Stabilization Of Phase Research Articles

Combined experimental and CALPHAD investigation of equimolar AlCoCrFeNiX (X=Mo,Ta,W) High-Entropy Alloys

Aiming to evaluate the effect of refractory metal additions to a quinary AlCoCrFeNi High-Entropy Alloy (HEA), three novel equimolar AlCoCrFeNi-X (X = Mo, Ta, W) HEAs were designed, arc-melted, annealed, and characterized by SEM-EDS, XRD and microhardness measurements. CALPHAD thermodynamic calculations were exploited to design compositions and thermal treatments of the selected HEAs as well as to predict constitution and interpret microstructure of the samples. On the other hand, the experimental results contributed to the validation of the in-house built GHEA thermodynamic database (including the Al, Co, Cr, Fe, Ni, Mo, Ta, W elements) used for the calculations. No TCP intermetallic was found to form in the quinary AlCoCrFeNi alloy. However, the formation of σ, Laves-C14 and μ phases was observed in the samples containing Mo, Ta, and W, respectively, in agreement with the most accepted VEC-based phases stabilization criteria. The addition of the refractory metals led to a microhardness increase for all the investigated alloys. Overall, good agreement was observed between experiments and calculations, especially for compositional trends and phase amounts, allowing the database validation and supporting its applicability to phase equilibria simulation in the six-component HEAs belonging to the Al–Co–Cr–Fe–Ni-X (X = Mo, Ta, W) systems.

Stabilization of various structural phases and magnetic properties of chemically synthesized Co-Ni-Ga nanoparticles

Polycrystalline Co-Ni-Ga ferromagnetic shape memory alloy nanoparticles with phase single austenite (A), martensite (M) and gamma (γ) structures have been obtained for the first time through a facile template-less chemical method. Average crystallite size of A, M and γ phase nanoparticles are 25 nm, 22 nm and 21 nm, respectively. All the synthesized nanoparticles exhibit soft ferromagnetic behavior with saturation magnetization varying from 21.22 to 77.65 emu/g and effective magnetic anisotropy of ∼105 J/m3 at 5 K. Ab initio studies have been performed to evaluate the magnetic moments of single A, M and γ phase. All the single phase nanoparticles have been ascertained to be in single-domain regime by estimating the single-domain size limit. This work showcases a simple methodology to prepare pure crystal phases in these nanoparticles. It also provides insight on the role of elemental precursors and processing conditions in designing Co-Ni-Ga nanoparticles for ferromagnetic shape memory applications.

Phase Noise Analysis Performance Improvement, Testing and Stabilization of Microwave Frequency Source

Phase Noise Analysis Performance Improvement, Testing and Stabilization of Microwave Frequency Source

Multiresponsive Behavior of the Pickering Emulsifier and Its Application for Collecting Small Oil Droplets in Water.

Responsive Pickering emulsions, with unique nanoparticle interfaces and sensitivity to external stimuli, significantly enhanced the stability and applicability of Pickering emulsions. Multifunctional composite material poly((2-(dimethylaminoethyl methacrylate)-b-(acrylate cyclodextrin))/Fe3O4 nanoparticles, namely P(DMAEMA-b-A-CD)/Fe3O4, with both multiresponsive characteristics and emulsifying capabilities had been designed to remove small oil droplets from water. Using the reversible addition-fragmentation chain transfer (RAFT) method, diblock polymers P(DMAEMA-b-A-CD) were grown in a controlled manner on the surface of Fe3O4. The Fe3O4 core showed responsiveness to a magnetic field, and the block copolymers prepared via the RAFT method demonstrated reactivity to both pH and CO2. The P(DMAEMA-b-A-CD)/Fe3O4 nanoparticles exhibited the capability to form Pickering/Oxford emulsions with exceptional stabilization properties. It could be observed that the introduction of CO2, acid, and a magnetic field led to the breakage of the emulsion, while the emulsion could be restabilized by removing the CO2 and the magnetic field or by adding alkali. Measurements of interfacial tension, ζ-potential, and contact angle demonstrated that the emulsification/breakdown mechanisms associated with pH and CO2/N2 were related to the surface wettability of the nanoparticles. In addition, the emulsifier had an excellent cycling capacity with at least 10 cycles by CO2/N2. Additionally, P(DMAEMA-b-A-CD)/Fe3O4 nanoparticles exhibited excellent stability in oil phases with large polarity differences and various real oil phases with different viscosities. Importantly, the P(DMAEMA-b-A-CD)/Fe3O4 nanoparticles could serve as functional materials for efficiently separating small oil droplets from water through the application of a magnetic field. Therefore, P(DMAEMA-b-A-CD)/Fe3O4 nanoparticles held promising potential as materials with economic and commercial value for oil-water separation applications.

