This paper describes the phase composition, morphological, chemical, and crystallographic properties of silicide phases in Cr–Fe–Si alloy ingots obtained through directional solidification, both before and after annealing. The samples had a general formula CrxFe _1-x Si2 with x = 0.1, 0.2, 0.3, and 0.4. Characterization of samples using various techniques (powder X-ray diffraction, transmission and scanning electron microscopy with electron backscatter diffraction, energy dispersive X-ray spectroscopy) showed that the use of a higher Cr concentration (x = 0.3 and 0.4) leads to suppression of the formation of the ε-FeSi metallic cubic phase. The amount of Cr involved in the substitution of Fe in α-, β-, and ε-Fe silicides does not depend on the nominal Cr concentration introduced into initial melts. Unlike the samples that underwent the free crystallization process, neither pure Si nor some other silicides (for example, Cr5Si3) or pure Si were found in the ingots of directional crystallization. The orientation relationships between the phases and the directions of growth of precipitates before and after annealing were established. Electrical conductivity, Seebeck coefficient and power factor were determined for the as grown and annealed ingots.

The mass synthesis of heavy REE-based beta-NaY0.5F4:Gd0.5@beta-NaLnF4:Yb/X @beta-Na(Y, Lu)F4 (Ln = Y, Yb, Lu; X = Er, Tm) nanoparticles via nanoseed-mediated heterogeneous crystallization, ensuring the fabrication of objects with a required morphology, crystal structure and photoluminescent properties, is presented. The optimal experimental parameters (x(Gd3+) = 0.5 and t = 15 min) for the synthesis of ultrafine (3-4 nm) hexagonal beta-NaY1-& khcy;F4:Gd & khcy; (x = 0 divided by 0.5) nanoseeds by high-temperature co-precipitation of acetate precursors in organic solvents were determined. The heterogeneous crystallization method was successfully applied to produce monodisperse beta-NaY0.5F4:Gd0.5@beta-NaLnF4:Yb/X@beta-Na(Y, Lu)F4 (Ln = Y, Yb, Lu; X = Er, Tm) nanoparticles with the "nanoseed @ active core @ inert shell" structure in the size range from 10 to 60 nm, which was confirmed by XRD and TEM analysis. Nanoparticles with the active beta-NaYbF4:Tm core demonstrate the best photoluminescence performance in the UV (lambda = 364 nm) and visible (lambda = 452 nm) spectral regions, exceeding the values of lutetium (by 3.4 and 3.9 times) and yttrium (by 7.6 and 9.3 times) counterparts. The heavy REE-based beta-NaY0.5F4:Gd0.5@beta-Na(Yb, Lu)F4:Yb/Er@beta-NaLuF4 nanoparticles exhibit the most efficient up- and downconversion photoluminescence in the visible and NIR ranges upon excitation at lambda = 978 nm. The proposed method was utilized for large-scale synthesis of heavy REE-based beta-NaY0.5F4:Gd0.5@beta-NaYbF4:Tm@beta-NaLuF4 nanoparticles with optimized cationic composition up to 80 g per production cycle which will facilitate their practical implementation in photonics and biotechnology.

LiRF4 (R = Y, Yb, Lu) nanoparticles (NPs), co-doped by Yb3+/Er3+ and Yb3+/Tm3+ ions, have been synthesized by high-temperature coprecipitation method. The influence of the molar ratio of precursors and the cation composition of matrices on the sizes and morphology of particles is investigated. The method of heterogeneous crystallization of these compounds using LiYF4 nanoseeds is optimized, which opens opportunities to controlled synthesis of LiRF4 NPs with required characteristics. Among the objects studied, LiYF4@LiYbF4:Tm3+@LiYF4 NPs demonstrate the most intense anti-Stokes photoluminescence in the UV (λ = 362 nm) and blue (λ = 450 nm) ranges, which exceeds the corresponding characteristics for β-NaYF4:Yb3+/Tm3+@NaYF4 particles. LiYF4@LiLuF4:Yb3+/Er3+@LiYF4 NPs are the most efficient IR converters in the (λ = 1530 nm) among the investigated isostructural matrices; their spectral-luminescence characteristics are close to those of the β-NaYF4:Yb3+/Er3+@NaYF4 compound with the equivalent degree of codoping. The results obtained give possibilities to consider LiYF4@LiYbF4:Tm3+@LiYF4 and LiYF4@LiLuF4:Yb3+/Er3+@LiYF4 NPs as a real alternative to the most widely used phosphors based on hexa-gonal β-NaYF4 host for photonics and biotechnology applications.

