High-pressure Transition Research Articles

Characterisation of the high-pressure structural transition and elastic properties in boron arsenic

This paper carries out the First principles calculation of the crystal structures (zinc blende (B3) and rocksalt (B1)) and phase transition of boron arsenic (BAs) based on the density-functional theory. Using the relation between enthalpy and pressure, it finds that the transition phase from the B3 structural to the B1 structural occurs at the pressure of 113.42GPa. Then the elastic constants C11, C12, C44, bulk modulus, shear modulus, Young modulus, anisotropy factor, Kleinman parameter and Poisson ratio are discussed in detail for two polymorphs of BAs. The results of the structural parameters and elastic properties in B3 structure are in good agreement with the available theoretical and experimental values.

Physics of spontaneous ignition of high-pressure hydrogen release and transition to jet fire

The aim of this study is to gain an insight into the physical phenomena underlying the spontaneous ignition of hydrogen following a sudden release from high-pressure storage and transition to sustained jet fire. The modelling and large-eddy simulation (LES) of the spontaneous ignition dynamics in a tube with a non-inertial rupture disk separating the high-pressure hydrogen storage and the atmosphere is described. Numerical experiments confirmed that due to the stagnation conditions a chemical reaction first commences in the tube boundary layer, and subsequently propagates throughout the tube cross-section. The dynamics of flame formation outside the tube, simulated by the LES model, has reproduced the combustion patterns, including vortex induced “flame separation”, which have been experimentally observed by high-speed photography. It is concluded that the LES model can be applied for hydrogen safety engineering, e.g. for the development of innovative pressure relief devices.

High-pressure magnetic transition in hcp-Fe

High-pressure experiments and ab initio calculations on the hexagonal close-packed (hcp) structure of pure iron were performed to investigate a pressure-induced magnetic transition and the equation of state in the pressure range of 0-107 and 0-400 GPa, respectively. The experimental data at room temperature showed a significant change in the cell parameter ratio at 55 GPa without any major structural changes occurring. Ab initio calculations at 0 K indicate that the change in the cell parameter ratio observed in the high-pressure experiments corresponds to a magnetic transition from an antiferromagnetic state to a nonmagnetic state. If the hcp-Fe is stable under inner core conditions, then the density of nonmagnetic hcp-Fe is ~6% denser than that of the inner core, as determined using the PREM model. This supports the view that the composition of the inner core should be composed of iron and a significant amount of lighter elements.

A first principles study of the thermal stability ofAm(MH4)n light complex hydrides

From the physical point of view, the cohesive energy of a reactant is preferable toits formation energy for characterizing its influence on the reaction processesfrom the reactants to the products. In fact it has been found that there is acertain correlation between the experimental hydrogen desorption temperatureand the cohesive energy calculated by a first principles method for a series ofAm(MH4)n (A = Li, Na, Mg;M = Be, B, Al) light complexhydrides (including Na2BeH4, Li2BeH4,NaAlH4,LiAlH4,Mg(AlH4)2,LiBH4 andNaBH4), which suggests that cohesive energy may be a useful physical quantity for evaluatingthe hydrogen desorption ability of complex hydrides, especially in cases whendehydrogenation products have unknown crystal structures, or may even be unknown. Tounderstand this correlation more deeply, the ionic interaction between A and theMH4 complex and the covalent interaction between M and H were calculatedand their contributions to the cohesive energy evaluated quantitatively.The calculated results show that the covalent M–H interaction in theMH4 complex is the dominant part of the cohesive energyEcoh (up to more than 75%) and hardly changes during high-pressure structural transitions ofAm(MH4)n. It was also found that low electronegativity of M or high electronegativity of A is responsiblefor the weak covalent M–H interaction and finally leads to the low thermodynamic stability ofAm(MH4)n, suggesting thatcomplex hydrides Am(MH4)n can be destabilized by partial substitution of M (A) with an element with electronegativitylower (higher) than Ms (As). This conclusion has been confirmed by lots of experimentalresults and may be a useful guideline for the future design of new complex hydrides of the typeAm(MH4)n.

High pressure transition in amorphous As2S3 studied by EXAFS

We report an in situ high pressure investigation of the structural change in vitreous As(2)S(3) up to 60 GPa using the diamond anvil cell and energy dispersive x-ray absorption spectroscopy. The main finding of the present study is a gradual elongation of the average As-S bond length, which takes place in the pressure range of 15-50 GPa. This change is interpreted as a signature of the coordination number increase around As atoms. The negative shift of the As K absorption edge position confirms the progressive metallization of the glass at high pressure. The observed changes are reversible after pressure release.

