Iron Manganite Research Articles

Nanocrystalline FeMnO3 Powder as Catalyst for Combustion of Volatile Organic Compounds.

The paper shows the obtaining of nanocrystalline iron manganite (FeMnO3) powders and their investigation in terms of catalytic properties for a series of volatile organic compounds. The catalyst properties were tested in the catalytic combustion of air-diluted vapors of ethanol, methanol, toluene and xylene at moderate temperatures (50-550 °C). Catalytic combustion of the alcohols starts at temperatures between 180 °C and 230 °C. In the case of ethanol vapors, the conversion starts at 230 °C and increases rapidly reaching a value of around 97% at 300 °C. For temperatures higher than 300 °C, the degree of conversion is kept at the same value. In the case of methanol vapors, the conversion starts at a slightly lower temperature (180 °C), and the degree of conversion reaches the value of 97% at a higher temperature (440 °C) than in the case of ethanol, and it also remains constant as the temperature increases. Catalytic combustion of the hydrocarbons starts at lower temperatures (around 50 °C), the degree of conversion is generally lower, and it increases proportionally with the temperature, with the exception of toluene, which shows an intermediate behavior, reaching values of over 97% at 430 °C. The studied iron manganite can be recommended to achieve catalysts that operate at moderate temperatures for the combustion of some alcohols and, especially, ethanol. The performance of this catalyst with regard to ethanol is close to that of a catalyst that uses noble metals in its composition.

How defects in lanthanum iron manganite perovskite structures promote the catalytic reduction of NO by CO

Adjusting the defect level during synthesis of A- and B-site deficient lanthanum iron manganite (LFM) perovskites shows that non-stoichiometry can beneficially influence the catalytic reactivity to N2 in the reduction of NO by CO on noble metal-free LFM-based perovskites. Optimal steering of La deficiency and the associated redox chemistry to reduce the near-surface regions during catalytic operation at low temperatures is the key factor. Surface enrichment by reducible B site cations and a proper design of structural defects resulting from the optimum introduction of La defects exclusively cause in-situ reduction of surface-near regions by CO oxidation, as well as formation of oxygen vacancies for enhanced NO and N2O reactivity. Excess doping with defects causes structural instability and continuous supply of oxygen from the catalyst bulk to the surface at elevated temperatures. Introduction of B site vacancies leads to surface enrichment by non-reducible lanthanum cations, causing suppressed catalyst activity undercutting even stoichiometric LFM.

Tailoring the metal-perovskite interface for promotional steering of the catalytic NO reduction by CO in the presence of H2O on Pd-lanthanum iron manganite composites

We steer the catalytic performance and morphology of Pd – lanthanum iron manganite (LFM) perovskite interfaces towards optimum NO+CO reactivity in presence of water by following different preparation approaches. Strong CO adsorption for samples without Pd-perovskite interface acts as an inhibitor for adsorption/dissociation of NO, while samples with an extended interface, additionally aided by H2O, show reduced CO poisoning. The optimized use of lattice oxygen for CO oxidation at the phase boundary and its replenishment from NO dissociation allows for the formation of more poisoning-resistant active sites for NO activation. Reaction of species from H2O dissociation with adsorbed CO assists further surface clean off. Enhanced NO reduction activity on the “de-poisoned” interface leads to a pronounced increase in N2 selectivity. Preferred production of NH3 at low NO and high CO and H2O concentration indicates that water gas shift intermediates are linked to increased surface hydrogen activity and increased NH3 formation.

