Increasing BT Content Research Articles

Evolution of Ferroelectricity in Sr0.6Ba0.4Nb2O6-BaTiO3 Solid Solution with a Strong Electrocaloric Effect.

In conventional knowledge, ferroelectric solid solutions were formed between members belonging to the same crystal structure family. Since both tungsten bronze and perovskite structures are constructed by connecting the corner-sharing oxygen octahedra, it offers a possibility for formatting an unusual solid solution between these two families. Herein, (1 - x)Sr0.6Ba0.4Nb2O6-xBaTiO3, (1 - x)SBN-xBT, solid solutions were synthesized and the solution mechanism was resolved from a structure viewpoint. With increasing BT content, the solid solution persists of tetragonal tungsten bronze structure, but the lattice parameter a (= b) decreases whereas c increases, resulting in the significant reduction of grains anisotropy. The ferroelectric-relaxor phase transition temperature shows a monotonic increase as x increases. However, the ferroelectricity evolution is not monotonous as a function of BT content because of the competitive effects of Ba and Ti on the property. As a result, the x = 0.10 ceramic shows the strongest ferroelectricity and a remarkable electrocaloric effect of 1.4 K near room temperature. This work challenges the traditional view of solid solution formation and provides an alternative way to modulate the structure and properties of ferroelectrics.

A P/N additive to optimise the flame retardancy, low dielectricity and mechanical properties of EP composites

For expanding the application of epoxy resin (EP) in semiconductor packaging, the P/N flame retardant containing azole ring, designated as BT, was designed, synthesized, incorporated into EP, and flame retardant EP (FREP) was prepared. These resins were tested in terms of their thermal stability, flame retardant properties, mechanical properties, and dielectric properties. Owing to the excellent biphasic flame retardancy of BT, the samples reached the V-0 class of UL-94 flammability standards at 5 wt% BT with a 35.3% Limited Oxygen Index (LOI), which is 31.7% higher than that of EP . At the addition of 15 wt% BT (i.e., EP/BT15), the cone calorimetry test indicated that the sample's total exotherm and peak exotherm rates were reduced by 34% and 42%, in comparison to pure EP, respectively. The mechanical properties of FREP improved, and the tensile and flexural strengths increased by 9% and 10%, respectively, at 10 wt% BT addition. Moreover, the dielectric constant and dielectric loss of FREP decreased with increasing BT content. In this work, a simple strategy for the preparation of EP with good transparency, mechanical properties, flame retardancy and low dielectric constant is provided.

Hard piezoelectric properties of lead‐free BiFeO3–BaTiO3 ceramics

AbstractHard piezoelectric properties are investigated in lead‐free BiFeO3–BaTiO3 (BF–BT) ceramics. Rhombohedral (R) phase ceramics of (1 – x)BF–xBT (x = 0.20–0.30) were prepared using a conventional solid‐state reaction and water‐quenching process. The R structure is observed in x = 0.20–0.275, and the R and tetragonal phases coexist at x = 0.30. The piezoelectric charge sensor coefficient (d33) and electromechanical planar coupling factor (kp) increase with increasing BT content, whereas the mechanical quality factor (Qm) decreases. The x = 0.20 ceramic shows the best hard piezoelectric properties: the highest Qm = 403 and the highest TC = 607°C. In contrast, x = 0.30 ceramic shows soft piezoelectric properties: d33 = 301 pC/N and kp = 0.33 with TC = 510°C. These results show that the BF–BT system in R‐phase‐rich region has good hard piezoelectric properties for transducer applications.

Optimization of fresh properties, rheological parameters and mechanical performances of grouts containing bentonite

