Formation Of Continuous Solid Solutions Research Articles

Solid Phase and Stability Investigation of a Co-Crystal in the l-Valine/l-Leucine System

Some amino acid systems are known to exhibit solid solution and/or co-crystal behavior upon crystallization, which significantly affects their phase diagrams and complicates the design of their purification processes. Such behaviors are observed in the l-valine/l-leucine system. In this work, the formation and stability of a 3:1 co-crystal of the two amino acids (designated as V3L) is further investigated. To accomplish the formation, liquid-assisted grinding, slurry equilibration, and sublimation experiments were performed and analyzed via HPLC and PXRD. Additionally, periodic DFT calculations were used to calculate lattice energies and determine the thermodynamics of possible solid phases. Experimental results show a clear metastability of the investigated V3L co-crystals when compared to its stable solid solution. The calculations underline the metastability and the possible formation of continuous solid solutions between l-valine and l-leucine since lattice energy differences between pure amino acids and mixed compositions are negligible. This previously unknown phase behavior can be used to assess the influence of V3L on the amino acid purification process and provides a basis for investigating similar systems with small energy differences between pure and mixed compositions in future studies. In addition, it demonstrates the particular variability of solid phases and their relationships in such simple but biologically important amino acid systems.

Crystal structure and electrochemical hydrogenation of HoNiIn1-xAlx (x = 0-1) solid solution

The influence of the substitution of indium by aluminum in HoNiIn compound at 873 K was investigated in the full concentration range by means of powder X-ray diffraction and EDX analysis. The formation of continuous solid solution was determined and changes of the unit cell parameters were calculated: HoNiIn1.0–0Al0–1.0 (ZrNiAl-type structure, space group P-62m, a = 0.74343(4)–0.69959(6) nm and c = 0.37472(3)–0.38289(4) nm, V = 0.17936(2)–0.16229(3) mn3). The best discharge capacity after electrochemical hydrogenation studies of HoNiIn1-xAlx solid solution is observed for battery prototypes with HoNiIn0.2Al0.8- and HoNiIn0.4Al0.6-based electrodes.

Band engineering of delafossite CuB1-xFexO2 (B = Al, Cr, Sc) solid solutions as photocathodes: Visible-light response and performance enhancement

The optimization of wide-bandgap semiconductor photoelectrodes for efficient visible-light response and enhanced photoelectrochemical activity is a major challenge in the field of hydrogen production from water splittin. To overcome this challenge, the integration of narrow-bandgap semiconductor photoelectrodes to form solid solutions has emerged as a promising strategy. Delafossite ABO2 compounds offer an ideal platform for this approach due to their family of materials with multiple compatible members and their ability to readily form solid solutions. In this study, we focus on the formation of continuous solid solutions by combining a narrow-bandgap semiconductor CuFeO2 photocathode with three typical wide-bandgap semiconductor CuBO2 (B=Al, Cr, Sc) photocathodes. The synthesis of these solid solutions was achieved using solid-state reaction and hydrothermal methods. Characterization of the optical properties confirms that CuB1-xFexO2 (0 < x < 1) solid solutions exhibit strong light absorption within the visible light region. Photoelectrochemical tests performed under visible light irradiation demonstrate excellent photoelectrochemical activity. Notably, the photocurrent densities of CuAl0.7Fe0.3O2, CuCr0.7Fe0.3O2, and CuSc0.8Fe0.2O2 photocathodes are approximately 7.29, 11.00, and 7.32 times higher, respectively, than those of the corresponding pure CuAlO2, CuCrO2, and CuScO2 photocathodes. Additionally, these solid-solution photocathodes exhibit significantly improved monochromatic incident photon-to-electron conversion efficiency. Attributed to the integration of Fe components, the bandgap and conduction band edge of CuBO2 (B=Al, Cr, Sc) materials are effectively decreased. The optimal photoactivity of CuB1-xFexO2 solid solutions under visible light irradiation is attained when the visible light response, reduction potential, and kinetic behavior of photogenerated carriers reach equilibrium. This finding underscores the importance of balancing these key factors to achieve superior performance in solid solution photocathodes. Based on our results, we summarize several universal principles for constructing high-performance solid solution photocathodes.

