Synthesis and characterization of CaFe2O4 nanoparticles via co-precipitation and auto-combustion methods

In this paper, the techniques for the synthesis of CaFe₂O₄ nanoparticles using the auto-combustion and co-precipitation methods are discussed. The effects of both methods on the microstructure and magnetic properties of the CaFe₂O₄ nanoparticles were compared. The CaFe₂O₄ powder was obtained after drying the synthesized sample via co-precipitation overnight in an oven at 80 °C. For auto-combustion method, the sol that was initially formed was gradually converted into a gel, which was then combusted at 250 °C. Finally, the CaFe₂O₄ nanoparticles were calcined at 550 °C. The different synthesis methods produced nanoparticles with different physical and magnetic properties in order to find an optimum size to be utilized for drug delivery applications. The results of the X-ray diffraction showed that both processes produced nanocrystals with an orthorhombic crystalline structure. It was noted from the measurements made with a transmission electron microscope (TEM) that the synthesis using the co-precipitation method produced nanoparticles with a size of about 10–20 nm, which was comparable with the size that was obtained when the auto-combustion method was used. The magnetic properties were investigated using a vibrating sample magnetometer (VSM), where the magnetic saturation (M_s) of CaFe₂O₄ for the sample synthesized using the co-precipitation method was 47.279 emu/g, which was higher than the magnetic saturation (M_s) of 31.10 emu/g obtained when the auto-combustion method was used. The hysteresis loops (Hc) for the samples were 17.380 G and 6.1672 G, respectively. Additionally, the elaborate properties mentioned above, such as the size and superparamagnetic properties of the synthesized CaFe₂O₄ nanoparticle size, were the characteristics required for drug delivery because the targeted therapy required nanoparticles with good magnetic properties, a suitable size, and which were non-toxic in order to have a potential application in targeted drug delivery systems.     

Structural and magnetic properties of Ce-doped strontium hexaferrite

Ce³⁺ ion substituted Sr-hexaferrite magnetic nanoparticles (MNPs), SrCe_xFe_12-xO₁₉ (0.0?≤?x?≤?0.5) MNPs, were fabricated by citrate sol-gel combustion approach. All products have been characterized using X-ray diffraction (XRD), Photoluminescence, scanning electron microscopy (SEM), elemental mapping (EDS), transmission electron microscopy (TEM) and vibrating sample magnetometer (VSM) at 300 and 10?K. The XRD pattern presents effective substitution of Ce³⁺ on the sites of strontium hexaferrite lattice. With Ce³⁺ doping, the lattice parameters a is almost unchanged, whereas c is a little increases with increasing the dopant contents. The hysteresis loops M-H showed the ferromagnetic nature of all elaborated. The saturation magnetization (M_s) and the remnant magnetization (M_r) are reduced with increasing Ce amount. All the elaborated products presented typically squarness ratio (M_r/M_s) around 0.5, indicating the existence of non-interacting single domain MNPs with a uniaxial anisotropy. The anisotropy fields (H_a) are found to be very large proving that all products are magnetically hard. With increasing the Ce content, H_a increases which indicate the strengthening of magnetic properties. Consequently, the values of coercive field (H_c) are enhanced, leading these products to be utilized in many uses, such as recording media and permanent magnets. ZFC and FC magnetizations curves indicated shifts of the blocking temperature (T_B) to lower temperatures with increasing Ce content. This is accredited to the reducing of particle size with Ce-substitution.     

Fast synthesis of SrFe12O19 hexaferrite in a single-mode microwave cavity

The M-type SrFe₁₂O₁₉ hexaferrite has been synthesized by a microwave solid state reaction process – a fast heating process – in a home-made 2.45 GHz single-mode microwave cavity. Starting from SrCO₃ and Fe₂O₃ mixtures (1:6 ratio), cold pressed samples have been heated up in the microwave electric field without needing any susceptor, demonstrating the good coupling of the precursors with this microwave mode in our experimental setup.After optimization of the experimental conditions, the properties of the obtained ceramics, including structure, microstructure and magnetic properties, are compared with those of ceramics synthesized by conventional solid state reaction. With that microwave process, it is found that SrFe₁₂O₁₉ ceramics prepared in less than 30 min exhibit magnetic properties similar to those of the same compound produced by a conventional process. This highlights the potentialities of the technique to synthesize hexaferrite ceramics.     

