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Lead iron niobate, Pb(Fe0.5Nb0.5)O3 (PFN), belongs to the family of multiferroic materials combining ferroelectric and antiferromagnetic ordering. Its properties to a large extent depend on the synthesis conditions. For applications it is important to obtain materials with large polarization and low electric leakage. In this paper we investigate the effect of processing parameters on the structural, electrical and magnetic behaviour of PFN ceramics prepared by the solid state method. The optimal calcination and sintering temperatures are found, which enable us to obtain ceramics with a large polarization Pmax = 28 μC/cm2 and dielectric permittivity eMax ≈ 55 000. We also find that increasing the calcination and sintering temperatures decreases diffuseness of the ferroelectric phase transition and shifts the Neel temperature to lower values, which might be due to a change of the distribution of Fe3+ and Nb5+ across the B-sites of the perovskite towards a more ordered structure.

Isolated nonmagnetic substitutional defect ions experience huge coupled electric magnetic interaction in the single-phase multiferroic BiFeO3. In the ferroelectric state above the magnetic Néel temperature TN, the electric environment generates a single symmetric electric field gradient (EFG) parallel to the electric polarization direction. Below TN, a distinct magnetic interaction arises, monitored by the probe nuclei via their magnetic moment. Two magnetic environments arise, given by the relative angle of the local magnetic moment within its easy magnetic plane with respect to the EFG orientation. The angle between field gradient orientation and magnetic field direction is the most stable fitting parameter. The magnetic interaction concomitantly increases the EFG dramatically which reflects an outstandingly large local magnetoelectric coupling. In the set of best fits, two different electric environments form concurrently with two distinctly different local magnetic fields. The magnetic ordering in BiFeO3 thus completely distorts the electric environment of the nonmagnetic probe nucleus. The implications for the local effect of dopants in BiFeO3 are discussed. A third probe environment arising independent of temperature is identified and associated with an iron vacancy., Physical Review B, 105 (9), ISSN:1098-0121, ISSN:0163-1829, ISSN:1550-235X, ISSN:0556-2805, ISSN:2469-9969, ISSN:1095-3795, ISSN:2469-9950

Composites of electroactive polymers and ferroelectric nanoparticles are promising for energy storage and electrocaloric applications. In this paper we report on synthesis and electrocaloric properties of P(VDF-TrFE-CFE)/ BaZr0.20Ti0.80O3 nanocomposites. BaZr0.20Ti0.80O3 (BZT) nanoparticles were synthesized via the hydrothermal route. The P(VDF-TrFE-CFE)/BZT composite films with varying amount (1.25 vol.% to 5 vol.%) of the nanoparticles were prepared by the solution casting method. The nanocomposite films showed a significant increase in the dielectric permittivity with the amount of nanoparticles. An increase in the polarization as well as in hysteresis losses with the amount of nanoparticles was observed. The direct electrocaloric effect was measured using a custom built quasi-adiabatic calorimeter. The P(VDF-TrFE-CFE)/BZT nanocomposite film with 5 vol.% BZT showed an electrocaloric temperature change of ~ 1.8 K at room temperature and an electric field of 50 MV/m, which is comparable to literature values.

The electrocaloric effect (ECE) in dielectrics is characterized by the isothermal entropy change ΔS and adiabatic temperature change ΔT induced by changes of external electric fields. The Maxwell relation, which relates changes of polarization P with temperature T (pyroelectric coefficient) under a fixed electric field E to ΔS for finite intervals in E, provides a convenient way to deduce the ECE from polarization data P(T, E). Hence, this method, known as the indirect method, is widely used in ECE studies in ferroelectrics. Here, we first present the thermodynamic consideration for the Maxwell relation. We then use the indirect method and P(T, E) from bipolar and unipolar polarization curves to deduce the ECE in the normal ferroelectric phase of a P(VDF-TrFE) copolymer. The deduced ECE using the P(T, E) from bipolar polarization curves exhibits a giant negative ECE. In contrast, the directly measured ECE in the same polymer shows the weak and normal ECE. We discuss the constraints of the indirect method and its relation to the polarization–electric field curves measured in practical ferroelectric materials.

We report on temperature-dependent studies of ultrasonic and dielectric properties of (x)0.5(Ba0.7Ca0.3)Ti03–0.5Ba(Ti0.8Zr0.2)O3(BCZT)/(1 − x)NiFe2O4 (BCZT/NFO) composite multiferroics and their relationship to the magnetoelectric (ME) effect in these materials. The most decisive factor in the maximization of the ME effect is the strong elastic softening of the BCZT phase at the phase transition between its ferroelectric phases with orthorhombic and tetragonal symmetry. The proximity of this phase transition to room temperature makes the system promising for practical applications of the ME effect. The magnetostrictive phase does not play any direct role in the determination of the ME temperature dependence because of its weakly temperature-dependent mechanical properties.

