Pure Barium Strontium Titanate Research Articles

Investigation of Barium Strontium Titanate (Ba0.95Sr0.05TiO3) synthesized via conventional solid-state reaction and co-precipitation route with diverse sintering temperatures

Barium Strontium Titanate (BST) includes ferroelectric material extensively studied due to its fascinating properties. Ba0.95Sr0.05TiO3 pellets have been prepared using two techniques of co-precipitation and solid-state reaction sintered at diverse temperatures of 900, 1000 ℃, 1100 ℃, and 1200 ℃ for 4 h. This study aimed to compare the two techniques based on the structural, microstructure, and electrical properties varied by sintering temperatures. The sample testing was performed using X-ray Diffraction (XRD), revealing that the coprecipitation needs a higher sintering temperature to obtain pure BST (1200 °C) compared to the solid-state route (1000 °C). The lattices and crystal sizes of both routes were not significantly different. The yields of the Scanning Electron Microscopy (SEM) characterization showed that both methods showed reduced porosity and larger grain size with increasing sintering temperature, but the co-precipitation produced higher density and less porosity than that of the solid-state technique. The hysteresis pattern was measured using Sawyer Tower, which resulted that the hysteresis loops of the precipitation were greater than the solid-state route in which the higher sintering temperature could broaden the loops. The effect of sintering temperature causes the dielectric constant to increase in both methods. Overall, the dielectric constant of all samples with the coprecipitation route is greater than the solid-state method. The highest dielectric constants for both routes are 589 (co-precipitation) and 216 (solid-state) at a frequency of 40 kHz and sintering temperature of 1200 °C. Thus, based on this study, co-precipitation is preferred to synthesize BST.

Microwave-Assisted Synthesized Gadolinium Doped Barium Strontium Titanate Nanostructures: Structural and Optical Properties for DSSC Applications

Gadolinium (Gd) doped barium strontium titanate (BST) was prepared using the microwave-assisted solid-state reaction method for dye sensitized solar cell (DSSC) applications. The optical properties and the structural analysis of the prepared samples reveal the optical band gap and the morphology. The XRD pattern of the annealed samples confirms the polycrystalline nature with the cubic crystal structure. When the dopant is added, the bandgap increases slightly from 3.11 to 3.27 eV. The J-V characteristics of DSSCs prepared with pure and doped BST were investigated. The efficiency of the DSSCs remained constant and there is a slight increase in the Jsc for highly doped samples under 1-sun illumination. Gadolinium doped barium strontium titanate shows variation in the J-V characteristics and could be a potential candidate for the solar photovoltaic applications.

Suppression of Acoustic Resonances in BST-Based Bulk-Ceramic Varactors by Addition of Magnesium Borate

This work presents a method for reducing acoustic resonances in ferroelectric barium strontium titanate (BST)-based bulk ceramic varactors, which are capable of operation in high-power matching circuits. Two versions of parallel-plate varactors are manufactured here: one with pure BST and one with 10 vol-% magnesium borate, Mg3B2O6 (MBO). Each varactor includes a 0.85-mm-thick ferroelectric layer. Acoustic resonances that are present in the pure BST varactor are strongly suppressed in the BST-MBO varactor and, hence, the Q-factor is increased over a wide frequency range by the addition of small amounts of a low-dielectric-constant (LDK) MBO. Although the tunability is reduced due to the presence of non-tunable MBO, the increased Q-factor extends the varactor’s availability for low-loss and high-power applications.