Synthesis of Co-Zr doped nanocrystalline strontium hexaferrites by sol-gel auto-combustion route using sucrose as fuel and study of their structural,magnetic and electrical properties

Sol-gel auto-combustion route using sucrose as fuel has been employed to synthesize nanocrystalline particles of SrZr_xCo_xFe_(12−2x)O₁₉ (0.0≤ x ≤1.0). The characterization of these materials has been done by TGA-DTA, FT-IR, XRD and EDS. SEM and TEM techniques have been used to study the structure and morphology. Magnetic properties have been investigated by VSM and Mössbauer spectroscopy (MS). The influence of calcination temperature on morphology and magnetic properties of samples is studied in a wide temperature range of 500–1100 °C. XRD analysis indicates the formation of pure single phase hexagonal ferrites at 900 °C. The crystallite size calculated using Scherrer equation lies in a narrow range of 21–33 nm. The crystallite size is small enough to obtain a suitable signal to noise ratio in high density recording medium. Substitution of Zr and Co for Fe has been found to have a profound effect on the structural, magnetic and electrical properties. Upon substitution saturation magnetization (M_S) first increases from 62.67 emu/g to 64.84 emu/g (up to x=0.4) followed by a decrease to 49.71 emu/g at x=1.0. There is a slow fall in coercivity (H_C) from 5785.74 (x=0.0) to 1796.51 Oe (x=1.0). Dielectric constant, dielectric loss tangent and AC conductivity in the frequency range 20 Hz to 120 MHz have been studied for all the compositions (x=0–1.0). The composition and frequency dependence of these dielectric parameters has been qualitatively explained.     

The role of Pb and annealing temperature on the structural,magnetic, optical and dielectric properties of W-type hexaferrite nanostructures

In this paper, W-type Sr_1-xPb_xCo₂Fe₁₆O₂₇ nanostructures were synthesized by auto-combustion sol-gel method. Then, the effects of annealing temperature and Pb contents on the structural, magnetic, optical, and dielectric properties of Sr_1-xPb_xCo₂Fe₁₆O₂₇ nanostructure were investigated. First, a gel of metal nitrates with a specific molar ratio with x different was prepared and then the gel was annealed at different temperatures for 4?h. To determine the annealing temperature of the samples, the prepared gel was examined by thermogravimetric analysis and differential thermal analysis. The morphology and crystal structure of the prepared samples were characterized by field emission scanning electron microscopy (FESEM) and X-ray diffraction pattern (XRD). The results of XRD patterns indicated that the annealing temperature of synthesized Sr_1-xPb_xCo₂Fe₁₆O₂₇ was reduced by increasing Pb contents. In addition, FESEM images showed that the microstructure of the samples was homogeneous and uniform, but since the samples have a magnetic property, the particles were aggregated. Fourier transform infrared analysis (FT-IR) was used to confirm the phase formation. The FT-IR results of the samples indicated that the tetrahedral and octahedral sites, which are the important attributes of hexaferrites, were formed. The magnetic properties of the samples were measured by vibrating sample magnetometer (VSM). The VSM results of the samples showed that because of increasing Pb content, the amount of saturation magnetization and that of magnetic coercivity decreased from 81.29 to 10.23?emu/g and 2285–477?Oe, respectively. The optical properties of the samples were investigated by ultraviolet–visible spectroscopy, which revealed that the energy gap decreases and the absorption peaks move towards longer wavelengths by increasing Pb content. The dielectric properties of the samples were investigated by the LCR meter. It was found that by increasing frequency, the dielectric constant (ε^′) and the dielectric loss (?) of the samples were decreased.     

