Yttrium substituted Co–Cu–Zn nanoferrite: A synergetic impact of Y3+ on enhanced physical properties and photocatalysis

Co_0.5Cu_0.25Zn_0.25Y_xFe_2-xO₄; (0≤x≤0.1; step 0.02) (CCZY) spinel ferrites were prepared by citrate technique. The prepared CCZY samples have crystallite sizes ranging from 21 to 34 nm. The nanoscale nature of the samples was, also, established by HRTEM micrographs. Even though the substitution route here involves the replacement of magnetic ions Fe³⁺ by a non-magnetic one Y³, the magnetization of CCZY nanoparticles did not show a continual decrease as expected. The nanoferrite Co_0.5Cu_0.25Zn_0.25Y_0.06Fe_1.94O₄, has a moderate value of saturation magnetization 63.45 emu/g (decreased with 11.55% than the pristine sample) and higher coercivity 416.44 Oe (increased with 21.83% than the pristine sample), which may be a suitable candidate for data storage applications. All CCZY nanoferrite have direct optical band gap within the range 1.57 eV–1.50 eV; which doesn't introduce a regular behavior with Y/Fe substitution process. Distinctively, the MB dye removal shows an optimum value with the nanoferrite CCZY (0.1), which gives a degradation efficiency of 95% after 60 min only. The outstanding increase in catalytic performance of the nanoferrite CCZY (0.1) was correlated with the size factor and saturation magnetization. The desirability function approach enabled to distinguish the optimal material (CCZY (0.1)) with the superior catalytic performance; the smallest size and convenient magnetic properties. Hence, the nanoferrite Co_0.5Cu_0.25Zn_0.25Y_0.1Fe_1.9O₄ can be utilized efficaciously for water treatment, via the safe photocatalytic process; without sabotaging the environment.     

Investigation of structural,magnetic and Mössbauer properties of Co2+ and Cu2+ substituted Ni–Zn nanoferrites

We investigated the effects of Co²⁺ and Cu²⁺ substitution on the super-exchange interactions in Ni–Zn nanoferrites. The cation distribution technique was taken into account to explain the results. To authenticate the cation distribution, we have estimated the cation distribution in the light of X-ray diffraction method, Mössbauer spectroscopic analysis, and magnetization study. Statistical model based on the cation distribution was used to calculate the Curie temperature. The values of magneton number n_B and Curie temperature T_C calculated by using the cation distribution is found to be in agreement with the experimentally obtained values.     

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.     

FTIR spectra and elastic properties of Cd-substituted Ni–Zn ferrites

Solid solutions Ni_0.5–x Cd _x Zn_0.5Fe₂O₄ (x = 0, 0.15, 0.30) were prepared by solid-state synthesis and characterized by FTIR spectroscopy. The FTIR spectra of synthesized ferrites showed two absorption bands (ν₁ and ν₂) in the range 400–600 cm^–1 belonging to tetrahedral (A) and octahedral (B) interstitial sites in the spinel lattice. The force constants for tetrahedral (K _t) and octahedral sites (K _o) were determined, as well as Young’s modulus (E), rigidity modulus (G), bulk modulus (B), Debye temperature (Θ_D), and velocity of transverse (V _t) and longitudinal (V _l) elastic waves. The relevant interionic cation–anion, cation–cation distances and bond angles are also reported.     

Synthesis and microwave absorption properties of Ni–Zn–Mn spinel ferrites

A series of Ni_0·5?xZn_0·3?xMn_0·2+2xFe₂O₄ ferrites was successfully prepared by the sol–gel autocombustion method. The structure and electromagnetic properties of the powders were characterised by X-ray diffraction, SEM and vector network analysis. The pure powders were formed by heating at 1200°C for 3 h in air, and grain sizes increased as the amount of substitution ranged from x?=?0·0 to x?=?0·25. For samples with x?=?0·1, a minimum reflection loss of ?27·57 dB was observed at 11·0 GHz with the less than ?10 dB absorption bandwidth at 8·0 GHz with 3·8 mm thickness. The results indicate that substitution with Mn and Zn ions can greatly improve the microwave absorption properties of NiFe₂O₄ ferrites.     

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,morphological, magnetic hysteresis and dielectric properties of cobalt substituted barium–lead hexagonal ferrites for technological applications

M-type, Ba_0.4Pb_0.6Fe_12-xCo_xO₁₉ (x = 0.00, 0.10, 0.20, 0.30, 0.40) hexaferrites, synthesized using citrate gel auto combustion method, and heated at 950 °C, 4 h for lossless applications. XRD analysis shows the development of the M-phase, along with PbM and hematite. The microstructural analysis reveals the stacking clusters of hexagonally shaped platelets. TEM image and SAED pattern of x = 0.3 composition shows polycrystalline nature and formed particles observed to fused with neighbouring particles. M − H loops of all samples reveal hard magnetic behaviour and possess multi-domain structure. The maximum saturation magnetization of 55.427 A m²/kg is observed in x = 0.10 composition and coercivity of prepared hexaferrites was found to vary from 0.058 T to 0.390 T. The cobalt substitution has a strong influence on the dielectric properties of prepared hexaferrites. The value of ac conductivity increases with cobalt substitution from x = 0.00 to x = 0.10, and followed by a reduction from x = 0.10 to x = 0.40. The same trend is observed for the dielectric constant. The low value of loss tangent for all compositions shows apt scope for lossless application.     