Phase transitions in praseodymium up to 23 GPa: An x-ray powder diffraction study

The lanthanide metal Pr has been studied by x-ray powder diffraction from 5 to 23 GPa with the aim of resolving the long-standing disagreements about the identity of the high-pressure phases, transitions, and structures of this element. We find that the distorted-fcc (d-fcc) phase observed above 7.4 GPa has the rhombohedral $hR24$ structure reported previously by Hamaya et al. and can definitely rule out the monoclinic structure proposed by other authors. At 13.7 GPa, the d-fcc phase starts to transform to another phase, Pr-VII, the structure of which is body-centered orthorhombic or a very slight distortion thereof. Pr-VII transforms to the $\ensuremath{\alpha}$-uranium phase at 20.5(5) GPa. In addition to identifying the phase transitions and structures, we have also resolved many of the disagreements between previous diffraction studies and show that almost all previous work is in agreement with the present study. The likely existence of the Pr-VII phase in a second lanthanide, Nd, suggests that it might be an additional member of the sequence of phases observed across the lanthanide elements.

High-Pressure Structural Transitions of Sc2O3 by X-ray Diffraction, Raman Spectra, and Ab Initio Calculations

The high-pressure behavior of scandium oxide (Sc(2)O(3)) has been investigated by angle-dispersive synchrotron powder X-ray diffraction and Raman spectroscopy techniques in a diamond anvil cell up to 46.2 and 42 GPa, respectively. An irreversible structural transformation of Sc(2)O(3) from the cubic phase to a monoclinic high-pressure phase was observed at 36 GPa. Subsequent ab initio calculations for Sc(2)O(3) predicted the phase transition from the cubic to monoclinic phase but at a much lower pressure. The same calculations predicted a second phase transition at 77 GPa from the monoclinic to hexagonal phase.

Phase-transition mechanism of h-BN [formula omitted]w-BN from first principles

We present ab initio calculations of the electron energy-loss near edge structure (ELNES) on hexagonal boron nitride to reveal the mechanism of its high pressure transition to wurtzite phase. Our simulated ELNES with the proposed phase-transition path of a 1/8 shift along [0001] for N atoms in h -BN is in excellent agreement with experimental data. Subsequent enthalpy calculation further confirmed the validity of this transition path. Our results support the experimental suggestion by Meng et al. [Y. Meng, H.-K. Mao, P.J. Eng, T.P. Trainor, M. Newville, M.Y. Hu, C.-c. Kao, J.F. Shu, D. Hausermann, R.J. Hemley, Nature Mater. 3 (2004) 111].

High-pressure transitions in MgAl 2O 4 and a new high-pressure phase of Mg 2Al 2O 5

Phase transitions in MgAl 2O 4 were examined at 21–27 GPa and 1400–2500 °C using a multianvil apparatus. A mixture of MgO and Al 2O 3 corundum that are high-pressure dissociation products of MgAl 2O 4 spinel combines into calcium–ferrite type MgAl 2O 4 at 26–27 GPa and 1400–2000 °C. At temperature above 2000 °C at pressure below 25.5 GPa, a mixture of Al 2O 3 corundum and a new phase with Mg 2Al 2O 5 composition is stable. The transition boundary between the two fields has a strongly negative pressure–temperature slope. Structure analysis and Rietveld refinement on the basis of the powder X-ray diffraction profile of the Mg 2Al 2O 5 phase indicated that the phase represented a new structure type with orthorhombic symmetry ( Pbam), and the lattice parameters were determined as a=9.3710(6) Å, b=12.1952(6) Å, c=2.7916(2) Å, V=319.03(3) Å 3, Z=4. The structure consists of edge-sharing and corner-sharing (Mg, Al)O 6 octahedra, and contains chains of edge-sharing octahedra running along the c-axis. A part of Mg atoms are accommodated in six-coordinated trigonal prism sites in tunnels surrounded by the chains of edge-sharing (Mg, Al)O 6 octahedra. The structure is related with that of ludwigite (Mg, Fe 2+) 2(Fe 3+, Al)(BO 3)O 2. The molar volume of the Mg 2Al 2O 5 phase is smaller by 0.18% than sum of molar volumes of 2MgO and Al 2O 3 corundum. High-pressure dissociation to the mixture of corundum-type phase and the phase with ludwigite-related structure has been found only in MgAl 2O 4 among various A 2+B 3+ 2O 4 compounds.

