Impact of Microstructure on Humidity Influence on Complex Impedance of Iron Manganite

This work deals with our continued research of oxide materials for potential application in gas/humidity sensing. We have made thick film samples using iron manganite powder synthesized by a sol-gel combustion method with a net-like structure, by screen printing on alumina substrate with PdAg interdigitated electrodes. The thick film samples were fired at two temperatures 600 and 800°C. The powder morphology was retained and only the organic compounds in the paste were burnt-out at 600°C, while at 800°C the thick film surface morphology was different where grain growth and individual particles can be observed. We measured complex impedance in a temperature and humidity chamber at room temperature (25°C) in the relative humidity range 30 – 90 % and frequency 100 Hz - 1 MHz. The thick film surface morphology has a significant influence on the effect of humidity on complex impedance. The complex impedance of thick films fired at 600°C was high and did not decrease noticeably with increase in relative humidity (RH), except for RH 80 and 90%, while thick film samples fired at 800°C had an overall lower impedance that reduced more noticeably with increase in RH 40–70% and even more for RH 80 and 90%.This is the peer-reviewed version of the paper:Nikolic, M.V., Vasiljević, Z.Z., Dojčinović, M.P., Vujančević, J., Radovanović, M., 2020. Impact of Microstructure on Humidity Influence on Complex Impedance of Iron Manganite, in: 2020 43rd International Spring Seminar on Electronics Technology (ISSE). Presented at the 2020 43rd International Spring Seminar on Electronics Technology(ISSE), IEEE. [https://doi.org/10.1109/ISSE49702.2020.9120967]Published version: [https://hdl.handle.net/21.15107/rcub_dais_10026

Structure, morphology and photocatalytic properties of CoxMg1-xFe2O4 (0<x<1) spinel ferrites obtained by sol-gel synthesis

Nanocrystalline cobalt magnesium ferrites with varying cobalt and magnesium content (CoxMg1-xFe2O4, 0<x<1) were synthesized using the sol-gel self-combustion method with citric acid as fuel, followed by calcination at 700 C for 2 hours. Structural characterization was performed using Xray diffraction (XRD), field emission scanning electron microscopy (FE-SEM) and Raman spectroscopy. It confirmed the formation of agglomerated nanocrystalline ferrites with an inverse cubic spinel structure. The optical band gap energy was determined using UV/Vis spectrophotometry. It reduced with increased Co content. Visible light photocatalytic activity was tested using natural and artificial light sources through a series of experimental degradations of the methylene blue (MB) solution

Influence of Co2+ ions on photocatalytic properties of MgFe2O4 ferrites

In this work, spinel magnesium cobalt ferrites (CoxMg1-xFe2O4, x = 0.0, 0.1, 0.3, 0.5, 0.7, 0.9) were synthesized by a sol-gel combustion method. Magnesium nitrate, cobalt nitrate and iron nitrate were used as oxidizers and citric acid was used as a reducing agent. The effects of cobalt ions on structural and morphological properties were investigated and characterized by X-ray diffraction (XRD), Raman spectroscopy, Field emission scanning electron microscope (FESEM) and Fourier transform infrared (FT-IR) spectroscopy. A cubic spinel structure formed with a varied distribution of cobalt and magnesium ions on tetrahedral and octahedral sites that depended on their content. All ferrite powders consisted of multigrain agglomerates. Optical properties were investigated by UV- vis spectrophotometry. The photocatalytic activity of as prepared samples was evaluated by measuring the rate of photodegradation reaction of methylene blue (MB) under visible light irradiation. After 240 min, compared to other samples, the sample labeled as Co0.1Mg0.9Fe2O4 showed the best rate of photodecomposition of MB resulting in reduction of 90% of its initial concentration

Visible light photocatalytic activity of nanocrystalline CoxMg1-xFe2O4 (x = 0-1)

The sol-gel combustion method was applied for synthesis of spinel magnesium cobalt ferrites CoxMg1-xFe2O4, with varying cobalt and magnesium content, x = 0.0, 0.1, 0.3, 0.5, 0.7, 0.9. Magnesium nitrate, cobalt nitrate and iron nitrate were used as oxidizers and citric acid was used as a reducing agent. Structural and morphological properties of the obtained ferrite powders were investigated and characterized by X-ray diffraction (XRD), Raman spectroscopy, Field emission scanning electron microscope (FESEM) and Fourier transform infrared (FT-IR) spectroscopy. Optical properties were investigated by UV-VIS spectrophotometry. A cubic spinel structure with multigrain agglomerates formed. Visible light photocatalytic activity of the spinel ferrite powder samples was evaluated by measuring the rate of photodegradation reaction of methylene blue (MB). After 240 min Co0.1Mg0.9Fe2O4 showed the best rate of photodecomposition of MB resulting in 90% of its initial concentration in an alkaline environment

