Phase Stability Research Articles

Computational investigation of the phase stability, electronic, optical, phonon spectrum, and elastic behavior of layered perovskites Ca2XO4 (X = Zr, Hf) for optoelectronic applications.

A significant class of solid-state materials, Ruddlesden-Popper (RP) perovskites are well-known for their rich chemical compositions that make them excellent electrocatalysts. Therefore, in this work, we conduct thorough analysis of RP perovskites, specifically Ca2XO4 (X = Zr, Hf). We delve into the structural, electronic, optical, and mechanical properties presenting their insights for the first time. Our investigations reveal that Ca2XO4 (X = Zr, Hf) exhibits stable tetragonal phase structures, with energies (E0) of - 10,522.93eV and - 33,520.14eV, respectively. The calculated in terms of the ground state determines to possess distinct values such as - 4.79 eV/atom for LiScTe2 and - 3.95 eV/atom for Ca2ZrO4 and Ca2HfO4. Notably, the semiconductor characteristics of Ca2ZrO4 and Ca2HfO4 are underscored by their respective wide direct band gap of 5.02eV and 5.30eV. Then, we discuss the optical parameters encompassing the dielectric function, absorption coefficient, optical conductivity, refractive index, and energy loss function. is described as ductile, whereas is defined as brittle. Our outcomes underscore remarkable ability of these materials to absorb ultraviolet radiation from the electromagnetic spectrum, positioning them as promising candidates for optoelectronic applications. We made these calculations by employing first-principles approach rooted in density functional theory (DFT) and utilizing the Perdew-Burke-Ernzerhof-Generalized Gradient Approximation (PBE-GGA) and Tran and Blaha-modified Becke-Johnson (TB-mBJ) functional within the WEIN2K framework. In this framework, Kramers-Kronig relations are used to obtain crucial optical parameters. Mechanical behavior is assessed by employing Voigt-Reuss-Hill approximation (VRH) fulfilling the Born's criteria which emphasizes that these materials are equally appropriate for a broad range of mechanical applications.

Electrode Elastic Modulus as the Dominant Factor in the Capping Effect in Ferroelectric Hafnium Zirconium Oxide Thin Films.

The discovery of ferroelectricity in hafnia based thin films has catalyzed significant research focused on understanding the ferroelectric property origins and means to increase stability of the ferroelectric phase. Prior studies have revealed that biaxial tensile stress via an electrode "capping effect" is a suspected ferroelectric phase stabilization mechanism. This effect is commonly reported to stem from a coefficient of thermal expansion (CTE) incongruency between the hafnia and top electrode. Despite reported correlations between ferroelectric phase fraction and electrode CTE, the thick silicon substrate dominates the mechanics and CTE-related stresses, negating any dominant contribution from an electrode CTE mismatch toward the capping effect. In this work, these discrepancies are reconciled, and the origin of these differences deriving from electrode elastic modulus, not CTE, is demonstrated. Pt/M/TaN/Hf0.5Zr0.5O2/TaN/Si devices, where M is platinum, TaN, iridium, tungsten, and ruthenium, were fabricated. Sin2(ψ)-based X-ray diffraction measurements of biaxial stress in the HZO layer reveal a strong correlation between biaxial stress, remanent polarization, and electrode elastic modulus. Conversely, a low correlation exists between the electrode CTE, HZO biaxial stress, and remanent polarization. A higher elastic modulus enhances the resistance to electrode elastic deformation, which intensifies the capping effect during crystallization, and culminates in the tandem restriction of out-of-plane hafnia volume expansion and preferential orientation of the polar c-axis normal to the plane. These behaviors concomitantly increase the ferroelectric phase stability and polarization magnitude. This work provides electrode material selection guidelines toward the development of high-performing ferroelectric hafnia into microelectronic devices, such as nonvolatile memories.

