Phase Transition Pressure Research Articles

Tuning the onset pressure of pressure-induced phase transition in indium phosphide by extrinsic doping

In-situ angle-dispersive X-ray diffraction (ADXRD) and Raman scattering were carried out to delineate the phase transitions under pressure in p-type zinc-doped indium phosphide (InP:Zn) at ambient temperature. The ADXRD measurements with pressure up to 17.3(2) GPa reveal that InP:Zn transforms from zinc-blende (ZB) to rock-salt (RS) structure in a pressure range of 8.1(2) - 8.6(1) GPa. The Raman scattering measurements indicate that the phase transition proceeds continuously over a wide range of pressure and reaches completion at the highest pressure applied (14.5(2) GPa) with significant metallization, as suggested by the disappearance of the transverse optical (TO) and longitudinal optical (LO) modes. In contrast, originally absent at ambient pressure, additional Raman shift of Zn local vibrational modes (LVMs), appeared at 276 cm-1 and 420.7(1) cm-1 within the pressure range of 2.2(1) up to 10.1(2) GPa, which can be attributed to Zn3P2 and VPZnInVP LO modes, respectively. The zero-pressure isothermal bulk moduli and its first order pressure derivatives for the zinc-blende InP:Zn are 79.44(2) GPa and 3.92(1), respectively. A total enthalpy change of about 45.45 KJ•mole-1 was derived for the ZB to RS structure transformation occurring at the pressure of 8.6(1) GPa. The present results suggest that diffusion of Zn in InP:Zn may have been governed by the modified substitution and interstitial (S–I) mechanism. Moreover, comparisons on the pressure-dependent behaviors in InP:Zn, InP:S, and InP:Fe extrinsically doped systems revealed that the exact type of the defects introduced into the lattice upon doping may have played crucial roles in the pressure-induced phase transitions.

Multi-phase equation of state of ultrapure hafnium to 120 GPa

Hafnium (Hf) is an industrially important material due to its large neutron absorption cross-section and its high corrosion resistance. When subjected to high pressure, Hf phase transforms from its hexagonal close packed α-Hf phase to the hexagonal ω-Hf phase. Upon further compression, ω-Hf phase transforms to the body centered cubic β-Hf phase. In this study, the high pressure phase transformations of Hf are studied by compressing and decompressing a well-characterized Hf sample in diamond anvil cells up to 120 GPa while collecting x-ray diffraction data. The phase transformations of Hf were compared in both a He pressure transmitting medium (PTM) and no PTM over several experiments. It was found that the α-Hf to ω-Hf phase transition occurs at a higher pressure during compression and lower pressure during decompression with a helium (He) PTM compared to using no PTM. There was little difference in the ω-Hf to β-Hf phase transition pressure between the He PTM and no PTM. The equation of state was fit for all three phases of Hf and under both PTM and no-PTM.

Effects of pseudopotentials and exchange-correlation functionals on phase transition of LaH10

To assess the effects of pseudopotentials and exchange-correlation functionals on trigonal to face-centered cubic phase transition of LaH10, we performed density functional theory based first-principles calculations by employing three-types of pseudopotentials with LDA (local density approximation) and GGA (generalized gradient approximation) exchange-correlation functionals. We found that the lattice parameters such as cell angle or cell volume and phase transition pressure exhibit a significant variation with LDA and GGA functionals whereas they exhibit a weak dependence on the pseudopotentials. In general, LDA calculations result in a lower phase transition pressure than GGA calculations. We also investigated the effects of pseudopotentials and exchange-correlation functionals on the electronic properties by calculating the total and partial density of state functions for face-centered cubic phase of LaH10 at 150 GPa. Computed electronic densities of states at the Fermi level are found to exhibit a weak dependence on the exchange-correlation functionals.

First-principles study of pressure-induced phase transitions, mechanical and thermodynamic properties of ThBC

First-principles calculations and particle swarm optimization algorithm are combined to predict the crystal structures in the pressure range from 0 to 100 GPa. Four phases of ThBC are determined, including the P4122, Cmcm, Cmce and Immm phases, in which the Cmcm, Cmce and Immm phases are newly predicted structures. The mechanical, electronic and thermodynamic properties of the four phases are investigated. According to the enthalpy–pressure and volume–pressure curves, the phase transition pressure from the P4122 phase to the Cmcm phase is 15 GPa, the Cmcm to the Cmce is 36 GPa and the Cmce to the Immm is 69 GPa. All the transitions belong to the first-order phase transition. Based on the calculated elastic constants, the P4122, Cmcm, Cmce and Immm phases exhibit brittle nature. The Young’s moduli show that the P4122 phase has the largest degree of anisotropy, and the Immm phase has the smallest. The calculated density of states reveal that the P4122, Cmcm, Cmce and Immm phases are all metallic.

