Ba0.5Sr0.5TiO3 Research Articles

Thickness-dependence of growth rate, dielectric response, and capacitance properties in Ba0.67Sr0.33TiO3/LaNiO3 hetero-structure thin films for film capacitor applications

This work reports the structure, growth rate, dielectric response, and capacitance properties of (100)-oriented Ba0.67Sr0.33TiO3 (BST)/LaNiO3 (LNO) hetero-structure thin films with varied BST layer thicknesses from 34 nm to 342 nm. The BST/LNO hetero-structure thin films were prepared by radiofrequency magnetron sputtering technique on Pt/SiO2/Si substrates. The XRD results showed that the compressive stress is relaxed at around 73 nm of BST layer, and above 119 nm of the BST layer thickness, the tensile stress has a significant effect on the crystal structure of the BST/LNO hetero-structure film. The growth rate of the BST films was thickness-dependent which was strongly related to the minimization of the strain energy. The dielectric constant of BST layer with the compressive stress increase from 177 to 2640 with the increase of BST layer thickness. The BST layer with the tensile stress showed a comparably stable dielectric constant of 2400. In addition, the capacitance properties and the electrical breakdown strength of BST/LNO hetero-structure thin films are also thickness-dependent, respectively. The electrical breakdown strength reached a maximum value of 1237 kV/cm in the BST/LNO hetero-structure thin film with ~73 nm BST layer.

Enhanced properties of SPEEK with incorporating of PFSA and barium strontium titanate nanoparticles for application in DMFCs

Novel blend nanocomposite proton-exchange membranes were prepared using sulfonated poly (ether ether ketone) (SPEEK), perfluorosulfonic acid (PFSA), and Ba0.9Sr0.1TiO3 (BST) doped-perovskite nanoparticles. The membranes were evaluated by attenuated total reflection, X-ray diffraction spectroscopy, water uptake, proton conductivity, methanol permeability, and direct methanol fuel cell test. The effect of two additives, PFSA and BST, were investigated. Results indicated that both proton conductivity and methanol barrier of the blend nanocomposite membranes improved compared with pristine SPEEK and the as-prepared blend membranes. The methanol permeability and the proton conductivity of the blend membrane containing 6 wt% BST obtained 3.56 × 10−7 cm2 s−1 (at 25 °C) and 0.110 S cm−1 (at 80 °C), respectively. The power density value for the optimum blend nanocomposite membrane (15 wt% PFSA and 6 wt% BST) (54.89 mW cm-2) was higher than that of pristine SPEEK (31.34 mW cm-2) and SPF15 blend membrane (36.12 mW cm-2).

Dielectric, ferroelectric and energy storage properties of lead-free (1-x)Ba0.9Sr0.1TiO3-xBi(Zn0.5Zr0.5)O3 ferroelectric ceramics sintered at lower temperature

Abstract Recently, ferroelectric ceramics with high maximum polarization, low remnant polarization and high electric breakdown strength (BDS) have attracted much attention due to their potential applications in energy storage capacitors. In this work, we show a novel kind of (Ba,Sr)TiO3 (BST)-based lead-free ferroelectric ceramics, i.e., (1-x)Ba0.9Sr0.1TiO3-xBi(Zn0.5Zr0.5)O3 (BST-xBZZ) solid solutions, which were fabricated by the traditional solid-state reaction process. By introducing the BZZ into BST with a content from 0.05 to 0.20, purely pseudocubic perovskite phases and highly dense structures are obtained. The increase of the BZZ content not only shifts the TC toward to lower temperature, but also induces strong relaxor behaviors with diffuse phase transition characteristics, thus improving the temperature stability of dielectric properties. Of special interest is the improved energy storage properties, which were systematically evaluated by measuring the polarization-electric field (P-E) hysteresis loops as a function of electric field, frequency and loading cycle. It is found that BT-0.15BZZ ceramic achieves a maximum energy density of 1.11 J/cm3, which is attributed to the improvement of BDS. In addition, relatively good frequency stability and fatigue resistance of this composition suggest its potential application in energy storage devices.

