Phase Separation Ordering Research Articles

Cationic mismatch effect on structural and magnetic behavior of La0.5-xEuxCa0.5-yBayMnO3 charge-ordered manganites

In this research, we have tried to investigate the effect of the cationic disorder on charge ordering and magnetic phase separation in La0.5-xEuxCa0.5-yBayMnO3 (x = 0, 0.05, and 0.1) compounds synthesized by using the sol-gel method. All the samples possess the same average ionic radius at A site <rA> and the same Mn3+/Mn4+ ratio. Our analysis confirmed the chemical composition by energy dispersive X-ray spectroscopy and verified the structural integrity and purity of the phase by X-ray diffraction, revealing an orthorhombic structure with Pnma space group, which is in agreement with the tolerance factor. The important mismatch effect observed in the substituted specimens induces drastic effects on the structural and microstructural properties. Magnetic measurements indicate a great reduction of Curie temperature for substituted samples (from 250 K for x = 0 to 90 K for x = 0.05 and 85 K for x = 0.1), which indicates a weakening of ferromagnetic double exchange interactions induced by cationic disorder. The Arrott plots and the magnetocaloric study of the Eu−based samples indicate the persistence of the antiferromagnetic charge-ordered state characterizing the pristine compound (x = 0) as well as the presence of a first-ordered metamagnetic transition for all the studied samples, which is ascribed to the presence of antiferromagnetic domains. Such transition induced the appearance of a shoulder peak near 100 K in the magnetic entropy change curves for high magnetic field values, resulting in an extra cooling efficiency.

Macroscopically ordered phase separation: A new strategy for improving the superconducting performance in Fe(Se, Te)

The phase separation commonly exists in Fe(Se, Te) and damages their superconducting performance. In this paper, we successfully tuned the phase separation in Fe(Se, Te) via adding FeF2 to the raw materials. A macroscopically ordered phase separation which exhibited submillimetre scale striations in width arranged along the c-axis was formed in the FeF2-added Fe(Se, Te), different from the commonly observed flower shape phase separation in FeF2-free Fe(Se, Te). Moreover, the two macroscopical separated phases were identified as FeSe0.6Te0.4 and FeSe0.4Te0.6. The regular phase separation morphology and the fixed phase composition enhanced the flux pinning behavior which induced the appearance of Δκ pinning and deferred the changing from point pinning to surface pinning with the raising temperature. As a result, Fe(Se, Te) with the macroscopically ordered phase separation overwhelms the common phase separation Fe(Se, Te) in Hc2, U0, and Jc. Notably, at 4.2 K, the critical current density Jc reaches 9.3 × 104 A/cm2 in self-field and 1.3 × 104 A/cm2 at 7 T which outclassed the reported values. Besides, the well-defined stoichiometry of the separated phase also lead to a higher Tc of 15.42 K with a narrower transition width of only 0.98 K. Overall, our work reveals the tuning of phase separation in Fe(Se, Te) in terms of phase morphology and stoichiometry, which is a new strategy for improving the superconducting performance in Fe(Se, Te).

Multivalency ensures persistence of a +TIP body at specialized microtubule ends

Microtubule plus-end tracking proteins (+TIPs) control microtubule specialization and are as such essential for cell division and morphogenesis. Here we investigated interactions and functions of the budding yeast Kar9 network consisting of the core +TIP proteins Kar9 (functional homologue of APC, MACF and SLAIN), Bim1 (orthologous to EB1) and Bik1 (orthologous to CLIP-170). A multivalent web of redundant interactions links the three +TIPs together to form a ‘+TIP body’ at the end of chosen microtubules. This body behaves as a liquid condensate that allows it to persist on both growing and shrinking microtubule ends, and to function as a mechanical coupling device between microtubules and actin cables. Our study identifies nanometre-scale condensates as effective cellular structures and underlines the power of dissecting the web of low-affinity interactions driving liquid–liquid phase separation in order to establish how condensation processes support cell function.

Formation of diffusion micro-pairs in the Ni68Mo20Al12 alloy

• The sign of the nteratomic interaction in a binary alloy changes with temperature. • Chemical bonds (ionic and covalent) exist in both solid and liquid states of an alloy. • New phases in ternary alloys form inside of diffusion micro-pairs formed in liquid. The article presents the results of an electron microscopic study of the Ni 68 Mo 20 A l 12 alloy. The results got serve as the basis for the conclusion that the chemical bonds between atoms in ternary alloys are carried out according to the principle of pair interaction. These data show that the separation of the studied ternary alloy into diffusion micro-pairs occurs already in the liquid state. When the temperature of the alloy drops to 1200 °C in the Mo/A l diffusion pair, the “ordering-phase separation” transition occurs, and Mo atoms and A l atoms take part in the formation of diffusion pairs with nickel. The article concluded that the starting point for the formation of the microstructure of alloys is the liquid state in which any alloy is in the process of its smelting. It is noted that high-entropy alloys, in which such diffusion micro-pairs cannot be formed due to hindered diffusion of atoms, are unlikely to have prospects for their use in industry.

