Ba0.5Sr0.5TiO3 Research Articles

The influence of the PZT buffer layer on electrophysical properties of MDM structures with the BST film

Films of the composition Ba0.8Sr0.2TiO3 (BST) were synthesized by the method of high-frequency (HF) sputtering on the buffer layer of a ferroelectric film of the composition PbZrxTi1-xO3 (PZT). Comparative results of electrophysical properties of three different metal--dielectric--metal (MDM)-structures are presented: Pt/BST/Ni, Pt/PZT/Ni, and Pt/PZT-BST/Ni. Keywords: metal--dielectric--metal structures, ferroelectric films of composition Ba0.8Sr0.2TiO3, a buffer layer, electrophysical properties.

Fabrication and Properties of Transparent BST Glass Ceramic Nanocomposites

The glass crystallization method was used to synthesize a nanocomposite material consisting of crystallites inside a glass-like matrix. In this study, we have studied the structural, optical, dielectric, and ferroelectric properties of crystals embedded in a glassy matrix. The melt quenching technique was used to prepare the Ba0.7Sr0.3TiO3 (BST) –Na2O–B2O3-SiO2 system. The heat treatment technique ranging between 650 and 800 °C were used to change the prepared glass to glass-ceramic samples. The presence of the amorphous phase and the crystalline precipitation phase in the amorphous matrix were showed in the X-ray diffraction patterns. The scanning electron microscope was used to study the morphology of the crystals. All glass-ceramic samples confirm the spherical-like nanocrystals structure. It was found that while the heat treatment temperature increased, the crystal size and crystallinity increased. The optical, dielectric, and ferroelectric properties of the synthesized samples depend upon their morphology and crystallinity.

Enhanced room-temperature electrocaloric effect in B and Mn modified Ba0.7Sr0.3TiO3 ceramics

Ba0.7Sr0.3TiO3 (BST) ceramic and Ba0.7Sr0.3TiO3 with 1 mol% B3+ ions and 0.5 mol% Mn2+ ions (BSTBM) ceramic are synthesized using citrate combustion technique. An enhanced electrocaloric effect has been reported in BSTBM ceramic. The addition of B3+ ions and Mn2+ ions lowers the sintering temperature of BST ceramic from 1275 °C to 1200 °C. The low temperature sintered BSTBM ceramics exhibit enhanced electrocaloric temperature change (△T = 1.92 K) accompany with large electrocaloric efficiency (△T/△E = 0.38 K m MV−1) under 50 kV/cm. The △T of BSTBM ceramic is eighty five percent higher than the value of BST ceramic.

Graphene/Ba0.7Sr0.3TiO3 heterostructure for uncooled infrared detectors

This paper proposes an uncooled infrared detector based on a heterostructure comprising Ba0.7Sr0.3TiO3 (BST) ceramic and graphene. The relationship between heterojunction current and ambient temperature was determined to further analyze the effect of BST phase transition on the graphene resistance. The current at 0.1 V increased by 0.3% and 4% as the temperature was increased to 27 and 31 °C, respectively. Thus, the rate of change within the phase transition temperature range was 0.9%/°C. These insights serve as a foundation for the development of graphene/ferroelectric heterostructures for application in uncooled infrared detectors.

A comparative study of microstructural, biological, and mechanical properties in 20H-80B and 20H-80S composite scaffolds

This article reports the fabrication, microstructural analysis, mechanical and biological properties of scaffolds synthesized from composites containing 20 At. % Ca10(PO4)6(OH)2 (HAP) and 80 At. % SrTiO3 (ST) (20H-80S), and 20 At. % Ca10(PO4)6(OH)2 and 80 At.% Ba0.5Sr0.5TiO3 (BST) (20H-80B). The microstructural analysis reveals the presence of reflections from both the monoliths along with smaller sized grain in 20H-80S (92.2 ± 4.5 nm). This resulted in improved mechanical strength compared to 20H-80B, which has a higher grain size (110.3 ± 5.1 nm) and higher porosity along with the biomineralization capacity of 20H-80B (Ca/P-1.64) which is found higher compared to 20H-80S (Ca/P-1.52). The higher porosity also reflected in high protein adsorption on 20H-80B. The scaffolds' cytocompatibility revealed the cell viability >90%, rendering the scaffolds suitable for bone tissue engineering applications.

