Non-stoichiometric NiZn ferrite by sol-gel processing

Non-stoichiometric Ni_0.5Zn_0.5Fe_2−xO_4−3/2x ferrites over a wide range of x = 0∼0.8 are synthesized by a sol-gel processing. Phase evolution, crystal structure and crystallite size of spinel ferrites are dependent on annealing temperature and the amount of Fe deficiency. The crystallite size of spinel increases with annealing temperature and grows faster in stoichiometric ferrites than that of non-stoichiometric. Fe deficiency results in the partial reduction of spinel ferrite to zincite ZnO. XRD indicates that the crystallization temperature of ZnO is increased to about 700 °C. Zincite reduces the number of ferrite crystallites and disfavors the growth of spinel ferrites. The lattice parameters decrease with Fe deficiency and are insensitive to the variation in composition in the samples annealed at lower temperature due to the segregation of ZnO and lattice expansion in the ultrafine crystallites.     

A crystal phase study of zinc hydroxide chloride in electric-arc-furnace dust

Chemical analysis shows that electric-arc-furnace (EAF) dust obtained from 13 steelmaking factories in Taiwan is composed chiefly of Fe (15–37%), Zn (7–28%) and Mn (1.55–3.99%) and that the mineral composition is mainly (Mn, Zn) Fe₂O₄, ZnO and ZnCl₂·4Zn(OH)₂·H₂O. It was also found that EAF dust exists as irregular agglomerates from 3 to 20 m in size and are made up of much smaller round particles from 0.3 to 1 m in size. ZnCl₂ gas in the dust condenses after passing through the EAF gas-cooler system binding small particles of Mn-Zn ferrite together. The agglutinative substance was identified as being ZnCl₂·4Zn(OH)₂·H₂O possibly arising from the interaction between ZnCl₂ and ZnO adhering to the Mn-Zn ferrite particles; a conjecture supported by the fact that EAF dust dissolves easily in hydrochloricacid solution leaving only loosely aggregated Mn-Zn ferrite material.     

An anomalous behaviour in the phase stability of the system Fe2O3 and NiO

Iron-nickel mixed oxides containing up to 50 mol% of NiO were prepared by firing the corresponding co-precipitated hydrous oxides; characterization was performed by X-ray diffraction, infrared spectroscopy, magnetic susceptibility, electrical conductivity and thermoelectric power measurements. A non-stoichiometric ferrite phase was formed when a sample containing 20 mol% NiO was sintered at 1050°C. This phase had two- to three-fold higher conductivity than either Fe₂O₃ or the stoichiometric ferrite (NiFe₂O₄). The thermoelectric power of this phase indicated a sharp change of charge carriers from n- to p-type near 350°C. This non-stoichiometric ferrite phase was stable only in a small temperature range and dissociated into -Fe₂O₃ and stoichiometric ferrite above 1200°C. Samples containing 5 and 10 mol% NiO also had small fractions of this non-stoichiometric ferrite phase when sintered at 1050°C.     

The preparation of zinc ferrite nanorods by using single ferrocenyl complex as precursor

Zinc ferrite nanorods were prepared by the decomposition of ferrocenyl complex [Zn(fca)₂] 1 (Hfca, ferroceneylacetone) as single source precursor. In this work, we presented a new and simple route to synthesize nanostructured ferrites by decomposition of ferrocene-based complexes without the assistance of catalysts or template, and successfully obtained zinc ferrite nanorods with perfect morphology. The synthesis of ZnFe₂O₄ nanorods was carried out via decomposition of zinc ferrocenyl complexes at the presence of sodium hypochlorite under hydrothermal condition without the attendance of catalysts or templates. The results show that ferrocenyl complexes play an important role in the control synthesis of good morphology ferrites. To our knowledge, this is the first report to describe the synthesis of nanostructured zinc ferrites based on one-step hydrothermal decomposition of zinc ferrocenyl complexes. This exploration provides a useful method to seek new nanomaterials with perfect morphology in the shape-controlled synthesis of complicated inorganic composition oxides.     

