Substitutional Solid Solutions Research Articles

Ag8GeS6(Se6)–Ag8GeTe6 SYSTEMS: PHASE RELATIONS, SYNTHESIS, AND CHARACTERIZATION OF SOLID SOLUTIONS

Phase equilibria in the Ag8GeS6-Ag8GeTe6 and Ag8GeSe6-Ag8GeTe6 systems were studied using differential thermal analysis and powder X-ray diffraction technique. The T-x phase diagrams were constructed. It has been found that both systems are partially quasi-binary and are characterized by the formation of continuous series of substitutional solid solutions between Ag8GeTe6 and high-temperature cubic modifications of Ag8GeS6 and Ag8GeSe6. When solid solutions are formed, the temperatures of polymorphic phase transitions of these compounds decrease. This leads to the stabilization of the ion-conducting cubic phase in the 40 mol% Ag8GeTe6 range of compositions at room temperature and below. The regions of homogeneity based on Ag8GeS6 and Ag8GeSe6 are 15 and 10 mol.%, respectively. The crystal lattice parameters of the identified solid solutions were calculated from the XRD data, and their linear dependence on the composition is shown

High entropy coating from AlCoCrCuFeNi alloy, obtained by laser alloying

The structural-phase state of the Al-Co-Cr-Cu-Fe-Ni system high-entropy alloy obtained by laser alloying of technically pure aluminium surface layers was investigated by XRD, EDX and metallographic analyses. It is shown that in the process of laser alloying the formation of an an ordered multicomponent substitution solid solution based on BCC lattice took place, which is typical for high-entropy alloys. The process of heterogeneous crystallization of high-entropy alloys AlCoCrCuFeNi and Al3CoCrCuFeNi was modeled taking into account cooling rates of the melt. It is established that the formation of the obtained structure is a consequence of high cooling rates of the melt and high content of aluminum in the laser alloying zone. The microhardness of the alloyed surface was higher compared to high-entropy alloys of this system obtained under equilibrium conditions and was equal to 6.59 GPa. Additional reasons that may affect the high values of microhardness are analysed.

Characterization of CrAl coating on stainless steel bipolar plates for polymer electrolyte membrane fuel cells

CrAl alloy coating has advanced potential to improve corrosion inhibition, hydrophobicity, and electrical conductivity for metallic BPs. The feasibility of CrAl coating for surface modification of the BPs is thoroughly examined through comparative analysis with stainless steel 316L (SS316L). The coated specimen can reach high polarization resistance (Rp) and 93% inhibition efficiency (η) from Tafel plots. Based on the various surface properties of CrAl coating, corrosion resistance mechanisms for substitutional solid solution and nanograin structures containing hydrophobic and low surface free energy are proposed.

Role of Ta in improving corrosion resistance of titanium alloys under highly reducing condition

Great improvement on corrosion resistance was achieved by adding small amount of Ta into ASTM Gr13 titanium alloy. Main contribution to the improved corrosion resistance originated from the stabilized passive film in terms of the prolonged time to passivity loss. OCP results showed that the OCP transition from the passive state to corroding one prolonged with the Ta content. This behavior was also supported by EIS results, where the loop shrinkage denoting the passivity loss was retarded and/or inhibited by the Ta addition. Microstructural analysis revealed that the added Ta functioned as both substitution element and solid solution one, leading to the growth of the precipitates including β-Ti phase and formation of the complex structured passive film. Especially, the prominent stability of the passive film observed for Gr13–1.0% Ta was ascribed to the high content of the Ta oxide in the passive film, meaning that the complex oxide film required the minimum amount of the Ta oxide to obtain the excellent stability of the passive film against the high concentrated acid solution.

Synthesis and photoluminescence properties of garnet red emitting CaY2Al4SiO12:Eu3+ phosphors

Eu3+ doped CaY2Al4SiO12 garnet phosphors were synthesized by using the sol-gel method. The crystal structure of the synthesized phosphors was characterized by X-ray diffraction and Rietveld refinements. The results of X-ray diffraction and Rietveld refinements of the powders sintered at 1400 °C showed the formation of a single phase and the effective concentration of Eu3+ ions in this garnet host lattice.The composition of the substitutional solid solutions of CaY2-xEuxAl4SiO12 (x = 0.01, 0.03, 0.06, 0.09, 0.12, and 0.15) exhibit efficient red photoluminescence peaking at 596 nm, which can be assigned to the 5D0 → 7F1 intra-configurational transition of Eu3+ located at the dodecahedral site in the garnet structure. The photoluminescence properties, such as excitation and emission spectra, decay curves, and quantum yield, are presented. The thermal stability of the as-prepared phosphors was determined. Additionally, the optical bandgap for the samples was estimated with UV–visible diffuse reflectance spectra using the Tauc relation. The correlation between the structural features and luminescence properties was determined. These phosphors with high thermal stability and high color purity can be potentially used in white-light-emitting diodes.

