Lead-free Sodium Bismuth Titanate Research Articles

Influence of NaOH Concentration on Structural, Morphological, Optical, and Electrical Characterization of Perovskite Sodium Bismuth Titanate Prepared by Hydrothermal Method

The hydrothermal method successfully prepares a lead-free sodium bismuth titanate (NBT) perovskite film. The prepared films were studied structurally, and morphologically using X-ray diffraction, and field-emission scanning electron microscopy (FESEM), respectively. Varying the concentration of NaOH showed a noticeable effect on the properties studied. Good crystallization of NBT perovskite films without impurities was obtained at 18 and 20 M concentrations, where the crystalline size was 14 nm according to the Scherer equation. Also, when varying the concentration of NaOH, a similar film thickness was obtained through a cross-section of the FESEM images. It was observed that there was a difference in the intensity of the peaks of the photoluminescence spectra of the prepared films with a change in the concentration of NaOH, which confirms a change in the concentration of oxygen vacancies. The activation energy of the prepared films was deduced from the Arrhenius plot, as it showed small values in the films prepared with a low concentration of NaOH. The results showed that the maximum value of mobility of NBT films was at 20 M of NaOH concentration through the Hall Effect.

Dynamic piezoelectric response facilitating lead-free ceramic to efficiently electrosynthesize hydrogen peroxide via oxygen reduction

Optimizing the interface property of the catalyst-electrolyte by the physical field modulation could improve the electrocatalytic performance, yet the associated investigations on the two-electron oxygen reduction reaction (2e− ORR) are still scarce. Herein, we develop a facile, green, and economic piezoelectricity-indued local electric field strategy based on the piezo-response of the polarized lead-free bismuth sodium titanate (P-BNT) ceramic under the dynamic operational conditions of ORR. The as-emerged electric field at the immediate vicinity of the ceramic catalyst surface greatly optimizes its adjacent OH- coverage from the alkaline electrolyte and lowers the local concentration of the HO2− product. Therefore, the adsorption ability of oxygen-containing intermediates during the ORR process is ameliorated, and the peroxide product disproportionation is simultaneously inhibited. Compared with the unpolarized ceramic catalyst, P-BNT prepared at a kilogram scale displayed excellent 2e- ORR selectivity over 90% in a wide potential window of 0.45 V in 0.1 M KOH with a summit of ∼100%, outmatching most state-of-the-art alkaline 2e− ORR catalysts. The current work could realize the improved electrosynthesis efficiency of hydrogen peroxide with practical application potentials, especially considering the environmentally-friendly, extensively-studied, and technically-mature lead-free piezoelectric BNT ceramic that can be facilely prepared in a low cost and large scale.

Optimizing strain response in lead-free (Bi0.5Na0.5)TiO3-BaTiO3-NaNbO3 solid solutions via ferroelectric / (non-)ergodic relaxor phase boundary engineering

Lead-free bismuth sodium titanate (Bi0.5Na0.5)TiO3 (BNT) and related solid solutions are potential piezoelectric materials for such applications as actuators and transducers if their excellent strain responses and piezoelectric properties can be optimized. In this work, a large strain response of 0.61% is achieved in lead-free (0.94-x%)(Bi0.5Na0.5)TiO3-0.06BaTiO3-x%NaNbO3 (x = 0 –6, BNT-6BT-xNN) ceramics with the composition of x = 3.5 in a pseudo-cubic structure. Coexistence of ferroelectric (FE) and relaxor (RE) domain structures is observed in all the unpoled ceramics and the enhanced strain response is believed to be related to the evolution of the ergodic relaxor (ER) and non-ergodic (NR) states thanks to the substitution of antiferroelectric NN. BNT-6BT-3.5NN is a critical composition near the FE/NR/ER phase boundary close to room temperature (RT) and its high strain response arises from a synergistic combination of a reversible electric-field-induced phase transition and an active domain switching in the mixed NR/ER state. This work provides new insights into the dynamic interplay between mesoscopic domains and macroscopic electrical properties in the BNT-based piezoceramics.

