Large Electrostrictive Coefficient Research Articles

A Highly Electrostrictive Salt Cocrystal and the Piezoelectric Nanogenerator Application of Its 3D-Printed Polymer Composite.

Ionic cocrystals with hydrogen bonding can form exciting materials with enhanced optical and electronic properties. We present a highly moisture-stable ammonium salt cocrystal [CH3C6H4CH(CH3)NH2][CH3C6H4CH(CH3)NH3][PF6] ((p-TEA)(p-TEAH)·PF6) crystallizing in the polar monoclinic C2 space group. The asymmetry in (p-TEA)(p-TEAH)·PF6 was induced by its chiral substituents, while the polar order and structural stability were achieved by using the octahedral PF6- anion and the consequent formation of salt cocrystal. The ferroelectric properties of (p-TEA)(p-TEAH)·PF6 were confirmed through P-E loop measurements. Piezoresponse force microscopy (PFM) enabled the visualization of its domain structure with characteristic "butterfly" and hysteresis loops associated with ferro- and piezoelectric properties. Notably, (p-TEA)(p-TEAH)·PF6 exhibits a large electrostrictive coefficient (Q33) value of 2.02 m4 C-2, higher than those found for ceramic-based materials and comparable to that of polyvinylidene difluoride. Furthermore, the composite films of (p-TEA)(p-TEAH)·PF6 with polycaprolactone (PCL) polymer and its gyroid-shaped 3D-printed composite scaled-up device, 3DP-Gy, were prepared and evaluated for piezoelectric energy-harvesting functionality. A high output voltage of 22.8 V and a power density of 118.5 μW cm-3 have been recorded for the 3DP-Gy device. Remarkably, no loss in voltage outputs was observed for the (p-TEA)(p-TEAH)·PF6 devices even after exposure to 99% relative humidity, showcasing their utility under extremely humid conditions.

Large electrostrictive response via tailoring ergodic relaxor state in Bi1/2Na1/2TiO3-based ceramics with Bi(Mn1/2Ce1/2)O3 end-member

Lead-free Bi1/2Na1/2TiO3 (BNT)-based relaxor ferroelectric ceramics with superior electrostrictive coefficient features have recently gained a lot of attention due to their application in high-precision displacement actuators. In this work, we propose an effective approach to enhance the electrostrictive effect via tuning the phase transition temperature around ambient temperature in BNT-based ceramics. Herein, a novel Bi(Mn1/2Ce1/2)O3 (BMnCe) modifier was adopted as an activator into 0.935Bi1/2Na1/2TiO3-0.065BaTiO3 (0.935BNT-0.065BT) for modifying the phase boundary (TF-R) around the ambient temperature. The compositional and temperature-dependent dielectric, ferroelectric, and electrostrain were systematically investigated. All samples exhibit a pure perovskite structure. Rietveld refinement revealed that the 0.935BNT-0.065BT ceramic presents a coexistence of rhombohedral (R3c) and tetragonal (P4bm) phases. As the BMnCe content increases, the tetragonal (P4bm) phase becomes more prevalent and eventually shifts into a pseudocubic phase. It was found that the addition of BMnCe can effectively tune the TF-R below ambient temperature and enhance the relaxor behavior. The polarization and electrostrain analysis revealed that the ferroelectric long-range order decreases with increasing BMnCe; specifically, a unique region emerges where remnant polarization, quasistatic d33, and negative strain abruptly drop. As a result, a high electrostrain (S) of 0.43 % with a normalized strain (Smax/Emax) of 716 pm/V was achieved at the critical composition (0.01 M concentration of BMnCe). More importantly, (0.935-x)BNT-0.065BT-xBMnCe (x = 0.01) shows a large electrostrictive coefficient (Q33) of 0.032 m4/C2 with a giant normalized electrostrictive coefficient (Q33/E) of 5.33ｘ10−9 m5/C2V at room temperature. Furthermore, the Q33 and Q33/E values show temperature insensitivity up to 120 °C, rendering the compound suitable for actuation-based devices. These results offer an effective avenue for designing high-performance BNT-based materials with giant electrostrictive coefficients.