Fabrication of Spike-Like Spherical Iron Manganite Nanoparticles for the Augmented Photocatalytic Degradation of Methylene Blue Dye

Fabrication of Spike-Like Spherical Iron Manganite Nanoparticles for the Augmented Photocatalytic Degradation of Methylene Blue Dye

THE STRUCTURAL, IMPEDANCE AND DIELECTRIC A FERRITE CORE OF IRON MANGANITE AND ITS COMPOSITE

THE STRUCTURAL, IMPEDANCE AND DIELECTRIC A FERRITE CORE OF IRON MANGANITE AND ITS COMPOSITE. Samples with single-phase MnFeO3 and multiphase MnFeO3/ZnFe2O4 (30/70), and MnFeO3/ZnFe2O4/LaMnO3 (30/40/30) have been successfully prepared as ferrite cores by the solid-state reaction method using high energy milling. Crystal structure, surface morphology, impedance, AC-conductivity and dielectric quantities, such as dielectric constant and dielectric loss have been studied. The crystalline structures for MnFeO3, ZnFe2O4, and LaMnO3 are hexagonal, cubic and monoclinic, The Rietveld program used for XRD analysis resulted in the composition fractions of single phase MnFeO3, multiphase MnFeO3/ZnFe2O4 (31/69), and MnFeO3/ZnFe2O4/LaMnO3 (31/40/29). The morphology of all samples has a heterogeneous shape and size with low porosity. The single-phase impedance of MnFeO3 is higher than the multiphase sample. The conductivity of the three samples has the same pattern, which is relatively constant at low frequencies and begins to increase at frequencies above 10 kHz. The dielectric constant and dielectric loss (tan 𝜕) have high values at low frequencies, decrease exponentially with increasing frequency and are relatively fixed at high frequencies.

All-Inorganic p-n Heterojunction Solar Cells by Solution Combustion Synthesis Using N-type FeMnO3 Perovskite Photoactive Layer.

This study outlines the synthesis and physicochemical characteristics of a solution-processable iron manganite (FeMnO3) nanoparticles via a chemical combustion method using tartaric acid as a fuel whilst demonstrating the performance of this material as a n-type photoactive layer in all-oxide solar cells. It is shown that the solution combustion synthesis (SCS) method enables the formation of pure crystal phase FeMnO3 with controllable particle size. XRD pattern and morphology images from TEM confirm the purity of FeMnO3 phase and the relatively small crystallite size (∼13 nm), firstly reported in the literature. Moreover, to assemble a network of connected FeMnO3 nanoparticles, β-alanine was used as a capping agent and dimethylformamide (DMF) as a polar aprotic solvent for the colloidal dispersion of FeMnO3 NPs. This procedure yields a ∼500 nm thick FeMnO3 n-type photoactive layer. The proposed method is crucial to obtain functional solution processed NiO/FeMnO3 heterojunction inorganic photovoltaics. Photovoltaic performance and solar cell device limitations of the NiO/FeMnO3-based heterojunction solar cells are presented.

Structural, morphological and textural properties of iron manganite (FeMnO3) thick films applied for humidity sensing

Iron manganite (FeMnO3) powder with a cubic (bixbyite, Ia3-) crystal structure was obtained by a solid state reaction. Thick film paste (powder + organic vehicles) was screen printed on alumina substrate with test interdigitated PdAg electrodes. Significant porosity (60.6%) composed of macropores (larger than 100 nm) was determined by Hg porosimetry, changing only slightly from the first extrusion run indicating a stable pore system. Hg porosimetry evaluation of thick film samples enabled estimation of true textural parameters of the thick film compared to powder. Impedance response of the thick film sensor was monitored in a humidity chamber in the relative humidity (RH) range 30–90%, at room temperature (25 °C) and frequency range from 42 Hz to 1 MHz. At 100 Hz the impedance reduced from 10.41 MΩ for RH 30% to 0.68 MΩ for RH 90%. Analysis of complex impedance using an equivalent circuit showed the dominant influence of grain boundaries. The sensor response and recovery was fast (several seconds) and a relatively low hysteresis value of 2.8% was obtained.

Synthesis and antibacterial activity of iron manganite (FeMnO3) particles against the environmental bacterium Bacillus subtilis.