Effect of Sintering Temperature on the Physical Properties of Ba0.6Sr0.4TiO3 Prepared by Solid-State Reaction

Barium Strontium Titanate (BST) ceramic materials are widely used in electronic devices due to their stable operation at high temperatures, high tunability, low tangent loss, low DC leakage, and alterable curie temperatures. While pure BST materials are usually produced at high sintering temperatures (1250 °C), there are limited studies on the temperature and duration of the sintering process to produce pure BST, synthesised from micro or even nano-sized raw materials. This study aims to determine the effective sintering temperature for producing pure BST material using a mixture of raw materials with a mean particle size of 0.4 μm after milled for 58 hours. The BaCO3, SrCO3, and TiO2 materials as raw materials for Ba0.6Sr0.4TiO3 synthesis were milled for 58 hours to produce a homogeneous mixture with a mean particle size of 0.4 μm. Sintering was carried out in a temperature range of 500-1100 °C for 1 hour. This study investigates the impact of sintering temperature on the physical properties and the purity of Ba0.6Sr0.4TiO3 powder using the x-ray diffraction method. The results showed that the Ba0.6Sr0.4TiO3 phase was formed at a sintering temperature of 700 °C. Pure BST material was formed at the sintering temperature of 1000 °C with a crystallite size of 41 nm. Whereas at a higher sintering temperature (1100 °C), the pure BST material formed produced a larger crystallite, sized at 43 nm with cubic structure. The synthesis temperature and duration recorded in this research are lower than recorded in the BST material preparation using the solid-state method. The results of this study indicate that the sintering temperature greatly affects the purity, crystal system and crystallite size of the Ba0.6Sr0.4TiO3 material produced. The sintering temperature of 1100 °C produces Ba0.6Sr0.4TiO3 material with the best physical properties because it has a cubic-shaped crystal system and the largest crystal size.

Sandwich-type composite multilayer films of strontium titanate and barium strontium titanate and their controllable dielectric properties

It is a challenge to reduce the dielectric loss and increase the tunability of pure barium strontium titanate (BST) films for microwave tunable application because these two properties change simultaneously. Herein, a novel composite of strontium titanate (ST) and potassium-doped BST (KBST) has been designed as ST/KBST/ST sandwich-type film with various ST and KBST layers. X-ray diffraction patterns show that the film exhibits cubic perovskite polycrystalline structure composed of BST and ST phase, mainly grow along (110) crystal plane with average grain size of less than 20 nm and decreasing BST phase/ST phase ratio with increasing film thickness. Scanning electron microscope shows that no interfacial layer can be observed, indicating that ST and KBST are fully compounded. Low dielectric loss and high tunability at -10 – 10 V and stable and excellent dielectric properties at 1 GHz are achieved, meeting the needs of microwave tunable application at high frequency. The surface structures are also studied by other analysis methods, and ST/MgBST/ST sandwich-type film is compared.

Structural, thermal and optoelectrical properties of pure and gadolinium doped barium strontium titanate for DSSC applications

A conventional method was adopted to prepare pure barium strontium titanate (BST) and gadolinium (Gd) doped BST nano perovskite (BSGT). The present investigation focused on various properties of as pure BST and BSGT for energy conversion applications. Cubic structure with Pm3/m space group was noticed in the structural mode of BST and BSGT by X-Ray diffraction analysis. Numerous functional groups related to BST and BSGT were assigned from Fourier-transform infrared peaks. The optical bandgap energy of BST decreased with the inclusion of Gd3+, which was investigated by UV–Vis spectrum. Electrical responses of prepared nano perovskite samples were identified by electrochemical impedance spectroscopy (EIS). Therefore, the IV characteristics were deliberated to study the BST and BSGT as photoanode for DSSC applications.

LOWERING THE SINTERING TEMPERATURE OF BARIUM STRONTIUM TITANATE BULK CERAMICS BY BARIUM STRONTIUM TITANATE-GEL AND BaCu(B₂O₅)

In this paper the influence of barium strontium titanate (BST) xerogel as a sinter additive and BaCu(B$_{2}$O$_{5}$) (BCB) as a liquid phase sintering aid on the sintering behavior of BST bulk ceramics is investigated. BST as well as BCB powders were synthesized via a mixed oxide route and BST gel via a sol-gel process. Compared to pure BST bulk ceramics, BST gel reduces the sintering start (onset temperature) by up to 174°C and increases the density for a sintering temperature of 1200°C. By adding BCB to the BST powder the sintering was completed much faster and the onset temperatures were reduced by 281°C and 312°C for 1 mol. % and 2.5 mol. %, respectively. With 2.5 mol. % BCB, the highest density of 96 % (5.41 g∙cm$^{-3}$) was achieved at 950°C.

