Stabilization Of Phase Research Articles

Enhanced Li+ conductivity of Li7La3Zr2O12 by increasing lattice entropy and atomic redistribution via Spark Plasma Sintering

Cubic Li7La3Zr2O12 (c-LLZO) is an ideal solid-state electrolyte for Li-ion batteries. The Li diffusivity at 24d site is a rate-determining step of the ionic conductivity. Aluminium is commonly used to synthesise c-LLZO. However, Al3+ prefers to occupy the 24d over 96h. To improve the ionic conductivity of Al-doped LLZO, minimizing the occupation of Al at 24d is shown to be crucial. In this work, SPS (Spark Plasma Sintering) is employed primarily due to its capability of metastable phase stabilization via a non-equilibrium process and ion redistribution related electromigration process. X-ray powder diffraction refinement reveals that occupancy of Al at 24d site decreased and lattice distortion index increase of SPS processed Al-doped c-LLZO. The lattice distortion index is closely tied to lattice entropy, i.e., configuration and vibrational entropy. Increasing lattice entropy can reduce the energy barriers between Al and Li’s 24d and 96h sites, stabilising Al3+ occupancy at 96h site. After SPS parameter optimisation, the high ionic conductivity of 2.6 × 10–4 S·cm-1 and low electronic conductivity of 10–7 S·cm-1. This study offers a new perspective on using SPS to modify the lattice structure, with potential benefits beyond simply densifying the samples. Highlighting the importance of high lattice entropy is favourable in enhancing ionic conductivity.

Super-swelling behavior of stacked lipid bilayer systems

Bilayer systems comprising lipid mixtures are the most well-studied model of biological membranes. While the plasma membrane of the cell is a single bilayer, many intra- and extra-cellular biomembranes comprise stacks of bilayers. Most bilayer stacks in nature are periodic, maintaining a precise water layer separation between bilayers. That equilibrium water separation is governed by multiple inter-bilayer forces and is highly responsive. Biomembranes re-configure inter-bilayer spacing in response to temperature, composition, or mass transport cues. In synthetic bilayer systems for applications in cosmetics or topical treatments, control of the hydration level is a critical design handle. Herein we investigate a binary lipid system that leverages key inter-bilayer forces leading to unprecedented levels of aqueous swelling while maintaining a coherent multilamellar form. We found that combining cationic lipids with bicontinuous cubic phase-forming lipids (lipids with positive Gaussian modulus), results in the stabilization of multilamellar phases against repulsive steric forces that typically lead to bilayer delamination at high degrees of swelling. Using ultra-small-angle X-ray scattering alongside confocal laser scanning microscopy, we characterized various super-swelled states of 1,2-dioleoyl-3-trimethylammonium-propane (DOTAP) and glycerol monooleate (GMO) lipids, as well as other analogous systems, at varied concentration and molar ratios. Through these experiments we established swelling profiles of various binary lipid systems that were near-linear with decreasing lipid volume fraction, showing maximum swelling with periodicity well above 200 nanometers.Graphical abstractConfocal fluorescence micrograph of super-swelled multilamellar structures in 90GMOD sample at 25 mM concentration. Inset plot shows intensity profile of orange line, with pink triangles indicating maxima.

Influence of bismuth oxide as a sintering aid on the densification of cold sintering of zirconia

In the past decades, Zirconia (ZrO2) has emerged as a promising technical ceramic, both as high temperature structural material and electrolyte for fuel cells, etc. The traditional synthesis of ZrO2 with spark plasma sintering (SPS) usually requires a sintering temperature as high as 1200 °C. General interest in lowering the sintering temperature to reduce energy consumption and thermal stresses has led to research on two promising routes – cold sintering via temperature-dependent chemical reactivity and sintering aids, which facilitates mass transport and improves densification. Here we combine both by developing a single-step sintering process benefitting from both water vapor through the in-situ conversion of Zr(OH)4 to ZrO2 and liquid phase Bi2O3 as a sintering aid. The resultant ZrO2 has a relative density above 80% with a sintering temperature as low as 900 °C, significantly higher than that of ZrO2 without sintering aids, which had a relative density of 54%, both sintered at 50 MPa. The dependence of porosity of sintered samples as a function of sintering pressure (range: 50 MPa–300 MPa) and temperature (range 400 °C–1200 °C) is mapped out as guidance for further material property design. A linear relationship between hardness and relative density was found, with a maximal hardness of 6.6 GPa achieved in samples with 30% porosity. In addition to sintered density, phase stabilization of tetragonal ZrO2 is enhanced at sintering temperature of 900 °C with water vapor and Bi2O3, respectively.