Non-ergodic – ergodic transition and corresponding electrocaloric effect in lead-free bismuth sodium titanate-based relaxor ferroelectrics

The ferroelectric refrigeration technology based on electrocaloric effect (ECE) is a promising environmental way to replace the gas compression refrigeration. Lead-free bismuth sodium titanate (NBT)-based relaxor ferroelectric ceramics have advantages of a large ECE within a wide temperature range around the depolarization temperature (Td), but the Td of pure NBT is too high to meet the application requirements. Here, we systematically studied the electrocaloric effect in (0.95-x)(Na0.5Bi0.5)TiO3-0.05SrTiO3-x(K0.5Na0.5)NbO3 ((0.95-x)NBT-0.05ST-xKNN) ceramics and its relation with the relaxor behavior. The addition of KNN enhances the relaxor character, and shifts the Td from 120 °C to a low temperature even below 0 °C. The directly measured ECE shows a peak of high ∆Tmax = 0.88 K (@ 60 °C) for x = 0.05 under an electric field of 40 kV/cm and a wide temperature span of 79 °C (≥ 80% of ∆Tmax). The x = 0.07 sample exhibits the optimal room-temperature ECE performance with a high ∆T30 °C = 0.71 K because the non-ergodic – ergodic phase transition occurs near room temperature. The electric field–temperature phase diagram reveals the origin of the enhanced ECE as the electric-field-induced transition between polar nanoregions (PNRs) and long-range ferroelectric domain.

Effect of Fe substitution on the structural, microstructural and dielectric properties of sodium bismuth titanate

Lead free sodium bismuth titanate (NBT) is widely being studied as an emerging room temperature multiferroic and as a ferroelectric material with potential to replace toxic lead based ceramics. Various elements can be substituted in the A-site or B-site to improve its electrical and magnetic properties. In this work, pure and Fe substituted NBT having the chemical formula Na0.5Bi0.5Ti(1-x)FexO3 (x = 0.00, 0.02) were synthesized using sol gel auto ignition method to study the effect of Fe substitution on the properties of NBT. XRD analysis confirmed the rhombohedral symmetry of the synthesized samples and the crystallite size of the samples were calculated using Scherrer’s formula. The morphological property of the samples was studied from the SEM images. UV–Visible Spectroscopy method was employed to study the optical properties of the samples. The dielectric properties of the samples were measured as a function of frequency in the range 100 Hz to 1 MHz at room temperature and also as a function of temperature in the range of 298 K- 473 K using an Agilent HP4284 LCR meter. Usual dispersive behavior of dielectric constant was observed for both the samples at the studied temperature range. Study of frequency and temperature dependence of the AC conductivity suggested that the conduction process in the materials is thermally activated. Jonchers’ universal power law was used to fit the AC conductivity curves to describe the dynamics of charge carrier with suitable conduction mechanism.

Ferroelectricity and Piezoelectricity of Na0.5Bi0.5TiO3 Nanotube Arrays: Implications for Functional Electronic Devices

Piezoelectric and ferroelectric properties of lead-free sodium bismuth titanate Na0.5Bi0.5TiO3 (NBT) nanotube arrays were studied using piezoresponse force microscopy. The nanotube arrays prepared by sol filling in the porous anodic aluminum oxide template with an exposure height of 30–55 nm and vertical arrangement demonstrated enhanced piezoelectric properties compared with the other nanotube structures and a large piezoelectric coefficient with regular domain states. We further prepared a metal/NBT nanotube arrays/metal capacitor for the study of ferroelectric and piezoelectric properties. The piezoelectric properties of NBT nanotube arrays were found to be much improved in a capacitor and finite element modeling attributes such improvement to the uniform electric potential distribution from the tip of the nanotube in the capacitor. The improved piezoelectric properties could make NBT nanotube arrays as a promising candidate for piezoelectric nanostructure devices.

