Na0.5Bi0.5TiO3 Research Articles

Enhancement of the phase, optical and dielectric studies of Bi0.5Na0.5TiO3 (BNT) based structure ceramics

The Mg-based dielectric ceramics of (Bi0.5Na0.5)(1−x)MgxTiO3, 0.00 ≤ x ≤ 0.04 was successfully synthesized by mixed oxide route at 850 °C for 2 hrs. The XRD result revealed the single phase monoclinic crystal structure without any secondary phases. The SEM image shows the uniform grain size, low porosity and denser microstructure of the samples. The grains size gradually increases from 1.58 µm to 2.70 µm due to mass transportation during the sintering process. The EDX analysis of the spectra of all the samples was investigated and reported the peaks of elemental compositions (i.e. Bi, O, Ti & Mg). The maximum dielectric constant (εr=1291) for the base composition were observed at 200 °C temperature. The abrupt increasing in tangent loss (tanδ) was reported above 200 °C temperature at frequency range (100 Hz–1 MHz). The TGA analysis shows the net loss (∼0.47 % by weight) was observed and the sample was sustained up to 850 °C calcine temperature.

Tailoring relaxor P4bm+P21ma phases in BNT-based ceramics for enhancing comprehensive energy storage properties

Tailoring relaxor phase is an effective strategy to enhance energy-storage properties (ESP) for Bi0.5Na0.5TiO3 (BNT)-based ceramics. Herein, we incorporate Na0.91Bi0.09Nb0.94Mg0.06O3 (NBNM) into BNT matrix to form a solid solution of BNT-xNBNM with x = 0.1–0.4. Rietveld refinements reveal that the composition with x = 0.3 has 46% relaxor tetragonal P4bm phase and 54% relaxor orthorhombic P21ma one, thus exhibiting a large normalized energy-storage density (Wrec/E = 0.015 J kV−1 cm−2) and a high efficiency (η = 87%) at 370 kV cm−1. The optimized composition also presents superior temperature stability with a variation of <±5% in the range of 20 °C–150 °C, outstanding frequency reliability with a variation of <±4% in the range of 5 Hz–500 Hz and excellent charge-discharge properties (discharge rate of 76 ns, current density of 1032 A cm−2 and power density of 129 MW cm−3 at 250 kV cm−1). The results demonstrate a successful strategy to design high performance Pb-free relaxor ferroelectrics for pulsed power capacitor applications.

Achieving giant electrostrain of above 1% in (Bi,Na)TiO3-based lead-free piezoelectrics via introducing oxygen-defect composition.

Piezoelectric ceramics have been extensively used in actuators, where the magnitude of electrostrain is key indicator for large-stroke actuation applications. Here, we propose an innovative strategy based on defect chemistry to form a defect-engineered morphotropic phase boundary and achieve a giant strain of 1.12% in lead-free Bi0.5Na0.5TiO3 (BNT)-based ceramics. The incorporation of the hypothetical perovskite BaAlO2.5 with nominal oxygen defect into BNT will form strongly polarized directional defect dipoles, leading to a strong pinning effect after aging. The large asymmetrical strain is mainly attributed to two factors: The defect dipoles along crystallographic [001] direction destroy the long-range ordering of the ferroelectric and activate a reversible phase transition while promoting polarization rotation when the dipoles are aligned along the applied electric field. Our results not only demonstrate the potential application of BNT-based materials in low-frequency, large-stroke actuators but also provide a general methodology to achieve large strain.

High-performance multifunctional piezoresistive/piezoelectric pressure sensor with thermochromic function for wearable monitoring

