A study of formation and photoluminescence properties of ZnO quantum dot doped zinc-alumino-silicate glass ceramic

Transparent Al₂O₃-SiO₂-ZnO-R₂O glass ceramics were fabricated by melting method. The effects of the different kind of alkali ions on the formation of the transparent glass ceramic were studied. X-ray diffraction and high resolution transmission electron microscope were measured to study the microstructure of the samples. The results showed that, transparent glass ceramic including ZnO quantum dots was obtained after heat treatment from 700 °C to 800 °C for the sample containing K₂O. While glasses containing Li₂O and Na₂O were opal after heat treatment. Photoluminescence properties of the K₂O contained samples were studied. It was found that the photoluminescence peak shifted to longer wavelength when the heat treatment temperature and time increased, which can be ascribed to the increasing of ZnO quantum dots size.     

Hydrothermal Synthesis and Characterization of PEG Stabilized Co3O4 nanoparticles

Polyethylene glycol stabilized Cobalt oxide, (Co₃O₄), nanoparticles were prepared via simple, one-step, inexpensive hydrothermal method. In this process, polyethylene glycol was used as a solvent and surfactant; gaseous NH₃ was used as an alkalinity additive. Investigation of the structural, morphological, thermal, and magnetic properties were carried out using X-ray diffraction (XRD), infrared spectroscopy (FT-IR), transmission electron spectroscopy (TEM), thermal analysis (TGA), and vibrating sample magnetometer (VSM), respectively. The nanocrystalline nature of the sample was confirmed by XRD and TEM. FT-IR measurement revealed that the O from C?CO coordinates with the surface of Co₃O₄ NP??s. Room temperature VSM measurement showed the ferromagnetic behavior of the product.     

Enhanced Ferromagnetic Properties of Co-doped ZnO DMS Nanoparticles

A systematic investigation was done to determine the structural, morphological and magnetic properties of Zn_0.8Co_0.2O nanoparticles synthesized by a simple autocombustion technique. XRD, FE-SEM and EDX measurements were implemented for the structural, morphological and compositional investigation of the product. Additionally VSM was used for the magnetic property investigations of the sample. The average particle size of the nanoparticles was estimated using Debye–Scherrer’s equation and found to be 20.8 nm. Magnetization measurements have shown that the particles have room-temperature ferromagnetic behavior with relatively high coercive fields. Magnetization and the coercive field of the sample increase by decreasing the temperature, as expected. FMR signal confirms the room-temperature enhanced ferromagnetic behavior without Co precipitates.     

Comparative Studies of Microwave and Sol–Gel-Assisted Combustion Methods of NiFe<Subscript>2</Subscript>O<Subscript>4</Subscript> Nanostructures: Synthesis,Structural, Morphological,Opto-magnetic,and Antimicrobial Activity

Nickel ferrite NiFe₂O₄ nanoparticles (NPs) were successfully synthesized by using nickel nitrate, ferric nitrate, citric acid, and ethyl cellulose as a surfactant by a simple sol–gel-assisted combustion method (SACM) and microwave-assisted combustion method (MACM). Structural, morphological, optical, and magnetic properties of the obtained powder were characterized by powder X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), photoluminescence (PL) spectroscopy, and vibrating sample magnetometry (VSM). XRD results show that the resultant powder was pure crystalline with cubic structure. The average crystalline size was found to be 18.8 and 10.2 nm synthesized by SACM and MACM, respectively. FT-IR spectra indicate the type of bonds between Ni–O and Fe–O (metal and oxygen). SEM images show that the morphology of the powder consists of well-defined structure. VSM results showed a ferromagnetic behavior of the sample. Antimicrobial activity of NiFe₂O₄ nanoparticles was performed. Both sample 1 (SACM) and sample 2 (MACM) show good inhibition in the zone 100 μg/ml. While comparing, sample 2 shows high inhibition than sample 1.     

