Potassium polytitanates intercalated with nickel ions and their thermal transformations

The intercalation of nickel ions into the layered structure of ultradispersed amorphous potassium polytitanate powder on treatment with an aqueous solution of nickel sulfate was studied. The limiting nickel content that can be attained by intercalation is 12.8 wt %. The nickel ion intercalation results in a decrease in the average particle size of potassium polytitanate and in the structural ordering. Heat treatment of the resulting intercalate promotes the formation of a nanocomposite consisting of the solid solution K_1.35(Ni _x Ti_{8 − x} )O₁₆ with the hollandite structure, Ti₂O₃, and, depending on the treatment schedule, either NiO nanocrystals or Ni metal.     

Ferromagnetism Induced by Substitution of the Iron(IV) Ion by an Unusual High‐Valence Nickel(IV) Ion in Antiferromagnetic SrFeO3

Novel cubic perovskites SrFe_1?xNi_xO₃ (0≤x≤0.5) with unusual high‐valence iron(IV) and nickel(IV) ions were obtained by high‐pressure and high‐temperature synthesis. Substantial magnetic moments of Ni^IV, which is intrinsically nonmagnetic with a nominal d⁶ electron configuration, were induced by the large magnetic moments of Fe^IV through orbital hybridization with oxygen. As a result, ferromagnetism with the transition temperature (T_c) above room temperature could be induced.     

Magnetic and Mössbauer effect study of YTi(Fe1−xNix)11

The magnetic properties and ⁵⁷Fe Mössbauer spectra of the compounds YTi(Fe_1−xNi_x)₁₁ were investigated. The compounds crystallize in a ThMn₁₂-type structure when x < 0.7. The substitution of nickel for iron results in an increase in Curie temperature with x < 0.5, and a peak is observed in the composition dependance of saturation magnetization at x = 0.07. The Mössbauer effect measurements were carried out at room temperature with x equal to 0.00, 0.04, 0.08 and 0.20. The best fits indicate that nickel atoms preferentially occupy the j and f sites. A maximum was found in the variation of hyperfine field as a function of nickel content, which is in good agreement with the results of magnetic measurements.     

Magnetische Eigenschaften der ternären Phase (Co x Ni1−x )11Se8

The composition range of the ternary body-centered tetragonal phase (Co _x Ni_1–x )₁₁Se₈ extends fromx=0.03 tox=0.37 at 580°C. The magnetic susceptibilities and their variation with temperature and composition were investigated within the temperature range from 100 to 300 K using a magnetic balance. The temperature dependence of the magnetic suceptibilities was found to be consistent with theCurie-Weiss law from which magnetic moments were derived. Assuming the magnetic moments as spin-only values each cobalt atom contributes two unpaired electrons. Change in composition did not affect the magnitude of the magnetic moments. Based on crystallographic and magnetic data a simple model for the mutual distribution of cobalt and nickel atoms could be constructed.

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Synthesis,Characterization, and Chemical Vapor Transport of Solid Solutions in the MgMoO4‐NiMoO4 System

Two solid solution series exist in the system MgMoO₄‐NiMoO₄. The α‐Ni_1–yMg_yMoO₄ solution series, isostructural to α‐NiMoO₄, is thermodynamically stable at ambient conditions for compositions between 0 % and about 75 % magnesium content. The solution series β‐Mg_1–xNi_xMoO₄, isostructural to MgMoO₄ and the high temperature β modification of NiMoO₄, is thermodynamically stable at ambient conditions for compositions with < 25 % nickel content. A complete solid solution series β‐Mg_1–xNi_xMoO₄ exists at higher temperatures (> 823 K). The transition temperature for the α → β transition decreases with increasing magnesium content. The coexistence of both polymorphs at room temperature in samples with a wide range of composition is a result of the kinetic inhibition of the phase transition β → α. The chemical vapor transport of β‐Mg_1–xNi_xMoO₄ solid solutions with chlorine was investigated. Crystals with a nickel content up to 25 % were synthesized in temperature gradients 1273 K → 1223 K or 1273 K → 1173 K. Deposited nickel richer crystals are destroyed during cooling down to room temperature due to the phase transition. The observed distinctive nickel enrichment during the transport process is in good agreement with predictions by thermodynamic modeling.     