Grouting is widely utilized in construction, offering numerous applications such as concrete repairs and soil stabilisation. However, the workability and strength of grout heavily depend on the water-to-binder (w/b) ratio, which can present certain challenges since a suitable grout should fulfil the requirements of the intended application. As substitutes for Portland cement in various applications, pozzolanic materials such as Bentonite offer numerous benefits including reduced environmental impact and providing chemical resistance. This study aims to investigate the optimum content of the main factors affecting the properties of the grout; bentonite replacement level (BT), superplasticiser dosage (SP) and w/b ratio using factorial design. A full factorial design was carried out to mathematically model the spread, flowability, cohesion, rheological parameters and compressive strength of grouts containing BT. Prediction models were developed to describe the effect of the different proportions. The developed models can be used further to optimise the proportions of the grout. The w/b ratio varied between 0.36 and 0.58, while the bentonite content and SP dosage were in the range of 0–6% and 0–0.8%, respectively. Results show that the spread of grout increased with increasing the SP dosage and w/b ratio and decreased with increasing BT content. Conversely, cohesion decreased with increasing the SP dosage and w/b ratio and increased with increasing BT content. The yield stress of the grout was influenced by the dosage of BT, SP and W/B. Increasing BT had approximately 2.2- and 1.42-times greater influence than increasing W/B and SP respectively. The plastic viscosity was affected, in order of significance, by the dosage of BT, SP and W/B. BT led to improvement of grout strength, while w/b ratio decreased the strength. Interactive effects of the parameters on the measured properties were also observed.

Nanoscale polar regions embedded within ferroelectric domains in Na1/2Bi1/2TiO3−BaTiO3

Relaxor ferroelectrics are an eminent group of functional materials, characterized by complex micro- and nanoscale structures, accounting for their enhanced piezoelectric properties. In the $(1\ensuremath{-}x){\mathrm{Na}}_{1/2}{\mathrm{Bi}}_{1/2}{\mathrm{TiO}}_{3}\text{\ensuremath{-}}x{\mathrm{BaTiO}}_{3}$ (NBT-BT) solid solution, the evolution of nanoscale domains and their hierarchical association with ferroelectric domains is investigated using conventional and scanning transmission electron microscopy on compositions with 6, 9, and 12 mol % BT. Short-range fluctuations in the local polar displacement (polar nanoregions, PNRs) account for a heterogeneous nanostructure at the morphotropic phase boundary (6 mol % BT). Platelike nanodomains of tetragonal $P4bm$ symmetry coexist with a minor volume fraction of rhombohedral $R3c$ nanodomains. Their overall population decreases with increasing BT content. However, ferroelectric $P4mm$ domains in the composition with 12 mol % BT still exhibit nanoscale regions, which deviate from the average polarization. Small volume fractions of both $P4bm$ and $R3c$ nanodomains remain embedded within the ferroelectric domains. This hierarchical domain configuration underpins the complex structural characteristics of NBT-based relaxor ferroelectrics.

Multiple property enhancement in bismuth ferrite‐based ferroelectrics by balancing nanodomain and relaxor state

AbstractBismuth ferrite‐barium titanate (BF‐BT)‐based ferroelectrics have received widespread attention due to its adjustable structure features and multifunctional characteristics. Property optimization (ferroelectricity, piezoelectricity, electrostrain, electrostriction) for different application scenarios can be realized by increasing BT content gradually, while it is still difficult to integrate multiple performance advantages in the same component. To solve the problem and achieve the simultaneous enhancement of property parameters, defect engineering was adopted in this work to balance domain configuration and relaxor state via selective oxides modification strategy. Compared with the nanodomain engineered relaxor ferroelectrics with improved electrostrain and degraded ferroelectricity, the defect‐mediated ceramics doped with MnO2 present both enhanced electrostrain and ferroelectricity. Multiscale structure analysis (crystal structure, defect structure, and domain structure) and property characterization (ferroelectricity, strain property, and leakage current density) suggested that the defect dipoles induced by Mn substitution can effectively refine domain size and maintain ferroelectric state at room temperature, and the easier domain switching caused by weak‐correlated polar dipoles greatly improves both the strain and ferroelectricity. Especially, the defect dipoles‐mediated nanodomain and property enhancement can be only observed in BFO‐Mn ceramics, and infeasible for other oxides (e.g., CuO and CeO2). We believe that this work can provide some guidance to modify electrical properties in BF‐BT‐based ferroelectrics.

