O3-based Ceramics Research Articles

Recent Developments in (K, Na)NbO3-Based Lead-Free Piezoceramics.

(K0.5Na0.5)NbO3 (KNN)-based ceramics have been extensively investigated as replacements for Pb(Zr, Ti)O3-based ceramics. KNN-based ceramics exhibit an orthorhombic structure at room temperature and a rhombohedral-orthorhombic (R-O) phase transition temperature (TR-O), orthorhombic-tetragonal (O-T) phase transition temperature (TO-T), and Curie temperature of -110, 190, and 420 °C, respectively. Forming KNN-based ceramics with a multistructure that can assist in domain rotation is one technique for enhancing their piezoelectric properties. This review investigates and introduces KNN-based ceramics with various multistructures. A reactive-templated grain growth method that aligns the grains of piezoceramics in a specific orientation is another approach for improving the piezoelectric properties of KNN-modified ceramics. The piezoelectric properties of the [001]-textured KNN-based ceramics are improved because their microstructures are similar to those of the [001]-oriented single crystals. The improvement in the piezoelectric properties after [001] texturing is largely influenced by the crystal structure of the textured ceramics. In this review, [001]-textured KNN-based ceramics with different crystal structures are investigated and systematically summarized.

Ultra-broad temperature insensitive Pb(Zr, Ti)O3-based ceramics with large piezoelectricity

The rapid growth of new electromechanical applications has increased the demand for ferroelectric ceramics with excellent piezoelectric properties and a wide temperature operating range. However, achieving robust piezoelectricity and temperature stability simultaneously in lead zirconate titanate (Pb(Zr, Ti)O3) based piezoelectric ceramics poses a significant challenge. This study proposes a new material system of 0.98Pb0.84Ba0.16(Zr2/3Ti1/3)O3–0.02Pb(Sb1/2Nb1/2)O3 + x wt.%Sm2O3 (PBZT-PSN-xSm) to address this challenge. Remarkably, the ceramics x = 0.4 demonstrate excellent piezoelectric properties (including piezoelectric coefficient d33 of 610 pC/N and Curie temperature TC of 290 °C) and favorable temperature stability (i.e., d33 varies less than 10 % within 25–200 °C). The high piezoelectric properties arise from the optimized phase fraction between rhombohedral (R) and tetragonal (T) phases and the increased grain size, which enhance the lattice distortion and the domain switching under electric fields, respectively. The superior temperature stability can be attributed to stable crystal structure and domain structure. These findings indicate that PBZT-PSN-xSm ceramics hold great promise for practical utilization in high-temperature transducers and sensors.

Superior energy storage performance and transparency in (K0.5Na0.5)(Nb0.97Ta0.03)O3-based ceramics

Lead-free transparent ferroelectric ceramics are an ideal material to meet the needs of pulsed power technology and optical transparency because of their excellent optical transparency and energy storage performances. However,...

Enhanced energy storage performance in Na(Nb,Ta)O3-doped Ba(Ti,Ca)O3-based ceramics through bidirectional optimization strategy

(1-x)(0.9Ba1.003Ti0.97Ca0.03O3–0.1(Bi0.51Na0.47)0.94Ba0.06TiO3)-xNa(Nb0.85Ta0.15)O3 (x = 0.03–0.15) ceramics were designed and fabricated through a bidirectional optimization strategy using traditional solid reaction method. The results revealed that the introduction of Na(Nb0.85Ta0.15)O3 increased the vacancy concentration at the A site, conducing to improved polarization and reduced grain size. The substitution at the B site disrupted the long-range ordered ferroelectric domains and generated polar nanodomains, leading to enhanced relaxation behavior. The optimum energy storage density of 3.57 J/cm3 and efficiency of 87.5% were simultaneously achieved under the electric field of 220 kV/cm in the sample with x = 0.09. Moreover, it also exhibits extremely high-power density (∼57 MW/cm3), ultrafast discharge time (∼103 ns), high discharge density (1.35 J/cm3), along with excellent temperature (30‒120 °C) and frequency stability (1‒100 Hz) under the equivalent electric field of 120 kV/cm. This novel design strategy provides theoretical guidance for the development of advanced electrical energy storage devices.