We consider a model of a nanocomposite based on non-interacting spherical single-domain ferroelectric nanoparticles of various sizes embedded in a dielectric matrix. The size distribution function of these nanoparticles is selected as a part of the Gaussian distribution from minimum to maximum radius (truncated normal distribution). For such nanocomposites, we calculate the dependences of the reversible part of the electric polarization, the electrocaloric temperature change, and the dielectric permittivity on the external electric field, which have the characteristic form of hysteresis loops. We then analyze the change in the shape of the hysteresis loops relative to the particle size distribution parameters. We demonstrate that for the same mean-square dispersion, the remanent polarization, coercive field, dielectric permittivity maximums, maximums and minimums of the electrocaloric temperature change depend most strongly on the most probable radius, moderately depend on the dispersion, and have the weakest dependency on the nanoparticle maximum radius. We calculated and analyzed the dependences of pyroelectric figures of merit on the average radius of the nanoparticles in the composite. The dependences confirm the presence of a phase transition induced by the size of the nanoparticles, which is characterized by the presence of a maxima near the critical average radius of the particles, the value of which increases with increasing dispersion of the distribution function., 25 pages, including 8 figures

The study of the electrocaloric effect in ensembles of ferroelectric nanoparticles is of significant interest for fundamental research and its practical applications in solidstate coolers. The exploration of electrocaloric cooling is of great importance to finding solutions to environmental and energyefficiency issues in currently available refrigeration technologies. In this work we calculated the polarization, electrocaloric temperature change, and dielectric permittivity of the nanocomposite containing non-interacting ferroelectric nanoparticles with different size distributions, and analyzed the dependences of polarization, dielectric permittivity and electrocaloric temperature change on the distribution function of the particles sizes. As anticipated, the properties of the nanocomposite approach that of the average size nanoparticles with a narrowing in the dispersion of particles sizes within the nanocomposite.

Studying multiferroic magnetoelectrics has been a focus field for the last decade and a half, and the exploration of new materials is one of the several aspects of this quest. Here we report on the synthesis and characterization of NiFe2O4-based multiferroic composites which employ (Ba,Ca)(Zr,Ti)O3 as the ferroelectric/piezoelectric component and NiFe2O4 as the magnetostrictive phase. We find that these composites show excellent magnetoelectric properties. Especially the composite with 30 vol% of NiFe2O4 has a converse ME coefficient approximately two times larger than the previously reported one for BaTiO3-CoFe2O4 composites. A relationship between the phase connectivity within these composites and the ME properties was explored by the time of flight secondary ion mass microscopy. We believe that our investigation will be helpful for the design of magnetoelectric materials as components of sensors and memory devices.

Solid-state refrigeration using the electrocaloric effect (ECE) in ferroelectric materials is a promising alternative to the conventional vapor-compression technology. In spite of growing interest to the investigation of the ECE, direct measurements of the effect are still rare. In this paper, we report on a modification of a differential scanning calorimeter for direct ECE measurements. The importance of proper estimation of the thermal correction factor and use of proper values of the heat capacitance for correct ECE measurements is discussed. The ECE measurements were performed for Ba(Zr0.2Ti0.8)O3 and Ba(Zr0.12Ti0.88)O3 bulk ceramics. Large electrocaloric temperature changes of 0.54 and 0.34 K are achieved under the application of an electric field of 2 kV/mm for the Ba(Zr0.12Ti0.88)O3 and Ba(Zr0.2Ti0.8)O3 samples, respectively. The relation between the directly measured ECE values and frequently used indirect estimation based on Maxwell's relations is discussed.

In this paper, we report on studies of the electrocaloric (EC) effect in lead-free (1−x)Ba(Zr0.2Ti0.8)O3–x(Ba0.7Ca0.3)TiO3 ceramics with compositions range between 0.32 ≤ x ≤ 0.45. The EC effect was measured directly using a modified differential scanning calorimeter. The maximum EC temperature change, ΔTdirect = 0.33 K under an electric field of 2 kV/mm, was observed for the composition with x = 0.32 at ~63°C. We found that the EC effect peaks not only around the Curie temperature but also at the transition between the ferroelectric phases with different symmetries. A strong discrepancy observed between the results of the direct measurements and indirect estimations points out that using Maxwell's equations is invalid for the thermodynamic nonequilibrium conditions that accompany only partial (incomplete) poling of ceramics. We also observe a nonlinearity of the EC effect above the Curie temperature and in the temperature range corresponding to the tetragonal ferroelectric phase.

Using Landau-Ginzburg-Devonshire theory and effective medium approximation, we analytically calculate typical dependences of the pyroelectric and electrocaloric coefficients on external electric field, temperature and radius for spherical single-domain ferroelectric nanoparticles. The considered physical model corresponds to the nanocomposite with small fraction of ferroelectric nanoparticles. Within the framework of the analytical model we establish how the size changes determine the temperature and field behavior pyroelectric and electrocaloric coefficients on example of BaTiO3 nanoparticles covered by a semiconducting shell and placed in a dielectric polymer. We show that by changing the particle size one can induce maxima of the pyroelectric coefficient and electrocaloric temperature variation, control their width, height and sign. Obtained analytical expressions allow selecting the interval of particle sizes, voltage, and/or temperature for which pyroelectric energy conversion and electrocaloric coefficient are optimal for applications. The observed size effect opens the possibility to control pyroelectric and electrocaloric properties of ferroelectric nanocomposites that can be important for their advanced applications in energy convertors and cooling systems., Comment: 28 pages, 9 figures, 2 tables, 4 appendixes

