In the present study, the temperature dependence of thermal expansion of iron-gallium borates Fe1–xGaxBO3—trigonal antiferromagnets with weak ferromagnetism—has been studied using X-ray diffraction analysis in the temperature range of 240–400 K. It has been found that the nature of thermal expansion changes significantly upon passing through the Néel point. It has been shown that, below the magnetic phase transition temperature, changes in the crystal lattice parameters are influenced by magnetostrictive deformations, as well as the temperature itself. Using the developed theoretical model, the temperature dependences of magnetoelastic constants for diamagnetically diluted Fe1–xGaxBO3 single crystals have been determined for the first time.
The mechanochemical synthesis and study of the structure of hydroxyapatite compounds with the substitution of calcium(II) cation for bismuth(III) cation has been carried out. Bismuth oxide and bismuth nitrate pentahydrate were used as a source of bismuth. It has been shown for the first time that, when using bismuth nitrate, the synthesis product contains a nitrate group, resulting in a multiphase system, whereas when using bismuth oxide, a monophase material with an apatite structure is synthesized, where the degree of substitution of calcium by bismuth can be increased up to 40 mol
Ab initio quantum-mechanical modeling has been employed to investigate the crystal structure of a bulk crystal of triclinic tungsten disulfide (WS2). The factors that influence the accuracy of representation of the triclinic phase have been established. The tetramerization process, defined as the formation of rhomboid metallic clusters of tungsten, observed irrespective of the approximation used, has been described. The destabilizing effect of the Peierls lattice distortion in the triclinic WS2, caused by a deficiency of valence electrons at tungsten, leading to the structural collapse of this phase, is revealed. The decisive role of isoelectronicity for isostructural transition metal dichalcogenides in determining the stability of bulk crystals is demonstrated using triclinic WS2 and ReS2 as an example.
The phase diagram of the ternary reciprocal system K,La||Cl,WO4 was studied using differential thermal, X-ray diffraction, and elemental analysis. Triangulation of the system into stable simplices was performed and confirmed by differential thermal analysis. The coordinates of binary eutectics in stable triangulating sections, four ternary eutectics, and one ternary peritectic in the K,La||Cl,WO4 ternary reciprocal system were determined. It was established that the K,La||Cl,WO4 system is irreversible, with exchange and complexation reactions occurring equally. Based on the stable and unstable sections revealed by differential thermal analysis (DTA) using the conversion method, the main chemical exchange reactions and the formation of binary salts in the K,La||Cl,WO4 system were determined. The possibility of synthesizing lanthanum tungstate in ionic melts of the K,La||Cl,WO4 system via an exchange reaction between salts of the unstable diagonal was revealed. The results of the chemical synthesis were confirmed by X-ray diffraction and elemental analysis.
A mixed cerium(IV)–zirconium(IV) phosphate was obtained for the first time under hydrothermal conditions. Based on X-ray diffraction, energy-dispersive X-ray spectroscopy analysis, and IR spectroscopy data, it was assigned the composition H2K2CeZr(PO4)4·xH2O. Using the crystallographic parameters of isostructural double cerium(IV) phosphates from X-ray powder diffraction data, the unit cell parameters of H2K2CeZr(PO4)4·xH2O were calculated: a = 6.6727(2) Å, b = 6.7462(2) Å, c = 17.3705(9) Å, V = 781.94(5), Z = 4 (space group Imma). The thermal behavior of the obtained compound was studied, and phase analysis of the thermolysis products was performed at each stage of mass loss. It was found that, for the initial structure, the decomposition process begins at temperatures below 500°C, and the final products at 1000°C are CePO4, KZr2(PO4)3, and K2CeZr(PO4)3.
The axial coordination of base molecules and ions on metalloporphyrins is a relevant approach to the preparation of molecular and structured materials for optoelectronics, catalysis, and biomimetics. In this work, we present the results of a comparative analysis of the thermodynamics and spectroscopy of the axial coordination of pyridine (Py), imidazole (Im), 1-methylimidazole (MeIm), 4-(1H-imidazol-1-yl)benzaldehyde (ImC6H4CHO), and N-methyl-2-(1H-imidazol-1-yl)-phenyl-3,4-fullero[60]pyrrolidine (ImC60) on manganese(III) porphyrins with different sets of substituents in the macrocycle depending on the reaction medium, in order to further develop the theory and optimization of the axial coordination processes. The influence of these factors on the stoichiometry of complexation and the stability of the axial complexes obtained is determined. The picture of the influence of the chemical structure and, therefore, the basicity of the axial ligand is complicated by the manifestation of steric effects during complex formation, while chloroform and toluene, as media for the reaction, have a very different effect on the equilibrium constant in a series of studied bases added to (Cl)MnOEP.
Single crystals of manganese arsenide and the MnAs0.93P0.07 solid solution based on it have been synthesized using the Stockbargar–Bridgman method. The crystal structure and composition of the samples have been determined using X-ray diffraction and X-ray spectral analysis. Calculations of the electronic structure and interatomic exchange integrals in the MnAs0.93P0.07 solid solution and pure MnAs revealed minor differences in the magnetic states of the atoms and the total energy of the crystal. The introduction of phosphorus led to compression of the manganese arsenide crystal lattice and a decrease in the magnetostructural phase transition temperature to 285 K. The maximum change in magnetic entropy for MnAs0.93P0.07 with a magnetic field changing from 0 to 8 T was 36 J/(kg K).
