Na0.5Bi0.5TiO3 Research Articles

Modulation of polarization behavior in Na0.5Bi0.5(Ti,Fe)O3-based heterostructure thin films for dielectric energy storage: Defect engineering study via an artificial aging process

Na0.5Bi0.5TiO3 (NBT)-based thin films are highly desired for energy storage owing to their high intrinsic polarization and Curie temperature under the current trend of electronic device integration and portability. However, the low energy density originating from the inferior anti-breakdown ability (EBD), as well as the limited space for improvement of the gap between maximum polarization and remanent polarization (Pm–Pr) is the main challenge for practical applications. Here, we propose a strategy to modulate polarization behavior of NBT-based heterostructure thin films. Na0.5Bi0.5(Ti0.97Fe0.03)O3 (NBFT) is taken as the basic component. Na0.5Bi0.5(Ti0.98Zr0.02)O3 (NBZT) and (Ba1-xSrx)TiO3 (BSxT, where x is set with gradient characteristics of 0, 0.1 and 0.2, respectively from near to far substrate ends) are chosen to fabricate NBFT/BSxT and (NBFT/NBZT)5/NBFT heterostructure thin films. Artificial aging process is carried out for modulating polarization behavior of both the heterostructure thin films. Time-dependent strain and defect migration are observed and analyzed, reflecting the structural relaxation characteristics of the thin films. After aging with treating, the recoverable energy storage density (Wrec) of NBFT/BSxT and (NBFT/NBZT)5/NBFT are increased from 46.78 to 66.95 J/cm3 and 66.57–67.64 J/cm3, respectively, with energy storage efficiency (η) increasing from 68.46% to 75.65% and 64.33%–70.76%, respectively at 20 kHz and room temperature. This research provides a new route to take usages of aging process for designing NBT-based thin film for dielectric energy storage.

A Stress Self-Adaptive Silicon/Carbon "Ordered Structures" to Suppress the Electro-Chemo-Mechanical Failure: Piezo-Electrochemistry and Piezo-Ionic Dynamics.

Construction of ordered structures that respond rapidly to environmental stimuli has fascinating possibilities for utilization in energy storage, wearable electronics, and biotechnology. Silicon/carbon (Si/C) anodes with extremely high energy densities have sparked widespread interest for lithium-ion batteries (LIBs), while their implementation is constrained via mechanical structure deterioration, continued growth of the solid electrolyte interface (SEI), and cycling instability. In this study, a piezoelectric Bi0.5 Na0.5 TiO3 (BNT) layer is facilely deposited onto Si/C@CNTs anodes to drive piezoelectric fields upon large volume expansion of Si/C@CNTs electrode materials, resulting in the modulation of interfacial Li+ kinetics during cycling and providing an electrochemical reaction with a mechanically robust and chemically stable substrate. In-depth investigations into theoretical computation, multi-scale in/ex situ characterizations, and finite element analysis reveal that the improved structural stability, suppressed volume variations, and controlled ion transportation are responsible for the improvement mechanism of BNT decorating. These discoveries provide insight into the surface coupling technique between mechanical and electric fields to control the interfacial Li+ kinetics behavior and improve structural stability for alloy-based anodes, which will also spark a great deal attention from researchers and technologists in multifunctional surface engineering for electrochemical systems.

Energy storage in epitaxial multilayered BiFeO3/Na0.5Bi0.5TiO3/La0.7Sr0.3MnO3 thin films

Lead-free dielectric film capacitors with fast charge-discharge rates are ideal for pulsed power capacitors, but their energy storage density lags behind. Lead-free epitaxial multilayered BiFeO3 (BFO)/Na0.5Bi0.5TiO3 (NBT)/La0.7Sr0.3MnO3 (LSMO) films were designed and fabricated by solution processing and the effects of bottom electrodes as well as BFO thickness on microstructures, electrical properties and energy storage performances were investigated. Compared with the NBT film on Pt/Ti/SiO2/Si substrate, the leakage current densities are significantly suppressed and polarizations are obviously improved for the multilayered BFO/NBT/LSMO films. The BFO/NBT/LSMO film with BFO thickness of about 60 nm exhibits a recoverable energy storage density of 37.0 J/cm3 under 2680 kV/cm and excellent performance stability. These results demonstrate that the epitaxial multilayered BFO/NBT/LSMO films are promising candidates for high-power energy storage applications.