Precipitation Behavior and Phase Stability in Al-Cu-Mg-Li-Sc Alloy During Aging

Precipitation Behavior and Phase Stability in Al-Cu-Mg-Li-Sc Alloy During Aging

Synthesis and High-pressure Properties of (Nd0.2Li0.2Ba0.2Sr0.2Ca0.2)TiO3 High-entropy Perovskite

The recent development of high-entropy perovskites has demonstrated their tremendous promise for various applications. To meet the expanding needs for extreme environment applications, however, the critical properties of high-entropy perovskite at high pressure remain to be disclosed. In the present work, an A-site high-entropy perovskite (Nd0.2Li0.2Ba0.2Sr0.2Ca0.2)TiO3 was synthesized. High-pressure investment on the phase stability, dielectric properties, and bandgap was conducted using diamond anvil cell combined with comprehensive in-situ measurements. The results reveal that (Nd0.2Li0.2Ba0.2Sr0.2Ca0.2)TiO3 remains the perovskite structure at the pressure up to ~15GPa. The grain resistance exhibits an exponential decrease with the increasing pressure, whilst an unusual change of the grain boundary resistance was observed at ~7GPa. Furthermore, (Nd0.2Li0.2Ba0.2Sr0.2Ca0.2)TiO3 shows a slight increase of the bandgap upon compression. Our multifaceted approach provides a comprehensive understanding of the high-pressure behavior of high-entropy perovskite, offering valuable insights for the design and optimization of advanced functional materials for high-pressure environments.

Formation of B2 Phase and its Phase Stability in Equiatomic Al-Cu-Fe-Ni-Ti High Entropy Alloy

Formation of B2 Phase and its Phase Stability in Equiatomic Al-Cu-Fe-Ni-Ti High Entropy Alloy

Testing the non-commutative charged Schwarzschild black hole surrounded by perfect fluid dark matter for thermodynamical features and weak gravitational lensing

This paper is devoted in studying the thermodynamical properties and weak gravitational lensing in the context of a non-commutative charged Schwarzschild black hole surrounded by perfect fluid dark matter. In this context, we study the geometric mass and thermal temperature to discuss the viability of the charged black hole solution by evaluating the specific heat, the phase transition and stability of the configuration. We also study the energy emission process of the black hole. From the thermodynamical properties, we conclude that our studied black hole solution is thermally stable. Moreover, we discuss gravitational lensing in the weak plasma field by considering uniform as well as non-uniform plasma and evaluate the deflection angle where we observe that the deflection angle in the case of uniform plasma is greater than that in non-uniform plasma. We also have studied the image magnification from the source’s brightness and observed that in uniform plasma case, the source image is more magnified than the non-uniform plasma.

A Low-jitter Charge-pumped PLL for LiDAR Detectors

A low-jitter charge-pumped phase-locked loop (CPPLL) with four-stage differential delay units is implemented in 180 nm standard CMOS technology. Not only a current-steering technique is adopted to eliminate charge injection and clock feed-through effects, but also a frequency divider with a retiming structure is used to ensure the high accuracy of the system feedback loop. The voltage-controlled oscillator adopts a gated-ring structure to achieve a stable and controllable clock. The prototype of the CPPLL occupies 0.184 , and results reveal that when the reference clock is 50 MHz, the output frequency is locked at 800 MHz accurately. The phase noise is as low as -140 dBc/Hz @1 MHz, with a peak-to-peak jitter of 4.36 ps. Meanwhile, an ultra-low root-mean-square (RMS) jitter of 0.161 ps is obtained. At the output spectrum of 800 MHz, the reference spur is merely -72 dBc. These results highlight the CPPLL's outstanding performance in phase noise, jitter, and stability, making it well-suited for high-precision integrated LiDAR.

Electronic interactions between SnO2 crystals and porous N-doped carbon nanoflowers accelerate electrochemical reduction of CO2 to formate