Dissemination of UTC(NIST) over 20 km of commercial optical fiber with active phase stabilization.

We demonstrate the transfer of a cesium frequency standard steered to UTC(NIST) over 20 km of dark telecom optical fiber. Our dissemination scheme uses an active stabilization technique with a phase-locked voltage-controlled oscillator. Out-of-loop characterization of the optical fiber link performance is done with dual-fiber and single-fiber transfer schemes. We observe a fractional frequency instability of 1.5 × 10-12 and 2 × 10-15 at averaging intervals of 1 s and 105 s, respectively, for the link. Both schemes are sufficient to transfer the cesium clock reference without degrading the signal, with nearly an order of magnitude lower fractional frequency instability than the cesium clocks over all time scales. The simplicity of the two-fiber technique may be useful in future long-distance applications where higher stability requirements are not paramount, as it avoids technical complications involved with the single-fiber scheme.

Stabilizing metastable ferroelectric tungsten trioxide phase at room temperature via solvothermal synthesis and millisecond pulsed laser irradiation

Epsilon tungsten trioxide (ε-WO3) has drawn much attention for its unique gas sensing and ferroelectric properties. However, the strong metastability of ε-phase makes it extremely difficult to stabilize the phase at room temperature. For a long time, it was believed that the ε-phase can only be stabilized by rapid solidification processing. In this study, ε-WO3 was stabilized by employing solvothermal synthesis and subsequent annealing, with the help of Cr- and Ti-dopants. Structural characterization using XRD, Raman and TEM analysis revealed that the as-annealed powders are a mixture of ε-WO3 and γ-WO3 and the fraction of ε-WO3 is directly correlated with the Cr- and Ti-doping levels. Rietveld refinement suggests that the maximum obtainable fractions of ε-phase in as-annealed WO3 are ∼68 % for Cr-doping and ∼87 % for Ti-doping. The growth mechanism is that solvothermal synthesis produced Cr- and Ti-doped W18O49 and subsequent annealing resulted in phase transition from W18O49 to ε-WO3. The XPS analysis reveals the phase stabilization mechanism to involve the interstitial sites of WO3 being occupied by Cr3+ and Ti4+ dopants, resulting in structure distortions. The fraction of ε-WO3 can be further improved to almost 100 % by introducing kinetic constraints using pulsed laser irradiation to rapidly melt and solidify the WO3 (in several milliseconds). A viable solvothermal synthesis route for ε-WO3 and the feasibility to produce ε-phase via additive manufacturing are illustrated in this work.

Phase stability and mechanical properties of the six-principal element TiVNbCrCoNi alloys

This study designed a series of six-principal element TiVNbCrCoNi alloys according to the maximum entropy principle under the constraint of valence electron concentration (VEC). The phase stability and mechanical properties were investigated. It was showed that at VEC levels below 5.2, the body-centered cubic (BCC)-structured solid-solution phase remained stable at room temperature. As VEC exceeded 8.0, the face-centered cubic (FCC)-structured solid-solution phase stabilized. In the VEC range of 5.2–8.0, (Co, Ni)Ti and Ni3Nb intermetallic compounds formed combining with the solid-solution phases. Both yield strength and ductility increased with increase of VEC in the BCC-structured solid-solution alloys. The phase stability was elucidated through First-principle and thermodynamic calculations, while the evolution of mechanical properties of solid-solution alloys was evaluated in terms of multiple parameters. The thermodynamic calculation achieved satisfactory accuracy after being adjusted to utilize atomic bond enthalpy instead of atomic electronegativity difference.

