Relaxor-ferroelectric Solid Solutions Research Articles

Enhanced energy storage performance and thermal stability in relaxor ferroelectric BNKT-BBN solid solution ceramics

Bi0.5Na0.5TiO3 (BNT)-based relaxor ferroelectrics have attracted considerable interest over the past decades as candidate materials to replace lead-based piezoelectrics because of their environmental friendliness. Moreover, owing to their high maximum polarization and high-power density resulting from their relaxor activity, BNT-based relaxor ferroelectrics have attracted attention as potential candidates for energy storage. Herein, bismuth layer-structured BaBi2Nb2O9 (BBN) was introduced into the perovskite binary material system 0.78(Bi0.5Na0.5TiO3)-0.22(Bi0.5K0.5TiO3) (BNKT). Compared to pure BNKT ceramics, BNKT-BBN exhibited improved relaxor behavior and suppressed grain growth. Moreover, an increase in BBN content increased the breakdown strength. Consequently, the energy storage efficiency increased from 32 % to 58 %. In addition, the thermal stability (ΔWrec/Wrec) remained below ∼5 % in the temperature range from room temperature to 200 °C. The findings of this study demonstrated that the introduction of BBN into BNT-based relaxor ferroelectrics is an effective way to improve energy storage performance and high temperature stability.

Polarization behavior in a compositionally graded relaxor–ferroelectric crystal visualized by angle-resolved polarized Raman mapping

Explaining the properties and functions of materials in terms of their atomic arrangements and inhomogeneous structures is a fundamental challenge for the development of ferroelectric oxides. Dielectric response, a fundamental property of matter, can be explained by long-wavelength polar lattice vibrations and dipole relaxations capable of responding to electrical bias; therefore spectroscopic methods, such as Raman spectroscopy, can be used to investigate its origin. Herein, we used angle-resolved polarized Raman mapping to investigate how phase boundaries and giant dielectric responses are related in a relaxor-Pb(Mg1/3Nb2/3)O3–ferroelectric-PbTiO3 (PMN-xPT) solid-solution system using a compositionally graded crystal, with gradual changes in polarization direction visualized by Raman mapping. The variation of the width of quasielastic light scattering with position reveals the following: The huge dielectric response observed in PMN-xPT is ascribable to the slowing down of a relaxation related to mesoscopic ferroelectric domains near the phase boundary, which is characteristic of relaxor–ferroelectric solid-solution systems and differentiates them from other ferroelectrics.

Origin of polar nanoregions from displacive correlation in relaxor ferroelectric Pb(Mg1/3Nb2/3)O3–PbTiO3

The existence of polar nanoregions (PNRs) which are widely accepted as a key factor contributing to ultrahigh piezoelectricity in relaxor-ferroelectric solid solutions is found to originate from local displacive correlations.

Achieving ultrahigh energy storage efficiency in local-composition gradient-structured ferroelectric ceramics

Although relaxor dielectric ceramic capacitors possess attractive features for high-power energy storage, their low energy storage efficiency (η) induces the dissipation of energy in the ceramics, thus significantly increasing their temperature and deteriorating their breakdown strength and lifetime in practical applications. Here, a new strategy for designing local-composition gradient-structured grains was proposed to improve the energy storage efficiency performance under a high-intensity electric field. To verify the applicability of the proposed strategy, the 0.9(K0.5Na0.5)NbO3–0.1Bi(Zn2/3Nb1/3)O3 relaxor-ferroelectric solid solution was employed for the experimental procedure. The gradient distribution of Zn from the grain interior to the grain boundary was achieved through the meticulous manipulation of different element diffusion behaviors. The resulting local-composition gradient structure could improve the relaxation behavior, while enhancing their dynamic response to external electric fields, thus decreasing dielectric nonlinearity and remarkably improving η performance under a high-intensity electric field. As a result, the η value of the ceramics decreased by a marginal extent until the electric field reached 326 kV cm−1, with a minimal variation of <±1.5%, demonstrating substantially higher performance than that of the well-studied lead-free nonlinear dielectric ceramics. Furthermore, by alleviating the local electric field concentration near the grain boundary, the unique structure could enhance the intrinsic breakdown of the dielectric material. Finally, through the proposed strategy, the optimum energy storage properties were obtained, namely, a high recoverable energy density of 4.01 J/cm3 and an ultrahigh energy efficiency of 97.1% at 326 kV cm−1. The proposed highly effective local-composition gradient-structured design offers a new paradigm for improving the energy storage efficiency of dielectric ceramic capacitors.

