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It is difficult to realize the balanced development of piezoelectric response {piezoelectric constant (d33) and strain} and temperature stability of potassium-sodium niobate ceramics. Here, we constructed one kind of lead-free piezoceramic system of 0.965K0.45Na0.55Nb0.96Sb0.04O3-0.035(Bi1-xHox)0.5Na0.5HfO3, and rhombohedral & tetragonal (R-T) multiphase coexistence maintains in a wide compositional range of x = 0.05–0.55. Greatly improved temperature stability of piezoelectric response is realized by doping rare earth Ho. Excellent temperature stability of both strain and d33 mainly originates from the weak temperature dependence of domain structure as well as the increased R-T phase transition temperature. As a result, the addition of rare earth Ho can boost temperature stability of potassium-sodium niobate-based ceramics.

It is still unclear about the association between ambient air pollution and attack risk of acute myocardial infarction (AMI) in South China. This study assessed the effects of short-term exposure to ambient air pollutants on hospital admission of AMI in Guangzhou, South China. We obtained the information on 19,622 hospital admissions of AMI from the Guangzhou Cardiovascular and Cerebrovascular Disease Event Surveillance System during the years from 2014 to 2017. Daily concentrations of air pollution data on particulate matter

Phase boundaries and composition design were explored to achieve both high piezoelectricity and favorable temperature stability in potassium-sodium niobate ceramics, using (1-x)(K,Na)(Nb,Sb)O3-xBi(Na,K)(Zr,Sn,Hf)O3 ceramics. A rhombohedral-tetragonal (R-T) phase boundary was constructed at x=0.035–0.04 by co-doping with Sb5+ and Bi(Na,K)(Zr,Sn,Hf)O3. More importantly, a superior temperature stability was observed in the ceramics with x=0.035, accompanying with a stable unipolar strain at room temperature to 100 °C. The ceramics with x=0.035 also exhibited improved piezoelectric properties (e.g., piezoelectric coefficient d33∼465 pC/N and electromechanical coupling factor kp=0.47) and Curie temperature (Tc∼240 °C). The Rietveld refinement and in-situ temperature-dependent piezoresponse force microscopy (PFM) results indicated that the enhancement of the piezoelectric properties was caused by the easy domain switching, high tetragonal fraction, and tetragonality, while the improved temperature stability mainly originated from the stable domain structures.

A resistive memory device based on the Ag/Bi1+δ(Fe0.95Zn0.05)O₃/SRO/Pt/TiO₂/SiO₂/Si(100) structure was prepared using radio frequency magnetron sputtering. The composition of the thin film element was analyzed by X-ray photoelectron spectroscopy and the thickness of the thin film was characterized by scanning electron microscope. Through the electrical test, we found that the device exhibited low operating voltage, which included VSET of about 0.1 V, VRESET of about -0.1 V, and VF of about 0.25 V. This facilitated the perfect integration of the device with the circuit design. Testing for 10,000 s at a substrate temperature of 85 °C, the device showed excellent retention. The I-V fitting curves of the resistive devices were analyzed. The low resistance state was in line with the ohmic mechanism and the high resistance state was in accordance with the Space Charge Limited Current mechanism. The resistance change of the device was attributed to the formation of Ag conductive filaments.

Ferroelectric electrocaloric (EC) materials represent a promising alternative for environment-friendly cooling technologies to replace vapor-compression-based refrigeration. The general strategy is to construct the relaxor phase transition around room temperature (RT) to improve the EC effect and expand its operating temperature. However, this strategy sacrifices the inherent EC response of ferroelectrics and needs a high excitation electric field (ΔE). Guided by the physical origin of the EC effect in ferroelectrics, we designed a lead-free BaTiO3-based ceramic to realize the close, successive ferroelectric–ferroelectric and ferroelectric–paraelectric (FP) transitions, which induce a broad metastable-phase-transition region near RT. In this ceramic, the ferroelectric polar matrix and reduced energy barriers greatly facilitate the polarization rotation/reversion, maintaining the strong ferroelectric polarization but large polarization change in a wide temperature range. We achieved a large EC coefficient ΔT/ΔE of >0.3–0.35 K mm kV−1 at a small ΔE of 5–15 kV cm−1, and a high temperature change ΔT of >0.9 K (40 kV cm−1). More importantly, our system exhibits a broad temperature span of a large EC effect, which greatly exceeds the performance of previous BaTiO3-based reports employing single FP relaxor transition, even twice wider than that of them. This work offers a new general solution to design EC materials with superior performances for practical EC cooling applications.

