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Sample records for accompanying high-pressure phase

  1. High-pressure phases of alumina

    Lyle, Matthew; Pickard, Chris; Needs, Richard

    2014-03-01

    Alumina (Al2O3) has been widely used as a pressure standard in static diamond anvil cell experiments and is a major chemical component of the Earth. So a detailed knowledge of its high-pressure stability is of great importance in both materials science and deep Earth science. A phase transition is known to occur at roughly 80-100 GPa between corundum and the Rh2O3 (II) structure. A second phase transition to the CaIrO3 structure occurs at even higher pressures. Here we present a computational structure search to reveal three additional structures which are competitive at these pressures but hitherto unknown to be stable in high-pressure alumina.

  2. High pressure phase transitions in Europous oxide

    The pressure-volume relationship for EuO was investigated to 630 kilobars at room temperature with a diamond-anvil, high-pressure cell. Volumes were determined by x-ray diffraction; pressures were determined by the ruby R1 fluorescence method. The preferred interpretation involves normal compression behavior for EuO, initially in the B1 (NaCl-type) structure, to about 280 kilobars. Between approx. =280 and approx. =350 kilobars a region of anomalous compressibility in which the volume drops continuously by approximately 2% is observed. A second-order electronic transition is proposed with the 6s band overlapping with the 4f levels, thereby reducing the volume of EuO without changing the structure. This is not a semiconductor-to-metal transition. In reflected light, this transition is correlated with a subtle and continuous change in color from brown-black to a light brown. The collapsed B1 phase (postelectronic transition) is stable between approx. =350 and approx. =400 kilobars. At about 400 kilobars the collapsed B1 structure transforms to the B2 (CsCl-type) structure, with a zero pressure-volume change of approximately 12 +/- 1.5%

  3. High-pressure phases of lead chalcogenides

    Research highlights: → We show that the intermediate phase transition for these compounds is not the GeS nor the TlI type structures, as previously reported, but the orthorhombic Pnma phase. → All these compounds are predicted to undergo a structural phase transition from the rocksalt to Pnma phase at about 8.13, 7.45 and 5.40 GPa for PbS, PbSe and PbTe respectively. → Further structural phase transitions from this intermediate phase to the CsCl phase have been predicted at about 25.3, 18.76 and 15.43 GPa for PbS, PbSe and PbTe respectively. - Abstract: Ab initio electronic structures have been carried out to find the pressure-induced structural phase transitions of lead chalcogenides (PbS, PbSe and PbTe) compounds. The zinc-blende, wurtzite, rocksalt, CsCl, GeS, TlI and orthorhombic Pnma phases are considered. Results show that the intermediate phase transition for these compounds is not the GeS nor the TlI type structures, as previously reported, but the orthorhombic Pnma phase. All these compounds are predicted to undergo a structural phase transition from the rocksalt to Pnma phase at about 8.13, 7.45 and 5.40 GPa for PbS, PbSe and PbTe respectively. Moreover, further structural phase transitions from this intermediate phase to the CsCl phase have been predicted at about 25.3, 18.76 and 15.43 GPa for PbS, PbSe and PbTe respectively.

  4. Equations of state for barium in high-pressure phases

    The universal equation of state with an arbitrary reference point presented by the author (Fang Zheng-Hua 1998 Phys. Rev. B 50 16 238) is applied successfully to the analysis of the experimental compression data of barium in different structural phases (I, II, and V). The comparison given in this paper shows that this equation suits for the isothermal compression behaviour of barium in the high-pressure phases (II and V) better than the Birch-Murnaghan equation. The applicability of equations of state for solids in high-pressure phases is also discussed. (author)

  5. Novel high-pressure phase of ZrO{sub 2}: An ab initio prediction

    Durandurdu, Murat, E-mail: murat.durandurdu@agu.edu.tr

    2015-10-15

    The high-pressure behavior of the orthorhombic cotunnite type ZrO{sub 2} is explored using an ab initio constant pressure technique. For the first time, a novel hexagonal phase (Ni{sub 2}In type) within P6{sub 3}/mmc symmetry is predicted through the simulation. The Ni{sub 2}In type crystal is the densest high-pressure phase of ZrO{sub 2} proposed so far and has not been observed in other metal dioxides at high pressure before. The phase transformation is accompanied by a small volume drop and likely to occur around 380 GPa in experiment. - Graphical abstract: Post-cotunnite Ni{sub 2}In type hexagonal phase forms in zirconia at high pressure. - Highlights: • A post-cotunnite phase is predicted for ZrO{sub 2} through an ab initio simulation. • Cotunnite ZrO{sub 2} adopts the Ni{sub 2}In type structure at high pressure. • The Ni{sub 2}In type structure is the densest high-pressure phase of ZrO{sub 2} proposed so far. • The preferred mechanism in ZrO{sub 2} differs from the other metal dioxides.

  6. Novel high-pressure phase of ZrO2: An ab initio prediction

    The high-pressure behavior of the orthorhombic cotunnite type ZrO2 is explored using an ab initio constant pressure technique. For the first time, a novel hexagonal phase (Ni2In type) within P63/mmc symmetry is predicted through the simulation. The Ni2In type crystal is the densest high-pressure phase of ZrO2 proposed so far and has not been observed in other metal dioxides at high pressure before. The phase transformation is accompanied by a small volume drop and likely to occur around 380 GPa in experiment. - Graphical abstract: Post-cotunnite Ni2In type hexagonal phase forms in zirconia at high pressure. - Highlights: • A post-cotunnite phase is predicted for ZrO2 through an ab initio simulation. • Cotunnite ZrO2 adopts the Ni2In type structure at high pressure. • The Ni2In type structure is the densest high-pressure phase of ZrO2 proposed so far. • The preferred mechanism in ZrO2 differs from the other metal dioxides

  7. High pressure phase transformation in iron under fast compression

    Bastea, M; Bastea, S; Becker, R

    2009-07-07

    We present experimental results on the solid-solid, {alpha} to {epsilon} phase transformation kinetics of iron under high pressure dynamic compression. We observe kinetic features - velocity loops - similar with the ones recently reported to occur when water is frozen into its ice VII phase under comparable experimental conditions. We analyze this behavior in terms of general ideas coupling the steady sample compression with phase nucleation and growth with a pressure dependent phase interface velocity. The model is used to predict the response of iron when steadily driven across the {alpha} - {epsilon} phase boundary on very short time scales, including those envisioned to be achieved in ultra-fast laser experiments.

  8. High-Pressure Phase Transition in Cyclo-octane

    GAO Ling-Ling; ZOU Guang-Tian; JIANG Sheng; LIU Dan; HAO Jian; JIN Yun-Xia; WANG Feng; WANG Qiu-Shi; LIU Jing; CUI Qi-Liang

    2008-01-01

    Structural behaviour of cyclo-octane under high pressure is studied by using a synchrotron x-ray source in a diamond anvil cell (DAC) up to 40.2 GPa at room temperature. The cyclo-octane firstly solidifies to the triclinic phase at 0.87 GPa. With the increasing pressure, the phase of cyclo-octane changes to the tetragonal phase at about 6.0 GPa and then transforms to amorphous phase above 18.2 GPa, which is kept till to 40.2 GPa. All the phase transitions of cyclo-octane are irreversible.

  9. High pressure phase transition in Pr-monopnictides

    Raypuria, Gajendra Singh, E-mail: sosfizix@gmail.com, E-mail: gsraypuria@gmail.com; Gupta, Dinesh Chandra [Condensed Matter Theory Group, School of Studies in Physics, Jiwaji University, Gwalior - 474011 (India); Department of Physics, Govt. K.R.G. P.G. Autonomous College, Gwalior - 474001 (India)

    2015-06-24

    The Praseodymium-monopnictides compounds have been found to undergo transition from their initial NaCl-type structure to high pressure body centered tetragonal (BCT) structure (distorted CsCl-type P4/mmm) using CTIP model. The calculated values of cohesive energy, lattice constant, phase transition pressure, relative volume collapse agree well with the available measured data and better than those computed by earlier workers.

  10. Isostructural Phase Transition of TiN under High Pressure

    ZHAO Jing-Geng; LI Yan-Chun; LIU Jing; YANG Liu-Xiang; YU Yong; YOU Shu-Jie; YU Ri-Cheng; LI Feng-Ying; CHEN Liang-Chcn; JIN Chang-Qing; LI Xiao-Dong

    2005-01-01

    @@ In situ high-pressure energy dispersive x-ray diffraction experiments on polycrystalline powder TiN with NaC1type structure have been conducted with the pressure up to 30.1 GPa by using a diamond anvil cell instrument with synchrotron radiation at room temperature. The experimental results suggest that an isostructural phase transition might exist at about 7GPa as revealed by the discontinuity of V/Vo with pressure.

  11. A subdivision algorithm for phase equilibrium calculations at high pressures

    M. L. Corazza

    2007-12-01

    Full Text Available Phase equilibrium calculations at high pressures have been a continuous challenge for scientists and engineers. Traditionally, this task has been performed by solving a system of nonlinear algebraic equations originating from isofugacity equations. The reliability and accuracy of the solutions are strongly dependent on the initial guess, especially due to the fact that the phase equilibrium problems frequently have multiple roots. This work is focused on the application of a subdivision algorithm for thermodynamic calculations at high pressures. The subdivision algorithm consists in the application of successive subdivisions at a given initial interval (rectangle of variables and a systematic test to verify the existence of roots in each subinterval. If the interval checked passes in the test, then it is retained; otherwise it is discharged. The algorithm was applied for vapor-liquid, solid-fluid and solid-vapor-liquid equilibrium as well as for phase stability calculations for binary and multicomponent systems. The results show that the proposed algorithm was capable of finding all roots of all high-pressure thermodynamic problems investigated, independent of the initial guess used.

  12. High-pressure phase transitions - Examples of classical predictability

    Celebonovic, Vladan

    1992-09-01

    The applicability of the Savic and Kasanin (1962-1967) classical theory of dense matter to laboratory experiments requiring estimates of high-pressure phase transitions was examined by determining phase transition pressures for a set of 19 chemical substances (including elements, hydrocarbons, metal oxides, and salts) for which experimental data were available. A comparison between experimental and transition points and those predicted by the Savic-Kasanin theory showed that the theory can be used for estimating values of transition pressures. The results also support conclusions obtained in previous astronomical applications of the Savic-Kasanin theory.

  13. New High-Pressure Phase in Fe2O3

    Tsuchiya, T.; Nishiyama, N.; Yusa, H.; Tsuchiya, J.; Funakoshi, K.

    2009-12-01

    Hematite Fe2O3, a prototype of trivalent transition metal oxides, crystallizes in the antiferromagnetic (AFM) insulating phase with the corundum structure at ambient conditions. Extensive studies have been carried out to clarify its structural, magnetic, and electronic evolutions under high pressure due to the broad interests in hematite from condensed matter physics to geosciences. The high-pressure phase relation in Fe2O3 is also substantial to understand geophysically important MgSiO3-Fe2O3 phase equilibria. Those are however still yet to be clarified as for example, some in situ X-ray diffraction measurements using the diamond anvil cell (DAC) reported a phase change from Rh2O3(II) (or orthorhombic Pv) to the CaIrO3-type structure over 60 GPa, while an experiment using the Kawai-type apparatus with sintered diamond (SD) anvils suggested to stabilize a different phase with an unidentified orthorhombic structure at much lower pressure of 40~45 GPa. On the other hand, recent theoretical and experimental investigations of non-magnetic sesquioxide compounds have revealed an emerging systematics of their high-pressure phase sequence (Tsuchiya et al., 2005; Tsuchiya et al., 2007; Yusa et al., 2008; Yusa et al., 2009). While the CaIrO3-type phase with six and eight disproportionate coordination polyhedra was found to stabilize in Al2O3 and Ga2O3 at megabar pressure, several other compounds such as In2O3 and Sc2O3 were reported to transform directly to a further denser phase with the α-Gd2S3 structure composed only of high eight-fold coordination polyhedra at much lower pressure. Similarly to these studies, we searched for a stable form of Fe2O3 under pressure theoretically by means of the density-functional structurally consistent LDA+U method and succeeded to discover a new phase transformation from Rh2O3(II) at the pressure fairly close to that reported by the SD experiment. The high-pressure phase however has different lattice constants suggested experimentally and

  14. High pressure phase transition in Nd2O3

    Rare-Earth (RE) sesquioxides are important materials, both scientifically as well as technologically for their existence in various polymorphic forms and wide variety of applications such as for laser rods, phosphors, refractory and abrasive materials etc. Like the RE metals, the physical properties of the RE sesquioxides are mainly affected by the partial filling of their inner 4f-electron shells leading to the well known effect, lanthanide contraction. As a consequence, depending on RE+3 cation radii, RE sesquioxides exist in three polymorphic modifications at ambient conditions viz. hexagonal, monoclinic and cubic structures. It has been observed that pressure also affects the stability of various polymorphs in RE sesquioxides. Cubic and monoclinic structured sesquioxides are known to undergo polymorphous transition to hexagonal phase under high pressure; however the role of high pressure on hexagonal structured sesquioxide is relatively less studied. With this motivation we have investigated high pressure behavior of Nd2O3 using energy dispersive X-ray diffraction (EDXRD) and Raman scattering techniques

  15. Phase Diagram of RDX Crystals at High Pressures and Temperatures

    Dreger, Zbigniew; Gupta, Yogendra

    2011-06-01

    A knowledge of the RDX phase diagram is important for understanding shock-induced decomposition of RDX. Vibrational spectroscopy and optical imaging in a diamond anvil cell were used to examine the RDX behavior at high pressures and temperatures. Interplay between three solid (α, γ, ɛ) , liquid, and decomposed phases was examined in experiments on single crystals at pressures up to 12.0 GPa and temperatures to 600 K. Several distinct pressure regions were found in the RDX response at elevated temperatures. The boundaries between the α, γ, and ɛ phases were determined with a triple point at 3.7 GPa and ~ 466 K. The α - γ phase transition was confirmed to be reversible and to occur at the same pressure 3.7 GPa, regardless of temperature. The ɛ-phase was found to exist only in a narrow range of pressures, from 2.8 to 6.0 GPa. Below and above these pressures, α- or γ-RDX crystals decompose or melt instead of transforming to ɛ-RDX. Both the α - ɛ and γ - ɛ transitions were irreversible at the phase boundaries. Decomposition kinetics of both the ɛ and γ phases were found to have a positive volumes of activation. Work supported by ONR and DOE/NNSA.

  16. Anomalous thermal expansion in the metallic phase of SmS under high pressure

    SmS exhibits a pressure-induced phase transition at 0.6 GPa from a semiconducting state to a rather metallic state accompanied with a change of Sm valence and volume compression. Using the X-ray diffraction technique under high pressures, we found local minima of the lattice constant of SmS in the metallic phase up to near 2 GPa. The pressure region of the volume minima coincides with that of the low-temperature increase and the humps of electrical resistivity. We succeeded in reproducing the volume minima by a phenomenological model of a Schottky-type behavior due to electronic gap suppressed by pressure

  17. High-Pressure Neutron Diffraction Study of Hydrous Phases

    Xu, H.; Zhu, J.; Zhang, J.; Hickmott, D.; Zhao, Y.

    2013-12-01

    Mineral phases containing water in the form of H2O or/and OH- are of considerable interest for many geological applications. For example, significant amounts of water are carried into the mantle via subduction of oceanic crust that contains hydrous minerals (such as serpentine). Thus studying hydrous minerals at elevated pressure (P) and temperature (T) is important in determining the mode and fate of water in the Earth's interior. Another example is gas hydrates, which are found in oceanic floor sediments, permafrost and the outer solar system. As these phases are stable only at high-P and/or low-T conditions, determination of their formation/decomposition kinetics and mechanisms require in situ high-P low-T capabilities. Because neutrons are sensitive to hydrogen (and its isotopes), high-pressure neutron diffraction is a powerful tool for such studies. Using the high-P, high-T or low-T apparatuses coupled with time-of-flight neutron diffraction, we have investigated the structures and stability of several simple hydroxides (e.g., brucite) and gas hydrates. Rietveld analysis of the obtained data allowed determination of unit-cell parameters, atomic positions and atomic displacement parameters at various P/T conditions. The bulk moduli, thermal expansion coefficients and other thermo-mechanical parameters have been determined, and the kinetics of dehydration and phase stability relations been discussed.

  18. Structural phase transitions of sodium nitride at high pressure

    Vajenine, G. V.; Wang, X.; Efthimiopoulos, I.; Karmakar, S.; Syassen, K.; Hanfland, M.

    2009-06-01

    The structural evolution of recently characterized sodium nitride Na3N as a function of pressure was investigated at room temperature by the angle-dispersive powder x-ray diffraction in a diamond-anvil cell up to 36 GPa. The rather open cubic anti- ReO3 -type structure stable at ambient pressure is followed by a series of four high-pressure modifications. Along the route, the coordination number for the nitride anion increases from 6 in Na3N-I to 8 in hexagonal Li3N -type Na3N-II , 9 in orthorhombic anti- YF3 -type Na3N-III , 11 in hexagonal Cu3P -type Na3N-IV , and finally 14 in cubic Li3Bi -type Na3N-V structures. The experimental data are compared to the results of total-energy calculations and are discussed with regard to the structural details of the five phases and their equations of state.

  19. High pressure equation of state for condensed phase thermodynamics

    Nogva, Stig-Erik

    2012-01-01

    In this study a search for an equation of state (EOS) that accurately predicts solids behaviour at both high pressure and temperature has been performed. Firstly, several two-parameter isothermal EOSs for solids under high pressure were investigated. The EOSs evaluated were the Murnaghan, Birch?Murnaghan, Vinet and pseudo-spinodal. The input parameters needed were found through parameter fitting of experimental data. The parameter fitting was done through a second order Murnagh...

  20. A New High Pressure Phase and the Equation of State of YbH2

    Staun Olsen, J.; Buras, B.; Gerward, Leif;

    1984-01-01

    High-pressure X-ray diffraction studies have been performed on YbH2 up to 28 GPa. A first order phase transition from an orthorhombic structure to a collapsed hexagonal structure with c/a = 1.34 has been observed at about 15 GPa. The transition is accompanied by a 5.2% decrease in volume. Fitting...... the V(P) data to Murnaghan's equation of state yields the bulk modulus B0 = 40.2 GPa and its pressure derivative B'0 = 4.75 for the orthorhombic phase. For the hexagonal phase we find the bulk modulus to be B = B0 = 138 GPa independent of pressure, i.e. B'0 = 0....

  1. High pressure behavior of P2O5 crystalline modifications: compressibility, elastic properties and phase transitions

    Solid phases of the P2O5 compound have rarely been studied under high pressure to date due to their record-high hygroscopicity. We present the results of in situ x-ray diffraction study of the structure of P2O5 molecular and polymeric modifications under pressures up to 11 GPa, as well as the results of an ultrasonic study of a molecular phase up to 2 GPa. At low pressures (0.3–0.7 GPa), there is a structural transformation in the molecular phase accompanied by a significant (7–8%) density increase. This phase transition is accompanied by a large increase of both the shear modulus (by 30–40%) and bulk modulus (by 20–25%). Compression curves of the molecular and polymeric covalent phases asymptotically converge to each other at 9–10 GPa and reach a density of 3.6–3.7 g cm−3. The polymeric modification is ‘typical’ for covalent oxides values of the bulk modulus and its derivative: B ≈ 35–40 GPa, B′P ≈ 3–4. The molecular phase has quite small values of the bulk and shear moduli (B ≈ 12 GPa, G ≈ 5 GPa). (paper)

  2. Unusually large structural stability of terbium oxide phase under high pressure

    High-pressure X-Ray diffraction studies on terbium oxide have been carried out up to a pressure of ∼35 GPa in a diamond anvil cell at room temperature. Terbium oxide, which exhibits the fluorite structure at ambient conditions, remains stable in its fluorite form up to a pressure of ∼27 GPa. Above 27 GPa, it undergoes a structural phase transition accompanied with broadening and appearance of new diffraction peaks. The large structural stability of the compound under pressure is thus unusual when compared with other rare earth sesquioxides, and has been attributed to the presence of Tb4+ ions. The XPS spectra on the sample confirms the presence of Tb4+ ions. The bulk modulus and its pressure derivative of the parent phase are evaluated and reported.

  3. High-pressure phase relations of CsD2PO4

    The high-pressure phase diagram of CsD2PO4 to 4.5 GPa and temperatures between 0 and 4700C is reported. Comparisons are made with CsH2PO4 and correlated with the isotope effect on the high-temperature high-pressure phase relations of KH2PO4

  4. High-pressure phases and compressibility of neptunium and plutonium compounds

    In this paper the diamond anvil technique for generation of pressure and its potential are briefly introduced. An overview is given on recent studies of the behavior of neptunium and plutonium compounds of the Bl (NaCl) and Cl (CaF2) types under high pressure. Most Bl-type compounds adopt the B2 (CsCl) form as a high-pressure structure, but tetragonal and rhombohedral high-pressure phases occur as well. Orthorhombic high-pressure phases exist for the dioxides. Bulk moduli were determined for all compounds studied. PuO2 is less compressible than dioxides of lighter actinides

  5. High pressure phase transitions for CdSe

    Bo Kong; Ti-Xian Zeng; Zhu-Wen Zhou; De-Liang Chen; Xiao-Wei Sun

    2014-05-01

    The structure and pressure-induced phase transitions for CdSe are investigated using first-principles calculations. The pressure-induced phase transition sequence WZ/ZB $\\to$ Rs $\\to$ $\\to$ CsCl for CdSe is drawn reasonably for the fist time, the corresponding transition pressures are 3.8, 29 and 107 GPa, respectively and the intermediate states between the structure and the CsCl structure should exist.

  6. High pressure phase transition and elastic properties of Lutetium chalcogenide

    Seddik, T., E-mail: sedik_t@yahoo.f [Laboratoire de Physique Quantique et de Modelisation Mathematique (LPQ3M), Departement de Technologie, Universite de Mascara, 29000 Mascara (Algeria); Semari, F. [Physics Department, Faculty of Sciences, University of Sidi-Bel-Abbes, 22000 (Algeria); Khenata, R., E-mail: khenata_rabah@yahoo.f [Laboratoire de Physique Quantique et de Modelisation Mathematique (LPQ3M), Departement de Technologie, Universite de Mascara, 29000 Mascara (Algeria); Bouhemadou, A. [Laboratory for Developing New Materials and their Characterisation, Department of Physics, Faculty of Sciences, University of Setif (Algeria); Amrani, B. [Laboratoire de Physique Quantique et de Modelisation Mathematique (LPQ3M), Departement de Technologie, Universite de Mascara, 29000 Mascara (Algeria)

    2010-01-01

    Using first-principles density functional calculation, the pressure induced structural phase transformation and mechanical properties of NaCl type (B1) structure in Lutetium chalcogenides (LuX: X=S, Se, Te) were studied by means of the full-potential augmented plane wave plus local orbitals (FP-APW+lo) method. The calculations were performed within the generalized gradient approximation (GGA) for the exchange-correlation potential. The calculated ground state properties such us lattice constants agree quit well with the experimental findings. We have determined the full set of first-order elastic constants and their pressure dependence, which have not been calculated and measured yet. The Debye temperature is estimated from the average sound velocity. To our knowledge this is the first quantitative theoretical prediction of the structural phase transition and elastic properties for these compounds and still awaits experimental confirmations.

  7. High pressure phase transition and elastic properties of Lutetium chalcogenide

    Using first-principles density functional calculation, the pressure induced structural phase transformation and mechanical properties of NaCl type (B1) structure in Lutetium chalcogenides (LuX: X=S, Se, Te) were studied by means of the full-potential augmented plane wave plus local orbitals (FP-APW+lo) method. The calculations were performed within the generalized gradient approximation (GGA) for the exchange-correlation potential. The calculated ground state properties such us lattice constants agree quit well with the experimental findings. We have determined the full set of first-order elastic constants and their pressure dependence, which have not been calculated and measured yet. The Debye temperature is estimated from the average sound velocity. To our knowledge this is the first quantitative theoretical prediction of the structural phase transition and elastic properties for these compounds and still awaits experimental confirmations.

  8. Structural phase transition of BaZrO{sub 3} under high pressure

    Yang, Xue; Li, Quanjun; Liu, Ran; Liu, Bo; Zhang, Huafang; Jiang, Shuqing; Zou, Bo; Cui, Tian; Liu, Bingbing, E-mail: liubb@jlu.edu.cn [State Key Laboratory of Superhard Materials, Jilin University, Changchun 130012 (China); Liu, Jing [Beijing Synchrotron Radiation Facility, Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100049 (China)

    2014-03-28

    We studied the phase transition behavior of cubic BaZrO{sub 3} perovskite by in situ high pressure synchrotron X-ray diffraction experiments up to 46.4 GPa at room temperature. The phase transition from cubic phase to tetragonal phase was observed in BaZrO{sub 3} for the first time, which takes place at 17.2 GPa. A bulk modulus 189 (26) GPa for cubic BaZrO{sub 3} is derived from the pressure–volume data. Upon decompression, the high pressure phase transforms into the initial cubic phase. It is suggested that the unstable phonon mode caused by the rotation of oxygen octahedra plays a crucial role in the high pressure phase transition behavior of BaZrO{sub 3}.

  9. On the high-pressure superconducting phase in platinum hydride

    Szczȩśniak, D.; Zemła, T. P.

    2015-08-01

    Motivated by the ambiguous experimental data for the superconducting phase in silane (SiH4), which may originate from platinum hydride (PtH), we provide a theoretical study of the superconducting state in the latter alloy. The quantitative estimates of the thermodynamics of PtH at 100 GPa are given for a wide range of Coulomb pseudopotential values ({μ }*) within the Eliashberg formalism. The obtained critical temperature value ({T}{{C}}\\in for {μ }*\\in ) agrees well with the experimental TC for SiH4, which may be ascribed to PtH. Moreover, the calculated characteristic thermodynamic ratios exceed the predictions of the Bardeen-Cooper-Schrieffer theory, implying the occurrence of strong-coupling and retardation effects in PtH. We note that our results may be of high relevance for future theoretical and experimental studies on hydrides.

  10. Mechanical behaviors and phase transition of Ho2O3 nanocrystals under high pressure

    Mechanical properties and phase transition often show quite large crystal size dependent behavior, especially at nanoscale under high pressure. Here, we have investigated Ho2O3 nanocrystals with in-situ x-ray diffraction and Raman spectroscopy under high pressure up to 33.5 GPa. When compared to the structural transition routine cubic -> monoclinic -> hexagonal phase in bulk Ho2O3 under high pressure, the nano-sized Ho2O3 shows a much higher onset transition pressure from cubic to monoclinic structure and followed by a pressure-induced-amorphization under compression. The detailed analysis on the Q (Q = 2π/d) dependent bulk moduli reveals the nanosized Ho2O3 particles consist of a clear higher compressible shell and a less compressible core. Insight into these phenomena shed lights on micro-mechanism studies of the mechanical behavior and phase evolution for nanomaterials under high pressure, in general.

  11. High-Pressure Induced New Phases and Properties in Typical Molecular Systems

    Cui, Tian

    2013-06-01

    High pressure introduces new phases by the rearrangement of atoms and reconfigurations of electronic states in materials, often with new physical and chemical phenomena. Study of the new phases in typical molecular systems under high pressure is an interesting subject, such as energy storage materials of solid hydrogen and polymeric nitrogen, hydrogen-rich compound with high-Tc superconductivity under high pressure, high pressure induced metallization of hydrogen, etc. High-pressure structures and pressure-induced phase transitions in the typical molecular solids, such as solid iodine, CHBr3, N2/CN, HBr/HCl, hydrogen-rich compounds (H2S, ZrH2, AsH3, BaReH9, etc.), and group IVA hydrides (Si2H6, Ge2H6, Sn2H6, etc.) are investigated extensively by means of first-principles density functional theory and extensive prediction strategies (molecular dynamics simulation, simulated annealing, soft mode phase transition, random structure-searching method and evolutionary methodology etc.). The new structures and new properties derived from pressure-induced phase transitions in these typical molecular systems have been observed. It is showed that high pressure provides a path for producing new materials with new properties.

  12. High pressure structural phase transitions of TiO2 nanomaterials

    Quan-Jun, Li; Bing-Bing, Liu

    2016-07-01

    Recently, the high pressure study on the TiO2 nanomaterials has attracted considerable attention due to the typical crystal structure and the fascinating properties of TiO2 with nanoscale sizes. In this paper, we briefly review the recent progress in the high pressure phase transitions of TiO2 nanomaterials. We discuss the size effects and morphology effects on the high pressure phase transitions of TiO2 nanomaterials with different particle sizes, morphologies, and microstructures. Several typical pressure-induced structural phase transitions in TiO2 nanomaterials are presented, including size-dependent phase transition selectivity in nanoparticles, morphology-tuned phase transition in nanowires, nanosheets, and nanoporous materials, and pressure-induced amorphization (PIA) and polyamorphism in ultrafine nanoparticles and TiO2-B nanoribbons. Various TiO2 nanostructural materials with high pressure structures are prepared successfully by high pressure treatment of the corresponding crystal nanomaterials, such as amorphous TiO2 nanoribbons, α-PbO2-type TiO2 nanowires, nanosheets, and nanoporous materials. These studies suggest that the high pressure phase transitions of TiO2 nanomaterials depend on the nanosize, morphology, interface energy, and microstructure. The diversity of high pressure behaviors of TiO2 nanomaterials provides a new insight into the properties of nanomaterials, and paves a way for preparing new nanomaterials with novel high pressure structures and properties for various applications. Project supported by the National Basic Research Program of China (Grant No. 2011CB808200), the National Natural Science Foundation of China (Grant Nos. 11374120, 11004075, 10979001, 51025206, 51032001, and 21073071), and the Cheung Kong Scholars Programme of China.

  13. Preparation of high-pressure phase boron nitride films by physical vapor deposition

    Zhu, P W; Zhao, Y N; Li, D M; Liu, H W; Zou Guang Tian

    2002-01-01

    The high-pressure phases boron nitride films together with cubic, wurtzic, and explosive high-pressure phases, were successfully deposited on the metal alloy substrates by tuned substrate radio frequency magnetron sputtering. The percentage of cubic boron nitride phase in the film was about 50% as calculated by Fourier transform infrared measurements. Infrared peak position of cubic boron nitride at 1006.3 cm sup - sup 1 , which is close to the stressless state, indicates that the film has very low internal stress. Transition electron microscope micrograph shows that pure cubic boron nitride phase exits on the surface of the film. The growth mechanism of the BN films was also discussed.

  14. High-pressure phases of group-IV, III-V, and II-VI compounds

    Mujica, A.; Rubio Secades, Ángel; A. Muñoz; Needs, R. J.

    2003-01-01

    Advances in the accuracy and efficiency of first-principles electronic structure calculations have allowed detailed studies of the energetics of materials under high pressures. At the same time, improvements in the resolution of powder x-ray diffraction experiments and more sophisticated methods of data analysis have revealed the existence of many new and unexpected high-pressure phases. The most complete set of theoretical and experimental data obtained to date is for the group-IVA elements ...

  15. The influence of peak shock stress on the high pressure phase transformation in Zr

    At high pressures zirconium is known to undergo a phase transformation from the hexagonal close packed (HCP) alpha phase to the simple hexagonal omega phase. Under conditions of shock loading, a significant volume fraction of high-pressure omega phase is retained upon release. However, the hysteresis in this transformation is not well represented by equilibrium phase diagrams and the multi-phase plasticity under shock conditions is not well understood. For these reasons, the influence of peak shock stress and temperature on the retention of omega phase in Zr has been explored. VISAR and PDV measurements along with post-mortem metallographic and neutron diffraction characterization of soft recovered specimens have been utilized to quantify the volume fraction of retained omega phase and qualitatively understand the kinetics of this transformation. In turn, soft recovered specimens with varying volume fractions of retained omega phase have been utilized to understand the contribution of omega and alpha phases to strength in shock loaded Zr.

