Sol Gel Self-combustion Method Research Articles

Effects of sintering temperature on the microstructure, electrical and magnetic characteristics of copper-zinc spinel ferrite with possibility use as humidity sensors

In this paper was investigated the effect of sintering temperature on a copper-zinc spinel ferrite, Cu0.5Zn0.5Fe2O4, synthesised by using a sol-gel self-combustion method, as material with possible to application in the field of humidity sensors. In order to highlight the influence of temperature treatment on the structure, electrical and magnetic properties, the powders of ferrite were annealed at various temperatures: 850 °C, 900 °C, 950 °C, 1000 °C and 1050 °C. For the analyzed samples, the X-ray diffraction investigations have revealed the phase composition and the average crystallite size. By using techniques scanning electron microscopy (SEM) and atomic force microscopy (AFM) were find the influence of the sintering temperature on some parameters like the porosity, homogeneity, shape and size of the crystallites. We have also investigated the temperature variation of the electrical conductivity, relative magnetic permeability and relative permittivity variation with frequency at room temperature. Finally, we analyzed the time response, variations of electrical conductivity and relative permittivity for various humidity levels and the perspectives of applicability copper-zinc spinel ferrite as humidity sensor.

Crystal structure and Cu/Fe K-edge analysis of Ba0.5Sr0.5Fe1-xCuxO3-δ (x = 0–0.2) and the influence on conductivity

Ba0.5Sr0.5Fe(1-x) CuxO3-δ (BSFC-x; x = 0–0.2) was synthesized and characterized. A sol-gel self-combustion method with mixed cation nitrate solutions and citric acid was used to synthesize BSFC-x precursors. Calcination was conducted in air at 850 °C for 6 h, followed by sintering in air at 1100 °C for 6 h. The phase, structure, and lattice parameters of the sintered BSFC-x were determined by X-ray diffraction (XRD). X-ray absorption near-edge spectroscopy (XANES) was used to analyze the oxidation state of the cation in the octahedron site (Cu/Fe). It showed that copper's oxidation state was predominantly 3+ due to oxygen octahedron neighbors in the crystalline symmetry and shifted to a lower oxidation state at 800 °C. The oxidation state was thought to be the predominant factor contributing to the overall conductivity through hole creation. The electrical analysis demonstrated semiconductor behavior at up to 500 °C that was influenced by the hole concentration, oxygen vacancies, and hopping distance. Above the maximum conductivity values, oxygen losses dominated the electrical response and disrupted the conductivity. Considering the doping quantity, the optimum doping was x = 0.1 with an electrical conductivity of ≈60 S/cm.

Low temperature sintering of (1-x-y) BaTiO3-xBiFeO3-yKVO3 composition

Abstract In this study, the composition of (1-x-y) BaTiO3-xBiFeO3-yKVO3 (x = 0.15; y = 0.01, 0.025) were successfully synthesized using a calcination at 700 °C for 2 h of mixed BaTiO3, BiFeO3, and KVO3. Previously, BaTiO3, BiFeO3, and KVO3 powders were respectively synthesized through oxalate co-precipitation, solid state reaction, and sol–gel self-combustion method. The substitution of 1 mol% and 2.5 mol% doped KVO3 successfully reduce the sintering temperature become ≈1050 °C from generally reported 1400⁰C-1500⁰C. The XRD pattern reveals the presence of a secondary phase which is also indicated by SEM images. Furthermore, the increase of KVO3 causes an increase of secondary phase then decrease the value of relative permittivity (er) and dissipation factor (tan δ).

Nanocrystalline SrMnO3 perovskite prepared by sol–gel self-combustion method for sensor applications

Oxide compound with perovskite-type structure, SrMnO3, was investigated in view of its application as capacitive and/or resistive humidity sensor. The compound presents a porous structure with prevailing open tubular pores systems and it was obtained by sol–gel self-combustion method using polyvinyl alcohol as colloidal medium, followed by heat treatment. Air relative humidity (RH) has a big influence on sensor electric capacity. The best sensitivity as capacitive humidity sensor was found at working frequency of 40 Hz over a wide range of relative humidity (0–98% RH). At this frequency, within the interval 0–98% RH the capacity increases by 1200%, and the resistance decreases by only 18%. The sensor has a good linearity of the logC vs. RH characteristics. The sensor exhibits very small hysteresis, and a short response time. The investigated material holds promise for humidity monitoring applications, taking into account the low cost, a wide range of relative humidity and a low-contamination impact, as well as for the realization of some electronic components, which requires good stability of resistivity in the presence of environmental humidity factors.

