Temperature-composition Phase Diagram Research Articles

Mannitol Crystallization at Sub-Zero Temperatures: Time/Temperature-Resolved Synchrotron X-ray Diffraction Study and the Phase Diagram.

Mannitol, a common pharmaceutical ingredient, exhibits complex polymorphism even in simple binary mannitol/water mixtures, with four crystalline forms observed. In this investigation, time/temperature-resolved synchrotron X-ray diffraction measurements are performed during freezing and thawing of mannitol/water mixtures. Mannitol crystallization depends strongly on the cooling rate and is initiated during cooling, if the cooling rate is lower than the critical cooling rate; otherwise, mannitol remains amorphous during freezing and crystallizes during subsequent heating above -30 °C. A temperature-composition phase diagram is constructed, reflecting eutectic and peritectic points and lower-temperature equilibria involving mannitol hemihydrate, hexagonal ice, and β-mannitol. Comparison of the experimental data with the phase diagram reveals that the mannitol crystallization behavior does not follow the equilibrium but appears to obey the Ostwald crystallization rule. Novel insights on equilibrium and kinetics phase relationships in mannitol/water systems could lead to improved formulations and manufacturing processes for pharmaceuticals and biopharmaceuticals.

Phase stability of monolayer Si1-xGex alloys with a Dirac cone.

The phase stability and electronic properties of two-dimensional Si1-xGex alloys are investigated via the first-principles method in combination with the cluster expansion and Monte Carlo simulations. The calculated composition-temperature phase diagram indicates that at low temperatures (below 200 K) monolayer Si1-xGex alloys energetically favor phase separation, whereas when the temperature is increased above 550 K, Si1-xGex alloys can be stabilized and thereby form solid solutions across the whole composition range. Special quasi-random structures were constructed to model the monolayer Si1-xGex. The Si1-xGex alloys are found to possess a robust Dirac cone against composition variation. These results provide a guideline for the experimental realization of Si1-xGex alloys and monolayer Si1-xGex alloys are believed to hold great potential for realization of applications in nanoelectronics and nano-optoelectronics.

Tailoring thermal expansion coefficient from positive through zero to negative in the compositional crossover alloy Ti50(Pd40Cr10) by uniaxial tensile stress

The precision control of thermal expansion is of fundamental interest and desirable for applications that require materials to retain their shape at different temperatures. In the present study, we propose that the thermal expansion coefficient can be tuned by uniaxial external stress for a single material embedded with nanoclusters, if the formation, growth or alignment of the nanoclusters depends on the external stress. We demonstrate the idea in a prototype alloy (Ti50(Pd40Cr10)) located at the compositional crossover region between martensite and strain glass in the temperature-composition phase diagram of Ti50(Pd50−xCrx). Its thermal expansion coefficient varies linearly from positive, through zero to negative values with increasing uniaxial tensile stress within 200 K ~ 300 K. The phase field simulations show that the volume fraction of nanoscale martensite variant favored by the external stress increases with stress, producing extra strain and compensating for the contraction of the austenite matrix on cooling. The degree of compensation leads to different thermal expansion coefficients. Such a tunable thermal expansion behavior occurs only in the crossover compositions between martensite and strain glass, providing a design recipe for searching new systems with similar behavior.

Effect of Cation Structure in Quinolinium-Based Ionic Liquids on the Solubility in Aromatic Sulfur Compounds or Heptane: Thermodynamic Study on Phase Diagrams.

Experimental and theoretical studies on thermodynamic properties of quinolinium-based ionic liquids (ILs) based on bis(trifluoromethylsulfonyl)imide anion (namely N-butyl-quinoloinium bis(trifluoromethylsulfonyl)imide, [BQuin][NTf2], N-hexylquinoloinium bis(trifluoromethyl-sulfonyl)imide, [HQuin][NTf2], and N-octylquinoloinium bis(trifluoromethyl-sulfonyl)imide, [OQuin][NTf2]) with aromatic sulfur compounds and heptane, as a model compound of fuel were examined in order to assess the applicability of the studied ionic liquids for desulfurization of fuels. With this aim, the temperature-composition phase diagrams of 13 binary mixtures composed of organic sulfur compounds (thiophene, benzothiophene, or 2-methylthiophene) or heptane and ionic liquid (IL) were investigated at ambient pressure. A dynamic method was used to determine the (solid–liquid) equilibrium phase diagrams in binary systems over a wide composition range and temperature range from T = 255.15 to 365.15 K up to the fusion temperature of ILs. The immiscibility gap with an upper critical solution temperature (UCST) was observed for each binary system under study. The influence of the alkane chain length of the substituent on the IL cation and of the sulfur compounds (the aromaticity of the solvent) was described. The experimental (solid + liquid) phase equilibrium dataset were successfully correlated using the well-known NRTL equation.