Comprehensive optimization of piezoelectric coefficient and depolarization temperature in Mn-doped Bi0.5Na0.5TiO3-Bi0.5K0.5TiO3-BaTiO3 lead-free piezoceramics

Lead-free Bi0.5Na0.5TiO3 (BNT) piezoelectric ceramics have the advantages of large coercive fields and high Curie temperatures. But the improvement of piezoelectric coefficient (d33) is usually accompanied by a huge sacrifice of depolarization temperature (Td). In this work, a well-balanced performance of d33 and Td is achieved in MnO2-doped 0.79(Bi0.5Na0.5TiO3)-0.14(Bi0.5K0.5TiO3)-0.07BaTiO3 ternary ceramics. The incorporation of 0.25 mol% MnO2 enhances the d33 by more than 40%, while Td remains almost unchanged (i.e., d33=181 pC/N, Td=184 °C). X-ray diffraction (XRD) shows that an appropriate fraction of the small axis-ratio ferroelectric phase (pseudo-cubic, Pc) coexists with the long-range ferroelectric phase (tetragonal, T) under this MnO2 doping. Piezoelectric force microscopy (PFM) has revealed a special domain configuration, namely large striped and layered macro domains embedded with small nanodomains. This study provides a distinctive avenue to design BNT-based piezoelectric ceramics with high piezoelectric performance and temperature stability.

Electric field-temperature phase diagram and electrical properties of (1-x)Na0.5Bi0.5TiO3 - xK0.5Bi0.5TiO3 ceramics

Electrically and thermally induced transitions between ferroelectric and relaxor states are of great significance in Na1/2Bi1/2TiO3 (NBT)-based materials due to their remarkable similarity to electromechanical properties. However, an in-depth understanding of the family of this material remains challenging, primarily due to its structural complexity and diverse behaviour with or without the presence of an external electric field. For enhancing NBT-based ceramics and enabling the analysis of their electric field temperature (E-T) phase diagrams, it has been suggested that K0.5Bi0.5TiO3 (KBT) could be used as a dopant material. This study thoroughly examines the electrical, microstructural, and ferroelectric (FE) properties of (1-x)NBT-xKBT ceramics. The incorporation of KBT into NBT, inducing a change in structural symmetry, reveals the coexistence of rhombohedral and tetragonal phases (x ∼ 0.2), as confirmed by X-ray diffraction. Using a modified KWW function, electrical modulus (EM) analysis illustrates a non-Debye-type relaxation process. Moreover, it is observed that temperature influences the transition of the material among its ferroelectric (FE), ergodic (ER), and non-ergodic (NR) relaxor phases. This report proposes that the E-T phase diagram can serve as a valuable tool for determining optimal conditions and selecting materials for electromechanical and actuator-based applications.

Local structure analysis of Bi0.5Na0.5TiO3–BaTiO3 solid solutions

Abstract Solid solutions of Bi0.5Na0.5TiO3 (BNT) and BaTiO3 (BT) with ABO3-type perovskite system is known to possess good ferroelectric properties. A local structural analysis and an electronic structure analysis of high-quality BNT-BT solid solutions were performed using synchrotron radiation X-rays to clarify the mechanism of the enhanced ferroelectric properties. The BNT-BT solid solution undergoes a series of phase transitions to tetragonal structures with space groups P4bm and P4mm. The local structure analysis revealed reduced off-center shift of A-site atoms resulting of the BT substitution. The local structure obtained by high-energy X-ray total scattering is consistent with the electronic structure obtained by X-ray absorption spectroscopy.

