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Conductivity in Mg doped lithium niobate (Mg:LN) plays a key role in the reduction of photorefraction and is therefore widely exploited in optical devices. However, charge transport through Mg:LN and across interfaces such as electrodes also yields potential electronic applications in devices with switchable conductivity states. Furthermore, the introduction of proton exchanged (PE) phases in Mg:LN enhances ionic conductivity, thus providing tailorability of conduction mechanisms and functionality dependent on sample composition. To facilitate the construction and design of such multifunctional electronic devices based on periodically PE Mg:LN or similar ferroelectric semiconductors, fundamental understanding of charge transport in these materials, as well as the impact of internal and external interfaces, is essential. In order to gain insight into polarization and interface dependent conductivity due to band bending, UV illumination, and chemical reactivity, wedge shaped samples consisting of polar oriented Mg:LN and PE phases were investigated using conductive atomic force microscopy. In Mg:LN, three conductivity states (on/off/transient) were observed under UV illumination, controllable by the polarity of the sample and the externally applied electric field. Measurements of currents originating from electrochemical reactions at the metal electrode-PE phase interfaces demonstrate a memresistive and rectifying capability of the PE phase. Furthermore, internal interfaces such as domain walls and Mg:LN-PE phase boundaries were found to play a major role in the accumulation of charge carriers due to polarization gradients, which can lead to increased currents. The insight gained from these findings yield the potential for multifunctional applications such as switchable UV sensitive micro- and nanoelectronic devices and bistable memristors. [ABSTRACT FROM AUTHOR]

We report the effects of hydrostatic pressure up to p~1.73GPa on the multiferroic and magnetoelectric properties of GdMn2O5 single crystals. The ferroelectric (FE) polarization can be enhanced at low pressures, while it decreased after reaching a maximum at p~1.30 GPa. This pressure induced variation of polarization can be ascribed to the combined results of Mn-Mn and Gd-Mn exchange striction under pressure. Our results show that the polarization induced by Mn-Mn interaction increases monotonously with increasing pressure and finally saturates above p≥1.30GPa. Interestingly, we find that a new FE phase appears in the temperature range of 31K-38K with pressure p≥0.88GPa. This new FE phase can be suppressed by magnetic field, but stabilized by pressure. The pressure-temperature (p-T) phase diagram of GdMn2O5 was obtained. Our analyses suggest that the pressure-induced new FE phase could arise from a non-collinear, incommensurate magnetic structure. [ABSTRACT FROM AUTHOR]

We report the effects of hydrostatic pressure up to p~1.73GPa on the multiferroic and magnetoelectric properties of GdMn2O5 single crystals. The ferroelectric (FE) polarization can be enhanced at low pressures, while it decreased after reaching a maximum at p~1.30 GPa. This pressure induced variation of polarization can be ascribed to the combined results of Mn-Mn and Gd-Mn exchange striction under pressure. Our results show that the polarization induced by Mn-Mn interaction increases monotonously with increasing pressure and finally saturates above p≥1.30GPa. Interestingly, we find that a new FE phase appears in the temperature range of 31K-38K with pressure p≥0.88GPa. This new FE phase can be suppressed by magnetic field, but stabilized by pressure. The pressure-temperature (p-T) phase diagram of GdMn2O5 was obtained. Our analyses suggest that the pressure-induced new FE phase could arise from a non-collinear, incommensurate magnetic structure. [ABSTRACT FROM AUTHOR]

Coexistence of two phases of AgNbO3 is shown to explain the experimentally observed polarization-electric field hysteresis loop better than either phase in isolation, based on detailed first-principles calculations of the structural changes and stabilities of different phases of this compound. Calculations confirm a ferroelectric phase transition, whereby the symmetry of the AgNbO3 crystal switches from antiferroelectric Pbcm to ferroelectric Pmc21, under an electric field of 9MV/cm. The calculated spontaneous polarization (0.61 C/m²) under this field compares well with the experimental value of 0.52 C/m². After transforming, the structure remains in the ferroelectric state even after the electric field is removed, despite the structure being energetically metastable. As the energy difference between the antiferroelectric and ferroelectric phases is only +0.5meV/f.u. and the potential energy barrier between them (~40 meV/f.u.) is comparable to thermal fluctuation energies, it is possible for these two phases to coexist at temperatures well below the paraelectric-antiferroelectric transition temperature (~626K). The exploitation of this phenomenon in AgNbO3 and related materials may provide a useful strategy for developing high-performance piezoelectric materials. [ABSTRACT FROM AUTHOR]

Coexistence of two phases of AgNbO3 is shown to explain the experimentally observed polarization-electric field hysteresis loop better than either phase in isolation, based on detailed first-principles calculations of the structural changes and stabilities of different phases of this compound. Calculations confirm a ferroelectric phase transition, whereby the symmetry of the AgNbO3 crystal switches from antiferroelectric Pbcm to ferroelectric Pmc21, under an electric field of 9MV/cm. The calculated spontaneous polarization (0.61 C/m²) under this field compares well with the experimental value of 0.52 C/m². After transforming, the structure remains in the ferroelectric state even after the electric field is removed, despite the structure being energetically metastable. As the energy difference between the antiferroelectric and ferroelectric phases is only +0.5meV/f.u. and the potential energy barrier between them (~40 meV/f.u.) is comparable to thermal fluctuation energies, it is possible for these two phases to coexist at temperatures well below the paraelectric-antiferroelectric transition temperature (~626K). The exploitation of this phenomenon in AgNbO3 and related materials may provide a useful strategy for developing high-performance piezoelectric materials. [ABSTRACT FROM AUTHOR]

Significant effect of semiconductor properties on domain configurations in ferroelectrics is demonstrated, especially in the case of doped materials. Phase field simulations are performed for ferroelectrics with space charges due to donors and electronic charge carriers. The free charges introduced thereby can act as a source for charge compensation at domain walls with uncompensated polarization bound charges. Results indicate that the equilibrium position of a domain wall with respect to its rotation in a head-to-head or a tail-to-tail domain configuration depends on the charge defect concentration and the Fermi level position. [ABSTRACT FROM AUTHOR]