Enhanced electric field-induced strain and electrostrictive response of lead-free BaTiO3-modified Bi0.5(Na0.80K0.20)0.5TiO3 piezoelectric ceramics

ABSTRACT Lead-free (1-x)Bi0.5(Na0.80K0.20)0.5TiO3-xBaTiO3 or (1-x)BNKT-xBT (x = 0 – 0.15 mol fraction) piezoelectric ceramics have been investigated. The optimum density was found for the ceramic sintered at 1125°C, corresponding 98 – 99% of their theoretical values. All ceramics had a single perovskite structure. The coexisting mixed tetragonal-rhombohedral phases all over the entire compositional range with tetragonal phase becoming superior at higher BT. The diffuse phase transition was promoted by the addition of BT. With increasing BT content, the Tm and Td values were found to decrease. Phase transition from ferroelectric (FE) phase to ergodic relaxor (ER) phase was also induced by the changes in BT content. These changes significantly suspended long-range ferroelectric order, then correspondingly reducing the Pr and Ec , resulting in an improvement of electrostrictive and electric field-induced strain responses. A significant increasing of electric field-induced strain response (Smax = 0.37% and d*33 = 630 pm/V) is noted for the x = 0.05 ceramic. Furthermore, high electrostrictive coefficient (Q33 ) of 0.0421 m4/C2 is observed for this composition, which was more than ~ 2 times (~108%) as compared to the pure BNKT ceramic. The studied results indicated these ceramics can be considered promising candidates for actuator applications.

Relationship between chemical composition, phase structure and piezoelectric property of BiFeO3–BaTiO3 ceramics near morphotropic phase boundary

The chemical composition and phase structure of (1−x)BiFeO3−xBaTiO3 (BF–xBT) ceramics near morphotropic phase boundary (MPB) are controversial so far. Particularly, no report mentioned BT content dependence of phase ratio of BF–xBT ceramics near MPB. Herein, BF–xBT (x = 0.24–0.38) ceramics with pure perovskite structure and dense microstructure were prepared by conventional sintering technics. The phase composition, electric resistivity, dielectric, ferroelectric and piezoelectric properties of the ceramics were systematically investigated. The results showed that the phase structure of the ceramics transforms from rhombohedral (R) to pseudocubic (pC) with increasing BT content, and the MPB with R-pC phase coexistence was determined in the range of 0.28 ≤ x ≤ 0.33. In addition, as BT content increases for the ceramics near MPB, the phase fraction of R decreases gradually from 75.3% for BF–0.28BT to 36.9% for BF–0.33BT. Especially for BF–0.31BT ceramics, the phase fraction of R (49.1%) and pC (50.9%) are almost equal to each other. Enhanced piezoelectricity and ferroelecricity were attained in the ceramics near MPB. Owing to more proper R/pC phase ratio and strong ferroelectricity, the best piezoelectric coefficient d33 = 190 pC/N was achieved in BF–0.31BT ceramics. This work revealed the relationship between chemical composition, phase structure and piezoelectric property of BF–BT piezoceramics near MPB, which is helpful to further improve the piezoelectric property of BF–BT via optimizing phase structure and/or composition engineering.

Competitive mechanism of temperature-dependent electrical properties in BiFeO3-BaTiO3 ferroelectrics controlled by domain evolution

To understand the structure nature and physical mechanisms of property evolution under electric and temperature fields, temperature-dependent electrical properties of bismuth ferrite-barium titanate (BiFeO3-BaTiO3, BF-BT) ceramics were analyzed from both static structure and domain dynamics. Intriguingly, temperature coefficient of remanent polarization (Pr) and negative strain (Sneg) changes from positive to negative as BT component increases, leading to a nearly zero temperature coefficient of Pr at critical component (BT=0.35). Combined with multi-scale structure characterization techniques and polarization switching/backswitching described by the temperature-dependent Ps and Ps-Pr, such behavior is explained by the evolution of domain size for the first time and a competitive mechanism is also proposed. That is, the evolution of macro stripe domain (0.25≤BT≤0.30) to nanodomain (0.35≤BT≤0.45) determines the transition from the dominated polarization switching process to the dominated backswitching process, further greatly determining the temperature-stability of strain properties: variation of unipolar strain changes from 136% (BT=0.25) to 25% (BT=0.45) with increasing BT content. We believe that these results significantly guide the performance improvement (especially temperature-dependent properties) of BF-BT solid solutions.