To meet the application of the pressure sensors in various conditions, a high-performance piezoresistive/piezoelectric (IOF) sensor with a thermochromic function has been designed and fabricated in this work, which consists of a color-changing piezoelectric film (BP) and a piezoresistive layer (FPM) laminated together. Benefiting from the reaction between the color-former and the developer in a temperature-dependent co-solvent, the thermochromic function in the IOF sensor can be achieved, showing from blue at 30 °C to white at 150 °C. Moreover, by introducing Bi0.5Na0.5TiO3 (BNT) piezoelectric material, the BP piezoelectric layer can provide 80 V output voltage, 1.398 V·kPa−1 sensitivity, and 30 ms response time, respectively. Electrical conductivity is imparted to the fabric through the introduction of MXene, and the FPM piezoresistive layer displays 0.835 kPa−1 sensitivity and 73 ms response time in a wide stress range of 0–300 kPa, respectively. When the IOF sensor is attracted to the human body and KN95 masks, it has good sensitivity to measure human behavior, breath airflow, and daily speaking signals, showing a promise to use in wearable monitoring. Summarily, the studied pressure sensor integrates the advantages of piezoresistive and piezoelectric sensors and may provide a new paradigm to develop multifunctional pressure sensors for wearable monitoring with temperature visualization.

Unraveling the discrepancy of temperature- and composition-dependent strain regulation in Bi0.5Na0.5TiO3 ceramics

For Bi0.5Na0.5TiO3 (BNT)-based materials, regulating temperature and composition could both induce giant electro-strain under the critical condition. Nevertheless, only the temperature-dependent regulation method achieved low hysteresis and maintained a high strain under high ergodic condition simultaneously. Herein, we investigated the origin of this discrepancy by means of matrix with close strain level. These two regulation methods exhibited different regulation mechanisms, especially for the microscopic structure (i.e., the discrepant lattice structure and polar entities). The A-site and BO6 octahedral-dependent vibration modes exhibited obvious discrepancies under the highly ergodic condition, while the shift was relatively small around relaxor/ferroelectric crossover. Additionally, polar entities also exhibited discrepant morphology (e.g., composition-regulated one exhibited striped domains, and temperature-regulated one possessed fuzzy signals with partial nanosized domains under the critical condition) and kinetic behaviors (e.g., under highly ergodic condition, temperature-regulated polar entities rebounded slowly at the initial unloading stage). In a word, relatively small structural discrepancies leaded to similar strain performance under the critical condition, while the increasing ergodicity accompanied by increasing structural discrepancies, which finally induced different strain performance under the high ergodic condition. This insight for designing the BNT-based materials with giant electro-strain and low hysteresis was useful to accelerate the industrialization of eco-friendly actuators.

Unveiling the high-temperature dielectric relaxation and conduction mechanisms in sol-gel derived LaFeO3 modified Sodium Bismuth Titanate ceramics

The lead-free NBT (Na0.5Bi0.5TiO3) ceramics doped with LaFeO3 having general chemical composition (1-x)Na0.5Bi0.5TiO3-(x)LaFeO3, where x = 0 and 0.05 (abbreviated as LFNBT0 and LFNBT5) were synthesized by sol-gel technique. These ceramics were characterized using X-Ray photoelectron spectroscopy to determine the elemental composition and chemical state of the samples whereas impedance spectroscopy was performed to investigate the electrical properties viz. dielectric constant, dielectric loss, impedance, modulus and conductivity over a wide temperature range (300–775 K) along with frequency (1 Hz - 1 MHz). XPS spectra at room temperature revealed the gradual reduction of valence states i.e., Fe3+ to Fe2+ and Ti4+ to Ti3+ resulting in the formation of oxygen vacancies in LFNBT system. A decrease in dielectric constant as well dielectric loss has been observed at room temperature i.e., from 898 to 541 and 0.75–0.25 respectively at 1 KHz frequency with the incorporation of LaFeO3 in the NBT. A phase transition from ferroelectric to para-electric phase is obtained at 583 K and 623 K for LFNBT0 and LFNBT5 respectively. The negative temperature coefficient of resistance (NTCR) behaviour is obtained from the analysis of impedance data. The Cole-Cole plots perceives the grain and grain boundary effect contribution of the materials with the non-Debye type of relaxation which is also confirmed by electric modulus data and aids in understanding of the transport phenomenon. The fitted conductivity data indicated that the conduction in the NBT system is governed by correlated barrier hopping (CBH). XPS analysis and activation energy values obtained from imaginary part of electrical impedance, modulus, and ac conductivity confirmed that the relaxation and conduction processes in LFNBT0 and LFNBT5 ceramics are attribute to the presence of oxygen vacancies.