单分散NixZn1-xFe2O4纳米颗粒的制备及其磁热效应

以乙酰丙酮金属盐为前驱体,三乙二醇为溶剂,采用多元醇法制备了镍锌不同配比的Ni_xZn_(1-x)Fe_2O_4(x=0,0.3,0.5,0.7和1.0)铁氧体,并通过X射线衍射仪(XRD),透射电子显微镜(TEM)和振动样品磁强计(VSM)等对样品的结构、形貌、磁性能和磁热性能进行了表征。结果表明:Ni_xZn_(1-x)Fe_2O_4铁氧体分散性较好,尺寸均一,形状近似球形,平均粒径为4~5 nm。Ni_xZn_(1-x)Fe_2O_4纳米颗粒在室温下表现出亚铁磁性,饱和磁化强度随着镍含量的增加先增大后减小,当x=0.5时达到最大值29.38 emu·g~(-1)。在382k Hz交变磁场作用下,Ni_(0.5)Zn_(0.5)Fe_2O_4铁氧体温度可升温至313 K,表现出较好的磁热性能。     

Geometrical structures,electronic states,and stability of NinAl clusters

Density‐functional with generalized gradient approximation (GGA) for the exchange‐correlation potential has been used to calculate the energetically global‐minimum geometries and electronic states of Ni_nAl (n = 2–8) neutral clusters. Our calculations predict the existence of a number of previously unknown isomers. All structures may be derived from a substitution of a Ni atom at marginal positions by an Al atom in the Ni_n+1 cluster. Aluminum atom remains on the surface of the geometrical configurations. Moreover, these species prefer to adopt three‐dimensional (3D) spacial forms at the smaller number of nickel atoms compared with the pure Ni_n+1 (n ≥ 3) configuration. Atomization energies per atom for Ni_nAl (n = 2–8) have the same trend as the binding energies per atom for Ni_n (n = 3–9). The stabilization energies reveal that Ni₅Al is the relatively most stable in this series. In comparison with the magnetic moment of pure metal nickel (0.6 μ_B), the average magnetic moment of Ni atom increases in Ni Al clusters except the Ni₃Al. Moreover, except the case of Ni₅Al, Ni average magnetic moment decreases when alloyed with Al atoms than that in pure Ni clusters, which originate the effective charge transferring from Al to Ni atoms. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2010     

Combined Experimental and Computational Studies of a Na2Ni1−xCuxFe(CN)6 Cathode with Tunable Potential for Aqueous Rechargeable Sodium‐Ion Batteries

Herein, potential‐tunable Na₂Ni_1?xCu_xFe(CN)₆ nanoparticles with three‐dimensional frameworks and large interstitial spaces were synthesized as alternative cathode materials for aqueous sodium‐ion batteries by controlling the molar ratio of Ni^II to Cu^II at ambient temperature. The influence of the value of x on the crystalline structure, lattice parameters, electrochemical properties, and charge transfer of the resultant compound was explored by using powder X‐ray diffractometry, density functional theory, cyclic voltammetry, galvanostatic charge–discharge techniques, and Bader charge analysis. Of the various formulations investigated, that with x=0.25 delivered the highest reversible capacity, superior rate capability, and outstanding cycling performance. These attributes are ascribed to its unique face‐centered cubic structure for facile sodium‐ion insertion/extraction and the strong interactions between Cu and N atoms, which promote structural stability.     

Solvent-Mediated Iodine Intercalation of a High-Tc Oxide Superconductor Bi2Sn1.8Ca1.2CU2Ox

The benzene-mediated iodine intercalation into the pseudo-layered superconductor Bi₂Sr_1.8Ca_1.2Cu₂O_x (2212) is an efficient way to prepare an intercalate with nominal composition IBi₂Sr_1.8Ca_1.2 Cu ₂O_x. Expansion by 22 percent along the crystallographic c-axis was observed but both a-and b-axes of the intercalates remained unchanged. The superconducting temperature (T_c) of 2212 phase decreased 10 K upon iodine intercalation. We report the First solvent-mediated intercalation reaction and preliminary characterizations of a presumably stage-1 phase IBi₂Sr_1.8Ca_1.2Cu₂O_x.     