Manipulation of metavalent bonding to stabilize metastable phase: A strategy for enhancing zT in GeSe

AbstractExploration of metastable phases holds profound implications for functional materials. Herein, we engineer the metastable phase to enhance the thermoelectric performance of germanium selenide (GeSe) through tailoring the chemical bonding mechanism. Initially, AgInTe2 alloying fosters a transition from stable orthorhombic to metastable rhombohedral phase in GeSe by substantially promoting p‐state electron bonding to form metavalent bonding (MVB). Besides, extra Pb is employed to prevent a transition into a stable hexagonal phase at elevated temperatures by moderately enhancing the degree of MVB. The stabilization of the metastable rhombohedral phase generates an optimized bandgap, sharpened valence band edge, and stimulative band convergence compared to stable phases. This leads to decent carrier concentration, improved carrier mobility, and enhanced density‐of‐state effective mass, culminating in a superior power factor. Moreover, lattice thermal conductivity is suppressed by pronounced lattice anharmonicity, low sound velocity, and strong phonon scattering induced by multiple defects. Consequently, a maximum zT of 1.0 at 773 K is achieved in (Ge0.98Pb0.02Se)0.875(AgInTe2)0.125, resulting in a maximum energy conversion efficiency of 4.90% under the temperature difference of 500 K. This work underscores the significance of regulating MVB to stabilize metastable phases in chalcogenides.

Single Crystal Seed Induced Epitaxial Growth Stabilizes α-FAPbI3 in Perovskite Solar Cells.

FAPbI3 stands out as an ideal candidate for the photoabsorbing layer of perovskite solar cells (PSCs), showcasing outstanding photovoltaic properties. Nonetheless, stabilizing photoactive α-FAPbI3 remains a challenge due to the lower formation energy of the competitive photoinactive δ-phase. In this study, we employ tetraethylphosphonium lead tribromide (TEPPbBr3) single crystals as templates for the epitaxial growth of PbI2. The strategic use of TEPPbBr3 optimizes the evolution of intermediates and the crystallization kinetics of perovskites, leading to high-quality and phase-stable α-FAPbI3 films. The TEPPbBr3-modified perovskite exhibits optimized carrier dynamics, yielding a champion efficiency of 25.13% with a small voltage loss of 0.34 V. Furthermore, the target device maintains 90% of its initial PCE under maximum power point (MPP) tracking over 1000 h. This work establishes a promising pathway through single crystal seed based epitaxial growth for achieving satisfactory crystallization regulation and phase stabilization of α-FAPbI3 perovskites toward high-efficiency and stable PSCs.

Phase stabilization of Fe doped SnS by solvothermal method and its structural, morphological and optoelectronic properties for photovoltaic applications

This letter reports the doping of Fe (Sn1-xFexS, x = 0, 0.002, 0.004, 0.006 and 0.008 M) in SnS by solvothermal method at a reaction temperature of 170 °C for a much reduced period of 90 min. The effect of Fe as a dopant on the phase purity, surface morphology, direct energy band gap and electrical resistivity of SnS is discussed in detail. Phase pure SnS formation is attained up to 6 % doping of Fe3+ at the cationic Sn2+ sites, whereas trivial formation of Sn2S3 as a secondary phase is observed along with SnS for SnS:Fe 8 % as evident from Raman, XRD, XPS and SAED analyses. Morphological studies showed the disruption of well-defined SnS nanorods upon the incorporation of Fe. The variations in direct energy band gap is well correlated with the effect of doping which in turn tuned the electrical transport properties of SnS without affecting its p-type conductivity.