Dopant tuned multi-functionality in barium titanate based lead-free piezoceramics

With the increased concerns on the toxicity of lead, the barium titanate (BT) has developed a vital lead-free ferroelectric material to replace lead-based one due to the extraordinary multi-functionality. However, to date the deep understanding on evolution mechanisms of multiple electro-related performances in single BT based ceramics is still limited, and the simultaneous enhancement or balanced development of comprehensive performance in BT ceramics face challenges. Here, a new lead-free ceramic system of Ba0.9+xSr0.1-xTi0.91Sn0.09O3 (BSTS, 0 ≤ x ≤ 0.1) was successfully prepared by the conventional solid-state reaction method, and the dopant tuned multi-functionality and underlying physical mechanism of performance evolutions were revealed in detail. The BSTS ceramics present R-O-T-C multiphase coexistence at a wider temperature range near room temperature, along with the structural features with flattened thermodynamic energy landscape and flexible polarization rotation. Accordingly, the enhanced piezoelectric coefficient (d33 = 600 pC/N), large electrostrictive coefficient (Q33 = 0.0405 m4/C2, E = 30 kV/cm), superior electrocaloric effect (ΔT = 0.77 K, E = 30 kV/cm) with a wider temperature span of 49 °C (ΔT > 0.5 K), and strong electrocaloric strength (ΔT/ΔE = 0.3857 K mm/kV, E = 5 kV/cm) are simultaneously attained under smaller electric field for BSTS ceramics. It exhibits a superior comprehensive performance than many reported BT based ceramics, which is suitable for more potential applications in the emerging fields of advanced functional devices, such as high precision displacement or strain actuators and zero-global-warming-potential refrigeration with larger capacity near room temperature. This work sheds insight into simultaneously optimizing different electro-related performances, and stimulates future studies on dopant tuned multi-functionality in BT based ceramics.

A Ferroelectric Aminophosphonium Cyanoferrate with a Large Electrostrictive Coefficient as a Piezoelectric Nanogenerator.

Hybrid materials possessing piezo- and ferroelectric properties emerge as excellent alternatives to conventional piezoceramics due to their merits of facile synthesis, lightweight nature, ease of fabrication and mechanical flexibility. Inspired by the structural stability of aminophosphonium compounds, here we report the first A3 BX6 type cyanometallate [Ph2 (i PrNH)2 P]3 [Fe(CN)6 ] (1), which shows a ferroelectric saturation polarization (Ps ) of 3.71 μC cm-2 . Compound 1 exhibits a high electrostrictive coefficient (Q33 ) of 0.73 m4 C-2 , far exceeding those of piezoceramics (0.034-0.096 m4 C-2 ). Piezoresponse force microscopy (PFM) analysis demonstrates the polarization switching and domain structure of 1 further confirming its ferroelectric nature. Furthermore, thermoplastic polyurethane (TPU) polymer composite films of 1 were prepared and employed as piezoelectric nanogenerators. Notably, the 15 wt % 1-TPU device gave a maximum output voltage of 13.57 V and a power density of 6.03 μW cm-2 .

A Ferroelectric Aminophosphonium Cyanoferrate with a Large Electrostrictive Coefficient as a Piezoelectric Nanogenerator

AbstractHybrid materials possessing piezo‐ and ferroelectric properties emerge as excellent alternatives to conventional piezoceramics due to their merits of facile synthesis, lightweight nature, ease of fabrication and mechanical flexibility. Inspired by the structural stability of aminophosphonium compounds, here we report the first A3BX6 type cyanometallate [Ph2(iPrNH)2P]3[Fe(CN)6] (1), which shows a ferroelectric saturation polarization (Ps) of 3.71 μC cm−2. Compound 1 exhibits a high electrostrictive coefficient (Q33) of 0.73 m4 C−2, far exceeding those of piezoceramics (0.034–0.096 m4 C−2). Piezoresponse force microscopy (PFM) analysis demonstrates the polarization switching and domain structure of 1 further confirming its ferroelectric nature. Furthermore, thermoplastic polyurethane (TPU) polymer composite films of 1 were prepared and employed as piezoelectric nanogenerators. Notably, the 15 wt % 1‐TPU device gave a maximum output voltage of 13.57 V and a power density of 6.03 μW cm−2.

