Search

In the present study, particular aspects of the large-signal switching properties and electromechanical hysteresis of the lead zirconate titanate (PZT)-type porous piezoceramics were studied in comparison with the dense piezoceramics of the same composition. Large-signal ferroelectric polarization and strain hysteresis loops were recorded at the bipolar electric fields in the range of 0 ÷ 5 kV/mm and in the frequency range of 0.01 ÷ 5 Hz. Measurements and analysis were performed by means of the electromechanical measurement system (STEPHV) and electromechanical response characterization program (STEP), combining large-signal modeling of the mechanical and electrical behavior of ferroelectric materials. [ABSTRACT FROM AUTHOR]

In this work, we report the preparation of BiFeO3/BiMnO3 (BFO/BMO) composite material, via the chemical substitution method, by adopting the sol-gel method. The X-ray diffraction studies confirmed the formation of two distinct phases in the prepared sample. Field emission scanning electron microscopic images revealed the two different morphologies, and the compositional studies verified the presence of the respective elements in these different grains. The dielectric constant value almost doubled in the composite sample than the single-phase BFO sample. The dielectric constant values at a frequency of 105 Hz were found to be 46 and 73 for the BFO and BFO/BMO samples, respectively. The remnant polarization value was found to reduce from 8.3 mC/cm² (for BFO) to 0.3 mC/cm² for biphasic BFO/BMO samples. [ABSTRACT FROM AUTHOR]

The dielectric constant and hysteresis loops of BaTiO3 ceramics with and without Pt implants were compared to determine the effect of the implant on the ceramic behavior. Ceramics with 90% relative density and 13.28 µm average grain size were analyzed. The results showed alterations in the ceramic's coercive field, remanent polarization, and dielectric constant with an implant. The metallic implant affected the internal structure of the BaTiO3 ceramic, which reduced the ferroelectric properties of the material. In principle, these alterations can be seen as drawbacks, but they open new applications. The results provide insights into the real impact of metallic implants on the ferroelectric properties of the samples. [ABSTRACT FROM AUTHOR]

Models of dielectric solids subject to large deformations are established by following a thermodynamic approach. The models are quite general in that they account for viscoelastic properties and allow electric and thermal conduction. A preliminary analysis is devoted to the selection of fields for the polarization and the electric field; the appropriate fields are required to comply with the balance of angular momentum and to enjoy the Euclidean invariance. Next, the thermodynamic restrictions for the constitutive equations are investigated using a wide set of variables allowing for the joint properties of viscoelastic solids, electric and heat conductors, dielectrics with memory, and hysteretic ferroelectrics. Particular attention is devoted to models for soft ferroelectrics, such as BTS ceramics. The advantage of this approach is that a few constitutive parameters provide a good fit of material behaviour. A dependence on the gradient of the electric field is also considered. The generality and the accuracy of the models are improved by means of two features. The entropy production is regarded as a constitutive property per se, while the consequences of the thermodynamic inequalities are made explicit by means of representation formulae. [ABSTRACT FROM AUTHOR]

The paper is devoted to the theoretical analysis and numerical implementation of a mathematical model of a nonlinear reaction–diffusion system on the COMSOL Multiphysics platform. The applied problem of the computer simulation of polarization switching in thin ferroelectric films is considered. The model is based on the Landau–Ginzburg–Devonshire–Khalatnikov thermodynamic approach and formalized as an initial-boundary value problem for a semilinear parabolic partial differential equation. The theoretical foundations of the model were explained. The user interface design application was developed with COMSOL Multiphysics. A series of computational experiments was performed to study the ferroelectric hysteresis and temperature dependences of polarization on the example of a ferroelectric barium titanate film. [ABSTRACT FROM AUTHOR]

Macroscopic properties of ferroelectrics are controlled by processes on the microscale, in particular the switching of crystal unit cells and the movement of domain walls, respectively. Besides these microscopic levels, the grains of a polycrystalline material constitute the mesoscopic scale. Interactions of grains with statistically distributed orientations, as a consequence of mechanical and electrostatic mismatch, give rise to for example, residual stress which in turn affects domain switching. A multiscale modeling thus has to incorporate at least three interacting scales. In this context, the condensed method has recently been elaborated as an efficient tool with low computational cost and effort of implementation. It is extended toward statistical distributions of grain sizes in a representative material volume element and amended with regard to the modeling of domain evolution. Each of the few parameters of the constitutive approach has a unique physical meaning and is adapted to available experimental values of macroscopic quantities of barium titanate taken from various sources. [ABSTRACT FROM AUTHOR]