THE SbBiTe2Se-SbBiTe2S PHASE DIAGRAM OF THE Sb-Bi-S-Se-Te SYSTEM

Using powder X-ray diffraction (PXRD) and differential thermal analysis (DTA), the phase equilibria of the SbBiTe2Se – SbBiTe2S section were studied, and its T-x diagram was constructed. The system is non-quasibinary, due to both initial phases melting in the temperature range. The system is stable below the solidus, which is characterized by the formation of continuous solid solutions (α-phase) with a tetradymite-like hexagonal structure. An analysis of the structural features of tetradymite and other tetradymite-like compounds shows that the substitution of atoms by related atoms is possible in all layers of the packet. In this work sulfur atoms in the central layer can be easily replaced by selenium atoms. This tendency allows us to expect the formation of the range of compositions in the BiSb-Te-Se-S system in which substitutions are realized in cationic and anionic positions. Lattice parameters were determined from the results of powder diffraction patterns. It has been established that the crystal lattice parameters of solid solutions change linearly with composition, which complies with the Vegards rule. Keywords: SbBiTe2Se – SbBiTe2S system, phase diagram, tetradymite-like structure, solid solutions, high entropy alloys.

THE SbBiTe2Se-SbBiTe2S PHASE DIAGRAM OF THE Sb-Bi-S-Se-Te SYSTEM

Using powder X-ray diffraction (PXRD) and differential thermal analysis (DTA), the phase equilibria of the SbBiTe2Se – SbBiTe2S section were studied, and its T-x diagram was constructed. The system is non-quasibinary, due to both initial phases melting in the temperature range. The system is stable below the solidus, which is characterized by the formation of continuous solid solutions (α-phase) with a tetradymite-like hexagonal structure. An analysis of the structural features of tetradymite and other tetradymite-like compounds shows that the substitution of atoms by related atoms is possible in all layers of the packet. In this work sulfur atoms in the central layer can be easily replaced by selenium atoms. This tendency allows us to expect the formation of the range of compositions in the BiSb-Te-Se-S system in which substitutions are realized in cationic and anionic positions. Lattice parameters were determined from the results of powder diffraction patterns. It has been established that the crystal lattice parameters of solid solutions change linearly with composition, which complies with the Vegards rule. Keywords: SbBiTe2Se – SbBiTe2S system, phase diagram, tetradymite-like structure, solid solutions, high entropy alloys.

MODELING THE PHASE DIAGRAM OF THE Tl9TbTe6–Tl4PbTe3–Tl9BiTe6 SYSTEM

The analytical multi 3D model of phase diagram of the Tl9TbTe6–Tl8Pb2Te6–Tl9BiTe6 system was obtained as temperature dependence on the composition using the Multipurpose Genetic Algorithm (MGA). It was determined that the system is characterized by the formation of continuous solid solutions with tetragonal Tl5Te3-type structure (δ-phase). The boundaries of the uncertainty band for the liquidus and solidus surfaces of the δ-phase and the TlTbTe2 compound are determined. The thermodynamic functions of mixing of the solid solutions depending on the composition and temperature are determined based on the model of regular solutions of non-molecular compounds. It was established that the δ-phase possess thermodynamic stability in the entire concentration interval

Взаємодія в системах Y2O3—Ln2O3 (Ln = Tb—Lu)

Based on the analysis of literature data from experimentally constructed phase diagrams of Y2O3 − Ln2O3 systems (Ln = Tb − Lu), as well as temperatures of polymorphic transformations of rare earth oxides (REE), tentative phase diagrams of Y2O3 − Ln2O3 systems (Ln = Tb − Lu) were constructed in wide intervals of temperatures and concentrations. Prediction of the binary phase diagrams structure of yttria − yttrium subgroup lanthanides systems was carried out on the basis of three principles: 1. Since double systems are formed by lanthanide oxides of one (yttrium) subgroup, it is very likely that in such systems continuous solid solutions will be formed between the components. 2. Intermediate binary phases are not formed in these systems. 3. The formation of continuous solid solutions occurs with a decrease in the temperatures of phase transformations in the solid state to a minimum shifted towards a lower transformation temperature of the system component. The forecast of the Y2O3 – Ln2O3 systems phase diagrams structure, where Ln = Tb – Lu, indicates the complete solubility of the components in the liquid and solid states. Binary compounds in the considered systems are not predicted. Phase transformations in the solid solutions on the basis of polymorphic modifications X, H, A, B and C of lanthanide oxides cascade at high temperatures by the peritectoid mechanism. Below 1850 °C regions of solid solutions with cubic C-structure of REE oxides are formed in the whole range of concentrations in the systems. Key words: REE oxides, yttria, polymorphs of REE oxides, phase diagram.

