Phase Transition Pressure Research Articles

Structural and thermodynamic properties of cubic sphalerite aluminum nitride under hydrostatic compression

The present work aims to investigate the structural phase stability and thermodynamic properties of aluminium nitride with cubic zinc-blende structure at normal and high pressures (up to 5 GPa) and high temperatures (up to 2000 K). In this study, we use the pseudopotential plane wave method within the framework of the density functional theory with the local density approximation for the exchange-correlation functional. The phase transition pressure has been determined and found to be in very good agreement with several theoretical data. The pressure and temperature dependences of thermodynamic properties are successfully presented, analyzed and discussed in details. Besides, the plasmon energy and microhardness are examined.

Elastic and thermophysical properties of BAs under high pressure and temperature

The pseudopotential plane-wave approach in the framework of the density functional theory, and the density functional perturbation theory with the generalized gradient approach for the exchange-correlation functional has been used to calculate the structural phase stability, elastic constants and thermodynamic properties of boron-arsenide (BAs) compound. The BAs compound transforms from the zincblende phase to rock-salt structure; the phase transition pressure was found to be 141.2 GPa with a volume contraction of around 8.2%. The thermodynamic properties under high pressure and temperature up to 125 GPa and 1200 K respectively were also determined, analyzed and discussed in comparison with other data of the literature. The systematic errors in the static energy were corrected using the bpscal EEC method. Our results agree well with those reported in the literature, where for example, our calculated melting temperature (2116 K) deviates from the theoretical one (2132.83 K) with only 0.8%, and the deviation between our result (1.86) of the Grüneisen parameter and the theoretical one (1.921) is only around 3.2%.

The phase transition and optical properties of Cr2+-doped ZnSe under high pressure

Abstract The phase transition pressure, electronic structure, optical properties and stability for ZnSe and Cr2+:ZnSe with different doping concentrations were calculated by first-principles calculation based on density-functional theory. The phase transition pressure was calculated by enthalpy-pressure relation. The introduction of dopant (Cr2+) reduces the phase transition pressure, and the phase transition pressure decreases with the increase of doping concentration. The high pressure enhances the degeneracy of Cr-d orbitals. Under the high-pressure conditions, the absorption peak positions of Cr2+:ZnSe have obvious blue-shift. Meanwhile, the stability of structures for ZnSe and Cr2+:ZnSe were further confirmed by defect formation energy and elastic constants.

Influence of nanofluid instability on thermodynamic properties near the critical point

Thermodynamic properties (isochoric heat capacity, critical and phase transition temperatures, pressure and thermal-pressure coefficient) of a nanofluid (2-propanol + TiO2) were experimentally studied near the critical point of the pure base fluid (2-propanol). Measurements were made using a high-temperature, high-pressure, nearly constant-volume adiabatic piezo-calorimeter that was designed for simultaneous measurements of caloric (CVVT) and density (PVT) properties of fluids along the near-critical isochores as a function of temperature in the two-phase and single-phase regions. The standard uncertainty of the density, temperature, pressure, thermal-pressure coefficient, and heat capacity measurements is estimated to be 0.1%, 0.02 K, 0.5%, 1.0%, and 1.5%, respectively. The measurements were made along a selected near-critical isochore of 282.68 kg·m−3 for a concentration of 0.132 mass fraction of TiO2 in the temperature range from (314 to 511) K. The measured CV and critical temperature data were interpreted in terms of finite-size scaling theory of critical phenomena for fluids confined in the finite-size media. The influence of finite size on the thermodynamic properties of the near- and supercritical fluid has been studied, along with thermal instability of the nanofluid (2-propanol + TiO2) at high temperatures (around 500 K).

Molecular dynamics simulations on the effect of nanovoid on shock-induced phase transition in uranium nitride

The Angular-Dependent Potential (ADP) proposed by Tseplyaev et al. was used to study the structural behavior of uranium nitride (UN) under shock pressure by molecular dynamics (MD) simulations. Based on the calculations of shock velocity US and particle velocity UP, the results show that a pressure-induced phase transition of Fm−3m→R−3m structure in UN occurs at 35 GPa, and it agrees well with experimental results of 30–32 GPa. We also considered the effect of nanovoid on the phase transition of UN crystal from Fm−3m to R−3m structure. It is found that the pressure of phase transition decreases with the increasing nanovoid diameter. The phase transition takes place firstly around nanovoid, companied by the nanovoid collapsing, and then spreads to the void-free regions in the process of shock loading. Due to different stresses at different direction the spreading velocity of phase transition perpendicular to the direction of shock wave is observed to be far faster than the one parallel to the direction of shock wave.

