Pressure-temperature Phase Diagram Research Articles

Effect of water on asphaltene-precipitation behavior of CO2-crude oil mixtures during CCUS processes

Water can extensively exist in reservoirs. Since the solubility of CO2 in water is not negligible under reservoir conditions, the aqueous phase should also be considered during the phase-behavior simulations of the CO2 flooding process. With the presence of an asphaltene phase and an aqueous phase, four phases (i.e., a vapor phase, a hydrocarbon phase, an asphaltene phase, and an aqueous phase) can coexist at a given thermodynamic equilibrium. In this study, a robust and efficient four-phase vapor–liquid-liquid-aqueous equilibrium calculation algorithm is applied to conduct four-phase vapor–liquid-asphaltene-aqueous equilibrium calculations by assuming asphaltene is a dense liquid phase. The algorithm is first validated by comparing the calculated asphaltene precipitation data with the presence of water against the experimental asphaltene precipitation data documented in the literature. The validation shows that the calculation results agree well with the experimental data, indicating that such algorithm can make reliable predictions of asphaltene precipitation with the presence of water. The validated algorithm is subsequently used to construct pressure–temperature (PT) and pressure-composition (Px) phase diagrams to study the effect of water on asphaltene precipitation under different pressure/temperature conditions and under the injection of CO2. We can conclude from the calculated results that although adding water to the reservoir fluid can cause obvious changes in the PT phase diagrams, it does not have a noticeable influence on the asphaltene precipitation onsets. However, it can be seen from the calculated Px phase diagrams that the presence of water during the CO2 flooding process can make asphaltene precipitated more easily. The maximum amount of asphaltene precipitation is decreased by the presence of water due to the fact that a considerable amount of CO2 is dissolved in the aqueous phase instead of the liquid hydrocarbon phase.

Collapse of metallicity and high-Tc superconductivity in the high-pressure phase of FeSe0.89S0.11

We investigate the high-pressure phase of the iron-based superconductor FeSe0.89S0.11 using transport and tunnel diode oscillator studies using diamond anvil cells. We construct detailed pressure-temperature phase diagrams that indicate that the superconducting critical temperature is strongly enhanced by more than a factor of four towards 40 K above 4 GPa. The resistivity data reveal signatures of a fan-like structure of non-Fermi liquid behaviour which could indicate the existence of a putative quantum critical point buried underneath the superconducting dome around 4.3 GPa. With further increasing the pressure, the zero-field electrical resistivity develops a non-metallic temperature dependence and the superconducting transition broadens significantly. Eventually, the system fails to reach a fully zero-resistance state, and the finite resistance at low temperatures becomes strongly current-dependent. Our results suggest that the high-pressure, high-Tc phase of iron chalcogenides is very fragile and sensitive to uniaxial effects of the pressure medium, cell design and sample thickness. This high-pressure region could be understood assuming a real-space phase separation caused by nearly concomitant electronic and structural instabilities.

A new order parameter model for the improper ferroelastic phase transitions in KMnF3 single crystal.

This paper proposes a new order parameter model which satisfactorily explains complicated symmetry changes, the temperature-pressure (T-P) phase diagram and elastic anomalies observed experimentally with the improper ferroelastic phase transitions in multiferroic KMnF3 single crystal. First, it is shown that the order parameter model is transformed according to the four-dimensional reducible representation of the wavevector star channel group. Second, based on the order parameter model and the singularity theory, the sixth-order structurally stable Landau potential model is constructed. Finally, the theoretical T-P phase diagram is plotted and the elastic anomalies possible for each of the phase transitions are discussed.

2.13 Ga Lawsonite/Barroisite-Bearing E-Morb Signature Metagabbro Associated with Spinel Metaperidotite from Itaguara (São Francisco Craton, Brazil): Oldest Blueschist-Facies Fragment of Oceanic Moho?