High-Performance Electrostrictive Relaxors with Dispersive Endotaxial Nanoprecipitations.

Ultrahigh-precision manufacturing and detection have highlighted the importance of investigating electrostrictive materials with a weak stimulated extrinsic electric field and a simultaneous large hysteresis-free strain. In this study, a new type of electrostrictive relaxor ferroelectric is designed by constructing a complex inhomogeneous local structure to realize excellent electrostrictive properties. A remarkably large electrostrictive coefficient, M33 (8 × 10-16 m2 V-2 ) is achieved. Through a combined atomic-scale scanning transmission electron microscopy and advanced in situ high-energy synchrotron X-ray diffraction analysis, it is observed that such superior electrostrictive properties can be ascribed to a special domain structure that consists of endotaxial nanoprecipitations embedded in a polar matrix at the phase boundary of the rhombohedral/tetragonal/cubic phases. The matrix contributes to the high strain response under the weak extrinsic electric field because of the highly flexible polarization and randomly dispersed endotaxial nanoprecipitations with a nonpolar central region, which provide a strong restoring force that reduces the strain hysteresis. The approach developed in this study is widely applicable to numerous relaxor ferroelectrics, as well as other dielectrics, for further enhancing their electrical properties, such as electrostriction and energy-storage capacity.

Large electrostrictive coefficient with optimized Electro-Strain in BNT-based ceramics with ergodic state

Electric field-induced high strain with low hysteresis and large electrostrictive coefficient are necessary for high-precision displacement actuators. Many works focused on achieve large strain through electric field-induced nonergodic-ergodic phase transition, while the accompanied large hysteresis hinders their practical application. Here, (1-x)(Bi0.54Na0.46)0.94Ba0.06TiO3-xSrTiO3 (BNBT-xST, x = 0.1, 0.2, 0.3, 0.4 and 0.5) ceramics are fabricated by a conventional solid state reaction method. The ergodic relaxor phase in BNBT ceramics was effectively regulated by doping SrTiO3. Finally, we achieve a high electro-strain of 0.17% with ultra-low hysteresis of 7.2% (@70 kV/cm) for × = 0.3 ceramics, and a large electrostrictive coefficient Q33 of 0.0251 m4/C2 (@70 kV/cm) with low strain hysteresis of 8.3% for × = 0.4 ceramics. This work provides a method for optimizing the strain-hysteresis trade-off and improving electrostrictive coefficient Q33 of BNT-based ceramics.

Achieving synergistic electromechanical and electrocaloric responses by local structural evolution in lead-free BNT-based relaxor ferroelectrics

• Inducing relaxor evolution by adjusting intrinsic A-site Na + /K + ratio. • Achieving large combined electromechanical and electrocaloric responses. • Realizing a larger electrocaloric endothermic peak at a low electric field. • Obtaining high electrocaloric strength and large electrostrictive coefficient. • Broadening the operating-temperature span. Self-actuating cooling materials based on synergistic electromechanical (EM) and electrocaloric (EC) responses are expected to lead next-generation of intelligent cooling devices. However, most current materials with the two responses present poor performance, narrow operation-temperature span and high driving electric field, and even contain toxic lead. Here, environmentally benign lead-free Bi 0.5 Na 0.5 TiO 3 -based (BNT) system was designed to achieve large combined response of two effects in a large temperature span by adjusting intrinsic A-site Na + /K + ratio to induce relaxor evolution. Simultaneously, high EC strength and large electrostrictive coefficient over a wide temperature range were obtained to resolve these challenges. The local-structural evolution is studied in detail to provide a theoretical basis for future application of this intelligent material. A novel asymmetric EC response presenting a larger endothermic peak was realized at a low electric field (<3 kV mm −1 ), which can provide a guideline for the development of low-driving-field EC materials to a certain extent. The phase-field simulation was performed to predict this unique behavior by describing the corresponding dipole coupling states under various electric fields.

