Order-disorder Transition Research Articles

He2+ irradiation response of structural evolution at different depths of MgO-Nd2(Zr1-xCex)2O7 composite ceramics used for inert matrix fuel

This paper reported the irradiation response of a 55 wt.% MgO-45 wt.% Nd2(Zr1-xCex)2O7 (abbreviated to M-NZCx, x = 0, 0.3 and 1) composite ceramics used as candidate inert matrix fuel under 500 keV He2+ ions with fluence of 1 × 1016–5 × 1017 ions/cm2. The irradiation-induced lattice expansion, amorphization of MgO and NZCx phases and order-disorder transition of Nd2(Zr1-xCex)2O7 pyrochlore were systemically explored via GIXRD, Raman and TEM techniques. And the detailed irradiation response at different depths of the typical M-NZC0.3 sample was especially investigated via GIXRD and TEM. The results showed that the lattice expansion ratios (Rs) of MgO (M), ordered pyrochlore (P) and disordered defect-fluorite (F) structures of NZCx pyrochlore in the samples under the same dose of He2+ irradiation were regular, which were ranged as the following order: RsM < RsP < RsF. And there was a belt-shaped damage aggregation zone located near interphase boundary at the maximum damage depth of M-NZC0.3 sample, which could be explained by the defect-absorption of boundary. And this defect-absorption of boundary was also found at any depth of M-NZC0.3 sample. This work systematically analyzed α-decay irradiation response of different phases in M-NZCx composite ceramics applying for inert matrix fuel.

Unveiling Enhanced Electrostatic Repulsion in Silica Nanosphere Assembly: Formation Dynamics of Body-Centered-Cubic Colloidal Crystals.

We demonstrate the effective establishment of long-range electrostatic interactions among colloidal silica nanospheres through acid treatment, enabling their assembly into colloidal crystals at remarkably low concentrations. This novel method overcomes the conventional limitation in colloidal silica assembly by removing entrapped NH4+ ions and enhancing the electrical double layer (EDL) thickness, offering a time-efficient alternative to increase electrostatic interactions compared with methods like dialysis. The increased EDL thickness facilitates the assembly of SiO2 nanospheres into a body-centered-cubic lattice structure at low particle concentrations, allowing for broad spectrum tunability and high tolerance to particle size polydispersity. Further, we uncover a disorder-order transition during colloidal crystallization at low particle concentrations, with the optimal concentration for crystal formation governed by both thermodynamic and kinetic factors. This work not only provides insights into assembly mechanisms but also paves the way for the design and functionalization of colloidal silica-based photonic crystals in diverse applications.

Crystallographic disorder-order transition of self-assembly FeCo mesocrystals independent of ligand

Mesocrystal with aligned small grains is an important type of block in building high performance artificial bulk materials. But it is difficult to obtain mesocrystal particles without the assistant of surface ligands due to their unclear formation process. In this study, mesocrystal FeCo nanoparticles were successfully synthesized by co-precipitation of Fe and Co atoms using hydrazine hydrate as reducing agent with an appropriate addition rate. A non-classic nucleation process and the formation of mesocrystal FeCo nanoparticles had been observed. Microstructure characterization reveals that the arrangement of grains inside particles gradually change from multi-orientation to mono-orientation with the change of addition rate of hydrazine. The hydrazine addition rate, ie the reducing rate of metal atoms plays an important role for the formation of mesocrystal particles. The obtained mesocrystal FeCo particles show good magnetic performance (the highest magnetization and lowest coercivity). The discovery of the influence of synthesis conditions on the formation of mesocrystals provide a useful way to control the microstructure and the performance of consisting nanostructures.

Morphologies of Comb-like Polyacrylic Acid/Polyacrylate Copolymers as Functions of the Degree of Derivatization with n-C22H45 Side Chains.

