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Synthesis (via solid-state reaction) and characterization (structure, microstructure, dielectric, electrical, and ferroelectric behavior) of brownmillerite polycrystalline material NaBiFe2O5 (NBFO) are discussed in this paper. The formation of a triclinic structure has been analyzed by the X-ray diffraction method. The morphology of the ceramic sample was analyzed using a field emission scanning electron microscope (FESEM) and energy-dispersive X-ray analysis (EDX). It is found that the grains are uniformly distributed through well-defined grain boundaries of the sample containing all the constituent elements (Na, Bi, Fe, and O). The study of both frequency (1 kHz–1MHz) and temperature (25–450 °C) dependent dielectric and AC-conductivity predicts the presence of Maxwell-Wagner type of dielectric dispersion and thermally activated relaxation mechanism of NBFO. The impedance spectra support the semiconducting behavior of the brownmillerite NBFO at high temperature. The resistance of the material falls with a rise in temperature favors the negative temperature coefficient resistance behavior of the material. The study of electric polarization suggests the possibility of the ferroelectric properties of the studied sample. The high dielectric constant and low tangent loss suggest the possibility of the material for device applications. [ABSTRACT FROM AUTHOR]

Synthesis (via solid-state reaction) and characterization (structure, microstructure, dielectric, electrical, and ferroelectric behavior) of brownmillerite polycrystalline material NaBiFe2O5 (NBFO) are discussed in this paper. The formation of a triclinic structure has been analyzed by the X-ray diffraction method. The morphology of the ceramic sample was analyzed using a field emission scanning electron microscope (FESEM) and energy-dispersive X-ray analysis (EDX). It is found that the grains are uniformly distributed through well-defined grain boundaries of the sample containing all the constituent elements (Na, Bi, Fe, and O). The study of both frequency (1 kHz–1MHz) and temperature (25–450 °C) dependent dielectric and AC-conductivity predicts the presence of Maxwell-Wagner type of dielectric dispersion and thermally activated relaxation mechanism of NBFO. The impedance spectra support the semiconducting behavior of the brownmillerite NBFO at high temperature. The resistance of the material falls with a rise in temperature favors the negative temperature coefficient resistance behavior of the material. The study of electric polarization suggests the possibility of the ferroelectric properties of the studied sample. The high dielectric constant and low tangent loss suggest the possibility of the material for device applications. [ABSTRACT FROM AUTHOR]

We report the preparation and characterization of vanadium substituted four-layer Aurivillius compound Bi5Fe1.5V0.5Ti2O15 using spin coating method. Ferroelectricity in the prepared films are confirmed from the well saturated polarization vs electric field (P-E) loops having remnant polarization (2 Pr) around 12.94 µC/cm2 at room temperature. In addition, low temperature P-E measurements show a decrease in Pmax and 2 Pr, which is attributed to the stabilization of defect dipole complexes and domain pinning, as seen in bismuth-based ferroelectrics. Additionally, this decrease in polarization is accompanied by an increase in imprint, confirming the presence of defect dipoles manifested as internal fields. [ABSTRACT FROM AUTHOR]

Today, great emphasis is placed on the creation of lead-free compounds that may be used in multi-functional equipment. This report describes the synthesis (through the solid-state technique) and physical characteristics (structural, electrical, and ferroelectric) of a polycrystalline Sr3Bi2WO9 compound (SBWO). A monoclinic crystal structure with cell parameters; a = 9.0285 Å, b = 16.6457 Å, c = 5.6787 Å with β = 93.13° is studied by analysis of X-ray diffraction method (crystallite size 100.77 nm). The purity, morphology, and elementary composition of elements were studied by SEM (grain size 0.582 μm) and EDX. The temperature-frequency variation of εr, tan δ, and σac were investigated. The drop in grain resistance value with increasing temperature demonstrates the NTCR property of the compound. It has been reported that the conduction process of the compound is based on a study of the modulus spectrum. SBWO is a possible choice for devices because it exhibits outstanding temperature-independent εr characteristics and reduced tanδ. Ferroelectric properties of the material (Ec=0.2655 kV/cm, Pr=0.00454 μC/cm2, Emax=2.478 kV/cm, and Pmax=0.0367 μC/cm2) shown by the electric field-dependent polarization at 25 °C. [ABSTRACT FROM AUTHOR]