Ferroelectric single crystals of a new lead-reduced Bi(Zn1/2Ti1/2)O3-PbZrO3-PbTiO3 (BZT-PZ-PT) ternary solid solution system have been grown for the first time by three different methods, namely high temperature solution growth (HTSG, or flux method), top-cooled solution growth (TCSG), and top-seeded solution growth (TSSG). The chemical and thermodynamic parameters, including the flux concentration, the soaking temperature and the cooling rate, have been optimized, leading to the growth of good quality BZT-PZ-PT crystals of pseudo-cubic morphology. A large size crystal of the dimensions of 2 x 2 x 0.5 cm³ has been obtained by the TSSG technique. The crystal structure is analyzed by means of X-ray powder diffraction. The highest ferroelectric Curie temperature TC of the grown crystals is found to be 320 °C by means of dielectric measurements. A remnant polarization of 32 µC/cm² is displayed with a coercive field of 15.4kV/cm. The high TC and large coercive field of the BZT-PZ-PT single crystal make this material a promising candidate for applications in high power electromechanical transducers that can operate in a wider temperature range and at high fields. [ABSTRACT FROM AUTHOR]

A low frequency and high amplitude rectangular voltage V has been applied during different increased duration to Twisted Surface Stabilized Ferroelectric Liquid crystal (TwFLC) samples in which the alignment layers of the two substrates were rubbed along two different directions between 0° and 90°. The optical bistability properties have been evaluated using the specific Mueller Matrix formalism that allows a simultaneous access, through a single-shot measurement, to different polarimetric coefficients. In this new approach, the ellipticity ∈R and the azimuthal αR polarimetric parameters, extracted from the birefringence Mueller Matrix MR will be considered in priority. Several significant parameters, such as the horizontal offset DV, the degree of asymmetry DA, the characteristic area S of the hysteresis loop, are used to characterize the degradation observed into the hysteretic behaviour of the samples, for different values of Ψ, at different duration T of exposure to V, before reaching the so-called stripes regime, giving a new experimental point of view concerning the evolution of the dynamic properties of the samples studied. The αR and the ∈R(V) hysteresis loops are specifically examined. Static mapping related to ∈R(T) is given too. Among the different possible physical origins of the observed degradation, the in-plane anchoring energy contribution will be particularly examined, and a theoretical model is proposed that also gives access to different physical parameters, through a new approach. [ABSTRACT FROM AUTHOR]

The role of internal field and exhaustion during ferroelectric switching was investigated by studying the dynamics of polarisation switching during the application of static electric fields at different points of the polarization-electric field (P-E) loop of a ferroelectric ceramic (PZT 5A). By simultaneously measuring polarization and strain changes during creep an insight into the evolution of the internal field during polarization switching was obtained. Electric field partial unloading tests were performed to estimate the magnitude of the effective internal field at different points of the P-E loop. Results show that the internal field increases proportionally with polarization reversal. A rate model that includes the effect of thermal fluctuations, internal field and exhaustion of nucleation sites during switching has been developed and applied to fit the polarization creep curves. The fitting of the creep curves in the sub-coercive region suggests that polarization hardening (increasing of internal field) is the mechanism controlling the polarization rate decay. At higher static applied electric fields the mechanism gradually changes and the exhaustion of the available nucleation sites becomes the main process responsible for the creep rate decay. [ABSTRACT FROM AUTHOR]

The scaling behaviors of dynamic hysteresis were investigated in serial rhombohedral Nb-doped Pb(Zr1-xTix)O3 (PZT) bulk ceramics as a function of frequency (f) and field amplitude (E0). Three distinct regions were plotted including linear loops, minor loops, and saturated loops with an increase of E0. When the external fields were over ∼1.5 times of coercive field (Ec), the scaling relations of saturated loops for these PZT ceramics could be expressed with an identical form as hysteresis area ∝ f 0.01E00.10, which indicated that similar ferroelectric systems with different compositions could display a uniform scaling law under high-E0 and low-f regions. [ABSTRACT FROM AUTHOR]

Aurivillius Bi5Ti3FeO15 (BTFO) multiferroic ceramics with different Cr-doped concentrations have been synthesized by the conventional solid state reaction method. The influences of Cr-doping concentrations on the structural, magnetic, dielectric, and ferroelectric properties of BTFO ceramics are investigated in detail. All these sintered Cr-substituted BTFO ceramics are determined to be layered perovskite Aurivillius structure by X-ray diffraction, as well as the lattice parameters a, b, and c are in good accordance with Vegard's law along with the Cr-doping concentration. The lattice distortion a/b for Aurivillius family decreases with increasing Cr-doping concentration. Moreover, Cr-doping can promote greatly the grain growth of BTFO samples confirmed from field emission scanning electron microscopy characterization. However, no obvious signs of the improvement in ferroelectric properties are found in Cr-doped BTFO ceramics, and abnormal ferroelectric polarization versus electric field (P-E) loops are observed as Cr-doping content is beyond 0.1. Similar [variant_greek_epsilon] (tanδ) versus frequency plots to those of the BTFO sample are exhibited when Cr-doping concentration is less than 0.1. Nevertheless, obvious dielectric dispersion phenomena are shown as the Cr-doping concentration is beyond 0.1, and this dispersion behavior becomes strong with further increasing Cr-doping concentration, which are clearly indicated by the appearance of dielectric loss relaxation peaks in the measurement frequency from 102 Hz to 106 Hz. In addition, the corresponding frequency to relaxation peak shifts towards high frequencies with the Cr-doping concentration. Finally, the same magnetic orderings for all these Cr-doped BTFO ceramics as those of the BTFO one, i.e., superparamagnetic state dominated with antiferromagnetic interaction, are unambiguously found, signifying that the predicted Fe3+-O-Cr3+ 180° ferromagnetic superexchange interaction based on the Goodenough-Kanamori (G-K) rule might not be achieved in BTFO ceramics through Cr substitution by the conventional solid state reaction. [ABSTRACT FROM AUTHOR]

