Alexander Naberezhnov

The rhombohedral phase with incommensurate modulation in Na1/2Bi1/2TiO3

The phase transition from tetragonal to rhombohedral phase in sodium bismuth titanate (NBT) is studied by means of neutron scattering. It is found that the rhombohedral phase has incommensurate modulation along the four-fold axis of the precursor tetragonal phase. The appearance of the incommensurate modulation is discussed on the symmetry grounds in the framework of the phenomenological theory of phase transitions.

Morphology and Magnetic Properties of Ferriferous Two-Phase Sodium Borosilicate Glasses

This contribution is devoted to the study of morphology and magnetic properties of sodium borosilicate glasses with different concentrations (15, 20, and 25 wt.%) of α-Fe2O3 in an initial furnace charge. These glasses were prepared by a melt-quenching method. For all glasses a coexistence of drop-like and two-phase interpenetrative structures is observed. The most part of a drop structure is formed by self-assembling iron oxides particles. All types of glasses demonstrate the magnetic properties and can be used for preparation of porous magnetic matrices with nanometer through dendrite channel structure.

Electrical Conductivity of NaNO2 Confined within Porous Glass

The AC electrical conductivity (σ) of polycrystalline NaNO2 and SiO2-NaNO2 composite, prepared by embedding of sodium nitrite into porous glasses with 7, 46 and 320 nm average pore diameter, have been studied at frequencies of 0.1 Hz–1 MHz within temperature range of 300–500 К. It was found a considerable increase of σ in sodium nitrite inclusions under restricted geometry conditions. A study of frequency dependences of σ shows a strong contribution of hopping mechanism to total electrical conductivity. The trend to reduction of activation energy of σ with decreasing of matrix pore diameter was revealed.

Nanoporous glasses with magnetic properties as a base of high-frequency multifunctional device making

Two types (microporous - Fe20-MIP and macroporous Fe20-MAP) porous magnetic matrices were prepared on base of Fe20 (60% SiO2-15% B2O3-5% Na2O-20% Fe2O3) alkali borosilicate glass. The average pore diameters were 5 nm for Fe20-MIP and 5 and 50 nm (bimodal distribution) for Fe20-MAP. The morphology, magnetic properties and coefficients of volume and linear magnetostriction have been studied for Fe20-MIP glass.

SEM and AFM studies of two-phase magnetic alkali borosilicate glasses

The morphology and composition of four types of two-phase alkali borosilicate glasses with magnetic atoms prepared by inductive melting have been studied. The results of scanning electron microscopy point to uniform distribution of Na, Si, and O atoms in these samples while magnetic iron atoms form ball-shaped agglomerates. The magnetic properties of these agglomerates have been confirmed by magnetic force microscopy. Atomic force microscopy had shown that in these samples two different morphological structures, drop-like and dendrite net, are formed. The formation of dendrite-like structure is a necessary condition for production of porous magnetic glasses. The obtained results allow us to optimize the melting and heat treatment processes leading to production of porous alkali borosilicate glasses with magnetic properties. The first results for nanocomposite materials on the basis of magnetic glasses containing the embedded ferroelectrics KH2PO4 demonstrate the effect of applied magnetic field on the ferroelectric phase transition.

Ultrabroadband Dielectric Spectroscopy of Lead-Free Relaxor Ferroelectric Na1/2Bi1/2TiO3

The results of the detailed study of the dielectric properties of single crystal Na 1/2 Bi 1/2 TiO 3 (NBT) in wide frequency (0.1 Hz–10 MHz) and temperature (300–1000 K) ranges are reported. Analyses of dispersion curves of the complex dielectric response within existing phenomenological models are done. Relaxation processes are identified and their dynamics are traced. Activation energies of Arrhenius’ relaxation processes are obtained by fitting. Besides we have found a relaxation process described by Vogel-Fulcher law, indicating that in the system occurs freezing at 370 K.