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Hexaferrite multiferroics: from bulk to thick films
摘要： We report studies of the structural and microstructural properties of Sr3Co2Fe24O41 in bulk form and as thick films. The precursor powders for the bulk form were prepared following the sol-gel auto-combustion method. The prepared pellets were synthesized at 1200 oC to produce Sr3Co2Fe24O41. The XRD spectra of the bulks showed the characteristic peaks corresponding to the Z-type hexaferrite structure as a main phase and second phases of CoFe2O4 and Sr3Fe2O7-x. The microstructure analysis of the cross-section of the bulk pellets revealed a hexagonal sheet structure. Large areas were observed of packages of hexagonal sheets where the separate hexagonal particles were ordered along the c axis. Sr3Co2Fe24O41 thick films were deposited from a suspension containing the Sr3Co2Fe24O41 powder. The microstructural analysis of the thick films showed that the particles had the perfect hexagonal shape typical for hexaferrites.
关键词： hexaferrite,microstructure,sol-gel auto-combustion,thick films,multiferroics
更新于2025-09-23 15:21:01
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Synthesis of Calcium Aluminate-Based Luminophores by the Citrate Nitrate Sol–Gel Process
摘要： Microwave-assisted sol–gel process was used to synthesize calcium aluminate and luminescent materials based on it, which find wide use in the manufacture of construction materials, catalysts, optical emission sources, and display devices. The major processes involved in the formation of crystalline calcium aluminate were identified resorting to powder X-ray diffraction, thermal analysis, scanning electron microscopy, and IR spectroscopy data. Synthetic steps have moderate activation energies in the 44–260 kJ/mol range. Luminescence characteristics of the obtained crystal phosphors were measured. The increase in the synthesis temperature to 1200°C and the increase in the activator concentration to 5 mol % enhance the luminescence of the Eu3+-activated calcium aluminate-based luminophore. Further increase in the concentration of the activator ions leads to luminescence quenching caused by the concentration effect.
关键词： calcium aluminate,sol–gel process,microwave treatment,europium(III) ions,crystal phosphor
更新于2025-09-23 15:21:01
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Dye-sensitized solar cell based on poly(?μ-caprolactone) gel polymer electrolyte and cobalt selenide counter electrode
摘要： In this work, gel-like polymer electrolytes were prepared by incorporating poly(ε-caprolactone) (PCL) into dimethylformamide (DMF)-potassium iodide (KI) liquid electrolytes. The optimized gel polymer electrolyte has the composition of 40 wt.% of PCL, 45 wt.% of DMF and 15 wt.% of KI with a conductivity of 2.72 × 10?3 S cm?1 at room temperature. Increase in conductivity with temperature is attributed to the increase in diffusion coefficient, D, number, n and mobility, μ of ions as determined from Nyquist plots fitting. Cobalt selenide (CoSe) was prepared by hydrothermal method and used as counter electrode catalysts in dye-sensitized solar cells (DSSCs). X-ray diffraction (XRD) studies show the formation of the as-prepared CoSe. The morphology and stoichiometric composition of CoSe were studied by field-emission scanning electron microscopy (FESEM) and energy dispersive X-ray spectroscopy (EDX). The PCL-DMF-KI gel polymer electrolytes were assembled into DSSCs with CoSe or platinum (Pt) as the counter electrodes. DSSC with CoSe counter electrode shows an efficiency of 6.74% while DSSC with Pt counter electrode yields an efficiency of 6.99%. Impedance studies of DSSCs suggest that the electrocatalytic reduction of triiodide, I3 ? by the CoSe is as good as Pt.
关键词： CoSe,PCL,Counter electrode,Gel polymer electrolyte,Dye-sensitized solar cells
更新于2025-09-23 15:21:01
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CaBi <sub/>4</sub> Ti <sub/>4</sub> O <sub/>15</sub> -based lead-free sol–gel composites for high-temperature application
摘要： 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 ?lms 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 con?rmed 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. ? 2018 The Japan Society of Applied Physics
关键词： ultrasonic transducer,high-temperature,sol–gel composites,lead-free,CaBi4Ti4O15
更新于2025-09-23 15:21:01
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Morphological, spectroscopic and photocatalytic properties of Eu3+:TiO2 synthesized by solid-state and hydrothermal-assisted sol-gel processes
摘要： Eu3+ doped TiO2 powders were synthesized by solid-state reaction and hydrothermal-assisted sol-gel process. They were characterized by X-ray diffraction, scanning electron microscopy and photoluminescence techniques. Both synthetic procedures yield the pure anatase phase of titania. The excitation and emission spectra and the decay profiles were measured for different thermal treatments of the samples, in order to investigate the effects of the synthesis conditions on the doping mechanism. The photocatalytic activity was investigated by measuring the degradation of methylene blue under UV light irradiation and a correlation between its efficiency and the luminescence performance has been proposed.