Magnetic Properties of Zn0.8(Fe0.1,Co0.1)O Diluted Magnetic Semiconductors: Experimental and Theoretical Investigation

Structural and magnetic properties of Zn_0.8(Fe_0.1, Co_0.1)O bulk diluted magnetic semiconductor have been investigated using X-ray diffraction (XRD) and magnetic measurements. TEM (Transmission Electron Microscopy) images confirmed the high crystallinity and grain size of Zn_0.8(Fe_0.1,Co_0.1)O powder, the samples were characterized by energy dispersive spectroscopy (EDS) to confirm the expected stoichiometry. This sample has been synthesized by co-precipitation route. The study of magnetization hysteresis loop measurements infers that the bulk sample of Zn_0.8(Fe_0.1,Co_0.1)O shows a well-defined hysteresis loop at T _c (200?K) temperature, which reflects its ferromagnetic behavior. Hydrogenation treatment was used for the control of phase separation. Based on first-principles spin-density functional calculations, using the Korringa?CKohn?CRostoker method (KKR) combined with the coherent potential approximation (CPA), the ferromagnetic state energy was calculated and compared with the local-moment-disordered (LMD) state energy. The mechanism of hybridization and interaction between magnetic ions in Zn_0.8(Fe_0.1,Co_0.1)O is also investigated.     

Correlation between the physical properties and the novel applications of Mg<Subscript>0.7</Subscript>Cu<Subscript>0.3</Subscript>Fe<Subscript>2</Subscript>O<Subscript>4</Subscript> nano-ferrites

Nano-ferrite of the general formula Mg_0.7Cu_0.3Fe₂O₄ was prepared by citrate-gel auto combustion method. The structure was studied by X-ray diffraction, Brunauer–Emmet–Teller, field emission scanning electron microscopy and energy dispersive X-ray spectroscopy analyses. The crystallite size of the investigated nano ferrite was ?39 nm. The magnetic hysteresis measurements at different temperatures (100, 170, 240, and 300 K) were performed using a vibrating sample magnetometer. A correlation between magnetic behavior and lattice strain has been established. Arrott plot has been employed to understand the magnetic behavior of nano-crystalline Mg_0.7Cu_0.3Fe₂O₄. The magnetic susceptibility was carried out using Faraday’s method. Magnetic constants such as Curie temperature, effective magnetic moment, saturation magnetization, and coercivity were obtained and reported. Based on UV diffuse reflectance spectroscopy studies, the optical band gaps are in the range from (1.3–1.9 eV), hence the investigated samples could act as visible light driven photo catalysts.     

Characterization of stain etched p-type silicon in aqueous HF solutions containing HNO3 or KMnO4

Stain etching of p-type silicon in hydrofluoric acid solutions containing nitric acid or potassium permanganate as an oxidizing agent has been examined. The effects of etching time, oxidizing agent and HF concentrations on the electrochemical behavior of etched silicon surfaces have been investigated by electrochemical impedance spectroscopy (EIS). An electrical equivalent circuit was used for fitting the impedance data. The morphology and the chemical composition of the etched Si surface were studied using scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) techniques, respectively. A porous silicon layer was formed on Si etched in HF solutions containing HNO₃, while etching in HF solutions containing KMnO₄ led to the formation of a porous layer and simultaneous deposition of K₂SiF₆ inside the pores. The thickness of K₂SiF₆ layer increases with increasing the KMnO₄ concentration and decreases as the concentration of HF increases.     

Synthesis of sodium and potassium aluminogermanate inorganic polymers

Synthesis of aluminogermanate inorganic polymers containing sodium as the charge-balancing ion was attempted by reacting NaAlO₂ solution with GeO₂ in an adaption of a sol-gel synthesis for aluminosilicate inorganic polymers. XRD and ²⁷Al MAS NMR suggested that only a small degree of reaction had occurred, based on the presence of unreacted GeO₂ and a trace of Na₃HGe₇O₁₆·4H₂O, with only a small amount of the tetrahedral aluminium characteristic of a true inorganic polymer. The addition of KOH markedly enhanced the reaction, producing a (Na,K) product with properties characteristic of a true inorganic polymer (an amorphous X-ray powder pattern and predominantly tetrahedral aluminium). An attempt to synthesise the potassium end-member aluminogermanate compound by replacement of the NaAlO₂ in the above synthesis with KAlO₂ produced only crystalline K(AlGeO₄)H₂O and K₃HGe₇O₁₆·4H₂O containing solely tetrahedral aluminium. Attempts to extend these syntheses to the gallium analogues of these aluminogermanate compounds were unsuccessful, producing only the crystalline products K(GaGeO₄)₆·7H₂O and K₃HGe₇O₁₆·4H₂O. Thus, the most successful sol-gel synthesis of a germanate compound with the properties of an inorganic polymer was of an aluminogermanate containing Na⁺ and K⁺ as the exchangeable cations.     

