The pseudo-potential PAW method of the density functional theory is employed to study the localization of superstoichiometric oxygen in ferrite CaBaFe 4 O 7 with the orthorhombic swedenborgite structure. The geometric characteristics of oxygen defects are determined by the crystal lattice relaxation procedure. It is shown that the formation of defects in calcium and barium coordination are energetically unfavorable. Oxygen intercalation into structural trigonal iron-oxygen and Kagomé layers is more favorable. In these layers, two edge-sharing Fe 2 O 5 bipyramides are formed instead of FeO 4 tetrahedra connected via one oxygen atom. The structural instability of ferrite CaBaFe 4 O 7 is shown to be caused by the population of anti-bonding 2 p O states during oxygen intercalation. The asymmetric location of the intercalated oxygen ion relative to the neighboring iron ions promotes the appearance of local electric polarization, which can induce ferroelectric effects in the presence of ferromagnetic order.

Ab initio calculations of the electronic structure and thermoelectric characteristics of low- and high-temperature phases of tin selenide, SnSe, with electronic and hole conductivity have been performed. It is shown that the calculations of thermoelectric properties on the basis of the Boltzmann-Onzager theory with consideration of carrier scattering on optical phonons lead to results in good agreement with experimental data. At temperatures below 600 K the modeling correctly reproduces the increased values of the figure-of-merit of electron-doped SnSe in comparison with almost stoichiometric or hole-doped selenide calculations. We explain anomalously high figure-of-merit values of the non-doped selenide at T > 600 K by the hole concentration increase due to oxidation of SnSe or the appearance of vacancies in the tin sublattice. For all the considered variants, i.e. for electron-doped low-temperature and high-temperature phases and low-temperature hole-doped phase, the modeling predicts the absence of figure-of-merit increase at exceeding some limiting concentration of current carriers.

Crystal structure and thermoelectric characteristics of the donor-doped CaMnO3-5 are significantly affected by doping elements and oxygen exchange with ambient air occurring at temperatures above 700 K. To investigate the role of dopants and oxygen nonstoichiometry in thermoelectric phenomena, polycrystalline Ca0.95Bi0.025Y0.025MnO3-5 was synthesized and the obtained temperature dependences of thermal and electronic parameters were studied by DFT calculation method. The electrical conductivity has shown to possess a polaronic character up to -700 K with low activation energy. An increase in temperature leads to formation of oxygen vacancies resulting in the appearance of vacancy states inside the band gap and a decrease in its width. The consequence of this is the observed gradual transition to the semiconductor behavior of electrical conductivity explicitly manifested above -1000 K. The obtained experimental figure of merit is shown to be almost an order of magnitude less than the corresponding theoretical one for bulk media, the main part of the deviation is related to the electrical conductivity of the ceramic specimen having a polycrystalline nature. We conclude that the thermoelectric properties of the donor-doped manganese oxide can be significantly improved employing bulk monocrystalline media.

The interaction of ultrashort laser pulses with transparent materials attracts increasing attention as a powerful technique of tailoring material properties. This technique is widely adopted in many applications based on 3D photonic structures in bulk optical materials among which optical glasses are of prime importance due to their relatively low cost, processability, and possibility of governing refractive index. Dynamics of laser-induced glass modification is still not completely understood while new laser sources and novel irradiation regimes, e.g., using spatiotemporally shaped beams, demonstrate a great potential for achieving predesigned material structures.

In this paper, the results of studying the formation conditions, crystal structure, thermal, spectral, and optical properties, as well as the electronic band structure of cobalt-doped zinc glycolate Zn 1 − x Co x (OCH 2 CH 2 O) (0˂x ≤ 0.2) are presented. Using X-ray powder diffraction data, it was shown that solid solutions are obtained by partial substitution of cobalt for zinc, while maintaining the crystal structure of Zn(OCH 2 CH 2 O). The vibrational spectra of Zn 1 − x Co x (OCH 2 CH 2 O) are identical to those of Zn(OCH 2 CH 2 O) and correlate completely with the results of structural analysis. As a result of heating in air at 600–900 °C, glycolate Zn 1x Co x (OCH 2 CH 2 O), where 0˂x ≤ 0.1, turns into oxide of the composition Zn 1 − x Co x O with wurtzite structure, whose powders have a deep green color (Rinman’s green). The UV-Vis-NIR spectra of Zn 1 − x Co x O contain bands typical of Co 2+ ion transitions in the tetrahedral environment. When Zn 1 − x Co x (OCH 2 CH 2 O) is heated in helium atmosphere, composites (1-x)ZnO:xCo:nC are formed that include a phase with wurtzite structure, metallic cobalt, and elemental carbon. The electronic band structure, optical characteristics, and isosurfaces of wave functions of pure and cobalt-doped zinc glycolate and oxide were calculated. This allowed us to establish the reasons for the increase in the band gap width in glycolate compared to the oxide and its decrease during doping.