Effect of poling on polarization alignment, dielectric behavior, and piezoelectricity development in polycrystalline BiFeO3–BaTiO3 ceramics

This study investigates the effect of poling electric field on polarization alignment, dielectric dispersion, relaxor feature, phase transition temperature (Tm), and piezoelectric properties evolution of (1–x)BiFeO3–xBaTiO3[(1–x)BF–xBT] ceramics with x = 0.26, 0.29, 0.32, and 0.35. The XRD pattern studies indicate that the application electric field induced the polarization alignment along with a significant change of the diffraction intensity of peaks, which gives rise to increasing piezoelectric properties. Simultaneously, the degree of dielectric dispersion and diffuse factor γ in the modified Curie–Weiss equation and Tm increase after applying the poling electric field. Moreover, the relaxor characteristics are more evident with increasing BT content. The dielectric behavior and relaxor feature may be attributed to the small random field domains resulting from local charge imbalance due to off‐valent substituents between A‐ and B‐site cation in (1–x)BF–xBT ceramics. Meanwhile, the application of the poling electric field probably increases the strength of the neighboring dipole–dipole interaction, giving the enhanced degree of dielectric dispersion and Tm.

Wavelength dependence of refractive index in lead-free Na0.5Bi0.5TiO3–BaTiO3 single crystals

Refractive indices of (1−x)Na0.5Bi0.5TiO3–xBaTiO3 (NBT–xBT, x=0, 0.06 and 0.08) single crystals were measured at room temperature after poled along pseudo-cubic crystallographic direction [001]. The refractive indices decrease dramatically when the wavelength increases for all crystals. At the same wavelength, refractive indices of NBT–xBT single crystals decrease with increasing BT content. Sellmeier dispersion equations were obtained by least square fitting, which can be used to calculate the refractive indices in low absorption wavelength range. Parameters connected to the energy band structure were determined by fitting single-oscillator dispersion equation. Similar to most oxygen-octahedral ferroelectrics, NBT–xBT crystals have the same dispersion behavior described by the refractive-index dispersion parameter. Dispersion energies take on covalent crystal values.

Dielectric, Ferroelectric, and Piezoelectric Properties of BiFeO3–BaTiO3 Ceramics

Perovskite solid solution ceramics of (1 − x)BiFeO3–xBaTiO3 (1 − x)BF–xBT, 0.2 ≤ x ≤ 0.45) with high electrical resistivity were prepared by solid‐state reaction method. Actual ferroelectric hysteresis loops and temperature dependence of dielectric constant of the ceramics were obtained. Ceramics of 0.7BF–0.3BT with small rhombohedral distortion show highest remnant polarization (Pr = 26.0 μC/cm2) and piezoelectric coefficient (d33 = 134 pC/N). Compositions with pseudo‐cubic symmetry (intermediate phases) show relaxor‐like dielectric anomaly. The values of Pr and d33 decrease with increasing BT content, from 24.8 μC/cm2 and 104 pC/N for 0.65BF–0.35BT to 8.2 μC/cm2 and 5 pC/N for 0.55BF–0.45BT.

Optical dispersion and interband transition in Na0.5Bi0.5TiO3-x%BaTiO3 lead-free relaxor ferroelectric single crystals

Optical properties of A-site disordered Na0.5Bi0.5TiO3-x%BaTiO3 (NBT-xBT) single crystals with three typical compositions were studied systematically. Refractive index as a function of wavelength was measured by Spectroscopic ellipsometry, and modified Sellmeier dispersion equations were obtained by the least square fitting. High optical transmittance (65%) over a wide transparent region (from 400 to 6000 nm) has been found in NBT-7.5BT, much higher than that of NBT and NBT-5BT. Optical band gap energies were calculated using the absorption coefficient through Tauc equation. With increasing BT content, refractive index and absorption coefficient decrease, while transmission and band gap energy increase.

Effect of sintering temperature on microstructure and piezoelectric properties of Pb-free BiFeO3–BaTiO3 ceramics in the composition range of large BiFeO3 concentrations

Lead-free (1-x)BiFeO3–xBaTiO3 [(1-x)BF-xBT] piezoelectric ceramics in the range of large BF concentrations were prepared by conventional oxide-mixed method at various sintering temperatures. The sintering temperatures have a significant effect on the microstructure of the ceramics, and the composition has a remarkable effect on optimal sintering temperature of the ceramics, which are closely related with piezoelectric properties. The grain size increased with increasing sintering temperature and the optimal sintering temperature increased with increasing BT content. The ceramics with x = 0.275 sintered at 990 °C exhibit enhanced electrical properties of d 33 = 136pC/N and k p = 0.312 due to the polarization rotation mechanisms at MPB and desired microstructure. These results show that the ceramic with x = 0.275 is a promising lead-free high-temperature piezoelectric material.

