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The ferroelectric crystals of triglycine sulphate-phosphate grown in a ferroelectric phase from solution of TGS and TGP salts have been investigated with respect to their pyroelectric and dielectric properties.

The piezooptic dispersion of the ferroelectric crystal Li 2 Ge 7 0 15 (LGO) was studied in the visible region of the spectrum at room temperatures between 278 K and 298 K. The results show an interesting photoelastic behavior. The piezooptic coefficient Cλ decreases with wavelength in the visible region up to a certain wavelength and then it shows a peak at sodium yellow wavelength and later on the usual reduction is observed. Thus there seems an optical zone in between 5400 A and 6200 A with an enhanced piezooptical behavior. This enhancement is observed to be very high, as high as 50%, when the crystal is stressesd along [001] and observation made along [100]. The height of this region is different for different orientations, though the width seems approximately the same.

Relaxor ferroelectric (1−x)Pb(Zn1/3Nb2/3)O3-xPbTiO3(PZNT) crystals were grown from PZNT-PbO high temperature solution by flux Bridgman, bottom seeded solution growth (BSSG) and gas-cooling methods. PZNT wafers cutting from flux Bridgman and BSSG-grown crystals were homogenous while serious inclusions were observed in PZNT wafers grown by the gas-cooling method. The -oriented PZNT crystals exhibited nearly the same dielectric/piezoelectric properties whatever the growth methods. However, the mechanical properties, such as Vickers' Microhardness Hv and fracture toughness Kc of the crystal grown by gas-cooling method were much inferior. It was suggested that BSSG method is a potential approach for growing large-size and high-quality PZNT crystals.

The use of high-dielectric ferroelectric crystals for THz generation is reviewed and recent progress in high-power THz signal generation is presented.

Infrared spectra of powdered 4-aminopyridinium tetrachloroantimonate(III) [4-NH 2 C 5 H 4 NH][SbCl 4 ] (abbreviation: 4-APCA) in the region of the internal vibrations of the 4-aminopyridinium cation (3600 and 400 cm −1 ) and in the temperature interval 10–300 K covering three structural phase transitions are presented and discussed. The results confirm the order–disorder mechanism of the phase transition at 245 K. The paraelectric–ferroelectric phase transition at 271 K is hardly visible in the infrared spectra, which is in agreement with its “displacive” nature of the transition suggested by the single crystal X-ray and ac calorimetric studies.

The topological method for studying phase transitions in ferroelectric crystals is described, which makes it possible to clearly represent the regularities of change in different macroscopic characteristics of a crystal in the presence of a cascade of phase transitions.

The electrochemical cell: Se|TGSesingle crystal |Se, with tri-glycine selenide as solid electrolyte was employed to observe the ferroelectric-paraelectric phase transition. The charge, which normally occurs on the surface of the ferroelectric crystal in the polar phase, is thus incorporated in the electrical double layer of the cell and can be precisely monitored. The pyroelectric currents can also be measured with this cell. The concentration changes on the surface of the single crystal after direct current polarization are observed.

The piezooptical (PO) parameters of the ferroelectric crystal Sn 2 P 2 S 6 with monoclinic symmetry are measured by an interferometric technique for the mechanical stress applied parallel to the three main crystallographic axes at light wavelength λ = 632.8 nm and room temperature (T = 293 K). Nine independent PO coefficients are determined experimentally. They exhibit quite large values: the largest measured component is π 11 = 15.6 pm N. The high PO coefficients presume potential applications of Sn 2 P 2 S 6 as high-efficient acousto-optic material.

The mechanism of polarization reversal in non-uniform telluric acid ammonium phosphate (TAAP) ferroelectric crystal has been found to be strongly influenced by an internal bias field distribution. It was shown that the internal bias field, originated from some structural defects can stabilize local domain structures, causing its fast spontaneous return to the original state. To reveal the effect of E b on the domain motion, measurements of the distribution of domain wall velocity during switching and spontaneous backswitching processes have been performed. A qualitative approach was proposed in order to find a distribution of the E b in the crystal.

Temperature dependence of the linear birefringence Δn and excess entropy ΔS in a phase transitions regions are presented for the (CH3NH3)5Bi2Cl11 and (CH3NH3)5Bi2Br11 ferroelectric crystals. We have confirmed that there is a linear relation between Δn and ΔS in the temperature range from 285 to 306 K and from 295 to 306 K for (CH3NH3)5Bi2Cl11 and (CH3NH3)5Bi2Br11 crystals, respectively. Our results imply that relation between the linear birefringence and excess entropy can be described by Landau theory.