Structure-property relationships in the lead-free piezoceramic system K0.5Bi0.5TiO3 - BiMg0.5Ti0.5O3

Distinctive structure-property relationships are revealed in the relaxor ferroelectric ceramic solid solution, (1-x)K0.5Bi0.5TiO3 - xBiMg0.5Ti0.5O3: 0.02 < x < 0.08. The constructed phase diagram and results of in-situ synchrotron X-ray diffraction provide explanations for temperature and electric field dependent anomalies in dielectric, ferroelectric and electromechanical properties. At room temperature a mixed phase tetragonal and pseudocubic phase field occurs for compositions 0 > x ≤ 0.07. As temperature rises to ≥150 °C, the ferroelectric tetragonal relaxor phase changes to a pseudocubic ergodic relaxor phase; this change in length scale of polar order is responsible for an inflection in relative permittivity - temperature plots. The transition is reversed by a sufficient electric field, thereby explaining the constricted form of polarisation-electric field loops measured at >150 °C. It is also responsible for a change in slope of the strain-electric field (S-E) plots which are relatively linear in the ferroelectric regime i.e. at temperatures up to 150 °C, giving unipolar strains of 0.11% at 20 °C and 0.14% at 150 °C (50 kV/cm field). The additional contribution from the effect of the field-induced pseudocubic to tetragonal transition, generates strains of ∼0.2% at 185 °C. Unusual for a piezoelectric solid solution, the maximum strains and charge coefficients (d33 = 150 pC/N, 20 °C) do not coincide with a morphotropic or polymorphic phase boundary.

High dielectric permittivity and electrostrictive strain in a wide temperature range in relaxor ferroelectric (1-x)[Pb(Mg1/3Nb2/3)O3-PbTiO3]-xBa(Zn1/3Nb2/3)O3 solid solutions

High electric field-induced strain with ultralow hysteresis, which is often generated based on electrostrictive effects in ferroelectric materials, is highly desired due to its potential applications in high-precision displacement actuators. In this paper, (1-x)[Pb(Mg1/3Nb2/3)O3-PbTiO3]-xBa(Zn1/3Nb2/3)O3 [(1-x)(PMN-PT)-xBZN] ceramics were fabricated by a solid-state reaction method. The effect of Ba(Zn1/3Nb2/3)O3 (BZN) content on dielectric and electrostrictive properties in relaxor ferroelectric PMN-PT solid solutions was investigated in detail by dielectric spectra, polarization-electric field (P-E) hysteresis loops and strain-electric field (S-E) curves. With an increasing BZN content, the temperature stability of the dielectric permittivity of (1-x)(PMN-PT)-xBZN is improved due to the formation of two coexistent phases. A high electrostrictive strain (~0.17% at 60 kV/cm) with an ultralow hysteresis (<10%) characteristic is obtained in a composition where x = 0.1725. The strain versus polarization (S-P) curves measured from 30 °C to 130 °C can be well fitted based on a quadratic relation, suggesting the dominating role of the electrostrictive effect. The longitudinal electrostrictive coefficient Q33 for this system ranges from 0.0254 m4/C2 to 0.0318 m4/C2. Our results suggest that (1-x)(PMN-PT)-xBZN ferroelectric ceramics are potential candidates for applications in capacitors and high-precision displacement actuators.

The origin of ultrahigh piezoelectricity in relaxor-ferroelectric solid solution crystals.

The discovery of ultrahigh piezoelectricity in relaxor-ferroelectric solid solution single crystals is a breakthrough in ferroelectric materials. A key signature of relaxor-ferroelectric solid solutions is the existence of polar nanoregions, a nanoscale inhomogeneity, that coexist with normal ferroelectric domains. Despite two decades of extensive studies, the contribution of polar nanoregions to the underlying piezoelectric properties of relaxor ferroelectrics has yet to be established. Here we quantitatively characterize the contribution of polar nanoregions to the dielectric/piezoelectric responses of relaxor-ferroelectric crystals using a combination of cryogenic experiments and phase-field simulations. The contribution of polar nanoregions to the room-temperature dielectric and piezoelectric properties is in the range of 50–80%. A mesoscale mechanism is proposed to reveal the origin of the high piezoelectricity in relaxor ferroelectrics, where the polar nanoregions aligned in a ferroelectric matrix can facilitate polarization rotation. This mechanism emphasizes the critical role of local structure on the macroscopic properties of ferroelectric materials.