Local structure analysis of BO6 (B = Fe, Cu) octahedron correlated with the magnetic properties of Cu-doped Ba0.5Sr0.5FeO3–δ

Perovskite-based Ba0.5Sr0.5Fe1–xCuxO3–δ (BSFCO-x, x = 0–0.2) was synthesized by sol–gel self-combustion method. The crystallinity was evaluated through X-ray diffraction, besides further local structure analysis, using X-ray absorption spectroscopy (XAS) showed a cubic symmetry for x = 0.05; 0.10, which was tetragonal at higher values, x = 0.15; 0.20. XAS analysis predicted the oxidation state (OS) of Cu to be a mixture of 3+ and 2+, while Fe includes 3+ and 4+. Conversely, the OS of Fe and Cu in the octahedron site influence the number of an unpair electron that determine the magnetic properties of perovskite. In addition, the magnetization for Ba0.5Sr0.5FeO3–δ is 0.172 emu g−1, originating from the ferromagnetic ordering Fe3+(t 2g 3 e g 2 )–O (2p)–Fe4+(t 2g 3 e g 1 ) interaction. This effect increase, due to the presence of oxygen vacancy in BSFCO-0.05, which weakens the d–p interaction of Fe-O, while the generation of higher Cu doping to increase the amount of Fe4+ leads to a decline in Cu3+. Therefore, Cu doping is confirmed to play a role in the paramagnetic–ferromagnetic transition.

Tailoring of structural and magnetic properties of nanosized lithium ferrites synthesized by sol–gel self-combustion method

In this study, we report the influence of Co2+ on structure and magnetic properties of nano-sized Li0.5−x/2Fe2.5−x/2CoxO4(where x = 0.0, 0.2, 0.4, 0.6, 0.8, 1.0) synthesized using sol–gel auto-combustion method. The X-ray diffractometric analysis of samples confirmed the formation of pure Li0.5−x2Fe2.5−x2CoxO4 nanoparticles ranges crystallite size from 36 to 43 nm with co-doping. There is a structural transformation from ordered P4332 to random Fd3m observed, which is caused by the localization of cobalt ions. RT-Mossbauer the showed presence of 57Fe in both sublattices. Position identification was performed based on the distribution of the over exchange fields and isomeric shift data. Magnetic measurements showed that the saturation magnetization increases to x ≤ 0.8 and then decreases with Co-content due to the change in cationic distribution. The cobalt substitution turns Li–Co ferrite from soft-magnet to hard-magnet.

Preparation and properties of solid electrolyte CaxBi1.7−xW0.3O3.45−0.5x electrolyte material by sol–gel combution method

CaxBi[Formula: see text]W[Formula: see text]O[Formula: see text] (CBW) ([Formula: see text], 0.05, 0.10, 0.15, 0.20, 0.30) electrolyte material were synthesized by sol–gel self-combustion method. The samples were characterized by thermogravimetric-differential thermogravimetric analysis(TG-DSC), X-ray diffraction, scanning electron microscopy (SEM), porosity and electrochemical impedance spectroscopy (EIS). The results show the powders CaxBi[Formula: see text]W[Formula: see text]O[Formula: see text] (CBW) with fluorite crystal structure can be obtained after the precursor was calcined at 760∘C. When sintered at 780∘C for 2[Formula: see text]h, the compact ceramic sintered with relative density higher than 97% can be obtained. The electrochemical studies showed that CaxBi[Formula: see text]W[Formula: see text]O[Formula: see text] (CBW) have high ionic conductivity after 780∘C sintering. The sample Ca[Formula: see text]Bi[Formula: see text]W[Formula: see text]O[Formula: see text] exhibits a conductivity of 0.07978 S[Formula: see text][Formula: see text][Formula: see text]cm[Formula: see text] at 750∘C, and the activation energy is 0.845[Formula: see text]eV, which is expected to be applied to the electrolyte materials for intermediate temperature solid oxide fuel cells (SOFC).

Nanocrystalline iron manganite prepared by sol–gel self-combustion method for sensor applications

The nanocrystalline iron manganite was be successfully synthesized, for capacitive humidity sensor application, by sol–gel self-combustion method using polyvinyl alcohol as colloidal medium, followed by heat treatment. The best performances as humidity sensor were found, at working frequency of 100 Hz: a high sensitivity over a wide range of relative humidity, 11–98% RH (the capacity increases by over 40 times); a good linearity of the logC vs. RH characteristics over the whole RH range, for all used frequencies. The sensor exhibits very small hysteresis, lower sensitivity to temperature, keeping linear characteristics and a short response time. The investigated material holds promise for humidity monitoring applications, taking into account the low cost, a wide range of relative humidity and a low-contamination impact.

