A high-entropy Ti0.2Zr0.2Hf0.2Nb0.2Ta0.2 alloy shows promise as a material for tensometric applications; however, data on its thermal stability at different temperatures are incomplete. Prepared samples were subjected to heat treatment (annealing in a vacuum) at 523 and 673 K for 0, 10, 25, 50, 100, 200, 400, and 800 h for X-ray diffraction studies and for 1, 2, 6, 10, 25, 50 100, 200, 400, and 800 h for measuring the microhardness of the solid solution. For all Ti0.2Zr0.2Hf0.2Nb0.2Ta0.2 samples, the chemical composition, lattice parameters, and the evolution of the microstructure and microhardness in the course of complete heat treatments are studied. The cast alloys prepared by repeated electric arc melting are found to form a bcc single-phase solid solution, which is characterized by dendritic grain growth and interdendritic segregation. During annealing at 523 K, the Ti0.2Zr0.2Hf0.2Nb0.2Ta0.2 alloy is thermally stable for 800 h and does not undergo phase transitions; however, isothermal holding leads to the formation of a nonequilibrium structure characterized by a high content of defects and concentration inhomogeneities. The decomposition of the solid solution takes place at the beginning stage of annealing at 673 K, and the long-term holding for 800 h favors the formation of multiphase structure. Whatever the annealing temperature (523, 673 K), the dendrite growth morphology changes. The behavior of time dependences of the microhardness correlates with X-ray diffraction data. In the course of annealing of experimental alloys at 523 K, no abrupt variations in the lattice parameter and hardness are observed. During annealing at 673 K, an abrupt increase in the microhardness from 365 to 560 HV and a change in the lattice parameter from 3.4128(1) to 3.3865(1) Å are observed, which indicate a phase transition. The data obtained allow us to determine the upper limit of the temperature range of operation of the alloy, which is 523 K.

Scandium is commonly known as a superior modifier for most alloys and compounds, substantially improving their phase stability and physical properties, as well as glass-forming ability. A special case is rare-earth based magnetic metallic glasses, which are an unique platform for intra-elemental substitution due to the chemical affinity of the lanthanides, yttrium and scandium. The latter, used as an alloying additive and being the smallest atom among the entire family, can drastically affect structure formation and magnetism in these metallic glasses. The main issue is that its modifying role is not well understood due to scarce information on the scandium effects in such rare-earth systems. This study is focused on thermal and magnetic analysis of some popular Gd-based BMGs redesigned with minor Sc additives. Here, we consider temperature behavior of specific heat capacity and entropy functions for both amorphous and crystalline phases to estimate the scandium effect on GFA and thermal stability of the glasses. As well, we inspect magnetic and magnetocaloric properties of these BMGs to understand whether this very expensive metal can radically improve the alloy magnetism and make these materials suitable for potential applications.

Russia has an impressive titanium mineral resource while the contribution into the global production of titanium concentrates is quite insignificant. The current annual demand of Russian enterprises for titanium raw materials is 40 times higher than its production. To improve and launch the processing of domestic titanium raw materials characterized by low quality and complex polymineral composition, new process solutions are required. These solutions should aim at the full extraction of TiO2 and related valuable components from the ore deposits whose development is planned or already started (for example, Afrikanda – perovskite-titanomagnetite deposit located on the Kola Peninsula). This report presents the results of studying the chemical and mineral compositions of perovskite and ilmenite concentrates with the purpose to assess the possibility of their joint processing using carbothermic reduction melting. Emission spectrometry, X-ray diffraction, electron microscopy, and X-ray spectral microanalysis were applied in these studies. It was found that the basis of the ilmenite gravity concentrate sample is modified ilmenite represented by leucoxenization products – pseudorutile and rutile, with their total content in the concentrate to be about 80 wt. %. Composition of other minerals (alumochromite, chromite, magnetite) includes titanium in the form of impurities – 2 – 3 wt. %. In the perovskite flotation concentrate sample titanium is contained in perovskite and titanite making up the bulk of the ore minerals of the concentrate. As for rare and rare-earth elements contained in the ilmenite sample – monazite having up to 33 wt. % Ce, and zircon were found. Perovskite sample contains rare-earth elements (REE concentration in wt. %) in loparite-(Ce) (22.8), aluminocerite-(Ce) (46.2), anсylite-(Ce) (51.3), torite (22.3), as well as in the main mineral – perovskite (2.8). With the exception of perovskite and loparite-(Ce), other REE-containing minerals are rare, and their share in total does not exceed 1 wt. %