Phase stabilization and optical response in the ultraviolet range, due to terbium concentration in hafnium oxide nanoparticles

This work reports the influence of terbium trivalent ions on growing kinetics and the phase in hafnium oxide nanoparticles, as well as response to radiation in the range from 256 to 286. The nanoparticles were obtained by the hydrothermal route maintaining the temperature constant and varying the reaction time and the terbium concentration. The results show a gradual change in the phase with the concentration of terbium trivalent ions, going from the monoclinic phase, present at low concentrations, to the tetragonal phase, which appears from dopant concentrations greater than 5% at., increasing in amount with concentration of dopant. These phases appear as two perfectly defined morphologies. Furthermore, there is a significant change in radiative lifetimes when the tetragonal phase appears.

STRUCTURAL, OPTICAL, AND VISIBLE-LIGHT DRIVEN PHOTACATALYTIC PROPERTIES OF Yb-DOPED BiVO4 NANOPARTICLES PREPARED VIA RAPID SONOCHEMICAL PROCESS

This work represents the synthesis and structural, morphological, and optical characterization of rare-earth Yb-doped BiVO4 materials with different Ytterbium (Yb3+) contents (0% - 5%). Yb-doped BiVO4 specimens in form of fine nanoparticles were synthesized by a rapid and facile sonochemical process. The structural and morphological characterizations were observed by X-ray diffraction technique (XRD), Fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM). Important optical properties of the prepared samples were investigated by the diffuse reflectance technique and the corresponding optical band gaps were calculated by the mean of the Kullbelka-Munk equation. From the characterized results, it is acknowledged that incorporated Yb dopant has a significant effect on the crystalline structure of BiVO4 by reducing in monoclinic phase in the pristine sample while the increasing Yb doping composition resulted in the mixed phases of monoclinic and tetragonal phases since Yb3+ ions could probably induce the stabilization of the tetragonal phase in BiVO4 material. Moreover, extensive doping with Yb3+ exhibits considerable influence on not only structural but also optical and relevant visible - driven photocatalytic properties of BiVO4 by means of the color degradation of RhB dye solution.

Doped and undoped ferroelectric HfO2: Role of Gd-doping in stabilizing the ferroelectric phase

Doped hafnium oxide was shown to exhibit a strong ferroelectric behavior. It was implied that doping allows the stabilization of a HfO2 non-centrosymmetric orthorhombic phase, a prerequisite for ferroelectric behavior. However, a number of reports showed comparable ferroelectric properties in undoped HfO2, although with different behaviors of the remanent polarization upon layer thickness. In this work, the ferroelectric properties and crystalline structure of doped and undoped HfO2 layers as a function of the layer thickness were studied. The results show similar properties for ultrathin layers. Indeed, both show a linear increase in the orthorhombic/tetragonal crystalline phase amount and of remanent polarization as a function of thickness up to 7 nm. For higher thicknesses, a strong increase in the monoclinic phase is observed in undoped layers alongside a strong decrease in the remanent polarization whereas, for doped layers, the remanent polarization continues to increase with thickness. The experimental results suggest that the stabilization of the undoped HfO2 orthorhombic ferroelectric phase is due to mechanical stress, which is particularly high in ultrathin layers but relaxes for thicker layers.

Unforeseen complications: a case of dengue shock syndrome presenting with multi-organ dysfunction in a subtropical region

OverviewDengue fever, a viral illness transmitted by the Aedes mosquito, is capable of causing a range of serious complications, including fulminant hepatic failure, renal dysfunction, encephalitis, encephalopathy, neuromuscular and ophthalmic disorders, seizures, and cardiomyopathy.Case descriptionThis report details the case of a 30-year-old lactating woman with no notable medical history who presented to the emergency department with symptoms of high-grade fever, altered mental status, and seizures. Upon imaging, bilateral infarcts in the thalami and cerebellar hemispheres were observed, consistent with cerebellitis and dengue encephalitis.Patient treatment and outcomeThe patient was admitted to the intensive care unit and received appropriate treatment. Following a critical phase and successful patient stabilization, she was transferred to a high dependency unit for a week before being discharged with recommendations for follow-up care.ConclusionThis case illustrates the broad spectrum of complications that can arise as a result of dengue infection and the importance of timely diagnosis and management in improving patient outcomes. Further investigation is required to better understand the mechanisms underlying these complications and to formulate specific guidelines for the prevention and treatment of dengue shock syndrome.

