Ba0.5Sr0.5TiO3 Research Articles

Resonant spectrum method for characterizing Ba0.5Sr0.5TiO3 based high overtone bulk acoustic wave resonators

This letter reports the use of the resonant spectrum method to characterize a high overtone bulk acoustic wave resonator (HBAR) which has a thin film ferroelectric BaSrTiO3 (BSTO) active layer on a YAG substrate. The HBAR works on the principle of electric field induced piezoelectricity of the thin film ferroelectric BSTO and exhibits switching functionality. From the parallel and series resonant frequencies of each of the multiple peaks in the frequency spectrum of the HBAR, the distribution of spacing of parallel resonance frequency and the distribution of effective coupling coefficient are studied and parameters like acoustic wave velocity, electromechanical coupling coefficient, elastic constant, and density for the thin film are determined. The influence of dc bias voltages on the distribution of the effective coupling coefficient and the electromechanical coupling coefficient is also reported. This letter also establishes the relationship between the relative tunability of the device capacitance and the electromechanical coupling coefficient.

Effect of coupling agents on the dielectric properties and energy storage of Ba0.5Sr0.5TiO3/P(VDF-CTFE) nanocomposites

Dielectric materials with high electric energy density and low dielectric loss are critical for electric applications in modern electronic and electrical power systems. To obtain desirable dielectric properties and energy storage, nanocomposites using Ba0.5Sr0.5TiO3 (BST) as the filler and poly(vinylidene fluoride-chlorotrifluoroethylene) as the matrix material are prepared with a uniform microstructure by using a newly developed process that combines the bridge-linked action of a coupling agent, solution casting, and a hot-pressing method. When a proper amount of coupling agent is used to modify the surface of the nanoparticles, the composite exhibits a higher dielectric constant and a more uniform microstructure. A dielectric constant of 95, dielectric loss of 0.25, and energy density of 2.7 J/cm3 is obtained in the nanocomposite with 30 vol.% of BST and 15 wt.% of coupling agent. The results suggest that the energy storage ability of the composites could be improved by the surface modification of the fillers and from the interface compatibility between the fillers and the polymer matrix.

Effects of temperature and electric field on upconversion luminescence in Er3+‐Yb3+ codoped Ba0.8Sr0.2TiO3 ferroelectric ceramics

AbstractOptical and electrical properties of 1%Er3+ and different Yb3+ content (1ExY) codoped Ba0.8Sr0.2TiO3 (BST) ferroelectric ceramics fabricated by the solid‐phase reaction were investigated. Under 980 nm pump condition, two green emission bands at 525 and 549 nm wavelength corresponding to, 2H11/2→4I15/2 and 2S3/2→4I15/2 transitions, and two red emission bands at 655 and 668 nm wavelength attributed to 4F9/2→4I15/2 transition are observed. The temperature‐sensing behaviors, calculated by the intensity ratio I525/I549 suggested that, the maximum sensitivity of the green emission of the 1E8Y‐BST ceramics is 1.07×10−2 K‐1 at 293 K. Furthermore, the maximum sensitivity of 1E6Y‐BST and 1E11Y‐BST ceramics were obtained around the Curie temperature. The fluorescence lifetime of 1E8Y‐BST ceramics for 2H11/2 level and 2S3/2 level shortened with the increase in the temperatures. Moreover, the upconversion (UC) luminescence intensity of 1E8Y‐BST decreased with the increase in the external electric field and had a mutation at the coercive electric field (Ec) of about 1.24 kV/cm, which revealed that the electric field had influence on the UC luminescence.

Powder selection for hydrothermally processed sol–gel composite barium strontium titanate capacitors

Ba0.7Sr0.3TiO3 (BST) capacitors for high frequency circuits have been fabricated at 175 °C on epoxy‐based copper‐clad printed circuit boards, having a glass transition temperature of ∼200 °C by hydrothermal processing of dried BST acetate‐based sol–gel powder slurries. The film thickness was 2–10 μm. BST powders were prepared respectively as ceramic derived powders processed from oxide mixtures fired to 1100 °C, sol–gel derived powders fired to 750 and 1100 °C, and a low temperature solution process dried at 500 °C. The performance of the capacitor was determined by both the dielectric properties of the powder and the interaction between the crystallizing gel and the powder surface. High relative permittivity is obtained for sol–gel derived powders fired to 750 °C, while high voltage tunability is a characteristic of the ceramic derived powders. Low temperature powders are ineffective. The difference is attributed to the nature of the crystalline interface formed between the surface of the powder particles and the hydrothermally crystallized BST formed from the dried gel within the composite. The optimum molar concentration of the hydrothermal solution was 0.1 M with a Ba content larger than that of the powder. Capacitor composites having a relative permittivity of up to 300 at 20 MHz were demonstrated.