Synthesis of Nanocrystalline Ba0,5Sr0,5FeO3-δ by Sol-gel Self-Combustion Method

Fuel cell is a one of device to convert chemical into proper electric energy, has some advantages including high efficiency, long term stability, fuel flexibility, environment friendly. To develop SOFC operates at intermediate temperature (500-700°C), it is necessary to figure out a cathode material capable of overcoming the low electrochemical reduction activity in oxygen at intermediate temperatures. Ba0,5Sr0,5FeO3-δ (BSF) has mixed ionic and electronic conductivity properties (MIEC). A sol-gel self-combustion method was used to synthesize BSF due to easier preparation and produces excellent result (high homogeneity and high reactivity) powder. Two conditions were set up in different pH, namely 0-1 and 6-7. The self-combustion reaction occurred on heating up to 220 °C and produced yield ashes. To acquire the calcination condition, the temperature was carried out at 500, 700, 900, 1000, and 1100 °C for 6 hours. In this study, the phase formation, structure, and crystallite size of BSF was characterized by make use of X-ray diffraction (XRD) data. The results show that BSF has cubic perovskite structure with space group pm3m (221), crystallite size 52 and 109 nm for pH 0-1 and 6-7 respectively.

Investigations on microstructure, electrical and magnetic properties of copper spinel ferrite with WO3 addition for applications in the humidity sensors

In the present study we report the structural, electrical, magnetic and humidity characteristics of copper ferrite with different percent on tungsten trioxide addition. The aim of this study was to obtain more stable and sensitive active materials for humidity sensors. In order to highlight the influence of tungsten on the structural, electrical and magnetic properties, the ferrite samples were fabricated via sol-gel self-combustion method and sintered for 30 min at 1000 °C with percent between 0 and 20% tungsten trioxide additions. The X-ray diffraction investigations showed the copper ferrite phase composition. The scanning electron microscopy revealed the influence of the substitution on characteristics of the crystallites and the profilometry showed the surface topography of samples. The investigation was focused on the variation of permittivity and electrical conductivity, in relation with tungsten trioxide addition, frequency and humidity. We have also, investigated the relevant magnetic characteristics of the copper ferrite material by highlighting the influence of tungsten trioxide addition on to Curie temperature and the permeability frequency characteristics. The data suggests that the copper ferrite with tungsten trioxide addition can be used as active material for humidity sensors.

Effects of Ce substitution at the A-site of LaNi0.5Fe0.5O3 perovskite on the enhanced catalytic activity for dry reforming of methane

Effects of Ce substitution at the A-site of LaNi0.5Fe0.5O3 perovskite on the enhanced catalytic activity for dry reforming of methane (DRM) were studied. La1-xCexNi0.5Fe0.5O3 mixed-oxide catalyst precursors were synthesized by a sol-gel self-combustion method. The CH4 and CO2 conversions increase for the samples with x=0.4–0.6. The used catalysts consist of Ni, CeO2, and (LaCe)(NiFe)O3. The metallic Ni phase provides the primary catalytic activity, while (LaCe)(NiFe)O3 perovskite dominates the enhanced catalytic activity. It is confirmed that the solubility of Ce in the perovskite is high under the DRM conditions. Our results suggest that the Ce3+ cation at the A-site of (LaCe)(NiFe)O3 is active for DRM, and the relevant mechanisms are discussed.

The study on nanogranular system manganites La–Pb–Ca–Mn–O which exhibits a large magnetoresistance near room temperature

In this paper, we have investigated the structure, transport properties and magnetoresistance of the La–Pb–Ca–Mn–O perovskite-manganite system within the temperature interval of 77–400 K and in magnetic field of 1.6 MA/m. Calcium as partial substitute for lead was introduced in the parent composition La0.6Pb0.4MnO3. Polycrystalline bulk samples were prepared by sol–gel self-combustion method and subsequent heat treatment at 1000 °C for 40–320 min. By a moderate substitution with Ca (Ca0.1), the Curie temperature increases by 10°, while for a bigger doping with Ca (Ca0.2), the Curie temperature decreases by 10° as compared with the sample without substitution. The samples exhibit a resistivity peak around 200–225 K, below the ferromagnetic ordering temperature (320–345 K). A negative and isotropic magnetoresistance has been obtained, which exhibits a peak in the temperature range 92–140 K, below electric transition temperature. By a moderate substitution with Ca (Ca0.1), the room temperature magnetoresistance increases (by 12%), while by a larger substitution with Ca (Ca0.2), the low temperature magnetoresistance increases (by 31% at 92 K).