Tunable Lower Critical Solution Temperature of Poly(butyl acrylate) in Ionic Liquid Blends

We describe the lower critical solution temperature (LCST)-type phase behavior of poly(butyl acrylate) (PBA) dissolved in hydrophobic 1-alkyl-3-methylimidazolium bis{(trifluoromethyl) sulfonyl}amide ionic liquids (ILs). The temperature-composition phase diagrams of these PBA/ILs systems are strongly asymmetric with the critical composition shifted to low concentrations of PBA. As the molecular weight increases from 5.0×103 to 2.0×104, the critical temperature decreases by about 67 °C, and the critical composition shifts to a lower concentration. Furthermore, the LCST of PBA/ILs system increases as increasing the alkyl side chain length in the imidazolium cation. Using IL blends as solvents, the LCST of PBA can be tuned almost linearly over a wide range by varying the mixing ratio of two ionic liquids without modifying the chemical structure of the polymers.

Thermo-Calc Determination of Phase Diagram of Si-B Binary System

Deep understanding of the Si-B binary system is mainly essential for producing solar-grade silicon from metallurgical-grade silicon (MG-Si) as raw material. The phase diagram and thermodynamic properties are the main pillars of this understanding, where the phase diagram is useful for determining the Si terminal solubility, which is necessary for the success of the solvent refining process, by careful examination of the solvus line. Since Si-B phase diagrams found in literature are old and based on old experimental data, Thermo-Calc software 2019b is used in this work to reassess the temperature–composition phase diagram of the Si-B binary system at pressure of 1 bar. The resulting phase diagram is compared with experimental and computed diagrams found in literature and used to deduce the different reactions, melting temperatures, and solubilities of Si in B and B in Si, and all the identified discrepancies are discussed. There are six single phases other than elemental boron and elemental silicon: liquid, diamond-Si solid solution, β-B solid solution, SiB3 solid solution, SiB6 considered as a stoichiometric compound, and SiBn solid solution. In addition, the phase diagram includes nine regions of two mixed phases, all of which are thoroughly discussed. The melting points of pure β-B and pure diamond-Si are determined. Two peritectic reactions are found, a eutectic reaction, and a peritectoid reaction. The maximum solubility of Si in B is found to be 5.37 Si mass percent at 2310.04 ± 0.025 K, while that of B in Si is found to be 0.41 B mass percent at 1657.56 ± 0.025 K.

Suppression of superconductivity by anisotropic strain near a nematic quantum critical point

High temperature superconductivity emerges in the vicinity of competing strongly correlated phases. In the iron-based superconductor $Ba(Fe_{1-x}Co_{x})_{2}As_{2}$, the superconducting state shares the composition-temperature phase diagram with an electronic nematic phase and an antiferromagnetic phase that break the crystalline rotational symmetry. Symmetry considerations suggest that anisotropic strain can enhance these competing phases and thus suppress the superconductivity. Here we study the effect of anisotropic strain on the superconducting transition in single crystals of $Ba(Fe_{1-x}Co_{x})_{2}As_{2}$ through electrical transport, magnetic susceptibility, and x-ray diffraction measurements. We find that in the underdoped and near-optimally doped regions of the phase diagram, the superconducting critical temperature is rapidly suppressed by both compressive and tensile stress, and in the underdoped case this suppression is enough to induce a strain-tuned superconductor to metal quantum phase transition.