关键词： TiO2:Eu,Solid-state,Optical spectroscopy,Anatase,Photocatalysis,Hydrothermal-assisted sol-gel
更新于2025-09-23 15:21:01
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Synthesis, DFT studies, fabrication, and optical characterization of the [ZnCMC] <sup>TF</sup> polymer (organic/inorganic) as an optoelectronic device
摘要： A novel carboxymethyl cellulose zinc thin film [ZnCMC]TF was fabricated using the sol–gel technique. Different characterization techniques such as Fourier-transform infrared spectroscopy (FTIR), Raman spectroscopy, ultraviolet–visible spectroscopy (UV-Vis), X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDX), and the optical properties were used to study the properties of [ZnCMC]TF. The molecular structure, FTIR, and optical properties were optimized. The Raman spectrum of the [ZnCMC]TF complex shows several bands in the range of 72–556 cm?1 due to (nZn–O) stretching and (Zn–O) bending, which is an obvious distinction between the FTIR and Raman spectra of [ZnCMC]TF. The optimization was performed using density functional theory (DFT) by DMol3 and Cambridge Serial Total Energy Package (CASTEP) program. The chemical structure was confirmed by spectroscopic and structural properties for both CMC and [ZnCMC]TF; the XRD results showed the same crystal structure (Monoclinic 2). [ZnCMC]TF has a larger grain size than CMC and has a similar behavior in the optical gap energy. The optical constants increased with increasing photon energy, refractive index n, absorption index k, and optical conductivity. The SEM images provide very good evidence in favor of the reaction of zinc transition metal with CMC for the formation of the [ZnCMC]TF complex. The resulting [CMC] spherical thin film and the [ZnCMC]TF polymeric nanorods were examined by different techniques including TEM and EDX. The optical properties obtained from the simulated FTIR, XRD, and CASTEP are in good agreement with those obtained from the experimental studies on CMC and ZnCMC. Based on the optical findings, [ZnCMC]TF is a promising candidate in applications such as solar cells and optoelectronic devices.
关键词： TEM,DMol3,zinc thin film,carboxymethyl cellulose,UV-Vis,DFT,optoelectronic devices,XRD,EDX,CASTEP,sol–gel technique,SEM,FTIR,optical properties,Raman spectroscopy
更新于2025-09-23 15:21:01
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Suppression of Ag migration by low-temperature sol-gel zinc oxide in the Ag nanowires transparent electrode-based flexible perovskite solar cells
摘要： Silver nanowires (Ag NWs) network is an excellent candidate as flexible transparent electrode applying in flexible perovskite solar cells, owing to their excellent electrical and optical properties. However, several problems including large surface roughness, chemical reaction between Ag and perovskite precursor, and migration of Ag limited the application in high performance perovskite solar cells. Aiming to solve these problems, the composite electrode combining the spray coated Ag nanowires and the low-temperature sol-gel zinc oxide was developed in this work. The optimized concentration and annealing temperature of sol-gel ZnO were 0.45 M and 150°C. The introduction of zinc oxide with suitable concentration caused slight impact on the transmittance and sheet resistant of transparent composite electrode, and promoted mechanical and chemical stability in air relative to the pristine Ag NWs electrode. The use of the composite flexible electrode could decrease the surface roughness of the Ag NWs electrode, passivate the reaction of perovskite and silver electrode, and prevent the migration of Ag. As a consequence, the performance of the flexible device significantly improved from 9.51% to 13.12%. Under the AM 1.5G constant illumination, the optimization device has a remarkably improved stability than pristine device. This study demonstrates that spray Ag NWs as bottom electrode is suitable for flexible perovskite solar cells. Meanwhile, it’s an effective method using sol-gel ZnO to construct composite electrode to promote the device performance and stability.
