O}}_{3}$ sample with tweed has been confirmed by the observation of optical second harmonic signals. The noncentrosymmetric point group is identified as $3m$ in agreement with earlier work on twinned $\mathrm{La}\mathrm{Al}{\mathrm{O}}_{3}$ but in contradiction with predictions of Landau-Ginzburg theory of simple ferroelastic wall structures.

Domain boundaries in lead phosphate, $\mathrm{P}{\mathrm{b}}_{3}{(\mathrm{P}{\mathrm{O}}_{4})}_{2}$, are investigated by using second harmonic generation (SHG) microscopy. It is revealed that they are polar while the bulk is a purely ferroelastic, centrosymmetric material. $\mathrm{P}{\mathrm{b}}_{3}{(\mathrm{P}{\mathrm{O}}_{4})}_{2}$ contains W and $W{}^{\ensuremath{'}}$ walls with different orientations. The SHG microscopy shows that both $W$ and $W{}^{\ensuremath{'}}$ walls are polar, in striking contrast to the bulk, where the macroscopic polarity is forbidden by symmetry. The strongest polarity is observed in the W walls with a local symmetry of monoclinic $m$. The $W{}^{\ensuremath{'}}$ walls are also monoclinic but with symmetry 2. This material is hence a new candidate for domain-boundary-induced ferroelectricity while the bulk remains fully inactive. An application of small stress to a W wall easily changes the boundary configuration without changing the type of domain boundary; i.e., the W-wall nature is conserved. While $\mathrm{P}{\mathrm{b}}_{3}{(\mathrm{P}{\mathrm{O}}_{4})}_{2}$ was so far suggested as a device material for acousto-optic switchers, the present study adds the possibility that light scattering can be modified also by electric fields.

Domain walls (DWs) of four typical ferroelastics, CaTiO3 (CTO), LaAlO3 (LAO), Pb3(PO4)2 (PPO), and BiVO4 (BVO), were observed by the second harmonic generation (SHG) microscopy, and the results were compared. The DWs of the examined ferroelastics are all polar. This fact does not depend on whether the crystal is an insulator (CTO, LAO, and PPO) or a semiconductor (BVO), on whether it has ferroelectric instability (CTO) or not (LAO, PPO, and BVO), or on the DW state, namely, whether the DW is crystallographically prominent or non-prominent. The symmetry of these DWs was determined from the SHG anisotropy, and it was clarified that they are a subgroup of the high temperature phase. In the cases of CTO and PPO, stress was applied to move the DW, and its polarity and symmetry were examined. The main characteristics did not change even when stress was applied. In all samples, uniform SHG was observed for each DW. This indicates that the DWs of the examined ferroelastics seem to be in a ferroelectric single domain state.

Ferroelastic domain boundaries in semiconductor bismuth vanadate, BiVO4, are examined using second harmonic generation microscopy. Although the bulk is centrosymmetric, domain boundaries produce homogeneous second harmonic (SH) signals. The polarization dependences of SH intensities exhibit strong anisotropy compatible with the polar symmetry m. The present results are compared with the experimental results of other ferroelastics we have observed so far. Unlike other ferroelastic materials, the directions of the SH maxima are in the same direction for all domain boundaries.

The effect of doping metal ions in ferroelastic Pb3(PO4)2 (PPO) on the polar nature of domain boundaries (DBs) was investigated using a second harmonic generation (SHG) microscope. It has been already reported that (DBs) of non-doped PPO is SH active and polar. The present study reveals that DBs of Ca-doped and Mg-doped PPO show greatly enhanced SH activity. This indicates that doping by metal ions enhances the polar nature of the DBs of PPO. This is important for future applications of DB nanotechnology. The enhancement of SH intensity is explained by a larger displacement of Ca2+ and Mg2+ ions in DBs due to smaller ionic radii. Analyses of the SH anisotropy experiments reveal that the symmetry-adapted W-wall belongs to monoclinic m and the non-adapted W'-wall to monoclinic 2. Both point groups are classified as the polar classes, which coincides with the case of pure PPO.

