Sodium Bismuth Titanate Ceramics Research Articles

Achieving Ultrahigh Electrocaloric Response in (Bi0.5Na0.5)TiO3-Based Ceramics through B-Site Defect Engineering.

Lead-free electrocaloric (EC) ferroelectrics are considered ideal for the next generation of environmentally friendly solid-state refrigeration materials. However, their inferior performance compared to lead-based materials significantly restricts their potential application. According to phase-field simulations, it is predicted that the pinning effect of a moderate number of defects can effectively enhance the reversible polarization response associated with the entropy change. Herein, sodium-bismuth titanate (BNT) ceramics with high spontaneous polarization are selected to construct B-site defects by introducing Li+ and Nb5+. Under an electric field of 6 kV mm-1, ultrahigh EC temperature changes of ΔTpos = 1.77 and ΔTneg = 1.49 K are achieved at 65 °C by direct measurement (ΔTneg > 1 K over 55-120 °C). Furthermore, ΔTneg remains above 0.70 K in the temperature range from 25 to 130 °C, exhibiting immense potential for practical applications. This study offers a promising direction for optimizing the EC response in defect systems.

Non-invasive thermal sensing and improved recoverable energy storage density of Bi0.5Na0.5TiO3: Er3+ doped multifunctional ferroelectric ceramic

In this work, Er3+ substituted bismuth sodium titanate ceramics with the chemical composition Bi0.5-xErxNa0.5TiO3 (x = 0.00, 0.01, 0.02, 0.03, 0.04, and 0.05) were synthesized using conventional solid state technique. The influence of Er3+ ions on structural, optical, ferroelectric, and temperature sensing properties have been investigated. The prepared ceramic powders were initially heated at a calcination temperature 850 °C to form single phase Bi0.5-xErxNa0.5TiO3 and finally sintered at temperature 1050 °C. Formation of pure phase compositions with rhombohedral crystal structure is confirmed through X-ray diffraction studies. The typical FTIR bands near 540, 860, 910 cm−1 confirmed the presence of Ti–O stretching of octahedral groups in the perovskite structure. The decent squared shaped saturated P-E hysteresis are obtained under an electric field of 60 ≤ E ≤ 70 kV/cm, and the loops become slimmer at higher Er3+ concentrations (x = 0.04). The efficiency of energy storage density increases with Er3+ doping and an improved recoverable energy storage (Wr = 2.73 J/cm3) and a higher efficiency (η = 70.77%) are obtained for Er content, x = 0.04. The photoluminescence spectra were recorded at two excitation wavelengths (488 nm and 980 nm). Two distinct green emission bands (529 nm and 550 nm) and one weak red emission band (670 nm) were observed at both excitation wavelengths. Increasing Er3+ content beyond (x > 0.03) leads to significant quenching of light emission due to cross relaxation process and non-radiative relaxations. The pump power dependency revealed that two photons were involved in the light upconversion process. The time-resolved fluorescence spectroscopy confirmed the decrease in lifetime with increasing Er3+ concentration. The absolute and relative sensitivity of the prepared ceramic at Er3+ concentration (x = 0.03) were found to be 0.47% K−1 at 523 K and 1.1% K−1 at 303 K, respectively. These optical and electrical properties open the possibility of realizing multifunctionality in the field of energy storage and opto-electronic applications.

Effect of sintering time on electrical, ferroelectric, and piezoelectric performances of microwave synthesized sodium bismuth titanate ceramics

Herein, we report the synthesis of sodium bismuth titanate (Na0.5Bi0.5TiO3/NBT), a lead-free ceramic prepared via a cost and time-effective microwave synthesis route. This work presents the investigation of microstructural, electrical, and optical characteristics of NBT ceramics. The formation of a single-phase NBT sample sintered for 30 and 40 min (denoted as NBT 30 and NBT 40) is confirmed by Rietveld refinement and Raman measurement. FTIR spectroscopy is used to characterize the single-phase nature and to confirm the presence of desired vibrational spectra in the perovskite structure. Tightly packed micron-sized grains are observed from the field emission scanning electron microscopy. Due to the A-site disorder present in the lattice, two diffuse types of dielectric anomalies are present in the temperature-dependent dielectric plot for both samples. The maximum dielectric constant values of 1475 and 1628 are found for NBT 30 and NBT 40 samples at the transition temperature. From temperature-dependent AC conductivity measurement, NBT 40 samples show a higher value of conductivity in comparison to NBT 30. The PE hysteresis loops confirm the ferroelectric character present in both samples. An improved piezoelectric coefficient is observed with increasing sintering time and is found to be 80 pCN−1 for NBT 40. The optical bandgap of materials is 3.03 and 3.1 eV for NBT 30 and NBT 40, respectively.