关键词： Ag nanowire electrode,Ag migration,Flexible perovskite solar cells,Sol-gel ZnO,Bending resistance
更新于2025-09-23 15:21:01
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Efficient N, Fe Co-Doped TiO2 Active under Cost-Effective Visible LED Light: From Powders to Films
摘要： An eco-friendly photocatalytic coating, active under a cost-effective near-visible LED system, was synthesized without any calcination step for the removal of organic pollutants. Three types of doping (Fe, N and Fe + N), with different dopant/Ti molar ratios, were investigated and compared with undoped TiO2 and the commercial P25 photocatalyst. Nano-crystalline anatase-brookite particles were successfully produced with the aqueous sol-gel process, also at a larger scale. All samples displayed a higher visible absorption and specific surface area than P25. Photoactivity of the catalyst powders was evaluated through the degradation of p-nitrophenol in water under visible light (>400 nm). As intended, all samples were more performant than P25. The N-doping, the Fe-doping and their combination promoted the activity under visible light. Films, coated on three different substrates, were then compared. Finally, the photoactivity of a film, produced from the optimal N-Fe co-doped colloid, was evaluated on the degradation of (i) p-nitrophenol under UV-A light (365 nm) and (ii) rhodamine B under LED visible light (395 nm), and compared to undoped TiO2 film. The higher enhancement is obtained under the longer wavelength (395 nm). The possibility of producing photocatalytic films without any calcination step and active under low-energy LED light constitutes a step forward for an industrial development.
关键词： aqueous sol-gel process,Fe/N doping,LED visible light,titania,photocatalysis
更新于2025-09-23 15:21:01
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Structural and dielectric properties of sol–gel derived Ba<sub>1–<i>x</i></sub>Sr<sub><i>x</i></sub>TiO<sub>3</sub> (0 ≤ <i>x</i> ≤ 0.5) ceramics for energy storage applications
摘要： Barium strontium titanate (Ba1–xSrxTiO3, BSTO: x = 0, 0.3 and 0.5) ceramics were prepared by sintering sol–gel derived BSTO powders at 1350 °C for 2 h. Average grain size of BSTO ceramics decreased from 15 to 2 μm with increasing Sr molar fraction. X-ray structural analysis revealed that BSTO ceramics exhibited tetragonal structure (x = 0 and 0.3) and transformed into cubic structure at high Sr molar fraction (x = 0.5) at room temperature. Dielectric constant of the BSTO ceramics was measured between ?60 and 180 °C and frequency range of 1–100 kHz. Temperature transition from ferroelectric to paraelectric phase (Curie temperature: TC) decreased linearly from 125 to ?30 °C as Sr molar fraction increased. The dielectric constant exhibited frequency-independent behavior in the frequency range investigated. A diffuse dielectric constant peak was evident for BSTO with Sr molar fraction of 0.5 due to the effect of fine-grained size. Polarization–electric field (P–E) at room temperature presented a well-defined hysteresis loop for BSTO (x = 0 and 0.3), indicating their ferroelectric characteristics. At a high Sr molar fraction of 0.5, the P–E loop became a linear relation, indicating a paraelectric phase. Energy storage density of BSTO with x = 0 was about 0.2 J/cm3; however, energy storage efficiency was less than 50%. After doping with Sr molar fraction of 0.5, energy storage density decreased to 0.1 J/cm3 but its energy storage efficiency significantly improved to 90%.
关键词： sol-gel method,dielectric,energy storage capacitors,barium strontium titanate
更新于2025-09-23 15:21:01
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Effect of the occupation of Ba and Ti sites on the structural, optical and dielectric properties of Sm-doped BaTiO3 ceramics
摘要： Sm-doped BaTiO3 powders have been synthesized with the help of the sol gel process. X-ray diffraction (XRD) patterns of the obtained powders, heat treated at a relatively low temperature (750 °C/3 h), revealed their crystallization in the pure perovskite structure without the presence of secondary phases. The occupation of the Ba and Ti sites by Sm in the BaTiO3 lattice and the evolution of the crystalline parameters as functions of the dopant content have been discussed based on XRD and Raman results. Dielectric measurements performed on the samples revealed a strong increasing diffuse character of the ferro-to-paraelectric phase transition with increasing Sm content. Moreover, the behavior of the permittivity as a function of frequency indicates that the samples are approaching their resonance frequency. The study of the conductivity showed the existence of a weak positive temperature coefficient of resistivity (PTCR) effect.
关键词： Sm-doped BaTiO3,dielectric properties,PTCR effect,perovskite structure,sol gel process
更新于2025-09-23 15:21:01