Crystalline Solid Solutions Research Articles

High-Pressure Monosulfide Solid Solution FexNi1−xS Phases: X-Ray Diffraction Analysis and Raman Spectroscopy

High-pressure high-temperature (HPHT) crystalline monosulfide solid solution (Mss) phases (FexNi1−xS, x = 0.90, 0.75, 0.50, 0.25), troilite (FeS I), and α-NiS of the Fe-Ni-S system were synthesized at 7 GPa and 900–1550 °C. The structural parameters of the obtained phases were refined by XRD using the Rietveld method. Factor group analysis revealed the number of active Raman modes for FeS I and α-NiS. Raman spectra of troilite, α-NiS, and Mss phases were obtained. It was shown that the Raman spectra of Mss phases and α-NiS have a similar topology. The Raman spectra of the experimental phases in the Fe-Ni-S system were analyzed with non-negative matrix factorization, which provided a meaningful concentration dependence of the spectral patterns. The spectral components were assigned to the FeS I and α-NiS structures. The structural and spectroscopic studies show linear dependencies of unit cell parameters and spectral components on composition and confirm the existence of a series of monosulfide solid solution FexNi1−xS.

Facile construction of a stable biomass-derived carbon-supported Al[sbnd]Zr composite with crystalline solid solution and Brønsted–Lewis dual acidity for efficient catalytic conversion of cellulose

Exploiting cellulose-derived levulinic acid (LA) in biorefinery has potential application prospects, and the development of efficient and stable catalysts is crucial yet challenging. In this study, a bimetallic synergy strategy was proposed to construct an efficient and durable solid acid catalyst with crystalline solid solution by a totally solid-phase method. Mechanical activation (MA)-treated precursor (metal salts, starch, and urea) was calcined to obtain a stable biomass-derived carbon (BC)-supported AlZr (MA-AZ/BC) composite, which was applied for catalytic conversion of cellulose to LA in aqueous-phase system. The results indicate that the synergistic effect of bimetallic crystalline solid solution and the existence of Brønsted–Lewis dual-acid sites in the MA-AZ/BC catalyst contributed to a cellulose conversion efficiency of 97.5 % and a LA yield of 67.1 %. Benefiting from the strong bimetal–support interaction, the MA-AZ/BC catalyst exhibited favorable stability and recoverability. On the basis of comprehensive analysis, a reaction mechanism of Brønsted–Lewis dual-acid sites for synergistic catalytic conversion of cellulose was proposed. This study provides a new idea for the rational design and environmentally friendly fabrication of functional BC-based catalysts for efficiently producing platform compounds derived from biomass.

Bridging the gap between high-entropy alloys and metallic glasses: Control over disorder and mechanical properties of coatings

High-entropy alloys (HEAs) and high-entropy metallic glasses (HEMGs) represent two intensively researched classes of materials with high technological interest for applications as functional coatings with high strength, hardness, toughness, and corrosion resistance. The distinctive structural difference between single-phase crystalline solid solutions for HEAs and liquid-like disorder for HEMGs generates a seemingly insuperable contrast. In this work, we demonstrate that we can deliberately choose between crystalline or glassy properties by introducing structural disorder in HfMoNbTiZr thin films of identical composition. Using pulsed laser deposition (PLD) at different growth conditions, we reproducibly tune the structure of HfMoNbTiZr coatings from crystalline to fully amorphous. We show that the level of disorder has a profound impact on the mechanical properties of the coatings using the hardness derived from nanoindentation measurements as an example. While the hardness of polycrystalline HfMoNbTiZr layers already exceeds the single-phase bulk value, the amorphous HfMoNbTiZr is even clearly harder, demonstrating a distinctive improvement with introducing disorder. Our findings bridge the two seemingly different concepts of HEAs and HEMGs and demonstrate that structural disorder is not a given material property. Instead, disorder can serve as a useful design parameter for customizing the properties of functional coatings.