The electrochemical carbon dioxide reduction reaction (CO2RR) to formic acid or formate is a highly effective approach for achieving carbon neutrality. However, multiple proton-coupling-electronic processes and the instability of the catalysts caused by surface poisoning greatly limit the overall efficiency of CO2RR to formate. Here, a facile method was developed to anchor ∼2.60 nm SnO2 crystals onto porous N-doped carbon nanoflowers (SnO2@N-GPC) for high-efficiency formate production. The maximum Faraday efficiency (FE) of the SnO2@N-GPC reached 96.3 % at −1.2 V vs reversible hydrogen electrode (RHE) and was more than 80.0 % in the potential region from −1.0 to −1.5 V vs RHE with ten hours of operating stability. The experimental results and density functional theory (DFT) calculations demonstrated that the electronic interactions between SnO2 and N-GPC precipitated by electron transfer from SnO2 to N-GPC at the interface improved the phase stability of the SnO2@N-GPC, which improved its stability for the CO2RR. Furthermore, the electronic interactions enhanced the adsorption of CO2 on the catalyst, accelerating the rate of the formation of key intermediates, and reducing the energy barrier of the rate-limiting step for generating formate. This study provides an efficient strategy for developing highly active and stable non-precious metal catalysts for the conversion of CO2 to high-value chemicals.

The influence of the elemental valence on the thermophysical properties of high entropy (La0.2Sm0.2Eu0.2Yb0.2Y0.2)2(Ce0.5Zr0.5)2O7 coatings for thermal barrier application

Commercial yttria-stabilized zirconia (YSZ) thermal barrier coatings (TBCs) are no longer sufficient for the stringent demands in the high operating temperature and excellent thermophysical properties of the high-performance gas turbines and aviation engines. High entropy ceramics, distinguished by their superior thermophysical properties, have risen as a potential substitute for TBCs. However, the realm of atmospheric plasma spraying (APS) in the creation of these advanced TBCs remains relatively unexplored. In this work, three distinct high-entropy (La0.2Sm0.2Eu0.2Yb0.2Y0.2)2(Ce0.5Zr0.5)2O7 coatings were developed through the meticulous alteration of spraying power. The effects of spraying power on the microstructure, valence states of constituent elements and thermophysical properties of the coatings were deeply investigated. The results indicated that all the as-sprayed coatings exhibit a defect fluorite structure. Spraying power does have a significant impact on the thermophysical properties of the coatings. With the decrease in spraying power, the thermal conductivity of the coatings shows a progressive reduction, whereas the coefficient of thermal expansion (CTE) exhibits a gradual increase. This trend is closely related to valence states of constituent elements in the coatings. The resulting coating exhibits a low thermal conductivity of 0.54 W⋅m-1⋅K-1, a high CTE of 11.22×10-6·K-1 and a superior phase stability at elevated temperatures.

Surface double defects-dominated TiO2 with high liquid phase stability for smart SERS sensing of dye additives in foods

Surface defect engineering is an effective strategy to regulate the physical and chemical properties of semiconductors for a wide range of applications. Herein, a surface-highly-reduced anatase TiO2 (R-TiO2) with double defects (surface oxygen vacancy defect and Ti3+ energy level defect) was developed as a plasmon-free surface-enhanced Raman scattering (SERS) substrate for ultrasensitive detection of food additives. Abundant surface oxygen vacancies enable R-TiO2 to exist stably in liquid phase, which realizes a smart SERS detection for dye target molecules due to evading fluorescent interference from analytes, while SERS enhancement of analytes cannot be observed on the solid phase substrate at all. Due to the joint contribution of surface double defects, a multi-channel charge transfer mode and a stronger Herzberg-Teller coupling between substrate and analyte are formed, which greatly enhance SERS effect of the substrate for sensitive detection of dye additives in foods with an enhancement factor of 1.6 × 106.

The structural, elastic, optoelectronic properties and hydrogen storage capability of lead-free hydrides XZrH3 (X: Mg/Ca/Sr/Ba) for hydrogen storage application: A DFT study