Sublattice alloy design of high-strength steels: Application of clustering and nanoscale precipitation of interstitial and substitutional solutes

Recent advances in high-strength steels for automobile applications or surface-hardened steels have attracted interest on controlling the nanoscale dispersion of alloy carbides/nitrides in ferrite. Particularly, B1-type carbide/nitride precipitation and metastable alloy clustering can be understood as the coupled ordering and compositional phase separation of interstitial alloying elements i and substitutional alloying elements s, i.e., "spinodal ordering". In this paper, the behavior of i–s clustering and alloy carbide/nitride precipitation is revealed by nanoscale characterization, theoretical calculations, and evaluations of mechanical properties. Physical measurements and density function theory-based analyses revealed that strong i–s attractive interaction is responsible for metastable i–s clustering, which clearly indicated "hidden" nanoscale inhomogeneity in solid solutions. Further, we discuss a concept termed interstitial sublattice engineering in bulk and at interphase boundary for strengthening of alloyed steels.

Improving the Molecular Packing Order and Vertical Phase Separation of the P3HT:O-IDTBR Blend by Extending the Crystallization Period of O-IDTBR.

The morphology with strong molecular packing order and gradient vertical composition distribution associated with efficient charge transport and collection is critical to achieve high performance in nonfullerene solar cells. However, the rapid solidification process of the active layer upon the fast removal of solvent usually results in a kinetically trapped state with undesired morphology. Herein, we proposed a strategy to extend the crystal growth time of the acceptor via a high-boiling-point additive that selectively dissolved the acceptor. This was enabled by adding dibenzyl ether (DBE) to the poly(3-hexylthiophene) (P3HT):O-IDTBR blend in chlorobenzene (CB) solution. The combination of the kinetic study by time-resolved ultraviolet-visible (UV-vis) absorption spectra and detailed morphological characterization allows us to correlate the crystallization kinetics with the microstructural transition. The results show that the crystal growth time of O-IDTBR increases from 3 to 60 s upon the addition of 0.75% DBE, leading to further evolution of the molecular order of O-IDTBR during the DBE-dominated drying period. Meanwhile, O-IDTBR has more time to migrate toward the substrate owing to the larger surface energy. In addition, the onset of the crystallization process of P3HT is brought forward from 8 to 6 s due to the reduced solvent quality, which favors P3HT to crystallize into a fibril network. As a result, an optimized morphology that features the enhanced molecular packing order of P3HT and O-IDTBR as well as the vertical compositional gradient of O-IDTBR is obtained. Devices based on the optimized blend show more balanced charge transport and suppressed bimolecular recombination, giving rise to an improved power conversion efficiency (PCE) from 4.29 ± 0.04 to 7.30 ± 0.12%.

Phase separation with ordering in aged Fe-Ni-Mn medium entropy alloy

High- and medium-entropy alloys are currently receiving significant attention. Understanding short-range ordering and nano-scaled phase separation concerning elemental interaction is a key to controlling phase stability for designing of high entropy alloys. In this study, we aim to clarify concurrent phase separation and ordering during aging of Fe-35Ni-35Mn (at%) medium-entropy alloy using advanced characterization techniques such as spherical aberration-corrected scanning transmission electron microscopy (Cs-corrected STEM) and three-dimensional atom probe (3DAP). Obvious age hardening occurs after aging at 500 °C for 96 h due to the formation of L10 ordered phase combined with phase separation. By aging at 400 °C or shorter time, obvious precipitation of the ordered phase is not detected but the radial distribution functions obtained by 3DAP present that enrichment of Ni and Mn nearby the same kinds of the element is observed, and this tendency is stronger for Mn. This result suggests that phase separation is induced by Mn clustering in the early stage of aging. A statistical thermodynamic model of phase stability considering L10 ordered structure is developed. The analyses using the model suggest that phase separation is not possible in a disordered state at 500 °C, therefore, nucleation of the L10 phase should precede phase separation at this temperature. On the other hand, phase separation is possible even in a disordered state at 400 °C, and ordering further enhances phase separation.