Using our experimental data for ns pulsed second harmonic generation (SHG) by periodically poled stoichiometric LiTaO3 (PPSLT) crystals, we consider in detail the mechanism underlying laser-induced damage in ferroelectric crystals. This mechanism involves generation and heating of free electrons, providing an effective kinetic pathway for electric breakdown and crystal damage in ns pulsed operation via combined two-photon absorption (TPA) and induced pyroelectric field. In particular, a temperature increase in the lattice of ≈1 K induced initially by ns SHG and TPA at the rear of operating PPSLT crystal is found to induce a gradient of spontaneous polarization generating a pyroelectric field of ≈10 kV/cm, accelerating free electrons generated by TPA to an energy of ≈10 eV, followed by impact ionization and crystal damage. Under the damage threshold for ns operation, the impact ionization does not lead to the avalanche-like increase of free electron density, in contrast to the case of shorter ps and fs pulses. However, the total number of collisions by free electrons, ≈1018 cm-3 (generated during the pulse and accelerated to the energy of ≈10 eV), can produce widespread structural defects, which by entrapping electrons dramatically increase linear absorption for both harmonics in subsequent pulses, creating a positive feedback for crystal lattice heating, pyroelectric field and crystal damage. Under pulse repetition, defect generation starting from the rear of the crystal can propagate towards its center and front side producing damage tracks along the laser beam and stopping SHG. Theoretical analysis leads to numerical estimates and analytical approximation for the threshold laser fluence for onset of this damage mechanism, which agree well with our (i) experiments for the input 1064 nm radiation in 6.8 kHz pulsed SHG by PPSLT crystal, (ii) pulsed low frequency 532 nm radiation transmission experiments, and also (iii) with the data published for other nonlinear crystals and operated wavelengths. [ABSTRACT FROM AUTHOR]

We have observed a sizable positive magnetocapacitance (∼5%-90%) in perovskite Pr0.55Ca0.45MnO3 and bilayer Pr(Sr0.1Ca0.9)2Mn2O7 system under 5 T magnetic field across 20-100 K below the magnetic transition point TN. The magnetodielectric effect, on the other hand, exhibits a crossover: (a) from positive to negative for the perovskite system and (b) from negative to positive for the bilayer system over the same temperature range. The bilayer Pr(Sr0.1Ca0.9)2Mn2O7 system exhibits a sizable anisotropy as well. We have also noticed the influence of magnetic field on the dielectric relaxation characteristics of these systems. These systems belong to a class of improper ferroelectrics and are expected to exhibit charge/orbital order driven ferroelectric polarization below the transition point TCO. Large magnetocapacitance in these systems shows a typical multiferroic behavior even though the ferroelectric polarization is small in comparison to that of other ferroelectrics. [ABSTRACT FROM AUTHOR]

We have investigated the polarization rotation and phase transition in [100]-oriented PZN-4.5%PT and PZN-8%PT single crystals on the basis of the single domain polarization rotation model. The dependence of both the polarization and the electrostrictive responses in ferroelectric crystals on the field at various temperatures has been numerically obtained. The numerical results have shown that both the polarization rotation and the phase transition are in nature determined by the electro-crystalline anisotropy constants. These constants are dependent on the composition of PZN-PT solution and ferroelectric properties of its components. Without considering the piezoelectric effect, the numerical results are in agreement with the experimental data. This paper is useful for better understanding of the polarization switching and the phase transition in ferroelectric crystals. [ABSTRACT FROM AUTHOR]

A concept of accurate liquid viscosity sensing, using bulk acoustic wave (BAW) resonators, is proposed. The proposed BAW resonators use thin ferroelectric films with the dc field induced piezoelectric effect allowing for generation of pure longitudinal acoustic waves in the thickness excitation mode. This makes it possible to utilize exclusively shear liquid particle displacement at the resonator side walls and, therefore, accurate viscosity evaluation. The BAW resonators with the dc field induced piezoelectric effect in 0.67BiFeO3-0.33BaTiO3 ferroelectric films are fabricated and their liquid viscosity sensing properties are characterized. The resonator response is analyzed using simple model of a harmonic oscillator damped by a viscous force. It is shown that the resonator Q-factor is inversely proportional to the square root of the viscosity-density product. The viscosity measurement resolution is estimated to be as high as 0.005 mPa·s, which is 0.5% of the water viscosity. [ABSTRACT FROM AUTHOR]

A self-consistent two-dimensional model of polarization switching in polycrystalline ferroelectrics is developed. It accounts for the statistical distribution of the local switching times due to the random spatial field distribution as well as for the feedback effect of the depolarization field changing during the switching process. Thereby the polarization response of each single-crystalline grain is modeled in the spirit of the Kolmogorov-Avrami-Ishibashi model while the electric field in the system is evaluated by a finite-element method at every iteration step. The results exhibit fair agreement with experiments on bulk ferroelectrics. [ABSTRACT FROM AUTHOR]

A master equation for describing the polar nanoregions (PNRs) dynamics with adaptive-volume-dependent activation energy barrier has been established based on mean field approximation to investigate the anomalous temperature- and frequency-dependent dielectric properties of relaxor ferroelectrics. In the proposed model, the activation energy was correlated with the applied electric field and mean volume of PNRs. By expressing the PNRs mean volume as a function of temperature and pressure, and then fitting it to some existing experimental data, the results obtained reproduced the experimentally observed dielectric response including the broad temperature- and frequency-dependent peaks, frequency shift and dispersion of susceptibility. Finally, it has been found that the pressure and applied electric field led to the decrease of the PNRs relaxation time, and thus the peak of the real part of the dielectric constant was shifted to a lower temperature, which is consistent with the existing experimental data. The present study shows that polar cluster dynamics provides a better understanding of the macroscopic dielectric properties of relaxor ferroelectrics. [ABSTRACT FROM AUTHOR]

In the frame of thermodynamic approach, it is shown that all the admissible values of the d33, d32, and d31 piezoelectric moduli of any orthorhombic (mm2) single crystal in the 3-dimensional (d33, d32, d31) space lie within a restricted area having the form of ellipsoid. The main parameters of this ellipsoid (the aspect ratios and the angles characterizing its orientation) depend only on the elastic constants of the crystal. Using the developed approach, the areas of the allowable values of piezoelectric moduli have been determined for six crystals: single-domain KNbO3 and 0.27Pb(In0.5Nb0.5)O3-0.40Pb(Mg1/3Nb2/3)O3-0.33PbTiO3 crystals possessing true orthorhombic symmetry and four polydomain macroscopically pseudoorthorhombic crystals-tetragonal BaTiO3 and PbTiO3 crystals with laminate 90° domain structure as well as rhombohedral 0.72Pb(Mg1/3Nb2/3)O3-0.28PbTiO3 and 0.93Pb(Zn1/3Nb2/3)O3-0.07PbTiO3 crystals, poled along the [011] direction of the prototype cubic cell. Four crystals from this set possess negative values of the longitudinal Poisson's ratio and are thus partially auxetics. [ABSTRACT FROM AUTHOR]