Unified and ultimate high-pressure phase of several nanolaminate Mn+1AXn (n = 1, 2, 3, etc.) ceramics from first principles

We did extensive research for the nanolaminate Mn+1AXn (n = 1, 2, 3, etc.) ceramics on their structural stability, in which the “M”, “A” and “X” dependence of the phase transition pressure is concluded. Mo2GaC presents multi-phase co-existence status at high pressure. The hexagonal P63/mmc to tetragonal P4/mmm transition is the common direct route for the N-containing MAX due probably to the high transition pressure. P63/mmc (No.194, α, β) α → β → P4/mmm transition might be the common route for the C-containing MAX due probably to the low α → β transition pressure. Nb2InN/Nb2GaN and Mo2InN present c-axis abnormal elongation at low pressures.

Structural analysis of terbium monopnictides under high pressure

In this work, theoretically study of structural, elastic, and mechanical properties of Terbium monopnictides TbX (X = P, As) in NaCl– B1 and CsCl–B2 phases are investigated using IIPM model. This model consists of Columbic interaction, three body interaction, polarizability effect and overlapping repulsive interaction operative up to second nearest neighbor. TbP and TbAs compounds exhibit structural phase transition from B1 to B2 phase at 46.3 GPa and 16.1 GPa pressure, respectively. The calculated structural phase transition pressures, bulk modulus and second order elastic constants are presented. Elastic constants and their related parameters such as Poisson's ratio, Young modulus and Shear modulus were also calculated. We have also predicted the pressure variation of the elastic and bulk modulus for B1 structure. We have compared our results with the available experimental and theoretical data.

Compression-rate dependence of pressure-induced phase transitions in Bi

It is qualitatively well known that kinetics related to nucleation and growth can shift apparent phase boundaries from their equilibrium value. In this work, we have measured this effect in Bi using time-resolved X-ray diffraction with unprecedented 0.25 ms time resolution, accurately determining phase transition pressures at compression rates spanning five orders of magnitude (10–2–103 GPa/s) using the dynamic diamond anvil cell. An over-pressurization of the Bi-III/Bi-V phase boundary is observed at fast compression rates for different sample types and stress states, and the largest over-pressurization that is observed is ΔP = 2.5 GPa. The work presented here paves the way for future studies of transition kinetics at previously inaccessible compression rates.

Powder conductor for pressure calibration applied to large volume press under high pressure

Pressure is the core of high-pressure science and technology, and the accuracy of pressure calibration is of much importance for high-pressure experiments and production. Although the pressure limit of the large volume press (LVP) continues to increase, there are no well solutions for in situ pressure calibration. In this study, using in situ high-pressure electrical performance measurement technology, two ideal calibration standard materials in powder conductors, cadmium phosphide (Cd3P2) and zinc telluride (ZnTe) with stable physical and chemical properties and obvious resistance change, are applied to pressure calibration in the LVP. In situ high-pressure synchrotron radiation x-ray diffraction was used to verify the phase transition pressure point of Cd3P2. The introduction of powder conductors for pressure calibration commits to establish a pressure system, which is safer, more stable to operate, and more accurate in experimental measurements for the LVP.

Investigation of structural, electronic and elastic properties of matlockite-type SrFI under high pressure: An Ab-initio study

In this study, Matlockite (PbFCl) type SrFI compound with a two-dimensional layered structure has been studied using density functional theory (DFT) and generalized gradient approximation (GGA) under high hydrostatic pressure. Calculations were made using the Siesta Method. In ambient conditions, matlockite type structures crystallize in tetragonal structure with space group P4/nmm. In nature, these structures are known as alkaline earth fluoro-halides. When gradually increasing pressures were applied to this structure, the phase transition was observed to the orthorhombic structure with space group Pmmn. In addition to these studies, some physical properties of SrFI, such as lattice parameters, bulk modulus, the derivative of the bulk modulus, and volume values were also calculated. On the other hand, total energy and enthalpy calculations were made to obtain the phase transition pressure values that are in good agreement with the experimental results. According to these calculations, phase transition pressure was predicted at about 44.8 GPa. Besides, how electronic and elastic properties of SrFI compound change with applied pressure were also examined. In the electronic structure calculations, about 5.09 eV band gap value was obtained for P4/nmm phase at 0 GPa pressure. Under increasing pressure, the 0.16 eV band gap value was calculated for the Pmmn phase of SrFI. According to these results, the stable phases obtained of the SrFI compound have semiconductor characters since the both phases have a conceivable band gap. In addition, elastic constants were calculated and two structures of SrFI were found to be mechanically stable.

