Stability Of Various Phases Research Articles

Coupled Insights into Structural, Electronic, and Optical Properties of GeTMS3(TM=Sc, Fe, Zn) Sulfide Perovskite across Different Phases: Ab Initio Study

The structural stability analysis of various phases of GeTMS3(TM=Sc, Fe, Zn) sulfide perovskite has been conducted utilizing the WIEN2k package. This investigation leverages density functional theory (DFT) within the full potential linearized augmented plane wave (FP-LAPW) method, employing GGA-mBJ potentials. The focus of this study has encompassed the computation of structural, magnetic, and optical attributes across distinct GeTMS3 phases. These materials have been identified as promising contenders for applications in photovoltaics and spintronics. The study reveals the stability of various phases, with the orthorhombic phase proving energetically favorable for GeScS3 and GeZnS3, and the tetragonal phase for GeFeS3. Magnetic analyses indicate favorable ferromagnetic behavior in GeFeS3 and nonmagnetic characteristics in GeScS3 and GeZnS3. Furthermore, electronic examinations unveil semimetallic and semiconducting behaviors in GeScS3 and GeZnS3 in the tetragonal, respectively, with GeFeS3 exhibiting a half-metallic nature in the orthorhombic phase. Optical properties illustrate their potential as light harvesters, displaying characteristics suitable for energy conversion applications. This study contributes to a deeper understanding of sulfide perovskite properties, offering insights into potential applications in diverse technological fields.

Evaluation of physical, mechanical and sliding wear properties of in-situ AB-TiC composite: a comparison with NAB alloy

The purpose of the present study is to evaluate the physical, mechanical and sliding wear properties/response of cast in-situ aluminium bronze (AB)-TiC [(Cu10Al3Fe)5TiC] composite and compare with cast nickel aluminium bronze (NAB) [Cu10Al5Ni5Fe] alloy. Sliding wear tests were conducted in dry and partially lubricant conditions using a pin-on-disc machine. A test material in the form of pin was evaluated against a rotating heat-treated EN-31 steel disc. Wear loss, frictional heating and friction coefficient properties were examined. The NAB alloy showed higher tensile strength (32.7%), compressive strength (7.68% at room temperature. and 4.18% at 500 °C), hardness (8.78%) and density (3.17%), whereas thermal conductivity of the AB-TiC composite was found 4.89% higher than NAB alloy. In dry sliding condition, composite outperformed NAB alloy in terms of wear resistance up to a critical applied load and/or sliding speed. Beyond this point, the wear behavior altered. Increasing sliding speed caused to reduce wear transition load. While friction coefficient showed mixed trend. Under lubricated wear test conditions, AB-TiC composite displayed considerably higher wear resistance (50.08%, 44.41% & 51.55%) and friction coefficient (26.37%, 40.75% & 14.96%) than the NAB alloy when tested in only oil, oil with 100 μm graphite and oil with 7–10 μm graphite respectively. Arrival of seizure in general caused significantly higher wear loss and temperature rise. In addition, it caused large adhesion of the specimen material to the disc surface. The reported wear behaviour of the samples has been validated using the features of wear surfaces and subsurface regions. The latter also permitted to comprehend the working wear processes. The analysis significantly shows good impacts of the oil lubrication (with and without solid particles) in terms of decreasing wear rate, frictional heating, and friction coefficient. Formation of steady lubricating film/layer was reported to be responsible for the better wear performance of the samples. Furthermore, irrespective of material composition and microstructure there exists a precise set of test parameters (e.g. load and speed) leading to optimal wear performance wherein the beneficial impacts of load bearing capability, thermal stability of various phases predominates.

The role of the A monovalent cation in the AVF3 perovskite series. A quantum mechanical investigation.

