Fabrication and electrical properties of barium strontium titanate thick films by modified sol–gel method

A modified sol–gel method has been developed to prepare for the barium strontium titanate (Ba_0.6Sr_0.4TiO₃, BST) thick films. The films were deposited on either Pd–Ag electroded alumina substrates (Pd–Ag/Al₂O₃) or silver electroded alumina (Ag/Al₂O₃) substrates by spin coating technique or screen printing technique. The thickness of the film was in the range of 2–10 μm. The key point of the process is to disperse fine-grained BST ceramic powders prepared by high energy ball mill into BST sol solution to form a slurry for spin coating and screen printing. In order to enhance the stability of the slurry and to avoid crack formation of the thick film, organic macromolecular poly-vinylpyrrolidone (PVP) was added to the sol solution. The structure and surface morphology of the films were studied by X-ray diffraction and Scanning Electron Microscope (SEM) techniques. It is revealed that the thick films exhibit pure perovskite phase and are crack-free, dense and homogeneous. The dielectric constant and loss tangent of the thick films are about 1200 and 0.01, at 10 °C and 1 KHz, respectively.     

Electrical and structural characterization of PTCR pure BaTiO3 nanopowders synthesized by sol–gel emulsion technique

BaTiO₃ ceramics have been widely studied for its application as multilayer ceramic capacitors. However, they have been reported to deviate from their insulating to semiconducting behavior upon doping, and are used as positive temperature coefficient (PTC) thermistors and transducers. In this work, sol–gel emulsion technique was used for synthesis of BaTiO₃ powders of various shapes and sizes. The synthesized powders were calcined at two different temperatures i.e. 750°C, and 1000°C. XRD revealed the powders to be primarily cubic in structure. Presence of tetragonality was noted in the powders calcined at 1000°C. Crystallite size was calculated for the powders calcined at 750°C and 1000°C. Average particle size of the prepared powders varied from 42 to 94?nm. The shape and size of the particles were dependent on the type and concentration of the surfactant used. The synthesized material showed positive temperature coefficient of resistivity (PTCR) behavior. From the recorded resistivity values a maximum of 10¹⁰ Ωcm was achieved. The ferroelectric to paraelectric transition temperature, Curie point, (T_c) was found to be at 75°C from the impedance spectroscopy analysis for the prepared material.     

Preparation of hafnium oxide thin films by sol–gel method

Hafnium oxide (HfO₂) films were grown on SiO₂/Si substrates by a sol–gel method, and their crystalline structure, microstructure and electrical properties were investigated. X-ray diffraction analysis indicated that the monoclinic HfO₂ films could be obtained by annealing at 500 °C. A transmission electron microscopy (TEM) image showed that the films were grown as a spherulite grain structure with a mean grain size of approximately 15 nm. The dielectric constant of the HfO₂ films of 300 nm was approximately 21.6, and the current–voltage measurements showed that the leakage current density of the HfO₂ films was approximately 1.14?×?10^?5 A/cm² at an applied electric field of 100 kV/cm. The sol–gel method-fabricated HfO₂ films are concluded to be feasible for MEMS applications, such as capacitive-type MEMS switches.     

Preparation and microwave properties of Mg doped barium strontium titanate (BSTO) ceramics sintered from Sol–Gel-derived powders

Studies on the Preparation and microwave properties of Mg doped barium strontium titanate (BSTO) ceramics sintered from Sol–Gel-derived powders. The crystal structure and microstructure of Ba_0.60Sr_0.40TiO₃ ceramics doped with Mg has been investigated. The microwave complex permittivity of BST ceramics doped with Mg powders is investigated in 100 MHz–6 GHz ranges by coaxial-transmission technique and the calculation of the equivalent medium theory. Experimental results showed that the typical cubic phase structure and the diffraction peaks of secondary phase that MgO phase become stronger with increasing Mg²⁺ content in the XRD pattern of the Mg doped BST ceramic sintered at 1250°C. The real part of the microwave complex permittivity of BSTM30 ceramic powders is excellent described by results of calculation of Bruggeman theory in wide powder content.     

Ferroelectric properties of Ba1−x Sr x TiO3 thin films synthesized by using novel sol–gel technique through carbonates

Ba_1?x Sr _x TiO₃ (BST) thin films were prepared on the substrate of Pt/Ti/SiO₂/Si by using novel sol–gel process through carbonates. The surface morphology and domain contrast of the films were investigated by atomic force microscopy (AFM), and the domain structures of the BST film were observed when AFM were operated in piezoelectric force microscopic (PFM) analysis and in the friction mode (FFM). The ferroelectric properties of the films were also investigated. It is shown that BST films obtained by the new sol–gel process through carbonates exhibit good properties.     

