Synthesis and magnetic properties of nickel ferrite nano-octahedra

High yield of nickel ferrite nano-octahedra with size distribution from 40 to 90 nm were synthesized through a simple hydrothermal method. The formation of faceted octahedra enclosed by {111} planes implies the much faster growth rate along 〈100〉 over 〈111〉 for face-centered cubic phase during hydrothermal process. Magnetic measurements indicated that the sample is soft-magnetic materials with much lower coercivity and much higher saturation magnetization compared to the nickel ferrite nano-crystals with similar size distribution but irregular shapes reported earlier.     

Al3+-modified elastic properties of copper ferrite

Ultrasonic pulse echo-overlap technique at 300 K (9 MHz) has been employed to study the elastic properties of Al³⁺-substituted CuFe₂O₄ spinel ferrite system. The longitudinal and transverse wave velocities are used to compute elastic moduli and these are corrected to the zero porosity by employing different models. Contrary to expectation, the magnitude of elastic moduli is found to decrease by 75% with only 30% of Al³⁺-substitution for Fe³⁺ in the system. The lowering of elastic stiffness is mainly due to residual stress-induced spontaneous cracking and presence of oxygen vacant sites in the material. The lower value of lattice energy for polycrystalline specimens as compared to their single crystalline counterparts have been explained in the light of an increase degree of disorientation at the grain boundary with Al³⁺-substitution.     

Spinel copper ferrite nanoparticles: Preparation,characterization and catalytic activity

The magnetic CuFe₂O₄ nanoparticles have been synthesized and characterized by various spectroscopic methods, including X‐ray diffraction (XRD), O K, Cu and Fe K ‐edge X‐ray absorption near edge structure (XANES), energy dispersive X‐ray analysis (EDX), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The azide‐alkyne cycloaddition by the reaction of various phenylacetylenes with a mixture of benzyl halides and NaN₃ and also three component (A³) coupling reaction of aldehyde, alkyne and amine catalyzed by CuFe₂O₄ nanoparticles under aerobic conditions led to the formation of the 1,4‐disubstituted‐1,2,3‐triazoles and propargylamines in excellent yields. The catalyst can be recovered by applying an external magnetic field for the subsequent cycloaddition reactions and reused without any tangible loss in catalytic efficiency.     

Annealing effect on the structural and magnetic properties of nickel ferrite thin films

Nickel ferrite is a soft magnetic material with inverse spinel structure. Soft ferrite films are used in microwave devices, integrated planar circuits, etc., because of their high resistivity. In this work, thin films of nickel ferrite were deposited on Si (100) substrate by using pulsed laser deposition (PLD) technique. The thickness of the film was measured by surface profilometer and also by X‐ray reflectivity (XRR). The films were annealed at three different temperatures to observe the effect on the structural and magnetic properties of the film. The films were characterised by X‐ray diffraction (XRD), Raman spectroscopy and vibrating sample magnetometer (VSM) to study the structural and magnetic properties. Copyright © 2010 John Wiley & Sons, Ltd.     

Complexing properties ofSchiff bases with copper and nickel ions

Summary The solution properties ofPPP,QPP, and their complexes with copper and nickel were investigated. The composition and stability of the complexes have been determined using the spectrophotometric method atT=25±1 °C, constant ionic strength (I=0.5M, adjusted with KNO₃) and a volume ratio of methanol/water of =0.10 and 0.16 forPPP andQPP, respectively, due to lower solubility ofQPP. The experimental results have been fitted to the theoretical equations using the computerized iterative method of successive approximation. The influence ofpH and addition of another benzene ring to the ligand molecule has been studied. The structures of isolated solid metal complexes withQPP were investigated by infrared and mass spectroscopy. The use ofPPP andQPP as analytical reagents for spectrophotometric determinations of copper and nickel is discussed.