Sharply focused pulses are required to modify transparent materials by femtosecond laser pulses. To model the modification process, it is necessary to compute the distribution of the electric field of the laser pulse at distances of the order of hundreds of microns from the focus. The frequently used paraxial approximation in the case of a sharp focus is not applicable. It is necessary to calculate a specific optical system. In the case when a parabolic mirror is used as a focusing element, the desired field distribution can be obtained using the Stratton–Chu integral (SCI). In this paper the generalization of the SCI to the case of a finite-time (femtosecond) pulse and a simplification of the SCI for the case of a large mirror located far from the focus are presented. This is typical for a wide range of practical problems. In addition, specific formulas of the SCI for frequently used polarizations of laser pulses are given. The main achievement of this paper is the development of extremely effective numerical methods of computing the SCI, which is the integral of a rapidly oscillating function. As an example, the calculation of the field of a focused laser pulse with a cylindrical intensity distribution along the radius (top-hat pulse) is given.

Vanadyl formate monohydrate VO(HCOO)2 center dot H2O has been synthesized by a facile two-stage method. The chemical and structural identity of the synthesized compound has been confirmed by X-ray diffraction, ther-mogravimetry, vibrational and absorption spectroscopy. It was established that during heating in water and ethylene glycol, VO(HCOO)2 center dot H2O leads to vanadyl hydroxide VO(OH)2 and vanadyl glycolate VO(OCH2CH2O) being formed. When heated in air or in helium at 300 degrees C and higher, VO(HCOO)2 center dot H2O transforms into vanadium pentoxide or sesquioxide, respectively. VO(HCOO)2 center dot H2O was used as a precursor for the synthesis of nanoscale vanadium sesquioxide (with an average particle size of 50 nm), which is stable under the normal conditions and is characterized by a lower metal-insulator transition temperature than the microsized (bulk) compound. The effect of transition temperature reduction for nanoscale vanadium sesquioxide agrees with the lower value of its unit cell volume (V = 296.74 angstrom 3) as compared with that for bulk V2O3 (297.7 angstrom 3). The main factor affecting the V2O3 particle size is the annealing temperature of precursor in inert atmosphere.

The calculations of Seebeck’s coefficient, conductivity and power functions for the electron-doped SrTiO_3, BaTiO_3 and CaTiO_3 compounds have been performed depending on temperature and current carrier concentration by employing ab initio method based on the electron density functional theory, on the Frohlich’s approach for the electron-phonon interaction and on the theory of Boltzmann–Onsager for the thermoelectric properties. The calculated Seebeck’s coefficient and conductivity correspond to experimental data. It is shown that for SrTiO_3 and BaTiO_3 the dependencies of power functions on the carrier concentration have maxima in the range of (200–250) × 10^{19} cm^{–3} at any temperature, while for CaTiO_3 the maxima are typical only at temperatures below 500 K. The temperature dependencies of the power function also confirm that such carrier concentration range is favorable for achieving high values of the SrTiO_3 figure of merit, while the maximally possible carrier concentration is necessary for optimal CaTiO_3 figure of merit.

The calculations of the electron-phonon relaxation time, Seebeck coefficient and conductivity were performed for cadmium oxide with oxygen vacancies and strontium titanate doped with niobium using the first-principle methods based on the electron density functional perturbation theory, Boltzmann theory and many-body theory of electron-phonon interaction. It is shown that the calculations of relaxation time based on the many-body theory lead to significantly more accurate results on transport characteristics than in the case of the standard approximation of a constant relaxation time. It is shown that interaction with defects has a significant effect on conductivity. Keywords: cadmium oxide, strontium titanate, electronic structure, PAW method, Boltzmann theory, transport characteristics.