Preparation of Integrated Passive Microwave Devices Through Inkjet Printing

Barium strontium titanate (BST) is a promising material for passive tunable microwave devices such as phase shifters or tunable matching networks. This publication covers the preparation of BST thick-films for microwave applications through inkjet printing. Two barium strontium titanate (BST) inks were prepared, printed on alumina substrates and sintered at different temperatures. The first ink was prepared with pure BST and sintered between 1100°C and 1200°C. The second ink was prepared with a BST–ZnO–B2O3 composition and was suitable to reduce the sintering temperature down to 800°C. The microstructure of the thick-films reveals the evolution of grain growth with increasing sintering temperature in the thick-films. Furthermore, a reaction with the substrate was observed for both inks at high sintering temperatures. The microwave characterization of the thick-films shows that for the permittivity and the tunability of the films, the effect of grain growth and reaction with the substrate compete against each other. Hence, the optimal microwave properties were achieved at a transition temperature, where first additional phases could already be observed. Even though, the properties are poorer for lower sintering temperatures, the investigations show that the preparation of silver- or gold-based metal–insulator–metal (MIM) structures through inkjet printing is possible with this composition. This allows various new design concepts for partly or fully inkjet printed passive microwave devices. Furthermore, it gives the opportunity for a future integration of passive tunable microwave devices in a low temperature co-fired ceramic (LTCC) fabrication process.

UV–visible spectra of perovskite iron-doped Ba0.72Sr0.28TiO3

The ultraviolet–visible spectra of the pure barium strontium titanate (Ba0.72Sr0.28TiO3) and the Fe3+-doped Ba0.72Sr0.28TiO3 were measured. The pure barium strontium titanate exhibited an ultraviolet (UV) absorption effect. The addition of Fe2O3 resulted in an increase of absorption wavelength. This red-shift effect was very strong even though the amount of Fe3+ was very small. The similar phenomenon was also observed in pure BaTiO3 and Fe3+-doped BaTiO3. The UV-absorption behavior was discussed in terms of Fe3+ replacing Ti4+ in the titanate with perovskite structure.

Electrophoretic Deposition Ba<sub>0.65</sub>Sr<sub>0.35</sub>TiO<sub>3</sub> Thick Films for Tunable Microwave Devices

Pure barium strontium titanate (Ba0.65Sr0.35TiO3) and MnO2-modified barium strontium titanate (Ba0.65Sr0.35TiO3-MnO2) thick films were fabricated by electrophoretic deposition technique. The structures and morphologies of the films were analyzed. The dielectric measurements were conducted on metal-insulator-metal capacitors using platinum as the bottom electrodes and gold as the top electrodes. The dielectric constants and dissipation factors of Ba0.65Sr0.35TiO3 and Ba0.65Sr0.35TiO3-15wt% MnO2 thick films were measured at a frequency of 1 MHz. The tunabilities of 12.5% and 9.3% were obtained for Ba0.65Sr0.35TiO3 and Ba0.65Sr0.35TiO3-MnO2 thick films under an applied electric field of 15 kV/cm, respectively. The dielectric properties of the present thick films were suitable for tunable microwave device applications.

