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Abstract: CuFe2O4/xCeO2 (x =0, 1, 5, 10 and 20wt%) nanocomposites have been prepared by urea–nitrate combustion method. The particle size of the as-prepared CuFe2O4/5wt% CeO2 nanocomposite is 5–10nm which has been revealed from TEM and HRTEM images. The as-synthesized materials have been sintered at four different temperatures (600, 800, 1000 and 1100°C) for 5h. The XRD analysis of the samples reveals that the prepared materials possess tetragonal structure and have the composite behaviour. The 1100°C sintered samples have further been characterized by FT-IR, UV–vis, SEM, ac electrical conductivity, dielectric constant, loss tangent, and Mössbauer spectra. The SEM images clearly show that CeO2 grows on the surface of the CuFe2O4. The electrical properties enumerate the ferrimagnetic behaviour of the synthesized materials. The Mössbauer spectra confirm both the inverse spinel structure of the prepared materials and the Fe3+ state of iron ions. [Copyright &y& Elsevier]

Abstract: An ever first attempt to synthesize nanocomposites of SnO2 coated CuFe2O4 has been made using urea–nitrate combustion method. Effect of various concentrations of SnO2 (1, 5, 10 and 20wt.%) at three different sintering temperatures viz., 800, 1000 and 1100°C for optimizing the compound formation has been studied individually. The synthesized materials were characterized by XRD, TEM, HRTEM, SAED, SEM, FT-IR, UV–vis, electrical conductivity and impedance spectra measurements. The XRD spectra reveal that 1100°C-sintered sample is of ultra pure and well-defined crystalline nature irrespective of the concentration of SnO2. The grain size of the materials has been found to get increased as a function of sintering temperature and the extent of SnO2 substitution. The TEM and HRTEM figures evidence the nanocrystalline nature of the product. SAED pattern confirms the presence of single phase and polycrystalline of the final product. The band gap values were calculated from UV–vis spectra, which confirm the lowest band gap value for the 5wt.% SnO2 added sample. The solid-state impedance and the electrical properties of the materials are in favour of the grain and grain boundary effect and the normal behavior of spinel compounds, respectively. [Copyright &y& Elsevier]

Abstract: Nanocrystalline CuFe2O4 and CuFe2O4/xSnO2 nanocomposites (x=0, 1, 5wt%) have been successfully synthesized by one-pot reaction of urea–nitrate combustion method. The transmission electron microscope study reveals that the particle size of the as synthesized CuFe2O4 and CuFe2O4/5wt%SnO2 are 10 and 20nm, respectively. The SnO2 coating on the nanocrystalline CuFe2O4 was confirmed from HRTEM studies. The resultant products were sintered at 1100°C and characterized by XRD and SQUID for compound formation and magnetic studies, respectively. The X-ray diffraction pattern shows the well-defined sharp peak that confirms the phase pure compound formation of tetragonal CuFe2O4. The zero field cooled (ZFC) and field cooled (FC) magnetization was performed using SQUID magnetometer from 2 to 350K and the magnetic hysteresis measurement was carried out to study the magnetic properties of nanocomposites. [Copyright &y& Elsevier]

Nanocomposites are a cohesive class of materials, which have many technological applications due to their excellent properties, realizable within the range of 1–100 nm sizes. Ferrite nanocomposites have been used as the potential candidate materials for photocatalytic and electrocatalytic anodes for oxidation of organic compounds like phenol, anodes for lithium batteries, inert anode for aluminium electrolysis, etc. Recently these are envisaged as an eco-friendly substitute for carbonaceous materials in electrochemical applications. In the present study the CuFe 2 O 4 /SnO 2 nanocomposites have been prepared by a novel combustion method. The TEM figure confirms the nanocrystalline nature of the as-synthesized product. XRD spectra show the well-defined crystalline nature and a phase transition of tetragonal to cubic on increased SnO 2 substitution. The band gap values calculated from the UV-Vis spectra are in the vicinity of semiconducting range. The maximum a.c. electrical conductivity of 1.75×10 -3 S · cm -1 was obtained for CuFe 2 O 4 /5% SnO 2 composition. The impedance spectrum also confirms the semiconducting behavior of the materials. [ABSTRACT FROM AUTHOR]