We report on precise experimental measurements with the Senarmont technique of optical birefringence in partly deuterated triglycine sulfate crystals (DTGS, deuteration degree x ≈ 0.7) and interpretation of the influence of ferroelectric phase transition (PT) on the birefringence. The critical phenomena observed, not too close to the PT point, are quantitatively analysed. The fluctuation effects are shown to be fairly well described in terms of the approach of first fluctuation correction to the Landau theory. We have derived spontaneous electrooptic characteristics of DTGS and revealed that deuteration improves those characteristics.

In this paper we report electro-optic (EO) sampling of THz pulses using ferroelectric crystal in the non-collinear Cherenkov phase-matching scheme, where an effective velocity matching is achieved in an EO crystal with a large refractive index in the THz frequency region. We demonstrate efficient THz EO sampling using LiNbO 3 and BaTiO 3 crystals in the Cherenkov- phase-matching scheme. It is shown that the efficiency of EO sampling with BaTiO3 is smaller than that with LiNbO 3 , even though the EO coefficient (r 33 ) of BaTiO 3 is three times higher than that of LiNbO 3 . The reason of the poor performance of BaTiO 3 is attributed to the strong absorption in the THz frequency region.

Polarized ferroelectric crystal lithium niobate wafers with different cuts are selected to offer differently charged surfaces. By induction of the mesenchymal stem cells differentiation into osteoblasts on different charged surfaces, the specific osteogenic-associated markers are assessed and the results illustrate that the positively charged wafer surface enhances rBMMSCs osteogenic differentiation.

The broadband quasi-phase-matching process in Ca0.28Ba0.72Nb2O6 was demonstrated and the relationships between crystal symmetries and second-harmonic patterns were studied. Considering the light-matter interaction, the frequency-doubled photons were found to be trapped by a centripetal force.

Low-frequency Raman spectra of a LiTaO3 ferroelectric crystal are studied in the temperature range 300–1273 K. The central peak associated with the relaxation susceptibility of the crystal lattice is recorded throughout the temperature range covered, including the temperatures both substantially lower and considerably higher than the Curie point (Tc = 900 K). The critical slowing down of the relaxation response time predicted by the Ginzburg-Landau-Devonshire theory is observed in the temperature range from 0.9Tc to 1.1Tc. In contrast to the critical slowing down, the width of the central peak γR increases below 0.9Tc and decreases above 1.1Tc with increasing temperature.

A novel probe technique, low frequency scanning probe acoustic microscope, was firstly developed based on the commercial atomic force microscope. The excitation frequency is in the range of several kHz up to teen-kHz, which is much lower than that in the conventional acoustic microscopes. The acoustic images of nanoscale domain structures in Pb(Mg1/3Nb2/3)O3-33%PbTiO3 single crystals were successfully visualized. Different electric polarizations show the variation of the elasticity in ferroelectrics, so the contrast of the acoustic images reflects the domain structure or the subsurface elasticity. In addition, the elasticity of the sample in response to the modulation of the excitation source is also discussed.

The time-dependent relaxation of retained polarization in unipolar methylammonium bromobismuthate, (CH3NH3)5Bi2Br11, single crystal was examined by optical observation of the domain structure. The polarization relaxation is attributed to the presence of a built-in internal bias field caused by structured disorder in the crystal. The internal field accounts for the broad spectrum of potential barriers for the domain walls. The slow polarization decay, in the long-time regime (t > 1 s), follows a stretched exponential and/or power-law function. On the assumption that relaxation centers (domains) are noninteracting, a distribution function of relaxation times is reconstructed. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

The polarization switching in methylammonium chlorobismuthate, (CH3NH3)5Bi2Cl11, single crystal was investigated by optical observations of the domain structure and switching current registration. It is shown that defects introduced during crystal growth influence the polarization switching kinetics. For the analysis of switching current data the statistical Avrami model of phase transformation kinetics was employed. Direct observation of the domain structure enabled us to verify the assumptions of the Avrami model in the case of non-uniform (CH3NH3)5Bi2Cl11 crystals. It is found that application of this model to non-uniform crystals can yield physically unclear values of some fitting parameters; e.g. the effective domain growth dimension is not constant with respect to the electric field. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

The fundamental optical absorption edge and dielectric permeability and its temperature and pressure dependence in the vicinity of phase transitions in (Sn 0.95 Zn 0.05 ) 2 P 2 S 6 ferroelectric crystals is measured . Based on these data, the p,T- phase diagram of (Sn 0.95 Zn 0.05 ) 2 P 2 S 6 crystals is built.