Effects of nickel content on the microstructure, microhardness and corrosion behavior of high-entropy AlCoCrFeNix alloys

In this study the effect of three different nickel concentration on the microstructure, hardness and corrosion properties of high entropy alloys (HEAs) from AlCrFeCoNi system as an alternative material for medical instruments fabrication was investigated. The analyzed HEAs were AlCrFeCoNix obtained by vacuum arc remelting from high purity raw materials and having nickel atomic ratio x = 1.0, 1.4 and 1.8. The microscopy examination revealed the dendritic morphology for the reference alloy (AlCrFeCoNi) and that the extent of the interdendritic areas increased with the concentration of nickel while Cr was more segregated in the interdendritic areas than in dendrites. Hardness values decreased as the percentage of nickel increased due to the dissolution of the precipitates in a nickel-rich matrix and consequently the formation of continuous solid solutions. The corrosion properties of the synthesized HEAs were evaluated using a potentiodynamic polarization method. The alloys were immersed in Simulated Body Fluid during one week and the corrosion parameters were recorded. The low corrosion rates, low corrosion currents and high polarization resistance attest the good stability of these HEAs in simulated biological environment indicating their possible use for surgical and dental instruments.

Vibrational spectra and optical properties ofFe1−xCrxVO4solid solutions: With a group theory analysis

The present manuscript reports vibrational spectra and optical studies of polycrystalline Fe1-xCrxVO4 solid solutions through FT-IR spectroscopy augmented with a group theory (G.T.) analysis and UV-Visible DRS spectroscopy. Full set of IR and Raman modes are determined by G. T. for various crystal symmetries in FeVO4-CrVO4 solid solutions where Triclinic, Monoclinic and Orthorhombic structures evolve with increasing Cr concentration. Experimentally obtained vibrational modes support the structural phase transitions and confirm formation of continuous solid solutions in Fe1-xCrxVO4. The Diffuse Reflectance Spectra (DRS) of Fe1-xCrxVO4 depicts the electronic structure and different optical transitions due to absorption of photon energy. The d-d transitions are manifested for all compounds in terms of crystal field stabilization energy (CFSE) caused by distorted lattice sites. The band gap energy of Fe1-xCrxVO4 is calculated using Tauc formula. It shows a red shift initially within triclinic structure then blue shift with the increase of Cr concentration. Urbach energy (Eu) tails in the spectra show the electronic structural disorder in Fe1-xCrxVO4 due to impurity energy levels of Cr ions within band gap region. It is observed that Eu decreases with the doping concentration due to the increase in crystal symmetry corresponding to the structural phase transitions in Fe1-xCrxVO4.

New Mixed Y0.5R0.5VO4 and RVO4:Bi Materials: Synthesis, Crystal Structure and Some Luminescence Properties

The results are reported on a precise crystal structure and microstructure determination of new mixed YVO4-based orthovanadates of Y0.5R0.5VO4 (R = Sm, Tb, Dy, Ho, Tm, Yb, Lu) as well as some Bi3+-doped RVO4 (R = La, Gd, Y, Lu) nano- (submicro-) materials. The formation of continuous solid solutions in the YVO4–RVO4 pseudo-binary systems (R = Sm, Tb, Dy, Ho, Tm, Yb, Lu) has been proved. The lattice constants and unit cell volumes of the new mixed orthovanadates were analyzed as a function of R3+ cation radius. The impact of crystal structure parameters on the energy band gap of the materials was studied by means of photoluminescence studies of the Bi3+-doped compounds.

Thermal Behaviour of Sm0.5 R 0.5FeO3 (R = Pr, Nd) Probed by High-Resolution X-ray Synchrotron Powder Diffraction.

Mixed ferrites Sm0.5Pr0.5FeO3 and Sm0.5Nd0.5FeO3 with orthorhombic perovskite structure isotypic with GdFeO3 were synthesized by solid-state reaction technique in air at 1473 K. Structural parameters obtained at room temperature prove a formation of continuous solid solutions in the SmFeO3–PrFeO3 and SmFeO3–NdFeO3 pseudo-binary systems. Sm0.5Pr0.5FeO3 and Sm0.5Nd0.5FeO3 show strongly anisotropic nonlinear thermal expansion: thermal expansion in the b direction is twice lower than in the a and c directions. The average linear thermal expansion coefficients of Sm0.5Pr0.5FeO3 and Sm0.5Nd0.5FeO3 in the temperature range of 298–1173 K are in the limits of (9.0–11.1) × 10−6 K−1, which is close to the values reported for the parent RFeO3 compounds. Subtle anomalies in the lattice expansion of Sm0.5Pr0.5FeO3 and Sm0.5Nd0.5FeO3 detected at 650–750 K reflect magnetoelastic coupling at the magnetic ordering temperature TN.