In close association with Paleoproterozoic retroeclogite and accretionary prism-related mica-quartz schist, a 2.13 Ga (metamorphic titanite U-Pb age) lawsonite/barroisite-bearing E-MORB signature metagabbro associated with spinel metaperidotite is found in the Itaguara Sequence from southern São Francisco craton, Brazil. Petrography and pressure-temperature equilibrium phase diagrams suggest that the metagabbro experienced blueschist-facies metamorphism, attaining peak metamorphic conditions at ~16 kbar and ~450 °C during subduction. The retrograde metamorphic path crossed epidote amphibolite-facies, in which the mineral assemblage found in metaperidotite (olivine, clinopyroxene, spinel, serpentine, chlorite, talc, and tremolite) was stable during a ca. 2.1 Ga continental collision-related exhumation that occurred between the Archean Campo Belo/Bonfim and Divinópolis complexes. This geological framework suggests that the metagabbro and adjacent spinel metaperidotite represent a subducted and exhumed blueschist-facies fragment of a Paleoproterozoic oceanic Mohorovičić (Moho) discontinuity, thus establishing the Itaguara metagabbro as the oldest-known occurrence of retrogressed blueschist and providing evidence for the activity of the modern-style plate tectonics more than 2 Gyr ago.

Pressure-induced evolution of structures and phase transition of technetium diboride

Using the particle swarm optimization algorithm, we conducted an extensive search for the high-pressure stable structure of technetium diboride (TcB2) within the pressure range of 0–400 GPa. At zero pressure, the P63/mmc (hP6-TcB2) structure is considered the ground state configuration. As the pressure increases, a structural transition from hP6-TcB2 to P6/mmm (hP3-TcB2) occurs at approximately 174.9 GPa. We discuss the bonding between the two distinct phases and analyze the contribution of different atomic bonds to maintaining their structural stability. Meanwhile, the temperature–pressure phase diagram of TcB2 was successfully determined for the first time through the quasi-harmonic approximation method. It is predicted that the transition pressure from hP6-TcB2 to hP3-TcB2 can be reduced to about 164 GPa at a room temperature of 300 K. These results provide valuable insights into the behavior of TcB2 under different temperature and pressure conditions and open up new possibilities for exploring its potential applications in a variety of environments.

Expanding the horizons of the thermodynamic landscape and optoelectronic properties of soft 2D hybrid perovskites MHy2PbX4

Comprehensive investigations revealed a pressure–temperature phase diagram for 2D hybrid perovskite MHy2PbI4, demonstrating its high structural elasticity and ability to generate polar phases mimicking its ferroelectric analogue MHy2PbBr4.

Thermoresponsive Polymers under Pressure with a Focus on Poly(N-isopropylacrylamide) (PNIPAM).

Pressure is a key variable in the phase behavior of responsive polymers, both for applications and from a fundamental point of view. In this feature article, we review recent developments, particularly applications of neutron techniques such as small-angle neutron scattering (SANS) and quasi-elastic neutron scattering (QENS), across the temperature-pressure phase diagram. These are complemented by kinetic SANS experiments following pressure jumps. In the prototype system poly(N-isopropylacrylamide) (PNIPAM), QENS revealed the pressure-dependent characteristics of hydration water around the lower critical solution temperature transition. The size, water content, and inner structure of the mesoglobules formed in the two-phase region depend strongly on pressure, as shown by SANS. Beside these changes at the phase transition, the mesoglobule formation at low pressure is determined by kinetic factors, namely the formation of a polymer-rich, rigid shell, which hampers further growth by coalescence. At high pressure, in contrast, the growth proceeds by diffusion-limited coalescence without any kinetic hindrance. The disintegration of the mesoglobules evolves either via chain release from their surface or via swelling, depending on the osmotic pressure of the water. Moreover, we report on the profound influence of pressure on the cononsolvency effect. In the temperature-pressure frame, the one-phase region is hugely expanded upon the addition of the cosolvent methanol. SANS experiments unveil the enthalpic and entropic contributions to the effective Flory-Huggins interaction parameter between the segments and the solvent mixture. QENS experiments demonstrate an increase in polymer associated water with pressure, whereas methanol is released. Correspondingly, the solvent phase becomes enriched in methanol, providing a mechanism for the breakdown of cononsolvency at a high pressure. Finally, we outline future opportunities for high-pressure studies of thermoresponsive polymers, with a focus on neutron methods.