Among the multiplicity of single-phase high-entropy alloys explored up to now, the TiZrHfNb one is accepted as thermally stable material that crystalizes into a single-phase body-centered cubic (BCC) solid solution. This HEA demonstrates exceptional structural stability at high temperatures, while its behavior under moderate thermal conditions (700 1300 K) has not been examined extensively so far. Here we address structure formation, phase transitions, thermal stability, and properties of the HEA under different thermal treatments. To do that, we synthesize the single-phase BCC alloy and analyze its structural evolution during long-time isothermal annealing as well as slow heating. In this study, we cover the temperature interval up to 1300 K and the annealing times up to 700 hours. In-situ X-ray diffraction combined with high-temperature measurements allow us to identify phase transformations in the HEA. The results reveal that BCC single-solid solution decomposes into several phases after isothermal annealing at 673 K for less than 200 hours. After prolonged homogenization, the system is a three-phase material consisting of two BCC and one HCP solid solutions. Ab initio simulations performed for the liquid phase indicate weak chemical interaction in the studied system and indirectly confirm the ability of the HEA to form single-phase solid solutions.

The features of the formation of crystalline and magnetic subsystems in the Eu1-xMn1+xO3 solid solution depending on the superstoichiometric manganese content were studied by X-ray diffraction analysis (XRD) and magnetometry. XRD showed that an increase in x led to significant decrease in the unit cell volume, which was accounted for by the occurrence of the manganese disproportionation reaction and subsequent redistribution of different valence manganese ions in nonequivalent positions as follows: $$\left({\mathrm{Eu}}_{1-x}^{3+}{\mathrm{Mn}}_{x}^{2+}\right)\left({\mathrm{Mn}}_{1-x}^{3+}{\mathrm{Mn}}_{x}^{4+}\right){\mathrm{O}}_{3}^{2-}$$ . The degree of orthorhombic and Jahn–Teller distortions decreased with increasing x. The temperatures of magnetic transitions due to manganese ions ordering in the B- and A-sublattices, high-temperature (T1) one and low-temperature (T2) one, respectively, were determined based on the temperature dependences of dM/dT. It was established that an increase in the Mn content reduced the temperature T1. Magnetization measurements performed in Eu0.94Mn1.06O3 in a low applied magnetic field demonstrated magnetization reversal at temperatures below T1.

Heterovalent element substitution is an effective way to optimize functional properties of the Y-Ba-Cu-O high-temperature superconductors. In this study, we analyze the effect of Y-Ca substitution on microstructure and critical current in YBa2Cu3O6.8 ceramics with transmission electron microscopy and magnetometry. The obtained results reveal that the substitution of Y3+ by Ca2+ initiates the formation of complicated microstructure consisting of Y(Ca)-123 matrix with multiple defects of different types and fine nanoscale Y-211 particles coherently coupled with the matrix. Depending on Ca doping, various microstructural defects such as dislocations, stacking faults, and effects associated with cationic disorder are observed. The magnetic and superconducting properties in Ca-substituted compositions Y-123 are discussed in terms of the sample microstructure morphology and the specificity of coupling between the basic Y(Ca)-123 phase and impurity particles of the Y-211 phase. We find that shape type and dispersion of the Y-211 precipitations are crucial to regulating both the critical current and the critical temperature in the ceramics.