Processing and properties of translucent bismuth sodium titanate ceramics

Lead-free bismuth sodium titanate piezoceramics were processed by a solid-state route with a novel precursor approach. By carefully controlling the processing parameters and sintering atmospheres, translucent ceramics with pore-free, homogeneous microstructures with exceptionally low dielectric loss at elevated temperatures. The pore-free microstructure can influence the operating life of a dielectric device positively, since pores and other microstructural defects are usually responsible for material failures within devices. Synchrotron and surface X-ray diffraction experiments revealed a clear dependence of the crystal structure on sintering parameters and defect chemistry. Microstructural analysis showed a dependency of a secondary phase on the sintering atmosphere. The grain size could be adjusted using a shortened grinding process instead of using the common methods like increasing calcining or sintering temperature.

Effects of rare-earth dopants on phase structure and electrical properties of lead-free bismuth sodium titanate-based ceramics

In this work, the effects of rare earth (RE) dopants on the phase structure, microstructure, and electrical properties of lead-free bismuth sodium titanate (BNT)-based ceramics were studied. Rare earth elements (i.e., Sm, Gd, Ho, Pr, Y, and Yb) were selected as the dopants to replace the Bi site of Bi0.5(Na0.8K0.2)0.5TiO3 ceramics. It was found that the addition of moderate RE ions reduced the temperature of ferroelectric-relaxor transition (Tf-r) and the dielectric maximum at lower temperature, while the slight influence on the dielectric maximum at higher temperature and microstructure were observed. Hereby, the three-stage evolution of phase structure after introducing RE ions was confirmed. A high piezoelectric coefficient d33 of ∼190 pC/N was achieved due to the improved dielectric constant in the state with stable electric field-induced ferroelectric phase. The high strain property and converse piezoelectric coefficient d33∗ of ∼340 pm/V were obtained in the state with the coexistence of nonergodic and ergodic relaxor phases when Tf-r approached room temperature. The degenerated overall electromechanical properties exhibited in the state with complete ergodic relaxor phase. This study affords a significant guidance for optimizing the piezoelectricity of BNT-based ceramics utilizing rare earth dopants.

Enhanced energy density in poly(vinylidene fluoride) nanocomposites with dopamine-modified BNT nanoparticles

Dielectric nanocomposites have attracted extensive attention since the potential application in the field of energy storage. Nevertheless, it is still a challenge to fabricate dielectric nanocomposites with high discharged energy density. Herein, lead-free bismuth sodium titanate (BNT) particles are used as filler in nanocomposite due to their outstanding dielectric properties. In this paper, BNT nanoparticles decorated by dopamine were employed to fabricate BNT@Dopa/poly(vinylidene fluoride) (PVDF) nanocomposites. Dielectric properties and energy storage performance of nanocomposites with BNT nanoparticles enhanced significantly. The maximum dielectric constant (er) of nanocomposites with BNT@Dopa nanoparticles was 14.15 at the frequency of 1 kHz. The discharged energy density (Udis) of nanocomposites with 3 vol% BNT@Dopa nanoparticles reached 13.09 J/cm3 at 430 kV/mm. The energy efficiency (η) of nanocomposites at 40 °C remained 53.62% at the electric field of 350 kV/mm. The nanocomposite with BNT@Dopa nanoparticles performed excellent fatigue endurance after 106 cycles. These results offer a practicable way to fabricate nanocomposites with high energy density.

Investigation of the mechanism of domain switching in different Na0.5Bi0.5TiO3 microstructures

Abstract Several researches have studied the physical properties of hydrothermally-synthesized low dimensional piezoelectric nanostructures. However, the obtained piezoelectric coefficient is not high and the relationship between physical properties and microstructures is still neglected. Here we report the piezoelectric and ferroelectric properties of different lead-free sodium bismuth titanate (Na0.5Bi0.5TiO3, NBT) microstructures synthesised with hydrothermal routes and give visualization of domain structures using piezoresponse force microscopy. The NBT nanowire exhibits better local piezoelectric response compared with NBT spherical aggregates and microcubes and other one-dimensional materials prepared by hydrothermal method and the large piezoelectric coefficient of nanowire was explained by observed regular stripe domain structures. Moreover, it is found that there are different domain configurations at the top and side of the nanowire under the external electrical fields, which don't change the regular stripe domain structure but lead to the movement of domain boundaries. By finite element modeling, it attributes to the different electric potential distributions from tip within the nanowire.