Phase boundary and electric field induced polarization rotation in lead-free Ba(Zr0.2Ti0.8)O3-(Ba0.7Ca0.3)TiO3

ABSTRACT Ba(Zr0.2Ti0.8)O3-x(Ba0.7Ca0.3)TiO3 (BZT-xBCT) is a promising lead-free ferroelectric system with high piezoelectricity. Here we carry out phenomenological calculations to explore phase stability and electric field induced phase transition. Study of free energy variation near phase boundaries revealed ultralow energy barrier in single orthorhombic phase region and phase coexistence around inter-ferroelectric transitions. The calculated critical electric field for tetragonal-orthorhombic transition is in reasonable agreement with experimental data. Temperature–composition phase diagram under [001], [011] and [111] oriented electric field are computed, and polarization rotation associated monoclinic structures are studied.

Quasi-Binary Transition Metal Dichalcogenide Alloys: Thermodynamic Stability Prediction, Scalable Synthesis, and Application.

Transition metal dichalcogenide (TMDCs) alloys could have a wide range of physical and chemical properties, ranging from charge density waves to superconductivity and electrochemical activities. While many exciting behaviors of unary TMDCs have been demonstrated, the vast compositional space of TMDC alloys has remained largely unexplored due to the lack of understanding regarding their stability when accommodating different cations or chalcogens in a single-phase. Here, a theory-guided synthesis approach is reported to achieve unexplored quasi-binary TMDC alloys through computationally predicted stability maps. Equilibrium temperature-composition phase diagrams using first-principles calculations are generated to identify the stability of 25 quasi-binary TMDC alloys, including some involving non-isovalent cations and are verified experimentally through the synthesis of a subset of 12 predicted alloys using a scalable chemical vapor transport method. It is demonstrated that the synthesized alloys can be exfoliated into 2D structures, and some of them exhibit: i) outstanding thermal stability tested up to 1230 K, ii) exceptionally high electrochemical activity for the CO2 reduction reaction in a kinetically limited regime with near zero overpotential for CO formation, iii) excellent energy efficiency in a high rate Li-air battery, and iv) high break-down current density for interconnect applications. This framework can be extended to accelerate the discovery of other TMDC alloys for various applications.

Melting loops in the phase diagram of individual nanoscale alloy particles: completely miscible Cu–Ni alloys as a model system

A modified thermodynamic approach to describe melting in isolated nanoscale materials is suggested. The Gibbs free energy change of nanoscale alloy particles is modeled as a function of composition, temperature and nucleus and particle sizes. Cu–Ni has been chosen as a model system due to the availability of thermodynamic data within the high-temperature interval 1300–1600 K. For the first time, “melting loops” in the temperature–composition phase diagram were calculated for nanoparticle of 25 and 80 nm, respectively. It is shown that such loops represent the equilibrium two-phase solid–liquid states and do not coincide with the limiting solubility curves—the solidus and the liquidus. This new finding leads to the “melting loop” concept concerning phase diagrams of nanoscale alloys introduced in this paper. It is found that Cu–Ni nanoparticles can melt in different ways, whereas the dominant transition mechanism is surface-induced melting that initiates from the surface and then proceeds toward the core region. The decrease in size causes also a change of the melting temperature, the temperature width of the phase transition, the solubility limit, the concentration width of the melting loop as well as a change of the shape and slope of the equilibrium curves of the two-phase region of the phase diagram. As expected, when the size of the nanoscale particle increases, the solidus temperature increases and the size-dependent phase diagram approaches the bulk phase diagram.

Thermodynamic aspects of the preparation of amorphous solid dispersions of Naringenin with enhanced dissolution rate.