The effect of Zn ion substitution on electromagnetic properties of low-temperature fired Z-type hexaferrite

The influence of Zn substitution on the densification, microstructure, lattice parameters and electromagnetic properties of planar Z-type hexaferrites, which have stoichiometric composition of Ba₃Co_2(10.8−x)Zn_2xCu_0.4Fe₂₄O₄₁, were investigated. The results show that the Zn²⁺ substitution has no obvious effect on the densification, but Z-type hexagonal phase can form and demonstrate typical planar anisotropic characteristics of soft magnetic materials (σ_r6.20 emu/g) in the range of x0.25. The of lattice parameters of planar a (0.588 nm) and axial c (5.25 nm) remain stable. At the certain temperatures, the sintered hexaferrites with an optimal density of about 4.62 g/cm³ show better electromagnetic properties for x=0.15 than the samples without Zn²⁺ incorporation: initial permeability of about 9.0, cut-off frequency of above 800 MHz, resisitivity of above 3.20 Ω cm and dielectric constant of less than 35.     

Synthesis and characterization of stable room temperature bulk ferromagnetic graphite

A novel and inexpensive chemical route leading to obtain macroscopic quantities of room temperature magnetic carbon is reported. This route consists of a controlled etching on the graphite structure, performed by a redox reaction in a closed system between graphite and CuO. X-ray diffraction suggests that this modified graphite could be represented by the coexistence of a matrix of pristine graphite and a foamy-like graphitic structure compressed along the c-axis. This material has a stable and strong ferromagnetic response even at room temperature where it can be attracted by any commercial magnet. At T = 300 K, the saturation magnetic moment, the coercive field and the remnant magnetization are 0.25 emu/g, 350 Oe and 0.04 emu/g, respectively.     

Synthesis and characterization of multiferroic BiFeO3 powders fabricated by hydrothermal method

The influence of processing parameters on phase formation and particle size of hydrothermally synthesized BiFeO₃ powders was investigated. BiFeO₃ powder was synthesized by dissolving bismuth nitrate and iron nitrate in KOH solution at temperatures ranging from 150 to 225 °C. X-ray diffraction patterns and scanning electron microscopy observation indicated that rod-like α-Bi₂O₃ phase was formed at initial stage of reaction and dissolved into ions to form thermodynamically stable BiFeO₃ phase. Single-phase perovskite BiFeO₃ has been formed using a KOH concentration of 8 M at a temperature of ≥175 °C in a 6 h reaction period. BiFeO₃ particle growth was promoted by lowering the KOH concentration, or increasing the duration time or reaction temperature. The effects of processing conditions on the formation of crystalline BiFeO₃ powders were discussed in terms of a dissolution–precipitation mechanism. The magnetization of the BiFeO₃ powders at room temperature showed a weak a ferromagnetic nature.     

Structural and magnetic properties of Ce-Y substituted strontium nanohexaferrites

Strontium nanohexaferrites substituted with Ce-Y were synthesized via citrate sol-gel combustion. Crystallography phase and morphology were verified by X-ray diffraction, electron microscope and Raman spectroscopy. The magnetization hysteresis loop (M vs. H) revealed the ferromagnetic behavior of all prepared products. The estimated saturation (M_s) and the remnant (M_r) magnetizations values are maximum for pristine SrY_0.5Ce_0.5Fe₁₁O₁₉ (i.e. x=0.5) and SrY_0.3Ce_0.3Fe_11.4O₁₉ (i.e. x?=?0.3) due to both Y³⁺ and Ce³⁺ contents. The obtained squareness ratio (M_r/M_s) values for substituted products are less than the value of 0.500 suggesting the uniaxial anisotropy for all substituted products. The magneto-crystalline anisotropy fields (H_a) values are very large indicating the hard-ferromagnetic features of all elaborated nanoparticles samples. It is found that H_a decreased with increasing both Y³⁺ and Ce³⁺ contents and is minimum for x?=?0.5, which imply the weakening of magnetic properties. Therefore, the coercive field (H_c) value is diminished due to Y³⁺ and Ce³⁺ substitutions and its minimum corresponds to x?=?0.3. The blocking temperatures (T_B) are estimated from ZFC and FC magnetizations experiments. It is observed that T_B shifts to higher temperatures with rising Y³⁺ and Ce³⁺ contents. This is ascribed to the reduction of particles size with Y and Ce substitutions.     