The ‘Ordering-Phase Separation’ Transition as a Microstructural Manifestation of the Electronic ‘Ionic Bond↔Covalent Bond’ Transition

The ‘Ordering-Phase Separation’ Transition as a Microstructural Manifestation of the Electronic ‘Ionic Bond↔Covalent Bond’ Transition

2D Side‐Chain Engineered Asymmetric Acceptors Enabling Over 14% Efficiency and 75% Fill Factor Stable Organic Solar Cells

AbstractThe charge transport and morphology of active layers are key considerations for device performance and stability in organic solar cells (OSCs). Such properties can be fine‐tuned via elaborate molecular design of fused‐ring electron acceptors (FREAs), especially conjugation extension and side chain engineering. In this work, N‐functionalized conjugation is explored in the design of high‐efficient asymmetric FREAs. The twisting of N‐conjugated side chains from backbone endows three FREAs with similar energy levels and light absorptions (≈850 nm edge). Their blends with PBDB‐T exhibit high charge carrier mobility and ordered phase separation. Excitingly, IPT2F‐TT based OSCs yield a champion power conversion efficiency (PCE) of 14.02% with a fill factor (FF) of 75.06%, outperforming PBDB‐T devices with IPT2F‐Th (12.52%, 71.20%), IPT2F‐Ph (13.13%, 72.11%), and octylated IPT‐2F (13.70%, 71.50%). The PCE over 14% and FF over 75% are among the highest values for 2D FREAs OSCs reported to date. More importantly, outstanding thermal stability and light soaking stability are observed with PCE over 12% maintained after thermal or light aging for 100 h. This work demonstrates N‐conjugated FREAs design as an effective strategy to simultaneously improve the photovoltaic performance and device stability for the OSCs.

Polarization Spinodal at Ferroelectric Morphotropic Phase Boundary.

Here, we report a new phenomenon of uniform and continuous transformation of a single polarization domain into alternating nanodomains of two polarization vectors with the same magnitude but different directions at ferroelectric morphotropic phase Boundary (MPB). The transformation is fully reversible and could enhance the piezoelectric coefficient d_{33}. Further free energy calculations illustrate that such a polarization "decomposition" process occurs within the region on the Landau free energy curve with respect to the polarization direction where the second derivative becomes negative, which is similar to spinodal instability in phase transformations such as spinodal ordering or isostructural phase separation (e.g., spinodal decomposition). This "polarization spinodal" uncovers a new mechanism of polarization switching that may account for the ultrahigh ahysterestic piezoelectric strain at the MPB. This work could shed light on the development of phase transition theory and the design of novel ferroelectric memory materials.

Short-Range Order Evolution in Nanocrystalline Mechanically Activated Fe–Cr Alloys in the Process of Annealing

Nanocrystalline Fe–Cr alloys synthesized from pure components in a planetary ball mill with a chromium content of 20–48 at % were annealed for 4 h at temperatures of Tan = 400–700°C. Short-range order (SRO) evolution and phase separation dependent on Tan were studied using Mossbauer spectroscopy and X-ray diffraction. The precipitation of the σ-FeCr phase was observed only in the samples with 48 at % of Cr at Tan = 600 and 700°C. For all the samples, the grain growth began most intensively from 400°C, and the higher the Cr content in an alloy, the smaller the final size of grains after Tan = 700°C. The analysis of behavior of the mean hyperfine field on Fe nuclei and distribution of the hyperfine field width depending on Tan, as well as fitting of Mossbauer spectra with spectral components corresponding to the α (Cr depleted) and α' (Cr rich) phases, demonstrated that the mechanically alloyed Fe-Cr samples were characterized by weak short-range separation passing at Tan = 400°C to a nearly statistically uniform distribution of atoms. Heterogeneous short-range order with the α and α' regions was formed in the alloys with 30 at % of Cr and more after annealing at 500–700°C. An analysis with the material balance equation led to our conclusion about the existence of the grain boundary segregations of Cr atoms.