We studied the temperature and pressure structural stability of 5 nm BaTiO3 particles by using high resolution synchrotron X-ray diffraction, high pressure Raman spectroscopy, and high pressure impedance technique. A coexistence of the tetragonal and orthorhombic phases is observed in 5 nm Barium titanate BaTiO3 particles with weight fractions 67(6.6)% and 33(8.0)% at ambient condition, respectively. In the temperature range from -123 °C to 177 °C, the phase boundaries of 5 nm BaTiO3 are diffusive and several phases coexist. Pressure dependent Raman spectra of 5 nm BaTiO3 indicates that there exist two phase transitions: the first is at 7.5 GPa when the coexisting phases of orthorhombic and tetragonal undergoes transition to tetragonal phase; the second is around 17.3 GPa when the tetragonal transforms to cubic phase. Observed transitions were confirmed by the high pressure impedance property measurement. [ABSTRACT FROM AUTHOR]

Oxygen vacancies (VO) and their migration and redistribution are believed to be the dominant factors resulting in the degradation of ferroelectrics. Thus, suppressing the formation and mobility of VO is quite crucial for the physical properties of ferroelectric materials. In this paper, the ab-biaxial strain effects on VO and their migration process in prototype perovskite ferroelectric BaTiO3 were studied by first principles total energy calculation. It is found that the formation energies for the two symmetrically inequivalent VO are enhanced under compressive strain. VO migration path between Vc (VO is located along the c-axis) and Vab (VO is located in the ab-plane) shows an 'S' shape. The VO migration barrier between Vc and Vab is enhanced by the compressive strain while lowered by the tensile strain. These results suggest that the ferroelectricity degradation induced by VO and their migration can be effectively mitigated by applying compressive strain. [ABSTRACT FROM AUTHOR]

We have proposed the polarization rotation theory to understand the underlying physics of the large piezoelectric effect in ferroelectric crystals by referring to the coherent rotation model in ferromagnetism. When both the electric field energy and crystalline anisotropy energy are taken into account, the polarization in BaTiO3 crystal can be rotated toward the field direction. The numerical results are in agreement with the experimental observations and have indicated the highly anisotropic polarization rotations and the field-induced-phases with different symmetries in the crystal. This theory is helpful for understanding the polarization reversal and the electromechanical effect in ferroelectric materials. [ABSTRACT FROM AUTHOR]

For ferroelectrics with a phase transition of the first order a double hysteresis loop of the polarization can be found close to TC. This behavior is explained using the Weiss field model taking into account that strain in the ferroelectric is induced by the polarization via the piezoeffect. The Weiss field model is looked at as a feedback loop where the polarization influences itself by the electrostatic interaction between the constituent dipoles. [ABSTRACT FROM AUTHOR]

A variant of piezo force microscopy was used to characterize the effect of strain on polarization in [(BaTiO3)n/(SrTiO3)m]p superlattices. The measurements were compared to theoretical predictions based on phase-field calculations. When polarization is constrained to be perpendicular to the substrate, the measured polarization and domain morphology agree quantitatively with the predictions. This case allows the presence of an internal electric field in the thin film to be identified. The measured trend in piezoelectric response with strain state was in qualitative agreement with predictions, and the differences were consistent with the presence of internal electrical fields. Clear differences in domain morphology with strain were observed; and in some cases, the lateral anisotropic strain appeared to influence the domain morphology. The differences in magnitude and morphology were attributed to the internal electric fields and anisotropic strains. [ABSTRACT FROM AUTHOR]

Using the phenomenological Landau thermodynamic theory, we have investigated the effect of external mechanical loads on the phase transition and physical properties of poly(vinylidene fluoride-trifluorethylene) [P(VDF-TrFE)] thin films. Quantitative calculation shows that the phase transition temperature, polarization, dielectric, pyroelectric, and piezoelectric properties are highly sensitive to external mechanical loads. External compressive stress increases the phase transition temperature and the out-of-plane polarization and decreases the out-of-plane dielectric constant below Tc, pyroelectric coefficient, and piezoelectric coefficient (absolute value) and vice versa. Compared with pervoskite-type ferroelectrics, the calculated results are opposite due to the different intrinsic parameters between pervoskite and polymer ferroelectrics, especially, electrostrictive constants. The ability to tailor the properties in ferroelectric P(VDF-TrFE) thin films with the mechanical load can offer a tremendously promising future for applications in multifunctional devices, such as agile mechanical sensors and transducers. [ABSTRACT FROM AUTHOR]

Ferroelectrics are essential components in a wide range of applications, including ultrasonic transducers, sensors, and actuators. In the single crystal form, relaxor-PbTiO3 (PT) piezoelectric materials have been extensively studied due to their ultrahigh piezoelectric and electromechanical properties. In this article, a perspective and future development of relaxor-PT crystals are given. Initially, various techniques for the growth of relaxor-PT crystals are reviewed, with crystals up to 100 mm in diameter and 200 mm in length being readily achievable using the Bridgman technique. Second, the characterizations of dielectric and electromechanical properties are surveyed. Boundary conditions, including temperature, electric field, and stress, are discussed in relation to device limitations. Third, the physical origins of the high piezoelectric properties and unique loss characteristics in relaxor-PT crystals are discussed with respect to their crystal structure, phase, engineered domain configuration, macrosymmetry, and domain size. Finally, relaxor-PT single crystals are reviewed with respect to specific applications and contrasted to conventional piezoelectric ceramics. [ABSTRACT FROM AUTHOR]