The domain boundaries of ferroelastic $\mathrm{LaAl}{\mathrm{O}}_{3}$ (LAO) are examined using a nonlinear optical second harmonic generation (SHG) microscope. Although bulk crystalline LAO possesses centro-symmetry and is inherently non-SH active, our three-dimensional observations reveal that the domain boundaries of LAO exhibit SH activity with almost the same magnitude within a boundary. The polarization dependence of the SH intensities shows strong anisotropy, which is explained by the polar trigonal point group, $3m$. The polar direction is found to be along the ${[111]}_{pc}$ axis and inclined from the domain boundary plane. It implies that the biquadratic coupling scheme of two order parameters could be the main origin of the emergence of polar nature at the domain boundary. Our experimental results together with those of $\mathrm{CaTi}{\mathrm{O}}_{3}$ suggest that the polar nature of the domain boundary in ferroelastic materials may be a ubiquitous phenomenon.

International audience; A compressive uniaxial mechanical stress is applied on ferroelastic CaTiO3 (CTO), and a change in the domain structure is observed under a polarization microscope and a second harmonic generation (SHG) microscope. New twin walls (TWs) appear perpendicular to the original TWs under stress. The SHG microscope observations and analyses confirm that this type of stress-induced TWs is polar, similar to the original TWs, and is crystallographically prominent with monoclinic symmetry m. A quantitative estimation of this stress-induced effect reveals that CTO is hard ferroelastic in the sense that the TW movement requires a large stress. A possible application of this phenomenon is discussed.

The second harmonic generation microscope (SHGM) constructs images of intensity distributions of SH waves produced by the interaction of fundamental waves with a polar material. We have developed this nonlinear optical microscope in order to make possible nondestructive, three-dimensional (3D) observations of various kinds of inorganic and organic materials. The SHGM can disclose also inverted domain structures of antiparallel spontaneous polarizations using the interference with the reference SH waves. The observation principle and several applications to structural characterizations of LiNbO3 and LiTaO3 quasi-phase matching devices, domain structure analyses of a relaxor/ferroelectric solid solution Pb(Zn1/3Nb2/3)O3-9%PbTiO3 at the morphotropic phase boundary, development of order parameter in a quantum paraelectric relaxor Li-doped KTaO3, and antiphase polar domain structures of muscle fibers and myofibrils are surveyed by stressing the high effectiveness of the SHGM as a tool of material diagnosis.

LiNbO3(LN)/LiTaO3(LT) superlattice thin films (SL) with several LT/(LN + LT) ratios and LN mono-layered films with several thicknesses are fabricated by the pulsed laser deposition (PLD) method. Structural analyses by XRD reveals that these films have a structure similar to those of LN and LT bulk crystals. The reduction of the point group symmetry from rhombohedral 3 m to monoclinic m is observed by SHG microscopy (SHGM). We compare LN/LT superlattice thin film and LN mono-layered thin films to observe how differently their point group symmetries deteriorate.

Temperature dependences of dielectric constant and second-harmonic generation (SHG) intensity of hexagonal (h-) YbFeO3 thin films deposited on yttrium stabilized zirconia (YSZ) (111) substrates were measured from 300 to 470 K. The results reveal that h-YbFeO3 film is ferroelectric below around 350 K. From the SQUID measurements, it is also concluded that this thin film is ferrimagnetic in the low-temperature range.

Non-destructive and contactless observations of the domain structures in a single crystal of solid solution Pb(Zn1/3Nb2/3)O3–9%PbTiO3 (PZN–9PT) was performed using the scanning second-harmonic generation (SHG) microscopy with the spatial resolution of optical wavelength scale. A novel method of the 2D mapping of SHG polarization dependence (Pol-D) is proposed. The result indicates that the Pol-Ds correspond well to the observed SHG images of domain structures. The directions of ferroelectric spontaneous polarizations are quantitatively analysed by comparing SHG images and the Pol-Ds. It is confirmed that PZN-9PT has the monoclinic symmetry at room temperature.

The first successful growth of La 1/2 Na 1/2 TiO 3 (LNTO) single crystals by floating zone method is reported. This growth requires specific atmosphere conditions to avoid vaporization of Na, and a post-growth annealing under dioxygen to get pure LNTO phase. We report, for the first time, dielectric measurements on a LNTO crystal, which confirm the quantum paraelectric behavior of this material.

Necessary conditions for the three-dimensional (3D) observation of polar domain structures using the second harmonic generation (SHG) interference microscope are examined. The essential point for the 3D observation is the use of an SHG tensor component with a negative wave-number misfit parameter Δk(= k2–2k1) between the wave-number k1 of the fundamental wave and k2 of the SH wave. The origin of this phenomenon is explained with the Fourier transform technique. Δk diagrams of the possible 3D observation are obtained for the sum-frequency generations in Mg doped LiNbO3 and BaTiO3.