  16. Simulation of the high-pressure phase equilibria of hydrocarbon-water/brine systems

    Zuo, You-Xiang; Stenby, Erling Halfdan; Guo, Tian-Min

    1996-01-01

    mixing rule to the energy parameter "a", (2) apply the revised MPT model (MPT2 model) to predict the effects of the coexisting water/formation water phase on the high-pressure phase behavior of reservoir oils/gas condensates, of which no experimental data is available.The predicted results indicate that...

  17. High Pressure Raman Scattering Study on the Phase Stability of DyVO4

    Patel, Nishant N.; Garg, Alka B.; Meenakshi, S.; Wani, B. N.; Sharma, S. M.

    2011-07-01

    High pressure Raman spectroscopic investigations have been carried out on rare earth orthovanadate DyVO4 upto 22 GPa. Abrupt changes and appearance of new modes were noted in Raman spectrum above 8 GPa with two phase coexistence over a pressure range of about 8-13 GPa The phase transition was found to be irreversible when pressure is released.

  18. Modeling and Experimental Studies on Phase and Chemical Equilibria in High-Pressure Methanol Synthesis

    van Bennekom, Joost G.; Winkelman, Jozef G. M.; Venderbosch, Robertus H.; Nieland, Sebastiaan D. G. B.; Heeres, Hero J.

    2012-01-01

    A solution method was developed to calculate the simultaneous phase and chemical equilibria in high-pressure methanol synthesis (P = 20 MPa, 463 phase and include dew point calculations. A modification of the

  19. Phase Transformation of BN Nanoparticles Under High Pressure Low Temperature Conditions

    Chen, Z.; Lai, Z. F.; Li, K.; Cui, D. L.; Lun, N.; Wang, Q. L.; Jiang, M. H.

    Phase transformation of BN nanoparticles under high pressure (580~860MPa) and low temperature (270~325°C) hot press conditions was investigated. It was found that the contents of orthorhombic boron nitride (oBN) and cubic boron nitride (cBN) increased with the increase of temperature and the prolonging of hot pressing time under high pressure conditions. At the same time, because of the intergrowth of hBN, oBN and cBN. there are strong interactions among these three phases.

  20. Nanosize effects assisted synthesis of the high pressure metastable phase in ZrO2

    Li, Quanjun; Zhang, Huafang; Liu, Ran; Liu, Bo; Li, Dongmei; Zheng, Lirong; Liu, Jing; Cui, Tian; Liu, Bingbing

    2016-01-01

    The size effects on the high pressure behaviors of monoclinic (MI) ZrO2 nanoparticles were studied using in situ high pressure synchrotron X-ray diffraction (XRD) and X-ray absorption spectroscopy (XAS). A size-dependent phase transition behavior under high pressure was found in nanoscale ZrO2. The normal phase transition sequence of MI-orthorhombic I (OI)-orthorhombic II (OII) occurs in 100-300 nm ZrO2 nanoparticles, while only the transition of MI-OI exists in ultrafine ~5 nm ZrO2 nanoparticles up to the highest experimental pressure of ~52 GPa. This indicates that the size effects preclude the transition from the OI to the OII phase in ~5 nm nanoparticles. Upon decompression, the OII and OI phases are retained down to ambient pressure, respectively. This is the first observation of the pure OI phase ZrO2 under ambient conditions. The bulk moduli of the MI ZrO2 nanoparticles were determined to be B0 = 192 (7) GPa for the 100-300 nm nanoparticles and B0 = 218 (12) GPa for the ~5 nm nanoparticles. We suggest that the significant high surface energy precludes the transition from the OI to the OII phase and the nanosize effects enhance the incompressibility in the ultrafine ZrO2 nanoparticles (~5 nm). Our study indicates that this is a potential way of preparing novel nanomaterials with high pressure structures using nanosize effects.

  1. Structural and magnetic phase transitions in NdCoAsO under high pressures

    We have investigated structural and magnetic phase transitions under high pressures in a quaternary rare-earth transition-metal arsenide oxide NdCoAsO compound that is isostructural to the high temperature superconductor parent phase NdFeAsO. The four-probe electrical resistance measurements carried out in a designer diamond anvil cell show that the ferromagnetic Curie temperature and antiferromagnetic Neel temperature increase with an increase in pressure. High pressure x-ray diffraction studies using a synchrotron source show a structural phase transition from a tetragonal phase to a new crystallographic phase at a pressure of 23 GPa at 300 K. The NdCoAsO sample remained antiferromagnetic and non-superconducting down to 10 K and up to the highest pressure achieved in this experiment, 53 GPa. A P-T phase diagram for NdCoAsO is presented from ambient conditions to P = 53 GPa and T = 10 K.

  2. High-pressure Sapphire Cell for Phase Equilibria Measurements of CO2/Organic/Water Systems

    Pollet, Pamela; Amy L. Ethier; Senter, James C.; Charles A. Eckert; Charles L. Liotta

    2014-01-01

    The high pressure sapphire cell apparatus was constructed to visually determine the composition of multiphase systems without physical sampling. Specifically, the sapphire cell enables visual data collection from multiple loadings to solve a set of material balances to precisely determine phase composition. Ternary phase diagrams can then be established to determine the proportion of each component in each phase at a given condition. In principle, any ternary system can be studied although te...

  3. Raman study of plastic crystal phase of cyclooctanol under high pressure with different compression rate

    Ren, Yufen; Cheng, Xuerui; Yang, Kun; Zhu, Xiang; Li, Haining; Wang, Yongqiang

    2015-12-01

    The cyclooctanol (C8H16O) has been investigated under high pressure with different compression rate using Raman spectroscopy. With lower compression rate, two-phase transformations are observed at around 0.4 and 1.1 GPa respectively. At around 0.4 GPa, solidification was observed while no any change presents in the Raman spectra, indicating plastic crystal phase formed. Further compressing to 1.1 GPa, most Raman peaks become sharper and more intense. Additionally, several new peaks present, meaning one ordered crystal phase occur at this pressure. While with higher compression rate, cyclooctanol maintains the liquid state during compression, indicating superpressuring liquid present. The result indicates compression rate plays one important role in phase transition of cyclooctanol. Finally, the phase transitions under high pressure are reversible. After depressurization to the ambient condition, the vibration spectra will return back to the original structure.

  4. High pressure phase transitions in scheelite structured fluoride: ErLiF4

    Our synchrotron based angle dispersive x-ray diffraction studies on scheelite structured ErLiF4 show that it undergoes two phase transitions, at ~11.5 and ~15.5 GPa to lower symmetry monoclinic phases, before becoming (irreversibly) amorphous at ~28 GPa. The first high pressure phase transformation to the fergusonite structure (space group I2/a) is found to be of thermodynamically second order. The second high pressure phase could be fitted to the P2/c space group, but detailed analysis rules out the wolframite structure (P2/c space group), common to many scheelite compounds under high pressures. We also suggest that despite the ionic character of the LiF4 tetrahedra, the compressibility of LnLiF4 (Ln=Eu–Lu) kind of scheelites is more affected by the LnF8 dodecahedra than the LiF4 tetrahedra. - Graphical abstract: Volume per formula unit of the scheelite and high pressure phases of ErLiF4 as a function of pressure. - Highlights: • ErLiF4 transforms to fergusonite and P2/c phase at high pressure. • Polyhedra of LnF8 affects compressibility of LnLiF4 (Ln=Eu–Lu) more than LiF4. • Amorphization pressure varies inversely in LnLiF4 with ionic size of Ln cation. • In ErLiF4a/c ratio reduces with pressure in contrast to reported increase in YLiF4

  5. Phase transitions in delafossite CuLaO2 at high pressures

    Structural stability of a transparent conducting oxide CuLaO2 at high pressures is investigated using in-situ Raman spectroscopy, electrical resistance, and x-ray diffraction techniques. The present Raman investigations indicate a sequence of structural phase transitions at 1.8 GPa and 7 GPa. The compound remains in the first high pressure phase when pressure is released. Electrical resistance measurements carried out at high pressures confirm the second phase transition. These observations are further supported by powder x-ray diffraction at high pressures which also showed that a-axis is more compressible than c-axis in this compound. Fitting the pressure dependence of unit cell volume to 3rd order Birch-Murnaghan equation of state, zero pressure bulk modulus of CuLaO2 is determined to be 154(25) GPa. The vibrational properties in the ambient delafossite phase of CuLaO2 are investigated using ab-initio calculations of phonon frequencies to complement the Raman spectroscopic measurements. Temperature dependence of the Raman modes of CuLaO2 is investigated to estimate the anharmonicity of Raman modes

  6. The high-pressure phase of alumina and implications for Earth's D″ layer

    Artem R. Oganov; Ono, Shigeaki

    2005-01-01

    Using ab initio simulations and high-pressure experiments in a diamond anvil cell, we show that alumina (Al2O3) adopts the CaIrO3-type structure above 130 GPa. This finding substantially changes the picture of high-pressure behavior of alumina; in particular, we find that perovskite structure is never stable for Al2O3 at zero Kelvin. The CaIrO3-type phase suggests a reinterpretation of previous shock-wave experiments and has important implications for the use of alumina as a window material i...

  7. Phase transitions in Cd3P2 at high pressures and high temperatures

    Yel'kin, F.S.; Sidorov, V.A.; Waskowska, A.;

    2008-01-01

    The high-pressure, high-temperature structural behaviour of Cd3P2 has been studied using electrical resistance measurements, differential thermal analysis, thermo baric analysis and X-ray diffraction. At room temperature, a phase transformation is observed at 4.0 GPa in compression. The experimen......The high-pressure, high-temperature structural behaviour of Cd3P2 has been studied using electrical resistance measurements, differential thermal analysis, thermo baric analysis and X-ray diffraction. At room temperature, a phase transformation is observed at 4.0 GPa in compression....... The experimental zero-pressure bulk modulus of the low-pressure phase is 64.7(7) GPa, which agrees quite well with the calculated value of 66.3 GPa using the tight-binding linear muffin-tin orbital method within the local density approximation. Tentatively, the high-pressure phase has an orthorhombic crystal...... structure with space group Pmmn (#59). The relative volume change at the phase transition is Delta V/V= -5.5%. Amorphization of the sample occurs above 25 GPa. A P-T phase diagram of Cd3P2 has been constructed. A metastable phase is observed at ambient conditions after heating the sample to above 600 K...

  8. First-principles prediction of a high-pressure hydrous phase of AlOOH

    Tsuchiya, Jun; Tsuchiya, Taku

    2011-02-01

    We have predicted a high-pressure hydrous phase of AlOOH stabilizing at ˜170 GPa by first-principles density-functional calculations. The structure predicted has a cubic pyrite-type AlO2 framework with interstitial H atoms forming symmetric hydrogen bonds, whose symmetry is assigned to the space group Pa3¯ (No. 205). The predicted δ-AlOOH to the pyrite-type phase sequence is analogous to a recent theoretical and experimental discovery of high-pressure phase evolution in InOOH and invokes the high-pressure phase relationship in SiO2, but the transition pressure is much greater in AlOOH than in InOOH. Relative enthalpies also indicate that the dissociation of this phase into a CaIrO3-type phase of Al2O3 plus ice X finally occurs at a further pressure of 300 GPa. The present results suggest that AlOOH has an unexpectedly wide stability range in pressure compared to common hydrous materials.

  9. Phase transitions in yttrium oxide at high pressure studied by Raman spectroscopy

    Raman spectra of Y2O3 single crystal were recorded at room temperature in a diamond anvil cell up to a pressure of 22 GPa. Two phase transitions were detected at pressures of 12 and 29 GPa. The different phases were identified with the three structures exhibited by rare-earth (RE) sesquioxides: cubic (C-type), monoclinic (B-type), and rhombohedral (A-type) phases. The first transition corresponds to the C rarrow B transformation and the second transition to the B rarrow A transformation. The reversibility of the two phase transitions as well as the evolution of the Y-O bonds under high pressure is discussed

  10. Structural Phase Transitions in AuIn2 at High Pressure

    Clark, S. M.; Speziale, S.; Voltolini, M.; Godwal, B. K.; Jeanloz, R.

    2007-12-01

    The intermetallic compound AuIn2 provides an analog for the high-pressure phases of SiO2, as it is initially in the Fm3m fluorite (CaF2) structure. Synchrotron-based angular-dispersive x-ray diffraction (Advanced Light Source beamline 12.2.2) reveals subtle anomalies in the pressure variation of normalized stress (F) versus Eulerian strain (f) around 3 GPa, coinciding with anomalies observed in fusion, transport and optical data, and potentially associated with the onset of an electronic phase transition. Our diamond-cell experiments (gasketted sample with methanol-ethanol pressure medium) show continuous broadening of diffraction peaks beyond 12 GPa, leading to amorphization near 24 GPa. On further increase of pressure, a crystalline phase appears around 28 GPa and persists upon unloading from 30 GPa to about 5 GPa, then reverting back to the original CaF2 phase. We find the sequence of pressure-induced phase transition documented for CaF2 (fluorite structure Fm3m - PbCl2 Pnma - Ni2In-type P63/mmc and a combination of PbCl2 and Ni2In) to be inadequate in fitting the observed high-pressure diffraction patterns of AuIn2. However, the post-cotunnite structure of PbCl2, BaCl2, BaBr2 and SnCl2 (P1121/c, Z=8) is able to account for most of the prominent peaks in our high-pressure diffraction patterns (a=10.983, b=9.875, c=4.350, À=96.6). Many oxides of geophysical interest occur in the CaF2 structure, and study of intermetallic compounds such as AuIn2 may prove useful in suggesting high-pressure metallic phases for these oxides.

  11. Phase stability of ε and γ HNIW (CL-20) at high-pressure and temperature

    Hexanitrohexaazaisowurtzitane (CL-20) is one of the few ingredients developed since World War II to be considered for transition to military use. Five polymorphs have been identified for CL-20 by FTIR measurements (α, β, γ, ε, ζ). As CL-20 is transitioned into munitions it will become necessary to predict its response under conditions of detonation, for performance evaluation. Such predictive modeling requires a phase diagram and basic thermodynamic properties of the various phases at high pressure and temperature. Therefore, the epsilon and gamma phases of CL-20 at static high-pressure and temperature were investigated using synchrotron angle-dispersive x-ray diffraction experiments. The samples were compressed and heated using diamond anvil cells (DAC). Pressures and temperatures achieved were around 5 GPa and 240 deg. C, respectively. The epsilon phase was stable to 6.3 GPa at ambient temperature. When heated at ambient pressure the epsilon phase was sustained to a temperature of 120 deg. C then underwent a transition to the gamma phase above 125 deg. C and then thermal decomposition occurred above 150 deg. C. Upon compression, the gamma phase underwent a phase transition at both ambient temperature and 140 deg. C. Pressure--volume data for the epsilon and gamma phase at ambient temperature and the epsilon phase at 75 deg. C were fit to the Birch-Murnaghan formalism to obtain isothermal equations of state

  12. High pressure phase transition in Zr–Ni binary system: A first principle study

    Mukherjee, Debojyoti, E-mail: debojyoti@barc.gov.in; Sahoo, B.D.; Joshi, K.D.; Gupta, Satish C.

    2015-11-05

    Total energy calculations have been performed on zirconium–nickel (with 50% nickel by atom) binary system to examine its structural stability under high pressure. The evolutionary structure search method in conjunction with density functional theory based projector augmented wave (PAW) method suggested that at zero pressure an orthorhombic phase with space group symmetry Cmcm is the lowest enthalpy structure, in agreement with the experiments. Further, it has been predicted that upon compression at ∼10 GPa, this structure will transform to a lower symmetry triclinic phase (space group P-1) which will remain stable up to ∼50 GPa, the maximum pressure of the present calculations. To support the results of our static lattice calculations, we performed lattice dynamic calculations also on Cmcm and P-1 structures. Lattice dynamic calculations correctly showed that at ambient condition the Cmcm phase is dynamically stable. Further, these calculations carried around the Cmcm to P-1 transition pressure predicted that the Cmcm phase will become unstable dynamically due to failure of acoustic zone boundary phonons, suggesting that the Cmcm to P-1 transition is phonon driven. For P-1 phase our calculations showed that this structure is dynamically stable not only at high pressures but also at ambient condition, indicating that at pressure lower than 10 GPa this phase could be a metastable structure. Further, we have calculated the elastic constants for both the phase at various pressures. - Highlights: • Pressure induced phonon driven orthorhombic to triclinic phase transformations in Zr–Ni binary system at ∼10 GPa. • Elastic and lattice dynamic stability of orthorhombic and triclinic phase. • Exploitation of evolutionary structure searching method to explore high pressure phase of Zr–Ni material.

  13. High pressure-low temperature phase diagram of barium: Simplicity versus complexity

    Desgreniers, Serge; Tse, John S.; Matsuoka, Takahiro; Ohishi, Yasuo; Li, Quan; Ma, Yanming

    2015-11-01

    Barium holds a distinctive position among all elements studied upon densification. Indeed, it was the first example shown to violate the long-standing notion that high compression of simple metals should preserve or yield close-packed structures. From modest pressure conditions at room temperature, barium transforms at higher pressures from its simple structures to the extraordinarily complex atomic arrangements of the incommensurate and self-hosting Ba-IV phases. By a detailed mapping of the pressure/temperature structures of barium, we demonstrate the existence of another crystalline arrangement of barium, Ba-VI, at low temperature and high pressure. The simple structure of Ba-VI is unlike that of complex Ba-IV, the phase encountered in a similar pressure range at room temperature. First-principles calculations predict Ba-VI to be stable at high pressure and superconductive. The results illustrate the complexity of the low temperature-high pressure phase diagram of barium and the significant effect of temperature on structural phase transformations.

  14. The Phase Transition of Eu2O3 under High Pressures

    JIANG Sheng; BAI Li-Gang; LIU Jing; XIAO Wan-Sheng; LI Xiao-Dong; LI Yan-Chun; TANG Ling-Yun; ZHANG Yu-Feng; ZHANG De-Chun; ZHENG Li-Rong

    2009-01-01

    Pressure-induced phase transition of cubic Eu2Oa is studied by angle-dispersive x-ray diffraction (ADXD) up to 42.3 GPa at room temperature. A structural transformation from a cubic phase to a hexagonal phase is observed,which starts at 5.0 GPa and finishes at about 13.1 GPa. The phase transition leads to a volume collapse of 9.0% at 8.6 GPa. The hexagonal phase of Eu2O3 maintains stable up to the highest experiment pressure. After release of pressure, the high-pressure phase transforms to a monoclinic phase. The pressure-volume data are fitted with the Birch-Murnaghan equation of state. The bulk moduli obtained upon compression from the fitting are 145(2) GPa and 151(6) GPa for the cubic and hexagonal phases, respectively, when their first pressure derivatives are fixed at 4.

  15. High-pressure high-temperature phase diagram of organic crystal paracetamol

    Smith, Spencer J.; Montgomery, Jeffrey M.; Vohra, Yogesh K.

    2016-01-01

    High-pressure high-temperature (HPHT) Raman spectroscopy studies have been performed on the organic crystal paracetamol in a diamond anvil cell utilizing boron-doped heating diamond anvil. Isobaric measurements were conducted at pressures up to 8.5 GPa and temperature up to 520 K in five different experiments. Solid state phase transitions from monoclinic Form I  →  orthorhombic Form II were observed at various pressures and temperatures as well as transitions from Form II  →  unknown Form IV. The melting temperature for paracetamol was observed to increase with increasing pressures to 8.5 GPa. This new data is combined with previous ambient temperature high-pressure Raman and x-ray diffraction data to create the first HPHT phase diagram of paracetamol.

  16. High-pressure high-temperature phase diagram of organic crystal paracetamol

    High-pressure high-temperature (HPHT) Raman spectroscopy studies have been performed on the organic crystal paracetamol in a diamond anvil cell utilizing boron-doped heating diamond anvil. Isobaric measurements were conducted at pressures up to 8.5 GPa and temperature up to 520 K in five different experiments. Solid state phase transitions from monoclinic Form I  →  orthorhombic Form II were observed at various pressures and temperatures as well as transitions from Form II  →  unknown Form IV. The melting temperature for paracetamol was observed to increase with increasing pressures to 8.5 GPa. This new data is combined with previous ambient temperature high-pressure Raman and x-ray diffraction data to create the first HPHT phase diagram of paracetamol. (paper)

  17. High-pressure and high-temperature study of the phase transition in anhydrite

    The high-pressure and high-temperature behaviors of anhydrite (CaSO4) are studied up to 53.5 GPa and 1800 K using double-sided laser heating Raman spectroscopy and x-ray diffraction in diamond anvil cells. The evidence of phase transition from an anhydrite structure to the monazite type was observed at about 2 GPa under cold compression. Another phase transition and a change in color of the sample from transparent to black have been also observed at a pressure of 33.2 GPa after laser heating. The new phase after laser heating persists to 53.5 GPa and 1800 K

  18. Free energy model for solid high-pressure phases of carbon.

    Schöttler, Manuel; French, Martin; Cebulla, Daniel; Redmer, Ronald

    2016-04-13

    Analytic free energy models for three solid high-pressure phases--diamond, body centered cubic phase with eight atoms in the unit cell (BC8), and simple cubic (SC)--are developed using density functional theory. We explicitly include anharmonic effects by performing molecular dynamics simulations and investigate their density and temperature dependence in detail. Anharmonicity in the nuclear motion shifts the phase transitions significantly compared to the harmonic approximation. Furthermore, we apply a thermodynamically constrained correction that brings the equation of state in accordance with diamond anvil cell experiments. The performance of our thermodynamic functions is validated against Hugoniot experiments. PMID:26974530

  19. Elements, Oxides, Silicates: High Pressure Phases With Implications for the Earth's Interior [Book Review

    Ahrens, Thomas J.

    1988-01-01

    A vitally important aspect of understanding the composition, structure, and processes acting within the solid Earth is obtaining a complete as possible knowledge of the fields of stability of the Earth's component minerals and their high-pressure polymorphs with respect to pressure and temperature. Liu and Bassett's book is the first effort which has focused on bringing together the available phase diagrams for the elements, oxides, and silicates that are relevant to the understanding of Eart...

  20. High-Pressure High-Temperature Phase Diagram of the Organic Crystal Paracetamol

    Smith, Spencer; Montgomery, Jeffrey; Vohra, Yogesh

    High-pressure high-temperature (HPHT) Raman spectroscopy studies have been performed on the organic crystal paracetamol in a diamond anvil cell utilizing boron-doped diamond as heating anvil. The HPHT data obtained from boron-doped diamond heater is cross-checked with data obtained using a standard block heater diamond anvil cell. Isobaric measurements were conducted at pressures up to 8.5 GPa and temperature up to 520 K in a number of different experiments. Solid state phase transitions from monoclinic Form I --> orthorhombic Form II were observed at various pressures and temperatures as well as transitions from Form II --> unknown Form IV. The melting temperature for paracetamol was observed to increase with increasing pressures to 8.5 GPa. Our previous angle dispersive x-ray diffraction studies at the Advanced Photon Source has confirmed the existence of two unknown crystal structures Form IV and Form V of paracetamol at high pressure and ambient temperature. The phase transformation from Form II to Form IV occurs at ~8.5 GPa and from Form IV to Form V occurs at ~11 GPa at ambient temperature. Our new data is combined with the previous ambient temperature high-pressure Raman and X- ray diffraction data to create the first HPHT phase diagram of paracetamol. Doe-NNSA Carnegie DOE Alliance Center (CDAC) under Grant Number DE-NA0002006.

  1. Superconducting H5S2 phase in sulfur-hydrogen system under high-pressure

    Ishikawa, Takahiro; Nakanishi, Akitaka; Shimizu, Katsuya; Katayama-Yoshida, Hiroshi; Oda, Tatsuki; Suzuki, Naoshi

    2016-01-01

    Recently, hydrogen sulfide was experimentally found to show the high superconducting critical temperature (Tc) under high-pressure. The superconducting Tc shows 30–70 K in pressure range of 100–170 GPa (low-Tc phase) and increases to 203 K, which sets a record for the highest Tc in all materials, for the samples annealed by heating it to room temperature at pressures above 150 GPa (high-Tc phase). Here we present a solid H5S2 phase predicted as the low-Tc phase by the application of the genetic algorithm technique for crystal structure searching and first-principles calculations to sulfur-hydrogen system under high-pressure. The H5S2 phase is thermodynamically stabilized at 110 GPa, in which asymmetric hydrogen bonds are formed between H2S and H3S molecules. Calculated Tc values show 50–70 K in pressure range of 100–150 GPa within the harmonic approximation, which can reproduce the experimentally observed low-Tc phase. These findings give a new aspect of the excellent superconductivity in compressed sulfur-hydrogen system. PMID:26983593

  2. Superconducting H5S2 phase in sulfur-hydrogen system under high-pressure.

    Ishikawa, Takahiro; Nakanishi, Akitaka; Shimizu, Katsuya; Katayama-Yoshida, Hiroshi; Oda, Tatsuki; Suzuki, Naoshi

    2016-01-01

    Recently, hydrogen sulfide was experimentally found to show the high superconducting critical temperature (Tc) under high-pressure. The superconducting Tc shows 30-70 K in pressure range of 100-170 GPa (low-Tc phase) and increases to 203 K, which sets a record for the highest Tc in all materials, for the samples annealed by heating it to room temperature at pressures above 150 GPa (high-Tc phase). Here we present a solid H5S2 phase predicted as the low-Tc phase by the application of the genetic algorithm technique for crystal structure searching and first-principles calculations to sulfur-hydrogen system under high-pressure. The H5S2 phase is thermodynamically stabilized at 110 GPa, in which asymmetric hydrogen bonds are formed between H2S and H3S molecules. Calculated Tc values show 50-70 K in pressure range of 100-150 GPa within the harmonic approximation, which can reproduce the experimentally observed low-Tc phase. These findings give a new aspect of the excellent superconductivity in compressed sulfur-hydrogen system. PMID:26983593

  3. A new high-pressure phase transition in natural Fe-bearing orthoenstatite

    Zhang, Jin S.; Dera, Przemyslaw; Bass, Jay D. (UC); (UIUC)

    2016-07-29

    Single-crystal X-ray structure refinements have been carried out on natural Fe-bearing orthoenstatite (OEN) at pressures up to 14.53 GPa. We report a new high-pressure phase transition from OEN to a monoclinic phase (HPCEN2) with space group P2{sub 1}/c, with a density change of {approx}1.9(3)%. The HPCEN2 phase is crystallographically different from low-pressure clinoenstatite (LPCEN), which also has P2{sub 1}/c symmetry. Upon release of pressure HPCEN2 reverts to OEN, and the transition pressure is bracketed between 9.96 and 14.26 GPa at room temperature. We find no evidence for a C2/c phase at high pressure. The lattice constants for the new phase at 14.26 GPa are a = 17.87(2), b = 8.526(9), c = 4.9485(10) {angstrom}, {beta} = 92.88(4){sup o} [{rho} = 3.658(9) g/cm{sup 3}]. Refinement of the new structure indicates rotation of tetrahedral chain as the key characteristic of this transition. This experiment points to the possibility of OEN and HPCEN2 as the stable phases in Earth's upper mantle.

  4. Free energy model for solid high-pressure phases of carbon

    Schöttler, Manuel; French, Martin; Cebulla, Daniel; Redmer, Ronald

    2016-04-01

    Analytic free energy models for three solid high-pressure phases—diamond, body centered cubic phase with eight atoms in the unit cell (BC8), and simple cubic (SC)—are developed using density functional theory. We explicitly include anharmonic effects by performing molecular dynamics simulations and investigate their density and temperature dependence in detail. Anharmonicity in the nuclear motion shifts the phase transitions significantly compared to the harmonic approximation. Furthermore, we apply a thermodynamically constrained correction that brings the equation of state in accordance with diamond anvil cell experiments. The performance of our thermodynamic functions is validated against Hugoniot experiments.

  5. 'Devil's Staircase'-Type Phase Transition in NaV2O5 under High Pressure

    The 'devil's staircase'-type phase transition in the quarter-filled spin-ladder compound NaV2O 5 has been discovered at low temperature and high pressure by synchrotron radiation x-ray diffraction. A large number of transitions are found to successively take place among higher-order commensurate phases with 2a x 2b x zc type superstructures. The observed temperature and pressure dependence of modulation wave number qc, defined by 1/z, is well reproduced by the axial next nearest neighbor Ising model. The qc is suggested to reflect atomic displacements presumably coupled with charge ordering in this system

  6. Free energy model for solid high-pressure phases of carbon

    Analytic free energy models for three solid high-pressure phases—diamond, body centered cubic phase with eight atoms in the unit cell (BC8), and simple cubic (SC)—are developed using density functional theory. We explicitly include anharmonic effects by performing molecular dynamics simulations and investigate their density and temperature dependence in detail. Anharmonicity in the nuclear motion shifts the phase transitions significantly compared to the harmonic approximation. Furthermore, we apply a thermodynamically constrained correction that brings the equation of state in accordance with diamond anvil cell experiments. The performance of our thermodynamic functions is validated against Hugoniot experiments. (paper)

  7. Development of high pressure two-phase choked flow analysis methodology in complex piping system

    Choked flow mechanism, characteristics of two-phase flow sound velocity and compressibility effects on flow through various piping system components are studied to develop analysis methodology for high pressure two-phase choked flow in complex piping system which allows choking flow rate evaluation and piping system design related analysis. Piping flow can be said choked if Mach number is equal to 1 and compressibility effects can be accounted through modified incompressible formula in momentum equation. Based on these findings, overall analysis system is developed to study thermal-hydraulic effects on steady-state piping system flow and future research items are presented. (Author)

  8. High-Pressure Low-Symmetry Phases of Cesium Halides from First Principle Techniques

    Nardelli, M. Buongiorno; Baroni, S.; Giannozzi, P.

    1994-01-01

    The relative stability of different high-pressure phases of various Cesium Halides is studied from first principles and analyzed using the Landau theory of phase transitions. We present results for CsI, CsBr, and CsCl up to pressures of about 100 GPa. A cubic-to-orthorhombic transition, driven by the softening of an acoustic phonon at the M point of the Brillouin zone, is competing with the cubic-to-tetragonal martensitic transition typical of these compounds. The phonon softening takes place...

