Response Of Relaxor Ferroelectrics Research Articles

Thermally-stable high energy-storage performance over a wide temperature range in relaxor-ferroelectric Bi1/2Na1/2TiO3-based ceramics

In this study, lead-free zirconium (Zr)-modified Bi1/2(Na0.78K0.22)1/2TiO3 (BNKT) ceramics were synthesized by the conventional solid-state reaction method. The co-existence of two phases (tetragonal; P4mm and cubic phases; Pm3‾m) with definite phase fractions were observed for all samples. The lattice parameters were gradually enhanced by the addition of Zr-content in the BNKT ceramics, which strongly support the relaxor-ferroelectric response. All of the samples are well-dense with no noticeable pores detected. Definite grains with clear grain boundaries were observed through SEM analysis. The temperature-dependent (25–200 °C) ferroelectric polarization response of all specimens were studied in detail under the constant applied electric field (60 kV cm-1). Thermally-stable high energy-storage properties (Wrec ≈ 0.72 J cm-3, and η ≈ 98%) with an extended operating temperature range (25–200 °C) within ±15% variation was observed for the Zr-modified BNKT composition. The enhancement of energy-storage properties can be attributed to the Zr addition, which increased the phase fraction of cubic crystal structure and assisted the ferroelectric to relaxor-ferroelectric phase transition. This study provides a comprehensive analysis of the energy-storage response of the lead-free ceramics for energy-storage devices.

Connecting the Multiscale Structure with Macroscopic Response of Relaxor Ferroelectrics

AbstractLead‐based relaxor ferroelectrics are characterized by outstanding piezoelectric and dielectric properties, making them useful in a wide range of applications. Despite the numerous models proposed to describe the relation between their nanoscale polar structure and the large properties, the multiple contributions to these properties are not yet revealed. Here, by combining atomistic and mesoscopic‐scale structural analyses with macroscopic piezoelectric and dielectric measurements across the (100–x)Pb(Mg1/3Nb2/3)O3–xPbTiO3 (PMN–xPT) phase diagram, a direct link is established between the multiscale structure and the large nonlinear macroscopic response observed in the monoclinic PMN‐xPT compositions. The approach reveals a previously unrecognized softening effect, which is common to Pb‐based relaxor ferroelectrics and arises from the displacements of low‐angle nanodomain walls, facilitated by the nanoscale polar character and lattice strain disorder. This comprehensive comparative study points to the multiple, distinct mechanisms that are responsible for the large piezoelectric response in relaxor ferroelectrics.

Multiscale field-induced structure of (1-x)Pb(Mg1/3Nb2/3)O3–xPbTiO3 ceramics from combined techniques

The vast majority of studies on field-induced changes in (1–x)Pb(Mg1/3Nb2/3)O3–xPbTiO3 (PMN–xPT) materials at the morphotropic phase boundary (MPB) have been performed on single crystals, while the more complex responses in polycrystalline materials have not yet been resolved. By using combined microscopy and diffraction techniques, this study aims to determine the structural changes induced by application of an electric field to two representative MPB compositions of the PMN–xPT family, namely, PMN–30PT with the initial Cm and Pm coexisting phases, and PMN–35PT with the P4mm and Pm phases. Both ceramic compositions are characterized by a hierarchical domain structure with domains present at different length-scales. Based on the applied field measurements, major contributing effects in both compositions are outlined and discussed with respect to the processes related to the monoclinic phase and the adaptive phase theory. It is shown that the highly mobile domain walls are largely involved, along with the field-induced polarization rotation in the monoclinic PMN–30PT, and a phase transition to a mainly tetragonal structure in PMN–35PT. These multiscale results elucidate important aspects of field-induced changes in PMN–xPT materials, contributing to the understanding of the complex electrical and electromechanical response of relaxor ferroelectrics.

High electrocaloric cooling power of relaxor ferroelectric BaZrxTi1–xO3 ceramics within broad temperature range

Electrocaloric effect (ECE) is much promising to realize high efficiency and environment friendly solution in solid cooling devices. Relaxor ferroelectrics are good candidates for the materials with high electrocaloric cooling power. In this paper, relaxor ferroelectric Ba(ZrxTi1–x)O3 (BZT, x = 0.2, 0.21, 0.22, 0.23) ceramics were prepared with their temperature change (ΔT) induced by the ECE and electrocaloric strength (ΔT/E) measured within broad temperature range. It is found that the BZT21 (x = 0.21) exhibits the largest ΔT of ∼4.67 K and a high ΔT/E value of ∼0.46 km/MV at 9.9 MV/m and 25 °C. BZT21 also exhibits apparent relaxor ferroelectric response, showing a very broad EC peak in the temperature interval between 15 °C and 50 °C. Moreover, the relationship between EC properties and relaxor features was analyzed by piezoresponse force microscopy test. The results reveal that more dispersed phase structures induce additional configurational entropy, which is in favor for the enhanced EC performance. The interplay and compromise between the kinetic and thermodynamic mechanisms of domain switching determines the optimal composition for the EC performances of the BZT ceramics.

