Relaxor State Research Articles

Низкотемпературная аномалия диэлектрических свойств наночастиц магнетита

This paper is devoted to study the dielectric response of magnetic alkali borosilicate glasses containing single-domain magnetite nanoparticles in the temperature range 5 - 100 K on heating and on cooling in magnetic fields from 0 to 14 T in the frequency range from 1 Hz to 160 kHz. It is shown, that an anomaly in the dielectric response is observed in the temperature range 15 - 50 K for single-domain magnetite nanoparticles. The position of this peculiarity is in good agreement with the transition to the relaxor state observed in the bulk material. The temperature hysteresis of this anomaly has been observed on heating and cooling, and it decreases with decreasing measurement frequency.

Relaxor ground state forced by ferroelastic instability in K0.5Bi0.5TiO3−Na0.5Bi0.5TiO3

The complex interplay of local disorder with the structure and dynamics and their role in enhancing the electromechanical response makes relaxor ferroelectric materials fascinating both from the scientific and technological standpoints. It is generally believed that in chemically disordered ferroelectric solid solutions, the normal ferroelectric state gradually yields to a relaxor ground state on increasing the concentration of localized (point-defect-like) random-field centers. That a different kind of process can spontaneously stabilize a relaxor ground state is less known, especially in the family of ferroelectric perovskites. We demonstrate the occurrence of this less-known phenomenon in $(1\ensuremath{-}x){\mathrm{K}}_{0.5}{\mathrm{Bi}}_{0.5}\mathrm{Ti}{\mathrm{O}}_{3}\text{\ensuremath{-}}(x){\mathrm{Na}}_{0.5}{\mathrm{Bi}}_{0.5}\mathrm{Ti}{\mathrm{O}}_{3}[(1\ensuremath{-}x)\mathrm{KBT}\ensuremath{-}(x)\mathrm{NBT}]$. Unlike the gradual evolution common to most ferroelectric solid solutions, KBT-xNBT exhibits an abrupt crossover from a normal ferroelectric ground state to a full-blown relaxor ground state for $xg0.58$. We show that this abrupt crossover to the relaxor state is caused by stabilization of an incommensurate-like/highly disordered $M$-point ferroelastic distortion in the ergodic/paraelectric temperature regime. The abrupt crossover manifests as composition driven anomalous changes in several important properties such as dielectric response, electromechanical properties, tetragonality, and coercive field, electrostrain, and mimics a scenario often encountered in composition driven interferroelectric transformations.

Emergence of reentrant relaxor behavior with enhanced electromechanical and electrocaloric effect in Ba0.95Ca0.05Sn0.09Ti0.91O3 ceramic

Both A- and B-site-substituted BaTiO3 ceramics are promising alternative relaxor materials to replace lead zirconium titanate as an actuator. With a motivation to improve electromechanical properties, a lead-free Ba0.95Ca0.05Sn0.09Ti0.91O3 (BCST) ceramic close to the polymorphic phase boundary composition is synthesized by solid-state reaction. X-ray diffraction and Raman spectroscopy confirm the coexistence of orthorhombic (Amm2) and tetragonal (P4 mm) phases at room temperature. Our low-temperature dielectric study reveals the appearance of a reentrant relaxor state from the ferroelectric state near ∼150 K and is attributed to the coexistence of short and long ferroelectric ordered regions and slowing down of domain dynamics in the smaller regions, similar to the reentrant spin glass state observed in the system Fe-xAu. This feature is confirmed through glass model fitting parameters [ωo = 2.66(±0.28) × 108 Hz, Tg = 110(±1) K, zv = 4.5(±0.3)], and Mydosh parameter (“K” ∼ 0.05). The field-induced polarization (P–E) and strain (S–E) curves show well-defined slim ferroelectric and “butterfly-like” loops with a large value of maximum strain of ∼0.12%, an electromechanical coefficient of d*33 ∼ 1113 pm/V, and an electrostrictive coefficient of Q11 ∼ 0.048 m4/C2 at room temperature.