The paper is devoted to the theoretical analysis and numerical implementation of a mathematical model of a nonlinear reaction–diffusion system on the COMSOL Multiphysics platform. The applied problem of the computer simulation of polarization switching in thin ferroelectric films is considered. The model is based on the Landau–Ginzburg–Devonshire–Khalatnikov thermodynamic approach and formalized as an initial-boundary value problem for a semilinear parabolic partial differential equation. The theoretical foundations of the model were explained. The user interface design application was developed with COMSOL Multiphysics. A series of computational experiments was performed to study the ferroelectric hysteresis and temperature dependences of polarization on the example of a ferroelectric barium titanate film.

Temperature scaling of dynamic ferroelectric hysteresis for the morphotropic phase boundary (MPB) compositions in xBiScO3–(1‐x‐y)PbZrO3–yPbTiO3 (xBS–(1‐x‐y)PZ–yPT, 0.018 ≤ x ≤ 0.264) ternary system was systematically investigated. The power‐law relation was obtained for remanent polarization Pr and temperature T, that is, Pr ∝ Tβ. It is interesting to find that the power‐law exponent β could be modulated by BiScO3 content x. With the increase of x from 0.018 to 0.264, β varies from −1.09398 to 2.44147. Transition of β from negative to positive produces in the vicinity of 0.054BS–0.476PZ–0.470PT ceramic. At this composition, the magnitude of β is very close to zero with value of only −0.01567, implying an almost temperature‐independent polarization characteristic of the ceramic. Comparing with the conventional PZT‐based piezoelectric ceramics that usually with negative exponent β, when x > 0.054, the xBS–(1‐x‐y)PZ–yPT ceramics show positive β value, so that the ferroelectric polarization is enhanced with increasing temperature. Such a positive temperature dependence of ferro‐/piezoelectric property makes the ternary system a promising candidate for high‐temperature applications. [ABSTRACT FROM AUTHOR]

[Display omitted] • Excellent Core@Shell nanostructures confirmed by TEM. • BaTiO 3 @Al 2 O 3 showing high dielectric constant ∼ 2400 with very low Tan δ ∼ 0.1. • AC conductivity behavior is satisfied with Jonscher's power law. • No frequency relaxation for BaTiO 3 @Al 2 O 3 , suitable for dielectric storage. • Confirmed P ∼ E hysteresis for BaTiO 3 @Al 2 O 3 with no dielectric relaxation. As-purchased BaTiO 3 , hydrothermally prepared BaTiO 3 , and BaTiO 3 @Al 2 O 3 core@shell nanostructures through heteronucleation method were confirmed for structure/microstructure through XRD/ FESEM/HRTEM. High static dielectric constant of 2450 is obtained for BaTiO 3 @Al 2 O 3 with a very low loss tangent (Tanδ ∼ 0.1), due to the outer thick insulating Al 2 O 3 layer over BaTiO 3. Jonscher's law and Modulus spectra show a non-Debye type broad relaxation obeying a modified KWW function for BaTiO 3 , with no relaxation for BaTiO 3 @Al 2 O 3 , due to the suppression of dipoles by Al 2 O 3. Higher dielectric field strength of ≥ 20 kV/cm was observed for BaTiO 3 @Al 2 O 3 through the ferroelectric hysteresis loops. [ABSTRACT FROM AUTHOR]

The presence of a spontaneous and switchable polarization is the defining property of a ferroelectric material. Such materials are indispensable in a countless number of industrial and scientific applications. Furthermore, the enhancement of ferroelectric property at reduced dimensions is crucial for continuous advancement in nanoelectronic applications. In this work, we investigate the onset of out-of-plane ferroelectricity in open-circuited stress-free BaTiO 3 ultrathin films by performing molecular dynamics simulations using the core–shell model potential. In doing so, we try to obtain electric polarization hysteresis loops using an appropriate range of external electric loading. It is found that out-of-plane ferroelectricity is suppressed in ultrathin films with thickness 10 or less than 10 unit cells, indicating that there exists a critical thickness for the emergence of out-of-plane ferroelectricity in ultrathin films. It is also found that the ultrathin films exhibit asymmetrical hysteresis loops slightly above the critical thickness. [ABSTRACT FROM AUTHOR]