Controlled Hydrothermal Synthesis and Structural Characterization of a Nickel Selenide Series

A series of nickel selenides (NiSe₂ microcrystals, Ni_1?xSe and Ni₃Se₂ microspheres) has been successfully synthesized through a convenient, low‐temperature hydrothermal method. A good nucleation and growth environment has been created by forming a uniform and transparent solution reaction system. The compositions (including the x value of Ni_1?xSe), phase structures, as well as the morphologies of nickel selenides, can be controlled by adjusting the Ni/Se ratio of the raw materials, the pH, the reaction temperatures and times, and so forth. The newly produced Se microspheres in the system have been used as both reactant and in situ template to the Ni_1?xSe microspheres. It is found that Ni_1?xSe microspheres act as the intermediate precursor during the formation of Ni₃Se₂ microspheres. Under certain conditions, hexagonal NiSe microspheres can be converted into rhombohedral NiSe nanowires in solution. The formation mechanisms of a series of nickel selenides has been investigated in detail by means of X‐ray diffraction (XRD) and scanning electron microscopy (SEM) analyses. This work has provided a general, simple, and effective method to control the composition, phase structure, and morphology of metal selenides in aqueous solution, which will be important for inorganic synthesis methodology and further applications of selenides.     

The distribution of nickel ions among octahedral and tetrahedral sites in NiAl2O4MgAl2O4 solid solutions

The cation distribution in NiAl₂O₄ and in the solid solutions Ni_xMg_1?xAl₂O₄ with x ranging from 0.01 to 0.55 has been studied by X-ray analysis, magnetic susceptibility and reflectance spectroscopy.The relative X-ray intensities of various reflections for each compound were measured and compared with intensities calculated for various models of cation distribution. Lattice parameters, magnetic moments of Ni²⁺, and the position of nickel absorption bands have also been measured. The results show that all specimens have a predominantly octahedral distribution for their nickel ions, and that there is a small change towards a random distribution when the quenching temperature is increased from 1273 to 1673°K.Both X-ray and magnetic results show that the fraction, α, of Ni²⁺ ions on tetrahedral sites varies with nickel content. For samples quenched from 1273°K, NiAl₂O₄ is 78% inverse, but between x = 1.0 and x = 0.25 the value of α decreases from 0.22 towards 0.1. Thus, the fraction of nickel on octahedral sites in the solid solutions is higher than in NiAl₂O₄. The effect is linked with an increase in Dq for the Ni²⁺ ion. Below x = 0.25, there is tentative evidence that α may increase. In nickel-dilute solutions the matrix as a whole is nearly normal, and it is suggested that Madelung energy may then be more effective in counteracting the octahedral stabilization of nickel. The same trend is observed in the specimens quenched from 1673°K.     

Rational Design and Controlled Synthesis of V-Doped Ni3S2/NixPy Heterostructured Nanosheets for the Hydrogen Evolution Reaction

Rational construction of high-efficiency and low-cost catalysts is one of the most promising ways to produce hydrogen but remains a huge challenge. Herein, interface engineering and heteroatom doping were used to synthesize V-doped sulfide/phosphide heterostructures on nickel foam (V-Ni₃S₂/Ni_xP_y/NF) by phosphating treatment at low temperature. The incorporation of V can adjust the electronic structure of Ni₃S₂, expose more active sites, and protect the 3D structure of Ni foam from damage. Meanwhile, the heterogeneous interface formed between Ni₃S₂ and Ni_xP_y can provide abundant active sites and accelerate electron transfer. As a result, the V-Ni₃S₂/Ni_xP_y/NF nanosheet catalyst exhibits outstanding activity in the hydrogen evolution reaction (HER) with an extremely low overpotential of 90 mV at a current density of 10 mA cm⁻² and stable durability in alkaline solution, which exceeds those most of the previously reported Ni-based materials. This work shows that rational design by interfacial engineering and metal-atom incorporation has a significant influence for efficient hydrogen evolution.     