Ca and Mn co-doped BiFeO3 (BFO) thin films were fabricated on (111) Pt/Ti/SiO2/Si substrates via a simple solution approach. Enhanced ferroelectric properties were obtained in these Ca and Mn co-doped BFO films, e.g., large remnant polarization value (Pr ∼ 89 μC/cm2) and large remnant polarization to saturated polarization ratio (Pr/Ps ∼ 0.84) for Bi0.90Ca0.10Fe0.90Mn0.10O3 film. X-ray diffraction and Raman spectra of these films showed that B-site Mn doping causes substantial structural transition toward orthorhombic phase and A-site Ca doping facilitates an evolution to tetragonal phase with higher crystal symmetry. The structural transitions are in favor of enhanced ferroelectric properties in the BFO films. The approach of A and B site co-doping is proved to be effective in enhancing ferroelectric performance in multiferroic BFO films. [ABSTRACT FROM AUTHOR]

Some point defects (i.e., oxygen vacancies) create deep trapping levels in the bandgap of the paraelectric phase ferroelectric crystals. Under applied DC field the traps release electrons via the Poole-Frenkel mechanism and become charged. The electric field of a point charge polarizes the crystal locally reducing its permittivity. In this paper a simple theory is proposed for calculating the DC field dependent apparent (measureable) permittivity of a paraelectric crystal with point charge defects. It is shown that the apparent permittivity of a paraelectric crystal may be sufficiently lower as compared with the defectless crystal. This reduction is in addition to the possible reduction of the apparent permittivity associated with the interfacial 'dead' layers and strain. [ABSTRACT FROM AUTHOR]

In polycrystalline BiMn2O5, a broad thermal stimulated depolarization current curve has been observed in the range from 10 K to 300 K and the pyroelectric coefficient determined. In magnetic susceptibility measurements reported in the literature, features appearing in the pyroelectric coefficient could also be identified for the same temperatures, suggesting a connection between electric and magnetic data above the Néel temperature. A detailed study of the dielectric constant from 240 K to 700 K for an extended range of frequencies revealed a broad maximum at low frequencies, characteristic of relaxor ferroelectrics, following Vogel-Fulcher relation. A freezing temperature of the polar nanoregions Tf = 512 K has been determined. This high temperature ferroelectric behavior is attributed to the Bi3+ in the distorted BiO8 cage. [ABSTRACT FROM AUTHOR]

The phase relation of tetragonal and cubic PbTiO3 and their unit-cell parameters have been determined by synchrotron x-ray diffraction at pressures up to 7.8 GPa and temperatures up to 1074 K with a cubic anvil apparatus. From these measurements, a pressure-temperature phase boundary between the tetragonal and cubic phases has been established. With increasing temperature or pressure, the c/a ratio of the ferroelectric, tetragonal PbTiO3 becomes closer to unity, suggesting that both heating and compression favor the paraelectric, cubic structure. Using a modified high-T Birch-Murnaghan equation of state and a thermal-pressure approach, we have derived the thermoelastic parameters of tetragonal and cubic PbTiO3, including the ambient bulk modulus K0, temperature derivative of bulk modulus at constant pressure, volumetric thermal expansivity, pressure derivative of thermal expansion, and temperature derivative of bulk modulus at constant volume. Our obtained K0 value for tetragonal PbTiO3 is consistent with previously reported results, while that for cubic PbTiO3 is smaller than earlier results probably due to differences in the experimental techniques used (cubic anvil apparatus versus diamond anvil cell) and related stress conditions of the samples. All other thermoelastic parameters for both tetragonal and cubic PbTiO3 have been determined for the first time. Compared with previous high-temperature data at atmospheric pressure, our P-V-T dataset for tetragonal PbTiO3 infers a pressure-induced crossover in volumetric thermal expansion from negative to positive between 0 and 1 GPa, an phenomenon that is of fundamentally interest and practically important. [ABSTRACT FROM AUTHOR]

Temperature-dependent dielectric permittivity of 0.94(Bi1/2Na1/2)TiO3-0.06BaTiO3 (BNT-6BT) lead-free piezoceramics was studied to disentangle the existing unclear issues over the crystallographic aspects and phase stability of the system. Application of existing phenomenological relaxor models enabled the relaxor contribution to the entire dielectric permittivity spectra to be deconvoluted. The deconvoluted data in comparison with the temperature-dependent dielectric permittivity of a classical perovskite relaxor, La-modified lead zirconate titanate, clearly suggest that BNT-6BT belongs to the same relaxor category, which was also confirmed by a comparative study on the temperature- dependent polarization hysteresis loops of both materials. Based on these results, we propose that the low-temperature dielectric anomaly does not involve any phase transition such as ferroelectric- to-antiferroelectric. Supported by transmission electron microscopy and X-ray diffraction experiments at ambient temperature, we propose that the commonly observed two dielectric anomalies are attributed to thermal evolution of ferroelectric polar nanoregions of R3c and P4bm symmetry, which coexist nearly throughout the entire temperature range and reversibly transform into each other with temperature. [ABSTRACT FROM AUTHOR]

A theoretical model for the electrocaloric effect (ECE) in relaxor ferroelectrics is presented. By solving a self-consistent relation for the ECE temperature change ΔT and minimizing numerically the mean field free energy for relaxors, the field and temperature dependence of ΔT is calculated. The corresponding harmonic Landau coefficient a=a(T), which differs from the ferroelectric case by always being positive, is derived from the spherical random bond-random field model, and the fourth-order coefficient b is treated as a phenomenological parameter, which can be either positive or negative. For b<0, a line of field-induced first-order relaxor-to-ferroelectric phase transitions exists in relaxors, which terminates at a liquid-vapor type critical point ECP,TCP. The critical behavior close to ECP,TCP is analyzed. It is shown that near the first-order phase transition a temperature or field interval or gap formally appears, where ΔT cannot be found. However, domain formation in the coexistence range should restore the continuous behavior of the ECE observed in real systems. Finally, it is shown that the ECE responsivity R1=ΔT/E reaches a maximum near the critical point, in agreement with recent experiments. [ABSTRACT FROM AUTHOR]