Lead metaniobate (PbNb 2 O 6 or PNO) belongs to the tetragonal tungsten bronze (TTB) family. There are three polymorphic forms of PNO: tetragonal (stable at high temperature), rhombohedral (stable at room temperature), and the metastable orthorhombic phase, which has ferroelectric properties. The metastable orthorhombic phase is formed by quenching from the high temperature tetragonal phase due to the reconstructive/sluggish tetragonal to rhombohedral phase transition. A suitable ionic substitution can also lead to the stable ferroelectric orthorhombic phase. Stabilization of the ferroelectric orthorhombic phase by ionic substitution, and the formation of ferroelectric relaxors with increased amounts of dopants is hereby reported for the compositions Pb (1-x) Bi (x/2 K (x/2) Nb 2 O 6 and Pb (1-x) Bi (x/2) Na (x/2) Nb 2 O 6. The solid solutions of PNO showed evidence of linked dielectric relaxation and ferroelectricity, validating the distinctive ferroelectric relaxor behaviour for the compositions Pb 0.6 Bi 0.2 K 0.2 Nb 2 O 6 and Pb 0.6 Bi 0.2 Na 0.2 Nb 2 O 6. As the concentrations of bismuth (Bi) and potassium/sodium (K/Na) dopants increased, the Curie temperature (Tc), or the temperature corresponding to the maximum dielectric permittivity (T m), dropped. By using the Uchino-Nomura relation as a modification of the Curie-Weiss law, it was established that the Pb 0.6 Bi 0.2 K 0.2 Nb 2 O 6 solid solution exhibit higher degree of diffuseness than Pb 0.6 Bi 0.2 Na 0.2 Nb 2 O 6 at the transitions. The width of the ferroelectric hysteresis loop increased as the percentage of dopants increased, from x = 0.1 to x = 0.3. At x = 0.4, a narrow ferroelectric hysteresis loop and a frequency-dependent Tm abruptly formed, which is indicative of a ferroelectric relaxor. [Display omitted] • Relaxor behavior of Bi and K/Na substituted solid solutions of PbNbO 6 was investigated. • The metastable ferroelectric orthorhombic phase of PbNbO 6 was stabilized by doping. • Characteristic relaxor behavior was evident for Pb 0.6 Bi 0.2 K 0.2 Nb 2 O 6 and Pb 0.6 Bi 0.2 Na 0.2 Nb 2 O 6. [ABSTRACT FROM AUTHOR]

Silicon semiconductor-insulator-semiconductor (SIS) structures with high-k dielectrics are a promising new material for photonic and CMOS integrations. The “diode-like” currents through the symmetric atomic layer deposited (ALD) HfO2/Al2O3/HfO2… nanolayers with a highest rectification coefficient 103 are observed and explained by the asymmetry of the upper and lower heterointerfaces formed by bonding and ALD processes. As a result, different spatial charge regions (SCRs) are formed on both insulator sides. The lowest leakages are observed through the stacks, with total Al2O3 thickness values of 8–10 nm, which also provide a diffusive barrier for hydrogen. The dominant mechanism of electron transport through the built-in insulator at the weak field E < 1 MV/cm is thermionic emission. The Poole-Frenkel (PF) mechanism of emission from traps dominates at larger E values. The charge carriers mobility 100–120 cm2/(V s) and interface states (IFS) density 1.2 × 1011 cm−2 are obtained for the n-p SIS structures with insulator HfO2:Al2O3 (10:1) after rapid thermal annealing (RTA) at 800 °C. The drain current hysteresis of pseudo-metal-oxide-semiconductor field effect transistor (MOSFET) with the memory window 1.2–1.3 V at the gate voltage |Vg| < ±2.5 V is maintained in the RTA treatment at T = 800–900 °C for these transistors.