The occurrence of the inverse (or negative) electrocaloric effect, where the isothermal application of an electric field leads to an increase in entropy and the removal of the field decreases the entropy of the system under consideration, is discussed and analyzed. Inverse electrocaloric effects have been reported to occur in several cases, for example, at transitions between ferroelectric phases with different polarization directions, in materials with certain polar defect configurations, and in antiferroelectrics. This counterintuitive relationship between entropy and applied field is intriguing and thus of general scientific interest. The combined application of normal and inverse effects has also been suggested as a means to achieve larger temperature differences between hot and cold reservoirs in future cooling devices. A good general understanding and the possibility to engineer inverse caloric effects in terms of temperature spans, required fields, and operating temperatures are thus of fundamental as well as technological importance. Here, the known cases of inverse electrocaloric effects are reviewed, their physical origins are discussed, and the different cases are compared to identify common aspects as well as potential differences. In all cases the inverse electrocaloric effect is related to the presence of competing phases or states that are close in energy and can easily be transformed with the applied field., Energy Technology, 6 (8), ISSN:2194-4296, ISSN:2194-4288

In this work, pyroelectric properties of composite films on the basis of poly(vinylidene fluoride-trifluoroethylene) copolymer with a various level of ferroelectric ceramics inclusions of barium lead zirconate titanate solid solution were investigated by the dynamic method. The composite films were prepared by the solvent cast method. The unusual spike-like dynamic response with a quasi-stationary component was observed. It is supposed that composite films may be effectively used for pyroelectric applications.

We report on the effect of an applied static magnetic field on the dielectric properties of ferroelectric relaxor/ferrimagnetic composites consisting of [Ba(Sn0.3Ti0.7)O3]0.8–[CoFe2O4]0.2 (BST0.8–CFO0.2). The pure Ba(Sn0.3Ti0.7)O3 (BST30) as well as the composites, were synthesized by solid state reaction method. The X-ray diffraction analysis confirmed that BST30 and CFO coexist in the composite without any secondary phase. The real and the imaginary part of the dielectric permittivity were studied as a function of temperature, with and without static magnetic field, respectively. Relaxor characteristics such as dielectric permittivity and its peak temperature are observed to vary with the magnetic field. This is explained in the context that the applied magnetic field creates magnetostriction in the ferrite phase which is transferred to the relaxor phase via the interface coupling. The strain in the relaxor phase results in the reorientation of local polarization entities, polar nano regions (PNRs), which alters the dielectric characteristics of the sample. This effect is explained in relation to local order parameter q(T) which is found to increase in a certain temperature range above the typical ferroelectric temperature regime with the application of magnetic field.

For advanced applications in modern industry, it is very important to reduce the volume of ferroelectric nanoparticles without serious deterioration of their polar properties. In many practically important cases, the fixed volume (rather than the fixed size) corresponds to realistic technological conditions of nanoparticles fabrication. The letter is focused on the theoretical study of the behavior of ferroelectric polarization, paramagnetoelectric coefficient and phase diagrams of semi-ellipsoidal nanoparticles with a fixed volume V. Our approach combines the Landau-Ginzburg-Devonshire phenomenology, the classical electrostatics, and the elasticity theory. Our results show that the size effects on the phase diagrams and polarization of semi-ellipsoidal BiFeO3 nanoparticles nontrivially depend on V. These findings provide a path to optimize the polar properties of nanoparticles by controlling their phase diagrams at a fixed volume.

In this work we address the peculiarities of the macroscopic responses in ternary 0.1Na0·5Bi0·5TiO3-0.6SrTiO3-0.3PbTiO3 (0.1NBT-0.6ST-0.3PT) solid solutions. These solid solutions exhibit a spontaneous first order relaxor to normal ferroelectric phase transition. The phase transition is accompanied by a broad dielectric relaxation which expands over 10 orders of magnitude in frequency just above the phase transition temperature. The temperature dependence of polarization shows that non-zero net polarization persists above the phase transition temperature. Below the phase transition temperature, it is not possible to describe the temperature dependence of polarization with a power law function which is valid in normal ferroelectrics. The piezoresponse force microscopy studies reveal that 0.1NBT-0.6ST-0.3PT solids solutions display several local polarization patterns which arise due to the bimodal distribution of grains in the ceramics. We associate the peculiar macroscopic responses to these complex polar structures and their different temperature behaviours.

The electrocaloric effect (ECE) in ferroelectric materials is a promising candidate for small, effective, low cost, and environmentally friendly solid state cooling applications. Instead of the commonly used indirect estimates based on Maxwell's relations, direct measurements of the ECE are required to obtain reliable values. In this work, we report on a custom-made quasi-adiabatic calorimeter for direct ECE measurements. The ECE is measured for two promising lead-free materials: Ba(Zr0.12Ti0.88)O3 and Ba(Zr0.2Ti0.8)O3 bulk ceramics. Adiabatic temperature changes of ΔTEC = 0.5 K at 355 K and ΔTEC = 0.3 K at 314 K were achieved under the application of an electric field of 2 kV/mm for the Ba(Zr0.12Ti0.88)O3 and Ba(Zr0.2Ti0.8)O3 samples, respectively. The quasi-adiabatic ECE measurements reliably match other direct EC measurements using a differential scanning calorimeter or an infrared camera. The data are compared to indirect EC estimations based on Maxwell's relations and show that the indirect measurements typically underestimate the effect to a certain degree.