Nonlinear dielectric susceptibility in relaxor ferroelectrics Pb(Zn1/3Nb2/3)O3-PbTiO3

ABSTRACTThe temperature dependence of the third-order nonlinear susceptibility ϵ3 in relaxor ferroelectrics (1-x)Pb(Zn1/3Nb2/3)O3-8%PbTiO3 was measured in the vicinity of critical endpoint, TCEP (172°C). It was found that ϵ3 takes positive values near TCEP and changes its sign to negative values at about 200°C. The nonlinear dielectric response of relaxor ferroelectrics was discussed on the basis of the Landau-Ginzburg-Devonshire free energy density.

A finite element phase field model for relaxor ferroelectrics

AbstractA mechanically coupled phase field model is presented for the domain evolution and mesoscopic response of relaxor ferroelectrics. In the model the spontaneous polarization is treated as order parameter. The model is derived from thermodynamic analysis including the material force theory. Random field theory is adopted to take the disorder of relaxor ferroelectrics into account. Results show that the model is capable of reproducing relaxor features, such as domain miniaturization, small remnant polarization and large piezoelectric response. Dependence of these features on the random field strength is discussed. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Internal Biasing in Relaxor Ferroelectric Polymer to Enhance the Electrocaloric Effect

The relaxor ferroelectric materials, because of their large and reversible electric field induced polarization, have been demonstrated to possess giant electrocaloric effect (ECE) over a broad temperature range, which are attractive for refrigeration with high energy efficiency and environmental friendliness. However, high electric fields are required to generate the giant ECE in these materials, posing challenge for these materials in practical cooling devices which also require high reliability and low cost. Here, a general approach is reported, for example, establishing an internal bias field in these relaxor ferroelectric polymers, to significantly improve ECE which can be induced at low electric fields. It is demonstrated that in a polymer blend (nanocomposite) with a properly controlled normal ferroelectric in nanophase dispersion in the relaxor polymer matrix, the charge neutrality in the blends can cause an internal biasing field, leading to more than 45% enhancement in the ECE at low electric field (≈50 MV m−1). This internal biasing approach provides a universal strategy to enhance other low field responses such as the electromechanical response in relaxor ferroelectrics.

Mesoscopic harmonic mapping of electromechanical response in a relaxor ferroelectric

Relaxor-ferroelectrics are renowned for very large electrostrictive response, enabling applications in transducers, actuators, and energy harvesters. However, insight into the dissimilar contributions (polarization rotation, wall motion) to the electromechanical response from electrostrictive strain, and separation of such contributions from linear piezoelectric response are largely ignored at the mesoscale. Here, we employ a band-excitation piezoresponse force microscopy (BE-PFM) technique to explore the first and second harmonics of the piezoelectric response in prototypical relaxor-ferroelectric 0.72Pb(Mg1/3Nb2/3)O3-0.28PbTiO3 (PMN-0.28PT) single crystals. Third order polynomial fitting of the second harmonic reveals considerable correlation between the cubic coefficient map and the first harmonic piezoresponse amplitude. These results are interpreted under a modified Rayleigh framework, as evidence for domain wall contributions to enhanced electromechanical response. These studies highlight the contribution of domain wall motion in the electromechanical response of relaxor ferroelectrics, and further show the utility of harmonic BE-PFM measurements in spatially mapping the mesoscopic variability inherent in disordered systems.

Large electrocaloric effect in Ba(Ti1−xSnx)O3 ceramics over a broad temperature region

A large electrocaloric effect (ECE) near room temperature is reported in Sn doped BaTiO3 ceramics. By tuning Ba(Ti1−xSnx)O3 compositions which also exhibit relaxor ferroelectric response to near the invariant critical point, the Ba(Ti1−xSnx)O3 bulk ceramics at x ∼ 0.12 exhibit a large EC coefficient (ΔT/ΔE =0.27*10−6K⋅mV−1) over a 50 K temperature range. In addition to that, the diffuse phase transition is successfully applied to broaden the EC peaks under low electric field. These properties added together indicate a general solution of the electrocaloric materials with high performance for practical cooling applications.