Enhanced Piezo-Photocatalytic Performance of Na0.5Bi4.5Ti4O15 by High-Voltage Poling.

The internal electric field within a piezoelectric material can effectively inhibit the recombination of photogenerated electron-hole pairs, thus serving as a means to enhance photocatalytic efficiency. Herein, we synthesized a Na0.5Bi4.5Ti4O15 (NBT) catalyst by the hydrothermal method and optimized its catalytic performance by simple high-voltage poling. When applying light and mechanical stirring on a 2 kV mm-1 poled NBT sample, almost 100% of Rhodamine B solution could be degraded in 120 min, and the reaction rate constant reached as high as 28.36 × 10-3 min-1, which was 4.2 times higher than that of the unpoled NBT sample. The enhanced piezo-photocatalytic activity is attributed to the poling-enhanced internal electric field, which facilitates the efficient separation and transfer of photogenerated carriers. Our work provides a new option and idea for the development of piezo-photocatalysts for environmental remediation and pollutant treatment.

Evolution between ferroelectric photovoltaic effect and resistance switching behavior engineered by the polarization field and barrier characteristics.

The bandgap and polarization field play a key role in the ferroelectric photovoltaic effect. However, narrow bandgap induced electrical conductivity always brings out a depression of the photovoltaic performances. Based on the mechanisms of the photovoltaic effect and resistance switching behaviors in ferroelectric materials, this work realizes an evolution between the two effects by engineering the polarization field and barrier characteristics, which addresses the trade-off issues between the bandgap and polarization for ferroelectric photovoltaic effect. SrCoOx (SC, 2.5≤x≤3) with multivalent transition is introduced into Na0.5Bi0.5TiO3 (NBT) matrix material to engineered the polarization field and barrier characteristics. (1-x)NBT-xSC (x=0.03, 0.05, 0.07) solid solution films present an evolution of ferroelectric photovoltaic effect to grow out of nothing again to the disappearance of the photovoltaic effect and the appearance of resistance switching behavior. The 0.95NBT-0.05SC film achieve the open-circuit voltage of 0.81 V and the short-circuit current of 23.52 µA/cm2, and the 0.93NBT-0.07SC film obtains the resistive switching behavior with switch ratio of 100. This work provides a practicable strategy to achieve the fascinating evolution between photovoltaic effect and resistive switching.

Improved dielectric energy storage performance of Na0.5Bi0.5TiO3-based lead-free relaxation ferroelectric ceramics achieved by domain structural regulation and enhanced densification

There is still a problem of low energy storage density in dielectric capacitors which is a core component of power systems. For the improvement of the energy storage density, the linear dielectric material CaTiO3 (CT) was introduced in Na0.5Bi0.5TiO3 (NBT) ceramics in this paper. By modifying the A site, a new relaxor ferroelectric ceramic was successfully synthesized and attained a recoverable density (Wrec) of 2.34 J/cm3 at x = 0.18. Moreover, the preparation process was optimized in this paper. Through the viscous polymer process (VPP) route, the energy density (WA) of 82NBT-18CTVPP ceramic further reaches 6.45 J/cm3 at 340 kV/cm, with efficiency (η) up to 75% and a Wrec of 4.82 J/cm3. At the same time, the change of Wrec is small at temperature (30–150 °C) and frequency (1 Hz–300 Hz), which demonstrates its excellent stability. The discharge power density reaches about 180 MW/cm3 and the discharge time is 0.117 μs, which indicates its excellent pulse discharge performance. The results show that 82NBT-18CT lead-free relaxation ferroelectric material is expected to become ideal for high-energy storage applications.