Pressure-induced linear enhancement of the superconducting transition in Nd0.8Sr0.2NiO2 thin films

We report the pressure (P) effect on the superconducting transition temperature T c and the upper critical field μ 0 H c2 of infinite-layer Nd0.8Sr0.2NiO2 thin films by measuring the electrical transport properties under various hydrostatic pressures to 4.6 GPa. At ambient pressure, it shows the clear superconducting transition with T c ∼ 10 K. Based on the evolution of resistance R(T), we found that the T c is monotonically enhanced to ∼14 K upon increasing pressure to 2.9 GPa. The constructed temperature–pressure phase diagram indicates that the calculated slope dT c/dP is about 1.14 K GPa−1 and the superconducting T c shows no signatures of saturation with pressure. It thus gives the possibility to further enhance T c by employing higher pressures or heterostructure engineering. In addition, the normalized slope of upper critical field μ 0 H c2(0) implies that the electron correlations are gradually decreasing with pressure, which exhibits an opposite evolution with superconducting T c. Our work further confirms the positive pressure effects in nickelate superconductors and gives more insight to further enhance its superconducting transition temperature.

Competitive nucleation and growth control of a- and c-axis YBCO films by metal organic deposition

This paper utilizes the TFA-MOD (Trifluoroacetate Metal-Organic Decomposition) method to prepare YB2C3O7-δ (YBCO) superconducting films on a LaMnO3 metal substrate. Using a self-made process curve, we investigate the nucleation and growth orientation of crystals at various temperatures under specific oxygen partial pressures (PO2). We successfully obtain an oxygen partial pressure-temperature phase diagram at a fixed time. This diagram provides critical insight into the trends that guide our regulation of parameters to ultimately achieve a relatively pure a-axis oriented YBCO film. Temperature and nucleation rate are important parameters that influence crystal nucleation orientation. The key conditions for producing a-axis-oriented YBCO films include low temperature, high Δμ, and extended crystallization time.

High-temperature and high-pressure thermal property measurements of SiO2 crystals.

The investigation of materials' behavior under high-temperature and high-pressure conditions, such as the correlation with structural characteristics and thermal properties, holds significant importance. However, the challenges associated with the experimental implementation have, to a certain extent, constrained such research endeavors. We utilized the ultrafast laser based non-contact thermal measurement method combined with an externally heated moissanite-anvil-cell to characterize the thermal conductivity of [10-10] oriented SiO2 crystals under high temperature (300-830K) and high pressure (0-15GPa) conditions. We investigated the impact of extreme conditions on the microstructure from both Raman spectroscopy and thermal perspectives. The presence of kinetic hindrances associated with the transformation of α-quartz to coesite and stishovite was identified and confirmed. It expands the comprehension and application of the SiO2 pressure-temperature phase diagram in this range and provides insights into the intricate relationship between extreme environments and material structure formation through the analysis of thermal characteristics.

First-principles lattice dynamics and thermodynamic properties of α-, θ-, κ- and γ-Al2O3 and solid state temperature-pressure phase diagram

γ-Al2O3 is a commonly observed high temperature alumina phase during Al-based alloy oxidation. Due to the partially ordered, defective nature of the spinel structure arising from the partial occupancy in the Al sites, first-principles prediction of the thermodynamic properties of γ-Al2O3 has been challenging. In this work, employing the first-principles quasiharmonic approach, we obtain the finite temperature thermodynamic properties of γ-Al2O3, including entropy, chemical potential, heat capacity, thermal expansion coefficient, and elastic constants and the results are compared with those calculated for the other three alumina phases, i.e., α-Al2O3, θ-Al2O3, and κ-Al2O3. The calculated lattice constants and the predicted relative phase stability under 0 K and 0 GPa, α>κ>θ>γ, are consistent with experimental values and existing calculations, respectively. Based on the results, we constructed the temperature-pressure phase diagram covering the four Al2O3 phases (α, κ, θ, γ), which could provide for experimentally synthesizing the different alumina phases.

High pressure–temperature phase diagram of ammonia hemihydrate

High pressure–temperature phase diagram of ammonia hemihydrate

Interplay of Kinetic Limitations and Disintegration: Selective Growth of Hexagonal Boron Nitride and Borophene Monolayers on Metal Substrates.

The CVD growth of bielemental 2D-materials by using molecular precursors involves complex formation kinetics taking place at the surface and sometimes also subsurface regions of the substrate. Competing microscopic processes fundamentally limit the parameter space for optimal growth of the desired material. Kinetic limitations for diffusion and nucleation cause a high density of small domains and grain boundaries. These are usually overcome by increasing the growth temperature and decreasing the growth rate. In contrast, the nature of molecular precursors with limited thermal stability can result in dissociation and preferential desorption, leading to an undesired or ill-defined composition of the 2D-material. Here we demonstrate these constraints in a combined low-energy electron diffraction and low-energy electron microscopy study by examining the selective formation of single-layer hexagonal boron nitride (hBN) and borophene on Ir(111) using a borazine precursor. We derive a temperature-pressure phase diagram and apply classical nucleation theory to describe our results. By considering the competing processes, we find an optimum growth temperature for hBN of 950 °C. At lower temperatures, the hBN island density is increased, while at higher temperatures the precursor disintegrates and borophene is formed. Our results introduce an additional aspect that must be considered in any high-temperature growth of bielemental 2D-materials from single molecular precursors.