The microstructure and energy storage properties of Ba0.3Sr0.7TiO3 crystallite thin films

Energy storage capacitors have gained much attention for their potential energy storage applications in pulse power system. In this paper, Ba0.3Sr0.7TiO3 (BST) crystallite thin films were prepared on Pt/Ti/SiO2/Si(100) substrates using a sol-gel method at different annealing temperatures from 650 to 850 °C. The films have a crystallite structure, in which amorphous phase forms a three-dimensional network structure and BST tiny grains are wrapped in it. The effects of annealing temperature on the phase structure, morphology, energy storage and dielectric properties of BST microcrystalline films were investigated. The grain size and the crystallinity increased with the increase of annealing temperature, and both pores and defects were produced on the surface when temperature reaches up to 750 °C. When annealing temperature increases, the breakdown strength and energy storage density increased initially, followed by an decrease. The optimal energy storage performance was achieved in the sample with the energy storage density of 31.6 J/cm3 at 3.0 M V/cm, while annealing at 700 °C. Moreover, the sample also exhibited a moderate dielectric constant (60) and a low dielectric loss (0.001).

Investigation of electrical, magneto-dielectric and transport properties of multiferroic (1 − x) BiFeO3–(x) BaSr0.7Ti0.3O3 solid solutions

To date, many efforts are underway on single-phase multiferroic material to obtain a compound with strong magneto-dielectric coupling, improved dielectric properties and insulation behavior for their practical applications. In this work, high-quality powders of the (1 − x)BiFeO3(BFO)–(x)Ba0.7Sr0.3TiO3(BST) solid solutions were obtained by simple sol–gel assisted route. A detailed study on the interplay between the dielectric, magneto-dielectric and transport properties in ceramic samples is presented. Dielectric analysis reveals anomalies in the proximity of Neel temperature, indicating small magneto-electric coupling, which was confirmed through capacitance versus magnetic field measurements. Analysis of dc electrical response indicates no signature of Poole Frenkel (PF) and Schottky emission (SE) mechanism, but a dominating space charge-limited conduction (SLCS) mechanism was found in the studied samples. It is demonstrated a significant decrease of the current density with the increase of the BST concentration, suppressing the oxygen vacancies presence leading to an oxidation states stabilization of the Fe ions with doping. The results of the ac conductivity analysis suggest a small-polarons hopping mechanism at low-temperature region followed by ionized oxygen vacancies transport in the high-temperature region.

Impact mechanism of gel’s alkali circumstance on the morphologies and electrical properties of Ba0.80Sr0.20TiO3 ceramics

Ba0.8Sr0.2TiO3 (BST) nanopowder was successfully synthesized by Pechini sol-gel method under different temperatures. Not only were BaCO3 impurity phase production and transition temperature from cubic to tetragonal phase respectively set at 440 °C and 800 °C, but also barium (Ba) resided in a 12-coordinate site of crystal lattice was set at 580 °C by the techniques of X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FT-IR). In addition, gels at pH 3–8 were used to prepare BST ceramics and the ceramics morphology was characterized by scanning electron microscope (SEM). The interrelationship between morphology and electrical properties, which were associated with precipitation phase on the crystal boundary of BST ceramics, was studied in detail. Finally, the optimal electrical properties of the ceramics were comprehensively displayed in this work, i.e., er = 8113.81, d33 = 78 pC/N, kp = 14.96%, and Qm = 85.08 at pH 5.