A study on separation of Mn and Fe from high-alumina ferruginous manganese ores by the carbothermal roasting reduction process

Carbothermal reduction followed by magnetic separation has been recognized as an effective recovery strategy to achieve separation of Mn and Fe from ferruginous manganese ores (Fe-Mn ores). However, it is difficult to improve the recovery of manganese more than 85% by changing carbothermic roasting reduction and magnetic separation. This work clarified the underlying reason for the poor separation with the magnetic separation process and proposed a promising process for the recovery of Fe and Mn from Fe-Mn ore. The effect of operating variables on recovery and separation of Mn and Fe from Fe-Mn ore is initially investigated during the carbothermic reduction roasting process followed by magnetic separation to reveal the underlying reason for the poor separation from Fe-Mn ores. Then, the stepwise reduction behaviors of the MnO-Fe₂O₃ and MnO-Fe₂O₃-Al₂O₃ systems were investigated to clarify that the formation of composite oxide Mn_1−xFe_xO (0 < x < 0.497) and hercynite (FeO·Al₂O₃) directly caused the poor separation of Fe and Mn from high-alumina Fe-Mn ores. Then, the stepwise reduction roasting behaviors of Mn_1−xFe_xO and FeO·Al₂O₃ were investigated by XRD, SEM-EDS and XPS analysis. After adjusting the experimental parameters, iron-rich products with a Fe recovery of 94.31% and a grade of 85.21% and manganese-rich product with a Mn recovery of 90.05% and a grade of 54.35% are obtained. The mass ratio of Mn/Fe increased to 8.5 in the manganese-rich product.     

Optimizing the performance of the RER magnetic separator for upgrading silica sands

Feed fractionation of a silica sand sample to a rare earth roll separator (RER) magnetic separator was found to be much more favorable for separation than the whole batch. The performance of the separator depends on both the size and the size distribution of the feed. The correlation between the different size fractions of the feed, e.g., ?0.6 + 0.106, ?0.6 + 0.211, and ?0.211 + 0.106 mm and the RER magnetic parameters, e.g., belt speed and splitter angle of inclination was statistically verified using the central composite design (CCD) to achieve the optimum performance of the separator to reduce the Fe₂O₃ content of the sand concentrate. About 56.6% removal of this contaminant was achieved with the whole feed ?0.6 + 0.106 mm at belt speed of 100 rpm and splitter angle inclination of 95°, whereas 84.3% reduction of Fe₂O₃ content was achieved with the separate size fractions under different belt speed and splitting angle inclination optima. The quality of the silica sand concentrate produced satisfies the requirement for both colorless glass and insulating glass fibers production.     

Mineralogical reconstruction of Titanium-Vanadium hematite and magnetic separation mechanism of titanium and iron minerals

In this paper, magnetization roasting - low-intensity magnetic separation was performed on a pre-concentration concentrate obtained from an Australian hematite containing titanium and vanadium to realize the separation of titanium and vanadium. The results showed that an iron concentrate with TFe (total iron) grade of 58.71%, iron recovery of 86.72% and V₂O₅ grade of 1.00%, V₂O₅ recovery of 93.97% could be obtained under the optimum roasting conditions (roasting temperature of 580 °C, total gas-flow rate of 1.44 m³/h, CO concentrate of 30%, roasting time of 20 min), meanwhile the iron tailings (i.e., TiO₂ concentrate) with TiO₂ grade of 43.76%, TiO₂ recovery of 63.42% was obtained. XRD analysis, phase iron chemical analysis, and magnetic analysis were conducted on the raw sample and the roasted products. The results showed that after magnetization roasting, the hematite and limonite in raw sample were transformed into magnetite with strong magnetism, and the vanadium hematite of hexagonal system was transformed into vanadium magnetite of equiaxed system. As the weakly magnetic ilmenite does not participate in the reaction during reduction roasting, the separation of ilmenite and vanadium can be easily achieved via magnetic separation.     