Synthesis of mixed-conducting oxide SrFeCo0.5O y powder by auto-combustion of citrate–nitrate gel

Mixed-conducting oxide SrFeCo_0.5O _y powders have been synthesized by auto-combustion of citrate–nitrate gel. The resulting powder is pure, homogeneous and possesses a reasonably fine particle size. Attempts have been made to understand the combustion process with the help of Differential Thermal Analysis (DTA) of the sample. The XRD, SEM and TEM studies on these powders confirmed that the method produces powder had greater composition uniformity, lower residual carbonate levels and smaller particle sizes.     

Dielectric and magnetic properties of sol–gel derived mullite-iron nanocomposite

Synthesis of highly crystallized mullite has been achieved at a temperature of 1000°C by sol–gel technique in presence of iron ions of different concentrations. XRD, FTIR spectroscopy, FESEM, LCR meter and HyMDC, Hysteresis measurement instrument, characterized samples. Mullite formation was found to depend on the concentration of the ions. The dielectric properties (dielectric constant, tangent loss and a.c. conductivity) of the composites have been measured, their variation with increasing frequency and concentration of the doped metal was investigated, and magnetic behavior was observed from the hysteresis loops. All the experimentations were performed at the room temperature. The composite showed a minimum dielectric constant of 3.26 at 0.002(M) concentration of iron at 1.5?MHz and the magnetic properties of nanocomposites suggest that the iron nanoparticles show hysteresis loop in 0.10?M, 0.15?M and 0.20?M , hence acts like typical paramagnetic materials as is the case for other iron-doped ferrisilicates.     

Synthesis and dielectric properties of Ba2TiSi2O8 glass-ceramics from the sol–gel process

The Ba₂TiSi₂O₈ glass-ceramics were prepared by sol–gel process using barium acetate, titanium butoxide, tetraethoxyorthosilicate and boric acid as raw materials. Because of the existence of glass and sintering additive, the Ba₂TiSi₂O₈ glass-ceramics can be sintered at 880 °C in air. The structure of sintered sample was characterized by means of XRD and SEM. XRD patterns showed that fresnoite Ba₂TiSi₂O₈ is the dominant crystalline phase in the sintered samples. SEM images indicated that the shape of Ba₂TiSi₂O₈ grains varied with the molar ratio of ([Ba(Ac)₂/Ti(OBuⁿ)₄/Si(OEt)₄]). With an increase of Si(OEt)₄ content, the length/diameter ratio of Ba₂TiSi₂O₈ grains decreases. The Ba₂TiSi₂O₈ glass-ceramics studied in this work have ?_r in the range of 6–12 (100 MHz) and demonstrate very low dielectric losses (tanδ <2?×?10^?3, 100 MHz). The experimental results suggested that the Ba₂TiSi₂O₈ glass-ceramics could be used as dielectric materials for low temperature co-fired ceramics (LTCC) process.     

Synthesis, formation and characterization of lead indium niobate–lead titanate powders

In this study, powders of lead indium niobate–lead titanate (1???x)Pb(In_1/2Nb_1/2)O₃–(x)PbTiO₃ (PINT) binary system near the morphotropic phase boundary (MPB) composition with x?=?38 mol% PbTiO₃ are synthesized with the conventional mixed oxide and the wolframite methods via a rapid vibro-milling technique for the first time. The preparation method and calcination temperature have been found to show pronounced effects on the phase formation behavior of the PINT powders. The stabilized perovskite phase form of PINT can be synthesized by the wolframite method, while precursor phases are still found in powders prepared by the conventional method. Finally, this study shows that the rapid vibro-milling mixing technique is effective in preparing the phase pure perovskite of PINT powders.     

Structure and dielectric properties of Ca-doped (Ba0.7Sr0.3) TiO3 thin films fabricated by sol–gel method

A wide range of Ca-doped (Ba_0.7Sr_0.3)TiO₃ (BST) thin films (from 0 to 20 mol%) have been prepared on Pt/Ti/SiO₂/Si (100) substrates by sol–gel technique. The structural and dielectric properties of BST thin films were investigated as a function of Ca dopant concentration. The results showed that the microstructure and dielectric properties of the BST films were strongly dependent on the Ca contents. With the Ca dopant concentration increasing, the grain size, dielectric constant and dielectric loss of the BST thin films decreased. As the content of Ca dopant reaches 10 mol%, the dielectric constant, dielectric loss, tunability, the value of FOM and the leakage current density are 281, 0.0136, 16.7%, 12.3 and 5.5?×?10^?6 A/cm², respectively.     