Effect of sputtering power and substrate bias on microstructure, mechanical properties and corrosion behavior of CoCrFeMnNi high entropy alloy thin films deposited by magnetron sputtering method

The CoCrFeMnNi high entropy alloy thin films with crystalline (solid solution) structure or amorphous state were fabricated by magnetron sputtering process at different target powers and different substrate bias. Effects of the target power and substrate bias on the characteristics of the CoCrFeMnNi thin films such as microstructures, morphology and surface topography, as well as mechanical properties and corrosion behavior were studied. Phase prediction was calculated by using thermodynamic and kinetic criteria under various deposition conditions. The enthalpy, entropy, δ and Ω parameters, and electronegativity differences influenced the solid solution stability of thin films. These parameters led to the formation of solid solutions with crystalline or amorphous structures under specific limits, which corresponded to the practical XRD and TEM analysis results. Using a substrate bias in the deposition of CoCrFeMnNi thin film changed the amorphous structure to a crystalline (solid solution (BCC + FCC)) at higher target powers (200 and 300 W). On the other hand, the film structure was entirely amorphous at all sputtering target powers without the substrate bias. The mechanical properties, such as hardness, Young's modulus, film strength, and fracture toughness of CoCrFeMnNi thin film, can be enhanced by using the substrate bias and increasing the sputtering power. The potentiodynamic polarization test in 3.5 wt% NaCl aqueous solution indicated that the deposition of CoCrFeMnNi thin films at different sputtering powers and without substrate bias could increase the corrosion resistance of 304 stainless steel substrate. Using the substrate bias of −100 V in the fabrication of CoCrFeMnNi thin film decreased the corrosion current density and increased its polarization resistance.

Nanocomposite versus solid solution formation in the TiSiN system

This work contributes to the ongoing scientific debate on the structure of TiSiN coatings. In order to illuminate the formation of a nanocomposite structure versus the formation of a Ti1-xSixN solid solution, a series of TiSiN coatings was synthesized and the influence of varying N2 pressures and the addition of Ar to the deposition atmosphere on the structure of TiSiN coatings was investigated in detail. The powdered TiSiN coatings all exhibited a lower lattice parameter than reported for TiN, which further decreased with increasing N2 pressure, at comparable elemental compositions. For all coatings the presence of a crystalline Ti1-xSixN solid solution as well as an amorphous SiNx phase fraction could be detected, where more Si was incorporated into the Ti1-xSixN solid solution at higher pressures, due to less energetic growth conditions and the additional kinetic activation stemming from Ar ions resulted in less Si incorporation. Density functional theory calculations showed that defects only play a subordinate role for the low observed lattice parameters.

Thermodynamic Stability Transitions and Coexistence of Two Polymorphs via Crystalline Solid Solutions: The T-X Phase Diagram of Salicylic Acid and 2,3-Dihydroxybenzoic Acid

Thermodynamic Stability Transitions and Coexistence of Two Polymorphs via Crystalline Solid Solutions: The T-X Phase Diagram of Salicylic Acid and 2,3-Dihydroxybenzoic Acid

Probing the Molecular and Macroscopic Structure of Solid Solutions by Dynamic Nuclear Polarization (DNP) Enhanced 13C and 15N Solid-State NMR Spectroscopy.

Crystallization is a widely used purification technique in the manufacture of active pharmaceutical ingredients (APIs) and precursor molecules. However, when impurities and desired compounds have similar molecular structures, separation by crystallization may become challenging. In such cases, some impurities may form crystalline solid solutions with the desired product during recrystallization. Understanding the molecular structure of these recrystallized solid solutions is crucial to devise methods for effective purification. Unfortunately, there are limited analytical techniques that provide insights into the molecular structure or spatial distribution of impurities that are incorporated within recrystallized products. In this study, we investigated model solid solutions formed by recrystallizing salicylic acid (SA) in the presence of anthranilic acid (AA). These two molecules are known to form crystalline solid solutions due to their similar molecular structures. To overcome challenges associated with the long 1H longitudinal relaxation times (T1(1H)) of SA and AA, we employed dynamic nuclear polarization (DNP) and 15N isotope enrichment to enable solid-state NMR experiments. Results of solid-state NMR experiments and DFT calculations revealed that SA and AA are homogeneously alloyed as a solid solution. Heteronuclear correlation (HETCOR) experiments and plane-wave DFT structural models provide further evidence of the molecular-level interactions between SA and AA. This research provides valuable insights into the molecular structure of recrystallized solid solutions, contributing to the development of effective purification strategies and an understanding of the physicochemical properties of solid solutions.