CoFeNiTix and CrFeNiTix high entropy alloy thin films microstructure formation

High entropy alloys (HEA) composition-structure relationships are crucial for guiding their design and applications. Here, we use a combined experimental and molecular dynamics (MD) approach to investigate phase formation during physical vapor deposition (PVD) of CoFeNiTix and CrFeNiTix HEA thin films. We vary titanium molar ratio from 0 to 1 to understand the role of a larger element in the alloy mixture. The experiments show that a high titanium content favors amorphous phase formation in the samples produced by magnetron co-sputtering. In contrast, a low titanium content results in the formation of a face-centered cubic (FCC) structure in both HEA families. This effect of titanium content on the stability of the amorphous and FCC phases is reproduced in PVD MD simulations. The threshold titanium molar ratio is identified to be ∼0.53 and ∼0.16 for the CoFeNiTix and CrFeNiTix films in the experiments, and ∼0.53 and ∼0.53 in the MD simulations. In addition, the atomistic modeling allows for energy versus volume calculations with increasing titanium content, which demonstrate the stabilization of the amorphous phase with respect to crystalline structures. To isolate the effect of atomic sizes, additional simulations are performed using an average-atom model, which disregards differences in atomic radii while preserving the average properties of the alloy. In these simulations, the energetic stability of the amorphous phase disappears. The combined experimental and simulation results demonstrate that the formation of the amorphous phase in HEA thin films generated by PVD is directly caused by the atomic size difference.

Role of Mg–O on phase stabilization in solution combustion processed rocksalt structured high entropy oxide (CoCuMgZnNi)O with high dielectric performance

High entropy oxide (CoCuMgZnNi)O with a phase pure rocksalt was synthesized using low-temperature solution combustion. The precursors were found to combust at 270 °C and 400 °C was considered to be the formation temperature. The high entropy rocksalt oxide (HERO) fully stabilized at 1000 °C shows a single-phase, fcc rocksalt structure with an Fm-3m space group. HERO displays one of its parent oxide Mg–O structural properties as both belong to the cubic family and had lattice parameters very close to each other. The lower cation systems exhibited a transition from spinel to rocksalt structure with the addition of Mg–O. Raman of HERO affirmed a completely disordered occupancy of various metal cations, the formation of HERO at 400 °C, and phase stabilization at 1000 °C. Dielectric measurements at room temperature showed high permittivity (κ) with magnitudes ∼1.9 × 103, 4.7× 101, and 0.9 × 101 at 100, 1k, and 100k Hz.

High‐Entropy Engineering for Broadband Infrared Radiation

AbstractDeveloping high‐performance infrared (IR) radiation materials with desired broadband emissivity, excellent thermal stability, and scalable fabrication processes is highly desirable for energy‐saving applications and heat dissipation. However, it remains a grand challenge to concurrently meet these requirements in existing IR radiation materials. Herein, a high‐entropy (HE) approach is employed to advance the IR radiation performance of spinel oxide. This strategy efficiently narrows the bandgap due to the enhanced electron transitions and the introduction of oxygen vacancies (Ov), variable‐valence behavior, and orbital hybridization. In addition, the lattice distortion effect lowers the symmetry of lattice vibration. Therefore, the resulting HE spinel oxide exhibits near‐blackbody radiation performance, with its emissivity approximately three times higher than that of the binary spinel oxide. Moreover, the entropy‐dominating phase stabilization effect contributes to impressive thermal stability (stable at 1300 °C for 100 h). This makes it suitable for high‐temperature thermal radiation applications, such as energy conservation in industrial high‐temperature furnaces. More importantly, the HE spinel oxide can be readily spray‐coated on various substrates. And the coating on stainless steel reaches an outstanding emissivity of 0.943 in the 0.78−16 µm wavelength range. All these merits render the HE approach competitive for the development of high‐emissivity and thermally stable thermal radiation materials.