Polarity Modulation Induced High Electrostrain Performance with Near-Zero Hysteresis in a (Sr0.7Bi0.2□0.1)TiO3-Based System

High-precision piezo actuators necessitate dielectrics with high electrostrain performance with low hysteresis. Polarity-modulated (Sr0.7Bi0.2□0.1)TiO3-based ceramics exhibit extraordinarily discrete multiphase coexistence regions: (i) the relaxor phase coexistence (RPC) region with local weakly polar tetragonal (T) and pseudocubic (Pc) short-range polar nanodomains and (ii) the ferroelectric phase coexistence (FPC) region with T long-range domains and Pc nanodomains. The RPC composition features a specially high and pure electrostrain performance with near-zero hysteresis (S ∼ 0.185%, Q33 ∼ 0.038 m4·C-2), which is double those of conventional Pb(Mg1/3Nb2/3)O3-based ceramics. Particular interest is paid to the RPC and FPC with multiscale characterization to unravel local structure-performance relationships. Guided by piezoelectric force microscopy, scanning transmission electron microscopy, and phase-field simulations, the RPC composition with multiphase low-angle weakly polar nanodomains shows local structural heterogeneity and contributes to a flat local free energy profile and thus to nanodomain switching and superior electrostrain performance, in contrast to the FPC composition with a macroscopic domain that shows stark hysteresis. This work provides a paradigm to design high-precision actuator materials with large electrostrain and ultralow hysteresis, extending our knowledge of multiphase coexistence species in ferroelectrics.

Giant electric field–induced strain in lead-free piezoceramics

Piezoelectric actuators are indispensable over a wide range of industries for their fast response and precise displacement. Most commercial piezoelectric actuators contain lead, posing environmental challenges. We show that a giant strain (1.05%) and a large-signal piezoelectric strain coefficient (2100 picometer/volt) are achieved in strontium (Sr)-doped (K,Na)NbO3 lead-free piezoceramics, being synthesized by the conventional solid-state reaction method without any post treatment. The underlying mechanism responsible for the ultrahigh electrostrain is the interaction between defect dipoles and domain switching. The fatigue resistance, thermal stability, and strain value (0.25%) at 20 kilovolt/centimeter are comparable with or better than those of commercial Pb(Zr,Ti)O3-based ceramics, showing great potential for practical applications. This material may provide a lead-free alternative with a simple composition for piezoelectric actuators and a paradigm for the design of high-performance piezoelectrics.

Enhanced energy storage performance of (Ba0.85Ca0.15) (Zr0.10Ti0.90) O3-based ceramics through a synergistic optimization strategy

Enhanced energy storage performance of (Ba0.85Ca0.15) (Zr0.10Ti0.90) O3-based ceramics through a synergistic optimization strategy

Structural origin of strongly diffused ferroelectric phase transition in Ba(Ti, Zr)O3-based ceramics

A significant broadening of the ferroelectric phase transition is an inherent characteristic of disordered polar systems, such as technologically important materials based on relaxor ferroelectrics. The origins of diffusion of the dielectric maximum are usually associated with chemical and structural heterogeneity, leading to local deviations of the Curie temperature in polar nanoregions giving rise to relaxor behavior. In this work, based on the results of crystal structure, dielectric, and ferroelectric properties investigation, we report a surprising broadening enhancement of the ferroelectric phase transition in (1-x)BaTi0.95Zr0.05O3-xPbTiO3 ceramics with x = 0.30. The values of its diffuseness parameters are similar to or even exceed those of common relaxor ferroelectrics, even though the studied ceramics does not demonstrate any frequency-dependent shift of dielectric maxima. Symmetry-mode analysis of the atomic displacements in the tetragonal phases provides direct evidence of the concentration-induced crossover between B-site and A-site driven ferroelectricity at x = 0.30. Structure-property correlations between polar distortion amplitudes, dielectric and ferroelectric behavior are observed, suggesting an increase in structural stiffness in the crossover region. This work shows a new structural mechanism of strongly diffused phase transition in ferroelectrics that consists of the interplay between atomic displacements of the A and B cations of the perovskite structure and, in principle, is not associated with the atomic disorder as such.