X-ray diffraction and thermogravimetric analysis methods were used to reveal conditions for the formation and thermal stability of cadmium oxosulfate Cd3O2SO4 synthesized by heating beta-Cd-2(OH)(2)SO4 in air. The crystal structure of Cd3O2SO4 was studied for the first time. It was shown that it is built by alternation of two types of blocks oriented parallel to the bc plane. The first type block consists of CdO8 clusters connected with each other by SO4 tetrahedra. The space between these blocks is occupied by blocks composed of tetragonal CdO5 pyramids connected with neighboring CdO8 blocks. The connections are carried out both through bridging oxygen atoms and oxygen atoms belonging to SO4 clusters. The unit cell parameters of Cd3O2SO4 are alpha=12.1762 (1) angstrom, b=6.85421 (5) angstrom, c=6.97322 (6) angstrom, beta=106.5578 (6)degrees, V=557.840 (8) angstrom(3), Z=4, sp. gr. C2/c. Vibrational spectroscopy data are in complete agreement with the crystal structure analysis. The UV-Vis-NIR spectra demonstrate the semiconducting nature of Cd3O2SO4 with the band gap of 3.45 eV stable at different heating temperatures. The energy band structure of Cd3O2SO4 has been studied by means of the first-principle pseudo-potential PAW method, VASP software package. The calculations performed point to a high probability of oxygen vacancies formation under the indicated synthesis conditions. However, the presence of vacancies does not lead to the appearance of vacancy bands inside the band gap, i.e., in accordance with experiment, they do not significantly affect the optical properties of Cd3O2SO4.

Colloidal-chemical transformations accompanying the thermal degradation of a homogeneous aqueous solution of nickel(II) ammoniac complexes are investigated by thermodynamic and kinetic methods. A competitive growth mechanism of β-Ni(OH)2 nano- and microcrystals in the solution bulk and on the solution–solid interface is proved. The weight growth rate for each of the kinetic routes is controlled by the kinetics of the first-order homogeneous reaction of $${\text{Ni}}\left( {{\text{N}}{{{\text{H}}}_{{\text{3}}}}} \right)_{6}^{{2 + }}$$ degradation. The reason for the competitive weight gain of the sol and β-Ni(OH)2 film lies in the different activation energies for $${\text{Ni}}\left( {{\text{N}}{{{\text{H}}}_{{\text{3}}}}} \right)_{6}^{{2 + }}$$ conversion to sol microcrystals (131.0 ± 27.0 kJ/mol) and to the film (94.0 ± 24.0 kJ/mol). This gives rise to the existence of two different temperature areas where sol or film growth is preferable. At 70–75°C, the sol and film growth rates are equal. An interpretation of the temperature-dependent colloidal growth mechanism of Ni(OH)2 crystals is proposed. The influence of the morphology and thickness of β-Ni(OH)2 films on their optical band gap width, photocatalytic and electrical activities is determined.

The calculations of the electron-phonon relaxation time, Seebeck coefficient and conductivity were performed for cadmium oxide with oxygen vacancies and strontium titanate doped with niobium using the first-principle methods based on the theory of electron density functional and its perturbations, Boltzmann theory and many-body theory of electron-phonon interaction. It is shown that the calculations of relaxation time based on the many-body theory lead to significantly more accurate results on transport characteristics than in the case of the standard approximation of a constant relaxation time. It is shown that interaction with defects has a significant effect on conductivity.

The thermodynamic stability borders and variations of oxygen non-stoichiometry in the perovskite-like molybdates Sr2MMoO6-delta, where M = Mn, Co, and Ni, are studied by using coulometric titration measurements. The data obtained are consistent with the reductive decomposition of Sr2NiMoO6-delta and Sr2CoMoO6-delta at small deviations of oxygen content 6-delta from its stoichiometric value. The manganite Sr2MnMoO6-delta exhibits considerably wider variations of delta at temperatures 1023 - 1223 K and oxygen pressures of 10(-8) - 10(-5) atm. The increase of the pressure results in Sr2MnMoO6-delta oxidative decomposition to Sr2MoO4 and Sr2Mn2O5 followed by oxidation of Sr2Mn2O5 to SrMnO3. The estimates based on density functional theory (DFT) are used to rationalize the results obtained.