We propose a method based on the switching current variation for determining the physical parameters of ferroelectric crystals. Algorithms providing for the separate and joint determination of parameters such as the surface tension σ and the kinetic coefficient β0 are presented.

This paper examines the engineered domain configurations and the macroscopic properties of ferroelectric crystals using an energy minimization theory. The energy minimizing domain configurations have been constructed, and their macroscopic properties have been calculated and compared well with experiments. The optimal domain configurations have also been identified.

In this report we present the first data on the switching processes in LaBGeO5 crystals in the temperature region up to transition point (Tc=533°C). At room temperature the crystal has an extremely high coercive field even at ultra low frequencies (Ec ∼ 150 kV/cm, f = 0.1 Hz) and a large switching time (near 0.3 s in step field mode). It is shown that the “normal” hysteresis loops can be observed at f = 50 Hz above 250°C up to Tc without typical for high-temperature ferroelectrics conductivity distortion. In the Merz-type rectangular pulse field mode some “nonclassical” features of switching processes were revealed above 400°C. That is the sharp dependence of the switching parameters on the prehistory of the samples. The sequence of forms of switching currents was found to be in the close connection with kind of preparation of the initial domain structure. It is shown that the mechanism of polarization reversal processes are different for multi- and single-domain initial state.

A new deflection phenomenon of light has been discovered in ferroelectric crystals that provides information about domain structures, their nucleation, and their dynamics: Illumination of a multi-domain crystal with a single light beam yields light patterns, if external electrical fields are applied. Deflection angles of up to ±8° are observed. We attribute this effect to light deflection from the boundaries of the domains. Besides providing a new method to study domains of any ferroelectric material, the method can be of practical importance for electro-optic beam scanning.

A central peak has been revealed in the Raman spectrum of ferroelectric crystals of lithium niobate LiNbO3 in the temperature range 80–300 K. It is shown that the extrapolation of the central peak, which manifests itself in inelastic-light-scattering spectra near the ferroelectric transition (Tc ∼ 1400 K), cannot account for the existence of the central peak so far from the phase transition.

The main physical properties of ferroelectric crystals are described, and the macroscopic and microscopic viewpoints are discussed along with some applications, such as in capacitors and nonlinear optics. The emphasis is on physical understanding, while the mathematical level is kept to a minimum or supplemented by graphical representations to make the article more accessible.

In this paper a variety of architectures of self-assembled halo-coordinated MX 6 octahedra in ferroelectric halogenoantimonates(III) and halogenobismuthates(III) is illustrated. The dielectric properties of a new ferroelectric [4-NH 2 C 5 H 4 NH][SbCl 4 ] are presented. The para-ferroelectric phase transitions mechanism (C2/c → Cc) at T c = 270.5K is discussed. The phase situation in the [4-NH 2 C 5 H 4 NH][MX 4 ] (where M = Sb, Bi and X = Cl, Br) family is compared.

A temperature dependence of hypersound velocities at transition from a paraelectric phase to ferroelectric phase in Sn2P2S6 crystals was investigated by Brillouin scattering spectroscopy. Based on these data, full set of elastic constants was determined. Similar measurements were also performed for Sn2P2(Se0.28S0.72)6 mixed crystals in the paraelectric phase near a Lifshitz point. The sound velocity indicatrices' evolution at transition from Sn2P2S6 to Sn2P2(Se0.28S0.72)6 was observed and softening of transverse acoustic phonons in the paraelectric phase near the Lifshitz point was found. An instability of the acoustic phonons is induced by an interaction with a soft optic mode which is the origin of an incommensurate phase appearance in mixed crystals Sn2P2(SexS1-x)6 with x > xLP=0.28.

Temperature dependence of the optical rotatory power (p) along the optical axis of pure and deuterated Rochelle salt single crystals has been given. Three phases of both crystals were examined and found to be optically active. The relation between spontaneous electrogyration (ρ s ) and spontaneous polarization (P s ) can be described by ρ s oc P 2 s . Moreover, the antipolar domains of pure and deuterated ferroelectric Rochelle salt crystals were found of the rotation twin-type not occurring in the enantiomorphic form, in contrast to those in other ferroelectric crystals, e.g., TGS-type and Pb 5 Ge 3 O 1 1 .