Realizing high-performance capacitive energy storage in lead-free relaxor ferroelectrics via synergistic effect design

Developing lead-free dielectric ceramics with outstanding energy storage properties has become urgent for dielectric capacitors. Herein, a synergistic effect design strategy has been proposed that combined the merits of relaxor ferroelectrics with high polarization/low remanent polarization and enhanced linear materials with relatively high polarization/ultrahigh dielectric breakdown strength. Hence, a novel lead-free 0.955Bi0.5Na0.5TiO3-0.045Ba(Al0.5Ta0.5)O3-based ceramics are engineered though introducing the enhanced linear dielectrics of 0.9CaTiO3-0.1BiScO3. A large recoverable energy density (Wrec∼3.13 J/cm3) and high efficiency (η∼88.4 %) as well as excellent power density (PD∼95.1 MW/cm3) and discharge speed (t0.9∼36 ns), along with superior stabilities, have been simultaneously realized. The piezoelectric force microscope measurements reveals that incorporating CT-BS generates more highly-dynamic polar nanoregions (PNRs), giving rise to rapid reversibility of PNRs with concurrently tailored energy storage performance. This study demonstrates synergistic effect design is a feasible and paradigmatic way to explore high-efficiency dielectrics for high-power energy storage applications.

Polarization-induced phase structure transition and change of photoluminescence in Er3+-doped (Ba, Ca)(Ti, Sn)O3-based multifunctional ceramics

Rare-earth elements-doped lead-free piezoelectric ceramics are a valuable multifunctional material. The Er3+-doped (Ba, Ca) (Ti, Sn)O3 (BCTS-Er) ceramics with various polymorphic phase transition (PPT) were synthesized through a traditional solid-state reaction route. The component with a coexisting phase structure of orthorhombic and tetragonal is abbreviated as BCTS-Er-I, and the component with a coexisting phase structure of rhombohedral and tetragonal is abbreviated as BCTS-Er-II. The BCTS-Er ceramic exhibits high piezoelectric properties (BCTS-Er-I: d33 = 260 pC/N; BCTS-Er-II: d33 = 310 pC/N) and strong green photoluminescence (PL) emission. The effects of polarization on the PL properties of the BCTS-Er ceramics with various PPT were systematically studied. Compared with the PL intensity of the unpoled sample, that of the poled BCTS-Er-I ceramics weakened by 70%, while that of the poled BCTS-Er-II ceramics increased by four times under the electric field at 10 kV/cm. The effect of polarization treatment on the PL properties of the BCTS-Er ceramics is attributed to the polarization-induced phase transition, lattice distortion, the symmetry of the host lattice, and domain reorientation. Compared with the unpoled samples, the PL intensity of the poled BCTS-Er-I samples with O-T phase structure weakened by 70%, while that of the poled BCTS-Er- II samples with R-T phase structure increased by 4 times under an electric field of 10 kV/cm.