Perovskite ferroelectrics and relaxor-ferroelectric solid solutions with large intrinsic electrocaloric response over broad temperature ranges

Electrocaloric materials have emerged as a viable technology for solid state heating/cooling and waste heat recovery applications. We provide a general methodology for theoretical analysis to both assess and guide the way in discovering new high performance electrocalorics.

High Temperature Acoustic Anomalies in PMN-PSN Solid Solution

We present an acoustic study of 0.55 PbMg1/3Nb2/3O3 - 0.45 PbSc1/2Nb1/2O3 relaxor ferroelectric solid solution in a wide temperature range, from 150 to 750 K. The longitudinal acoustic wave velocity and attenuation were measured by the ultrasonic pulse-echo technique at frequency 10 MHz. The strong anomalies observed in the longitudinal sound velocity and attenuation versus temperature were found to correlate with the temperature range of the relaxor ferroelectric state. Attenuation peaks were observed at characteristic temperatures of relaxors, i.e., at TB (Burns temperature) and T* (an additional significant temperature). The results are compared with the acoustic behavior of PbMg1/3Nb2/3O3.

The Change in Domain Structures from Tweed in Rhombohedral Phase to Twin Structure in Orthorhombic One with Stress in Relaxor Ferroelectric Solid Solutions

Rhombohedral ellipsoidal domains, tetragonal circular ones, orthorhombic star ones, and dark domains consisted of fluxes of platelets were found to be induced on the (001)cub plane in 24PIN-46PMN-30PT crystals by shear stresses applied along [001]cub direction through Vickers micro-indentation. Bright star orthorhombic domains along [110]cub direction and the dark domains of nano-inclusions along [100]cub and [110]cub directions correspond to the creation and annihilation of thin platelet domains for the shuffling model, respectively. Two kinds of dielectric dispersions were found in depoled 24PIN-46PMN-30PT: one is the relaxor type and the other normal one at higher temperatures than the relaxor type.

Poling and Depoling Effects on Dielectric Properties and Domain Structures in Relaxor 24Pb(In1/2Nb1/2)O3–46Pb(Mg1/3Nb2/3)O3–30PbTiO3 near a Morphotropic Phase Boundary Composition

The temperature dependence of the complex relative permittivity in a relaxor ferroelectric solid solution 24Pb(In1/2Nb1/2)O3–46Pb(Mg1/3Nb2/3)O3–30PbTiO3 (PIN–PMN–PT) crystal poled and depoled was measured from room temperature to 200 °C at various frequencies. The poled sample exhibits transitions from the ferroelectric (FE) phase to the relaxor (RE) phase on heating, and after that, the depoled one exhibits those from the RE phase to the glassy freezing phase on cooling. An RE-type dielectric dispersion with a weak frequency (f) dependence was observed. Such a dielectric dispersion in the RE state was found to be based on tweed domain structures observed by polarization light microscopy (PLM) and piezoelectric force microscopy (PFM) due to the competition between the antiferroelectric (AFE) and FE coupling in the RE state. The temperature dependence of complex permittivity with resonance- and relaxor-type dielectric dispersions in the poled and depoled samples was characterized by hierarchical domain structures.

The Effect of Pressure on the Poling Condition in Lead-based Relaxor Ferroelectric Solid Solutions

The Effect of Pressure on the Poling Condition in Lead-based Relaxor Ferroelectric Solid Solutions

Dielectric characterization of (1-x)pmn-xpt (x = 0.07 and 0.10) ceramics synthesized by an ethylene glycol-based soft chemical route

Materials based on relaxor ferroelectrics have become one of the most important families of functional materials being explored for such applications as sensors/actuators, micro-electromechanical systems (MEMS), non-volatile random access memories, and high-energy-density capacitors. Fabrication of high-quality relaxor-based ceramics remains, however, a challenging task. In this work, a new soft chemical synthetic method for the preparation of the complex perovskite-based relaxor ferroelectric solid solutions, (1-x)Pb(Mg(1/3)Nb(2/3))O(3)-xPbTiO(3) was developed using ethylene glycol as the solvent. Ceramics with compositions of x = 0.07 and 0.10 were prepared and it was found that a 10% stoichiometric excess of Pb(2+) was required to compensate for lead oxide volatility at the high temperatures used for sintering. The ceramics produced by this method show excellent dielectric properties at room temperature, such as a high dielectric constant (~20 000) and low loss over a large temperatures range (tan δ < 0.01 between 20 and 200°C). The temperature dependence of the dielectric constant exhibits typical relaxor ferroelectric behavior, fitting a quadratic law which describes the high-temperature slope of ε'(T) peak. The frequency dispersion of the temperature of maximum permittivity satisfies the Vogel-Fulcher law.

