BaxSr1-xTiO3 Research Articles

Rapid fabrication of Ba1–xSrxTiO3 ceramics via reactive flash sintering

Ba1–xSrxTiO3 (BST) ceramics are promising dielectric materials. However, their fabrication is usually laborious, requiring long preparation stages and high temperatures, which are not favorable for tuning the grain size and dielectric properties. In this study, (Ba1–xSrx)TiO3 (x = 0.1, 0.3, 0.5) ceramics were produced via reactive flash sintering (RFS) of a mixture of BaCO3, SrCO3 and TiO2 powders at 900 °C and relatively short times (15–90 s). The electric field (E-field) with a strength of 400 V/cm and the current densities of 25–75 mA mm−2 were applied during RFS. Once the Sr2+ content increased, the incubation time for the RFS decreased, suggesting that the addition of Sr2+ facilitated the RFS process. At the RFS time above 15 s, a single-phase Ba0.6Sr0.4TiO3 perovskite structure was formed. When the time and the applied current density increased, both the densities and grain sizes within the ceramics increased. This increased the real part (ε’) of the complex permittivity compared to that of the conventionally sintered (CS) ceramic. Moreover, the enhancement of mass transport by E-field-induced oxygen vacancies was considered the predominant mechanism of RFS in the production of BST ceramics.

Ionic radius effect on structural and electrical properties of barium strontium titanate thin films

The effect of ion radius on the structural and electrical properties of the perovskite oxide Ba1-x SrxTiO3 thin film is investigated in this work. X-ray diffraction analysis confirmed the formation of phase perovskite structures. Investigations of ceramic microstructures and mechanical properties showed their dependence on the value of ratio x. X-ray diffraction (XRD) and Field emission scanning electron microscopy (FESEM) are used to study the crystallographic aspects of the materials. The XRD pattern changed from tetragonal to cubic as x rose. FESEM images revealed the particle size varied with the values of x increased. The results show that as the ion radius varies, the crystal structure undergoes distortions, affecting the symmetry and stability of the BaSrTiO3 thin films. Electrical properties change depending on the change in particle size.

Flash sintering of tunable dielectric Ba0.6Sr0.4TiO3 electroceramics

Ba(1-x)SrxTiO3 (BST) is a crucial dielectric material in tunable devices for modern wireless communication technologies, owing to high dielectric tunability and low dielectric loss. However, the conventional processing of BST ceramics requires a high sintering temperature of about 1350 ºC. In this work, we demonstrate the feasibility of using Flash sintering (FS) and corresponding maps to process Ba0.6Sr0.4TiO3 ceramics, resulting in a 350 ºC decrease in sintering temperature and 7 h reduction in sintering process time. The Flash-sintered BST exhibits a finer grain microstructure, lower dielectric loss, and significantly higher K-factor (figure of merit for tunability) when compared to conventionally sintered BST, unequivocally meeting the application criteria for tunable materials. Our findings highlight the effectiveness of FS as an alternative method for the rapid sintering of BST, while also opening up possibilities for further research into more efficient sintering processes for electroceramics.

Ferroelectric polarization-electric field promoted S-scheme CdSe/BaxSr1-xTiO3 for highly efficient solar hydrogen evolution

Coupling the ferroelectric polarization and internal electric field to realize effective separation and migration of photogenerated charges is highly attractive for accomplishing efficient photocatalytic hydrogen production. In this work, an internal electric field modulated S-scheme heterostructure was fabricated by depositing CdSe on ferroelectric BaxSr1-xTiO3 (BxST) through an in-situ growth method. Because of the oriented powerful electron transport driven by the strong spontaneous polarization and internal electric field, the as-synthesized CdSe/BxST heterojunctions demonstrated excellent solar to H2 performance. Without the addition of noble metal cocatalyst, 7% CdSe/B0.8ST exhibited a H2 evolution rate of 1971.8 µmol g-1 h−1 with an apparent quantum yield of 12.1% at 365 nm. Moreover, the obtained heterojunction catalysts exhibit good stability after 12 h continuous irradiation. This work provides a viable strategy on the utilization of ferroelectric polarization and internal electric field strategy to promote charge transfer and separation of S-scheme photocatalysts.