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.     

Morphology tailoring and enhanced electrochemical properties of Cd–Zn co-doped NiO nanorods for high performance supercapacitor

A systematic approach has been introduced to synthesize Cd–Zn co-doped NiO nanostructures with different ratios such as Cd_0.07Zn_0.03NiO, Cd_0.05Zn_0.05NiO, Cd_0.03Zn_0.07NiO and Cd_0.01Zn_0.09NiO for supercapacitor applications. The XRD studies has confirmed the phase purity with average crystallite size of 40 nm. The SEM characterization has shown that the morphology of nanostructures was tuned from particles to nano-rods structure with increasing the at. % concentration of Zn doping. Optical properties revealed that band gap and recombination rate have strong co-relation with specific capacitance. The CV results have confirmed the pseudocapacitive nature of the as prepared nanostructures and maximum specific capacitance (1485.19 Fg^-1) was measured for Cd_0.03Zn_0.07NiO which is superior than numerous reported values of NiO. The GCD results of Cd_0.03Zn_0.07NiO performed at 1 A/g scan rate, exhibited excellent charging-discharging ability with high cyclic retention of 82.8%. High capacitance and superior stability of Cd_0.03Zn_0.07NiO material indicate it as a potential candidate for supercapacitor applications.     

Determination of surface area and porosity of sol–gel derived ceramic powders in the system TiO2–SiO2–Al2O3

The surface characteristics of ternary ceramic powders in the system TiO₂–SiO₂–Al₂O₃ prepared by a sol–gel technique were studied through nitrogen gas adsorption at liquid nitrogen temperature and application of the Brunauer–Emmett–Teller (BET) equation. The total surface area, total pore volume and pore radius of the powders were calculated through the construction of plots relating the amount of nitrogen gas adsorbed V₁ and the thickness of the adsorbed layer t (V₁−t plots). These results permitted the detection of the different types of pores present in the samples. In a first approximation, the V₁−t plots seem to demonstrate the correctness of the results obtained for the total specific area of the investigated samples. The influence of thermal treatment (drying, calcination) on the surface characteristics of the investigated powders was assessed.     

A study of the structural and morphological properties of Ni–ferrite,Zn–ferrite and Ni–Zn–ferrites functionalized with starch

Zinc–ferrite, nickel–ferrite and mixed nickel–zinc ferrites were successfully synthesized via the thermal decomposition method from acetylacetonate complexes. To control the particle size and enhance dispersibility in an aqueous medium, starch, a natural and biocompatible compound, was used for the first time for coating such magnetic powders. X-ray powder diffraction (XRPD) was performed to study the structural properties of all samples. The presence of a single-phase spinel structure as well as the cation distribution in both sites of all investigated magnetic powders was confirmed. The values of unit cell parameters obtained from the results of the Rietveld analysis decreased, while the average crystallite size increased with increasing Ni²⁺ content. The average microstrain parameters unambiguously showed a change in the spinel structure with cation distribution. Scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS) and Fourier transform infrared spectroscopy (FTIR) analyses were also utilized to characterize the synthesized materials, corroborating the XRPD data. The obtained results indicated that functionalization by starch was successfully achieved.     

A critical role of pH in the colloidal synthesis and phase transformation of nano size α-Al2O3 with high surface area

This paper demonstrates the critical role of pH in the colloidal (i.e. sol-gel) synthesis of nano size α-Al₂O₃. Investigation, based on X-ray diffraction pattern, indicates that the transformation of α-Al₂O₃ from gels obtained at high pH⩾7, undergoes via formation of boehmite (gel→AlOOH→γ-Al₂O₃→α-Al₂O₃). On the other hand, the transformation of α-Al₂O₃ at low pH (⩽6) follows the gel→γ-Al₂O₃ →α-Al₂O₃ sequence. The transmission electron microscopy reveals that the particle size of the α-Al₂O₃ decreases from ≈750 to ≈70 nm with decreasing pH from 12 to 2.5, respectively. The α-Al₂O₃ with large surface area (≈130 m²/g) is obtained when it is processed at low pH (2.5). The true powder density of the α-Al₂O₃ sample derived at pH=2.5 is observed to be 3.92 g/cm³ after sintering at 1450 °C, due to fine particles. The isoelectric point (iep) and ξ of the α-Al₂O₃ are found to be 8.7 and 9.2 when synthesized at pH 2.5 and 12, respectively.     