Amorphous ternary solid dispersions of poorly water-soluble Naringenin (NRG) in Poloxamer 188 (POX) and Neusilin US2 (NSL) were prepared in a Hot- Melt Extruder (HME) using the principle of Low-Temperature Solubilization (LTS). Before HME, the NRG-POX solid-state interaction was investigated using Flory Huggins (F-H) theory. Construction of the composition-phase diagram showed Gibbs free energy to be negative close to the melting temperature of NRG, indicating a miscible system. The temperature-composition phase diagram provided insights on the phase behavior of the active-polymer solid dispersion system. The interactions and phase behavior predicted within the framework of the F-H theory were further investigated using Differential Scanning Calorimetry (DSC), X-Ray Diffraction (XRD), Hot Stage Microscopy (HSM) and Fourier-transform infrared spectroscopy (FT-IR). Based on the findings, amorphous solid dispersions of NRG were prepared via HME, which demonstrated a significant increase in the dissolution rate (p≤0.05). The enhancement of the dissolution rate is due to conversion from crystalline to amorphous form, as confirmed by DSC and XRD. The amorphous NRG prepared in the current study exhibited a release of 77% at the end of 2h, which is an increment of 250% from that of pure crystals.

Phenomenological theory of phase transitions in the MPB region of (1−x)Pb(Mg1/3Nb2/3)O3-xPbTiO3 single crystals

ABSTRACTA higher-order Landau–Ginzburg–Devonshire theory is proposed to describe phenomenologically the complex phase transitions in the MPB region of the relaxor ferroelectric (1−x)Pb(Mg1/3Nb2/3)O3-xPbTiO3(PMN-PT) single crystals. Using the singularity theory, a structurally stable 10th-order potential with four varying expansion coefficients (a1, a11, a2 and a12) depending on temperature and composition is found out. By studying on two- and three-dimensional sections of a four-dimensional phase diagram a1-a11-a2-a12 in the space of phenomenological parameters, the range of coefficient parameters by which the structural stability of the potential model can be guaranteed is determined. The theoretical temperature-composition phase diagram is constructed and it is shown that this is in good agreement with both recent experimental data and first-principle calculation for the symmetry change. Moreover, temperature dependence of dielectric constants for various compositions is studied.

Micellar Fd3m cubosomes from monoolein – long chain unsaturated fatty acid mixtures: Stability on temperature and pH response

HypothesisControl of the nanostructure of self-assembled systems may be achieved through manipulation of surfactant molecular packing and interfacial curvature. In order to phase engineer the inverse micellar cubosomes in some monoolein-fatty acid systems, lipids with wedge shaped molecular geometry were incorporated to promote the formation of this phase, that is of interest as potential sustained released nanocarriers. ExperimentsLiquid crystalline nanoparticle dispersions of monoolein with some cis unsaturated fatty acids were prepared and their partial temperature-composition phase diagrams and structure were established using high throughput Small Angle X-ray Scattering (SAXS) and cryogenic transmission electron microscopy (cryo-TEM). The pH responsiveness of these systems was evaluated in the presence of phosphate buffered saline (PBS). FindingsThe partial temperature-composition phase diagrams of five nanoparticle formulations containing monoolein and unsaturated fatty acids were established and identified the presence of micellar cubosomes in each of these systems. The results indicate that temperature, fatty acid concentration and structure, as well as pH all directly impact the formation and stability of this phase. Low energy inverse micellar cubic to emulsion phase transformations were identified in the monoolein with oleic acid and vaccenic acid systems at physiological temperatures that may be advantageous for staged therapeutic release strategies in nanomedicine.

High-pressure melting equilibrium of chiral compounds: A practical study on chlorinated mandelic acids under carbon dioxide atmosphere

Chiral molecules pose great research potential related to their wide applications in various industries due to the different biological effects of enantiomers. Chiral temperature-composition (melting) phase diagrams are widely available for atmospheric pressure, and those are frequently applied to predict the maximal efficiency of enantioseparation. However, self-disproportionation of enantiomers has already been observed in gas antisolvent fractionation as well. Here, we present the first chiral temperature-composition phase diagrams under carbon dioxide pressure. Chiral temperature-composition phase diagrams of 2-, 3- and 4-chloromandelic acids were determined experimentally. High pressure differential scanning calorimetry and the visual first and last melting point method were used simultaneously to determine the temperature-composition phase diagrams of the compounds. Results were compared to the atmospheric phase diagrams. At 16 and 20 MPa pressures modest melting point depressions of 10−18 °C were observed for any enantiomeric compositions, while the eutectic composition remained practically unaffected. The Schröder–van Laar and Prigogine–Defay equations, widely accepted for the prediction of atmospheric temperature-composition phase diagrams of enantiomeric mixtures, were proved to be applicable also in the presence of a soluble pressurized gas.