Large electrostrictive coefficients of BaTiO&lt;sub&gt;3&lt;/sub&gt;-based lead-free ceramics

AbstractMicro-displacement actuators have important applications in aerospace, semiconductor, industry and other fields. Now most of the lead-based piezoelectric ceramics are used in the market. In consideration of environmental protection and legal restriction, it is urgent to develop lead-free ceramic materials with excellent electrostrictive properties. As a kind of ABO&lt;sub&gt;3&lt;/sub&gt;-type ferroelectrics, (Ba,Ca)(Ti,Zr)O&lt;sub&gt;3&lt;/sub&gt; lead-free ceramics have attracted a lot of attention because of their high piezoelectricity. In this work, (Ba&lt;sub&gt;0.85&lt;/sub&gt;Ca&lt;sub&gt;0.15&lt;/sub&gt;)(Ti&lt;sub&gt;0.9&lt;/sub&gt;Zr&lt;sub&gt;0.1&lt;/sub&gt;)O&lt;sub&gt;3&lt;/sub&gt; (BCTZ) ceramics with high electrostrictive coefficient are prepared by the solid-state method. The effects of sintering temperature on the structures and electrical properties of BCTZ ceramics are studied. The results show that the sintering temperature can help to improve density and grain growth of BCTZ ceramic.There are no impurity phases in the BCTZ ceramic systems, and all samples show ABO&lt;sub&gt;3&lt;/sub&gt;-type perovskite structures. At room temperature, the crystal structure of BCTZ ceramic forms coexistence of orthogonal (O)-tetragonal (T) phase. The dielectric peak of BCTZ ceramic is widened, and the Curie temperature reaches a maximum value of 110 ℃ when &lt;i&gt;T&lt;/i&gt;&lt;sub&gt;s&lt;/sub&gt; = 1300 ℃. With the increase of sintering temperature, the dielectric peak of BCTZ ceramic gradually becomes narrowed, and the Curie temperature of ceramic moves toward low temperature.As the sintering temperature is 1300 ℃, the grain size of BCTZ ceramic is 1 μm, the large electrostrictive coefficient &lt;i&gt;Q&lt;/i&gt;&lt;sub&gt;33&lt;/sub&gt; (5.84 × 10&lt;sup&gt;–2&lt;/sup&gt; m&lt;sup&gt;4&lt;/sup&gt;/C&lt;sup&gt;2&lt;/sup&gt;) can be obtained, which is about twice that of traditional PZT ceramic. This may be attributed to combination of the surface effect caused by grain size of BCTZ ceramic with the strong ionic nature of A-O chemical bond. In addition, although BCTZ ceramic has an O-T phase boundary near room temperature, the electrostrictive coefficient &lt;i&gt;Q&lt;/i&gt;&lt;sub&gt;33&lt;/sub&gt; of ceramic has good temperature stability in a range of 25–100 ℃. It shows that the crystal phase and temperature have no effect on the electrostrictive coefficient of BCTZ lead-free ceramic. It provides a new idea for designing the high electrostrictive properties of lead-free piezoelectric ceramics with potential applications.

Feasible Way to Achieve Multifunctional (K, Na)NbO3-Based Ceramics: Controlling Long-Range Ferroelectric Ordering.