Polymers with crystallizable side chains have numerous applications, and their properties depend on their crystal morphologies and phase separation. Structural analysis on a wide spatial scale plays an important role in controlling the thermal properties and higher-order structures of these polymers. In this study, we elucidated the melting and crystallization processes of copolymers with varying crystallizable side-chain fractions over a wide spatial range. Differential scanning calorimetry revealed that the enthalpies of melting and crystallization increased linearly with increasing crystallizable side-chain fraction. The results of wide-angle X-ray scattering indicated that the crystal lattice was hexagonal. Conversely, spherulite-like higher-order architectures with linear structures and radial spreading were observed in the highly crystallizable components, but no micrometer-scale structures were observed in the less crystallizable components. In situ small-angle X-ray scattering was used to elucidate the phase separation and mixing processes. Lamellar crystallites were observed at crystallizable side-chain fractions of >55 wt.%, whereas small crystallites were observed at fractions of <45 wt.%. At temperatures above the order-disorder transition temperature, density fluctuations caused by correlation holes were observed. These properties have a strong effect on the crystallizable side-chain fraction.

Structure and evolution of disordered deep-charge phases in NaxCrO2 Na-ion battery electrodes

Layered sodium chromium oxide, O3–NaCrO2, is a promising electrode material for Na-ion batteries due to the high thermal stability, high rate-capability, and good coulombic efficiency of the material. However, it is well-known that the material loses crystallinity and the ability to store Na-ions reversibly when taken to high states of charge. While the structural identity of the disordered state has been investigated, a bulk structural model has so far been lacking, as has the mechanism for the order-disorder transition from the P′3-NaxCrO2 (the last crystalline phase observed during charge) to the disordered state. In this work, we combine pair distribution function analysis from total X-ray scattering and powder X-ray diffraction to obtain a complete structural model for the disordered O3-like NaxCrO2 forming at high states-of-charge, and from operando pair distribution function analysis and X-ray absorption spectroscopy, we elucidate the structural evolution of the order-disorder transition and shed new light on the Cr-migration in the disordered state, which is the cause of the irreversibility of the Na-ion storage.

Ab Initio-Based Modeling of Thermodynamic Cyclic Voltammograms: A Benchmark Study on Ag(100) in Bromide Solutions.

Experimental cyclic voltammograms (CVs) measured in the slow scan rate limit can be entirely described in terms of the thermodynamic equilibrium quantities of the electrified solid-liquid interface. They correspondingly serve as an important benchmark for the quality of first-principles calculations of interfacial thermodynamics. Here, we investigate the partially drastic approximations made presently in computationally efficient calculations for the well-defined showcase of an Ag(100) model electrode in Br-containing electrolytes, where the nontrivial part of the CV stems from the electrosorption of Br ions. We specifically study the entanglement of common approximations in the treatment of solvation and field effects, as well as in the way macroscopic averages of the two key quantities, namely, the potential-dependent adsorbate coverage and electrosorption valency, are derived from the first-principles energetics. We demonstrate that the combination of energetics obtained within an implicit solvation model and a perturbative second order account of capacitive double layer effects with a constant-potential grand-canonical Monte Carlo sampling of the adsorbate layer provides an accurate description of the experimental CV. However, our analysis also shows that error cancellation at lower levels of theory may equally lead to good descriptions even though key underlying physics such as the disorder-order transition of the Br adlayer at increasing coverages is inadequately treated.

On the atomic ordering in the B-sublattice of high-entropy perovskites

Atomic ordering in perovskites has been the subject of intensive research for decades. With the growing interest in high-entropy perovskites (HEP), the issue of atomic ordering is now reaching a new level of significance. Many multi-cationic perovskites have already been synthesized, and some of them exhibit atomic ordering. Therefore, the problems of estimating the phase transition temperature of atomic ordering, determining the type of emerging atomic order, and the distribution of cations in ordered sublattices need to be addressed. In this work, based on the unstrained elastic cation-anion bonds model, we develop a Monte Carlo calculation scheme of atomic order-disorder phase transitions in the B-sublattice of perovskites with arbitrary composition and apply it to the case of HEP. We find that HEP’s may experience rock-salt type atomic ordering, while preserving considerable configurational entropy and essentially becoming ordered disordered perovskites. For many HEP’s, whose synthesis has been already reported in literature or which await their synthesis, we estimate the phase transition temperature Tod, reduced cubic lattice parameters, and the composition of the ordered sublattices. Finally, we derive a simple relation for the estimation of Tod from normalized standard deviation of the unstrained cation-anion bond lengths of atoms in the B-sublattice, which can be easily calculated.

Direct Observation of Twin van der Waals Molecular Chains.