The synthesis and characterization of nickel and cobalt ferrite nanopowders obtained by different methods

The ferrite materials, especially of nickel and cobalt, are popular due to their unique mechanical and magnetic properties. The single phase NiFe2O4 and CoFe2O4 ferrites were synthesized by three methods: the high frequency plasma chemical synthesis, the sol-gel self-combustion, and the co-precipitation technology combined with the hydrothermal synthesis method. Magnetic properties, crystallite size, the specific surface area of synthesized products are characterized. Nanopowders synthesized in the high frequency plasma have a specific surface area in the range of 28–30 m2/g (the average particle size 38–40 nm, crystallite size ~40 nm), but a wider particle size distribution is in the range of 10–100 nm with some particles of 200 nm. The ferrite nanopowders obtained by the sol-gel self-combustion and hydrothermal synthesis method have the specific surface area of 40 ± 3 and 60 ± 5 m2/g (average particle size 25–30 nm and 19–26 nm, crystallite size 10–20 nm and 12–20 nm), respectively. Cobalt ferrites after synthesis are characterized by the saturation magnetization MS of 75 emu/g (for plasma chemical synthesis), 53 emu/g (for the self-combustion method), and 57 emu/g (hydrothermal synthesis). The saturation magnetization for nickel ferrites is 44, 29 and 30 emu/g, respectively. After the thermal treatment up to 900 oC the particle size of all ferrites increases, but their magnetic properties are approaching those of monolithic ferrites.DOI: http://dx.doi.org/10.5755/j01.ct.67.1.15824

Evaluation of Antioxidant and Cytotoxicity Activities of Copper Ferrite (CuFe2O4) and Zinc Ferrite (ZnFe2O4) Nanoparticles Synthesized by Sol-Gel Self-Combustion Method

Spinel copper ferrite (CuFe2O4) and zinc ferrite (ZnFe2O4) nanoparticles were synthesized using a sol-gel self-combustion technique. The structural, functional, morphological and magnetic properties of the samples were investigated by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), Transmission electron microscopy (TEM) and vibrating sample magnetometry (VSM). XRD patterns conform to the copper ferrite and zinc ferrite formation, and the average particle sizes were calculated by using a transmission electron microscope, the measured particle sizes being 56 nm for CuFe2O4 and 68 nm for ZnFe2O4. Both spinel ferrite nanoparticles exhibit ferromagnetic behavior with saturation magnetization of 31 emug−1 for copper ferrite (50.63 Am2/Kg) and 28.8 Am2/Kg for zinc ferrite. Both synthesized ferrite nanoparticles were equally effective in scavenging 2,2-diphenyl-1-picrylhydrazyl hydrate (DPPH) free radicals. ZnFe2O4 and CuFe2O4 nanoparticles showed 30.57% ± 1.0% and 28.69% ± 1.14% scavenging activity at 125 µg/mL concentrations. In vitro cytotoxicity study revealed higher concentrations (>125 µg/mL) of ZnFe2O4 and CuFe2O4 with increased toxicity against MCF-7 cells, but were found to be non-toxic at lower concentrations suggesting their biocompatibility.

CuCr2O4 Spinel Ceramic Pigments Synthesized by Sol-Gel Self-Combustion Method for Solar Absorber Coatings

A series of CuCr2O4 spinel ceramic pigments have been successfully synthesized via a facile and cost-effective sol-gel self-combustion method. The reaction mechanism was systematically studied using the corresponding characterization technologies. The results suggested that CuCr2O4 spinel ceramic pigments could be obtained at annealing temperature of 600 °C for 1 h, and the size, morphology, and crystallinity of CuCr2O4 spinel were greatly influenced by the annealing temperature. The as-burnt powder and CuCr2O4 spinel ceramic pigment were then employed to fabricate thickness sensitive spectrally selective (TSSS) paint coatings by a convenient spray-coating technique. The results revealed that spectral selectivity of TSSS paint coatings based on CuCr2O4 spinel ceramic pigments was much better than that of paint coatings based on the as-burnt powders. Furthermore, the effect of surface features of TSSS paint coatings on its optical property and hydrophobicity was investigated in detailed.