Coupled magnetic and structural transition in topological antiferromagnet EuAgAs under high pressure

Recently, EuAgAs and its derivatives have emerged as a promising platform for studying the interplay of transports, magnetism and topology. Herein, we report construction of a temperature-pressure phase diagram for antiferromagnetic Dirac semimetal EuAgAs, through electrical transport, synchrotron x-ray diffraction and Raman spectroscopy measurements in diamond anvil cells at high pressures up to 48.6 GPa. At Pc1∼3–5 GPa, we found a pressure-induced magnetic phase transition with accompanying a structural P63/mmc→Pnma transition. In the pristine antiferromagnetic phase, negative colossal magnetoresistance is observed mainly below the Néel temperature TN along with a field-induced metamagnetic transition; in the emergent magnetic phase, however, it is evident both above and below the magnetic critical temperature TC yet with no field-induced metamagnetic transition. These distinct features lead us to argue a ferromagnetic-like state for EuAgAs above Pc1, which is further supported by observation of a T5/3 temperature dependence of low-temperature resistance, a characteristic of marginal Fermi-liquid state expected to exist close to a ferromagnetic instability by spin fluctuations in metallic ferromagnets. At Pc2∼20 GPa, a possible phase transition of electronic origin may take place, which is revealed jointly by change of a T5/3→T5/2 temperature dependence of low-temperature resistance and change in slope of linear-in-T resistance at high temperatures.

Coexistence of zigzag antiferromagnetic order and superconductivity in compressed NiPSe3

NiPSe3 is regarded as a bandwidth-controlled Mott insulator, distinct from the widely studied Mott insulating magnetic graphene MPSe3 (M = Mn and Fe) family. By employing high-pressure synchrotron X-ray diffraction, we observe two structural transitions as a function of pressure. With the help of first-principles calculations, we discover the antiferromagnetic (AFM) moment directions of NiPSe3 switch from out-of-plane to in-plane and the honeycomb layers slide relative to each other at the first structural transition. The in-plane AFM order persists until the second structural transition, whereupon the two-dimensional (2D) structure assumes a more three-dimensional (3D) character. A bandwidth-controlled Mott insulator-metal transition (IMT) occurs between the two structural transitions at Pc ~ 8.0 GPa, concomitant with the emergence of superconductivity with Tc ~ 4.8 K. The superconductivity in NiPSe3 emerging in the 2D monoclinic phase coexists with the in-plane AFM order and continues into the 3D trigonal phase. Our electronic structure calculations reveal that the IMT and superconductivity in NiPSe3 are both related to the enhanced Se2− 4p and Ni2+3d electronic hybridizations under pressure. From these results, we construct a temperature-pressure electronic phase diagram of NiPSe3, revealing interesting relationships between magnetism and superconductivity.

Exploring the configuration space of elemental carbon with empirical and machine learned interatomic potentials

We demonstrate how the many-body potential energy landscape of carbon can be explored with the nested sampling algorithm, allowing for the calculation of its pressure-temperature phase diagram. We compare four interatomic potential models: Tersoff, EDIP, GAP-20 and its recently updated version, GAP-20U. Our evaluation is focused on their macroscopic properties, melting transitions, and identifying thermodynamically stable solid structures up to at least 100 GPa. The phase diagrams of the GAP models show good agreement with experimental results. However, we find that the models’ description of graphite includes thermodynamically stable phases with incorrect layer spacing. By adding a suitable selection of structures to the database and re-training the potential, we have derived an improved model — GAP-20U+gr — that suppresses erroneous local minima in the graphitic energy landscape. At extreme high pressure nested sampling identifies two novel stable structures in the GAP-20 model, however, the stability of these is not confirmed by electronic structure calculations, highlighting routes to further extend the applicability of the GAP models.