The relative stability of various phases of five AVF3 compounds (A = Li, Na, K, Rb and Cs) is investigated starting from the cubic (C) Pm3̄m (221) prototype structure, with five atoms (one formula unit) in the primitive cell. To the authors' knowledge, only three of these compounds have been investigated experimentally (Na, K and Rb), and they are reported as being cubic. The picture emerging from the present simulation is quite different: CsVF3 and RbVF3 are dynamically stable in the cubic structure, KVF3 is tetragonal, with space group (SG) I4/mcm (no. 140) and 10 atoms in the unit cell; note, however, that an orthorhombic Pnma (62) phase (four formula units) exists, which is not a subgroup of I4/mcm (140), and is very close in energy to the tetragonal phase. Further symmetry lowering is observed in the Na and Li compounds that are orthorhombic. The energy gain and volume reduction with respect to the cubic aristotype increase along the series K, Na and Li, and is very large for the last two compounds. Both FM and AFM solutions have been explored, and they show a very similar path along the SG modifications. The present scheme for determining the lowest energy SG is general, and can be applied to any perovskite. The B3LYP full range hybrid functional and the Hartree-Fock (HF) Hamiltonian, an all-electron Gaussian type basis set and the CRYSTAL code have been used.

Phase Relations of Ni2In-Type and CaC2-Type Structures Relative to Fe2P-Type Structure of Titania at High Pressure: A Comparative Study

Density functional theory (DFT) based on first-principles calculations was used to study the high-pressure phase stability of various phases of titanium dioxide (TiO2) at extreme pressures. We explored the phase relations among the following phases: the experimentally identified nine-fold hexagonal Fe2P-type phase, the previously predicted ten-fold tetragonal CaC2-type phase of TiO2, and the recently proposed eleven-fold hexagonal Ni2In-type phase of the similar dioxides zirconia (ZrO2) and hafnia (HfO2). Our calculations, using the generalized gradient approximation (GGA), predicted the Fe2P → Ni2In transition to occur at 564 GPa and Fe2P → CaC2 at 664 GPa. These transitions were deeply investigated with reference to the volume reduction, coordination number decrease, and band gap narrowing to better determine the favorable post-Fe2P phase. Furthermore, it was found that both transitions are mostly driven by the volume reduction across transitions in comparison with the small contribution of the electronic energy gain. Additionally, our computed Birch–Murnaghan equation of state for the three phases reveals that CaC2 is the densest phase, while Ni2In is the most compressible phase.

Discovery of New Ti-Based Alloys Aimed at Avoiding/Minimizing Formation of α” and ω-Phase Using CALPHAD and Artificial Intelligence

In this work, we studied a Ti-Nb-Zr-Sn system for exploring novel composition and temperatures that will be helpful in maximizing the stability of β phase while minimizing the formation of α” and ω-phase. The Ti-Nb-Zr-Sn system is free of toxic elements. This system was studied under the framework of CALculation of PHAse Diagram (CALPHAD) approach for determining the stability of various phases. These data were analyzed through artificial intelligence (AI) algorithms. Deep learning artificial neural network (DLANN) models were developed for various phases as a function of alloy composition and temperature. Software was written in Python programming language and DLANN models were developed utilizing TensorFlow/Keras libraries. DLANN models were used to predict various phases for new compositions and temperatures and provided a more complete dataset. This dataset was further analyzed through the concept of self-organizing maps (SOM) for determining correlations between phase stability of various phases, chemical composition, and temperature. Through this study, we determined candidate alloy compositions and temperatures that will be helpful in avoiding/minimizing formation of α” and ω-phase in a Ti-Zr-Nb-Sn system. This approach can be utilized in other systems such as ω-free shape memory alloys. DLANN models can even be used on a common Android mobile phone.

The Effect of Configurational Entropy of Mixing on the Design and Development of Novel Materials

The configurational entropy of mixing (∆Smix) has a profound influence on the stability of various phases in different materials at intermediate and high temperatures. Recently, it has been observed that ∆Smix can be used as an important tool to design novel multicomponent materials with fascinating properties. ∆Smix affects ∆Gmix and tends to stabilize the FCC/ BCC/HCP multicomponent solid solutions over brittle phases including compounds. This opens up vistas to design novel solid solution-based materials with improved mechanical, functional properties. Accordingly, multicomponent and multiprinciple alloys were developed in 2004, and subsequently, novel ceramics and polymers have been designed. The present paper is intended to provide an insight into the role of ∆Smix to design novel metallic, ceramic as well as polymeric materials.

Phonons, phase transitions and thermal expansion in LiAlO2: an ab initio density functional study.

