S. N. Sul’yanov

Mechanochemical Synthesis of Nonstoichiometric Fluorite Ca{sub 1-x} La{sub x} F{sub 2+x} Nanocrystals from CaF{sub 2} and LaF{sub 3} Single Crystals

The nonstoichiometric Ca1−xLaxF2+x phase (x ≥ 0.1) is obtained by mechanochemical synthesis from CaF2 and LaF3 single crystals. This phase is the first representative of fluorite fluorides obtained by mechanochemical synthesis in the MFm-RFn systems (m < n ≤ 4). The average grain size ranges within 10–30 nm. The temperature dependence of ionic conductivity of the mechanochemically synthesized phase pressurized at 600 MPa (at its high-temperature portion at temperatures exceeding 200–250°C) coincides with the conductivity of the single crystals of the same composition (Ca0.8La0.2F2.2). The activation energy of ionic conductivity (0.95 eV) corresponds to migration of interstitial fluoride ions in the crystal bulk. Mechanochemical synthesis of a multicomponent fluoride material with nanometer grains opens a new chapter in the chemistry of inorganic fluorides. A decrease of the sintering temperature of the powders with nanometer grains is very important for preparing dense fluoride ceramics of complicated compositions and other polycrystalline forms of fluoride materials.

Mechanochemical synthesis of nonstoichiometric nanocrystals La1 − yCayF3 − y with a tysonite structure and nanoceramic materials from CaF2 and LaF3 crystals

The nonstoichiometric phases La1 − yCayF3 − y (y = 0.15, 0.20) with a tysonite (LaF3) structure have been prepared for the first time by the mechanochemical synthesis from CaF2 and LaF3 crystals. The average size of coherent scattering regions is approximately equal to 10–30 nm. It has been shown that the compositions of the phases prepared by the mechanochemical synthesis are inconsistent with the phase diagram of the CaF2-LaF3 system. The “mechanohydrolysis” of the La1 − yCayF3 − y phase has been observed for the first time. Under these conditions, the La1 − yCayF3 − y phase partially transforms into lanthanum calcium oxyfluoride for a milling time of 180 min with intermediate sampling. The La1 − yCayF3 − y nanoceramic materials have been prepared from a powder of the mechanochemical synthesis product by pressing under a pressure of (2–6) × 108 Pa at room temperature. The electrical conductivity of the synthesized materials at a temperature of 200°C is equal to 4.9(6) × 10−4 S/cm, and the activation energy of electrical conduction is 0.46(2) eV. These data for the nanoceramic materials coincide with those obtained for migration of fluorine vacancies in single-crystal tysonite fluoride materials.

Properties of nanocomposites based on crosslinked elastomeric polyurethane and ultrasmall additives of single-wall carbon nanotubes

It is shown for the first time that the addition of ultrasmall amounts of single-wall carbon nanotubes leads to a significant increase in the main mechanical characteristics of the crosslinked poly(urethane urea) elastomer. The elastic modulus and the tensile strength pass through maxima as the nanotube concentration is increased from 0 to 0.018 wt %; at a nanotube concentration of 0.002 wt %, the maximum values of the modulus and strength are higher by factors of 2.5 and 1.5, respectively, than the corresponding values for the unfilled polymer. The thermomechanical, spectral, and structural characteristics of nanomodified elastomers are investigated, and possible causes of change in their mechanical parameters are discussed.

Equation of state and structural phase transitions in iron-based Ba3TaFe3Si2O14 langasite at high hydrostatic pressures

Synchrotron X-ray diffraction studies of the structural characteristics of Ba3TaFe3Si2O14 langasite are performed at high hydrostatic pressures (up to 60 GPa) created in a diamond anvil cell. At pressures up to 20 GPa, the Mössbauer absorption spectra for 57Fe nuclei and the Raman spectra are recorded. Two structural phase transitions at P ≈ 5.5 and 20 GPa are observed. The first transition corresponds to the displacements of light oxygen atoms and to an increase in the local symmetry of 3f oxygen tetrahedra surrounding iron ions. The second one is accompanied by a pronounced change in the lattice parameter c, and the unit cell volume undergoes a stepwise drop as large as 8.6%. An appreciable decrease in the parameter c at the structural transition should result in a significant increase in the exchange coupling constants between iron ions in neighboring ab planes underlying the giant increase in the Néel temperature in this crystal at pressures exceeding 20 GPa.