Sol-Gel-Prepared Nanoparticles of Mixed Praseodymium Cobaltites-Ferrites.

Two series of nanocrystalline powders of PrCo1 − xFexO3 (x = 0.1, 0.3, 0.5, 0.7 and 0.9) of high purity were obtained by sol-gel citrate method at 700 and 800 °C. The formation of continuous solid solution with an orthorhombic perovskite structure (sp. group Pbnm) was observed. A peculiarity of the PrCo1 − xFexO3 solid solution is the lattice parameter crossovers, which occurred at certain compositions and revealed in the pseudo-tetragonal or pseudo-cubic metric. An average crystallite size of the PrCo1 − xFexO3 samples estimated from the analysis of the angular dependence of the X-ray diffraction (XRD) line broadening varies between 30 and 155 nm, depending on the composition and synthesis temperature.

Phase diagram of the Nd2Fe14B–Sm2Fe14B pseudo-binary system

The phase relations in the (1−x)Nd2Fe14B–xSm2Fe14B system over the whole concentration range have been studied by means of X-ray powder diffraction (XRD), differential thermal analysis (DTA) and scanning electron microscopy with energy-dispersive X-ray spectroscopy. Crystal structure parameters for all studied compositions of (Nd1−xSmx)2Fe14B have been determined by full-profile Rietveld refinements. These results revealed that all intermediate alloys of (Nd1−xSmx)2Fe14B are similar to the end member of the investigated system, Nd2Fe14B, with a tetragonal structure (space groupP42/mnm). The formation of continuous solid solutions has been found in this system. The normalized lattice parameters and unit-cell volumes of (Nd1−xSmx)2Fe14B solid solutions decrease linearly with increasing Sm content. The DTA measurements show that the melting temperature of (Nd1−xSmx)2Fe14B increases linearly with increasing Sm content and no metastable phases were detected. Based on the DTA data and XRD results, a tentative phase diagram for the pseudo-binary system Nd2Fe14B–Sm2Fe14B has been constructed.

Structural Behaviour of EuCoO&lt;sub&gt;3 &lt;/sub&gt;and Mixed Cobaltites-Ferrites EuCo&lt;sub&gt;1&lt;/sub&gt;&lt;sub&gt;−&lt;/sub&gt;&lt;sub&gt;x&lt;/sub&gt;Fe&lt;sub&gt;x&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt;

Crystal structure of the mixed cobaltites-ferrites EuCo1−xFexO3, obtained by solid state reaction in air at 1573 K, has been studied by means of X-ray powder diffraction technique. It was found that all samples synthesized adopt orthorhombic perovskite structure. Obtained values of structural parameters indicate formation of continuous solid solution in the EuCoO3−EuFeO3 system. Thermal behaviour of the EuCoO3 structure has been investigated in the temperature range of 298–1173 K by means of in situ high-resolution powder diffraction technique applying synchrotron radiation. Strong anomalies in the lattice expansion have been detected between 580 K and 800 K, which are evidently connected with the transitions of Co3+ ions to the higher spin states and further metal-insulator transition occurred in EuCoO3 at about 600 K.

Synthesis and characterization of cadmium-calcium hydroxyapatite solid solutions

A series of cadmium-calcium hydroxyapatite solid solutions was prepared by an aqueous precipitation method. By various means, the characterizations confirmed the formation of continuous solid solutions over all ranges of Cd/(Cd+Ca) atomic ratio. In the results, both lattice parameters a and c display slight deviations from Vegard’s rule when the Cd/(Cd+Ca) atomic ratio is greater than 0.6. The particles change from smaller acicular to larger hexagonal columnar crystals as the Cd/(Cd+Ca) atomic ratio increases from 0–0.60 to 0.60–1.00. The area of the phosphate peak for symmetric P-O stretching decreases with the increase in Cd/(Cd+Ca) atomic ratio, and the peak disappears when the Cd/(Cd+Ca) atomic ratio is greater than 0.6; the two phosphate peaks of P-O stretching gradually merge together for the Cd/(Cd+Ca) atomic ratio near 0.60. These variations can be explained by a slight tendency of larger Cd ions to occupy M(2) sites and smaller Ca ions to prefer M(1) sites in the structure.