Suppression of Metamagnetic Transitions of Martensitic Type by Particle Size Reduction in Charge-Ordered La0.5Ca0.5MnO3

In this paper, we have studied the effect of size reduction on charge ordering (CO) and magnetic phase separation in La0.5Ca0.5MnO3. The magnetic ground state at low temperature shifts from ferromagnetic (nanoparticles) to CO-antiferromagnetic (bulk) with increasing annealing temperature. The studied samples exhibit relevant phenomena such as Griffiths phase and training effect. Magnetic field cycling can stabilize ferromagnetic or antiferromagnetic domains, depending on the temperature value as well as the sample’s nature. For the compound sintered at 1200 °C, step-like metamagnetic transitions of martensitic type were observed at 4 K, indicating the presence of weak spin-phonon coupling. The disappearance of magnetic phase separation at 4 K (the sample is purely antiferromagnetic) can be a possible origin for the occurrence of such transitions. Lowering the sintering temperature leads to the disappearance of martensitic transitions. The obtained results indicate that the occurrence of step-like metamagnetic transition of martensitic type necessarily requires the onset of a long-range CO-antiferromagnetic state.

Chemical Bonds in Metallic Alloys

This review article represents a summary of completed, original work, embodying the results of extensive laboratory and theoretical investigations as well as new interpretations of existing problems in Materials Science. Using the examples of a number of binary Ni-base and Fe-base alloys, the TEM method has shown that the main reason for the precipitation of particles of a new phase is the chemical interactions that always exist between all atoms of an alloy, both in the solid and in the liquid state. It has been found experimentally that the sign of the chemical interaction energy in many alloys changes with a temperature change (the ‘orderingphase separation’ transition). It has been shown that the cause of the ‘ordering-phase separation’ transition is the electronic ‘ionic bond ↔ covalent bond’ transition. Such a transition takes place when delocalization of a couple of the valence electrons occurs on the A and B atoms simultaneously with the hybridization of a couple of the valence electrons on the B atoms. All these discoveries radically change the existing ideas about diffusion phase transformations in alloys. Keywords: Phase Transitions; Chemical Interactions; Ordering; Phase separation; ‘Ordering-Phase Separation’ Transition; ‘Ionic Bond ↔ Covalent Bond’ Electronic Transition

Formation of Diffusion Pairs as an Initial Stage in the Process of Decomposition of Alloys

The paper discusses the researches that formed the basis of the study of the transition of “ordering-phase separation” and the reasons for such transition occurrence. Experimental results have presented what diffusion pairs are and how they occur in binary and multicomponent alloys. The paper illustrates that the chemical bonds between atoms are realized on the principle of pair interaction in both solid and liquid states of the alloy. The process of separating a multi-component ABC alloy into diffusion pairs A/B, A/C, and B/C occurs in a liquid solution, where the diffusion mobility of atoms is very high, and the resistance of the environment is relatively low. The driving force of such a process is the chemical attraction between like and unlike atoms, that is, the tendency to phase separation and the tendency to ordering. Quenching the liquid alloy into the water fixes a microstructure consisting of microscopic areas corresponding in composition to one or another diffusion pairs. The paper shows what exactly should be done so that such a branch of science as Materials Science could get rid of the empirical approach when creating new alloys.

Scalable synthesis of fluorescent organic nanodots by block copolymer templating

Scalable synthesis of fluorescent organic nanodots by block copolymer templating

Highly efficient removal of fluoride from aqueous media through polymer composite membranes

Abstract Different aluminum and calcium based particles, montmorillonite (MMT), zeolites (NaY), bayerite (BAY) and hydroxyapatite (CaHAp), were compared and evaluated for water defluorination. The effect of parameters such as temperature of the medium, concentration (mass of adsorbent), reaction time and pH on the defluorination capacity were studied for the particles with best performance. MMT and CaHAp adsorbents showed increased fluoride rejections in batch experiments (≈45 and 100%). The defluorination capacity of MMT is influenced by the concentration and pH, while for CaHAp is independent of the evaluated parameters within the measured range. Further, polymer composite membranes based on poly(vinylidene fluoride-hexafluoropropylene) (PVDF-HFP) and the adsorbents with higher defluorination capacity were prepared by thermally induced phase separation in order to produce active filters for fluoride removal from water. The composite membranes presented a homogeneous porous structure with degrees of porosity ranging between ≈20 and 76% and average pore size in the micron range. The permeability of the composite membranes ranged between 12,500 and 10,000 L/h·m2·bar. A maximum fluoride rejection of 68% was obtained after 6 filtrations for the CaHAp/P(VDF-HFP) composite membranes. Thus, the composite membranes of P(VDF-HFP) with MMT and CaHAp show suitable performance for defluorination in water purification systems.