It is challenging to achieve highly tunable multifunctional properties in one piezoelectric ceramic system through a simple method due to the complicated relationship between the microscopic structure and macroscopic property. Here, multifunctional potassium sodium niobate [(K, Na)NbO3 (KNN)]-based lead-free piezoceramics with tunable piezoelectric and electrostrictive properties are achieved by controlling the long-range ferroelectric ordering (LRFO) through antimony (Sb) doping. At a low Sb doping, the slightly distorted NbO6 octahedron and the softened B-O repulsion well maintain the LRFO and induce plenty of nanoscale domains coexisting with a few polar nanoregions (PNRs). Thereby, the diffused rhombohedral-orthorhombic-tetragonal (R-O-T) multiphase coexistence with distinct dielectric jumping is constructed near room temperature, by which the nearly 2-fold increase in the piezoelectric coefficient (d33 ∼ 539 pC/N) and the temperature-insensitive strain (the unipolar strain varies less than 8% at 27-120 °C) are obtained. At a high Sb doping, the LRFO is significantly destroyed, leading to predominant PNRs. Thus, a typical relaxor is obtained at the ferroelectric-paraelectric phase transition near room temperature, in which a large electrostrictive coefficient (Q33 = 0.035 m4/C2), independent of the electric field and temperature, is obtained and comparable to that of lead-based materials. Therefore, our results prove that controlling the LRFO is a feasible way to achieve high-performance multifunctional KNN-based ceramics and is beneficial to the future composition design for KNN-based ceramics.

Piezoelectric performance of Zr-modified lead-free BiFeO3-BaTiO3 ceramics

The structural evolution and the variation in the electrical properties of 0.67Bi1.03FeO3–0.33BaTi1-xZrxO3 (BF33BT-100xZr with x = 0.00–0.05) piezoelectric ceramics were studied. An enhanced static piezoelectric coefficient (d33) οf 248 pC/N, with a high Curie temperature (TC) of approximately 400 °C, was obtained near the morphotropic phase boundary (MPB). The room-temperature dynamic piezoelectric coefficient (d33*) was found to gradually increase from 460 to 620 pm/V as the temperature was increased to 100 °C. A large electrostrictive coefficient (Q33) of 0.018–0.032 m4/C2 in the temperature range of 25–100 °C was obtained for the BF33BT-3Zr ceramic. The enhancement of the ferroelectric and piezoelectric responses of the ceramic with increasing temperature is associated with the thermal facilitation of domain switching. A strong relationship was observed between the crystalline structure and the functional properties of the investigated ceramic series, creating a viable paradigm for future research into lead-free piezoelectric ceramics.

Large Electrostrictive Coefficient in a Two-Dimensional Hybrid Perovskite Ferroelectric.

Two-dimensional (2D) hybrid organic-inorganic perovskites (HOIPs) are attracting tremendous interest for their great scientific and technological potential in photovoltaics and optoelectronics. Although the ferroelectricity in 2D HOIPs has been greatly developed, however, to date no phosphonium-based 2D HOIP ferroelectrics have yet been found. Meanwhile, electrostriction plays an important role in the electromechanical behavior of ferroelectrics, while it has never been reported for 2D HOIP ferroelectrics. Here, we present the first phosphonium-based 2D HOIP ferroelectric (EATMP)PbBr4 (EATMP = (2-aminoethyl)trimethylphosphanium) with a direct bandgap of 2.84 eV. Notably, (EATMP)PbBr4 possesses a high Curie temperature of 534 K, which is the highest among all reported 2D HOIP ferroelectrics. Moreover, it exhibits a large electrostrictive coefficient of about 3.96 m4 C-2 as well, far exceeding those of PVDF (1.3 m4 C-2) and inorganic ones (∼0.034-0.096 m4 C-2). With excellent ferroelectric and piezoelectric properties and the merit of easy fabrication, (EATMP)PbBr4 shows great potential in applications for future smart devices of actuators, transducers, and sensors.

Large electrostrictive coefficient with high electro‐strain dominated by modified ergodic state in BNT‐based solid solutions

AbstractFor ferroelectric electrostrictors, shifting their Curie temperature TC to the ambient temperature is an effective way to enhance their electrostrictive effect. However, the enhanced electrostrictive coefficient Q33 in this way is often accompanied with an inferior electro‐strain. In this work, by introducing CaZrO3/BaZrO3 as the special kind of solid solution, with an effective regulation on the ergodic state, we simultaneously realize a larger room‐temperature electrostrictive coefficient Q33 (~0.04337 m4/C2) with a superior electro‐strain (~0.41%) in Bi0.5Na0.5TiO3‐based relaxor ferroelectric ceramics. The ions substitution with larger radius in either A‐site or B‐site of perovskite structure tends to facilitate the evolution from ferroelectric tetragonal phase P4mm to relaxor tetragonal phase P4bm along with the decrease in polarity in crystal, thereby shifting the transition temperature TF‐R below room temperature. As a result of the effective regulation on the ergodic state, a large electro‐strain with low hysteresis, just like electrostrictors, is successfully realized in BNT‐based ferroelectric ceramics. Our investigation provides an effective way to simultaneously enhance the electrostrictive coefficient Q33 and electro‐strain for practical applications in precisely controlled displacement.