Flow characteristics and dispersion during the vertical anthropogenic venting of supercritical CO2 from an industrial scale pipeline

Pressurized pipelines represent the most reliable and cost effective way of transporting captured CO2 from fossil fuel-fired electricity generation plants for subsequent sequestration. Leakage of CO2 through a small puncture is the most common form pipeline failure during normal operation; such failures could lead to fracture. The study of pipeline depressurization and inventory dispersion behavior is of paramount importance for assessing the possibility of fracture propagation and the impact of CO2 pipeline releases on the surrounding environment. A large-scale fully instrumented pipeline (258 m long, 233mm i.d.) was constructed to study the pressure response, phase transition and dispersion of gaseous, dense and supercritical phase CO2 during vertical leakage through a 15 mm diameter orifice. The fluid pressures and temperatures in the pipeline were recorded to study the pressure response and phase transition inside the pipeline. Video cameras and CO2 concentration sensors were used to monitor the formation of the visible cloud and the gas concentration distribution in the far-field. There was a “two cold, intermediate hot” phenomenon during the vertical release in the dense and supercritical release due to the dry ice particle accumulation near the orifice. The intersection of the jet flow and settling CO2 mixture resulted in complex visible cloud forms in dense CO2 release.

NO2···NO2 Contacts under Compression: Testing the Forces in Soft Donor–Acceptor Interactions

Intermolecular forces and energies are not directly observable and cannot be retrieved from a crystal structure determination, which simply pictures the resulting equilibrium between forces. In this work, using compression to sample the repulsive part of potentials, we show that high pressure studies may give insight in the nature of intermolecular forces. We focus our attention on controversial π* ← n interactions between NO2 groups, which exhibit several conformations. Using X-ray diffraction and ab initio calculations, we describe the high pressure behavior and phase transition of 4-amino-4′-nitrobiphenyl. To deepen our understanding of the nature of NO2···NO2 interactions, we used several theoretical tools, including pairwise atomic potential energies and forces. The results show that this interaction is associated with a mild stabilization. Since the repulsive forces are experimentally found to be weaker than those of other contacts, we conclude that also the attractive forces are weak, although in e...

Perspective: High pressure transformations in nanomaterials and opportunities in material design

Pressure and temperature phase transitions of nanomaterials often differ significantly from those of their bulk parents, offering novel approaches for the engineering of original materials. The importance or even the dominance of surface atoms in the nanoworld enhances the effects of environment, geometry, and intercalation. In the present article, we explore the current knowledge of these effects, as evidenced in the high pressure phase diagrams of nanomaterials such as nanocrystals, carbon nanotubes, fullerites, graphene, and other 2D systems, as well as nanoporous structures like clathrates or zeolites. Recent advances and future challenges in the use of extreme thermodynamic conditions to develop new functional nanomaterials, composites, or devices will be reviewed, along with the specificities of the experimental environment required for these investigations.

Anomalous pressure effect on the thermal conductivity of ZnO, GaN, and AlN from first-principles calculations

In this paper, the lattice thermal conductivities of bulk ZnO, GaN, and AlN in the normal-pressure wurtzite phase and high-pressure rocksalt phase at room temperature are investigated by solving the phonon Boltzmann transport equation based on first-principles calculations. The results show that the thermal conductivities of the rocksalt ZnO, GaN, and AlN close to the phase-transition pressure are reduced by 73%, 91%, and 34%, respectively, compared to that of corresponding normal-pressure wurtzite structures. Additionally, the thermal conductivity of wurtzite ZnO and GaN exhibits unexpectedly nonmonotonic dependence on pressure; however, for wurtzite and rocksalt AlN the thermal conductivity increases monotonically with the increase of pressure. Detailed phonon mode analysis reveals that the enhanced lattice anharmonicity is responsible for the depressed thermal conductivity of the rocksalt phase. By evaluating the relative contributions of dominant factors affecting lattice thermal conductivity, we find that the nonmonotonic response of thermal conductivity to pressure in wurtzite ZnO and GaN is attributed to the interplay of group velocity and phonon relaxation time. This study provides quantitative understanding of lattice thermal conductivity of ZnO, GaN, and AlN considering the pressure-induced phase transition and highlights the importance of pressure in manipulating lattice thermal conductivity.