The study of basic crystal structure, dielectrics, magnetic and electrical characteristics of a high temperature sintered dysprosium (Dy) substituted bismuth ferrite (BFO) ceramic material, Bi(Fe0.90Dy0.10)O3 (abbreviated as BFDO10) has been reported in this work. The solid-state reaction (SSR) technique is adopted for synthesizing the material. Study of the X-ray diffraction (XRD) data shows an orthorhombic symmetry. The approximate crystallite size is found to be 29 nm. The field emission scanning electron micrograph (FESEM) shows a high density grains of the sample and energy dispersive X-ray micro-analysis (EDXMA) reveals the presence of its basic components. The extensive analysis of the dielectric and electrical properties of the sample was carried out within a frequency from 1 kHz to 1000 kHz and temperature ranges from 25 to 500 °C. A study of the impedance spectroscopy reveals a negative temperature coefficient of resistance (NTCR) behavior and a non-Debye type of dielectric relaxation process of the compound. The ac-conductivity (σac) of the material follows Jonscher's universal power law. A study of the electric field polarization confirms the enhancement in remnant polarization and coercive field. The magnetic property shows an enhancement in ferromagnetic orders by virtue of this doping. Moreover, several other interesting features which could be utilized for modern device applications also specified in this article. [ABSTRACT FROM AUTHOR]

Ferroelectric crystals show spontaneous electric polarization even in the absence of an electric field. Lead hydrogen arsenate (LHA) is a member of the group of Lead hydrogen phosphate (LHP) type ferroelectric crystals. We have modified earlier two sub-lattice pseudospin model (PLCM) Hamiltonian for LHA crystal. phonon anharmonic terms, four body interaction terms, and extra spin-lattice terms have been added to the model. For the LHA crystal, formulas for Cochran's frequency, dielectric constant, and loss tangent have been determined using Green's function approach, and a strong agreement is displayed when comparing our theoretical results to other researchers' experimental findings. [ABSTRACT FROM AUTHOR]

The 180° light scattering experiment has been performed in SrTiO3single crystal under uniaxial stress in order to clarify the physical origin of the Broad Doublet (BD). Especially, the polarization analyses of the BD are made in the stress-induced quantum ferroelectric state (the stress ofσ= 19.4 kgf/mm2is applied along the [001]cdirection atT= 16.5 K). The analyses clearly show that the physical origin of the BD is “not” the second sound. The real physical origin of the BD is predicted to be a transverse acoustic mode propagating inside the ferroelectric regions. [ABSTRACT FROM AUTHOR]

Nanoscale structural and polar behavior in abalone and clamshell have been studied using the scanning probe techniques. Untreated pristine sample surfaces were probed to realize their intrinsic electrical properties. While prominent polarization switching under opposite bias field is observed in the clusters of nanograins of the abalone shell, the piezoelectric phase contrasts remained confined mostly at the grain-grain boundary regions in the clamshell. These shells mostly comprised of centrosymmetric CaCO3, the observed polar responses is attributed to the structural distortion initiated by the intra-granular organic phase of the biopolymers. The biopolymer-nanocrystalline layered (as found in abalone shell) or 3:1 composite structure (as found in clamshell) bear an analogy with the piezoelectric composites, where due to the stretching/twisting of the biopolymers under external mechanical stress, the piezoelectric responses get originated owing to the intrinsic electromechanical coupling. [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]

Effect of nanocrystalline size of the particles on ferroelectric properties of KNbO3 is studied. Properties like hysteresis parameters, phase transition temperatures and domain morphology in nanocrystallites were studied by using P-E hysteresis, differential scanning calorimetry (DSC) and transmission electron microscopy (TEM) techniques, respectively. Nanocrystalline KNbO3 compound was synthesized by a modified polymerized complex method and room-temperature structural phase was characterized by X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy. Field emission gun-scanning electron microscopy (FEG-SEM) was used to reveal the size and morphology of the particles. It was found that the present nanoparticles of sizes ranging from 50 to 250 nm bears polarization values <1 μC/cm2, and undergo cubic-tetragonal and tetragonal-orthorhombic phase transitions at 312 and 87 °C respectively. Although the value of polarization is small as compared to the bulk reported in the literature, the nature of P-E loops along with phase transitions and presence of 60, 90 and 180° domain structures indicates retention of ferroelectric nature in KNbO3 even at the nanolevel. [ABSTRACT FROM AUTHOR]

Computer simulation of repolarization and inverse piezoeffect is realized by Monte-Carlo method in polymer ferroelectric materials, observed in AC electric field with different frequencies and amplitudes. For describing the interactions between the segments of polymer chains, Lennard-Jones potential was used with additional term describing exchange short-range orientational interactions. We investigate the influence of temperature and parameters of external electric field on the hysteresis curve area, which determines the absorption coefficient. It is shown that for ferroelectric systems there is a frequency of the external field, which accounts for the maximum absorptivity. [ABSTRACT FROM AUTHOR]

Superfast domain wall motion during merging of elongated domains in potassium titanyl phosphate (KTP) single crystals with C2v symmetry has been studied. The model of the [100]-oriented superfast wall formation resulting in appearance of the switching current peaks has been proposed. The fitting of the measured double-maxima current peaks has allowed extracting the [100]-oriented wall velocity. The obtained values are close to the results obtained by analysis of the domain kinetics video records. The mobility and threshold fields for superfast domain walls have been obtained. [ABSTRACT FROM AUTHOR]