Microstructure and Dielectric Properties of Gradient Composite BaxSr1-xTiO3 Multilayer Ceramic Capacitors.

Multilayer ceramic capacitors (MLCCs) prepared using Ba1-xSrxTiO3 (BST) ceramics exhibit high dielectric constants (~1000), low dielectric loss (<0.01), and high breakdown voltage, with particularly significant tunability in dielectric properties (>50%) and with poor temperature stability. Doping-dominated temperature stability improvements often result in unintended loss of dielectric properties. A non-doping method has been proposed to enhance the temperature stability of BST capacitors. The composite gradient multilayer (CGML) ceramic capacitors with BaxSr1-xTiO3, where 0.5 < x < 0.8, as the dielectric, were prepared using a tape-casting method and sintered at 1250 °C. There exists a dense microstructure and continuous interface between the BaxSr1-xTiO3 thick film and the Pt electrodes. CGML ceramic capacitors feature a high dielectric constant at 1270, a low dielectric loss of less than 0.007, and excellent frequency and temperature stability. The capacitor showcases remarkable dielectric properties with a substantial tunability of 68% at 100 kV/cm, along with a notably consistent tunability ranging from 20% to 28% at 15 kV/cm across temperatures spanning from 30 to 100 °C, outperforming single-component BST-MLCCs in dielectric performance.

Huge dielectric properties of lead-free BaxSryLi0.6Ti1.67O3 ceramics

BaxSr1-xTiO3 (BST) is a new type of composite ceramic with high dielectric constant, low dielectric loss, stable structure and environmental friendliness, which has become the focus of current research. BST ceramics are widely used in dielectric capacitors, but they have the disadvantages of high sintering temperatures and high energy consumption. In this paper, Li2CO3 is added as a flux to reduce the sintering temperature of BST ceramic. The BaxSryLi0.6Ti1.67O3 (BSLT) ceramic was prepared using the solid phase method. The effects of different Ba/Sr ratios and sintering temperatures on the microstructure and dielectric properties of the BSLT ceramics were investigated. The results suggest that the Ba0.15Sr0.25Li0.6Ti1.67O3 ceramic owns the optimal dielectric constant of 7.11 × 106 and relatively low dielectric loss of 2.2 at 500 °C and 1 kHz when the sintering temperature is 1190 °C.

Temperature and E-Poling Evolution of Structural, Vibrational, Dielectric, and Ferroelectric Properties of Ba1-xSrxTiO3 Ceramics (x = 0, 0.1, 0.2, 0.3, 0.4 and 0.45).

Lead-free Ba1-xSrxTiO3 (BST) (x = 0, 0.1, 0.2, 0.3, 0.4 and 0.45) ceramics were successfully prepared via the solid-state reaction route. A pure perovskite crystalline structure was identified for all compositions by X-ray diffraction analysis. The basic phase transition temperatures in these ceramics were studied over a wide temperature range. A change in symmetry from a tetragonal to cubic phase was detected, which was further proven by phonon anomalies in composition/temperature-dependent Raman spectra. The incorporation of Sr2+ into BaTiO3 (BT) lead to a shift in the phase transitions to lower temperatures, suppressing the ferroelectric properties and inducing relaxor-like behavior. Therefore, it was reasonable to suppose that the materials progressively lack long-range ordering. The initial second-harmonic generation (SHG) measurements demonstrated that the cubic phase of BST ceramics is not purely centrosymmetric over a wide temperature interval. We discussed the possible origin of the observed effects, and showed that electric field poling seems to reconstruct the structural ordering destroyed by the introduction of Sr2+ to BT. In the first approximation, substitution of Sr for larger Ba simply reduced the space for the off-central shift in Ti in the lattice and hence the domain polarization. A-site cation ordering in BST and its influence on the density of electronic states were also explored. The effect of doping with strontium ions in the BST compound on the density of electronic states was investigated using ab initio methods. As the calculations showed, doping BT with Sr2+ atoms led to an increase in the bandgap. The proposed calculations will also be used in the subsequent search for materials optimal for applications in photovoltaics.