Discerning perturbed assembly of lipids in a model membrane in presence of violacein

Violacein is a naturally found pigment that is used by some gram negative bacteria to defend themselves from various gram positive bacteria. As a result, this molecule has caught attention for its potential biomedical applications and has already shown promising outcomes as an antiviral, an antibacterial, and an anti-tumor agent. Understanding the interaction of this molecule with a cellular membrane is an essential step to extend its use in the pharmaceutical paradigm. Here, the interaction of violacein with a lipid monolayer formed at the air–water interface is found to depend on electrostatic nature of lipids. In presence of violacein, the two dimensional (2D) pressure–area isotherms of lipids have exhibited changes in their phase transition pressure and in-plane elasticity. To gain insights into the out-of-plane structural organization of lipids in a membrane, X-ray reflectivity (XRR) study on a solid supported lipid monolayer on a hydrophilic substrate has been performed. It has revealed that the increase in membrane thickness is more pronounced in the zwitterionic and positively charged lipids compared to the negatively charged one. Further, the lipid molecules are observed to decrease their tilt angle made with the normal of lipid membrane along with an alteration in their in-plane ordering. This has been quantified by grazing incidence X-ray diffraction (GIXD) experiments on the multilayer membrane formed in an environment with controlled humidity. The structural reorganization of lipid molecules in presence of violacein can be utilized to provide a detailed mechanism of the interaction of this molecule with cellular membrane.

Effect of compositional variability due to thermal instability on critical phenomena in n-hexane + IL mixture

Isochoric heat capacity of binary n-hexane + IL (1-octyl-3-methylimidazolium chloride, abbreviated as [C8C1im]Cl) along the fixed isochore of 255.13 kg∙m−3 as a function of temperature near the critical point of pure solvent (n-hexane) have been measured. The measurements were performed for the selected concentration of 0.0089 mol fraction of IL in the three-, two-, and one-phase regions over a temperature range from (308 to 527) K at pressures to 4 MPa. The measurements were performed using a high-temperature, high-pressure, nearly constant-volume adiabatic calorimeter. The combined expanded uncertainty of the density (ρ), temperature (T), concentration (x), and isochoric heat capacity (CV) measurements at the 0.95 confidence level with a coverage factor of k = 2 is estimated to be 0.0015, 15 mK, 0.0001, and 0.03, respectively. The possibility of the chemical reactions occurring during isochoric heat capacity measurements at high temperatures has been discussed. The onset of the effects of thermal decomposition on the isochoric heat capacity of binary n-hexane + [C8C1im]Cl mixture was found at temperatures above approximately 420 K. The addition of n-hexane into the IL made little change in thermal stability of IL. The liquid–vapor phase transition parameters (TS=509.88 ± 0.05 K, ρS=255.13 kg∙m−3, and PS = 3.1175 MPa) have been measured using the technique based on isochoric heat capacity abrupt behavior. Addition of the IL (0.0089 mol fraction) increases the phase transition temperature of pure n-hexane by 2.17 K, while the phase transition pressure increases by 0.0734 MPa.

Modeling and experimental studies of quartz and stishovite and the effects of metal dopants on the quartz-to-stishovite pressure-phase transition

Solid-state density functional theory has been employed to study the vibrational and electronic structures of quartz and stishovite as a function of pressure, as well as the effects of Al, Fe, and Ni dopants on the quartz-to-stishovite pressure-phase transition. The calculated Raman-active modes and band gaps are presented and compared to those obtained experimentally. Calculated changes in the enthalpy of the neat and doped crystals suggest that Al decreases the quartz-to-stishovite transition pressure, whereas Fe and Ni increase the transition pressure.

