Borate glasses with a high content of lanthanum oxide are promising materials for the design of high refraction index optical media, although the fine tuning of their properties requires a detailed understanding of their atomic structure. We consider glasses of two systems: La2O3-xNb2O5-(1-x)B2O3 and La2O3-xTa2O5-(1-x)B2O3 with the refraction index varied approximately from 1.7 to 2.0. The local atomic structure of metal atoms is studied by Xray absorption fine structure (XAFS) spectroscopy: the environment of La atoms is probed by La L3-edge XANES, and of Ta atoms - by Ta L3-edge EXAFS. We propose a new approach for the analysis of La L3-XANES which allows a smooth variation of the coordination number N in addition to a commonly used variation of interatomic distances R. The proposed "N,R-fit" approach is verified by the application of a more commonly used method "FitIt" for a quantitative analysis of La L3-XANES spectra. The results of the analysis show that the number of nearest oxygen neighbors of La atoms increases with the increase of M2O5 (M = Ta, Nb) content achieved by the decrease of B2O3 content. On the contrary, the number of nearest oxygen neighbors of M = Ta, Nb atoms is approximately constant and changes occur in the next coordination shells. According to the results of EXAFS analysis, the second and third coordination shells are different for Ta and Nb despite their chemical similarity. And this difference correlates with the discrepancy in maximal content of metal oxide in the glass composition - 20 mol.% for Ta2O5 and 30 mol.% for Nb2O5.

A study of the phase transformation in technically pure titanium under different types of deformation has been performed: upset under high pressure and high hydrostatic-pressure torsion (HPT). A set of modern methods of the study included microindentation, X-ray diffraction, transmission electron microscopy, as well as EXAFS-spectroscopy in synchrotron radiation for detailed studying a local atomic structure of phases. The correlation between the phase transformation course and the deformation method has been found. It has been shown that in contrast to pressure without a shear component, the shear deformation under high pressure at room temperature contributes to the occurrence of a high-temperature β-phase with a local atomic order different from that in the initial phase.

Effect of single-doping by Ag2O (8 mol.%), Au2O (0.016 mol.%), Rb2O (8 mol.%), Nd2O3 (0.5 mol.%), Er2O3 (0.5 mol.%) on the structure and optical properties of zinc-phosphate (PZ) glasses was studied. Crystal-chemical similarity of local structures of the dopants in these glasses and in the revealed for them reference crystals of corresponding chemical composition was established by XANES/EXAFS. The specifics of this principle for each of the glasses was determined. Combining the obtained parameters of the embedded metal's local structure with TEM, absorption and photoluminescence (PL) data, the presence of color centers (ionic dimers, nanoclusters, nanoparticles (NPs)), their specific type and optical performances were determined. It was shown that Nd, Er are homogeneously distributed in as-prepared PZ glass without clustering, retaining their PL properties. Formation of Ag, Au, Rb color centers and Au NPs in as-prepared single-doped PZ glasses were studied.

Photonic crystals obtained by the modified Stöber method with the natural sedimentation of nanospheres is investigated. The surfaces of the silica nanospheres are investigated using atomic-force microscopy. The surfaces of all samples have a cauliflower structure. The structure of the photonic crystals is studied by the method of small-angle synchrotron radiation scattering (SASRS). The SASRS curves exhibit two or three regions with different scattering intensities. Three original techniques for analyzing the data obtained are proposed. Periodicity in the dependence of the logarithm of intensity on the scattering vector at the smallest wavenumbers, related to scattering from nanospheres, is found. The influence of the water/TEOS molar ratio on the size and concentration of these particles is revealed. Particles of two types (nanospheres and subglobules) are observed at low water concentrations (6–8 mol/L), whereas at water concentrations of 13–23 mol/L the particles are of three types (nanospheres, subglobules, and grains). The morphology of the detected particles is estimated.