In this study, we report on investigation of the electrocaloric (EC) effect in lead-free Ba(SnxTi1-x)O3 (BSnT) ceramics with compositions in the range of 0.08 ≤ x ≤ 0.15 by the direct measurement method using a differential scanning calorimeter. The maximum EC temperature change, ΔTEC-max = 0.63 K under an electric field of 2 kV/mm, was observed for the composition with x = 0.11 at ∼44 °C around the multiphase coexistence region. We observed that the EC effect also peaks at transitions between ferroelectric phases of different symmetries. Comparison with the results of indirect EC measurements from our previous work shows that the indirect approach provides reasonable estimations of the magnitude of the largest EC temperature changes and EC strength. However, it fails to describe correctly temperature dependences of the EC effect for the compositions showing relaxor-like behaviour (x = 0.14 and 0.15) because of their non-ergodic nature. Our study provides strong evidence supporting that looking for multiphase ferroelectric materials can be very useful to optimize EC performance.\ud

Dense nanocrystalline barium strontium titanate Ba0.6Sr0.4TiO3 (BST) ceramics with an average grain size around 40 nm and very small dispersion were obtained by spark plasma sintering at 950°C and 1050°C starting from nonagglomerated nanopowders (~20 nm). The powders were synthesized by a modified “Organosol” process. X-ray diffraction (XRD) and dielectric measurements in the temperature range 173–313 K were used to investigate the evolution of crystal structure and the ferroelectric to paraelectric phase transformation behavior for the sintered BST ceramics with different grain sizes. The Curie temperature TC decreases, whereas the phase transition becomes diffuse for the particle size decreasing from about 190 to 40 nm with matching XRD and permittivity data. Even the ceramics with an average grain size as small as 40 nm show the transition into the ferroelectric state. The dielectric permittivity e shows relatively good thermal stability over a wide temperature range. The dielectric losses are smaller than 2%–4% in the frequency range of 100 Hz–1 MHz and temperature interval 160–320 K. A decrease in the dielectric permittivity in nanocrystalline ceramics was observed compared to submicrometer-sized ceramics.

We study the electrocaloric (EC) effect in bulk BaTiO$_3$ (BTO) using molecular dynamics simulations of a first principles-based effective Hamiltonian, combined with direct measurements of the adiabatic EC temperature change in BTO single crystals. We examine in particular the dependence of the EC effect on the direction of the applied electric field at all three ferroelectric transitions, and we show that the EC response is strongly anisotropic. Most strikingly, an inverse caloric effect, i.e., a temperature increase under field removal, can be observed at both ferroelectric-ferroelectric transitions for certain orientations of the applied field. Using the generalized Clausius-Clapeyron equation, we show that the inverse effect occurs exactly for those cases where the field orientation favors the higher temperature/higher entropy phase. Our simulations show that temperature changes of around 1 K can in principle be obtained at the tetragonal-orthorhombic transition close to room temperature, even for small applied fields, provided that the applied field is strong enough to drive the system across the first order transition line. Our direct EC measurements for BTO single crystals at the cubic-tetragonal and at the tetragonal-orthorhombic transitions are in good qualitative agreement with our theoretical predictions, and in particular confirm the occurrence of an inverse EC effect at the tetragonal-orthorhombic transition for electric fields applied along the [001] pseudo-cubic direction., 12 pages, 11 figures

The lead-free ferroelectric 0.5Ba(Zr0.2Ti0.8)O3 − 0.5(Ba0.7Ca0.3)TiO3 (BCZT) is a promising component for multifunctional multiferroics due to its excellent room temperature piezoelectric properties. Having a composition close to the polymorphic phase boundary between the orthorhombic and tetragonal phases, it deserves a case study for analysis of its potential for modern electronics applications. To obtain magnetoelectric coupling, the piezoelectric phase needs to be combined with a suitable magnetostrictive phase. In the current article, we report on the synthesis, dielectric, magnetic and magnetoelectric characterization of a new magnetoelectric multiferroic composite consisting of BCZT as a piezoelectric phase and CoFe2O4 (CFO) as the magnetostrictive phase. We found that this material is multiferroic at room temperature and manifests a magnetoelectric effect larger than that of BaTiO3 −CoFe2O4 bulk composites with similar content of the ferrite phase.

The electrocaloric effect (ECE) of BaZr$_{x}$Ti$_{1-x}$O$_3$ (BZT) is closely related to the relaxor state transition of the materials. This work presents a systematic study on the ECE and the state transition of the BZT, using a combined canonical and microcanonical Monte Carlo simulations based a lattice-based on a Ginzburg-Landau-type Hamiltonian. For comparison and verification, experimental measurements have been carried on BTO and BZT ($x=0.12$ and $0.2$) samples, including the ECE at various temperatures, domain patterns by Piezoresponse Force Microscopy at room temperature, and the P-E loops at various temperatures. Results show that the dependency of BZT behavior of the Zr-concentration can be classified into three different stages. In the composition range of $ 0 \leq x \leq 0.2 $, ferroelectric domains are visible, but ECE peak drops with increasing Zr-concentration harshly. In the range of $ 0.3 \leq x \leq 0.7 $, relaxor features become prominent, and the decrease of ECE with Zr-concentration is moderate. In the high concentration range of $ x \geq 0.8 $, the material is almost nonpolar, and there is no ECE peak visible. Results suggest that BZT with certain low range of Zr-concentration around $x=0.12 \sim 0.3 $ can be a good candidate with relatively high ECE and simutaneously wide temperature application range at rather low temperature.