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Komplexbildende Eigenschaften vonSchiffschen Basen mit Kupfer- und Nickelionen

Zusammenfassung Die Eigenschaften vonPPP,QPP und ihrer Komplexe mit Kupfer und Nickel in Lösung wurden untersucht. Zusammensetzung und Stabilität der Komplexe wurde bei 25±1 °C, konstanter Ionenstärke (I=0.5M, eingestellt mit KNO₃) und einem. Methanol/Wasser-Volumenverhältnis von =0.10 und 0.16 fürPPP bzw.QPP (bedingt durch die geringere Löslichkeit vonQPP) bestimmt. Die experimentellen Ergebnisse wurden mittels eines Algorithmus zur sukzessiven Approximation an die theoretischen Gleichungen angepaßt. Der Einfluß despH-Werts und eines weiteren aromatischen Rings am Liganden wurden studiert. Die Strukturen der isolierten festen Komplexe mitQPP wurden mittels IR- und Massenspektroskopie untersucht. Die Verwendung vonPPP undQPP als analytische Reagenzien zur spektrophotometrischen Bestimmung von Kupfer und Nickel wird diskutiert.

     

Structure and electrical properties of oxygen-deficient strontium copper niobate

The transport properties of Sr_5.66 Cu_0.14Nb_2.20 O_11.30 double perovskite, which enters the homogeneity region of (Sr_1-y Cu _y )₆–_2x Nb_2+2x O_11+3x solid solution, are concerned. The total conductivity is differentiated into terms over wide ranges of temperatures and oxygen partial pressures $ p_{O_2 } $ p_{O_2 } in dry and humid atmospheres. When $ p_{O_2 } $ p_{O_2 } is low or high, a test sample has dominant electron transport of n- or p-type, respectively. In air ($ p_{O_2 } $ p_{O_2 } = 0.21 atm), the p-type electron conductivity term increases with temperature elevation. In a humid atmosphere ($ p_{H_2 O} $ p_{H_2 O} = 0.02 atm), a sample is capable of a reversible incorporation of water occlusion from the gas phase; as a result, some proton conductivity term appears and ion transference numbers increase over a wide range of $ p_{O_2 } $ p_{O_2 } values.     

氧化锌修饰的铁酸铜催化剂水煤气变换性能研究(英文)

以250~400℃为活性测试温区,研究了氧化锌修饰的铁酸铜催化剂的水煤气变换性能。发现以2.5%ZnO修饰的催化剂表现出较高的催化活性,N2物理吸附、SEM、XRD、H2-TPR和CO2-TPD表征结果表明,适量ZnO的引入不仅能够促使CuFe2O4晶相发生转变,而且可以增强催化剂还原性能和增加弱碱性和中强碱性位点数量,同时也可改善铜铁之间的相互作用,从而提高了CuFe2O4的催化活性。     

Preparation and properties of metallacyclobutanes of nickel and palladium

Bis(phosphine)-3,3-dimethylnickela- and palladacyclobutanes have been prepared by intramolecular C-H insertion reaction of the corresponding dineopentyl metal complexes. Nickelacyclobutane complexes decompose when heated thereby undergoing competitive carbon-carbon bond cleavage to give isobutene and ethylene, with reductive elimination affording 1,1-dimethylcyclopropane and skeletal isomeri-zation of the metallacyclic ring yielding 3-methyl-1-butene, whereas the palladium analog gave no significant amounts of CC bond cleavage products.Added phos-phine was seen to have an effect on CC bond scission of nickelacyclobutane complexes. Nickelacyclobutane complexes in solution are thought to be in equilibrium with olefin-coordinated nickel-carbene complex on the basis of available experimental evidence from hydrogenolysis, carbene-trap reactions with olefins and reaction with carbon monoxide     

Synthesis and electrical properties of dense Bi2Al4O9

Bi₂Al₄O₉ ceramics are difficult to sinter to greater than 80% theoretical density due to peritectic decomposition at 1,070 °C. A novel processing method is discussed where a high-bismuth oxide-based liquid is used as a sintering aid. After sintering, the high bismuth oxide phase is removed by leaching with 40% acetic acid. The resulting samples are phase pure and ∼91% dense. The grain size varies in a wide range with the average grain size of ∼1 μm. The electrical properties of these ceramics were measured as functions of temperature (550–850 °C) and oxygen partial pressure (6×10⁻⁶–1 atm). The total conductivity was separated into electronic and ionic contributions. The low ionic conductivity indicates that the material is not an ‘intrinsically defective fast ion conductor’. The ionic conductivity is due almost exclusively to compensating oxygen vacancies related to impurities. With increasing temperature and decreasing oxygen partial pressure, the electronic conduction dominates over the ionic conduction.     