Hierarchical Domain Structures in Relaxor 24Pb(In1/2Nb1/2)O3–46Pb(Mg1/3Nb2/3)O3–30PbTiO3 near a Morphotropic Phase Boundary Composition Grown by Bridgman Method

The domain structures of the lead-based relaxor ferroelectric solid solution single crystal, 24Pb(In1/2Nb1/2)O3 (PIN)–46Pb(Mg1/3Nb2/3)O3 (PMN)–30PbTiO3 (PT), near a morphotropic phase boundary (MPB) composition grown by the Bridgeman method were studied by polarized light microscopy (PLM), piezoresponse force microscopy (PFM) and scanning electron microscopy (SEM). The change in domain structures with poling from rhombohedral spindlelike domains of 3–5 µm width to orthorhombic domains of ∼20 µm width with rectangular cells with a size of 3–5 µm, characterized with an antiferroelectic double hysteresis loop in the electric field-induced strain behavior, was found. Such domain structures were microscopically identified from SEM images as small circular tetragonal defects, planar monoclinic defects such as edge and screw dislocations with Burgers vector b along <110>cub and/or <100>cub directions and their agglomerate rectangular orthorhombic defects, also characterized by PFM. Hierarchical domain structures are discussed from the viewpoints of domain structures due to defects such as edge and screw dislocations originating in the chemical order region (COR) and the piezoelectric responses and dielectric properties.

Hierarchical Domain Structures in Relaxor 24Pb(In1/2Nb1/2)O3–46Pb(Mg1/3Nb2/3)O3–30PbTiO3near a Morphotropic Phase Boundary Composition Grown by Bridgman Method

The domain structures of the lead-based relaxor ferroelectric solid solution single crystal, 24Pb(In1/2Nb1/2)O3 (PIN)–46Pb(Mg1/3Nb2/3)O3 (PMN)–30PbTiO3 (PT), near a morphotropic phase boundary (MPB) composition grown by the Bridgeman method were studied by polarized light microscopy (PLM), piezoresponse force microscopy (PFM) and scanning electron microscopy (SEM). The change in domain structures with poling from rhombohedral spindlelike domains of 3–5 µm width to orthorhombic domains of ~20 µm width with rectangular cells with a size of 3–5 µm, characterized with an antiferroelectic double hysteresis loop in the electric field-induced strain behavior, was found. Such domain structures were microscopically identified from SEM images as small circular tetragonal defects, planar monoclinic defects such as edge and screw dislocations with Burgers vector b along cub and/or cub directions and their agglomerate rectangular orthorhombic defects, also characterized by PFM. Hierarchical domain structures are discussed from the viewpoints of domain structures due to defects such as edge and screw dislocations originating in the chemical order region (COR) and the piezoelectric responses and dielectric properties.

Analysis of the Piezoelectric Performance of Modern 0–3-Type Composites Based on Relaxor-Ferroelectric Single Crystals

Effective piezoelectric coefficients e 33*, d 33*, g 33*, and h 33*, squared figures of merit d 33*g 33* and dh *gh *, and other related parameters of novel 0–3 and 0–3–0 composites based on single crystals of relaxor-ferroelectric solid solutions of (1−x)Pb(Mg1/3Nb2/3)O3−xPbTiO3 are studied using the effective field method, effective medium method and finite element method. The volume-fraction dependences of a number of parameters and figures of merit are determined using the above methods and compared for composites with aligned prolate spheroidal inclusions. Four parameter ratios that determine interconnections between the effective electromechanical constants of the 0–3-type composites are first introduced. These parameter ratios are used to interpret the longitudinal dielectric and piezoelectric response of composite structures with prolate inclusions that exhibit high piezoelectric activity. The role of piezoelectric anisotropy and activity of the composite components in forming the longitudinal piezoelectric effect is analysed. Specific novel composite architectures with high piezoelectric sensitivity (longitudinal and hydrostatic) are identified and discussed.