Magnetoelectric (ME) materials are of utmost interest in view of both fundamental understanding and novel desirable applications. Despite its smallness, the linear ME effect has been shown to control spintronic devices very efficiently, e.g., by using the classic ME antiferromagnet Cr₂O₃. Similar nano-engineering concepts exist also for type-I multiferroic single phase materials like BiFeO₃ and BiMnO₃. Record high ME response has been realized in stress-strain coupled multiphase magnetoelectrics like PZT/FeBSiC composites, enabling applications in sensors. In type-II multiferroics, whose ferroelectricity is due to modulated magnetic ordering, the ME coupling is of fundamental interest. Higher-order ME response characterizes disordered systems, which extend the conventional multiferroic scenario toward ME multiglass (e.g., Sr(1-x)MnxTiO₃).

Ceramic solid solutions Bi 4 (V 1−x Zr x ) 2 O 11−z (I), (Bi 1−y La y ) 4 V 2 O 11−z (II) and (Bi 1−y La y ) 4 (V 0.96 Zr 0.05 ) 2 O 11−z (III) with x < 0.30, y < 0.20, were prepared by the solid state reaction method and were investigated by means of various experimental techniques. The low temperature ferroelectric α-phase exists in the solid solutions with x, y ≤ 0.05. The phase transition to paraelectric β-phase was revealed in these compositions by the dielectric spectroscopy, SHG and DTA/DSC methods. Dielectric permittivity measurements confirmed an effect of the domain walls “pinning” due to the presence of oxygen vacancies inherent to the bismuth vanadate based structures. Switching of ferroelectric domains by an external electric field was observed in Piezoresponse Force Microscopy experiments.

The crystal structure, magnetic and local ferroelectric properties of polycrystalline Bi 1− x Gd x FeO 3 ( x = 0.1, 0.2, 0.3) samples were investigated at room temperature. Gadolinium substitution was found to induce a polar-to-polar R 3 c → Pn 2 1 a structural phase transition at x ≈ 0.1. Increasing the content of the substituting element suppressed the spontaneous polarization in Bi 1− x Gd x FeO 3 , resulting in a ferroelectric–paraelectric Pn 2 1 a → Pnma phase transition at 0.2 x 3 seems to be related to A-site substitution by rare-earth ions with a large difference in ionic radius with respect to Bi 3+ . The effect of the magnetically active Gd 3+ substitution on the low-temperature magnetic properties of Bi 1− x Gd x FeO 3 samples is also discussed.

“Multiglass” materials with simultaneous occurrence of two different glassy states extend the frame of conventional multiferroicity, which is devoted to crystalline materials with coexisting uniform long-range electric and magnetic ordering. The concept applies to Sr0.98Mn0.02TiO3 ceramics, where A-site substituted Mn2+ ions are at the origin of both a polar and a spin cluster glass. Spin freezing is initiated below the dipolar glass temperature, Tg e ≈ 38 K, which is seemingly indicated by a divergence of the nonlinear susceptibility, χ3. Below Tg m ≈ 34 K both glass phases are independently verified by memory and rejuvenation effects. Biquadratic interaction of the Mn2+ spins with ferroelectric correlations of their off-center pseudospins in the incipient ferroelectric host crystal SrTiO3 explains the high spin glass temperature and comparably strong third-order magnetoelectric coupling between the polar and the magnetic degrees of freedom. Preliminary results on the related compound K0.97Mn0.03TaO3 favorably comply with the magnetoelectric multiglass concept.

Investigation of crystal structure, dielectric, magnetic and local ferroelectric properties of the diamagnetically substituted Bi 1− x A x FeO 3− x /2 (A=Ca, Sr, Pb, Ba; x =0.2, 0.3) polycrystalline samples has been carried out. It has been shown that the heterovalent A 2+ substitution result in the formation of oxygen vacancies in the host lattice. The solid solutions have been found to possess a rhombohedrally distorted perovskite structure described by the space group R 3 c . Piezoresponse force microscopy has revealed signs of existence of the ferroelectric polarization in the samples at room temperature. Magnetization measurements have shown that the magnetic state of these compounds is determined by the ionic radius of the substituting elements. A-site substitution with the biggest ionic radius ions has been found to suppress the spiral spin structure of BiFeO 3 giving rise to the appearance of room-temperature weak ferromagnetism.

