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[en] We estimate the thickness and ordering temperature of an antiferromagnetic and passivation surface oxide through exchange bias coupling. The surface NiO, which is generated through the exposure of a Ni/Cu(001) surface to oxygen, is taken as a model system on which to perform the estimation. Since no exchange bias is found in the surface NiO/Ni/Cu(001), we have built a sandwich structure of NiO/n ML Ni/10 ML Co/Cu(001) to measure the n dependence of exchange bias. With n ⩽ 2, a large exchange bias field is found above 300 K, which could be due to the direct contact between the oxides and the Co layer. With 3 ⩽ n ⩽ 6, a smaller exchange bias field is found with a blocking temperature of 190 K. This implies that the thickness of NiO is, at most, 3 ML. Discovering the thickness and ordering temperature of the surface NiO provides us to explore the potential applications by using surface NiO
[en] We investigated the surface oxidation behavior of cube-textured polycrystalline nickel at various oxidation conditions. Cube-textured NiO film was formed on a cube-textured polycrystalline nickel regardless of oxidation conditions but different growth behavior of NiO crystals was observed depending on the oxidation conditions. The introduction of water vapor into O2 did not affect the texture evolution, but rough and porous microstructure was developed. Microstructure of NiO film tends to be denser as the oxygen partial pressure increases. It is interesting that peak of theta - two theta diffraction pattern started to get stronger in air atmosphere and plane became the major texture in the substrate oxidized in high purity argon gas. Small amount of high index crystallographic plane NiO peak crystal was observed when N2Owas used as an oxidant while only plane crystal was formed in dry O2 atmosphere. Flat and smooth surface was changed into rough faceted one when ramping rate to oxidation temperature was faster. The grain size of NiO was decreased when the oxygen partial pressure was low. It was also observed that the modification of nickel surface suppressed the development of texture.
[en] Complete text of publication follows. The aim of this study was to prepare nickel oxide nanoparticles obtained from aqueous solutions using radiation energy. While works dealing with radiation preparation of nickel nanoparticles are quite numerous, reports dealing with radiation preparation of nickel oxide are rather scarce. Properties of NiO and other catalysts are affected by the method of preparation. It varies the purity, the size of crystallites, the stoichiometry, the specific surface area, the surplus oxygen, and the amount of active catalytic centres. Particle size uniformity and high chemical purity of prepared materials are advantages of radiation method. Five basic aqueous solutions containing nickel formate and other compounds, including hydrogen peroxide, polyvinyl alcohol (PVA), and isopropyl alcohol (IPA), were used for preparation of nickel oxide. Prepared solutions were irradiated by accelerated electrons with doses in the range 0 200 kGy. During irradiation, the solutions changed their colour due to the formation of solid phase. In few cases, the formation of true colloid was observed. With increasing dose up to 80 kGy, the yield of the solid phase increases. Changes caused by irradiation were determined by UV/VIS spectrophotometry in the range of 190-900 nm. The solid phase from the solutions irradiated with the optimum dose of 80 kGy was separated via ultrafiltration and carefully dried. The composition of the solid phase was determined via X-ray powder diffraction. From diffractograms the size of crystallites was determined. The specific surface area was measured using isothermal adsorption of nitrogen from gas mixture hydrogen - nitrogen. Catalytic activity was studied by catalytic degradation of aqueous solution of hydrogen peroxide. Rate constants were measured at four temperatures. The solid phase was annealed under vacuum at 200 deg C for 2 hours. The characteristics of annealed and unannealed materials were compared using all previously mentioned methods. The solid phase formed was found to be pure non-stoichiometric nickel oxide in all studied solutions; the size of the particles was calculated to be in order of tenth of nm. The catalytic activity of samples was determined to be significantly higher compared to commercial non-stoichiometric NiO (LACHEMA). The obtained results indicate that radiation technique is a viable and very promising method for preparation of highly pure NiO catalysts with uniform small-sized particles.