Reciprocal space temperature-dependent phonons method from ab-initio dynamics

We present a robust reciprocal-space implementation of the temperature-dependent effective potential method, our implementation can scale easily to large cell and long sampling time. It is interoperable with standard ab-initio molecular dynamics and with Langevin dynamics. We prove that both sampling methods can be efficient and accurate if a thermostat is used to control temperature and dynamics parameters are used to optimize the sampling efficiency. By way of example, we apply it to study anharmonic phonon renormalization in weakly and strongly anharmonic materials, reproducing the temperature effect on phonon frequencies, crossing of phase transition, and stabilization of high-temperature phases.

Mg and Al-induced phase transformation and stabilization of Ga2O3-based γ -phase spinels

Ga2O3 films were deposited on (100) MgAl2O4 spinel substrates at 550, 650, 750, and 850 °C using metal-organic chemical vapor deposition and investigated using x-ray diffraction and transmission electron microscopy. A phase-pure γ-Ga2O3-based material having an inverse spinel structure was formed at 850 °C; a mixture of the γ-phase and β-Ga2O3 was detected in films grown at 750 °C. Only β-Ga2O3 was determined in the films deposited at 650 and 550 °C. A β- to γ-phase transition occurred from the substrate/film interface during growth at 750 °C. The growth and stabilization of the γ-phase at the outset of film growth at 850 °C was affected by the substantial Mg and Al chemical interdiffusion from the MgAl2O4 substrate observed in the energy-dispersive x-ray spectrum. Atomic-scale investigations via scanning transmission electron microscopy of the films grown at 750 and 850 °C revealed a strong tetrahedral site preference for Ga and an octahedral site preference for Mg and Al. It is postulated that the occupation of these atoms in these particular sites drives the β-Ga2O3 to γ-phase transition and markedly enhances the thermal stability of the latter phase at elevated temperatures.

Unconventional Nonequilibrium Phase Stabilization in FeNi Alloy Examined by Positron Annihilation Spectroscopy

The equilibrium FeNi alloy prefers face centered cubic (fcc) phase whereas the formation of metastable phases through certain low‐temperature synthesis methods is obscure. FeNi alloy exhibiting nonequilibrium body centered cubic (bcc) structure beyond 5 at% Ni is obtained through chemical reduction at 453 K with noticeable lattice shrinkage. Positron lifetime analysis and Doppler broadening spectroscopy are employed to probe the correlation between defects and phase stability. The mean lifetime of the chemically synthesized alloys is larger than 300 ps, implying an average of 7‐vacancy cluster. The modified two‐state trapping model reveals defect concentration in the range of , on par with irradiated alloys. Significant deviation in the high‐momentum component between the bulk and chemically synthesized samples is correlated to the changes in 3d electrons. The Fe and FeNi alloy uncover significant contraction in d‐band of Fe which facilitates bcc phase stabilization above 5 at% Ni through cluster vacancy formation.

Chirality transfer to harness mesophase transitions in liquid crystal mixtures containing an oxadiazole derivative

ABSTRACT Chiral liquid crystal mixtures are an important field of research in the development of these materials. The main advantage of chiral liquid crystal mixtures is their ability to produce an optically active three-dimensional structure. Moreover, 1,3,4-oxadiazoles have been widely used as electron-transporting/hole-blocking materials or emitting layers in electroluminescent diodes and nonlinear optical materials owing to their interesting properties. Here, we investigate the phase transitions in a mixture of a chiral oxadiazole derivative liquid crystal, EOS-12, and a traditional nematic liquid crystal, E7. EOS-12 is miscible with the E7 matrix at all concentrations. The mesomorphic properties of these mixtures were studied using differential scanning calorimetry (DSC), polarised optical microscopy (POM) and digital colourimetry analysis. In addition, the cholesteric pitch is measured using the Grandjean-Cano technique and photophysical studies were performed in solutions and films. Mixtures show polymorphism depending on the concentration and temperature: nematic, chiral nematic, TGBA*, and smectic phases. A temperature-concentration phase diagram was established using POM. Stabilisation of the SmA phase is observed with a greater temperature range than the constituents of the mixture. According to these results, the properties of the mixture can be used to create various material functionalities, depending on the composition of the mixture.