Mixing Behavior of a Poly(ethylene glycol)-Grafted Phospholipid in Monolayers at the Air/Water Interface

Mixed phospholipid monolayers hosting a poly(ethylene glycol) (PEG)-grafted distearoylphosphatidylethanolamine with a PEG molecular weight of 5000 (DSPE-PEG5000) spread at the air/water interface were used as model systems to study the effect of PEG-phospholipids on the lateral structure of PEG-grafted membrane-mimetic surfaces. DSPE-PEG5000 has been found to mix readily with distearoylphosphoethanolamine-succinyl (DSPE-succynil), a phospholipid whose structure resembles closely that of the phospholipid part of the DSPE-PEG5000 molecule. However, properties of mixed monolayers such as morphology and stability varied significantly with DSPE-PEG5000 content. In particular, our surface pressure, epifluorescence microscopy (EFM), and Brewster angle microscopy (BAM) studies have shown that mixtures containing 1-9 mol % of DSPE-PEG5000 form stable condensed monolayers with no sign of microscopic phase separation at surface pressures above approximately 25 mN/m. Yet, at 1 mol % of DSPE-PEG5000 in mixed monolayers, the two components have been found to behave nearly immiscibly at surface pressures below approximately 25 mN/m. For monolayers containing 18-75 mol % of DSPE-PEG5000, a high-pressure transition has been observed in the low-compressibility region of their isotherms, which has been identified on the basis of continuous BAM imaging of monolayer morphology, as reminiscent of the collapse nucleation in a pure DSPE-PEG5000 monolayer. Thus, the comparative analysis of our surface pressure, EFM, and BAM data has revealed that there exists a rather narrow range of mixture compositions with DSPE-PEG5000 content between 3 and 9 mol %, where somewhat homogeneous distribution of DSPE-PEG5000 molecules and high pressure stability can be achieved. This finding can be useful to "navigating" through possible mixture compositions while developing guidelines to the rational design of membrane-mimetic surfaces with highly controlled bio-nonfouling properties.

Characterization of the High-Pressure Structural Transition and Thermodynamic Properties in Sodium Chloride: A Computational Investigation on the Basis of the Density Functional Theory

Using first-principles calculations, the elastic constants, the thermodynamic properties, and the structural phase transition between the B1 (rocksalt) and the B2 (cesium chloride) phases of NaCl are investigated by means of the pseudopotential plane-waves method. The calculations are performed within the generalized gradient approximation to density functional theory with the Perdew-Burke-Ernzerhof exchange-correlation functional. On the basis of the third-order Birch-Murnaghan equation of states, the transition pressure Pt between the B1 phase and the B2 phase of NaCl is determined. The calculated values are generally speaking in good agreement with experiments and with similar theoretical calculations. From the theoretical calculations, the shear modulus, Young's modulus, rigidity modulus, and Poisson's ratio of NaCl are derived. According to the quasi-harmonic Debye model, we estimated the Debye temperature of NaCl from the average sound velocity. Moreover, the pressure derivatives of elastic constants, partial differentialC11/partial differentialP, partial differentialC12/partial differentialP, partial differentialC44/partial differentialP, partial differentialS11/partial differential P, partial differentialS12/partial differentialP, and partial differentialS44/partial differentialP, for NaCl crystal are investigated for the first time. This is a quantitative theoretical prediction of the elastic and thermodynamic properties of NaCl, and it still awaits experimental confirmation.

Electronic, electrical and thermodynamic properties of Ca 5Si 3 by first principles calculations and low temperature experimental techniques

A combined experimental and computational study of the Ca 5Si 3 phase is presented. Its’ electronic structure and lattice stability are investigated by first principles methods: four different crystal lattices have been investigated by means of density functional theory (DFT) calculations and pseudopotentials within the generalized-gradient approximation using the VASP code. The Ca 5Si 3 phase is predicted to undergo an high pressure transition: the lattice transition tI32(Cr 5B 3-type) → tI32(W 5Si 3-type) has been predicted by DFT to occur at 14.9 GPa. The electronic and band structure of the tI32 Cr 5B 3-type lattice is calculated and discussed. The Ca 5Si 3 phase ground state structure is predicted to be a metal with a peaked density of states below the Fermi energy and a sharp minimum right above it. Experimentally the low temperature resistivity and heat capacity of the Ca 5Si 3 phase have been measured between 2 and 300 K and discussed in view of our computational predictions and available literature. The Ca 5Si 3 tI32(Cr 5B 3-type) standard pressure polymorph exhibits a metallic temperature dependence of the electric conductivity in agreement with the DFT predictions.