Is electrostrain &amp;gt;1% in oxygen deficient Na0.5Bi0.5TiO3 a composition effect?

Abstract For over two decades Na0.5Bi0.5TiO3 (NBT) -based lead-free piezoelectrics have attracted attention due to its ability to exhibit large electric-field driven strain. Compared to the popular Pb(Zr, Ti)O3 (PZT)-based piezoelectrics, which exhibit electrostrain of about 0.3%, the derivatives of NBT-based lead-free piezoelectrics at the ergodic—non ergodic relaxor crossover exhibit larger electric-field driven strain ∼0.45%. In recent years, there has been a concerted effort to increase the maximum electrostrain in lead-free piezoceramics. Recent reports suggest that oxygen deficient NBT- based piezoceramics can exhibit electrostrain ∼1%. In this paper we explore this phenomenon and show that the ultra high electric field driven strain measured is primarily a consequence of reducing the thickness of the disc dimension below 500 microns and not an exclusive effect of the composition.

Mixed ionic–electronic conduction and defect chemistry of (Na0.5Bi0.5TiO3)1−x(BiCoO3)x (0 ≤ x ≤ 0.06) solid solutions

Incorporation of BiCoO3 induces n-type electronic conduction into NBT to make it a mixed ionic-electronic conductor with high conductivity.

Simultaneous improvement of polarization and bandgap by finite solid solution engineering.

A narrow-bandgap-induced potential field always results in decreased photovoltaic performance. Here, a finite solid solution was designed to explore the simultaneous improvement of the polarization property and bandgap obtained from the critical effect in which BiMnO3 (BM) enters the Na0.5Bi0.5TiO3 (NBT) crystal lattice, resulting in a strong lattice expansion; by contrast, the incorporation of Mn without a d-orbital weakened the orbital hybridization accompanied by Jahn-Teller (J-T) distortion to reduce the optical bandgap. A narrow bandgap of 2.90 eV and polarization of 65.9 μC cm-2 were achieved by finite solid solution engineering. The open-circuit voltage and the short-circuit current with a BM doping component of 0.04 reached as high as 1.1 V and 0.0132 mA cm-2, respectively. This work provides an optimized strategy for the mutual benefit of the polarization and bandgap by finite solid solution engineering.

Interfacial Oxygen Octahedral Coupling-Driven Robust Ferroelectricity in Epitaxial Na0.5Bi0.5TiO3 Thin Films.

The oxygen octahedral rotation (OOR) forms fundamental atomic distortions and symmetries in perovskite oxides and definitely determines their properties and functionalities. Therefore, epitaxial strain and interfacial structural coupling engineering have been developed to modulate the OOR patterns and explore novel properties, but it is difficult to distinguish the 2 mechanisms. Here, different symmetries are induced in Na0.5Bi0.5TiO3 (NBT) epitaxial films by interfacial oxygen octahedral coupling rather than epitaxial strain. The NBT film grown on the Nb:SrTiO3 substrate exhibits a paraelectric tetragonal phase, while with La0.5Sr0.5MnO3 as a buffer layer, a monoclinic phase and robust ferroelectricity are obtained, with a remanent polarization of 42 μC cm-2 and a breakdown strength of 7.89 MV cm-1, which are the highest record among NBT-based films. Moreover, the interfacial oxygen octahedral coupling effect is demonstrated to propagate to the entire thickness of the film, suggesting an intriguing long-range effect. This work provides a deep insight into understanding the structure modulation in perovskite heterostructures and an important avenue for achieving unique functionalities.

Integrating a Ferroelectric Interface with a Well-Tuned Electronic Structure in Lithium-Rich Layered Oxide Cathodes for Enhanced Lithium Storage

Li-rich layered oxides (LLOs) are considered promising candidates for new high-energy-density cathode materials for next-generation power batteries. However, their large-scale applications are largely hindered by irreversible Li/O loss, structural degradation, and interfacial side reactions during cycling. Herein, we demonstrate an integration strategy that tunes the electronic structure by La/Al codoping and constructs a ferroelectric interface on the LLOs surface through Bi0.5Na0.5TiO3 (BNT) coating. Experimental characterization reveals that the synergistic effect of the ferroelectric interface and the well-tuned electronic structure can not only promote the diffusion of Li+ and hinder the migration of On- but also suppress the lattice volume changes and reduce interfacial side reactions at high voltages up to 4.9 V vs Li+/Li. As a result, the modified material shows enhanced initial capacities and retention rates of 224.4 mAh g-1 and 78.57% after 500 cycles at 2.0-4.65 V and 231.7 mAh g-1 and 85.76% after 200 cycles at 2.0-4.9 V at 1C, respectively.