Entropic Control of Bonding, Guided by Chemical Pressure: Phase Transitions and 18-n+m Isomerism of IrIn3.

As with other electron counting rules, the 18-n rule of transition metal-main group (T-E) intermetallics offers a variety of potential interatomic connectivity patterns for any given electron count. What leads a compound to prefer one structure over others that satisfy this rule? Herein, we investigate this question as it relates to the two polymorphs of IrIn3: the high-temperature CoGa3-type and the low-temperature IrIn3-type forms. DFT-reversed approximation Molecular Orbital analysis reveals that both structures can be interpreted in terms of the 18-n rule but with different electron configurations. In the IrIn3 type, the Ir atoms obtain largely independent 18-electron configurations, while in the CoGa3 type, Ir-Ir isolobal bonds form as 1 electron/Ir atom is transferred to In-In interactions. The presence of a deep pseudogap for the CoGa3 type, but not for the IrIn3 type, suggests that it is electronically preferred. DFT-Chemical Pressure (CP) analysis shows that atomic packing provides another distinction between the structures. While both involve tensions between positive Ir-In CPs and negative In-In CPs, which call for the expansion and contraction of the structures, respectively, their distinct spatial arrangements create very different situations. In the CoGa3 type, the positive CPs create a framework that holds open large void spaces for In-based electrons (a scenario suitable for relatively small T atoms), while in the IrIn3 type the pressures are more homogenously distributed (a better solution for relatively large T atoms). The open spaces in the CoGa3 type result in quadrupolar CP features, a hallmark of low-frequency phonon modes and suggestive of higher vibrational entropy. Indeed, phonon band structure calculations for the two IrIn3 polymorphs indicate that the phase transition between them can largely be attributed to the entropic stabilization of the CoGa3-type phase due to soft motions associated with its CP quadrupoles. These CP-driven effects illustrate how the competition between global and local packing can shape how a structure realizes the 18-n rule and how the temperature can influence this balance.

Stabilizing High-Temperature α-Li3PS4 by Rapidly Heating the Glass.

High-temperature metastable phases exhibit superior characteristics compared to those of thermodynamically stable phases at room temperature. Although optimization of the compositions and crystallizations from glasses contribute to the stabilization of metastable phases at room temperature, the stabilization of the high-temperature α-Li3PS4 phase is not yet reported. α-Li3PS4 was successfully stabilized at room temperature, instead of the middle-temperature β-Li3PS4 phase, via rapid heating to crystallize the Li3PS4 glass. The obtained electrolyte exhibited a high ionic conductivity of >10-3 S cm-1 at room temperature. The crystallization of the glass via rapid heating overcame the thermodynamic limitations in the preparation of the metastable crystals. Further development of materials via nonequilibrium states should contribute to the design of high-performance materials.

PHASE RELATIONS IN THE Ag8SiS6–Ag8SiTe6 SYSTEM AND CHARACTERIZATION OF SOLID SOLUTIONS

Argyrodite family compounds and phases based on them are valuable ecologically friendly functional materials that exhibit a number of functional propreties, such as thermoelectric, photoelectric, optical, and other. On the other hand, having Cu+ and Ag+ ion conductivity, they are ionic conductors, and can be used as electrochemical sensors, electrodes, or electrolyte materials in solid-state batteries, displays, etc. In the present paper, phase relations in the Ag8SiS6–Ag8SiTe6 system were studied by differential thermal analysis and X-ray diffraction phase techniques and a T-x phase diagram was constructed. It is established that the system is quasi-binary and is characterized by the formation of a continuous series of substitutional solid solutions between Ag8SiTe6 and HT- Ag8SiS6 compounds. With the formation of solid solutions, the temperature of the polymorphic transition of the Ag8SiS6 decreases. This leads to the stabilization of the ion-conducting cubic phase in the range of compositions 30 mol. % Ag8SiTe6 at room temperature and below. The homogeneity regions based on RT-Ag8SiS6 are 10 mol. %. According to XRD data, the crystal lattice parameters of the obtained solid solutions were calculated and a their linear dependence on the composition is shown

Stabilization of metallic phase in nanostructured hollow V2O3 spheres prepared by ultrasonic spray pyrolysis