Preparation and magnetic properties of Zn-Cu-Cr-La ferrite and its nanocomposites with polyaniline

Nanosized Zn(0.6)Cu(0.4)Cr(0.5)Fe(1.5-x)La(x)O(4) (x=0 - 0.06) ferrites doped with La are synthesized by a rheological phase reaction method. Polyaniline (PANI)/ferrite nanocomposites are prepared by in situ polymerization method. The structure, morphology and ferromagnetic property of ferrite powders and nanocomposites are characterized by X-ray powder diffractometer (XRD), transmission electron microscope (TEM), Fourier transform infrared spectra (FTIR), UV-visible spectroscopy (UV), thermogravimetric analysis (TGA) and vibrating sample magnetometer (VSM). The results indicate that the PANI and nanosized ferrite powders can be combined effectively. The polymers can reduce the agglomeration of nanosized ferrite particles to some extent, which is good for the dispersedness and stabilization of nanoparticles. The PANI/ferrite nanocomposites under applied magnetic field exhibit the hysteretic loops of the ferromagnetic nature. The magnetic properties of nanocomposites are tailored by controlling the ferrite content.     

Structure and properties of bivalent nickel and copper complexes with pyrazine-amide-thioether coordination: stabilization of trivalent nickel

Acyclic pyrazine-2-carboxamide and thioether containing hexadentate ligand 1,4-bis[o-(pyrazine-2-carboxamidophenyl)]-1,4-dithiobutane (H(2)bpzctb), in its deprotonated form, has afforded light brown [Ni(II)(bpzctb)](1)(S=1) and green [Cu(II)(bpzctb)](2)(S=1/2) complexes. The crystal structures of 1.CH(3)OH and 2.CH(2)Cl(2) revealed that in these complexes the ligand coordinates in a hexadentate mode, affording examples of distorted octahedral M(II)N(2)(pyrazine)N'(2)(amide)S(2)(thioether) coordination. Each complex exhibits in CH(2)Cl(2) a reversible to quasireversible cyclic voltammetric response, corresponding to the Ni(III)/Ni(II)(1) and Cu(II)/Cu(I)(2) redox process. The E(1/2) values reveal that the complexes of bpzctb(2-) are uniformly more anodic by approximately 0.2 V than those of the corresponding complexes with the analogous pyridine ligand, 1,4-bis[o-(pyridine-2-carboxamidophenyl)]-1,4-dithiobutane (H(2)bpctb), attesting that compared to pyridine, pyrazine is a better stabilizer of the Ni(ii) or Cu(i) state. Coulometric oxidation of the previously reported complex [Ni(II)(bpctb)] and 1 generates [Ni(III)(bpctb)](+) and [Ni(III)(bpzctb)](+) species, which exhibit a LMCT transition in the 470--480 nm region and axial EPR spectra corresponding to a tetragonally elongated octahedral geometry. Complex 2 exhibits EPR spectra characteristic of the d(z(2)) ground state.     

Low-temperature sol-gel synthesis of modified nickel ferrite

A low-temperature method has been developed for preparing nickel ferrite doped with cobalt and copper (Ni_0.9Co_0.1Cu_0.1Fe_1.9O_{4 − δ}). This method provides the target product at 170–200°C with nanosized particles. The role of ammonium nitrate in the considerable reduction of ferrite synthesis temperature was studied.     

Investigations on structural,electrical and magnetic properties of nickel substituted La-ferrites

Nanocrystalline nickel substituted La-ferrites, LaNi_xFe_1−xO₃ (where x = 0, 0.2, 0.4, 0.6 and 1.0) were synthesized by sol–gel autocombustion method. X-ray diffraction (XRD) technique was used to confirm the phase formation. The lattice parameter (a) decreases with increase of Ni content. The surface morphology and elemental analysis of the samples were studied by using scanning electron microscopy (SEM) and energy dispersive X-ray spectrometer (EDS). The electrical properties of the samples were measured by two-probe method. The hysteresis parameters viz. saturation magnetization (M_s), coercivity (H_C) and remanence (M_r) are reported as a function of nickel content. The substitution of nickel plays an important role in changing the structural, electrical and magnetic properties of La-ferrites.     