Highly improved dielectric behaviour of ferronematic nanocomposite for display application

We report the investigation of influence of nickel zinc ferrite magnetic nanoparticles (NZFO (Ni_0.5Zn_0.5Fe₂O₄)) on phase transition, optical and dielectric properties in a nematic liquid crystal (NLC). The interaction of NZFO nanoparticles with NLC was confirmed by the formation of ferronematic droplets due to the transfer of magnetic orientational effect onto the underlying NLC matrix. The doping results in shift of nematic to isotropic transition to low-temperature region. An enhancement in the value of refractive index is observed in the nematic region after the addition of NZFO nanoparticles. The dielectric constant of NLC was remarkably enhanced by 10 times after doping, which is found to be maximum at 0.1 wt% concentration of NZFO nanoparticles. The decrease in the value of dissipation factor in low-frequency region shows that the magnetic nanoparticles are able to trap ionic impurities effectively. The obtained results suggest that the optimum amount of doping concentration is 0.1 wt% of NZFO nanoparticles in NLC due to high dielectric constant with low dissipation factor and high refractive index with high dispersive power at room temperature.     

Magnetische Eigenschaften der ternären Phase (Fe x Ni1-x )11Se8

The partial substitution of nickel by iron in the body centered tetragonal crystal structure of the ternary compound (Fe _x Ni_1–x )₁₁Se₈ is restricted to the range of 0.04<x<0.23 at 580°C. The magnetic properties of samples with different compositions were studied by susceptibility measurements in the temperature region from 100 to 300 K. The continuous addition of Fe atoms resulted in a decreasing temperature dependence of the magnetic susceptibilities. Only for compositions withx0.14 an approximatedCurie—Weiss behaviour was observed. The Fe-rich samples (x>0.14) showed a very high constant paramagnetism which could not be interpreted asPauli paramagnetism. The evaluation of magnetic moments was based on the assumption that only the Fe atoms contribute to the temperature dependence of the magnetic susceptibilities. The actual value of the magnetic moments is supposed to be affected by magnetic interactions between neighbouring Fe atoms. The extrapolation of the magnetic moments towardsx=0 is compatible with a magnetic moment of 3.87 _B corresponding to three unpaired d-electrons per Fe atom. According to the negativeWeiss constants derived fromCurie—Weiss law antiferromagnetic interactions at low temperatures can be expected.

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Synthesis of uniform-sized bimetallic iron–nickel phosphide nanorods

We synthesized uniform-sized nanorods of iron–nickel phosphides from the thermal decomposition of metal–phosphine complexes. Uniform-sized (Fe_xNi_1−x)₂P nanorods (0x1) of various compositions were synthesized by thermal decomposition of Ni–trioctylphosphine (TOP) complex and Fe–TOP complex. By measuring magnetic properties, we found that blocking temperature and coercive field depend on Ni content in the nanorods. Both parameters were more sensitive to doping compared with bulk samples.     

Dielectric behaviour in Ni0.65Zn0.35CuxFe2.xO4 ferrites

A series of samples of the type Ni_0.65Zn_0.35Cu_xFe_2–xO₄ (x=0, 0.1, 0.2, 0.3, 0.4 and 0.5) were prepared by means of a ceramic technique. The existence of a single phase was confirmed in X-ray studies. The dielectric constantK and dielectric lossD were measured at different temperatures at a frequency of 1 kHz. The pronounced increase in the dielectric constant at the transition temperature is due to the phase transformation from the ferrimagnetic to the paramagnetic state. The decrease in the dielectric loss with temperature is due to the reduction in the relaxation time of the hopping electrons and holes. The Tawfik constant was calculated in the ferrimagnetic state and was found to be correlated to the dielectric constant.

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Zusammenfassung Mittels einer Keramiktechnik wurde eine Reihe von Proben des Types Ni_0.65Zn_0.35Cu_xFe_2–xO₄ mitx=0, 0.1, 0.2, 0.3, 0.4 und 0.5 hergestellt. In Röntgendiffraktionsuntersuchungen wurde die Existenz von Single-Phasen bestätigt. Bei verschiedenen Temperaturen und einer Frequenz von 1 kHz wurde die DielektrizitätskonstanteK und der dielektrische VerlustD gemessen. Die ausgesprochene Erhöhung der Dielektrizitäts-konstante bei der Umwandlungstemperatur kann der Phasenumwandlung vom ferromagnetischen in den paramagnetischen Zustand zugeschrieben werden. Die Abnahme des elektrischen Verlustes mit steigender Temperatur kann durch kleinere Relaxationszeiten der springenden Elektronen und Löcher erklärt werden. Für den ferromagnetischen Zustand wurde auch die Tawfik-Konstante berechnet, die in Korrelation mit der Dielektrizitäts-konstante gefunden wurde.