Temperature-insensitive piezoelectric properties of lead-free BiFeO3–BaTiO3 ceramics with high Curie temperature

Temperature-insensitive high piezoelectric strain and low strain hysteresis (Hs) with high Curie temperature (TC) are desirable for piezoelectric actuator applications. The excellent room-temperature piezoelectric performance (d33 = 309 pC/N and d33∗ = 458 pm/V) with very high TC = 482 °C have achieved in 0.67Bi1.03FeO3-0.33Ba1-xLaxTiO3 ceramics. Furthermore, a small variation in the piezoelectric strain (ΔST = 13%) in the temperature range of 25 °C–125 °C with low strain hysteresis (Hs = 12%) and a large average electrostrictive coefficient (Q33 = 0.03 m2/C4) leads to a high figure of merit for piezoelectric actuators. The structural origin of the high piezoelectric performance is related to the crystal structure morphotropic phase boundary and maximum crystal structure lattice distortion (90° ̶ αR = 0.12° and cT/aT = 1.008). While the physical origin is mainly attributed to the soft ferroelectric effect by La3+ as donor doping on Ba2+-site that significantly reduces the coercive field and makes it easy to switch ferroelectric polarization under the applied electric field. We believe that this breakthrough in lead-free ceramics opens a new development window for temperature-insensitive piezoelectric properties for the high-temperature commercial applications.

Frequency-dependent ferro-antiferro phase transition and internal bias field influenced piezoelectric response of donor and acceptor doped bismuth sodium titanate ceramics

The influence of donor (La3+) and acceptor (Sc3+) dopant on structural and electrical properties of lead-free Bi0.5Na0.5TiO3 (BNT) ceramics system was investigated. Both donor and acceptor substitutions induced a structural transformation of pure BNT ceramics from a rhombohedral to a pseudocubic structure. Splitting of the (111)pc peak in pure BNT was considered symmetry identification for a rhombohedral structure. A micrometer level grain size (1.70 μm–2.81 μm), dense microstructure with good ferroelectric and piezoelectric performance (d33=56−45pC/N) was obtained. The 3% La content BNT ceramic shows an improved dielectric property. The Curie temperature increases from 355 °C for pure BNT to 365 °C for donor-doped and 370 °C for acceptor-doped BNT. The donor doping created cationic vacancies; acceptor doping induces oxygen vacancies that stabilized the polarization level. Maximum remnant polarization (Pr) value has been obtained for 3% La-doped (Pr=27μC/cm2) and 5% Sc-doped (Pr=20μC/cm2) BNT system. Bipolar strain increased with the increase in donor dopant concentration resulting in a large electrostrictive coefficient (Q11 ∼ 0.0122%–0.045%) has been obtained. Electric field-induced unipolar strain value was enhanced to its maximum value (Smax = 0.14%) for 3% La content with normalized strain d33∗=209pm/V and Smax = 0.13% for 5% Sc with normalized strain d33∗=155pm/V at an applied electric field of 70 kV/cm and 50 kV/cm, respectively. The enhanced strain was considered to be associated with low internal bias field and maximum polarization level. In terms of capacitive response, 5% Sc holds a maximum current (∼0.017 mA) during polarization switching.