We present results of piezoresponse force microscopy studies on “uniaxial” relaxors Sr x Ba1− x Nb2O6 (SBN) and on “cubic” relaxors Pb[Mg1/3Nb2/3]1− x Ti x O3 (PMN-PT). The chosen compositions exhibit a spontaneous transition from the ergodic relaxor into the ferroelectric state. In both materials static regions of non-zero piezoresponse were found above the corresponding transition temperature. We attribute them to large polar nanosized regions (PNRs), which are “frozen” on the experimental time scale. The temperature evolution of the observed structures was investigated. It has been found that in PMN-PT these quasi-static PNRs are larger and exist in a broader temperature range than those in SBN.

Dielectric relaxation of BaTi1− x Sn x O3 ceramics is investigated by means of dielectric spectroscopy. The gradual crossover from ferroelectric to relaxor behavior is characterized by vanishing of the contribution due to domain walls and appearance of relaxation related to reorientation of polar nanosized regions. Typical behavior of relaxors is observed only in ceramics with x = 0.30, while the compositions with 0.175 ≤ x ≤ 0.25 show coexistence of both ferroelectric and relaxor features. The relaxor properties are supposed to be due to both weak random fields and disorder inherent in pure BaTiO3.

OA hybrid Relaxor/ferroelectric ceramic/ceramic composites have shown to be promising in generating large electromechanical strain at moderate electric fields. Nonetheless, the mechanisms of polarization and strain coupling between grains of different nature in the composites remain unclear. To rationalize the coupling mechanisms we performed advanced piezoresponse force microscopy (PFM) studies of 0.92BNT–0.06BT–0.02KNN/0.93BNT–0.07BT (ergodic/non-ergodic relaxor) composites. PFM is able to distinguish grains of different phases by characteristic domain patterns. Polarization switching has been probed locally, on a sub-grain scale. k-Means clustering analysis applied to arrays of local hysteresis loops reveals variations of polarization switching characteristics between the ergodic and non-ergodic relaxor grains. We report a different set of switching parameters for grains in the composites as opposed to the pure phase samples. Our results confirm ceramic/ceramic composites to be a viable approach to tailor the piezoelectric properties and optimize the macroscopic electromechanical characteristics.

The orthorhombically distorted perovskite NaMnF$_{3}$ has been predicted to become ferroelectric if an $a=c$ distortion of the bulk $Pnma$ structure is imposed. In order to test this prediction, NaMnF$_{3}$ thin films were grown on SrTiO$_{3}$ (001) single crystal substrates via molecular beam epitaxy. The best films were smooth and single phase with four different twin domains. In-plane magnetization measurements revealed the presence of antiferromagnetic ordering with weak ferromagnetism below the N\'eel temperature $T_N=66$ K. For the dielectric studies, NaMnF$_{3}$ films were grown on a 30 nm SrRuO$_{3}$ (001) layer used as a bottom electrode grown via pulsed laser deposition. The complex permittivity as a function of frequency indicated a strong Debye-like relaxation contribution characterized by a distribution of relaxation times. A power-law divergence of the characteristic relaxation time revealed an order-disorder phase transition at 8 K. The slow relaxation dynamics indicated the formation of super-dipoles (superparaelectric moments) that extend over several unit cells, similar to polar nanoregions of relaxor ferroelectrics., Comment: 4 pages, 3 figures

In this work, the nanoscale electromechanical properties of Pb-based perovskites that are currently the main candidates for piezoelectric applications are investigated by Piezoresponse Force Microscopy (PFM). Local response is compared with that studied via conventional technique. The effect of local polarization switching by mechanical force is demonstrated. This effect may limit the functionality of the films in piezoelectric applications. Local piezoelectric nonlinearity, as well as the nanoscale degradation are also studied by PFM. These measurements demonstrate that the defects may act as pinning centers for domain walls and thus influence nanoscale properties. Finally, local properties of ferroelectric relaxors are presented.

Pb (ZrxTi1−x)O3 (PZT) thin films with (111) texture were deposited onto commercially available Pt/Ti/SiO2/Si substrates via the sol–gel technique. Piezoforce microscopy (PFM) was then used to analyse the evolution of domain populations as a function of the Zr content x. Domain structures of virgin films, local piezoelectric properties of individual grains and piezoelectric histograms were studied in films with different compositions (x = 0.2–0.6), which cover both the tetragonal and rhombohedral sides of the phase diagram. In films with low Zr content mainly single-domain grains were observed. As the Zr content increased, a larger fraction of polydomain grains was found. The local piezoelectric response measured inside sufficiently big grains indicated that the strongest piezoelectric effect occurs in PZT30/70 (x = 0.3) films. This was attributed to two different effects: high out-of-plane polarization achieved due to the (111) texture and influence of the dielectric constant. In tetragonal films with their lower dielectric constants the electric field seen by a ferroelectric is higher as compared to other compositions, giving rise to an apparent increase of the effective piezoelectric response measured by PFM. The analysis of the domain images indicated that sol–gel derived PZT films are slightly self-polarized near the free surface. With increasing Zr/Ti ratio, the variation of domain populations resulted in reversing the sign of the average piezoelectric response at x≈0.3. It is demonstrated that PFM histograms are extremely sensitive to PZT composition and can be used as a signature of complex domain structures in ferroelectric thin films.