Ceria–Zirconia-Supported Ruthenium Catalysts for Hydrogen Production by Ammonia Decomposition

Commercial cerium–zirconium oxide supports (Ce0.5Zr0.5O2, Ce0.75Zr0.25O2, and Ce0.4Zr0.5Y0.05La0.05O2) were used to prepare Ru/CeZrOx catalysts. According to the XRD and IR spectroscopy data, the supports consist of ceria-based substitutional solid solutions. The specific surface areas of supports and catalysts are similar and range from 71–89 m2/g. As shown by TEM and XRD methods, the size of support particles equals 6–11 nm. According to the TEM data, the size of ruthenium particles does not exceed 1.3 nm. The catalyst activity in the ammonia decomposition process was studied. The Ru/Ce0.75Zr0.25O2 catalyst at temperature 500 °C and GHSV 120,000 h−1 demonstrated the highest hydrogen productivity of 53.3 mmol H2/(gcat·min) and compares well with the best results reported in the literature. The kinetics of ammonia decomposition reaction were calculated using the Temkin–Pyzhov exponential expression. The developed mathematical model well described the experimental data. The studied catalysts demonstrated high activity for the ammonia decomposition reaction.

Magnetic characteristics of solid solutions Ni1–xMxMnSb (M = Ti, V, Cr)

The results of an experiment on the study of the crystal and magnetic structures of substitutional solid solutions of the Ni0.90M0.10MnSb (M = Ti, V, Cr) systems using thermal neutron diffraction in the temperature range ~ 3–300 K are presented. It is found that all the studied compositions have ferromagnetic ordering along the c axis. In the spectra of Ni0.90V0.10MnSb and Ni0.90Cr0.10MnSb solid solutions, a reflection appears in the region 2Θ = 28.6°, which indicates the formation of antiferromagnetic ordering. It has been found that this reflection disappears at a temperature T = 75 K in Ni0.90V0.10MnSb, while it is observed in the spectrum of Ni0.90Cr0.10MnSb over the entire temperature range under study. Within the framework of density functional theory (DFT), an ab initio calculation of the crystal structure and magnetic moments for Ni1–xMxMnSb (M = Ti, V, Cr; x = 0; 0.125; 0.250) was carried out. It has been established that titanium, vanadium, and chromium ions participate in electron transfer only with Mn and Sb ions. The DFT results predict the existence of magnetic moments for Ti, V, and Cr ions. It was found that the spins of Ti, V, and Cr ions are antiferromagnetically coupled with the spins of Mn and Ni ions. The results obtained are of interest for the development of new concepts and models of structural design, which makes it possible to synthesize fundamentally new functional materials with already specified physical properties.

Dynamics of cluster structure change in melts that forms a continuous series of solid solutions during equilibrium and nonequilibrium crystallization

The article describes the dynamics of changes in the melt structure during cooling of solid substitution solutions in the process of quasi-equilibrium (CRC) and non-equilibrium explosive crystallization (NRCC), taking into account clustering processes. The boundaries of the transition to the solid state are determined as the structure of clusters changes during crystallizations of the KRK and NRK types. The boundaries are determined taking into account the critical overheating and pre-crystallization supercooling relative to the liquidus line . It is determined that during quasi–equilibrium crystallization, the melt changes its structure in the following sequence , and during non-equilibrium explosive crystallization - in the sequence . The phase rule is used to calculate the first crystals that appeared during various types of crystallization. Alloy cooling curves describing various types of alloy crystallization.