Large electrostrictive effect and high energy storage performance of Pr3+-doped PIN-PMN-PT multifunctional ceramics in the ergodic relaxor phase

The photoluminescence, dielectric relaxation, ferroelectric hysteresis, and field-induced strain properties of Pr3+-doped 0.24Pb(In1/2Nb1/2)O3-0.42Pb(Mg1/3Nb2/3)O3-0.34PbTiO3 (PIN-PMN-PT:Pr3+) multifunctional ceramics have been investigated. It was found that Pr3+ doping enhanced the dielectric diffuseness and relaxation behavior of PIN-PMN-PT ceramics. Slim P-E loops and S-E curves appear in PIN-PMN-PT:Pr3+ ceramics when the Pr3+ doping concentration reaches 1.4 mol%. Local domain configurations associated with phase transitions were investigated by piezoresponse force microscopy (PFM). Large electrostrictive coefficient Q33 (˜0.03 m4/C2) and high energy-storage efficiency η (92%) were obtained in 2 mol% Pr3+-doped PIN-PMN-PT ceramic in the ergodic relaxor (ER) phase at room temperature. The giant electrostrictive effect and excellent energy-storage performance are related to the field-induced dynamic behavior of polar nanoregions (PNRs). The results show that the PIN-PMN-PT:Pr3+ system is an excellent multifunctional material for making electromechanical and energy storage devices.

Large electrostrictive properties in lead-free BaTiO3–ZnSnO3 solid solutions

A new lead-free perovskite piezoelectric solid solution (1−x)BaTiO3–xZnSnO3 (BT–xZS) was designed and fabricated using the traditional solid-state reaction method. The introduction of ZnSnO3 was found to shift the high-temperature cubic phase of BaTiO3 to lower temperatures. At room temperature large electrostrictive coefficient up to 0.0452 m4 C−2 was obtained in BT–0.10ZS ceramic, which is much larger than the traditional electrostrictive material Pb(Mg1/3Nb2/3)O3 and recently reported lead-free electrostrictive systems. The large electrostrictive response of BT–xZS ceramics makes them quite potential to be applied to new solid-state actuators.

Enhanced temperature stability and tailored electromechanical response in (Ba0.85Ca0.15)(Zr0.1Ti0.9)O3 piezoceramics through rare earth modification

(Ba,Ca)(Zr,Ti)O3 piezoceramics are deemed as one of potential lead-free alternatives to commonly used lead-based piezoelectric ceramics because of their high piezoelectric properties. However, in the process of improving their electrical properties, it tends to cause significant deterioration of thermal, frequency, and fatigue stability for electromechanical response, which will impede the commercialization of piezoelectric materials. Herein, we designed a strategy using the rare earth to modify BCZT lead-free piezoceramics so as to solve the above mentioned challenges. In this work, for Ho-modified BCZT lead-free ceramics, we achieved not only high electromechanical response with Smax/Emax = 550 pm/V and large piezoelectric coefficient d33 = 521 pC/N, but also the enhanced temperature stability featured by < 2% variation for d33 in the general operating temperature range of 20 °C and 70 °C. In addition, large electrostrictive coefficient Q33 of 0.045 m4/C2 was also realized in this modified materials while still maintaining good temperature stability. More interestingly, this modified materials also performed excellent fatigue endurance, evidenced by < 3% variation for the remnant polarization (Pr) and Smax/Emax after 105 cycles. The complex impedance spectra verified that the boosted fatigue resistance was mainly attributed to the decrease of the defect density originating from the reduced oxygen vacancies. These results demonstrate that the introduction of rare earth into BCZT is an effective way to tailor temperature stability and electromechanical responses.

Thermally-stable large strain in Bi(Mn0.5Ti0.5)O3 modified 0.8Bi0.5Na0.5TiO3-0.2Bi0.5K0.5TiO3 ceramics

(1-x)[0.8Bi0.5Na0.5TiO3-0.2Bi0.5K0.5TiO3]-xBi(Mn0.5Ti0.5)O3 (x = 0–0.06, BNKMT100x) lead-free ferroelectric ceramics were prepared via solid state reaction method. Bi(Mn0.5Ti0.5)O3 induces a structure transition from rhombohedral-tetragonal morphotropic phases to pseudo-cubic phase. Moreover, the wide range of compositions within x = 0.03–0.055 exhibit large strain of 0.31%–0.41% and electrostrictive coefficient of 0.027–0.041 m4/C2. Especially, at x = 0.04, the large strain and electrostrictive coefficient are nearly temperature-independent in the range of 25–100 °C. The impedance analysis shows the large strain and electrostrictive coefficient originate from polar nanoregions response due to the addition of Bi(Mn0.5Ti0.5)O3.