LiNbO3(LN)/LiTaO3(LT) superlattice thin films are fabricated by the pulsed laser deposition method with several LT/(LN+LT) ratios including LN and LT mono-layered films. These films are found to be epitaxial and have clear superlattice structure by x-ray diffraction technique with both in-plane and out-of-plane configurations. However, SHG microscopic observations of these films reveal that the point group symmetry is monoclinic m, different from 3 m of LN and LT bulk crystals.

A short review of the study of thermal properties of the nanostructured ferroelectrics is given. An application of the modern calorimetric technique to a comparative study of phase transitions in the ferroelectric nanostructured materials (polycrystalline and epitaxial thin films, superstructures, ferroelectric heterostructures, substrate-induced ferroelectricity) is considered.

Temperature dependences of optical second harmonic generation (SHG) and light transmissivity are measured on a single crystal of multiferroic BiFeO3. SHG intensity exhibits a peak around the Neel temperature. The origin of this anomalous behavior could be attributed to rearrangements of ferroelectric micro-domain structures caused by spin-lattice coupling enhanced by ferroelectric order parameter.

LiTaO3(LT)/LiNbO3(LN) super-lattice thin films with different LT/LN ratios are fabricated on (0001) sapphire (α-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 θ–2θ and in-plane φ-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.

Dielectric properties of KH2PO4 (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°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.

Relaxor/ferroelectric super lattice films Pb(Sc 1/2 Nb 1/2 )O 3 /PbTiO 3 (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.

Optical second harmonic generation (SHG) and birefringence Δn 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 P312. The critical index of the order parameter is determined to be 0.5 from the birefringence measurement in the vicinity of TC.

A transparent BaTiO3 particle/polymer hybrid was synthesized from a Ba–Ti double alkoxide modified with an organic ligand and its refractive index and second harmonic generation were studied. BaTiO3 particles modified with 2-vinyloxyethanol (ethylene glycol monovinyl ether, EGMVE) were polymerized with methyl methacrylate (MMA) yielding the transparent BaTiO3 particle/poly MMA hybrid. X-ray photoelectron spectra indicated that the formation of chemical bonds between BaTiO3 nanoparticles and the organic matrix. The refractive indexes of the hybrid films depended on the crystallite size of BaTiO3 nanoparticles and the volume fractions of BaTiO3 and polymer phases. The hybrid film synthesized at BaTiO3/8EGMVE/30H2O/PMMA revealed a refractive index of 1.65 at 589 nm with an Abbe number of 54. The hybrid film exhibited a second harmonic wave of 532 nm on irradiation with a fundamental wave of 1,064 nm.

Ferroelectric domain structures of BiFe 0 3 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.

The temperature dependence of the heat capacity of thin epitaxial films BaTiO3/MgO is studied by the dynamic 3ω 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.

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.

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 BaTiO 3 /MgO epitaxial thin films by dynamical 3ω 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 T c 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 (BaTiO 3 ) n /(Sr TiO 3 ) m /Sr TiO 3 were obtained for the first time for the films with the average thicknesses near 100 nm.

Optical second harmonic (SH) intensities and dielectric constants of Li doped KTaO 3 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 1/3 Nb 2/3 )O 3 -PbTiO 3 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 KTaO 3 .

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.

Single crystals of K1-xLixTaO3 (KLT) with different Li concentrations are grown by the self-flux method. Li concentrations in the crystals are determined by second-harmonic-generation microscope observations. Complex dielectric constants of KLT are measured in the temperature range from 20 K to room temperature and the frequency range from 5 Hz to 1 MHz. The results are analyzed using the Cole–Cole plot and the Vogel–Fulcher law. For x>4.4%, two semicircles of the Cole–Cole plot appear in a specific temperature region. These two relaxation processes can be explained by the different types of dynamics of Li dipole moments. The activation energy Ea and the characteristic frequency ν0 are determined from the fitting of the two models. It is found that Ea does not show strong Li concentration dependence. The origin of the phenomenon is discussed using a polar nanoregion picture.

In order to elucidate the origin of the characteristic dielectric response of CaCu 3 Ti 4 O 12 (CCTO), we synthesize c-axis oriented multilayer thin films composed of alternative layers of CCTO and an insulator CaTiO 3 (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 - iκ are performed on pure KTaO 3 and K 0.93 Li 0.07 TaO 3 single crystals by using a spectroscopic ellipsometer in temperature range from room temperature to 10 K. At room temperature, experimentally obtained complex dielectric constants ϵ* = ϵ1−iϵ2 of both crystals are analyzed by the classical Drude model. Temperature dependence of the imaginary part ϵ 2 of K 0.93 Li 0.07 TaO 3 shows a small but distinct change around 70 K. The origin of the anomalous behavior is discussed.