Molecular modeling of diphenylalanine peptide nanotubes (FF PNT) is performed using PM3 method in HyperChem. The study focuses on the polar properties of FF PNT structures having different chiralities (L, D) and conformations (α-helix, β-sheet). The results show that the optimized structures for L-PNT possess higher polarization in both conformations (0.023 C/m2 - α, 0.04 C/m2 - β) compared with D-PNT (0.016 C/m2 - α, 0.014 C/m2 - β). The water structures inside PNT are investigated, too. The hexagonal ice/water structures used for these models are analyzed in respect to the XRD data recently obtained. [ABSTRACT FROM AUTHOR]

We present a new technique of fabricating the extended-shape electrodes with dendrite channels for formation of the multi-domain state in lithium niobate (LN). The dendrite structure of NaCl created by drying drops of protein-NaCl solution was used for electrode patterning. The linear dependence of the dendrite sizes on drying time has been revealed. The high resolution visualization of the static domain structures created using dendrite electrodes allowed revealing formation of quasi-periodic domain arrays. The produced LN plates with multi-domain regions will be used for manufacturing of the pyroelectric field generators with focusing effect for bioprinting. [ABSTRACT FROM AUTHOR]

We present the results of experimental study of the local switching in single crystals of relaxor ferroelectric Ni-doped strontium barium niobate with various initial domain states using conductive tip of scanning probe microscope. We investigated the domain growth in as-grown domain structure and initial domain states created by: (i) scanning by biased tip, (ii) in-field cooling, and (iii) scanning by electron beam. The dependences of effective domain radius on the voltage and pulse duration were derived. The shape factor, domain wall mobility, and start voltage were revealed. The obtained results can be used for the domain engineering in ferroelectrics. [ABSTRACT FROM AUTHOR]

We present the nanoscale piezoresponse of ultrasonically synthesized reduced graphene oxide-hydroxyapatite (rGO-HAP) nanocomposite using Piezoresponse Force Microscopy (PFM). The piezoresponse in rGO (thickness ∼ 12 nm) is homogeneous in the unfolded region than that of the folded region. Variation in the confined piezo response of rGO-HAP nanocomposite studied at different regions having pure rGO, HAP nanorod (NR) and HAP NR intercalated rGO sheets. Under biasing, the polarization switching of the HAP NR intercalated rGO nanosheets is examined. Based on the PFM data analysis, it is implied that piezoelectricity of HAP intercalated rGO nanosheets is mainly created through the hydroxyl ions along the c-axis which prompts noncentrosymmetry in the structure. [ABSTRACT FROM PUBLISHER]

We calculate the spontaneous polarization as a function of temperature for a mixed crystal ofclose to the tricritical point. This calculation of the spontaneous polarization is performed using the effective field approximation for the dipolar () and higher order (quadrupolar and octopolar) interactions for the mixed system ofat concentrations fromto. Our calculations show that as thedecreases with increasing the concentrationx, first order (discontinuous) transition which occurs at low concentrationsbecomes tricriticaland then the second order (continuous) transitionin. Dipolar and also higher order (quadrupolar and octopolar) interactions are needed to explain the mechanism of ferroelectric – paraelectric transition in. [ABSTRACT FROM PUBLISHER]

The concept of background dielectric constant proposed by Tagantsev, together with the distinction between critical and non-critical electric polarizations as a natural extension for the order parameter of ferroelectric phase transitions, is critically discussed. It is argued and exemplified that, even if these quantities can be very useful for obtaining qualitative and semi-quantitative results from phenomenological modeling, they cannot be introduced in a self-consistent manner. [ABSTRACT FROM PUBLISHER]

Polarization rotation and dielectric property of epitaxial PbTiO3thin films have been investigated using a phenomenological approach. Occurrence of monoclinic and triclinic structures is determined by electromechancial boundary conditions. With increasing temperature and strain anisotropy, monoclinic structure (MC) becomes more favorable than triclinic structure on the polarization path. In general, high permittivity can be obtained around monoclinic-orthorhombic transition. Strain anisotropy may have a significant impact on the dielectric response. Critical field for monoclinic-orthorhombic transition decreases with decreasing strain magnitude or increasing strain anisotropy. Under equal but opposite in-plane strain, rather high dielectric tunability can be obtained at medium electric field. [ABSTRACT FROM AUTHOR]