Perovskite hydrides are promising materials for hydrogen capacity application to achieve the US DOE on-board criteria. We have investigated novel perovskite hydrides XZrH3 (X: Mg/Ca/Sr/Ba) for H2 storage and transportation applications. In this study we investigates the physical properties of XZrH3 light materials for solid-state hydrogen storage application by incorporating the DFT framework with the CASTEP code. We have theoretically examined the structural, mechanical, electronic, optical, and hydrogen storage properties of these materials. The selected compounds were fully relaxed and optimized in the cubic phase space group Pm-3 m. Structural phase stability was confirmed through thermodynamic, and mechanical analyses. Mechanical properties, evaluated based on Poisson’s ratio, the Puagh’s ratio, and Cauchy pressure, indicate the ductile behavior with a preference for ionic bonding. The electronic structure analysis reveals the metallic behavior of these materials. Optical calculations were also performed to provide additional insights into the physical properties of H2 compounds. The gravimetric hydrogen storage capacities were calculated as 2.55, 2.25, 1.66, and 1.31 wt% for MgZrH3, CaZrH3, SrZrH3, And BaZrH3 hydrides respectively. The identified properties of XZrH3 suggest that these materials could significantly enhance hydrogen storage systems, with potential integration into existing energy technologies, offering a pathway toward more efficient and sustainable hydrogen-based solutions.

Enhanced photocatalytic and supercapacitor performance of CeO2 nano foam integrated MWCNT and rGO nanocomposites

In this study, Cerium oxide nanoparticles (CeO2 NPs) with foam like morphology were prepared using the Moringa Oleifera seed extract-assisted green synthesis method. The prepared CeO2 NPs were integrated respectively with reduced graphene oxide (CeO2/rGO) and multi-walled carbon nanotubes (CeO2/MWCNT) via a simple one-pot reflex method. The structural and morphological features and elemental characteristics, including the physico-chemical and thermal characteristics of the samples, were assessed. The photocatalytic degradation ability of the catalyst was tested against Alizarin Red (AR) and Safranin (SF) dyes. Under sunlight, degradation efficiencies of 92.62%, 95.46%, and 99.62% were achieved against Safranin dye by CeO2, CeO2/MWCNT, and CeO2/rGO, respectively. The XRD analysis shows the structural phase stability of the nanocatalyst even after five cycles. The supercapacitor characteristics of all anode electrode samples were assessed. Moreover, the specific capacitance values of 370, 413, and 554 Fg-1 were measured using cyclic voltammetry at a scan rate of 5 mV/s for CeO2, CeO2/MWCNT, and CeO2/rGO, respectively. After undergoing 3000 charge-discharge cycles, the hybrid CeO2/rGO nanocomposite revealed admirable cycling stability with an 8.6% decrease in its specific capacitance. According to the results, the green-mediated CeO2/rGO heterojunction nano semiconducting materials are promising candidates for twin applications in photocatalysis and supercapacitors.

Sb-anchoring single-crystal engineering enables ultra-high-Ni layered oxides with high-voltage tolerance and long-cycle stability

Ni-rich layered oxides are promising cathodes for Li-ion batteries, but the inherent structural defects result in severe surface/bulk degradation during long cycling, especially at high cutoff voltage. Herein we propose a Sb-anchoring single-crystalline engineering to enhance the microstructural and electrochemical stability of ultra-high-Ni layered oxides, where the surface-enriched Sb doping inhibits Li-Ni mixing, suppressing the undesired layered to mixed/rock-salt phase transformation; the bulk-doped Sb rivets into Ni sites, reinforcing the bulk phase stability; the single-crystal endows enhanced crack resistance and reduced surface area, preventing surface parasitic reactions and the subsequent proliferation of cathode electrolyte interfaces. In-situ XRD reveals an essential correlation between cycle stability and phase reversibility, whereas Sb doping into both surface and bulk structures showcases a continuous anchoring effect, largely enhancing the phase transformation reversibility. DFT calculations prove a high oxidation tolerance, as Ni2+ diffusion barrier is higher than the pure cathode. A representative Li(Ni0.9Co0.05Mn0.05)0.99Sb0.01O2 cathode exhibits a high-voltage up to 4.6V, and a Li(Ni0.9Co0.05Mn0.05)0.99Sb0.01O2//graphite full-cell demonstrates an ultra-high capacity retention of 93.4% after 1000 cycles at 1C in 3.0−4.2V. This simple and efficient cathode engineering will promote the promising application of Ni-rich layered oxides in high-energy Li-ion batteries.