By using a second-order time-dependent Ginzburg--Landau model, we simulate the polarization hysteresis behavior of a ferroelectric system subjected to a sinusoidal electric field. We examine polarization hysteresis loop structure as a function of both field amplitude and field frequency. Departing from previous work, the relationship between these field parameters and loop structure is quantified by considering the Fourier transform spectra of the time series of polarization. These spectra are used to determine deforming factors that measure the amplitude- and frequency-dependent distortions of hysteresis loop structures from ellipticity. Our results agree with experimental observations, thus validating the model. [ABSTRACT FROM AUTHOR]

With the motivation of realizing the high performance graphene-based nonvolatile memory devices, we fabricate and characterize reliable and robust ferroelectric field-effect transistor (FFETs), which are composed of single-layer graphene (SLG) and lead-zirconate-titanate (PZT). After completing all of the fabrication steps, the samples are annealed in vacuum to improve the device characteristics. Through systematic analyses, we investigate an optimal vacuum-annealing condition for improving the memory characteristics of the device. At annealing temperatures at 250–300 °C, both the electrical conduction properties of the SLG channel and the capacitive-coupling abilities of the SLG/PZT/Pt stack are dramatically improved because of the elimination of chemical residues and/or molecular oxygens. Consequently, the vacuum-annealed SLG-PZT FFET displays a great improvement of data retention (∼72% after 10 year) and a large memory window (∼4.1 V). We believe the present study can provide alternative avenues for exploring unprecedented graphene-based memory structures. [ABSTRACT FROM AUTHOR]

(100-x) BaTiO3(BT)-(x) CoFe2O4(CFO) (X = 10, 20 and 30 wt%) composites were prepared through conventional solid state reaction method by mixing two individual phases by weight. Structure and surface morphology of the composites were observed using X-ray diffraction and Scanning electron microscopy respectively. Polarization study of the BT-CFO composites was done by measuring the polarization (P) against the electric field (E) up to 30 KV/cm, pattern observed showed good ferroelectric behaviour with Pmax= 4.10 µC/cm2for BT-CFO/90-10. In order to estimate the effect of magnetic phase on ferroelectric nature of BT, dielectric and magnetoelectric measurements were also done on the composites and are presented here. [ABSTRACT FROM PUBLISHER]

Piezoelectric lead zirconate titanate (PZT) ceramic-cement composites using a high volume of ceramic content (80%) in 0–3 connectivity were fabricated. Piezoelectric Force Microscope (PFM) characterization was carried out and ferroelectric hysteresis behavior of the composites were investigated. Domain configurations of PZT ceramic can be seen at the interfacial zone of PZT-cement composites. Ceramic particles were seen to bind well with the cement matrix. The ferroelectric hysteresis loop at 50 Hz and 10–25 kV/cm showed a slim loop with low loss behavior for this type of composite due to increase in the PZT ceramic in 0-3 PZT-cement composites. [ABSTRACT FROM AUTHOR]

In this study we take the view that frequency dependence of ferroelectric hysteresis is a result of direct competition between the speed of polarization evolution and the speed of external loading. We used the Ginzburg–Landau kinetic equation to evaluate the evolution of polarization vectors. We also devised a polycrystal model with a core–shell grain configuration to reflect the effect of the grain-boundary (GB) affected zone. The phase-field results showed that the coercive field tended to increase with frequency, but remnant polarization increased only slightly while the dielectric constant and piezoelectric constant d 33 , tended to decrease. We also found that, while both hysteresis and butterfly loops exhibited the familiar sharp tails at low frequencies, the tails disappeared and the loops became elliptic- and kidney-shaped, respectively, at high frequencies. The calculated low-frequency phenomena are widely supported by experiments, but the high-frequency ones are not commonly found in the literature. We substantiated both types of findings with details of the underlying domain dynamics. They clearly showed a complete 180° polarization reversal at low frequencies, but stopped mostly at 90° at high frequencies. We also examined the influence of the kinetic coefficient and the loading amplitude, and found that, as either increases, the elliptic and kidney shapes of the loops would occur at a higher frequency. The calculated grain-size effects indicated that the remnant polarization, dielectric constant, and d 33 all decreased with decreasing grain size. This is again widely supported by experiments. But we also found that the grain-size effect of coercive field is more complicated. It may increase or decrease, and it is the magnitude of spontaneous polarization of the GB affected zone that determines its outcome. [ABSTRACT FROM AUTHOR]