We have used the ab initio density functional theory technique to understand the phase transitions and structural changes in various high temperature/pressure phases of LiAlO2. The electronic band structure as well as phonon spectra is calculated for various phases as a function of pressure. The phonon entropy used for the calculations of Gibbs free energy is found to play an important role in the phase stability and phase transitions among various phases. A sudden increase in the polyhedral bond lengths (Li/Al-O) signifies the change from the tetrahedral to octahedral geometry at high-pressure phase transitions. The activation energy barrier for the high-pressure phase transitions is calculated. The phonon modes responsible for the phase transition (upon heating) from high pressure phases to ambient pressure phases are identified. Moreover, ab initio lattice dynamics calculations in the framework of quasi-harmonic approximations are used to study the anisotropic thermal expansion behavior of γ-LiAlO2.

First-principles reinvestigation of bulk WO3

Using first-principles calculations, we analyze the structural properties of tungsten trioxide WO3 . Our calculations rely on density functional theory and the use of the B1-WC hybrid functional, which provides very good agreement with experimental data. The hypothetical high-symmetry cubic reference structure combines several ferroelectric and antiferrodistortive (antipolar cation motions, rotations and tilts of oxygen octahedra) structural instabilities. The instability related to antipolar W motions combines with those associated to oxygen rotations and tilts to produce the biggest energy reduction, yielding a P21/c ground state. This non-polar P21/c phase is only different from the experimentally reported Pc ground state by the absence of a very tiny additional ferroelectric distortion. The calculations performed on a stoichiometric compound so suggest that the low temperature phase of WO3 is not intrinsically ferroelectric and that the reported ferroelectric character might arise from extrinsic defects such as oxygen vacancies. Independently, we also identify never observed R3m and R3c ferroelectric phases with large polarizations and low energies close to the P 21/c ground state, which makes WO3 a potential antiferroelectric material. The relative stability of various phases is discussed in terms of the couplings between different structural distortions, highlighting a very complex interplay involving improper-like couplings up to fourth order in the energy expansion in the cubic phase.

Enhancements in Fraction Measurements and Flow Modeling for Multiphase Flowmeters

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 170853, “Enhancements in Fraction Measurements and Flow Modeling for Multiphase Flowmeters,” by A. Lupeau, OneSubsea, and G. Jolivet, D. Chazal, M. Fiore, C. Toussaint, B. Fournier, and F. Hollaender, Schlumberger, prepared for the 2014 SPE Annual Technical Conference and Exhibition, Amsterdam, 27–29 October. The paper has not been peer reviewed. With more than a decade of experience acquired using Venturi/gamma ray multiphase flowmeters (MPFMs), further gains in measurement quality and operational robustness have been achieved. This paper will illustrate how enhancements in fraction measurements using multienergy gamma ray attenuation and a more comprehensive analysis of the gamma ray spectrum have been developed and implemented to provide greater measurement accuracy and stability, leading to enhanced performances in multiphase-flow measurements. Introduction Increasing industry interest in MPFMs has led to numerous developments in the search for the technology (or, more generally, combination of technologies) most capable of providing multiphase-flow measurements in a wide range of conditions with high levels of accuracy and moderate sensitivity to input parameters and their variations. Several manufacturers have revised their operating principles over the past few years. These revisions include replacing either one or several core-measurement blocks; providing optional added measurements to improve accuracy; or completely changing operating principles, either to replace existing meters or to target specific markets. Two core technologies have proved very reliable in the field of multiphase metering: Venturi meters for flow velocities and gamma ray measurements to determine flowing fractions. A key benefit of fraction measurements based on gamma ray attenuation is that it offers a straight path of measurement across the fluids independently of their distribution, whether oil-, water-, or gas-continuous, and therefore offers the ability to identify dispersed fluids entrapped in other phases. Such measurements also can be performed at a very high level of accuracy. Venturi meters, for their part, benefit from a simplicity of structure as well as a lack of reliance upon strong assumptions about the distribution and stability of various phases in flow. While those two technological blocks have been at the core of most multiphase meters, implementations vary somewhat. First, in a majority of cases, a single-energy gamma ray measurement is used, and only a single piece of information is obtained from that measurement, typically related to the split between gas and liquid phases linked to mixture density. Additional information is required to determine the fraction of all three phases; this generally requires performing measurements at multiple locations. In such situations, the multiplicity of measurements raises issues regarding how representative it is to correlate observations performed at multiple locations at the same time in inherently chaotic and unstable flows.