In this study, the effect of R (R= Y, Pr, Nd, Sm, Eu, Lu) substitution on crystal structure and properties HTS compositions R1-xCaxBa2Cu3Oy. The XRD results showed that the substitution of Y / R in Y-123 leads to the disappearance of spikes in the linear and volumetric coefficients of thermal expansion. Mechanical activation showed that the composition of Nd-123 demonstrates enhanced chemical stability with respect to water vapor and CO2 when exposed to air.

Physicochemical features of the YBa2Cu3O6 + δ superconductor synthesized via ceramic route and subjected to a kind of modification by long-term exposure to an atmosphere with low pH2O have been studied by X-ray diffraction, thermal analysis, and magnetometry. The resulting material had a high degree of saturation with air components at room temperature and 30% humidity, up to 1.5 wt % in 30 days, which is not inherent in YBa2Cu3O6 + δ.

For Y1-xCaxBa2Cu3Oy with varying oxygen and calcium content, the change of crystal structure at cooling from room temperature to 80 K has been investigated. The main change is associated with a shift of apical oxygen atoms. Using determined unit cell parameters as function of temperature, the coefficients of linear thermal expansion have been calculated as alpha(X) = 1/X.(dX/dT), where. X = a, b, c - unit cell dimensions. For the compound without calcium all alpha(X) values demonstrate anomalous behavior such as growing at cooling in temperature interval T-1 divided by T2 similar to 150 divided by 225 K. The calculation of electronic structure at temperatures above, below and within this interval shows the appearance of the electronic states density peak for Ba and O4 atoms. It is explained by the localization of charge carriers with the participation of the lattice distortion in a form of apical CueO bond compression. As the material Y0.9Ca0.1Ba2Cu3Oy regardless of the oxygen content possess low and constant coefficient of thermal expansion along all crystallographic directions, that makes this material suitable for superconducting films and other composites. (C) 2015 Elsevier B.V. All rights reserved.

The crystal structure of the high-temperature Y1–x Ca x Ba2Cu3O6.8 superconductor has been studied in a temperature range of 80–300 K using low-temperature X-ray diffraction analysis; its microstructure has been studied by scanning and transmission electron microscopy. Changes of the bond length in the structure of principal phase and precipitation topology of impurity phases and their compositions have been analyzed. An addition of calcium was shown to increase the environmental tolerance of the principal Y123 phase and its microhardness and ensures the low unchanged coefficient of thermal expansion. All of the facts indicate that the material can be used to manufacture composite superconducting articles.

The degradation processes of YBa 2 Cu 3 O 6.77 (3) films 600 nm thick deposited on substrates from a textured (100) foil of the Ni-W alloy with the YSZ (Y 2 O 3 + ZrO 2 ) (100 nm) and CeO 2 (50 nm) buffer layers at 200°C in air have been investigated. It has been shown that the degradation proceeds in the same manner as in the bulk ceramic materials with the same oxygen content, namely, initially the single-phase material with the orthorhombic structure laminates into the fractions depleted (the main fraction) and enriched with oxygen. After holding for more than 20 h, the oxygen-depleted fraction is first subjected to the structural phase transformation with the transition of the orthorhombic structure into the cubic one, which is associated with the redistribution of barium and yttrium atoms over their sites in the presence of water vapors.

The effect of doping on the temperature evolution of the crystal structure of the YBa2Cu3O y high-temperature superconductor has been investigated. The crystal structure of Y1 − x Ca x Ba2Cu3Oy (x = 0, 0.1; y = 6.6, 6.8, 6.95) has been studied using the full-profile analysis with X-ray powder diffraction data in the temperature range 100–300K. The unit cell parameters, the bond lengths, and the calculated linear and volume coefficients of thermal expansion are characterized by a nonmonotonic behavior in the temperature range ∼160–225 K. Samples with the oxygen content y = 6.6–6.8 in both systems (with x = 0 and 0.1) have negative linear coefficients of thermal expansion at low temperatures. A possible reason for the anomalous behavior can be the change in the state of the electronic subsystem. The data analysis confirms that the doping mechanisms upon oxygen introduction, and when Y is substituted for Ca are different.