Ferroelectric, pyroelectric and piezoelectric properties of CeO2-doped Na0.5Bi0.5TiO3 ceramics

Lead-free sodium–bismuth titanate (Na0.5Bi0.5TiO3, NBT) nanoceramics synthesized by sol–gel method were doped with CeO2 by using solid-state method from 0.0 to 5.0 wt%. The effects of CeO2-doped NBT on structure and microstructure as well as electrical properties were investigated. X-ray analysis shows that CeO2 diffuses into the lattice of NBT to form a solid solution and form morphotropic phase boundary between rhombohedral and tetragonal phase structure in NBT during the sintering process. The electrical properties of NBT ceramics have been greatly improved by doping certain amount of CeO2. The NBT-0.6 wt% CeO2 shows improvement in dielectric properties at room temperature with the highest dielectric constant at 10 kHz (em′ = 1276, tan δ = 0.03 and Tm = 370 °C), high remanent polarization (Pr = 56 μC cm−2) and low coercive field (Ec = 53 kV cm−1). Piezoelectric properties were enhanced with the doping, where the piezoelectric constant d33 = 90 pC N−1 and enhance in mechanical coupling factor k33 = 0.44. The results suggest that the NBT-0.6 CeO2 ceramics can be a suitable material for sensor, actuator or memory device application.

Self-Polarization in Epitaxial Fully Matched Lead-Free Bismuth Sodium Titanate Based Ferroelectric Thin Films.

The Bi0.5Na0.5TiO3-based ferroelectric is one of the most promising candidates for environment-friendly lead-free ferroelectric/piezoelectric materials for various applications such as actuators and micro-electromechanical systems. The understanding and tailoring of the ferro-(piezo-)electric properties of thin films, however, are strongly hindered by the formation of the defects such as dislocations, ion vacancies in the film, as well as by the complexity of the interface between the film and the substrate. An ideal system for the study of the polarization behavior in the ferro-(piezo-)electric film would be a fully matched system. In this work, monocrystalline 0.89Bi0.5Na0.5TiO3-0.11BaTiO3 thin films were epitaxially grown on (001)-oriented Nb-doped SrTiO3 substrates using a sol-gel technique. The films were almost fully lattice- and thermally matched with the substrate, thus avoiding the impact of dislocations and thermal stress. The films were self-poled by a built-in electric field, originating from the sedimentation of heavier atoms during the film preparation. As a consequence, an upward self-polarization was introduced into the films, giving rise to asymmetric phase hysteresis loops and domain switching current responses. These results highlight the importance of the interface complexity for the self-polarization of piezoelectric thin films, even for fully matched films, which will therefore facilitate the control of properties of piezoelectric films and their applications for various functional devices.

Structural, optical, and Raman studies of Gd doped sodium bismuth titanate

The effects of gadolinium (Gd) on lead free sodium bismuth titanate (Na0.5Bi0.5TiO3, NBT) ceramics are investigated. X-ray diffraction (XRD) studies indicate that perovskite phase (rhombohedral, R3c) is formed for all Gd doped NBT (Gdx:NBT) compositions (x = 0, 0.02, 0.04, 0.06, 0.08). XRD peak shifts to the higher angles for all compositions except for x = 0.08. Amphoteric nature of Gd in NBT sites are observed i.e., it occupies Bi-site up to x = 0.06 and then distributes to Ti-site. Octahedral distortion (c/a) increases in the range 0.02 ≤ x ≤ 0.06 and then decreases. Raman spectra suggest that the introduction of Gd+3 ion induces structural changes without disturbing the long range order. The material can be readily excited using UV (360 nm) and shows emission peaks at ~592 nm and 687 nm. Optical property evaluation indicates that the lowest band gap (Eg = 2.78 eV) is observed at x = 0.08. When x > 0.04, the photoluminescence (PL) intensity decreases indicating the onset of concentration quenching. The critical energy distance (found to be 14 Å) and Dexter's theory based analysis indicate that concentration quenching is attributable to multipole-multipole (specifically dipole-dipole) interactions in the system. Commission International de Eclairage (CIE) chromatic color coordinates are reported for all doped systems; the observed patterns mirror PL analysis results. For instance, PL intensity shrinks beyond 4 at%; this corresponds to a regression in the CIE trajectory with respect to concentration.