Spectrally selective Cu1.5Mn1.5O4 spinel ceramic pigments for solar thermal applications

In this work, Cu1.5Mn1.5O4 spinel ceramic pigments have been successfully prepared by a facile and cost-effective sol–gel self-combustion method and annealed at a temperature ranging from 500 °C to 900 °C for 1 h.

Effect of sintering temperature on the structural and magnetic properties of MgFe2O4 ceramics prepared by spark plasma sintering

Spark plasma sintering (SPS) is a powerful technique to produce fine grain dense ferrite at low temperature. This work was undertaken to study the effect of sintering temperature on the densification, microstructures and magnetic properties of magnesium ferrite (MgFe2O4). MgFe2O4 nanoparticles were synthesized via sol–gel self-combustion method. The powders were pressed into pellets which were sintered by spark plasma sintering at 700–900°C for 5min under 40MPa. A densification of 95% of the theoretical density of Mg ferrite was achieved in the spark plasma sintered (SPSed) ceramics. The density, grain size and saturation magnetization of SPSed ceramics were found to increase with an increase in sintering temperature. Infrared (IR) spectra exhibit two important vibration bands of tetrahedral and octahedral metal-oxygen sites. The investigations of microstructures and magnetic properties reveal that the unique sintering mechanism in the SPS process is responsible for the enhancement of magnetic properties of SPSed compacts.

Humidity sensor characteristics and electrical properties of Ni–Zn–Dy ferrite material prepared using different chelating-fuel agents

Humidity sensor characteristics and electrical properties of Ni–Zn ferrite material doped with Dy were studied after synthesis via sol–gel self-combustion method. In order to obtain different micro configurations of the material reflected in different porosities, four different fuel agents were involved: citric acid, tartaric acid, cellulose and urea. XRD and XPS techniques were used to certify the composition. The influence of fuel agent and structural features on the electrical properties of ferrite sintered pellets was investigated at room temperature as a function of frequency and humidity. Because the electrical characteristics of a porous material can significantly affect by the humidity, the electrical measurements were carried out in controlled humidity environments. Conduction mechanism is explained in terms of fuel agent influence on phase composition, grain size value, cation distribution and induced strain within spinel lattice by dissolution of voluminous Dy3+ ions. The humidity sensors applicative characteristics of the material are highlight by analyzing the sensitivity, response and recovery times of nickel–zinc–dysprosium ferrite used as active material.

Synthesis of Nickel and Cobalt Ferrite Nanopowders and Selected Properties of Polycarbonate Composites with Nickel Ferrite

NiFe2O4 and CoFe2O4 have been synthesized by sol-gel self-combustion method and high frequency plasma chemical synthesis. Structure and magnetic properties of the synthesized products have been characterized. All the synthesized ferrites are nanocrystalline single phase materials with specific surface area of 30-40 m2/g and calculated particle size of 30-40 nm. Ni and Co ferrites synthesized by high-temperature plasma route are characterized by saturation magnetization Ms of 44,2 emu/g and 75,4 emu/g, remanent magnetization Mr of 10,0 and 32,0 emu/g and coercivity Hc of 74 Oe and 780 Oe, respectively. NiFe2O4 (2 – 10 wt. %) has been introduced in a polycarbonate (PC) matrix by melt compounding. Magnetic as well as elastic properties of PC matrix nanocomposites are increased along with growing NiFe2O4 content.

Effects of Dy3+ substitution on the structural and magnetic properties of Ni0.5Zn0.5Fe2O4 nanoparticles prepared by a sol-gel self-combustion method

A series of Ni-Zn ferrite nanoparticles with a nominal composition Ni0.5Zn0.5DyxFe2-xO4 (x=0.000–0.100 with steps of 0.025) was prepared by a simple sol-gel self-combustion method. The effects of composition and calcined temperatures on their morphology, specific area, magnetic properties and radio frequency heating rate are studied. It is found that all the Dy3+ substituted Ni-Zn ferrites exhibit typical spinel structure. Moreover, Dy3+ substitution can notably reduce the average crystal size and enhance the specific area of Ni-Zn ferrite. The value of specific area reaches 29.25m2/g when x is 0.1, about five times higher than that of Ni0.5Zn0.5Fe2O4 sample. With the increase of Dy3+ content, all the values of Ms, Mr and Hc increase first and then decrease, and they maximize to 67.801emu/g (Ms), 11.10 (Mr) and 79.89G (Hc), improving about 28%, 208% and 92%, respectively, compared with those of Ni0.5Zn0.5Fe2O4, when calcined at 1073K and x is 0.025. In addition, the heating rate of Dy-substituted samples are also enhanced markedly.