  9. Phase transition induced strain in ZnO under high pressure.

    Yan, Xiaozhi; Dong, Haini; Li, Yanchun; Lin, Chuanlong; Park, Changyong; He, Duanwei; Yang, Wenge

    2016-01-01

    Under high pressure, the phase transition mechanism and mechanical property of material are supposed to be largely associated with the transformation induced elastic strain. However, the experimental evidences for such strain are scanty. The elastic and plastic properties of ZnO, a leading material for applications in chemical sensor, catalyst, and optical thin coatings, were determined using in situ high pressure synchrotron axial and radial x-ray diffraction. The abnormal elastic behaviors of selected lattice planes of ZnO during phase transition revealed the existence of internal elastic strain, which arise from the lattice misfit between wurtzite and rocksalt phase. Furthermore, the strength decrease of ZnO during phase transition under non-hydrostatic pressure was observed and could be attributed to such internal elastic strain, unveiling the relationship between pressure induced internal strain and mechanical property of material. These findings are of fundamental importance to understanding the mechanism of phase transition and the properties of materials under pressure. PMID:27173609

  10. The high-pressure phase of alumina and implications for Earth's D″ layer

    Oganov, Artem R.; Ono, Shigeaki

    2005-01-01

    Using ab initio simulations and high-pressure experiments in a diamond anvil cell, we show that alumina (Al2O3) adopts the CaIrO3-type structure above 130 GPa. This finding substantially changes the picture of high-pressure behavior of alumina; in particular, we find that perovskite structure is never stable for Al2O3 at zero Kelvin. The CaIrO3-type phase suggests a reinterpretation of previous shock-wave experiments and has important implications for the use of alumina as a window material in shock-wave experiments. In particular, the conditions of the stability of this phase correspond to those at which shock-wave experiments indicated an increase of the electrical conductivity. If this increase is caused by high ionic mobility in the CaIrO3-type phase of Al2O3, similar effect can be expected in the isostructural postperovskite phase of MgSiO3 (which is the dominant mineral phase in the Earth's D″ layer). The effect of the incorporation of Al on the perovskite/postperovskite transition of MgSiO3 is discussed. PMID:16040809

  11. The dynamic response of high pressure phase of Si using phase contrast imaging and X-ray diffraction

    Lee, H. J.; Galtier, E.; Xing, Z.; Gleason, A.; Granados, E.; Tavella, F.; Schropp, A.; Seiboth, F.; Schroer, C.; Higginbotham, A.; Brown, S.; Arnold, B.; Curiel, R.; Peterswright, D.; Fry, A.; Nagler, B.

    2015-11-01

    Static compression studies have revealed that crystalline silicon undergoes phase transitions from a cubic diamond structure to a variety of phases including body-centered tetragonal phase, an orthorhombic phase, and a hexagonal primitive phase. However, the dynamic response of silicon at high pressure is not well understood. Phase contrast imaging has proven to be a powerful tool for probing density changes caused by the shock propagation into a material. With respect to the elastic and plastic compression, we image shock waves in Si with high spatial resolution using the LCLS X-ray free electron laser and Matter in Extreme Conditions instrument. In this study, the long pulse optical laser with pseudoflat top shape creates high pressures up to 60 GPa. We also measure the crystal structure by observing the X-ray diffraction orthogonal to the shock propagation direction over a range of pressure. In this talk, we will present the capability of simultaneously performing phase contrast imaging and in situ X-ray diffraction during shock loading and will discuss the dynamic response of Si in high pressure phases

  12. Phase transformation and fluorescent enhancement of ErF3 at high pressure

    Li, Wentao; Ren, Xiangting; Huang, Yanwei; Yu, Zhenhai; Mi, Zhongying; Tamura, Nobumichi; Li, Xiaodong; Peng, Fang; Wang, Lin

    2016-09-01

    Pressure-induced phase transformation and fluorescent properties of ErF3 were investigated here using in-situ synchrotron X-ray diffraction and photoluminescence up to 32.1 GPa at room temperature. Results showed that ErF3 underwent a reversible pressure-induced phase transition from the β-YF3-type to the fluocerite LaF3-type at 9.8 GPa. The bulk moduli B0 for low- and high-pressure phases were determined to be 130 and 208 GPa, respectively. Photoluminescencent studies showed that new emission lines belonging to the transition of 2H11/2→4I15/2, 4S3/2→4I15/2, and 4F9/2→4I15/2 appeared during phase transition, suggesting pressure-induced electronic band splitting. Remarkably, significant pressure-induced enhancement of photoluminescence was observed, which was attributed to lattice distortion of the material under high pressure.

  13. High-pressure Phase Equilibria for Binary Ethanol System Containing Supercriticai CO2

    朱虎刚; 田宜灵; 陈丽; 秦颖; 冯季军

    2001-01-01

    High-pressure phase behavior of supercritical (SC) CO2+ethanol system was investigated at 333.2 K,348.2K, 353.2K, 368.2K, 413.2K and 453.2K and pressure from 2.0MPa to 14.3MPa. The measurement was carried out in a cylindrical autoclave with a moveable piston and a window for adjustment and observation of phase equilibria at given T and p. The samples were taken from two coexisting phases and were analyzed to obtain their compositions. It is shown that the solubility of SC CO2 in ethanol increases drastically with pressures at the given temperature, but the content of ethanol in CO2-rich phase increase faintly.

  14. Anomalous phase transition of InN nanowires under high pressure

    Tang, Shun-Xi; Zhu, Hong-Yang; Jiang, Jun-Ru; Wu, Xiao-Xin; Dong, Yun-Xuan; Zhang, Jian; Yang, Da-Peng; Cui, Qi-Liang

    2015-09-01

    Uniform InN nanowires were studied under pressures up to 35.5 GPa by using in situ synchrotron radiation x-ray diffraction technique at room temperature. An anomalous phase transition behavior has been discovered. Contrary to the results in the literature, which indicated that InN undergoes a fully reversible phase transition from the wurtzite structure to the rocksalt type structure, the InN nanowires in this study unusually showed a partially irreversible phase transition. The released sample contained the metastable rocksalt phase as well as the starting wurtzite one. The experimental findings of this study also reveal the potentiality of high pressure techniques to synthesize InN nanomaterials with the metastable rocksalt type structure, in addition to the generally obtained zincblende type one. Project supported by the National Natural Science Foundation of China (Grant Nos. 50772043, 51172087, and 11074089).

  15. High-Pressure Torsion of Ti: Synchrotron characterization of phase volume fraction and domain sizes

    Bolmaro, Raúl E.; Sordi, Vitor L.; Ferrante, Maurizio; Brokmeier, Heinz-Günter; Kawasaki, Megumi; Langdon, Terence G.

    2014-08-01

    Rods of grade 2 Ti were processed by Equal-Channel Angular Pressing (ECAP) (phi = 120° at 573 K) employing 2, 4 and 6 passes. The same billets were further deformed by High- Pressure Torsion (HPT) at room temperature, varying both the hydrostatic pressure (1 and 6 GPa) and the number of rotations (n = 1 and 5). The ECAP and HPT samples were studied by synchrotron radiation at DESY-Petra III GEMS line. On the ECAP samples, textures were thus determined while for both ECAP and HPT samples the measurements were further analyzed by MAUD. Domain sizes and phase volume fractions were determined as a function of the radial direction of the samples. Alpha and Omega phases were detected in different amounts depending mostly on hydrostatic pressure and shear deformation. These transition phases can be pressure-induced during HPT processing and the results of Vickers microhardness measurements were related to the processing parameters and to the amounts of these phases.

  16. Structural phase transformations of GaN and InN under high pressure

    We present the results of an ab initio study of the relative stability of structural phases of GaN and InN materials at high pressures. Both the local density and generalized gradient approximations for the exchange-correlation potential have been used in the calculations. The wurtzite, zinc-blende and rocksalt structures are considered. Comparisons with the available experimental data reveal a roughly better agreement with respect to previous calculations. In many cases, the generalized gradient approximation results are found to differ significantly from those of the local density approximation

  17. A Steinberg-Guinan model for High-Pressure Carbon, Diamond Phase

    Orlikowski, D; Correa, A; Schwegler, E; Klepeis, J

    2007-07-27

    Since the carbon, diamond phase has such a high yield strength, dynamic simulations must account for strength even for strong shock waves ({approx} 3 Mbar). We have determined an initial parametrization of two strength models: Steinberg-Guinan (SG) and a modified or improved SG, that captures the high pressure dependence of the calculated shear modulus up to 10 Mbar. The models are based upon available experimental data and on calculated elastic moduli using robust density functional theory. Additionally, we have evaluated these models using hydrodynamic simulations of planar shocks experiments.

  18. Phase Behavior at High Pressure of the Ternary System: CO2, Ionic Liquid and Disperse Dye

    Helen R. Mazzer

    2012-01-01

    Full Text Available High pressure phase behavior experimental data have been measured for the systems carbon dioxide (CO2 + 1-butyl-3-methylimidazolium hexafluorophosphate ([bmim] [PF6] and carbon dioxide (CO2 + 1-butyl-3-methylimidazolium hexafluorophosphate ([bmim] [PF6] + 1-amino-2-phenoxy-4-hydroxyanthraquinone (C.I. Disperse Red 60. Measurements were performed in the pressure up to 18 MPa and at the temperature (323 to 353 K. As reported in the literature, at higher concentrations of carbon dioxide the phase transition pressure increased very steeply. The experimental data for the binary and ternary systems were correlated with good agreement using the Peng-Robinson equation of state. The amount of water in phase behavior of the systems was evaluated.

  19. The high-pressure phase behavior and compressibility of 2,4,6-trinitrotoluene

    Stevens, Lewis L.; Velisavljevic, Nenad; Hooks, Daniel E.; Dattelbaum, Dana M. (LANL)

    2008-10-24

    The phase stability and isothermal compression behavior of 2,4,6-trinitrotoluene (TNT) have been established to 26.5 GPa using angle-dispersive x-ray diffraction. P-V isotherms derived from the high-pressure x-ray spectra displayed a slight density hysteresis around 4.0 GPa and a sharp discontinuity at - 20.0 GPa. The latter transition is ascribed to a monoclinic-to-orthorhombic first-order phase transition in TNT. The conversion of the isothermal P-V data to the shock velocity-particle velocity plane revealed a deviation from linearity at low u{sub p}, a cusp associated with the phase transition at high u{sub p}, and general agreement with the wealth of unreacted Hugoniot data on TNT.

  20. The high-pressure phase stability of 2,4,6-trinitrotoluene (TNT)

    Bowden, P. R.; Chellappa, R. S.; Dattelbaum, D. M.; Manner, V. W.; Mack, N. H.; Liu, Z.

    2014-05-01

    2,4,6-trinitrotoluene (TNT) is a widely used explosive that is relatively insensitive to initiation by shock loading. While the detonation properties of TNT have been extensively reported, the high pressure-temperature (P-T) stability of TNT has not been investigated in detail. At ambient conditions, TNT crystallizes in a monoclinic lattice (space group P21/a), and our previous X-ray diffraction (XRD) measurements at room temperature suggested a phase transition to orthorhombic (space group Pca21) at ~20 GPa. In this work, we have performed in-situ synchrotron XRD and vibrational spectroscopy measurements along the room temperature isotherm to investigate phase stabilities up to 18 GPa. While our Raman spectroscopy measurements indicate spectral changes at ~2 GPa, careful XRD measurements reveal that the monoclinic phase persists up to 10 GPa.

  1. The high-pressure phase stability of 2,4,6-trinitrotoluene (TNT)

    2,4,6-trinitrotoluene (TNT) is a widely used explosive that is relatively insensitive to initiation by shock loading. While the detonation properties of TNT have been extensively reported, the high pressure-temperature (P-T) stability of TNT has not been investigated in detail. At ambient conditions, TNT crystallizes in a monoclinic lattice (space group P21/a), and our previous X-ray diffraction (XRD) measurements at room temperature suggested a phase transition to orthorhombic (space group Pca21) at ∼20 GPa. In this work, we have performed in-situ synchrotron XRD and vibrational spectroscopy measurements along the room temperature isotherm to investigate phase stabilities up to 18 GPa. While our Raman spectroscopy measurements indicate spectral changes at ∼2 GPa, careful XRD measurements reveal that the monoclinic phase persists up to 10 GPa.

  2. Nanosecond Ultrasonics to Study Phase Transitions in Solid and Liquid Systems at High Pressure and Temperature

    This report describes the development of a high-frequency ultrasonic measurement capability for application to the study of phase transitions at elevated pressure and temperature. We combined expertise in various aspects of static high-pressure technique with recent advances in wave propagation modeling, ultrasonic transducer development, electronic methods and broadband instrumentation to accomplish the goals of this project. The transduction and electronic systems have a demonstrated bandwidth of 400 MHz, allowing investigations of phenomena with characteristic times as short as 2.5 nS. A compact, pneumatically driven moissanite anvil cell was developed and constructed for this project. This device generates a high-pressure environment for mm dimension samples to pressures of 3 GPa. Ultrasonic measurements were conducted in the moissanite cell, an LLNL multi-anvil device and in a modified piston cylinder device. Measurements for water, and elemental tantalum, tin and cerium demonstrate the success of the methods. The γ-α phase transition in cerium was clearly detected at ∼0.7 GPa with 75 MHz longitudinal waves. These results have direct application to important problems in LLNL programs, as well as seismology and planetary science

  3. Nanosecond Ultrasonics to Study Phase Transitions in Solid and Liquid Systems at High Pressure and Temperature

    Bonner, B P; Berge, P A; Carlson, S C; Farber, D L; Akella, J

    2007-03-21

    This report describes the development of a high-frequency ultrasonic measurement capability for application to the study of phase transitions at elevated pressure and temperature. We combined expertise in various aspects of static high-pressure technique with recent advances in wave propagation modeling, ultrasonic transducer development, electronic methods and broadband instrumentation to accomplish the goals of this project. The transduction and electronic systems have a demonstrated bandwidth of 400 MHz, allowing investigations of phenomena with characteristic times as short as 2.5 nS. A compact, pneumatically driven moissanite anvil cell was developed and constructed for this project. This device generates a high-pressure environment for mm dimension samples to pressures of 3 GPa. Ultrasonic measurements were conducted in the moissanite cell, an LLNL multi-anvil device and in a modified piston cylinder device. Measurements for water, and elemental tantalum, tin and cerium demonstrate the success of the methods. The {gamma}-{alpha} phase transition in cerium was clearly detected at {approx}0.7 GPa with 75 MHz longitudinal waves. These results have direct application to important problems in LLNL programs, as well as seismology and planetary science.

  4. Phase relations in the Fe-FeSi system at high pressures and temperatures

    Fischer, Rebecca A.; Campbell, Andrew J.; Reaman, Daniel M.; Miller, Noah A.; Heinz, Dion L.; Dera, Przymyslaw; Prakapenka, Vitali B. (UC); (Maryland)

    2016-07-29

    The Earth's core is comprised mostly of iron and nickel, but it also contains several weight percent of one or more unknown light elements, which may include silicon. Therefore it is important to understand the high pressure, high temperature properties and behavior of alloys in the Fe–FeSi system, such as their phase diagrams. We determined melting temperatures and subsolidus phase relations of Fe–9 wt% Si and stoichiometric FeSi using synchrotron X-ray diffraction at high pressures and temperatures, up to ~200 GPa and ~145 GPa, respectively. Combining this data with that of previous studies, we generated phase diagrams in pressure–temperature, temperature–composition, and pressure–composition space. We find the B2 crystal structure in Fe–9Si where previous studies reported the less ordered bcc structure, and a shallower slope for the hcp+B2 to fcc+B2 boundary than previously reported. In stoichiometric FeSi, we report a wide B2+B20 two-phase field, with complete conversion to the B2 structure at ~42 GPa. The minimum temperature of an Fe–Si outer core is 4380 K, based on the eutectic melting point of Fe–9Si, and silicon is shown to be less efficient at depressing the melting point of iron at core conditions than oxygen or sulfur. At the highest pressures reached, only the hcp and B2 structures are seen in the Fe–FeSi system. We predict that alloys containing more than ~4–8 wt% silicon will convert to an hcp+B2 mixture and later to the hcp structure with increasing pressure, and that an iron–silicon alloy in the Earth's inner core would most likely be a mixture of hcp and B2 phases.

  5. Phase relations in the Fe-FeSi system at high pressures and temperatures

    Fischer, Rebecca A.; Campbell, Andrew J.; Reaman, Daniel M.; Miller, Noah A.; Heinz, Dion L.; Dera, Przymyslaw; Prakapenka, Vitali B.

    2013-07-01

    The Earth's core is comprised mostly of iron and nickel, but it also contains several weight percent of one or more unknown light elements, which may include silicon. Therefore it is important to understand the high pressure, high temperature properties and behavior of alloys in the Fe-FeSi system, such as their phase diagrams. We determined melting temperatures and subsolidus phase relations of Fe-9 wt% Si and stoichiometric FeSi using synchrotron X-ray diffraction at high pressures and temperatures, up to ~200 GPa and ~145 GPa, respectively. Combining this data with that of previous studies, we generated phase diagrams in pressure-temperature, temperature-composition, and pressure-composition space. We find the B2 crystal structure in Fe-9Si where previous studies reported the less ordered bcc structure, and a shallower slope for the hcp+B2 to fcc+B2 boundary than previously reported. In stoichiometric FeSi, we report a wide B2+B20 two-phase field, with complete conversion to the B2 structure at ~42 GPa. The minimum temperature of an Fe-Si outer core is 4380 K, based on the eutectic melting point of Fe-9Si, and silicon is shown to be less efficient at depressing the melting point of iron at core conditions than oxygen or sulfur. At the highest pressures reached, only the hcp and B2 structures are seen in the Fe-FeSi system. We predict that alloys containing more than ~4-8 wt% silicon will convert to an hcp+B2 mixture and later to the hcp structure with increasing pressure, and that an iron-silicon alloy in the Earth's inner core would most likely be a mixture of hcp and B2 phases.

  6. High-pressure phase transitions of CaRhO3 perovskite

    Shirako, Yuichi; Kojitani, Hiroshi; Akaogi, Masaki; Yamaura, Kazunari; Takayama-Muromachi, Eiji

    2009-09-01

    High-pressure phase transitions of CaRhO3 perovskite were examined at pressures of 6-27 GPa and temperatures of 1,000-1,930°C, using a multi-anvil apparatus. The results indicate that CaRhO3 perovskite successively transforms to two new high-pressure phases with increasing pressure. Rietveld analysis of powder X-ray diffraction data indicated that, in the two new phases, the phase stable at higher pressure possesses the CaIrO3-type post-perovskite structure (space group Cmcm) with lattice parameters: a = 3.1013(1) Å, b = 9.8555(2) Å, c = 7.2643(1) Å, V m = 33.43(1) cm3/mol. The Rietveld analysis also indicated that CaRhO3 perovskite has the GdFeO3-type structure (space group Pnma) with lattice parameters: a = 5.5631(1) Å, b = 7.6308(1) Å, c = 5.3267(1) Å, V m = 34.04(1) cm3/mol. The third phase stable in the intermediate P, T conditions between perovskite and post-perovskite has monoclinic symmetry with the cell parameters: a = 12.490(3) Å, b = 3.1233(3) Å, c = 8.8630(7) Å, β = 103.96(1)°, V m = 33.66(1) cm3/mol ( Z = 6). Molar volume changes from perovskite to the intermediate phase and from the intermediate phase to post-perovskite are -1.1 and -0.7%, respectively. The equilibrium phase relations determined indicate that the boundary slopes are large positive values: 29 ± 2 MPa/K for the perovskite—intermediate phase transition and 62 ± 6 MPa/K for the intermediate phase—post-perovskite transition. The structural features of the CaRhO3 intermediate phase suggest that the phase has edge-sharing RhO6 octahedra and may have an intermediate structure between perovskite and post-perovskite.

  7. The phase diagram of solid hydrogen at high pressure: A challenge for first principles calculations

    Azadi, Sam; Foulkes, Matthew

    2015-03-01

    We present comprehensive results for the high-pressure phase diagram of solid hydrogen. We focus on the energetically most favorable molecular and atomic crystal structures. To obtain the ground-state static enthalpy and phase diagram, we use semi-local and hybrid density functional theory (DFT) as well as diffusion quantum Monte Carlo (DMC) methods. The closure of the band gap with increasing pressure is investigated utilizing quasi-particle many-body calculations within the GW approximation. The dynamical phase diagram is calculated by adding proton zero-point energies (ZPE) to static enthalpies. Density functional perturbation theory is employed to calculate the proton ZPE and the infra-red and Raman spectra. Our results clearly demonstrate the failure of DFT-based methods to provide an accurate static phase diagram, especially when comparing insulating and metallic phases. Our dynamical phase diagram obtained using fully many-body DMC calculations shows that the molecular-to-atomic phase transition happens at the experimentally accessible pressure of 374 GPa. We claim that going beyond mean-field schemes to obtain derivatives of the total energy and optimize crystal structures at the many-body level is crucial. This work was supported by the UK engineering and physics science research council under Grant EP/I030190/1, and made use of computing facilities provided by HECTOR, and by the Imperial College London high performance computing centre.

  8. Correlated structural and electronic phase transformations in transition metal chalcogenide under high pressure

    Li, Chunyu; Ke, Feng; Hu, Qingyang; Yu, Zhenhai; Zhao, Jinggeng; Chen, Zhiqiang; Yan, Hao

    2016-04-01

    Here, we report comprehensive studies on the high-pressure structural and electrical transport properties of the layered transition metal chalcogenide (Cr2S3) up to 36.3 GPa. A structural phase transition was observed in the rhombohedral Cr2S3 near 16.5 GPa by the synchrotron angle dispersive X-ray diffraction measurement using a diamond anvil cell. Through in situ resistance measurement, the electric resistance value was detected to decrease by an order of three over the pressure range of 7-15 GPa coincided with the structural phase transition. Measurements on the temperature dependence of resistivity indicate that it is a semiconductor-to-metal transition in nature. The results were also confirmed by the electronic energy band calculations. Above results may shed a light on optimizing the performance of Cr2S3 based applications under extreme conditions.

  9. High pressure Raman scattering study on the phase stability of LuVO 4

    Rao, Rekha; Garg, Alka B.; Sakuntala, T.; Achary, S. N.; Tyagi, A. K.

    2009-07-01

    High pressure Raman spectroscopic investigations have been carried out on rare earth orthovanadate LuVO 4 upto 26 GPa. Changes in the Raman spectrum around 8 GPa across the reported zircon to scheelite transition are investigated in detail and compared with those observed in other vanadates. Co-existence of the zircon and scheelite phases is observed over a pressure range of about 8-13 GPa. The zircon to scheelite transition is irreversible upon pressure release. Subtle changes are observed in the Raman spectrum above 16 GPa which could be related to scheelite ↔ fergusonite transition. Pressure dependencies of the Raman active modes in the zircon and the scheelite phases are reported.

  10. Turbulence modelling of high-pressure convective boiling two-phase flows

    This article is a contribution to the modelling of multidimensional high-pressure convective boiling two-phase flows relative to PWR's thermal hydraulics conditions. Postulating that the turbulence is one possible physical mechanism for heat removal from the wall towards the two-phase flow core, this work focuses on modelling turbulent transport terms in the momentum and energy balance equations. Using the pioneering work of Sato et al., the momentum and the energy balance equations are derived for a two-phase mixture. Such a system can be expressed as a combination of parameters, which include the local void fraction as well as the fluid velocity profile, the wall shear stress and the eddy diffusivity. By specifying a closure relation for this last parameter, a numerical solution can be obtained. As a preliminary step towards a numerical solution, the turbulent structure of the two-phase flow is expressed as a linear superposition of an inherent liquid turbulence and an additional one due to the bubble agitation. On the basis of this theory, the mixture velocity and temperature profiles can be predicted provided that the local void fraction and the wall shear stress are known. The model is then tested against the experimental data bank DEBORA (Garnier et al.,) which is devoted to the study of high pressure boiling flows. The first results are encouraging for the mechanical part but some discrepancies are observed on temperature profiles for boiling tests. This work should be continued in order to (i) improve the model especially for the thermal aspects and (ii) identify the key parameters responsible for the heat flux limitation (DNB). (author)

  11. The high-pressure phase transformations of PbO2

    Using a diamond-anvil high-pressure cell, an in situ X-ray diffraction study of PbO2 to about 240 kbar at room temperature has revealed the following phase transformations: rutile → αPbO2 → tetragonal fluorite → cubic fluorite with increasing pressure. The volume change for the transition rutile → αPbO2 is about -2% and for the transition αPbO2 → tetragonal fluorite is about -6%, nearly constant within the pressure range of investigation. The volume difference between the tetragonal and the cubic fluorite-type phases is negligibly small. Both the tetragonal and the cubic fluorite-type phases cannot be preserved after removal of the pressure, even after heating by the laser. Both phases have been found to revert to αPbO2 at one atmospheric pressure. Optically, the colour of αPbO2 changes from an opaque black to transparent red with increasing pressure. The tetragonal fluorite-type phase, which exists in the pressure range between about 90 and 180 kbar at room temperature, is slightly transparent with very dark red or brown colour, and the cubic fluorite-type phase is dark red and transparent. (orig.)

  12. Novel high-pressure phases of AlP from first principles

    Liu, Chao; Hu, Meng; Luo, Kun; Yu, Dongli; Zhao, Zhisheng; He, Julong

    2016-05-01

    By utilizing a crystal structure prediction software via particle swarm optimization, this study proposes three new high-pressure phases of aluminum phosphide (AlP) with high density and high hardness, in addition to previously proposed phases (wz-, zb-, rs-, NiAs-, β-Sn-, CsCl-, and Cmcm-AlP). These new phases are as follows: (1) an I 4 ¯ 3d symmetric structure (cI24-AlP) at 55.2 GPa, (2) an R 3 ¯ m symmetric structure (hR18-AlP) at 9.9 GPa, and (3) a C222 symmetric structure (oC12-AlP) at 20.6 GPa. Based on first-principle calculations, these phases have higher energetic advantage than CsCl- and β-Sn-AlP at ambient pressure. The independent elastic constants and phonon dispersion spectra are calculated to check the mechanical and dynamic stabilities of these phases. According to mechanical property studies, these new AlP phases have higher hardness than NiAs-AlP, and oC12-AlP has the highest hardness of 7.9 GPa. Electronic band structure calculations indicate that NiAs- and hR18-AlP have electrical conductivity. Additionally, wz-, zb-, and oC12-AlP possess semiconductive properties with indirect bandgaps, and cI24-AlP has a semiconductive property with a direct bandgap.

  13. The high pressure-temperature phase behavior of 2,4,6-trinitrotoluene (TNT)

    Bowden, Patrick; Chellappa, Raja; Dattelbaum, Dana; Manner, Virginia; Mack, Nathan; Liu, Zhenxian

    2013-06-01

    2,4,6-trinitrotoluene (TNT) is a widely used explosive that is relatively insensitive to initiation by shock loading. While the detonation properties of TNT have been extensively reported, the high pressure-temperature (P - T) stability of TNT has not been investigated in detail. In addition, there are no studies that have determined the effects of pressure on the stability of the liquid phase. At ambient conditions, TNT crystallizes in a monoclinic lattice (space group P21 / a) , and our previous x-ray diffraction (XRD) measurements at room temperature suggested a phase transition to orthorhombic (space group Pca21) at ~20 GPa. In this work, we have performed in situ synchrotron XRD and vibrational spectroscopy measurements at various P - T conditions along isothermal and isobaric pathways to confirm previously reported phase transitions, and investigate phase stabilities up to 30 GPa and 500°C. Using all the available data, we have established the first comprehensive high P - T phase diagram of TNT, including the melting line as a function of pressure. While our synchrotron IR and Raman spectroscopy measurements indicate spectral changes at ~2 GPa, careful XRD measurements (hydrostatic, He medium and non-hydrostatic) reveal that the monoclinic phase is likely stable up to 20 GPa. We will present a self-consistent P - V - T equation of state derived from the reported structural and vibrational data.

  14. Structure determination of the high-pressure phase of CdSe

    Structural phase transition sequence of CdSe has been investigated at pressures up to 60 GPa under quasi-hydrostatic conditions using synchrotron X-ray diffraction. A phase transition from the wurtzite type (B4) to the NaCl-type (B1) structure has been observed, followed by another phase transition to an orthorhombic structure at 27 GPa, in agreement with previous reports. We show that this high-pressure orthorhombic phase has a Pnma symmetry rather than being a Cmcm-symmetric structure as previously suggested. From our observations, the appearance of the new reflections and reflection splitting with increasing pressure is due to the change of atomic relative positions in crystal lattice and the difference in the compression ratio of lattice parameters for the Pnma structure, and we find no evidence for the third phase transition reported previously. The pressure-induced phase transition of CdSe has been further confirmed by the density-functional theory calculations.

  15. Phase transition and equation of state of paratellurite (TeO2) under high pressure

    Liu, Xun; Mashimo, Tsutomu; Kawai, Nobuaki; Sekine, Toshimori; Zeng, Zhaoyi; Zhou, Xianming

    2016-07-01

    The Hugoniot data for TeO2 single crystals were obtained for pressures up to ∼85 GPa along both the (a-axis) and (c-axis) directions using a velocity interferometer system for any reflector and inclined-mirror method combined with a powder gun or two-stage light gas gun. The Hugoniot-elastic limit of TeO2 was determined to be 3.3–4.3 GPa along the c-axes. The shock velocity (U s) versus particle velocity (U p) relation for TeO2 shows a kink around U p = 1.0 km s‑1, which suggests a phase transition completes at ∼26 ± 2 GPa. The Hugoniot relations of the low and high pressure phase are given by U s = 3.13(5) + 1.10(6)U p for U p 1.0 km s‑1, respectively. First-principles geometry optimizations based on the generalized gradient approximation after Perdew, Burke and Ernzerhof method were also performed on TeO2. It suggested that a continuous structure distortion occurs up to 22 GPa, and the lattice parameters b and c abruptly increase and decrease at 22 GPa, respectively, indicating a first-order phase transition to the cotunnite structure phase. The equation of state of the cotunnite phase TeO2 is discussed based on the experimental and simulation results.

  16. High-pressure phase transition of MH3 (M: Er, Ho)

    Hou, Pugeng; Tian, Fubo; Li, Da; Chu, Binhua; Zhao, Zhonglong; Liu, Bingbing; Cui, Tian

    2014-08-01

    Motivated by the potential high temperature superconductivity in hydrogen-rich materials, high-pressure structures of ErH3 and HoH3 were studied by using genetic algorithm method. Our calculations indicate that both ErH3 and HoH3 transform from P-3c1 structure to a monoclinic C2/m structure at about 15 GPa, and then transforms into a cubic Fm-3m structure at about 40 GPa. ErH3 and HoH3 adopt the same P63/mmc structure with space group P63/mmc at above about 220 and 196 GPa, respectively. For ErH3, the P63/mmc phase is stable up to at least 300 GPa, while for HoH3, a phase transformation P63/mmc → Cmcm occurs at about 216 GPa, and the Cmcm phase is stable up to at least 300 GPa. The P-3c1 ErH3 and HoH3 are calculated to demonstrate non-metallic character, and the other phases are all metallic phases.

  17. Synthesis of Novel Extended Phases of Molecular Solids at High Pressures and Temperatures

    This study is for in-situ investigation of chemical bonding and molecular structure of low z-elements and simple molecular solids at high pressures and temperatures using 3rd-generation synchrotron x-ray diffraction. To understand the contribution of the empty d-electron orbital of Mg in relation to the formation of molecular solids like MgO, which is one of the important Earth lower mantle materials and MgB2, which has recently been the focus of intense superconducting material research, we have performed double-sided laser heating experiments using a diamond anvil cell (DAC). Understanding the structural stability and the formation of the above Mg-compounds requires studying Mg itself as well as the relevant compounds. BL10XU at the Spring-8 was used to study phase stability and make accurate equation of state (EOS) determinations of Mg coupled with external heating and the double-sided laser heating technique. Monochromatic x-ray at 30 keV (0.4135 (angstrom)) was focused to about 40 (micro)m at the sample and the diffracted x-ray were recorded using a high-resolution image plate (3000 x 3000 pixels with a 0.1 mm resolution per pixel). EOS parameters for hcp and bcc Mg were determined by fitting to a Birch-Murnaghan equation. An isothermal compression of Mg at 300 K up to 100 GPa provides EOS parameters (B0, B0(prime), and V0) comparable for both hcp and bcc phases, which is similar to the cases for hcp and fcc phases measured in cobalt and xenon. Similar EOS parameters for both low and high pressure phases with a very small or no measurable volume discontinuity at the phase transition pressure suggests that the hcp-bcc structural transition of Mg may be driven by a stacking fault due to a shear instability as seen in xenon and cobalt. Compared to the recent estimation determined using a large volume press [1], our B0 is smaller by more than 10% suggesting that the difference may be due to non-hydrostatic conditions. The phase boundary of Mg up to 650 K was

  18. High pressure phase diagram of CeCoGe2.2Si0.8

    We have investigated the temperature-pressure phase diagram of the heavy fermion compound CeCoGe2.2Si0.8 by DC magnetic susceptibility measurements, χDC(T), under high pressure. The Néel temperature of TN = 4 K in zero pressure is reduced by pressure up to 3 kbar. At higher pressures antiferromagnetic order appears to gradually transform into a spin glass like-state. Magnetic field decreases both TN and the spin glass freezing temperature Tf. At 3 T and 6.5 kbar a divergence of χDC(T) is observed with a power law that is consistent with a disorder-dominated quantum criticality.