The van der Waals (vdW) assemblies are the most common structures of materials. However, direct mapping of intermolecular electron clouds of a vdW assembly has never been obtained, even though the intramolecular electron clouds were visualized by atomic-resolution techniques. In this report, we unprecedentedly mapped the intermolecular electron cloud of the assemblies of ethanol molecules via ethyl groups with high-resolution atomic force microscopy and scanning tunneling microscopy at 5 K, leading to the first visualization of vdW molecular chains, in which ethanol molecules assemble into twin vdW molecular chains in a reverse parallel configuration on the Ag(111) plane. Furthermore, spontaneous order-disorder transitions in the chain were dynamically observed, suggesting its unusual properties different from those of 2D vdW materials. These findings provide an "eye" to see the atomic world of vdW materials.

Effects of Ni addition on the order–disorder transitions of Fe–Pt intermetallic compounds: An experimental study on Fe–Ni–Pt phase diagrams

The Fe–Pt based intermetallic compounds exhibit good chemical stability and unique magnetic properties, where Ni is an important additional element to optimize the magnetic properties or obtain the outstanding catalytic performances of the Fe–Pt based alloys. Knowledge of how Ni addition affects the order–disorder transitions of the Fe–Pt intermetallics is thus necessary; however, the related information is limited. Therefore, in this work, the phase diagrams of the Fe–Ni–Pt system were experimentally investigated, and as a result, the isothermal sections of the Fe–Ni–Pt system at 600 and 900 °C, as well as the vertical sections of Fe80Ni20–Pt80Ni20 and Fe50Pt50–Ni50Pt50 were constructed. Based on these results, the influences of Ni addition on the crystal stabilities and phase transformations of the ordered Fe–Pt intermetallics have been well described. The results show that the L10-FePt and L10-NiPt phases form a ternary continuous solid solution of L10-(Fe,Ni)Pt, whereas Ni can dissolve in the L12-Fe3Pt and L12-FePt3 phases as high as 57.0 at.% and 26.0 at.% at 600 °C, respectively. The selective occupancy of Ni atoms has been predicted, which should depend on the alloy composition. For both the L10-(Fe,Ni)Pt and L12-FePt3 phases, when Pt contents are less than their stoichiometric values, Ni atoms will preferentially occupy the Pt sublattice, forming as many nearest-neighbor Fe−Pt bonds as possible. All these results can correlate the alloy compositions, annealing temperatures and crystal structures to both magnetic and catalytic properties, thus providing a basis for optimizing the Fe–Ni–Pt alloys towards enhanced magnetic or catalytic performances.

Optimizing Co content in intermetallic L10-FeCoPt nanoparticles to enhance the electrocatalytic performance

The L10-FeCoPt nanoparticles with ultra-small size, highly ordered structure, and various Co contents have been successfully obtained by annealing the wet-chemical synthesized nanoparticles. The addition of third-element Co into L10-FePt nanoparticles would increase the grain size, facilitate the disorder-order transition, and enhance the saturation magnetization and coercivity. The better permanent magnet properties and maximum electrocatalytic HER activity of L10-FeCoPt nanoparticles were achieved when added the moderate Co content (4.5 % and 8.5 %). The hydrogen evolution reaction (HER) kinetics and density functional theory revealed that the Co atom would promote the hybridization of Fe-3d and Pt-5d orbitals and increase the hydrogen adsorption free energy to closer to 0. Optimization of Co content to a suitable range would generate higher permanent magnetic properties and suitable surface energy, which facilitated the proton transformation and lowered the Tafel slope to follow the Volmer-Tafel process in HER. This work illustrates that optimizing third-element content in Pt-based magnetic intermetallic is a feasible strategy to operate the electrocatalytic reaction pathway and enhance the electrocatalytic performance.

Phase Transitions, Dielectric Response, and Nonlinear Optical Properties of Aziridinium Lead Halide Perovskites.

