Search

Nanostructured hollow Co3O4 spheres are synthesized by ultrasonic spray pyrolysis. Nanocrystals forming the sphere structure have different sizes and packing density, depending on the synthesis conditions. The samples are studied by X-ray diffraction, scanning electron microscopy, low-temperature nitrogen adsorption, vacuum pycnometry, and Raman and X-ray photoelectron spectroscopies. The field and temperature dependences of magnetization show that the magnetic properties and the Neel temperature of Co3O4 hollow spheres are determined by the size and packing density of nanocrystals.

To create different oxygen nonstoichiometry in oxide samples of NdSr2Mn2O7 + δ, we have used a two-step method of synthesis, which makes it possible to achieve different oxygen nonstoichiometry of the samples. Oxygen nonstoichiometry is formed by two methods: quenching at certain temperatures and annealing at certain values of oxygen partial pressure. The value of oxygen nonstoichiometry is determined by the mass of oxygen emitted from the sample during the decomposition of samples of NdSr2Mn2O7 + δ to simple oxides. We have determined oxygen nonstoichiometry in NdSr2Mn2O7 + δ when recording external parameters such as pressure and temperature. The study of samples of NdSr2Mn2O7 + δ using thermogravimetry and X-rays revealed phase separation—two phases with the same cation composition, having different oxygen content. By example of a sample of NdSr2Mn2O7 + δ tempered from 1000°C and having oxygen nonstoichiometry of +0.09, we have proposed a crystallographic criterion of manifestation of phase separation in Ruddlesden–Popper (R–P) phases—a sharp change in the manganese-oxygen bond lengths. Measurements of the electrical dc resistance in the samples of NdSr2Mn2O7 have been performed in the temperature range of 5–300 K and magnetic fields up to 7 T using the standard 4-probe method. A magnetoresistive effect up to 400% was found in the studied oxides, which is nonlinearly dependent on their oxygen nonstoichiometry.

Magnetic and structural transitions in NdBaMn2−xTixO6 (x = 0, 0.2) samples obtained by the topotactic procedure at 1373 K and lgPO2=−19 atm are studied by low-temperature X-ray diffraction and magnetometry in 1–5 T fields. Undoped double manganite undergoes a reversible ferromagnet—antiferromagnet magnetic phase transition at ТN = 278 K without changing symmetry. The 20 mol.% titanium substitution for manganese causes a decrease in symmetry from the tetragonal space group P4/mmm to the orthorhombic space group Pmmm and a shift of magnetic transitions to lower temperatures. Oxide NdBaMn2O6 demonstrates high values of the magnetocaloric effect in the temperature range 250–315 K.

The static magnetization of CsNa5M3(MoO4)6 single phase molybdates, where M = Co, Ni, and Mn, is measured at 4–300 K in magnetic fields of up to 20 kOe. It is shown that the materials are paramagnetic. Magnetization as a function of temperature is described using the Curie–Weiss law. The intrinsic magnetic moments of the phases are found to be 9.759 (Co), 6.958 (Ni), and 12.203 Bohr magnetons for manganese molybdates. It is concluded that the charge state of Co, Ni, and Mn cations in the compounds is +2.

An amorphous-nanocrystalline Gd2O3 powder with a specific surface area of 155 m2/g has been prepared using pulsed electron beam evaporation in vacuum. The nanopowder consists of 20- to 500-nm agglomerates formed by crystalline nanoparticles (3-12 nm in diameter) connected by amorphous-nanocrystalline strands. At room temperature, the Gd2O3 nanopowder exhibits a paramagnetic behavior. The phase transformations occurring in the powder have been investigated using differential scanning calorimetry and thermogravimetry (40-1400°C). The amorphous phase of the nanopowder is thermally stable up to a temperature of 1080°C. It has been found that the amorphous phase has an inhibitory effect on the temperature of the polymorphic transformation from the cubic phase into the monoclinic phase. It has been revealed that, compared with the microcrystalline powder, the Gd2O3 nanopowder is characterized by a complete quenching of photoluminescence. © 2013 Pleiades Publishing, Ltd.

This work was supported by the Russian Foundation for Basic Research, project no. 10-03-96043-r_Urals_a. Temperature dependencies of density (by the gamma-penetrating method), electrical resistivity (by the contact-less method in rotating magnetic field), and magnetic susceptibility (by the Faraday method) of Sn-Bi alloys with near-eutectic compositions are investigated. The alloy with eutectic composition, Sn -58% (mass) Bi, is shown to differ significantly in the electron structure from hypo- and hypereutectic ones. The melt overheating above the given temperature provides the hysteresis of the properties sensitive to electron structure.

This study was supported by the Russian Foundation for Basic Research (grant no. 07-02-01049). Results are given of an investigation of magnetic susceptibility, electrical resistance, and density of Al62Cu25.5 5Fe(12.5) alloy in the solid and liquid states. It is found that the behavior of the investigated properties at temperatures above the melting point is abnormal. The results are discussed assuming the existence of long-lived (metastable) microregions in the melts.