  19. High-Pressure Phase Behavior of Polycaprolactone, Carbon Dioxide, and Dichloromethane Ternary Mixture Systems

    Gwon, JungMin; Kim, Hwayong [Seoul National University, Seoul (Korea, Republic of); Shin, Hun Yong [Seoul National University of Science and Technology, Seoul (Korea, Republic of); Kim, Soo Hyun [Korea Institute of Science and Technology, Seoul (Korea, Republic of)

    2015-04-15

    The high-pressure phase behavior of a polycaprolactone (Mw=56,145 g/mol, polydispersity 1.2), dichloromethane, and carbon dioxide ternary system was measured using a variable-volume view cell. The experimental temperatures and pressures ranged from 313.15 K to 353.15 K and up to 300 bar as functions of the CO{sub 2}/dichloromethane mass ratio and temperature, at poly(D-lactic acid) weight fractions of 1.0, 2.0, and 3.0%. The correlation results were obtained from the hybrid equation of state (Peng-Robinson equation of state + SAFT equation of state) for the CO{sub 2}-polymer system using the van der Waals one-fluid mixing rule. The three binary interaction parameters were optimized by the simplex method algorithm.

  20. A dynamic study of the warm-up phase of a high-pressure mercury lamp

    A time-dependent two-dimensional computational fluid model has been adopted to investigate the dynamic behavior of the high-pressure mercury lamp during the last phase of the warm-up period. The model solves the combined momentum, continuity, energy, and electric field equations for the plasma and the energy equation for the wall. Two models have been compared. The first takes convection into account and is called ''convection model.'' The second, which neglects this term, is termed ''convectionless model.'' Good agreement between the predictions and experimental data from literature has been obtained. It is found that the convection affects the lamp performance by increasing the mercury losses behind the electrodes and the mercury-evaporation time.

  1. High-pressure phase equilibrium data for the (carbon dioxide + L-lactide + ethanol) system

    Highlights: • Equilibrium data are important for polymerization of L-lactide at high pressure. • Addition of ethanol causes a reduction in pressure to obtain a homogeneous region. • Experimental results were modeled using the Peng–Robinson (PR) equation of state. - Abstract: Experimental phase equilibrium values (cloud points) for the ternary system involving carbon dioxide, L-lactide and ethanol have been measured in order to provide fundamental values to conduct the polymerization reaction in supercritical carbon dioxide medium. The experiments were performed using a variable-volume view cell over the temperature range from 323 K to 353 K, system pressure between 9 MPa and 25.0 MPa and different mole ratios of ethanol to L-lactide (0.5:1, 1:1 and 1.5:1). Phase transitions of vapour-liquid types were observed. The experimental results were modelled using the Peng–Robinson (PR) equation of state with the Wong–Sandler (PR–WS) mixing rule, providing a good representation of the experimental phase equilibrium values

  2. High-pressure light scattering apparatus to study pressure-induced phase separation in polymer solutions

    Xiong, Yan; Kiran, Erdogan

    1998-03-01

    A new high-pressure time- and angle-resolved light scattering apparatus has been developed to study the kinetics of phase separation in polymer solutions and other fluid mixtures under pressure at near- and supercritical conditions. The system consists of a high-pressure polymer loading chamber, a solvent charge line, a variable-volume scattering cell (with a built-in movable piston connected to a pressure generator, and an expansion rod driven by an air-actuated diaphragm), and a recirculation pump which are all housed in a temperature-controlled oven. The system is operable at pressures up to 70 MPa, and temperatures up to 473 K. The scattering cell is a short path-length cell made of two flat sapphire windows that are separated by 250 μm. It is designed to permit measurements of transmitted and scattered light intensities over an angle range from 0° to 30°. A linear image sensor with 256 elements is used to monitor the time evolution of the scattered light intensities at different angles. With this sensor, the angle range from 2° to 13° is scanned at a sampling rate of 3.2 ms/scan. The pressure quenches are achieved by movement of the air-actuated movable expansion rod, or by the movement of the piston with the aid of the pressure generator to bring about either rapid (at rates approaching 2000 MPa/s) or slow pressure changes in the system. Quench depth is also adjustable, and very deep (70 MPa) or very shallow (as low as 0.1 MPa) pressure quenches are readily achievable. The temperature and the pressure of the solution in the scattering cell, and the transmitted and scattered light intensities at different angles are recorded in real time through a computerized data acquisition system before and during phase separation. The experimental system is especially suited to follow the kinetics of phase separation in polymer solutions and to assess the metastable and unstable regions where phase separation proceeds by the nucleation and growth, and the spinodal

  3. Hexagonal ice transforms at high pressures and compression rates directly into "doubly metastable" ice phases.

    Bauer, Marion; Winkel, Katrin; Toebbens, Daniel M; Mayer, Erwin; Loerting, Thomas

    2009-12-14

    We report compression and decompression experiments of hexagonal ice in a piston cylinder setup in the temperature range of 170-220 K up to pressures of 1.6 GPa. The main focus is on establishing the effect that an increase in compression rate up to 4000 MPa/min has on the phase changes incurred at high pressures. While at low compression rates, a phase change to stable ice II takes place (in agreement with earlier comprehensive studies), we find that at higher compression rates, increasing fractions and even pure ice III forms from hexagonal ice. We show that the critical compression rate, above which mainly the metastable ice III polymorph is produced, decreases by a factor of 30 when decreasing the temperature from 220 to 170 K. At the highest rate capable with our equipment, we even find formation of an ice V fraction in the mixture, which is metastable with respect to ice II and also metastable with respect to ice III. This indicates that at increasing compression rates, progressively more metastable phases of ice grow from hexagonal ice. Since ices II, III, and V differ very much in, e.g., strength and rheological properties, we have prepared solids of very different mechanical properties just by variation in compression rate. In addition, these metastable phases have stability regions in the phase diagrams only at much higher pressures and temperatures. Therefore, we anticipate that the method of isothermal compression at low temperatures and high compression rates is a tool for the academic and industrial polymorph search with great potential. PMID:20001064

  4. Investigation of new phases in the Ba-Si phase diagram under high pressure using ab initio structural search.

    Shi, Jingming; Cui, Wenwen; Flores-Livas, José A; San-Miguel, Alfonso; Botti, Silvana; Marques, Miguel A L

    2016-03-01

    Barium silicides are versatile materials that have attracted attention for a variety of applications in electronics and optoelectronics. Using an unbiased structural search based on a particle-swarm optimization algorithm combined with density functional theory calculations, we investigate systematically the ground-state phase stability and the structural diversity of Ba-Si binaries under high pressure. The phase diagram turns out to be quite intricate, with several compositions stabilizing/destabilizing as a function of pressure. In particular, we identify novel phases of BaSi, BaSi2, BaSi3, and BaSi5 that might be synthesizable experimentally over a wide range of pressures. Our results not only clarify and complete the previously known structural phase diagram, but also provide new insights for understanding the Ba-Si binary system. PMID:26923068

  5. Phase Transitions of Triflate-Based Ionic Liquids under High Pressure.

    Faria, Luiz F O; Ribeiro, Mauro C C

    2015-11-01

    Raman spectroscopy has been used to study phase transitions of ionic liquids based on the triflate anion, [TfO](-), as a function of pressure or temperature. Raman spectra of ionic liquids containing the cations 1-butyl-3-methylimidazolium, [C4C1Im](+), 1-octyl-3-methylimidazolium, [C8C1Im](+), 1-butyl-2,3-dimethylimidazolium, [C4C1C1Im](+), and 1-butyl-1-methylpyrrolidinium, [C4C1Pyr](+), were compared. Vibrational frequencies and binding energy of ionic pairs were calculated by quantum chemistry methods. The ionic liquids [C4C1Im][TfO] and [C4C1Pyr][TfO] crystallize at 1.0 GPa when the pressure is increased in steps of ∼ 0.2 GPa from the atmospheric pressure, whereas [C8C1Im][TfO] and [C4C1C1Im][TfO] do not crystallize up to 2.3 GPa of applied pressure. The low-frequency range of the Raman spectrum of [C4C1Im][TfO] indicates that the system undergoes glass transition, rather than crystallization, when the pressure applied on the liquid has been increased above 2.0 GPa in a single step. Strong hysteresis of spectral features (frequency shift and bandwidth) of the high-pressure crystalline phase when the pressure was released stepwise back to the atmospheric pressure has been found . PMID:26457868

  6. Strength and structural phase transitions of gadolinium at high pressure from radial X-ray diffraction

    Lattice strength and structural phase transitions of gadolinium (Gd) were determined under nonhydrostatic compression up to 55 GPa using an angle-dispersive radial x-ray diffraction technique in a diamond-anvil cell at room temperature. Three new phases of fcc structure, dfcc structure, and new monoclinic structure were observed at 25 GPa, 34 GPa, and 53 GPa, respectively. The radial x-ray diffraction data yield a bulk modulus K0 = 36(1) GPa with its pressure derivate K0′ = 3.8(1) at the azimuthal angle between the diamond cell loading axis and the diffraction plane normal and diffraction plane ψ = 54.7°. With K0′ fixed at 4, the derived K0 is 34(1) GPa. In addition, analysis of diffraction data with lattice strain theory indicates that the ratio of differential stress to shear modulus (t/G) ranges from 0.011 to 0.014 at pressures of 12–55 GPa. Together with estimated high-pressure shear moduli, our results show that Gd can support a maximum differential stress of 0.41 GPa, while it starts to yield to plastic deformation at 16 GPa under uniaxial compression. The yield strength of Gd remains approximately a constant with increasing pressure, and reaches 0.46 GPa at 55 GPa

  7. Phase equilibrium data and thermodynamic modeling of the system (CO2 + biodiesel + methanol) at high pressures

    Highlights: → We measured phase behavior for the system involving {CO2 + biodiesel + methanol}. → The saturation pressures were obtained using a variable-volume view cell. → The experimental data were modeled using PR-vdW2 and PR-WS equations of state. - Abstract: The main objective of this work was to investigate the high pressure phase behavior of the binary systems {CO2(1) + methanol(2)} and {CO2(1) + soybean methyl esters (biodiesel)(2)} and the ternary system {CO2(1) + biodiesel(2) + methanol(3)} were determined. Biodiesel was produced from soybean oil, purified, characterized and used in this work. The static synthetic method, using a variable-volume view cell, was employed to obtain the experimental data in the temperature range of (303.15 to 343.15) K and pressures up to 21 MPa. The mole fractions of carbon dioxide were varied according to the systems as follows: (0.2383 to 0.8666) for the binary system {CO2(1) + methanol(2)}; (0.4201 to 0.9931) for the binary system {CO2(1) + biodiesel(2)}; (0.4864 to 0.9767) for the ternary system {CO2(1) + biodiesel(2) + methanol(3)} with a biodiesel to methanol molar ratio of (1:3); and (0.3732 to 0.9630) for the system {CO2 + biodiesel + methanol} with a biodiesel to methanol molar ratio of (8:1). For these systems, (vapor + liquid), (liquid + liquid), (vapor + liquid + liquid) transitions were observed. The phase equilibrium data obtained for the systems were modeled using the Peng-Robinson equation of state with the classical van der Waals (PR-vdW2) and Wong-Sandler (PR-WS) mixing rules. Both thermodynamic models were able to satisfactorily correlate the phase behavior of the systems investigated and the PR-WS presented the best performance.

  8. High pressure monoclinic phases of Sb{sub 2}Te{sub 3}

    Souza, S.M.; Poffo, C.M.; Triches, D.M. [Departamento de Engenharia Mecanica, Universidade Federal de Santa Catarina, Campus Universitario Trindade, S/N, C.P. 476, 88040-900 Florianopolis, Santa Catarina (Brazil); Lima, J.C. de, E-mail: fsc1jcd@fisica.ufsc.br [Departamento de Fisica, Universidade Federal de Santa Catarina, Campus Universitario Trindade, S/N, C.P. 476, 88040-900 Florianopolis, Santa Catarina (Brazil); Grandi, T.A. [Departamento de Fisica, Universidade Federal de Santa Catarina, Campus Universitario Trindade, S/N, C.P. 476, 88040-900 Florianopolis, Santa Catarina (Brazil); Polian, A.; Gauthier, M. [Physique des Milieux Denses, IMPMC, CNRS-UMR 7590, Universite Pierre et Marie Curie-Paris 6, 4 Place Jussieu, 75252 Paris Cedex 05 (France)

    2012-09-15

    The effect of pressure on nanostructured rhombohedral {alpha}-Sb{sub 2}Te{sub 3} (phase I) was investigated using X-ray diffraction (XRD) and Raman spectroscopy (RS) up to 19.2 and 25.5 GPa, respectively. XRD patterns showed two new high pressure phases (named phases II and III). From a Rietveld refinement of XRD patterns of {alpha}-Sb{sub 2}Te{sub 3}, the unit cell volume as a function of pressure was obtained and the values were fitted to a Birch-Murnaghan equation of state (BM-EOS). The best fit was obtained for bulk modulus B{sub 0}=36.1{+-}0.9 GPa and its derivative B{sub 0}{sup Prime }=6.2{+-}0.4 (not fixed). Using the refined structural data for {alpha}-Sb{sub 2}Te{sub 3}, for pressures up to 9.8 GPa, changes in the angle of succession [Te-Sb-Te-Sb-Te], in the interaromic distances of Sb and Te atoms belonging to this angle of succession and in the interatomic distances of atoms located on the c axis were examined. This analysis revealed an electronic topological transition (ETT) along the a and c axes at close to 3.7 GPa. From the RS spectra, the full widths at half maximum (FWHM) of the Raman active modes of {alpha}-Sb{sub 2}Te{sub 3} were plotted as functions of pressure and showed an ETT along the a and c axes at close to 3.2 GPa. The XRD patterns of phases II and III were well reproduced assuming {beta}-Bi{sub 2}Te{sub 3} and {gamma}-Bi{sub 2}Te{sub 3} structures similar to those reported in the literature for {alpha}-Bi{sub 2}Te{sub 3}.

  9. Mirrored continuum and molecular scale simulations of the ignition of high-pressure phases of RDX

    Lee, Kibaek; Joshi, Kaushik; Chaudhuri, Santanu; Stewart, D. Scott

    2016-05-01

    We present a mirrored atomistic and continuum framework that is used to describe the ignition of energetic materials, and a high-pressure phase of RDX in particular. The continuum formulation uses meaningful averages of thermodynamic properties obtained from the atomistic simulation and a simplification of enormously complex reaction kinetics. In particular, components are identified based on molecular weight bin averages and our methodology assumes that both the averaged atomistic and continuum simulations are represented on the same time and length scales. The atomistic simulations of thermally initiated ignition of RDX are performed using reactive molecular dynamics (RMD). The continuum model is based on multi-component thermodynamics and uses a kinetics scheme that describes observed chemical changes of the averaged atomistic simulations. Thus the mirrored continuum simulations mimic the rapid change in pressure, temperature, and average molecular weight of species in the reactive mixture. This mirroring enables a new technique to simplify the chemistry obtained from reactive MD simulations while retaining the observed features and spatial and temporal scales from both the RMD and continuum model. The primary benefit of this approach is a potentially powerful, but familiar way to interpret the atomistic simulations and understand the chemical events and reaction rates. The approach is quite general and thus can provide a way to model chemistry based on atomistic simulations and extend the reach of those simulations.

  10. Traction and nonequilibrium phase behavior of confined sheared liquids at high pressure

    Gattinoni, Chiara; Heyes, David M.; Lorenz, Christian D.; Dini, Daniele

    2013-11-01

    Nonequilibrium molecular dynamics simulations of confined model liquids under pressure and sheared by the relative sliding of the boundary walls have been carried out. The relationship between the time-dependent traction coefficient, μ(t), and the state of internal structure of the film is followed from commencement of shear for various control parameters, such as applied load, global shear rate, and solid-liquid atom interaction parameters. Phase diagrams, velocity and temperature profiles, and traction coefficient diagrams are analyzed for pure Lennard-Jones (LJ) liquids and a binary LJ mixture. A single component LJ liquid is found to form semicrystalline arrangements with high-traction coefficients, and stick-slip behavior is observed for high pressures and low-shear velocities, which is shown to involve periodic deformation and stress release of the wall atoms and slip in the solid-liquid boundary region. A binary mixture, which discourages crystallization, gives a more classical tribological response with the larger atoms preferentially adsorbing commensurate with the wall. The results obtained are analyzed in the context of tribology: the binary mixture behaves like a typical lubricant, whereas the monatomic system behaves like a traction fluid. It is discussed how this type of simulation can give insights on the tribological behavior of realistic systems.

  11. High-pressure electron-resonance studies of electronic, magnetic, and structural phase transitions. Progress report

    Research is described in development of a high-pressure electron-resonance probe capable of operating down to 1.50K temperatures. The apparatus has been used to measure the EPR of a sample of DPPH at room temperature and zero pressure. EPR has been used to measure valence field instabilities in alloy systems. Studies have been done on metal-insulator transitions at high pressure, and are briefly described

  12. Prediction of new high pressure phase of TaB{sub 3}: First-principles

    Zhang, Xiaozheng [College of Science, Inner Mongolia University of Technology, Hohhot 010051 (China); State Key Laboratory of Rare Earth Resource Utilization, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun 130022 (China); Zhao, Erjun, E-mail: ejzhao@yahoo.com [College of Science, Inner Mongolia University of Technology, Hohhot 010051 (China); Wu, Zhijian, E-mail: zjwu@ciac.ac.cn [State Key Laboratory of Rare Earth Resource Utilization, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun 130022 (China)

    2015-05-25

    Highlights: • Crystal structure of TaB{sub 3} is predicted using the evolutionary algorithm USPEX code. • The structural and mechanical properties of tantalum borides are investigated by DFT. • The stable phases are found by enthalpy-pressure relationship and convex hull. • oC16–TaB{sub 3} has a estimated hardness (41.2 GPa) and indentation strength (22.8 GPa). • High pressure is advantageous to syntheses of ruthenium Triborides oC16–TaB{sub 3}. - Abstract: The phase stability, elastic, mechanical, dynamical and electronic properties of tantalum borides, i.e., Ta{sub 2}B, TaB, Ta{sub 3}B{sub 4}, Ta{sub 5}B{sub 6}, TaB{sub 2} and TaB{sub 3}, have been investigated by first-principles. The calculated convex hull indicates that at ambient conditions, the ground state phases are tI12–Ta{sub 2}B, oC8–TaB, oC22–Ta{sub 5}B{sub 6}, oI14–Ta{sub 3}B{sub 4}, and hP3–TaB{sub 2}; while at 75 GPa, they are tI12–Ta{sub 2}B, oC8–TaB, oC22–Ta{sub 5}B{sub 6}, oI14–Ta{sub 3}B{sub 4}, hP3–TaB{sub 2} and oC16–TaB{sub 3}; oC8–TaB, oC22–Ta{sub 5}B{sub 6}, oI14–Ta{sub 3}B{sub 4}, oC16–TaB{sub 3} are the most stable phases at 120 GPa. The enthalpy-pressure relationship reveals that the hP3–TaB{sub 2} is the most stable below 75 GPa, while the predicted oC16–TaB{sub 3} becomes the most stable above 75 GPa. Combining the estimated hardness (41.2 GPa) and indentation strength (22.8 GPa) for oC16–TaB{sub 3}, it is suggested that oC16–TaB{sub 3} is hard or potential superhard. Since it is not available experimentally, further experimental synthesis could be rewarding.

  13. Melting phase relations in the system H2O - NH3 at high pressure

    Sugimura, E.; Hirose, K.; Komabayashi, T.; Ohishi, Y.; Hirao, N.; Dubrovinsky, L. S.

    2012-12-01

    The density models of Uranus and Neptune constrained by their gravitational moments from Voyager mission suggest that mantles of these planets may be predominantly comprised of water (H2O), methane (CH4), and ammonia (NH3). The impurities in pure water would greatly influence the phase relations in the water-rich system expected in the icy mantle, which must be known to construct a plausible planetary model. One of important effects of the impurity is on the liquidus temperature (Tliq), since it decides the actual presence of solid phase within the icy mantle. In order to determine Tliq in H2O-rich region of the H2O - CH4 - NH3 ternary system, the melting phase relations in the H2O - CH4 and H2O - NH3 systems must be accurately known. However, previous melting experiments on each binary system were limited to several gigapascals, thus need to be explored to higher P-T conditions for application in interiors of Uranus and Neptune. We have investigated high-pressure (P) and -temperature (T) melting phase relations in the H2O - NH3 system based on a combination of visual observation and angle-dispersive x-ray diffraction (XRD) measurements at BL10XU, SPring-8. High-P-T conditions were generated in an externally-resistive heated diamond anvil cell (DAC). Starting material was 20wt% NH3 aqueous solution whose composition was checked via Tliq of the solution measured in a DAC at near atmospheric pressure. The aqueous solution was loaded into a gold-lined hole in a preindented rhenium gasket in order to insulate the sample from rhenium. Pressure was determined from the unit-cell volume of gold liner. Melting and freezing of the sample were detected by monitoring disappearance/appearance of diffraction peaks of solid and diffuse scattering of liquids, as well as observing melting/crystallization of crystal grains under microscope. Up to 20 GPa at room temperature, in addition to ice VII, diffraction peaks of bcc-like phase, which is most likely to be the reported phase VI

  14. Effect of Nb additions on the microstructure, thermal stability and mechanical behavior of high pressure Zr phases under ambient conditions

    Research highlights: → We analyze the influence of Nb additions on the shear-induced α → ω → β phase transformations in pure Zr by high pressure torsion (HPT). → Nb reduces the transition pressures and increases the transformation kinetics. → High pressure phases are retained under ambient conditions due to the presence of an internal stress. → Post-HPT annealing allows to fabricate bimodal/biphase nanostructures with enhanced mechanical behavior. - Abstract: This paper analyzes the influence of Nb on the shear-induced α → ω → β transformation taking place when processing Zr by high pressure torsion (HPT) under suitable conditions of pressure and shear. With that purpose, pure Zr and Zr-2.5%Nb were processed by HPT at room temperature and at pressures ranging from 0.25 to 6 GPa using 5 anvil turns. Nb causes a further reduction of the transition pressures, which are already lower when applying shear besides pressure. Thus, the transition pressure to the β phase is reduced at least 100 times in the Zr-Nb alloy. Alloying with Nb decreases the grain size of the transformed phases, significantly enhances their thermal stability and increases their UTS and elongation to failure. Selected post-HPT annealing treatments lead to the development of very tough, multiphase Zr and Zr-Nb with bimodal grain size distributions. The retention of the high pressure phases under ambient conditions is explained by the development of a high internal stress during processing. This stress is measured by synchrotron radiation diffraction at HZB-BESSY II. It is proposed that the presence of Nb reduces the internal stress level required for the retention of the high pressure phases.

  15. 77 FR 3281 - High Pressure Steel Cylinders From China; Scheduling of the Final Phase of Countervailing Duty...

    2012-01-23

    ... 7, 2011. See 76 FR 61937 (Oct. 6, 2011) and the newly revised Commission's Handbook on E-Filing... COMMISSION High Pressure Steel Cylinders From China; Scheduling of the Final Phase of Countervailing Duty and... cylinders, provided for in subheading 7311.00.00 of the Harmonized Tariff Schedule of the United...

  16. Quenching ilmenite with a high-temperature and high-pressure phase using super-high-energy ball milling.

    Hashishin, Takeshi; Tan, Zhenquan; Yamamoto, Kazuhiro; Qiu, Nan; Kim, Jungeum; Numako, Chiya; Naka, Takashi; Valmalette, Jean Christophe; Ohara, Satoshi

    2014-01-01

    The mass production of highly dense oxides with high-temperature and high-pressure phases allows us to discover functional properties that have never been developed. To date, the quenching of highly dense materials at the gramme-level at ambient atmosphere has never been achieved. Here, we provide evidence of the formation of orthorhombic Fe2TiO4 from trigonal FeTiO3 as a result of the high-temperature (>1250 K) and high-pressure (>23 GPa) condition induced by the high collision energy of 150 gravity generated between steel balls. Ilmenite was steeply quenched by the surrounding atmosphere, when iron-rich ilmenite (Fe2TiO4) with a high-temperature and high-pressure phase was formed by planetary collisions and was released from the collision points between the balls. Our finding allows us to infer that such intense planetary collisions induced by high-energy ball milling contribute to the mass production of a high-temperature and high-pressure phase. PMID:24763088

  17. Mechanical behaviors and phase transition of Ho{sub 2}O{sub 3} nanocrystals under high pressure

    Yan, Xiaozhi [Institute of Atomic and Molecular Physics, Sichuan University, Chengdu 610065 (China); Center for High Pressure Science and Technology Advanced Research (HPSTAR), 1690 Cailun Rd., Pudong, Shanghai 201203 (China); Ren, Xiangting [Institute of Atomic and Molecular Physics, Sichuan University, Chengdu 610065 (China); He, Duanwei, E-mail: duanweihe@scu.edu.cn, E-mail: yangwg@hpstar.ac.cn [Institute of Atomic and Molecular Physics, Sichuan University, Chengdu 610065 (China); Institute of Fluid Physics and National Key Laboratory of Shockwave and Detonation Physic, China Academy of Engineering Physics, Mianyang 621900 (China); Chen, Bin [Center for High Pressure Science and Technology Advanced Research (HPSTAR), 1690 Cailun Rd., Pudong, Shanghai 201203 (China); Yang, Wenge, E-mail: duanweihe@scu.edu.cn, E-mail: yangwg@hpstar.ac.cn [Center for High Pressure Science and Technology Advanced Research (HPSTAR), 1690 Cailun Rd., Pudong, Shanghai 201203 (China); High Pressure Synergetic Consortium (HPSynC), Geophysical Laboratory, Carnegie Institution of Washington, 9700 S Cass Avenue, Argonne, Illinois 60439 (United States)

    2014-07-21

    Mechanical properties and phase transition often show quite large crystal size dependent behavior, especially at nanoscale under high pressure. Here, we have investigated Ho{sub 2}O{sub 3} nanocrystals with in-situ x-ray diffraction and Raman spectroscopy under high pressure up to 33.5 GPa. When compared to the structural transition routine cubic -> monoclinic -> hexagonal phase in bulk Ho{sub 2}O{sub 3} under high pressure, the nano-sized Ho{sub 2}O{sub 3} shows a much higher onset transition pressure from cubic to monoclinic structure and followed by a pressure-induced-amorphization under compression. The detailed analysis on the Q (Q = 2π/d) dependent bulk moduli reveals the nanosized Ho{sub 2}O{sub 3} particles consist of a clear higher compressible shell and a less compressible core. Insight into these phenomena shed lights on micro-mechanism studies of the mechanical behavior and phase evolution for nanomaterials under high pressure, in general.

  18. Development and testing of a new apparatus for the measurement of high-pressure low-temperature phase equilibria

    Fonseca, José M.S.; von Solms, Nicolas

    2012-01-01

    A new apparatus for the study of high-pressure phase equilibria at low temperatures using an analytical method was designed, assembled and tested. The apparatus was specially developed for the study of multi-phase equilibria in systems containing hydrocarbons, water and hydrate inhibitors, at tem...... the study of the system methane+water. An equilibrium point for the quaternary system methane+n-hexane+methanol+water is also presented....

  19. On the use of distorted fcc structures for describing high-pressure phases

    The paper describes distorted lattices that can be derived from the face-centred cubic Bravais lattice. Crystallographic principles are outlined and it is discussed how various lattices can be identified from the observed splitting of X-ray powder diffraction lines. Examples are taken from recent high-pressure studies of actinide rocksalt structure compounds and cerium metal. (orig.)

  20. An approximate approach of heat transfer accompanied by phase transition

    Low temperature heat (solar energy, geothermal energy, industrial and domestic waste heat) is widely available for many applications. Energy storage of that heat is now of great importance because the key to the effective and widespread use of low temperature heat is its adaptation to the energy requirements. From this point of view, storage tanks based on the phase change principal are one interesting alternative. Phase change material (PCM) is particularly attractive due to its ability to provide a high-energy storage density and its characteristics to store heat at a constant temperature corresponding to the phase transition temperature of the heat storage material. That is why the problem of the heat transfer accompanied by phase transition is of mine interest to the practice. Heat storage system with the PCM and shell-and-tube type is analysed by Lacroix [6]. Several authors, using mathematical models of different complexity, studied this type of. latent heat storage unit. Heat-of-fusion storage materials for law temperature storage in the temperature range 0-120oC are reviewed by Abhat [5] and Reiter and Rota [4]. Hamdan and Elweer [3] have investigated a melting process of a solid phase. In the present study, the phase change problem of the PCM is analysed in another type of heat storage system. We use closed tubes (capsules) filled with PCM and the heat transfer fluid (HTF) flowing in the shell space of the heat exchanger (Fig.1). The heat process is analysed in terms of both radial and axial direction and is linked to the convective heat transfer from the HTF. As it is known [2,3] the transient heat transfer in PCM can be described by the well-known heat conduction equation applied for various phase conditions and the energy balance on the interface given by the Stephan's equation. The later determines the rate of moving of the interface and in this manner the space areas where the heat conduction equations have corresponding coefficients. The application

  1. A new phase of ThC at high pressure predicted from a first-principles study

    Guo, Yongliang; Qiu, Wujie; Ke, Xuezhi; Huai, Ping; Cheng, Cheng; Han, Han; Ren, Cuilan; Zhu, Zhiyuan

    2015-08-01

    The phase transition of thorium monocarbide (ThC) at high pressure has been studied by means of density functional theory. Through structure search, a new phase with space group P 4 / nmm has been predicted. The calculated phonons demonstrate that this new phase and the previous B2 phase are dynamically stable as the external pressure is greater than 60 GPa and 120 GPa, respectively. The transformation from B1 to P 4 / nmm is predicted to be a first-order transition, while that from P 4 / nmm to B2 is found to be a second-order transition.

  2. Phase changes induced by guest orientational ordering of filled ice Ih methane hydrate under high pressure and low temperature

    Low-temperature and high-pressure experiments were performed with filled ice Ih structure of methane hydrate under pressure and temperature conditions of 2.0 to 77.0 GPa and 30 to 300 K, respectively, using diamond anvil cells and a helium-refrigeration cryostat. Distinct changes in the axial ratios of the host framework were revealed by In-situ X-ray diffractometry. Splitting in the CH vibration modes of the guest methane molecules, which was previously explained by the orientational ordering of the guest molecules, was observed by Raman spectroscopy. The pressure and temperature conditions at the split of the vibration modes agreed well with those of the axial ratio changes. The results indicated that orientational ordering of the guest methane molecules from orientational disordered-state occurred at high pressures and low temperatures, and that this guest ordering led to the axial ratio changes in the host framework. Existing regions of the guest disordered-phase and the guest ordered-phase were roughly estimated by the X-ray data. In addition, above the pressure of the guest-ordered phase, another high pressure phase was developed at a low-temperature region. The deuterated-water host samples were also examined and isotopic effects on the guest ordering and phase changes were observed.