Synthesis of zinc oxide nanostructures during zinc oxidation by sub-and supercritical water

Solid zinc (Zn)_S and liquid zinc (Zn)_L are oxidized by water with the formation of zinc oxide (ZnO) nanostructures and the evolution of hydrogen. The maximum rate of this process, called chemical supercondensation by water (CSW), is realized on approaching the melting temperature of zinc from the left and right with increasing density of supercritical water. The CSW process begins with the formation of (ZnO) _n clusters via the reaction (Zn)_S,L + nH₂O = [(Zn)_S,L · (ZnO) _n ] + nH₂, followed by their subsequent growth at n > 7 in the exothermal process of epitaxy on (Zn)_S and coagulation of (ZnO) _n in (Zn)_L. The CSW of (Zn)_S leads predominantly to the formation of nanowires and nanorods, while the CSW of (Zn)_L practically always proceeds with the formation of nanoparticles. The rate of (Zn)_S oxidation increases with the thickness of a layer converted into ZnO. This is related to the self-heating and local melting of (Zn)_S in the course of CSW. The complete CSR of (Zn)_S plates and cylinders results in the formation of highly porous nanostructural ceramics.     

Effects of Iron Deficiency Content on Electromagnetic Performance of LiZn Ferrites

The polycrystalline Li_0.35Zn_0.3Fe_2.35?x O_4?δ ferrites with different iron-deficient contents (x = 0.000 ～0.235) have been synthesized via a solid-state method. Based on the deconvoluted X-ray photoelectron spectroscopy (XPS) spectra of Fe 2p for LiZn ferrites, the Fe²⁺ and Fe³⁺ ion percent contents have been estimated via the area proportion of each peak, respectively. With the increase of iron-deficient content (x), the ion percent ratio of Fe²⁺/Fe³⁺ shows a monotone decrease. Furthermore, according to the equivalent circuit of ferrite of a “brick wall” model, resistivity and permittivity frequency spectra (100 Hz ～1 MHz) of LiZn ferrites have been investigated, and LiZn ferrites show grain boundary and grain characteristics at low and high frequencies, respectively. In addition, the ferromagnetic resonance (FMR) linewidth has been separated to anisotropy and porosity line broadening contributions by an approximate calculation based on a spin-wave approach.     

Low temperature solution synthesis and characterization of ZnO nano-flowers

Synthesis of flower-shaped ZnO nanostructures composed of hexagonal ZnO nanorods was achieved by the solution process using zinc acetate dihydrate and sodium hydroxide at very low temperature of 90 °C in 30 min. The individual nanorods are of hexagonal shape with sharp tip, and base diameter of about 300-350 nm. Detailed structural characterizations demonstrate that the synthesized products are single crystalline with the wurtzite hexagonal phase, grown along the [0 0 0 1] direction. The IR spectrum shows the standard peak of zinc oxide at 523 cm⁻¹. Raman scattering exhibits a sharp and strong E₂ mode at 437 cm⁻¹ which further confirms the good crystallinity and wurtzite hexagonal phase of the grown nanostructures. The photoelectron spectroscopic measurement shows the presence of Zn, O, C, zinc acetate and Na. The binding energy ca. 1021.2 eV (Zn 2p_3/2) and 1044.3 eV (Zn 2p_1/2), are found very close to the standard bulk ZnO binding energy values. The O 1s peak is found centered at 531.4 eV with a shoulder at 529.8 eV. Room-temperature photoluminescence (PL) demonstrate a strong and dominated peak at 381 nm with a suppressed and broad green emission at 515 nm, suggests that the flower-shaped ZnO nanostructures have good optical properties with very less structural defects.     

