The structural origin of the germanate anomaly in glasses, which involves complex Ge–O coordination environments, is frequently studied using crystalline analogs. This study aims to provide reliable spectroscopic fingerprints by performing a detailed structural and thermal analysis of crystalline A4Ge9O20 model systems with A = Li, Na, K. The compounds were synthesized via melt crystallization and characterized using powder X-ray diffraction (PXRD), differential scanning calorimetry (DSC), and Raman spectroscopy techniques. The results demonstrate clear cation-dependent crystallization pathways. The Li-containing system predominantly forms Li2Ge7O15 in mixture with Li4Ge9O20, indicating a preference for thermodynamically stable phases. The Na-system successfully yields the target Na4Ge9O20 compound. In contrast, the K-system primarily produces the likely metastable K2Ge4O9 phase with a significant amorphous fraction, highlighting the role of kinetic limitations. This comparative study demonstrates that the size of the alkali cation is a critical factor for controlling phase formation under identical stoichiometric and thermal conditions.

The crystallization of glasses used for immobilization of radioactive waste is generally undesirable due to potential disruption of the matrix structure with subsequent migration of radionuclides into the environment. However, glass crystallization, being a natural consequence of the establishment of equilibrium in the system, can be employed in the controlled synthesis of glass ceramics having predictable properties and structures. The paper discusses the results of crystallization in the glass-forming system Na2O-Cs2O-B2O3-SiO2 leading to the formation of ordered phases. During crystallization from borosilicate melt, cubic cesium borosilicate CsBSi2O6, as described in the space group I-43d, and orthorhombic Cs2B2Si3O10 (Cmce), were found with different Na2O/Cs2O ratios. A variety of techniques were employed to characterize the generated crystals. Single crystal x-ray diffraction (SXRD) was applied to identify the crystal structure. The crystalline arrangement of the crystals was confirmed using powder x-ray diffraction (PXRD) analysis. The Raman spectra and images of these crystalline phases are reported here for the first time.

The crystallization of glasses used for immobilization of radioactive waste is generally undesirable due to potential disruption of the matrix structure with subsequent migration of radionuclides into the environment. However, glass crystallization, being a natural consequence of the establishment of equilibrium in the system, can be employed in the controlled synthesis of glass ceramics having predictable properties and structures. The paper discusses the results of crystallization in the glass-forming system Na2O-Cs2O-B2O3-SiO2 leading to the formation of ordered phases. During crystallization from borosilicate melt, cubic cesium borosilicate CsBSi2O6, as described in the space group I-43d, and orthorhombic Cs2B2Si3O10 (Cmce), were found with different Na2O/Cs2O ratios. A variety of techniques were employed to characterize the generated crystals. Single crystal x-ray diffraction (SXRD) was applied to identify the crystal structure. The crystalline arrangement of the crystals was confirmed using powder x-ray diffraction (PXRD) analysis. The Raman spectra and images of these crystalline phases are reported here for the first time.

Functional porous materials actively used as sorbents and membranes have complex microstructural morphologies that satisfy different requirements for industrial or medical purposes. In order to apply porous membranes, the sizes, shapes and orientations of their pores, along with their densities, surface-to-volume ratios and spatial distributions, need to be carefully considered. Thus, the possibility to alter the properties of porous materials during the production process via their structural alteration becomes a priority. For example, improved production methods can help to enhance the performance of sorbents used in waste treatment. This paper presents the results of a study of the structure and physico-chemical properties of glasses of the Na2O/K2O-B2O3-SiO2-GeO2 system and porous glasses obtained from them. Changes in the structure of the initial glasses when sodium is replaced with potassium at constant ratios of glass-forming cations were estimated based on the results of Raman spectroscopy. At a ratio of K2O/Na2O contents of about 0.6, nonlinear dependencies of the density and temperature of the glass transition on the size of the alkaline cation are characterized by kinks. The characteristics of seven porous materials were determined according to the method of low-temperature adsorption-desorption of nitrogen. It is demonstrated that the microstructure of a porous material depends on the composition and structure of the initial glass. The results of the sorption of cesium from the solution correlate well with changes in the structure of the initial glasses when replacing sodium with potassium. The volume of micropores is shown to increase with an increase in the number of coordinated germanium atoms in the glass [6]Ge, while the specific surface area and volume of mesopores depend more on the ratio of [4]B and [3]B in the composition of borate superstructural groupings. As a result, the porous glass in which sodium oxide is completely replaced by potassium oxide has optimal characteristics regarding Cs sorption and stability.