Modeling structure–properties relations in compositionally disordered relaxor dielectrics at the nanoscale

The solid solution Ba1−xSrxTiO3 (BSTO) displays dielectric response that is highly tunable, while also exhibiting low losses in a broad frequency regime, including the microwave band. Therefore, there is a need for a better understanding of the influence of the BSTO microstructure on its relaxor properties and performance in a variety of technological applications. Since the local polarization in BSTO is strongly dependent on composition, so is its response to an applied AC field. In this work, we have adopted a phase field method to study the frequency-dependent dielectric response of this system while accounting for the local fluctuations in the solid-solution composition. By utilizing a thermodynamic potential that includes spatial dependence on the averaged Sr content, we connected relaxor-like features in the dielectric dispersion to local spatial inhomogeneities, such as average size of Sr- or Ba-rich regions, across a wide range of temperatures. These results show that the adopted simple coarse-grained approach to the relaxor problem is sensitive enough to reveal correlations between the frequency and temperature dependence of the dielectric response and modulations in the material morphology and microstructure.

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

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

Dielectric, piezoelectric and energy storage properties of large grain Ba1−xSrxTiO3 (BST) ceramic system for 0.17 ≤ x ≤ 0.26

The ferroelectric, energy storage, piezoelectric, and electrostrictive properties of the Ba1-xSrxTiO3 (BST) ceramic system for different Sr contents was synthesized using the solid-state reaction technique. At room temperature, pure tetragonal crystal structure was confirmed for the large grain ceramics, by the X-ray diffraction study for all compositions with coexistence of phases for x = 0.26. The dielectric measurement showed the maximum values of the dielectric constant, εr = 6434.33 at the Curie temperature, Tc = 42°C for x = 0.26. The maximal polarization (Pmax = 11.15μC/cm2) and remnant polarization (Pr = 4.67μC/cm2) was obtained with the low value of coercive field Ec = 317 V/cm. Increasing the Sr content, Wtot and Wrec reach 91.67 mJ/cm3 and 79.36 mJ/cm3, and a maximal energy storage efficiency (η) of 86.57% was achieved for x = 0.26, also the electrostrictive coefficient was calculated as 0.048 m4/C2 with a conversepiezoelectric coefficient 220 pm/V.

Study on the charge carrier transport property generated by photo/piezo synergy field over barium strontium titanate

The combination of piezoelectric catalysis and photocatalysis has garnered significant attention in the fields of pollutant degradation and water splitting. However, the charge carrier transport property remains unclear due to the difficulty in observing nanocrystal polarization during the reaction process. This study aimed to address this issue by preparing Ba1−xSrxTiO3 (BST) solid solutions using the solid-phase method and examining the effect of ion doping on piezoelectricity-photocatalytic activity. The photocatalysis and local piezoelectric catalysis coupling was evaluated through water decomposition and dye degradation. Interestingly, the introduction of local piezoelectric catalysis had the opposite effect: it reduced photocatalytic hydrogen production but increased the rate of photocatalytic RhB degradation. The possible mechanism was proposed that the different adsorption of H+ and radicals on the catalysts would affect the direction of the local piezoelectric potential and then change the photo-generated carriers' transfer path.

Strontium-induced phase, energy band and microstructure regulation in Ba1−xSrxTiO3photocatalysts for boosting visible-light photocatalytic activity

The polyacrylamide gel method has been developed for fabrication of Ba1−xSrxTiO3(BST) photocatalysts. The structure, surface morphology, band gap and photocatalytic activity of BST photocatalysts can be regulated by adjusting thexvalue.

