V. B. Fetisov

Electrochemical dissolution of Co3O4 in acidic solutions

The cyclic voltammetry method was used to study the regularities of the electrochemical behavior of cobalt cobaltite in an acidic medium. It is shown that cathodic reduction of Co3O4 in the studied range of potentials of +1.0 to −0.8 V is a multistage process occurring according to the scheme: In the following anodic half-cycle, formation of the CoO protoxidic phase is continued from such sources as Co3O4 − δ and metallic cobalt. At the potentials to the positive of +0.25 V, the process of absorption of the superstoichiometric oxygen is realized within the region of homogeneity of the CoO1 + δ protoxidic phase. The dependence of the rate of the chemical stage of the process on the potential sweep direction and also a significant increase in the rate of stage II at the second and further electrode polarization cycles was explained within the theory of nucleation and diffusion of charged particles in the electric field.

THE DIFFUSION OF TRACER OXYGEN ATOMS IN NI FERRITES

Oxygen tracer diffusion in polycrystalline nickel ferrites Ni(1−x)Fe(2+x)O(4) (x=0.1; 0.2; 0.4) at temperatures of 450–700 °C was studied. The number of 18O atoms diffusing to the sample was determined using the 18O(p,α)15N nuclear reaction at the energy of the primary beam particles equal to 762 keV. The nuclear physical experiments were performed on a 2 MV Van de Graaff accelerator. It has been established the oxygen diffusion is characterized by relatively small activation energy (0.89 eV for x=0.2) and low pre-exponential factors (∼10−13 cm2/s for x=0.2). These results suggest that oxygen diffusion in the ferrites under consideration occurs by means of structural vacancies with their concentration about 10−9–10−11.

Anomalous currents under cyclic polarization of magnetite electrode in acidic medium

An anomalous phenomenon was observed in acidic solutions in cyclic voltammetric curves in the studies of electrochemical behavior of magnetite. It consisted in appearance of the reverse current: a cathodic response under the anodic potential sweep. It was shown that the direct and reverse currents follow the same regularities. Analysis of experimental data allows concluding that both currents correspond to the same process: Fe3O4 + 8H+ + 2e → 3Feaq2+ + 4H2O. Appearance of anomalous currents on polarization curves of magnetite occurs if the following conditions are observed: irreversibility of the given electrochemical reaction under the given mode experimental parameters; incompleteness of reaction at the cathodic halfcycle stage; layer-by-layer dissolution when the electrode surface is continually refreshed.

Effect of Cation Ordering on the Electrochemical Properties of (MgCr 2 O 4 ) x (Fe 3 O 4 ) 1 - x Solid Solutions

We have studied the influence of long- and short-range cation order on the crystallographic, electrical, and electrochemical properties of (MgCr2O4)x(Fe3O4)1 − x solid solutions. A mathematical model has been proposed which ensures an adequate description of the composition dependences of these properties. Short-range cation order on the octahedral site of the spinel structure has been shown to have a significant effect on these properties at x < 0.5. The results of this study demonstrate that the electrochemical reduction process is highly sensitive to structural features of the (MgCr2O4)x(Fe3O4)1 − x solid solutions.

“Latent” oxygen-transport properties of YBa2Cu3O6 + δ

High-temperature superconductors possessing anastonishing and still not properly understood prop-erty, high-temperature superconductivity (HTSC),remain the focus of much attention [1]. At the sametime, another their advantage—relatively high oxy-gen ion conductivity—was noted already at the earli-est stage of the discovery of high-temperature super-conductors [2, 3].It is worth noting that diffusion coefficients foundby different authors for the same high-temperaturesuperconductors differ by many orders of magnitude.For example, the O