Approach to a block polymer precursor from poly(3-hexylthiophene) nitroxide-mediated in situ polymerization for stabilization of poly(3-hexylthiophene)/ZnO hybrid solar cells

A cross-linked block copolymer poly(3-hexylthiophene)-b-poly(zinc dimethacrylate) (P3HT-b-PZn(MA)₂), which acted as precursor for the preparation of poly(3-hexylthiophene)/ZnO (P3HT/ZnO) hybrid film by in-situ hydrolysis, was rationally designed and synthesized via nitroxide-mediated in-situ polymerization of zinc methacrylate (Zn(MA)₂) using poly(3-hexylthiophene) alkoxyamine (P3HT-TIPNO) as macroinitiator for the purpose of stabilizing the P3HT/ZnO hybrid solar cells. The cross-linking was confirmed by the insolubility of the film in organic solvents and Fourier-transform infrared experiment. With the function of the cross-linked template, the diffusion of ZnO nanoparticles prepared by in-situ hydrolysis could be lowered to suppress the formation of large aggregations, which favored the formation of a better and more stable interpenetrating network and provided more heterojunction interfaces for exciton dissociation. As a result, the inverted device based on cross-linked P3HT/ZnO hybrid film obtained by in situ hydrolyzing P3HT-b-PZn(MA)₂ block copolymer yielded a power conversion efficiency of 0.45% under AM 1.5G illumination from a calibrated solar simulator with an intensity of 100 mW/cm², and the deterioration of the photoconversion performance was suppressed in the hybrid solar cells with the cross-linked P3HT/ZnO compared to cells with non-cross-linked P3HT/ZnO obtained by in situ hydrolyzing P3HT-TIPNO/Zn(MA)₂ blend film.     

Surface-induced time-dependent instability of ZnO based thin-film transistors

We report on the surface-induced time-dependent instability of ZnO based thin-film transistors (ZnO-TFTs) with interdigitated source/drain (S/D) electrodes. As time elapsed, a considerable shift of threshold voltage (V_T) was observed (by ~ − 16 V) from our TFT. Contact angle of de-ionized water on ZnO surface also changed from 30° to 110°, revealing time-dependent surface state change. According to X-ray photoemission spectroscopy (XPS) measurements, the Zn 2p_3/2 core-level peak and the valence band maximum (VBM) of aged ZnO surface shifted to the higher binding energy by 0.3 eV, which implies a downward energy band bending of the ZnO back channel-surface. We conclude that without passivation layer any bottom gate ZnO-TFT meets the surface-induced electrical instabilities due to the time-dependent conductance of ZnO surface.     

Electrical conductivity studies of copper-substituted and non-substituted Ni-Zn mixed ferrites

The electrical conductivity of Ni-Zn and copper-substituted Ni-Zn ferrites is investigated in the range 300 to 1000 K. It is seen that the plots of log against 10³/T exhibit a linear relationship. There are four distinct regions exhibited by the Ni-Zn ferrite. However, with the substitution of copper there appears to be gradual disappearance of the fourth region. Also for the samples of Ni-Zn ferrite with more than 80% Zn, there are only three regions in the variation of log with 10³/T. The breaks and discontinuities are attributed to several sources. The electrical conduction in these ferrites is explained on the basis of a hopping mechanism. The activation energy in the paramagnetic region is found to be more than that for the ferri magnetic region. This is attributed to the effect of the magnetic ordering in the conduction process.     

Zinc Ferrite Nanoparticles: New Preparation Method and Magnetic Properties

In this work, single phase zinc ferrite (ZnFe₂ O ₄) nanoparticles with a mean crystallite size of 12 nm were successfully prepared just by high energy wet milling of metallic Zn and Fe powders and water as the raw materials, without any subsequent heat treatments. Variation of the magnetization with respect to temperature was studied by Faraday balance. Room temperature M–H curve of the as-milled powder has an s-shape, which shows it has ferrimagnetic order. To investigate the effect of annealing on magnetic properties of the as-milled powder, it was annealed at different temperatures from 150 to 800 °C and characterized by XRD and magnetometry. The results show that cation distribution of the as-milled nanoparticles is different from that of the bulk zinc ferrite (normal spinel) and by annealing it changes drastically, and finally, it changes to that of the bulk one.     