Oxygen vacancy effect on ionic conductivity and relaxation phenomenon of Sr&lt;sub&gt;&lt;i&gt;x&lt;/i&gt;&lt;/sub&gt;Ba&lt;sub&gt;1–&lt;i&gt;x&lt;/i&gt;&lt;/sub&gt;Nb&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;6&lt;/sub&gt; ceramics

Due to the various risks caused by lead, the research of lead-free ferroelectric functional ceramics has been one of research hotspots recently. And relaxor ferroelectrics have an important position in materials for ceramic capacitor due to their low temperature change rate and large electrostrictive coefficient. However, the lead-free Sr&lt;sub&gt;&lt;i&gt;x&lt;/i&gt;&lt;/sub&gt;Ba&lt;sub&gt;1–&lt;i&gt;x&lt;/i&gt;&lt;/sub&gt;Nb&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;6&lt;/sub&gt; ceramic is a non-filled tungsten bronze structural material whose Curie temperature can be adjusted by changing the proportion of Sr composition. The increase of Sr concentration in ceramic can cause relaxor behavior and improve dielectric constant and ferroelectric properties. In this work, Sr&lt;sub&gt;&lt;i&gt;x&lt;/i&gt;&lt;/sub&gt;Ba&lt;sub&gt;1–&lt;i&gt;x&lt;/i&gt;&lt;/sub&gt;Nb&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;6&lt;/sub&gt; (&lt;i&gt;x&lt;/i&gt; = 0.4, 0.5 and 0.6, abbreviated as SBN40, SBN50 and SBN60, respectively) ceramics are prepared by a high-temperature solid-state reaction process. The dielectric properties and the impedances of the Sr&lt;sub&gt;&lt;i&gt;x&lt;/i&gt;&lt;/sub&gt;Ba&lt;sub&gt;1–&lt;i&gt;x&lt;/i&gt;&lt;/sub&gt;Nb&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;6&lt;/sub&gt; ceramics are investigated in detail. It is worth noting that the high-temperature diffusion for the Sr&lt;sub&gt;&lt;i&gt;x&lt;/i&gt;&lt;/sub&gt;Ba&lt;sub&gt;1–&lt;i&gt;x&lt;/i&gt;&lt;/sub&gt;Nb&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;6&lt;/sub&gt; has not been studied before. Furthermore, the analysis of high-temperature dielectric behavior and impedance of lead-free functional ceramics is important for the application of functional ceramics in the high-temperature environment. The temperature of phase transition for SBN40, SBN50 and SBN60 are 401.15 K, 355.15 K, and 327.15 K, respectively, which are obtained from the modified Curie-Weiss law. The result shows that the increase of Sr composition leads the phase transition temperature from ferroelectric to paraelectric phase to decrease. In addition, the calculated value of diffusion phase transition parameter &lt;i&gt;γ&lt;/i&gt; for SBN40, SBN50 and SBN60 are 1.53, 1.90 and 1.94, respectively, showing that it is close to an ideal relaxor ferroelectric with the Sr content increasing in SBN ceramics at low temperature. In addition, it is noticed that a similar diffusion appears in at high temperature. This phenomenon is unrelated to the phase transition, but it is corresponding to high temperature dielectric relaxation which is related to oxygen vacancy. As expected, the impedance spectroscopic data present a thermally activated relaxation phenomenon. Finally, activation energy for conduction and relaxation are calculated from the impedance and dielectric data through the Arrhenius law. Comparing the activation energy values for conduction and relaxation, it can be obviously concluded that the trap-controlled conduction process should be responsible for the relaxation process of sample. And the hopping of ions, caused by oxygen vacancies, plays a critical role in the dielectric relaxation process at high temperature.