The structural stability, thermal expansion, oxygen exchange thermodynamics, and thermochemical storage (TCS) capacity of perovskite-like Sr0.25Ca0.75MnO3-delta and Ruddlesden-Popper SrCa3Mn3O10-delta manganites are studied by the combined use of experimental techniques, thermodynamic modeling of the defect formation reactions, and energy calculations utilizing density functional theory (DFT). It is argued that conservative estimates of the storage capacity can be made by the use of the Dulong-Petit limit for high-temperature heat capacity and oxygen partial enthalpy independent of both temperature and oxygen content. The respectively recalculated literature data and the obtained results show that the thermodynamic limit for the TCS capacity (~800 kJ/kg) of Sr0.25Ca0.75MnO3-delta is one of the highest at thermal cycling within the oxygen partial pressure range of 10(-4)-0.21 atm. At the same time, the storage capacity of SrCa3Mn3O10-delta achieves only about 600 kJ/kg. The TCS cycling tests demonstrate the stability of SrCa3Mn3O10-delta while a decline in the energy storage capacity is observed for Sr0.25Ca0.75MnO3-delta. According to the EDX analysis, this effect may reflect surface degradation of Sr0.25Ca0.75MnO3-delta. The energy storage capacities of SrCa3Mn3O10-delta and Sr0.25Ca0.75MnO3-delta decrease to 510 and 560 kJ/kg, respectively, because of the rather sluggish reduction kinetics. It is concluded that further improvement of manganites as energy storage materials can be achieved using new doping strategies.

This article presents new findings obtained from the study of formation conditions, crystal structure, thermal, spectral, optical properties and electronic band structure of zinc glycolate Zn(OCH2CH2O). This compound was synthesized by heating the solutions of zinc formate Zn(HCOO)2middot2H2O in ethylene glycol (A) or in a mixture of ethylene glycol and distilled water (B). The crystal structure of Zn(OCH2CH2O) has been studied using the X-ray powder diffraction method. It is shown that the crystal structure is built via zigzag joining of [Zn4O12C8H16] tetracycles with the tetrahedrally coordinated zinc (ZnO4). Zinc atoms inside the tetracycles and the tetracycles themselves are interconnected with oxygen bridges. Complex anions OCH2CH2O2-are bonded to zinc atoms by chelation. The unit cell parameters of Zn(OCH2CH2O) are as follows: the tetragonal structure, space group I41/a (88-2), Z = 16, a = b = 11.08673(9) A, c = 11.5902(1) A, V = 1424.62(2) A3. The IR and Raman spectra of Zn(OCH2CH2O) correlate fully with the results of structural analysis. Under UV excitation, the luminescence spectra of Zn(OCH2CH2O) samples synthesized following the methods (A) and (B) are characterized by emission maxima at 460 nm (blue luminescence) and 540 nm (yellow-green luminescence), respectively. Yellow-green luminescence is due to the presence of an ad-mixture of zinc oxide nanoparticles of size 10 nm in the sample. The electron density functional method is employed to study the electronic band structure and chemical bonding in Zn(OCH2CH2O). It is shown that the 3dZn orbitals are covalently bonded to 2pO orbitals so that an octagon is formed, where the zinc atoms of four neighboring ZnO4 tetrahedrons are linked through their vertices. The feasibility of synthesizing a layered structure of Zn(OCH2CH2O) is analyzed on the basis of ab initio calculations and Voigt-Reuss-Hill theory.(c) 2022 Elsevier B.V. All rights reserved.

The calculations of Seebeck's coefficient, conductivity and power functions for the electron-doped SrTiO3, BaTiO3 and CaTiO3 compounds have been performed depending on temperature and current carrier concentration by employing ab initio method based on the electron density functional theory, on the Frohlich's approach for the electron-phonon interaction and on the theory of Boltzmann--Onsager for the thermoelectric properties. The calculated Seebeck's coefficient and conductivity correspond to experimental data. It is shown that for SrTiO3 and BaTiO3 the dependencies of power functions on the carrier concentration have maxima in the range of (200-250)·1019 cm-3 at any temperature, while for CaTiO3 the maxima are typical only at temperatures below 500 K. The temperature dependencies of the power function also confirm that such carrier concentration range is favorable for achieving high values of the SrTiO3 figure of merit, while the maximally possible carrier concentration is necessary for optimal CaTiO3 figure of merit. Keywords: Ca, Sr, Ba titanates, PAW method, electronic structure, thermoelectric properties.