An electro-mechanically coupled phase field model for ferroelectric domain evolution is introduced. Based on Gurtin's concept of a microforce balance, a generalized Ginzburg-Landau evolution equation is derived from the second law of thermodynamics. The thermodynamic potential is formulated for transversely isotropic material behavior by adopting a coordinateinvariant formulation. The model is reduced to 2D and implemented into a finite element framework. The numerical simulations concern the microstructure evolution in mechanically clamped BaTiO3 single-crystals. In the second part of this contribution Keip et al. [1], the poling behavior of ferroelectric composites and polycrystals is investigated with regard to size effects and the influence of a discontinuous order parameter field across grain boundaries. (© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]

Molecular dynamics (MD) simulations of ferroelectric materials have improved tremendously over the last few decades. Specifically, the core-shell model has been commonly used for the simulation of ferroelectric materials such as barium titanate. However, due to the computational costs of MD, the calculation of ferroelectric hysteresis behaviour, and especially the stress-strain relation, has been a computationally intense task. In this work a molecular statics algorithm, similar to a finite element method for nonlinear trusses, has been implemented. From this, an algorithm to calculate the stress dependent continuum deformation of a discrete particle system, such as a ferroelectric crystal, has been devised. Molecular statics algorithms for the atomistic simulation of ferroelectric materials have been previously described. However, in contrast to the prior literature the algorithm proposed in this work is also capable of effectively computing the macroscopic ferroelectric butterfly hysteresis behaviour. Therefore the advocated algorithm is able to calculate the piezoelectric effect as well as the converse piezoelectric effect simultaneously on atomistic and continuum length scales. Barium titanate has been simulated using the core-shell model to validate the developed algorithm. [ABSTRACT FROM AUTHOR]

In this study, compositions in the 0.2Pb(Zn1/3Nb2/3)O3-0.8Pb(Zr1/2Ti1/2)O3 based systems will be developed based on the material engineering approach (processing vs. electrical properties). This work involves the fabrication of high purity PZN-PZT based in ceramic forms, and a study of La2O3 addition on phase formation, microstructures and electrical properties was investigated which are especially important from the viewpoint of the development of practical piezoelectric materials. The effect of La2O3 addition was characterized on microstructure and electrical properties of PZN-PZT. Amounts of 0.05-1 wt% La2O3 were doped on 0.2PZN-0.8PZT. All compositions of powders were uniaxially pressed in pellets and sintered at the temperature 1250°C with dwell time 2 h. Phase and microstructure development, dielectric and ferroelectric properties of ceramics were characterized by XRD, SEM, LCR meter and Modified Sawyer-Tower Circuit respectively. In addition, the values of permittivity maximum and the temperature of permittivity maximum were substantially decreased by La-doping and these results show increased Pr, Ps and strain level but decreased Ec. [ABSTRACT FROM AUTHOR]

In this study, compositions in the 0.2Pb(Zn1/3Nb2/3)O3-0.8Pb(Zr1/2Ti1/2)O3based systems will be developed based on the material engineering approach (processing vs. electrical properties). This work involves the fabrication of high purity PZN-PZT based in ceramic forms, and a study of La2O3addition on phase formation, microstructures and electrical properties was investigated which are especially important from the viewpoint of the development of practical piezoelectric materials. The effect of La2O3addition was characterized on microstructure and electrical properties of PZN-PZT. Amounts of 0.05–1 wt% La2O3were doped on 0.2PZN-0.8PZT. All compositions of powders were uniaxially pressed in pellets and sintered at the temperature 1250°C with dwell time 2 h. Phase and microstructure development, dielectric and ferroelectric properties of ceramics were characterized by XRD, SEM, LCR meter and Modified Sawyer–Tower Circuit respectively. In addition, the values of permittivity maximum and the temperature of permittivity maximum were substantially decreased by La-doping and these results show increased Pr, Psand strain level but decreased Ec. [ABSTRACT FROM PUBLISHER]