Structural and Electrocaloric Investigation of the Lead and Strontium Modified Bismuth Sodium Titanate Ceramics

The Structural and Electrocaloric characteristics of Pb and Sr Modified Bismuth Sodium Titanate, i.e. Bi0.25Na0.35Sr0.3Pb0.1TiO3 (BNSPT) is reported. BNSPT Ceramics was synthesised by the traditional solid-state mixed oxide method. Stoichiometry-weighted constituent oxide and carbonates are mixed for 2 h in an acetone media and then calcined at 800 °C for 6 h. X-ray diffraction confirms the formation of a single-phase crystal structure. Further, lattice parameters were calculated using the Reitveld refined data and crystallite size was calculated by Debye-Scherrer’s equation. The dried powder was compacted in to pellets and sintered at 1250 °C for 2 h. The temperature dependence of maximum polarization was obtained from the P-E loop at a different temperature range from room temperature to 200 °C. The Electrocaloric properties of the BNSPT were measured by 500 V/cm using the Standard Thermodynamics Maxwell relation.

Achieving high energy storage density under low electric field in modified bismuth sodium titanate ceramics

Achieving high energy storage density under low electric field in modified bismuth sodium titanate ceramics

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.

Effect of Gd3+ doping on structural, vibrational, dielectric, and ferroelectric properties of Bi0.5Na0.5TiO3 ceramic

The effect of adding Gadolinium on bismuth sodium titanate ceramics on structure and electrical characteristics with the chemical formula (Bi 1-x Gd x ) 0.5 Na 0.5 TiO 3 (x = 0.00, 0.02, 0.04, 0.06,0.08 and 0.10) (BGNT) were examined using a solid-state reaction approach. The pure perovskite rhombohedral phase is visible without any secondary phase for all of the compositions in the X-ray diffraction pattern. A comprehensive investigation of Raman spectra revealed the vibrational and phonon modes of the molecular structure. The dielectric investigation of sintered samples in temperature and frequency dependence revealed two dielectric peaks attributable to factors generated by phase transitions from ferroelectric to antiferroelectric and antiferroelectric to paraelectric. With a low remanent polarization ( Pr = 0.65 µC/cm 2 ) and a coercive field ( Ec = 8.62 kV/cm), the polarisation hysteresis (P–E) loop demonstrated optimal electrical performances.

Characterization of modified lead-free ferroelectric sodium-bismuth titanate ceramics

Influence of dopants on structure, microstructure, dielectric and ferroelectric properties of ferroelectric-relaxor (Na0.5Bi0.5)TiO3 ceramics modified by Ba2+ cations and overstoichiometric additives (SiO2 and Na2O) was studied. Changes in structure, microstructure, and dielectric parameters were observed depending on solid solutions compositions.

Enhanced electrical and photocatalytic activities in Na0.5Bi0.5TiO3 through structural modulation by using anatase and rutile phases of TiO2

This paper deals with an in-depth analysis on the role of the microstructure phase of titanium dioxide (TiO2) precursor in sodium bismuth titanate (Na0.5Bi0.5TiO3, hereafter represented as NBT) ceramics prepared through the hydrothermal method. The comparison of the grain size, microstructure, crystal structure, and electrical properties of the NBT ceramics is carried out using anatase and rutile TiO2. NBT ceramics with anatase TiO2 (denoted by NBTA) displayed superior dielectric and ferro/piezoelectric properties along with the additional functionality in terms of photocatalysis. Systematic studies of functional properties such as piezoelectric, ferroelectric, and dielectric stressed the far-reaching influence of effects on grain size. The mechanisms and functional properties of grain quantitative effects are also discussed. Grain boundaries volume fraction increment has decreased the dielectric peak but increased the diffusiveness in the case of the NBT with rutile TiO2 precursor (denoted as NBTR). Similarly, elastic stiffness increment restricts the movement of the domain wall and led to a decrement in remnant polarization along with an increase in the values of the corresponding piezoelectric coefficient in fine-grain NBTR samples.