Dysregulation of Phase Separation in Cancer

Liquid-liquid phase separation leads to demixing of proteins from solution and results in a dense, protein-rich phase, which co-exists with a light phase depleted of protein. Recent findings support a model in which phase separation is the biophysical driving force for the formation of membrane-less organelles in the cell, such as stress granules, nucleoli and nuclear speckles. Current open questions are: (i) How is phase separation propensity encoded in the protein sequence, (ii) are dense liquid droplets used as reaction compartments in the cell, and (iii) is physiological phase separation disrupted in disease states? To address them, we study the interaction of the tumor suppressor Speckle-type POZ protein (SPOP), a substrate adaptor of a ubiquitin ligase, with its substrates. SPOP localizes to different liquid membrane-less organelles in the cell nucleus, where it encounters its substrates, but it is never found diffuse in the cell. However, its recruitment mechanism to these organelles is not understood. Here, we show for the first time that SPOP undergoes liquid-liquid phase separation with substrate proteins, and that this mechanism underlies its recruitment to membrane-less organelles. Multivalency of SPOP and substrate for each other drive their ability to phase separate. Moreover, we present strong evidence that the SPOP/substrate assemblies are active ubiquitination compartments in vitro and in cells. SPOP cancer mutations reduce the propensity for phase separation and tune the material properties of mesoscale assemblies. In the cell, cancer mutants fail to localize to the proper organelles and to recruit substrate. We propose that SPOP has evolved a propensity for phase separation in order to target substrates localized in membrane-less compartments. Our results provide mechanistic insights into the contributions of structured and disordered domains to phase separate, enzymatic activity inside liquid organelles, and disruption of phase separation by cancer mutations.

Multicomponent alloys: Regularities in the formation of microstructures

We have experimentally discovered and described earlier the phase transition “ordering – phase separation” and the electronic transition “ionic bond ↔ covalent bond” for binary alloys. In this article it is shown that the ternary alloys ABC in a liquid state are separated into microscopic sites with a chemical composition corresponding to the diffusion couples A/B, A/C or B/C. The causes of such separations are discussed. It was shown that within each diffusion pair the same processes of formation of microstructures occur, including the “ordering-phase separation” transition, as in the corresponding binary alloys.

The magnetic state of the weakly anion-excess manganite LaMnO3+δ

This paper deals with the magnetic state of the weakly anion-excess lanthanum manganite LaMnO3+δ (δ ≈ 0.0375). The temperature and field dependences of the magnetic moment of single crystal samples are studied in detail for temperatures of 2–350 K in different fields up to 5 T along the c-axis. The field dependence of the observed singular temperature points, such as those for magnetic ordering, magnetic vitrification, and magnetic phase separation, is recovered. The magnetic field behavior of several of the singular points is found to be interrelated. These results are fully consistent with models of magnetic phase separation that predict the formation of self-localized states such as nanoscale ferromagnetic droplets in a bulk antiferromagnetic matrix.

A Ladder-type Heteroheptacene 12H-Dithieno[2',3':4,5]thieno[3,2-b:2',3'-h]fluorene Based D-A Copolymer with Strong Intermolecular Interactions toward Efficient Polymer Solar Cells.

Ladder-type electron-donating units for D-A copolymers applied in polymer solar cells usually comprise multiple tetrahedral carbon bridges bonded with out-of-plane alkyl chains for desirable solubility for device processing. However, molecular packing of resultant copolymers in the solid state and charge transport within devices are also impeded in spite of with multiple fused aromatic backbones. To mitigate this issue, a structurally well-defined ladder-type electron-donating heteroheptacene, 12H-dithieno[2',3':4,5]thieno[3,2-b:2',3'-h]fluorene (DTTF) with an extended conjugated backbone and a single tetrahedral carbon bridge attached with two bulky alkyl chains was designed and synthesized. The copolymerization of DTTF with 4,7-bis(4-hexylthiophen-2-yl)benzo[c][1,2,5]thiadiazole (DTBT) afforded a soluble D-A copolymer (PDTTF-DTBT) with a medium optical band gap of 1.72 eV and low-lying HOMO level at -5.36 eV. PDTTF-DTBT unprecedentedly exhibits strong intermolecular stacking ability and presents preferential face-on orientation on both ZnO and PEDOT:PSS layers. The improved packing order and appropriate phase separation of both the copolymer and PC71BM in the bulk heterojunction blend on the ZnO layer over on the PEDOT:PSS layer lead to much improved power conversion efficiency of ∼8.2% in the inverted solar cell device, among the highest for reported ladder-type D-A copolymers. The research demonstrates that it is an effective method to incorporate a single tetrahedral carbon bridge to the molecular center of a ladder-type heteroacene with heavily extended π-conjugation to prepare D-A copolymers toward highly efficient PSCs.