Enhanced energy storage performance of Ba 0.4 Sr 0.6 TiO 3 ceramics: Influence of sintering atmosphere

Abstract Ba0.4Sr0.6TiO3 (BST) powders were prepared by hydrothermal method, the ceramics were sintered in N2, air and O2 atmosphere respectively. The effect of sintering atmosphere on the microstructure, dielectric properties, and energy storage performance of BST ceramics were investigated. The grain size of the BST ceramics sintered in O2 atmosphere was reduced to 0.44 µm, indicating the grain growth was significantly inhibited with increasing oxygen partial pressure due to the lack of oxygen vacancy. Dielectric relaxation behavior was observed in the BST ceramics, and the degree of which was increased with increasing oxygen partial pressure. BST ceramics sintered in O2 atmosphere showed the largest critical breakdown strength of 16.72 kV/mm, at which the highest energy storage density of 1.081 J/cm3 and a moderate energy storage efficiency of (73.78%) were obtained. The dependence of energy-storage properties on applied field was also investigated, it was found that the energy storage density increased with increasing applied filed while the energy storage efficiency decreased with increasing applied filed.

Giant Enhancement of Polarization and Strong Improvement of Retention in Epitaxial Ba0.6Sr0.4TiO3‐Based Nanocomposites

In Ba0.6Sr0.4TiO3 (BSTO)‐based epitaxial nanocomposite films increased P r values are demonstrated by up to a factor of 3 compared to standard BSTO films. A strongly reduced temperature coefficient of polarization retention is also obtained, i.e., 0.07% °C−1 compared to 0.24% °C−1. Piezopoling with only marginal leakage current is also achieved up to 200 °C, the highest temperature studied. The origin of the improved performance is the incorporation of Sm2O3 nanopillars in the films which acted as stiff vertical nanoscaffolds, inducing a strong tetragonal distortion in the BSTO (up to 1.033(7) in terms of the out‐of‐plane/in‐plane lattice dimensions). The films have comparable performance to industry‐standard Pb(Zr,Ti)O3 films, at the same time as being Pb‐free.

Enhanced energy storage density of Ba0.4Sr0.6TiO3 ceramics with additive of Bi2O3-B2O3-ZnO glass

The Ba0.4Sr0.6TiO3 (BST) ceramics with Bi2O3-B2O3-ZnO (BBZ) glass additive were prepared by the solid state reaction route. Microstructural observation demonstrates that the average grain size reduces obviously with increasing glass additive. The dielectric constant decreases and the dielectric breakdown strength (BDS) increases as glass additive increases. The energy storage density of ceramics with 5wt% glass additive is 0.62J/cm3 attributed to the relatively high dielectric constant and BDS. These results indicate that this material is a promising candidate for energy storage capacitor devices.

Enhanced dielectric properties and suppressed leakage current density of PVDF composites flexible film through small loading of submicron Ba0.7Sr0.3TiO3 crystallites

Ba0.7Sr0.3TiO3 (BST) crystallites prepared by sol–gel technique are incorporated into poly(vinylidene fluoride) PVDF matrix by solution casting technique. Cuboid shape of crystallite has been confirmed by high resolution transmission electron microscopy. PVDF composite films exhibit high dielectric constant and very low leakage current density. The dielectric constant ~22 (at 1 kHz) has been obtained for composites containing 11 vol% of BST crystallite; which is ~3 times higher than the dielectric constant of the pure PVDF (~7.9). Moreover, the leakage current density with same loading of BST crystallite increased only by one order (i.e. 10−7Amp/cm2 for pure PVDF to 10−6Amp/cm2). The observed value of leakage current density is very small as compared to earlier reports. The dielectric loss was found to be 0.02–0.03 at 1 kHz, which is also very small. The improved dielectric behavior is attributed to the improved interface between PVDF and BST crystallite and, the suppressed leakage current density might be arising due to smaller conducting pathways at interface.