Structural transition, large strain induced by B-site equivalent doping with Hf4+ ions in BNT-based ceramics

A series of HfO2-modified (Bi0.475Na0.405K0.055Li0.015)0.95Ba0.05Ti(1-x)HfxO3 (x = 0–0.015) lead-free ceramics were prepared. Results of detailed characterizations showed that the addition of HfO2 had little influence on the grain size, and all of the samples showed the pure perovskite structure. As the Hf4+ content increases, the samples changed from the normal ferroelectric phase to the ergodic relaxor state at room temperature, and the ceramics with x = 0.01 showed a high electro-strain of 0.295% at 6 kV/mm. Therefore, this study provides a new insight into of how the HfO2 addition influences the ferroelectric property of the BNT-based ceramics by B-site substitution.

High-energy storage performance in BaTiO3-based lead-free multilayer ceramic capacitors

Abstract

Improper relaxor state in(Ca1−xSrx)8[AlO2]12(MoO4)2

Dielectric and elastic properties of aluminate-sodalite-type oxides, ${({\mathrm{Ca}}_{1\ensuremath{-}x}{\mathrm{Sr}}_{x})}_{8}{[\mathrm{Al}{\mathrm{O}}_{2}]}_{12}{(\mathrm{Mo}{\mathrm{O}}_{4})}_{2}$ with $x=1/16$ and 1/4, are investigated in the present study. A well-defined improper ferroelectric phase transition is demonstrated in the composition of $x=1/16$ by the onset of spontaneous strain and sharp anomalies in the dielectric and elastic responses around 600 K. As the Sr concentration increases to $x=1/4$, strong frequency dispersion appears in the dielectric and elastic responses, indicating that the system changes into a short-range ordered state. The dielectric and elastic anomalies are found to follow a single Vogel-Fulcher equation over a wide frequency range from ${10}^{\ensuremath{-}1}$ to ${10}^{6}\phantom{\rule{0.16em}{0ex}}\mathrm{Hz}$. The present results suggest an improper relaxor state at the composition of $x=1/4$, in which polar nanoregions form under spatially heterogeneous strain due to differences in the local coordination environments around Ca and Sr.

Nature of polar state in 0.67BiFeO3–0.33BaTiO3

This study was conducted to understand the nature of the polar state in the morphotropic phase boundary composition 0.67BiFeO3–0.33BaTiO3 (0.67BF–0.33BT). Both the unpoled and poled specimens exhibit an average cubic structure. The poling induces a 0.14% increase in the lattice parameter. Macrodomains are absent both in the initial and polar state of 0.67BF–0.33BT. A typical relaxor-type dielectric anomaly was observed (Tf = ~ 627 K, TB = ~ 820 K). The remnant polarization (Pr), maximum value of electrostrain (Sm), and magnitude strain at Ec in the bipolar mode (Sneg) increase clearly during heating (Pr, ~ 40 µC/cm2; Sm, 0.191% under 40 kV/cm at 453 K). Unlike Bi0.5Na0.5TiO3-based nonergodic relaxors, the first-cycle bipolar electrostrain loops indicate that the minimum strain on the negative side of the bipolar strain curves is negative. Furthermore, the slopes of the relative permittivity versus log frequency plots in unpoled (− 21) and poled (− 23) specimens are similar. The transition between the relaxor state and ferroelectric-like state does not involve a clear dielectric anomaly even in the poled specimen.

Macroscopic polarization in the nominally ergodic relaxor state of lead magnesium niobate

Macroscopic polarity and its dynamic response to external electric fields and temperature in the nominally ergodic relaxor phase of pristine lead magnesium niobate crystals and ceramics, Pb(Mg1/3Nb2/3)O3 (PMN), were investigated. Dynamic pyroelectric measurements provide evidence for persistent macroscopic polarity of the samples. Annealing experiments below and above Burns temperature of polarized samples relate this polarity to the presence of polar nano-entities and their dynamics. The dc electric field strength required for macroscopic polarization reversal is similar to the amplitude of the ac field where dynamic nonlinear dielectric permittivity reaches its maximum. Consequently, the aforementioned maximum is related to the reorientation of polar nano-entities. The results question the existence of an ergodic state in PMN below Burns temperature.