Relaxor behaviour and nonlinear dielectric properties of lead-free BZT–BZN composite ceramics

To improve the dielectric performance of Ba(Zr0.2Ti0.8)O3-based ceramics, (1-x) Ba(Zr0.2Ti0.8)O3-xBi(Zn2/3Nb1/3)O3 composite ceramics (as short as (1-x) BZT20-xBZN) were synthesised using a solid-state reaction. The effects of Bi(Zn2/3Nb1/3)O3 on the microstructure and dielectric properties were studied. Stable cubic symmetry and polar nanoregions (PNRs)-related first-order Raman modes were observed as the amount of BZN increased. The 0.94BZT20–0.06BZN sample exhibited improved dielectric constants with a higher degree of relaxor behaviour (γ = 1.91). BZN-dependent dielectric nonlinearity was observed under an applied electric field. The evolution of the relaxor behaviour and dielectric nonlinearity in the (1-x) BZT20-xBZN composite ceramics were related to PNRs variations. The largest figure of merit (~65) was obtained for the 0.94BZT20–0.06BZN ceramics, while the dielectric tunability was 75%.

Conduction properties of acceptor-doped BaTiO3–Bi(Zn1/2Ti1/2)O3-based ceramics

A series of acceptor-doped ceramics based on the solid solution, (1-x)BaTiO3–xBi(Zn1/2Ti1/2)O3 (BT-BZT), where x = 0.1, 0.2, 0.3, 0.4, were prepared via solid-state synthesis to investigate the effect of doping and BZT content on conduction properties. Impedance spectroscopy measurements showed an increase in conductivity through acceptor doping with Mg on the Ti-site ( $${\text{Mg}}_{{{\text{Ti}}}}^{^{\prime\prime}}$$ ). Ceramics of the composition, 0.80BaTiO3–0.20Bi(Zn1/2Ti1/2)O3 with 3 mol% $${\text{Mg}}_{{{\text{Ti}}}}^{^{\prime\prime}}$$ , showed the highest conductivity in this study at 1.28 mScm−1 (~ 600 °C), an order of magnitude improvement over the stoichiometric composition. Variable pO2 impedance measurements revealed p-type conductivity in the grain while EMF measurements showed that above ~ 550 °C, ions are the dominant charge carriers (transference number, ti = 0.91 at 735 °C). Similarly, all 3 mol% Mg-doped compositions above x = 0.1 were primarily ionic conductors with transference numbers above ti = 0.79 (735 °C). X-ray diffraction data showed a pseudocubic primary phase for all samples with evidence of additional impurity phases accompanying samples with 3 mol% $${\text{Mg}}_{{{\text{Ti}}}}^{^{\prime\prime}}$$ or greater.

Relation between dielectric permittivity and electrocaloric effect under high electric fields in the Pb(Mg1/3Nb2/3)O3-based ceramics

The correlation between dielectric permittivity and electrocaloric (EC) temperature change (ΔTEC) has been investigated in (1 − x)Pb(Mg1/3Nb2/3)O3−xPbTiO3 (PMN–100xPT, with x = 0, 0.05, and 0.10) relaxor ferroelectric ceramics. At a given electric field, both peak temperatures, including the temperature of the permittivity peak (Tm) and the temperature of the maximum of the ΔTEC (TEC max) increase with increasing PT content. The peak of the dielectric permittivity is, regardless of the applied electric field, always at a higher temperature than is the TEC max, and the temperature gap between both maxima progressively increases with increasing applied DC bias. This is particularly true above the threshold field, which induces the long-range ordered ferroelectric state. The results, which are explained in terms of the electric field–temperature phase diagram of relaxor systems, thus reveal that Tm can only roughly mark the temperature of the upper boundary of the temperature–electric field window, where the EC responsivity (ΔTEC/ΔE) is the highest.

Effects of Sintering Method and BaTiO3 Dopant on the Microstructure and Electric Properties of Bi (Fe0.9Al0.05Yb0.05) O3-Based Ceramics