Influence of particle sizes on the electronic behavior of ZnxCo1−xFe2O4 spinels (x = 0.2, 0.3)

The effect of composition and particle size on the electrical and magnetic behavior of ZnxCo1−xFe2O4 spinels (x=0.2 and 0.3) has been studied. Powdered samples of these ferrites have been synthetized by the liquid mix technique and hydrothermal method (in sub and supercritical conditions), leading to average particle sizes of ca. 50 and 10nm, respectively. They have been characterized by means of X-ray diffraction, Thermogravimetric analysis, Energy-Dispersive X-ray Spectroscopy and impedance and magnetic measurements. Permittivity values up to ca. 500 were registered at 375K, which remained almost constant at moderate frequencies, between 103 and 106Hz. Stabilization of polarization phenomena is very sensitive to grain size and composition. Dielectric behavior evolves to a relaxor ferroelectric response when grain size becomes nanometric and, particularly, when the sample shows high monodispersion. The conduction mechanism and type of majority charge carriers have been established from Seebeck measurements. The x=0.3 sample, prepared in supercritical water for the first time, exhibits homogeneous particle size distribution, superparamagnetic behavior and Curie temperature lower than those corresponding to similar microsized samples. The electronic response of the ferrites obtained in supercritical conditions is interpreted considering the possible short scale polarization of nanodomains.

Giant Electrocaloric Response Over A Broad Temperature Range in Modified BaTiO3 Ceramics

A giant electrocaloric effect (ECE) near room temperature is reported in a lead‐free bulk inorganic material. By tuning Ba(ZrxTi1–x)O3 compositions which also exhibit relaxor ferroelectric response to near the invariant critical point, the Ba(ZrxTi1–x)O3 bulk ceramics at x ∼ 0.2 exhibit a large adiabatic temperature drop of 4.5 K, a large isothermal entropy change of 8 J kg−1 K−1, and a large EC coefficient (|ΔTc/ΔE| = 0.52 × 10−6 KmV−1 and ΔS/ΔE = 0.93 × 10−6 J m kg−1 K−1 V−1) over a 30 K temperature range. These properties added together indicate a general solution of the electrocaloric materials with high performance for practical cooling applications.

Influence of the critical point on the electrocaloric response of relaxor ferroelectrics

The electrocaloric effect (ECE), i.e., the conversion of electric energy into heat, is of great importance for application in new generation cooling or heating devices that would be friendlier to the environment. Here, utilizing direct measurements of the ECE change of the temperature ΔT via a high resolution calorimeter, we study the ECE as a function of the magnitude of the electric-field step E in the vicinity of the critical point in several bulk relaxor ferroelectric ceramic systems. Relatively large ΔT of ∼2 to 3 K were obtained at modest fields of 90 kV/cm, even in the case of ceramic materials. The effective responsivity ΔT/E as a function of the electric field shows a characteristic peak near the critical point, which demonstrates the importance of proximity to the critical point for the enhancement of the electrocaloric effect. Experimental results are in good agreement with the theoretical calculations based on the spherical random-bond random-field model.

Heat Capacity Response of Relaxor Ferroelectrics Near the Morphotropic Phase Boundary

The influence of the electric bias field on the sequence of monoclinic phase transitions between the tetragonal and rhombohedral phases was studied by heat capacity measurements in PMN 1 − x PT x single crystal with x = 0.295. It is shown that besides the cubic to tetragonal (C-T) phase transition also tetragonal to monoclic C (T-M C ) phase transition exhibit a critical point at certain critical bias field value, thus terminating a line of first order transitions. It is shown by field cooled and zero-field cooled polarization experiments that similar critical point also exists in 9/65/35 PLZT ceramics.

Non-linear dielectric properties in based-PMN relaxor ferroelectrics

The investigation of the non-linear dielectric response in ferroelectric materials has become one of the most important issues in the field of ferroelectricity due to its technological and scientific interest. Rather, from the practical point of view the understanding of the non-linear dielectric properties is essential to improve the performance of ferroelectric multilayer capacitors and actuators devices, which commonly operate at high field levels. On the other hand, the non-linear (NL) dielectric response to large electric fields has been revealed as a powerful technique to investigate the physical origin of the dielectric relaxor state. In this work, low frequency dielectric measurements were performed in 0.9[Pb(Mg 1/3Nb 3/2)O 3]–0.1PbTiO 3 (PMN–PT) relaxor ceramics in a wide frequency and temperature range. The non-linear dielectric properties were investigated by using the measurements of the dielectric permittivity of the PMN–PT as a function of the dc “bias” driving field. The obtained results were analyzed within the framework of the current models for the dielectric response of relaxor ferroelectrics.

Infrared dielectric response of relaxor ferroelectrics

In the article we discuss the dielectric response of relaxor-type complex perovskites in the phonon-frequency region on the basis of a rich collection of experimental data accumulated in our laboratory by numerous infrared spectroscopy investigations over the past decade. The effect of the cation occupational disorder and of the nanoscopic inhomogeneous polarisation on the infrared response is considered in the framework of the factor-group symmetry analysis and the effective-medium approach. Polar mode assignment and comparison of the mode parameters of different materials is facilitated by systematic evaluation of mode-plasma frequencies. Whenever possible, the results are presented in form of tables convenient for further analysis or by comparison with results of other techniques, including ab-initio calculations. Infrared properties of other non-perovskite relaxors are briefly mentioned.