The electronic energy-band structure of the PrBaCo2O5 + δ cobaltite at the oxygen content close to 5.5 are calculated by the first-principle PAW methods. The semiconductor–metal phase transition at 5 + δ = 5.5 is shown to be a result of the transition of cobalt atoms in the octahedral environment from the high-spin to low-spin state. The cause of the appearance of the metallic conduction is an increase in the energy of antibonding eg states of pyramidal cobalt atoms, and, as a result, they are at the Fermi level, thereby determining the metallic character of the system. The effect of a deviation of the oxygen content from 5.5 on the energy-band structure and the conductivity is studied. The semiconductor–metal transition is shown can be observed only in a narrow range of the values of 5 + δ lower 5.5.

The ab initio calculated defect formation energies are used for assessment of high-temperature thermodynamic functions that govern the appearance of oxygen vacancies in PrBaCo2-xMxO6-δ, where M = Fe, Co, Ni and Cu. The free energy of oxygen vacancy formation is shown to depend on the dopant and total oxygen content in the cobaltite. The experimentally observed trend for the oxygen vacancy concentration to increase with the atomic number of 3d dopants from Fe to Cu is explained as a result of the decrease of bond strength. The preferable location of oxygen vacancies near impurity atoms is accompanied by an anisotropic redistribution of electronic charge density. The most pronounced development of this effect in the case of iron doping leads to a low probability of tetrahedrally coordinated iron to exist in the layered cobaltites. It is shown that the calculated enthalpies of defect formation satisfactorily explain the experimentally observed changes of oxygen non-stoichiometry in the doped cobaltite. The energy barriers for oxygen jumps are found to vary only weakly at the doping thus suggesting rather insignificant dependence of the oxygen ion conductivity on 3d dopant nature. The earlier findings and results in the present work are indicative of promising properties combination in PrBaCo2-xNixO6-δ for the application as an electrode material in IT-SOFCs.

The computational modeling within a density functional theory was applied for simulations of electronic spectra and calculations of structural and energy characteristics of the cubic double perovskite oxides Sr2Mg1-xNixMoO6-delta, where x = 0, 0.5, and 1. The oxygen stoichiometric molybdates are antiferromagnetic semiconductors with an energy gap near 2 eV. The energy-based arguments show that anti-site cation disorder may contribute to the structural stability of the molybdates. It is found that nickel doping is favorable for mitigated chemical expansion. The replacement of magnesium by nickel is accompanied by the contribution of Ni3d states to the valence band while leaving hybrid Mo4d-O2p states in the conduction band virtually unchanged. It is shown that the compounds under study are thermodynamically unstable in heavily reducing conditions which is confirmed by experimental results. The appearance of oxygen deficiency in Sr2Mg1-xNixMoO6-delta results in the formation of oxygen vacancy associated donor states near the bottom of the conduction band and the transition from the intrinsic to degenerate semiconductor. It is suggested that the influence of nickel dopants on the energy and density of the donor states may help to explain variations of the conducting properties with doping level. (C) 2021 Elsevier B.V. All rights reserved.

We apply mathematical modelling to study heat transfer processes during fire refining of blister copper in a ladle-furnace unit. A ladle-furnace unit was designed to test the refining technology using bottom blowing in a bubble mode by gaseous reducing agents (hydrocarbons) and an oxidiser. Mathematical modelling allows the properties of a real process to be described based on mathematical formalisation of physical laws and regularities. It was proposed to use gaseous reducing agents, rather than expensive residual fuel, as a liquid-reducing agent. The use of gaseous reducing agents in the bottom blowing mode produces higher technical and economic indicators of the process. In addition, some technological operations were transferred directly to the ladle, thereby eliminating the need for re-melting and heating of refined copper. One of the identified problems was the need to maintain the predetermined thermal regime, which provides the very possibility of both performing refining operations and introducing a gaseous reagent (determining the hydro-gas-dynamic parameters) into the melt during bottom blowing. An original method for considering the thermal effects of chemical reactions in mathematical models was presented using an example of exothermic reactions during oxidative refining. The use of two different methods of analysis allowed a comprehensive assessment of the influence of the main exothermic reactions on the thermal regime of the refining process. The presented mathematical models can be used for determining the specific effect of various technological parameters (composition and fuel consumption, temperature and degree of blast enrichment, lining design, etc.) on the dynamics of changes in the temperature field of the melt and the technical and economic parameters of melting as a whole.