Nanocrystalline iron manganite powder was synthesized using the sol–gel combustion process, with glycine as fuel. It was further calcined at 900 °C for 8 h, resulting in the formation of a loose cubic FeMnO3 powder with a small specific surface area, net-like structure and plate-like particles as confirmed by XRD, N2 physisorption, FESEM and TEM analyses. The metal ion release was studied by ICP-OES and showed that less than 10 ppb of Fe or Mn ions were released by leaching in water, but 0.36 ppm Fe and 3.69 ppm Mn was found in LB (Luria–Bertani) bacterial medium. The generation of reactive oxygen species (ROS) was monitored in distilled water and bacterial medium and showed that FeMnO3 particles do not generate O2˙− ions with or without UV irradiation, but synthesize H2O2 and show an antioxidative effect. Besides the higher stability of FeMnO3 particles in aqueous solution they showed an inhibitory effect on Bacillus subtilis growth in LB medium even at low concentrations (0.01 mg ml−1), but not in BHI medium even at 1 mg ml−1. This study points out that the mechanism of antibacterial action of engineered metal oxides needs continued investigation and specific experimental controls.

Dielectric Properties of Nanocrystalline Yttrium Iron Manganites Synthesized by Sol–Gel Method

Hexagonal yttrium manganites, YMnO3, exhibit multiferroic behavior and doping suitable cations at the either Y-site or Mn-sites can significantly influence the structural and electrical properties. Nanocrystalline Fe3+-doped YMnO3 manganites substituting at the Y-sites having the general formula Y1-xFexMnO3 with x = 0, 0.1, 0.15, 0.20, 0.25 were synthesized by sol–gel method and were sintered at 1100 °C for 1 h. X-ray diffraction (XRD) studies confirmed the hexagonal phase of the samples and various structural parameters viz. lattice constant, crystallite size, X-ray density were evaluated from the XRD data. The crystallite size of the nanocrystalite manganites ranges from 39 to 63 nm. Investigation on the dielectric properties such as dielectric constant and dielectric loss of the samples was done using an impedance analyzer. The studies showed large increase in dielectric constant and dielectric loss for higher Fe3+-doped manganites i.e. for x ≥ 0.20. Temperature variation of dielectric properties revealed a ferroelectric phase transitions which shift to lower temperature with the increase of Fe3+ ion substitution.

Nanowires assembled from iron manganite nanoparticles: Synthesis, characterization, and investigation of electrocatalytic properties for water oxidation reaction

Abstract

Influence of humidity on complex impedance and dielectric properties of iron manganite (FeMnO3)

Bulk samples of iron manganite with a cubic $$Ia\bar{3}$$ crystal structure were obtained by solid state synthesis (combination of milling and calcination) of starting hematite (Fe2O3) and manganese carbonate (MnCO3) powders followed by sintering green samples at 1000 °C for 4 h. Structural characterization performed by XRD and SEM analysis confirmed the formation of iron manganite in the form of a porous network of grains and pores with average particle size of 530 and 430 nm, respectively. The influence of humidity on complex impedance and dielectric properties was monitored in the relative humidity range 30–90% in a climatic chamber in the frequency range 42 Hz–1 MHz at working temperatures of 25 and 50 °C. At the lowest frequency of 42 Hz the impedance reduced with relative humidity from 57.9 (RH 30%) to 3.21 MΩ (RH 90%) at 25 °C, and from 23.3 (RH 30%) to 1.3 MΩ (RH 90%) at 50 °C that is approximately 20 times. Analysis of complex impedance using an equivalent circuit showed the dominant influence of grain boundaries. The influence of grains (bulk) was taken into account for higher relative humidity values (70% at 25 °C and 60% at 50 °C) that is related to the mechanism of water interaction with the sample surface. The dielectric constant and loss tangent decreased with increase in frequency in accordance with the Maxwell–Wagner type interfacial polarization mechanism and also increased with increase in relative humidity.

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.