The structure of borosilicate glass and glass-ceramic materials of two compositions with different Cs/Na ratios was studied using Raman spectroscopy. The materials were synthesized in two different modes. The anionic environment of cesium in the glass and the structural rearrangements of the network during the formation of crystalline phases have been studied. X-ray diffraction patterns of glass-ceramic samples made it possible to determine the only crystalline phase CsBSi2O6, the structure of which was not clearly determined. The glass-ceramics of the studied composition can be used to immobilize cesium by incorporating it into the crystalline phases of the CsBSi2O6 composition, while sodium is retained in the glassy matrix. These studies showed that the composition of the crystalline phase does not depend on the initial ratio of alkali cations, while the proportion of the ordered and amorphous phases is controlled by the kinetics of the melt cooling process.

Borosilicate glasses have long been the preferred form for immobilizing high-level radioactive wastes. However, a significant drawback of glass-matrices involves the low rate of loading with radionuclides. One of the approaches to solving this problem envisages a multiphase glass system with crystalline inclusions. The present work aims to study model borosilicate glasses and glass-ceramics containing Cs atoms serving as a radionuclide simulator. Two approaches for the synthesis of glass-ceramics were used: directed crystallization, and pressing followed by annealing. The structure of initial borosilicate glasses and glass-ceramic samples obtained by these means was studied using Raman spectroscopy. An X-ray diffraction analysis was applied to identify crystalline phases. The morphology and composition of the crystalline phase was evaluated using scanning electron microscopy. The obtained results showed that the structure and properties of the synthesized glass-ceramic material is determined by the composition of initial glasses. Due to the ratio of modifying cations in glasses at a constant boron-to-silicon ratio, the crystalline phases identified in glass-ceramics are significantly affected by the anionic structure. The formation and growth of crystals was also established to be dependent on the technological scheme of synthesis.

Within the kinetic-atomistic approach, a new approach is proposed for constructing the temperature dependence of the stationary velocity of propagation of the solid–liquid interface (SLI) in metals: aluminum, copper, and iron with different crystallographic orientations. The considered temperature range includes the range of maximum allowable overheating/overcooling values for each of the metals. A significant modification to the well-known kinetic model with the Wilson–Frenkel (WF) diffusion constraint, which is used to construct the response function, is made. An atomistic simulation of the processes of melting/crystallization of metals aluminum, copper, and iron is carried out over the entire temperature range using three interaction potentials of the “embedded atom” family. By comparing the simulation results with the data of the modified kinetic model, the response function of the interface velocity in the range of maximum allowable overheating/overcooling values in metals is constructed using the least squares criterion. The use of the modified WF kinetic model in calculations significantly improves the accuracy of the response function over the considered temperature range. The resulting temperature dependence of the interface velocity is diffusion-limited and is described by the same equation for each metal over the considered temperature range.

Borosilicate glasses have long been the preferred form for immobilizing high-level radioactive wastes. However, a significant drawback of glass-matrices involves the low rate of loading with radionuclides. One of the approaches to solving this problem envisages a multiphase glass system with crystalline inclusions. The present work aims to study model borosilicate glasses and glass-ceramics containing Cs atoms serving as a radionuclide simulator. Two approaches for the synthesis of glass-ceramics were used: directed crystallization, and pressing followed by annealing. The structure of initial borosilicate glasses and glass-ceramic samples obtained by these means was studied using Raman spectroscopy. An X-ray diffraction analysis was applied to identify crystalline phases. The morphology and composition of the crystalline phase was evaluated using scanning electron microscopy. The obtained results showed that the structure and properties of the synthesized glass-ceramic material is determined by the composition of initial glasses. Due to the ratio of modifying cations in glasses at a constant boron-to-silicon ratio, the crystalline phases identified in glass-ceramics are significantly affected by the anionic structure. The formation and growth of crystals was also established to be dependent on the technological scheme of synthesis.

The action of an ultrashort laser pulse on a thin gold film was studied using a single-speed nonequilibrium combined continuum-atomistic model, which was further developed in the work. Three ablation modes were studied: supercritical expansion, phase explosion and mechanical spallation. The simulation results are compared with experimental data. The dependence of the amount of removed substance on the fluence of laser radiation was obtained.

— Properties of porous materials prepared from glasses of the Na 2 O–B 2 O 3 –SiO 2 –GeO 2 system have been studied using low-temperature nitrogen adsorption/desorption measurements. The results demonstrate that germanium substitution for silicon in the glasses studied leads to an increase in pore volume at SiO 2 /GeO 2 ratios of down to 0.5. The porous glass with this composition has the largest specific surface area and micro- and mesopore volumes. We assume that the observed changes in the porosity parameters of glass in the case of complete germanium substitution for silicon are related to structural features of the borogermanate glass network, associated with B–O–B bond breaking and the formation of non-bridging oxygen atoms.