Reaction amplification with a gain: Triplet exciton–mediated quantum chain using mixed crystals with a tailor-made triplet sensitizer

Photochemical valence bond isomerization of a crystalline Dewar benzene (DB) diacid monoanion salt with an acetophenone-linked piperazinium cation that serves as an intramolecular triplet energy sensitizer (DB-AcPh-Pz) exhibits a quantum chain reaction with as many as 450 product molecules per photon absorbed (Φ ≈ 450). By contrast, isomorphous crystals of the DB diacid monosalt of an ethylbenzene-linked piperazinium (DB-EtPh-Pz) lacking a triplet sensitizer showed a less impressive quantum yield of ca. Φ ≈ 22. To establish the critical importance of a triplet excited state carrier in the adiabatic photochemical reaction we prepared mixed crystals with DB-AcPh-Pz as a dilute triplet sensitizer guest in crystals of DB-EtPh-Pz. As expected from their high structural similarities, solid solutions were easily formed with the triplet sensitizer salt in the range of 0.1 to 10%. Experiments carried out under conditions where light is absorbed by the triplet sensitizer-linked DB-AcPh-Pz can be used to initiate a triplet state adiabatic reaction from 3DB-AcPh-Pz to 3HB*-AcPh-Pz, which can serve as a chain carrier and transfer energy to an unreacted DB-EtPh-Pz where exciton delocalization in the crystalline solid solution can help carry out an efficient energy transfer and enable a quantum chain employing the photoproduct as a triplet chain carrier. Excitation of mixed crystals with as little as 0.1% triplet sensitizer resulted in an extraordinarily high quantum yield Φ ≈ 517.

Designing Organic π-Conjugated Molecules for Crystalline Solid Solutions: Adamantane-Substituted Naphthalenes.

We showcase herein organic crystalline solid solutions (CSSs) based on the simplest polycyclic aromatic hydrocarbon (PAH) scaffold, naphthalene, stabilized by dispersion forces induced by adamantane substitution. High thermal stability of the host and guest molecules synthesized by cross-coupling of dibromonaphthalene derivatives and 4-(1-adamantyl)phenyl boronic ester enabled formation of crystals by sublimation. We could generate binary monocrystalline solid solution systems proven by X-ray crystallography, the first system of designed CSSs stabilized exclusively via dispersion forces with structural evidence. These observations are additionally supported by lattice energy calculations and spectroscopic examinations. For the generation of CSSs, it is of utmost importance that the host and guest molecules have similar lattice energies and spatial compatibility. We anticipate that the thermostable organic CSS design demonstrated herein would be beneficial for functional materials and further investigation towards materials with unique properties.

Terminal crystalline solid solutions, solubility enhancements and T-X phase diagram of salicylic acid - 4-hydroxybenzoic acid.

The binary T-X phase diagram of salicylic acid (SA) and 4-hydroxybenzoic acid (4HBA) has been constructed from 20 °C to melting, revealing a partially miscible system with an eutectic composition of 27.3 mol% 4HBA in SA. Terminal crystalline solid solutions were obtained at the extremes of the phase diagram with solid-state miscibility limits below 0.4% at 20 °C. The limited phase boundaries could be captured experimentally by both DSC analyses at around melting temperature and solid-liquid equilibria studies at 20 °C in two solvent systems. The NRTL model was applied to regress phase boundaries and generate the final binary T-X phase diagram. The NRTL model was also used to regress solubility data, and reproduce the ternary SA/4HBA/solvent phase diagram at 20 °C and 1 atm. 4HBA was obtained as two crystal forms, viz. anhydrate and monohydrate. It is shown how the monohydrate of 4HBA is less miscible with SA in the solid state than the anhydrous form of 4HBA. As compared to pure SA and 4HBA, the crystalline solid solutions exhibited significant changes in physical properties that are relevant for organic and pharmaceutical materials in the context of impurity effects. A lattice incorporation of just 0.2 mol% 4HBA in SA caused a 10% reduction in melting enthalpy and a 66% solubility increase in 40 wt% MeOH in H2O. The reasons for this thermodynamic effect are discussed.

Impurity-induced acceleration of polymorphic conversion via crystalline solid solutions and the T–X phase diagrams of salicylic acid and 3-hydroxybenzoic acid

Binary T–X phase diagrams of salicylic acid and two monotropic polymorphs of 3-hydroxybenzoic acid showing divergence in thermodynamic stability leading to acceleration of polymorphic conversions.

Rapid solid-state metathesis reactions for the formation of cobalt–iron monoboride solid-solutions and investigation of their water splitting electrocatalytic activity

Rapid solid-state metathesis (SSM) reactions between four reactants form crystalline solid-solution cobalt iron monoborides. These mixed metal borides show improved HER activity that primarily correlates with higher cobalt content.