Synthesis and characterization of nanocrystalline barium strontium titanate powders prepared by citrate precursor method

Nanocrystalline and well dispersed barium strontium titanate (BST) powders were prepared by a novel and simple citrate precursor method. This method involved direct crystallization of a white precursor from a stable solution in the citric acid (CA)–ethylene glycol (EG)–tetrabutyl titanate–M 2+ (M = Ba, Sr) system under a specific pH value range. Subsequent heat treatment of the precursor at 850 °C led to a pure phase BST powder. TG/DTA was used to examine the decomposition behaviour of the precursor. The crystalline phase and morphology of the BST powders were investigated by XRD and TEM. It was found that the BST powders synthesized by citrate precursor process were more homogeneous and uniform than that obtained by the citrate gel method.

Pb 0.3 Sr 0.7 TiO 3 thin films for high-frequency phase shifter applications

Pb 0.3 Sr 0.7 TiO 3 ( PST 30 ) thin films were synthesized on platinized silicon (Pt∕Si) and lanthanum aluminate (LAO) substrates using chemical solution deposition technique. The films on LAO substrate were highly (100) oriented, whereas the films on Pt∕Si substrate were polycrystalline. The low dielectric loss in the PST30∕LAO films makes them attractive for fabricating tunable dielectric devices. An eight-element coupled microstrip phase shifter was fabricated on PST30∕LAO film and tested in the frequency range ∼15–17GHz. The maximum figure of merit (κ=phase shift per dB loss) of ∼56°∕dB was obtained for PST30 film, which was better than commonly observed value in pure barium strontium titanate films. This makes PST30 a potential candidate material for further investigations for microwave applications.

Model for interface formation and the resulting electrical properties for barium–strontium–titanate films on silicon

The interface formation between sputtered barium strontium titanate (BST) films and both Si and SiO2 substrate surfaces has been followed using real-time spectroscopic ellipsometry and the mass spectrometry of recoiled ions. In both substrates an intermixed interface layer was observed and subcutaneous Si oxidation occurred. A model for the interface formation is proposed in which the interface includes an SiO2 film on Si, and an intermixed film on which is pure BST. During the deposition of BST the interfaces films were observed to change in time. Electrical characterization of the resulting metal–BST interface capacitors indicates that those samples with SiO2 on the Si surface had the best electrical characteristics.

Barium strontium titanate powder obtained by polymeric precursor method

Pure barium strontium titanate powder, with Ba/Sr ratio of 80/20 was prepared by the polymeric precursor method (also called Pechini process). The powder was obtained after a calcination at 800 °C for 8 h and characterized by XRD, IR, BET and SEM. The requirements to avoid barium carbonate as a secondary phase are presented and discussed in detail.

Fabrication of SiO 2-doped Ba 0.85Sr 0.15TiO 3 glass–ceramic films and the measurement of their pyroelectric coefficient

SiO 2-doped Ba 0.85Sr 0.15TiO 3 (SBST) glass–ceramic (g–c) films with perovskite structure have been prepared on Pt/Ti/SiO 2/Si substrates by sol–gel technique. Differential thermal analysis (DTA), X-ray diffraction (XRD) and atomic force microscopy (AFM) are employed to analyze the synthesize process and microstructure of SBST g–c films. The ferroelectricity and crystallization behavior of SBST films are discussed. It is found that the starting synthesize temperature of SBST15 film is larger than that of pure barium strontium titanate (BST) film for about 60 °C. The grain sizes decrease and the ferroelectricity of SBST g–c films is degenerated, but their loss tangent and leakage current density decrease with increasing SiO 2 contents. The temperature coefficient of dielectric (TCD) and the pyroelectric coefficient γ of the films are measured. The results show that TCD and the pyroelectric coefficient γ of SBST5 film at 20–25 °C are, respectively, 4.6% °C −1 and 8.1×10 −8 C cm −2 K −1, which is about 2/3 value of the pure BST films. BST g–c film with 5 mol% SiO 2 dopant is hopeful to be the advanced candidate material for uncooled infrared focal plane arrays (UFPAs) applied at near room temperature.