Fabrication and electrical characterization of solution-processed all-oxide transparent NiO/TiO2 p-n junction diode by sol–gel spin coating method

Solution-processed all-oxide transparent NiO/TiO₂ p-n junction was fabricated using sol–gel spin coating method. The optical properties of the NiO and TiO₂ films were studied by transmittance and absorbance spectra. The optical band gaps of NiO and TiO₂ films were determined by optical absorption method and found to be 3.83 eV and 3.74 eV, respectively. The current–voltage characteristics of the oxides based p-n junction showed a rectifying behavior. The junction parameters such as ideality factor and barrier height were calculated using thermionic emission model, Chenug, and Norde method. The barrier height and ideality factor values of the diode were obtained to be 0.59 eV and 9.8, respectively.     

Influence of the pH of li-rich Li1.2Mn0.54Ni0.13Co0.13O2 on the electrochemical performance by sol–gel method

Abstract

The positive electrode material of the lithium-rich layered oxide has poor capability, and its cycle stability and rate characterizations have not been satisfactory. The lithium-rich cathode material Li_1.2Mn_0.54Ni_0.13Co_0.13O₂ with different particle sizes was obtained by adjusting the pH by sol–gel method. The results show that the electrochemical performance of the material is optimal at pH = 9.0. It initial discharge capacity of 262.5 mAh/g at 0.1 C between 2.0 and 4.8 V. The high reversible discharge capacities is still of 161.0 and 133.7 mAh/g after 100 cycles at 0.5 C and 2 C, with a high capacity retention of 80.46% and 84.14%, respectively. This excellent electrochemical performance is attributed to smaller and uniform particles     

Structure and properties of Zn-doped CoFe2O4 thin films via a sol–gel method

Zn-doped cobalt ferrite Co_0.9Zn_0.1Fe₂O₄ (CZFO) films with the spinel structure were fabricated on Pt(111)/Ti/SiO₂/Si(100) using a sol-gel method, and the effect of annealing temperature and time on structure and magnetic properties of the CZFO thin films were investigated. The coercivity and saturation magnetization of the films are not sensitive to annealing time, and increase with a rise in the annealing temperature below 800 °C. The CZFO thin films annealed at 800 °C show the best crystallization and the highest coercivity (3.5 kOe), and above 800 °C, the coercivities of the films decrease as a result of formation of multi-domains, while the saturation magnetization comes to stable.     

Synthesis, formation and characterization of lead zinc niobate–lead zirconate titanate powders via a rapid vibro-milling method

In this study, an approach to synthesizing pyrochlore-free lead zinc niobate – lead zirconate titanate powders with a formula xPb(Zn_1/3Nb_2/3)O₃–(1???x)Pb(Zr_1/2Ti_1/2)O₃ (when x?=?0.1–0.5) by a mixed oxide synthetic route via a rapid vibro-milling has been developed. The formation of perovskite phase in calcined PZN-PZT powders has been investigated as a function of calcination temperature by TG-DTA and XRD techniques. Powder morphology and chemical composition have been determined with SEM and EDX techniques. The potential of a vibro-milling technique as a significant time-saving method to obtain single-phase PZN-PZT powders at low calcination temperature is also discussed. The results indicate that at calcination condition of 900 °C for 2 h, with heating/cooling rates of 20 °C/min single-phase PZN-PZT powders can be obtained for every composition ratio between x?=?0.1–0.5.     

Mathematical Simulation of Arc Suppression by Devices with a Liquid–Metal Contact

The problem of simulation of the arc-suppression process in the case of switching off high-current dc circuits by devices with a liquid–metal working medium is considered. Since devices with a liquid–metal contact are designed to switch specific power circuits, the possibility of joint consideration of the electrical circuit and the switch is used to optimize the shutdown process. The obtained mathematical model allows with the use of the known temperature profile of the dynamic arc to calculate the main dynamic characteristics of the arc discharge, such as current, voltage, conductivity, temperature, and the trunk conductor radius. It is shown that, if the real temperature profile of the arc is not known, calculation of such integral characteristics of the arc-suppression process as current, resistance and intensity of the arc trunk can be carried out with the use of an equivalent temperature profile. On the basis of the obtained mathematical model, a calculation methodology is developed for the process of circuitry cutout by an apparatus with liquid–metal contacts with a change in the topological structure of the circuit being switched off during the commutation process.     