Electronic, mechanical, and vibrational properties of calcium lanthanum sulfide solid solution: A DFT study

The combination of optical and mechanical properties of calcium lanthanum sulfide (CLS) makes it an attractive material for optical applications. CLS is a γ-phase La2S3/CaS solid solution above 50:50 La2S3/CaS. Experiments have characterized the effect of composition on the structural, thermal, and optical properties. However, the effect of impurities and other defects, such as porosity, on resulting properties is difficult to deconvolute. We used the density functional theory (DFT) simulations to characterize the effect of La2S3/CaS relative fractions on structural, electronic, mechanical, and vibrational properties of single crystalline CLS solid solutions. We find a decrease in the stiffness with CaS fraction and confirm the experimentally observed increase in the lattice parameter with La2S3 fraction. We also characterized the point defects, including sulfur vacancies, oxygen substituting sulfur, oxygen, and sulfur impurities on lanthanum sublattice vacant sites, and sulfur substituting calcium (vS, OS, OLa, and SLa, respectively). Our defect studies in 90:10 CLS find the neutral charge state configuration to be energetically favorable for all tested configurations except for the sulfur vacancies (vS).

Mechanical Alloying in Zeolitic Imidazolate Framework for Enhanced Photocatalytic Dye Degradation.

A ball milling approach has been performed for isostructural ZnZIF-8 and CoZIF-8 in a 1:1 molar ratio to produce the amorphous (a) solid solution state (aZn0.5Co0.5ZIF-8). It further transformed to a crystalline (c) solid solution state (cZn0.5Co0.5ZIF-8) by exposing 95% relative humidity (RH) at 25 °C for 72 h. Unique heterometal solid solution structure and high catalytic active sites of aZn0.5Co0.5ZIF-8 showed excellent photocatalytic performance for the degradation of methylene blue dye under visible light source. The catalytic efficiency of aZn0.5Co0.5ZIF-8 (97.9%) is much higher than the pristine (p) as well as the amorphous state (a) of ZnZIF-8/CoZIF-8 and cZn0.5Co0.5ZIF-8.

Polymorphic Solid Solutions in Molecular Crystals: Tips, Tricks, and Switches.

Crystal polymorphism has been a topic of much interest for the past 20 years or so, especially since its scientific (and legal) importance to the pharmaceutical industry was realized. By contrast, the formation of solid solutions in molecular crystals has been overlooked despite its long-standing prevalence in the analogous field of inorganic crystals. Wilfully forgotten, crystalline molecular solid solutions may be very common in our world since molecular compounds are rarely produced with 100% purity, and impurities able to form solid solutions are difficult to reject via recrystallization. Given the importance of both polymorphism and solid solutions in molecular crystals, we share here some tips, tricks, and observations to aid in their understanding. First, we propose a nomenclature system fit for the description of molecular crystalline solid solutions capable of polymorphism (tips). Second, we highlight the challenges associated with their experimental and computational characterization (tricks). Third, we show that our recently reported observation that polymorph stabilities can change by virtue of solid solution formation is a general phenomenon, reporting it on a second system (switches). Our work focuses on the historically important compound benzamide forming solid solutions with nicotinamide and 3-fluorobenzamide.

High‐entropy oxides: Harnessing crystalline disorder for emergent functionality

AbstractHigh‐entropy materials defy historical materials design paradigms by leveraging chemical disorder to kinetically stabilize novel crystalline solid solutions comprised of many end‐members. Formulational diversity results in local crystal structures that are seldom found in conventional materials and can strongly influence macroscopic physical properties. Thermodynamically prescribed chemical flexibility provides a means to tune such properties. Additionally, kinetic metastability results in many possible atomic arrangements, including both solid‐solution configurations and heterogeneous phase assemblies, depending on synthesis conditions. Local disorder induced by metastability, and extensive cation solubilities allowed by thermodynamics combine to give many high‐entropy oxide systems utility as electrochemical, magnetic, thermal, dielectric, and optical materials. Though high‐entropy materials research is maturing rapidly, much remains to be understood and many compositions still await discovery, exploration, and implementation.