Structural, ferroelectric, pyroelectric, and dielectric study of Bi0.5Na0.5TiO3 ceramics synthesized with precursors obtained by the sol–gel method and doped with lanthanum

This study examines the ferroelectric, pyroelectric, and dielectric properties of La-doped bismuth sodium titanate ceramics Bi0.5Na0.51−xLaxTiO3 (BNLT), using amounts of 0–6.7 at. % La. The precursor powders used to make dense BNLT ceramics were obtained via the sol–gel method using the acetic acid route. All samples were calcined at 700 °C for 1 h and sintered at 1150 °C for 30 min in an encapsulated crucible to avoid Na and Bi volatilization yielding relative densities equal to or higher than 94%. The obtained x-ray diffraction patterns, typical of the perovskite structure, confirm the incorporation of lanthanum into the lattice, which evolved from a rhombohedral phase to a mixture of rhombohedral and cubic structures at higher concentrations. The thermogravimetry and differential scanning calorimetry results indicate that the crystallization of precursor powders of BNT takes place between 500 and 700 °C. In addition, the scanning electron microscopy micrographs reveal a decrease in grain size from 4.5 to 0.5 µm with increasing La content. The ferroelectric hysteresis curves show that the best ferroelectric properties were obtained for BNT 1.3% La, where the obtained values of remnant polarization and coercive field were Pr = 29 µC/cm2 and Ec = 39 kV/cm, respectively. At this concentration, the pyroelectric response shows a higher value, four times higher than the pyroelectric signal of pure BNT.

Investigation of Ga doping for non-stoichiometric sodium bismuth titanate ceramics

The electrical properties of Ga3+ doping Na0.5Bi0.5TiO3-based oxygen ionic conductors were studied. The Na0.52Bi0.47Ti1−xGaxO3−δ (x = 0, 0.01, 0.015, 0.02) samples were fabricated by the means of traditional solid-state reaction. The results of AC impedance measurements showed that the bulk conductivity of Na0.52Bi0.47Ti1−xGaxO3−δ samples decreased monotonously with the increase of Ga3+ doping concentration. At 673 K, the bulk conductivity of the Na0.52Bi0.47Ti0.98Ga0.02O3−δ sample is 7.19 × 10–4 S/cm, which is lower than that of the Na0.52Bi0.47TiO3−δ sample under the identical test temperature. The highest total conductivity emerged in the Na0.52Bi0.47Ti0.99Ga0.01O3−δ (x = 0.01) sample with 1.387 × 10–4 S/cm at 623 K, which demonstrated that the slight Ga3+ doping supported the enhancement of the total conductivity. A relaxation peak was observed in Na0.52Bi0.47Ti1−x GaxO3−δ compounds. As the Ga3+ ions were introduced into the Na0.52Bi0.47TiO3−δ compound, there was an increasing trend of the relaxation activation energy educed by the internal friction test. In addition, the oxygen relaxation height decreased with Ga3+ doping, which suggested that the introduction of Ga3+ ions resulted in the decrease of mobile oxygen vacancy.

Effect of Cobalt Additions on the Microstructure and Properties of Sodium Bismuth Titanate Ceramics

Single-phase (Na0.5Bi0.5)(Ti1 – xCox)O3 (x = 0–0.1, ∆х = 0.02) ceramic samples have been prepared by solid-state reactions, and their structure, microstructure, and dielectric properties have been studied. In all of the synthesized samples, a perovskite phase with a pseudocubic unit cell has been identified. Partial substitutions of cobalt cations for titanium cations increase the unit cell volume of the samples. We have studied the dielectric properties of the ceramics. The increased room temperature dielectric permittivity of the samples can be interpreted as evidence that the acceptor doping performed in this study has an advantageous effect on the piezoelectric properties of the sodium bismuth titanate ceramics.