Deposition of Zn–Co by constant and pulsed current

The initial stages of both Zn–Co and Zn electrodeposition were investigated by electrochemical quartz crystal microgravimetry (EQCM). The initial electrode mass growth, determined under both pulse and constant current conditions, was much higher than predicted by Faraday's law. This was explained in terms of the precipitation of scarcely soluble compounds of zinc on an electrode surface. The EQCM data confirm that the hydroxide suppression mechanism explains the anomalous Zn and Co codeposition. A nonuniform adsorption of brightener (benzalaceton) on the profiled surface was concluded on the basis of plating distribution investigations. The additive adsorbs to a greater extent on the surface projections.     

Synthesis and enhanced gas sensing properties of flower-like ZnO/α-Fe2O3 core-shell nanorods

This paper reports a facile two-step synthesis route for the preparation of flower-like ZnO/α-Fe₂O₃ nanorods (NRs). Flower-like ZnO NRs with the average diameter about 810 nm and length about 4.5 µm were firstly synthesized via a chemical solution method, and then ZnO NRs was coated with a continuous α-Fe₂O₃ layer to form ZnO/α-Fe₂O₃ core-shell structure through an ionic-layer adsorption and reaction method. The gas-sensing results show that the ZnO/α-Fe₂O₃ NRs exhibit excellent sensitivity, selectivity, and response-recovery capacity to ethanol vapor at a low optimum temperature of 240 °C. In particular, compared with pure ZnO NRs and α-Fe₂O₃ nanoparticles (NPs), the ZnO/α-Fe₂O₃ NRs show an obvious improvement in gas sensing properties. The substantial improvement of sensing properties may be attributed to the unique microstructure and heterojunction formed between ZnO and α-Fe₂O₃.     

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.     

Complex permittivity andpermeability of Zn–Co substituted Z type hexaferrite prepared by citrate sol–gel process

Abstract

A series of Z type hexaferrite samples with composition Ba₃Co_xZn_{2 -x}Fe₂₄O₄₁ (x varying from 0·0 to 2·0 in steps of 0·4) were prepared by a citrate sol-gel process. Samples were characterised by TG-DSC, X-ray diffraction, and scanning electron microscopy. Complex permittivity and permeability, and dielectric and magnetic losses were studied as a function of measurement frequency, composition, and annealing temperature. The dependence of natural resonant frequency on annealing temperature as well as on cobalt content was investigated in the range 100 MHz to 6 GHz. Reflection loss has been calculated as a function of frequency according to transmission line theory.     

Preparation and characterization of Co2+ substituted Li–Dy ferrite ceramics

Stoichiometric compositions of ferrites with the chemical formula Li_0.5?0.5xCo_xFe_2.4?0.5xDy_0.1O₄ with x=0, 0.25, 0.5, 0.75, 1.0 were prepared by the standard double sintering ceramic method. X-ray diffraction analysis confirmed the cubic spinel structure of the prepared samples. The structural, morphological and magnetic properties were studied by X-ray diffraction, infra-red spectroscopy (IR), scanning electron microscopy (SEM), vibrating sample magnetometry (VSM) and ac susceptibility measurements. Lattice constant, grain size and density increase whereas porosity decreases with the increase in Co²⁺ substitution. IR measurements show the characteristic ferrite bands. Spectral absorption bands were observed in IR spectroscopic analysis at ν₁=564?601 cm^?1, ν₂=486?519 cm^?1 and ν₃=551?578 cm^?1. The cation distribution estimated by the X-ray diffraction is supported by magnetization and susceptibility studies. The saturation magnetization decreases from 44.25 to 17.14 emu/g whereas coercivity remarkably increases from 240.69 to 812.14 emu/g with increasing Co²⁺ substitution. The mechanisms involved are discussed.     

Direct and facile synthesis of Li–Sr–Zn ferrites via low temperature solution combustion route

Li–Sr–Zn nanoferrites i.e. Li_0.25Sr_0.5–xZn_xFe_2.25O₄, where ‘x’ varies from 0–0.5, have been synthesized using a low temperature solution combustion method which proves to be an efficient and economical technique for synthesizing these type of nanoferrites. The as-synthesized nanoferrites have cubic spinel structure as characterized by X-ray powder diffraction. Powder XRD and TEM (Transmission Electron Microscopy) characterization also evidence that the crystallite and particle size are in close agreement to each other. Mössbauer spectroscopy studies demonstrate that there is a gradual transition from ferrimagnetic to superparamagnetic character, which is also supported by the saturation magnetization and coercivity values. At room temperature, the nanoferrites were found to be superparamagnetic with negligible coercivities approaching towards zero while saturation magnetization values were found to be in the range 6.87–30.10 emu g⁻¹. The frequency dependent dielectric constant and loss values are in accordance with Koop׳s model. These nanoferrites show great potential in high density recordings, magnetic nanodevices and biomagnetic applications.