  3. High-Pressure Phase Equilibria in Systems Containing CO2 and Ionic Liquids

    Sedláková, Zuzana; Wagner, Zdeněk; Aim, Karel

    Catalogue : Zagreb Inventors Association, 2011, s. 131. [International Invention Show (silver medal awarded) /36./. Zagreb (HR), 09.11.2011-12.11.2011] R&D Projects: GA ČR GP203/09/P141; GA AV ČR IAA400720710 Institutional research plan: CEZ:AV0Z40720504 Keywords : high pressure * ionic liquid * carbon dioxide Subject RIV: CF - Physical ; Theoretical Chemistry

  4. Study of film thickness on fuel rod under high pressure and high temperature steam-water two phase flow

    The liquid film thickness on the fuel rod is measured by ultrasonic echo technique under high temperature and high pressure steam-water two phase flow. As quality is increased, film thickness is decreased. The film thickness is about 0.2 mm at 9% of quality under 1 MPa. It was found from test data that disturbance wave is not measured clearly and change of film is small. (author)

  5. Metamagnetic behaviour and phase diagram of Lu.sub.2./sub.Fe.sub.17./sub. under high pressure

    Kamarád, Jiří; Arnold, Zdeněk; Medvedeva, I. V.; Kuchin, A. G.

    242-245, - (2002), s. 876-878. ISSN 0304-8853 R&D Projects: GA ČR GA202/99/0184; GA AV ČR IAA1010018 Grant ostatní: RFBR(RU) 99-02-16935 Institutional research plan: CEZ:AV0Z1010914 Keywords : magnetic phase diagram * high pressure * metamagnetism * rare-earth intermetallic compounds Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 1.046, year: 2002

  6. Ergot alkaloids in rye flour determined by solid phase cation-exchange and high pressure liquid chromatography with fluorescence detection

    Storm, Ida Drejer; Have Rasmussen, Peter; Strobel, Bjarne W.; Hansen, Hans Christian Bruun

    2008-01-01

    Abstract Ergot alkaloids (EAs) are mycotoxins which are unavoidable contaminants of cereal products, particularly rye. A method was compiled employing clean-up by cation-exchange solid phase extraction, separation by high-pressure liquid chromatography under alkaline conditions and fluorescence detection. It is capable of separating and quantifying both C8-isomers of ergocornine, a-ergocryptine, ergocristine, ergonovine, and ergotamine. The average recovery was 61?10 % with limits ...

  7. High-Pressure Torsion of Ti: Synchrotron characterization of phase volume fraction and domain sizes

    Bolmaro, Raúl E; Sordi, Vitor L.; Ferrante, Maurizio; Brokmeier, Heinz-Günter; Kawasaki, Megumi; Terence G. Langdon

    2014-01-01

    Rods of grade 2 Ti were processed by Equal-Channel Angular Pressing (ECAP) (phi = 120° at 573 K) employing 2, 4 and 6 passes. The same billets were further deformed by High- Pressure Torsion (HPT) at room temperature, varying both the hydrostatic pressure (1 and 6 GPa) and the number of rotations (n = 1 and 5). The ECAP and HPT samples were studied by synchrotron radiation at DESY-Petra III GEMS line. On the ECAP samples, textures were thus determined while for both ECAP and HPT samples the m...

  8. High-pressure phase transition and properties of spinel ZnMn2O4

    Åbrink, S.; Waskowska, A.; Gerward, Leif;

    1999-01-01

    X-ray photoelectron spectroscopy, magnetic measurements, and a single-crystal x-ray structure determination at normal pressure have shown that Jahn-Teller active manganese ions in ZnMn2O4 are present in one valence state (III) on the octahedral sites of the spinel structure. The high-pressure beh......X-ray photoelectron spectroscopy, magnetic measurements, and a single-crystal x-ray structure determination at normal pressure have shown that Jahn-Teller active manganese ions in ZnMn2O4 are present in one valence state (III) on the octahedral sites of the spinel structure. The high...

  9. The piston-cylinder apparatus for in-situ structural investigations of high-pressure phases of gas hydrates with the use of synchrotron radiation

    Mirinski, D S; Larionova, E G; Kurnosov, A V; Ancharov, A I; Dyadin, Y A; Tolochko, B P; Sheromov, M A

    2001-01-01

    The piston-cylinder apparatus for the investigation of high-pressure gas hydrate phases by the powder diffraction method is presented. The first results concerning the nature of the high-pressure gas hydrate phase in the sulfur hexafluoride-water system are reported.

  10. The stability of Al,Fe-bearing phase H and a new pyrite-type hydroxide at high pressures

    Nishi, M.; Kuwayama, Y.; Tsuchiya, J.; Irifune, T.

    2015-12-01

    Water plays an important role in the structure, dynamics, and evolution of planets because hydrogen can affect the physical properties and stabilities of constituent minerals in the planets. Since alumimous phase H (MgSiO4H2-AlOOH) is stable over the entire pressure range of the lower mantle, the hydrated subducting plate may deliver a certain amount of water into the bottom of the Earth's mantle (Tsuchiya 2013, Nishi et al. 2013, Ohira et al. 2014, Walter et al. 2015). Compositional analysis of phase H grains synthesized from natural serpentine shows the presence of the Fe component in this phase (Nishi et al., 2015). This result suggests that phase H would also form solid solutions with ɛ-FeOOH, since ɛ-FeOOH is isostructural to phase H and δ-AlOOH. Moreover, an ab initio calculation has recently predicted that the new high pressure form of AlOOH, which has pyrite-type structure, would be stabilized at pressures above 170 GPa (Tsuchiya and Tsuchiya, 2011). Although this pyrite-type hydroxide has been found in InOOH, this structure in AlOOH has not been reported by experimental studies. Here we examine the composition and stability of Al,Fe-bearing phase H using a multi-anvil apparatus combined with sintered diamond anvils. Results show that large amounts of Fe and Al are partitioned into phase H relative to bridgmanite. Fe likely affects the stability of phase H in the lower mantle. Also, we conducted high pressure experiments on pure δ-AlOOH by using laser-heated diamond anvil cell (DAC) techniques up to 200 GPa and 2,500 K. In-situ X-ray diffraction (XRD) measurements indicated that the transition from the δ-AlOOH to the pyrite-type structure occurs at high pressures above 190 GPa. Our experimental results exhibited a density reduction of 2.6 wt.% through the structural transition, and both experimental data plots and theoretical calculations showed similar compressibilities of δ-AlOOH and pyrite-type AlOOH. In recent years, hundreds of extra

  11. Two-phase convection in the high-pressure ice layer of the large icy moons: geodynamical implications

    Kalousova, K.; Sotin, C.; Tobie, G.; Choblet, G.; Grasset, O.

    2015-12-01

    The H2O layers of large icy satellites such as Ganymede, Callisto, or Titan probably include a liquid water ocean sandwiched between the deep high-pressure ice layer and the outer ice I shell [1]. It has been recently suggested that the high-pressure ice layer could be decoupled from the silicate core by a salty liquid water layer [2]. However, it is not clear whether accumulation of liquids at the bottom of the high-pressure layer is possible due to positive buoyancy of water with respect to high-pressure ice. Numerical simulation of this two-phase (i.e. ice and water) problem is challenging, which explains why very few studies have self-consistently handled the presence and transport of liquids within the solid ice [e.g. 3]. While using a simplified description of water production and transport, it was recently showed in [4] that (i) a significant fraction of the high-pressure layer reaches the melting point and (ii) the melt generation and its extraction to the overlying ocean significantly influence the global thermal evolution and interior structure of the large icy moons.Here, we treat the high-pressure ice layer as a compressible mixture of solid ice and liquid water [5]. Several aspects are investigated: (i) the effect of the water formation on the vigor of solid-state convection and its influence on the amount of heat that is transferred from the silicate mantle to the ocean; (ii) the fate of liquids within the upper thermal boundary layer - whether they freeze or reach the ocean; and (iii) the effect of salts and volatile compounds (potentially released from the rocky core) on the melting/freezing processes. Investigation of these aspects will allow us to address the thermo-chemical evolution of the internal ocean which is crucial to evaluate the astrobiological potential of large icy moons. This work has been performed at the Jet Propulsion Laboratory, California Institute of Technology, under contract to NASA. [1] Hussmann et al. (2007), Treatise of

  12. Thermal expansion study on high-pressure phases of SmS

    We have measured the thermal expansion coefficient αL(T) of SmS under pressure up to 21.6kbar. In the golden phase, an excitation gap Δ inferred from αL(T) decreases with increasing pressure. When the system enters the metallic phase from the golden phase, Δ collapses suddenly to zero, and simultaneously, a huge sharp anomaly appears in the αL(T) curve, reflecting the magnetic phase transition

  13. Natural gas exploitation by carbon dioxide from gas hydrate fields - high-pressure phase equilibrium for an ethane hydrate system

    Natural gas hydrate fields which have a large amount of methane and ethane deposits in the subterranean Arctic and in the bottom of the sea at various places in the world, have become the object of public attention as a potential natural gas resource. Here the idea of natural gas exploitation from natural gas hydrate fields combined with CO2 isolation using CO2 hydrate has been presented. As a fundamental study, high-pressure phase behaviour for the ethane hydrate system was investigated in a high-pressure cell up to a maximum pressure of 100 MPa, following a previous study of CO2 and methane hydrates. Consequently, the phase equilibrium relationship of an ethane hydrate-water-liquid ethane mixture was obtained in the temperature range from 290.4 to 298.4 K and over a pressure range of 19.48 to 83.75 MPa. The observed phase boundary corresponds to the three-phase coexisting line with non-variant quadruple point of ethane hydrate-water-liquid ethane-gaseous ethane at 288.8 K and 3.50 MPa, similar to the CO2 hydrate-water-liquid CO2 system. (Author)

  14. Ambient-condition growth of high-pressure phase centrosymmetric crystalline KDP microstructures for optical second harmonic generation.

    Ren, Yan; Zhao, Xian; Hagley, Edward W; Deng, Lu

    2016-08-01

    Noncentrosymmetric potassium dihydrogen phosphate (KH2PO4 or KDP) in the tetragonal crystal phase is arguably the most extensively studied nonlinear optical crystal in history. It has prolific applications ranging from simple laser pointers to laser inertial confinement fusion systems. Recently, type IV high-pressure KDP crystal sheets with a monoclinic crystal phase having centrosymmetric properties have been observed. However, it was found that this new crystal phase is highly unstable under ambient conditions. We report ambient-condition growth of one-dimensional, self-assembled, single-crystalline KDP hexagonal hollow/solid-core microstructures that have a molecular structure and symmetry identical to the type IV KDP monoclinic crystal that was previously found to exist only at extremely high pressures (>1.6 GPa). Furthermore, we report highly efficient bulk optical second harmonic generation (SHG) from these ambient condition-grown single-crystalline microstructures, even though they have a highly centrosymmetric crystal phase. However, fundamental physics dictates that a bulk optical medium with a significant second-order nonlinear susceptibility supporting SHG must have noncentrosymmetric properties. Laue diffraction analysis reveals a weak symmetry-breaking twin-crystal lattice that, in conjunction with tight confinement of the light field by the tubular structure, is attributed to the significant SHG even with sample volumes <0.001 mm(3). A robust polarization-preserving effect is also observed, raising the possibility of advanced optical technological applications. PMID:27574703

  15. Formation of metastable phases in magnesium–titanium system by high-pressure torsion and their hydrogen storage performance

    No binary phases exist in the Mg–Ti binary equilibrium phase diagram and the two elements are totally immiscible even in liquid form. This study shows that four metastable phases (two with the bcc and fcc structures and two with the hcp structures) are formed in the Mg–Ti system by severe plastic deformation (SPD) through the process of high-pressure torsion (HPT). Investigation of hydrogenation properties reveals that these metastable phases are decomposed to pure Mg and Ti during heating before they can absorb the hydrogen in the form of ternary Mg–Ti hydrides. First-principles calculations show that the hydrogenation reaction should occur thermodynamically, and ternary Mg–Ti hydrides with the cubic structure should form at low temperature. However, the slow kinetics for this reaction appears to be the limiting step. Calculations show that the binding energy of hydrogen increases and the thermodynamic stability of hydrides undesirably increases by addition of Ti to Mg

  16. Structural phase transitions of ionic layered PbFX (X = Cl−or Br–) compounds under high pressure

    The PbFX (X = Cl–or Br–) compounds crystallize in tetragonal structure with space group P4/nmm. High pressure X-ray diffraction studies carried out on PbFCl compound reveals that it undergoes pressure induced structural transitions at ∼18 GPa and ∼38 GPa to orthorhombic and monoclinic (P21/m) phases respectively. Like PbFCl, a similar phase transition from tetragonal to orthorhombic phase is observed in PbFBr at intermediate pressure. These phase transitions seem to be similar to the transitions involving other matlockite structure compounds such as BaFX (X = Cl–, Br–or I–). PbFCl has a larger structural stability range compared to BaFCl and is attributed to the large anisotropic coordination of the Pb2+ and Cl–ions

  17. Modelling three-phase releases of carbon dioxide from high-pressure pipelines

    Martynov, S.; S. Brown; Mahgerefteh, H.; Sundara, V.; Chen, S.; Zhang, Y.

    2014-01-01

    This paper describes the development and experimental validation of a three-phase flow model for predicting the transient outflow following the failure of pressurised CO2 pipelines and vessels. The choked flow parameters at the rupture plane, spanning the dense-phase and saturated conditions to below the triple point, are modelled by maximisation of the mass flowrate with respect to pressure and solids mass fraction at the triple point. The pertinent solid/vapour/liquid phase equilibrium data...

  18. High-pressure phase of the cubic spinel NiMn2O4

    Åsbrink, S.; Waskowska, A.; Olsen, J. Staun;

    1998-01-01

    It has been observed that the fee spinel NiMn2O4 transforms to a tetragonal structure at about 12 GPa. The tetragonal phase does not revert to the cubic phase upon decompression and its unit-cell constants at ambient pressure are a(0)=8.65(8) and c(0)=7.88(15) Angstrom (distorted fee). Within thr......). The bulk modulus of the cubic phase is 206(4) GPa....

  19. High-pressure high-temperature synthesis of novel binary and ternary nitride phases of group 4 and 14 elements

    Dzivenko, D. A.; Horvath-Bordon, E.; Zerr, A.; Miehe, G.; Kroll, P.; Boehler, R.; McMillan, P.F.; Riedel, R.

    2008-01-01

    Our recent experiments on high-pressure high-temperature synthesis of novel ternary nitrides of group 4 and 14 elements are presented. Dense carbon nitride imide, C2N2(NH), was synthesized for the first time in a laser heated diamond anvil cell (LH-DAC) at pressures above 27 GPa and temperatures around 2000 K. Based on results of the electron diffraction-, EELS-and SIMS-measurements combined with theoretical calculations the structure of this new C-N-H phase was suggested to be of the defect-...

  20. Structural phase transition and elastic properties of thorium pnictides at high pressure

    Kuldeep Kholiya; B R K Gupta

    2007-04-01

    In the present paper we have pointed out the weaknesses of the approach by Aynyas et al [1] to study the structural phase transition and elastic properties of thorium pnictides. The calculated values of phase transition pressure and other elastic properties using the realistic and actual approach are also given and compared with the experimental and previous theoretical work.

  1. High pressure studies of the phase transition in the ferroelectric Sn2P2S6

    Dzhavadov, Leonid N.; Ryzhov, Valentin N.

    2016-06-01

    We apply a method of pulse-adiabatic modulation of pressure to obtain heat capacity and thermal expansion of ferroelectric Sn2P2S6 in the vicinity of the second order phase transition at pressures to 5 kbar. The phase transition in Sn2P2S6 does not change its nature and stays second order in the whole range of pressure currently studied. The earlier conclusion on the tricritical features of the phase transition in Sn2P2S6 cannot be confirmed. Discontinuities of heat capacity and thermal expansion perfectly fit the Ehrenfest equation that expected in the mean field theories. An excellent performance of the Ehrenfest formula in a wide range of pressures establishes phase transition in Sn2P2S6 as an almost ideal mean field phase transition.

  2. High pressure Laue diffraction and its application to study microstructural changes during the α → β phase transition in Si

    Popov, D., E-mail: dpopov@carnegiescience.edu; Park, C.; Kenney-Benson, C.; Shen, G. [High Pressure Collaborative Access Team, Geophysical Laboratory, Carnegie Institution of Washington, Argonne, Illinois 60439 (United States)

    2015-07-15

    An approach using polychromatic x-ray Laue diffraction is described for studying pressure induced microstructural changes of materials under pressure. The advantages of this approach with respect to application of monochromatic x-ray diffraction and other techniques are discussed. Experiments to demonstrate the applications of the method have been performed on the α → β phase transition in Si at high pressures using a diamond anvil cell. We present the characterization of microstructures across the α–β phase transition, such as morphology of both the parent and product phases, relative orientation of single-crystals, and deviatoric strains. Subtle inhomogeneous strain of the single-crystal sample caused by lattice rotations becomes detectable with the approach.

  3. High pressure Laue diffraction and its application to study microstructural changes during the α → β phase transition in Si

    An approach using polychromatic x-ray Laue diffraction is described for studying pressure induced microstructural changes of materials under pressure. The advantages of this approach with respect to application of monochromatic x-ray diffraction and other techniques are discussed. Experiments to demonstrate the applications of the method have been performed on the α → β phase transition in Si at high pressures using a diamond anvil cell. We present the characterization of microstructures across the α–β phase transition, such as morphology of both the parent and product phases, relative orientation of single-crystals, and deviatoric strains. Subtle inhomogeneous strain of the single-crystal sample caused by lattice rotations becomes detectable with the approach

  4. High-pressure phase transitions in rare earth metal thulium to 195 GPa

    We have performed image plate x-ray diffraction studies on a heavy rare earth metal, thulium (Tm), in a diamond anvil cell to a pressure of 195 GPa and volume compression V/Vo = 0.38 at room temperature. The rare earth crystal structure sequence, hcp → Sm-type → dhcp → fcc → distorted fcc, is observed in Tm below 70 GPa with the exception of a pure fcc phase. The focus of our study is on the ultrahigh-pressure phase transition and Rietveld refinement of crystal structures in the pressure range between 70 and 195 GPa. The hexagonal hR- 24 phase is seen to describe the distorted fcc phase between 70 and 124 GPa. Above 124 ± 4 GPa, a structural transformation from hR 24 phase to a monoclinic C 2/m phase is observed with a volume change of - 1.5%. The equation of state data shows rapid stiffening above the phase transition at 124 GPa and is indicative of participation of f-electrons in bonding. We compare the behavior of Tm to other heavy rare-earths and heavy actinide metals under extreme conditions of pressure.

  5. Synthesis of new Diamond-like B-C Phases under High Pressure and Temperatures

    Ming, L. C. [University of Hawaii; Zinin, P. V. [University of Hawaii; Sharma, S. K. [University of Hawaii

    2014-04-22

    A cubic BC3 (c-BC3) phase was synthesized by direct transformation from graphitic phases at a pressure of 39 GPa and temperature of 2200 K in a laser-heated diamond anvil cell (DAC). A combination of x-ray diffraction (XRD), electron diffraction (ED), transmission electron microscopy (TEM) imaging, and electron energy loss spectroscopy (EELS) measurements lead us to conclude that the obtained phase is hetero-nano-diamond, c-BC3. The EELS measurements show that the atoms inside the cubic structure are bonded by sp3 bonds.

  6. High-pressure phase behaviour of poly(D-lactic acid), trichloromethane, and carbon dioxide ternary mixture systems

    Highlights: • The high pressure phase behaviour of poly(D-lactic acid), trichloromethane and carbon dioxide ternary mixtures was measured. • The experimental data shows the characteristics of the LCST behaviour of (polymer + solvent + gas) systems. • The hybrid equation of state for the (polymer + carbon dioxide) system was used to correlate the experimental data. - Abstract: The high pressure phase behaviour of poly(D-lactic acid) (Mw = 359,000), trichloromethane, and carbon dioxide ternary mixture systems is presented in this study. Cloud and bubble point pressures were measured using a variable volume view cell at temperatures (313.15 to 363.15) K and pressures up to 33.6 MPa. The hybrid equation of state for the polymer-carbon dioxide system was used to correlate the experimental results. The van der Waals one-fluid mixing rule with three adjustable binary interaction parameters was used for all correlations. The binary parameters were optimised using the simplex method algorithm

  7. Pressure-induced phase transitions in GeS under high pressures

    Dias, Ranga; Yoo, Choong-Shik

    2012-02-01

    We have studied the pressure-induced structural and electronic phase transitions of layered GeS (Pnma) to 30 GPa, using micro-Raman spectroscopy and electrical resistivity measurements in diamond anvil cells. The result shows a steady decrease in resistivity to that of metal at around 18 GPa. The visual appearance of GeS supports the insulator-metal transition: initially black GeS becomes opaque and eventually reflective with increasing pressure. The Raman result indicates that the metallization is preceded by a structural phase transition, presumably to the previously predicted Cmcm structure.

  8. A route to possible civil engineering materials: the case of high-pressure phases of lime

    A. Bouibes; Zaoui, A.

    2015-01-01

    Lime system has a chemical composition CaO, which is known as thermodynamically stable. The purpose here is to explore further possible phases under pressure, by means of variable-composition ab initio evolutionary algorithm. The present investigation shows surprisingly new stable compounds of lime. At ambient pressure we predict, in addition to CaO, CaO2 as new thermodynamically stable compound. The latter goes through two phases transition from C2/c space group structure to Pna21 at 1.5 GPa...

  9. Compressibility of the high-pressure rocksalt phase of ZnO

    Recio, J.M.; Blanco, M.A.; Luana, V.;

    1998-01-01

    We report the results of a combined experimental and theoretical investigation on the stability and the volume behavior under hydrostatic pressure of the rocksalt (B1) phase of ZnO. Synchrotron-radiation x-ray powder-diffraction data are obtained from 0 to 30 GPa. Static simulations of the ZnO B1...... in the range of 160-194 GPa. For its zero-pressure first derivative, the experimental and theoretical data yield a value of 4.4+/-1.0. Overall, our results show that the ZnO B1 phase is slightly more compressible than previously reported. [S0163-1829(98)07537-7]....

  10. Phase relation of CaSO4 at high pressure and temperature up to 90 GPa and 2300 K

    Fujii, Taku; Ohfuji, Hiroaki; Inoue, Toru

    2016-05-01

    Calcium sulfate (CaSO4), one of the major sulfate minerals in the Earth's crust, is expected to play a major role in sulfur recycling into the deep mantle. Here, we investigated the crystal structure and phase relation of CaSO4 up to ~90 GPa and 2300 K through a series of high-pressure experiments combined with in situ X-ray diffraction. CaSO4 forms three thermodynamically stable polymorphs: anhydrite (stable below 3 GPa), monazite-type phase (stable between 3 and ~13 GPa) and barite-type phase (stable up to at least 93 GPa). Anhydrite to monazite-type phase transition is induced by pressure even at room temperature, while monazite- to barite-type transition requires heating at least to 1500 K at ~20 GPa. The barite-type phase cannot always be quenched from high temperature and is distorted to metastable AgMnO4-type structure or another modified barite structure depending on pressure. We obtained the pressure-volume data and density of anhydrite, monazite- and barite-type phases and found that their densities are lower than those calculated from the PREM model in the studied P-T conditions. This suggests that CaSO4 is gravitationally unstable in the mantle and fluid/melt phase into which sulfur dissolves and/or sulfate-sulfide speciation may play a major role in the sulfur recycling into the deep Earth.

  11. Equilibrium Between Phases of Matter: Supplemental Text for Materials Science and High-Pressure Geophysics

    Jacobs, M.H.G.; Oonk, H.A.J.

    2012-01-01

    The Second Volume of Equilibrium between Phases of Matter, when compared with the First Volume, by H.A.J. Oonk and M.T. Calvet, published in 2008, amounts to an extension of subjects, and a deepening of understanding. In the first three sections of the text an extension is given of the theory on iso

  12. Structural phase transitions in IrO2 at high pressures

    Structural transformations in iridium dioxide (IrO2) were investigated using first-principles calculations up to a pressure of 50 GPa at 0 K. The phase transformation from the rutile-type to the pyrite-type structure was confirmed at 8-15 GPa. Although structures of the CaCl2-type and α-PbO2-type are observed in other metal dioxides, such as SiO2, GeO2, and SnO2, our calculations indicated that these structures are metastable in IrO2. Our calculations explain experimental observations which show the direct transformation from the rutile-type to the pyrite-type structures in IrO2. The bulk modulus of the pyrite-type phase calculated in this study is in good agreement with the experimental value. The non-magnetic state is stable relative to the ferromagnetic and antiferromagnetic states in all IrO2 phases. The calculated electronic density of states suggests that the pyrite-type phase is metallic

  13. Hybrid functionals and electronic structure of high-pressure phase of CdO

    Joshi, K.B.; Paliwal, U. [Department of Physics, M. L. Sukhadia University, Udaipur 313001 (India); Sharma, B.K. [Department of Physics, University of Rajasthan, Jaipur 302004 (India)

    2011-05-15

    The electronic band structure and density of states (DOS) of B2-phase cadmium oxide (CdO) are computed following the first-principles linear combination of atomic orbitals method applying the CRYSTAL code. The PBE correlation functional coupled with Becke's ansatz for exchange is considered for calculations. The electronic band structure and DOS are examined considering HF, B3LYP and hybrid schemes. Hybrid functionals are used with 25, 15, 10 and 5% mixing of Fock exchange with PBE-GGA. Depending on the correlation functionals, and different mixings in the hybrid schemes, B2-phase CdO may have an indirect positive band gap, a negative band gap or a zero gap. The effect of pd repulsion originating from pd hybridisation is visible in the calculated band structures. (Copyright copyright 2011 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  14. Formation of collapsed tetragonal phase in EuCo2As2 under high pressure

    The structural properties of EuCo2As2 have been studied up to 35 GPa, through the use of x-ray diffraction in a diamond anvil cell at a synchrotron source. At ambient conditions, EuCo2As2 (I4/mmm) has a tetragonal lattice structure with a bulk modulus of 48 ± 4 GPa. With the application of pressure, the a axis exhibits negative compressibility with a concurrent sharp decrease in c-axis length. The anomalous compressibility of the a axis continues until 4.7 GPa, at which point the structure undergoes a second-order phase transition to a collapsed tetragonal (CT) state with a bulk modulus of 111 ± 2 GPa. We found a strong correlation between the ambient pressure volume of 122 parents of superconductors and the corresponding tetragonal to collapsed tetragonal phase transition pressures.

  15. Structural phase transition and failure of nanographite sheets under high pressure: a molecular dynamics study

    Nanographite sheets under high compressive stresses at ambient temperature have been investigated through molecular dynamics simulations using the Tersoff-Brenner potential. Nanographite undergoes a soft to hard phase transition at a certain compressive stress, about 15 GPa. With increasing compressions, the bonding structures of nanographite are changed, interlayer sp3-bonds are formed, and nanographite transforms into a superhard carbon phase (SCP). Further compressions lead to the instabilities of the SCP. Although the detailed lattice structure of the SCP remains elusive, its compressive strength can approach 150 GPa, comparable to that of diamond. The maximum failure stresses of nanographite sheets are sensitive to the inter-and intra-layer interstices. Our results may explain paradoxical experimental results in the available literature

  16. THE GENERALIZED MAXIMUM LIKELIHOOD METHOD APPLIED TO HIGH PRESSURE PHASE EQUILIBRIUM

    CARDOZO-FILHO Lúcio

    1997-01-01

    Full Text Available The generalized maximum likelihood method was used to determine binary interaction parameters between carbon dioxide and components of orange essential oil. Vapor-liquid equilibrium was modeled with Peng-Robinson and Soave-Redlich-Kwong equations, using a methodology proposed in 1979 by Asselineau, Bogdanic and Vidal. Experimental vapor-liquid equilibrium data on binary mixtures formed with carbon dioxide and compounds usually found in orange essential oil were used to test the model. These systems were chosen to demonstrate that the maximum likelihood method produces binary interaction parameters for cubic equations of state capable of satisfactorily describing phase equilibrium, even for a binary such as ethanol/CO2. Results corroborate that the Peng-Robinson, as well as the Soave-Redlich-Kwong, equation can be used to describe phase equilibrium for the following systems: components of essential oil of orange/CO2.

  17. In-situ Phase Transformation and Deformation of Iron at High Pressure and Temperature

    Miyagi, Lowell

    2009-01-01

    With a membrane based mechanism to allow for pressure change of a sample in a radial diffraction diamond anvil cell (rDAC) and simultaneous infra-red laser heating, it is now possible to investigate texture changes during deformation and phase transformations over a wide range of temperature-pressure conditions. The device is used to study bcc (alpha), fcc (gamma) and hcp (epislon) iron. In bcc iron, room temperature compression generates a texture characterized by (100) and (111) poles paral...

  18. Structural study of the high-pressure antiferroelectric phase of CsH2PO4

    A three-dimensional neutron diffraction study has been carried out on the pressure-induced antiferroelectric phase of CsH2PO4. At 100.70K and a hydrostatic pressure of 3.6 kbar, the unit cell parameters are a = 15.625(9), b = 6.254(2), c = 4.886(1) A, β = 108.08(3)0 and Z = 4. Atomic parameters were determined using full-matrix least-squares methods which yield final agreement indices: R(F2) = 0.0715, R/sub w/(F2) = 0.0807 and S = 2.13. The structure is nearly consistent with the monoclinic space group P21/a but refinement in P21 yields a slightly better fit. The structure is markedly different from those of the paraelectric and ferroelectric phases with large relative displacements (nearly 1 A) of Cs+1 and PO4-3 groups in the x-z plane. Hydrogens bonding in b-chains, which are disordered in the paraelectric phase, show antiferroelectric order

  19. High pressure phase transformation in yttrium sulfide(YS): A first principle study

    First principles calculations have been carried out to analyze structural, elastic and dynamic stability, of YS under hydrostatic compression. The comparison of enthalpies of rocksalt type (B1) and CsCl type cubic (B2) structures determined as a function of compression suggests the B1→B2 transition at ∼ 49 GPa. Various physical quantities such as zero pressure equilibrium volume, bulk modulus, and pressure derivative of bulk modulus have been derived from the theoretically determined equation of state. The single crystal elastic constants derived from the energy strain method agree well with the experimental values. The activation barrier between B1 and B2 phases calculated at transition point is ∼ 17/mRy/formula unit. Our lattice dynamic calculations show that at ambient condition, the B1 phase is lattice dynamically stable and frequencies of phonon modes in different high symmetry directions of Brillouin zone agrees well with experimental values. The B2 phase also is dynamical stable at ambient condition as well as at ∼ 49 GPa, supporting our static lattice calculation

  20. A molecular dynamics study of ambient and high pressure phases of silica: structure and enthalpy variation with molar volume.