We present an extensive study of the luminescence characteristics of Mn impurity ions in a YAl3(BO3)4:Mn crystal, in combination with X-ray fluorescence analysis and determination of the valence state of Mn by XANES (X-ray absorption near-edge structure) spectroscopy. The valences of manganese Mn2+(d5) and Mn3+(d4) were determined by the XANES and high-resolution optical spectroscopy methods shown to be complementary. We observe the R1 and R2 luminescence and absorption lines characteristic of the 2E ↔ 4A2 transitions in d3 ions (such as Mn4+ and Cr3+) and show that they arise due to uncontrolled admixture of Cr3+ ions. A broad luminescent band in the green part of the spectrum is attributed to transitions in Mn2+. Narrow zero-phonon infrared luminescence lines near 1060 nm (9400 cm−1) and 760 nm (13,160 cm−1) are associated with spin-forbidden transitions in Mn3+: 1T2 → 3T1 (between excited triplets) and 1T2 → 5E (to the ground state). Spin-allowed 5T2 → 5E Mn3+ transitions show up as a broad band in the orange region of the spectrum. Using the data of optical spectroscopy and Tanabe–Sugano diagrams we estimated the crystal-field parameter Dq and Racah parameter B for Mn3+ in YAB:Mn as Dq = 1785 cm−1 and B = 800 cm−1. Our work can serve as a basis for further study of YAB:Mn for the purposes of luminescent thermometry, as well as other applications.

The content of metal ions and their valence state for three Ni x Cu y Mn 3-x-y BO 5 compositions were estimated by EXAFS and XANES spectroscopy methods. In all three compositions, the copper y content did not exceed 0.25; in the third composition, some manganese ions entered the compound not only in the trivalent, but also in the divalent state. A detailed study of the magnetic properties showed that two magnetic transitions are observed in all compositions: one in the region of 60-75 K, and the second in the region of 10 K. Based on the exchange interactions calculated within the framework of the empirical model, the magnetic ordering temperatures for two- and three-lattice magnets were determined and it was assumed that the magnetic transition in the region of 60-75 K is associated with the ordering of magnetic moments in positions 2 and 3. Keywords: ludwigites, magnetic phase transition, indirect exchange interactions.

Chromium (Cr) is reported to be hazardous to environmental components and surrounding biota when levels exceed allowable thresholds. As Cr is extensively utilized in different industries, thereby comprehensively studied for its toxicity. Along with Cr, the applications of nano-Cr or chromium oxide nanoparticles (Cr2O3-NPs) are also expanding; however, the literature is scarce or limited on their phytotoxicity. Thereby, the current work investigated the morpho-physiological insights of macro- and nanoparticles of Cr in Hordeum vulgare L. plants. The increased accumulation and translocation of Cr under the exposure of both forms disturbed the cellular metabolism that might have inhibited germination and growth as well as interfered with the photosynthesis of plants. The overall extent of toxicity was noticeably higher under nanoparticles’ exposure than macroparticles of Cr. The potential cue for such phytotoxic consequences mediated by Cr nanoparticles could be an increased bioavailability of Cr ions which was also supported by their total content, mobility, and factor toxicity index. Besides, to support further these findings, synchrotron X-ray technique was used to reliably identify Cr-containing compounds in the plant tissues. The X-ray spectra of the near spectral region and the far region of the spectrum of K-edge of Cr were obtained, and it was established that the dominant crystalline phase corresponds to Cr2O3 (eskolaite) from the recorded observations. Thus, the obtained results would allow revealing the mechanism of macro- and nanoparticles of Cr induced impacts on plant at the tissue, cellular- and sub-cellular levels.

The study of TiNiCu alloy samples in the initial state after quenching by EXAFS revealed the dependence of the local atomic structure of the alloys on the copper content. Studies of the structure of alloys by X-ray diffraction (XRD) using synchrotron radiation with a wavelength of 0.8 Å showed that in the initial state after quenching, the alloys are in an amorphous state. After isothermal crystallization of alloys at a temperature of 500° C for 300 s, it was found that samples of alloys with a copper content of more than 30 at.% after crystallization became so brittle that they were unsuitable for further research. This is a consequence of the peculiarities of the local atomic structure of the alloys identified by the EXAFS method. Temperature intervals and the nature of alloy phase martensitic transformations (MT) were determined by differential scanning calorimetry (DSC).