MAS-NMR support for Hench model in the case of bioactive glass microspheres

The structural changes occurred in bioactive glass microspheres belonging to the system SiO₂–Na₂O–P₂O₅–CaO–K₂O–MgO incorporating yttrium were investigated before and after soaking in simulated body fluid (SBF) by X-ray diffraction (XRD) and ³¹P and ²⁹Si magic angle sample spinning nuclear magnetic resonance (MAS-NMR). The addition of yttrium to the bioactive glass composition induces changes in the behavior of the glass microspheres in SBF. The XRD analysis proves that after the immersion in SBF a crystalline hydroxyapatite-like phase is developed on the microspheres surface. The ²⁹Si and ³¹P MAS-NMR results show that silicate species with two and three bridging oxygens per SiO₄ tetrahedra and PO₄ monomeric units are present in the glass structure. After immersion in SBF, new silicate species with four bridging oxygens appear as result of silica-gel layer formed on microspheres surface. The formation of crystalline hydroxyapatite-type layer is reflected by the occurrence of narrow components in ³¹P MAS-NMR spectra. The NMR results support the Hench model for bioactive glasses behavior in biological environments.     

Phase Separation in Electron Doped Iron-Selenide K0.8Fe1.6Se2 Superconductor by Scanning X-ray Nano-Diffraction

A new family of high temperature superconductors, the heavily electron doped iron-selenides, like K_0.8Fe_1.6Se₂, has been attracting high interest since they show both 30 K superconductivity, with missing hole pockets questioning the s_± pairing model, and unusually high magnetic moments. The hot debate is between coexistence versus phase separation and on the possible divergence of surface from bulk structure. Here, we provide direct evidence for a nanoscale phase separation in a single crystal of K_0.8Fe_1.6Se₂, where a first magnetic phase, with superlattice modulation $(\sqrt{5}\times\sqrt{5})$ , coexists with a second nonmagnetic phase, with a second superlattice modulation ( $\sqrt{2} \times\sqrt{2}$ ), below 520?K using transmission X-ray diffraction. The mapping of the spatial distribution of the two phases is measured by scanning X-ray nanodiffraction using a 300×300 nm² X-ray spot. The complex spatial phase separation clarifies the coexistence of superconductivity and magnetism in the same sample.     

Synthesis and Characterization of Ferromagnetic Nickel Nanoparticles

Nickel nanoparticles on mass production scale have been prepared using a modified polyol process with Ni(CH₃COO)₂?4H₂O, NaOH, 1,2 propandiol and hydrazinium hydroxide (N₂H₄?H₂O). A?mixture of face centered cubic (fcc) metallic nickel nanoparticles with 12 nm diameter were obtained. We have experimentally studied the structure of nanoparticle by X-ray and Scanning Electron Microscopy (SEM, EDS). The magnetic properties of the prepared Ni film have been studied by Ferromagnetic Resonance (FMR) technique, Vibrating Sample Magnetometer (VSM) and Vector Network Analyzer (VNA). The effective g-factor and magnetic anisotropy constant were determined as g _eff=2.25 and K _eff=85?Oe, respectively.     

Creation of Ferromagnetic Properties in Ni-Doped Na<Subscript>2</Subscript>WO<Subscript>4</Subscript>—Effect of Hydrogenation Post-treatment

Pure and Ni-doped sodium tungstate (Na₂WO₄) powders were synthesised by simultaneous crystallisation method. The effects of Ni doping on the structural, optical, and magnetic properties of the host Na₂WO₄ powder were studied. The study of X-ray diffraction shows that the incorporated Ni ions occupy locations in interstitial positions and substitution for W ion in the Na₂WO₃ lattice. A monophase cubic structure was obtained when the as-crystallised Na₂WO₄ powder was doped with Ni ions or annealed in hydrogen gas atmosphere (hydrogenation). The optical properties were studied by diffuse reflectance spectroscopy (DRS) technique. It was established that the direct bandgap of Na₂WO₄ exhibits red shift from 4.6 to 3.50 eV with Ni doping and blue shift to 5.13 eV with hydrogenation. The purpose of the present study is to study conditions necessary to prepare powders having room-temperature ferromagnetic (RT-FM) properties. Therefore, the Na₂WO₄ nano-powder was doped with Ni ions. RT-FM properties were obtained with Ni-doped Na₂WO₄ that was strongly enhanced by hydrogenation so that the energy product (EP) was increased by 213 %. This enhancement was attributed to the enhancement of the magnetic medium for the spin-spin (S-S) interaction inside the crystalline medium. In general, an experimental relationship was established between O vacancies, optical absorption, and magnetic properties of the studied crystal. Thus, it was proved, for the first time, the possibility of producing Na₂WO₄ having RT-FM, where magnetic characteristics can be tailored by doping and post-treatment under H₂ atmosphere, thus a new potential candidate to be used in magnetic applications of ferroelectric crystals.     

