Vol 54, No 3 (2018)

The effect of ascorbic acid additions on the growth mechanism of thin PbSe films produced by hydrochemical deposition has been studied by atomic force microscopy (AFM). A fractal analysis of AFM images of the lead selenide films has shown that their formation follows the “cluster–particle” aggregation mechanism. The fractal dimension assessed by the box-counting method is 2.26 at an average grain size of ~150 nm. From the transmission spectra of the films grown at deposition times from 20 to 120 min, we have evaluated their optical band gap, which has been shown to decrease from 0.595 to 0.53 eV with increasing deposition time. These values are attributable to the manifestation of quantum size effects in the grown PbSe films.

Fe-containing nanoparticles have been grown for the first time on the surface of multiwalled carbon nanotubes by metalorganic chemical vapor deposition using iron acetylacetonate, Fe(acac)₃, as a precursor. The resultant hybrid nanomaterial has been characterized by X-ray diffraction, scanning electron microscopy, high-resolution transmission electron microscopy, and thermogravimetric analysis. The results demonstrate that the synthesized material consists of multiwalled carbon nanotubes whose surface is decorated with iron nanoparticles.

This paper presents a detailed study of phase formation processes in the AgNO₃–Sb₂O₃–MoO₃ system during heating in air. The compositions of the solid-state reaction products have been determined using thermogravimetry and qualitative X-ray diffraction. The results demonstrate that, at a final heat treatment temperature of 1023 K, synthesis yields a range of Ag_2–xSb_2–xMo_xO₆ compounds with the pyrochlore structure and 0.0 ≤ x ≤ 2.0. The structural parameters of the synthesized phases have been refined by the Rietveld method in space group Fd3̅m and their electrical conductivity has been measured.

This paper presents a systematic SEM–EDS study of polished sections of individual skeletal and dendritic ferrospheres in the–0.04 + 0.032 mm size fraction, isolated from fly ash from the combustion of brown coal from the Berezovskoe field. The ferrospheres are characterized by a wide range of variations in the macrocomponent composition of local areas. We have identified groups of globules whose overall composition as well as the composition of local areas on their polished sections can be represented by general equations for component concentrations: SiO₂ = f(FeO), SiO₂ = f(Al₂O₃), and CaO = f(SiO₂). Such equations make it possible to identify the nature of the mineral precursors involved in the formation of the globules. FeO-rich skeletal ferrospheres with low CaO concentration originate from the thermochemical transformation of pyrite and illite associates. Skeletal and dendritic ferrospheres with monotonically increasing CaO and SiO₂ concentrations are formed from pyrite and montmorillonite associates, with the participation of a melt containing quartz and decomposition products of Ca-humates of the initial coal. Skeletal and dendritic spinel ferrite crystallization is due to a magnesium aluminate spinel “seed,” resulting from the thermal transformation of illite and montmorillonite from the parent coal. The observed increase in glass phase concentration and the change from the skeletal type of crystallization to a dendritic in the ferrospheres containing ≤64 wt % FeO and ≥6.5 wt % CaO are due to the low concentration of the spinel-forming cations Fe²⁺ and Fe³⁺ in the melt and the increase in the percentage of [Fe³⁺O₂]⁻ and [Fe₂³⁺ O₅]⁴⁻ ferrite complexes with an increase in the degree of oxidation of the melt.

We have identified linear correlations between the molecular refractions R_mol (cm³/mol) of crystals and the ionic radii r_i (Å) of the cations in the RF₃ rare-earth trifluoride homologous series: R_mol = 8.33r_i + 0.102 for R = La–Nd and R_mol = 13.03r_i–4.42 for R = Sm–Lu. The fact that the RF₃ rare-earth trifluorides can be divided into two groups is related to the morphotropic transition from the LaF₃ (tysonite) structure to the β-YF₃ structure. The correlation found here for RF₃ crystals with the β-YF₃ structure because the electronic structure of Y (4d¹5s²) differs from that of Sm–Lu (4f^6–145d^0–16s²) in that it has no 4f electrons.

An all-vapor phase MCVD process has been proposed for the fabrication of fiber preforms with a Yb₂O₃–Al₂O₃–P₂O₅–SiO₂ multicomponent glass core. We have investigated the tubular preform collapse into a rod and demonstrated approaches capable of preventing P₂O₅ losses in the central part of the core during the collapse process. Preforms with a flat, perfect step-index profile have been fabricated.

Ceramic Pb(Fe_1–xSc_x)_2/3W_1/3O₃ samples with 0 ≤ x ≤ 1 have been prepared and characterized by X-ray diffraction, Mössbauer spectroscopy, and dielectric and pyroelectric measurements. The stoichiometry ranges of the perovskite solid solutions in this system have been identified, their structural parameters have been determined, and their dielectric permittivity, dielectric loss tangent, resistivity, and thermally stimulated depolarization current have been measured as functions of temperature. The composition dependences of the dielectric properties for the solid solutions have been obtained. The solid solutions have been shown to exhibit ferroelectric relaxor properties, with a well-defined maximum in their permittivity in the range 180–250 K.

This paper examines the effect of pulsed laser irradiation on the electrical properties of n-type semiconductor ferroelectric ceramics (based on a (Ba,Sr)TiO₃ solid solution) with a planar contact configuration. The elemental compositions and surface morphologies of the material before and after laser irradiation are compared using scanning electron microscopy data. In the framework of the well-known Heywang model for the positive temperature coefficient of resistance effect, we calculate the resistance of the material as a function of temperature for the paraelectric phase and determine parameters of grain boundaries that ensure good agreement between the experimental data and theoretical curves.