The mechanism of the low-temperature formation of barium hexaferrite

We have investigated the formation of barium hexaferrite via the coprecipitation method. Fine precursor powders were obtained with coprecipitation from water and ethanol solutions of various reagent salts. The coprecipitates were calcined at 300–800 °C for 0–50 h. The samples were characterized with X-ray powder diffraction, thermal analysis, electron microscopy and magnetometry. The formation of barium hexaferrite was a combination of two competing mechanisms and was not influenced by the reagent salts or the solvent. The formation temperature of the barium hexaferrite was reduced to 500 °C by optimizing the coprecipitation conditions.     

Synthesis, characterization and optical properties of Mg(OH)2 micro-/nanostructure and its conversion to MgO

Magnesium hydroxide (Mg(OH)₂) micro- and nanostructures have been synthesized by a single step hydrothermal route. Surface morphology analysis reveals the formation of micro- and nanostructures with varying shape and size at different synthesis conditions. Structural investigations by X-ray diffraction (XRD) and transmission electron microscopy (TEM) confirm that the synthesized material is Mg(OH)₂ with hexagonal crystal structure. An optical band gap of 5.7 eV is determined for Mg(OH)₂ nanodisks from the UV–vis absorption spectrum. A broad emission band with maximum intensity at around 400 nm is observed in the photoluminescence (PL) spectra of Mg(OH)₂ nanodisks at room temperature depicting the violet emission, which can be attributed to the ionized oxygen vacancies in the material. Furthermore, Mg(OH)₂ has been converted to MgO by calcination at 450 °C. Optical studies of the MgO nanodisks have shown an optical band gap of 3.43 eV and a broadband PL emission in the UV region. Mg(OH)₂ and MgO nanostructures with wide-band gap and short-wavelength luminescence emission can serve as a better luminescent material for photonic applications.     

Fabrication of highly dispersed crystallized nanoparticles of barium strontium titanate in the presence of N,N-dimethylacetamide

Highly dispersed nanoparticles of barium strontium titanate (BST) were successfully synthesized by hydrolysis method using N,N-dimethylacetamide as a solvent at 120 °C and 140 °C. X-ray diffraction analysis (XRD) showed that the as-prepared particles presented a perovskite polycrystalline structure. The result of transmission electron microscopy (TEM) images revealed the particle size in the range of 5-30 nm. The composition without any annealing treatment characterized with the parallel plate capacitor method displayed good dielectric properties.     

Synthesis of porous iron oxide ceramics using Greek wooden templates and mill scale waste for EMI applications

The scope of this study is the synthesis of low cost iron oxide ceramics with porous structure for lightweight Electromagnetic Interference (EMI) shielding applications, using mill scale waste as the initial material, utilizing Greek wood templates. These wood-templated iron oxide (Fe₂O₃) ceramics were prepared by impregnation of inorganic precursor solution, derivated from mill scale waste, into four different kinds of Greek native wood templates; pine, fir, poplar and beech, followed by thermal treatment.Scanning Electron Microscopy (SEM) was used to investigate the microstructure of the prepared wood-templated iron oxide specimens. Their iron and oxygen contents were validated by Scanning Electron Microscopy-Energy-Dispersive X-ray Spectroscopy (SEM-EDX) and their mineralogical composition by X-ray Powder Diffractometry (XRD). The wooden substances were found to be completely removed and the synthesized Fe₂O₃ (hematite) was confirmed by XRD, as a single phase. It is also demonstrated that the structures of the iron oxide were hierarchically porous developed according to the wood templates. Moreover, the pore shape and size distribution showed a dependence on the calcination temperature and wood template. Specifically, the temperature increase from 1000 °C to 1200 °C created larger but less pores in μm scale. Finally these low cost iron oxide ceramics exhibited electrical (mainly) and magnetic properties suitable for electromagnetic shielding applications.     