ФАЗОВЫЕ ПЕРЕХОДЫ В ТВЕРДЫХ РАСТВОРАХ НА БАЗЕ CDAS2 ПРИ ДАВЛЕНИЯХ ДО 50 ГПА

Research has been performed into baric dependences between electrical resistance and thermo-EMF of eutectic solid solutions based on cadmium diarsenide of various compositions (Cd0.97Zn0.03As2 and Cd0.95Zn0.05As2) at pressures from 16 to 50 GPa and room temperature. Pressures were created in a chamber with conducting diamond anvils that served as contacts with the sample. Structural changes were recorded by changing electrical resistance and thermo-EMF. When replacing cadmium atom, zinc forms closer bonds with arsenic, which must result in the crystal lattice strengthening and higher pressures of phase transitions. Solid solutions preserve phase transitions observed in pure cadmium diarsenide. An increase in the crystal lattice stability of the solutions is confirmed compared to initial cadmium diarsenide. It is shown that with an increase in the zinc concentration pressures of phase transitions are shifted into the zone of higher pressures. The compounds preserve electronic conductivity in the range of pressures under consideration. At pressures higher than 30 GPa the thermo-EMF values become close to zero. This may be due to both an increase on concentrations of minority charge carriers and the impact of additional donating levels in the forbidden zone of solid solutions.

Modeling of the removal mechanism of monocrystalline silicon-based on phase change-dislocation theory and its edge chipping damage during micro-grinding

The micro-grinding of complex meso/micro-components of hard and brittle materials have attracted much attention in recent years. However, little related knowledge was accumulated, and there is a lack of quantitative evaluation of edge chipping damage, which is a major drawback. A theoretical model was established to further analyze the material removal mechanism under the action of single grain, considering the pressure phase transition, dislocation nucleation, and crack growth. An evaluation factor Fr of edge chipping damage was proposed to provide a reference for evaluating micro-grinding quality. Besides, the theoretical results were verified using the nano-scratch test. The experimental results proved that the proposed evaluation factor was an efficient tool to describe and predict micro-grinding quality.

Phase Relations in the Ni–S System at High Pressures from ab Initio Computations

Based on the ab initio calculations within the density functional theory and crystal structure prediction algorithms, the structure and stability of compounds in the Ni–S system at pressures of 100–400 GPa were determined. As a result, a homologous series of discrete compounds (Ni and S) consisting of Ni14S-C2/m, Ni13S-R3̅, Ni12S-R3̅, Ni5S-C2/m, Ni4S-P1̅, and Ni3S-Cmcm is revealed. We also confirmed the absence of the stable Fe-bearing compounds between Fe and Fe2S in the studied pressure range. At the Earth’s core pressures, 4 wt % of sulfur can be dissolved in solid fcc-Ni without deformation of the structure. Significant deformations in the Ni structure occur at sulfur contents from 4 to 15 wt %. In contrast, up to 0.45 wt % of sulfur could be dissolved in hcp-Fe at 350 GPa and 0 K. For Ni3S, two phases with space groups I4̅ and Cmcm were predicted. Ni3S-I4̅ is stable at least from 100 GPa, whereas above 330 GPa, it transforms into Ni3S-Cmcm. The pressure of phase transition is almost independent of temperature. The Ni2S is stable in the entire pressure range and undergoes a single-phase transition from the Pnma- to P6̅2m-phase at 266 GPa and 0 K with a Clapeyron slope of 5 MPa/K. The S-rich sulfide NiS3 is characterized by Im3̅m symmetry and is thermodynamically stable from 100 to 318 GPa. Our new data on Ni sulfides might be important to constrain detailed thermodynamic models for Fe–Ni-bearing Earth and planetary cores.

Phase Equilibrium and Density of CO2 + Acetic Acid Systems from 308.15 to 338.15 K and 15 to 45 MPa.

Using a high-pressure phase equilibrium apparatus and vibrating-tube densimeter, phase transition pressures of CO2 (1) + acetic acid (2) binary systems with x2 = 0.000, 0.107, 0.163, 0.222, and 1.000 were measured under temperatures from 308.15 to 338.15 K. Besides, the densities at the same composition and temperature under pressure from 15 to 45 MPa were also detected, and the volumes of mixing (ΔVm) were calculated. Three prediction models (SRK EOS, PC-SAFT EOS, and TS model) were introduced to predict and correlate the density of binary systems, which was found to have positive relationships with temperature and acetic acid concentration and a negative relationship with pressure. Thereinto, the variation trend of CO2 density with pressure tends to be flat under high pressure, and which of acetic acid density increased linearly with pressure. ΔVm are negative, and their absolute value increases with the increase of temperature and the decrease of pressure. The work herein could provide a theoretical guide and basic data for supercritical CO2 extraction technology and CO2 application in oil field development.