The ceramic compositions near the morphoptropic boundary of the systems Pb(Mg 1/3 Nb 2/3 )O 3 -PbTiO 3 (PMN-PT) and Pb(Mg 1/3 Nb 2/3 )O 3 -PbTiO 3 -Pb(Mg 1/2 W 1/2 )-O 3 (PMN-PT-PMW) have been prepared using the high disperse magnesium oxide precursor. Domain structure and piezoelectric hysteresis loops have been studied by the piezoelectric force microscopy (PFM) method. Ordering of the domain patterns has been revealed in the PMW doped ceramics. The decreasing of the ferroelectric phase transition temperature, while the enhancement of dielectric permittivity and piezoelectric d 33 and | d| 31 coefficients has been shown to be governed by the PMW content.

Low-frequency dielectric studies were performed on the fine-grain ceramics of BaTiO3 doped with 2.5 mol% of non-ferroelectric perovskite La(Mg1/2Ti1/2)O3 (BT:2.5% LMT). In addition to the permittivity and P–E hysteresis loop measurements as a function of temperature, local electromechanical properties of BT:2.5% LMT were analysed by piezoresponse force microscopy. It was found that the temperature evolution of the dielectric properties detected by macroscopic methods (average over many grains) is similar to that observed on the nanoscale level (in a single grain). BT:2.5% LMT was revealed to exhibit the typical features of both the ferroelectric and the relaxor. The observed dielectric behaviour is discussed in terms of heterovalent substitution at both A-(Ba2+/La3+) and B-(Ti4+/Mg2+) perovskite sites.

Effects of the Pb(Mg1/2W1/2)O3 additive on structure, phase transitions, dielectric and piezoelectric properties of Pb(Mg1/3Nb2/3)O3-PbTiO 3 close to the morphotropic boundary have been studied. The additive is shown to influence the diffuseness of phase transitions, domain structure and peizoelectric properties of the ceramics depending on their structure and morphology.

Dielectric and ferroelectric properties of ceramic solid solutions (Pb0.98−xBaxLa0.02) (Sn0.35Zr0.55Ti0.10)O3 (I) and (Pb0.98−xBax)(Sn0.35Zr0.55Ti0.10Nb0.02)0.995O3 (II), x = 0.09–0.13 have been studied. It was found out that ferroelectric properties are promoted by addition of Nb cations. With increasing x relaxor behavior becomes evident in the both systems.

The local electromechanical response of epitaxial thin films of relaxor ferroelectric PbMg1/3Nb2/3O3 (PMN) was studied at room temperature using Piezoresponse Force Microscopy (PFM). In the virgin films, no piezoelectric contrast was detected. An onset of the polar state was induced locally by applying an external bias to the tip. After removing the voltage, a relaxation of the locally induced polarization was observed. The relatively small threshold electric field and short critical time for onset of the polar state, and the relatively long relaxation time are discussed in terms of peculiarities of both PFM technique and thin films.

High-quality SrBi2Ta2O9 single crystals were grown by self-flux solution method. According to x-ray topography the crystals with layered habitus and typical dimensions up to ∼ 7 × 5 × 0.05 mm3 show perfect (001)-orientation with the edges directed along [110] axes. The quality of the crystals was also confirmed by high-field measurements, which did not detect any ferroelectric hysteresis along the c-axis crystallographic direction thus confirming that the polarization vector lies entirely in the a-b plane. Sharp phase transition (Tc = 350°C) with well-defined Curie-Weiss behavior above the transition was found. Examination of the domain structure revealed well-faceted 90° domains forming due to mechanical twinning above the transition to ferroelectric phase.

BaTiO3 ceramics doped with 2.5 mol% of non-ferrolectric perovskite La(Mg1/2Ti1/2)O3 (BT:2.5%LMT) were dielectrically investigated at macroscopic and nanoscale (by Piezoresponse Force Microscopy) levels. The results of dielectric study performed on bulk ceramics were compared with those of individual grains. BT:2.5%LMT was revealed to exhibit the typical features of both ferroelectric and relaxor behaviour.

Strontium bismuth tantalate (SBT) ultrathin films with thickness about 40 nm have been prepared by a chemical solution deposition (CSD) method based on the synthesis of a Ta-glycolate derivative. Layers of the precursor solution diluted with 2-ethyl-1-hexanol were spin-coated onto Pt/TiO2/SiO2/(100)Si substrates. Crystallisation was carried out in oxygen at 650 °C by Rapid Thermal Processing (RTP). Topography of the films was observed by Scanning Force Microscopy (SFM). The piezoresponse mode of the SFM equipment was used to perform the nanoscale observation of the ferroelectric domain structure of the SBT ultrathin films and to measure piezoelectric hysteresis loops. The macroscopic ferroelectric response was measured on capacitors prepared after the deposition on the film surfaces of top platinum electrodes of ∼0.05 mm2 of area.