Acceptor and donor co-doped titanium dioxide (TiO2) materials have a colossal permittivity (CP), a low dielectric loss, and a good temperature/frequency stability, showing an immense potential for microelectronics and high-energy storage devices. In this study, we propose to decode the role of acceptors and donors on CP dielectric properties in TiO2 by doping a series of A3+ acceptors or B5+ donors. A reduced dielectric loss of tan δ 105 is displayed in B5+-TiO2 accompanied by a high dielectric loss (>0.40). Both of them possess an obvious temperature/frequency sensitivity. Inversely, an additive effect with CP and low dielectric loss appears in A3+ and B5+ co-doped TiO2 over a broad temperature/frequency range, e.g., a giant er value (5.7–9.6 × 104) and a low tan δ value (0.05–0.096) are achieved in a paradigm system of (Gd0.5Nb0.5)xTi1−xO2. The XPS analysis indicates that introducing A3+ causes the appearance of , while the B5+ substitution can afford an extra electron to transform Ti4+ to Ti3+. The introduced cations and generated defects combine together to form an electron-pinned defect-dipole and cause a strong dipole polarization. These defects can also facilitate the internal barrier layer capacitance and surface barrier layer capacitor effects, leading to a higher CP property.

In this work, (0.99 − x)(K0.5Na0.5)(Nb0.965Sb0.035)O3–0.01SrZrO3–x(Bi0.5Na0.5)ZrO3 ceramics were selected to show how a phase engineering strategy (PES) affects the strain properties in potassium sodium niobate (KNN)-based ceramics. The application of PES resulted in the coexistence of multiple phases in KNN-based ceramics accompanied by an increased diffuseness of ferroelectricity and decreased domain size. The strain properties, including the dependencies of strain on composition, temperature and fatigue behavior, were evaluated by considering the phase structure, domain configuration and microstructure. The improved room-temperature strain properties of the KNN-based ceramics with PES originated from the converse piezoelectric response, domain switching and possible electric-induced phase transition, which resulted from the coexistence of multiple phases and complex domain configuration. The enhanced temperature stability mainly originated from the converse piezoelectric response. Endurable fatigue resistance (no degradation within 100–105 electric cycles) and a high electrostriction coefficient (Q33 = 0.035 m4 C−2) were observed in the ceramics with x = 0.03 and 0.05, respectively. This study provides a systematic analysis of the effects of PES on strain properties in KNN-based ceramics.

The understanding of high piezoelectricity in potassium sodium niobate (KNN)-based ceramics with a new phase boundary has been limited to unpoled samples. Here, the phase structure, domain structure, and phenomenological theory were studied on both unpoled and poled samples by taking (0.99 − x)(K0.48Na0.52)(Nb0.955Sb0.045)O3–0.01SrZrO3–x(Bi0.5Ag0.5)ZrO3 ceramics as an example. Shifting the phase transition temperatures to room temperature can result in the coexistence of a ferroelectric matrix containing an orthorhombic–tetragonal (O–T) coexisting phase and rhombohedral (R)-related polar nanoregions (PNRs), and then the miniature and nanoscale domain structure can be demonstrated. During the poling process, the R phase-related PNRs can facilitate domain switching and polarization rotation, resulting in a single domain structure and enhanced evidence of the R phase. Therefore, high piezoelectricity originates from a single domain feature as well as the diffused multi-phase coexistence in association with R phase related PNRs. This study provides a systematic approach to understand the physical mechanisms of enhanced piezoelectricity in KNN-based ceramics.