Nanocrystalline Cubic Phase Scandium-Stabilized Zirconia Thin Films.

The cubic zirconia (ZrO2) is attractive for a broad range of applications. However, at room temperature, the cubic phase needs to be stabilized. The most studied stabilization method is the addition of the oxides of trivalent metals, such as Sc2O3. Another method is the stabilization of the cubic phase in nanostructures-nanopowders or nanocrystallites of pure zirconia. We studied the relationship between the size factor and the dopant concentration range for the formation and stabilization of the cubic phase in scandium-stabilized zirconia (ScSZ) films. The thin films of (ZrO2)1-x(Sc2O3)x, with x from 0 to 0.2, were deposited on room-temperature substrates by reactive direct current magnetron co-sputtering. The crystal structure of films with an average crystallite size of 85 Å was cubic at Sc2O3 content from 6.5 to 17.5 mol%, which is much broader than the range of 8-12 mol.% of the conventional deposition methods. The sputtering of ScSZ films on hot substrates resulted in a doubling of crystallite size and a decrease in the cubic phase range to 7.4-11 mol% of Sc2O3 content. This confirmed that the size of crystallites is one of the determining factors for expanding the concentration range for forming and stabilizing the cubic phase of ScSZ films.

Two-dimensional lead halide perovskite lateral homojunctions enabled by phase pinning

Two-dimensional organic-inorganic hybrid halide perovskites possess diverse structural polymorphs with versatile physical properties, which can be controlled by order-disorder transition of the spacer cation, making them attractive for constructing semiconductor homojunctions. Here, we demonstrate a space-cation-dopant-induced phase stabilization approach to creating a lateral homojunction composed of ordered and disordered phases within a two-dimensional perovskite. By doping a small quantity of pentylammonium into (butylammonium)2PbI4 or vice versa, we effectively suppress the ordering transition of the spacer cation and the associated out-of-plane octahedral tilting in the inorganic framework, resulting in phase pining of the disordered phase when decreasing temperature or increasing pressure. This enables epitaxial growth of a two-dimensional perovskite homojunction with tunable optical properties under temperature and pressure stimuli, as well as directional exciton diffusion across the interface. Our results demonstrate a previously unexplored strategy for constructing two-dimensional perovskite heterostructures by thermodynamic tuning and spacer cation doping.

Ultrabroadband two-dimensional electronic spectroscopy in the pump-probe geometry using conventional optics.

We report ultrabroadband two-dimensional electronic spectroscopy (2D ES) measurements obtained in the pump-probe geometry using conventional optics. A phase-stabilized Michelson interferometer provides the pump-pulse delay interval, τ1, necessary to obtain the excitation-frequency dimension. Spectral resolution of the probe beam provides the detection-frequency dimension, ω3. The interferometer incorporates active phase stabilization via a piezo stage and feedback from interference of a continuous-wave reference laser detected in quadrature. To demonstrate the method, we measured a well-characterized laser dye sample and obtained the known peak structure. The vibronic peaks are modulated as a function of the waiting time, τ2, by vibrational wave packets. The interferometer simplifies ultrabroadband 2D ES measurements and analysis.

Search for eutectic high entropy alloys by integrating high-throughput CALPHAD, machine learning and experiments

We present a comprehensive study on the identification of eutectic high entropy alloys (EHEAs) through integration of CALculation of PHAse Diagrams (CALPHAD), machine learning (ML), and experimental data. By performing high-throughput CALPHAD calculations to obtain the temperature differences between liquidus and solidus phases (ΔT) and employing gradient descent optimization to identify local minima in ΔT surface, we obtained a reliable dataset for EHEAs across 5–6 component alloy families, which effectively addresses current limitations in both the quality and availability of EHEA data. In conjunction with literature-based experimental data, this dataset serves as the foundation for ML models trained with an XGBoost classifier. The physical descriptors with the most significant effects on the classification of eutectics and non-eutectics are identified. Our study reveals that configurational entropy alone yields a remarkable 98% classification accuracy, elucidating its dual role in phase stabilization and melting point depression. For the first time, an explicit phase selection rule to identify eutectics has been derived from an artificial neural network model, which facilitates efficiently screening EHEAs without resorting to CALPHAD nor ML models. This study presents a robust, data-driven strategy applicable not only to EHEAs but also to a broader range of alloy systems.