Dielectric constants of complex perovskite oxide (Ba 1 − x La x ) (Ti 1 − x Cr x ) 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 CaCu 3 Ti 4 O 12 (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.

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(Sc 1/2 Nb 1/2 )O 3 (PSN) and PbTiO 3 (PT) superlattice thin films are processed on single-stepped SrTiO 3 (001) substrates by the pulsed laser deposition (PLD) technique. SrRuO 3 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 2θ of superlattice reflection. Real part of dielectric constant is about 350 at room temperature in the frequency range of 10 2 -10 5 Hz.

Li-doped KTaO3, K(1-x)Li x TaO3 (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, Td and Tp. 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 Tp. The present experiments support that KTL is a real relaxor.

Some new features of the polarization switching processes in the high temperature (T c = 533°C) ferroelectric LaBGeO 5 crystal regarding the stability of the domain structure are discussed. The shape of the switching current for different values of the electric field in rectangular pulses is described in the framework of the model taking into account the possible heterogeneity of the crystal—the different probability of the domain nucleation in different parts of the crystal. Stability of the mono-domain state was studied by means of pyroelectric measurements. The “natural” domain structure and artificial one are visualized.

The thermochromic phase transitions of the merocyanine J-aggregate monolayers on the binary counter-ion subphases containing a pair of Mg 2+ and Cd 2+ (Mg 2+ /Cd 2+ subphase) or that of Zn 2+ and Cd 2+ (Zn 2+ /Cd 2+ subphase) were investigated by the visible reflection spectroscopy. The temperature of the subphase was controlled between 40 °C and a freezing temperature of the aqueous subphases. In addition to the phases of the J-band at 595 and 618 nm, a new phase of the J-band at 614 nm was found at the temperatures below 10 °C for both subphases. Although one of the ion species in the binary counter-ion subphase is different, the transition behaviors on the Mg 2+ /Cd 2+ and Zn 2+ /Cd 2+ subphases were almost the same, suggesting that not the atomic number but the hydrated ionic radius influences the phase transition of the merocyanine J-aggregates.

The monolayer of amphiphilic merocyanine dye (MD) molecules at the air-water interface was observed by the grazing incidence X-ray diffraction (GIXD) method. At the air-water interface, the MD molecules formed two-dimensional crystallites (J-aggregates), whose excitonic absorption bands were located at longer wavelength than the monomer band. The structural analysis on the MD J-aggregate was carried out, and, using the determined structure, the relationship between the molecular arrangement and the energy shift of the visible absorption band upon crystallization was clarified. For the calculation of the energy shift, simple formulas were derived on the basis of molecular exciton theory. It was revealed that not only the transition dipole moment interaction but also the electric dipole moment interaction among the molecules plays an important role in the energy shift.

Using a simple methodology based on the classical Bragg–Brentano X-ray geometry we have evidenced at room temperature a pseudo-cubic phase and a monoclinic (Pm) phase in thin films of PbSc1/2Nb1/2O3 (PSN) and (PbSc1/2Nb1/2O3)0.57–(PbTiO3)0.43 (PSN–PT) respectively, the latter compound corresponding to a morphotropic phase boundary (MPB) composition. Depending on the substrate and the thickness, different domains configuration are obtained. Competition between epitaxial and thermal stress induces a complex structural evolution with temperature which is different from that of ceramic samples. Indeed PSN films transform from a pseudo-cubic (triclinic) phase towards a cubic phase whereas in PSN–PT, a succession of transformations from a pure Pm phase toward a tetragonal (possibly non polar) phase is observed, a cubic phase never being reached up to 950 K.

The recently found chromic phase transition of merocyanine J-aggregates monolayer on the aqueous subphase containing Cd 2 + and Mg 2 + was investigated by the grazing-incidence X-ray diffraction method. The evidence of the structural difference between the phases of J-band at 620 nm and 590 nm was obtained by the investigations on the monolayers prepared at the different molar ratios of Cd 2 + and Mg 2 + . The change in a Bragg's peak was observed at the ratio of the ions, where the J-band wavelength also exhibited the discrete shift. The relationship between the obtained results and the phase diagram determined by the shift of the J-band wavelength was also discussed from the viewpoint of the formation mechanism of J-aggregate crystallites.