An unexpected high-pressure stability domain for a lower density polymorph of benzophenone

For over a century, it was thought that the crystalline polymorph II of benzophenone does not possess a stable domain in the pressure–temperature phase diagram. With a combination of new experimental results and literature data, this case of crystalline dimorphism has finally been solved and it is shown that form II possesses a stable domain at high pressure and high temperature, even though its density is lower than that of form I, the stable form under ordinary pressure and temperature conditions. The phase diagram of benzophenone is a clear demonstration of the fact that to understand the phase behaviour of a chemical substance both the exchange of heat (due to the change in intermolecular interactions) and work (due to the change of volume at a given pressure) need to be taken into account.

Temperature-pressure phase diagram of confined monolayer water/ice at first-principles accuracy with a machine-learning force field

Understanding the phase behaviour of nanoconfined water films is of fundamental importance in broad fields of science and engineering. However, the phase behaviour of the thinnest water film – monolayer water – is still incompletely known. Here, we developed a machine-learning force field (MLFF) at first-principles accuracy to determine the phase diagram of monolayer water/ice in nanoconfinement with hydrophobic walls. We observed the spontaneous formation of two previously unreported high-density ices, namely, zigzag quasi-bilayer ice (ZZ-qBI) and branched-zigzag quasi-bilayer ice (bZZ-qBI). Unlike conventional bilayer ices, few inter-layer hydrogen bonds were observed in both quasi-bilayer ices. Notably, the bZZ-qBI entails a unique hydrogen-bonding network that consists of two distinctive types of hydrogen bonds. Moreover, we identified, for the first time, the stable region for the lowest-density 4cdot {8}^{2} monolayer ice (LD-48MI) at negative pressures (<−0.3 GPa). Overall, the MLFF enables large-scale first-principle-level molecular dynamics (MD) simulations of the spontaneous transition from the liquid water to a plethora of monolayer ices, including hexagonal, pentagonal, square, zigzag (ZZMI), and hexatic monolayer ices. These findings will enrich our understanding of the phase behaviour of the nanoconfined water/ices and provide a guide for future experimental realization of the 2D ices.

A trust-region-based phase envelope construction algorithm

Pressure-temperature (PT) and pressure-composition (Px) phase diagrams play an important role in various chemical and petroleum engineering applications. Lots of algorithms based on the Newton-Raphson method have been proposed to numerically construct PT/Px phase envelopes. No attempt is made to improve the computational efficiency of such Newton-Raphson solution method. This work develops a new trust-region-based algorithm to replace the Newton-Raphson method to provide more robust and efficient phase envelope construction calculations. We first convert the phase envelope construction problem into a minimization problem by defining a least-squares objective function. We then apply the trust-region optimization method with an exact subproblem solver to minimize the objective function. We follow the general strategy proposed by Michelsen (1980) to develop the revised phase envelope construction algorithm. We demonstrate the good performance of the trust-region-based algorithm by comparing it with the conventional Newton's method. The computational results indicate that the new trust-region-based algorithm is more robust and cost-effective than the Newton-based algorithm.

Pressure effect of the charge density wave transition on Raman spectra and transport properties of 2H−NbSe2

Charge density wave (CDW) order is widely existing and fundamentally important in solid-state physics. However, several critical issues regarding the vibrational and electronic subsystems and their coupling still need to be better understood. Here, we tune the electrical transport and collective vibrational excitation, i.e., phonon and amplitude mode, by pressure in a prototype charge density wave material, $2H\text{\ensuremath{-}}{\mathrm{NbSe}}_{2}$. A complete pressure-temperature phase diagram is revisited. The anomaly in Hall and magnetoresistivity at CDW critical temperature, ${T}_{\mathrm{CDW}}$, was suppressed by the pressure. In the Raman spectroscopy measurements, the appearance of CDW amplitude mode is accompanied by the freezing of the two-phonon mode. The frequency of CDW amplitude mode under pressure follows modified mean-field theory with power-law scaling $(\ensuremath{\beta}=0.18)$. The renormalization of the Raman phonon across the CDW transition and the mean-field temperature dependence of CDW amplitude mode emphasized the importance of electron-phonon coupling in the formation of CDW state in $2H\text{\ensuremath{-}}{\mathrm{NbSe}}_{2}$. Our work clarifies the complex vibrational and electronic subsystems and sheds light on the mechanism of the charge density state in $2H\text{\ensuremath{-}}{\mathrm{NbSe}}_{2}$.