Comprehending the underlying mechanism behind directly/indirectly obtained large electrocaloric response in Bi0.5Na0.5TiO3-based relaxor ferroelectrics

Lead-free ferroelectric electrocaloric (EC) materials are promising candidates for the next generation of cooling materials. Bi0.5Na0.5TiO3 (BNT)-based relaxor ferroelectrics, one of the most representative EC materials, exhibit a superior electrocaloric effect (ECE) near the depolarization temperature (Td). However, there are more and more concerns over the reliability of the widely used indirect measurement method. Here, to comprehend the difference between indirectly and directly obtained ECE results in BNT-based system, the applicability of indirect measurement (based on Maxwell equation) was critically analyzed with respect to the reliable direct measurement (based on heat flow). As evidenced in prototypical BNT-based compositions with different Td values, the dynamic behaviors of local polar structures including ferroelectric domains and polar nano-sized regions (PNRs), can largely affect the measured polarization and thus affect the reliability of indirect measurement. After systematically comparing and analyzing the composition-, temperature-, electric field (E-field)-dependent ECE results obtained from indirect and direct ways, the applicable working regions for the indirect method were determined. This work reveals the underlying mechanism behind direct and indirect ECE measurements, providing the “indirect + direct” experimental strategy for effectively evaluating the ECE performance in BNT-based relaxor ferroelectrics.

Giant Energy Storage Density with Antiferroelectric-Like Properties in BNT-Based Ceramics via Phase Structure Engineering.

Driven by the information industry, advanced electronic devices require dielectric materials which combine both excellent energy storage properties and high temperature stability. These requirements hold the most promise for ceramic capacitors. Among these, the modulated Bi0.5 Na0.5 TiO3 (BNT)-based ceramics can demonstrate favorable energy storage properties with antiferroelectric-like properties, simultaneously, attaching superior temperature stability resulted from the high Curie temperature. Inspired by the above properties, a strategy is proposed to modulate antiferroelectric-like properties via introducing Ca0.7 La0.2 TiO3 (CLT) into Bi0.395 Na0.325 Sr0.245 TiO3 (BNST) ((1-x)BNST-xCLT, x = 0.10, 0.15, 0.20, 0.25). Combining both orthorhombic phase and defect dipole designs successfully achieve antiferroelectric-like properties in BNST-CLT ceramics. The results illustrate that 0.8BNST-0.2CLT presents superior recoverable energy storage density ≈8.3 J cm-3 with the ideal η ≈ 80% at 660kV cm-1 . Structural characterizations demonstrate that there is the intermediate modulated phase with the coexistence of the antiferroelectric and ferroelectric phases. In addition, in situ temperature measurements prove that BNST-CLT ceramics exhibit favorable temperature stability over a wide temperature range. The present work illustrates that BNT-based ceramics with antiferroelectric-like properties can effectively enhance the energy storage performance, which provides novel perspectives for the subsequent development of advanced pulsed capacitors.

B-site ion driven morphotropic phase transformation in NN-BT-ABO3 lead-free ceramics through chemical pressure

Forming morphotropic phase boundary (MPB) is crucial to improve the piezoelectric properties of lead-free NaNbO3-BaTiO3-xABO3 (NN-BT-xABO3) ceramics. In this work, four NN-BT-xABO3 systems (ABO3 = K0.5Bi0.5TiO3 (KBT), Bi0.5Na0.5TiO3 (BNT), K0.5Bi0.5ZrO3 (KBZ), and Bi0.5Na0.5ZrO3 (BNZ)) were constructed to analyze the relationship between ABO3 characteristic and phase transformation behavior. The results showed that the NN-BT-xKBT/xBNT systems underwent ferroelectric tetragonal (T)-relaxor ferroelectric T phase transformation with d33 ∼ 150 pC/N and kp ∼ 0.2 in NN-BT-0.11KBT and NN-BT-0.09BNT compositions, while the NN-BT-xKBZ/xBNZ systems underwent ferroelectric T- ferroelectric rhombohedral (R) morphotropic phase transformation with improved d33 ∼ 256 pC/N and kp ∼ 0.31 in NN-BT-0.04BNZ composition. The B-site ion radius was found to be a key factor in inducing phase transformation. The incorporation of small Ti4+ ions tends to break the long ordering of ferroelectrics, inducing the normal-relaxor ferroelectric phase transformation, however, the appearance of the R phase in NN-BT-xAZrO3 compositions was attributed to the chemical pressure caused by buckled Zr-O-Zr bonds as larger Zr4+ ions enter the NN-BT matrix lattices. This study will deepen the understanding of the ferroelectric phase transformation mechanism in the lead-free NaNbO3 material system and provide a guidance for designing morphotropic NN-based lead-free piezoelectric ceramics.