The processes of polarization switching in LaBGeO 5 (LBGO) crystals are studied in details for the triangle and pulse electric field in the wide temperature range from room temperature (RT) to Tc = 530°C. It is revealed that the temperature dependence of a coercive field (f = 0.1 Hz) has an exponential form and this field reaches a value 150 kV/cm at the RT. The temperature evolution of the switching time and the form of the switching current are obtained in the mode of the successive solitary pulses and in the steady conditions. The features of “non-classical” behavior are noted (the dependence of switching parameters on the prehistory of samples, frequency dependence of the switching time). It is shown that the stable artificial domain structure at RT with the periodicity of 200 μm can be obtained by applying about 300–350 V/mm near 300°C. The stable domain structure was contrasted by means of SHG microscope probing.

Optical second-harmonic generation (SHG) in SrTi16O3 (STO16) and SrTi18O3 (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 36K. However, neutron and X-ray diffraction analyses indicate that no structural change appears at low temperature in STO18, and STO16 under the electric field. By taking into account the fact that the SHG is sensitive to the local polar-order, the combined studies reveals that the long-range order of polar phase does not develop on the both crystals and is frozen in local regions.

Compounds in the pseudo-binary BaTiO3-Ba(Fe1/2Ta1/2)O-3 system have been synthesized at 1500degreesC in air and characterized by X-ray and electron diffraction as well as impedance analysis and Mossbauer spectroscopy. The symmetry of Ba(Fe1/2Ta1/2)O-3 is found to be trigonal with the space group P3m1. Two solid solutions exist in the BaTi1-xFex/1Tax/1O3 system at room temperature. The first (SS1) is in the composition range 0 less than or equal to x less than or equal to 0.07 and is tetragonal, P4mm, while the second broader solid solution, (SS2) 0.12 less than or equal to x less than or equal to 1, is trigonal and has the space group P3ml. The conductivity becomes higher with reduced amount of Ti in the structure. The activation energy of conductivity differs between the two solid solutions, 0.80eV for SS1 and 0.30eV for SS2, which indicates different mechanisms. The maximum of the real part of the pemittivity recorded for compounds in SS1 decreases towards room temperature with increasing amount of Fe/Ta doping and a high dielectric constant of around 7000 is found for BaTi(0.94)Fc(0.03)Ta(0.03)O(3). (C) 2004 Elsevier Inc. All rights reserved.

The oxygen isotope exchange of 16O by 18O 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 Tc 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.

The domain structure in K2Cd2xMn2(1-x)(SO4)3 (x=0.5, 0.7 and 0.9) langbeinite crystals is studied with the aid of optical polarization microscopy. It is shown that the domain walls in ferro-elastic langbeinites separate enantiomorphous orientation states. These orientation states appear in the phase with the symmetry 23 in connection with the hypothetic phase transition . In the phase with the symmetry 222, these domain walls are transformed to those separating ferroelastic domains with the opposite signs of enantiomorphism. It is revealed that one enantiomorphous domain can only transform to the other via a thick layer of the parent phase with symmetry. The results for the volume thermal expansion are presented. It is shown that the isolated point at the x,T-phase diagram of K2Cd2xMn2(1-x)(SO4)3 solid solutions corresponds to the concentration x=0.6.

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, π/2, −π/2 and π, between SH waves generated in a sample and a homogeneous SHG plate. Inverted domain structures in MgO:LiNbO 3 were successfully obtained: they grow in a wedge-like 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.

To understand the mechanism of thermochromic phase transition of a J-aggregate monolayer of a merocyanine dye (MD, 3-caboxymethyl-5-[2-(3-octadecyl-benzothiazolin-2-ylidene)ethylidene]rhodanine) on aqueous subphases containing Mg2+ and Cd2+ ions, the molecular vibrational investigation was performed by using external infrared (IR) reflection absorption spectroscopy. The in situ observation indicates that, on increasing the subphase temperature from 19.5 to 34.5 °C, IR bands observed at 1177 and 1126 cm-1 for the J-aggregate monolayer shift to 1188 and 1146 cm-1, respectively; the shift is reversible and exhibits a thermal-hysteresis. These spectral changes correspond well to the thermochromic behavior of the visible absorption band of the J-aggregate (J-band), where the J-band shift is observed between 620 and 595 nm. The ab initio calculation of the normal modes were carried out on the MD molecule to assign the IR bands near 1183 and 1136 cm-1, indicating that they are attributed by the vibrational modes...