The (1 − x) Bi (Fe0.9Al0.05Yb0.05) O3–xBaTiO3 (BFAYO-x BTO) ceramics were synthesized by microwave sintering (MWS) and conventional sintering (CS) methods. The crystal structure, surface morphology, dielectric and ferroelectric properties were investigated. XRD patterns show that BTO tetragonal and BFO rhombohedral phases coexist in both MWS and CS samples, and that the diffraction peaks of MWS samples shift to lower angles due to the larger ionic radius of Ba2+ compared with Bi3+. The lattice constant of BFAYO-x BTO ceramics increases with the increase of BTO content. It was found that the average grain size of the MWS ceramic is much smaller than that of the CS ceramic. Dielectric measurements reveal that the dielectric loss and dielectric constant increase with BTO content increasing. The introduction of BTO into BFAYO-based ceramic contribute to the enhancement of the dielectric relaxation behavior. The P–E hysteresis loops demonstrate that the remnant polarization (Pr) and the coercive field (EC) of the MWS samples are smaller than those of the CS samples. Pr and EC first increase, then decrease and then increase again with the increase of BTO content. The maximum and minimum values of the remnant polarization were obtained at x = 0.25 and 0.3, respectively.

Review of Sintering Technologies, Structural Characteristics, and Piezoelectric Properties of NKN-Based Lead-Free Ceramics

The (Na1−xKx)NbO3-based (NKN-based) lead-free piezoelectric ceramics have been extensively investigated from the beginning of this century to replace the Pb(Zr1−xTix)O3-based piezoelectric ceramics. The sintering of the NKN-based ceramics is difficult because they are soluble in water, and Na2O evaporation, which degrades the piezoelectric properties of the specimen, occurs during sintering. CuO was used as a sintering aid to improve the sinterability and to reduce the sintering temperature of the NKN ceramics. The NKN-based ceramics with various polymorphic phase boundary (PPB) structures such as orthorhombic–tetragonal PPB, rhombohedral–orthorhombic PPB, and rhombohedral–tetragonal PPB structures were developed to enhance the piezoelectric properties. The specimen with the rhombohedral–tetragonal PPB structure has been reported to show excellent piezoelectric properties. Recently, NKN-based ceramics with various pseudocubic-based PPB structures were reported, and they exhibited enhanced piezoelectric properties with good thermal stability. In this manuscript, the sintering of NKN-based ceramics and the various PPB structures developed for improving their piezoelectric properties are discussed in detail.

Pseudocubic-based polymorphic phase boundary structures and their effect on the piezoelectric properties of (Li,Na,K)(Nb,Sb)O3-SrZrO3 lead-free ceramics

CuO-added 0.96(LixNa0.5-xK0.5)(Nb1-ySby)O3-0.04SrZrO3 ceramics were sintered at 1020 °C for 6 h. Various crystal structures were synthesized in these specimens by controlling the Li2CO3 (x) and Sb2O5 (y) contents: pseudocubic, orthorhombic-pseudocubic polymorphic phase boundary (PPB), tetragonal-pseudocubic PPB, orthorhombic-tetragonal-pseudocubic PPB, and orthorhombic-tetragonal PPB structures. The pseudocubic structure developed in these specimens was similar to the R3m rhombohedral structure instead of the Pm3m cubic structure because the specimens with a pure pseudocubic structure showed good ferroelectric and piezoelectric properties. The piezoelectric properties of the specimens were influenced by their crystal structures. The specimen with the tetragonal-pseudocubic PPB structure showed the best piezoelectric properties because this structure was similar to the tetragonal-rhombohedral morphotropic phase boundary structure developed in Pb(Zr1-xTix)O3-based ceramics. In particular, the specimen with the tetragonal-pseudocubic PPB structure corresponding to x = 0.05 and y = 0.065 showed the largest d33 and kp values of 431 pC/N and 0.43, respectively.