BST-P(VDF-CTFE) nanocomposite films with high dielectric constant, low dielectric loss, and high energy-storage density

Free-standing, flexible, and transparent ceramic-polymer nanocomposite films with a uniform thickness of about 5 μm were fabricated using a simple spin-coating process, in which the polymer solution with a high concentration was used. Ba0.5Sr0.5TiO3 (BST) nanoparticles and P(VDF-CTFE) 91/9 mol.% (VC91) copolymer were used as ceramic filler and polymer matrix, respectively. Microstructures, dielectric properties, and energy-storage performances of the BST-VC91 nanocomposite films have been investigated. With increasing volume fraction of BST, the dielectric constant increases, while the dielectric loss decreases. A dielectric constant of about 38.4 at 100 Hz associated with a dielectric loss of only about 0.02 was obtained in the nanocomposite film with 40 vol% of BST. It is experimentally found that the temperature dependences and the frequency dispersions of dielectric properties were strongly influenced by the volume fraction of BST, especially at high temperatures. Good temperature stability and small frequency dispersion of dielectric constant can be obtained in the BST-VC91 nanocomposite films with 40 vol% and 50 vol% of BST, which are also associated with a low dielectric loss. It is concluded that the motion of the polymer chains is the micro-origin of the relaxation process observed at high temperatures. With increasing volume fraction of BST, the dielectric breakdown strength decreases, while the maximal polarization and remnant polarization increase. The maximal charge-energy density and discharge-energy density of about 21.7 J/cm3 and 7.5 J/cm3 are obtained in the BST-VC91 nanocomposite film with 30 vol% BST under 2500 kV/cm, which are more than 2 times larger than those observed in pure VC91 film under the same electric field.

Investigation of structural and optical properties of oblique angle sputter deposited barium strontium titanate nanostructures

Oblique angle sputtered Ba0.5Sr0.5TiO3 (BST) nanotextured films were characterized with attention to their optical and structural properties. The optical band gap values included a low value of 2.82 eV for the sample sputtered at 75˚ oblique angle and a high value of 3.65 eV for the sample sputtered at 0˚. Refractive index at the wavelength of 400 nm increased from 1.377 to 2.320 with increasing oblique angle. X-ray diffraction studies revealed polycrystalline nature of deposited films exhibiting perovskite structure. Williamson-Hall analysis showed that the average crystallite sizes increased with increasing oblique angle for the samples deposited using collimator in deposition process. Atomic force microscopy showed that the surface roughness increased from 0.143 nm to 3.143 nm by increasing oblique angle. The dependence of optical band gap, refractive index, thickness, roughness, crystallite size, strain, and surface morphology on oblique angle was investigated.

Electrical Photoconductivity of Ta2O5 Doped Based on Ba0,5S0,5TiO3 Thin Film

Ba0,5Sr0,5TiO3 (BST) thin films were deposited on Si (100) p-type substrates using a chemical solution deposition (CSD) methode and doped with 0%, 2.5%, 5%, 7.5%, 10% tantalum pentaoxide (Ta2O5). Chemical Solution Deposition Methode (CSD) used the spin coating techniques with a rotational speed of 3000 rpm for 30 seconds. BST thin films annealed at a temperature 850 oC, then characterized by, LCR meter for electrical conductivity characterization. The result shows that electrical conductivity and dielectric constant value of BST and Ta2O5 doped based on BST (BSTT) thin films are in the range semiconductor materials. The electrical conductivity values obtained increased when the higher intensity light is used whereas resistance value could decrease if the light intensity is increased. Dielectric values obtained in the range from 7.29 to 16.11. The addition of tantalum pentaoxide dopant will increases electrical conductivity value of BST thin films. Electrical conductivity data show that BST thin films have shown the characteristic of the photoconductivity.