Nanoparticles of LiRF4 (R = Y, Yb, Lu), activated with Yb3+/Er3+ and Yb3+/Tm3+ ions, were obtained by the high-temperature co-precipitation method. The influence of the precursor molar ratio and the cationic composition of matrices on their dimensionality and morphology was studied. A method for the heterogeneous crystallization of these compounds using LiYF4 nanoseeds was optimized, which opens up opportunities for controlled synthesis of LiRF4 nanoparticles with controllable characteristics. Among the studied objects, LiYF4@LiYbF4:Tm3+@LiYF4 nanoparticles demonstrate the most intense anti-Stokes photoluminescence in the UV (λ = 362 nm) and blue (λ = 450 nm) ranges, exceeding similar indicators for β-NaYF4:Yb3+/Tm3+@NaYF4 particles. LiYF4@LiLuF4:Yb3+/Er3+@LiYF4 nanoparticles are the most efficient converters of IR radiation in the λ = 1530 nm range among the investigated isostructural matrices and exhibit similar spectral-luminescent properties to the β-NaYF4:Yb3+/Er3+@NaYF4 compound with an equivalent degree of codoping. The obtained results allow considering LiYF4@LiYbF4:Tm3+@LiYF4 and LiYF4@LiLuF4:Yb3+/Er3+@LiYF4 nanoparticles as a real alternative to the most widely used phosphors based on the hexagonal matrix β-NaYF4 for photonics and biotechnology applications.

Solid electrolyte nanoceramics Pr _1-y SryF _3-y (y = 0.03, sp. gr. P3̅c1 ) were obtained by high-energy milling of melt-grown crystals, followed by cold pressing. The phase composition, microstructure, morphology, and electrical properties of nanoceramics were studied using X-ray diffraction analysis, electron microscopy, and impedance spectroscopy. The room-temperature conductivity of the synthesized Pr0.97Sr0.03F2.97 nanoceramics (σcer = 1.7 × 10−7 S/cm) is much lower than the conductivity of the original single crystal (σcrys = 4.0 × 10−4 S/cm), which is due to its low ( 75 _1-y SryF _3-y nanopowder make it possible to process single-phase highly conductive ceramics. The proposed method for the synthesis of ceramic fluoride nanomaterials as a technological form of solid electrolytes is a promising way for further developments in the field of creating fluorine-ion current sources and fluorine gas sensors.

In this study, an approach for the facile and versatile synthesis of multicomponent superionic nanofluorides is proposed. The results of synthesis optimization of the tysonite-type LaF3 and La0.95Sr0.05F2.95 (sp. gr. P (3) over bar c1) nanopowders with a particle size up to 100 nm by the trifluoroacetate precursors thermal decomposition under various conditions (dynamic vacuum and ambient atmosphere) are presented. The produced samples are characterized by X-ray diffraction, electron microscopy, and differential scanning calorimetry. Decarbonization annealing of the initial nanopowders in air at 773 K is urgent for the effective elimination of amorphous carbon formed as a result of the metal-organic precursors decomposition. The nanoceramics were pressed to a theoretical density of 75-80 % and their ion-conducting properties were measured using impedance spectroscopy. The conductivity of decarbonized La0.95Sr0.05F2.95 composition, obtained in a dynamic vacuum, is 1 x 10(-3) S/cm at 500 K, which exceeds the performance of undoped LaF3 ceramics by approximately 60 times. The conductive properties of nanoceramics, produced from decarbonized vacuum-synthesized powders, are 5 times higher (1 x 10(-3) Sm/cm) compared to mechanochemically fabricated ones. Air-synthesized (773 K) La0.95Sr0.05F2.95 ceramics are conducted significantly worse, although no traces of pyrohydrolysis were detected. Thus, the precursors thermal decomposition method opens up great prospects for the advanced production of ion-conducting nanomaterials based on multicomponent fluoride compounds for solid electrolyte design.

Thin manganese silicide films were obtained on mica by magnetron sputtering from targets of three types. The microstructure and elemental composition of the targets and films were studied by scanning electron microscopy and reflection electron diffraction. The phase composition and structure of the films over depth (cuts) were controlled by scanning and transmission electron microscopy. It has been shown that, when depositing films from poly- and single-crystal targets of higher manganese silicide, in contrast to a target from sintered Мn and Si powders, one can obtain polycrystalline films of higher manganese silicide of the Mn4Si7 composition after subsequent 1-h annealing at a temperature of 800 K and a pressure of 10–3 Pa.

Hot pressing of a Si single crystal in the bulk of electrolytic Cr powder at 1213 K, with subsequent annealing in air, leads to the formation of an intermediate polycrystalline silicide layer at the interface between the initial components. The phase composition and microstructure of the transition layer and its vicinity were investigated by scanning electron microscopy, X-ray energy-dispersive microanalysis, and electron backscatter diffraction. The transition layer has a crystal structure of the hexagonal phase of chromium disilicide (sp. gr. P 6 2 22). An additional annealing up to 120 h leads to insignificant recrystallization of small grains into larger ones.