Synthesis of nano-sized Yb3Al5O12 powders by the urea co-precipitation method

Nano-sized polycrystalline ytterbium aluminum garnet (YbAG, Yb₃Al₅O₁₂) powders were successfully synthesized by a simple urea co-precipitation method. The thermal behavior of the YbAG precursor was investigated. The calcined amorphous YbAG precursor was directly converted to 20–30 nm monophase YbAG at as low as temperature 900 °C, without any other intermediate phases. The nano-sized YbAG powders calcined at 900 °C distributed evenly with a slight aggregation, and the specific surface area of the powders reached 29.7 m² g⁻¹. The absorption spectrum of the YbAG powders was measured, and there were two strong absorption peaks centered at 931 and 965 nm. The results did not correspond to the absorption peaks of Yb:YAG crystal exactly, as the lattice parameters were different between YbAG and YAG.     

Spin-glass behavior and redox catalytic properties of room temperature produced ZnCrMnO4

Recognizing the multifunctional capability of spinels, synthesis, and properties of oxide spinel with an equal concentration of Jahn Teller active Mn³⁺ and geometrically frustrated Cr³⁺ with non-magnetic Zn²⁺ have been explored. ZnCrMnO₄, resulting from the room temperature oxidation reaction, has an average crystallite size of 16 nm. Nearly 25% of Zn occupies the octahedral sites along with Cr and Mn, as revealed by the successful structural refinement in the Fd-3m space group. Electron microscopic results confirm cubic spinel formation. Raman spectrum shows the disordered nature of the spinel. X-ray photoelectron spectral (XPS) analysis establishes mixed valences of manganese ((III), (IV)) and chromium ((III) and (VI)). ZnCrMnO₄ displays electronic transitions typical of Mn³⁺ and Cr³⁺ in its UV–Visible diffuse reflectance spectrum. Spin-glass frustration at 26 K, followed by an antiferromagnetic ordering at 10 K, is noticed for the sample from the magnetic measurements. The sample exhibits a surface area of 138 m²/g (BET measurements) and catalyzes the oxidation of aromatic alcohols (phenol, benzyl alcohol) and reduction of nitroaromatics efficiently.     

四苯基卟啉锶配合物的合成及发光性能

利用醋酸锶与四苯基卟啉反应,合成了四苯基卟啉锶配合物。利用元素分析、红外、核磁共振等对该配合物进行了结构表征。采用紫外-可见吸收光谱、荧光光谱和循环伏安法研究了该配合物的光电性能。四苯基卟啉锶配合物紫外-可见吸收光谱有一个强的吸收峰和一个次强的吸收峰,分别为428、457 nm。荧光光谱有一个强的发射峰和一个弱的发射峰,分别为610、676 nm。循环伏安法测得其氧化峰电位为1.558 V和1.051 V。与四苯基卟啉相比,四苯基卟啉锶紫外吸收发生红移,而荧光发射发生蓝移。     

A comparative study of the synthesis of nanocrystalline Yttrium Aluminium Garnet using sol-gel and co-precipitation methods

Nanocrystalline yttrium aluminium garnet (nYAG) powder has been synthesized via sol-gel and co-precipitation methods using nitrate precursors. Thermal evolution and crystallisation kinetics of both the methods were investigated. The optimised calcination condition for the formation of nYAG was also examined. It was found that a complete transformation to nYAG was observed at 925 °C/2 h and 1000 °C/1 h for the coprecipitation and sol-gel samples respectively. An intermediate YAlO₃ phase was formed at 900 °C in all powders regardless of the synthesis methods. The powder morphologies obtained from TEM revealed very similar particle sizes for the two routes (20–30 nm); whilst the extent of agglomeration was higher for the sol-gel method. It was also observed that by controlling the pH in a narrow range, maintaining the precipitate processing temperature and dehydrating excess OH- ions in the precipitates using n-butanol treatment, the extent of agglomeration was further reduced in the co-precipitated nYAG powder.