Improvement of magnetoelectric coupling effect in Ba0.8Sr0.2TiO3-Co0.5Cu0.5Fe2O4 multiferroic fluids by tuning the composition

Ba0.8Sr0.2TiO3 (BST) and Cu0.5Co0.5Fe2O4 (CCFO) nanopowders were prepared by hydrothermal method and chemical coprecipitation, respectively. Barium strontium titanate nanopowder–nano mixed oxides containing copper, cobalt, and iron (BST-CCFO) multiferroic fluids with different mass ratios (mBST/mCCFO = 1:2, 1:1, and 2:1) were prepared by using dimethyl silicone oil and silane coupling agent. Effect of mass ratio on the magnetoelectric performance was comparatively investigated. X-ray diffraction (XRD) showed that the BST and CCFO powders had no secondary phases, which are tetragonal perovskite structure and cubic spinel structure, respectively. Scanning electron microscopy (SEM) showed that the average grain size of BST and CCFO was 26.34 nm and 26.82 nm, respectively. The agglomeration of BST nanopowder was serious. Under the external magnetic field, the BST-CCFO multiferroic fluid will form a chain structure due to the directional movement of magnetic particles, thus enhancing the dielectric properties and ferroelectric properties of multiferroic fluid. The chain structure under the action of magnetic field will change the motion of ferroelectric particles, so that the magnetoelectric coupling effect of multiferroic fluid is significantly enhanced, which is much higher than that of the same type of magnetoelectric composite ceramics. This study is expected to provide a new way to improve the magnetoelectric coupling effect of multiferroic materials.

Application Of Ba0.5Sr0.5TiO3 (Bst) Film Doped With RuO2 (0%, 2%, 4% and 6%) On A Rice-Stalk Cutting Robot Model Based On A Line Follower With Hc-05 Bluetooth Control

Ba0.5Sr0.5TiO3 (BST) film doped with RuO2 with varying concentrations (0%, 2%, 4%, and 6%) on a p-type (100) silicon substrate has been successfully grown using the Chemical Solution Deposition (CSD) method and spin coating at a rotational speed of 3000 rpm for 30 seconds. The film on the substrate was then heated at 850 oC for 15 hours. BST film+RuO2 variations were characterized for their sensitivity as a light sensor. BST film+RuO2 variations were tested with a varied light source and reflective surface colors. Thin films have a range at the visible light wavelength, so LED lights were used as the light source in the present study. The light source selected was the blue LED because it had a high contrast in differentiating between dark and light-colored surfaces. Various electronic circuits assisted sensitivity characterization with the aim to produce a sensor that is highly sensitive to light. The response of BST film+ RuO2 variations differed according to the RuO2 doping concentration. BST film doped with RuO2 6% had a very good response to changes in light, so this film was applied as the line detector sensor in the line follower-based rice-stalk cutter model with an HC-05 Bluetooth control. Before being integrated with the microcontroller, the output voltage of the BST film was strengthened using an op-amp circuit so that the microcontroller could read the output voltage of the BST film.

Unraveling the relationship between bulk structure and exposed surfaces and its effect on the electronic structure and photoluminescent properties of Ba0.5Sr0.5TiO3: A joint experimental and theoretical approach

In this paper, we conducted a combined experimental and theoretical investigation of bulk and (001) surface properties of a Ba0.5Sr0.5TiO3 (BST) material synthesized by the polymeric precursor method. Characterization techniques, such as X-ray diffraction (XRD), Raman spectroscopy, ultraviolet-visible diffuse reflectance spectroscopy, field-emission scanning electron microscopy (FE-SEM) and photoluminescence (PL), were employed to disclose the structural, electronic, and optical properties of BST. Structural analysis confirmed the BST tetragonal symmetry, showing the relevant fingerprints of structural distortions, while the crystallographic morphologies were observed in the FE-SEM images. The theoretical results evidenced the structural disorder along the tetragonal BST phase, corroborating the central role of the bonding environment in the electronic and PL properties of the material. Moreover, the (001) surface results indicated that Esurf values depend on the chemical environment of exposed surfaces following the bonding character along with A-O and Ti-O paths, which also affects the electronic structure of surface-oriented BST.