    Rajappa, Chitra; Sringeri, S Bhuvaneshwari; Subramanian, Yashonath; Gopalakrishnan, J

    2014-06-28

    Extensive molecular dynamics studies of 13 different silica polymorphs are reported in the isothermal-isobaric ensemble with the Parrinello-Rahman variable shape simulation cell. The van Beest-Kramer-van Santen (BKS) potential is shown to predict lattice parameters for most phases within 2%-3% accuracy, as well as the relative stabilities of different polymorphs in agreement with experiment. Enthalpies of high-density polymorphs - CaCl2-type, α-PbO2-type, and pyrite-type - for which no experimental data are available as yet, are predicted here. Further, the calculated enthalpies exhibit two distinct regimes as a function of molar volume-for low and medium-density polymorphs, it is almost independent of volume, while for high-pressure phases a steep dependence is seen. A detailed analysis indicates that the increased short-range contributions to enthalpy in the high-density phases arise not only from an increased coordination number of silicon but also shorter Si-O bond lengths. Our results indicate that amorphous phases of silica exhibit better optimization of short-range interactions than crystalline phases at the same density while the magnitude of Coulombic contributions is lower in the amorphous phase. PMID:24985659

  1. Recycling of water of high pressure cleaning of pipes. Phase 1. Quality demands and economical aspects

    According to the regulation 6.1 in the current licence Surface Water Pollution Law (WVO, abbreviated in Dutch) of October 10, 1997, ECN carried out the first phase of a study on the title subject with respect to pipes applied in oil and gas exploration. In the present situation water of the so-called pipe-cleaner is transported via a seapipe after precipitation and membrane filtration. Next to the quality demands and economical aspects attention is paid to a number of environmental aspects

  2. Structural properties of the zircon- and scheelite-type phases of YVO4 at high pressure

    Wang, X.; Loa, I.; Syassen, K.; Hanfland, M.; Ferrand, B.

    2004-08-01

    The laser host material yttrium orthovanadate YVO4 with a tetragonal zircon-type structure has been studied by angle-dispersive powder x-ray diffraction in a diamond anvil cell up to 26GPa (T=300K) . In situ diffraction confirms that the compound undergoes a nonreversible transformation to a scheelite-type structure at a pressure of 8.5GPa . The equations of state of the zircon and scheelite phases and changes in internal structural parameters are reported. The effect of pressure on the distorted tetrahedral and dodecahedral coordinations of the V and Y ions, respectively, is discussed.

  3. Structural variety beyond appearance: high-pressure phases of CrB4 in comparison with FeB4.

    Zhang, Yunkun; Wu, Lailei; Wan, Biao; Zhao, Yan; Gao, Rui; Li, Zhiping; Zhang, Jingwu; Gou, Huiyang; Mao, Ho-kwang

    2016-01-28

    Employing particle swarm optimization (PSO) combined with first-principles calculations, we systemically studied high-pressure behaviors of hard CrB4. Our predictions reveal a distinct structural evolution under pressure for CrB4 despite having the same initial structure as FeB4. CrB4 is found to adopt a new P2/m structure above 196 GPa, another Pm structure at a pressure range of 261-294 GPa and then a Pmma structure beyond 294 GPa. Instead of puckering boron sheets in the initial structure, the high-pressure phases have planar boron sheets with different motifs upon compression. Comparatively, FeB4 prefers an I41/acd structure over 48 GPa with tetrahedron B4 units and a P213 structure above 231 GPa having equilateral triangle B3 units. Significantly, CrB4 exhibits persistent metallic behavior in contrast with the semiconducting features of FeB4 upon compression. The varied pressure response of hard tetraborides studied here is of importance for understanding boron-rich compounds and designing new materials with superlative properties. PMID:26692374

  4. High-pressure phase transition makes B4.3C boron carbide a wide-gap semiconductor

    Hushur, Anwar; Manghnani, Murli H.; Werheit, Helmut; Dera, Przemyslaw; Williams, Quentin

    2016-02-01

    Single-crystal B4.3C boron carbide is investigated through the pressure-dependence and inter-relation of atomic distances, optical properties and Raman-active phonons up to ~70 GPa. The anomalous pressure evolution of the gap width to higher energies is striking. This is obtained from observations of transparency, which most rapidly increases around 55 GPa. Full visible optical transparency is approached at pressures of  >60 GPa indicating that the band gap reaches ~3.5 eV at high pressure, boron carbide is a wide-gap semiconductor. The reason is that the high concentration of structural defects controlling the electronic properties of boron carbide at ambient conditions initially decreases and finally vanishes at high pressures. The structural parameters and Raman-active phonons indicate a pressure-dependent phase transition in single-crystal natB4.3C boron carbide near 40 GPa, likely related to structural changes in the C-B-C chains, while the basic icosahedral structure appears to be less affected.

  5. Polyamorphic phase transition of Yb-based metallic glass at high pressure

    li, L.; Li, R.; Liu, H.; Chupas, P.

    2013-12-01

    A family of Yb-based bulk metallic glasses (BMG) has been fabricated based on strong liquid characteristic and excellent glass-forming ability. Using a diamond anvil cell with high-energy synchrotron X-ray, the total scattering of metallic glass Yb-Mg-Zn was studied at pressure up to 30GPa in a hydrostatic isopropanol pressure-medium. The local structure was investigated through direct Fourier transformation of the structure factor [S(Q)], pair distribution function (PDF) [G(r)] with background correction. Polyamorphic phase transition is achieved because smaller atoms are extruded into the clearance of the larger rare earth atoms and 4f electrons delocalized. Phase transition from a low-density state to a high-density state occurs, smaller atoms can be extruded is one of two reasons for the high compressibility of rare earth BMG. The second reason is the delocalization of 4f electrons, which can induce the volume collapse of rare earth atoms.

  6. In-situ Phase Transformation and Deformation of Iron at High Pressure andTemperature

    Miyagi, Lowell; Kunz, Martin; Knight, Jason; Nasiatka, James; Voltolini, Marco; Wenk, Hans-Rudolf

    2008-07-01

    With a membrane based mechanism to allow for pressure change of a sample in aradial diffraction diamond anvil cell (rDAC) and simultaneous infra-red laser heating, itis now possible to investigate texture changes during deformation and phasetransformations over a wide range of temperature-pressure conditions. The device isused to study bcc (alpha), fcc (gamma) and hcp (epislon) iron. In bcc iron, room temperature compression generates a texture characterized by (100) and (111) poles parallel to the compression direction. During the deformation induced phase transformation to hcp iron, a subset of orientations are favored to transform to the hcp structure first and generate a texture of (01-10) at high angles to the compression direction. Upon further deformation, the remaining grains transform, resulting in a texture that obeys the Burgers relationship of (110)bcc // (0001)hcp. This is in contrast to high temperature results that indicate that texture is developed through dominant pyramidal {2-1-12}<2-1-13> and basal (0001)-{2-1-10} slip based on polycrystal plasticity modeling. We also observe that the high temperature fcc phase develops a 110 texture typical for fcc metals deformed in compression.

  7. A route to possible civil engineering materials: the case of high-pressure phases of lime

    Bouibes, A.; Zaoui, A.

    2015-07-01

    Lime system has a chemical composition CaO, which is known as thermodynamically stable. The purpose here is to explore further possible phases under pressure, by means of variable-composition ab initio evolutionary algorithm. The present investigation shows surprisingly new stable compounds of lime. At ambient pressure we predict, in addition to CaO, CaO2 as new thermodynamically stable compound. The latter goes through two phases transition from C2/c space group structure to Pna21 at 1.5 GPa, and Pna21 space group structure to I4/mcm at 23.4 GPa. Under increasing pressure, further compounds such as CaO3 become the most stable and stabilize in P-421m space group structure above 65 GPa. For the necessary knowledge of the new predicted compounds, we have computed their mechanical and electronic properties in order to show and to explain the main reasons leading to the structural changes.

  8. High-pressure high-temperature phase diagram of gadolinium studied using a boron-doped heater anvil

    Montgomery, J. M.; Samudrala, G. K.; Velisavljevic, N.; Vohra, Y. K.

    2016-04-01

    A boron-doped designer heater anvil is used in conjunction with powder x-ray diffraction to collect structural information on a sample of quasi-hydrostatically loaded gadolinium metal up to pressures above 8 GPa and 600 K. The heater anvil consists of a natural diamond anvil that has been surface modified with a homoepitaxially grown chemical-vapor-deposited layer of conducting boron-doped diamond, and is used as a DC heating element. Internally insulating both diamond anvils with sapphire support seats allows for heating and cooling of the high-pressure area on the order of a few tens of seconds. This device is then used to scan the phase diagram of the sample by oscillating the temperature while continuously increasing the externally applied pressure and collecting in situ time-resolved powder diffraction images. In the pressure-temperature range covered in this experiment, the gadolinium sample is observed in its hcp, αSm, and dhcp phases. Under this temperature cycling, the hcp → αSm transition proceeds in discontinuous steps at points along the expected phase boundary. From these measurements (representing only one hour of synchrotron x-ray collection time), a single-experiment equation of state and phase diagram of each phase of gadolinium is presented for the range of 0-10 GPa and 300-650 K.

  9. First principles study of isostructural phase transition in Sb2Te3 under high pressure

    The structural properties, electronic band structure and Bader charge of Sb2Te3 under hydrostatic pressure were simulated using density functional theory in order to study isostructural phase transitions (IPT) in Sb2Te3. The theoretical results showed that the axial ratio c /a did not exhibit any anomaly below 6 GPa. The variations of bond lengths were discontinuous at 2.5 GPa, which suggested considerable changes in interatomic interactions and provided sound support to the IPT. The effective charges of Sb and Te atoms showed significant discontinuous variations at 2.5 GPa, which revealed a strong redistribution of the electronic charge density and considerably changed interactions among bonding atoms. Thus, the IPT is originated from the considerable variation in the electronic charge density. (copyright 2015 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  10. Phase equilibrium of binary system carbon dioxide - methanol at high pressure using artificial neural network

    Interest in supercritical fluids extraction (SFE ) is increasing throughout many scientific and industrial fields. The common solvent for use in SFE is carbon dioxide. However, pure carbon dioxide frequently fails to efficiently extract the essential oil from a sample matrix, and modifier fluids such as methanol should be used to enhance extraction yield. A more efficient use of SFE requires quantitative prediction of phase equilibrium of this binary system, carbon dioxide - methanol. The purpose of the current research is modeling carbon dioxide - methanol system using artificial neural network (ANN). Results of ANN modeling has been compared with experimental data as well as thermodynamic equations of state. The comparison shows that the ANN modeling has a higher accuracy than thermodynamic models. (author)

  11. High volumetric hydrogen density phases of magnesium borohydride at high-pressure: A first-principles study

    Fan Jing; Bao Kuo; Duan De-Fang; Wang Lian-Cheng; Liu Bing-Bing; Cui Tian

    2012-01-01

    The previously proposed theoretical and experimental structures,bond characterization,and compressibility of Mg(BH4)2 in a pressure range from 0 to 10 GPa are studied by ab initio density-functional calculations.It is found that the ambient pressure phases of meta-stable I41/amd and unstable P-3ml proposed recently are extra stable and cannot decompose under high pressure.Enthalpy calculation indicates that the ground state of F222 structure proposed by Zhou et al.[2009 Phys.Rev.B 79 212102]will transfer to I41/amd at 0.7 GPa,and then to a P-3m1 structure at 6.3 GPa.The experimental P6122 structure (α-phase) transfers to I41/amd at 1.2 GPa.Furthermore,both I41/amd and P-3m1 can exist as high volumetric hydrogen density phases at low pressure.Their theoretical volumetric hydrogen densities reach 146.351 g H2/L and 134.028 g H2/L at ambient pressure,respectively.The calculated phonon dispersion curve shows that the I41/amd phase is dynamically stable in a pressure range from 0 to 4 GPa and the P-3ml phase is stable at pressures higher than 1 GPa.So the I41/amd phase may be synthesized under high pressure and retained to ambient pressure.Energy band structures show that they are both always ionic crystalline and insulating with a band-gap of about 5 eV in this pressure range.In addition,they each have an anisotropic compressibility.The c axis of these structures is easy to compress.Especially,the c axis and volume of P-3m1 phase are extraordinarily compressible,showing that compression along the c axis can increase the volumetric hydrogen content for both I41/amd and P-3m1 structures.

  12. Elastic behaviour and phase stability of pyrophyllite and talc at high pressure and temperature

    Gatta, G. Diego; Lotti, Paolo; Merlini, Marco; Liermann, Hanns-Peter; Lausi, Andrea; Valdrè, Giovanni; Pavese, Alessandro

    2015-04-01

    The compressional behaviour of (triclinic) pyrophyllite-1 Tc was investigated by means of in situ synchrotron single-crystal diffraction up to 6.2 GPa (at room temperature) using a diamond anvil cell. Its thermal behaviour was investigated by in situ synchrotron powder diffraction up to 923 K (at room pressure) with a furnace. No evidence of phase transition has been observed within the pressure range investigated. The α angle decreases whereas the β and γ angles increase with P, with the following linear trends: α( P) = α 0 - 0.203(9)·Δ P, β( P) = β 0 + 0.126(8)·Δ P, and γ( P) = γ 0 + 0.109(5)·Δ P (angles in ° and P in GPa). P- V data fits with isothermal Murnaghan and third-order Birch-Murnaghan Equations of State yield: K T0 = 47(3) GPa and K' = 6.6(14) for the M-EoS fit, K T0 = 47(4) GPa and K' = 7.3(19) for a III-BM-EoS fit, with the following anisotropic compressional scheme: β a : β b : β c = 1.06:1:4.00. The evolution of the "Eulerian finite strain" versus "normalized stress" leads to: Fe(0) = 47(3) GPa as intercept value and regression line slope with K' = 7.1(18). A drastic and irreversible change of the thermal behaviour of pyrophyllite-1 Tc was observed at 700 modelled between 298 and 773 K following the equation α V( T) = α 0(1 - 10 T -1/2), with α V298 K = 2.2(2) × 10-5 K-1 [with V 0 = 424.2(1) Å3 and α 0 = 5.5(3) × 10-5 K-1] and thermal anisotropic scheme α a : α b : α c = 1.20:1:2.72. By linear regression, we obtained: V( T)/ V 0 = 1 + α 0V· T = 1 + 3.1(2) × 10-5 ( T - T 0). The thermal behaviour of talc-1 Tc was investigated by in situ synchrotron powder diffraction up to 1,173 K (at room- P) with a furnace. At 423 K, the diffraction pattern was indexable with a monoclinic unit-cell but with a doubling of the c-axis (as expected for the 2 M-polytype). At T > 1,123 K, an irreversible transformation occurs, likely ascribable to the first stage of the T-induced de-hydroxylation. Between 423 and 1,123 K, the β angle

  13. High-temperature- and high-pressure-induced formation of the Laves-phase compound XeS2

    Yan, Xiaozhen; Chen, Yangmei; Xiang, Shikai; Kuang, Xiaoyu; Bi, Yan; Chen, Haiyan

    2016-06-01

    We explore the reactivity of xenon with sulfur under high pressure, using unbiased structure searching techniques combined with first-principles calculations, which identify a stable XeS2 compound crystallized in a Laves phase with hypercoordinated (16-fold) Xe at 191 GPa and 0 K. Taking the thermal effects into account, we find that increasing the temperature could further stabilize it. The formation of XeS2 is a consequence of pressure-induced charge transfer from Xe to S atoms and the delocalization of Xe 5 p and S 3 p electrons. Meanwhile, the stabilization into a Laves phase of XeS2 is the result of delocalized chemical bonding and the need for optimum structure packing. The present discussion of the formation mechanism in XeS2 is general, and conclusions can be used to understand the formation of other Laves-phase compounds and the Xe chemistry that allows closed-shell Xe to participate in chemical reactions.

  14. Phase diagram of ZrZn2 at high pressure: Low-temperature features and elusive superconductivity

    Studies of the AC magnetic susceptibility and electrical resistivity of polycrystalline samples of ZrZn2, synthesized at high pressure, were performed at pressures up to 4.5 GPa and temperatures down to 0.4 K. The evolution with pressure of the line of ferromagnetic phase transformations qualitatively agrees with numerous previous data, though the transition temperature is highly sensitive to the quality and history of samples. Upon approaching zero temperature, the transition line bends toward the pressure axis as dictated by the Nernst theorem. An additional feature of the phase diagram was discovered in the samples with the highest Curie temperature (25-26 K). The electrical resistance of these samples drastically decreases near 1.4-1.8 K at ambient pressure. The temperature of this resistive transition does not change much with pressure and crosses the Curie line at a pressure near 1.2 GPa, seemingly forming some sort of tetracritical point. Application of magnetic fields up to 2 T suppresses the transition that one may expect if superconductivity is involved. However, heat capacity measurements do not show any anomaly at the transition, which resembles the case described by Pfliederer et al. [Nature (2001) 58

  15. The role of equilibrium volume and magnetism on the stability of iron phases at high pressures

    The present study provides new insights into the pressure dependence of magnetism by tracking the hybridization between crystal orbitals for pressures up to 600 GPa in the known hcp, bcc and fcc iron. The Birch–Murnaghan equation of state parameters are; bcc: V0 = 11.759 A3/atom, K0 = 177.72 GPa; hcp: V0 = 10.525 A3/atom, K0 = 295.16 GPa; and fcc: V0 = 10.682 A3/atom, K0 = 274.57 GPa. These parameters compare favorably with previous studies. Consistent with previous studies we find that the close-packed hcp and fcc phases are non-magnetic at pressures above 50 GPa and 60 GPa, respectively. The principal features of magnetism in iron are predicted to be invariant, at least up to ∼6% overextension of the equilibrium volume. Our results predict that magnetism for overextended fcc iron disappears via an intermediate spin state. This feature suggests that overextended lattices can be used to stabilize particular magnetic states. The analysis of the orbital hybridization shows that the magnetic bcc structure at high pressures is stabilized by splitting the majority and minority spin bands. The bcc phase is found to be magnetic at least up to 600 GPa; however, magnetism is insufficient to stabilize the bcc phase itself, at least at low temperatures. Finally, the analysis of the orbital contributions to the total energy provides evidence that non-magnetic hcp and fcc phases are likely more stable than bcc at core earth pressures. (paper)

  16. Developing a platform for high-resolution phase contrast imaging of high pressure shock waves in matter

    Schropp, Andreas; Patommel, Jens; Seiboth, Frank; Arnold, Brice; Galtier, Eric C.; Lee, Hae Ja; Nagler, Bob; Hastings, Jerome B.; Schroer, Christian G.

    2012-10-01

    Current and upcoming X-ray sources, such as the Linac Coherent Light Source (LCLS) at the Stanford Linear Accelerator Center (SLAC, USA), the SPring-8 Angstrom Compact Free Electron Laser (SACLA, Japan), or the X-ray Free Electron Laser (XFEL, Germany) will provide X-ray beams with outstanding properties.1, 2 Short and intense X-ray pulses of about 50 fs time duration and even shorter will push X-ray science to new frontiers such as, e. g., in high-resolution X-ray imaging, high-energy-density physics or in dynamical studies based on pump-probe techniques. Fast processes in matter often require high-resolution imaging capabilities either by magnified imaging in direct space or diffractive imaging in reciprocal space. In both cases highest resolutions require focusing the X-ray beam.3, 4 In order to further develop high-resolution imaging at free-electron laser sources we are planning a platform to carry out high-resolution phase contrast imaging experiments based on Beryllium compound refractive X-ray lenses (Be-CRLs) at the Matter in Extreme Conditions (MEC) endstation of the LCLS. The instrument provides all necessary equipment to induce high pressure shock waves by optical lasers. The propagation of a shock wave is then monitored with an X-ray Free Electron Laser (FEL) pulse by magnified phase contrast imaging. With the CRL optics, X-ray beam sizes in the sub-100nm range are expected, leading to a similar spatial resolution in the direct coherent projection image. The experiment combines different state-of-the art scientific techniques that are currently available at the LCLS. In this proceedings paper we describe the technical developments carried out at the LCLS in order to implement magnified X-ray phase contrast imaging at the MEC endstation.

  17. Characterization of boron nitride phase transformations in the Li–B–N system under high pressure and high temperature

    Highlights: • The characterization of cBN phase transformation in Li3N melt is revealed under HPHT. • A simultaneous precipitation and dissolution of cBN in Li3BN2 melt is proved. • The BN phase transition behaviors of Li3N–hBN and Li3N–cBN system is not equivalent. • The results provide a clue for further improvement of the quality of direct sintering of cubic boron nitride. - Abstract: The possible phase transformations of boron nitride in the Li–B–N system have been discussed by the chemical reactions of Li3N, hBN and cBN at the conditions of 5.0 GPa and 1300–1500 °C. The results of the reaction between Li3N and hBN shows that certain Li–B–N eutectic compound(s) which were produced in the thermodynamical stable region of cBN have no catalytic effect for cBN growth. It indicates that a certain irreversible BN precipitation/dissolution process takes place in Li3N melt. However, the reaction between Li3N and hBN is preferential when Li3N, hBN and cBN coexist in Li–B–N system, and the regrowth of cBN is observed, namely the morphology of cBN changing from irregular to fine shape crystals with well-facetted (1 1 1) surface. Furthermore, the estimated sizes of regrown cBN are almost same as those of the raw cBN. This indicates a simultaneous cBN dissolution and precipitation process in Li3N + hBN/cBN system under high pressure and high temperature

  18. Characterization of boron nitride phase transformations in the Li–B–N system under high pressure and high temperature

    Guo, W., E-mail: guowei1982cry@163.com [College of Physics and Optoelectronics, Taiyuan University of Technology, Taiyuan 030024 (China); National Key Lab of Superhard Materials, Jilin University, Changchun 130012 (China); Shi, Y. [College of Chemistry and Chemical Engineering, Taiyuan University of Technology, Taiyuan 030024 (China); Yang, P. [College of Physics and Optoelectronics, Taiyuan University of Technology, Taiyuan 030024 (China); Ma, H.A.; Jia, X. [National Key Lab of Superhard Materials, Jilin University, Changchun 130012 (China); Wang, S., E-mail: wangshuang@tyut.edu.cn [College of Chemistry and Chemical Engineering, Taiyuan University of Technology, Taiyuan 030024 (China)

    2015-09-25

    Highlights: • The characterization of cBN phase transformation in Li{sub 3}N melt is revealed under HPHT. • A simultaneous precipitation and dissolution of cBN in Li{sub 3}BN{sub 2} melt is proved. • The BN phase transition behaviors of Li{sub 3}N–hBN and Li{sub 3}N–cBN system is not equivalent. • The results provide a clue for further improvement of the quality of direct sintering of cubic boron nitride. - Abstract: The possible phase transformations of boron nitride in the Li–B–N system have been discussed by the chemical reactions of Li{sub 3}N, hBN and cBN at the conditions of 5.0 GPa and 1300–1500 °C. The results of the reaction between Li{sub 3}N and hBN shows that certain Li–B–N eutectic compound(s) which were produced in the thermodynamical stable region of cBN have no catalytic effect for cBN growth. It indicates that a certain irreversible BN precipitation/dissolution process takes place in Li{sub 3}N melt. However, the reaction between Li{sub 3}N and hBN is preferential when Li{sub 3}N, hBN and cBN coexist in Li–B–N system, and the regrowth of cBN is observed, namely the morphology of cBN changing from irregular to fine shape crystals with well-facetted (1 1 1) surface. Furthermore, the estimated sizes of regrown cBN are almost same as those of the raw cBN. This indicates a simultaneous cBN dissolution and precipitation process in Li{sub 3}N + hBN/cBN system under high pressure and high temperature.

  19. Application of phase-modulated dispersion interferometry to electron-density diagnostics of high-pressure plasma

    Phase-modulated dispersion interferometry (PMDI) is a technique for measuring the electron density in plasmas that was first developed for large fusion reactors. In this paper, we demonstrate the potential of PMDI for the diagnostics of microplasma generated at high pressures. PMDI can eliminate the effect of nondispersive components in the refractive-index variation on the measurement; therefore, most of the variation of the refractive index induced by the variation of gas density is eliminated by signal processing, contributing to accurate electron-density determination in microplasmas. The measurement results for a pulsed-dc microplasma in an atmospheric-pressure helium gas flow revealed that the electron density of the microplasma was in the range between 4 × 1013 and 1.4 × 1014 cm−3, and our PMDI system had a temporal resolution of 110µs and a sensitivity of the line-integrated electron density of 7 × 1011 cm−2. (fast track communication)

  20. Crystal structure of SrGeO3 in the high-pressure perovskite-type phase

    Akihiko Nakatsuka

    2015-05-01

    Full Text Available Single crystals of the SrGeO3 (strontium germanium trioxide high-pressure phase have been synthesized successfully at 6 GPa and 1223 K. The compound crystallizes with the ideal cubic perovskite-type structure (space group Pm-3m, which consists of a network of corner-linked regular GeO6 octahedra (point-group symmetry m-3m, with the larger Sr atoms located at the centers of cavities in the form of SrO12 cuboctahedra (point-group symmetry m-3m in the network. The degrees of covalencies included in the Sr—O and the Ge—O bonds calculated from bond valences are 20.4 and 48.9%, respectively. Thus, the Ge—O bond of the GeO6 octahedron in the SrGeO3 perovskite has a strong covalency, comparable to those of the Si—O bonds of the SiO4 tetrahedra in silicates with about 50% covalency. The thermal vibrations of the O atoms in the title compound are remarkably suppressed in the directions of the Ge—O bonds. This anisotropy ranks among the largest observed in stoichiometric cubic perovskites.

  1. High-pressure high-temperature synthesis of novel binary and ternary nitride phases of group 4 and 14 elements

    Dzivenko, D A; Horvath-Bordon, E; Miehe, G; Riedel, R [FB Materialwissenschaft, TU Darmstadt, Petersenstrasse 23, 64287 Darmstadt (Germany); Zerr, A [LPMTM-CNRS, Universite Paris Nord, 99 Av. J.B. Clement, 93430 Villetaneuse (France); Kroll, P [Department of Chemistry, UTA, Arlington, Texas 760019-0065 (United States); Boehler, R [Hochdruckgruppe, MPI fuer Chemie, J.-J.-Becher-Weg 27, 55128 Mainz (Germany); McMillan, P F [Department of Chemistry, UCL, 20 Gordon Street, London WC1 H0AJ (United Kingdom)], E-mail: dzivenko@materials.tu-darmstadt.de

    2008-07-15

    Our recent experiments on high-pressure high-temperature synthesis of novel ternary nitrides of group 4 and 14 elements are presented. Dense carbon nitride imide, C{sub 2}N{sub 2}(NH), was synthesized for the first time in a laser heated diamond anvil cell (LH-DAC) at pressures above 27 GPa and temperatures around 2000 K. Based on results of the electron diffraction-, EELS-and SIMS-measurements combined with theoretical calculations the structure of this new C-N-H phase was suggested to be of the defect-wurtzite type. Farther, macroscopic amounts of a new oxynitride of zirconium having cubic Th{sub 3}P{sub 4}-type structure, c-Zr{sub 2.86}(N{sub 0.88}O{sub 0.12}){sub 4}, were synthesized at high pressures and temperatures using a multi-anvil apparatus. Earlier this structure was observed for binary nitrides of zirconium(IV) and hafnium(IV) synthesized in microscopic amounts in a LH-DAC. The lattice parameter of c-Zr{sub 2.86}(N{sub 0.88}O{sub 0.12}){sub 4} was found to be a{sub 0} = 6.7549(1) A which is slightly larger than that of c-Zr{sub 3}N{sub 4}. Isotropic bulk and shear moduli of c-Zr{sub 2.86}(N{sub 0.88}O{sub 0.12}){sub 4} of B{sub 0} = 219 GPa and G{sub 0} = 96 GPa, respectively, were determined from the compression and nanoindentation measurements. The Vickers microhardness, H{sub V}(1), of the porous (about 30 vol. %) sample of c-Zr{sub 2.86}(N{sub 0.88}O{sub 0.12}){sub 4} was measured to be 12 GPa, similar to that of single crystal {delta}-ZrN.

  2. Phase equilibrium data and thermodynamic modeling of the system (CO{sub 2} + biodiesel + methanol) at high pressures

    Pinto, Leandro F.; Segalen da Silva, Diogo Italo [Department of Chemical Engineering, Federal University of Parana, CEP 81531-990, Curitiba, PR (Brazil); Rosa da Silva, Fabiano; Ramos, Luiz P. [Department of Chemistry, Federal University of Parana, CEP 81531-990, Curitiba, PR (Brazil); Ndiaye, Papa M. [Department of Chemical Engineering, Federal University of Parana, CEP 81531-990, Curitiba, PR (Brazil); Corazza, Marcos L., E-mail: corazza@ufpr.br [Department of Chemical Engineering, Federal University of Parana, CEP 81531-990, Curitiba, PR (Brazil)

    2012-01-15

    Highlights: > We measured phase behavior for the system involving {l_brace}CO{sub 2} + biodiesel + methanol{r_brace}. > The saturation pressures were obtained using a variable-volume view cell. > The experimental data were modeled using PR-vdW2 and PR-WS equations of state. - Abstract: The main objective of this work was to investigate the high pressure phase behavior of the binary systems {l_brace}CO{sub 2}(1) + methanol(2){r_brace} and {l_brace}CO{sub 2}(1) + soybean methyl esters (biodiesel)(2){r_brace} and the ternary system {l_brace}CO{sub 2}(1) + biodiesel(2) + methanol(3){r_brace} were determined. Biodiesel was produced from soybean oil, purified, characterized and used in this work. The static synthetic method, using a variable-volume view cell, was employed to obtain the experimental data in the temperature range of (303.15 to 343.15) K and pressures up to 21 MPa. The mole fractions of carbon dioxide were varied according to the systems as follows: (0.2383 to 0.8666) for the binary system {l_brace}CO{sub 2}(1) + methanol(2){r_brace}; (0.4201 to 0.9931) for the binary system {l_brace}CO{sub 2}(1) + biodiesel(2){r_brace}; (0.4864 to 0.9767) for the ternary system {l_brace}CO{sub 2}(1) + biodiesel(2) + methanol(3){r_brace} with a biodiesel to methanol molar ratio of (1:3); and (0.3732 to 0.9630) for the system {l_brace}CO{sub 2} + biodiesel + methanol{r_brace} with a biodiesel to methanol molar ratio of (8:1). For these systems, (vapor + liquid), (liquid + liquid), (vapor + liquid + liquid) transitions were observed. The phase equilibrium data obtained for the systems were modeled using the Peng-Robinson equation of state with the classical van der Waals (PR-vdW2) and Wong-Sandler (PR-WS) mixing rules. Both thermodynamic models were able to satisfactorily correlate the phase behavior of the systems investigated and the PR-WS presented the best performance.

  3. Random phase disturbances and tolerance on amplitude and phase spread in driver of two-beam accelerator with accompanying wave

    One investigates into effect of random phase disturbances on particle dynamics at extraction of UHF power from two-beam accelerator driver with accompanying wave. Paper presents the simulation results of beam dynamics in the driver depending on the value of phase disturbances. One determines tolerances for spread in values of amplitude and phase of wave in driver power extractors

  4. Calculation of stability of sodic phases in high-pressure metapelites and observation of Sambagawa metamorphic rocks

    Kouketsu, Y.; Enami, M.