Lead zirconate titanate (PZT) ceramics have been extensively used for electronic applications due to their ability to couple mechanical and electrical energy, a so-called piezoelectric effect. This effect is caused by the shift of Ti4+or Zr4+ion relative to neighbouring atoms. The movement of the ions due to an external load causes reorientation of the ferroelectric polarization. Microscopically, the detail of the shift of Ti ion, reflecting polarization switching behaviour, can be analyzed by X-ray absorption near-edge structure (XANES) technique. The aim of this project is to investigate the shift of Ti4+ion in PZT under the application of electric field by in-situ X-ray absorption technique. For this project, the special custom-built high voltage sample chamber installed at synchrotron XANES beam line at Synchrotron Light Research Institute, Thailand, was employed to conduct the experiment. XANES spectrum of bulk PZT was collected under the different amplitudes of an applied electric field. Ti K-edge X-ray absorption spectra were analyzed by IFEFFIT software package. The results showed that the pattern of XANES changed with the alternation of the applied field amplitude. The change of XANES spectrum was caused by the movement of Ti4+ion reflecting the change of ferroelectric polarization. From the analysis, it was found that this technique could be used to investigate the Ti4+ion shifting of PZT bulk ceramics. [ABSTRACT FROM AUTHOR]

Results of direct measurements of electrocaloric effect and polarization are mutually compared in solid solutions 0.4Na1/2Bi1/2TiO3-(0.6-x)SrTiO3-xPbTiO3. Three temperature regions are distinguished in respect of a phase transition temperature. Above the phase transition, electrocaloric effect is determined by orientation of polar nanoregions by electric field. In wide temperature regions above and below the phase transition temperature, the difference between results, obtained from direct electrocaloric effect measurements and from polarization hysteresis loops, is explained by temperature dependence of concentration of polar nanoregions, oriented by electric field. Existence of a common ΔT(P) curve for all temperatures in the ferroelectric state indicates that polarization can be treated as a parameter, which solely determines electrocaloric effect in this state. [ABSTRACT FROM AUTHOR]

Charge transport in integrated ferroelectric capacitors Pt/PZT/Pt/Ti/SiO2/Si is studied. The PZT films prepared with 15% of Pb excess by sol-gel deposition show the (111) textured polycrystalline structure. The current flowing through PZT grains is shown to be significantly larger than the current flowing along grain boundaries. Ferroelectric hysteresis loops, current-voltage dependences, short-circuited photocurrent under film illumination by light with photon energy 2.7 eV are measured. The modified method of depolarization hysteresis loops is used to indicate the absolute value of non-switchable polarization. It is shown experimentally that depolarization with compensating bias or film illumination can change the film switching behavior. [ABSTRACT FROM PUBLISHER]

The ferroelectric and photovoltaic properties of BaTiO3films at the nanoscale are considered. The switching and scaling of the coercive field in the hetero epitaxial BaTiO3films with thickness 3–50 nm are investigated in condenser. At the nanoscale there is competing of extrinsic (domain-driven) and intrinsic homogeneous (Landau-Ginzburg) mechanisms. The conversion efficiency of the Bulk Photovoltaic Effect at the nanoscale could be extremely large. It is experimentally shown for heteroepitaxial BaTiO3films with thickness 20 and 40 nm. For nanoscaled BaTiO3films the conversion efficiency is 4,5 orders of magnitude larger as compared to the bulk crystals. [ABSTRACT FROM PUBLISHER]

In this work we have studied by our theoretical approach a density and a spontaneous polarization behavior of the Ni-doped LiMO3(M˭Ta or Nb), according to the rate of Ni, the calculated values and the curves of the spontaneous polarization Ps and the density show that the mechanism of substitution of Ni in LiMO3is described by two vacancy models: the first is [Li1−5x−3yMx−yNi4yΔ4x][M]O3for %N < 3 and the second one is [Li1+5x−13yNi5y−xΔ4 (2y−x)][M1−(x−y)Ni(x−y)] O3for. [ABSTRACT FROM AUTHOR]

The strong dependence of the domain kinetics on the applied field and the thickness of the surface layers produced by proton exchange has been revealed in congruent lithium niobate. The correlated nucleation leads to formation of self-assembled structures consisting of isolated domains. Formation of the nanodomains in front of the domain wall results in its continuous motion. The pronounced self-organization effect leads to formation of broad domain boundaries and ensembles of isolated nanodomains consisting of nanodomain chains and nets. The obtained effects were attributed to highly non-equilibrium switching conditions caused by retardation of the bulk screening of depolarization field. [ABSTRACT FROM AUTHOR]

The increase and relaxation of the conduction current caused by formation of intergrown charged domain walls (CDW) during polarization reversal have been studied in stoichiometric lithium niobate. The 103-104times increase of the conduction current was revealed in the temperature range 100-200°C. The current, measured during polarization reversal, consists of the conventional switching current and the conduction current along CDW dominating for T>200°C. The model based on the complex conductivity pathway along CDW was proposed. The current data were analyzed in terms of the Kolmogorov-Avrami model taking into account the input of the CDW conductivity. [ABSTRACT FROM AUTHOR]