Electrostrictors offer unique advantages over piezoelectrics, including no poling process, temperature stability and hysteresis-free strain characteristics. Learning from the distinction between disordered and ordered ABI0.5BII0.5O3 perovskite-structured electrostrictors, the electrostrictive effect enhances with a smaller active space for B ions. Here, we propose a novel design strategy to arouse the potential capacity of electrostriction in BaTiO3-based materials by A-site Li+–Ho3+ ion-pairs engineering. In this way, limited active space for a Ti-site is expected due to the contracted oxygen octahedron around ion-pairs, resulting in smaller polarization per unit magnitude of electric field but a larger strain per unit magnitude of polarization and therefore an enhanced longitudinal electrostrictive coefficient Q33. A systematic analysis evidenced that Li+ and Ho3+ ions tend to occupy the neighboring Ba-sites in one unit cell of BaTiO3, and directly form Li+–Ho3+ ion-pairs along the [001] direction. Besides, partial fragmented domain patterns induced by local structural heterogeneity due to the involvement of ion-pairs are detected in samples with higher dopants, benefiting suppression of hysteresis in strain curves. Consequently, the (Li, Ho) co-doped BaTiO3 ceramics by A-site engineering exhibit giant Q33 up to 0.06 m4 C−2 which is superior to other lead-bearing/free electrostrictive materials, meeting the requirement of a thermal stability (20–150 °C) – low hysteresis (

For perovskite ferroelectric oxides, the composition-induced transition from ferroelectrics to relaxors can enhance their electrostrictive coefficient Q33 remarkably, and has been attracting more and more attention in recent years. Achieving a larger electro-strain response is one of the most original driving forces for pursuing higher Q33 values, while the two are often incompatible. Herein, taking the promising relaxor ferroelectric Na0.5Bi0.5TiO3 (NBT) as the research object, we report the excellent electrostriction-like electro-strain behaviors (0.41% ≤ Suni ≤ 0.46%, 25 ≤ T ≤ 125 °C; Suni exhibits only 2.23% decline after 105 cycles) together with a series of enhanced Q33 values (0.029–0.047 m4 C−2). Accompanied by the reconstruction of de-coupled A–O interactions, the electric-field-induced relaxor to ferroelectric state transition contributes to the superior electro-strain behaviors, while the enhanced Q33 will greatly degenerate during this transition process. In contrast to the non-hysteretic electrostriction observed in linear dielectrics, for NBT-based relaxor ferroelectrics, the peculiar coexistence of ferroelectric in-phase a0a0c+ and anti-phase a−a−a− tiltings is suggested to contribute to the enhanced electrostriction-like behaviors observed in this work. These observations indicate that NBT-based systems can be considered as a potential family of peculiar lead-free electrostrictors for application in the field of actuators.

For eco-friendly bismuth sodium titanate (Bi0.5Na0.5TiO3)-based materials, ultrahigh poling strain (Spol) is always accompanied with a sizable remnant strain (Srem), which severely restricts the cycling reliability of their superior electro-strain. Composition engineering is an effective way of eliminating Srem, but Spol will be sacrificed as well, leading to an overall inferior electro-strain. Here, by composition engineering and subtle criticality confinement, a giant recoverable electro-strain (S > 0.7%, realizing Srem modulation without Spol sacrifice) with reduced hysteresis is reported in BNT-based relaxor ferroelectrics, which can be kept at a high level (

Ultrasonic energy harvesting has been developed as a promising power solution for implantable medical devices (IMDs) to perform tasks such as diagnosis, therapy, and monitoring. However, most current ultrasonic electronics use toxic lead-based piezoelectric materials (e.g., lead zirconate titanate) as core components and feature bulk or flat structures, representing common barriers to the development of future IMDs that should be eco-friendly and long-term fixation in the implanted position. Here, we present a KNN composite-based lead-free piezoelectric helix for ultrasonic transcutaneous energy harvesting. The device contains multilayer components (a matching layer, lead-free composites, a copper foil, and a Parylene-C film) to form a final self-supporting helix harvester, which can adapt to cylindrical objects (e.g., blood vessels) to maintain fixation. Nanodomain-induced high-performance ( d33 ∼ 465 pC N−1) KNN ceramic was fabricated and further processed into 1–3 composites to enhance electromechanical coupling properties and mechanical flexibility. The developed prototype can be excited ultrasonically to generate adjustable power output up to ∼22.97 mW cm−2. The generated electricity was stored in capacitors and used to operate light-emitting diodes. Further ex vivo tests showed that the device is still sufficient to support wireless energy transfer through porcine tissues, demonstrating the great potential of the lead-free piezoelectric helix for IMDs.