Structural properties and Doping effects of ferroelectric ceramics (Na0.2Bi0.3Zr0.5) TiO2

Lead free Sodium Bismuth Titanate Zirconate (Na0.2Bi0.3Zr0.5) TiO2 or NBZT Solid solution were prepared by Mixed Oxide Conventional route. Moreover, their Phase Structure and luminescence properties were investigated for storage device applications. Primarily XRD analysis indicated that mixed phase structure at the higher annealing temperature. X ray powder Diffraction Data were used for a quantitative Structural investigation. SEM results for spherical and cuboid particles were observed. Based on results we can say that average grain diameter for NBZT is around 100-200 nm. Ferroelectrics perovskites has optical properties, which is shown in photo luminescence emission and absorption Spectra. Photoluminescence arises when excited by photon so in this present work excitation band at 390 nm (3.2 eV).we say that hard and soft Ferro electric ceramics. Peaks are observed between 2.76 eV to 4.10 eV from the emission spectra. Absorption spectra are used for excitation wavelength.

Recoverable Self-Polarization in Lead-Free Bismuth Sodium Titanate Piezoelectric Thin Films.

Bismuth sodium titanate, Bi0.5Na0.5TiO3 (BNT), is a promising lead-free ferroelectric material. However, its potential applications have not been fully explored, mainly because of the complex domain structure arising from its intricate phase transitions. A deep and thorough study of its domain structure and polarization switching behavior will greatly help with understanding the polarization nature and with promoting future applications. In this work, we demonstrate that BNT polycrystalline films possess a highly ordered out-of-plane polarization (self-polarization) and randomly oriented in-plane polarizations. Interestingly, the inherent nature of polarization in the BNT films does not allow for the nonvolatile domain writing, as the switched polarization spontaneously and rapidly reverses to the initial orientation state once the external poling electric field is removed, making the self-polarization recoverable. Such a stable self-polarization vanishes gradually with temperature increasing over 150 °C but starts to recover to its initial state upon cooling down to 250 °C, and entirely recovers once the temperature is reduced to below 200 °C. Such interesting properties of BNT films are attributed to the combined effects of the free charges at the Pt electrode, (detected) cation vacancies at the oxide/Pt interface and the defects in oxide lattices. Our results make a step closer to fully understand the nature of polarization and related piezoelectricity in BNT. Such films with recoverable self-polarization are of great interest for applications as sensors, actuators, and transducers that can operate particularly under high temperatures and high electric field conditions.

Controllable synthesis and growth mechanism of lead free bismuth sodium titanate nanowires

Abstract Highly uniform lead-free piezoelectric bismuth sodium titanate (Bi 0.5 Na 0.5 TiO 3 , BNT) nanowires were successfully synthesized via a hydrothermal method. Synthesized at a stirring speed range of 300–1000 rpm, the compositions and orientations of BNT nanowires were well controlled. The effects of stirring speeds on the formation of BNT nanoparticles and nanowires in the hydrothermal processes were systematically investigated. The BNT nanowires with a high aspect ratio were proven to be single crystals with [110] growth direction from high-resolution TEM analysis. The mechanism of growth of BNT nanowires out of nanoparticles in the hydrothermal processes was proposed.