    2010-12-01

    P-T pseudosection analyses of high-pressure metapelites from several subduction related regions were carried out by using the computer program Perple_X 07 in order to determine the mineral equilibrium, particularly the stability of sodic phases, in the model system MnO-Na2O-K2O-CaO-FeO-MgO-Al2O3-SiO2-H2O. Metapelites from Sambagawa, Western Alps, New Caledonia, Greece, and South Tianshan were selected for these analyses. Although the occurrence of sodic pyroxene in these metapelite samples is free or very rare, all the samples are considered to have undergone high-pressure metamorphism under blueschist-eclogite facies conditions. The bulk rock compositions of these metapelites have relatively low XNa [=Na/(Al + Na)] values. Therefore, the rare occurrences of sodic pyroxene in these samples are possibly due to their characteristic bulk rock compositions, although this has not been proved yet. The calculation results for the stability of sodic phases under the blueschist and eclogite facies conditions indicate the following. (1) Sodic pyroxene in the studied metapelites is stable only under higher-pressure conditions of P > 2.5 GPa, although its stable P-T range increases toward the lower-pressure side with increasing XNa value of the bulk-rock composition. (2) Paragonite and glaucophane are stable throughout the wide XNa range of bulk-rock compositions of host rocks under the blueschist and quartz-eclogite facies conditions. (3) The stability field of paragonite enlarges with the presence of CO2 in the metamorphic fluid. Thus, the high stability of paragonite and glaucophane in metapelites and the close relationship between the stability of sodic pyroxene and the bulk-rock composition explain why omphacite-bearing metapelites are rarely found. Observations of Sambagawa metapelites were carried out on the basis of these results. In the Besshi region of the Sambagawa belt, quartz grains with a high residual pressure of up to 0.8 GPa extensively occur as inclusions in

  5. A new fullerene network phase obtained from C.sub.70./sub. at high-pressure and high-temperature

    Marques, L.; Skorokhod, Yuriy; Soares, R.

    2015-01-01

    Roč. 9, č. 9 (2015), s. 535-538. ISSN 1862-6254 Institutional support: RVO:68378271 Keywords : fullerenes * high-pressure synthesis * X-ray diffraction * density functional calculations Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 2.142, year: 2014

  6. The local phase transitions of the solvent in the neighborhood of a solvophobic polymer at high pressures

    Budkov, Yu. A.; Vyalov, I. I.; Kolesnikov, A. L.; Georgi, N.; Chuev, G. N.; Kiselev, M. G.

    2014-11-01

    We investigate local phase transitions of the solvent in the neighborhood of a solvophobic polymer chain which is induced by a change of the polymer-solvent repulsion and the solvent pressure in the bulk solution. We describe the polymer in solution by the Edwards model, where the conditional partition function of the polymer chain at a fixed radius of gyration is described by a mean-field theory. The contributions of the polymer-solvent and the solvent-solvent interactions to the total free energy are described within the mean-field approximation. We obtain the total free energy of the solution as a function of the radius of gyration and the average solvent number density within the gyration volume. The resulting system of coupled equations is solved varying the polymer-solvent repulsion strength at high solvent pressure in the bulk. We show that the coil-globule (globule-coil) transition occurs accompanied by a local solvent evaporation (condensation) within the gyration volume.

  7. The local phase transitions of the solvent in the neighborhood of a solvophobic polymer at high pressures

    Budkov, Yu. A., E-mail: urabudkov@rambler.ru [G.A. Krestov Institute of Solution Chemistry of the Russian Academy of Sciences, Ivanovo (Russian Federation); National Research University Higher School of Economics, Moscow (Russian Federation); Department of Chemistry, Lomonosov Moscow State University, Moscow (Russian Federation); Vyalov, I. I. [Istituto Italiano di Tecnologia, via Morego 30, Genova 16163 (Italy); Kolesnikov, A. L. [Ivanovo State University, Ivanovo (Russian Federation); Institut für Nichtklassische Chemie e.V., Universitat Leipzig, Leipzig (Germany); Georgi, N., E-mail: bancocker@mail.ru [Max Planck Institute for Mathematics in the Sciences, Leipzig (Germany); Chuev, G. N. [Max Planck Institute for the Physics of Complex Systems, Dresden (Germany); Institute of Theoretical and Experimental Biophysics, Russian Academy of Science, Pushchino, Moscow Region (Russian Federation); Kiselev, M. G. [G.A. Krestov Institute of Solution Chemistry of the Russian Academy of Sciences, Ivanovo (Russian Federation); Department of Chemistry, Lomonosov Moscow State University, Moscow (Russian Federation)

    2014-11-28

    We investigate local phase transitions of the solvent in the neighborhood of a solvophobic polymer chain which is induced by a change of the polymer-solvent repulsion and the solvent pressure in the bulk solution. We describe the polymer in solution by the Edwards model, where the conditional partition function of the polymer chain at a fixed radius of gyration is described by a mean-field theory. The contributions of the polymer-solvent and the solvent-solvent interactions to the total free energy are described within the mean-field approximation. We obtain the total free energy of the solution as a function of the radius of gyration and the average solvent number density within the gyration volume. The resulting system of coupled equations is solved varying the polymer-solvent repulsion strength at high solvent pressure in the bulk. We show that the coil-globule (globule-coil) transition occurs accompanied by a local solvent evaporation (condensation) within the gyration volume.

  8. Synchrotron X-ray diffraction studies of phase transitions and mechanical properties of nanocrystalline materials at high pressure

    The behavior of nanocrystals under extreme pressure was investigated using synchrotron x-ray diffraction. A major part of this investigation was the testing of a prototype synchrotron endstation on a bend magnet beamline at the Advanced Light Source for high pressure work using a diamond anvil cell. The experiments conducted and documented here helped to determine issues of efficiency and accuracy that had to be resolved before the construction of a dedicated ''super-bend'' beamline and endstation. The major conclusions were the need for a cryo-cooled monochromator and a fully remote-controllable pressurization system which would decrease the time to change pressure and greatly reduce the error created by the re-placement of the diamond anvil cell after each pressure change. Two very different types of nanocrystal systems were studied, colloidal iron oxide (Fe2O3) and thin film TiN/BN. Iron oxide nanocrystals were found to have a transition from the γ to the α structure at a pressure strongly dependent on the size of the nanocrystals, ranging from 26 GPa for 7.2 nm nanocrystals to 37 GPa for 3.6 nm nanocrystals. All nanocrystals were found to remain in the α structure even after release of pressure. The transition pressure was also found, for a constant size (5.7 nm) to be strongly dependent on the degree of aggregation of the nanocrystals, increasing from 30 GPa for completely dissolved nanocrystals to 45 GPa for strongly aggregated nanocrystals. Furthermore, the x-ray diffraction pattern of the pressure induced α phase demonstrated a decrease in intensity for certain select peaks. Together, these observations were used to make a complete picture of the phase transition in nanocrystalline systems. The size dependence of the transition was interpreted as resulting from the extremely high surface energy of the α phase which would increase the thermodynamic offset and thereby increase the kinetic barrier to transition that must be overridden with pressure. The

  9. Synchrotron X-ray diffraction studies of phase transitions and mechanical properties of nanocrystalline materials at high pressure

    Prilliman, Gerald Stephen

    2003-09-01

    The behavior of nanocrystals under extreme pressure was investigated using synchrotron x-ray diffraction. A major part of this investigation was the testing of a prototype synchrotron endstation on a bend magnet beamline at the Advanced Light Source for high pressure work using a diamond anvil cell. The experiments conducted and documented here helped to determine issues of efficiency and accuracy that had to be resolved before the construction of a dedicated ''super-bend'' beamline and endstation. The major conclusions were the need for a cryo-cooled monochromator and a fully remote-controllable pressurization system which would decrease the time to change pressure and greatly reduce the error created by the re-placement of the diamond anvil cell after each pressure change. Two very different types of nanocrystal systems were studied, colloidal iron oxide (Fe{sub 2}O{sub 3}) and thin film TiN/BN. Iron oxide nanocrystals were found to have a transition from the {gamma} to the {alpha} structure at a pressure strongly dependent on the size of the nanocrystals, ranging from 26 GPa for 7.2 nm nanocrystals to 37 GPa for 3.6 nm nanocrystals. All nanocrystals were found to remain in the {alpha} structure even after release of pressure. The transition pressure was also found, for a constant size (5.7 nm) to be strongly dependent on the degree of aggregation of the nanocrystals, increasing from 30 GPa for completely dissolved nanocrystals to 45 GPa for strongly aggregated nanocrystals. Furthermore, the x-ray diffraction pattern of the pressure induced {alpha} phase demonstrated a decrease in intensity for certain select peaks. Together, these observations were used to make a complete picture of the phase transition in nanocrystalline systems. The size dependence of the transition was interpreted as resulting from the extremely high surface energy of the {alpha} phase which would increase the thermodynamic offset and thereby increase the kinetic barrier

  10. Collapse of CuO Double Chains and Suppression of Superconductivity in High-Pressure Phase of YBa2Cu4O8

    Nakayama, Atsuko; Onda, Yusuke; Yamada, Shuhei; Fujihisa, Hiroshi; Sakata, Masafumi; Nakamoto, Yuki; Shimizu, Katsuya; Nakano, Satoshi; Ohmura, Ayako; Ishikawa, Fumihiro; Yamada, Yuh

    2014-09-01

    The crystal structure and electrical resistivity of YBa2Cu4O8 (Y124) were studied under high pressure up to 18 GPa using diamond-anvil cells, respectively, in order to clarify its conduction mechanism. Y124 causes the first-order phase-transition into the orthorhombic Immm at pressure around 11 GPa. The high-pressure phase (HPP) also shows the superconductivity, while the manner of temperature dependence of electrical resistance and the pressure dependence of transition temperature, Tc, drastically change above 11 GPa. The CuO2 plane persists in HPP but the CuO double chains collapse with the phase transition and transform into three-dimensional Cu-O network, resulting in the renewal of conduction system.

  11. An environment-dependent interatomic potential for silicon carbide: calculation of bulk properties, high-pressure phases, point and extended defects, and amorphous structures

    An interatomic potential has been developed to describe interactions in silicon, carbon and silicon carbide, based on the environment-dependent interatomic potential (EDIP) (Bazant et al 1997 Phys. Rev. B 56 8542). The functional form of the original EDIP has been generalized and two sets of parameters have been proposed. Tests with these two potentials have been performed for many properties of SiC, including bulk properties, high-pressure phases, point and extended defects, and amorphous structures. One parameter set allows us to keep the original EDIP formulation for silicon, and is shown to be well suited for modelling irradiation-induced effects in silicon carbide, with a very good description of point defects and of the disordered phase. The other set, including a new parametrization for silicon, has been shown to be efficient for modelling point and extended defects, as well as high-pressure phases.

  12. An environment-dependent interatomic potential for silicon carbide: calculation of bulk properties, high-pressure phases, point and extended defects, and amorphous structures.

    Lucas, G; Bertolus, M; Pizzagalli, L

    2010-01-27

    An interatomic potential has been developed to describe interactions in silicon, carbon and silicon carbide, based on the environment-dependent interatomic potential (EDIP) (Bazant et al 1997 Phys. Rev. B 56 8542). The functional form of the original EDIP has been generalized and two sets of parameters have been proposed. Tests with these two potentials have been performed for many properties of SiC, including bulk properties, high-pressure phases, point and extended defects, and amorphous structures. One parameter set allows us to keep the original EDIP formulation for silicon, and is shown to be well suited for modelling irradiation-induced effects in silicon carbide, with a very good description of point defects and of the disordered phase. The other set, including a new parametrization for silicon, has been shown to be efficient for modelling point and extended defects, as well as high-pressure phases. PMID:21386297

  13. Laser-driven phase transitions in aqueous colloidal gold nanoparticles under high pressure: picosecond pump-probe study.

    Hashimoto, Shuichi; Katayama, Tetsuro; Setoura, Kenji; Strasser, Michael; Uwada, Takayuki; Miyasaka, Hiroshi

    2016-02-14

    Pump-probe transient extinction spectroscopy was used to analyze 355 nm picosecond laser heating-induced phenomena in 60 nm-diameter aqueous gold nanoparticles (AuNPs) under a high pressure of 60 MPa. Kinetic spectroscopy revealed that a supercritical layer surrounding the AuNP nucleated with a lifetime of approximately 1 ns during its dynamic expansion and decay for a fluence of 19.6 mJ cm(-2). Moreover, in the post-mortem transmission electron micrographs we observed a number of fragments, a small percentage of size-reduced cores, and erupted particles among the intact particles after 60 shots, suggesting that evaporation occurred under laser illumination. The particle temperature calculation indicated that evaporation begins with a liquid droplet AuNP surrounded by a supercritical layer at temperatures below the boiling point of gold. By applying high pressure, we obtained a clear picture of the evaporation event, which was not possible at ambient pressure because bubble formation caused particle temperatures to rise uncontrollably. In this study, we shed light on the critical role of the supercritical layer formed around the AuNP under high pressure during laser-induced evaporation. PMID:26812175

  14. First-principles study on the phase transition, elastic properties and electronic structure of Pt3Al alloys under high pressure

    Highlights: • The phase transition of Pt3Al alloys occurs at 60 GPa. • The elastic modulus of Pt3Al alloys increase with increasing pressure. • The cubic structure has good resistance to volume deformation under high pressure. • The pressure enhances the hybridization between Pt atom and Al atom. - Abstract: The phase transition, formation enthalpies, elastic properties and electronic structure of Pt3Al alloys are studied using first-principle approach. The calculated results show that the pressure leads to phase transition from tetragonal structure to cubic structure at 60 GPa. With increasing pressure, the elastic constants, bulk modulus and shear modulus of these Pt3Al alloys increase linearly and the bond lengths of Pt–Al metallic bonds and the peak at EF decrease. The cubic Pt3Al alloy has excellent resistance to volume deformation under high pressure. We suggest that the phase transition is derived from the hybridization between Pt and Al atoms for cubic structure is stronger than that of tetragonal structure and forms the strong Pt–Al metallic bonds under high pressure

  15. Determination of the phase boundary of the omega to beta transition in Zr using in situ high-pressure and high-temperature X-ray diffraction

    Ono, Shigeaki, E-mail: sono@jamstec.go.jp [Research and Development Center for Ocean Drilling Science, Japan Agency for Marine-Earth Science and Technology, 2-15 Natsushima-cho, Yokosuka-shi, Kanagawa 237-0061 (Japan); Kikegawa, Takumi [High Energy Acceleration Research Organization, 1-1 Oho, Tsukuba 305-0801 (Japan)

    2015-05-15

    The high-pressure behavior of zirconium has been examined using the synchrotron X-ray diffraction technique to a pressure of 38 GPa and a temperature of 800 K employing a hydrothermal diamond anvil cell technique. The structural transition from the ω to the β phase was observed. This transition has a negative dP/dT gradient, which is in general agreement with those reported in previous studies. The transition boundary was determined to be, P (GPa)=41.2–0.025×T (K). The negative slope of the transition, dP/dT, determined in our study using the diamond anvil cell technique was less than half that estimated by the previous study using a large press apparatus. - Graphical abstract: Experimental results and phase boundary of the ω–β transition in Zr. - Highlights: • X-ray diffraction patterns of zirconium were measured by the synchrotron experiments. • High-pressure experiments were performed by an external-heated diamond anvil cell. • Phase diagram of zirconium was determined at high pressures and high temperatures. • Phase boundary between omega and beta transition has a negative dP/dT slope.

  16. A density functional study of the high-pressure chemistry of MSiN2(M = Be, Mg, Ca): prediction of high-pressure phases and examination of pressure-induced decomposition

    Rebecca Römer, S.; Kroll, Peter; Schnick, Wolfgang

    2009-07-01

    Normal pressure modifications and tentative high-pressure phases of the nitridosilicates MSiN2 with M = Be, Mg, or Ca have been thoroughly studied by density functional methods. At ambient pressure, BeSiN2 and MgSiN2 exhibit an ordered wurtzite variant derived from idealized filled β-cristobalite by a C1-type distortion. At ambient pressure, the structure of CaSiN2 can also be derived from idealized filled β-cristobalite by a different type of distortion (D1-type). Energy-volume calculations for all three compounds reveal transition into an NaCl superstructure under pressure, affording sixfold coordination for Si. At 76 GPa BeSiN2 forms an LiFeO2-type structure, corresponding to the stable ambient-pressure modification of LiFeO2, while MgSiN2 and CaSiN2 adopt an LiFeO2-type structure, corresponding to a metastable modification (24 and 60 GPa, respectively). For both BeSiN2 and CaSiN2 intermediate phases appear (for BeSiN2 a chalcopyrite-type structure and for CaSiN2 a CaGeN2-type structure). These two tetragonal intermediate structures are closely related, differing mainly in their c/a ratio. As a consequence, chalcopyrite-type structures exhibit tetrahedral coordination for both cations (M and Si), whereas in CaGeN2-type structures one cation is tetrahedrally (Si) and one bisdisphenoidally (M) coordinated. Both structure types, chalcopyrite and CaGeN2, can also be derived from idealized filled β-cristobalite through a B1-type distortion. The group-subgroup relation of the BeSiN2/MgSiN2, the CaSiN2, the chalcopyrite, the CaGeN2 and the idealized filled β-cristobalite structure is discussed and the displacive phase transformation pathways are illustrated. The zero-pressure bulk moduli were calculated for all phases and have been found to be comparable to compounds such as α- Si3N4, CaIrO3 and Al4C3. Furthermore, the thermodynamic stability of BeSiN2, MgSiN2 and CaSiN2 against phase agglomerates of the binary nitrides M3N2 and Si3N4 under pressure are examined.

  17. Study of cements silicate phases hydrated under high pressure and high temperature; Etude des phases silicatees du ciment hydrate sous haute pression et haute temperature

    Meducin, F.

    2001-10-01

    This study concerns the durability of oil-well cementing. Indeed, in oil well cementing a cement slurry is pumped down the steel casing of the well up the annular space between it and the surrounding rock to support and protect the casing. The setting conditions of pressure and temperature may be very high (up to 1000 bar and 250 deg C at the bottom of the oil-well). In this research, the hydration of the main constituent of cement, synthetic tri-calcium silicate Ca{sub 3}SiO{sub 2}, often called C{sub 3}S (C = CaO; S = SiO{sub 2} and H H{sub 2}O), is studied. Calcium Silicate hydrates are prepared in high-pressure cells to complete their phase diagram (P,T) and obtain the stability conditions for each species. Indeed, the phases formed in these conditions are unknown and the study consists in the hydration of C{sub 3}S at different temperatures, pressures, and during different times to simulate the oil-well conditions. In a first step (until 120 deg C at ambient pressure) the C-S-H, a not well crystallized and non-stoichiometric phase, is synthesized: it brings adhesion and mechanical properties., Then, when pressure and temperature increase, crystallized phases appear such as jaffeite (Ca{sub 6}(Si{sub 2}O{sub 7})(OH){sub 6}) and hillebrandite (Ca{sub 2}(SiO{sub 3})(OH){sub 2}). Silicon {sup 29}Si Nuclear Magnetic Resonance (using standard sequences MAS, CPMAS) allow us to identify all the silicates hydrates formed. Indeed, {sup 29}Si NMR is a valuable tool to determine the structure of crystallized or not-well crystallized phases of cement. The characterization of the hydrated samples is completed by other techniques: X- Ray Diffraction and Scanning Electron Microscopy. The following results are found: jaffeite is the most stable phase at C/S=3. To simulate the hydration of real cement, hydration of C{sub 3}S with ground quartz and with or without super-plasticizers is done. In those cases, new phases appear: kilchoanite mainly, and xonotlite. A large amount of

  18. Supercooling of aqueous dimethylsulfoxide solution at normal and high pressures: Evidence for the coexistence of phase-separated aqueous dimethylsulfoxide solutions of different water structures

    Kanno, H.; Kajiwara, K.; Miyata, K.

    2010-05-01

    Supercooling behavior of aqueous dimethylsulfoxide (DMSO) solution was investigated as a function of DMSO concentration and at high pressures. A linear relationship was observed for TH (homogeneous ice nucleation temperature) and Tm (melting temperature) for the supercooling of aqueous DMSO solution at normal pressure. Analysis of the DTA (differential thermal analysis) traces for homogeneous ice crystallization in the bottom region of the TH curve for a DMSO solution of R =20 (R: moles of water/moles of DMSO) at high pressures supported the contention that the second critical point (SCP) of liquid water should exist at Pc2=˜200 MPa and at Tc2<-100 °C (Pc2: pressure of SCP, Tc2: temperature of SCP). The presence of two TH peaks for DMSO solutions (R =15, 12, and 10) suggests that phase separation occurs in aqueous DMSO solution (R ≤15) at high pressures and low temperatures (<-90 °C). The pressure dependence of the two TH curves for DMSO solutions of R =10 and 12 indicates that the two phase-separated components in the DMSO solution of R =10 have different liquid water structures [LDL-like and HDL-like structures (LDL: low-density liquid water, HDL: high-density liquid water)] in the pressure range of 120-230 MPa.

  19. Structural phase transition of edge-sharing copper oxide Ca0.85CuO2 under high pressure

    MAI Wenjie; ZHANG Gongmu; QIN Xiaomei; CHEN Liangchen; LI Fengying; YU Richeng; LIU Jing; JIN Changqing

    2004-01-01

    The perovskite-like structure compound Ca0.85- CuO2 has interesting structural properties: it has infinite one-dimensional edge-sharing copper-oxygen chains as well as partial occupancy of the Ca sites resulting in an incommensurate superstructure. In situ high-pressure energy dispersive X-ray diffraction measurements on polycrystalline powder Ca0.85CuO2 have been performed by using diamond anvil cell (DAC) instrument with synchrotron radiation. The results for the first time show that edge-sharing copper oxide Ca0.85CuO2 undergoes a structural transition at 14.5 GPa, and furthermore the structural transition is reversible.

  20. High-pressure-high-temperature phase relations of MgGeO3 : First-principles calculations

    Tsuchiya, Taku; Tsuchiya, Jun

    2007-09-01

    The high-pressure-high-temperature behavior of MgGeO3 has been investigated by first-principles computations. It is found that at 300K , the first transformation from ilmenite to orthorhombic perovskite at 24-38GPa is followed by the second one to the CaIrO3 structure at 51-56GPa . Quasiharmonic free energy calculations suggest that the first transformation has a negative Clapeyron slope ( -9.3MPa/K at 1000K ), whereas the second one has a less temperature-sensitive positive Clapeyron slope ( +7.8MPa/K at 1000K ). It is also confirmed that the LiNbO3 structure does not have its own stability P,T conditions. Pressure dependence of the Goldschmidt tolerance factor indicates a clear correlation between distortion of the perovskite structure and relative stability of perovskite and postperovskite structures.

  1. High-pressure phases in shock-induced melt of the unique highly shocked LL6 chondrite Northwest Africa 757

    Hu, Jinping; Sharp, Thomas G.

    2016-07-01

    Northwest Africa 757 is unique in the LL chondrite group because of its abundant shock-induced melt and high-pressure minerals. Olivine fragments entrained in the melt transform partially and completely into ringwoodite. Plagioclase and Ca-phosphate transform to maskelynite, lingunite, and tuite. Two distinct shock-melt crystallization assemblages were studied by FIB-TEM analysis. The first melt assemblage, which includes majoritic garnet, ringwoodite plus magnetite-magnesiowüstite, crystallized at pressures of 20-25 GPa. The other melt assemblage, which consists of clinopyroxene and wadsleyite, solidified at ~15 GPa, suggesting a second veining event under lower pressure conditions. These shock features are similar to those in S6 L chondrites and indicate that NWA 757 experienced an intense impact event, comparable to the impact event that disrupted the L chondrite parent body at 470 Ma.

  2. High-pressure phase behaviour of the binary system {CO2 + cis-decalin} from (292.75 to 373.75) K

    The phase behaviour of the {CO2 (1) + cis-decalin (2)} binary system has been experimentally studied at temperatures ranging from (292.75 to 373.75) K. Saturation pressures, ranging from (15.9 to 490.5) bar, were obtained using a variable volume high-pressure cell by visual observation of phase transitions at constant overall composition. For this system, no literature data are available and the results obtained in this study reveal the occurrence of vapor-liquid, liquid-liquid, and vapor-liquid-liquid phase transitions in the investigated temperature range. A total of 133 experimental points are reported including bubble points, dew points, liquid-liquid phase equilibria, and coordinates of the three-phase line. The experimental data can be reasonably predicted by the PPR78 model in which the temperature-dependent binary interaction parameter is calculated by a group contribution method

  3. High Pressure and high temperature phase transition in FeTiO3: implications for the deep interior of giant planet

    Hamane, D.; Zhang, M.; Yagi, T.; Yanming, M.

    2011-12-01

    The discovery of the structural phase transition of perovskite into a CaIrO3-type phase at high pressures invites the investigation of further phase transitions in order to understand the deep interior of giant planet. Recent experimental studies for FeTiO3 have detected a new dissociation to a dense compound assemblage rather than the CaIrO3-type phase at high pressures. Since the phase relation of FeTiO3 is expected to be significant for estimating the ultrahigh-pressure behavior of ABX3 compounds such as MgSiO3, we investigated the phase transition in FeTiO3 up to 80 GPa and 2600K by synchrotron X-ray diffraction using a laser-heated diamond anvil cell and analytical transmission electron microscopy observations. We conclude that FeTiO3 ilmenite transforms into the following phase(s) with increasing pressure: FeTiO3 (perovskite) at 18-30 GPa, 1/2 Fe2TiO4 (Ca2TiO4-type) + TiO2 (OI-type) at 30-45 GPa and high temperature, FeO (wüstite) + TiO2 (OI) at 30-45 GPa and low temperature, and 2/3 FeO (wüstite) + 1/3 FeTi3O7 (orthorhombic phase) above 45 GPa. We also estimates the structural model of FeTi3O7 phase by using the particle swarm optimization simulation, and Rietveld refinement based on this model structure gave an excellent fit with the experimentally obtained X-ray diffraction pattern. This new high-density FeTi3O7 structure consists of the polyhedra for monocapped prisms FeO7, bicapped prisms TiO8, and tricapped prisms TiO9 with Imm2 symmetry. The dense compound assemblage found in FeTiO3 is promising for investigating the behavior of ABX3 compounds under ultrahigh pressures, and our experimental results suggest that the AB3X7 type oxide instead of cotunnite SiO2 may produce the denser assemblage even in the silicate system at ultra high pressure. This new model has not yet been proposed as a candidate, but our suggestion will be important for predicting the mineral assemblage in the deep interiors of giant planets.

  4. Compressibility and phase transformations of AgInSe{sub 2} from high-pressure X-ray diffraction studies

    Orlova, N.S.; Turtsevich, G.A.; Bodnar, I.V. [Institute of Solid State and Semiconductor Physics, Minsk (Belarus)

    1994-06-01

    The compound AgInSe{sub 2} is one of the A{sup I}B{sup III}C{sup VI}{sub 2} ternary semiconductors, which exhibit unique optical properties and are highly promising materials for use in nonlinear optics and semiconductor engineering. Their elastic properties are of great importance and yet, unlike other characteristics, remain inadequately studied. In particular, the elastic constants were determined only for AgGaS{sub 2} and AgGaSe{sub 2}. The compressibilities were measured for a number of CuB{sup III}C{sup VI}{sub 2} compounds and for three Ag compounds AgGaS{sub 2}, AgGaSe{sub 2}, and AgGaTe{sub 2}. No data on the compressiblity of AgInC{sup VI}{sub 2} compounds is available in the literature. The compressibilities along the major directions of AgInS{sub 2} crystals with the chalcopyrite structure were reported. In this work, we studied the compressibility of AgInSe{sub 2} using high-pressure X-ray diffraction analysis.

  5. Observation of phase transformations in LiMn2O4 under high pressure and at high temperature by in situ X-ray diffraction measurements

    This work presents the diffraction features of lithium-manganese oxide in extreme pressure and temperature conditions used as positive electrode materials in lithium-ion batteries. Energy-dispersive X-ray diffraction yield reliable description of material lattice, its distortion and chemical stability under high pressure and at high temperature (HP/HT). The phase evolution as a function of pressure and temperature is reported and analyzed in the LiMn2O4 sample. A comparison with another tetragonal spinel shows the influence of the Jahn-Teller effect on the HP/HT structure of this class of materials.

  6. Effects of grinding-induced grain boundary and interfaces on electrical transportation and structure phase transition in ZnSe under high pressure

    Jie, Yang; Pei, Wang; Guo-Zhao, Zhang; Xiao-Xue, Zhou; Jing, Li; Cai-Long, Liu

    2016-06-01

    Interface and scale effects are the two most important factors which strongly affect the structure and the properties of nano-/micro-crystals under pressure. We conduct an experiment under high pressure in situ alternating current impedance to elucidate the effects of interface on the structure and electrical transport behavior of two ZnSe samples with different sizes obtained by physical grinding. The results show that (i) two different-sized ZnSe samples undergo the same phase transitions from zinc blend to cinnabar-type phase and then to rock salt phase; (ii) the structural transition pressure of the 859-nm ZnSe sample is higher than that of the sample of 478 nm, which indicates the strong scale effect. The pressure induced boundary resistance change is obtained by fitting the impedance spectrum, which shows that the boundary conduction dominates the electrical transport behavior of ZnSe in the whole experimental pressure range. By comparing the impedance spectra of two different-sized ZnSe samples at high pressure, we find that the resistance of the 478-nm ZnSe sample is lower than that of the 859-nm sample, which illustrates that the sample with smaller particle size has more defects which are due to physical grinding. Project supported by the National Natural Science Foundation of China (Grant Nos. 11404133 and 11374121) and the Program of Science and Technology Development Plan of Jilin Province, China (Grant No. 20140520105JH).

  7. High-Pressure Microfluidics

    Ogden, Sam

    2013-01-01

    In this thesis, some fundamentals and possible applications of high-pressure microfluidics have been explored. Furthermore, handling fluids at high pressures has been addressed, specifically by creating and characterizing strong microvalves and pumps. A variety of microstructuring techniques was used to realize these microfluidic devices, e.g., etching, lithography, and bonding. To be able to handle high pressures, the valves and pumps need to be strong. This necessitates a strong actuator ma...

  8. Phase transitions and equation of state of CsI under high pressure and the development of a focusing system for x-rays

    The phase transitions and equation of state of ionic solid cesium iodide were studied under high pressure and room temperature in a diamond anvil cell. The studies were carried out using both energy dispersive and angular dispersive diffraction methods on synchrotron radiation sources over the pressure range from atmospheric pressure to over 300 gigapascals (3 million atmospheres). CsI undergoes a distinct phase transition at about 40 GPa, a pressure that is much lower than the reported insulator-metal transition at 110 GPa, from the atmospheric pressure B2(CsCl) structure to an orthorhombic structure. At higher pressures, a continuous distortion in the structure was observed with a final structure similar to a hcp lattice under ultra high pressure. No volume discontinuity was observed at the insulator-metal transition. The newly found transition sequence is different from the result of previous static compression studies. The current structure has a smaller unit cell volume than the previous assignment. This has resolved a long existing controversy among the previous static compression studies, the dynamic compression studies, and the theoretical studies. The current results also explain the apparent discrepancy between the present study and the previous static studies. We also present the development of a focusing system for high energy x-rays (> 12 keV) that is particularly suited for high pressure diffraction studies. This system uses a pair of multilayer coated spherical mirrors in a Kirkpatrick-Baez geometry. A focused beam size less than 10 micron in diameter can be readily achieved with sufficient intensity to perform diffraction studies. 93 refs., 46 figs., 15 tabs

  9. Phase behaviour and thermodynamic modelling for the system (grape seed oil + carbon dioxide + ethanol) at high pressures

    This short communication reports phase equilibrium data (cloud points), employing the synthetic static method, for the system {grape seed oil (GSO) + carbon dioxide (CO2) + ethanol} up to T = 343.15 K and 22.53 MPa. Experimental results were modelled using the Peng-Robinson equation of state with the classical van der Waals quadratic mixing rule (PR-vdW2). It is shown that the thermodynamic model is able to represent satisfactorily the phase behaviour of the system investigated

  10. Polymorphism of iron at high pressure: A 3D phase-field model for displacive transitions with finite elastoplastic deformations

    Vattré, A.; Denoual, C.