Rietveld refinement is used to investigate the crystal structure of prepared (0.965 – x)(K0.48Na0.52)NbO3–xBiInO3–0.035(Bi0.5Na0.5)ZrO3 (KNN-xBI-BNZ) ceramics. From refined results, the distortion degree of crystal structures in KNN-xBI-BNZ ceramics presents a rising trend with BiInO3 modification, which is in keeping with the results of diffuseness. The spontaneous polarization (Ps) is also calculated using refined structural parameters. The submicron domains are observed when x = 0.004, which presents good electrical properties (d33 = 317 pC/N, Tc = 336 °C) simultaneously. Excellent thermal stability of ceramics modified with BiInO3 is observed in a broad temperature range.

To achieve high piezoelectricity and the corresponding good temperature stability of BaTiO3 (BT) ceramics, a new system of (1-x-y) BaTiO3 – yCaTiO3 – x(BaZr1-zHfz)O3 (BT-yCT-xBZHz) was designed. The O-T phase boundary was observed at 0.065 ≤ x ≤ 0.085, 0.08 ≤ y ≤ 0.12 and 0 ≤ z ≤ 1.0 near room temperature. Due to the O-T phase boundary, the enhancement of electrical properties (d33 = 500 pC/N, kp = 0.52, Pr = 14.0 μC/cm2 and er = 2800), large strain (∼0.23%) and d33* = 1100 pm/V (10 kV/cm) can be obtained. Moreover, temperature-dependent electrical properties were investigated in detail, and a reliable performance was realized due to high TC (>100 °C). The d33* was demonstrated to be temperature-insensitive from 16 °C to 60 °C (varying less than 7%), which is superior to the reported BT-based ceramics. Besides, d33 and Pr fluctuate less than 22% in this temperature range, also showing an usable stability. We believe that this work can be beneficial to facilitate an increasing adoption of lead-free BT-based piezoceramics for practical applications.

Multitudinous topological configurations spawn oases of many physical properties and phenomena in condensed-matter physics. Nano-sized ferroelectric bubble domains with various polar topologies (e.g., vortices, skyrmions) achieved in ferroelectric films present great potential for valuable physical properties. However, experimentally manipulating bubble domains has remained elusive especially in the bulk form. Here, in any bulk material, we achieve self-confined bubble domains with multiple polar topologies in bulk Bi0.5Na0.5TiO3 ferroelectrics, especially skyrmions, as validated by direct Z-contrast imaging. This phenomenon is driven by the interplay of bulk, elastic and electrostatic energies of coexisting modulated phases with strong and weak spontaneous polarizations. We demonstrate reversable and tip-voltage magnitude/time-dependent donut-like domain morphology evolution towards continuously and reversibly modulated high-density nonvolatile ferroelectric memories., Experimentally manipulating bubble domains remains elusive especially in the bulk form of ferroelectrics. Here, the authors achieve self-confined bubble domains with multiple polar topologies in bulk Bi0.5Na0.5TiO3 ferroelectrics, demonstrating reversible and donut-like domain morphology evolution.

The influence of relaxor behavior on strain behavior is less investigated in potassium sodium niobate [(K, Na)NbO3, KNN] ceramics. Here, we report novel phenomena in the temperature-dependent strain behavior with the electric field of KNN-based ceramics with relaxation characteristics. The strain temperature stability is electric field dependent below the threshold electric field: temperature-dependent strain can be effectively improved by increasing the applied electric fields, while it remains almost electric field independent above the threshold electric field. Such a macroscopic property change can be well consistent with the following microscopic domain structure evolution. Little voltage dependence is found above a certain voltage by employing voltage-dependent piezoresponse hysteresis loops and domain switching under different temperatures, implying the contribution of domain behavior to the change of strain. Ergodic polar nanoregions (PNRs) are induced by the high-density domain walls among nanodomains in the relaxor samples, as revealed by the atomic-resolution polarization mapping with Z-contrast. The facilitated domain switching due to the lowered energy barrier and nearly vanished polarization anisotropy based on the PNRs with nanoscale multiphase coexistence can promote the electric field compensation for temperature effect. This work demonstrates the contribution of relaxor behavior to the electric field dependence of strain temperature stability in KNN-based ceramics.