CALPHAD modeling of [formula omitted]- carbide dual ordering in Fe-Al-C ternary alloys

A novel four-sublattice model for the κ phase, denoted as (Fe, Al)3(Fe, Al)1(C, Va)1(C, Va)3 was proposed to improve the thermodynamic prediction, such as equilibrium composition, phase stability of κ-carbide in Fe-Al-C system. The sublattice model explains the transformation from the disordered FCC solid solution to the ordered κ-carbide via concurrent ordering of substitutional and interstitial atoms. The dual ordering model can restrict the irregular contribution of configurational entropy arising at 20 at% C composition, which is an issue with the existing thermodynamic databases. For the CALPHAD assessment, κ-carbide was considered as a single, individual phase that is in equilibrium with the liquid, austenite (γ), ferrite (α) or other intermetallic and carbide phases in the Fe-Al-C system. The formation energy calculated from density functional theory (DFT) showed that Fe3Al–L12 phase is energetically more favorable than the Fe3AlC–E21 phase, and C atoms in sublattice IV are not energetically favorable at all. The assessed parameters provided better accuracy than the existing database in the calculations of isothermal sections, liquidus projection, invariant reactions, and low-temperature phase compositions. The model is highly suitable for the low temperature (<800 °C) phase predictions. Thus, the improved Fe-Al-C model lays the foundation for the thermodynamic and kinetic studies of κ-carbide for designing new Fe-Mn-Al-C alloys and optimizing the heat treatment processes.

First-principles study of the electronic, vibrational, thermodynamic properties and phase stability of orthorhombic KClO4 under pressure

The purpose of this study is to deeply understand the basic physical properties of potassium perchlorate (KClO4) as a typical ionic energetic material under pressure. KClO4 Received attention for its widespread use in explosives, fireworks, safety matches and rocket propellants. In this paper, we systematically study the basic physical properties of KClO4 under 0-20 GPa pressure, including electrons, mechanical, vibrations, and thermodynamic parameters, based on density functional theory (DFT). The accuracy of the calculations was verified by optimizing the lattice parameters of the crystal structure and comparing them with previous experimental values. Electronic structure analysis revealed that KClO4 is a broadband gap nonconductor. Electronic density of states (DOS) analysis revealed strong covalent bonding between Cl-O bonds. Based on the phonon information, this study calculates the thermodynamic properties of KClO4 and analyzes a function of the relevant thermodynamic quantities under pressure. Combined with the structural phase transition phenomena observed in high pressure experiments, we analyze the dynamic and mechanical instability. These analyses help to understand the behavior of KClO4 under high pressure conditions and are crucial for its application in energetic materials.

Thermo-Physical Properties of Hexavalent Tungsten W6+-Doped Ta-Based Ceramics for Thermal/Environmental Barrier Coating Materials

The CaTa0.8WO6 ceramic was fabricated by a solid-state reaction for thermal/environmental barrier coating (Thermal and Environmental Barrier Coating) applications, and the microstructures, mechanical and thermal properties were investigated. The result showed CaTa0.8WO6 has a lower thermal conductivity (1.05 W·m−1·K−1 at 900 °C) than 8 wt.% yttria-stabilized zirconia and the doped Ta-based ceramics with Mg2+, Yb3+, Zr4+ and Nb5+, indicating that hexavalent tungsten element W6+ doping effectively reduces thermal conductivity and improves thermal insulation performance of Ta-based ceramics. The thermal expansion rates curve without inflection points resulting from phase transition indicates that CaTa0.8WO6 has excellent high-temperature phase stability. Since the Young’s modulus and Pugh’s ratio of CaTa0.8WO6 ceramics were lower than those of various valence states doping Ta-based ceramics, which means that CaTa0.8WO6 has better damage tolerance.

Toward predictable phase structures in high-entropy oxides: A strategy for screening multicomponent compositions

The recent surge in interest in high-entropy oxides (HEOs) as a novel class of ceramic materials can be attributed to the remarkable performance enhancements caused by both the complexity of their chemical composition and the simplicity of their structure. The extensive range of components presents challenges to the implementation of HEOs, rendering it difficult to predict the phase structure prior to the final synthesis. Herein, semi-empirical methods based on various parameters, including ΔX, VEC, ΔSmix, ΔHmix and δ, were utilized to determine the phase stability of rock salt, spinel, perovskite and fluorite structures. The combination of δ with ΔX, VEC, ΔSmix, and ΔHmix, in graphical form, is an effective indicator for determining the phase stability of rock salt, perovskite and fluorite structures. The spinel structure is stabilized outside the range of the other three structures. The phase formation rules were further verified with two newly designed and prepared HEOs via X-ray diffraction and high-resolution transmission electron microscopy. The HEOs show potential for functional applications, e.g., methyl orange degradation.