Structural and High-Pressure Properties of Rheniite (ReS2) and (Re,Mo)S2

Rhenium disulfide (ReS2), known in nature as the mineral rheniite, is a very interesting compound owing to its remarkable fundamental properties and great potential to develop novel device applications. Here we perform density functional theory (DFT) calculations to investigate the structural properties and compression behavior of this compound and also of the (Re,Mo)S2 solid solution as a function of Re/Mo content. Our theoretical analysis is complemented with high-pressure X-ray diffraction (XRD) measurements, which have allowed us to reevaluate the phase transition pressure and equation of state of 1T-ReS2. We have observed the 1T-to-1T’ phase transition at pressures as low as ~2 GPa, and we have obtained an experimental bulk modulus, B0, equal to 46(2) GPa. This value is in good agreement with PBE+D3 calculations, thus confirming the ability of this functional to model the compression behavior of layered transition metal dichalcogenides, provided that van der Waals corrections are taken into account. Our experimental data and analysis confirm the important role played by van der Waals effects in the high-pressure properties of 1T-ReS2.

Hadron–Quark Phase Transition in the SU (3) Local Nambu–Jona-Lasinio (NJL) Model with Vector Interaction

We study the hadron–quark hybrid equation of state (EOS) of compact-star matter. The Nambu–Jona-Lasinio (NJL) local SU (3) model with vector-type interaction is used to describe the quark matter phase, while the relativistic mean field (RMF) theory with the scalar-isovector δ-meson effective field is adopted to describe the hadronic matter phase. It is shown that the larger the vector coupling constant GV, the lower the threshold density for the appearance of strange quarks. For a sufficiently small value of the vector coupling constant, the functions of the mass dependence on the baryonic chemical potential have regions of ambiguity that lead to a phase transition in nonstrange quark matter with an abrupt change in the baryon number density. We show that within the framework of the NJL model, the hypothesis on the absolute stability of strange quark matter is not realized. In order to describe the phase transition from hadronic matter to quark matter, Maxwell’s construction is applied. It is shown that the greater the vector coupling, the greater the stiffness of the EOS for quark matter and the phase transition pressure. Our results indicate that the infinitesimal core of the quark phase, formed in the center of the neutron star, is stable.

Fracture criterion and control plan on CO2 pipelines: Theory analysis and full-bore rupture (FBR) experimental study

Pressurized pipelines are the most reliable and cost-effective option for the long-distance transportation of CO2 from an emitter to an onshore storage site. Propagating or unstable factures are considered catastrophic pipeline failures, resulting in a massive escape of inventory within a short period of time. The decompression curve for CO2 exhibits a large drop in decompression wave speed at the phase transition pressure, leading to a higher driving force for crack propagation. The study of fracture control plans is very important for assessing the possibility of fracture propagation and preventing unstable fracturing along CO2 pipelines. Three full-bore rupture (FBR) experiments were performed using an industrial-scale (258 m long, 233 mm inner diameter) CO2 pipeline with initial CO2 states of gaseous, dense and supercritical phases, respectively. The relation between the decompression velocity and the pipeline fracture propagation velocity was analyzed during the process of buried CO2 pipeline release. A fracture propagation criterion was established for the buried CO2 pipeline. For the gaseous CO2 leakage, the pressure plateau corresponding to the decompression wave velocity only appeared near the closed end of the pipeline. For the dense CO2 leakage, the pressure plateau corresponding to the decompression wave velocity was observed near the saturation pressure after rapid decompression. For the supercritical CO2 leakage, the pressure plateau corresponding to the decompression wave velocity was observed in the stage when the supercritical CO2 transformed into the two phases of gas and liquid. Compared with the gaseous and dense CO2, for the supercritical CO2, the initial decompression wave velocity was the smallest, and the requirement of the pipeline safety factor was the highest.

Insight into the phase transition, elastic and thermodynamic properties of BeS compound under high pressure and temperature from the first principle calculation

Based on the first principle plane wave pseudopotential and generalized gradient approximation (GGA) method, the phase, elastic and thermodynamic properties of BeS compound at pressure ranging from 0 to 175 GPa are calculated. After studying the energy-volume and entropy difference-pressure of the zinc blende, NiAs, NaCl and CsCl structures of BeS compound in depth, we consider the zinc blende and NiAs structures as two stable structures for BeS compound. The phonon spectra and elastic constants reveal that zinc blende and NiAs structures are also structurally and mechanically stable at ambient conditions. Furthermore, the phase transition pressure from zinc blende structure to NiAs structure is 58.615 GPa. Intriguingly, the anisotropies of the elastic and sound velocities of BeS are found to exhibit anisotropic characteristics, which is the first comprehensive study on the mechanical properties of BeS compound. Notably, we report for the first time the thermodynamic properties of NiAs structure, such as the Debye temperature, specific volume heat capacity, which shows great potential in the further study on the properties of BeS compound.