Pressure‐induced ferroelectric‐relaxor phase transition in (Bi0.5Na0.5)TiO3‐based ceramics

AbstractIn this work, the effects of composition, temperature, and poling on the phase transition behavior under hydrostatic pressure of lead‐free (1‐x)[(0.98Bi0.5Na0.5Ti0.995Mn0.005O3‐0.02BiAlO3)]‐xNaNbO3 (BNT‐BA‐xNN) ceramics were investigated. It was found that hydrostatic pressure can induce a phase transformation from ferroelectric (FE) to relaxor (RE). Meanwhile, the FE‐RE phase transition pressure (PFR) tends to decrease as the NN addition increases. Moreover, increasing temperature exhibits a similar effect that is, reducing PFR. The reduced PFR were considered to result from the reduced FE stability and increasing proportion of RE phase. However, PFR was obviously enhanced after poling, which can be attributed to the induced FE phase and the formation of macrodomains with application of an electric field. These results will aid in understanding the phase transition behavior of BNT‐based relaxor ferroelectrics for applications under hydrostatic pressure.

Structural and electronic properties of wurtzite, zincblende and rocksalt Al1 − xInxN ternary alloys at ambient and high pressure

ABSTRACTAlthough AlInN is originally a wurtzite structure, zincblende and rocksalt are other potential phases. It will be interesting to have a comparative study of the physical properties of this compound in various phases. A DFT-based study of wurtzite, zincblende and rocksalt phases of AlInN alloys is carried out. Structural (lattice parameter, bulk modulus) and electronic properties (energy band gap, and electron effective mass) of the Al1 − xInxN alloys are investigated, at ambient pressure, throughout the whole range of indium contents for all considered phases. High pressure effects on the studied parameters are also examined, with the phase transition pressures computed for different values of In concentrations, and compared with available data. Structural density functional calculations are performed with Perdew–Burke–Ernzerhof gradient-corrected functional for solids (PBEsol), while electronic structure is computed with the modified Becke–Johnson (TB-mBJ) potential exchange to ensure a better accuracy of calculated the band gaps. Alloy randomness is taken into account using a special quasi-random structure.

Superconductivity induced by hydrostatic pressure effect in LaO0.5F0.5Bi(S0.9Se0.1)2

Electrical resistivity of LaO0.5F0.5Bi(S0.9Se0.1)2 have been measured at a temperature range of 2.8 ∼ 300 K by applying several hydrostatic pressures. Pressure-induced superconducting phase was observed above a pressure P of 0.85 GPa and Tc increased from 2.86 K to 8.42 K. The sudden increase of Tc in LaO0.5F0.5Bi(S0.9Se0.1)2 results from the structural phase transition from tetragonal (P4/nmm) to monoclinic (P21/m). Structural phase transition pressure Pc of LaO0.5F0.5Bi(S0.9Se0.1)2 is higher than that of LaO0.5F0.5BiS2. The increase of Pc is ascribed to the suppression of the displacement parameter of the in-plane chalcogen site induced by chemical pressure of Se-substitution.

The electrical behaviors of anatase titanium dioxide(TiO2) nanoparticles under high pressure

Electrical behaviors of anatase TiO2 nanoparticles were investigated at high pressure. Resistive switching effect was observed at different pressures and enhanced with pressure. The I-V characteristic curves show stable resistive switching performance as a function of pressure and also indicate that the optimal properties appear below 21.4 GPa. The larger current at high pressure was obtained, which should be ascribed to the semiconductor-metallic transformation. The conductive mechanism was discussed and high pressure phase transitions play a key role in resistive switching behaviors.

High pressure phase equilibrium data for carbon dioxide, methyl methacrylate and poly (dimethylsiloxane) systems

This paper investigates high-pressure phase transitions for the binary system carbon dioxide (CO2) + methyl methacrylate (MMA) and for the ternary system CO2 + MMA + poly (dimethylsiloxane) vinyl terminated (PDMS-V). The experiments were carried out using the static-synthetic method in a stainless steel equilibrium cell with a variable-volume, including piston and sapphire window, at temperatures of 323.15, 333.15, 343.15 and 353.15 K and the molar fraction ranging from 0.6949 to 0.9499 and 0.6833 to 0.9444 for the binary and ternary systems, respectively. For the binary system, phase transition was determined from the liquid region to the two-phase region. High miscibility of carbon dioxide in MMA was observed with a significant volumetric expansion of the liquid phase. The surfactant PDMS-V was added to this binary system in order to investigate its effect on the phase behavior. For the ternary system CO2 + MMA + PDMS-V, phase transitions were observed from the liquid homogeneous phase until the two-phase region. The results indicate that the addition of PDMS-V led to a small increase in the phase transition pressure, and for the liquid-liquid region a large increase in the phase transition pressure of the system occurred at all temperatures.