O’Keeffe (1973), using PbF2 as an example, proposed to consider the presence of a low melting entropy in fluoride compounds as a criterion for high anionic conductivity: ΔSfus < 20 J/(mol K). To test this criterion, data on entropy ΔSfus were analyzed for 38 fluorides (1 ≤ n ≤ 4) with a ionic bond and different types of crystal structure. It has been shown that a low entropy of melting is a necessary but not sufficient condition for high anionic conductivity in fluoride crystals. A low ΔSfus value is typically a consequence of the existence of polymorphic or diffuse (Faraday) transitions in fluoride compounds. Structural types of fluorides with high ionic conductivity have been identified, including the highly symmetric structures of fluorite CaF2, tysonite LaF3, and the α-modification of YF3. The results obtained can be used to search for, model, and synthesize new fluoride solid electrolytes.
The precipitation of basic bismuth nitrate by adding a bismuth nitrate solution to an aqueous ammonia solution was studied using X-ray diffraction, chemical analysis, differential thermal analysis, IR spectroscopy, BET, and electron microscopy. It was found that, at pH 10–11 and 22 ± 2°C, basic bismuth nitrate of the composition Bi6O7(OH)2(NO3)2⋅2H2O precipitates, and, upon treatment with water at 90 ± 5°C, a compound of the composition Bi6O7(OH)2(NO3)2 is formed. These basic bismuth nitrates, unlike the compound [Bi6O5(OH)3](NO3)5⋅3H2О used in engineering and medicine, contain fewer nitrate ions, are insoluble in water, and are finely crystalline.
The reaction between [ZrF4(dmso)2] and monodentate phosphoryl-containing ligand 1-Ac-2-[Ph2P(O)]C6H10 (L'), which contains two asymmetric carbon atoms and is a racemic mixture of the two enantiomers (1R,2S) and (1S,2R), was studied in a Me2SO–СН2Сl2 mixture using 19F1H NMR spectroscopy. Based on the analysis of the 19F1H NMR spectra and taking into account the concept of heterotopy of organic compounds, the resonance signals were assigned, and a conclusion was drawn regarding the formation of the racemic and meso diastereomers of the octahedral zirconium complex cis-[ ZrF_4L_2^' ]. For the first time, the value of the spin–spin coupling constant between fluorine atoms in trans position to each other was determined for zirconium fluoride complexes JF'F” = 205 Hz.
Microcrystalline single-phase mixed lanthanum–samarium–gadolinium zirconate (LaSmGd)2/3Zr2O7 with a pyrochlore structure was prepared. The heat capacity of (LaSmGd)2/3Zr2O7 was measured by relaxation, adiabatic, and differential scanning calorimetry in the temperature range of 2–1865 K. The obtained data set on the heat capacity of (LaSmGd)2/3Zr2O7 was smoothed using various methods and used to calculate the thermodynamic functions of (LaSmGd)2/3Zr2O7.
The mechanism of adsorption of WO_4^2 - tungsten ions on Fe3O4 magnetite nanoparticles from aqueous solutions at pH 5 was studied for the first time. Integrated studies of Fe3O4 nanoparticles after sorption of WO_4^2 - ions from aqueous solutions were carried out using electron microscopy, energy dispersive X-ray spectrometry, microcalorimetry, and X-ray photoelectron and IR spectroscopy. The presence of tungsten on the surface of magnetite particles after sorption was established. Thermodynamic parameters were determined from the approximation of adsorption isotherms at temperatures of 20, 30, 40°C using the Langmuir and Freundlich equations. The adsorption process was found to be exothermic. The standard adsorption enthalpy Δ H^∘ = −7.07 kJ/mol was comparable with the molar interaction enthalpy derived from direct microcalorimetric measurements ( Δ H^∘ = −10.17 kJ/mol). Relying on the thermodynamic parameters and IR and X-ray photoelectron spectroscopy data, it was assumed that adsorption was predominantly implemented via physical adsorption mechanism involving electrostatic interaction between WO_4^2 - and the Fe3O4 surface.
NiFe2O4 nanoparticles with average size of 17 ± 2 nm (saturation magnetization 32 emu/g, coercive force 112 Oe) have been synthesized by the joint alkaline precipitation of nickel(II) and iron(II) ions followed by oxidation with atmospheric oxygen. It has been found that, in addition to the ferrospinel phase (a = 8.329 ± 0.001 Å), the product contains 9.6 wt
Variants of development of digital twins of the isobaric phase diagram of the ternary system LiCl–UCl3–KCl in the form of computer 3D models are considered. Three variants of the phase diagram model are proposed, depending on the number of binary compounds in the UCl3–KCl system. The first variant accounts for the formation of one binary compound K2UCl5, wherein the ternary system is triangulated by the quasi-binary section LiCl–K2UCl5 into two eutectic subsystems. The second variant considers the formation of three compounds: K2UCl5, K3UCl6, and KU2Cl7. The system is triangulated by the LiCl–K2UCl5 section into two subsystems, in each of which the eutectic invariant transformation is preceded by the decomposition of binary compounds. In a third, hypothetical variant, based on the formation of two compounds, K2UCl5 and K3UCl6, the occurrence of three invariant transformations is assumed. The models are constructed across the entire temperature range and account for both the high-temperature phase regions with a melt and the subsolidus regions. The presented digital twins are not only a tool for further study of the LiCl–UCl3–KCl system but also provide predictive opportunities for experimental investigation, depending on the chosen variant of the UCl3–KCl system structure.