High strength‐ductility combination in low‐density dual phase high entropy alloys

High strength and good ductility combination make it appealing for advanced structural and functional applications. However, enhancing strength typically reduces ductility due to their inverse correlation. FCC, BCC, L12, and B2 phases are most commonly found in high-entropy alloys (HEAs), which are the subject of extensive research to tweak their mechanical properties. We present a systematic microstructure-oriented mechanical property investigation for a newly developed low-density dual-phase high entropy alloy (LDDP-HEA) with varying phase fractions. In this study, Al15Cu20Fe25Ni30Ti10 HEA was designed by phase formation rules and heat treated at 800, 900, and 1000 °C for 24 h, followed by water quenching to investigate phase stability and their effect on mechanical properties. A combination of FESEM, EBSD, EDS, XRD, microhardness, and compression tests were carried out to investigate the microstructural characteristics and mechanical properties of the HEAs. The LDDP-HEA exhibited an excellent combination of mechanical properties with a high yield strength of ∼1675 MPa, ultimate compressive strength of ∼2250 MPa, and elongation to fracture of ∼10 % in the as-cast condition. The strength and low density of the alloy lead to superior specific compressive yield strength of 240 MPa g−1 cm3 and 121.70 MPa g−1 cm3 in as-cast and heat treated at 1000 °C conditions, respectively.

Vapor-liquid-liquid equilibria for the water + 1-butanol + CPME mixture

In this contribution we have carried out vapor-liquid-liquid equilibrium (VLLE) determinations for the Water + 1-Butanol + cyclopenthyl methyl ether (CPME) mixture, where no previous information is reported. Measurements were performed with a commercial Fisher VLE/VLLE 602 equilibrium cell at 101.3 kPa and the Wisniak's L/K test is used to ensure the thermodynamic consistency for the two pairs of V-La and V-Lo phases at VLLE. Additionally, we have predicted the three-phase line of this system by performing modified multiphase flash calculations coupled with a phase stability restriction, where the system was modelled with the SAFT-VR-Mie equation of state. The VLLE of the ternary mixture was excellently predicted by only fitting binary interaction parameters to the phase equilibrium of each constituent binary mixture. This system has two partially miscible binaries in Water + 1-Butanol and Water + CPME, which makes the ternary liquid-liquid system a type II equilibrium envelope. The two binaries are connected through a zeotropic three-phase line.

Unraveling the Phase Behavior and Stability of Surfactant-Free Microemulsions: From Molecular Interactions to Macroscopic Properties.

Surfactant-free microemulsions (SFMEs), formed in mixed ternary systems such as water/ethanol/oil, have garnered substantial interest due to their unique properties and broad applications in areas such as enzyme-catalyzed reactions and nanoparticle synthesis. In this work, we conducted an in-depth investigation of the spontaneous nucleation and stabilization mechanisms of SFMEs, employing experimental techniques, molecular dynamics (MD) simulations, and Flory-Huggins (F-H) theory. The formation of multiscale nanostructures (characteristic scales of ∼1 and ∼100 nm) and their interfacial charging characteristics in SFMEs have been revealed experimentally. MD simulations investigated the structure and stability on the microscopic scale, enhancing our understanding of molecular interactions within these microemulsions. Our theoretical analysis revealed that the stability of mesoscopic nanodroplets within SFMEs hinges on a delicate balance between mixing entropy and internal energy. Equilibrium between these energies results in stable nanodroplet solutions, showcasing a delicate balance that can be manipulated by adjusting the volume fractions of the components and their interaction parameters. This research not only advances the theoretical understanding of SFMEs but also highlights their potential in industrial applications, emphasizing the importance of integrating theoretical and experimental approaches to develop functional nanostructured materials.