Ba0.6Sr0.4TiO3 Thin Films Deposited by Spray Coating for High Capacitance Density Capacitors

Metal‐insulator‐metal (MIM) capacitors with Ba0.6Sr0.4TiO3 (BST) thin films as insulating layers are fabricated using a novel, fast, and low‐cost method. On one hand, the process lies in the swift, continuous, and scalable synthesis of BST nanoparticles using the supercritical fluid technology and, on the other hand, the nonpyrolytic spray coating of thin films using colloidal nanocrystals as ink. The authors focus on the deposition process of thin and uniform layer. A dispersed colloidal suspension based on BST nanoparticles is deposited on a hot copper substrate. A 200 nm thick dielectric film is successfully obtained. Electrical characterizations of Cu/BST/Al MIM structure demonstrate a state‐of‐the‐art capacitance density almost reaching 1 µF cm−2 within an operating voltage range of ±1 V. Moreover, an annealing process of the dielectric layer and the final MIM capacitor at 90 °C during 15 h brings a significant decrease of the leakage current by three decades from mA cm−2 to µA cm−2.

Analysis of saturation currents and barrier height of Ta2O5 doped based on Ba0,5S0,5TiO3 photodiode

Ba0,5Sr0,5TiO3 (BST) thin films have been prepared on Si (100) p-type substrates using a chemical solution deposition (CSD) method and doped with 0%, 2.5%, 5%, 7.5%, 10% tantalum pentaoxide (Ta2O5). Chemical Solution Deposition Method (CSD) used the spin coating techniques with a rotational speed of 3000 rpm for 30 seconds. BST thin films annealed at a temperature 850 °C. Various electrical parameters such as saturation current, series resistance and barrier height have been calculated from the analysis of experimental I–V results and discussed in detail. The series resistance was found from the experiment of 42.8 MΩ, 7.9 MΩ, 7.2 MΩ, 2.03 MΩ, 1.2 MΩ for variation doping content. The saturation current of 22.3 μA, 2.7 μA, 9.7 μA, 4.82 μA, 4.50 μA was obtained in BST thin film with variation doping content. Then, the barrier height of 0.56 eV, 0.62 eV, 0.58 eV, 0.54 eV, 0.60 eV was obtained in BST thin film with variation doping content. The optical characterization and analysis microstructure such as XRD, EDX were discussed in detail.

Existence of internal domains in (Bi0.5La0.5FeO3)(1-x)–(Ba0.7Sr0.3TiO3)x solid solution and their effects on magnetic and dielectric behaviour

A significant experimental effort has been undertaken to evaluate the doping effect of La3+at Bi-site in solid solutions of BiFeO3 (BFO) and Ba0.7Sr0.3TiO3 (BST) through various techniques like x-ray diffraction, magnetic measurements, and frequency and/or temperature dependent impedance spectroscopy. The magnetic isotherm at room temperature in La doped BFO (BLFO)-BST solid solution indicates weak ferromagnetism due to improvement in the homogeneous canted spin structure. The elusive nano-sized domain structure inside the grains of 40% BST co-doped BLFO was observed by a scanning electron microscopy technique. The domains and domain boundaries are generally formed inside the grain due to strained/unstrained lattice defects and/or mismatch with the substitution of ions of different sizes at the A and B sites. An equivalent circuit model (internal barrier layer capacitor), based on domain, domain boundary, and grain boundary relaxations, has been established to justify the enhancement of the dielectric response with BST concentrations.

Enhanced Piezocatalytic Performance of (Ba,Sr)TiO3 Nanowires to Degrade Organic Pollutants

The discovery of piezocatalysts opens up a new route to wastewater decontamination. The piezoelectricity of barium titanate nanocrystals induced by ultrasonic vibration was found effective to degrade organic pollutants. In the present work, the products of (Ba,Sr)TiO3 (BST) nanocrystals with different morphologies including nanowires (NWs), nanoparticles (NPs) and their composite were synthesized by a template hydrothermal method. And, the piezocatalytic behavior of them was thoroughly investigated with respect to a possible influence of lowered phase transition temperature on the piezocatalytic behavior. It was found that the elongated BST nanowires were more effective in degrading dye pollutants in comparison with the pure BaTiO3 nanowires and BST nanoparticles, which makes the BST nanowires a better candidate as piezocatalyst. The catalytic nature of the stress induced dye degradation was confirmed by the detection of free radicals and intermediate products during the degradation process. The improveme...