Evolution of Relaxor Behavior in Multiferroic Pb(Fe2/3W1/3)O3-BiFeO3 Solid Solution of Complex Perovskite Structure

Mutiferroic materials like bismuth ferrite BiFeO3 have attracted much interest in the last decade due to their promising potential for such applications as spintronics and magnetoelectric data storage devices. On the other hand, relaxor ferroelectrics have been intensively studied for their complex structures with quenched disorder and polar nanoregions which play an important role in their outstanding piezoelectric performance. Much less studied are the single-phase multiferroics that exhibit ferroelectric and/or magnetic relaxor behavior and the correlation between their structure and intricate magneto-electric interactions. In this work, we investigate the evolution of the structure and relaxor behavior in the solid solution between the complex perovskite multirelaxor Pb(Fe2/3W1/3)O3 [PFW] and canonical multiferroic BiFeO3 [BFO], (1-x)PFW-xBFO (with a solubility limit of x = 0.30). The temperature dependences of the dielectric permittivity and loss tangent measured in the frequency range from 100 Hz to 1 MHz indicate characteristic relaxor ferroelectric properties for compositions of x ≤ 0.15, with a frequency-dependent dielectric permittivity peak and its temperature, Tm, satisfying the Vogel-Fulcher law. Detailed studies of the evolution of the relaxor behavior with composition reveal that Tm decreases firstly with a small amount (x = 0.05) of BFO substitution and then increases with further increase of BFO concentration. The degree of relaxor character, as defined by ΔTm [Tm (1 MHz) - Tm (100 Hz)], increases monotonously with increasing BFO content, signifying an enhancement of relaxor behavior with BFO substitution, which is confirmed by the Lorenz-type quadratic variation of the static permittivity. A temperature - composition phase diagram is constructed in terms of the characteristic Burns temperature (TB) and freezing temperature (Tf), which delimits a paraelectric state (PE) above TB, a non-ergotic relaxor state (NR) below Tf, and an ergotic relaxor state (ER) in between. The observed enhancement of relaxor behavior is explained by an increase in the number and size distribution of polar nanoregions in the ER phase, resulting from increased compositional and charge disorders as a result of BFO substitution. The evolution of relaxor behavior and its microscopic mechanisms studied in this work are insightful for a better understanding the multirelaxor properties in multiferroics. Moreover, further substitution of BFO (x ≥ 0.2) flattens the permittivity curves and leads to a temperature-stable variation of high dielectric constant (≈ 103) in a wide temperature range, making the PFW-BFO solid solution attractive for such applications as high energy density capacitors.

Lead-free Na0.4K0.1Bi0.5TiO3 ceramic: Poling effect and enhancement in electromechanical and piezoelectric voltage coefficient

The effect of electric poling on the piezoelectric properties of the sintered Na0.4K0.1Bi0.5TiO3 is studied with varying poling field and temperature. An optimized poling condition (EP =50 kVcm, TP =110 °C) exhibited a high piezoelectric voltage (g33∼ 85 mV m/N) and charge coefficients (d33∼193pC/N). A combination of electric field induced irreversible transformation from polar nano regions embedded in a non-polar relaxor state to a long-range ordered ferroelectric state and increase in the structural ordering are responsible for the observed high piezoelectric properties. A mechanism is discussed to reveal the origin of high voltage coefficient due to poling, where the decrease of dielectric permittivity can facilitate high g33. This investigation provides an approach for designing the high performance Na0.4K0.1Bi0.5TiO3based materials suitable for sensors and energy harvesting applications.

Phase evolution in (1−x)(Na0.5Bi0.5)TiO3-xSrTiO3 solid solutions: A study focusing on dielectric and ferroelectric characteristics

In the present work, the nature of phase evolution of (1−x)(Na0.5Bi0.5)TiO3-xSrTiO3 (NBT-xST) solid solutions with x of 0–0.6 is revealed by characterizing the dielectric and ferroelectric properties. Two unique dielectric anomalies associated with high-temperature nanoregions (PNRs) in the ergodic relaxor (ER) state and low-temperature PNRs in the nonergodic relaxor (NR) state are identified. Characteristic temperatures, including TB,TRT∗, Tm, Td and TT∗, are determined in fresh and poled states on the basis of the characteristics of the evolution of these two dielectric anomalies. The whole evolution of the transition from the NR state to the ER state is reflected by the temperature-dependent polarization versus electric field (P-E) hysteresis loops, i.e., from the square loops, via the double-like loops, to the slim loops. The characteristic temperatures, including TP-N, TN-R and TR-dis, are determined by the characteristics of the evolution of P-E loops. Accordingly, a phase diagram of NBT-xST was constructed according to these characteristic temperatures. Most importantly, the relationship between polarization responses and heterogeneous polar phase coexistence has been established and a schematic diagram is given. This work will help to understand the phase evolution and its impact on the macroscopic properties of NBT and the associated NBT-based solid solutions.

