S. A. Petrova

Magnetic susceptibility of nanostructural manganite LaMnO3 + δ produced by mechanochemistry method

The mechanochemical method is shown to be a relatively simple method for producing nanostructural manganites LaMnO3 + δ with crystallite size D ≥ 10 nm. An increase in the treatment duration in a planetary mill from 1 to 13 h decreases the size D and increases microstrains. The Curie temperature of the nanostructural manganites decreases insignificantly and the phase transition is smeared as D decreases. A decrease in the unit-cell volume and the temperature dependences of the inverse magnetic susceptibility 1/χ(T) indicate an increase in the Mn4+ ion concentration with the milling duration. The variation of the magnetic properties of LaMnO3 + δ nanostructural powders is explained by the competition of a number factors, such as variations of the composition, the cation-sublattice defect structure, the size effect, and the microstrain level.

Oxygen Isotope Exchange between Gaseous Phase Enriched with 18O Isotope and Nanocrystal Oxides LaMnO3+δ Obtained by Severe Plastic Deformation

The kinetics of the isotope exchange between gaseous oxygen enriched with the 18O isotope and two LaMnO3+δ oxide samples – a nanopowder and a bulk nanocrystal – has been studied. The 18O isotope concentration has been measured by the acceleration nuclear microanalysis method. The coefficients of the volume and the nanograin boundary self-diffusion of oxygen have been evaluated at 500 °C. They are equal to 3.5·10 −20 and 1.5·10 −13 cm2/s, respectively.

Grain boundary self-diffusion of tracer 18O atoms in nanocrystalline oxide LaMnO3 + δ

Diffusion coefficients of tracer 18O atoms at boundaries of nanograins of LaMnO3 + δ oxide have been measured in the temperature range of 400–500°C. The samples of the nanocrystalline oxide are prepared with the use of the shockwave loading method. The concentration profile of the tracer atoms after diffusion annealing is measured with the use of the nuclear microanalysis method. The activation energies of the grain boundary diffusion amounts to about 2 eV and the boundary width is ∼0.05 nm. The measured coefficients of the grain boundary diffusion at 500°C exceed the corresponding coefficients of the volume diffusion by seven orders of magnitude.

Effect of mechanical activation on the morphology and structure of hydroxyapatite

We have studied the effect of grinding in planetary mills on the phase composition, morphology, and water content of hydroxyapatite powder. The results indicate that milling for even relatively short times, which reduces the average particle size by a factor of 2, causes the monetite present in the unmilled powder to disappear and reduces the crystallite size of the hydroxyapatite. The fraction of nanoparticles in the powder is then 98% and remains constant during further milling. Milling for longer times leads to hydroxyapatite amorphization. For an average size of large particles R ≥ 1 μm, the surface area of the particles per unit volume, E (cm−1), is determined only by R (E ∼ 1/R).

Synthesis, structure, and conductivity of substituted bismuth niobate Bi7Nb2O15.5

Structural and electrochemical characteristics of substituted bismuth niobates Bi6.95Y0.05Nb2-yMyO15.5±δ, where M = Fe or Zr, have been reported. The homogeneity ranges of solid solutions and crystallochemical parameters have been determined by means of X-ray powder diffraction and electron microscopy with X-ray microanalysis. The compatibility of niobates with an electrode material based on lanthanum manganite has been assessed. The electrical conductivity of sintered samples has been studied by impedance spectroscopy. It has been shown that the change of the dopant type does not lead to a noticeable change in conductivity.

Synthesis, structure, and conductivity of BINBVOX ceramics

The preparation and the structure and transport characteristics of Bi4V2 − xNbxO11 (BINBVOX) were studied. A comparative analysis of the synthesis of solid solutions was performed. The sintering of ceramics and the electrical conductivity as a function of temperature, composition and partial oxygen pressure were studied.

Synthesis, region of existence, structural characteristics, and conductivity of BI(CR, FE)VOX solid solutions

The results of our studies of solid solutions of the general composition Bi4V2 − xFex/2Crx/2O11 − δ are presented. The crystal-chemical parameters of different polymorphic modifications of BIMEVOX were determined. The particle size distribution was determined by laser diffraction and optical microscopy. The surface of sintered preforms was studied by scanning electron microscopy. The conductivity of sintered poly-crystalline samples as a function of temperature and composition was studied by impedance spectroscopy. The conductivity was depends on the procedure for the synthesis of solid solutions. The most promising compositions were revealed.

Thermally activated transformations in stable and metastable copper(II) pyrovanadate polymorphs

The structural transformations of α- and β′-Cu2V2O7 phases over the entire temperature range of their existence and α → β′-Cu2V2O7 and β′ → β-Cu2V2O7 polymorphic transitions in α-Cu2V2O7 are described from the crystal-chemical standpoint. Variations in the parameters of the polyhedral blocks of the α-Cu2V2O7 structure implies that the greatest deformations occur with a negative and near-zero bulk thermal expansion in the range from room temperature to 400°C. The compression and rotation of vanadium-oxygen diortho groups is accompanied by unbending of zigzag copper-oxygen chains, with the distances between them unchanged, which is the reason for the anomalous volume expansion of the structure. Thermal distortion of β′-Cu2V2O7 is insignificant. The thermal expansion coefficients (TECs) of unit cell parameters are as follows: αa = −1.36 × 10−5 1/K, αb = 1.95 × 10−5 1/K, αc = 1.37 × 10−5 1/K, αβ = −0.18 × 10−5 1/K, and αV = 1.93 × 10−5 1/K. We demonstrate that the low-temperature Cu2V2O7 phase can be formed without admixtures of metastable β-Cu2V2O7 upon slow cooling (at about 1 K/min) of the high-temperature phase.

Electrochemical characteristics, thermal and chemical compatibility in the La0.7Sr0.3CoO3 electrode-γ-BIFEVOX electrolyte system

The electrochemical characteristics and compatibility of components of the electrode-electrolyte system, where the electrolyte is chosen to be γ-BIFEVOX compositions crystallizing in a stable tetragonal phase and the cathode material is chosen to be composite electrodes of composition La0.7Sr0.3CoO3 + Bi4V1.7Fe0.3O11 − δ, were studied.

Some features of the preparation, structure, and properties of BICUTIVOX

This work continues the search for optimal preparation methods and studies of structural and transport characteristics of BICUTIVOX solid solutions of the general composition Bi4V2 − xCux/2Tix/2O11 − δ (x = 0.0−0.35).