High‐Entropy Phase Stabilization Engineering Enables High‐Performance Layered Cathode for Sodium‐Ion Batteries

AbstractO3‐type layered oxides are considered as one of the most promising cathode materials for rechargeable sodium‐ion batteries (SIBs) due to their appealing energy density and feasible synthesis. Nevertheless, it undergoes complicated phase transitions and pronounced structural degradation during the cycling of charge/discharge process, rendering severe volumetric strain and poor cycling performance. Herein, a zero‐strain high‐entropy NaNi0.2Fe0.2Mn0.35Cu0.05Zn0.1Sn0.1O2 cathode for SIBs is presented by high‐entropy phase stabilization engineering. It is verified that this low‐nickel cobalt‐free high‐entropy cathode can deliver a highly reversible phase evolution, zero volumetric strain, and a significantly improved cycling performance in full cells (87% capacity retention after 500 cycles at 3.0 C). Combining X‐ray absorption spectra and first‐principles calculations, the varied elemental functions in the high‐entropy framework are clearly elucidated, namely, Ni/Fe/Cu acts as charge compensators, while Mn/Zn/Sn serve as interlayer slipping inhibitors through enhanced charge localization besides their stable valence states. By addressing the volumetric strain and cycling instability concerns for O3‐type cathode materials, this work presents a promising strategy for inhibiting irreversible phase transitions and structural degradation in intercalation electrodes, which significantly boosts the development of commercially feasible cathodes for high‐performance SIBs.

Low oxidation conditions in pulsed laser deposition enhance polarization without degradation of endurance and retention in Hf0.5Zr0.5O2 films

Interplay between oxygen vacancies and the stabilization of the ferroelectric orthorhombic phase in doped HfO2, as well as the resulting impact on endurance and retention, is far from being well understood. In Hf0.5Zr0.5O2 (HZO) thin films, it is commonly found that high polarization occurs usually at the the expense of robustness upon cycling due to the polarization–endurance dilemma. It has been reported that HZO thin films grown by pulsed laser deposition under the mixed Ar and O2 atmosphere exhibit a high polarization. Here, we show that this strategy enables functional properties tuning, allowing to obtain HZO films with high polarization at low oxidation conditions without degradation of endurance and retention.

Anomalous polarization-switching phenomena and noteworthy pyroelectricity in ferroelectric Hf0.5Zr0.5O2 polycrystalline films

Hafnia-based oxide thin films exhibit unconventional robust ferroelectricity at the nanoscale, paving the way for advancements in next-generation nanoelectronics. However, the stability and dynamics of ferroelectric polarization in hafnia-based oxides films, particularly at the nanoscale, warrant further exploration. In this study, we delve into the factors influencing the formation of the ferroelectric phase. Our findings illuminate that the confinement effect of the capped layer enhances the stabilization of the metastable orthorhombic phase, thereby bolstering its ferroelectricity and endurance. Furthermore, we identify an unprecedented polarization-switching behavior in HfO2-based ferroelectric films, characterized by a decrease in the remanent polarization and an increase in the coercive field as the temperature drops. This peculiar phenomenon can be ascribed to the reduction in the long-range interaction of polarization dipoles upon cooling, as evidenced by the dielectric spectrum. The diminished long-range interaction results in the emergence of nanodomains and a re-entrant relaxer behavior, offering novel insights into the origin of ferroelectricity and the stability of ferroelectric polarization in hafnia-based thin films. Given the commendable compatibility of Hf0.5Zr0.5O2 films with Si substrates and a pyroelectric coefficient of −62.1 μC/m2·K, they emerge as a prime candidate for sensor device applications.