Synthesis, characterization and dielectric properties of nanometer-sized barium strontium titanates prepared by the polymeric citrate precursor method

Barium strontium titanate (BST) powders of the formula Ba1 − xSrxTiO3 (0 ≤ x ≤ 1) have been prepared for the first time by the polymeric precursor route using citric acid and ethylene glycol. Pure BSTs were obtained at 500 °C. These oxides were found to have the cubic structure, which is retained even after heating at 800 °C. Detailed X-ray studies on samples sintered at 1100 °C show weak tetragonal distortion for BaTiO3, while the other BSTs retain their cubic structure. The particle size of the sintered oxides increases from 55 nm for BaTiO3 to 88 nm for SrTiO3, from X-ray line-broadening studies. The nano-sized grains are reasonably stable to sintering (the particle size for BaTiO3 changes from 25 nm at 500 °C to 55 nm at 1100 °C). The dielectric constant of the sintered oxides decreases from 510 for BaTiO3 (x = 0) to 190 for SrTiO3 (x = 1) at 100 kHz. The dielectric loss decreases from 0.05 for BaTiO3 to 0.001 for SrTiO3 at 100 kHz. No ferroelectric transition was observed in either the dielectric studies or by differential scanning calorimetry.

Dielectric properties of sol–gel-derived MgO:Ba0.5Sr0.5TiO3 thin-film composites

Alternate layer deposition of heterostructured magnesium oxide (MgO):barium strontium titanate (BST) thin films is demonstrated to be an approach to synthesize dielectric films with a higher figure of merit for microwave dielectric applications. The dielectric constant and the dielectric tunability are modified by MgO insertion. The dramatic reduction in the dielectric loss tangent effectively increased the figure of merit of the heterostructured thin films as compared to the pure BST films. The significant reduction in the dielectric loss tangent values has been attributed to the minute solid solubility of MgO in the BST lattice and the induced microstructural modifications induced by the MgO layers in thin films.

Porous Behavior and Dielectric Properties of Barium Strontium Titanate Synthesized by Sol−Gel Method in the Presence of Triethanolamine

This investigation presents a novel method of preparation of barium strontium titanate (BST) from [Ba(2,4-pentadionate)-Sr(2,4-pentadionate)-Ti(OC3H7)4-TEA-i-PrOH-water] system. Triethanolamine (TEA) was used as an additive, which prevents the precipitation of oxides from the alcoholic titanium isopropoxide solution in the presence of excess water. An increasing molar ratio of water from 4.5 to 6.5 did not show any precipitation in the precursor sols in the presence of triethanolamine. Thermal behavior of the xerogel was studied by thermal gravimetric analysis (TGA). X-ray diffraction (XRD) indicated that the pure BST phase was crystallized at 900 °C. Triethanolamine was observed to influence the porous behavior of the final powders. Pore diameter of the powder calcined at 900 °C, was increased from 0.013 μm to 0.080 μm when the molar ratio of triethanolamine increased from zero to four. Therefore, a porous powder of BST was obtained at a higher molar ratio of triethanolamine. Porous behavior was also studied with respect to water and heat treatment, and explained with the help of density measurements and scanning electron microscopy (SEM). A low dielectric constant was obtained for the highly porous BST as compared with the high value for dense material.

Computer Simulation of Direct-Current Field Dependence of the Dielectric Constant of Al2O3-Doped Barium Stronium Titanate in the Paraelectric State

Effects of a DC field on the real part of the relative dielectric constant of Al2O3-doped barium strontium titanate for application in phased array antennas have been studied. The real part of the relative dielectric constant of the specimens decreases when the applied DC field is increased. The tunability is about 24% for barium strontium titanate doped with 1 wt% Al2O3. Curve fitting only works well for pure barium strontium titanate. The real part of the relative dielectric constant of Al2O3-doped barium strontium titanate decreases rapidly before 1.0 kV/cm and slowly after 1.0 kV/cm when compared to the data obtained by curve fitting. This can be explained by the space charge polarization theory.