Phase equilibria in the Tl–TlI–Te system and thermodynamic properties of the Tl5Te3−xIx solid solution

The Tl–TlI–Te ternary system was investigated by using the DTA and XRD analyses, microhardness and EMF measurements, leading to the construction of important polythermal and isothermal sections as well as the projection of the liquidus surface. Determined were the fields of primary crystallization and the types and coordinates of non- and monovariant equilibria. The system features the formation of continuous solid solutions (δ-phase) between the Tl5Te3 and Tl5Te2I compounds. The homogeneity area of the δ-phase completely covers the Tl5Te2I–Tl5Te3–Tl2Te subsystem. The partial molar thermodynamic functions (ΔG‾,ΔH‾,ΔS‾) of thallium as well as the standard integral thermodynamic functions of the Tl5Te3−xIx solid solution (for various x) were calculated based on the results of the EMF measurements.

Formation of continuous solid solutions near the minimum point of a phase diagram

A model of structure ordering in alloys of the compositions corresponding to the minimum points of phase diagrams with continuous series of solid solutions was proposed based on calculating the concentration dependence of the energy of mixing and the results of X-ray powder diffraction study of solid solutions in the systems Sb-As, Sb2Se3-Bi2S3, and Cu-Mn.

Characterization of Cd1−x Zn x Se thin films deposited at low temperature by chemical route

Optoelectronic technologically important pseudo-binary Cd1−xZnxSe thin films with a variable composition (0 < x < 1) has been developed by chemical bath deposition method. The objective to study growth kinetics, physical, microscopic, compositional, optical, electrical and structural changes. Cd1−xZnxSe have been deposited on non-conducting glass substrate in tartarate bath containing Cd+2 and Zn+2 ions with sodium selenosulphate with an aqueous alkaline medium at 278 K. The quality and the thickness of the films are depends upon deposition temperature, deposition time and pH, etc. X-ray diffraction (XRD), atomic absorption spectroscopy, optical absorption, scanning electron microscopy and thermoelectric technique characterized the films. The XRD study indicates the polycrystalline nature in single cubic phase over whole range of composition. Analysis of absorption spectra gave direct type band gap, the magnitude of which increases non-linearly as zinc content in the film is increased and dc electrical conductivity at room temperature was found to decreases from 10−7 to 10−8 (Ω cm)−1. All the films show n-type conductivity. The promising features observed are the formation of continuous solid solutions in a single cubic phase.

Peculiarities in the electronic band structures of Cr∕Cu multilayered nanostructures and Cr1−xCux metastable alloy films: Ab initio linearized-augmented plane-wave and experimental optical studies

A set of Cr1−xCux alloy films with 0&amp;lt;x&amp;lt;1 and Cr∕Cu multilayered films (MLFs) has been prepared by dc sputtering onto glass substrates kept at 293K. The x-ray diffraction study reveals the formation of continuous solid solutions in bcc structures for the Cr1−xCux alloy films with x&amp;lt;0.3 and in fcc structures for x&amp;gt;0.3. The structural instability of Cr1−xCux alloy films near x≈0.3 is discussed in terms of band structures of Cr–Cu alloys with bcc and fcc types of structure, and related to the dramatic changes of the density of states at the Fermi level. The optical properties of Cr1−xCux alloy films can be classified into two groups, representing the film structures. The fcc-bcc structural transformation results in the appearance of interband absorption at 2eV in the optical-conductivity spectra of alloy films, which originates from Cr. The observed changes in the experimental optical properties of Cr1−xCux alloy films are explained in terms of band structures of Cr–Cu alloys. The comparison between experimental and modeled optical properties of Cr∕Cu MLF enables us to conclude that the interfacial alloy regions of about 1.6–2.2nm in thickness are spontaneously formed during the Cr∕Cu MLF fabrication. In addition, it was understood that the main features of electronic band structures for pure Cr and Cu sublayers of a few nanometers in Cr∕Cu MLF resemble greatly those of the bulk Cr and Cu.

Crystal growth and characterization of Yb 3+-doped Gd 3Ga 5O 12

Single crystals of (Yb x Gd 1− x ) 3Ga 5O 12 (0.0 ≤ x ≤ 1.0) have been grown by the micro-pulling-down method. Formation of continuous solid solutions with a garnet structure was confirmed. Composition dependence of the lattice constant, thermal diffusivity, specific heat capacity and thermal conductivity was investigated. Assignment of the Yb 3+-energy levels in Gd 3Ga 5O 12-host lattice has been performed by using absorption, emission and Raman spectroscopy measurements at both, room temperature and at 12 K.