Nanostructured crystals of Sr 1− x R x F 2+ x fluorite phases and their ordering: 6. Microindentation analysis of crystals

Hardness, crack resistance, brittleness, and effective fracture energy have been studied for crystals of 24 fluorite phases Sr1 − xRxF2 + x (R are 14 rare earth elements (REEs); 0 < x ≤ 0.5) and SrF2 grown by the Bridgman method from a melt. These characteristics change nonlinearly with an increase in the REE content for Sr1 − xRxF2 + x (0 < x ≤ 0.5) with R = La, Nd, Sm, Gd, and Lu; it is maximum in the range x < 0.1 for all REEs. The changes in a number of REEs have been traced for an isoconcentration series of Sr0.90R0.10F2.10 crystals (R = La, Nd, Sm, Gd, Ho, Er-Lu, or Y) and crystals (similar in composition) with R = Tb and Dy. The hardness of Sr1 − xRxF2 + x crystals is higher by a factor of ∼2–3 than that of SrF2. The effect of decrease in microstresses in SrF2 crystals is confirmed by the isomorphic introduction of R3+ ions into this crystalline matrix.

Reactions on single-walled nanotubes: 2. Reactions on the nanosized surface of nanotubes in liquid hydrocyanic acid

Chemical reactions stimulated by γ-radiation in liquid hydrocyanic acid (HCN) in the presence of single-walled edcarbon nanotubes (SWCNTs) have been studied. The polymerization of HCN on the surface of nanotubes occurs several times more rapidly than in pure HCN, and the set of radiolysis products becomes poorer. It is likely that the approach of polymerizing reagents on the nanosized surface is limited by specific mutual orientations. Furthermore, the CN and H radicals add to the walls of the nanotubes and the nanotubes become soluble in water, ethanol, and acids.

Anion conductivity of a Ce0.95Gd0.05O0.075F2.85 solid electrolyte

An oxygen-containing CeF3-based solid electrolyte with the composition Ce0.95Gd0.05O0.075F2.85 has been prepared by Bridgman growth from a melt using a Gd2O3-containing starting mixture, and its ionic conductivity σ has been measured. The σ of the oxyfluoride at 400°C is 5 × 10−3 S/cm, which is }~ 200 times the σ of single crystals of the well-known superionic oxide conductor Zr0.88Y0.12O1.94. The present results demonstrate the feasibility of obtaining a large number of oxyfluoride solid electrolytes based on rare-earth trifluorides with the tysonite (LaF3) structure via reactions between fluorides and oxides (of the same rare-earth element or different rare earths) in a melt, followed by melt solidification. They can be proposed as gasimpermeable conducting membranes of low-temperature potentiometric oxygen sensors.

Structure and physicochemical properties of thin film photosemiconductor cells based on porphine derivatives

Photosemiconductor thin films based on two organic porphine derivatives have been investigated. These compounds have different pendent groups; the film morphology, along with the specific fabrication technique, is determined to a great extent by these groups. The films have been fabricated by vacuum sputtering and using the Langmuir−Schaefer method. According to the atomic force microscopy (AFM) data, the Langmuir−Schaefer films are more homogeneous than the sputtered ones. It is shown that the sputtered films based on substituted porphine have a looser stacking than the initial analog. A spectroscopy study revealed a bathochromic shift of the Soret band in the Langmuir−Schaefer films–sputtered films series. This shift is explained by the increase in the concentration and size of molecular aggregates in sputtered films. It is shown that a polycrystalline C60 fullerene film deposited onto an amorphous substituted porphine layer improves the photoelectric characteristics of the latter. Both the time stability of the photodiode structure and its ampere‒watt sensitivity increase (by a factor of 10 in the transition regime). The steady-state current does not change. The effect of polarity reversal of the photovoltaic signal is observed in a planar С60‒substituted metalloporphine heterostructure, which is similar to the pyroelectric effect. The polarity reversal can be explained by the contribution of the trap charge and discharge current at the interface between the amorphous photosemiconductor and crystalline photosemiconductor to the resulting photoelectric current.

Structure formation in crystallizing ferroelectric polymers

The structure of ferroelectric copolymers of vinylidene fluoride with hexafluoropropylene is investigated using wide-angle x-ray diffraction. It is shown that the crystallization of extruded films of vinylidene fluoride-hexafluoropropylene copolymers brings about the formation of the nonpolar α modification and, possibly, the polar αp modification. An increase in the hexafluoropropylene content in the copolymer leads to a decrease in the degree of perfection of the α (αp) phase, on the one hand, and a reduction of its volume fraction, on the other hand.

POLARCALC: A program for calculating the linear-polarization factor using an area detector

A graphical interface program has been developed to determine the linear-polarization factor of a monochromatic X-ray beam when analyzing scattering from an amorphous object. An area coordinate detector is used in measurements. The change in intensity over the azimuthal angle at a constant diffraction angle is interpolated by a theoretical cosine dependence, which contains the polarization factor.