Enhanced hydrogen barrier performance of ZrH1.8 via yttria-zirconia composite film developed through the ECD-MAO technique

To address the inherent shortcomings of the direct micro-arc oxidation method, this study employed a combination of electroplating and micro-arc oxidation techniques. This approach successfully fabricated a hydrogen permeation barrier film on the surface of ZrH1.8, featuring a yttria-stabilized zirconia (YSZ) composite oxide. The prepared composite film layer underwent thorough evaluations, encompassing assessments of its microstructure, phase structure, adhesion strength, thickness, barrier properties, and hydrogen permeation performance. The findings indicated that the electroplated yttrium layer contributes to the stabilization of the tetragonal phase of zirconia (T-ZrO2) during the micro-arc oxidation process, thereby enhancing the discharge behavior of the film layer. By employing this treatment method, the content of T-ZrO2 in the film layer increased to 26.70%, and the film became denser with a thickness of 60.93 μm. Additionally, the adhesion strength between the film layer and the substrate significantly improved, reaching 75.95 N, with a hardness of 393.24 HV. Furthermore, the film layer exhibited an increased hydrogen release temperature of 680 °C, demonstrating excellent performance as a hydrogen permeation barrier.

Unraveling the crucial contribution of additive chromate to efficient and stable alkaline seawater oxidation on Ni-based layered double hydroxides

Seawater electrolysis to generate hydrogen offers a clean, green, and sustainable solution for new energy. However, the catalytic activity and durability of anodic catalysts are plagued by the corrosion and competitive oxidation reactions of chloride in high concentrations. In this study, we find that the additive CrO42− anions in the electrolyte can not only promote the formation and stabilization of the metal oxyhydroxide active phase but also greatly mitigate the adverse effect of Cl− on the anode. Linear sweep voltammetry, accelerated corrosion experiments, corrosion polarization curves, and charge transfer resistance results indicate that the addition of CrO42− distinctly improves oxygen evolution reaction (OER) kinetics and corrosion resistance in alkaline seawater electrolytes. Especially, the introduction of CrO42− even in the highly concentrated NaCl (2.5 M) electrolyte prolongs the durability of NiFe-LDH to almost five times the case without CrO42−. Density functional theory calculations also reveal that the adsorption of CrO42− can tune the electronic configuration of active sites of metal oxyhydroxides, enhance conductivity, and optimize the intermediate adsorption energies. This anionic additive strategy can give a better enlightenment for the development of efficient and stable oxygen evolution reactions for seawater electrolysis.

Fabrication and Characterization of novel high internal phase bigels with high mechanical properties: Phase inversion and personalized edible 3D food printing

In this paper, bigels systems were prepared by using 20 wt% palm stearin (POs) structured soybean oil oleogels and 80 wt% xanthan gum hydrogels in different ratios of polyglycerol polyricinoleate (PGPR). The proportion of PGPR in bigels was changed to explore the phase inversion and stabilization mechanism of bigels by multiple microscopy techniques, and the mechanical properties have been evaluated by the rheology analysis and 3D printability. When the PGPR content was less than 0.4 wt%, bigels presented as the O/W type. As the PGPR content was 1.0 wt% and 1.2 wt%, the bigel presented as the W/O type with a high internal phase, and a high level of droplets dispersed closely within an oil phase. The increase in PGPR content slowed down the nonlinear viscoelastic behavior under large strains. In terms of 3D printing capability, bigels (oleogels containing 20 wt% POs) showed an unsatisfactory 3D printing capability. However, with the increase of POs and PGPR content, more plastic and printable W/O high internal phase bigels were obtained due to the formation of a more stable, homogeneous, and strong ink. In addition, the bigels systems were investigated for the preparation of 3D biscuit printing, and it was found that the K′ value of W/O bigels batter (1511.39) was larger than that of O/W bigels batter (1394.82), showing greater hardness and better 3D printing performance. These findings could facilitate the broadening of bigels systems that could be applied for 3D biscuit printing.