Hybrid organic-inorganic lead halide perovskites are promising candidates for next-generation solar cells, light-emitting diodes, photodetectors, and lasers. The structural, dynamic, and phase-transition properties play a key role in the performance of these materials. In this work, we use a multitechnique experimental (thermal, X-ray diffraction, Raman scattering, dielectric, nonlinear optical) and theoretical (machine-learning force field) approach to map the phase diagrams and obtain information on molecular dynamics and mechanism of the structural phase transitions in novel 3D AZRPbX3 perovskites (AZR = aziridinium; X = Cl, Br, I). Our work reveals that all perovskites undergo order-disorder phase transitions at low temperatures, which significantly affect the structural, dielectric, phonon, and nonlinear optical properties of these compounds. The desirable cubic phases of AZRPbX3 remain stable at lower temperatures (132, 145, and 162 K for I, Br, and Cl) compared to the methylammonium and formamidinium analogues. Similar to other 3D-connected hybrid perovskites, the dielectric response reveals a rather high dielectric permittivity, an important feature for defect tolerance. We further show that AZRPbBr3 and AZRPbI3 exhibit strong nonlinear optical absorption. The high two-photon brightness of AZRPbI3 emission stands out among lead perovskites emitting in the near-infrared region.

Melting and defect transitions in FeO up to pressures of Earth's core-mantle boundary.

The high-pressure melting curve of FeO controls key aspects of Earth's deep interior and the evolution of rocky planets more broadly. However, existing melting studies on wüstite were conducted across a limited pressure range and exhibit substantial disagreement. Here we use an in-situ dual-technique approach that combines a suite of >1000 x-ray diffraction and synchrotron Mössbauer measurements to report the melting curve for Fe1-xO wüstite to pressures of Earth's lowermost mantle. We further observe features in the data suggesting an order-disorder transition in the iron defect structure several hundred kelvin below melting. This solid-solid transition, suggested by decades of ambient pressure research, is detected across the full pressure range of the study (30 to 140 GPa). At 136 GPa, our results constrain a relatively high melting temperature of 4140 ± 110 K, which falls above recent temperature estimates for Earth's present-day core-mantle boundary and supports the viability of solid FeO-rich structures at the roots of mantle plumes. The coincidence of the defect order-disorder transition with pressure-temperature conditions of Earth's mantle base raises broad questions about its possible influence on key physical properties of the region, including rheology and conductivity.

Critical systematic investigation of the Cd–Ce system: phase stability and Gibbs energies of formation and equilibria via thermodynamic description

Abstract The CALPHAD (CAlculation of PHAse Diagrams) technique is used in the critical remodeling of the Cd–Ce system. On the basis of new experimental data in the literature, the excess Gibbs energies of the solution phase expression (liquid, bcc, fcc, and hcp_A3) are described using the Redlich–Kister equation. Four compounds (Cd3Ce, Cd6Ce, Cd11Ce, and Cd17Ce2) are treated as stochiometric compounds. Two intermetallic compounds (Cd2Ce and Cd58Ce13), which exhibit a little homogeneity range, are treated as a two-sublattice model. Two thermodynamic models are used for the CdCe and bcc. Model I is to model the compound CdCe and bcc-Ce separately. Model II is to use the formula (Cd, Ce)0.5(Cd, Ce)0.5(Va)3 to describe the compound CdCe with a CsCl-type structure (B2) and cope with the disorder–order transition from bcc-A2 to bcc-B2. The present work shows that four eutectic reactions, three peritectic reactions, two eutectoid reactions, one peritectoid transformation and three congruent reactions are observed, and the stoichiometric compound Cd17Ce2 is only stable from 804 to 882 °C in the Cd–Ce system.

Dynamics, statistics, and task allocation of foraging ants.

Ant foraging is one of the most fascinating examples of cooperative behavior observed in nature. It is well studied from an entomology viewpoint, but there is currently a lack of mathematical synthesis of this phenomenon. We address this by constructing an ant foraging model that incorporates simple behavioral rules within three task groups of the ant colony during foraging (foragers, transporters, and followers), pheromone trails, and memory effects. The motion of an ant is modeled as a discrete correlated random walk, with a characteristic zigzag path that is congruent with experimental data. We simulate the foraging cycle, which consists of ants searching for food, transporting food, and depositing chemical trails to recruit and orient more ants (en masse) to the food source. This allows us to gain insights into the basic mechanism of the cooperative interactions between ants and the dynamical division of labor within an ant colony during foraging to achieve optimal efficiency. We observe a disorder-order phase transition from the start to the end of a foraging process, signaling collective motion at the population level. Finally, we present a set of time delay ODEs that corroborates with numerical simulations.