Pressure Induced Superconductivity inCaFe2As2

CaFe2As2 has been found to be exceptionally sensitive to the application of hydrostatic pressure and can be tuned to reveal all the salient features associated with FeAs superconductivity without introducing any disorder. The ambient pressure, 170 K, structural/magnetic, first-order phase transition is suppressed to 128 K by 3.5 kbar. At 5.5 kbar a new transition is detected at 104 K, increasing to above 300 K by 19 kbar. A low temperature, superconducting dome (T(c) approximately 12 K) is centered around 5 kbar, extending down to 2.3 kbar and up to 8.6 kbar. This superconducting phase appears to exist when the low pressure transition is suppressed sufficiently, but before the high pressure transition has reduced the resistivity too dramatically.

Combined High Pressure and Subzero Temperature Phase Transition on the Inactivation of Escherichia coli ATCC 10536

Combined high pressure and subzero temperature phase transition was performed to inactivate Escherichia coli ATCC 10536 at 200 MPa. Inactivation was compared among atmospheric pressure inactivation (APFI), pressure assisted freezing inactivation (PAFI), pressure assisted thawing inactivation (PATI), and pressure shift freezing inactivation (PSFI). Phase transition characteristics of microbial suspension were concurrently analyzed to investigate its influence on microbial inactivation. Phase transition temperature of E. coli ATCC 10536 suspension decreased to -23.8°C at 200 MPa, which is observed from the phase transition plateau. Supercooling was observed from nucleation temperature (-25°C) of PAFI. PATI resulted in the most inactivation of 4.37 log reduction, followed by PAFI and PSFI in decreasing order. APFI showed no efficacy of inactivation for E. coli ATCC 10536. Synergistic effect of high pressure, subzero temperature, and phase transition was expected for microbial inactivation.

High-pressure phase transition inRb6C60

High-pressure and high-temperature studies have been carried out on the alkali metal--intercalated fullerene system ${\text{Rb}}_{6}{\text{C}}_{60}$ by performing x-ray diffraction (XRD), x-ray absorption, and Raman spectroscopy measurements. All of these techniques allow the obtaining of complementary information on the high-pressure behavior and evolution of the studied system. In particular, the occurrence of a reversible transition has been clearly identified at around 35 GPa both at 600 K and at room temperature by XRD and Raman spectroscopy, respectively. The XRD data show that the high-pressure phase is compatible with a hexagonal unit-cell structure with $a=8.360(2)\text{ }\text{\AA{}}$ and $c=14.830(7)\text{ }\text{\AA{}}$ at 43 GPa and 600 K. In correspondence with such transition, the Raman spectra exhibit an abrupt change in the frequency of the normal vibrations. By coupling the information obtained with the different experimental techniques, we suggest that the high-pressure structural transition is accompanied by the formation of two-dimensional polymers of ${\text{C}}_{60}$.

Effect of aliphatic chain length on stability of poly(ethylene glycol)-grafted phospholipid monolayers at the air/water interface

The monolayer behavior of phosphatidylethanolamines bearing aliphatic chains of different length, C 16 and C 18, and grafted with PEG chains of molecular weight 2000, DPPE-PEG2000 and DSPE-PEG2000, respectively, was studied at the air/water interface. Comparative analysis of the surface pressure–molecular area ( π– A) isotherms, Brewster angle microscopy (BAM) and atomic force microscopy (AFM) data has provided a new insight in the nature of the high-pressure transition observed in the isotherms of both DPPE-PEG2000 and DSPE-PEG2000 monolayers. This high-pressure transition appears in the low compressibility region of the two PEG2000–phospholipid isotherms at remarkably different surface pressures, at ∼26 and ∼19 mN/m for DPPE-PEG2000 and DSPE-PEG2000, respectively. The transition has been found to originate from the monolayer collapse. As visualized by BAM and AFM, fluid DPPE-PEG2000 and DSPE-PEG2000 monolayers are unable to sustain high pressures and collapse through the formation of micellar defects in the monolayer structure as a result of 2D to 3D relaxation of an overcompressed film.

Rh2O3(II)-type structures inGa2O3andIn2O3under high pressure: Experiment and theory

