Interaction and transformation of metastable defects in intercalation materials

Non-equilibrium defects often dictate macroscopic functional properties of materials. In intercalation hosts, widely used in rechargeable batteries, high-dimensional defects largely define reversibility and kinetics. However, transient defects briefly appearing during ionic transport have been challenging to capture, limiting the understanding of their life cycle and impact. Here, we overcome this challenge and track operando the interaction and impact of metastable defects within NaxNi1-xMnyO2 intercalation hosts in a charging sodium-ion battery. Three-dimensional coherent X-ray imaging reveals transformation and self-healing of a metastable domain boundary, glissile dislocation loop, and stacking fault. A local strain gradient suggests a quantifiable difference in ion diffusion, coincident with the macroscopic change in diffusion coefficient. Analysis of the unexpected defect anisotropy highlights the importance of mesostructure, suggesting a possible control approach and disputing the rigidity of the framework layers. The shared nature of oxygen framework layers makes our results applicable to a wide range of intercalation materials.

Research of Thermodynamic Conditions for Gas Hydrates Formation from Methane in the Coal Mines

This article is focused on solving the problem of power supply for the mining and industrial regions of Ukraine. This problem is caused by a significant import dependence on natural gas, the lack of efficient technologies in the integrated development of the energy resources of gas-coal deposits and the deterioration of social and economic, as well as environmental conditions in mining regions. As a promising direction for solving the problem of rational use of methane from coal mines and reducing the hazardous gas emissions into the atmosphere, the implementation of gas hydrate technologies into the technological complex of a coal mine has been proposed. The Clausius-Clapeyron equation has been improved for the conditions of gas hydrates formation, which considers the presence of an excess in non-equilibrium defects and is supplemented, taking into account the thermal effect of phase transformations, with all the time positive thermal effect of the defects relaxation. It has been revealed that one can intentionally control the relaxation energy of defects by the thermodynamic stimulus of phase transformations in the process of hydrate formation. The experimental dependences have been determined of the change in hydrate accumulation on the time of hydrate formation, with the methane hydrates production and taking into account the parameters of pressure and temperature. It has been revealed that the maximum fast time of hydrate formation at T = 1°C and P = 10 MPa is the time which amounts to 2.5 hours. The experimental dependences have been determined of the gas hydrates formation out of a methane-air mixture of degassing holes, on the methane concentration, on pressure and temperature parameters. It has been determined that the greater the methane concentration in the mixture, the greater must be the pressure in the system for the gas hydrates formation.

Defect Chemistry and Basic Properties of Non-Stoichiometric PuO2

The basic properties of PuO2−x were reviewed, and the equilibrium defects in PuO2−x were evaluated from the experimental data of the oxygen potential and electrical conductivity as well as the Ab-initio calculation results. Consistency among various properties was confirmed, and the mechanistic models for thermal property representations were derived.

The Features of Structure Formation in Mechanically Activated Powder Mixture 3Ti+Al in the Thermal Explosion Mode

The experimental investigation of structure formation processes in preliminary mechanically activated powder mixture 3Ti + Al was carried out. The synthesis was realized in the thermal explosion mode with the use of high-frequency induction heating. The characteristic features of structure and phase formation in this system by quenching of the mixture at different annealing times were installed. It was shown, that the processes of structure-phase formation occur in the following sequence: chemical reaction - structural relaxation - thermal relaxation - thermal equilibrium. The time-temperature intervals of Ti3Al strictly single-phase compound existence with various concentrationsof non-equilibrium defects of the structure were established.

The Study of Pyrite Surface Properties and Effect Mechanism with Xanthate Caused by the Microscopic Crystal Structure and Defects

The pyrite in the nature, due to the differences of the semiconductor properties caused by crystal structure and the presence of defects, will be bound to seriously affect the surface state and surface-activity of the mineral, eventually make the process of electrochemical reaction and flotation behavior change in the solution. Starting from the microscopic point of view, this article would study the affect mechanism of crystal structure and defects on the pyrite surface properties and the electrochemical reaction process. Studies have shown, because of the existence of the strong Fe-S covalent bond and determinate equilibrium defects, make the Fermi level and valence state of partial surface element change, accordingly lead to special semiconductor and surface properties of pyrite, ultimately affect the process of pyrite electrochemical flotation.

Models of Mutual Solubility Increasing under the Pulse Loading

Since 1975 a so-called anomalous mass-transfer in metals and alloys under pulse loading is being investigated in the Institute of Metal Physics. This phenomenon remains to be a challenge to theoreticians. Besides, one more phenomenon (observed at the same systems) was discovered – formation of metastable alloys (solutions, and, sometimes, ordered phases), with solubility limits far exceeding the equilibrium values and depending on the deformation rate. Since formation of nonequilibrium phases is also typical for alloys under irradiation, it seemed natural for us to use some of concepts and models invented in the “materials under irradiation” community. We propose 3 types of models for description of metastable solid solution formation in diffusion couple under pulse loading: 1) flux balance for both components at the interface with account of non-equilibrium defects generated during pulse loading; 2) “ballistic jump” concept, which had been invented by George Martin et al. for materials under irradiation or ball-milling, combined with another Martin’s kinetic model (1994) of diffusion; 3) modification of such a concept for the case of non-equilibrium interstitial defects. Non-equilibrium phase diagrams obtained by all 3 models are built and compared with experimental data which reflect a qualitative correspondence to one another.