Study of the transport properties of composite solid electrolytes LiClO4-MgAl2O4

Magnesium-aluminum spinel MgAl2O4 was synthesized by mechanical treatment of a mixture of hydroxides followed by treatment of the solution at 80 ° C and sintering at 850° C. The obtained nanocrystalline sample with a specific surface area of 100 m2/g were used for the preparation of composite solid electrolytes (1-x) LiClO4-xMgAl2O4. It was shown that conductivity increases with the spinel concentration and goes through a maximum of 1.35·10-2 S/cm at 150 °C for composite 0.3LiClO4-0.7MgAl2O4.

Particularities of changes in internal structure of nanocrystalline Ni under mechanical loading

Molecular dynamics study of the plasticity nucleation mechanisms in a Ni nanocrystalline sample under shear loading in the constrained conditions was carried out. The studied Ni sample consisted of nine grains of the same size with large misorientation angles relative to each other. In one of the directions, grippers were simulated, to which compressive forces and shear with a constant velocity were applied. In two other directions, periodic boundary conditions were used. It is shown that plasticity nucleation occurs in the region of the triple junction. At the same time, in the region of the triple junction, in the zone of which the stacking fault will be formed, tensile stresses are realized along one of the adjacent grain boundaries, and compressive stresses occur along the other. An increase in stresses in the triple junction zone leads to the formation of a stacking fault, which moves to the volume of one of the grains. Another mechanism of plasticity in nanocrystalline nickel is the migration of grain boundaries, which leads to a significant change in grain sizes.

Фаза Имри-Ма в нанокристаллическом ферромагнетике

A possibility of appearing a disordered Imry–Ma state induced by fluctuations of the anisotropy easy axis direction in a nanocrystalline sample in the case of a weak exchange interaction between crystallites has been studied. A phase diagram of the system has been built in variables “the characteristic crystallite size–the exchange integral of the intercrystallite interaction.” The characteristic value of statistic fluctuations of the crystallographic anisotropy has been estimated, and the dependences of the coercive field on the crystallite size have been found for systems of various space dimensions.

Magnetic field-dependent spin structures of nanocrystalline holmium

The results are reported of magnetic field-dependent neutron diffraction experiments on polycrystalline inert-gas condensed holmium with a nanometre crystallite size (D = 33 nm). At T = 50 K, no evidence is found for the existence of helifan(3/2) or helifan(2) structures for the nanocrystalline sample, in contrast with results reported in the literature for the single crystal. Instead, when the applied field H is increased, the helix pattern transforms progressively, most likely into a fan structure. It is the component of H which acts on the basal-plane spins of a given nanocrystallite that drives the disappearance of the helix; for nanocrystalline Ho, this field is about 1.3 T, and it is related to a characteristic kink in the virgin magnetization curve. For a coarse-grained Ho sample, concomitant with the destruction of the helix phase, the emergence of an unusual angular anisotropy (streak pattern) and the appearance of novel spin structures are observed.

Magnetic and nuclear structure of goethite (α-FeOOH): a neutron diffraction study

The magnetic structure of two natural samples of goethite (α-FeOOH) with varying crystallinity was analyzed at 15 and 300 K by neutron diffraction. The well crystallized sample has thePb′nmcolor space group and remained antiferromagnetic up to 300 K, with spins aligned parallel to thecaxis. The purely magnetic 100 peak, identifying this color space group, was clearly resolved. The nanocrystalline sample shows a phase transition to the paramagnetic state at a temperature below 300 K. This lowering of the Néel temperature may be explained by the interaction of magnetic clusters within particles. The nuclear structure, refined with the Rietveld and pair distribution function methods, is consistent with reports in the literature.

Preparation of Eu3+-Doped Rutile TiO2 Nanocrystals at Room Temperature by a Sonochemical Method

Lanthanide-doped semiconductors find usage in a wide variety of applications. In this work, Eu3+-doped rutile TiO2 nanocrystals have been successfully prepared at room temperature by a sonochemical method. The nanocrystalline sample has been characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM) techniques. A possible mechanism is proposed to explain the formation of Eu3+-doped TiO2 nanomateirals. Additionally, the characteristic emissions of Eu3+ can be found upon excitation in the region of TiO2 absorption, indicating that an energy transfer from TiO2 to Eu3+ occurs for the doped sample.

Torsion-Impedance in Soft Magnetic Amorphous and Nanocrystalline Wires

The measurements of magneto-impedance,, have been performed, at the frequency f = 1 MHz, on amorphous and nanocrystalline wires under the application of torsion stress ( = 0-125 rad/m). At , exhibit single-peak due to the axial easy direction of the wires. The torsion-impedance,, is defined as the impedance change with at the condition of the axial field H = 0. We found that at the low torsion , shows a maximum at = 0.87 and 5.23 rad/m for the amorphous and the nanocrystalline samples, respectively; with increasing ,of the amorphous wire decreases monotonously and tends to the saturation, but of the nanocrystalline sample shows two more peaks at = 70.65 and 104.67rad/m. These results have been discussed considering the modification of domain structure by the applied torsion.

Thermal Annealing Dependence of High-Frequency Magnetoimpedance in Amorphous and Nanocrystalline FeSiBCuNb Ribbons

The magnetoimpedance (MI) effect in Fe73.5Si13.5B9Nb3Cu1 melt-spun amorphous ribbons has been studied in the frequency range (1–500 MHz). Isothermal heating treatments in a furnace have been employed to nanocrystallize the ribbons (1 h at 565 °C in a vacuum of 10–3 mbar), while other samples were annealed at lower temperatures (400 and 475 °C during 1 h), in order to evaluate the influence of the annealing temperature on the MI effect. The high-frequency impedance was measured using a technique based on the reflection coefficient measurements of a specific transmission line by using a network analyzer. Frequency dependence of the MI ratio, ΔZ/Z, and both resistive, ΔR/R, and reactive, ΔX/X, components of magnetoimpedance were measured in the amorphous and annealed states, at different temperatures. A maximum value of the MI ratio of about 50% at a driving frequency of 18 MHz is obtained in the nanocrystalline (annealed at 565 °C) ribbon. Maxima for R/R of about 81% at 85 MHz and ΔX/X around 140% at 5 MHz were also achieved. It is revealed that the microstructural evolution in the nanocrystalline sample leads to a magnetic softening, an optimum domain structure and a permeability which is sensitive to frequency and applied magnetic field, generating a large MI response.

Behaviour of impurity elements during the weathering of ilmenite

X-ray spectromicroscopy has been applied to the characterization of weathered ilmenite sand samples from Australian localities. X-ray absorption near edge spectroscopy (Xanes) studies were performed at the K-edges of the major elements Fe and Ti and minor impurity elements Mn and Cr. An extended suite of reference samples with crystallite sizes ranging from 1 nm to μm size were measured to establish if the absorption edge characteristics were influenced by crystal size effects. No changes were detected for oxides of Cr3+, Fe3+ or Ti4+, but the mixed Fe2+/Fe3+ oxide, Fe3O4, showed an edge shift to higher energies (by 1.5 eV) in a nanocrystalline sample. The Xanes study of a composite ilmenite grain with an unweathered primary ilmenite core and a highly weathered rim showed that Fe was present as Fe2+ in the core and Fe3+ in the rim whereas Mn was present as Mn2+ in both core and rim. Chromium, which is incorporated into the grains during weathering, is present predominantly as Cr3+, although minor (~15%) Cr6+ also occurs in highly weathered grains. The absorption K-edges of Fe3+ and Mn2+ are shifted markedly (by 2–3 eV) to higher energies in titanate phases relative to the binary oxides Fe2O3 and MnO.