Magnetic Photocatalysts Based on Nanocrystalline Manganese-Doped Titanium Dioxide

Manganese-doped anatase with a nanosized morphology (as spherically shaped nanoparticles) has been synthesized under hydrothermal conditions. It has been shown that manganese is incorporated into the titanium dioxide structure to form substitutional solid solutions. At high dopant concentrations, part of the introduced manganese goes to the formation of α-MnO2. A significant increase in the optical activity in the visible range and a decrease in the bandgap width down to ~2.4 eV are observed for manganese-doped anatase because of the appearance of extrinsic (multivalent Mn ions) and intrinsic compensating (oxygen vacancies) defects. It has been found that manganese-doped samples are diluted magnetic semiconductors, and the magnetic characteristics increase with increasing manganese content. All manganese-containing samples demonstrate photocatalytic activity in the degradation reaction of indigo carmine when irradiated with visible light. The degree of dye degradation depends on the content of manganese in the samples and reaches 90%.

Chemical Deposition of CdxPb1 – xS/CdyS Thin-Film Composite Structures

Thin films of CdxPb1 – xS (0 ≤ x ≤ 0.094) substitutional solid solutions of cubic structure B1 (space group Fm) were prepared by chemical deposition and characterized by X-ray diffraction, scanning electron microscopy, EDX elemental analysis, and Raman spectroscopy. Once the cadmium sulfate concentration in the batch reached some critical value (0.1 mol/L), the films formed involved two autonomous phases: CdxPb1 – xS substitutional solid solutions and hexagonal cadmium sulfide CdyS of structure В4 (space group P63mc). The method and its parameters as proposed are efficient for manufacturing heterostructures in the CdS–PbS system in one-pot deposition.

The thermodynamic and mechanical properties of Earth-abundant metal ternary boride Mo2(Fe,Mn)B2 solid solutions for impact- and wear-resistant alloys

Substitutional solid solutions of the Mo2FeB2–Mo2MnB2 system exhibit high stability and a sufficient level of mechanical properties to be used as a reinforcement phase in high-manganese alloys (steels), providing both impact- and wear-resistance.

Synthesis of Co-Ni Alloy Particles with the Structure of a Solid Substitution Solution by Precipitation in a Supercritical Carbon Dioxide.

Mixed Co-Ni bimetallic systems with the structure of a solid substitution solution have been synthesized using the supercritical antisolvent precipitation (SAS) method, which uses supercritical CO2 as an antisolvent. The systems obtained have been characterized in detail using X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), Fourier-transform infrared (FTIR) spectroscopy, and magnetostatic measurements. It has been found that Co-enriched systems have a defective hexagonal close-packed (hcp) structure, which was described by a model which embedded cubic fragments of packaging into a hexagonal close-packed (hcp) structure. It has been shown that an increase in water content at the precipitation stage leads to a decrease in the size of cubic fragments and a more uniform distribution of them in Co-enriched systems. It has also been shown that mixed systems have the greatest coercivity in the line of samples. Ni-enriched bimetallic systems have a cubic close-packed (ccp) structure with modified crystal lattice parameters.

Activity of Mono-, Bi-, and Trimetallic Catalysts Pt-Ni-Cr/C in the Bicyclohexyl Dehydrogenation Reaction.

The influence of metals with different redox properties and a carbon carrier on the activity of mono-, bi- and trimetallic Pt-Ni-Cr/C catalysts has been studied in the bicyclohexyl dehydrogenation reaction as the hydrogen release stage in hydrogen storage. An increase in the conversion (X > 62%) of bicyclohexyl and selectivity for biphenyl (S > 84%) was observed on trimetallic catalysts Pt-Ni-Cr/C compared with the monometallic catalyst Rt/C (X > 55%; S > 68%). It has been established that the increase in the conversion of bicyclohexyl and selectivity for biphenyl in the dehydrogenation reaction on trimetallic catalysts is due to an increase in the activity of Pt nanoparticles in the vicinity of local Cr-Ni clusters of solid substitution solutions.

