A. V. Fokin

Ferroelectrics properties of nanosize KDP particles

The low frequency dielectric permittivity measurements were performed on the KDP nanosize particles system. The highly dispersed objects were obtained by introducing of ferroelectric material into the pores of different dielectric matrixes. The significant shift of transition temperature from the bulk value as well as the transition broadening for the KDP particles samples was observed.

Calorimetric and dielectric studies of ferroelectric sodium nitrite confined in a nanoscale porous glass matrix

Heat-capacity measurements of the sodium nitrite confined in a nanoscale porous glass matrix show that the intermediate incommensurate phase, present in the bulk, has disappeared and that the first-order ferroelectric transition becomes suppressed and gradual. The ferroelectric transition temperature is shifted considerably to lower temperatures. Two noncritical dielectric modes were observed; however, the observed giant growth of the dielectric constant on heating through the transition temperature TC is shown to be mainly due to the electrode polarization effect.

Ferroelectric phase transitions in materials embedded in porous media

Abstract Large quantities of highly dispersed ferroelectric objects were obtained by impregnation of two porous dielectric matrixes (porous glass and artificial opal) with molten ferroelectric materials (NaNO2, KH2PO4 (KDP)). The diameters of ferroelectric nanoparticles may be varied from about 100 nm to 3–4 nm. The neutron scattering measurements for NaNO2 particles and low frequency dielectric permittivity measurements for NaNO2, KDP and Rochelle salt particles were performed on such nanosize particles systems. The significant shift of transition temperature from the bulk value for KDP particles as the transition broadening for NaNO2 and KDP particles was observed.

Capacity and thermal conductivity of a nanocomposite chrysolite asbestos-KDP (KH2PO4)

A nanocomposite chrysotile-KDP (KH2PO4) was prepared. KDP was introduced into empty nanochannels of chrysotile asbestos with diameters of ∼5 nm. Thermal conductivity κ and heat capacity at a constant pressure Cp of the samples of chrysotile asbestos and nanocomposite chrysotile asbestos-KDP were measured in a temperature range of 80–300 K. Based on the analysis of the behavior of temperature dependences κ(T) and Cp(T) of the composite, temperatures of the ferroelectric transition TF for KDP in nanochannels of chrysotile asbestos were determined. It turned out to be equal to ∼250 K at TF ∼ 122 K for massive KDP samples.

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.

Electrical conductivity and superconductivity of ordered indium-opal nanocomposites

The electrical conductivity is measured experimentally and the parameters of the superconducting transition are determined in a regular spatial network of multiply connected submicron-sized indium grains embedded in voids of an ordered opal dielectric matrix. The In-opal nanocomposite was prepared by pressure injection of the molten metal into voids of opal samples. Arrays of In grains of different sizes were produced by properly varying the characteristic geometric sizes of the opal voids, which offered the possibility of observing quantitative and qualitative changes in the temperature dependence of electrical resistance and studying the size effects on the critical temperature and critical magnetic field in the In-opal nanocomposites. It was found that, as the coherence length becomes comparable to the size of the superconducting grains, the parameters of the superconducting transition in the nanocomposite increase sharply.

Optoacoustic conversion in suspensions: The competition of mechanisms and statistical characteristics

Optoacoustic conversion in diluted suspensions under the effect of nanosecond laser pulses is considered. The mode of operation with moderate values of the laser fluence is studied theoretically and experimentally. In this mode, a competition of the thermooptical and cavitation mechanisms of sound conversion is observed, which leads to considerable fluctuations of the acoustic response from one laser pulse to another. Analytical expressions for the basic characteristics of the acoustic signal are obtained. A simulation of the statistical characteristics of the cavitation contribution to the signal is performed using the Monte Carlo method. The experiment is based on the use of second harmonic pulses of a YAG laser and test suspensions. The histograms of the amplitudes of acoustic signals can be used to discriminate between the mechanisms of optoacoustic conversion and also can serve as the basis for diagnosing a low content of an insoluble phase in a liquid.

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.

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.

Resistance and magnetic susceptibility of superconducting lead embedded in nanopores of glass

This paper reports on a study of the resistance and differential magnetic susceptibility χac of lead embedded in nanosized glass pores with a diameter of ∼7 mm, which was performed at temperatures of 6–300 K and magnetic fields of up to 6 T. The field dependence of the resistance R(H) and the temperature dependences of the real, χ″(T), and imaginary, χ″(T), parts of magnetic susceptibility reveal indications of superconducting phase transitions associated with the volume and surface superconductivity of Pb nanopar ticles. The measurements of the field dependence of resistance have been used to set up the Hc-Tc phase diagram and to carry out a comparison with the study of the heat capacity performed on the same samples.