Characterization of wet processed (Ni, Zn)-ferrites for CO2 decomposition

Ultrafine (Ni, Zn)-ferrites were prepared by two different methods of coprecipitation and hydrothermal synthesis, and their oxygen-deficient ferrites (ODF) produced by hydrogen reduction were investigated on the efficiency of CO₂ decomposition. The crystalline sizes of (Ni, Zn)-ferrites were less than 30 nm with high Brunauer–Emmett–Teller (BET) surface areas, ranging from 77 to 172 m² g^–1. The (Ni, Zn)-ferrites by hydrothermal synthesis resulted in smaller crystalline sizes, higher BET surface areas and better efficiencies of CO₂ decomposition than by coprecipitation. Compared with the binary NiFe₂O_4– ferrite, the ternary (Ni _x , Zn_1–x ) Fe₂O_4– ferrites showed higher efficiency for CO₂ decomposition, indicating a potential catalyst for the reduction of CO₂ emission in the environmental atmosphere.     

Influence of cerium substitution on structural,magnetic and dielectric properties of nanocrystalline Ni–Zn ferrites synthesized by combustion method

Nickel–Zinc (Ni–Zn) ferrites substituted by cerium (Ce) and having the chemical composition Ni_0.5Zn_0.5Ce _x Fe_2?x O₄ (x?=?0.00, 0.02, 0.04, 0.06, 0.08 and 0.10) were synthesized by combustion method using the organic fuel urea as reducing agent. The effects of cerium substitution on the structural, magnetic and dielectric properties of Ni–Zn compounds have been evaluated. X-ray diffraction patterns indicate that the Ni_0.5Zn_0.5Ce _x Fe_2?x O₄ crystallizes into cubic spinel structure initially and secondary phase emerged along with main spinel phase when the Ce³⁺ content is increased. The elemental composition analysis confirms the stoichiometric presence of expected elements in the samples. Scanning electron microscope and high-resolution transmission electron microscope images reveal the nature of grain growth and the particle size of the synthesized samples. Fourier transform infrared spectroscopy confirms the formation of spinel phase and predicted the shifting of bands corresponding to Fe–O vibrations towards higher wavenumbers compared to undoped Ni–Zn ferrite. Magnetic characterization studies reveal that the substitution of Ce³⁺ into the Ni–Zn ferrite leads to a significant change in saturation magnetization and coercivity values. A plot of dielectric constant (?′) versus applied electrical frequency measured at room temperature shows the normal dielectric behavior of the spinel ferrites. The introduction of Ce³⁺ rare earth ions into Ni–Zn ferrites samples is found to affect the values of both dielectric constant and AC conductivity.     

Green and low temperature synthesis of nanocrystalline transition metal ferrites by simple wet chemistry routes

Crystalline and nanostructured cobalt （CoFe2O4）, nickel （NiFe2O4）, zinc （ZnFe2O4） and manganese （MnFe2O4） spinel ferrites are synthesized with high yields, crystallinity and purity through an easy, quick, reproducible and low-temperature hydrothermal assisted route starting from an aqueous suspension of copredpitated metal oxalates. The use of water as a reaction medium is a further advantage of the chosen protocol. Additionally, the zinc spinel is also prepared through an alternative route combining copredpitation of oxalates from an aqueous solution with thermal decomposition under reflux conditions. The nanocrystalline powders are obtained as a pure crystalline phase already at the extremely low tem- perature of 75 ℃ and no further thermal treatment is needed. The structure and microstructure of the prepared materials is investigated by means of X-ray powder diffraction （XRPD）, while X-ray photoelectron spectroscopy （XPS） and inductively coupled plasma-atomic emission spectroscopy （ICP-AES） analyses are used to gain information about the surface and bulk composition of the samples, respectively, confirming the expected stoichiometry. To investigate the effect of the synthesis protocol on the morphology of the obtained ferrites, transmission electron microscopy （TEM） observations are performed on selected samples. The magnetic properties of the cobalt and manganese spinels are also investigated using a superconducting quantum device magnetometer （SQUID） revealing hard and soft ferrimagnetic behavior, respectively.     