Crystal structure and electrical properties of textured Ba2Bi4Ti5O18 ceramics

Highly textured Ba2Bi4Ti5O18 ceramic was prepared by spark plasma sintering (SPS). X-ray diffraction of the ceramics revealed the coexistence of a major ferroelectric phase (Space group, SG: B2cb) and a minor paraelectric phase (SG: I4/mmm) at room temperature. A diffused phase transition was observed at around 240 °C. The evolution of the switching current peaks in the electric current vs. electric field (I-E) loops with increasing temperature was interpreted by the structural changes and temperature dependent polarisation reversal processes. The slim polarisation vs. electric field (P-E) loops, the extra switching current peaks in the I-E loops and the non-zero piezoelectric d33 coefficient indicate that Ba2Bi4Ti5O18 is a relaxor ferroelectric material. The recoverable energy density (0.41 ± 0.01 J/cm3) of Ba2Bi4Ti5O18 ceramics in the perpendicular direction to the SPS pressing direction is close to that of Pb(Mg1/3Nb2/3)O3-based ceramics. The obtained results suggest Ba2Bi4Ti5O18 ceramics might be promising for energy storage applications.

Effect of Mn-doping on dielectric and energy storage properties of (Pb0.91La0.06)(Zr0.96Ti0.04)O3 antiferroelectric ceramics

Bulk ceramics with high recoverable energy density (Wre) and energy efficiency (η) play a critical role in the development of pulsed power systems for miniaturization and lightweight. The orthorhombic phase (Pb,La)(Zr,Ti)O3-based antiferroelectric (AFE) ceramics have been regarded as one of the most promising candidates for pulsed power system applications due to their relatively high energy storage density and efficiency. However, the main drawback of orthorhombic phase (Pb,La)(Zr,Ti)O3-based AFE ceramics is relatively low dielectric breakdown strengthen (DBS), which has always restricted the improvement of energy storage density. In this study, an effectively method to increase DBS by the introduction of Mn has been proposed. The relative density of orthorhombic phase (Pb0.91La0.06)(Zr0.96Ti0.04)O3 (PLZT) ceramics was improved by Mn-doping. And the introduction of Mn can decrease the tolerance factor (t) of PLZT ceramics because the radius of Mn2+ is larger than that of B-site Zr4+/Ti4+, and thus enhancing antiferroelectricity. Meanwhile, the effects of Mn-doping on the phase structure, microstructure and dielectric properties of PLZT ceramics have been studied thoroughly in this study. It is found that the highest Wre of 7.65 J/cm3 is obtained at 1.0 mol% Mn-doped PLZT ceramic, which is obviously larger than that of undoped PLZT ceramic (5.71 J/cm3). These results suggest that the Mn-doped PLZT ceramics are potential energy storage materials in pulsed power systems.

Polarization orientation dependence of piezoelectric losses in soft lead Zirconate-Titanate ceramics

Dielectric, elastic and piezoelectric losses are investigated in soft Pb(Zr,Ti)O3-based piezoelectric ceramics in terms of polarization direction dependence of the properties. The difference of the mechanical quality factor at the resonance and anti-resonance frequencies were obtained by the impedance method. The polarization angle of the samples varied from 0 (E//PS) to 90 degree (E⊥PS) for “effective” k31 and k33 vibrating modes. The change in the piezoelectric losses is dominant in comparison to the dielectric or elastic losses in both vibration modes.

Mechanical properties enhancement in potassium-sodium niobate lead-free piezoceramics: the impact of chemical modifications

The development of (K0.44Na0.52Li0.04)(Nb0.86Ta0.10Sb0.04)O3-based (KNL-NTS) ceramics is attracting great interest because of environmental concerns. Most of the efforts have been concentrated on improving the electrical properties. However, it is desirable to develop ceramics with good electrical response and high mechanical properties. Therefore, the evaluation of the mechanical properties is substantial and little studied. The aim of this work is to study the mechanical properties of KNL-NTS lead free ceramics doped with Zr evaluating the effects that can give rise to improved mechanical properties. Our results show that the crystalline phase, size and shape of grains in the ceramics are affected by the doping amount. We found that the microstructure does have a close relationship to the mechanical response, more specifically; a uniform and fine grain microstructure is suitable to lead high mechanical strength. Based on these results, the chemical modifications with Zr4+ ions have a significantly positive influence on hardness, strength and fracture toughness values of KNL-NTS ceramics.