In the development of nanostructured V2O3 materials, the topical issue is to elucidate the factors that affect the temperature of a metal-insulator transition (MIT). In this work, we study the structural, magnetic and electrical properties of V2O3 thin-walled microsphere prepared by spray-pyrolysis (SP). Low-temperature XRD and TEM revealed that SP-microspheres contain the anisotropic (50×20 nm) nanocrystallites with a preferred (001)-orientation along the sphere surface and show moderate biaxial compressive stresses. SP-aggregates exhibit a high concentration of intercrystallite boundaries and inner pores, which induce high lattice microstrains. Structural, magnetic and electrical properties showed no evidence of MIT down to 100 K. NMR investigations indicated that antiferromagnetic areas appear at temperatures below 115 K. Comparative studies were performed on V2O3 50 nm nanoparticles prepared by thermolysis using the same parent vanadyl solution. The findings suggest that a high defect concentration and microstrains rather than compressive stresses lead to the suppression of MIT.

Quantification of strain and its impact on the phase stabilization of all-inorganic cesium lead iodide perovskites

•CsPbI3 nanoplates are epitaxially grown on muscovite mica single-crystal substrates •Lattice strain is present and found to increase with decreasing nanoplate thickness •The strained epitaxy enhances the metastable perovskite high-T phase stability The high-temperature perovskite γ-phase of CsPbI3 readily undergoes phase transition at ambient conditions to a low-temperature non-perovskite δ-phase with a poorer optoelectronic performance, thus hindering commercialization of these materials in photovoltaics. Here, we present the epitaxial growth of CsPbI3 nanoplates on muscovite mica single-crystal substrates and demonstrate that the high-temperature phase stability of these nanoplates is enhanced by a strained interface. Strain is measured as a function of nanoplate thickness on a single-particle level through spatially resolved structural and optical characterizations and is found to increase with decreasing thickness. From quantitatively tracking the CsPbI3 phase transition for thin (<400 nm) and thick (>400 nm) nanoplates, we observe a larger fraction of thin nanoplates still maintaining their high-temperature phase after 1 month compared with their thick counterparts. These findings establish a relationship between strain and phase transition kinetics, which is critical for rational design of stable perovskite-based optoelectronic devices. The high-temperature perovskite γ-phase of CsPbI3 readily undergoes phase transition at ambient conditions to a low-temperature non-perovskite δ-phase with a poorer optoelectronic performance, thus hindering commercialization of these materials in photovoltaics. Here, we present the epitaxial growth of CsPbI3 nanoplates on muscovite mica single-crystal substrates and demonstrate that the high-temperature phase stability of these nanoplates is enhanced by a strained interface. Strain is measured as a function of nanoplate thickness on a single-particle level through spatially resolved structural and optical characterizations and is found to increase with decreasing thickness. From quantitatively tracking the CsPbI3 phase transition for thin (<400 nm) and thick (>400 nm) nanoplates, we observe a larger fraction of thin nanoplates still maintaining their high-temperature phase after 1 month compared with their thick counterparts. These findings establish a relationship between strain and phase transition kinetics, which is critical for rational design of stable perovskite-based optoelectronic devices.

Tailoring SnO2 Defect States and Structure: Reviewing Bottom-Up Approaches to Control Size, Morphology, Electronic and Electrochemical Properties for Application in Batteries.

Tin oxide (SnO2) is a versatile n-type semiconductor with a wide bandgap of 3.6 eV that varies as a function of its polymorph, i.e., rutile, cubic or orthorhombic. In this review, we survey the crystal and electronic structures, bandgap and defect states of SnO2. Subsequently, the significance of the defect states on the optical properties of SnO2 is overviewed. Furthermore, we examine the influence of growth methods on the morphology and phase stabilization of SnO2 for both thin-film deposition and nanoparticle synthesis. In general, thin-film growth techniques allow the stabilization of high-pressure SnO2 phases via substrate-induced strain or doping. On the other hand, sol-gel synthesis allows precipitating rutile-SnO2 nanostructures with high specific surfaces. These nanostructures display interesting electrochemical properties that are systematically examined in terms of their applicability to Li-ion battery anodes. Finally, the outlook provides the perspectives of SnO2 as a candidate material for Li-ion batteries, while addressing its sustainability.