     

Structural, magnetic and dielectric properties of Sc modified (1 − y)BiFeO3–yBaTiO3 ceramics

In this study, the bulk ceramics with general formula (1 − y)BiFe_1−xSc_xO₃–yBaTiO₃ (x = 0.1–0.3, y = 0.1–0.3 mol%) were prepared by the traditional solid-state method. Their structural, magnetic, dielectric properties were investigated. X-ray diffraction analysis indicated that all samples crystallized in pure perovskite structure. The structural phase transition from R3c to Pm-3m occurred when the amount of BaTiO₃ exceeded 20 mol%. The room temperature M–H curves were obtained and scandium doping could decrease the magnetic coercive field. Thus the soft magnetic property of prepared solid solutions could be improved. Frequency dependence of dielectric constant and loss were studied. The results indicated that addition of an appropriate amount of scandium could reduce the dielectric loss. The dielectric losses of 0.7BiFe_1−xSc_xO₃–0.3BaTiO₃ (x = 0, 0.1, 0.2, 0.3) at 1 kHz were 0.104, 0.094, 0.043 and 0.057 respectively.     

Single Phase Formation,Cation Distribution,and Magnetic Characterization of Coprecipitated Nickel-Zinc Ferrites

X-ray diffraction, scanning electron microscopy, and vibrating sample magnetometry were used to investigate the structural, morphological, and magnetic properties of Ni_1-xZn_xFe₂O₄ nanosubmicron powders (x = 0–0.8). The samples were prepared by a coprecipitation method at temperatures between 600 and 1100 degree Celsius for five hours. The lattice constant, average size of coherent scattering regions, and cation distribution were analyzed by Rietveld refinement of the X-ray diffraction measurements. Scanning electron micrographs showed that the particle size increased from the nano- to the submicron scale as the zinc content increased from x = 0 to x = 0.8. The magnetization as functions of temperature and applied magnetic field were measured on the single-phase samples obtained at an annealing temperature of 1100 degrees Celsius. The derived saturation magnetization and Curie temperature were compared to those of the bulk counterparts reported previously and discussed based on finite-size effects and possible nonmagnetic impurities. The influence of zinc substitution on the magnetic exchange interactions were studied based on molecular-field theory for compositions of 0 ≤x ≤ 0.4.     

Influence of ceramic process and Eu content on the composite multiferroic properties of the Ba6−2xLn2xFe1+xNb9−xO30 TTB system

The present work reports the optimisation of the composition and elaboration process of Ba_6−2xLn_2xFe_1+xNb_9−xO₃₀ (0.6 < x < 1.0), a composite multiferroic below 440 K. Both firing and sintering conditions have been investigated in order to lower the two spurious phases content and to improve the ceramic quality. The Eu content has also been varied, with subsequent adjustment of cationic content to maintain charge compensation and site occupancies. The evolution of phase content, dielectric and magnetic properties has been evaluated with respect to these parameters. It was found that optimal processing parameters allow a significant improvement of dielectric properties but leave magnetic properties unaffected. Eu content modification impacts both the dielectric and magnetic properties of the TTB samples and changes their dielectric behaviour from ferroelectric to relaxor.     

Nickel Oxidation State and Magnetic Properties of Hole-Doped and Reduced Nd2−xSrxNiOyCompounds

The NiK-edge XANES of reduced Nd_2−xSr_xNiO₄samples shows an increase of Ni³⁺content with Sr³⁺concentration. The appearance of mixed valence Ni²⁺/Ni³⁺produces a change in the magnetic properties of the system. The Nd³⁺sublattice orders antiferromagnetically atT_N∼13–20 K forx=0.4, 0.5, and 0.6, due to the interactions of Ni–Nd sublattices. Forx=0.8 this order begins to disappear because of the effect of the low spin state Ni³⁺created at the NiO₄planes. Additionally, the reduced family Nd_2−xSr_xNiO_y(y<4) shows the disappearance of Ni³⁺, the decrease of Ni²⁺with respect to the nonreduced form, and the appearance of Ni⁺. All the compounds of the reduced family show AF order at low temperature.