Electrical Properties of Lead-Free Relaxor Ferroelectric Solid Solution Single Crystal (Na1/2Bi1/2)TiO3–BaTiO3 Grown by Bridgman Method

Lead-free relaxor ferroelectric solid solution single crystals of (Na1/2Bi1/2)TiO3–BaTiO3 (NBT-BT) grown by the Bridgman method without the flux of Bi2O3 and Na2O have good optical quality and electrical properties. It was found that their transition from the rhombohedral phase to the tetragonal phase occurs at about 250 °C, accompanied by isotropization. Moreover, the domain wall structure changes with heating, and dielectric dispersion gradually disappears at 250 °C. Relative permittivity increases with further heating and shows a peak at Ta of 340 °C with the appearance of brightness in a polarizing microscope, accompanied by a small frequency dispersion in tan δ. Polarization–electric field (P–E) hysteresis loops reveal a narrow shape without saturation with increasing electric field due to random fields based on defects at A-sites in perovskite compounds. Strain (S) versus electric field curves under bipolar fields reveal a slightly piezoelectric behavior without polarization reversal. The value of d33 (Smax/Emax) was estimated to be about 250 pm/V at room temperature.

Polarization orientation effect and combination of electromechanical properties in advanced0.67Pb(Mg1/3Nb2/3)O3–0.33PbTiO3 single crystal/polymer composites with 2–2 connectivity

A comparative study on the effective piezoelectric properties and hydrostaticpiezoelectric response is first carried out for advanced 2–2 composites based onsingle crystals of relaxor-ferroelectric solid solutions. Different orientationsof domains and different poling directions of components are taken intoconsideration in the analysis of the effective longitudinal piezoelectric coefficientsd33*,e33*,g33* and hydrostaticpiezoelectric coefficients dh*, eh* and gh*. The important role of the polarization orientation effect and the effectof combination of the electromechanical properties in attaining the largeeffective parameters is shown for the parallel-connected 2–2 single-domain0.67Pb(Mg1/3Nb2/3)O3–0.33PbTiO3/polyvinylidene fluoride composite. In particular, near extremum points of the effectiveparameters, this composite is characterized by the piezoelectric coefficientsg33*≈500 mV m N−1,|dh*|≈400 pC N−1,|eh*|≈40 C m−2,and gh*≈400 mV m N−1. Three piezo-sums are first found to describe major contributions of the piezoelectric coefficientsdij*,eij* andgij* todh*,eh* andgh*, respectively, in the vicinity of absolute maxima (minima) of the aforementionedhydrostatic parameters. Advantages concerned with the presence of the single crystal(either single-domain or polydomain) in the studied 2–2 composites are discussed inconnection with their piezoelectric activity, sensitivity and hydrostatic response.

Effects of Pressure on Piezoelectric and Dielectric Responses of Relaxor Ferroelectric Solid Solution Pb(Mg1/3Nb2/3)O3–PbTiO3 Binary System Ceramics near a Morphotropic Phase Boundary Composition

The piezoelectric and dielectric properties of Pb(Mg1/3Nb2/3)O3–PbTiO3 (PMNT) ceramics with compositions near a morphotropic phase boundary (MPB) were investigated under pressures p up to 700 MPa at 25 °C. The resonance and antiresonance frequency characteristics of impedance and phase in the k31 mode for PMNT (67/33) and (69/31) ceramics were observed under various pressures. The effect of pressure on their responses were clearly observed. The electromechanical coupling coefficient k31 in the k31 mode increases and the electromechanical quality factor Q decreases with increasing p at pressures lower than 100 MPa. The decrease in Q with p is due to the scattering of ultrasonic waves from the domain boundary. The relative permittivity εr increases with increasing p. Such increases in both k and εr with p seem to be related to the increase in topographical domain-wall density associated with monoclinic distortions. At pressures higher than 100 MPa, their electromechanical suppression in PMNT ceramics occurs at each pressure, corresponding to the electromechanical coupling coefficient k. εr increases with pressure-induced electromechanical suppression. The change in εr with such suppression corresponds to k. Such a phenomenon seems to be due to the increase in piezoelectric load based on the increase in complex domain wall density coming from the increase in free energy with pressure.

Pressure-modulated free energy change in piezoelectric and dielectric responses for relaxor ferroelectric solid solution Pb(Mg1∕3Nb2∕3)O3–PbTiO3 binary system single crystal and ceramics near a morphotropic phase boundary composition

The electromechanical and dielectric responses in transverse and longitudinal modes for relaxor ferroelectric solid solution Pb(Mg1∕3Nb2∕3)O3–PbTiO3 (PMNT) near a morphotropic phase boundary composition were investigated under hydrostatic pressures up to 700MPa at 25°C. The effect of pressure on their responses remarkably appeared. Their electromechanical suppression in PMNT single crystal and ceramics occurs at each pressure, corresponding to electromechanical coupling coefficient k. The permittivity ε increased with pressure-induced electromechanical suppression. The change in ε with such suppression corresponds to k. Such phenomena were considered to be due to the increase in piezoelectric load based on decrease of domain size coming from increase in free energy with pressures.