Effect of hot pressing temperature on dielectric and energy storage properties of Ba0.6Sr0.4TiO3/ poly(vinylidene fluoride) composites

0–3 Ba0.6Sr0.4TiO3 (BST) / poly(vinylidene fluoride) (PVDF) composites were prepared via tape casting and then followed by hot pressing (HP) method. The effect of HP temperature on the microstructure, dielectric properties and energy storage density of the composites were investigated. With the increase of HP temperatures, the dielectric constant increases, whereas the dielectric loss decreases first and then increases. The energy storage density increases first and then decreases. And the composites exhibit a high dielectric tunability (> 85.6 %) and flexibility. Furthermore, the composites display optimal dielectric properties when the HP temperature is 120 °C, the values of dielectric constant and loss are 42.19 and 0.034, respectively. Particularly, compared with the composites formed under HP at room temperature (RT) (1.23 J/cm3) and the pure PVDF matrix (2.8 J/cm3). The values of energy storage density of composites with HP at 120 °C (4.1 J/cm3) has been improved 3.33 times and 1.47 times, respectively. The composites with tunable microstructure and dielectric properties show good potential in supercapacitor and energy storage devices.

Elasticity study of textured barium strontium titanate thin films by X-ray diffraction and laser acoustic waves

Ba0.65Sr0.35TiO3 (BST) thin films of 300 nm were deposited on Pt(111)/TiO2/SiO2/Si(001) substrates by radio frequency magnetron sputtering. Two thin films with different (111) and (001) fiber textures were prepared. X-ray diffraction was applied to measure texture. The raw pole figure data were further processed using the MTEX quantitative texture analysis software for plotting pole figures and calculating elastic constants and Young’s modulus from the orientation distribution function (ODF) for each type of textured fiber. The calculated elastic constants were used in the theoretical studies of surface acoustics waves (SAW) propagating in two types of multilayered BST systems. Theoretical dispersion curves were plotted by the application of the ordinary differential equation (ODE) and the stiffness matrix methods (SMM). A laser acoustic waves (LAW) technique was applied to generate surface acoustic waves (SAW) propagating in the BST films, and from a recursive process, the effective Young’s modulus are determined for the two samples. These methods are used to extract and compare elastic properties of two types of BST films, and quantify the influence of texture on the direction-dependent Young’s modulus.

Fabrication and dielectric properties of Ba0.6Sr0.4TiO3 / acrylonitrile–butadiene–styrene resin composites

Ba0.6Sr0.4TiO3 (BST)/acrylonitrile–butadiene–styrene (ABS) composites were prepared via solution casting method. Effects of volume fraction of BST on microstructure and dielectric properties of composites were studied. Dielectric constants were simulated by Lichtenecker, Maxwell, Landzu–Lifishitz, and Yamada models. It was found that the permittivity of BST/ABS resin composites increases from 4.5 to 18 while loss tangent from 0.021 to 0.082 at 1 kHz with BST fillers increasing from 10 to 40 vol%. The permittivity value calculated by Yamada’s model matched well with the experimental results and the deviation was less than 2% with a shape factor (n) of 3.2. The dielectric tunability of the composites improved with increasing the amount of BST fillers. Dielectric properties of ABS resins were enhanced by increasing BST fillers due to the interface polarization mechanism. The development of BST/ABS dielectric functional composites broadens the range of candidate materials for 3D printed electronic devices.

Flexoelectric Induced Caloric Effect in Truncated Pyramid Shaped Ba0.67Sr0.33TiO3 Ferroelectric Material

Solid state refrigeration based on ferroelectric materials can potentially be competing in not-in-kind refrigeration technology. However, their functionality is currently limited to Curie temperatures. Through this article, authors have attempted to describe an unexplored component of the stress-driven caloric effect, obtainable beyond the Curie point. The phenomenon, termed as the flexocaloric effect (FCE), relies on inhomogeneous straining of the crystal lattice to induce polarization in centrosymmetric crystals (flexoelectricity). For this study, a truncated pyramid geometry was selected, and the dependence of sample height on caloric capacity was studied. A peak temperature change of 1.75 K (313 K) was estimated for Ba0.67Sr0.33TiO3 (BST) ceramics employing a truncated pyramid configuration.