Core-Shell Structure and Dielectric Properties of Ba0.6Sr0.4TiO3@ Fe2O3 Ceramics Prepared by Co-Precipitation Method

Ba0.6Sr0.4TiO3 (BST) ceramic materials have been widely used in the field of multilayer ceramic capacitors. Surface modification through the surface coating to form a heterogeneous layer could effectively improve the dielectric properties. In this work, BST powders were prepared by a co-precipitation method. The effects of reaction conditions on the microstructure of the BST powder were investigated. The reaction temperatures significantly affected the morphology of BST powder, and the rhombic-type particles were obtained with the reaction temperature around 80 °C. Meanwhile, the BST@Fe2O3 was prepared by the chemical precipitation method using BST powders with rhombic-type microstructure as “core”, and the so-called “core-shell” microstructure was confirmed in the BST@Fe2O3 powder. Then, BST@x wt%Fe2O3 (x = 2.5, 5, 7.5, and 10, denoting the different content of Fe2O3) ceramics were further prepared, and the influence of “core-shell” structure on the phase structure, microstructure, and dielectric properties was investigated. With the increasing of Fe2O3 content, the ferroelectric–paraelectric phase transition temperature shifts toward lower temperatures, and dielectric peaks gradually become broad and frequency-dependent, which may be due to inconsistent chemical composition from core to shell.

Impedance Spectroscopy and ac Conductivity in Ba0.5Sr0.5TiO3-Ca10(PO4)6(OH)2 Ceramic Composites: An Electrical Approach to Unveil Biocomposites.

We report bioceramic composites of varying concentrations of Ba0.5Sr0.5TiO3 (BST) and Ca10(PO4)6(OH)2 (HAP) for the analysis of electrical properties. The motivation is to predict the suitability of the composites for bio-electrets or the practical possibility in designing electro-active scaffolds. X-ray diffraction (XRD) and field-emission scanning electron microscopy (FESEM) are used to analyze the microstructural evolution of the composites. A systematic variation in the grain and crystallite sizes is noticed from the FESEM and XRD, along with the presence of Sr5(PO4)3(OH) (SAP). The temperature and frequency variations of the dielectric properties of the composites are studied. Modeling of the dielectric properties with the microstructural properties and at. % of the monolith BST is presented. Cole-Cole formalism is adopted to model the electrical behavior of the synthesized composites. Furthermore, the ac conductivity analysis reveals that Mott's variable range hopping (VRH) conduction is the most appropriate formalism that successfully describes the conduction process. The established Mott's VRH is also related to the polarization mechanisms active in the specimens. Our study projects a correlation between the electrical and biological properties by predicting the protein adsorption behavior from the perspective of impedance spectroscopy.

Enhanced electrocaloric effect at room temperature in Mn2+ doped lead-free (BaSr)TiO3 ceramics via a direct measurement

(Ba1−xSrx)(MnyTi1−y)O3 (BSMT) ceramics with x = 35, 40 mol% and y = 0, 0.1, 0.2, 0.3, 0.4, 0.5 mol% were prepared using a conventional solid-state reaction approach. The dielectric and ferroelectric properties were characterized using impedance analysis and polarization-electric field (P–E) hysteresis loop measurements, respectively. The adiabatic temperature drop was directly measured using a thermocouple when the applied electric field was removed. The results indicate that high permittivity and low dielectric losses were obtained by doping 0.1–0.4 mol% of manganese ions in (BaSr)TiO3 (BST) specimens. A maximum electrocaloric effect (ECE) of 2.75 K in temperature change with electrocaloric strength of 0.55 K·(MV/m)−1 was directly obtained at ∼21 °C and 50 kV/cm in Ba0.6Sr0.4Mn0.001Ti0.999O3 sample, offering a promising ECE material for practical refrigeration devices working at room temperature.

Tunable Microwave Device Fabrication on Low‐Temperature Crystallized Ba0.5Sr0.5TiO3 Thin Films by an Alternating Deposition and Laser Annealing Process

AbstractThis article demonstrates a method to fabricate crystalline Ba0.5Sr0.5TiO3 (BST) thin films at a lower temperature of ≈300 °C using an excimer laser by an alternating depositing and annealing process. Firstly, a BST thin film with a thickness of ≈120 nm is deposited at 300 °C (laser energy of ≈2 J cm−2) and subsequently laser annealed (66 mJ cm−2) at 300 °C. This process is repeated five times to obtain thicker device quality films. XRD patterns, TEM, Raman, and UV–Vis–NIR spectroscopy confirm that phase formation of BST thin films has taken place. The band edge value for BST thin films is observed to decrease systematically from 4.65 eV (amorphous, 300 °C) to 3.56 eV (5‐layers, crystalline, 300 °C). A varactor device with a Circular Patch Capacitor (CPC) structure is patterned on the five‐stage laser annealed BST thin films processed at 300 °C, which shows a microwave tunability of 34% at 1 GHz compared to conventionally deposited BST films (prepared at 700 °C). This study provides a way for fabricating ferroelectric thin film based tunable devices at low temperatures, making the process compatible with low melting substrates in flexible electronics and other situations where there is a temperature constraint.