Predominance diagrams of uranium and plutonum species in both lithium chloride–potassium chloride eutectic and calcium chloride

Electro-reduction of spent nuclear fuel has the potential to significantly reduce the amount of high level waste from nuclear reactors. Typically, spent uranium and plutonium are recovered via the PUREX process leading to a weapons-grade recovery; however, electro-reduction would allow spent nuclear fuel to be recovered effectively whilst maintaining proliferation resistance. Here, we present predominance diagrams (also known as Littlewood diagrams) for both uranium and plutonium species in molten lithium chloride–potassium chloride eutectic (LKE) at 500 °C and in calcium chloride at 800 °C. All diagrams presented depict regions of stability of various phases at unit activity in equilibrium with their respective dissociated ions. The diagrams thermodynamically define the electrochemical system leading to predictions of reaction conditions necessary to electrochemically separate species. The diagrams have been constructed using a pure thermodynamic route; identifying stable species within the molten salt with an assumption of unit activity for each of the phases. These thermodynamically predicted diagrams have been compared to the limited available experimental data; demonstrating good correlation. The diagrams can also be used to predict regions of stability at activities less than unity and is also demonstrated.

Phase Transition of Random Ising Model: Comparison of Glass Like Phase and Random Ordered Phase

The glass like phase proposed by Katsura et al. and the random ordered phase by Oguchi et al. are treated in a unified way for the Ising system with bond randomness. The molecular field approximation is used and the stability of various phases is discussed by comparing the free energies. The distribution function or the probability for the effective field is considered. It is shown that the method of Katsura et al. corresponds to taking the distribution function as site-independent and the random ordered phase is obtained by taking the probability as site-dependent. Taking the probability for both the magnitude and the sign of the effective field as site-dependent, the transitions to the ferromagnetic, antiferromagnetic and glass like phase from the paramagnetic state are discussed. The transition temperature to the glass like phase is shown to never exceed the ferro- or antiferromagnetic transition temperature. Thus, the glass like phase is possible only in the restricted region of the phase diagram.

Thermodynamic stability of various phases of zinc tin oxides from ab initio calculations

Thermodynamic stabilities of various phases in ZnO–SnO2 systems were investigated based on the Gibbs energy obtained from density functional theory (DFT) calculations. The pressure–temperature (p–T) phase diagram was determined; the coexistence of ZnO and SnO2 was the most stable phase in the low temperature region at zero external pressure, while Zn2SnO4 with the inverse spinel structure and ZnSnO3 with the lithium niobate structure were stable at the high temperature and high pressure region. Various octahedral configurations of the inverse spinel structures of Zn2SnO4 were considered. The calculated results showed feasible agreement with experimental data on the phase stability and explained well the experimental observation of the mixed state of Zn2SnO4, ZnO and SnO2 at mid-range temperatures and pressures. Considering the atomic structures, bulk moduli and thermodynamic stabilities, the local density approximation calculations were found to describe experimental observations more accurately than the generalized gradient approximation calculations. The phase transitions in the ZnO–SnO2 system were found to be dominated by the changes in both the Zn–O bond length and the coordination number of Zn, rather than changes in the bond length of Sn–O and the coordination number of Sn.

Phase transformation B1 to B2 in TiC, TiN, ZrC and ZrN under pressure

Phase stability of various phases of MX (M = Ti, Zr; X = C, N) at equilibrium and under pressure is examined based on first-principles calculations of the electronic and phonon structures. The results reveal that all B1 (NaCl-type) MX structures undergo a phase transition to the B2-structures under high pressure in agreement with the previous total-energy calculations. The B1-MX structures are dynamically stable under very high pressure (210-570 GPa). The pressure-induced B2 (CsCl-type) MC phases are dynamically unstable even at high pressures, and TiN and ZrN are found to crystallize with the B2-structure only at pressures above 55 GPa. The first-order B1-to-B2 phase transition in these nitrides is not related to the softening of phonon modes, and the dynamical instability of B2-MX is associated with a high density of states at the Fermi level.