Pyro-photocatalytic Coupled Effect in Ferroelectric Bi0.5Na0.5TiO3 Nanoparticles for Enhanced Dye Degradation

Advanced oxidation processes (AOPs), achieved through the continuous attack of reactive oxygen species (ROS), are considered the most efficient way to mineralize organic pollutants. Among them, photocatalysis is the most environmentally friendly strategy for pollution mitigation but is hampered by low conversion efficiency. By exploiting the coupling effect without changing the properties of the semiconductor, the application of pyroelectric fields can significantly improve the catalytic performance. The degradation rate of rhodamine B by Bi0.5Na0.5TiO3 (BNT) nanoparticles under temperature fluctuations and visible light irradiation was up to 98%. The performance was enhanced by 216.54% and 31.48% compared to the pyroelectric catalysis and photocatalysis alone, respectively. The improved performance is due to the introduced pyroelectric potential with the imposition of temperature fluctuations, which can make the domains enhance the polarization of ferroelectrics, thus promoting the charge separation. This method can significantly advance the coupled pyro-photocatalytic reaction of ferroelectric semiconductors and also can enable the synergistic utilization of multiple energy sources such as solar and thermal energy, which is a promising strategy for environmental remediation.

Achieving high energy storage performances in high-entropy epitaxial Na0.5Bi0.5Ti0.7Hf0.1Zr0.1Sn0.1O3 thin film

Lead-free Na0.5Bi0.5TiO3 (NBT) exhibiting large polarization and a high Curie temperature can be considered as a promising candidate for dielectric capacitors. The large polarization switching hysteresis and low breakdown field, however, restrict the performance optimization. Herein, epitaxial NBT-based high-entropy Na0.5Bi0.5Ti0.7Hf0.1Zr0.1Sn0.1O3 (NBTHZS) films are designed and prepared by solution-based processing. Compared with the NBT film, the polarization switching hysteresis is depressed and the breakdown field is significantly improved for the NBTHZS film due to the high-entropy effects. Therefore, the NBTHZS film achieves a ∼16 times enhancement of energy density (from 5.1 J/cm3 of the NBT film to 81 J/cm3 of the NBTHZS film) and a high efficiency of 74.1% as well as an excellent performance reliability. The results shed light on enhancing dielectric energy storage properties of NBT-based films by forming high-entropy structures.

Enhanced energy storage performance achieved in Na0.5Bi0.5TiO3–Sr0.7Bi0.2TiO3 ceramics via domain structure and bandgap width tuning

Dielectric capacitors have attracted considerable attention owing to their excellent performance, including high charge-discharge rate as well as good temperature stability and fatigue resistance. Na0.5Bi0.5TiO3(NBT)-based ceramics are considered to be one of the most prospective lead-free dielectric materials because of their unique phase transition and relaxation characteristics. However, the energy storage performance obtained in the currently available materials is not satisfactory. We propose a synergetic optimization strategy through composition design and domain engineering in 0.74Na0.5Bi0.5TiO3-0.26Sr0.7Bi0.2TiO3 (NBSBT) ceramic, i.e., by simultaneously refining the grain size and widening the bandgap width, which facilitates a large breakdown strength and ΔP (Pm–Pr). A high dielectric constant and low remnant polarization is beneficial for obtaining improved energy storage properties. Piezoelectric force microscopy revealed that the introduction of NaNbO3(NN) disrupts the microdomains of the NBSBT ceramics and promotes the generation of polar nano-regions. An excellent energy storage density (Wrec) of 4.83 J/cm3 and a moderate efficiency (η) of 87.4% are obtained at the optimum composition of 0.85NBSBT-0.15NN. These characteristics demonstrate that (1-x)NBSBT-xNN based ceramics are promising candidate materials for high-temperature energy storage devices and provide an effective strategy for the design of next-generation dielectric capacitors.