The content of transition‐metal ions and their valence state for three compositions of NixCuyMn3−x−yBO5 are estimated by the methods of X‐ray absorption spectroscopy. In all the three compositions, the copper content does not exceed 0.25. One of the compositions has manganese ions both in the trivalent and bivalent states according to the K‐edge position. The calculations of the total energies of various cation‐ordered structures using the software package Wien2K show that copper ions predominately occupy one site, namely, 2(2d). The measurements of the magnetic properties show two types of magnetic transitions in all the three compositions, with one of them being in the range of 60–75 K and the other one at 10 K. Based on the exchange interactions calculated in the framework of the empirical model, magnetic ordering temperatures are estimated for two‐ and three‐sublattice structures and the magnetic transition in the range of 60–75 K is supposed to be connected with magnetic moment ordering in sites 2 and 3.

The local crystalline environment of Ni and Cu atoms in the quasi-binary TiNi-TiCu shape memory alloys containing 30 and 40 at.% Cu has been studied using EXAFS spectroscopy. Amorphous melt-spun alloy ribbons have been crystallized by isothermal annealing or by exposing to a short (10 ms) electric pulse. Analysis of the EXAFS spectra has shown that electropulse crystallization has a more noticeable effect on the local atomic structure of austenite compared to martensite. In particular, it leads to a decrease in the local disorder of atoms in the Cu coordination shells, a decrease in the lengths of Cu-Ni and Cu-Cu bonds, hinders an increase in the lattice parameter of the austenite phase and stabilizes its crystal structure. The observed changes in the local atomic structure of the austenite phase of the alloys contribute to the improvement in the shape memory properties.

Методами спектроскопии EXAFS и XANES были оценены содержание металлических ионов и их валентное состояние для трех составов NixCuyMn3-x-yBO5. Во всех трех составах содержание меди y не превысило 0.25; в третьем составе часть ионов марганца вошли в соединение не только в трехвалентном, но и в двухвалентном состоянии. Подробное исследование магнитных свойств показало, что во всех составах наблюдается два магнитных перехода: один в районе 60-75 K, а второй в районе 10 K. На основании вычисленных в рамках эмпирической модели обменных взаимодействий были определены температуры магнитного упорядочения для двух- и трехподрешеточного магнетика и сделано предположение, что магнитный переход в районе 60-75 K связан с упорядочением магнитных моментов в позициях 2 и 3. Ключевые слова: людвигиты, магнитный фазовый переход, косвенные обменные взаимодействия.

Poly( p -xylylene)–molybdenum oxide nanocomposite thin films of different thicknesses and inorganic filler content are synthesized by low-temperature vapor deposition polymerization. The structure of the nanocomposites and its evolution during thermal annealing is studied by wide angle X-ray scattering and X-ray absorption spectroscopy. It is found that the molybdenum oxide nanoparticles are amorphous in both the as-deposited and annealed composite films. The short-range order characteristic of orthorhombic molybdenum trioxide is preserved in the nanoparticles; however, a noticeable disordering of the structure together with a decrease in the effective oxidation state of molybdenum are revealed. Both an increase in the filler content and thermal annealing lead to a decrease in the bandgap of the composites, which is related to the increase in the nanoparticle size. It is shown that thermal annealing improves the stability of the resistive switching (RS) characteristics in memristors based on the synthesized nanocomposites, which creates an opportunity for the application of these materials as the active layer of memristive devices.