VO2: Orbital competition, magnetism, and phase stability

The relative phase stability of VO${}_{2}$ is one of the most fundamental issues concerning the metal-insulator transition in this material but has been so far largely unexplored theoretically. We investigate the relative stability of various phases of VO${}_{2}$ using different levels of energy functionals within density functional theory (DFT). It is found that straightforward applications of several popular energy functionals, including the Heyd-Scuseria-Ernzerhof (HSE) hybrid functional, result in a wrong prediction for the ground state of VO${}_{2}$. In particular, although the HSE and DFT+$U$ methods are able to produce a band gap in the M${}_{1}$ phase, they strongly favor the formation of local magnetic moments, a result that clearly disagrees with experiments. We also examine the effect of the occupation and the redistribution of the $d$ derived ${t}_{2g}$ (i.e., ${d}_{xz}$, ${d}_{yz}$, and ${d}_{{x}^{2}\ensuremath{-}{y}^{2}}$) orbitals of V atoms on the calculated relative phase stability of VO${}_{2}$. We find that a small change in $d$ occupation can result in a drastically different theoretical prediction. With the introduction of an orbital-dependent potential, a complete separation between the ${d}_{{x}^{2}\ensuremath{-}{y}^{2}}$ derived valence band and ${d}_{xz}$ and ${d}_{yz}$ derived conduction bands in the M${}_{1}$ phase is achieved, resulting in a slight redistribution of the $d$ occupation and a more faithful account of the polarization of the ${t}_{2g}$ orbitals. This slight rearrangement of the $d$ occupation also leads to a relative phase stability of VO${}_{2}$ (including structural and magnetic phases) that agrees well with experiment.

Small-Angle and Wide-Angle X-Ray Scattering Study of Slow Relaxation Following Phase Transitions of New Bolaamphiphiles Based on N-(12-Betainylamino-Dodecane)-octyl β-D-Glucofuranosiduronamide Chloride

ABSTRACT In the present study, we investigated the polymorphism and its time-dependence of a new series of bolaamphiphile molecules based on N-(12-Betainylamino-dodecane)-octyl β-D-Glucofuranosiduronamide Chloride. To obtain six members of this series, the length of the main bridging chain and the lateral chain were varied in order to modify the hydrophilic–lipophilic balance. Another chemical modification was to introduce a diacetylenic unit in the middle of the bridging chain to study the influence of the π–π stacking on the supramolecular organization of these molecules. Dry bolaamphiphiles self-organize in supramolecular structures such as lamellar crystalline structure, Lc; lamellar gel structure, Lβ′; lamellar fluid structure, Lα; and lamellar isotropic structure, L. Thermal hysteresis of these structures, following phase transitions, are investigated by small-angle and wide-angle X-ray scattering. Once the thermal cycle is accomplished, the system remains in the kinetically stabilized undercooled high-temperature phase at the temperature of 20°C. Subsequently, the time-dependence of the relaxation to the thermodynamically stable phase is followed, and very slow relaxation for a period on the order of hours or days is observed. The study of the polymorphism and the stability of various phases of this new series of bolaamphiphiles—which are issued from natural primary resources (sugar beet and wheat) and thus interesting for potential application in pharmaceutical, cosmetics, or food industry—was undertaken in this work.

First-principles study of phase stability of Ti2N under pressure

A first-principles study of phase stability of various phases of Ti${}_{2}$N under normal conditions and as a function of pressure was carried out. Among the \ensuremath{\epsilon} and \ensuremath{\delta}\ensuremath{'}phases of Ti${}_{2}$N that are observed experimentally, \ensuremath{\epsilon}-Ti${}_{2}$N is the most stable. The \ensuremath{\delta}\ensuremath{'} phase can only exist at high temperature due to the soft acoustic modes at the $X$ point. The origin of the tetragonal structure of both the \ensuremath{\epsilon} and \ensuremath{\delta}\ensuremath{'} phases is supposed to be caused by the tetragonal local lattice distortion around a nitrogen vacancy. Based on the results of the total-energy and phonon-spectrum calculations at zero temperature, the following sequence of phase transformation in Ti${}_{2}$N under pressure is predicted: \ensuremath{\epsilon}-Ti${}_{2}$N (space group P4/mnm), $P$ $=$ 77.5 GPa \ensuremath{\rightarrow} Au${}_{2}$Te type (space group C2/m), $P$ $=$ 86.7 GPa \ensuremath{\rightarrow} Al${}_{2}$Cu type (space group I4/mcm). The present study shows that, to correctly predict relative phase stability, the peculiarities of the phonon spectra of the materials under investigation have to be properly accounted for.