A thin Al2O3 layer was atomic layer deposited on a 50 - or 70 nm-thick, polycrystalline Mn-doped BiFeO3 (BFMO) thin film to fabricate a dielectric/ferroelectric bi-layer capacitor. The thin Al2O3 layer worked as a tunnel switch to improve the ferroelectric performance of the BFMO films. The BFMO thin film and BiFeO3 film contains a high density of charged defects, such as oxygen vacancies, Bi vacancies, and Fe2+ ions reduced from Fe3+, which induce a large leakage current and cause instability of ferroelectric polarization in one direction. An asymmetric hysteresis loop and severe depolarization was observed in the BFMO capacitor due to the local field induced by the defect complexes that are mainly formed near the Pt/BFMO interface from interactions between charged defects. Depositing a thin Al2O3 tunnel switch layer reduced these detrimental phenomena, which could be attributed to a decrease in the amount of oxygen vacancies as well as the suppression of polarization back-switching after the polarization switching and during non-switching. The defects in the BFMO films also caused domain wall pinning during the relaxation time so the switching speed decreased with increasing relaxation time. Adopting an Al2O3 tunnel switch layer also improved this problem. [ABSTRACT FROM AUTHOR]

Ferroelectric films usually have phase states and physical properties very different from those of bulk ferroelectrics. Here we propose free-standing ferroelectric-elastic multilayers as a bridge between these two material systems. Using a nonlinear thermodynamic theory, we determine phase states of such multilayers as a function of temperature, misfit strain, and volume fraction φp of passive elastic material. The numerical calculations performed for two classical ferroelectrics-PbTiO3 and BaTiO3-demonstrate that polarization states of multilayers in the limiting cases φp→1 and φp→0 coincide with those of thin films and bulk crystals. At intermediate volume fractions, however, the misfit strain-temperature phase diagrams of multilayers differ greatly from those of epitaxial films. Remarkably, a ferroelectric phase not existing in thin films and bulk crystals can be stabilized in BaTiO3 multilayers. Owing to additional tunable parameter and reduced clamping, ferroelectric multilayers may be superior for a wide range of device applications. [ABSTRACT FROM AUTHOR]

We report on the optical characterization of Yb3+ doped BaMgF4 nonlinear fluoride crystal grown by the Czochralski technique. Low temperature absorption spectroscopy reveals that Yb3+ incorporates into the matrix at four well differentiated centers. High resolution site selective experiments have been performed to determine the energy level schemes associated with the major Yb3+ centers detected in the system. The fluorescence decay times recorded at 10 K under selective excitation are analyzed for each Yb3+ center. The spectroscopic behavior of the codoped Yb3+:Na+:BaMgF4 system has been also investigated. Codoping with Na+ eliminates two Yb3+ centers present in the singly doped Yb3+:BaMgF4 crystal. The charge compensation mechanisms and site location for Yb3+ in the fluoride matrix are discussed. [ABSTRACT FROM AUTHOR]

In this work, we investigated structural, electrical, and magnetic properties of ferroelectric PbZr0.2Ti0.8O3 (PZT) and ferrimagnetic/ferroelectric [CoFe2O4(CFO)/PZT] bilayers grown on (100)LaAlO3 (LAO) substrates supplied with bottom 50 nm thick LaNiO3 electrodes. Interestingly, structural and electrical properties of the PZT layer exhibited remarkable changes after the top-layer CFO deposition. X-ray diffraction data suggested that both the c- and a-domains exist in the PZT layer and the tetragonality of the PZT decreases upon the top-layer deposition. A variation in the electrical properties of the PZT layer upon the CFO deposition was investigated by polarization versus voltage (P-V), capacitance versus voltage (C-V), and capacitance versus frequency (C-f) measurements. The CFO deposition induced a slight decrease of the remnant polarization and more symmetric behavior of P-V loops as well as led to the improvement of fatigue behavior. The tentative origin of enhanced fatigue endurance is discussed based on the measurement results. These results were corroborated by local piezoelectric measurements. Ferrimagnetic property of the CFO/PZT bilayer was confirmed by magnetic measurement at room temperature. [ABSTRACT FROM AUTHOR]

[100] oriented Sr0.75Ba0.25Nb2O6 relaxor crystals have been studied by means of acoustic emission (AE) over a wide 20-400 °C temperature range. Both the Burns temperature, Td = 350 °C, and the intermediate temperature, T* = 183°C, and the susceptibility maximum temperature, Tm (59 °C on heating and 47 °C on cooling), have been successfully detected. Dependent upon the external electric field, the Tm exhibits a local minimum near 0.25 kV/cm accompanied by pronounced AE maximum in a manner which had recently been detected in Pb(Mg1/3Nb2/3)O3-0.33PbTiO3 by Dul'kin et al. [Appl. Phys. Lett. 94, 252904 (2009)] and in Pb(Sc1/2Ta1/2)O3 by Dul'kin et al. [Phys. Rev. B 82, 180101(R) (2010)], whereas the T* increases monotonically, similar to that which had recently been revealed in BaTiO3 by Dul'kin et al. [Appl. Phys. Lett. 97, 032903 (2010)] with a rate of 7.5 K cm/kV. An observed Tm behavior is discussed from the point of view of the existence of the random electric field components along the [100] direction in Sr0.75Ba0.25Nb2O6 crystals. [ABSTRACT FROM AUTHOR]

Ho3+-Yb3+ co-doped bismuth titanate ferroelectric thin films were prepared by a chemical solution deposition method on fused silica substrates and their up-conversion luminescence characteristics excited by a 980 nm diode laser were investigated. The two emission bands centered at 546 and 656 nm in the emission spectra can be assigned to 5F4 + 5S2 → 5I8 and 5F5 → 5I8 transitions of Ho3+ ions, respectively. A bright green emission was observed even when the laser pumping power was relatively low. The dependence of the emission intensity on the pumping power indicated that the up-conversion emission in the thin films was a two-photon process. The up-conversion emission mechanism is discussed in detail. This study suggests that Ho3+ and Yb3+ co-doped Bi4Ti3O12 thin films can be applied to the fabrication of new multifunctional photoluminescence ferroelectric thin-film devices. [ABSTRACT FROM AUTHOR]