Comprehensive temperature-stable energy storage performance in core-shell structural Na0.5Bi0.5TiO3@SrSn0.1Ti0.9O3-(Bi2O3-B2O3-SiO2) composites via morphology engineering

In this paper, morphology engineering was developed to optimize the overall temperature-stable energy storage performance of ceramic capacitors. First, SrSn0.1Ti0.9O3 (SST) particles were coated on Na0.5Bi0.5TiO3 (NBT) rods to form "core-shell" NBT@SST rods by a co-precipitation method to improve the relaxor behavior. And the rods were compounded with the Bi2O3-B2O3-SiO2 (BBS) glass to dense into NBT@SST-BBS composites. The nanorods morphology of ceramic grains can increase the charge storage sites to induce higher polarization value. The moderate-εr SST shell with highly lattice matching could lower the interfacial polarization between ceramic and glass phase so as to boost the breakdown strength. Comparatively, composites with nanorod morphology can reach the highest recoverable energy density of 2.19 J/cm3 at 229 kV/cm with superior temperature stability (Δε/ε150 °C ≤ 15% at 30–395 °C). We hope this work will give guidance to fabricate the next-generation dielectric capacitors through morphology engineering.

The Influence of BaTiO3 Content on the Energy Storage Properties of Bi0.5Na0.5TiO3-Bi(Mg2/3Nb1/3)O3 Lead-Free Ceramics

Na0.5Bi0.5TiO3 (NBT)-based ceramics are promising lead-free candidates for energy-storage applications due to their outstanding dielectric and ferroelectric properties derived from large polarization. However, the high coercive field and large remnant polarization are unfavorable for practical applications, and thus NBT-based ceramics with relaxation behavior via doping/forming solid solutions with other elements/components have been widely studied. In this work, BaTiO3 (BT) was introduced to the 0.94Na0.5Bi0.5TiO3-0.06Bi(Mg2/3Nb1/3)O3 system by a conventional solid-state reaction to form a homogeneous solid solution of 0.94[(1−x)Na0.5Bi0.51TiO3-xBaTiO3]-0.06Bi(Mg2/3Nb1/3)O3 (BNT-100xBT-BMN). As the BT content increased, the proportion of the rhombohedral R3c phase increased while that of the tetragonal P4bm phase decreased, leading to the maximum Pmax (38.29 μC/cm2) and Eb (80 kV/cm) obtained in BNT-7BT-BMN (x = 0.07) composition. Specifically, the optimal energy storage properties of Wrec ~ 1.02 J/cm3 and η ~ 62.91% under 80 kV/cm were obtained in BNT-7BT-BMN ceramics, along with good temperature stability up to 200 °C, which are promising factors for future pulse power applications.

Multi‐Effects Coupled Nanogenerators for Simultaneously Harvesting Solar, Thermal, and Mechanical Energies

AbstractAs a result of the widespread use of small‐scale and low‐power electronic devices, the demand for micro‐energy sources has increased, in particular the potential to harvest the wide variety of energy sources present in their surrounding environment. In this paper, a novel coupled nanogenerator that can realize energy harvesting for multiple energy sources is reported. Based on the unique electrical properties of ferroelectric Bi0.5Na0.5TiO3 (BNT) materials, it is possible to combine a photovoltaic cell, pyroelectric nanogenerator, and triboelectric‐piezoelectric nanogenerator in a single element to harvest light, heat, and mechanical energy simultaneously. To evaluate the effectiveness of coupling for different materials, a Yang coupling factor (kC,Q) is defined in terms of transferred charge, where BNT has the largest kC,Q of 1.29 during heating, indicating that BNT has the best coupling enhancement compared to common ferroelectric materials. This new criterion and novel device structure therefore provide a new basis for the future development of coupled nanogenerators which are capable of harvesting multiple sources of energy.