Exploring shape memory and self-healing behavior in sodium and zinc neutralized ethylene/methacrylic acid (EMAA) ionomers

Polymeric materials with self-healing and shape memory capabilities have gained increasing attention for their potential applications across various industries. In this study, zinc and sodium ionomers were systematically investigated using a multi-faceted approach, including rheological analysis, Fourier-transform infrared spectroscopy (FTIR), dynamic mechanical thermal analysis (DMTA), X-ray diffraction (XRD), and self-healing and shape memory assessments. Rheological analysis revealed distinct viscosity profiles among the ionomers, with EMAA-Zn 1706 exhibiting higher viscosity at low frequencies and a pronounced thinning behavior across the frequency range. FTIR analysis provided insights into the ionomers' molecular structures and functional groups. DMTA results illuminated the viscoelastic behavior and phase transitions of the ionomers. Peaks in the tan delta curve indicated order-disorder transitions and crystalline melting temperatures, influencing their mechanical properties. XRD patterns revealed low-angle peaks associated with clusters or localized regions within the ionomers. Additionally, characteristic peaks pointed to degrees of crystallinity and ordered packing. Self-healing assessments demonstrated varying healing efficiencies, with values ranging from 40 % to 60 % for EMAA-Zn 9945 and EMAA-Na 2000, while EMAA-Zn 1706 exhibited lower healing efficiency, not surpassing 20 %, attributed to its distinct rheological characteristics. Shape memory experiments were conducted in both torsion and fold-deploy modes, revealing remarkable shape fixations, with all ionomers exceeding 99 % in torsion and 95 % in the fold-deploy method. In aqueous environments, shape memory returns remained above 90 %, underscoring the water's influence on the shape memory effect. The exceptional shape memory performances and varying self-healing efficiencies of these ionomers highlight their versatility and significance in addressing practical challenges, paving the way for tailored materials with promising applications in numerous fields.

Order-disorder transition and thermal behavior of paracelsian-type MGa2Ge2O8 (M = Sr, Ba) compounds

Two Ga–Ge disordered feldspar-related compounds MGa2Ge2O8 (M = Sr, Ba) with paracelsian topology were synthesized for the first time using the melt crystallization methods (1300–1400 °C) and rapid cooling. Their stability was studied under high-temperature conditions using in situ single-crystal (up to 1000 °C) and powder (up to 1050 °C) X-ray diffraction. Both compounds are stable in the studied temperature range. The refinement of the crystal structure of BaGa2Ge2O8 at different temperatures does not demonstrate any ordering processes. The thermal expansion of both compounds has anisotropic character (αmax/αmin = 3.7 and 3.9 for SrGa2Ge2O8 and BaGa2Ge2O8, respectively), wherein the maximum and minimum expansion is observed within the bc plane. The anisotropy degree of MGa2Ge2O8 increases as the size of extraframework cation increasing. Simultaneously this process leads to the decreasing of MGa2Ge2O8 stability range. The influence of the crystallization procedure on order-disorder process of MGa2Ge2O8 is discussed.

Predicting large comprehensive refrigeration performance of plastic crystals by compositing carbon architectures for room temperature application

Plastic crystals PE (pentaerythritol) possess colossal barocaloric effect (BCE) that is promising for solid-state refrigeration; however, the high phase transition temperature (&amp;gt; 400 K) and low thermal conductivity (&amp;lt;0.5 W·m−1·K−1) greatly hinder its practical application at room temperature. Here, we propose to complex plastic crystal (PC) with carbon nanotube/graphene architectures (CNT-Gra) to form [PC/CNT-Gra] composites and investigate the BCE based on molecular dynamics simulations. It is found that phase transition temperature of molecular order to disorder can be tuned by alloying PA (neopentane) or NPG (neopentyl glycol) into PE imbedded in CNT-Gra architectures. Importantly, we find that PE0.8PA0.2/CNT-Gra and PE0.75NPG0.25/CNT-Gra demonstrate both giant isothermal entropy changes ΔS (∼200 J·kg−1·K−1) and adiabatic temperature change ΔT (∼18 K) at room temperature. The large BCE mainly comes from the order–disorder transition of PC molecules imbedded in CNT-Gra architectures through analysis of the dynamic process of the composites. Importantly, the thermal conductivity of these campsites is as high as ∼10 W·m−1·K−1, enabling efficient thermal exchange that is vital for improving cooling performance of the cyclic refrigeration process. This work provides important insights for designing PC-based composites with optimized comprehensive cooling performance for potential room temperature refrigeration.