Radiation damage in magnesium-doped lithium niobate crystals, created by low-mass, high-energy ions which have transmitted the entire crystal thickness, leads to an enhanced electrical dark conductivity as well as an enhanced photoconductivity. Experimental results on the electrical properties after ion exposure are given, and an asymmetric dependence of the conductivity as well as refractive index changes on the irradiation geometry with respect to the ferroelectric axis is revealed. [ABSTRACT FROM AUTHOR]

The stabilization effect, an increase of the reverse transition temperature TC with ferroelectric aging time, was recently found in acceptor doped ferroelectrics. Such an effect has found a microscopic explanation in the symmetry-conforming principle of point defects, which also accounts for a similar stabilization effect in ferroelastic/martensite materials. However, such a microscopic model is difficult to use to make a quantitative/semiquantitative evaluation of the aging process. In the present work, we propose a single-domain thermodynamic model that provides a semiquantitative fit to the experimentally observed stabilization kinetics. Furthermore, it predicts a new aspect of ferroelectric aging: the decrease of latent heat ΔH of the reverse transition with aging time. Such a prediction was confirmed via experimental differential scanning calorimetry results. [ABSTRACT FROM AUTHOR]

(Pb0.87La0.02Ba0.1) (Zr0.7Sn0.24Ti0.06)O3 (PLBZST) antiferroelectric ceramics with the addition of 0-9 wt. % excess PbO were fabricated by the conventional solid-state reaction process, and their microstructure, dielectric, and pyroelectric properties were systemically investigated. When excess PbO content was less than 9 wt. %, two pyrochlore phases were formed along with the perovskite phase. Compared with common specimens, PLBZST antiferroelectric ceramics with excess PbO exhibited a higher pyroelectric coefficient and a lower dielectric loss, which are beneficial for the development of pyroelectric devices. Around the Curie temperature, as the excess PbO increased from 0 wt. % to 9 wt. %, PLBZST ceramics' pyroelectric coefficient increased from 1600 μC/m2K to 4000 μC/m2K, and the figure of merit increased from 40 × 10-5 Pa-0.5 to 140 × 10-5 Pa-0.5 under a 400 V/mm dc field. The largest figure of merit of 200 × 10-5 Pa-0.5, which is about 8 times higher than that of conventional phase transition materials barium strontium titanate (BST), was obtained in PLBZST ceramics with 6 wt. % excess PbO when a 600 V/mm dc bias field was applied. Therefore, improvement of pyroelectric property is beneficial for the development of infrared detectors. [ABSTRACT FROM AUTHOR]

Hyper-Raman scattering is used to investigate the vibrations in two prototypical relaxors, PbMg1/3 Nb2/3 O3 and PbMg1/3 Ta2/3 O3 (PMT). First-order scattering from polar modes is clearly observed. Most of the triply-degenerate cubic vibrations are split into doublets and their frequencies compare very well to that of PbTiO3 in its tetragonal phase. Their shape and scattering intensities are sensitive to the local chemical ordering and ferroelectric distortions. For example, the tendency toward 1:1 local ordering on the B-site in PMT is clearly evidenced. These results demonstrate the strong potentiality of hyper-Raman scattering as structural probe of complex perovskites. [ABSTRACT FROM AUTHOR]

In this paper, a surface-layer model is established to study the axial polarization distributions and critical diameters of nanowires with different surface compositions. Analytical solutions are obtained based on this model, which are validated by the ab initio results for small-size nanowires and can also predict the behaviors of large-size specimen. Compared to the traditional Landau-Ginzburg-Devonshire theory using an extrapolation length, the present model describes more microstructure information of the surface-layer, and is thus capable of characterizing the influences of different surface compositions. Furthermore, this model may shed insight into the mechanisms of the size effect and polarization distribution patterns in nanoscale ferroelectrics. [ABSTRACT FROM AUTHOR]

In this paper, we report the dielectric and ferroelectric response of compositionally graded bilayer and trilayer composites consisting of BaTiO3 (BT) and 0.975BaTiO3-0.025Ba(Cu1/3Nb2/3)O3 (BTBCN). Two types of graded bilayer samples were synthesized, one with same thickness of BT and BTBCN while other with different layer thicknesses. The graded trilayer sample consisted of BT layer sandwiched between two BTBCN layers of equal thickness. Scanning electron microscopy and transmission electron microscopy images showed a sharp interface with needle-shape domains across the interface. The domain size on BT side was found to be larger than that on BTBCN side. The temperature dependence of dielectric response for all composite systems was found to exhibit shifting in characteristic Curie peak compared to constituent material which was associated to coupling between layers. Moreover, the differences in grain size, tetragonality, domain mobility of each layer was found to perturb the electrical response of composite. The polarization mismatch between uncoupled BT and BTBCN established internal electric field in composite specimen and defined new polarization states in each layer by perturbing free energy functional of the composite specimen. Dynamic hysteresis behaviors and power-law scaling relations of all specimens were determined from polarization-electric field hysteresis loop measurements as a function of frequency. All systems were found to exhibit similar dynamic scaling relationships. Hysteresis area , Pr, and EC decreased with increasing frequency due to delayed response but increased with increasing applied electric field due to enhancement of driving force. Trilayer system was found to exhibit strong internal-bias field and double hysteresis behavior. The coupling effect resulting due to polarization mismatch between layers had substantial influence on the dynamic hysteresis behavior and power-law scaling relations. [ABSTRACT FROM AUTHOR]

In this work we demonstrate by transmission electron microscopy and piezoresponse force spectroscopy that the polarization direction in hydrothermally synthesized lead titanate (PbTiO3) nanorods can be changed from parallel to the nanorod axis to perpendicular to it by a simple heat treatment above the Curie temperature. The heat treatment also introduced 90° domains, caused a rearrangement of the surface and a reduction in the amounts of defects. The polarization of the heat-treated nanorods could be successively switched in the direction perpendicular to the nanorod axis. This control of the polarization in PbTiO3 nanorods opens up possibilities of tailoring the ferroelectric properties and is therefore highly relevant for the use of ferroelectric nanorods in devices. [ABSTRACT FROM AUTHOR]