Universal converse flexoelectricity in dielectric materials via varying electric field direction

ABSTRACT Flexoelectricity is a symmetry independent electromechanical coupling phenomenon that outperforms piezoelectricity at micro and nanoscales due to its size-dependent behavior arising from gradient terms in its constitutive relations. However, due to this gradient term flexoelectricity, to exhibit itself, requires specially designed geometry or material composition of the dielectric material. First of its kind, the present study put forward a novel strategy of achieving electric field gradient and thereby converse flexoelectricity, independent of geometry and material composition of the material. The spatial variation of the electric field is established inside the dielectric material, Ba0.67Sr0.33TiO3 (BST), by manipulating electrical boundary conditions. Three unique patterns of electrode placement are suggested to achieve this spatial variation. This varying direction of electric field gives rise to electric field gradient, the prerequisite of converse flexoelectricity. A multi-physics coupling based theoretical framework is established to solve the flexoelectric actuation by employing isogeometric analysis (IGA). Electromechanically coupled equations of flexoelectricity are solved to obtain the electric field distribution and the resulting displacements thereby. The maximum displacements of 0.2 nm and 2.36 nm are obtained with patterns I and II, respectively, while pattern III can yield up to 85 nm of maximum displacement.

Matching conflicting oxidation conditions and strain accommodation in perovskite epitaxial thin-film ferroelectric varactors

Perovskite oxide materials of the general chemical formula ABO3 are a rich playground for epitaxial stacks of different functional layers for novel device applications. In the example of a tunable metal–insulator–metal ferroelectric varactor (tunable capacitor) made from the highest conducting perovskite SrMoO3 as an electrode and the tunable dielectric Ba0.5Sr0.5TiO3 (BST), we show how the extremely conflicting oxidation potentials can be conciliated in a fully functional heterostructure. Controlling the growth kinetics by the substrate temperature, oxygen pressure, and oxidation time, the formation of the non-conducting Mo6+ states can be effectively suppressed and the BST cation stoichiometry can be tuned. The cumulative impact of the cation nonstoichiometry, epitaxial strain, and oxygen deficiency in the BST films leads to the expansion of their c-axis lattice parameter via the formation of point defects. The dielectric permittivity of 440, the high tunability of 3.5, and the quality factor of 50 are achieved for the varactors at the frequency of 1 GHz. It turns out that the varactor performance is anti-correlated to the tetragonal lattice distortion of BST, which itself is interrelated to the oxidation conditions. The mechanism of the leakage current through oxygen deficient BST layers of the varactors is analyzed within the combined scenarios of the space-charge limited current and Poole–Frenkel field-assisted emission from traps. The achieved high capacitance per unit area of 0.04 pF/μm2 and moderate leakage currents of 0.025 μA/pF make these varactors suitable for applications in microwave microelectronic devices.

Fabrication of Flexible Multilayer Composite Capacitors Using Inkjet Printing.

This paper shows a straightforward method for printing multilayer composite capacitors with three dielectric layers on flexible substrates. As known from multilayer ceramic chip capacitors (MLCCs), it is possible to create a parallel connection of the layers without enlarging the needed area. Hence, the overall capacitance is increased, as the capacitances of the single dielectric layers add up. To realize printed capacitors, a special ceramic/polymer composite ink is used. The ink consists of surface-modified Ba0.6Sr0.4TiO3 (BST), a polymeric crosslinking agent and a thermal initiator, which allows an immediate polymerization of the ink, leading to very homogenous layers. The dielectric behavior of the capacitors is examined for each completed dielectric layer (via impedance spectroscopy) so that the changes with every following layer can be analyzed. It is demonstrated that the concept works, and capacitors with up to 3420 pF were realized (permittivity of ~40). However, it was also shown that the biggest challenge is the printing of the needed silver electrodes. They show a strong coffee stain effect, leading to thicker edge areas, which are difficult to overprint. Only with the help of printed supporting structures was it possible to lower the failure rate when printing thin dielectric layers.

Effect of NiO interface coating on thermal and mechanical properties in Ba<sub>0.8</sub>Sr<sub>0.2</sub>TiO<sub>3</sub>/Cu matrix composites

Ba0.8Sr0.2TiO3 (BST) particles are an effective reinforcement to reduce the coefficient of thermal expansion of Cu composites because of their negative thermal expansion behavior during phase transformation. However, improving interface bonding is still the key point to further study. In this study, NiO interface coating is employed in the BST/Cu composite to improve interface bonding. NiO interface coating of the composite broadens the phase transformation temperature range of BST particles. Accordingly, the average thermal expansion of the composite in the temperature range of 30–250°C is reduced from 12.99×10−6 to 11.71×10−6 °C−1. In addition, the mechanical properties of the composite are considerably enhanced. In specific, the yield strength and the compressive strength are increased by 72.8% and 41.3%, respectively. This work verifies that NiO interface coating can effectively improve the interface bonding in the BST/Cu composite and further enhance the properties of the composite. The results imply that the NiO-BST/Cu composite has great potential for application in the future.