The electrocaloric effect (ECE) is significantly critical for environmentally friendly cooling technologies to replace vapor compression-based refrigeration. Lead-free bismuth sodium titanate-based ferroelectrics have attracted considerable attention because of their depolarization process, which can induce a high ECE. However, their high depolarization temperature (

Preferable temperature stability of ferroelectric and strain properties can be achieved in potassium sodium niobate (KNN)-based ceramics compared to that of other lead-free piezoelectric material systems, giving it greater potential for use in electronic devices once the temperature reliability issue related to the piezoelectric constant (

Electromechanical actuators with toxic lead-based electrostrictive materials dominate the market of high-precision electronics devices, so one of urgent aims becomes how to explore the new generation of ecofriendly electrostrictive materials with superior electrostriction behaviors. Herein, a strategy of modifying the active space for the B-site in lead-free relaxor ferroelectrics arouses the potential capacity of electrostriction, including K

Lead-free relaxor ferroelectrics (RFEs) exhibit a broader variety of phenomena in comparison with the "canonical" lead-containing compositions, rendering them attractive for newly multifunctional materials with low-cost and eco-friendly processing. Here, guided by the characteristics of relaxor ferroelectrics, lead-free (1

The inherent disadvantage of lead-free potassium sodium niobate (KNN)-based ceramics is the severe temperature instability of piezoelectric charge coefficient (d

Simultaneous improvement of piezoelectricity and temperature stability is vital for developing high-performance KNN-based lead-free materials. Here, effects of CaTiO3 on phase structure, piezoelectricity and temperature stability of (1 – x)[0.95(K0.5Na0.5)NbO3–0.05(Bi0.5Na0.5)ZrO3]–xCaTiO3–0.2%MnO2 ceramics were studied. It was found that the orthorhombic-tetragonal phase transition temperature can be gradually decreased by increasing CaTiO3 content. Particularly, the improved strain temperature stability (strain varied

The elimination of lead in piezoelectric applications remains challenging. Since the advances in the piezoelectricity were found in the perovskite family in 2000, studies into lead-free piezoelectric materials have grown exponentially in the fields of condensed matter physics and materials science. In this review, we highlighted the compelling physical properties of lead-free piezoelectric perovskite materials and summarized their state-of-the-art progress, with an emphasis on recent advances in the piezoelectric effect. We mainly introduced the unique advances in lead-free perovskites piezoelectric bulk materials, along with the descriptions of phase boundaries, domain configurations, and piezoelectric effects, and then the main physical mechanisms of high piezoelectricity were summarized. In particular, the applications of lead-free materials were also introduced and evaluated. Finally, challenge and perspective are featured on the basis of their current developments. This review provides an overview of the development of lead-free piezoelectric perovskite materials in the past fifteen years along with future prospects, which may inspire material design toward practical applications based on their unique properties.

For the bismuth sodium titanate (BNT)-based materials, the thermal depolarization temperature (Td) is always an obstacle for practical applications. Recently, BNT/ZnO composite has provided one method to resist the thermal depolarization, and however, Td values just increase to a small extent and the conclusions derive from ZnO merely. A universal selection principle for the oxides will be helpful for us to choose the suitable oxides to effectively resist the thermal depolarization, which is desperately demanded but still lacks in BNT/oxide composites. Here, we report that the deferred thermal depolarization can be also obtained in piezoelectric Bi0.5(Na0.8K0.2)0.5TiO3: Al2O3(BNKT:Al2O3) composites. Td is deferred to the higher temperatures (from 116 °C to 227 °C) with increasing Al2O3 contents, as evidenced by the temperature dependence of dielectric, ferroelectric and piezoelectric properties. In addition, the piezoelectricity of BNKT:0.15Al2O3 remains stable at a high temperature (∼210 °C). And, the thermal deviatoric stress from the coefficients of thermal expansion (CTE) discrepancies between Al2O3 and BNKT matrix provides a stronger stabilization force than the ions diffusion-induced destabilization force, resulting in the ultimate deferred thermal depolarization and the significantly increased Td values. In particular, according to the results from the representative BNT/oxides (i.e., ZnO, Al2O3, ZrO2, HfO2) composite, the oxide selection principle (regulating several competing factors) is given to form the appropriate thermal resistant BNT/oxide composite, which may further open the door for piezoelectric BNT-based materials from the research and application scope.