Abstract: The La3+ substituted nanocrystalline strontium ferrite has been prepared by citrate combustion method using metal nitrate salts as cation precursors and citric acid as a fuel. The structural characteristics of the compounds have been evaluated using XRD and FTIR. The existence of the single-phase perovskite structure with nanocrystalline size has been confirmed from the X-ray powder diffraction patterns. The stretching and bending vibrations of the metal cations are confirmed from the FTIR spectra. The electrical conductivity of the materials is found to increase with increasing temperature measured by using a modified four-probe technique. The electrochemical behavior has been studied by using potentiostatic polarization method in KOH solutions at two different concentrations of 1 and 2M. From the polarization studies it has been found that the material La0.4Sr0.6FeO3 gives the lowest corrosion rate of 0.001mmpy in 1M KOH solution. [Copyright &y& Elsevier]

The non-stoichiometric perovskite-type oxide SrFeO3−δ was prepared by Co-precipitation method using metal nitrate salts as cation precursors and NaOH solution as the precipitating agent. From the thermogravimetric analysis, the strontium orthoferrite phase formation was found to be complete at 550 °C. The XRD spectra showed the synthesized compound to be of orthorhombic structure. The FTIR spectra confirm the characteristic peaks of SrFeO3−δ stretching and bending vibrations. The submicron size of the synthesized compound was showed by scanning electron microscope. The physical properties such as density, porosity and hardness were also carried out. The DC electrical conductivity measurements gave the maximum value of 84 S cm−1 for the 1000 °C sintered sample. The electrochemical behavior of the 800 and 1000 °C sintered SrFeO3−δ electrode was performed in alkaline KOH solution by potentiostatic polarization and electrochemical impedance spectroscopy. [Copyright &y& Elsevier]

Metallic ferrites are investigated as prospective materials for different applications especially as anodes in extractive metallurgy. CuFe2O4, one of the important ferrites, is envisaged for substituting the carbon anode in Hall–Heroult cells. A single step combustion process has been used for the synthesis of CuFe2O4 powder from cupric nitrate, ferric nitrate and urea. The experimental conditions for maximum conversion efficiency of the precursor powders have been optimized. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM) have confirmed the formation, structure and homogeneity of the as-prepared powders. The detailed physical, electrical and structural characterization of the materials have been carried out for the specimens obtained on sintering at different temperatures up to 1000 °C. [Copyright &y& Elsevier]

Abstract: Ultrafine powders of nanocrystalline CuFe2O4 and CuFe2O4/10wt.% SnO2 nanocomposites are prepared by a urea–nitrate combustion method. Phase pure and highly crystalline CuFe2O4 (tetragonal structure) and CuFe2O4/SnO2 (cubic structure) are obtained after sintering at 1100°C. The average particle size is 10–20 and 20–30nm, respectively. Both the nanoferrite anodes have an excellent specific capacity of greater than 800mAhg−1 versus Li metal. It is concluded that SnO2 doping improves the coulombic efficiency of copper ferrite anodes from 65 to 99.5% via an enhanced structural stability. [Copyright &y& Elsevier]

Awareness in environmental hygiene and escalation in the energy cost in electrometallurgical industries have necessitated a reauditing of the production technologies, more so in the case of aluminium as it is a highly energy intensive process. Metal aluminates are of interest due to their technological applications in aggressive environments. The preparation of the metal aluminates usually involves the solid state reaction (SSR) of the corresponding metal oxides or sulphates at high temperatures. The present investigation is the preparation of MgAl2O4 using the metal oxides by solid state synthesis. The compacts were sintered at high temperatures and their properties such as particle size, density, porosity, hardness, ac electrical conductivity and dielectric behaviour were evaluated. The phase formation and structural properties have been ascertained by XRD, FTIR, TG/differential thermal analysis (DTA) and scanning electron micrograph (SEM) studies. The sinterability characteristics of the materials strongly dependent on the temperature of the processing. The XRD patterns confirm the phase formation of MgAl2O4. The FTIR spectra show the structural details of the synthesized compound. From the SEM micrographs, it is revealed that the agglomeration process progresses with the increasing temperature. The ac electrical conductivity and dielectric behaviour of aluminates strongly depend upon sintering time, temperature and spinel formation. [Copyright &y& Elsevier]