Finding optimal conditions and investigating the structure & morphology of cobalt/magnesium ferrite based cubic spinels (CoxMg1-xFe2O4) as photocatalysts

Cobalt/magnesium ferrites with various mole percentage ratio of the metals (obtained structures are CoxMg1-xFe2O4 with x being 0, 0.1, 0.3, 0.5, 0.7, 0.9, 1.0) were synthesized by sol-gel combustion synthesis using glycine as fuel, following the rules of propellant chemistry. The powders were then sintered at 700 °C for 3 hours. Obtained powders were characterized by X-Ray diffraction (XRD), scanning electron microscopy (SEM), Raman spectroscopy, UV/vis diffuse reflectance spectroscopy (DRS). Investigation of the magnetic properties was also conducted by vibrating sample magnetometry (VSM). The obtained powders were proved to be phase-pure cubic spinels which formed agglomerated micrograins. Series of photocatalytic experiments of methylene blue degradation were done. The influence of different experimental conditions was investigated including variations of: pH values, concentrations of the pollutant, masses of the photocatalyst, different light sources and therefore different light irradiation. Interesting results, including enhancement of the degradation rate with the introduction of cobalt into MgFe2O4 and decrease of the degradation rate with further increase of cobalt content and formation of hard agglomerates, open new possibilities for further investigation of the utilisation of Co/Mg ferrites as photocatalysts

Humidity and Temperature Sensing of Mixed Nickel–Magnesium Spinel Ferrites

Temperature- and humidity-sensing properties were evaluated of NixMg1-x spinel ferrites (0 ≤ x ≤ 1) synthesized by a sol-gel combustion method using citric acid as fuel and nitrate ions as oxidizing agents. After the exothermic reaction, amorphous powders were calcined at 700 °C followed by characterization with XRD, FTIR, XPS, EDS and Raman spectroscopy and FESEM microscopy. Synthesized powders were tested as humidity- and temperature-sensing materials in the form of thick films on interdigitated electrodes on alumina substrate in a climatic chamber. The physicochemical investigation of synthesized materials revealed a cubic spinel Fd3¯m phase, nanosized but agglomerated particles with a partially to completely inverse spinel structure with increasing Ni content. Ni0.1Mg0.9Fe2O4 showed the highest material constant (B30,90) value of 3747 K and temperature sensitivity (α) of −4.08%/K compared to pure magnesium ferrite (B30,90 value of 3426 K and α of −3.73%/K) and the highest average sensitivity towards humidity of 922 kΩ/%RH in the relative humidity (RH) range of 40–90% at the working temperature of 25 °C

Investigating NTC thermistor, ferroelectric and electric properties of Fe2TiO5

Pure phase orthorhombic pseudobrookite (Fe2TiO5) was synthesized using a modified sol-gel method. Bulk samples were obtained by uniaxial pressing of the obtained powder into compacts sintered at 900 °C for 2 h. A noticeable NTC thermistor effect was noted with a B20/55 value of 5747 K and high resistivity of 45 MΩcm at 25 °C. A non-linear current-voltage characteristic was observed in the voltage range (0.2–1100 V) at room temperature (25 °C). Non-saturated (lossy) P-E loops were obtained at both measured frequencies (100 Hz and 1 kHz) more expressed for the higher measured frequency, with the maximal polarization of 0.291 C/cm2 and remanent polarization of 0.123 °C/cm2 for 20 kV/cm2 and 1 kHz. Complex impedance measured in the temperature range 20–330 °C enabled analysis of the contribution of grain boundary and grains to the conduction mechanism. Bulk conductivity data determined in this temperature range was analyzed using Jonscher’s universal dielectric response model and showed that the conduction process followed the nearest neighbor hopping conduction mechanism