MnO2-doped 0.99(0.36BiScO3-0.64PbTi1-xCexO3)-0.01Bi(Zn0.5Ti0.5)O3 (BS-PTC-BZT-MnO2) ceramics are fabricated by the solid-state method. Here, it's firstly reported that Ce element can reduce dielectric loss (tan δ) and suppress the decrease of piezoelectric constant (d33) simultaneously. Effects of Ce contents on the structure and electrical properties of BS-PTC-BZT-MnO2 ceramics are studied. The ceramics (x = 0.02) with MPB (rhombohedral-tetragonal) possess low dielectric loss (tan δ = 1.36%, 1 kHz) and high piezoelectric constant (d33 = 360 pC/N) simultaneously, which is superior to most reported BS-PT. Besides, excellent comprehensive properties including high Curie temperature (TC = 422 °C), large dielectric constant (ɛr = 1324), and high remnant polarization (Pr = 35.1 µC/cm2) are obtained. Asymmetric S-E and P-E hysteresis loops indicate that defects and oxygen vacancies are induced by multi-valence elements (Ce and Mn), which is the origin for reducing tan δ. In addition, good thermal stability of piezoelectric and dielectric properties is observed. These results indicate that Ce and Mn co-doped BS-PTC-BZT-MnO2 ceramics can be well applied as power electronic devices under high temperature.

Because of their high toxicity, lead-based materials in electronic devices must be replaced by lead-free piezoelectric materials. However, some issues remain that hinder the industrial applications of these alternative ceramics. Here, we report the construction of a 0-3-type ceramic composite (KNNS–BNKZ:xZnO), where the Sb-doped ZnO submicronic particles were randomly distributed throughout the potassium–sodium niobate-based ceramic matrix. In this (K,Na)NbO3 (KNN)-based ceramic composite, superior temperature stability, excellent piezoelectric properties, and a high Curie temperature were simultaneously achieved. The unipolar strain varied from +20 to −16% when the temperature was increased from 23 to 200 °C in KNNS–BNKZ:xZnO with x = 0.75. By increasing the ZnO content from x = 0 to x = 5.0, the Curie temperature was increased from 227 to 294 °C. More importantly, the piezoelectric coefficient remained high (d33 = 480–510 pC/N) for a wide range of compositions, x = 0.25–1.0. Transmission electron micros...

(1 − x)K0.40Na0.60Nb0.96Sb0.04O3–x(Bi0.92Nd0.08)0.5Na0.5ZrO3 (KNNS–xBNNZ) lead-free piezoceramics have been synthesized by a conventional solid state sintering method, and the effects of BNNZ content on their phase structure and electrical properties were investigated. The phase boundary of rhombohedral–orthorhombic–tetragonal (R–O–T) has been formed in the composition range of 0.030 ≤ x ≤ 0.040. An optimal comprehensive performance (e.g., d33 ~ 470 ± 10 pC/N, kp ~ 0.50 ± 0.02, TC ~ 283 °C, er ~ 1950, tanδ ~ 0.043, Strain ~ 0.135%, and d33* ~ 450 pm/V) is obtained in the ceramics with x = 0.035. Moreover, a relatively good component stability of piezoelectric properties (d33 ~ 402–470 pC/N, kp ~ 0.485–0.524, Strain ~ 0.133–0.135%, and d33* ~ 443–450 pm/V) is gained in a broad component range from 0.030 to 0.045, which is benefited from the contribution of multiphase boundary (R–O–T, R–T). Therefore, we believe that KNNS–xBNNZ ceramics opens a window for the practical applications in piezoelectric material markets.