Eighty years have past since the discovery of the first ferroelectric crystal, rochelle salt, by Valasek in 1921. In perovskite compounds, the ferroelectricity was discovered in BaTiO 3 at the early stage of the 1940's in USA, Russia and Japan. 10 years later, the antiferroelectricity was first discovered in PbZrO 3 at 1951 by Sawaguchi, Shirane and Takagi [51S2]. From the following bibliography of perovskite and its related compounds until 1955, we can easily imagine vivid activities and enthusiasm in this field all over the world. This reminds us recent every effort and passion to search and understand high-temperature superconductors. When we looked hack over this golden era of ferroelectricity, we realize so many interesting ideas were proposed.

The effect of photoelastic relaxation is investigated using triglycine sulfate ferroelectric crystals as an example. The optical and deformation contributions to the photoelastic relaxation are described, and their percentage in the combined effect is determined. Consideration is given to the temperature dependences of the relaxation amplitudes of the path difference and birefringence, which are induced by mechanical stress.

A ferroelectric crystal with charge-free surface conditions contains polarized domains which can form a flux closure with zero net polarization. In the presence of an external electric field, the flux closure in a two-dimensional continuum reorients its spontaneous polarization to align with the field. Based on this concept of ferroelectric switching coupled with mechanical straining, we demonstrate the working principle of a ferroelectric nano-actuator. The behavior of the actuator is explored under the action of electro-mechanical loading and its mechanism is simulated with a 2D phase-field model. The design of nano-actuator is modified to achieve greater actuation displacements by bending a thin device.

Nonlinear optics studies the class of phenomena occurring when an intense light field, typically from a laser source, modifies the optical properties of a transparent material in a nonlinear way. The polarization \(\vec{P}(\vec{x},t)\) of the material can be written as a power series in the field strength \(\vec {E}(\vec{x},t)\) : $$\vec{P}=\chi^{(1)}\vec{E}+\chi^{(2)}\vec{E}^{2}+\chi^{(3)}\vec{E}^{3}+\cdots $$ where χ (i) is the i-order optical susceptibility of the material. Nonlinear phenomena arise from the nonzero value of the χ (2) susceptibility in noncentrosymmetric crystals. A large class of nonlinear materials (among them LN, KTP, BBO, and LBO) has been studied and used since 1960’s for up/down-conversion of the existing laser sources to wavelength regions which are not directly accessible otherwise. Some of these materials also belong to ferroelectrics, and this feature can be exploited to engineer the orientation of their nonlinear susceptibility. One of the earliest and most commonly used material is LiNbO3 (LN), because of its high nonlinear coefficient (d 33≈27 pm/V) and its wide transparency range from the UV to the mid IR (0.3÷5 μm). A technique giving access to d 33 in LN for optimizing nonlinear conversion processes, named quasi-phase-matching (QPM), was thought even before the first fabrication of this material. About 20 years later, the first experimental demonstration of this idea was obtained, and nowadays periodic poling of ferroelectrics crystals is a widely spread technology making these devices world-wide used and commercially available.

This is the peer reviewed version of the following article: Blue SHG enhancement by silver nanocubes photochemically prepared on a RbTiOPO4 ferroelectric crystal, which has been published in final form at http://doi.org/10.1002/adma.201401603. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Use of Self-Archived Versions, Silver nanocubes with low size dispersion have been selectively photo-deposited on the positive surface of a periodically poled RbTiOPO 4 ferroelectric crystal. The obtained nanocubes show preferential orientations with respect to the substrate suggesting ep itaxial growth. The plasmonic resonances supported by the nanocubes are exploited to enhance blue SHG at the domain walls, This work has been supported by the Spanish Government under projects MAT2010–17443, MAT2011–29255-C02–02 and MAT2013– 43301-R, Comunidad de Madrid under grant S2009/1756 and Generalitat de Catalunya under project 2009SGR235

The ferrobielastic properties (ferroic properties of the second order) earlier theoretically predicted for lead germanate uniaxial ferroelectric crystals are justified experimentally. It is demonstrated that single-domain samples are formed upon cooling to temperatures below the Curie point under uniaxial mechanical stresses corresponding to a combination of mechanical stresses σ11σ13 or σ22σ23. The macroscopic mechanism of this phenomenon is considered.

The switching kinetics in ferroelectrics in the bulk polarization switching stage and in the final stage of the process are studied. Consideration is given to the specific case of switching of intrinsic ferroelectrics with 180° domains. A complete system of equations describing the switching processes and taking into account the change in repolarization in the course of a phase transformation is derived. The solution of this system is found. All the main characteristics of the switching process are calculated; namely, the evolution of the domain size distribution function is revealed and the time dependences of the domain density and flux are determined. An expression describing the variation in repolarization with time is obtained. The mechanisms of domain growth are studied. An equation for calculating the switching current and its variation with time is derived. A method is proposed for determining a number of constants for ferroelectric crystals by studying the switching current evolution.