The preparation of lead-free bismuth sodium titanate ceramics via the solid state combustion technique

ABSTRACTLow calcined temperature, high density and good dielectric properties of BNT ceramics successfully prepared by the solid state combustion technique and glycine was used as fuel to reduce the reaction temperature. The effects of calcination temperature (500–900°C) and sintering temperature (1100–1150°C) on phase formation, microstructure and dielectric properties of (Bi0.5Na0.5)TiO3 (BNT) ceramics were investigated. The phase purity, crystal structure and microstructure of the samples were tested using X-ray diffraction (XRD) and scanning electron microscopy (SEM). It was found that the pure rhombohedral perovskite structure of BNT powders were observed from the sample calcined at 650°C, which is lower than the solid state reaction technique by ∼200°C. The purity phase was detected in all ceramic samples. The microstructure of the BNT powders exhibited an almost-spherical morphology and a highly agglomerated form. The average grain size of the ceramics was increased with increase sintering temperature. The TF-R and Tm were slightly increased with the increase of sintering temperature. The highest density and the best dielectric properties was obtained by sample sintered at temperature of 1120°C. The solid state combustion technique is a new alternative for reduction of calcined temperature, improvement of densification and modify of dielectric properties to prepared BNT ceramics.

Role of strain and lattice distortion on ferroelectric and piezoelectric properties of bismuth magnesium zirconate substituted sodium bismuth titanate ceramics

Effect of weak ferroelectric perovskite, bismuth magnesium zirconate [Bi(Mg0.5Zr0.5)O3] substitution in lead-free sodium bismuth titanate [(Na0.5Bi0.5)TiO3] ceramics is studied. Influence of substitution on intrinsic and extrinsic contribution and impact on ferroelectric and piezoelectric properties are investigated. Improved spontaneous polarization (Ps), increased remnant polarization (Pr), decreased coercive field (Ec) and high piezoelectric coefficient (d33) are obtained for x = 0.01 mole fraction of Bi(Mg0.5Zr0.5)O3 substitution due to decrease in rhombohedral lattice distortion and homogeneous strain. Small rhombohedral lattice distortion (δr) and minimum homogeneous strain (δ) are the primary intrinsic parameters which favours the extrinsic parameters such as mobility of non-180° domain reorientation, domain switching and domain wall motion. Enhanced mobility softens the coercive field and increases remnant polarization to maximum. Reduced rhombohedral lattice distortion, low strain and enhanced mobility are the key factors for enhanced piezoelectric constant, highest remnant polarization and decreased coercive field in non-MPB (1 − x)(Na0.5Bi0.5)TiO3–xBi(Mg0.5Zr0.5)O3 solid solutions.

Substitutional effect of bismuth ferrite on the electrical properties of sodium bismuth titanate ceramics

Lead free sodium bismuth titanate ceramics was substituted with bismuth ferrite in low mole fraction and the influence of substitution on the dielectric constant, Curie temperature, depolarization temperature, remnant polarization, coercive field and piezoelectric coefficient were studied. Rhombohedral R3c symmetry is maintained for all mole fractions. Dielectric constant decreases and small deviation arises in Curie temperature on bismuth ferrite substitution. No significant change in depolarization temperature (Td) is observed on bismuth ferrite substitution. Spontaneous and remnant polarization increases and piezoelectric coefficient is enhanced up to x = 0.01 mol fraction and then decreases. Also coercive field decreases up to x = 0.01 mol fraction and then increases. Reduced remnant polarization, dielectric constant and increased coercive field are due to hardening effect induced by the acceptor Fe3+ cation in the B-site of sodium bismuth titanate. Formation of Ti4+ cation and oxygen vacancies restricts domain wall motion and suppresses domain reorientation which decreases the extrinsic contribution to piezoelectric coefficient and hence d33 decreases.

Electrocaloric effect and luminescence properties of lanthanide doped (Na1/2Bi1/2)TiO3 lead free materials

Polycrystalline lead-free Sodium Bismuth Titanate (NBT) ferroelectric ceramics doped with rare earth (RE) element are prepared using solid state reaction method. Optical, ferroelectric, and electrocaloric properties were investigated. The introduction of RE3+ ions in the NBT host lattice shows different light emissions over the wavelength range from visible to near infrared region. The ferroelectric P-E hysteresis loops exhibit an antiferroelectric-like character near room temperature indicating possible existence of a morphotropic phase boundary. The enhanced electrocaloric response was observed in a broad temperature range due to nearly merged phase transitions. Coexistence of optical and electrocaloric properties is very promising for photonics or optoelectronic device applications.