Improving the accuracy of multisided travelling wave determination of location of a fault in a power line by means of the difference–distance-measuring technique

The double-ended travelling wave method of determination of location of a fault in electrical networks has significant errors due to changes in the propagation velocity of electromagnetic waves. We have developed a travelling wave method of improving the accuracy of location of a fault determination in power transmission lines that is based on navigation algorithms. The method is applicable to lines with branches. The distance to fault determination for the developed method is up to twice as accurate as the double-ended travelling wave location of a fault method. The accuracy of the developed method is less influenced by external factors (change of sag, soil resistance, the instantaneous value of the current at the fault time) than is the accuracy of the double-ended travelling wave location of a fault method. The proposed method allows reducing the errors in determining distance to the location of a fault, and its accuracy is less affected by external factors. The developed method can be incorporated into existing and prospective devices based on travelling wave methods of location of a fault determination.     

Highly dispersive optical solitons with a polynomial law of refractive index by Laplace–Adomian decomposition

Journal of Computational Electronics - This paper presents a numerical study of highly dispersive optical solitons that maintain a cubic–quintic–septic nonlinear (also know as...     

Scan–rescan reproducibility of segmental aortic wall shear stress as assessed by phase-specific segmentation with 4D flow MRI in healthy volunteers

Objective

The aim was to investigate scan–rescan reproducibility and observer variability of segmental aortic 3D systolic wall shear stress (WSS) by phase-specific segmentation with 4D flow MRI in healthy volunteers.

Materials and methods

Ten healthy volunteers (age 26.5?±?2.6 years) underwent aortic 4D flow MRI twice. Maximum 3D systolic WSS (WSSmax) and mean 3D systolic WSS (WSSmean) for five thoracic aortic segments over five systolic cardiac phases by phase-specific segmentations were calculated. Scan–rescan analysis and observer reproducibility analysis were performed.

Results

Scan–rescan data showed overall good reproducibility for WSSmean (coefficient of variation, COV 10–15%) with moderate-to-strong intraclass correlation coefficient (ICC 0.63–0.89). The variability in WSSmax was high (COV 16–31%) with moderate-to-good ICC (0.55–0.79) for different aortic segments. Intra- and interobserver reproducibility was good-to-excellent for regional aortic WSSmax (ICC?≥?0.78; COV?≤?17%) and strong-to-excellent for WSSmean (ICC?≥?0.86; COV?≤?11%). In general, ascending aortic segments showed more WSSmax/WSSmean variability compared to aortic arch or descending aortic segments for scan–rescan, intraobserver and interobserver comparison.

Conclusions

Scan–rescan reproducibility was good for WSSmean and moderate for WSSmax for all thoracic aortic segments over multiple systolic phases in healthy volunteers. Intra/interobserver reproducibility for segmental WSS assessment was good-to-excellent. Variability of WSSmax is higher and should be taken into account in case of individual follow-up or in comparative rest–stress studies to avoid misinterpretation.

     

The effect of sintering temperature and time on the growth of single crystals of 0.75 (Na<Subscript>0.5</Subscript>Bi<Subscript>0.5</Subscript>)TiO<Subscript>3</Subscript>–0.25 SrTiO<Subscript>3</Subscript> by solid state crystal growth

Materials in the (Na_0.5Bi_0.5)TiO₃–SrTiO₃ system are of interest for use as lead-free piezoelectric actuators due to high electric-field induced strains. Piezoelectric properties may be further improved by growing single crystals but as yet work on single crystal growth in this system is limited. In the present work, single crystals of composition 0.75 (Na_0.5Bi_0.5)TiO_3?0.25 SrTiO₃ were grown by solid state crystal growth (SSCG) on [001] SrTiO₃ seed crystals and the dependence of crystal growth distance and matrix grain growth on sintering temperature investigated. Electron backscattered diffraction and X-ray diffraction analysis show that the single crystals grow epitaxially on the seed crystals. Energy dispersive spectroscopy indicates that the grown crystals are slightly Na-deficient, while X-ray photoelectron spectroscopy indicates the presence of oxygen vacancies. Single crystal growth distance, mean matrix grain size and grain size distribution as a function of sintering temperature and time are presented. Increasing the sintering temperature increases both single crystal and matrix grain growth rates. The optimum single crystal growth temperature is found to be 1250°C. The effect of sintering temperature on the single crystal and matrix grain growth behavior is explained using the mixed control mechanism of microstructural evolution.