Effect of Film Thickness on the Self-Assembly of CBABC Symmetric Pentablock Terpolymer Melts under 1D Confinement: A Dissipative Particle Dynamic Study.

The study investigates the impact of film thickness on the phase behavior of pentablock terpolymers, denoted as C3B3A6B3C3, when subjected to wall confinement by utilizing the dissipative particle dynamics method. Phase diagrams were constructed to elucidate how factors such as block-block interaction strength, film thickness, and wall properties affect the self-assembly structures. In cases where the wall exhibits no preference for any of the blocks, lamellae phases with orientations perpendicular to the wall are observed. The order-disorder transition (ODT) temperature is found to be influenced by the interaction between the polymer and the wall in thin confinement scenarios. When the wall displays a preference for specific blocks, the orientation of lamellae structures undergoes variations. Lamellae tend to align parallel to the wall when the wall favors A or C blocks, and they orient perpendicularly when B blocks are favored. Furthermore, the mechanical properties of the lamellae structures are related to the conformations of the polymer chains. Structures where chains predominantly adopt a loop conformation exhibit enhanced elastic properties. The ratio of looping to bridging conformations can be adjusted by altering the film thickness and wall selectivity.

Assessment of the partial saddle point approximation in field-theoretic polymer simulations.

Field-theoretic simulations are numerical treatments of polymer field theory models that go beyond the mean-field self-consistent field theory level and have successfully captured a range of mesoscopic phenomena. Inherent in molecularly-based field theories is a "signproblem" associated with complex-valued Hamiltonian functionals. One route to field-theoretic simulations utilizes the complex Langevin (CL) method to importance sample complex-valued field configurations to bypass the signproblem. Although CL is exact in principle, it can be difficult to stabilize in strongly fluctuating systems. An alternate approach for blends or block copolymers with two segment species is to make a "partial saddle point approximation" (PSPA) in which the stiff pressure-like field is constrained to its mean-field value, eliminating the signproblem in the remaining field theory, allowing for traditional (real) sampling methods. The consequences of the PSPA are relatively unknown, and direct comparisons between the two methods are limited. Here, we quantitatively compare thermodynamic observables, order-disorder transitions, and periodic domain sizes predicted by the two approaches for a weakly compressible model of AB diblock copolymers. Using Gaussian fluctuation analysis, we validate our simulation observations, finding that the PSPA incorrectly captures trends in fluctuation corrections to certain thermodynamic observables, microdomain spacing, and location of order-disorder transitions. For incompressible models with contact interactions, we find similar discrepancies between the predictions of CL and PSPA, but these can be minimized by regularization procedures such as Morse calibration. These findings mandate caution in applying the PSPA to broader classes of soft-matter models and systems.

Pressure-Modulated Anomalous Organic-Inorganic Interactions Enhance Structural Distortion and Second-Harmonic Generation in MHyPbBr3 Perovskite.

Organic-inorganic halide perovskites possess unique electronic configurations and high structural tunability, rendering them promising for photovoltaic and optoelectronic applications. Despite significant progress in optimizing the structural characteristics of the organic cations and inorganic framework, the role of organic-inorganic interactions in determining the structural and optical properties has long been underappreciated and remains unclear. Here, by employing pressure tuning, we realize continuous regulation of organic-inorganic interactions in a lead halide perovskite, MHyPbBr3 (MHy+ = methylhydrazinium, CH3NH2NH2+). Compression enhances the organic-inorganic interactions by strengthening the Pb-N coordinate bonding and N-H···Br hydrogen bonding, which results in a higher structural distortion in the inorganic framework. Consequently, the second-harmonic-generation (SHG) intensity experiences an 18-fold increase at 1.5 GPa, and the order-disorder phase transition temperature of MHyPbBr3 increases from 408 K under ambient pressure to 454 K at the industrially achievable level of 0.5 GPa. Further compression triggers a sudden non-centrosymmetric to centrosymmetric phase transition, accompanied by an anomalous bandgap increase by 0.44 eV, which stands as the largest boost in all known halide perovskites. Our findings shed light on the intricate correlations among organic-inorganic interactions, octahedral distortion, and SHG properties and, more broadly, provide valuable insights into structural design and property optimization through cation engineering of halide perovskites.