Enhanced electrical properties of Cr2O3 addition NBT‐based high‐temperature piezoelectric ceramics

AbstractOwing to industrial and technological developments, there has been an increasing demand for piezoelectric ceramics that can function at temperatures of 500°C or higher. Na0.5Bi4.5Ti4O15 (NBT) with its high Curie temperature (TC) of 650°C is a typical bismuth layer–structured ferroelectric. However, its relatively low piezoelectric coefficient (d33 ∼ 16 pC/N) hinders its potential application at high temperatures. In this study, compositions of Ca0.05(Na0.5Bi0.5)0.95Bi4Ti4O15 with different additions of Cr2O3 (CNBT–Cr100x) were designed based on previous studies on Ca2+‐doped NBT piezoceramics, and the effects of the addition on the structural and electrical properties were investigated. The d33 value of CNBT–Cr20 was as high as 29 pC/N, almost twice higher than that of pure NBT ceramics. This increase was investigated in depth using X‐ray diffraction refinement and piezoelectric force microscopy in terms of intrinsic and extrinsic contributions. The Ps values of CNBT and CNBT–Cr20 were almost equal. The density of the domain walls of CNBT–Cr20 was significantly higher than that of CNBT, indicating that the increase of d33 of CNBT–Cr20 is mainly due to the increase in the extrinsic contribution. The CNBT–Cr20 ceramic exhibited excellent properties with a high TC of 655°C, a high d33 of 29 pC/N, and a resistivity high than 106 Ω cm at 500°C, demonstrating its potential for applications at high temperatures such as 500°C.

Enhanced energy storage performance of Bi0.5Na0.5TiO3-based ceramics via grain tuning and relaxor construction

Relaxor ferroelectrics have become competitive candidates in energy storage applications owing to their relatively high maximum polarization, high breakdown strength, and relatively low remnant polarization. Here, Bi0.5Na0.5TiO3 (BNT) with large polarization was selected as the base composition, and Sr0.7Bi0.2Ti0.8Hf0.2O3 (SBTH), as a dopant, was added into BNT to improve its relaxor behavior and decrease the grain size. A series of (1-x)Bi0.5Na0.5TiO3-xSr0.7Bi0.2Ti0.8Hf0.2O3 (abbreviated as (1-x)BNT-xSBTH, x = 0.1, 0.2, 0.3 and 0.4) ceramics were synthesized. The addition of SBTH resulted in the increase in structural disorder, as confirmed by the red-shift in Raman spectra, the enhancement of the relaxor characteristic and the fast response of the domains in local poling measurements. As a result, excellent energy storage properties (with the recoverable energy storage density of 5.5 J/cm3 and efficiency of 85.9 % at 410 kV/cm) were realized in the 0.6BNT-0.4SBTH sample. Moreover, the sample also exhibited excellent thermal stability (20 °C to 200 °C) and frequency insensitivity (0.5–500 Hz). These results suggest that BNT-based relaxor ferroelectric ceramics modulated by SBTH possess great potential in dielectric energy-storage capacitors.

Texture performance of lead-free Bi1/2Na1/2TiO3–BaZrO3 ceramics

The effect of Bi1/2Na1/2TiO3 (BNT) template on texture development of 0.94Bi1/2Na1/2TiO3-0.06BaZrO3 (BNT-BZ) ceramics was investigated. Employing plate-like BNT templates, textured BNT–BZ ceramics were developed through conventional solid-state reaction (CSSR) and reactive-templated grain growth following a tape-casting process. Structural results show that all compositions crystallized into simple perovskite phase. Introduction of BNT templates into BNT-BZ ceramics stabilized the ferroelectric state and enhance dielectric constant, field-induced strain, and piezoelectric coefficient. Enhancement in electromechanical properties of the textured ceramics were more pronounced in comparison with conventionally processed BNT-BZ ceramics and their composite counterparts. Direct comparison of the BNT-BZ ceramics developed by CSSR with their textured counterparts showed that the dielectric constant (ε) of textured samples increased 32%, piezoelectric constant (d33) 70% and field-induced strain (Smax) increased 141%. The results obtained from the structure and electromechanical properties confirm that texture engineering play an important role in improving the piezoelectric properties of ceramics.