Study on the Flexoelectricity of BST Film Multilayer Structure

Single layer and bilayer Y3+-doped Ba0.65Sr0.35TiO3 (BST) thin-film cantilever beam, of which the single BST film thickness is 500 nm, was prepared on a composite silicon substrate. The flexoelectric coefficients of both types of BSTs were measured using a low frequency vibration method. The flexoelectric coefficient of the bilayer BST film multilayer structure is 1.66 μC/m, which doubles the effective flexoelectric coefficient comparing to the single layer BST. In addition, we discussed the effective piezoelectric coefficient of the BST film multilayer structure, which can reach as much as 2.08×10-10C/N due to the scaling effect.

Changes in the structural and electrophysical properties of Ba0.8Sr0.2TiO3 films with decreasing thickness

Abstract Comparative studies of structural and electrophysical properties were performed for Ba0.8Sr0.2TiO3 (BSTO) films with the thickness of 100 nm, 120 nm and 350 nm. The surface morphology, the domain structure and local polarization switches were explored in the ferroelectric phase whereas high-frequency capacitance–voltage characteristics were measured in the paraelectric phase at 121°С. It was shown that good crystalline properties of the BSTO surface and grains are preserved until the thickness of ceramic layers decrease to 100 nm. The surface roughness did not exceed 2 – 4 nm and the average radius grains was in the range of 64 – 87 nm. Polarization domains induced with a microscope tip were stable and are conserved for several hours. Electrophysical properties of Ba0.8Sr0.2TiO3 films in the paraelectric phase strongly depend on the thickness of layers of BSTO ceramics. Effective dielectric permittivity of BSTO in the limit of weak fields decreases when the film thickness decreases from 350 nm to 100 nm from 920 to 400.

Effect of sintering temperature on microstructure, crystal structure and dielectric performance of Ba0.67Sr0.33TiO3 ceramics prepared by a novel direct coagulation casting via high valence counter ions (DCC-HVCI) method

Perovskite Ba0.67Sr0.33TiO3 (BST) ceramics with improved dielectric performance were fabricated by a novel direct coagulation casting via high valence counter ions (DCC-HVCI) method using 0.5 mol% MgO as the coagulation agent. The influence of sintering temperature on micromorphology, crystal structure, and dielectric performance of BST ceramic components was systematically evaluated. The densification rate of BST samples could reach the maximum at a heating temperature around 1305 °C and end up approximately at 1380 °C. As increasing the sintering temperature from 1400 to 1550 °C, the relative density of BST ceramics decreases from 98.82 ± 0.16% to 96.72 ± 0.06%, and the mean grain size drops gradually from 9.96 to 4.68 μm. The increased sintering temperature promotes the lattice expansion due to Ti4+ replacement at B site by Mg2+, as well as the generation of oxygen vacancies. In addition, as increasing sintering temperature, the dielectric permittivity (εr) of BST ceramic components decreases first and then slightly increases, while the dielectric loss (tanδ) of ceramics shows the opposite trend. The results indicate that the initial tanδ increase is mainly attributed to the lattice expansion of BST ceramics, and the subsequent loss reduction results from the easily localized conduction electrons on Mg2+ sites reducing the carrier concentration. The samples sintered at 1550 °C show the lowest dielectric loss (tanδ≈0.013), which is significantly reduced by an order of magnitude compared with that of dry-pressed samples (tanδ≈0.262).

Electro-optic properties of Ba0.8Sr0.2TiO3 thin film

Electro-optic properties of Ba0.8Sr0.2TiO3 (BST) film with a thickness of 1 μm deposited on the MgO (001) substrate by the rf sputtering have been studied. Structural features of the film were identified by X-ray diffraction method. It was shown, that the BST film exhibited a predominantly linear EO behavior under the applied static electric field, that have been explained according to the strong compressive stresses in the film. The polarization distribution across the gap between the electrodes when electric field is applied was also investigated experimentally and calculated. The linear EO coefficient of Ba0.8Sr0.2TiO3 film with a thickness of 1 μm film was found to be rc = 99.4 p.m./V, that is promising for various EO applications, for example, high performance EO modulator.