Structural,dielectric and magnetic properties of Bi–Mn doped SmFeO3

We have studied the structural, magnetic, dielectric and impedance properties of the Sm_1-xBi_xFe_1-yMn_yO₃ [SmFeO₃ (SFO), Sm_0.9Bi_0.1FeO₃ (SBFO), Sm_0.9Bi_0.1Fe_0.9Mn_0.1O₃ (SBFMO)] polycrystalline samples synthesized by solid-state reaction method. Rietveld refinement of room temperature (RT) powder x-ray diffraction pattern confirms the orthorhombic crystal structure with Pnma/Pbnm space group. The average particle size of Bi doped and co-doped (Bi–Mn) samples determined from SEM analysis are 5.6 μm and 5.2 μm, respectively. Room temperature field-dependent magnetization increases, suggesting the presence of magnetic contribution due to the Rare earth-Fe ion interaction which persists even at RT. However, with co-doping of Bi and Mn, a decrease in magnetization is observed, which corresponds to the dilution of Fe³⁺-Fe³⁺ interactions due to the presence of Mn³⁺ ions. The observed values of magnetization at 90 kOe for Bi doped sample is (2.87 emu/g) approximately two times and for codoped (0.7 emu/g) sample is nearly half of that of pristine sample (1.51 emu/g). Dielectric measurements as a function of frequency/temperature and impedance analysis using equivalent circuit model reveal grain and grain boundary contributions of SBFO (at high temperature) and SBFMO (for all temperature) samples towards the electrical properties indicating the electrically heterogeneous nature of these samples. However, for SFO sample grain contribution is dominant. Observed value of dielectric constant varies from ~10³-10⁴ with Bi–Mn doping. The conduction mechanism of the studied samples has been explained by considering Jonscher power law. Arrhenius law fitting of AC conductivity data manifests two types of conduction mechanisms in these samples. The depressing nature of the semicircular arc observed in the Nyquist plot of all the samples indicates the presence of a non-Debye type of relaxation.     

Effects of excess NaClO4 on phases,size and magnetic properties of Ni–Zn ferrite powders prepared by combustion synthesis

Ni_0.4Zn_0.6Fe₂O₄ powders were prepared by combustion synthesis with different amount of NaClO₄. Phases, particle size and magnetic properties of the powders and annealed powders were systematically investigated using scanning electron microscopy (SEM), X-ray diffraction (XRD), energy dispersive spectrometer (EDS) and vibrating sample magnetism (VSM). The excess content of NaClO₄ offered significant advantages with respect to the size, morphology and magnetic properties of the powders. After annealing, sub-micro ferrite spherical powders with spinel phase in a range of 500–800 nm can be obtained. With the increase of the NaClO₄ content, the saturation magnetization of the powders shows a maximum value at 68.8 emu/g when w=0.4, whereas the coercivity stayed nearly constant. The maximum saturation of annealed powders by combustion synthesis is much higher than the range reported in the literature.     

Optimization of the magnetic properties and microstructure of Co–La substituted strontium hexaferrite by varying the production parameters

The aim of this paper was to improve the magnetic properties of magnetoplumbite-type (M-type) strontium hexaferrite substituted with Co²⁺–La³⁺ produced by conventional ceramic forming techniques. The effect on the magnetic properties of varying the composition of the target compound Sr_1−xLa_xFe_12−yCo_yO₁₉ and the primary and secondary firing temperatures was investigated. Microstructure studies and XRD phase analysis indicated that optimum values of the remanent magnetization B_r and coercive field H_cj were obtained with a primary firing temperature of 1240 °C and a final firing temperature of 1180 °C, where (x=y)_th ¹=0.15, (y/x)_exp ²=0.75 and the molar ratio of ferric oxide to strontium oxide=5.8. The optimized magnetic properties obtained under these conditions were B_r=4070 Gs, H_cj=4710 Oe, (H_k/H_cj)=82.     