CURRENT DIRECTIONS OF THEORETICAL DEVELOPMENTS REGARDING THE USE OF IRON-BASED ALLOYS

The article proves that important achievements of theoretical developments regarding the use of iron-based alloys are the scientific works of domestic researchers. Thus, in the dissertation research of Karpets M.V. for the first time, the phase composition, microstructure and physicо-mechanical properties of alloys of the Сr-Ni-Co-Fe-Cu-Al system in the concentration range (0-3 mol) of the content of chemical elements were systematically investigated. It was established that in the studied system, due to the high entropy of mixing, only simple solid substitution solutions based on fcc and bcc structures are formed, which are characterized by a high complex of physical and mechanical properties that are not inherent to any of the constituent components. It is substantiated that the main factor of phase formation in high-entropy alloys is the value of the average electron concentration of the alloy. The interval of values ​​of the average electron concentration, in which bcc or fcc structures exist, depends on the rate of crystallization of the melt and the presence of elements prone to liquation in the alloy. Stabilizing elements of solid solutions based on phases with bcc (Al, Cr) and fcc (Cu, Ni, Co) structures were established. A significant scientific achievement should be considered the first developed high-entropy CrMnFeCoNi2Cu alloy based on a solid solution with an fcc phase structure, capable of being deformed by rolling at room temperature by 98% without the appearance of cracks or tears. Its phase composition, microstructure, and physical and mechanical properties at all stages of deformation were studied. It is shown that, for the first time in Ukraine, during cold rolling in the high-entropy CrMnFeCoNi2Cu alloy, similar to pure metals and alloys with an fcc structure, a rolling texture with the main component appears. The article provides examples of other theoretical developments regarding the use of iron-based alloys.

THE CHROMIUM AND COBALT DISTRIBUTION IN THE DIFFUSION LAYER OF STEEL X35CrNi2-3 DURING THERMОDIFFUSION SATURATION

For parts of machines and equipment operating under the influence of aggressive media, abrasive, high temperatures, the creation of a hard, wear-resistant surface is an urgent task. Cobalt is used as a binder to create hard alloy materials that work under these conditions. It was of interest to evaluate the possibility of using cobalt as an additive in complex thermal diffusion chromium plating of structural steel. The article describes the features of thermal diffusion saturation of steel X35CrNi2-3 with chromium and cobalt at a temperature of 1000°C. A technique for analyzing the obtained coating is presented, based on the possibilities of X-ray spectral microanalysis of the diffusion layer on transverse microsections of the obtained samples. The elemental composition of the diffusion layer was monitored using the JEOL JSM-6460 LV universal scanning (scanning) electron microscope. The microstructure was studied using the optical metallographic microscope Axio Observer D1.m. The X-ray phase analysis was carried out with the Rigaku Ultima IV diffractometer. The hardness measurement was carried out with the FM-800 microhardness tester at a load of 50 g. Data were obtained on the distribution of chromium and cobalt in the surface layer of steel. It is shown that the resulting thermal diffusion coating consists mainly of a substitutional solid solution based on Cr‒Fe‒Co with bcc lattice and chromium carbides. The average diffusion coefficients of chromium in the α-phase of chromium were determined to be DCr = 3,22·10‒15 м2/с; in the γ-phase of iron DCr = 9,41·10‒15 м2/с. The diffusion coefficient of cobalt in the γ-phase of iron DCo = 7,89·10‒15 м2/с. The depth of the outer coating on the sample was about 15–20 µm, the depth of the diffusion layer of chromium in the base metal was about 70 µm, and that of cobalt was about 40 µm. The maximum hardness of the outer surface layer was 1740 HV, the diffusion layer in the base metal was 900–560 HV, and the base metal was about 510 HV.

Ablation performance of C/C-ZrC-SiC composites with in-situ YSi2-doped ZrC-SiC-ZrSi2 coating under oxyacetylene torch

C/C-ZrC-SiC composites with in-situ formed ZrC-SiC-ZrSi2 coating (ZS) and YSi2-doped ZrC-SiC-ZrSi2 coating (YZS) were prepared by reactive melting infiltration (RMI). The ablation behavior was investigated under the oxyacetylene torch with heat fluxes of 2.38 and 4.18 MW/m2. Results showed that YZS exhibited a more integrated scale and lower ablation rates after ablation due to the doping of YSi2. The Y2O3 and ZrO2 phases could form substitutional solid solutions during ablation, which had a dense structure and could lower the surface temperature of composites. Meanwhile, Y2O3 could inhibit the phase transition of ZrO2, promoting the sintering of ZrO2 during ablation.