Mixed Ni-Mg Spinel Ferrites Used as Materials for Charge Storage Electrodes

Problems that countries all over the world have in common are dependence of economy and energy production on fossil fuels. There is a growing need for energy production and storage routes that are safe for the environment, renewable, efficient and cheap. One of the directions in which science is moving forward is discovering materials suitable for use in batteries and supercapacitors to improve their operating potential, electrical capacity or biocompatibility. The objective is also to synthesize materials for batteries or supercapacitors that are cheap, consist of earth abundant elements and have high electrochemical activity. In this work, mixed nickel-magnesium ferrites NixMg1−xFe2O4, with x being 0, 0.1, 0.3, 0.5, 0.7, 0.9 and 1, were synthesized via sol-gel combustion synthesis with citric acid used as fuel and nitrate ions used as oxidizing agents. Combusted powders were calcined at 700 °C. The structure and morphology of the powders were characterized with X-ray diffraction method (XRD), field emission scanning electron microscopy (FESEM), Raman and FTIR spectroscopy. The band gap was calculated by using UV/Vis diffuse reflectance spectroscopy (DRS). Samples were cast on nickel foam and tested as energy storage materials in a three-electrode setup in 3 M KOH aqueous solution as electrolyte. The methods used were cyclic voltammetry (CV) and constant current chronopotentiometry to obtain galvanostatic charge-discharge (GCD) curves. Results show that all of the synthesized materials show battery-type charge storage in alkaline electrolyte due to the formation of metal cation oxyhydroxides. With increasing nickel content, electrochemical activity drops. The highest value of capacity, 34.3 mA h g-1 at the current density of 500 mA g-1 is ascribed to magnesium ferrite, MgFe2O4

Mixed Ni-Mg Spinel Ferrites Used as Materials for Charge Storage Electrodes

Problems that countries all over the world have in common are dependence of economy and energy production on fossil fuels. There is a growing need for energy production and storage routes that are safe for the environment, renewable, efficient and cheap. One of the directions in which science is moving forward is discovering materials suitable for use in batteries and supercapacitors to improve their operating potential, electrical capacity or biocompatibility. The objective is also to synthesize materials for batteries or supercapacitors that are cheap, consist of earth abundant elements and have high electrochemical activity.In this work, mixed nickel-magnesium ferrites NixMg1−xFe2O4, with x being 0, 0.1, 0.3, 0.5, 0.7, 0.9 and 1, were synthesized via sol-gel combustion synthesis with citric acid used as fuel and nitrate ions used as oxidizing agents. Combusted powders were calcined at 700 °C. The structure and morphology of the powders were characterized with X-ray diffraction method (XRD), field emission scanning electron microscopy (FESEM), Raman and FTIR spectroscopy. The band gap was calculated by using UV/Vis diffuse reflectance spectroscopy (DRS). Samples were cast on nickel foam and tested as energy storage materials in a three-electrode setup in 3 M KOH aqueous solution as electrolyte. The methods used were cyclic voltammetry (CV) and constant current chronopotentiometry to obtain galvanostatic charge-discharge (GCD) curves. Results show that all of the synthesized materials show battery-type charge storage in alkaline electrolyte due to the formation of metal cation oxyhydroxides. With increasing nickel content, electrochemical activity drops. The highest value of capacity, 34.3 mA h g-1 at the current density of 500 mA g-1 is ascribed to magnesium ferrite, MgFe2O4

Mixed Ni-Mg Spinel Ferrites Used as Materials for Charge Storage Electrodes

Problems that countries all over the world have in common are dependence of economy and energy production on fossil fuels. There is a growing need for energy production and storage routes that are safe for the environment, renewable, efficient and cheap. One of the directions in which science is moving forward is discovering materials suitable for use in batteries and supercapacitors to improve their operating potential, electrical capacity or biocompatibility. The objective is also to synthesize materials for batteries or supercapacitors that are cheap, consist of earth abundant elements and have high electrochemical activity.In this work, mixed nickel-magnesium ferrites NixMg1−xFe2O4, with x being 0, 0.1, 0.3, 0.5, 0.7, 0.9 and 1, were synthesized via sol-gel combustion synthesis with citric acid used as fuel and nitrate ions used as oxidizing agents. Combusted powders were calcined at 700 °C. The structure and morphology of the powders were characterized with X-ray diffraction method (XRD), field emission scanning electron microscopy (FESEM), Raman and FTIR spectroscopy. The band gap was calculated by using UV/Vis diffuse reflectance spectroscopy (DRS). Samples were cast on nickel foam and tested as energy storage materials in a three-electrode setup in 3 M KOH aqueous solution as electrolyte. The methods used were cyclic voltammetry (CV) and constant current chronopotentiometry to obtain galvanostatic charge-discharge (GCD) curves. Results show that all of the synthesized materials show battery-type charge storage in alkaline electrolyte due to the formation of metal cation oxyhydroxides. With increasing nickel content, electrochemical activity drops. The highest value of capacity, 34.3 mA h g-1 at the current density of 500 mA g-1 is ascribed to magnesium ferrite, MgFe2O4