Structural, magnetic, and electrical property of nanocrystalline perovskite structure of iron manganite (FeMnO3)

In this work, nanostructure FeMnO3 perovskite material was synthesis by sol–gel auto combustion method using the glycine as a chelating agent for the first time in the literature. The synthesized materials were investigated structural, electrical, and magnetic properties by various characterization techniques. The X-ray diffraction reveals that the density and specific surface value are 2.54 g/cm3 and 1.468 m2/g, respectively. FE-SEM investigated surface morphology in the nanoscale region. The FeMnO3 material is existing antiferromagnetism at room temperature. Electrical property such as dielectric constant, tangent loss, and impedance spectrum, Nyquist plot with an equivalent circuit, AC conductivity, and electric modulus was analysed. The real part of permittivity, dielectric tangent loss with varying with temperature shows that the behaviour of Maxwell–Wagner relaxation in the FeMnO3 might be observed oxygen vacancy. The Nyquist plot gives more information-related electrical conduction process and individual contribution of grain and grain boundaries. The resistance (Ω) and capacitance (farads) values are varied with increasing temperature. An electric modulus value is varied under suppression electrode polarization and shows the effect of bulk and grain boundaries.

Comparative studies of structural and electrical properties of yttrium iron manganites prepared by ceramic method and sol-gel auto combustion method

ABSTRACTPolycrystalline yttrium iron manganites – YMn1-xFexO3 (with x = 0.0, 0.1, 0.15, 0.20) were synthesized by ceramic method and sol-gel auto-combustion method. XRD confirmed the formation of hexagonal phase in all samples. The hexagonal a– and c- parameters for the samples prepared by the sol-gel method are found to be closer to the stoichiometric values. The room temperature frequency variation of electrical properties such as dielectric constant, dielectric loss and ac conductivity showed a dispersive behavior for all the samples. The values of dielectric constant and dielectric loss are found to be lower for the sol-gel prepared samples.

Wet coprecipitation preparation of perovskite-type iron manganite nano powder pure phase using nitrate precursors: structural, opto-electronic, morphological and photocatalytic activity for degradation of Nile blue dye

A pure phase of iron manganite nano powder has been prepared by the wet coprecipitation route using nitrate precursors subject to heat treatment at 650 °C for 4 h in air. The structural, opto-electronic, thermal and morphological properties of iron manganite nano powder were investigated by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), energy-dispersive X-ray spectroscopy (EDX), and UV–Vis diffuse reflectance spectroscopy (UV–Vis DRS). XRD results showed that a pure phase nano powder iron manganite with perovskite-type structure is formed. FESEM results showed that an average size of the iron manganite nano particles at about 64 nm with a narrow particle size distribution. UV–vis DRS reveal the optical band gap of 1.901 eV (652 nm) with a strong absorption at visible region of solar light. The photcatalytic activity of pure phase nano powder iron manganite perovskite catalyst displayed an excellect activity in degradation of Nile blue organic dye with 95% efficiency and 86% TOC removal in 80 min of irradiation.

Structural and electrical studies of sol–gel synthesized nanocrystalline hexagonal yttrium iron manganite ceramics

Hexagonal yttrium manganites, YMnO3, are interesting materials for their multiferroic behavior. Substituting suitable cations either at the Y-site or Mn-site offers great opportunities to produce a variety of manganites and tune their properties. Nanocrystalline yttrium iron manganites with the compositional formula Y[Formula: see text]Fe[Formula: see text]MnO3, [Formula: see text] = 0.0, 0.10, 0.15, 0.20 and 0.25, were synthesized by sol–gel autocombustion method. The prepared samples were heated at 1100[Formula: see text]C for 1 h. Another set of samples with compositional formula YFe[Formula: see text]Mn[Formula: see text]O3, [Formula: see text] = 0.0, 0.10, 0.15, 0.20 and 0.25, were also synthesized by the same method and heated at 1100[Formula: see text]C for 1 h. Various characterizations were done on these manganite systems synthesized by substituting iron at different sites. X-ray diffraction (XRD) technique studied the structure of the samples and analysis of XRD patterns confirmed the formation of hexagonal phase in the samples. Structural parameters such as lattice constants, crystallite size, theoretical density, etc. were determined using the XRD data. The unit cell dimensions have been found to agree with the standard data and the Debye–Scherrer crystallite size obtained from XRD data ranges from 42 nm to 77 nm. The room temperature frequency variations of electrical properties such as dielectric constant, dielectric loss and AC conductivity were measured in the range of 100 Hz–2 MHz and the variations showed a dispersive behavior for all the samples. The various measurements and the results obtained were studied and discussed in the paper.