Ионно-плазменное осаждение многокомпонентных пленок с заданным законом распределения состава по толщине

A method is proposed for ion-plasma deposition of thin multicomponent films with the ability to control the component composition in thickness (gradedfilm) with a change in the pressure of the working gas according to a given law. Using the BaxSr1-xTiO3 (BSTO)perovskite-type structure as an example, the calculated (Monte Carlo simulation) and experimental dependences of the component composition of films and their deposition rate on the pressure of the working gas were obtained. As an example, the possibility of deposition of BSTO films with a linear distribution of composition by their thickness.

Ion-plasma deposition of multicomponent films with a given law of composition distribution by thickness

A method is proposed for ion-plasma deposition of thin multicomponent films with the ability to control the component composition in thickness (graded film) with a change in the pressure of the working gas according to a given law. Using the BaxSr1-xTiO3 (BSTO)perovskite-type structure as an example, the calculated (Monte Carlo simulation) and experimental dependences of the component composition of films and their deposition rate on the pressure of the working gas were obtained. As an example, the possibility of deposition of BSTO films with a linear distribution of composition by their thickness. Keywords: ion-plasma deposition, thin multicomponent films, composition control.

Alkali Metal Cations as Charge‐Transfer Bridge for Polarization Promoted Solar‐to‐H2 Conversion

AbstractUtilization of spontaneous polarization electric field of ferroelectric materials to realize the spatial separation and fast transfer of photogenerated charges has been regarded as a promising strategy to fabricate highly efficient photocatalysts. Herein, a novel heterostructure is constructed by coupling potassium poly(heptazine imide) (K‐PHI) with ferroelectric BaxSr1‐xTiO3 (BxST) through a facile electrostatic self‐assembly strategy. The ionic species of K‐PHI can neutralize the polarized charges in BxST to form intimate interfacial contact, substantially boosting the internal electric field. Notably, K+ cations intercalated into K‐PHI act as charge‐transfer bridge to promote migration and separation of photogenerated charge carriers. As a result, a significantly improved H2‐evolution rate of 1087.4 µmol h−1 g−1 with an apparent quantum yield (AQY) of 8.05% at 420 nm is achieved over 5% K‐PHI/B0.8ST, standing among the best polymeric carbon nitride‐based photocatalysts reported up to date. Moreover, the extreme stability of the catalysts is evidenced by remaining outstanding catalytic performance even after storage for half a year. This strategy can be extended to other alkali metal (Na+ and Cs+) modified polymeric materials, highlighting the key role of the bridging ions in constructing polarized heterostructure, which sheds light on the design of ferroelectric‐assisted photocatalysts.

The Mechanism of a Film-Forming Medium during the RF Deposition of Ferroelectric Ceramics of the BaxSr1–xTiO3 Composition

The Mechanism of a Film-Forming Medium during the RF Deposition of Ferroelectric Ceramics of the BaxSr1–xTiO3 Composition

Optimized Tunability of Barium Strontium Titanate Thin Films onto Different Plates with Proper Buffer Layers

Misfit strain, polarization, permittivity, and tunability of Ba x Sr1−x TiO3 (BST) thin films on various substrates with varied buffer layers are calculated by a modified thermodynamic model. The lattice parameters of the LaAlO3 (LAO), CaTiO3 (CT), BaZr0.25Ti0.75O3 (BZT), and MgO buffer layers grow consecutively as does the thermal expansion coefficient (TEC) of the Si, Ti, Ni, and stainless steel (SS) substrates. When the TEC of substrates is bigger (such as Ni, SS) than that of the films, introducing buffer layers with larger lattice parameters (such as BZT, MgO) can improve the permittivity and tunability. Conversely, inserting buffer layers with smaller lattice parameters (such as LAO, CT) can enhance the dielectric response when the TEC of substrates is smaller (such as Si, Ti) than that of the films. The relationship between the TEC of substrate and the lattice parameter of buffer layer is primarily linear for achieving high tunability. According to several references, introducing LaNiO3 buffer layers can significantly increase the tunability of BST solid solutions prepared on Si‐based substrates, which is in line with the estimated rule. This law offers a guide for choosing the best substrate and buffer layer when producing BST films with strong dielectric response.