[en] Quaternary nickel orthophosphates, ANi4(PO4)3 (A=Alkali metals) have been extensively investigated because they show interesting properties such as ionic conductivities, optical, and magnetic behaviors. They are built up from NiO6 octahedra and PO4 tetrahedra. These basic building blocks are connected via common oxygen atoms to form the three-dimensional frameworks and the alkali metal ions reside in the empty space. For NaNi4(PO4)3, two different structures have been reported and this can be caused by the different reaction conditions. While NaNi4(PO4)3 prepared as single crystals with the use of NaCl flux at 1373 K crystallizes in the space group Amam and show a partial disorder of one of the PO4 tetrahedra, NaNi4(PO4)3 and KNi4(PO4)3 synthesized with alkali metal nitrate at 1073 K as powders adopt an ordered structure with the space group Pnnm. As far as we know, no structural studies of KNi4(PO4)3 from single crystal diffraction data have been reported yet and RbNi4(PO4)3 is a new compound. In this paper we report on the synthesis and structural investigations using single crystals of two nickel orthophosphates, KNi4(PO4)3 and RbNi4(PO4)3
[en] Highlights: • 3D ordered macroporous NiO/Al nanothermite synthesised by integrating colloidal crystal template and magnetron sputtering. • The morphology and heat release of the designed nanomaterials can be controlled by different aluminizing times. • Significantly enhanced energy output, with 71.5% of the theoretical value, increased by 260-1530 J·g−1 than other systems. • Obtained NiO/Al system exhibits lowered ignition temperature (about 460 °C), reduced impurities and less gas production. • This NiO/Al nanothermite film has the great potential applications in the field of microinitiators. The performances of nanothermites largely rely on a meticulous design of nanoarchitectures and the close assembly of components. Three-dimensionally ordered macroporous (3DOM) NiO/Al nanothermite film has been successfully fabricated by integrating colloidal crystal template (CCT) method and controllable magnetron sputtering. The as-prepared NiO/Al film shows uniform structure and homogeneous dispersity, with greatly improved interfacial contact between fuel and oxidizer at the nanoscale. The total heat output of 3DOM NiO/Al nanothermite has reached 2462.27 J·g−1 at optimal the deposition time of 20 min, which is significantly more than the values of other NiO/Al structural systems that have been reported before. Intrinsic reduced ignition temperature (onset temperature) and less gas production render the wide applications of 3DOM NiO/Al nanothermite. Moreover, this design strategy can also be readily generalized to realize diverse 3DOM structured nanothermites.
[en] Magnetic profiles of FM/AF/FM trilayers (FM=ferromagnet, AF=antiferromagnet), as a function of AF thickness t have been investigated by bulk magnetization and polarized neutron reflectivity measurements. DC magnetization results show a t-dependence of the magnetization reversal. From the analysis of polarized neutron reflectivity in conjunction with the DC magnetization we conclude that the thickness dependence of magnetization reversal is a direct consequence of domain wall formation across NiO
[en] Bi-stable switching effect has been studied in nickel oxide films with three different thicknesses. The best sample of our experiments was 150-nm NiO film. Its resistance ratio between high and low states was 3.6 in endurance measurement. The maximum resistance ratio in I-V curve could reach two orders of magnitude, and it could endure over 200 times of reverse processes with the ratio remaining about 1.46. This indicates that the nickel oxide has potential to be a promising material on resistance random access memory
[en] Discrepancies between short-circuit diffusion data derived from nickel oxide bicrystals and specimens produced by the oxidation of nickel has led to a requirement for thin film nickel oxide specimens of controlled microstructure and impurity level that can be produced independently of the oxidation process. RF magnetron sputtering of nickel oxide has been used to produce thin films intended for this application. The as-deposited films contain excess oxygen compared to stoichiometric nickel oxide and exhibit strong preferred orientation. Annealing in argon leads to oxygen deficient films. The reduction in porosity which accompanies the annealing leads to the formation of through-thickness cracks in the films. Subsequent oxygen tracer studies demonstrate that the cracks give rise to excessive oxygen transport through the films compared to that expected for thermally oxidised scales. The microstructural anomalies produced by the annealing process mean that the required microstructures were not achieved and these films are not useful analogues of thermal nickel oxide scales. (author)
[en] The purpose of present work is investigation of catalytic ability ofaluminium hydride in the reduction of nickel oxide and formation magneticnickel powders. Investigations was carried out on plasma-chemical equipment