Dependence of lanthanum local atomic structure in borate glasses La2O3-Nb2O5-B2O3 upon component composition was studied combining XANES, computer simulations using crystal chemical similarity (CCS) of a shortrange order in glass and crystal, and multidimensional interpolation of spectra as the function of structural parameters. By this approach, the values of La-O bond lengths and angles in chains O-La-O were determined. Comparison of the obtained radial and angle distribution functions of oxygen atoms around La in the studied glasses with the same functions of the reference crystals revealed that within the existing CCS of La local structure in glasses and in B3LaO6, there is a decrease in the average length of La-O bonds by - 0.1 & ANGS; and decrease of FWHF by - 0.2 & ANGS; in the radial distribution of nearest O atoms, under retaining angle distribution of these atoms. It was shown that the ratio of intensities of the first two peaks in experimental La L3-edge XANES is an effective fingerprint of the number of nearest oxygen neighbors of lanthanum. Using the dependence of this ratio upon the component composition of glasses, the changes in the local structure of La under decreasing of B2O3 fraction from 72.5 to 47.5% were determined.

The effects related to the conversion of magnetic structures of a Cu2MnBO5 ferrimagnet to a Cu2GaBO5 antiferromagnet under the Mn3+→Ga3+ substitution were studied. The properties of four single crystal samples with the gallium concentration x = 0.04, 0.11, 0.17, 0.25 were examined. The chemical composition and valence state of the samples were determined by X-ray absorption spectroscopy element-sensitive technique. Distribution of the 3d metal ions over crystallographic positions was studied using the first principal calculations by Wien2k program. The evolution of the magnetic properties was investigated by the measurements of the temperature and field dependences of magnetization, dc and ac magnetic susceptibility. In agreement with the previous study of the structure evolution of Cu2Mn1-xGaxBO5 solid solutions, the critical concentration upon a change in the magnetic ordering type was found in the range x = 0.17÷0.25. The non-monotonic behavior of magnetization in terms of the gallium content was found in the concentration range of 0.04÷0.17. A complex pattern of magnetic phase transitions belonging to the concentration phase boundary was obtained in the compounds with gallium being within the range x = 0.17÷0.25. One could observe the splitting of the peaks of the real part of ac-susceptibility of the high-temperature phase transition in the Cu2MnBO5-like phase (x = 0.04, 0.11) and that of the low-temperature one at the concentration boundary (x = 0.17, 0.25) with different frequency and orientational dependence. The type and origin of the multiple phase transitions observed in the studied samples were analyzed.

Методом полимеризации на поверхности из газовой фазы синтезированы образцы тонкопленочных композитов на основе поли-пара-ксилилена и оксида молибдена с различной толщиной и концентрацией неорганического наполнителя. Методами рентгеновского рассеяния и спектроскопии поглощения рентгеновского излучения исследована структура синтезированных композитов и ее изменение при термическом отжиге. Обнаружено, что наночастицы оксида молибдена как в исходных, так и в отожженных образцах остаются аморфными. При этом в наночастицах сохраняются элементы локального порядка, характерные для орторомбического триоксида молибдена, однако происходит заметное разупорядочение структуры с понижением эффективной степени окисления молибдена. Увеличение концентрации наполнителя и отжиг приводят к уменьшению ширины запрещенной зоны в наночастицах оксида молибдена, что, по всей видимости, связано с увеличением размера наночастиц. Показано, что отжиг приводит к улучшению стабильности характеристик резистивного переключения в мемристорах на основе синтезированных композитов, что открывает возможность использования данных материалов в качестве активного слоя мемристивных устройств.

The work considers the rotational and translational oscillations of three cylinders differing in terms of the ratio of the length to the cylinder diameter (aspect ratio). The cylinders are suspended in the test section of a low velocity wind tunnel on a wire suspension equipped with steel springs. In the equilibrium position, the axis of the cylinders is directed horizontally and parallel to the freestream velocity vector. Under the influence of the air flow, the cylinders can execute rotational or translational oscillations. The two suspension springs are equipped with semiconductor strain gauges that measure the periodically changing tension of the springs during oscillations. The analog signal from the strain gauges is transmitted to a PC oscilloscope, which transmitted it in digital form to a computer. After calibration of the device and decoding of the signal, the frequencies and amplitudes of translational oscillations in the vertical direction and rotational oscillations around the horizontal axis passing through the center of the cylinder and perpendicular to the freestream velocity vector are determined. It turns out that in the studied range of cylinder elongations there is a transition from rotational to translational oscillations. A cylinder with an aspect ratio of 1.9 performs steady rotational oscillations under the influence of wind, and their amplitude increases with increasing air-flow velocity. The previously proposed mathematical model correctly predicts rotational oscillations. The square of the amplitude of rotational oscillations is a linear function of the Strouhal number if the velocity of the air flow is sufficiently large. Translational oscillations of the cylinder with an aspect ratio of 1.9 are damped. A decrease in the aspect ratio of the cylinder down to 1.5 is accompanied by a decrease in the amplitudes of rotational vibrations. At low air-flow velocities, translational oscillations with a small amplitude are registered. Further reducing the aspect ratio to 1.0 eliminates rotational oscillations entirely. The amplitude of translational oscillations increases. Translational oscillations occur in a limited range of air-flow velocities.