Local ferroelectric properties of single crystals (CH 3 NH 3 ) 5 Bi 2 Br 11 (MAPBB) are investigated by Scanning Probe Microscopy (SPM) in a piezoelectric contact mode. The SPM signal proportional to the effective piezoelectric coefficient, d eff , is measured along with the standard topography. Both ferroelectric domain imaging and local hysteresis measurements are performed at room temperature in the close vicinity of the phase transition temperature (T c 39°C). Lamellar domain structure with the phase contrast due to 180° domains is observed for the surfaces perpendicular to the polar direction. Local hysteresis loops acquired by SPM are well saturated with the average coercive voltage of ∼15 V. The shape of the loops is found to depend on the stiffness of the SPM cantilever. Local studies are complemented with the macroscopic measurements (polarization, piezoelectric coefficient, dielectric permittivity) performed in the temperature range including T c (20-39°C). The mechanisms of the domain contrast and prospects of using MAPBB for high-density data storage are discussed.

In this work, the frequency relaxation of the dielectric permittivity of BaBi 2 Ta 2 O 9 (BBT) and BaBi 2 Nb 2 O 9 (BBN) ceramics is investigated in the wide temperature range. Both compositions feature behavior typical for relaxor ferroelectrics including the strong frequency dispersion of the permittivity, the pronounced shift of its temperature maximum with frequency, and the absence of the macroscopic polarization even far below the dielectric peak temperature. The frequency dispersion of the real and imaginary parts of the permittivity is analyzed in the approximation of the uniform distribution of relaxation times. It is found that BBT has a narrower relaxation time spectrum, which broadens faster on cooling, as compared to that of BBN. It is suggested that such a behavior may result from the different level of cation substitution of Bi 3+ with Ba 2+ in both ceramics. The obtained parameters of relaxation spectra are compared with those of conventional relaxor ferroelectrics.

Dielectric properties of solid solutions PbTiO 3 -Pb(Mg 1/3 Nb 2/3 )O 3 (I), PbTiO 3 -Pb(Mg 1/3 W 1/3 )O 3 (II), PbTiO 3 -Pb(Sc 1/3 Nb 1/3 )O 3 (III), PbZrO 3 -Pb(Mg 1/3 W 1/3 )O 3 (IV) have been studied. Vogel-Fulcher approach has been used for description of relaxor properties of ceramics I with x = 0.20-0.24 and II with x = 0.45. Applicability of the power distribution function for evaluation of the diffuse phase transition parameters of ceramics I-IV has been proved.

Theelectrocaloric effect (ECE) in ferroelectric materials is a promising mechanism for the development of small, effective, low cost, and environmentally friendly solid state refrigerators. During the last decade, an increased interest has been paid to studies of this effect. Getting reliable values requires direct measurements of the ECE instead of the frequently used indirect estimates based on Maxwell's relation. In this paper, we report on the modification of a differential scanning calorimeter for direct ECE measurements. The importance of proper estimation of the heat capacitance and thermal losses for the correct ECE measurements is discussed. The ECE was measured for bulk ceramics Ba(Zr 0.2 Ti 0.8 )O 3 . The temperature change reaches a value of ΔT EC = 0.44 K at 305 K under an electric field of 2 kV/mm. The obtained data are compared with results of the evaluation of the indirect ECE.

This paper presents an extract of modifications of lead magnesium niobate–lead titanate in order to optimize its electrocaloric properties. Electrocaloric entropy (Δ S EC ) and temperature changes (Δ T EC ) are measured in a temperature range from −5 °C up to 100 °C using differential scanning calorimetry. The influence of dopants (Li + , Mn 2+ , Sr 2+ , Ta 5+ ) on the electrocaloric effect as well as on microstructure, dielectric and ferroelectric behavior is investigated. The maximum of relative permittivity can be shifted to lower or higher temperatures depending on the added dopant and decreased ferroelectric hysteresis losses were observed for all altered compositions. For the undoped PMN–8PT ceramics maximum Δ T EC of 0.58 K and Δ S EC of 0.51 J kg −1 K −1 were measured, when applying an electric field of 2 kV mm −1 at 30 °C. The electrocaloric temperature change showed lower values for all doped PMN–8PT. Remarkably, this is accompanied with an increase of the entropy change for the Li-doped sample.

The phase state of solid solutions Pb[Zr 1 m x (Fe 0.5 Nb 0.5 ) x ]O 3 (0

The dielectric and ferroelectric properties of Pb[(Mg0.5W0.5 )1 – x Ti x ]1 – y Sn y O3 (x = 0.4–0.5, y = 0–0.15) solid solutions are studied. The results are used to elucidate the origin of the relaxor state developing in a temperature range between the para- and ferroelectric phases.

In this study we report on the dielectric, ferroelectric, and piezoelectric properties of the conventional polyvinylidene fluoride/trifluoroethylene, P(VDF-TrFE), copolymer of composition 70/30 mol.% with fillers on the basis of lead zirconate titanate (PZT). (Pb0.75Ba0.24Sr0.01)(Zr0.53Ti0.47)O3 (BPZT) fillers with concentrations from 10 to 50 vol.% are additional components in the P(VDF-TrFE) piezoelectric polymer. Dielectric spectroscopy and the characterization of ferroelectricity and piezoelectricity in the P(VDF-TrFE)/BPZT composites are performed over a wide temperature range from 150 to 420 K. The dependence of the effective dielectric permittivity for the composites under investigation on the filler concentration is analyzed by the Lichtenecker mixing rule. The approximation model of effective medium is also applied to explain the impact of BPZT fillers on the ferroelectric and piezoelectric properties of P(VDF-TrFE)/BPZT composites.