Pressure-temperature Phase Diagram Research Articles

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

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

Temperature-Dependent Structural Evolution of Ruddlesden-Popper Bilayer Nickelate La3Ni2O7.

A recent article ( J. Am. Chem. Soc. 2024, 146, 7506-7514) details a pressure-temperature (P-T) phase diagram for the Ruddlesden-Popper bilayer nickelate La3Ni2O7 (LNO-2222) using synchrotron X-ray diffraction. This study identifies a phase transition from Amam (#63) to Fmmm (#69) within the temperature range of 104-120 K under initial pressure and attributes the I4/mmm (#139) space group to the structure responsible for the superconductivity of LNO-2222. Herein, we examine the temperature-dependent structural evolution of LNO-2222 single crystals at ambient pressure. Contrary to the symmetry increase and the established Amam-Fmmm phase boundary, we observe an enhancement in the Amam reflections as temperature decreases. This work not only delivers high-quality crystallographic data of LNO-2222 using laboratory X-rays across various temperatures but also enhances the understanding of the complex crystallographic behavior of this system, contributing insights to further experimental and theoretical explorations.

Methylammonium Lead Iodide across Physical Space: Phase Boundaries and Structural Collapse.

Hybrid perovskites exhibit complex structures and phase behavior under different thermodynamic conditions and chemical environments, the understanding of which continues to be pivotally important for tailoring their properties toward improved operational stability. To this end, we present for the first time a comprehensive neutron and synchrotron diffraction investigation over the pressure-temperature phase diagram of the paradigmatic hybrid organic-inorganic perovskite methylammonium lead iodide (MAPbI3). This ambitious experimental campaign down to cryogenic temperatures and tens of kilobars was supported by extensive ab initio molecular dynamics simulations validated by the experimental data, to track the structural evolution of MAPbI3 under external physical stimuli at the atomic and molecular levels. These combined efforts enable us to identify the mechanisms underpinning structural phase transitions, including those exhibiting negative thermal expansion across the boundary between the cation-ordered low-temperature phase and the dynamically disordered high-pressure cubic phase. Our results bring to the fore how pronounced octahedral distortions at high pressures ultimately drive the structural collapse and amorphization of this material.

The phase diagram and strengthening behavior of compositionally complex carbides under high pressure

AbstractThe application of compositionally complex carbides under extreme conditions has garnered significant attention. The phase diagram compositionally complex transition metal carbide (Ta0.2Nb0.2Hf0.2Zr0.2V0.2)C for synthesis under high‐pressure and high‐temperature has been systematically investigated for the first time, and a pressure‐induced decrease in the compositionally complex carbides phase formation temperature was observed. The asymptotic Vickers hardness and bulk modulus of (Ta0.2Nb0.2Hf0.2Zr0.2V0.2)C reached 24.0 GPa and 311.3 GPa. The bulk modulus demonstrates an approximate 30% improvement compared to the average values of individual carbides, indicating that it possesses relatively competitive mechanical properties within the compositionally complex carbides group. The Claperon equation has been utilized to predict the lattice contraction of compositionally complex carbides during phase formation, and the physical mechanism of the high‐pressure strengthening has been proposed accordingly. In summary, the research of pressure–temperature phase diagram and the high‐pressure strengthening mechanism lay a valuable theoretical basis for the structural design and performance optimization of novel compositionally complex carbides.

Phase Diagram, Glassy Dynamics and Crystallization Kinetics of the Biobased Polyester Poly(ethylene 2,5-furanoate) (PEF).

We report the pressure-temperature (P-T) phase diagram, the origin of the subglass dynamics, and the crystallization kinetics of the biobased polyester poly(ethylene 2,5-furanoate) (PEF), through dielectric spectroscopy (DS) measurements performed as a function of temperature and pressure. The phase diagram comprises four different "phases"; glass, quenched melt, crystalline, and normal melt. The cold crystallization temperature, T cc, increases linearly with pressure (according to the Clausius-Clapeyron equation) as dT cc/dP | P →0 ∼ 240 K·GPa-1 and is accompanied by a small change in specific volume (ΔV = 0.028 cm3/g). This contrasts with the stronger dependence of the glass temperature, T g , with a pressure coefficient, dT g /dP | P →0, of 383 K·GPa-1, typical of rigid polymers. With the application of pressure, we address the molecular origin of the subglass β-process through the apparent activation volume, a quantity accessible only by pressure experiments. Moreover, increasing pressure densifies the segmental process but blocks the β-process, with possible implications in the gas-barrier properties. The crystallization kinetics from the quenched melt to the cold-crystallized state was explored by thermodynamics (differential scanning calorimetry, DSC), dynamics (DS), and structure (via simultaneous X-ray scattering at small (SAXS) and wide (WAXS) angles) following different routes within the phase diagram. Interestingly, all probes followed the same sigmoidal kinetics (of the Avrami type) with comparable time scales. Inspection of the evolution of the dielectric strength for the different dynamic processes during isothermal crystallization (at T c = 402 K; P = 0.1 MPa) revealed the absence of the restricted amorphous fraction (RAF) at the early stages of crystallization. This observation is in line with the proposed mesomorphic phase-an intermediate phase formed during crystallization in the absence of chain folding, as suggested by G. Strobl. Subsequent growth of the RAF followed the same Avrami kinetics as identified by the thermodynamic and structural probes. Shallow quenches within the P-T phase diagram identified experimental routes for keeping PEF in the metastable quenched amorphous state for long times.

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

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

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

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

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

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

Coexistence of zigzag antiferromagnetic order and superconductivity in compressed NiPSe3

Coexistence of zigzag antiferromagnetic order and superconductivity in compressed NiPSe3

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.