Coating of nano-sized ionically conductive Sr and Ca doped LaMnO3 films by sol–gel route

In this study, Sr and Ca doped LaMnO₃ thin ceramic films were coated on Al₂O₃ substrates by using a sol–gel route as the cathode material for SOFC. Nitrate precursors were used for the preparation of the thin film coating solution, and methanol and acetyl acetone were also used as the solvent and chelating agent, respectively. After the solution was prepared, an Al₂O₃ single crystal substrate was dipped into the solution. Then it was fired at 500 °C and annealed at 1025 °C for the crystallization. Coated films were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), focused ion beam (FIB) and atomic force microscopy (AFM). Conductivity of the coated films was measured by the four probe Van der Pauw method. XRD, SEM, AFM and FIB characterizations of the coated film showed that the LaMnO₃ phase was formed, surface of the films was uniform and had homogenously distributed pores sized about 10 nm, mean grain size was about 60–80 nm and the film thickness was about 180 nm. The specific resistivity of the film was calculated to be 0.524 Ω m.     

Structural and magnetic properties of erbium doped nanocrystalline Li–Ni ferrites

A series of nanocrystalline Li_0.25Ni_0.5Fe_2.25−xEr_xO₄ (x=0.00, 0.02, 0.06, 0.08, and 0.10) ferrite powders, having a cubic spinel crystal structure and a low value of coercivity, was synthesized by the sol–gel auto-combustion route. The structure, morphology and magnetic properties of the prepared nanoferrites were characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and the magnetic property measurement system (MPMS). A well-defined single phase spinel structure is confirmed in all the samples by X-ray diffraction analysis. The lattice parameters of the samples increase slightly with increasing the erbium content. The crystallite size of the Er-doped samples is smaller than that of pure Li–Ni ferrite, and decrease regularly in the range of 36.0–14.5 nm. It has been observed that the magnetic properties of these ferrites are strongly influenced by the added erbium content. The magnetic measurements indicate that saturation magnetization (M_s) and coercivity (H_c) decrease gradually with the increase of Er content in the lattice.     

Structural,optical and magnetic properties of Zn1−xCoxO prepared by the sol–gel route

Effects of Co doping on the structural, optical and magnetic properties of ZnO samples prepared by the sol–gel method are reported. The X-ray diffraction, X-ray photoelectron spectroscopy and UV–visible spectroscopy confirmed the substitution of Co ions on Zn sites without changing the wurtzite structure. No segregated secondary phases or Co rich clusters were detected. Optical absorption spectra of the samples exhibit a blue shift in the absorption band edge with increasing dopant concentration. The photoluminescence measurements show a blue shift in UV emission peak with the increase in Co concentration and a slight shift in the green emission band at around 509 nm which gets suppressed for higher sintering temperature. The field dependence of magnetization observed at room temperature exhibits clear ferromagnetic behavior. Efforts have been made to fit the experimental M–H data using the magnetic polarons model (BMP) which involves localized carriers and magnetic cations. The calculated concentration of the BMPs is found to be below the typical percolation threshold in ZnO. Thus BMP model alone is not sufficient to explain the room temperature ferromagnetic behavior in ZnO. To know the exact magnetic ordering in the system, we also attempted to fit temperature dependent magnetization curves with the Curie–Weiss Law which shows antiferromagnetic ordering in all samples.     

Synthesis and magnetic properties of La3+-Co2+ substituted strontium ferrite particles using modified spray pyrolysis–calcination method

The purpose of the research was to improve the intrinsic magnetic properties of strontium ferrite by substituting lanthanum and cobalt for strontium and iron. The salt-assisted ultrasonic spray pyrolysis (SA-USP) following calcination process were used to from La-Co substituted strontium ferrite particles (La_xSr_1-xFe_12-yCo_yO₁₉), and their compositional dependent magnetic properties systemically investigated. All the samples were calcined at 1050 °C for 1 h in an air atmosphere to yield single-phased hexagonal particles several hundred nanometers to microns in size. A saturation magnetization of 70.76 emu/g and a coercivity 7265 Oe were obtained at a composition of La_0.25Sr_0.75Fe_11.75Co_0.25O₁₉. The amount of Co was reduced to obtain an optimized saturation magnetization of 71.40 emu/g and a coercivity of 7572 Oe at a composition of La_0.25Sr_0.75Fe_11.8Co_0.2O₁₉.     