NO sensitivity of perovskite-type electrode materials La0.6Ca0.4B′1−xB″xO3±δ (B′ = Mn, Cr; B″ = Ni, Fe, Co; x = 0, 0.1, …, 0.6) in mixed potential sensors

Perovskite-type electrode materials of the compositions La0.6Ca0.4B′1−xB″xO3±δ (B=Mn, Cr; B″=Ni, Co, Fe; x=0, …, 0.6) were investigated with regard to their NO sensitivity and the cross-sensitivity to NO2 and propylene in a potentiometric solid electrolyte measuring setup. The highest NO sensitivity was found for nickel and iron manganites with x=0.2 and 0.3. Dependencies on the NO gas concentration were found using impedance spectroscopy. For some materials, the catalytic conversion of NO, NO2, methane and propene was determined by thermal investigation in the temperature range of 25–800°C.

Structural and catalytic characterization of nanostructured iron manganite

In this work the self-combustion method was applied to synthesize simple iron manganite (FeMnO3) nanopowders. Among the various methods known, the self-combustion method allows a good control over the size of the material particles. According to this method the thermal energy for the synthesis of manganite crystallites is supplied by a fast exothermic combustion reaction. The final product is a finely divided powder. The procedure offers the advantage of producing ultra-fine, homogeneous reproducible multicomponent ceramic powders with precise stoichiometry.We determined a series of structural and catalytic properties of nanostructured materials obtained by this method. The catalytic activity of the nanocrystalline iron manganite for the combustion of acetone vapors and of some hydrocarbons diluted in air was studied. The perovskite thus obtained has a favorable microstructure for obtaining catalysts for the combustion of the gases and vapors.

Iron Manganites Synthesis by the Soft Chemistry Method

ABSTRACTThe iron manganites FexMn(3−x)O4 synthesis by soft chemistry method have been studied. The main difficulty is to obtain single phase spinel with high Mn content (0.4< x < 1.3). Oxalate precursor powders of these materials with controlled shape and nanoscopic size have been prepared. The precursors are then heat treated with a H2/H2O/N2 gas mixture at low temperature. The resulting stoechiometric spinels are metastable phases with high specific surface area and are highly reactive toward oxygen. Therefore, these oxide can be oxidized in air at low temperature in order to produce mixed valence defect manganites FexMn(3−x)O4+δ with a good reproducibility on the oxygen content. Although, some problems persist for the higher Mn contents, as the oxygen partial pressure for the reduction must be controlled precisely in order to produce the stoechiometric spinel at low temperature. The development of a low temperature reduction system, with oxygen partial pressure controlled by oxygen electrochemical pumping, is in progress.

Aging of iron manganite negative temperature coefficient thermistors

“Aging,” defined as the drift of resistance with temperature after 1000 h, was investigated for iron manganite temperature coefficient thermistors. For these devices, aging is relatively large, about 10%. The cationic distributions before and after aging were determined by Mössbauer spectroscopy. These distributions explain all the x-ray diffraction and correlated electrical data. The origin of the aging observed on iron manganites thermistors has been identified. It is due to the migration of Fe3+ ions from tetrahedral to octahedral sites of the spinel structure in order to reach a structural equilibrium.