Low-Temperature Dielectric Response of Relaxor Ferroelectrics and Related Disordered Materials

This paper reviews the characteristic dielectric dispersion of relaxor ferroelectrics PbMg⅓Nb2/3O3, and (Pb1- x La x )(Zr y Ti1-y )1-x/4O3 and ferroelectric BiScO3-PbTiO3 solid solutions in the frequency range of 100 Hz–2 THz. In relaxors the main dielectric dispersion at high temperatures appears in the microwave and mm-wave region, which softens and broadens on cooling. Distribution of relaxation times below room temperature is very broad and below freezing temperature it results in nearly frequency independent dielectric loss in the entire available frequency range. The broad distribution of relaxation times stems from structural inhomogeneities which cause random fields and have influence on the distribution of activation energies for hopping of disordered ions. Landau-type thermodynamic model was proposed for explanation of the distribution of relaxation times. Besides the frequency independent dielectric loss, additional dielectric relaxation of not thermally activated origin was observed in BiScO3-64%PbTiO3 below 1 GHz.

Dielectric response of relaxor ferroelectrics in the time-domain

Dielectric response of relaxor ferroelectrics was analyzed in the time-domain by evaluating the relaxation-time (τ) distribution of Pb(Mg1/3Nb2/3)O3-10 mol % PbTiO3 using the method of Tikhonov regularization. The distribution function g(τ) became exponentially broad and flat as temperature approached a certain critical point (∼230 K), indicating the advent of the frozen polar domains with infinitely long τ in a matrix of the thermally activated dynamic polar domains. The dielectric response of the high-temperature relaxation part was then separately estimated with the help of the two-states-polarization model. The estimated g(τ) of the relaxation part showed logarithmic Gaussian behavior, which manifested an ergodicity in the thermally activated flips of dynamic polarizations at high temperatures. In contrast to this, a resonance kernel was postulated to describe the dielectric response of the frozen polar domains at lower temperatures.

Thermal exfoliation and crystallographic transformation of single-crystal metal oxides induced by He-ion implantation

We report on the thermal exfoliation of 7 μm thick films from 3.8 MeV He ion-implanted single-crystal 0.955 Pb(Zn1/3Nb2/3)O3–0.045 PbTiO3 [(PZN–PT) with 4.5% PT] by rapid thermal processing. Comparison with z-cut LiNbO3 shows a significantly higher exfoliation threshold temperature in PZN–PT for the same implantation conditions. Unusually large strains in the through-implanted layer are induced in the relaxor ferroelectric PZN–PT upon ion implantation leading to a crystallographic phase transformation in that material that is not observed in LiNbO3. Depth profile analysis of the refractive index shows a much larger refractive index modulation due to nuclear collisions than in LiNbO3. The higher exfoliation temperature observed for PZN–PT, despite a larger impact of the ion implantation on material structure, suggests that the electronic polarizability and elastic response of relaxor ferroelectrics near the morphotropic phase boundary have a significant impact on the crack propagation process responsible for thermally induced exfoliation.

Effect of defect-induced internal field on the aging of relaxors

The effect of a defect-induced internal field on the dielectric response of relaxor ferroelectrics is investigated using a Monte Carlo simulation. It was observed that only at a small temperature range near the temperature of the dielectric maximum does the susceptibility decrease markedly due to the internal field. This temperature range increases with enhancing internal field. We found that the susceptibility is almost independent of the internal field width at low internal field width, and then decreases linearly with enhancing internal field width. This dependence of the susceptibility on the internal field width is very similar to the relation of the dielectric constant with logarithmic aging time, which probably suggests a linear dependence of the internal field on the logarithm of the aging time. The frequency dependence of the susceptibility aging is sensitive to the temperature. With increasing temperature, the curve of the susceptibility change against logarithmic frequency varies from concave to approximately linear, and then to convex, which is in agreement with the recent aging rate measurement.

Optical Properties and Model of Relaxor Ferroelectrics

Phenomenological approach to a relaxor theory is developed and some experi-mental results in the support of this theory are received. The optical absorption spectrum, luminescent emission and photoconductivity are investigated in the wide temperature region in PbMg 1/3 Nb 2/3 O 3 . On the basis of this data the density of states on the impurity band and the velocity of charge carrier localization are found. The probability distribution of relaxation time, g (ln( ))dln( ), is found analytically as the function of the density of states in the impurity polaron band. The temperature dependences of dielectric response of relaxor ferroelectrics are described in the framework of the Landau-Ginzburg-Devonshire theory of phase transitions. The properties of local centers and polaron localization dynamics are studied.