A. A. Naberezhnov

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.

Effect of electric field on neutron scattering in lead magnoniobate

The temperature dependence of the intensity of the Bragg and the transverse component of quasi-elastic neutron scattering from the single-crystal model relaxor PbMg1/3Nb2/3O3 (PMN) has been studied for various applied electric fields. It is shown that application of a field E>Eth ≈1.6 kV/cm increases the elastic scattering intensity and reduces the intensity of the transverse diffuse-scattering component and that, below 230 K and for E>6 kV/cm, the elastic-scattering intensity saturates while the temperature-dependent part of the transverse diffuse-scattering component becomes practically suppressed. The measured temperature and field dependences of the intensity of type (h00) and (hh0) Bragg reflections provide supportive evidence both for the presence of considerable lead-ion displacements relative to the ideal perovskite sites and for the existence in strong electric fields of an induced transition to the ferroelectric phase below 250 K.

Structure and dielectric response of Na1 − xKxNO2 nanocomposite solid solutions

This paper reports on the results of the investigation into the thermal evolution of the structure and dielectric properties of Na1 − xKxNO2 solid solutions (x = 0, 0.05, 0.10) embedded in porous glass with an average pore diameter of 70 ± 10 Å in the range 300–447 K, i.e., in the ferro-and paraelectric phases. The structural properties of the bulk and nanostructured materials are compared. It is shown that the introduction of small amounts of potassium brings about a noticeable change in the intensity ratio of the elastic Bragg peaks, while leaving the space group characterizing the structure of these nanocomposites unaffected. An increase in the potassium fraction does not result in a substantial decrease in the phase transition point. Measurements of the dielectric response have revealed that an increase in the potassium content gives rise to a marked “hardening” of the lattice in the premelting state, which reduces dielectric losses.

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.

Dielectric properties of the P(VDF60/Tr40) copolymer in the porous glass matrix

The dielectric properties and electrical conductivity of the composite material, which was prepared by incorporating the P(VDF60/Tr40) copolymer into the porous glass matrix (the average pore diameter is approximately equal to 320 nm), and the bulk sample of the P(VDF60/Tr40) copolymer have been investigated in the temperature range 290–440 K. It is revealed that the incorporated material is characterized by an increase in the melting temperature and a considerable decrease in the temperature at which the ferroelectric phase formed in polymer inclusions becomes unstable. It is shown that charge transfer in the composite material occurs predominantly through channels filled with the polymer.

Critical neutron scattering in a uniaxial relaxor Sr0.6Ba0.4Nb2O6

This paper reports on the results of an investigation into the temperature evolution of the critical scattering of neutrons in the strontium barium niobate crystal SBN60 in a zero field and in applied external direct-current (dc) electric fields. It has been shown that the observed critical scattering consists of two components that are adequately described by a Lorentzian and a Lorentzian squared. These components differently depend on the temperature and the momentum transfer vector. The application of an external electric field significantly suppresses the second component.

Atomic dynamics of tin nanoparticles embedded into porous glass

The method of resonant nuclear inelastic absorption of synchrotron radiation has been used to study the phonon spectrum for tin nanoparticles (with a natural isotope mixture) embedded into a porous glassy (silica) matrix with an average pore diameter of 7 nm in comparison to the analogous spectrum of bulk tin enriched with 119Sn isotope. Differences between the spectra have been observed, which are related to both the dimensional effects and specific structural features of the porous glass-tin nanocomposite. Peculiarities in the dynamics of tin atoms embedded into nanopores of glass are interpreted in terms of a qualitative model of the nanocomposite structure.

Investigation of longitudinal vibrations of -O-H groups in chrysotile asbestos by neutron scattering and polarized infrared spectroscopy

The specific features of the vibrational spectra of chrysotile asbestos, which is a natural mineral that represents a system of closely packed tubular fibers with an outer diameter of ∼30 nm, an inside diameter of ∼5 nm, and a length up to a centimeter and more, have been investigated using neutron scattering and polarized infrared spectroscopy. This material can serve as a natural matrix for the preparation of nanostructures by filling channels with various materials.

Temperature dependences of the order parameter for sodium nitrite embedded into porous glasses and opals

The temperature dependences of the order parameter η(T) for sodium nitrite NaNO2 embedded in porous glasses with average pore diameters of 320 and 20 nm, as well as in artificial opals, have been investigated. It has been demonstrated that the dependence η(T) for sodium nitrite in the porous glass almost coincides with that for the bulk material, whereas this dependence for NaNO2 in opals differs substantially from that observed in the bulk material and from those previously determined for sodium nitrite in porous glasses with average pore diameters of 3 and 7 nm. It has been revealed that the dependence of the order parameter for sodium nitrite in opals exhibits a temperature hysteresis (approximately equal to 8 K). The temperature dependence η(T) has been described using a simple model, which takes into account the nanopore diameter distribution existing in artificial opals.

Surface and volume superconductivity of Pb embedded in nanopores

The heat capacity of lead embedded in glass nanopores (7 nm in diameter) and bulk lead was studied in the temperature range 2–40 K without a magnetic field and in magnetic fields of 1–8 T. The properties of lead nanoparticles and bulk lead were compared. The results obtained allowed us to separate the surface superconductivity from the volume superconductivity. The temperature dependence of the heat capacity of lead nanoparticles was shown to exhibit two superconducting transitions above and below the transition temperature for bulk lead (Tc = 7.2 K), which are associated with the surface and volume superconductivity. The upper critical fields Hc3 for the surface superconductivity and Hc2 for the volume superconductivity were determined. It turned out that these fields for Pb nanoparticles are two orders of magnitude higher than those for bulk lead. The “superconductor-normal metal” phase diagrams were constructed for lead nanoparticles. The study established an increase in the density of low-frequency excitations in Pb nanocrystals as compared to bulk Pb and a difference in the electronic heat capacity of Pb nanoparticles as compared to bulk Pb.