Probing the Coexistence of Ferroelectric and Relaxor States in Bi0.5Na0.5TiO3-Based Ceramics for Enhanced Piezoelectric Performance.

To tackle the global restriction on the use of lead-based materials, a feasible strategy of developing a piezoelectric ceramic with a ferroelectric- and relaxor-coexisted hybrid state is proposed in order to reduce the energy barrier as well as to assist polarization rotation. A significantly enhanced piezoelectric coefficient, d33, of 173 pC/N along with a broadened high-temperature stability above 300 °C has been obtained. Further probing via piezoresponse force microscopy unveils the grain boundary-governed domain structures with complicated configurations, suggesting close correlations with the coexistence of ferroelectric and relaxor states. This work demonstrates a recipe for establishing a novel grain-based ferroelectric-relaxor hybrid state with improved piezoelectric performance, which can further be beneficial for realistic applications.

Effect of bismuth doping on structural and electrical properties of 0.9(BaZr0.2Ti0.8O3)–0.1(Ba0.7Ca0.3TiO3) ceramic

The (Ba0.97Ca0.03)1−3y/2BiyZr0.18Ti0.82O3 ceramic system was prepared by the conventional solid-state sintering technique. The effect of bismuth substitution has been investigated via X-ray diffraction, Scanning electron microscopy, dielectric, electric and ferroelectric measurements. X-ray diffraction showed that these compounds crystallized, at room temperature, in tetragonal P4mm space group symmetry for BCTZ10 and BCTZ10–0.02Bi compounds and in cubic symmetry with space group Pm3‾m for y = 0.06; 0.08 and 0.1 compositions distorted perovskite structures. SEM images were used to observe the microstructure. The effect of the crystal structure change and microstructure features on the dielectric and ferroelectric properties of our new BCTZ10-yBi ceramic system has been discussed. The dependence of the permittivity on temperature indicated a crossover from a normal ferroelectric, for both BCTZ10 and BCTZ10–0.02 ceramics, to a relaxor state for 0.06 < y ≤ 0.1 composition compounds. The enhancement of the dielectric properties was marked by the shift of Tm to room temperature, the increase of the maxim of permittivity and the improvement of the relaxor behavior that characterizes optimal composition due to Bi3+ substitution. BCTZ10–0.06Bi ceramic exhibit the highest εrm', with a value of 11508 at 1 kHz, at Tm of 270 k near room temperature. Both BCZT10 and BCZT-0.02Bi ceramics exhibit a hysteresis loops signature of ferroelectric behavior at room temperature. While doped BCZT-0.02Bi show just a non linear evolution of P vs. E, the increase of the spontaneous and remnant polarizations: Ps from 0.063 μC/mm2 to 0.073 μC/mm2 and Pr from 0.028 μC/mm2 to 0.040 μC/mm2 for BCZT10 and BCZT10–0.02Bi compositions, respectively, is an evidence of the enhancement of ferroelectric properties as a result of bismuth substitution on BCZT10. The electrical properties of our new BCTZ10-yBi ceramic system may be largely tunable and could be attractive for non-volatile random access memory devices.

Synthesis and characterization of Bi0.5Na0.5TiO3-BaTiO3-K0.5Na0.5NbO3 ceramics for energy storage applications

Structural, microstructural, dielectric, ferroelectric and piezoelectric properties of the (0.95-x)Bi0.5Na0.5TiO3–0.05BaTiO3-xK0.5Na0.5NbO3 (BNT-BT-KNN) lead-free ceramics with 0.0 ≤ x ≤ 0.06 were studied. Samples were synthesized through the mechanochemically activated solid-state method and structurally characterized by X-ray diffraction (XRD) and Raman-spectroscopic studies, whereas the microstructure of all samples was analyzed by Field Emission Scanning Electron Microscopy (FE-SEM). When KNN concentration and temperature were increased, the transition from a ferroelectric to relaxor state was detected by ferroelectric-loop measurements. Furthermore, the high-energy storage efficiency values at room temperature obtained for samples with x ≥ 0.04 confirm the suitability of these ceramics for energy storage applications.