Enhanced piezo-catalytic H2O2 production over Bi0.5Na0.5TiO3 via piezoelectricity enhancement and surface engineering

The piezo-catalytic hydrogen peroxide (H2O2) production is a promising alternative to traditional anthraquinone oxidation process, but it remains a challenging task. The low conversion efficiency of mechanical energy and the limitedsurface-active sites are the challengings for improving reaction efficiency. Moreover, piezo-catalysts are difficult to prepare in large quantities, limiting the industrial application. To address this issue, this study utilized piezoelectricity enhancement and surface engineering to regulate the Bi0.5Na0.5TiO3 (BNT) for piezo-catalytic H2O2 production. We successfully synthesized an efficient and stable piezo-catalyst, Ag-loaded Bi0.5Na0.5TiO3-AgNbO3 solid solution (Ag/BNT-AN), that was applied to two-channel H2O2 production. The piezo-catalytic activity of Ag/BNT-AN piezo-catalyst was greatly improved through joint regulation of enhancing piezoelectricity by Ag and Nb co-substitution, as well as promoting O2 reduction and H2O oxidation reactions by surface modification with Ag nanoparticals and hydroxyl groups. The optimal Ag/BNT-AN piezo-catalyst displayed H2O2 production rates of 469 µmol g−1 h−1 under ultrasonic vibration, which was 13 times higher than pure BNT. Additionally, the study found that H2O2 could also be synthesized when the catalyst was subjected to simple stirring as mechanical stress, indicating the potential of Ag/BNT-AN to harness low-frequency mechanical energy. This work provides an effective strategy for regulating piezo-catalysts and presents a catalyst design paradigm at the kilogram level.

Development of Lead Free Magnetoelectric Materials for Magnetic Field Sensor applications

(100-x) Na0.5Bi0.5TiO3 (NBT)-(x) NiFe2O4 (NFO)(x = 0, 20, 40, 60, 80 and 100) composites are synthesized using conventional solid state reaction method. Crystal structure studies are performed by using X-ray Diffraction technique (XRD) and the Rietveld analysis of XRD patterns confirms the co-existence of cubic (NFO) and rhombohedral (NBT) symmetry with Fd- 3m and R3c space groups, respectively. Micro-structural study reveals the formation of combination of composite phases and its inter-coupling grains. The average grain sizes and area percentage of each phase for the composites are calculated using Image J software. The Magnetisation versus Magnetic field (M-H) hysteresis loops show soft magnetic behavior of composites with variation in Saturation magnetization (MS) and Coercivity (HC). A maximum MS (34 emu/g) and low HC (15 Oe) is obtained for (80) NFO - (20) NBT composite.The Polarization – Electric field (P-E) analysis shows that the maximum saturation polarization (PS) is obtained for (60)NBT-(40)NFO sample and is attributed to the leakage current generated by conductive NFO phase. The coupling between the ferrite and ferroelectric phase is studied based on the magnetoelectric voltage coefficient(αME). The maximum (αME) of 1.82 mV/cm-Oe is obtained for (80)NBT -(20)NFO sample and this is almost 80% higher than the previously published literature on NBT-NFO composites. This can be attributed to the uniform distribution of grains with each ferroelectric phase surrounded by ferrite phase as shown in the morphological study.