The effect of mole fraction on the phase transition of BaxSr1-xTiO3 ceramic from cubic to tetragonal assisted by Rietveld analysis

The displacive phase transition in BaxSr1-xTiO3 (BST) ceramic due to the mole fraction differences was investigated using x-ray diffraction assisted by Rietveld analysis. Detailed Rietveld analysis showed that BST undergoes a structural phase transformation from cubic to tetragonal phase. Average crystallite size and microstrain present in the powders were studied using the Wilson and Debye–Scherrer equation. The crystal structure of samples was refined by the Rietveld method, and an expansion on the unit cell parameters was determined. These analyses revealed an increment in the unit cell strain and an increase in the crystallite size when the mole fraction was increased.

Studies on Electrical Energy Storage Density in Lead-Free Ferroelectric Ba1-x SrxTiO3 (x = 0.1, 0.3, and 0.7) Capacitors

Structure, phonon, and energy storage density were studied in Sr2+-substituted lead-free ferroelectric Ba1-x SrxTiO3 (BSTx) (x = 0.1, 0.3, and 0.7) samples, prepared using solid state reaction techniques, utilizing X-ray diffraction, Raman, and ferroelectric polarization measurement techniques. The system is tetragonal for x = 0.1 with large c/a ratio at room temperature. The tetragonal anisotropy decreases with increasing x, and becoming cubic for x > 0.3. All these structural properties change due to change in the c/a ratio upon rising temperature. Temperature dependent phonon spectroscopic results (80-500 K) indicate reduction in tetragonal to cubic phase transition temperature upon increasing x due to reduction in tetragonal anisotropy (c/a). Overdamping of ~90 cm-1 E-soft phonon mode and a dramatic decrease in the intensity of ~160 cm-1 A-mode were observed at around the tetragonal ferroelectric to cubic paraelectric phase. Using UV-Vis optical absorption spectra, the optical band gaps of these compounds were calculated as 1.73, 1.7, and 1.68 eV as a function of increasing the dopant concentration (x). The energy storage densities of these electrically polled BSTx capacitors were estimated using the polarization hysteresis loops. For x = 0.7, a large energy storage density (Ure) of 20 Joule/cm3 with the efficiency of 57 % was estimated at applied electrical field of 88 kV/cm. Close to Tc large dielectric constant and high energy density values of BSTx capacitors indicate its possible application in high energy storage and pulse power devices. These results will be presented in detail at the meeting.

A novel room-temperature synthesis technique for producing high-density Ba1-xSrxTiO3 and PbZryTi1-yO3 composites

The ability to synthesize capacitors at room temperature has great cost-saving potential compared to energy-intensive conventional sintering techniques which involve extended periods at high temperature. In this work, several compositions in the Ba1-xSrxTiO3 (BST) and PbZryTi1-yO3 (PZT) series were synthesized conventionally and densified via a room-temperature fabrication (RTF) process. The BST and PZT particles were coated and mixed with an aqueous solution of Li2MoO4 (LMO), which acts as a binder. The novel techniques presented in this work, including the usage of a vacuum-assisted pellet die and a bath sonicator in combination, were designed to increase the density of the resultant pellets. Relative densities as high as 96.1% were achieved for BST x = 0.5, 96.9% for BST x = 0.45%, and 95.1% for PZT y = 0.5 RTF pellets using LMO as a binder. These composites are the densest room-temperature fabricated composites reported to date. In addition, the effect of mixing particles with two different size distributions was analyzed for composites produced with PZT particles. The dielectric properties of all these dense RTF composites were measured at temperatures ranging from 150 °C to − 60 ℃ and compared with those of conventionally sintered electroceramics with the same compositions.