Copper nanoparticles-modified Na0.5Bi4.5Ti4O15 micron-sheets as a highly efficient and low cost piezo-photocatalyst

The coupling of piezoelectric effect and metal surface modification is an effective way to improve photocatalytic performance. Herein, we prepared a new piezoelectric heterojunction catalyst by depositing Cu nanoparticles on the surface of lead-free Na0.5Bi4.5Ti4O15 (NBT) piezoelectric micron-sheets. Under the simultaneous excitation of light and stirring, NBT@6.4 wt%Cu photocatalyst exhibits excellent piezo-photocatalytic activity, in which the degradation rate of methyl orange (MO) solution can reach 96% within 120 min, and the rate constant kobs value is as high as 24.67 × 10−3 min−1, which is ∼ 13 times larger than that of pure NBT photocatalyst under the excitation of light. The improved piezo-photocatalytic performance is attributed to that the deposition of Cu nanoparticles and the high piezoelectric properties of NBT facilitates the transfer and separation of photogenerated carriers. This work provides a new option for designing high-performance piezo-photocatalysts for pollutant treatment.

Phase transition and energy storage properties of Bi0.5Na0.5TiO3–Bi(Mg2/3Nb1/3)O3 lead-free ceramics

Bi0.5Na0.5TiO3 (BNT) lead-free ceramics have been extensively studied due to their excellent dielectric, piezoelectric and ferroelectric properties. The phase structure and functionalities of BNT can be feasibly adjusted by doping/forming solid solutions with other elements/components. In this work, Bi(Mg2/3Nb1/3)O3 (BMN) was introduced into BNT by a conventional solid-state reaction to form a homogeneous solid solution of (1-x)(Bi0.5Na0.5)TiO3-xBi(Mg2/3Nb1/3)O3 (BNT-xBMN) with a perovskite structure. With the increase of BMN content, a phase transition from rhombohedral R3c to tetragonal P4bm has been confirmed by XRD, along with shifting the ferroelectric-paraelectric phase transition temperature to lower temperatures with broadening dielectric peaks. Furthermore, an optimized recoverable energy density of 1.405 J/cm3 was achieved for BNT-0.10BMN ceramics under a low applied electric field of 140 kV/cm, which is mainly attributed to the transformation from ferroelectric to ergodic relaxor phase.

Effective Complex Permittivity of Random Composite Media: PVDF/(Na&lt;sub&gt;1/2&lt;/sub&gt;Bi&lt;sub&gt;1/2&lt;/sub&gt;)TiO&lt;sub&gt;3&lt;/sub&gt;

The present study discusses the fabrication of non-lead ceramic/polymer composites employing (Na1/2Bi1/2)TiO3 (NBT) ceramic powder as a filler and poly(vinylidene fluoride); PVDF as a polymer matrix. The NBT (volume fraction, ϕ = 1) ceramics were synthesized using the conventional mixed-oxide method followed by the high-energy ball milling method whereas (1-ϕ)PVDF/ϕ(Na1/2Bi1/2)TiO3; 0 ≤ ϕ ≤ 0.3 composites were prepared from a melt-mixing process. It was observed that the real and imaginary parts of dielectric permittivity, ac conductivity, and longitudinal piezoelectric charge coefficient increase with the increase in NBT-content. Different dielectric mixing models were presented to determine the effective complex permittivity of the composites. Five dielectric mixture equations have been chosen to test the acceptability of experimental data. It was revealed that theoretical models as given by Bruggman, Rother-Lichtenecker, and modified Rother-Lichtenecker show good agreement with the experimental results of filler-concentration dependent alteration of effective relative permittivity and loss factor of the PVDF/NBT composite. A mathematical model of first-order exponential growth has also been proposed, which fitted excellently the experimental data (r2 &gt; 0.998).