The characteristics of nonequilibrium heat transfer of copper, such as thermal conductivity and heat capacity, are obtained in a wide temperature range (300 ≤ T ≤ 5700 K), including the region of melting-crystallization phase transformations by mathematical modeling. As is known, there are two mechanisms of heat transfer in a solid body: by elastic vibrations of the lattice and by free electrons. When determining these characteristics of copper heat transfer, the lattice and electronic components were taken into account. Modeling of the characteristics of heat transfer of the copper electronic subsystem in this work is based on the use of quantum statistics of the electron gas using the Fermi–Dirac integrals. The properties of the phonon subsystem were determined within the framework of the atomistic approach. The interaction potential of particles of the “embedded atom” family EAM was used for modeling. The simulation results were compared with the results of alternative calculations. The total heat capacity and thermal conductivity of copper, obtained by summing the electronic and phonon components, are compared with the experimental data.

The paper presents results of structural calculations carried out on the alkali borate glasses using physico-chemical modeling based on Gibbs energy minimisation. Standard heat capacity, entropy and enthalpy of for-mation values for lithium, sodium and potassium borates are estimated by regression analysis for use as the input data for the models taking into account the error of the initial data. The correction of the physicochemical model was made using results of Raman spectroscopy. The dependence of the maximum of the "borate anomaly" on the number of non-bridging oxygen atoms was shown. It was found that the most obvious changes in the dependence of properties occur in the regions of N1 and N2 compositions, which are characterized by the appearance of asymmetric triangles Bo2O- and BoO22-in glasses, correspondingly.

Методом низкотемпературной адсорбции/десорбции азота определены характеристики пористых материалов, полученных из стекол системы Na 2 O–B 2 O 3 –SiO 2 –GeO 2 . Показано, что при замещении кремния на германий наблюдается увеличение объема пор в изученных стеклах вплоть до состава с соотношением SiO 2 /GeO 2 , равным 0.5. Пористое стекло этого состава характеризуется наибольшими удельной поверхностью, объемами микро- и мезопор. Кроме того, мы предположили, что изменение пористых характеристик стекла в случае полного замещения кремния на германий связано со структурными особенностями борогерманатной сетки, обусловленными разрывом связей B–O–B с образованием немостиковых атомов кислорода.

The article is devoted to the problem of constructing equations of state with deep entry into metastable regions (overheating/undercooling) of the molten and crystalline phases of aluminum. For mathematical modeling of hydrodynamic processes, the knowledge of the equations of state is the source of the most important information about the dependence of the thermodynamic properties of a substance on the microscopic internal structure. Moreover, for modeling, the equations of state are required in the form of smooth analytical dependencies with the characteristics of metastable states. Molecular dynamics simulation was used as the main tool for obtaining the equations of state. Based on the results of molecular dynamics calculations, the work obtained mutually consistent single-phase equations of state for molten and crystalline aluminum in tabular form. For tabular values, the approximating analytical dependences of low degrees were obtained. The results are presented in the form of tables and graphs. The thermodynamic consistency of the resulting equations is investigated. The simulation results of this work are compared with the equations of state for aluminum obtained by other authors.

Despite numerous investigations, the thermodynamic properties of potassium silicates remain apparently contradictory. In situ experiments are complicated by the unstable behavior of a K2O–SiO2 melt in the region of compositions with a high potassium oxide content. In this paper, we study the structure of melts by the method of physicochemical modeling, taking into account the results of high-temperature Raman spectroscopy. To do this, the Raman spectra were curve-fitted, taking into account the second coordination sphere of silicon atoms. From the interpretation of the spectra of K2O–SiO2 glasses and melts having a K2O content of up to 55 mol.%, quantitative characteristics of the system were obtained. Since available information on the thermodynamic properties of potassium silicates is known to be contradictory, coordinated thermodynamic characteristics of potassium silicates, some of which were evaluated, were used as input data for modeling. Structural modeling of glasses and melts of the K2O–SiO2 system was carried out across a range of compositions up to 60 mol.% potassium oxide. The database of structural units of melts of the potassium silicate system, updated according to experimental data, will find practical application in chemistry, geochemistry and engineering fields.

Министерство науки и высшего образования Российской Федерации Российское химическое общество им.Д.И.Менделеева Секция по химической термодинамике и термохимии Научного совета РАН по физической химии Сибирское Отделение Российской Академии Наук Институт неорганической химии им.А.В.Николаева СО РАН

A structure–property correlation has been developed, which makes it possible to choose the optimal values of the enthalpy of formation of alkali metal borates, for which, according to the data of various experimental works and reference publications, wide variations are observed. Using this correlation, the enthalpy of formation of unstudied alkali metal borates can be reasonably estimated. It has been found that the contribution of B 2 O 3 to the enthalpy of formation is the same not only for alkali metal borates but also for Ba, Ca, and Pb borates, for whose enthalpy of formation a structure–property correlation has also been established. This suggests the suitability of the obtained correlations for estimating the enthalpy of formation in the borate series, where the value is known only for one member of the series, as well as the possibility of estimating the enthalpy of formation of mixed borates of different metals.