The dielectric response in Bi4Ti3O12single crystals was studied at subswitching conditions at relative low temperatures (20–250°C) and frequencies (100 mHz to 10 kHz) both in-plane and out-of-plane. Electron-holes are likely to be the major charge carriers in both orientations although oxygen vacancies contribute as well. This scenario is supported by ferroelectric hysteresis loop measurements in both directions, showing aging in the c-axis direction but not in the a-direction. The absorption of blue laser light (3 eV) above approximately 150°C confirmed the main role of electron-hole carriers in conductivity at low temperatures. [ABSTRACT FROM AUTHOR]

Ferroelectric materials, such as lead zirconate titanate, lanthanum-doped lead zirconate titanate, and BaTiO3, are being considered, or are already being employed, for a large number of applications including nanopositioning, high-speed valves for fuel injectors, ultrasonic transducers, high-speed camera shutters and autofocusing mechanisms, energy harvesting, and pico air vehicle design. Their advantages include nanometer positioning resolution, broadband frequency responses, moderate power requirements, the capability for miniaturization, and complementary actuator and sensor capabilities. However, they also exhibit creep, rate-dependent hysteresis, and constitutive nonlinearities at essentially all drive levels due to their noncentrosymmetric nature. In this article, we model the hysteretic dependence of strains and polarizations on input fields and stresses using the homogenized energy model framework. At the domain level, the minimization of the Gibbs energy densities yields linear constitutive relations. Nonlinearities and hysteresis due to dipole switching are modeled at the grain level using the Boltzmann theory to specify the evolution of dipole fractions that serve as internal variables. In the final step of the development, stochastic homogenization, based on the assumption that interaction fields and driving forces are manifestations of underlying densities, is used to construct nonlinear constitutive relations for the bulk material. It is demonstrated that these relations are amenable to subsequent development of distributed system models. The article includes significant discussion regarding the mechanisms that produce hysteresis in ferroelectric materials. The capability of the framework for characterizing various hysteretic phenomena, including creep and various rate dependencies, is illustrated by validation with lead zirconate titanate and lanthanum-doped lead zirconate titanate data. [ABSTRACT FROM AUTHOR]

Abstract: For various piezoceramic actuator applications, the active materials are exposed to mechanical bias stresses. Such mechanical loading strongly modifies the hysteretic transfer characteristic of the actuators. An appropriate approach to model the hysteretic characteristic is based on the Preisach operator. However, the classical Preisach model is incapable of reflecting the influence of mechanical loading. The scope of the present study is, thus, the development of a generalized Preisach model incorporating the impact of compressive stress. To accomplish this goal, the effects of stress and mechanical creep on the polarization hysteresis are characterized by means of measurements. For our model, we take advantage of an analytic Preisach distribution function, introduced in our recent work. This function is extended to a formulation incorporating uniaxial compressive bias stress. As the results clearly demonstrate, the utilized distribution function is very promising to be further extended with respect to mechanical creep behavior. [Copyright &y& Elsevier]

Abstract: The glasses with composition (50−X)PbO–XSrO-25TiO2-25B2O3 (where X=0, 5, 10 and 15mol%) were prepared using conventional quenching technique. The T g, T c, density and CTE of the glass samples were measured. The T g observed to increase with increasing concentration of SrO, while the T c first decreased and then increased. The glass samples were converted to glass ceramics by following two stage heat treatment schedule. The glass ceramic samples were characterized by XRD, SEM and dielectric measurements. The XRD results revealed the formation of ferroelectric lead titanate as a major crystalline phase in glass ceramics. Additional phases observed include Sr2B2O5 and PbB2O4. The room temperature (RT) dielectric constant of glass and glass ceramics are in the range of 100–120 which is promising for capacitor application. [Copyright &y& Elsevier]

Abstract: In various ferroelectric actuator applications, the active material is exposed to mechanical prestress. This is often caused by unintended clamping, such as for smart materials with embedded ferroelectric components. In other cases, the stress is applied on purpose to enhance the transducer performance or to prevent from tensile forces. Hence, the development of models, describing the transducer behavior under combined, electro-mechanical loading conditions is essential. In our previous work, we proposed an analytic weight function for the scalar Preisach hysteresis oper- ator. The model was further enhanced to describe the dynamic material behavior of piezoceramic actuators. Here, we address the influence of uniaxial mechanical prestress on the polarization hysteresis by conducting measurements on lead zirconate titanate samples. A parameter study is performed to investigate, how the weight function can be extended to a formulation incorporating prestress. The resulting simulations coincide very well with measurements. [Copyright &y& Elsevier]