Structural and magnetic properties of nanocrystalline zinc-doped metal ferrites (metal=Ni; Mn; Cu) prepared by sol–gel combustion method

In this work, nanocrystalline M–Zn ferrites (M=Ni; Mn; Cu) with compositions of M_1?xZn_xFe₂O₄ (x=0.0, 0.2 and 0.4) were synthesized from metal nitrate precursors by rapid the sol–gel combustion method using diethanolamine (DEA) as the fuel. As-synthesized powders were calcined at 1000 °C for 4 h. The crystal structures and morphologies of these compounds were characterized by X-ray diffraction (XRD) and field-emission scanning electron microscopy (FE-SEM), respectively. The chemical interaction of ferrite powders was investigated by Fourier transform infrared spectroscopy (FTIR). The magnetic properties of after-calcined nanoparticles were measured at room temperature using a vibrating sample magnetometer (VSM). The single phase spinel cubic structure formation is confirmed by XRD and FTIR results. Meanwhile FE-SEM micrographs show the appearance of both undoped and Zn-doped ferrite ceramic samples. In addition, the VSM analyses indicate that the Zn content has a significant influence on the magnetic properties such as saturation magnetization (M_s) and coercivity (H_c).     

Microstructure and properties of CaO–ZrO2–SiO2 glass–ceramics prepared by sintering

For the development of a new wear resistant and chemically stable glass-ceramic glaze, the CaO–ZrO₂–SiO₂ system was studied. Compositions consisting of CaO, ZrO₂, and SiO₂ were used for frit, which formed a glass-ceramic under a single stage heat treatment in electric furnace. In the sintered glass-ceramic, wollastonite (CaSiO₃) and calcium zirconium silicate (Ca₂ZrSi₄O₁₂) were crystalline phases composed of surface and internal crystals in the microstructure. The internal crystal formed with nuclei having a composition of Ca_1.2Si_4.3Zr_0.2O₈. The CaO–ZrO₂–SiO₂ system showed good properties in wear and chemical resistance because the Ca₂ZrSi₄O₁₂ crystals positively affected physical and mechanical properties.     

Effect of sintering temperature electrical properties of ZNR doped with Pr–Co–Cr–La

The microstructure, electrical properties, and dielectric characteristics of the ZNR (zinc oxide-based nonlinear resistors), which are composed of zinc oxide-based ceramics doped with Pr–Co–Cr–La, were investigated at different sintering temperatures (1240, 1245, 1250, 1255, 1260, and 1300 °C). The increase of sintering temperature led to more densified ceramics, whereas it decreased the nonlinear properties and breakdown voltage. The highest nonlinearity was obtained from 1240 °C, with 79.3 in nonlinear coefficient and 0.3 μA in leakage current. As the sintering temperature increased, the donor density increased from 0.90 × 10¹⁸ to 2.59 × 10¹⁸/cm³, and the barrier height decreased from 1.90 to 0.67 eV, and the dielectric dissipation factor increased from 0.0874 to 0.2839.     

Photocatalytic degradation of methanol on titania and titania–silica aerogels prepared by non-alkoxide sol–gel route

Titania and titania–silica aerogels were prepared by alkoxide or non-alkoxide sol–gel route and subsequent supercritical drying with carbon dioxide at low temperature. The resulting aerogels having high surface area and mesoporosity were used as photocatalysts for gas phase methanol degradation reaction. Photocatalytic degradation reactions were carried out on titania and titania–silica aerogels, and commercial Degussa P-25 titania. The photocatalytic activities of titania and titania–silica aerogels were higher than that of the P-25. While the conversion of methanol degradation over the P-25 catalyst was only 50–60%, that for the titania aerogel was observed to be above 98% due to the higher specific surface area and the well developed mesoporous structure. In spite of lower titania contents, much higher surface area and high dispersion of titania of titania–silica aerogel gave rise to the high photocatalytic activity in comparison to those of titania aerogels. Moreover, titania–silica aerogel was also used for the photodegradation and adsorption hybrid system. It was observed that the high removal efficiency for methanol was caused by the combination of higher catalytic activity and adsorption capacity.     