Microstructure and electrical properties of microwave sintered Nb-doped NBT ceramics

Nb5+-doped sodium bismuth titanate (NBT) ceramics ((Na0.5Bi0.5)1-x/2Ti1-xNbxO3 where x = 0, 0.005, 0.01 and 0.015) were obtained by microwave assisted solid state reaction route and microwave sintered at 1000 ?C. Microwave processing technique was chosen for the sintering as it is a powerfulmethod which enables sintering in a short time with fast heating rate avoiding grain growth. The influence of Nb5+-doping on microstructure and electrical properties of the NBT ceramics was studied. X-ray diffraction analyses revealed that solubility limit of niobium in NBT lattice is up to 1mol%, as with further increase in niobium concentration pyrochlore appeared. Microstructure of all the ceramics was investigated by field emission scanning electron microscopy and it was observed that the average grain size decreased with doping. Temperature dependent dielectric study was carried out for all the ceramics at different frequency. All ceramics show diffusive dielectric behaviour around Tm and introduction of Nb even increases compositional fluctuation compared to the parent NBT. Nb-doping shifts the Tm toward lower temperature. Leakage current study showed that for whole range of electric field ohmic type conduction mechanism is dominant for all the ceramics. Room temperature polarization-electric field (P-E) hysteresis loop confirms the ferroelectric behaviour of all the ceramics.

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.

Physical properties and sinterability of pure and iron-doped bismuth sodium titanate ceramics

Pure (BNT) and iron-doped bismuth sodium titanate (Fe-BNT) ceramics were produced according to the formula Bi0.5Na0.5Ti1−xFexO3−0.5x, where x = 0 to 0.1. The addition of Fe2O3 enables decreasing the sintering temperature to 900 °C in comparison with 1075 °C for pure BNT, whilst also achieving lower porosities and greater densities. This is attributed to oxygen vacancy generation arising from substitution of Fe3+ onto the Ti4+ site of the BNT perovskite structure, and the resulting increase in mass transport that this enables during sintering. X-ray diffraction (XRD) analysis of Fe-BNT samples shows single-phase BNT with no secondary phases for all studied Fe contents, confirming complete solid solution of Fe. Rietveld refinement of XRD data revealed a pseudocubic perovskite symmetry (Pm-3m), and unit cell lengths increased with increasing Fe content. Scanning electron microscopy (SEM) showed that average grain size increases with increasing Fe content from an average grain size of ~ 0.5 μm in (x = 0) pure BNT to ~ 5 μm in (x = 0.1) Fe-doped BNT. Increasing Fe content also led to decreasing porosity, with relative density increasing to a maximum > 97% of its theoretical value at x = 0.07 to 0.1. The addition of Fe to BNT ceramics significantly affects electrical properties, reducing the remnant polarization, coercive field, strain and desirable ferroelectric properties compared with those of pure densified BNT. At room temperature, a high relative permittivity (ɛ′) of 1050 (x = 0.07) at an applied frequency of 1 kHz and a lower loss factor (tanδ) of 0.006 (x = 0.1) at an applied frequency of 300 kHz were observed by comparison with pure BNT ceramics.

Ion dynamics of non-stoichiometric Na0.5+xBi0.5-xTiO3-δ: A degradation study

Sodium bismuth titanate, a well-known piezoelectric material is reported as the new family of fast oxide ion conductors. In the current study, we investigated the influence of A-site non-stoichiometry on the electrical conductivity and ion dynamics of sodium bismuth titanate ceramics. For this, we synthesized the system Na0.5+xBi0.5-xTiO3–δ with x = −0.02, −0.01, 0.00, 0.01 and 0.02. The samples synthesized were almost single phase with rhombohedral (R3c) symmetry. The scanning electron micrographs showed the formation of dense grains with bulk density > 96%. The microstructure appeared to be very sensitive to non-stoichiometry. The conductivity data isotherms with frequency showed non-linear variation and were well fitted with Jonscher power law. We have observed super linear frequency dependent behaviour in Bi rich composition and sub-linear behaviour with the increase in Na content. To study the degradation mechanism, Na0.5+xBi0.5-xTiO3-δ (x = −0.01, 0.00, 0.01) samples were kept in reducing environment for 48 h. Further, for the analysis of conduction mechanism and the qualitative/quantitative estimation of charge carriers before and after reducing conditions, various models were used.