Achieving comprehensive temperature-stable energy storage properties in core-shell Na0.4K0.1Bi0.5TiO3@(SrZrO3-BiMg0.5Sn0.5O3)@SiO2 ceramics via a multi-scale synergistic optimization

At present, to improve the energy storage properties and wide-range temperature stability synergistically is the bottleneck of Na0.5Bi0.5TiO3 (NBT)-based energy storage ceramics. In this paper, it is expected to breakthrough this bottleneck through a multi-scale synergistic optimization (including composition, structure and preparation) integrated by the design of core–shell structure. This unique structure is constructed by coating SrZrO3-BiMg0.5Sn0.5O3 (SZ-BMS) on the surface of Na0.4K0.1Bi0.5TiO3 (NKBT), and then coating SiO2 glass to prepare NKBT@(SZ-BMS)@SiO2 ceramics. The SZ-BMS phase plays multi roles in alleviating interfacial polarization, domain reconstruction and defect regulation. The outer SiO2 layer benefits to grain size refinement and defect control. The energy storage performance of NKBT@(SZ-BMS)@SiO2 ceramics are affected by the BMS amount. When the BMS amount is 15 mol%, high breakdown strength of 301 kV/cm and polarization of 29.1 μC/cm2 are achieved in the ceramics. Ultimately, large recoverable energy density of 3.94 J/cm3 with high efficiency of 87.1% are simultaneously obtained. It also has an ultra-wide temperature stability (30–467 ℃) of dielectric properties and excellent thermal endurance of energy storage within 20–150 ℃. The prepared NKBT@(SZ-BMS)@SiO2 ceramic is a favorable alternative for temperature-stable energy storage capacitors.

Structure, Electrical Properties, and Thermal Stability of the Mn/Nb Co-Doped Aurivillius-Type Na0.5Bi4.5Ti4O15 High Temperature Piezoelectric Ceramics

In order to meet the urgent need for high temperature piezoelectric materials with a Curie temperature over 400 °C, the Mn/Nb co-doped strategy has been proposed to improve the weak piezoelectric performance of the Aurivillius-type Na0.5Bi4.5Ti4O15 (NBT) high temperature piezoelectric ceramics. In this paper, the crystal structure, electrical properties, and thermal stability of the B-site Mn/Nb co-doped Na0.5Bi4.5Ti4-x(Mn1/3Nb2/3)xO15 (NBT-100x) ceramics were systematically investigated by the conventional solid-state reaction method. The crystal structural analysis results indicate that the NBT-100x ceramics have typical bismuth oxide layer type phase structure and high anisotropic plate-like morphology. The lattice parameters and the grain sizes increase with the B-site Mn/Nb co-doped content. The electrical properties were significantly improved by Mn/Nb co-doped modifications. The maximum of the piezoelectric coefficient d33 was found to be 29 pC/N for the NBT-2 ceramics, nearly twice that of the unmodified NBT ceramics. The highest values of the planar electromechanical coupling factor kp and thickness electromechanical coupling factor kt were also obtained for the NBT-2 ceramics, at 5.4% and 31.2%, respectively. The dielectric spectroscopy showed that the Curie temperature Tc of the Mn/Nb co-doped NBT-100x ceramics is slightly higher than that of unmodified NBT ceramics (646 °C). The DC resistivity of the NBT-2 ceramics is higher than 106 Ω∙cm at 500 °C. All the results together with the good thermal stability demonstrated the Mn/Nb co-doped ceramics as an effective method to improve the NBT based piezoelectric ceramics and the potential candidates of the Mn/Nb co-doped NBT-100x ceramics for high temperature piezoelectric applications.

Clarification on phase transition behaviors by local strain engineering in Bi1/2Na1/2TiO3–SrTiO3‐based ternary ceramics

AbstractThe stabilization of ergodicity plays an important role in realizing large strain in a Bi1/2Na1/2TiO3 (BNT)‐based relaxor, which is strongly related to the degree of random fields with respect to the randomly distributed different cations. To clarify the effects of different ionic radii, this study investigated and compared the microstructures, crystal structures, phase transition behaviors, and electrical properties of BNT–ST‐based ternary ceramics by modifying BiMeO3 (where Me = Al and Fe). It was observed that the stabilized relaxor states are different between BiFeO3‐/and BiAlO3‐modified BNT–ST ternary ceramics. As a result, it is suggested that phase transition (more precisely, the stabilization of ergodicity) can be influenced by the different internal strain in BNT–ST‐based ternary ceramics.