Real time in situ x-ray diffraction study of the crystalline structure modification of Ba0.5Sr0.5TiO3 during the post-annealing

We report about an in situ study of crystalline structural changes during thermal treatment of a Ba0.5Sr0.5TiO3 (BSTO) film grown on MgO. The study covers the complete cycle of heating, annealing and cooling and reveals simultaneous phenomena of phase transitions and strain evolution, which have been characterized by in situ 2D reciprocal space mapping (2D-RSM) using high-resolution synchrotron x-ray diffraction in coplanar and grazing incidence geometries. In this way, temperature induced phase transformation from the BSTO2 to the BSTO1 phase has been monitored and the appearance of a further crystalline phase was detected. Moreover, for both BSTO phases, transitions between in-plane compressive and tensile states have been determined during thermal treatment. Furthermore, a contraction of the out-of-plane lattice components has been observed during the annealing phase while the in-plane lattice components remain leading to the change of the residual in-plane strain towards tensile state. The in situ 2D-RSM findings provide valuable and versatile insights into strain engineering and structure modification upon thermal treatment.

Fine-grained silica-coated barium strontium titanate ceramics with high energy storage

The fine-grained silica-coated Ba0.3Sr0.7TiO3 (BST) ceramics were prepared by conventional solid-phase sintering method, the size of matrix materials which were produced by oxalate co-prepared method is about 100 nm. With the increase of the content silica, the grain size of ceramic dropped from 2 µm (pure BST) to 300 nm (Ba0.3Sr0.7TiO3-3 wt% SiO2) and the polarization of ceramic decreased under the same applied electric field, but the energy storage efficiency increased significantly. At the same time, the dielectric breakdown strength (BDS) increased significantly with the decrease of grain size and the addition of SiO2. For Ba0.3Sr0.7TiO3-3 wt% SiO2 ceramic, due to the small grain size, the BDS increased from 130 kV/cm to 380 kV/cm, its discharge energy storage density is 1.52 J/cm3 while the energy storage efficiency reaches 82.2%. The discharge energy density of the Ba0.3Sr0.7TiO3-3 wt% SiO2 ceramic increased to 3.3 times than that of pure Ba0.3Sr0.7TiO3 ceramic.

Tunable metamaterial device for THz applications based on BaSrTiO3 thin film

Design, fabrication and characterization of an active single-negative metamaterial device in the terahertz (THz) spectrum is presented. The device is constructed by vertical split-ring unit cells which incorporate a Ba0.6Sr0.4TiO3 (BST) thin film whose dielectric constant can be altered by applying DC bias to change the capacitance of the split-ring resonators. A numerical model of the device that predicts a resonant frequency as a function of BST dielectric constant is presented. The resonant frequency shift due to the applied DC bias is experimentally verified and correlated with the model. The resonant frequency shift occurs as a direct result of the bias controlled index of refraction change in BST which significantly enhances the device response speed and durability compared with previously demonstrated micro-electro-mechanical systems based tunable metamaterial devices. In addition, this device can be used to characterize dielectric properties of the tunable oxide thin films in low THz spectrum (such as tunability) for many applications.

Strong impact of SrTiO3/TiO2 buffer layer on epitaxial growth and dielectric response of Ba0.7Sr0.3TiO3 thin films on MgO

We demonstrate a significant improvement in the epitaxial growth of perovskite dielectric films on MgO by introducing a SrTiO3 (STO)/TiO2 buffer layer, which enhances their dielectric response. 270-nm-thick (001)-epitaxial (Ba,Sr)TiO3 (BST) films were deposited by pulsed laser deposition on STO/TiO2-buffered MgO with a SrRuO3 (SRO) bottom electrode. The film directly deposited on SRO/MgO grew in a three-dimensional mode, resulting in a rough and poorly crystalline film with an almost relaxed strain. On the other hand, the film with a buffer layer grew in a two-dimensional mode, resulting in a flat and highly crystalline film with a large compressive strain (−0.80%). As a result, the paraelectric-to-ferroelectric phase transition temperature increased by 220 °C and an out-of-plane dielectric constant exceeding 1000 was achieved.