The study presents a comparative analysis of the structures of dried films of bacterial cellulose (BC) produced by bacteria of the Gluconacetobacter hansenii GH-1/2008 strain under static conditions of cultivation on nutrient media with different carbon sources, such as glucose, sucrose, maltose, fructose, and lactose. It was found that the supramolecular structure of the films is a three-dimensional network composed of orientationally ordered microfibrils with an average diameter from 30 to 60 nm, which consist of crystalline and amorphous regions. An analysis of the powder X-ray diffraction patterns demonstrated that the crystalline regions of microfibrils are formed by cellulose I. Depending on the composition of the nutrient medium, the degree of crystallinity of the films varies in the range from ~20 to 90%. It was found that, regardless of the carbon source, the top and bottom surfaces of BC films have different microstructures defined by static conditions of cultivation. Thus, the top surface of gel films contains pores with a diameter of up to 500 nm, whereas a wider pore size distribution (up to 600 nm) is observed on the bottom surface. The difference between the average pore sizes on the top and bottom surfaces varies from 95 to 180 nm and from 100 to 200 nm, respectively. The measurements of the mechanical properties of the films showed that the films produced by the cultivation on media containing fructose and sucrose have the maximum strength, whereas the films produced using lactose and maltose have the minimum strength. The data on the BC productivity of the GH-1/2008 strain were obtained.

Soft viscoelastic nanocomposites based on entangled linear wormlike micelles of cationic surfactant eru-cyl bis(hydroxyethyl)methylammonium chloride and aluminosilicate clay halloysite nanotubes with a surface charge triggered by pH were prepared and studied by rheometry, n-potential measurements, thermogravimetric analysis, and cryo-TEM. It was shown that the nanotubes induce an increase of viscos-ity, which can be attributed to their incorporation into the network of entangled wormlike surfactant micelles via the attachment of micellar endcaps to the surfactant double layer on the surface of the nan-otubes. The junctions between the micelles and the nanotubes were visualized by cryo-TEM. The soft nanocomposites demonstrate peculiar flow curves with two shear thinning regions and a plateau between them. The two slopes were attributed to the orientation of the nanotubes (at lower shear rates) and then of the micellar worms (at higher shear rates) along the direction of flow. The intermediate vis-cosity plateau may represent a stable flow when all nanotubes are oriented, while the micellar worms are not. The nanocomposite system was shown to be pH responsive. Its viscosity increases by 30 times with increasing pH from 4 to 9, which was explained by increasing surface charge of the nanotubes favoring the interaction with oppositely charged WLMs. Such soft materials with easily triggered rheological prop-erties are very promising for various applications.(c) 2022 Elsevier B.V. All rights reserved.

The phase composition, microstructure, and interphase interfaces of the disordered CrSi2-FeSi2 solid solution obtained by spontaneous crystallization (before and after annealing) have been investigated by scanning, transmission electron microscopy, electron diffraction, and X-ray energy dispersive spectrometry. The as-grown samples contained the phases of CrSi2 with the P6422 hexagonal structure and FeSi2 with the P4/mmm tetragonal structure. Annealing of the samples led to the phase transformation of tetragonal FeSi2 into the orthorhombic modification Cmca. Precipitates of cubic iron monosilicide FeSi with space group P213, nano-precipitates of Si and silicon silicide Cr5Si3 with a tetragonal structure I4/mcm were observed inside the FeSi2 grains. Impurities of interstitial Cr atoms with a concentration up to 2.0 at% are found in iron (di)silicides grains in all samples. The structure of the CrSi2 phase remains unchanged after annealing; the concentration of impurity iron atoms is about 0.7 at%. Orientation relationships between the crystal lattices of the phases are established and strains due to the mismatch of the crystal lattices are determined.

Branched polyacrylonitrile has been synthesized via anionic polymerization with the 1,4-diazabicyclo[2.2.2]octane–ethylene oxide initiating system. The degree of branching has been determined by means of NMR spectroscopy and indirectly confirmed by viscometry of the dilute solutions. Solutions of binary mixtures of the branched PAN with the industrial linear polymer in dimethyl sulfoxide with different ratio of the components have been prepared; their rheological behavior has been investigated. It has been shown that the introduction of the branched polymer in a solution of linear PAN allows significant decrease in the mixed solutions viscosity at equal total fraction of the polymer. The addition of branched PAN in a solution of the linear PAN has increased the total concentration of the polymer in the system favoring the increase in the viscosity of the mixed solution, but the viscosity has been significantly lower than this of the equally concentrated solution of the linear polymer. Investigation of the frequency dependences of the components of complex shear modulus of these solutions has revealed that the increase in the viscoelastic properties is mainly due to the increase in the elasticity modulus. Exponent of the frequency dependence of the loss modulus in the terminal zone has not been changed, whereas this of the elasticity modulus has been decreased to 0.4 over the entire range of the ratio between the branched and linear PAN. The specific relaxation time has been decreased with the increase in the fraction of linear PAN. Thermal behavior of linear and branched PAN has been investigated by means of DSC. The performed study has revealed the possibility of preparation of the mixed films and fibers based on linear and branched polyacrylonitrile.