High-pressure transitions of ${\mathrm{Ga}}_{2}{\mathrm{O}}_{3}$ and ${\mathrm{In}}_{2}{\mathrm{O}}_{3}$ were examined by using a laser-heated diamond-anvil cell combined with in situ x-ray diffractometry at pressures up to $108\phantom{\rule{0.3em}{0ex}}\mathrm{GPa}$ and $20\phantom{\rule{0.3em}{0ex}}\mathrm{GPa}$, respectively. To predict the transition pressure to high-pressure phases, first principles static lattice energy calculations based on the density functional theory were also performed. ${\mathrm{Rh}}_{2}{\mathrm{O}}_{3}(\mathrm{II})$ phases were confirmed as post corundum phases for both ${\mathrm{Ga}}_{2}{\mathrm{O}}_{3}$ and ${\mathrm{In}}_{2}{\mathrm{O}}_{3}$ at about $37\phantom{\rule{0.3em}{0ex}}\mathrm{GPa}$ and $7\phantom{\rule{0.3em}{0ex}}\mathrm{GPa}$, respectively. The transition pressures determined by high-pressure experiments are almost consistent with those by theoretical computations. In regard to the present sesquioxides, a link of transition from corundum to perovskite was not confirmed. The ${\mathrm{Rh}}_{2}{\mathrm{O}}_{3}(\mathrm{II})$ phases converted to corundum phases under decompression at room temperature. The bulk modulus of ${\mathrm{Rh}}_{2}{\mathrm{O}}_{3}(\mathrm{II})$ phase in ${\mathrm{Ga}}_{2}{\mathrm{O}}_{3}$ and ${\mathrm{In}}_{2}{\mathrm{O}}_{3}$ were determined as $271\ifmmode\pm\else\textpm\fi{}10\phantom{\rule{0.3em}{0ex}}\mathrm{GPa}$ and $169\ifmmode\pm\else\textpm\fi{}4\phantom{\rule{0.3em}{0ex}}\mathrm{GPa}$ with their pressure derivatives fixed at 4, respectively.

Displacive mechanisms and order-parameter symmetries for the A7-incommensurate-bcc sequences of high-pressure reconstructive phase transitions in Group Va elements

The high-pressure structural transitions observed in the Group Va elements P, As, Sb, and Bi are described by displacive atomic mechanisms. A theoretical analysis of the proposed mechanisms shows that two different structural paths are followed relating the low-pressure A7 structure to the highest-pressure bcc structure. One structural path gives rise to the host-guest structures found in As, Sb, and Bi, whereas another path yields the incommensurate P IV structure recently disclosed in P. The incommensurate character of the host-guest and P IV structures is shown to be imposed by the energetically most favorable path relating the A7 and bcc structures.

X-ray diffraction study of high pressure transition in InOOH

We performed high-pressure and high-temperature X-ray diffraction experiments on InOOH using laser heated diamond anvil cells. After heating at 1300 K, pyrite-type InOOH was formed at 14 GPa and it was stable up to at least 30 GPa. Pyrite-type InOOH partially transformed back to distorted rutile-type InOOH after recovery. The lattice constant and unit-cell volume of pyrite-type InOOH were determined to be a0 = 5.3151(8) A and V0 = 150.15 (7) A3 at ambient conditions, respectively. The density difference between pyrite-type and distorted rutile-type InOOH was 5% at ambient condition.

Compression mechanism and pressure-induced amorphization ofγ−ZrW2O8

The structure of $\ensuremath{\gamma}\text{\ensuremath{-}}\mathrm{Zr}{\mathrm{W}}_{2}{\mathrm{O}}_{8}$ has been optimized at zero pressure and also at $V∕{V}_{0}=0.97$ by means of density functional theory calculations using the B3LYP functional. As previously found for $\ensuremath{\alpha}\text{\ensuremath{-}}\mathrm{Zr}{\mathrm{W}}_{2}{\mathrm{O}}_{8}$, tungsten polyhedra are stiffer than zirconium octahedra in $\ensuremath{\gamma}\text{\ensuremath{-}}\mathrm{Zr}{\mathrm{W}}_{2}{\mathrm{O}}_{8}$. However, contrary to what has been found for $\ensuremath{\alpha}\text{\ensuremath{-}}\mathrm{Zr}{\mathrm{W}}_{2}{\mathrm{O}}_{8}$, all first coordination polyhedra in the $\ensuremath{\gamma}$ phase are less compressible than the unit cell. Volume reduction in $\ensuremath{\gamma}\text{\ensuremath{-}}\mathrm{Zr}{\mathrm{W}}_{2}{\mathrm{O}}_{8}$ is, thus, mainly accomplished by polyhedral tilting. Upon pressure increase, the distance between the terminal oxygen and W atoms from the nearest polyhedra decreases by as much as 3.66% (for the pair O101-W6). Accordingly, a further reduction in the zirconium tungstate molar volume with the high-pressure transition to the amorphous phase should bring several oxygen atoms within the threshold of bond formation to W. $\mathrm{O}\phantom{\rule{0.2em}{0ex}}1s$ photoelectron spectra provide further experimental evidence on the formation of additional W-O bonds in amorphous zirconium tungstate. These new W-O bonds should enable the metastable retention of the amorphous phase upon pressure release.