High refractive glasses in the La2O3-Nb2O5-B2O3 (LNB) system were synthesized by the melt-quenching technique and correlations between their compositions and structural features were clarified. It was found that the refraction index of the LNB glasses is tunable from 1.71 to 1.98 by the variation of the Nb2O5 fraction from 5 to 30 mol%. The infrared spectroscopy analysis implies on the presence of three and four coordinated borate units, as well as six coordinated niobium atoms. The X-ray absorption (La L-3-edge and Nb K-edge XANES and EXAFS) spectroscopy and total X-ray scattering results show that niobium atoms maintain octahedral oxygen coordination despite the wide variation of the Nb2O5 content, while average lanthanum coordination number is versatile and changes from similar to 8 to similar to 10. The interatomic distance values testify that the niobium octahedra in the glass network are connected only "by corners". The stability of niobium local atomic structure implies that the main source of the changes in the optical properties of studied glasses is the variation of the Nb2O5 content. The deeper understanding of the local atomic structure of the high refractive index LNB glasses paves ways for the development of new glass wafers for cutting-edge augmented reality devices. (c) 2022 Elsevier B.V. All rights reserved.

The crystallization mechanisms and kinetics in amorphous Ti50Ni25Cu25 alloy produced by different methods of amorphization have been studied by X-ray diffraction at room temperature and in situ synchrotron diffraction upon heating up to 823 K. One of the amorphous states was obtained by melt quenching (MQ) at a cooling rate of approximate to 10(6) K/s. The other amorphous state was realized in a polycrystalline alloy of the same composition by high pressure torsion by four revolutions of the movable anvil (HPT4). Differential scanning calorimetry was used to determine the temperatures of crystallization and glass transition, as well as a change of the thermal effect as a function temperature. It is shown that the amorphous states under consideration substantially differ in the mechanisms and temperature parameters of crystallization. The amorphous phase produced by HPT4 was found to be less stable with respect to heating than the amorphous phase obtained by MQ. The origins of the difference in the crystallization kinetics of the amorphous phases obtained by MQ and HPT4 are discussed.

Electrical transport in polycrystalline rare earth oxymolybdates Lri(2)MoO(6) (Ln = La, Pr, and Nd) was investigated using theoretical and experimental methods. The theoretical approach consisted of geometrical-topological analysis, bond valence site energy (BVSE) simulation, and density functional theory (DFT) calculations. The BVSE modeling revealed that ionic conductivity can occur only by oxygen migration. The DFT calculations showed the roughly equal value of the energy barriers to oxygen migration in all oxymolybdates (less than 0.85 eV). The oxygen pressure-dependent isotherms of Ln(2)MoO(6) (Ln = La, Pr, and Nd) at 1 x 10(-18)-0.21 atm show a mixed ionic and electronic conductivity mechanism in the temperature range of 700-900 degrees C. The total conductivity reached 10(-5) S/cm at 800 degrees C for Ln(2)MoO(6) and Nd2MoO6 and 10(-3) S/cm at 800 degrees C for Pr2MoO6. All three layered oxymolybdates Ln(2)MoO(6) (Ln = La, Pr, and Nd) exhibit proton conductivity in a humid atmosphere.