Using a flash evaporation method from a precursor synthesized by a vacuum-pulse method, Mn1.1Sb films with different thicknesses of 20, 60, 120, 240, and 800 nm were obtained on glass substrates. According to XRD data, the composition and crystal structure of the films corresponded to the original Mn1.1Sb precursor. The results of magnetic measurements indicated a dependence of the magnetic properties on the film thickness. As the thickness increased, the magnetic properties of the films approached those of the precursor. It was found that the ponderomotive force of Mn1.1Sb films sharply increased in the ferromagnetic state, from 40 mg for thin films of 20–60 nm to 230 mg for films with a thickness of 800 nm. Upon heating the 20- to 60-nm films to 750 K and subsequent cooling to liquid nitrogen temperature, the magnetization values corresponded to paramagnetic levels; these partially transitioned to ferrimagnetic values in films thicker than 100 nm. A model considering the influence of surface van der Waals forces, particularly absorption during heating–cooling cycles, on the transition from ferromagnetic to paramagnetic states in Mn1.1Sb films of various thicknesses is discussed.
A method for manufacturing Ba0.55La0.45F2.45 nanopowders by mixing reagents in a microreactor with counter-current intensively swirled flows (MRISF-CC-1) was investigated. The phase composition of the product was influenced by the concentrations of the initial materials and the flow rates of their solutions. The concentrations of the reagents and solution flow rates providing the production of single-phase solid solutions were determined: Cnitrate = 0.15 mol/L and C_NH_4F = 0.40 mol/L at solution flow rates from 1.1 to 3.5 L/min; Cnitrate = 0.30 mol/L and C_NH_4F = 0.80 mol/L at solution flow rates of 3.5 L/min; and Cnitrate = 0.45 mol/L and C_NH_4F = 1.2 mol/L at solution flow rates of 1.1 L/min. The compositions of single-phase products corresponded to the as-batch compositions, and nanoparticles had a high degree of homogeneity. The developed method can be scaled up to manufacture large batches of nanoscale particles.
Porous anodic alumina (por-Al2O3) is of great scientific interest due to its potential for use in nanoelectronics and nanosensors. Por-Al2O3 was formed by anodic oxidation of aluminum foil in an etidronic acid-based electrolyte at various temperatures (T = 5–40°C) and represents arrays of ordered nanopores with diameters ranging from 80 to 110 nm. Using EPR spectroscopy, oxygen vacancies (F+ centers) were detected in all samples, and their concentrations were calculated. Photoluminescence (PL) of por-Al2O3 consists of two bands: at λ1 = 454 nm and λ2 = 585 nm (T = 5–25°C) and at λ1 = 465 nm and λ2 = 635 nm (T = 40°C). It was established that F+ centers are responsible for the PL band at λ1. It was discovered that the contribution to the PL at λ2 comes from nonparamagnetic defects formed as a result of the incorporation of molecular fragments from the electrolyte into the sample structure during anodization. The mechanisms of PL in porous Al2O3 synthesized in etidronic acid were elucidated for the first time, and it was shown that the electrolyte temperature can be used to control the defect concentration and PL intensity.
The literature data on the standard enthalpies of formation of a number of crystalline rare-earth trifluorides are considered. These data are obtained mainly by two methods: EMF and FC, but there are some discrepancies between them. The reasons for the discrepancy in the data may be experimental difficulties, such as the formation of high-temperature hardened modifications of trifluorides during the combustion of metals in a fluorine atmosphere. In the EMF method, the presence of impurities in the samples under study can lead to additional potential-forming reactions, the thermodynamic characteristics of which have been calculated. In addition, the influence of the surface state at the phase boundaries, including the formation of an oxide film, and the composition of the gas phase have been considered. A new set of standard enthalpies of formation for crystalline rare-earth trifluorides have been recommended.
The decomposition of cobalt acetylacetonate in a mixture with oxygen was studied using a thermodynamic approach to construct chemical vapor deposition diagrams. The calculations were performed using the database and software of the Electronic Materials Properties Database. The process was assumed to proceed in a quasi-equilibrium regime on a chemically inert substrate in the reactor temperature range of 473–1073 K at a pressure of 1.333 or 101 325 Pa. Calculations indicate that MOCVD processes can produce films containing, depending on the conditions, cobalt and cobalt oxides CoO and Co3O4, as well as various complexes of these phases, including mixtures with carbon. The results of this study may be useful for producing cobalt-containing coatings.