Scattering of hot charge carriers in solid solutions of dielectric crystals with substitutional disorder

The spatial distribution of the components that make up the substitutional solid solution is non-uniform. The randomness of substitution leads to the formation of a random potential acting on secondary electrons in the conduction band and holes in the valence band. The random potential is one of the factors that significantly affect the migration, localization, and recombination of a given charge carriers. The influence of another factor, the energy structure of the conduction band, was considered for a substitutional solid solution of the AxB1−xC type in the model of multiple parabolic branches of the electron dispersion law. The transport mean free paths for the cases of elastic scattering of electrons by potential fluctuations and inelastic scattering of electrons by LA and LO phonons were calculated. It was shown that the presence of several parabolic branches of the electron dispersion law in the conduction band in all cases leads to a significant reduction in transport mean free paths compared to the model of one parabolic branch of the electron dispersion law in the conduction band.

Insights into mixed metal sulfides of MnxSn1-xS2 for high-performance supercapacitors

• Substitutional solid solution Mn x Sn 1-x S 2 can be easily synthesized. • Mn 0.33 Sn 0.67 S 2 delivers the highest capacitance electrochemical performances. • The content of Mn plays a crucial role in the lattice parameter and electrochemical properties. • Mn 0.33 Sn 0.67 S 2 //AC achieves excellent energy density of 15.68 Wh kg −1 at 0.15 kW kg −1 . A variety of mixed metal sulfides of Mn x Sn 1-x S 2 nanoflowers were synthesized by a facile one-step template-free solvothermal method and their ability of capacitive energy storage were evaluated as potential supercapacitor electrode materials. Substitutional solid solutions of Mn x Sn 1-x S 2 with various chemical compositions can easily be produced by varying the Mn/Sn molar ratio in the reactants. Among these sulfides, Mn 0.33 Sn 0.67 S 2 exhibits the highest electrochemical performance with a high specific capacitance of 1118.92 F g −1 at 1 A g −1 , great rate capacity and superb cycling stability. Because of its increased electrochemical active sites, altered microstructure, and improved electrical conductivity brought on by lattice distortion and the synergistic effect of elemental substitution, Mn 0.33 Sn 0.67 S 2 exhibits good performance. What’s more, an asymmetric supercapacitor of Mn 0.33 Sn 0.67 S 2 //AC (activated carbon) possesses a high energy density (15.68 Wh kg −1 at 150.1 W kg −1 ). Thus, Mn doped tin sulfides highlight widely applicable to advance high-performance energy storage technology.

Synthesis of Co2+ doped Cadmium borate nanopowder for luminescent applications

Nanoparticles embedded in host materials exhibit a wide variation in properties, viz., photocatalytic activity, luminescence to name a few. In the present study, Cadmium borate was taken as a host in which addition of Cobalt (Co2+) was done through precipitation method. X ray diffraction (XRD) studies revealed only Cadmium borate peaks (indicating the replacement of Co2+ ions at Cd2+ sites, forming a substitutional solid solution), while morphology was found to be agglomerated irregular particles. Photoluminescent studies indicated their possible application for yellowish green coloured emission.

STUDY OF PHASE FORMATION PROCESSES IN CER-CER TYPE INERT MATRICES BASED ON OXIDE COMPOUNDS

The purpose of this work is to study the processes of phase formation in the samples (1-x)ZrO2 – xAl2O3 ceramics depending on the variation of the oxide components, as well as to establish changes in the structural parameters and degree of crystallinity. The choice of zirconium and aluminum oxides as the basis for cer-cer inert matrices for nuclear fuel is due to their physical, chemical, structural and mechanical properties, the combination of which will produce a new type of ceramics with great potential in the field of nuclear fuel. These oxide compounds have high thermal stability and resistance to high temperatures, which also allows their use as a basis for disperse nuclear fuel for new-generation hightemperature nuclear reactors. The method of mechanochemical milling followed by thermal annealing was chosen to obtain ceramics based on oxide compounds. The choice of grinding conditions, as well as the subsequent thermal annealing was chosen to initiate the processes of phase transformations and structural changes as a result of thermal influence and partial relaxation of the deformation distortions and metastable formations initiated during grinding. The X-ray diffraction method was chosen as the main method to study the processes of phase transformation and structural changes. During the studies it was found that the addition of aluminum oxide leads to the structural ordering of the main monocline phase ZrO2, as well as the formation of solid solutions of substitution and introduction. At equal concentrations of the oxide components using the method of X-ray phase analysis was established polymorphic phase transformation in zirconium dioxide, the presence of which indicates the processes of phase transformation arising from the addition of zirconium oxide and changes in the phase formation processes.