Effects of crystal chemistry and local random fields on relaxor and piezoelectric behavior of lead-oxide perovskites

Random electric fields caused by the disordered distribution of heterovalent cations over the equivalent crystallographic positions are often considered to be the main reason of the relaxor behavior and the associated giant electromechanical response. Some models relate the development of the relaxor state to the crystal chemical properties of the constituent ions. In this work the functions of random fields and ferroactive cations are compared in perovskite solid solutions in the desirable for technological applications composition range of morphotropic phase boundary. The crystal structure, dielectric and ferroelectric properties, piezoelectric effect and electrostriction are investigated in technologically important ceramic solid solutions PbzBa1−z(Mg1/3Nb2/3)m(Zn1/3Nb2/3)y(Ni1/3Nb2/3)nTixO3 with substitutions in A (Pb2+ by Ba2+)- and B (Ti4+ by [B2+1/3Nb5+2/3]4+) perovskite sublattices. Two composition sections of the system are designed; in both of them the concentration of ferroactive ions, Pb2+ and Ti4+, respectively, varies within the same range of 15%, but the strength of quenched random electric fields changes significantly only in B-substituted ceramics. Similar behavior is found in both sections, including the same sequence of structural phase transitions and transformations from normal ferroelectric to relaxor state and similar evolution of properties with concentration. The results clearly demonstrate that the role of crystal chemical factors in the development of relaxor behavior and electromechanical performance of lead-oxide materials is not less important than that of quenched random fields. The mechanisms of the observed behavior are discussed in the frame of existing theoretical models.

Superior electrostrictive coefficient of 6BNT-4SCxBT lead-free relaxor ferroelectrics with Ca2+ substitution

In this study, lead-free 0.6(Bi0.5Na0.5)TiO3-0.4(Sr0.7-xCaxBi0.2)TiO3 ceramics (abbreviated as 6BNT-4SCxBT, x=0, 0.05, 0.10, 0.15 and 0.20 mol) were prepared by a traditional solid-state method. The effects of Ca2+ on phase structure, state transformation, ferroelectric and energy storage properties, and electrostrictive performance of 6BNT-4SCBT-x ceramics were comprehensively investigated. Co-occupied Bi3+, Na+, Sr2+ and Ca2+ ions induced the inhomogeneous distribution of A-site ions and charge, which resulted in polar nano-regions (PNRs) for relaxor ferroelectrics. 6BNT-4SCxBT ceramics present the ergodic relaxor state of polar rhombohedral PNRs and weakly polar tetragonal PNRs at room temperature. When the Ca2+ content was increased, 6BNT-4SC0.01BT ceramics showed the properties of weakly polar tetragonal PNRs (with lowest Tp~71 °C). 6BNT-4SCxBT ceramics exhibit electrostrictive effect Q33 (~0.045 m4/C2) and high energy storage efficiency. Moreover, large Q33 (>0.0421 m4/C2) indicates good electrical field stability. This result is a significant advancement in the area of lead-free electrostrictive materials, which has a great prospect in BNT-based ceramics.

Ferroelectric and piezoelectric properties of (Bi1/2K1/2)(ZrxTi1−x)O3 lead-free ceramics

We report the effect of Zr substitution for Ti on the ferroelectric and piezoelectric properties of lead-free (Bi1/2K1/2)TiO3 (BKT) ceramics. Dense ceramics of (Bi1/2K1/2)(ZrxTi1−x)O3 with x up to 0.06 were fabricated by sintering of hydrothermally derived fine powders. The investigation of the crystal structure and dielectric properties revealed that the Zr substitution decreased the tetragonal lattice distortion of BKT and stabilized the relaxor state. The coercive electric field was found to be decreased monotonically with increasing the Zr content, while the largest remanent polarization of 26 μC cm−2 was observed at x = 0.04. As a result, the ceramic with x = 0.04 showed an enhanced piezoelectric d33 constant of 140 pC N−1.

Electric-Field-Induced Phase Transformation and Frequency-Dependent Behavior of Bismuth Sodium Titanate-Barium Titanate.