Impact of Hot-Melt Extrusion Processing Conditions on Physicochemical Properties of Amorphous Solid Dispersions Containing Thermally Labile Acrylic Copolymer

For successful formulation of amorphous solid dispersions (ASDs) using hot-melt extrusion, it is imperative to understand the effect that heat and shear rate has on the physicochemical properties of the excipient. In this study, we investigated the influence of hot-melt extrusion parameters on solvent-free binary ASDs of ibuprofen (IBU), a model active pharmaceutical ingredient, in methacrylic acid-ethyl acrylate copolymer type A, 1:1, EUDRAGIT® L100-55 (EUD). To evaluate the impact of barrel temperature, screw speed, and residence time on EUD mass average molar mass and IBU release profile, size-exclusion chromatography and dissolution testing were used, respectively. The optimal conditions were established for IBU loadings less than 40 wt. %. For ASD formulations prepared using the ideal variables, spectral and thermal analyses confirmed that, under dry conditions at a temperature of 25°C, IBU remained amorphous during an 18-month storage period. After 28 months, formulations with active pharmaceutical ingredient content above 30 wt. % started to recrystallize. A temperature–composition phase diagram, constructed using melting point depression and glass-transition temperature measurements of IBU–EUD mixtures, correlated well with the long-term physical stability. The effect that minor-to-moderate polymer degradation within the extrudates has on their long-term physical stability and dissolution characteristics is analyzed and discussed.

Accelerated Search for BaTiO3-Based Ceramics with Large Energy Storage at Low Fields Using Machine Learning and Experimental Design.

The problem that is considered is that of maximizing the energy storage density of Pb‐free BaTiO3‐based dielectrics at low electric fields. It is demonstrated that how varying the size of the combinatorial search space influences the efficiency of material discovery by comparing the performance of two machine learning based approaches where different levels of physical insights are involved. It is started with physics intuition to provide guiding principles to find better performers lying in the crossover region in the composition–temperature phase diagram between the ferroelectric phase and relaxor ferroelectric phase. Such an approach is limiting for multidopant solid solutions and motivates the use of two data‐driven machine learning and design strategies with a feedback loop to experiments. Strategy I considers learning and property prediction on all the compounds, and strategy II learns to preselect compounds in the crossover region on which prediction is carried out. By performing only two active learning loops via strategy II, the compound (Ba0.86Ca0.14)(Ti0.79Zr0.11Hf0.10)O3 is synthesized with the largest energy storage density ≈73 mJ cm−3 at a field of 20 kV cm−1, and an insight into the relative performance of the strategies using varying levels of knowledge is provided.

Reemergence of superconductivity by 4d transition-metal Pd doping in over-doped 112-type iron pnictide superconductors Ca0.755La0.245FeAs2

In 112-type iron-based superconductors (IBSs), rare earth (e.g. La) doping enhanced antiferromagnetic (AFM) order and 3d transition-metal (e.g. Co, Ni) doping induced reemergence of superconductivity (SC) in the over-doped regime (non-SC) are of particular interest, providing a significant opportunity to further understand the relationship between SC and AFM order in IBSs. Recently, 4d transition-metal Pd-doped 112-type Ca1-yLayFe1-xPdxAs2 (x > 0.2, 0 ≤ y ≤ 0.3) compounds, which crystallized in new orthorhombic and tetragonal structures, have been identified (Inorg. Chem. 56 3030 (2017)). However, none of them exhibit SC, probably due to the oversubstitution of Pd for Fe. Here, to reveal the impact of slight Pd doping on the over-doped Ca1-yLayFeAs2 and compare to 3d Co/Ni doping series, single crystals of Ca0.755La0.245Fe1-xPdxAs2 with 0 ≤ x ≤ 0.08 are successfully grown using the self-flux method. We find that, upon only a small amount of Pd doping (x = 0.013), bulk SC with a maximum Tc of 28.5 K is reemerged, in contrast to the case with high Pd doping level. Moreover, based on the electrical resistivity and magnetization data, we construct the temperature-composition (T–x) phase diagram, the shape of which, particularly for the region where the AFM and SC phases coexist microscopically, is almost identical to that of Ca0.76La0.24Fe1-xNixAs2, but is distinctly different from that of Ca0.74La0.26Fe1-xCoxAs2, presumably due to the presence of complex doping mechanism in 112-type IBSs. Finally, for one selected single crystal with x = 0.013, superconducting properties including critical current density, vortex pinning mechanism, and vortex diagram are systematically studied by magnetization, magneto-optical imaging, and magneto-resistivity measurements. Our work provided more insight into the phase diagrams and superconducting properties of 112-type IBSs, allowing better understanding of its superconducting mechanism and developing the potential applications.

