I. V. Golosovsky

Structure of magnetic nanoclusters in ferriferous alkali borosilicate glasses

The crystal structure of two-phase and porous alkali borosilicate glasses with embedded magnetic atoms has been investigated using X-ray powder diffraction. It has been shown that, during the preparation of two-phase (nonporous) glasses, the α-Fe2O3 phase undergoes a transition to magnetite (Fe3O4) with the formation (at particular concentrations of α-Fe2O3 in the initial mixture) and stabilization of the β-Fe2O3 phase. The characteristic sizes of nanoparticles of iron oxides (Fe3O4 and β-Fe2O3) in these glasses have been determined. For two types of porous glasses (namely, the macroporous glass Fe20-MAP and the microporous glass Fe20-MIP), the occupancies of the octahedral (Fe2+) and tetrahedral (Fe2+/Fe3+) iron positions in magnetite have been found.

Diffraction studies of the crystalline and magnetic structures of γ-Fe2O3 iron oxide nanostructured in porous glass

The crystalline and magnetic structures of γ-Fe2O3 maghemite synthesized in porous glass in the form of nanoparticles with a mean diameter of 106(2) Å have been determined by the neutrons and synchrotron radiation diffraction methods. Nanostructured maghemite with the spinel structure has vacancies in the octahedral and tetrahedral positions. The magnetic structure corresponds to the usual ferrimagnetic type. The measured magnetic moments are much lower than the moments in a usual sample. Moreover, the moments are strongly different in the octahedral and tetrahedral positions; this difference is explained by the difference in the exchange interaction for moments in different positins.

Structure of KD 2 PO 4 Embedded in a Porous Glass

The temperature evolution of the crystal structure of KD 2 PO 4 (DKDP) embedded in a porous glass with 7 nm pore diameter has been studied by neutron diffraction in temperature interval 90 K-308 K. It is shown that confined DKDP forms interconnected clusters with characteristic size of 18(0.5) nm. The structure of this nanocomposite material is found to be monoclinic and corresponds to the space group P 2 1 . The lattice parameters and characteristic cluster size are temperature independent and do not reveal any peculiarities in the vicinity of expected ferroelectric phase transition of 223 K.

Unit-cell parameters of nanoparticles embedded in porous glasses: Neutron-diffraction studies

The size effect on the unit-cell parameters of low-melting metal nanoparticles, e.g., bismuth, gallium, selenium, tin, and lead, embedded in porous glasses with a pore size of 7 nm is studied using neutron diffraction. The applicability of the continuum model for description of the lattice parameters of nanoscale systems taking into account the interaction between nanoparticles and the host matrix s discussed.

Electrophysical properties of carbon nanocomposites based on nanodiamonds irradiated with fast neutrons

The electrophysical properties of nanoporous carbon composites consisting of a nanometer-sized pyrolytic carbon matrix and nanodiamonds have been analyzed. It has been shown that the power-law dependence of the electrical resistivity on the thickness of the pyrolytic carbon layer D on a log-log scale has an inflection for D = 1 Å. It has been found that the temperature dependence of the electrical resistivity of the nanocomposite is described by an exponential function with an exponent of 1/4 for both unirradiated samples and samples irradiated with fast neutrons. This is characteristic of variable-range hopping conductivity in the case of strong localization in systems with semiconductor conductivity in the presence of a local disorder. With an increase in the neutron fluence, the electrical resistivity of the studied material changes very significantly (by several hundred percent) and nonmonotonically. This result is associated with the transformation of the structure of the graphite-like matrix and with possible graphite-diamond phase transitions.

Low-temperature phase transition in nanostructured MnO embedded within the channels of MCM-41-type matrices

High-resolution x-ray-diffraction experiments of antiferromagnetic MnO nanostructured within the channels of mesoporous MCM-41 matrices reveal an unusual transition from a distorted, trigonal phase to a cubic phase at about 40 K, well below the magnetic transition temperature of 120 K. The disappearance of the structural distortion is accompanied by an increase of the unit-cell parameter, amplitude of atomic motion, and the appearance of inner stresses. Such behavior drastically differs from the behavior known for the bulk compound.

High-resolution x-ray diffraction study of MnO nanostructured within a MCM-48 silica matrix with a gyroidal system of channels

Antiferromagnetic MnO was synthesized within a mesoporous matrix MCM-48 with a gyroidal system of channels. Synchrotron radiation studies reveal that the embedded nanoparticles have a ribbonlike shape and a length of about 53(3) A . The peculiar diffraction line shape shows the loss of long-range atomic order. In spite of positional disorder, a transition from a cubic structure to a rhombohedral one, similar to the transition known for the bulk, is observed.