Synthesis of manganese–zinc ferrite by powder mixing using ferric oxide from a steel mill acid recovery unit

With the aim of producing fine-grained manganese–zinc (Mn–Zn) ferrite at the end of a calcination process at moderate temperatures, this study consisted, at first, of an “electrochemically designed” powder mixing by wet-ball milling a mixture of manganese (MnO₂), zinc (ZnO), and iron (Fe₂O₃ granules produced by an acid recovery unit of a Brazilian steelmaker, milled to fine sizes using alkaline media) –based raw materials. This mixing/milling resulted in improved size reduction when compared to milling without any alkali addition. Further, noticeable size reduction was achieved when elemental Zn was used in place of ZnO, especially when ammonia was used as the medium. Calcination of the alkaline-milled mixture of MnO₂ + ZnO + Fe₂O₃ at 1200 °C allowed obtaining well-crystallized single-phase Mn–Zn ferrite, whereas calcination of the MnO₂ + ZnO + Fe₂O₃ mill-mixed in 100% NH₄OH at 1200 °C produced the highest saturation magnetization in the as-calcined state.     

Evolution and temperature dependence of ZnO formation by high power sonication

The sonochemical reaction between varying concentrations of zinc nitrate hexahydrate (Zn(NO₃)₂·6H₂O) and hexamethylenetetramine (C₆H₁₂N₄) in a 150 W dual transducer sonicator resulted in different phases of zinc compounds. Single phase zinc oxide (ZnO) was exclusively obtained in the case of 0.05 M. By tracking the products synthesized at 50 °C, zinc hydroxide (Zn(OH)₂) was formed in the first 40 min and replaced by ZnO after prolonged sonication. Zn(OH)₂ was also present in a mixed phase with ZnO when the reagent concentration was reduced to 0.01 M. The increase in the synthesis temperature up to 80 °C reduced defects and free radicals but introduced zinc hydroxide nitrate hydrate (Zn₅(OH)₈(NO₃)₂(H₂O)₂) which is a dominant phase from the reaction between highly concentrated reagents (0.1 M). High temperature and sonication power in this system tend to cause agglomerations into irregular microparticles.     

Decomposition of CO2 and CO into carbon with active wüstite prepared from Zn(II)-bearing ferrite

CO₂ decomposition reaction into carbon was studied at 300 °C using the H₂-reduced Zn(II)-bearing ferrite which consisted of the Zn(II) oxide and the active wüstite. The H₂-reduced Zn(II)-bearing ferrite was prepared from Zn(II)-bearing ferrite by the reduction with H₂ gas at 300 °C. The wüstite (FeO) in the H₂-reduced Zn(II)-bearing ferrite had a higher value (=0.97, active wüstite) than those of the normal wüstites (0.90<<0.95) prepared at high temperatures (>570 °C). The decomposition reaction of CO₂ proceeds in two steps: (1) CO₂ reduction to CO, and (2) CO decomposition into carbon. In the initial stage, the reduction of CO₂ into CO takes place, accompanying both the oxidation of the active wüstite to the slightly oxidized wüstite, and the transformation of active wüstite and Zn(II) oxide into the Zn(II)-bearing ferrite. After the reaction of the initial stage attains equilibrium of an apparent state of rest, the adsorbed CO is decomposed into carbon, associated with the transformation of the slightly oxidized wüstite and the Zn(II) oxide into the Zn(II)-bearing ferrite.     

Highly conductive and transparent In-doped zinc oxide thin films deposited by chemical spray using Zn(C5H7O2)2

Highly conductive and transparent indium-doped zinc oxide, ZnO, thin films were deposited on sodocalcic glass substrates by chemical spray, using zinc acetylacetonate, Zn(C₅H₇O₂)₂, and doped with indium chloride. Substrate temperature, dopant concentration in the starting solution and the kind of alcohol used as a solvent (methanol, ethanol and isopropanol) were varied in order to optimize deposition conditions. The lowest resistivity value of was obtained with ethanol at a substrate temperature of 475 °C and a [In]/[Zn]=2.5 at % ratio in the starting solution. The mobility and the carrier concentration values were in the order of and , respectively. For optimal deposition conditions no preferential growth was found. Surface morphology was altered depending on the kind of alcohol used, producing a rough surface with isopropanol than with methanol or ethanol. Transmittance average was of the order of 85%, at 550 nm.