Control of ferroelectric phase transition in nano particulate NBT–BT based ceramics

Abstract Lead free relaxor NBT–BT based ceramic compositions were prepared using sol–gel method. The samples were sintered around 1140 °C for 3–4 h in the air. The characterization was done using X-ray diffraction (XRD), filed emission scanning electron microscope (FESEM), energy dispersive spectrometry (EDS), Raman, Fourier transform infrared (FTIR), dielectric and P – E loop measurements. The XRD patterns recorded at room temperature confirmed the phase formation of the samples. From FESEM micrographs, the particle sizes were estimated for calcined powders and are found to be in the range of 50–70 nm. The analysis of both Raman and FTIR spectral data of the samples also indicated the distortion of NBT lattice with the addition of Ba 2+ and Nd 3+ ions. It was found that the dielectric and piezoelectric properties of NBT–BT compositions beyond the morphotrophic phase boundary (MPB) are rather sensitive to the presence of tetragonal phase in addition to the rhombohedral phase. NBT ceramics exhibit a decrease in diffusive factor with increasing BT content, implying a degradation of relaxor feature leading to the normal ferroelectric nature. The ceramic samples employed in the present study exhibited variation in P – E hysteresis loops.

Structure and electrical properties of ternary BiFeO3-BaTiO3-PbTiO3 high-temperature piezoceramics

In the current work, the bulk ternary (0.85-x) BiFeO3-xBaTiO3-0.15PbTiO3 (BF-BTx-PT, x=0.08–0.35) system has been studied as a potential high-temperature piezoceramics. Samples with various content of BT were prepared via solid-state route, and pure perovskite phase was confirmed by X-ray diffraction. The temperature dependence of dielectric constants confirmed the decrease of Curie temperature with increasing BT content. It was found that the morphotropic phase boundary (MPB) composition of BF-BTx-PT ceramics was in the vicinity of x=0.15, which exhibits optimal properties with piezoelectric constant d33 of 60 pC/N, high Curie temperature of 550 °C, and low sintering temperature of 920 °C. Measurements also showed that the depoling temperature was 300 °C, about 150 °C higher than that of commercialized PZT ceramics, which indicated good temperature stability. BF-BTx-PT ceramics are promising candidates for high temperature applications.

DC conductivity and magnetic properties of piezoelectric–piezomagnetic composite system

A series of composites (1−x) (Ni0.8Zn0.2Fe2O4)+x (BaTiO3), where x=0%, 20%, 40%, 60%, 80% and 100% BT content, have been prepared by the standard ceramic technique, then sintered at 1200°C for 8h. X-ray diffraction analysis shows that the prepared composites consist of two phases, ferrimagnetic and ferroelectric. DC electrical resistivity, thermoelectric power, charge carriers concentration and charge carrier mobility have been studied at different temperatures. It was found that the DC electrical conductivity increases with increasing BT content. The values of the thermoelectric power were positive and negative for the composites indicating that there are two conduction mechanisms, hopping and band conduction, respectively. Using the values of DC electrical conductivity and thermoelectric power, the values of charge carrier mobility and the charge carrier concentration were calculated. Magnetic measurements (hysteresis loop and magnetic permeability) show that the magnetization decreases by increasing BT content. M–H loop of pure Ni0.6 Zn0.4 Fe2O4 composite indicates that it is paramagnetic at room temperature and that the magnetization is diluted by increasing the BT content in the composite system. The value of magnetoelectric coefficient for the composites decreases by increasing BT content for all the compositions except for 40% BT content, which may be due to the low resistivity of magnetic phase compared with the BT phase that causes a leakage of induced charges on the piezoelectric phase. Since both ferroelectric and magnetic phases preserve their basic properties in the bulk composite, the present BT–NZF composite are potential candidates for applications as pollution sensors and electromagnetic waves.

