A. Yu. Pichugin

Synthesis of Highly Dispersed Boron Carbide from Nanofibrous Carbon

The results of a study of the synthesis of fine-grained boron carbide powder and some of its characteristics are presented in the article. Boron carbide was obtained by synthesis from elements (boron and nanofibrous carbon (NFC)) in an inert gaseous atmosphere. The presence of boron carbide in the samples was established by X-ray phase analysis. The impurity content was determined by X-ray fluorescence spectroscopy. The shape and size of the boron carbide particles were determined by transmission and scanning electron microscopy with the use of local energy-dispersive X-ray microanalysis; this made it possible to determine that boron and carbon were mostly present in them. The specific surface area and porosity of the samples were determined using the BET method. The thermo-oxidative stability of boron carbide was studied by simultaneously using thermogravimetry and differential scanning calorimetry. The synthesized boron carbide at a temperature of 1900°C and holding time of 15–40 min had an impurity content no higher than 1.5 wt % and particle sizes of 100–500 nm.

Magnetic and electrical properties of cation-substituted sulfides MexMn1 − xS (Me = Co, Gd)

The temperature dependences of the specific magnetization σ and the electrical resistivity ρ of MexMn1 − xS single crystals (Me= Co, Gd; x= 0.05) have been studied in the temperature range 80 K < T < 1000 K. The samples under study have revealed the presence of a spontaneous magnetic moment below the Néel temperature (TN) and ferromagnetic clusters in Gd0.05Mn0.95S in the temperature range 146 K < T < 680 K. Substitution of gadolinium for manganese initiates a transition from p-type to n-type conduction. The change in the conduction type is accompanied by an increase in the electrical resistivity at 300 K by approximately one order of magnitude and, accordingly, by a decrease in the activation energy. The magnetic and electrical properties of the crystals under study have been interpreted in terms of the cluster model with temperature-dependent ferromagnetic exchange and an electron localized in this cluster.

Nonuniform Magnetic States and Electrical Properties of

The real and imaginary parts of magnetic permeability at the three frequencies 100 Hz, 1 kHz and 10 kHz and magnetic moment in magnetic field H = 0.05 T in the SmXMn1-XS(0.1 ≤ × ≤ 0.25) solid solutions at the temperatures 5 K-300 K were measured. Magnetization curves were measured in the range of fields - 9 T <; H <; 9 T at the temperatures T = 5 K, 50 K. Non-linear behavior of the magnetization versus field, residual magnetic moment, logarithmic dependence of imaginary parts of the magnetic permeability maximum on frequency and sharp drop of Im(μ) at T <; 40 K for compound Sm0.25Mn0.75S were found. The electrical resistivity of the SmXMn1-XS(0.15 <; x <; 0.25) solid solution in the range of temperatures 80 K-300 K were measured. Minimum and maximum in the temperature dependence of the resistivity were found respectively at T = 220 K for X = 0.15 and at T = 100 K for X = 0.2 compounds. This behavior is explained a result of the mobility edge movement and the disorder of the deformation and spin density fluctuations with short-range order.

{\rm Sm}_{\rm X}{\rm Mn}_{1-{\rm X}}{\rm S}

XRD data on the layered vanadium-substituted copper-chromium disulfides (CuCr1−xVxS2, x = 0−0.4) are compared with the data obtained by X-ray emission and photoelectron spectroscopies.

Solid Solutions

This paper reports on the results of investigations of the thermal properties and thermal conductivity of single crystals of homogeneous solid solutions FexMn1 − xS with a cubic NaCl structure, which have been prepared by the cation substitution for divalent manganese ions in manganese monosulfide. It has been revealed that the heat capacity and thermal conductivity exhibit anomalies in the range of the magnetic transition. The cation substitution is accompanied by an increase in the phase transition temperature.

XES investigation of the layered vanadium-substituted copper-chromium disulfides

In the work X-ray K edges of chromium dichalcogenides CuCr1-xMx′S2 (M = V, Fe; x = 0-0.40) and MCrX2 (M = Cu, Ag, Na; X = O, S, Se) were studied experimentally and theoretically. Comparison of fine structures of experimental XANES spectra obtained using a synchrotron radiation source and theoretical absorption spectra modelled using FDMNES software package allows one to study the influence of types of intercalate M, chalcogene X and also the effect of the cation substitution of chromium atoms by vanadium and iron on XANES structure of K edges in CuCr1-xMx′S2 and MCrX2.

Heat capacity and thermal conductivity of FexMn1 − xS single crystals

In the work, X-ray and Auger microprobe studies of the surface of crystals prepared from powder samples of CuCr1−xVxS2 disulfides (x = 0÷0.11) by crystallization from melt in the sulfur vapor atmosphere. Sample slabs cut from ingots include crystalline layered blocks with different orientation of copper-containing extended linear inclusions separated by disulfide matrix layers. The results of the microprobe analysis of regions with copper-containing inclusions and the regions adjacent to them are presented.

Xanes of X-ray absorbtion K edges of chromium dichalcogenides CuCr1-xM′xS2 and MCrX2

Abstract2p3/2,1/2 Photoelectron spectra of single crystalline specimens of chromium-copper disulfides CuCrS2 and CuCr0.85V0.15S2 are studied. It is shown that the spectra of single crystalline specimens substantially differ from the corresponding spectra of chromium-copper disulfides in the powder state.

X-ray and Auger microprobe studies of vanadium-doped layered chromium-copper disulfide crystals

Fe0.27Mn0.73S single crystals were studied. A magnetic transition is detected near 197 K, which is accompanied by anomalies of the thermal, electrical, and resonant properties.