Nanostructured Ceramics of Potassium Sodium Bismuth Titanate: Hydrothermal Synthesis and Piezoelectric Response at Morphotropic Phase Boundary

Potassium Sodium Bismuth Titanate (KNBT) ceramics, with the general formula (1 - x)K0.5Bi0.5TiO3 -xNa0.5Bi0.5TiO3, have been synthesized following hydrothermal route, starting with solid solutions of pure perovskite nanoceramics of KBT and NBT in desired stoichiometric weight ratios, followed by sintering between 850°C and 1000°C for few hours. Pure KNBT nanoceramics with perovskite structure, having mean particle size around 30 nm, could be obtained. Morphology of the samples is found to depend strongly on composition. A change of composition results in a phase change, as evident from X-ray structure analysis. This phase change is a result of rhombohedral to tetragonal morphotropic phase boundary (MPB) in the sample with x around 0.80. Composition dependent occurrence of MPB leads to formation of needle like structures with micrometer length scales. These are typical of tetragonal lamellar structures, suggesting partial induction of tetragonal polar order from rhombohedral structure at MPB. Dielectric and piezoelectric properties, such as dielectric constant and loss, piezoelectric coefficients and figures of merit, exhibit threshold maxima in their values at the composition corresponding to MPB. These values reported for a lead-free piezoceramic, synthesized by a comparatively simple hydrothermal route, are highly promising, and comparable to well-known PZT.

Dielectric, ferroelectric, and energy storage properties in dysprosium doped sodium bismuth titanate ceramics

In this work, Na0.5(Bi1-xDyx)0.5TiO3 (0 ≤ x ≤ 15%) ceramics were prepared via solid state reaction method and were characterized. A stable and pure perovskite phase was revealed by X-ray diffraction analysis for all compositions and a symmetry change from rhombohedral to orthorhombic phase was detected beyond 10% of Dy substitution. The incorporation of Dy3+ into Sodium Bismuth Titanate (Na0.5Bi0.5TiO3) matrix allows a substantial decrease of the coercive field, an increase in the resistivity, and leads to a high stability of the dielectric permittivity (∆ɛ/ɛ(150 °C) ≤ ± 15%) over a wide temperature range. Furthermore, this system was found to exhibit improved energy storage properties at high temperatures with a maximum energy density of 1.2 J/cm3 obtained for 2%Dy composition at 200 °C. The obtained results are very promising for energy storage capacitors operating at high temperatures.

Phase Formation and Phase Transitions in Nonstoichiometric Sodium Bismuth Titanate Ceramics

We have studied the phase formation, microstructure, and dielectric and ferroelectric properties of (Na0.5–xBi0.5)TiO3 and (Na0.5Bi0.5 + x)TiO3 nonstoichiometric ceramics with Na/Bi 0.05 have anomalies near 900 K, confirming the presence of Bi4Ti3O12 as an impurity phase, which is accompanied by an increase in the spontaneous polarization of these samples.

Effect of composition induced transition in the optical band-gap, dielectric and magnetic properties of Gd doped [formula omitted] complex perovskite

The optical band-gap, dielectric and magnetic properties of gadolinium doped sodium bismuth titanate ceramics, Na0.5Bi0.5−xGdxTiO3 (NBT:xGd) with x=0,0.005,0.01,0.015and0.02, sintered by the conventional solid-state reaction were studied at room temperature. The X-ray diffraction (XRD) patterns revealed that the doping with Gd3+ ions into the ceramics resulted in rhombohedrally distorted perovskite structure. The microstructure morphology observed through the Scanning Electron Microscopy (SEM) are generally submicron level with the presence of micro-pores close to the grain boundary regions. It was found that band-gap energy values, Eg decreased with Gd-doping, being 3.247 and 3.151 eV for x=0 and 0.02, respectively. The dielectric properties of NBT:xGd samples were predominantly due to the interfacial effects at lower frequencies due to the presence of oxygen vacancies. Further, the long-range interaction between the Gd3+ ions changed the diamagnetic behavior in NBT samples to paramagnetic in the NBT:xGd ceramics.