The focus on piezoelectric ceramics based on the potassium sodium niobate system began in 2004. After years of dedicated research, these materials can be considered one of the most promising lead-free piezoceramics with comprehensive performance. While their structure–property relationships are still not completely understood, the thermal stability issue is partly resolved, which leaves further room for phase-boundary engineering. Technological advancement has recently focused on using base metals as inner electrodes for multilayer actuators, which provides cost benefits as compared to lead zirconate titanate devices. The remaining challenges, however, such as poor sinterability and weak reproducibility of functional properties, still hinder extensive applications of these materials.

To further balance the relationship between piezoelectricity and temperature stability, the (0.975 – y)NaNbO3-yBaTiO3-0.025BaZrO3 (y = 0–0.20) ceramics are developed by constructing a wide tetragonal phase region. Effects of BaTiO3 on the relationships among phase structure, electrical properties, and temperature dependence are investigated. With increasing BaTiO3 contents, the ceramics endure the structural evolutions from orthorhombic phase to tetragonal phase, and then to relaxor cubic phase. A wide tetragonal phase zone of 24–180 °C can be realized in the ceramics with y = 0.08, together with an enhanced piezoelectric coefficient d33 = 215 pC/N. Intriguingly, excellent temperature stability of unipolar strain (Suni) and piezoelectric coefficient (d33) are observed in the ceramics with y = 0.08 within 20–180 °C. This work provides an alternative way to enhance piezoelectricity and temperature stability in lead-free piezoceramics.

(1−x−y)(K0.45Na0.55)NbO3–yBi0.5Na0.5ZrO3–xBaHfO3–0.2%MnO2 ceramics without antimony have been fabricated by the conventional solid-state method, and influences of Bi0.5Na0.5ZrO3 and BaHfO3 contents on their structure and electrical properties are studied. Composition modification can result in the formation of rhombohedral–orthorhombic–tetragonal phase coexistence in the ceramics (y = 0.04 and 0.01 ≤ x ≤ 0.02 as well as x = 0.01 and 0.04 ≤ y ≤ 0.045). In the region of this phase boundary, the ceramics exhibit both enhanced piezoelectric properties (d33 ~ 385 pC/N, kp ~ 51%, S ~ 0.157%) and high Curie temperature (TC ~ 320 °C). Especially, good comprehensive properties and the absence of antimony make the material more environmentally friendly.

Although phase boundary engineering has made notable progress in improving the electrical properties of (K,Na)NbO3-based piezoceramics, lattice distortion and spontaneous polarization of multiphase coexisting systems are a few of the remaining concerns. Here, new research employing XRD Rietveld refinement was performed to explore crystal structures, phase fractions and atomic parameters of Fe2O3-added (0.995-x)K0.48Na0.52NbO3-xBi0.5Na0.5ZrO3-0.005BiScO3 ceramics. The distortion of the oxygen octahedron and the spontaneous polarization were presented. Central cation displacement provides a much larger contribution to polarization and the electric dipole moment in orthorhombic phase is much larger than that in tetragonal phase. Benefiting from tetragonal-orthorhombic phase coexistence and lattice distortion, optimized ferroelectric and piezoelectric properties (d33 ∼ 381 pC/N, Pr ∼ 20.47 μC/cm2) were obtained. The ceramic still holds a large d33 (313 pC/N) after up to 300 ℃ of thermal annealing. A series of material constants was also calculated and compared to lead-based ones.

Ternary 0.99(0.36BiScO 3 -0.64PbTiO 3 )-0.01Bi(M 1 M 2 ) 0.5 O 3 (BS-PT-BM 1 M 2 ) ceramics were prepared by the solid-state reaction method, where M 1 and M 2 respectively stand for bivalent and quadrivalent elements (M 1 =Sn, Pb, Ni, Sr, Ba, Ca, Cu, Mg and Mn, M 2 = Hf, Sn, Zr, Si, Ce and Mn). Effects of different elements on their structure and electrical properties were studied in detail. It was found that the formation of MPB by optimizing the doped elements can enhance electrical properties ( d 33 = 500 pC/N, ɛ r = 2013, tan δ = 0.024 at 100 kHz). Interestingly, different electrical properties can be induced by choosing the doped elements. For example, a high d 33 can be realized by doping M 1 = Sn, Pb or Sr (M 2 = Ti) as well as M 2 = Hf, Sn or Zr (M 1 = Zn), and the dielectric loss can be suppressed by doping Ce or Mn. In addition, large bipolar strain (S = 0.25–0.46%) as well as high remanent polarization ( P r = 34.7–46.4 µC/cm 2 ) can be observed for all doped elements, which were superior to pure BS-PT ( P r = 32 µC/cm 2 and S = 0.18%), and high T C ( T C = 417–443 °C) can be attained in all the ceramics. We believe that the addition of ABO 3 -type compounds with optimum elements can enhance electrical properties of BS-PT ceramics.

