A. V. Prokof’ev

Effect of a photonic band gap in the optical range on solid-state SiO2 cluster lattices — opals

It is shown that synthetic opals — cubic face-centered lattices of SiO2 clusters — are systems which exhibit a number of properties of photonic crystals in the visible-light range. By filling the voids (pores) in such lattices with different materials it is possible to vary the optical contrast of the medium and to obtain crystals of both the lattice of spheres type and its three-dimensional replica. It is shown that under conditions of identical optical contrast and in the presence of an additional optical inhomogeneity of the spheres, the transparency of the lattice of spheres is lower than that of its replica based on homogeneous media. A refractive index modulation of 1.266 was achieved in the lattice of spheres.

Fabrication of regular three-dimensional lattices of submicron silicon clusters in an SiO2 opal matrix

Silicon is now the most important material in modern solid-state electronics. Regular systems of silicon nanoclusters containing up to 1014 cm−3 elements were obtained in a sublattice of opal (SiO2) voids. By using three-dimensional dielectric matrix-carriers similar to opal, it may be possible to obtain three-dimensional ensembles of semiconductor nanodevices. Various parameters of these “opal-silicon” nanocomposites were measured.

Heat transport over nonmagnetic lithium chains in LiCuVO4, a new one-dimensional superionic conductor

The thermal conductivity of three single-crystal samples of the quasi-one-dimensional spin system of LiCuVO4 with different concentrations of defects (primarily, vacancies on the lithium sublattice) was measured along the crystallographic a axis (along the nonmagnetic lithium chains) in the temperature interval 5–300 K. An increase in thermal conductivity from that of the crystal lattice was revealed for T>150–200 K. This increase can be accounted for only by assuming LiCuVO4 to be a superionic conductor. This assumption was confirmed by measuring its electrical conductivity in the temperature interval 300–500 K. Li+ ions move over vacancies on the lithium sublattice (conducting channels) and act as charge carriers in LiCuVO4. It is shown that LiCuVO4 is a fairly good superionic conductor with application potential.

Electrical conductivity and permittivity of the one-dimensional superionic conductor LiCuVO4

The electrical conductivity σa and permittivities ɛa, ɛb, and ɛc of a LiCuVO4 single crystal have been measured along the a, b, and c crystallographic axes, respectively, in the temperature range 300–390 K at a frequency of 103 Hz. The temperature dependences σ(T) and ɛ(T) were found to be typical for superionics.

Thermal conductivity of a new type of regular-structure nanocomposites: PbSe in opal pores

Samples of an opal-based nanocomposite with PbSe embedded chemically into opal voids have been produced. Their thermal conductivity (in the 16–100-K range), the Seebeck coefficient (16–100 K), and electrical resistivity (5–100 K) have been measured. The thermal conductivity data permit a conclusion that a new type of substance has been produced, namely, nanocomposites having a regular structure, with each nanocomponent being a microcrystal. A concept of quasi-chemical bonding forming in nanocomponent lattices is introduced.

Spinon thermal conductivity of-(CuO2)-spin chains in LiCuVO4

The thermal conductivity κtotb of the quasi-one-dimensional (S=1/2) Heisenberg antiferromagnet LiCuVO4 with uniform (-CuO6-) spin chains aligned parallel to the b axis in a crystal with an orthorhombically distorted inverse spinel structure is measured in the temperature range 10–300 K. The spinon component κmchain of the thermal conductivity is separated out.

Structural characterization of opal-based photonic crystals in the visible range

For structural characterization of periodic three-dimensional systems with submicron-scale lattice parameters (optical photonic crystals), is analogous to the use of visible light of x-rays. It is shown that specular reflectance and transmittance spectra of opal do indeed yield information on the lattice period and structural perfection of photonic crystals.

Specific features in the thermal conductivity of synthetic opals

Data on the thermal conductivity ϰph of the cluster lattice of synthetic opals are analyzed. All opals are divided into two groups according to the temperature dependence of their ϰph. These are opals-1, whose thermal conductivity behaves like ϰph(T) of quasi-crystalline materials, and opals-2, with a ϰph(T) dependence typical of classical amorphous solids. Possible reasons for this difference are considered. An attempt is made to explain the complex temperature hysteresis in ϰph(T) observed earlier in opals-2.

Electrical, galvanomagnetic, and thermoelectric properties of PbSe in the void sublattice of opal

A study of transport phenomena, namely, electrical resistivity, thermopower, Hall coefficient, and magnetoresistance of p PbSe synthesized in opal voids has been carried out in the 4–300 K range. The parameters of the semiconducting material have been determined at different void filling levels. An anomalous behavior of the hole mobility associated with surface scattering from insulating opal-matrix walls has been observed.

Investigation of polarization magnetooptic responses of a low-concentration ferrofluid

A highly sensitive laser polarization-optical technique was developed and applied to investigations of a ferrofluid, which was placed in a magnetic field. A colloid solution of magnetite in kerosene was used as a sample. It was shown that the magnetooptic response of this substance is reliably registered at a volume solid-phase content of down to ~10–5. It was revealed that within a very wide range of changes in the solution concentration, a quadratic dependence of the observed birefringence value on the low-intensity field (up to several tens of oersted) is retained.