The microscopic model of a crystal consisting of finite size particles is proved to be more realistic for many ferroelectric crystals than the models with pointwise particles. Two ideas naturally appeared when deriving the continuum approximations for this model. The first one is to consider a crystal as micropolar media, which is the continuum analog for the microscopic model with particles having rotational degrees of freedom. The second idea is to use the many-field approximation. A particular problem of the negative Poisson ratio, having no place in a model with pointwise particles, is also discussed. Finally, a new mechanism of the lock-in transition in a crystal supporting the incommensurate phase is offered.

The studies of superlattices in ferroelectric crystals have made a rapid progress since 1980s. A superlattice is composed of modulated domains on the micron scale, controllable with modern techniques. It reveals a number of novel physical properties of optical and acoustic character. In this paper, we review recent advances in developing new techniques for fabrication and characterization of ferroelectric superlattices, and in exploring new physical effects for applications. The outlook for superlattice applications is briefly described.

The influence of nonequilibrium electrons on the domain structure and switching of ferroelectrics (photodomain effect) has been investigated in ferroelectric crystals and ceramics. In the present paper, this effect is observed and explained as a result of the domain walls screening in frame ofYshibashi-Takagi theory.

The chaotic oscillations of polarization of ferroelectric crystal in LCR -resonance circuit were under investigation. There were made experiments with irradiated TGS-crystal and then was constructed the model which allows to calculate the lower ranhges of the onset of chaos for such crystal.

It has recently been shown that single-crystal solid solution ferroelectric crystals can have dramatically improved electromechanical properties compared to conventional transducer materials. This discovery has stimulated research aimed at understanding the atomic structures of these materials and identifying parameters controlling the growth of large crystals. We have investigated PZN-type relaxors with the stoichiometry Pb(Zn 1/3 2+ Nb 2/3 5+ )O 3 , using the first-principles ab initio projector mixed-basis method. We have analyzed well-converged structures and energetics of both P4/mmm space group [001] stacking vs. P3m1 [111] stacking. The atomic positions in each compositional structure are relaxed using calculated forces and a velocity-based MD relaxation method. The calculations reveal a preference for P3m1 [111] stackings.

The diffusive-reflectance (30°) IR spectroscopy was used to explore IR-optical properties of needle-like SbSI (antimony sulphoiodide) and SbSI:Cl (chloride modified) crystals and μ-crystals (powders). It turned out to be possible to follow paraelectric-ferroelectric (PE-FE) phase transition influence on IR-spectrum as well as to observe the effect of Cl introduction into SbSI structure. Anisotropy in the water adsorption was also observed for unmodified SbSI.

Temperature dependence of the linear birefringence (1.b.) in TGSe and TGFB crystals has been studied with a high temperature resolution. Temperature derivatives of the 1.b. are compared with the specific heat transients measured for these crystals.

The problem of critical size in ferroelectric crystals and films is considered within the mean-field theory. It is shown that, when the boundary conditions are correctly chosen, the critical size can be either very small or even absent; i.e., ferroelectricity can exist in one unit cell.

In the present work the Raman spectra of the family of ferroelectric crystals A 3 B 2 C 9 (where A=Cs, Rb; B=Sb, Bi; C=Br) are given and the assignment of some high frequency bands is fulfilled. The conclusion about the possible differences of the structures of the crystals Rb 3 Bi 2 Br 9 and Rb 3 Sb 2 Br 9 from the well-known and thoroughly investigated structure of the Cs 3 Bi 2 Br 9 crystal is made. It is shown that anharmonic interaction of vibrations can give rise to anomalous T -dependence of spectra in the low frequency region. For a crystal having methyl-ammonium (MA) groups the strong anharmonic effects can generate a very complicated structure around internal fundamental frequencies of the MA group which may be considered as a result of the phase transition effects.

The influence of isomorphous substitution and high hydrostatic pressure on the behavior of the fundamental absorption edge (AE) inSn(Pb)2P2S(Se)6 ferroelectric crystals is studied. It is shown that the AE in these crystals is caused by an electron-phonon interaction, and oscillation frequencies of interacting phonons correspond to oscillations of the[P2S(Se)6]4− anion sublattice. Baric and concentration changes of the Uhrbach rule parameters are analyzed.