A comparative study of the magnetic and microwave properties of Al3+ and In3+ substituted Mg–Mn ferrites

The effect of substitution of diamagnetic Al³⁺ and In³⁺ ions for partial Fe³⁺ ions in a spinel lattice on the magnetic and microwave properties of magnesium–manganese (Mg–Mn) ferrites has been studied. Three kinds of Mg–Mn based ferrites with compositions of Mg_0.9Mn_0.1Fe₂O₄, Mg_0.9Mn_0.1Al_0.1Fe_1.9O₄, and Mg_0.9Mn_0.1In_0.1Fe_1.9O₄ were prepared by the solid-state reaction route. Each mixture of high-purity starting materials (oxide powders) in stoichiometric amounts was calcined at 1100 °C for 4 h, and the debinded green compacts were sintered at 1350 °C for 4 h. XRD examination confirmed that the sintered ferrite samples had a single-phase cubic spinel structure. The incorporation of Al³⁺ or In³⁺ ions in place of Fe³⁺ ions in Mg–Mn ferrites increased the average particle size, decreased the Curie temperature, and resulted in a broader resonance linewidth as compared to un-substituted Mg–Mn ferrites in the X-band. In this study, the In³⁺ substituted Mg–Mn ferrites exhibited the highest saturation magnetization of 35.7 emu/g, the lowest coercivity of 4.1 Oe, and the highest Q×f value of 1050 GHz at a frequency of 6.5 GHz.     

On the magnetic, mechanical and rheological properties of rubber–nickel nanocomposites

Rubber–nickel nanocomposites were synthesized by incorporating freshly prepared nanometric nickel particles in two different matrices namely natural rubber and neoprene rubber according to specific recipes for various loadings of nano nickel and the cure characteristics of these composites were evaluated. The maximum torque values register an increase with the increase in loading of nickel in both composites and this is attributed to the non-interacting nature of nickel nanoparticles with rubber matrices. The cure time of natural rubber composites decreases with increase in the content of nickel, and in neoprene rubber cure, time increases with increase in filler content. In natural rubber, the curing reaction seems to be activated by the presence of nickel particles. The magnetization studies of the composites reveal that the magnetic properties of nickel are retained in the composite samples. The elastic modulus of natural rubber and neoprene rubber are largely improved by the incorporation of nickel particles.     

CSA doped polyaniline/CdS organic–inorganic nanohybrid: Physical and gas sensing properties

Camphor sulfonic acid (CSA) doped polyaniline/CdS nanohybrid materials were prepared by chemical oxidative polymerization method and characterized by field emission scanning electron microscopy (FESEM) and Fourier transform infrared (FTIR) spectroscopy. It is proved that there is a strong synergetic interaction between the CSA and polyaniline–CdS nanohybrid. Gas sensing measurements showed that the gas sensor based on the CSA doped PANi–CdS nanohybrid had high sensor response (75%), good selectivity (for H₂S) and stability (97.34%), as well as comparatively short recovery time to H₂S, operating at room temperature. The enhanced gas sensing performance of the nanohybrid is due to the high surface area of the CSA doped PANi–CdS hybrids and the p–n heterojunction formed between p-type polyaniline and n-type CdS nanoparticles.     

Physical–chemical properties of nanopowders and ceramic samples of REE orthophosphates

A series of physical–chemical studies of a series of binary REE orthophosphate systems has been performed: LaPO₄–DyPO₄–H₂O, LaPO₄–YPO₄–H₂O, LaPO₄–LuPO₄–H₂O, YPO₄–LuPO₄–H₂O, and YPO₄–ScPO₄–H₂O. Nanopowders of Ln'_{1 ?x}Ln'_x PO₄ · nH₂O orthophosphates have been synthesized by the sol–gel method using direct and reverse precipitation techniques. Ceramic samples were produced from the nanopowders, and their physical–mechanical properties were determined depending on the thermal treatment temperature and duration. The ceramic samples’ thermal behavior has been investigated by the dilatometry method. The results have been compared depending on the technique of nanopowder synthesis.     

Physical properties and electrochemical performance of molybdenum–lead-germanate glasses and glass ceramics

Glasses and glass ceramics of the xMoO₃(100?x)[7GeO₂·3PbO] system where x=0–30 mol% MoO₃ were synthesized and characterized in order to obtain information about the structural correlations and the relationship between structure and physical properties in these materials. Changes of the FTIR, UV–vis and EPR data are discussed in view of the glass network structural changes determined by the evolution of molybdenum ions state, glass composition and MoO₃ concentration.The spectroscopic studies indicate that with increasing of MoO₃ content a fraction of the Mo⁶⁺ ions convert Mo³⁺ and Mo⁵⁺ ions. Accordingly, these modifications cause the depolymerization of the host network, the increase of the structural disorder and formation of GeO₂ and PbMoO₄ crystalline phases. The shape of EPR spectra is modified by the increase of the MoO₃ concentration indicating that molybdenum ions exists in glass and glass ceramics in more than one valence state. The EPR spectra contain a broad line located at g～5.2 and, for the samples with a MoO₃ content up to x≥15 mol%, the presence of the hyperfine structure characteristic for the Mo⁵⁺ ions can be observed, too.The electrochemical performances of the glass and glass ceramics samples with x=10 and 30 mol% MoO₃ were demonstrated by cyclic voltammetry.     