Site occupancy effects of Mg impurities in BaTiO3

A first-principles based atomistic model is developed to investigate intrinsic effects of Mg incorporation into A- and B-sites of BaTiO3. We find that the replacement of Ba by Mg at A-site positions generates local electric dipoles due to Mg off-centering along [001] directions, which increase the Curie temperature and decrease the cell volume. The inverse dependence is observed for B-site doped compositions, where the defect dipoles decrease the Curie temperature and expand the volume. Temperature-composition phase diagrams are constructed for both site locations and the effect of the two types of defects on the switching process is investigated. The theoretical predictions are used to shed light on experimental results of Mg-doped ceramics manufactured to induce a given occupation site. The comparison indicates that the incorporation of Mg into the B-site is thermodynamically favorable whereas the properties observed for the A-site ceramics cannot be explained from the intrinsic effects described by the model.

Phase structure and quasi-single-domain mechanism in Pb(Mg1/3Nb2/3)O3-xPbTiO3 single crystals near morphotropic phase boundary

Based on the domain configuration analysis, we demonstrate that orthorhombic (O) phase is a structural bridge between the rhombohedral (R) and tetragonal (T) phase in Pb(Mg1/3Nb2/3)O3-xPbTiO3 (PMN-xPT) crystals near the morphotropic phase boundary (MPB), as illustrated in the composition-temperature phase diagram. After poling along the polar direction, domain patterns in PMN-0.30PT, PMN-0.33PT, and PMN-0.37PT single crystals are found to accord with quasisingle-domain configurations (1R*, 1O*, and 1T*) after removal of the electric field. Furthermore, by the thermodynamic theory analysis, the quasisingle-domain states present one dominant domain and other adjacent domains owing to partial depolarization. Our results provide a reliable and nondestructive method to identify the phase structures near the MPB region in the PMN-xPT and other similar relaxor-ferroelectric single crystals.

Determination of drug-polymer solubility from supersaturated spray-dried amorphous solid dispersions: A case study with Efavirenz and Soluplus®

Amorphous solid dispersions (ASDs) are found to be a well-established strategy for overcoming limited aqueous solubility and poor oral bioavailability of active pharmaceutical ingredients (APIs). One of the main parameters affecting ASDs physical stability is the API solubility in the carrier, because this value determines the maximal API load without a risk of phase separation and recrystallization. Phase-diagrams can be experimentally obtained by following the recrystallization of the API from a supersaturated homogeneous API-polymer solid solution, commonly produced by processes as solvent casting or comilling, which are very time-consuming (hours). The work deals with the construction of a temperature-composition EFV-Soluplus® phase diagram, from a thermal study of recrystallization of a supersaturated solid solution (85 wt% in EFV) generated by spray drying. This supersaturated solution is kept at a given annealing temperature to reach the equilibrium state and the amount that still remains dispersed in the polymer carrier at this equilibrium temperature is determined by means of the new glass transition temperature of the binary mixture. From our knowledge, this is the first study employing a fast process (spray drying) to prepare a supersaturated solid solution of an API in a polymer aiming to determine a temperature-composition phase diagram. The EFV solubility in Soluplus ranges from 20 wt% at 25 °C to 30 wt% at 40 °C. It can be a very useful preformulation tool for researchers studying amorphous solid dispersions of Efavirenz in Soluplus, to assist for predicting the stability of EFV-Soluplus ASDs at different EFV loadings and under different thermal conditions.