Synthesis and characterization of Co-Fe Prussian blue nanoparticles within MCM-41

A Prussian blue analogue, K_0.84Co_1.08[Fe(CN)₆] is prepared by reaction between [Fe(CN)₆]³⁻ in aqueous solution and ion-exchanged Co²⁺ in the channels of MCM-41. Powder X-ray diffraction, transmission electron microscopy, thermogravimetric analysis, nitrogen adsorption/desorption isotherms, diffuse reflectance UV-vis absorption spectroscopy and magnetic measurements were employed to characterize the product. The results show that the Prussian blue analogue is in nanoparticles within the channels and the hexagonal phase of MCM-41 remains intact during the reactions. A particle size effect on optical and magnetic properties of the nanoparticles was observed.     

Anomalous behaviour of the magnetic hysteresis loop in the α-Fe2O3/SiO2 nanocomposite

The α-Fe₂O₃/SiO₂ nanocomposite containing 45 wt.% of hematite was prepared by the sol-gel method and characterized by using X-ray diffractometer (XRD), transmission electron microscopy (TEM), and superconducting quantum interference device (SQUID) magnetometer. TEM microscopy showed spherical particles with average size about 10 nm, whereas XRD diffraction confirmed the formation of the hematite phase. The magnetic measurements showed anomalous behavior of the hysteresis loops including decrease of high field isothermal magnetization and overlap of initial, remagnetization and magnetization curves. This anomalous behavior represents a novel effect for α-Fe₂O₃/SiO₂ nanocomposites. We conjecture that a field-induced antiferromagnetic coupling between nanoparticles may produce this effect.     

Biologically formed hollow cuprous oxide microspheres

Hollow cuprous oxide (Cu₂O) microspheres with a diameter of ca. 1.8 μm are prepared by using yeast as template. The possible mechanism for the formation of the hollow Cu₂O spheres is revealed. The biotemplated sample is investigated by means of X-ray diffraction (XRD), scanning electron microscopy (SEM) and ultraviolet–visible (UV–vis) absorption spectra. The sample consists of the crystalline Cu₂O microspheres with diameters of about 59.5 nm and lattice parameter of 4.264 Å. The observed optical band gap of the product indicates that the blue–shift effect occurs, which is attributed to the hollow Cu₂O microspheres.     

The structural,dielectric and magnetic study of cobalt based spinel ferrites and polypyrrole composites

The CoFe₂O₄ was prepared via co-precipitation route, and in situ polymerization was used to prepare the polypyrrole, for the fabrication of nanocomposite. Two-point probe techniques, X-ray diffraction (XRD), as well as vibrating sample magnetometer (VSM) were used to investigate the electrical, magnetic, and structural characteristics of all the synthesized samples. In nanocomposites with higher ferrite concentrations, XRD peaks became more intense, and their widths becomes narrowed. The ferrite content enhanced the dc resistivity as well activation energy of the materials. The hysteresis loop identified the ferromagnetic property. The super paramagnetic behavior has been observed in samples PF1 (with 25% ferrites) and PF2 (having 50% ferrite ratio). These two samples might be employed in hyperthermia, which is a cancer therapy approach.

     

Curie temperature enhancement in partially disordered Sr2FeReO6 double perovskites

Two samples of the double perovskite Sr₂FeReO₆ have been synthesized by (1) soft-chemistry procedures and (2) high-pressure methods. The sample prepared by a soft-chemistry technique presents 75% of Fe/Re cationic order whereas the one prepared by the application of high external pressure generates a complete Fe/Re cationic order. Both materials have been characterized by X-ray diffraction, neutron powder diffraction and magnetic measurements. The magnetic properties of both oxides have been compared, observing that the specimen prepared via soft-chemistry procedures presents an enhanced Curie temperature of 445 K, although the sample prepared under high-pressure techniques displays a superior saturation magnetization. This behavior is explained as a consequence of the presence, in the partially disordered sample, of Fe-rich islands containing strong Fe-O-Fe antiferromagnetic couplings, able to nucleate and lock the ferromagnetic interactions of the ordered regions, thus increasing the global Curie temperature of the partially disordered material.