Dielectric and magnetic properties of substituted Li–Zn ferrite thick films clouded over a half wavelength microstrip rejection filter

Li_0.35–0.5x Mg _x Zn_0.3Fe_2.35–0.5x O₄ nanoparticles (x = 0, 0.14, 0.28, 0.42, 0.56, and 0.70) were prepared by low-cost combustion synthesis at relatively low temperature. Thick films of Li–Mg–Zn ferrite were prepared by screen printing method and characterized by XRD and microwave characteristics at microwave frequencies (within X- and Ku-bands) by overlay technique using λ/2 rejection filter. The influence of magnesium content x on the resonance frequency, quality factor, effective dielectric constant, complex permittivity, complex permeability, microwave conductivity, and penetration depth was explored.     

Structural and magnetic properties of steel slag based glass–ceramics

Crystallisation of magnetite in multicomponent glass melts was investigated. Structural features and magnetic properties were tested using X-ray diffraction, scanning electron microscope techniques, vibrating sample magnetometer and Mössbauer spectroscopy at room temperature. The results show that the magnetite phase was detected in the glass–ceramic samples after heat treatment at higher crystallisation temperature (over 900°C). Fe²⁺ and Fe³⁺ ions contribute to the formation of magnetite crystal. Various crystal morphologies were observed. Isomer shift values suggest that Fe³⁺ and Fe²⁺ are in tetrahedral and octahedral coordination respectively. The saturation magnetisation tends to increase with the crystallisation temperature.     

Structural and electrical properties of sol–gel-derived Al-doped bismuth ferrite thin films

Al-doped BiFeO₃ (BiFe_(1?x)Al_xO₃) thin films with small doping content (x=0, 0.05, and 0.1) were grown on Pt(111)/TiO₂/SiO₂/Si substrates at the annealing temperature of 550 °C for 5 min in air by the sol–gel method. The crystalline structure, as well as surface and cross section morphology were studied by X-ray diffraction and scanning electron microscope, respectively. The dielectric constant of BiFeO₃ film was approximately 71 at 100 kHz, and it increased to 91 and 96 in the 5% and 10% Al-doped BiFeO₃ films, respectively. The substitution of Al atoms in BiFeO₃ thin films reduced the leakage current obviously. At an applied electric field of 260 kV/cm, the leakage current density of the undoped BiFeO₃ films was 3.97×10^?4 A/cm², while in the 10% Al-substitution BiFeO₃ thin films it was reduced to 8.4×10^?7 A/cm². The obtained values of 2P_r were 63 μC/cm² and 54 μC/cm² in the 5% and 10% Al-doped BiFeO₃ films at 2 kHz, respectively.     

Mechanical properties of sol–gel prepared nanocomposite coatings in the presence of titania and alumina-derived nanoparticles

Hybrid nanocomposite coatings were prepared by sol–gel method using silica, titania and alumina nanoparticles derived from their alkoxides precursors; in the presence of 3-glycidoxypropyl-trimethoxysilane (GPTMS) and bisphenol A (BPA) on 1050 aluminium alloy substrate. The effect of type and ratio of nanoparticles on mechanical behaviour of the coatings were investigated by dynamic mechanical thermal analysis (DMA) and nanoindentation experiments. DMA results demonstrated that the values of the glass transition temperature (T_g) and the temperature at maximum tan (δ), (T_t) as well as the storage modulus of the hybrid samples depend mainly on the silane content and titania to alumina molar ratio of nanoparticles in the coating composition. In addition, nanoindentaion experiments were performed to study the mechanical properties such as hardness, elastic modulus and E/H ratio for the nanocomposite hybrid coatings. Nanoindentation results indicate that the homogenous reinforced structure was formed in the surface of nanocomposite coating with incorporation of titania and alumina-derived nanoparticles. The incorporation of TiO₂ in comparison with AlOOH nanoparticles in the GPTMS-based coatings showed an improving effect on E/H ratio.