In recent years, the awareness of energy, environment and economy for the metallurgical industries, has necessitated the development of mixed oxide-based oxygen-evolving anode materials to avoid the emission of greenhouse gases, such as CO2, CO, and CF6, during electrolysis. In this regard, the noncarbon anode material Ni1−xMgxFe2O4 (x=0.0, 0.3, 0.6, 0.9) has been prepared by nonconventional citrate gel process using metal nitrate salts as cation precursors and citric acid as a chelating agent. The X-ray analysis showed the existence of single-phase spinel structure with increase of lattice parameter and tetrahedral radius with increasing Mg2+ ion concentration, as against a decrease in density. The FT-IR spectra show the characteristic features of the synthesized ferrite compounds. The DC electrical conductivity increases with increasing temperature. It also increases with an increase of Mg2+ ion concentration and reaches a maximum value of 3.3 S cm−1 at x=0.6 at which, the activation energy for conduction is found to be minimum. The effect of the Mg2+ substitution on the electrocatalytic activity of the electrodes towards the oxygen evolution reaction (OER) is studied by using steady state potentiostatic polarization measurements in alkaline KOH solution. The Roughness factor (Rf) and the Double layer capacitance (Cdl) of the synthesized electrodes were measured by using Electrochemical Impedance Spectroscopy. The chemical stability of the Ni0.4Mg0.6Fe2O4 electrode, which is observed to possess optimum properties, was ascertained in a saturated cryolite–alumina melt at the 960 °C, the operating temperature of aluminium electrolysis. [Copyright &y& Elsevier]

Abstract: Fine crystalline LaFeO3 and antimony-substituted compounds have been prepared by co-precipitation method. The as synthesized materials have been sintered at 1000°C for single-phase compound formation and evaluated for their electrical and structural properties. TG/DTA studies ascribed that the precursor powders have undergone rapid changes during the transformation of LaFeO3 and substituted compounds. XRD data reveal the presence of well-defined sharp peaks, indicating the single-phase perovskite structure of LaFeO3 and polycrystalline structure of LaFeO3 and Sb2O3 compounds. The FT–IR spectra exhibit an absorption band corresponding to Fe–O stretching vibration, which is shifted on the substitution of Sb3+ ions. The temperature dependent d.c. conductivity shows the semiconducting behavior of the synthesized materials. The band gap values are found to increase upto x =0.4 and decrease on further increase in concentrations of the Sb3+ ions. The decrease in dielectric constant with increasing frequency explained the Maxwell–Wagner Interfacial polarization model. [Copyright &y& Elsevier]

Abstract: A series of Sn4+ substituted NiFe2O4 with general formula Ni1−x Sn x Fe2O4 (x =0.0, 0.2, 0.4, 0.6, and 0.8) has been prepared by novel combustion synthetic method. The prepared compounds have been sintered at 1000°C and evaluated for their structural and electrical properties. XRD studies reveal the synthesized compounds are nanocrystalline size with cubic structure. The Fourier transform infrared (FT-IR) spectra show the characteristic features of the synthesized ferrite compounds. The UV–vis spectra reveal the optical band gap of the synthesized compounds. The dc electrical conductivity of the compounds found to increase with increasing measuring temperature. A maximum dc electrical conductivity of 6.0Scm−1 was obtained at a measuring temperature of 1000°C in the composition of x =0.8, for which the activation energy for conduction is found to be minimum. [Copyright &y& Elsevier]

The structural and electrical properties of magnesium-substituted nickel ferrite having the general formula of Ni1-xMgxFe2O4 (x=0, 0.3, 0.6, 0.9) has been studied as a function of magnesium ion concentration. The materials have been prepared by citrate gel process using metal nitrate salts as a cation precursors and citric acid as gelating agent. The powder X-ray diffraction pattern confirms fcc structure for the synthesized compound. The variation of lattice parameter and the tetrahedral radius increases with increase in Mg2+ ion concentration. The AC electrical parameters such as dielectric constant (#x03B5;′) and loss tangent (tan δ) for all the systems have been studied as a function of frequency in the range 50 Hz to 10 kHz at room temperature. A maximum DC electrical conductivity of 3.3 S cm-1 was obtained at a temperature of 1000°C and a AC electrical conductivity of 10.94×10-6at 10 kHz was observed in the composition x=0.6 i.e. for Ni0.4Mg0.6Fe2O4 compound which may be due to the maximum Fe2+ concentration in the octahedral sites. The dielectric constant follows the Maxwell''s–Wagner interfacial polarization and the relaxation peaks were observed in the dielectric loss properties. The FTIR spectra show the characteristic peaks of ferrite sample. The morphological features were studied using scanning electron microscope. [Copyright &y& Elsevier]