To study the fundamental essence of core losses and to achieve an accurate core loss separation formula, a dynamic finite-element model for the nonlinear hysteresis loop of laminations has been established. In the model, Maxwell's equations are solved for the hysteresis character in the magnetic lamination, using the Galerkin finite-element method, where the hysteresis is represented by an energetic hysteresis model. Based on the simulation results, the magnetic characteristics, skin effect, time delay, and magnetic field distribution are discussed. Then, core losses, particularly excess losses, affected by the magnetic characteristics are carefully examined. It is concluded that excess current loss formula is only applicable for the cases where skin effect is negligible and the sum of hysteresis losses and eddy current losses can more generally represent total losses. [ABSTRACT FROM AUTHOR]

Abstract: Piezoelectric composites made from lead zirconate–titanate ceramic and cement have recently been developed as sensors in smart concrete structures due to their compatibility with the host concrete structure. However there is difficulty in poling the composite due to the insulating nature of the cement phase. In this work, carbon powder was used as a conducting phase in the composites at up to 2.0% by volume. The ferroelectric properties of the composites were investigated. For the same electric field, composites with added carbon were found to have higher polarization values. Therefore, this suggests that carbon could be added as a conducting phase to lead zirconate–titanate ceramic–cement composites in order to improve their polarization. [Copyright &y& Elsevier]

Abstract: A simple and effective method of solid state reaction followed by quenching process is used to prepare multiferroic Er3+ and La3+ doped BiFeO3 ceramics. X-ray diffraction patterns indicated that these ceramics were of single-phase perovskite structure. Doping with La enhanced the dielectric, ferroelectric and ferromagnetic properties of BiFeO3. A-site substitution with the La and Er ions has been found to suppress the spiral spin structure of BiFeO3 giving rise to the appearance of room-temperature weak ferromagnetism. The enhanced multiferroic properties are attributed to the enhanced magnetoelectric interaction, which results from the La and Er substitution-induced destruction of the spin cycloid. [Copyright &y& Elsevier]

Lead magnesium niobate titanate (PMN-PT)-Portland cement (PC) composites were produced. PMN- PT amount used in this work were 30, 50, and 70% by volume. The effects of PMN-PT content (using 30%, 50%, 70% PMN-PT) and stress on the ferroelectric polarization-electric field (P-E) hysteresis of the composites are reported in this present work. From the results, it was found that there was an increase in the instantaneous remnant polarization (Pir) when PMN- PT amount increased while Pir was found to decrease when the stress was increased from 0 to 57 MPa. [ABSTRACT FROM AUTHOR]

Lead magnesium niobate titanate (PMNT)-Portland cement (PC) composites were produced. PMNT amount used in this work was 50% by volume. The ferroelectric (P-E) hysteresis behaviors were investigated as function of both frequency and electric field for all composites. From the results, it was found that there was an increase in both the instantaneous remnant polarization (Pir) and coercive field (Eic) when the applied field increased from 5 kV/cm to 20 kV/cm, Pir was found to increase from 1.5 to 9.8 μC/cm2 and Eic waas found to increase from 3.4 to 13.8 kV/cm. On the other hand, Pir and Eic were found to reduce from 11.1 to 8.8 μC/cm2 and from 10.8 to 15.3 kV/cm respectively, when the frequency was increased from 30-90 Hz; ascribed to the delayed response of the polarization reversal to the varying external field. [ABSTRACT FROM AUTHOR]

For the numerical simulation of non-linear piezoelectric material behavior, we use a constitutive relation that is based on a decomposition of the physical quantities dielectric displacement and mechanical strain into a reversible and an irreversible part. Therein, we set the irreversible part of the dielectric displacement equal to the irreversible electric polarization and express the irreversible mechanical strain by a polynomial ansatz of the irreversible electric polarization. The reversible parts of mechanical strain and dielectric displacement are further described by the linear piezoelectric constitutive law. We apply a Preisach hysteresis operator to compute the irreversible polarization from the history of the driving electric field. Furthermore, the entries of the piezoelectric modulus tensor are assumed to be functions of the electric polarization. To efficiently solve the non-linear system of partial differential equations, we have developed a quasi-Newton scheme and use the finite element (FE) method for the numerical solution. This FE scheme has been applied to numerically calculate the dynamic behavior of a piezoelectric disc and a stack actuator. The obtained results compare well to measured data. [ABSTRACT FROM AUTHOR]

