Gayane Chilingaryan

Samples of natural glass (translucent obsidian) and artificial glass obtained from natural perlite raw material and similar in composition to obsidian were irradiated at room temperature by γ‑photons with an average energy of 1.25 MeV in different doses up to 1300 kGy from a ⁶⁰Co radiation source. It is known that γ-radiation affects the optical properties of glass depending on the composition as well as on the presence of defects in the glass framework. The analysis was carried out using the methods of absorption, luminescence, Raman, and EPR spectroscopy depending on the γ-irradiation doses. A comparison of the transmission, photoluminescence, Raman, and EPR spectra for obsidian and perlite glass was carried out. The difference transmission spectra between non-irradiated and irradiated samples made it possible to isolate the absorption bands for which Fe³⁺ ions in different coordination are responsible. Upon excitation with a laser with a wavelength of 473 nm, visible to the naked eye green–red photoluminescence was observed in natural and synthetic glasses before and after irradiation. Raman spectra upon excitation with a wavelength of 785 nm in both types of studied glasses before and after irradiation showed vibrational frequencies characteristic of glass matrices and a band associated with water in the silicate network of glass. In addition, during the registration of the Raman spectra, an intense asymmetric photoluminescence band was observed in the 850–950 nm region. EPR measurements showed three signals characteristic for Fe³⁺ ions with g-factors of ~6.0, ~4.2 and ~2.0 in natural and synthetic glasses. In the region of the specified doses of γ-irradiation, obsidian and perlite glass turned out to be resistant to the formation of NBOHC paramagnetic defects.

A supercapacitor is an energy storage device that has the advantage of rapidly storing and releasing energy compared to traditional batteries. One powerful method for creating a wide range of materials is combustion synthesis, which relies on self-sustained chemical reactions. Specifically, solution combustion synthesis involves mixing reagents at the molecular level in an aqueous solution. This method allows for the fabrication of various nanostructured materials, such as binary and complex oxides, sulfides, and carbon-based nanocomposites, which are commonly used for creating electrodes in supercapacitors. The solution combustion synthesis offers flexibility in tuning the properties of the materials by adjusting the composition of the reactive solution, the type of fuel, and the combustion conditions. The process takes advantage of high temperatures, short processing times, and significant gas release to produce well crystalline nanostructured materials with a large specific surface area. This specific surface area is essential for enhancing the performance of electrodes in supercapacitors. Our review focuses on recent publications in this field, specifically examining the relationship between the microstructure of materials and their electrochemical properties. We discuss the findings and suggest potential improvements in the properties and stability of the fabricated composites based on the results.

Semitransparent gray color obsidian samples (bulk and powder) were irradiated at room temperature by Co⁶⁰ radiation source with the γ-photon average energy of 1.25 MeV and different doses from 5 to ~500 kGy. It is known that γ-irradiation influences the optical properties of glass materials depending on the composition as well as on the presence of defects in the glass matrix. Analysis of obsidian samples was carried out by absorption and reflection spectroscopy in the UV, visible, and IR ranges, as well as by EPR measurements for characterization of semitransparent gray color obsidian depending on the γ-irradiation of different doses. The difference in transmittance spectra between the pristine sample and those irradiated with different doses made it possible to distinguish three absorption bands at 368, 386, and 442 nm, which are responsible for Fe³⁺ ions in different environments. The content of hydroxyl OH groups, determined from the absorption in the band at ~4500 cm^–1, does not change in the range of used doses. The EPR measurements showed three signals with g-factors of ~6.0, ~4.2, and ~2.0 characteristic for Fe³⁺ ions, the intensities of which increase with increasing irradiation doses. Obsidian turned out to be resistant to the formation of NBOHC paramagnetic defects in the region of the indicated doses of γ-irradiation.

Samples of natural zeolite from the Nor-Kokhb deposit (Armenia), as well as its chemically and thermally modified by the microwave method in comparison with the traditional method, were studied. It was shown that the process of microwave processing proceeds 3 times faster than the traditional one. X-ray diffraction analysis shows that the main mineral in the zeolite samples under study is clinoptilolite. According to the results of optical and EPR spectroscopy, the presence of Fe³⁺ ions in the framework and extraframework positions of the zeolite was revealed. The study of diffuse reflection spectra allows to conclude that zeolite is a wide-band material with a bandgap of 4.14 eV.

Ni@C nanocomposites in a graphite-like carbon matrix and cobalt nanoparticles in carbon nanotubes were obtained by solid-phase pyrolysis of nickel phthaloc

Nanoparticles of iron (α-Fe) and iron oxide (Fe3O4) with a core-shell structure (α-Fe core, Fe3O4 shell) covered with additional graphite-like ca