The phase composition, microstructure, and interphase interfaces of the disordered CrSi2-FeSi2 solid solution obtained by spontaneous crystallization (before and after annealing) have been investigated by scanning, transmission electron microscopy, electron diffraction, and X-ray energy dispersive spectrometry. The as-grown samples contained the phases of CrSi2 with the P6422 hexagonal structure and FeSi2 with the P4/mmm tetragonal structure. Annealing of the samples led to the phase transformation of tetragonal FeSi2 into the orthorhombic modification Cmca. Precipitates of cubic iron monosilicide FeSi with space group P213, nano-precipitates of Si and silicon silicide Cr5Si3 with a tetragonal structure I4/mcm were observed inside the FeSi2 grains. Impurities of interstitial Cr atoms with a concentration up to 2.0 at% are found in iron (di)silicides grains in all samples. The structure of the CrSi2 phase remains unchanged after annealing; the concentration of impurity iron atoms is about 0.7 at%. Orientation relationships between the crystal lattices of the phases are established and strains due to the mismatch of the crystal lattices are determined. Keywords: chromium disilicide, iron disilicide, interphase interfaces, transmission electron microscopy, energy dispersive X-ray spectrometry.

The structural features of the poly(N-vinylpyrrolidone)–La(NO3)3 ⋅ 6H2O composite hydrogel were studied by scanning and transmission electron microscopy. The La(NO3)3 ⋅ 6H2O powder, which was used for the preparation of the composite, was shown to contain also hexagonal prismatic crystals with an edge of ~1.8 µm and needle-like crystals with a width of 1 µm and a length of up to 50 µm. During the composite formation, the La(NO3)3 ⋅ 6H2O powder is hydrolyzed in the bulk of the hydrogel, and lanthanum is uniformly distributed in the matrix. However, flower-like structures up to 20 µm in diameter are formed on the surface of the composite. These structures are composed of lanthanum- and oxygen-rich nanorods. Transmission electron microscopy studies of dried hydrogels showed that the composite hydrogel and flower-like inclusions have an amorphous structure.

Evolution of the morphology of cellulose solutions in N-methylmorpholine-N-oxide during coagulation with a “soft” coagulant, isobutyl alcohol, at different temperatures is considered. Using optical interferometry and transmitted and scanning electron microscopy the mechanism of phase separation of the system to form a polymer phase is studied depending on the temperature of alcohol. It is shown that, in the case of a room temperature coagulant, a heterogeneous film with a droplet texture enlarging over thickness appears along the precipitation front. At a high temperature of alcohol the coagulation of the solution occurs in two stages. At the first stage the penetration of the coagulant into the jet of spinning solution leading to the formation of vacuoles occurs. The phase separation of the solution proceeds within the vacuoles as microreactors to form a polymer-concentrated shell and a polymer-diluted phase in the vacuole cavity. At the second stage the coagulant diffuses through the vacuole shell into the bulk of the solution and causes its uniform coagulation. The process of vacuole formation is visualized. The transverse cleavage of the film is analyzed by energy dispersive X-ray spectroscopy. The difference in the content of C, N, and O atoms on the walls of vacuoles and in the region of a film with a uniform cellular morphology is established.

Rheometry, small-angle neutron scattering, and cryo-transmission electron microscopy were combined to investigate the structure and properties of mixed wormlike micelles (WLMs) of zwitterionic (oleylamidopropyl dimethyl betaine) and anionic (sodium dodecylsulfate) surfactants. This system demonstrates the formation of giant linear long-lived WLMs, which even at extremely low surfactant concentration reach a sufficient length to entangle with each other and form a three-dimensional temporally persistent network. Stability of these micelles can be due to electrostatic attraction between the headgroups of the anionic and zwitterionic surfactants and favorable volume/length hydrophobic ratio in the surfactant mixture. Heating of these systems leads to the transition of temporally persistent network with predominantly elastic properties into transient network exhibiting viscoelasticity, which is due to the shortening of long-lived WLMs. At increasing surfactant concentration, the long-lived linear micelles transform into fast-breaking branched micelles, which is due to the screening of electrostatic interactions by salt released from the dissociated surfactant molecules. The transition results in the drop of viscosity and approaches the system to the behavior of Maxwell fluid with a single relaxation time. The observed structural transitions strongly affecting the rheological properties can be exploited in various applications of zwitterionic surfactants. (C) 2021 Elsevier B.V. All rights reserved.