Abstract: Polycrystalline ceramics of 1− x[Na0.5Bi0.5TiO3]− x[BiFeO3] (NBT–BFO) were synthesized by the modified Pechini''s method to study their magnetic and magnetoelectric properties. A series of solid solutions exhibiting magnetoelectric output were formed when two iso-structural compounds Na0.5Bi0.5TiO3 (NBT) and BiFeO3 (BFO) were combined. Polarization-electric field hysteresis loops revealed that the maximum polarization (∼23μC/cm2 for x =0.1) decreased continuously with the increase of BFO content, following a hard doped effect. Piezoelectric charge coefficient (d 33)=41pC/N was obtained for the ceramics with x =0.1 and the value continues to decrease with the composition. Magnetic hysteresis loops represent the canted antiferromagnetic nature for x ≤0.6 and ferromagnetic-like behavior for the BFO-rich compositions. Magnetoelectric coupling was determined by measuring the magnetoelectric voltage coefficient which is ∼12.4mV/cm-Oe at an ac magnetic field of 10Oe (1kHz), for x =0.1 sample. [Copyright &y& Elsevier]

Abstract: The ferroelectric, magnetic and magnetoelectric properties of (x) NiFe2O4 [NFO]+(1−x) Pb0.93La0.07(Zr0.60Ti0.40)O3 [PLZT] composites, where (x=0, 0.15, 0.30, 0.45, and 1) synthesized using double sintering ceramic method were studied. Structural analysis of these composites using X-ray diffraction (XRD) techniques confirms presence of both the phases in the composite without any impurity or intermediate phase. The scanning electron microscopy (SEM) images recorded in backscattered mode was used to study the microstructure and investigate connectivity scheme in composites. Observation of well saturated ferroelectric hysteresis loops for PLZT phase and their composites, and magnetic hysteresis loops for NFO and composites samples confirms the ferroelectric and magnetic nature of the samples. The magnetoelectric (ME) coefficient (dE/dH) was noted as a function of dc magnetic field for two different orientations viz. transverse and longitudinal and different content of magnetostrictive–piezoelectric phases. Maximum value of static ME voltage coefficient obtained for transverse orientation was 8.9mV/cm∗Oe in 15% NFO+85%PLZT bulk composites. [Copyright &y& Elsevier]

Lead zirconate titanate (PZT)-cement composites of 0-3 connectivity were produced and the effects of the frequency and electric field on the ferroelectric polarization-electric field (P-E) hysteresis of the composites were investigated. It was found that there was an increase in both the instantaneous remnant polarization (Pir) and coercive field (Eic) when the applied field increased. The instantaneous remnant polarization (Pir) was found to reduce when the frequency was increased. The ferroelectric hysteresis loops only existed when the composites were subjected to lower frequency; i.e. at 20 and 40 Hz. At higher frequency, the loops tended to stretch out, showing more of a lossy characteristic. [ABSTRACT FROM AUTHOR]

Lead Zirconate Titanate (PZT)-cement composites of 0-3 connectivity were produced and the effects of PZT particle size and PZT content on the ferroelectric hysteresis behavior were investigated. It is clear from the hysteresis measurements that the particle size has a strong influence on the polarization-electric field loop of composites with smaller particle sizes of 75 μm and 212 μm the loops were found to exhibit a lossy characteristic. At 425 μm particle size, the composite exhibits a more typical ferroelectric hysteresis loop. There is also a significant increase in the remnant polarization with increasing particle size where the composite of 425 μm was found to have a significantly higher instantaneous remnant polarization (Pir) in comparison to the composites with smaller particle sizes. Furthermore, Pir was found to increase as PZT volume increases from 40-60%, while coercive field (Eic) decreased and reached a saturated value when PZT volume content is 60%. [ABSTRACT FROM AUTHOR]