Authors gratefully acknowledge the support of the National Natural Science Foundation of China (NSFC Nos. 51722208 and 51332003) and the Fundamental Research Funds for the Central Universities (2012017yjsy111). Authors thank Mrs. Wang Hui (Analytical & Testing Center of Sichuan University) for performing the FE-SEM measurements.

In the past, accompanied by the highly asymmetric bipolar strain-electric field (S-E) loop, the ultrahigh strain can be realized in bismuth sodium titanate (BNT)-based ceramics mainly by the B site doping, which seriously restricts the further opening of the research and application scope. Here, regardless of A or/and B sites doping, we observed an ultrahigh unipolar strain response (S = 0.53–0.56% and d33* = 883–933 pm/V, 60 kV/cm) in [Bi0.5(Na0.82-xK0.18Lix)0.5](1-y)Sry(Ti1-zTaz)O3 ceramics by chemical modifications, accompanied by the even higher unipolar strain (∼0.63%, 90 kV/cm) and large field signal (d33* = 990 pm/V, 50 kV/cm). Moreover, the symmetrical bipolar S-E loop is also obtained in this system. In particular, we strictly illuminate the origin of the composition-induced giant strain from the view of the microscopic (A-O bonds weakening), mesoscopic (the coexistence of metastable small-sized ferroelectric domain structures and ergodic relaxor phase), and macroscopic (Tf-r shifting) perspectives. We believe that this work can provide a simple but effective way to optimize the strain behavior in BNT-based ceramics.

(LiBi)-doped CaBi2Nb2O9 (CBN) ceramics were synthesized by the conventional solid-state sintering method. The effects of (LiBi) additives on the crystalline structure were explored by Rietveld refinements. The results showed that pseudo-tetragonal distortion was induced by (LiBi) additives when x ≥ 0.35. This structural distortion increased the spontaneous polarization along a-axis and decreased the quits spontaneous polarization along b-axis, which was beneficial to the polarization switching, thus promoting the ferroelectricity and decreasing the coercive field (EC) of CBN based ceramics. The Ca0.60(Li0.5Bi0.5)0.40Bi2Nb2O9 (CBNLB-40) ceramics possess the optimum ferroelectric property with 2Pr of 10 μC/cm2 and a coercive field (EC) lower than 100 kV/cm. Moreover, it exhibits a good ferroelectric fatigue-free property within 107 switched cycles. This work may provide a new method to promote the performance of Aurivillius ferroelectric-based non-volatile memory devices.

The intensive demands of microelectronics and energy-storage applications are driving the increasing investigations on the colossal permittivity (CP) materials. In this study, we designed a new system of Dy and Nb co-doped TiO2 ceramics [(Dy0.5Nb0.5)xTi1–xO2] with the formation of secondary phases, and then the enhancement of overall dielectric properties (er ∼ 5.0–6.5 × 104 and tan δ < 8%) was realized in the broad composition range of 0.5 ≤ x ≤ 5%. More importantly, effects of secondary phases on microstructure, dielectric properties, and stability were explored from the views of defect-dipoles and internal barrier layer capacitance (IBLC) effect. According to the defect-dipoles theory, the CP should mainly originate from Nb5+, and the Dy3+ largely contributes to the decreased dielectric loss. Both CP and low dielectric loss were obtained for co-doping with Dy3+ and Nb5+. Besides, the Dy enrichment induced the formation of secondary phases, which were regarded as the low loss unit dispersed into the cer...