R. G. Zakharov

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.

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 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.

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.

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).

Phase relations in the Zn2V2O7-Cu2V2O7 system from room temperature to melting

Phase relations in the Zn2V2O7-Cu2V2O7 system were studied by high-temperature X-ray diffraction and differential thermal analysis. The major phase constituents of the system are solid solutions based on Zn2V2O7 and Cu2V2O7 polymorphs and their coexistence regions. The generation of α-Zn2 − 2xCu2xV2O7 solid solution, where 0 ≤ x ≤ 0.30, leaves almost unchanged the stabilization temperature of the high-temperature zinc pyrovanadate phase. The α-Cu2 − 2xZn2xV2O7 homogeneity range is 5 mol % Zn2V2O7. In the range 0.050 ≤ x ≤ 0.09 from 20 to ∼ 620°C, there is the two-phase field of α-Cu2V2O7 and β-Cu2V2O7 base solid solutions. At still higher temperatures, β-Zn2 − 2xCu2xV2O7 and α-Cu2 − 2xZn2xV2O7 coexist in the mixed-phase region. β-Zn2 − 2xCu2xV2O7 solid solution, where 0 ≤ x ≤ 0.30, exists above 610 ± 5°C. The extent of the β′-Cu2V2O7-base solid solution is 9 to 65 mol % Zn2V2O7 at 615 ± 5°C, expanding to 0 mol % Zn2V2O7 with rising temperature.

Structure and electrical conductivity of cobalt-doped Bi26Mo10O69

The existence boundaries, structures, and transport parameters of Bi1 − xCox[Bi12O14]Mo5O20 ± δ and Bi[Bi12O14]Mo5 − yCoyO20 ± δ solid solutions, which have a unique columnar structure, were studied. Electrical conductivity in these solid solutions was studied by impedance spectroscopy.

Structural phase transitions in nanoscaled systems with Jahn-Teller ions

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