In this paper, we report the dielectric and ferroelectric response of compositionally graded bilayer and trilayer composites consisting of BaTiO3 (BT) and 0.975BaTiO3-0.025Ba(Cu1/3Nb2/3)O3 (BTBCN). Two types of graded bilayer samples were synthesized, one with same thickness of BT and BTBCN while other with different layer thicknesses. The graded trilayer sample consisted of BT layer sandwiched between two BTBCN layers of equal thickness. Scanning electron microscopy and transmission electron microscopy images showed a sharp interface with needle-shape domains across the interface. The domain size on BT side was found to be larger than that on BTBCN side. The temperature dependence of dielectric response for all composite systems was found to exhibit shifting in characteristic Curie peak compared to constituent material which was associated to coupling between layers. Moreover, the differences in grain size, tetragonality, domain mobility of each layer was found to perturb the electrical response of composite. The polarization mismatch between uncoupled BT and BTBCN established internal electric field in composite specimen and defined new polarization states in each layer by perturbing free energy functional of the composite specimen. Dynamic hysteresis behaviors and power-law scaling relations of all specimens were determined from polarization-electric field hysteresis loop measurements as a function of frequency. All systems were found to exhibit similar dynamic scaling relationships. Hysteresis area , Pr, and EC decreased with increasing frequency due to delayed response but increased with increasing applied electric field due to enhancement of driving force. Trilayer system was found to exhibit strong internal-bias field and double hysteresis behavior. The coupling effect resulting due to polarization mismatch between layers had substantial influence on the dynamic hysteresis behavior and power-law scaling relations. [ABSTRACT FROM AUTHOR]

The photoluminescence of Pr doped (Bi0.5Na0.5)TiO3 ferroelectric ceramics prepared by conventional solid-state reaction were investigated. A bright red emission is observed at room temperature, which ascribed to 1D2→3H4 transition. The excitation bands are mainly located at 440 ∼ 505 nm, which is adaptable to the emission band of commercial blue light-emitting diodes (LEDs) chips. The optimal emission intensity was also obtained when Pr doping level was 0.003 mol. Meanwhile, the enhanced ferroelectric properties were obtained by Pr doping. The results show that Pr doped (Bi0.5Na0.5)TiO3 ceramics as a multifunctional material may be useful for white LEDs, sensor, and optical-electro integration. [ABSTRACT FROM AUTHOR]

In ferroelectric superlattices (SLs), the short-range interactions and intermixing between contacting dissimilar materials can lead to the formation of interfacial nanolayers with physical properties different from those of both constituents. We demonstrate theoretically that such nanolayers can give rise to a sizable dependence of the SL permittivity on the period even in the paraelectric regime. The results of dielectric measurements performed for coherent Ba0.8Sr0.2TiO3-Ba0.4Sr0.6TiO3 SLs are qualitatively consistent with the theoretical predictions. At the same time, the experimental data indicate that other factors also contribute to the variation of the permittivity with the period in ferroelectric superlattices and multilayers. [ABSTRACT FROM AUTHOR]

Physical processes taking place at the surface and its vicinity are so rich and versatile that sometimes seems to be inexhaustible subject of fundamental researches, which open new ways of technical applications. In particular theoretical and experimental researches of the versatile flexoelectric phenomena at nanoscale remain hot topic during last 10 years. Among them the special attention attracts the spontaneous flexoelectric effect inherent to nanosized and nanostructured ferroelectrics, as originated from the intrinsic polarization inhomogeneity near the surface of the system. The effect revealed in 2009 is very important, since it leads to the strong increase of effective flexoelectric coefficients values due to size effect. So that at small sizes the spontaneous flexoeffect strongly influences polar, piezoelectric and dielectric properties as well as the correlation radius. Motivated by above argumentation the author review describes the way of nanoscale ferroelectric properties and phase diagram calculations in the framework of Landau-Ginzburg-Devonshire thermodynamic theory with special attention to flexoelectric effect contribution. The comparison of obtained results with available experimental data is given whenever possible. The review highlights recent calculations, which have shown that the spontaneous flexoelectric effect and chemical pressure can be the physical reason of ferroelectric phase conservation and reentrance observed in spherical ferroelectric nanoparticles up to 5 nm sizes. Fundamental results devoted to the finding of "forbidden" shear surface wave propagating near the surface of all ferroelectrics due to omnipresent flexoelectric coupling are discussed. These missed surface waves are waiting for experimental observation, which could be the source of unique information about surface impact on the dynamics, structural peculiarities and possible phase transitions induced by the surface. Also we analyze how significantly the flexoelectric coupling can change static and dynamic polar properties in ferroelectrics, govern the formation and growth of unusual domains structures and influence optic and acoustic soft modes. The special attention in the review in paid to recent results, which have shown that flexocoupling induces soft acoustic mode in response of spatially modulated phase appearance in flexoelectrics. We'd like to underline that theoretical and experimental studies of flexoelectricity and related phenomena in nanosized and bulk ferroelectrics are very important for applications in nanoelectronics and memory devices, opening the way of true minimization of multilayer ceramic capacitors, piezoelectric transducers, pyroelectric elements and ferroelectric memories. [ABSTRACT FROM AUTHOR]

Downscaling of magnetoelectric random access memory device (MELRAM) is considered by studying an example of the hybrid structure based on ferroelectric-magnetostrictive metal. Elastic mechanism of magnetoelectric interaction is analyzed by numerical modeling taking into account inhomogeneous distribution of anisotropic strain, ferroelectric polarization and electric field. The proposed shape of the cell allows to decrease the inhomogeneity of the strain in the magnetic subsystem and to achieve remarkable dynamic characteristics for a nanometric device sized nm3: we adopted an input voltage of V0 = 90 mV and obtained a switching time tS = 1.1 ns, an output readout voltage VME = 4.7 mV, and an ultra-low energy consumption 13 aJ/bit. [ABSTRACT FROM AUTHOR]

Here we demonstrate a method to tune a ferroelectric imprint, which is stable in time, based on the coupling between the non-switchable polarization of ZnO and switchable polarization of PbZrxTi(1-x)O3. SrRuO3/PbZrxTi(1-x)O3/ZnO/SrRuO3 heterostructures were grown with different ZnO thicknesses. It is shown that the coercive voltages and ferroelectric imprint vary linearly with the thickness of ZnO. It is also demonstrated that the ferroelectric imprint remains stable with electric field cycling and electric field stress assisted aging. [ABSTRACT FROM AUTHOR]