Exchange bias in Ba0.4Sr0.6TiO3/La0.7Sr0.3MnO3 heterostructures

This work relates to the integration of the two-layer stack of the proposed multiferroic structure onto silicon substrates. Ba1-xSrxTiO3 is an excellent material for room-temperature voltage-tunable dielectric applications due to its high (ε=6000) dielectric constant. In this study we choose a composition of Ba0.4Sr0.6TiO3 (BST), which is cubic and paraelectric at 300K, and transforms to a ferroelectric tetragonal phase upon cooling through the Curie temperature (TC) at 200K. The main focus of the present work is to study what happens when BST is placed in contact with a room temperature ferromagnetic layer such as La0.7Sr0.3MnO3 (LSMO). In this study, the magnetic properties of a BST (200nm)/LSMO (63nm) heterostructure was compared to that of a single LSMO layer (63nm). Both films were deposited onto MgO/TiN buffered Si (100) using pulsed laser deposition (PLD) and a domain matching epitaxy (DME) paradigm. X-ray diffraction (XRD) measurements showed that these films were of single phase and epitaxial in nature, with an unrelaxed lattice strain of ∼0.2% that was predominately composed of thermal and defect-induced strain. The magnetic measurements showed that the Curie temperature (TC) of LSMO remained unchanged at 350K when the BST was in contact with the LSMO layer. Interestingly, at 4K both the coercive field (Hc) and the exchange bias (HEB) of the BST/LSMO heterostructure as compared to the lone LSMO film increased significantly from 400 to 800 Oe and from 155 to 305 Oe, respectively. These differences were found to disappear above 200 K, the ferroelectric TC of the BST over-layer. This strongly suggests that the observed changes in the magnetic behavior of the heterostructure was the result of stress and/or charge redistributions that resulted when the BST layer transformed from the cubic (paraelectric) to tetragonal (ferroelectric) phase at low temperature.

Bistable Capacitance Performance-Induced Ambipolar Charge Injected Based on Ba0.6Sr0.4TiO3 by an Inlaid Zr–Hf–O Layer for Novel Nonvolatile Memory Application

In this paper, we present a distinguished hysteresis behavior by a few nanometers inlaid Zr–Hf–O (ZHO) layer between the Ba0.6Sr0.4TiO3(BST) film and the metal Pt electrode. The capacitance–voltage curve shows an insignificant change in the range of 0.3–1 MHz. The excellent retention property showing the difference of high state and low state is estimated as about 23.0% and 12.5% after one year and ten years, which might be caused by the deeper trap in an interdiffusion layer. The possible mechanism is proposed that the BST/ZHO interface exists as an interdiffusion, which could create additional defects and ambipolar charge injection causing the hysteresis behavior due to a postdeposition annealing process. The device can be employed as a promising candidate for applying in novel nonvolatile memory device.

Influence of the vicinal surface on the anisotropic dielectric properties of highly epitaxial Ba0.7Sr0.3TiO3 thin films.

Epitaxial thin films of Ba0.7Sr0.3TiO3 (BST) were grown on the designed vicinal single-crystal LaAlO3 (001) substrates to systematically investigate the evolution of microstructures and in-plane dielectric properties of the as-grown films under the strains induced by surface step terraces. Anisotropic dielectric properties were observed, which can be attributed to different tetragonalities induced by vicinal LaAlO3 substrates with miscut orientations along the [100] and [110] directions with different miscut angles of 1.0°, 2.75° and 5.0°. A terrace geometric model with both compressive and tensile strained domains in the BST film was established, which is in good agreement with the experimental results. Our experimental studies not only shed new light on the heteroepitaxial growth mechanism, but also provide a promising platform for the design and integration of high performance device applications.