Reduction in emissions of nitrogen oxides, particulate matter, and polycyclic aromatic hydrocarbon by adding water-containing butanol into a diesel-fueled engine generator

Three groups of n-butanol–diesel blends with 0, 0.5, and 1.0wt.% water-content were investigated to simulate the hydrated butanol produced by acetone–butanol–ethanol fermentation and a simple distillation treatment. Both 30-day standing and centrifugal test results showed that 15wt.% n-butanol (BT) was the minimum additive ratio to stabilize the 1.0wt.% water content diesel blend, while those blends that contained 0 or 0.5wt.% water could remain as stable one-phase clear liquids by adding just 5wt.% BT. These stable diesel blends were further examined in a heavy-duty diesel-fueled engine generator (HDDEG). Using BT-diesel blends increased the indicated specific fuel consumption (ISFC) because of the lower heating value of n-butanol, while the micro-explosions that occurred could reduce the ISFC when using 0.5wt.% water-containing BT-diesel blends. NOx emissions increased with the increasing BT content at a low additive ratio (5–15wt.%), and reduced when adding a higher amount of BT (>15wt.%). PM, total-PAHs, and total-BaPeq emissions were all significantly reduced when the increasing BT additive ratio contained either 0, 0.5, or 1.0wt.% water because of the lower sulfur and higher oxygen fuel contents. On the other hand, the CO emission level went up with the addition of BT. Notably, the diesel blends with 0.5wt.% water only slightly increased ISFC when low fractions of BT were added, i.e. 0.40% and 0.81% ISFC increases with the addition of 5 and 10wt.% BT, respectively. In addition, there were significantly lower NOx, PM, Total-PAHs and Total-BaPeq, emissions with the blends than with regular diesel. With the aim of achieving both good energy performance and less pollutant emissions, the 5 and 10wt.% BT additive with 0.5% water content blends were the most suitable for practical use in an HDDEG without any engine modifications or changes in controls.

Structural, dielectric and piezoelectric studies of (1−x)PLSZNT–xBaTiO3 ceramics

(1 − x )Pb 0.973 La 0.012 Sr 0.015 (Zr 0.53 Ti 0.47 ) 0.9845 Nb 0.01 O 3 – x BaTiO 3 polycrystalline solid solutions abbreviated hereafter as (1 − x )PLSZNT– x BT, where x (BT) = 0.1, 0.2, 0.3, 0.4 and 0.5 have been fabricated through high-temperature solid-state reaction technique and investigated for phase formation evolution, microstructural studies, apparent density, dielectric behavior and piezoelectric properties. Introduction of BT into PLSZNT lattice showed a single-phase ferroelectric tetragonal structure, and further increment of BT content resulted in stabilizing the ferroelectric tetragonal (FE TET ) perovskite phase. Microstructure, apparent density, dielectric behavior and piezoelectric coefficients were examined as a function of BT content. It was perceived that BT diffusion into PLSZNT was homogeneous, and increasing BT enhanced the grain growth and dielectric response till x = 0.5. TEM studies of calcined powders revealed an average particle size ranging from 22 to 84 nm. The study of dielectric and piezoelectric properties of the sintered and poled samples indicate that increasing BT content influenced both the parameters, respectively. The substitution till x = 0.5 evidently increased dielectric and piezoelectric properties with a relatively decreasing Curie temperature in the PLSZNT–BT ceramic system which may be applicable for possible capacitor, sensor and actuator applications.

Dielectric properties of (1 − x)Pb(Zr 0.52Ti 0.48)O 3–( x)BaTiO 3 ceramics under uniaxial compressive pre-stress

Effects of uniaxial compressive pre-stress on the dielectric properties of ceramics in PZT–BT solid-solution system are investigated. The physical properties measurements reveal that the addition of BT into PZT results in the increase of grain size and microstructural heterogeneity, except for the density which sees the opposite trend. The dielectric properties measured under stress-free condition show a gradual increase of the dielectric constant with increasing BT content, while the dielectric loss tangent is not considerably different. The dielectric properties under the uniaxial compressive pre-stress of the PZT–BT ceramics are observed at stress levels up to 15 MPa using a uniaxial compressometer. The results clearly show that both the dielectric constant and the dielectric loss tangent of the PZT–BT ceramics increase significantly with increasing applied stress. Larger changes in the dielectric properties with the applied stress are observed in the PZT-rich compositions. The experimental observations have been attributed to the increase of the domain wall motions from the application of the compressive pre-stress.