Typical superparamagnetism with improved electrical properties of nano modified bismuth ferrite multiferroic composites

Multiferroic composites with the chemical formula, (0.5) BiFeO₃ + (0.5) Ni_0.5Zn_0.5Fe₂O₄, in bulk and nano forms were synthesized by preparing bismuth ferrite (BiFeO₃ or BFO) in bulk (B) and nano (N) forms and nickel zinc ferrite (Ni_0.5Zn_0.5Fe₂O₄or NZFO) in nano form. Single phase BFO was synthesized using conventional solid-state reaction as well as sol-gel autocombustion methods and NZFO powders were prepared by using sol-gel autocombustion method, respectively. X-ray diffraction (XRD) studies reveal the existence of rhombohedrally distorted perovskite structure for BFO and cubic spinel phase for NZFO in single phase as well as composite samples. Microstructural studies and energy dispersive spectroscopy (EDS) data reveal the formation of grains, intergranular porosities and chemical purity of the synthesized samples. Dielectric and AC conductivity measurements confirm the existence of space charge polarization along with the small polaron model in these composites. Ferroelectric and magnetic studies show that there was a considerable enhancement in the ferroelectric and magnetic orders for the nano form of the BFO (N) + NZFO composite. The observed remnant polarization values 2.80388 & 7.75901 μC/cm², saturation magnetization values 37.96072 & 40.47491emu/gm for bulk BFO (B) + NZFO and nano BFO (N) + NZFO composites, respectively. Interestingly, both the samples exhibit superparamagnetic behaviour at room temperature with coercivities close to zero. This typical behaviour is attributed to the corresponding anisotropic contributions originated from the individual constituents. The observed variations in BFO (N) + NZFO sample attributed to the corresponding structural modifications brought about by the variations due to its size effect in the present work.     

新型镍离子亲和色谱介质的制备及其性能考察

以氯甲基化聚苯乙烯交联微球(氯球)为载体基质、N,N-二甲基甲酰胺(DMF)为溶剂、N,N-二异丙基乙胺(DIEA)催化,将合成的Lys(Boc)-OEt、氯乙酸乙酯连接到微球上。经水解使羧基裸露,与Ni²⁺螯合,制得新型镍离子亲和色谱介质。将其应用于His-Lys-Tyr三肽及Phe-His-Thr三肽纯化研究。以不含组氨酸的六肽作为杂质模型,用所制备的镍离子亲和介质进行分离。结果表明,所制备的镍离子亲和介质对两个含组氨酸的三肽具有很好的亲和作用,并实现了与不含组氨酸六肽的分离。     

Preparation, electrochemical and spectral properties of N-methyl-pyridylethynyl nickel porphyrins

A series of nickel N-methyl-pyridylethynylporphines were synthesized and their electrochemical and absorption properties were studied. UV-visible spectra of these complexes show that the absorption red-shifts of the nickel porphyrins are as significant as the zinc analogues. Although the reduction potential shifts caused by the electron-withdrawing substituents are not as large as the zinc complexes, the first reduction potentials of the nickel porphyrins are more positive than those of the zinc counterparts. In addition, the redox behaviors of these nickel porphyrins are similar to those of the zinc analogues.     

Mechanical and electrical properties of Ni0.65Zn0.35CuxFe2−xO4 ferrite

A series of samples in the system Ni_0.65Zn_0.35Cu_xFe_2?xO₄ (x=0.0, 0.1, 0.2, 0.3, 0.4 and 0.5) were prepared by the usual ceramic technique. X-ray analysis showed that they were cubic spinel (single phase). Young's modulus, the dielectric loss and the change in capacitance under mechanical stress were measured for the samples. Young's modulus decreased with increasing Cu content. This is due to the fact that Cu²⁺ ions entered the lattice substitutionally for Fe³⁺ ions at the octahedral sites, creating lattice vacancies gave rise to lattice strain. The minimum value of the dielectric loss corresponding tox=0.3 may be due to the formation of lattice vacancies retarding the jump frequency to be far from the frequency of the applied a.c. field. The increase in capacitance of the samples with mechanical stress may be explained via the mechanism of dielectric polarization.