Preparation and dielectric properties of polyimide/Ba0.7Sr0.3TiO3 nanocomposite film

Ba0.7Sr0.3TiO3 (BST) nanoparticles were incorporated into polyimide (PI) matrix to obtain the nanocomposite films via solution casting method. The prepared BST/PI nanocomposite films were thoroughly characterized. X-ray diffraction measurements revealed that these films were amorphous in nature.They exhibited high thermal stability up to 519°C in nitrogen atmosphere with 5% weight loss, and high glass transition temperature up to 311°C. The nanocomposite films exhibited good mechanical properties. Dielectric constant of the film increases from 3.23 to 11.8 at 1 Hz frequency, as the BST content increases from 0 to 5 wt%, which is mainly due to the high dielectric constant of BST.

Porous (Ba,Sr)TiO3 ceramics for tailoring dielectric and tunability properties: Modelling and experiment

3D Finite Element Method simulations were employed in order to describe tunability properties in anisotropic porous paraelectric structures. The simulations predicted that properties of a ceramic can be tailored by using various levels of porosity. Porous Ba0.6Sr0.4TiO3 (BST) ceramics have been studied in order to investigate the influence of porosity on their functional properties. The BST ceramics with various porosity levels have been obtained by solid-state reaction. Lamellar graphite in different concentration of 10, 20 and 35 vol.%was added as sacrificial pore forming agent. The structural, microstructural, dielectric and tunability properties were investigated. By comparison with dense BST ceramic, porous samples present a fracture mode transformation from intragranular to an intergranular fracture and a decrease of grain size. Lower dielectric constants, low dielectric losses, but higher values of tunability than in the dense material were obtained in the porous BST structures as a result of local field inhomogeneity generated by the presence of air pores-ceramic interfaces.

Enhanced electrocaloric effect in Mn + Y co-doped BST ceramics near room temperature

Electrocaloric effect (ECE) of Ba0.67Sr0.33TiO3 (BST) and Mn+Y co-doped BST (BSTMY) ceramics prepared using citrate-nitrate combustion derived powders was investigated. The densification and dielectric strength can be improved by Mn+Y co-doping and citrate-nitrate combustion processes. The maximum electrocaloric temperature change (ΔT) in BSTMY is much larger than that in BST. Large ΔT of 2.63K and electrocaloric strength of 0.0239KcmkV−1 are obtained in BSTMY ceramic at room temperature.

Domain wall motions in BST ferroelectric thin films in the microwave frequency range

The existence of domain wall motion at microwave frequencies and its contribution to the ferroelectric complex permittivity is shown by evaluating the dielectric properties of BaSrTiO3 (BST) thin films as a function of the incident power. Even at low AC field amplitudes, the presence of the domain walls and the correlated motions (vibration and jumps) result in sensitivity of the dielectric properties to the incident field amplitude. Although the contribution of domain wall motion to the real part of the permittivity is not preponderant (less than 10%), it represents more than 50% of the material's global dielectric losses. This illustrates the importance to consider domain wall motion even in the microwave frequency region and the necessity to take into account the applied AC field amplitude (and thus the incident power) when characterizing ferroelectric materials. The present study has been realized on BST thin films, elaborated by pulsed laser deposition on MgO/Ir substrates.

Fabrication, characterisation and dielectric properties of KH550 modified BST/PVDF nanocomposites with high dielectric strength

Ba0.6Sr0.4TiO3 (BST)/poly(vinylidene fluoride) (PVDF) 0–3 nanocomposites with BST nanoparticle contents of 10–40 vol% were prepared by tape casting method. The BST nanoparticles with ∼60 nm crystal size and accurate atomic ratio were synthesised by sol–gel method. The effect of the BST nanoparticle contents on the microstructure and dielectric properties of BST/PVDF nanocomposites were investigated. The BST/PVDF nanocomposites system declares that feasibility of applying low contents nanoparticles to form a homogeneous distribution in polymer matrix, higher dense interface connectivity, thereby providing a significant improvement to the dielectric strength and energy storage density; meanwhile, the nanocomposites possess high dielectric tunability. In this study, the maximum dielectric strength ∼287.12 kV/mm and energy storage density ∼5.15 J/cm3 were obtained in 10 vol% BST/PVDF nanocomposites, respectively. Moreover, the nanocomposite possesses high dielectric tunability ∼62.6% at 58 kV/mm, which proposed the nanocomposites suitable for tunable microwave devices, supercapacitors and energy storage device applications at high-voltage environment.