Viewing high entropy alloys through glasses: Linkages between solid solution and glass phases in multicomponent alloys

High entropy alloys (HEAs) represent highly promising multicomponent crystals that form concentrated solid solutions (CSSs) and may violate traditional thermodynamic rules of mixing, ultimately leading to excellent physical properties. For a deeper understanding, we investigate seven CSSs, including Co-Cr-Ni-Fe-Mn elements, at experimentally relevant compositions and conditions, through molecular simulations, and we use 1-1 comparisons to corresponding glass state characteristics, attained through rapid cooling protocols. We determine the behavior of various structural features, including the configurational entropy for a set of CSSs in their crystalline and vitreous states numerically. We employ swap Monte Carlo (MC) simulations, in combination with the reversible scaling method, to efficiently compute the configurational entropy (${S}_{\text{conf}}$), and show that the entropic rule of mixing is not always adequate for predicting alloy formation. We study the stability and formability of crystalline solid solutions, as well as glasses, while following the thermodynamics of ${S}_{\text{conf}}$. An apparent entropic similarity between CSSs and corresponding glasses leads us to use a Kauzmann-like ansatz, relating the CSSs at ${S}_{\text{conf}}\ensuremath{\rightarrow}0$ with the emergence of a CSS order-disorder transition, at temperature ${T}_{OD}$. In the context of glasses, a comparison between kinetic and thermodynamic fragilities allows the association of sluggish diffusion onset to a drop in ${S}_{\text{conf}}$ at ${T}_{K}$. Analogously, we classify CSSs as ``strong'' or ``fragile'' in the sense of their ability to migrate across CSS crystal configurations at high temperatures, distinguishing its formability. We argue that the magnitude of ${T}_{OD}$ may be an excellent predictor of CSS single-phase stability, which appears to scale with well-known HEA predictors, in particular we notice that VEC and ${T}_{OD}$ have in relation to the others a significantly large Pearson correlation coefficient, much larger than most other observables (except $\mathrm{\ensuremath{\Delta}}{H}_{\text{mix}}$).

Enantioselectivity of chiral dihydromyricetin in multicomponent solid solutions regulated by subtle structural mutation.

Multicomponent crystals of a chiral drug with non-chiral components have attracted increasing attention in the application of enantiomer purification and regulation of the physicochemical properties of crystalline materials. Crystalline solid solutions provide opportunities for fine-tuning material properties because of continuously adjustable component stoichiometry ratios. The synthesis, crystal structure, thermodynamics and solid-state enantioselectivity of a series of multicomponent crystals of chiral dihydromyricetin (DMY) with caffeine (CAF) or theophylline (THE) were investigated and the results reveal how the subtle change of molecular structure of the coformer dictates the enantiomer selectivity in multicomponent cocrystals. A series of multicomponent cocrystal solvates of chiral DMY with CAF and THE were synthesized by the slurry cocrystallization method in acetonitrile. Although most racemic mixtures crystallize as racemic compounds or conglomerates, both DMY-CAF and DMY-THE crystallize as chiral solid solutions, unveiled by pseudo-binary melt phase diagrams and pseudo-ternary solution phase diagrams. Crystal structures of Rac-DMY-CAF, R,R-DMY-CAF, Rac-DMY-THE and R,R-DMY-THE are reported for the first time via single-crystal X-ray diffraction, displaying two distinct types of solid solution differing in mixing scale of enantiomers spanning several orders of magnitude. Surprisingly, this remarkable impact on enantiomer discrimination was simply achieved by the reduction of a methyl group of CAF to the THE coformer, which was further rationalized from their crystal structures and intermolecular interactions. Collectively, this work has demonstrated that a subtle change in the molecular structure of a coformer can regulate enantioselectivity in crystalline materials, guiding the purification of chiral racemic compounds via the cocrystallization method and the design of solid-solution crystalline materials.

Processing Gray Selenium in Phosphonium-Based Ionic Liquids.

The dissolution of gray selenium in tetraalkylphosphonium acetate ionic liquids was investigated by UV-vis, NMR, and Raman spectroscopy as well as quantum chemical calculations and electrochemical methods. Acetate anions and tetraalkylphosphonium cations facilitate the formation and stabilization of oligoselenides Sen2- and cationic Se species in the ionic liquid phase. Chemical exchange of selenium atoms was demonstrated by variable-temperature 77Se NMR experiments. Additionally, uncharged cycloselenium molecules exist at high selenium concentrations. Upon dilution with ethanol, amorphous red selenium precipitates from the solution. Moreover, crystalline Se1-xTex solid solutions precipitate when elemental tellurium is added to the mixture as confirmed by powder X-ray diffraction and Raman spectroscopy.

Solubility enhancements through crystalline solid solutions, the non-linear Tammann diagram and the T–X phase diagram of salicylic acid–benzoic acid

The T–X phase diagram of salicylic acid–benzoic acid discloses significant miscibility in the solid-state. The two crystalline solid solutions result in 87% and 19% solvent solubility increases, respectively, relative to the pure components.