Study of effect of temperature on phase transition pressure of GaAs and GaSb

We have presented the pressure induced phase transition of GaAs and GaSb from zinc blende (ZB) to rocksalt (NaCl) structure associated by using realistic interaction potential model (RIPM), which is modified by taking effect of temperature. This model consists of coulomb interaction, three body interaction and short range overlap repulsive interaction up to second neighbor. Phase transition pressures are associated with a sudden collapse in volume showing the occurrence of first order phase transition. The phase transition pressure (Pt) and volume collapse obtained from this model show a reasonable agreement with experimental and theoretical results.

Unusual grain coarsening behavior of bismuth under high pressure

It is well known the atomic diffusion caused by high temperature leads to conspicuous grain coarsening, which is of crucial importance to the properties of materials. High pressure usually slows down the diffusion rate of atoms and refines the grain size. In this study, using synchrotron angle dispersive x-ray diffraction (ADXRD) techniques, we observed an abnormal grain coarsening behavior of bismuth (Bi) stemming from the high pressure phase transition at room temperature, demonstrating that the grain coarsening can also be triggered by pressure. Two factors mainly give raise to this unusual coarsening behavior of Bi: (1) the nucleation rate of new phase is very slow during transformation according to the kinetics study of the phase transition in Bi, which inhibits the grain refinement; (2) the liquid interphase in the phase transition process enables the recrystallization of Bi under high pressure. Our experiment results are consistent with the previous theoretical calculations, which is crucial for describing the nucleation and growth process and clarifying the phase transition mechanisms in Bi.

Theoretical study of CaO, CaS and CaSe via first-principles calculations

Abstract ab initio Calculations were performed to study the properties of CaO, CaS and CaSe alkaline earth chalcogenides in the B1 (NaCl) and B2 (CsCl) phases. The calculations were based on the density functional theory (DFT) within generalized gradient approximation (GGA). Results of structural properties (equilibrium lattice parameters, bulk moduli, its first pressure derivative) of both phases, and results of the properties of phase transition from B1 to B2 phase (transition pressure, compression ratio at the phase transition) were reported. Elastic properties of the B1 phase of these compounds, such as elastic constants C11, C12, and C44, shear modulus (G), Young's modulus (E), Poisson’s ratio (σ), Kleinman parameter (ξ), and anisotropy factor (A) were investigated at ambient conditions. The band structure and density of states were studied, too, for the B1 structure of these compounds. The results are in good agreement with the available experimental and other theoretical results.

DFT study of [BH4]− rotation in pressure-driven phase transition of MBH4

The pressure-induced phase transitions of MBH4 (M = Na, K) have been studied using first-principles calculations. The optimized results indicate that their high-pressure phases are space group P42/nmc, which have the same symmetry as the C-substructure of their low-pressure phases. The result of [BH4]− rotational barrier shows that rotational barrier will increase with the increase of external pressure. The rotational energy barrier of KBH4 is larger than that of NaBH4 at same pressure due to larger radius of potassium atom, which can explain why potassium borohydride has a lower phase transition pressure. The theoretical rotation barrier obtained with Tkatchenko-Scheffler correction is higher and is more sensitive to change under different pressures than that without vdW correction.

Structural stability and thermodynamic properties of BSb under high pressure and temperature

The pseudopotential plane-wave method in the framework of density functional theory with the generalized gradient approximation for the exchange-correlation functional has been adopted to calculate the phase stability and thermodynamic properties of BSb under high pressure and temperature. The BSb compound transforms from the most stable zinc-blende phase to the rock-salt one and the pressure of the phase transition is around 60 GPa, which is in excellent agreement with the available theoretical data. The thermodynamic properties, such as bulk modulus, heat capacity, entropy, thermal expansion coefficient, Debye temperature, and Grüneisen parameter of BSb with stable zinc-blende structure are determined in the temperature range of 0–1200 K and the pressure up to the phase transition pressure. In addition, the electronic polarizability, plasmon energy, microhardness, melting temperature, and the thermal conductivity at 300 K are also predicted for BSb in zinc-blende structure. It is believed that these results will be quite helpful not only to understand the investigated properties of this less studied compound but also useful for the future applications in semiconductor based devices.

Pressure-induced structural phase transition and electrical properties of Cu2S

The structural phase transition and electrical properties of Cu2S have been investigated by X-ray diffraction and electrical resistance measurements at pressures up to 41.3 GPa in diamond anvil cell. A new high pressure phase is found above 22.3 GPa, which probably has a tetragonal structure. It is observed that the electrical resistance exhibits an insulating behavior at high pressures and low temperature. After the pressure is released, the high pressure phase transforms back to original monoclinic phase. This study sheds light on the electrical transport properties of Cu2S, as well as to improve our understanding of its high pressure phase transition behavior.