The electric field response of the lead-free solid solution (1−x)Bi0.53Na0.47TiO3–xBaTiO3 (BNT–BT) in the higher BT composition range with x = 0.12 was investigated using in situ synchrotron X-ray powder diffraction. An introduced Bi-excess non-stoichiometry caused an extended morphotropic phase boundary, leading to an unexpected fully reversible relaxor to ferroelectric (R–FE) phase transformation behavior. By varying the field frequency in a broad range from 10−4 up to 102 Hz, BNT–12BT showed a frequency-dependent gradual suppression of the field induced ferroelectric phase transformation in favor of the relaxor state. A frequency triggered self-heating within the sample was found and the temperature increase exponentially correlated with the field frequency. The effects of a lowered phase transformation temperature TR–FE, caused by the non-stoichiometric composition, were observed in the experimental setup of the freestanding sample. This frequency-dependent investigation of an R–FE phase transformation is unlike previous macroscopic studies, in which heat dissipating metal contacts are used.

Electric field-induced strain in Sr(Hf0.5Zr0.5)O3-modified Bi0.5(Na0.8K0.2)0.5TiO3 piezoelectric ceramics

Lead-free Sr(Hf0.5Zr0.5)O3-modified Bi0.5(Na0.8K0.2)0.5TiO3 (SHZ-BNKT) ceramics were synthesized using a conventional solid-state, mixed-oxide method. In complex solid solutions such as BNKT, the role of a ternary additive is important because it can break up the long-range dipole order, which destabilizes the ferroelectric phase leading to relaxor behavior. In this system, as verified by x-ray diffraction, SHZ was incorporated into the BNKT perovskite lattice throughout the studied compositional range. The coexistence of tetragonal and rhombohedral phase was observed for x = 0.00 and with the addition of SHZ, a transition to pseudocubic symmetry was observed, which is indicative of the onset of relaxor behavior. To characterize the relaxor properties of the material, the polarization–electric field hysteresis, dielectric, and electric-field-induced strain behaviors were studied as a function of composition. The temperature-dependent dielectric spectra showed frequency dependence for all the SHZ-modified BNKT ceramics, which is a typical characteristic of relaxor ferroelectrics. Furthermore, constriction in polarization loops and an absence of negative strain in the bipolar strain measurement for SHZ-modified BNKT compositions confirms that the addition of SHZ significantly disrupts the ferroelectric order. The addition of 2 mol. % SHZ in BNKT markedly enhanced the electric field-induced strain from 0.10% (for pure BNKT) to 0.33% (for 2% SHZ-BNKT). The corresponding normalized strain coefficient (d33∗=Smax/Emax) increased from 196 pm/V to 663 pm/V at a moderate electric field of 50 kV/cm. These results indicate that BNKT–SHZ ceramics can be designed for an improved strain response via a cation substitution-induced relaxor state for electromechanical actuator applications.

Tailoring the Structure, Energy Storage, Strain, and Dielectric Properties of Bi0.5(Na0.82K0.18)0.5TiO3 Ceramics by (Fe1/4Sc1/4Nb1/2)4+ Multiple Complex Ions

The effects of (Fe1/4Sc1/4Nb1/2)4+ (FSN) multiple complex ions on the structure and electrical properties of Bi0.5(Na0.82K0.18)0.5Ti(1-x)(Fe1/4Sc1/4Nb1/2)xO3 (BNKT-xFSN) ceramics were studied. The FSN complex ions induces the phase transition from ferroelectric state to relaxor state. The coercive field and remanent polarization decrease rapidly with the increase of FSN content. With the increase of the external electric field, the energy storage density of BNKT-xFSN ceramics gradually increases and reaches the maximum value of 0.96 J/cm3 (90 kV/cm) at x=0.09, and the corresponding efficiency is 62%. Meanwhile, the field-induced strain of BNKT-0.07FSN ceramic increases from 0.13% at 50 kV/cm to 0.43% at 80 kV/cm, and the corresponding electrostrictive coefficient Q33 reaches the maximum value of 0.0213 m4/C2. BNKT-xFSN relaxed ceramics with pseudo-cubic structure have large electrostrictive coefficients when TF-R is near room temperature. The local composition inhomogeneity by FSN complex ions at B-sites induces the relaxor characteristics of BNKT-xFSN ceramics.