CaBi4Ti4O15-based lead-free sol–gel composites for high-temperature application

CaBi4Ti4O15 (CBiT)-based lead-free sol–gel composites were developed for high-temperature ultrasonic transducer application. In this study, two types of lead-free sol–gel solution, Ba0.7Sr0.3TiO3 (BST) and Bi4Ti3O12 (BiT), were used for consistency to fabricate ∼50-µm-thick CBiT/BST and CBiT/BiT films on 3-mm-thick titanium substrates by a sol–gel spray technique. BST and BiT were chosen because of their high dielectric constant and high Curie temperature, respectively, in addition to their being lead-free materials. A thermal cycle test was carried out between RT and 600 °C, and clear multiple echoes were confirmed during three thermal cycles for both materials. In addition, the sensitivity of CBiT/BiT was higher than that of CBiT/BST although a higher poling temperature is required for CBiT/BiT. Therefore, an ultrasonic transducer potential for high-temperature application was successfully demonstrated.

Effect of post-annealing on the chemical state and crystalline structure of PLD Ba0.5Sr0.5TiO3 films analyzed by combined synchrotron X-ray diffraction and X-ray photoelectron spectroscopy

A Ba0.5Sr0.5TiO3 (BSTO) thin film was grown on a MgO (100) substrate by pulsed laser deposition. The interrelation between the results derived from X-ray photoelectron spectroscopy (XPS) and 2D-reciprocal space maps (2D RSMs) recorded in high resolution diffraction produce complementary information about the chemical state and about the crystalline structure. Both methods confirm the presence of two BSTO1 and BSTO2 phases in the as-deposited and in the post-annealed states, having two chemical environments, two out-of-plane lattice parameters c1 and c2 and two tetragonal distortion ratios D1 and D2. Using the advantages of a combined study, the BSTO1 phase corresponds to the perovskite phase while the BSTO2 phase belongs to a BSTO phase having high tetragonal distortion with respect to the perovskite BSTO1 phase.The post-annealing has induced a transformation from BSTO1 phase to the BSTO2 phase in the surface layer and in the bulk of the BSTO film in addition to the appearance of a further crystalline phase corresponding to a third chemical state. This represents an important and a novel finding in the understanding of the influence of the post-thermal treatment on the structure and the chemical states of the BSTO film which could be accordingly monitored by XRD and XPS. In fact, upon post-annealing, a proportion of BSTO1 perovskite phase decreases while a strained BSTO2 phase increases and a newly formed BaTiO3-like phase appears.

Strong pyro-electro-chemical coupling of Ba0.7Sr0.3TiO3@Ag pyroelectric nanoparticles for room-temperature pyrocatalysis

In this work, a strong pyro-electro-chemical coupling effect of the sol-gel-synthesized Ba0.7Sr0.3TiO3 (BST) pyroelectric nanoparticles was discovered and its application for room-temperature pyrocatalytic dye decomposition was also developed. Through harvesting 25–50 °C cold-hot alternation energy, BST nanoparticles can obviously decompose Rhodanmine B dye with a decomposition efficiency of 90%. The pyro-electro-chemical coupling is on basis of product of the pyroelectric effect and the electrochemical effect, which can be proved by the observed intermediate reaction products of superoxide radicals (•O2-) and hydroxyl radicals (•OH). The enhanced pyrocatalytic activity of pyroelectric BST@Ag (1.5 wt%) nanoparticles is obtained with a decomposition efficiency of 99% for Rhodanmine B dye, which may be due to the coating silver on BST surface impeding the recombination of pyroelectrically-induced positive and negative electric charges. The strong pyro-electro-chemical performance makes the pyroelectric BST@Ag nanoparticles potential in wastewater decomposition through utilizing cold-hot fluctuation thermal energy.