High Pressure Phase Transitions in Yttria, Y2O3

We have carried out neutron inelastic scattering measurement of the phonon density of states and lattice dynamic calculations for Y2O3 using ab-initio density functional perturbation theory and interatomic potential model. The calculations are found to be in good agreement with experimental data, indicating that the potential model can be used for the calculation of phase diagram of Y2O3. The model is then used for free energy calculation to understand the stability of various phases as a function of pressure and temperature.

Silica- and sulfate-bearing rock coatings in smelter areas: Part II. Forensic tools for atmospheric metal(loid)- and sulfur-isotope compositions

Black silica- and sulfate-bearing rock coatings in the Greater Sudbury area, Canada provide a record of atmospheric processes and emitted particulate matter associated with historical smelting operations in this area. Coating samples collected over the Greater Sudbury region are characterized with scanning electron microscopy, electron microprobe analysis, laser ablation inductively coupled mass-spectrometry, S-stable isotope measurements and micro X-ray fluorescence. On the micrometer scale, Cu, Pb, As, Se and S occur in close association within metal–sulfate rich layers composed of Fe- and Cu-sulfates. The concentrations of these and other elements do not represent their chemical proportions in the smelter plumes due to dissolution–precipitation processes, element substitutions and the stability of various phases involved in the coating formation. On the regional scale, the atomic ratios of Pb:Ni, As:Ni and Se:Ni decrease in the coatings with increasing distance from the smelting centers. This observation is consistent with higher wet deposition rates of small diameter Pb, As and Se-bearing primary sulfate aerosols (<2.5μm), compared to larger diameter (>2.5μm) Ni-bearing particulate matter. The mixing of primary (higher δ34S values) and secondary (lower δ34S values) sulfates explains the δ34S values of sulfates within the coatings close to smelting centers and the decrease in these values is attributed to the decrease in the ratio of primary to secondary sulfates with distance from the smelting centers. The information preserved in mineral surface-coatings together with an understanding of stoichiometry, geochemical processes and former environmental conditions provide a valuable record of atmospheric compositions, mixing, scavenging, deposition rates and oxidation processes, and the nature and source of anthropogenic releases to the atmosphere.

Spin-Triplet Pairing Induced by Hund's Rule Exchange in Orbitally Degenerate Systems: Hartree-Fock Approximation

We discuss the spin-triplet pairing mechanism induced by the Hund rule ferromagnetic exchange. We include explicitly the e ect of interband hybridization and treat the problem by starting from an extended Hubbard model for a doubly degenerate band, making the simplest Hartree Fock approximation for the part involving the pairing and the Hubbard interaction. The conditions of stability of various phases are determined as a function of both band lling and microscopic parameters. The phase diagram contains regions of stability of the spin-triplet superconducting phase coexisting with either saturated or non-saturated ferromagnetism. Phase diagrams for the cases of constant density of states and that of square lattice have been provided. The in uence of hybridization on the stability of considered phases, as well as the temperature dependences of magnetic moment and the superconducting gap are also discussed.

Phase transitions and thermodynamic properties of yttria, Y2O3: Inelastic neutron scattering shell model and first-principles calculations

Yttria (Y${}_{2}$O${}_{3}$) is a well-known ceramic material extensively used in industry. We report new neutron inelastic scattering measurement of the phonon density of states (PDOS) and lattice dynamic calculations using the ab-initio density functional theory and interatomic potential model, which are found to be in good agreement with each other. The model is then used in extensive free-energy calculation to understand the stability of various phases as a function of pressure and temperature. We find that one of the Y-O bonds shows a very large compression with increasing pressure, involving change of coordination around the Y atoms. This seems to provide the mechanism of the transition from the monoclinic phase to the hexagonal phase at the high pressure. We find that this transition is displacive in nature, and we also identify how the change of coordination affects the phonon spectra of the various phases.