    2016-07-01

    A thermodynamically consistent framework for combining nonlinear elastoplasticity and multivariant phase-field theory is formulated at large strains. In accordance with the Clausius-Duhem inequality, the Helmholtz free energy and time-dependent constitutive relations give rise to displacive driving forces for pressure-induced martensitic phase transitions in materials. Inelastic forces are obtained by using a representation of the energy landscape that involves the concept of reaction pathways with respect to the point group symmetry operations of crystal lattices. On the other hand, additional elastic forces are derived for the most general case of large strains and rotations, as well as nonlinear, anisotropic, and different elastic pressure-dependent properties of phases. The phase-field formalism coupled with finite elastoplastic deformations is implemented into a three-dimensional Lagrangian finite element approach and is applied to analyze the iron body-centered cubic (α-Fe) into hexagonal close-packed (ɛ-Fe) phase transitions under high hydrostatic compression. The simulations exhibit the major role played by the plastic deformation in the morphological and microstructure evolution processes. Due to the strong long-range elastic interactions between variants without plasticity, a forward α → ɛ transition is energetically unfavorable and remains incomplete. However, plastic dissipation releases considerably the stored strain energy, leading to the α ↔ ɛ ↔α‧ (forward and reverse) polymorphic phase transformations with an unexpected selection of variants.

  11. The nonlinear anomalous lattice elasticity associated with the high-pressure phase transition in spodumene: A high precission static compression study

    Ullrich, A; Miletich, R; 10.1007/s00269-009-0300-8

    2010-01-01

    The high-pressure behavior of the lattice elasticity of spodumene, LiAlSi2O6, was studied by static compression in a diamond-anvil cell up to 9.3 GPa. Investigations by means of single-crystal XRD and Raman spectroscopy within the hydrostatic limits of the pressure medium focus on the pressure ranges around similar to 3.2 and similar to 7.7 GPa, which have been reported previously to comprise two independent structural phase transitions. While our measurements confirm the well-established first-order C2/c-P2(1)/c transformation at 3.19 GPa (with 1.2% volume discontinuity and a hysteresis between 0.02 and 0.06 GPa), both unit-cell dimensions and the spectral changes observed in high-pressure Raman spectra give no evidence for structural changes related to a second phase transition. Monoclinic lattice parameters and unit-cell volumes at in total 59 different pressure points have been used to re-calculate the lattice-related properties of spontaneous strain, volume strain, and the bulk moduli as a function of pr...

  12. The disproportionation reaction phase transition, mechanical, and lattice dynamical properties of the lanthanum dihydrides under high pressure: A first principles study

    Yang, Jin-Wen; Gao, Tao; Gong, Yan-Rong

    2014-06-01

    The pressure-induced disproportionation reaction phase transition, mechanical, and dynamical properties of LaH2 with fluorite structure under high pressure are investigated by performing first-principles calculations using the projector augmented wave (PAW) method. The phase transition of 2LaH2 → LaH + LaH3 obtained from the usual condition of equal enthalpies occurs at the pressure of 10.38 GPa for Perdew-Wang (PW91) functional and 6.05 GPa for Ceperly-Adler (CA) functional, respectively. The result shows that the PW91 functional calculations agree excellently with the experimental finding of 11 GPa of synchrotron radiation (SR) X-ray diffraction (XRD) of Machida et al. and 10 GPa of their PBE functional theoretical result. Three independent single-crystal elastic constants, polycrystalline bulk modulus, shear modulus, Young's modulus, elastic anisotropy, Poisson's ratio, the brittle/ductile characteristics and elastic wave velocities over different directions dependences on pressure are also successfully obtained. Especially, the phonon dispersion curves and corresponding phonon density of states of LaH2 under high pressure are determined systematically using a linear-response approach to density functional perturbation theory (DFPT). Our results demonstrate that LaH2 in fluorite phase can be stable energetically up to 10.38 GPa, stabilized mechanically up to 17.98 GPa, and stabilized dynamically up to 29 GPa, so it may remain a metastable phase above 10.38 GPa up to 29 GPa, these calculated results accord with the recent X-Ray diffraction experimental finding and theoretical predictions of Machida et al.

  13. Phase stability, physical properties of rhenium diboride under high pressure and the effect of metallic bonding on its hardness

    Highlights: •The transition pressure Pt between the ReB2–ReB2 and MoB2–ReB2 phases is firstly determinate. •The single-bonded B–B feather remains in ReB2 compounds. •A semiempirical method to evaluate the hardness of crystals with partial metallic bond is presented. •The large hardness (39.1 GPa) of ReB2–ReB2 indicate that it is a superhard material. •The zigzag interconnected B–Re and B–B covalent bonds underlie the ultraincompressibilities. -- Abstract: Using first-principles calculations, the elastic constants, thermodynamic property and structural phase transition of rhenium diboride under pressure are investigated by means of the pseudopotential plane-waves method, as well as the effect of metallic bond on its hardness. Eight candidate structures of known transition-metal compounds are chosen to probe for rhenium diboride ReB2. The calculated lattice parameters are consistent with the experimental and theoretical values. Based on the third order Birch–Murnaghan equation of states, the transition pressure Pt between the ReB2–ReB2 and MoB2–ReB2 phases is firstly determinate. Elastic constants, shear modulus, Young’s modulus, Poisson’s ratio and Debye temperature are derived. The single-bonded B–B feather remains in ReB2 compounds. Furthermore, according to Mulliken overlap population analysis, a semiempirical method to evaluate the hardness of multicomponent crystals with partial metallic bond is presented. Both strong covalency and a zigzag topology of interconnected bonds underlie the ultraincompressibilities. In addition, the superior performance and large hardness (39.1 GPa) of ReB2–ReB2 indicate that it is a superhard material

  14. High-pressure phase behavior of MnTiO3: decomposition of perovskite into MnO and MnTi2O5

    Okada, Taku; Yagi, Takehiko; Nishio-Hamane, Daisuke

    2011-04-01

    The phase relations and compression behavior of MnTiO3 perovskite were examined using a laser-heated diamond-anvil cell, X-ray diffraction, and analytical transmission electron microscopy. The results show that MnTiO3 perovskite becomes unstable and decomposes into MnO and orthorhombic MnTi2O5 phases at above 38 GPa and high temperature. This is the first example of ABO3 perovskite decomposing into AO + AB2O5 phases at high pressure. The compression behavior of volume, axes, and the tilting angle of TiO6 octahedron of MnTiO3 perovskite are consistent with those of other A2+B4+O3 perovskites, although no such decomposition was observed in other perovskites. FeTiO3 is also known to decompose into two phases, instead of transforming into the CaIrO3-type post-perovskite phase and we argue that one of the reasons for the peculiar behavior of titanate is the weak covalency of the Ti-O chemical bonds.

  15. High-pressure structural phase transitions in TiO sub 2 and synthesis of the hardest known oxide

    Ahuja, R

    2002-01-01

    Despite great technological importance and many investigations, a material with a measured hardness comparable to that of diamond or cubic boron nitride has yet to be identified. Our combined theoretical and experimental investigations led to the discovery of a new polymorph of titanium dioxide, where titanium is ninefold coordinated to oxygen in the cotunnite (PbCl sub 2) structure. Hardness measurements on this phase, synthesized at pressures above 60 GPa and temperatures above 1000 K, reveal that this material is the hardest oxide yet discovered. Furthermore, it is one of the least compressible (with a measured bulk modulus of 431 GPa) and hardest (with a microhardness of 38 GPa) polycrystalline materials studied so far.

  16. Study on two-phase flow dynamics in steam injectors II. High-pressure tests using scale-models

    Analytical and experimental studies have been conducted on large-scale steam injectors for a next-generation reactor. The steam injectors are simple, compact, passive steam jet pumps for a steam-injector-driven passive core injection system (SI-PCIS) or steam-injector-driven primary loop recirculation system (SI-PLR). In order to check the feasibility of such large-scale steam injectors we developed the separate-two-phase flow models installed in the PHOENICS Code, and scale-model tests were conducted for both SI-PCIS and SI-PLR. A 1/2 scale SI-PCIS model achieved a discharge pressure of almost 8 MPa with 7 MPa steam and 0.4 MPa water, and a 1/5 scale SI-PLR model attained a discharge pressure of 12.5 MPa with 3 MPa steam and 7 MPa water. Both results are in good agreement with the analysis, confirming the feasibility of both systems. The systems will help to simplify the next generation of BWRs.

  17. High pressure phase transitions in Mg{sub 1-x}Ca{sub x}O: Theory

    Srivastava, Anurag; Chauhan, Mamta [Advanced Material Research Lab, Indian Institute of Information Technology and Management, Gwalior (India); Singh, R.K. [Department of Physics, ITM University, Gurgaon (India); Padegaonker, Rishikesh [Indian Embassy School, Sana (Yemen)

    2011-08-15

    We have analysed a B1 {yields} B2 structural phase transitions in Mg{sub 1-x}Ca{sub x}O solid solutions and their ground state properties by using first principle density functional theory and charge transfer interaction potential (CTIP) approach. The effects of exchange-correlation interactions are handled by the generalized gradient approximation with Perdew-Burke-Ernzerhof type parameterization. CTIP approach includes the long range modified Coulomb with charge transfer interactions and short range part of this model includes the van der Waals as well as Hafemeister Flygare type overlap repulsive interactions. The study observes a linear variation of calculated transition pressure, bulk modulus and lattice parameter of Mg{sub 1-x}Ca{sub x}O as a function of Ca composition. The observed results for the end point members are in agreement to their experimental counterparts and the deviations have been discussed. (Copyright copyright 2011 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  18. Construction of a Direct Water-Injected Two-Stroke Engine for Phased Direct Fuel Injection-High Pressure Charging Investigations

    Somsel, James P.

    1998-01-01

    The development of a water injected Orbital Combustion Process (OCP) engine was conducted to assess the viability of using the powerplant for high altitude NASA aircraft and General Aviation (GA) applications. An OCP direct fuel injected, 1.2 liter, three cylinder, two-stroke engine has been enhanced to independently inject water directly into the combustion chamber. The engine currently demonstrates low brake specific fuel consumption capability and an excellent power to weight ratio. With direct water injection, significant improvements can be made to engine power, to knock limits/ignition advance timing, and to engine NO(x) emissions. The principal aim of the testing was to validate a cyclic model developed by the Systems Analysis Branch at NASA Ames Research Center. The work is a continuation of Ames' investigations into a Phased Direct Fuel Injection Engine with High Pressure Charging (PDFI-ITPC).

  19. Experimental study of simulating high pressure steam-water to-phase flow with sulfur hexafluoride gas and ethyl alcohol liquid

    Mist flow appears in various industrial plants and machines; nuclear power plants, chemical plants, heat exchangers, steam turbines, and so on. Behaviors of droplet have effects on heat and mass transfer process on them. As for a steam generator of a nuclear power plant, mist flow appears at primary and secondary separator. These apparatus separates steam and droplet. Droplet erodes steam turbine blade and gives it too much damage. In order to prevent it, we must clarify the behavior of droplet; i.e. diameter and its distribution. Clarification of droplet behavior at actual pressure and temperature of a steam generator is very difficult and it costs too much and takes long time to develop a steam generator. It is needed, therefore, to develop a new experimental method. One of the best ways is to use alternate fluids of which properties as same as that of high pressure and high temperature steam-water system. We have developed the new experimental method and simulated actual pressure steam-water two phase flow using Sulfur Hexafluoride gas and ethyl alcohol liquid two-phase flow at low pressures and atmospheric temperature. The specific objectives of this study are to: (1) simulate easily a high pressure and high temperature steam-water system by using alternative fluids; (2) confirm that Sulfur Hexafluoride and ethyl alcohol system at atmospheric temperature and low pressure is able to simulate steam-water system. For measuring drop diameter, the laser diffraction technique was applied. Further, the photographs of the droplets were taken by the video camera. The drop diameter decreased as increasing gas velocity and it was found that drop diameter was about 100∼200μm under the simulation condition of 6MPa and 280 .deg. C

  20. Synthesis of new cubic C3N4 and diamond-like BC3 phases under high pressure and high temperature

    In this report, we discuss the progress in synthesis of new binary phases from B-C-N triangle in DAC under high-pressure and high-temperature (HPHT) conditions: cubic C3N4 (c-C3N4) and diamond-like BC3 (d-BC3) phase. These two phases have been synthesized by direct transformation from graphitic phases under HPHT conditions. The c-C3N4 phase was recovered at ambient conditions from the graphite-like C3N4 (g-C3N4) phase subjected to pressures between 21 and 38 GPa in a diamond anvil cell, laser-heated to temperatures between 1600 and 3000 K. The x-ray diffraction data on the new phase are best explained by a cubic unit cell with the lattice parameters a = 3.878±0.001 A. The synthesis of the c-C3N4 phase has been also conducted in a large volume press at pressure 25 GPa and temperature 20000C. X-ray peaks of c-C3N4 phase obtained in the large-volume press are weaker than those of diamonds. Application of the UV Raman spectroscopy revealed that UV Raman spectrum of the g-C3N4 is substantially different from that measured with visible Raman spectroscopy. It has two strong peaks at 690 cm-1 and at 986 cm-1 assigned to different types of the ring (s-triazine ring) breathing modes. A diamond-like BC3 has been synthesized at temperature 2033 ± 241 K and at pressure 50 GPa. The conclusion about the phase transition from graphitic BC3 (g-BC3) to d-BC3 phase was made from the analysis of Raman scattering data. The Raman spectrum of the novel d-BC3 displays all the peaks but one at 671 cm-1 characteristic to Raman spectra the B doped diamond. The peaks pattern of the d-BC3 suggests that this phase could become a superconductor at low temperatures

  1. On the Chemical Evolution of Upper Mantle of the Early Earth—An Experimental Study on Melting of the Silicate Phase in Jilin Chondrite at High Pressures

    谢鸿森; 方虹; 等

    1989-01-01

    Relatively old ages of chondrites(normally around 4.5Ga)suggest that their parent bodies did not experience any mely-fractionation under high temperature and high pressure conditions pertaining to the interior of terrestrial plaets.Therefore,it is reasonable to take chondrites as starting materials in the study of the chemical evolution of the early earth.The sillicate phase in the Jilin chondrite (H5)was chosen for this purpose because it possesses a chemical composition similar to that of the primitive mantle.The melting experiment was carried out at 20-30 k bar and has rsulted in a product which contains1-5% melts in addition to solid cryustal phase.The chemical composition of the melt phases and the partitioning of various elements between the coexisting silicate melts are geochemically similar to those of anatectic rocks on the earth.This can thus serve as the basis for discussing the chemical evolution of the early upper mantle.

  2. Elastic Constants at High Pressure, Solid-Liquid Phase Boundaries and Equations of State for Solid and Liquid Copper and 316-Stainless Steel

    Hayes, Dennis

    1999-06-01

    Prior accurate measurements of sound speed on the Hugoniot for copper and 316-SS are used to construct complete equations of state for solid and liquid phases. Differences between calculated bulk and observed elastic sound-speed in the solid are used to infer high-pressure elastic constants. At higher pressures, where the shocked state is entirely liquid, data are sufficient to construct the EOS including an accurate estimate for Grüneisen's ratio. The liquid EOS also reasonably describes some low-pressure, high-temperature properties, including density, sound speed, variation of sound speed with temperature, and thermal expansion, lending confidence to its accuracy. Results are comparable for each metal: the shear modulus increases along the Hugoniot and then drops precipitously toward zero as the pressure nears the liquid-phase boundary. In the liquid, Grüneisen's ratio is observed to be constant and agrees with the value measured for the liquid at zero pressure. The state below which this constancy holds is identified as the smallest pressure on the Hugoniot at which melting is complete. The gap between pure solid and pure liquid is identified as the mixed-phase region and in the case of copper, its size and location are in reasonable agreement with published ab initio calculations of Moriarty. Confidence in calculated temperature and entropy is less then that in pressure, volume and energy owing to uncertainties in specific heats.

  3. Experimental study of simulating high pressure steam-water two-phase flow with sulfur hexafluoride gas and ethyl alcohol liquid (droplets behavior of downward mist flow)

    The full text follows. Mist flow appears in various industrial plants and machines; nuclear power plants, chemical plants, heat exchangers, steam turbines, and so on. Behaviors of droplet have effects on heat and mass transfer process on them. As for nuclear power plants, droplet diameters of downward mist flow have an important effect on peak-clad-temperature (PCT) at loss of coolant accidents (LOCA). Reliability of two-fluid model computer codes to predict gas-liquid two-phase flow relies on the experimental database. We simulated actual pressure steam-water two-phase flow using Sulfur Hexafluoride gas and ethyl alcohol liquid two-phase flow at low pressures. The specific objectives of this study are to: (1) simulate easily a high pressure and high temperature steam-water system by using alternative fluids; (2) clarify the diameter of droplet which does not break up any more (stable droplet diameter) in the blow down phenomenon of LOCA; (3) extend the downward mist flow database to lower liquid-to-gas density ratio. We carried out the experiment of downward mist flow with two kinds of fluids: Sulfur Hexafluoride (SF6) and ethyl alcohol (C2H5OH) as gas and liquid phase, respectively. Those fluids can simulate a high pressure and temperature steam-water system of 6 MPa, and 550 K at the condition of the lower pressure and atmospheric temperature (0.5 MPa and 300 K, respectively). The physical properties of SF6 and C2H5OH are as same as steam-water system. The density ratio and surface tension, which affect on the diameter of droplet, of SF6 / C2H5OH at 0.5 MPa and 300 K is about 30 and 2.1 10-2 N/m, respectively. SF6 is widely used in electronic equipment as insulating gas. It stays in the same chemical state under the condition of atmospheric temperature and chemical decomposition due to thermal energy is not developed below 770 K. Experimental conditions of superficial gas and liquid velocities were 1.5 m/s-10 m/s and 0.01 m/s-0.03 m/s, respectively. The system

  4. Rapid determination of sixteen sulfonylurea herbicides in surface water by solid phase extraction cleanup and ultra-high-pressure liquid chromatography coupled with tandem mass spectrometry.

    Yan, Cuimin; Zhang, Beibei; Liu, Wenyuan; Feng, Feng; Zhao, Yonggang; Du, Hui

    2011-11-15

    A sensitive and very fast analytical method has been developed for the simultaneous quantification of sixteen sulfonylurea herbicides in surface water. An ultra-high-pressure liquid chromatography coupled with tandem mass spectrometry method with solid phase extraction for sample cleanup has been developed for screening sixteen sulfonylurea herbicides (oxasulfuron, thifensulfuron-methyl, cinosulfuron, metsulfuron methyl, sulfometuron methyl, triasulfuron, rimsulfuron, ethametsulfuron methyl, sulfosulfuron, tribenuron methyl, bensulfuron methyl, iodosulfuron methyl, pyrazosulfuron ethyl, prosulfuron, chlorimuron ethyl, ethoxysulfuron) in water samples simultaneously within 12 min. Water samples were acidified, and the target herbicides were extracted by passing through ProElut C18 extraction cartridges. After drying by nitrogen flow, the cartridges were eluted with elution solvents, and the eluate was then evaporated to dryness, redissolved and analyzed. The mobile phase composed of 0.02% formic acid and acetonitrile using gradient elution. A triple quadrupole mass spectrometer equipped with an electrospray ionization source operated in the positive ion with selective reaction monitoring mode. Each of the analytes in all the samples was monitored using protonated molecule and its two characteristic fragment ions for confirmation. The limits of detection for all analytes were below 1.0 ng/mL, except for sulfosulfuron and prosulfuron, and limits of quantitation were between 1 and 8 ng/mL for this method. Three water types were used for the validation of the method. PMID:21983197

  5. An experimental study of two-phase critical flow with non-condensable gas in a small-diameter pipe at high pressure and normal temperature

    An experimental study is performed on two-phase critical flow with non-condensable gas in a small diameter pipe at high pressure and normal temperature. T2GDM, which is a test section for measuring void fraction inside, is used on KAREI non-condensable gas two-phase critical flow test facility which has the existing test section T2. The gamma densitometer for void fraction measurement is composed of a sealed gamma ray source, a shielding equipment, a radiation detector, a signal processing unit and a traversing system. The measurement results show that a lot of void is generated while passing through the test section. Experimental data of critical flow rates are generated using two test section of T2 and T2GDM. The results show that the critical flow rates decrease rapidly with the increase of the volumetric gas fraction. The experiments are simulated with the MARS2.1 code. The simulation results show that the modified Henry-Fauske model in the MARS2.1 code predicts well the measured critical flow rates when the non-condensable gas is not injected, while it over-predicts the flow rates when the non-condensable gas is injected

  6. Infrared Spectra of High Pressure Carbon Monoxide

    Evans, W J; Lipp, M J; Lorenzana, H E

    2001-09-21

    We report infrared (IR) spectroscopic measurements of carbon monoxide (CO) at high pressures. Although CO is one of the simplest heteronuclear diatomic molecules, it displays surprisingly complex behavior at high pressures and has been the subject of several studies [1-5]. IR spectroscopic studies of high pressures phases of CO provide data complementing results from previous studies and elucidating the nature of these phases. Though a well-known and widely utilized diagnostic of molecular systems, IR spectroscopy presents several experimental challenges to high pressure diamond anvil cell research. We present measurements of the IR absorption bands of CO at high pressures and experimentally illustrate the crucial importance of accurate normalization of IR spectra specially within regions of strong absorptions in diamond.

  7. High-pressure phase behaviors of ZnTiO3: ilmenite-perovskite transition, decomposition of perovskite into constituent oxides, and perovskite-lithium niobate transition

    Akaogi, M.; Abe, K.; Yusa, H.; Kojitani, H.; Mori, D.; Inaguma, Y.

    2015-06-01

    High-pressure high-temperature phase transitions of ZnTiO3 ilmenite were examined using multianvil apparatus up to 25.5 GPa and 1,500 °C and diamond anvil cell to 26.5 GPa and about 2,000 °C. Combined results of the multianvil quench experiments and in situ diamond anvil cell experiments indicated that at about 10 GPa and 1,200 °C ZnTiO3 ilmenite transforms to orthorhombic perovskite which is converted to lithium niobate phase on release of pressure. The boundary of the ilmenite-provskite transition is expressed by P(GPa) = 15.9 - 0.005 T (°C). The high-pressure experiments also indicated that at 20-24 GPa and 1,000-1,400 °C ZnTiO3 orthorhombic perovskite dissociates into rocksalt-type ZnO + baddeleyite-type TiO2 which are recovered, respectively, as wurtzite-type ZnO and α-PbO2-type TiO2 at 1 atm. The boundary of the perovskite dissociation is expressed by P(GPa) = 8.7 + 0.011 T (°C). Molar volume changes of ZnTiO3 at ambient conditions were estimated as -4.7 % for the ilmenite-perovskite transition and -3.5 % for the perovskite decomposition into the oxides. The absence of CaIrO3-type postperovskite in ZnTiO3 is consistent with that dissociation of ZnTiO3 perovskite into the oxides has the larger molar volume change than -1 to -2 % of the perovskite-postperovskite transition in various ABO3 compounds and with previous data that ABO3 perovskites with relatively ionic B-O bonds do not transform to the postperovskite. The transition behaviors of ZnTiO3 are similar to those of MnTiO3 and FeTiO3, but ZnTiO3 perovskite dissociates into the constituent oxides.

  8. Deuterium high pressure target

    The design of the deuterium high-pressure target is presented. The target having volume of 76 cm3 serves to provide the experimental research of muon catalyzed fusion reactions in ultra-pure deuterium in the temperature range 80-800 K under pressures of up to 150 MPa. The operation of the main systems of the target is described: generation and purification of deuterium gas, refrigeration, heating, evacuation, automated control system and data collection system

  9. Deuterium High Pressure Target

    Perevozchikov, V; Vinogradov, Yu I; Vikharev, M D; Ganchuk, N S; Golubkov, A N; Grishenchkin, S K; Demin, A M; Demin, D L; Zinov, V G; Kononenko, A A; Lobanov, V N; Malkov, I L; Yukhimchuk, S A

    2001-01-01

    The design of the deuterium high-pressure target is presented. The target having volume of 76 cm^3 serves to provide the experimental research of muon catalyzed fusion reactions in ultra-pure deuterium in the temperature range 80-800 K under pressures of up to 150 MPa. The operation of the main systems of the target is described: generation and purification of deuterium gas, refrigeration, heating, evacuation, automated control system and data collection system.

  10. High pressure gas target

    Gelbart, W.; Johnson, R. R.; Abeysekera, B.

    2012-12-01

    Compact, high pressure, high current gas target features all metal construction and semi-automatic window assembly change. The unique aspect of this target is the domed-shaped window. The Havar alloy window is electron beam welded to a metal ring, thus forming one, interchangeable assembly. The window assembly is sealed by knife-edges locked by a pneumatic toggle allowing a quick, in situ window change.

  11. Distinction of synthetic dl-α-tocopherol from natural vitamin E (d-α-tocopherol) by reversed-phase liquid chromatography. Enhanced selectivity of a polymeric C18 stationary phase at low temperature and/or at high pressure.

    Yui, Yuko; Miyazaki, Shota; Ma, Yan; Ohira, Masayoshi; Fiehn, Oliver; Ikegami, Tohru; McCalley, David V; Tanaka, Nobuo

    2016-06-10

    Separation of diastereomers of dl-α-tocopherol was studied by reversed-phase liquid chromatography using three types of stationary phases, polymeric ODS, polymeric C30, and monomeric ODS. Polymeric ODS stationary phase (Inertsil ODS-P, 3mmID, 20cm) was effective for the separation of the isomers created by the presence of three chiral centers on the alkyl chain of synthetic dl-α-tocopherol. Considerable improvement of the separation of isomers was observed on ODS-P phase at high pressure and at low temperature. Complete separation of four pairs of diastereomers was achieved at 12.0°C, 536bar, while three peaks were observed when the separation was carried out either at 12.0°C at low pressure or at 20°C at 488bar. Higher temperature (30.0°C) with the ODS-P phase resulted in only partial separation of the diastereomers even at high pressure. Only slight resolution was observed for the mixture of diastereomers with the C30 stationary phase (Inertsil C30) at 12.0°C and 441bar, although the stationary phase afforded greater resolution for β- and γ-tocopherol than ODS-P. A monomeric C18 stationary phase did not show any separation at 12.0°C and 463bar. The results suggest that the binding site of the polymeric ODS-P phase is selective for flexible alkyl chains that provided the longest retention for the natural form, (R,R,R) form, and the enantiomer, (S,S,S) form, of dl-α-tocopherol. PMID:27157422

  12. Phase diagram of the La-Si binary system under high pressure and the structures of superconducting LaSi5 and LaSi10

    The La-Si binary phase diagram under a high pressure of 13.5 GPa was experimentally constructed. New superconducting silicides LaSi5 and LaSi10 were found, which have peritectic decomposition temperatures at 1000 and 750 deg. C, respectively. The single crystal X-ray structural analysis revealed that there are two polymorphs in LaSi5. The α-form obtained by heating a molar mixture of LaSi2 and 3 Si at about 700 deg. C or by a rapid cooling from 1000 deg. C under pressure crystallizes with the space group C2/m and the lattice parameters a=15.11(3), b=4.032(6), c=8.26(1) A, and β=109.11(1)o. The β-form obtained by a slow cooling from 800-950 deg. C to 600 deg. C under pressure has the same space group but with slightly different lattice parameters, a=14.922(7), b=3.906(2), c=8.807(4) A, and β=107.19(1)o. The β-form is formed during the incomplete transformation of the α-form on cooling, and has always been obtained as a mixture with the α-form. The compound can be characterized as a Zintl phase with a polyanionic framework ∞3[Si5]3- with large tunnels running along the b axis hosting lanthanum ions. In the β-form, three of the five Si sites are disordered. The two polymorphs contain one dimensional sila-polyacene ribbons, Si ladder polymer, running along the b axis. The α-form showed superconductivity with the transition temperature Tc of 11.5 K. LaSi10 crystallizes with the space group 63/mmc and the lattice parameters a=9.623(4), c=4.723(3) A. It is composed of La containing Si18 polyhedra (La-Si18) of hexagonal beer-barrel shape, which form straight columns by stacking along the c-axis via face sharing. One-dimensional columns of La-Si18 barrels are edge-shared, and bundled with infinite Si trigonal bipyramid chains via corner sharing. The Si atoms in the straight chains have a five-fold coordination. LaSi10 became a superconductor with Tc=6.7 K. The ab initio calculation of the electric band structures showed that α-LaSi5 and LaSi10 are metallic, and

  13. High-pressure phase behaviour measurement of (CO2 + ethylene glycol dimethacrylate) and (CO2 + di-ethylene glycol dimethacrylate) binary mixture systems

    Highlights: → Binary mixtures of CO2 + EGDMA and CO2 + DEGDMA have been studied. → Isothermal experimental data were determined from 313.2 to 363.2 K. → A static method with a variable-volume view cell was used. → The experimental data was correlated well using the Peng-PR model. - Abstract: Ethylene glycol dimethacrylate (EGDMA) and di-ethylene glycol dimethacrylate (DEGDMA) are two of the most wildly used di-functional monomers in the polymer industry. The EGDMA and DEGDMA are applied to cross-linking polymerisation for improving the physical and chemical properties of synthesized polymers. However, residual and unreacted EGDMA and DEGDMA applied to the synthesis of dental composite and super-absorption polymer poses a health threat. This problem can be solved by using supercritical CO2, which has high diffusivity and causes polymer swelling. To design and operate the supercritical fluid extraction process using scCO2, high pressure phase behaviour data are required. The pressure-composition (P-x) isotherms for the (CO2 + EGDMA) and (CO2 + DEGDMA) binary mixture systems were measured using the static method with a variable-volume view cell at temperatures ranging from (313.2 to 363.2) K. The experimental data correlation was performed using the Peng-Robinson equation of state (PR-EOS) and the Van der Waals one fluid mixing rule. The critical constants for the PR-EOS were estimated by the Joback method and the Marrero-Gani method. The acentric factor was estimated by the Lee-Kesler method. The Marrero-Gani method showed better correlation results than the Joback method and the EGDMA is more soluble in the supercritical carbon dioxide than the DEGDMA.

  14. Phase transitions and photoinduced transformations at high pressure in the molecular donor-acceptor fullerene complex (Cd(dedtc)2)2 · C60

    The Raman spectra of crystals of C60 fullerene-cadmium diethyldithiocarbamate molecular donor-acceptor complexes (Cd(dedtc)2)2 · C60 were measured at pressures of up to 17 GPa, and the crystal lattice parameters of these complexes were determined at pressures of up to 6 GPa. An increase in pressure up to ∼2 GPa leads to changes in the Raman spectra, which are manifested by splitting of the intramolecular Hg(1)-Hg(8) phonon modes and by softening of the Ag(2) mode of the C60 molecule. A further increase in pressure up to 17 GPa does not induce significant new changes to the Raman spectra, while a decrease is accompanied by the reverse transformation at a pressure of about 2 GPa. The pressure dependence of the lattice parameters also exhibits a reversible feature at 2 GPa related to a jumplike decrease in compressibility. All these data are indicative of a phase transition in the vicinity of 2 GPa related to the formation of covalent bonds between C60 molecules and, probably, the appearance of C120 dimers in fullerene layers. It was also found that, in the pressure interval from 2 to 6.3 GPa, the Raman spectra of complexes exhibit photoinduced transformations under prolonged exposure to laser radiation with a wavelength of λ = 532 nm and power density up to 5000 W/cm2. These changes are manifested by splitting and softening of the Ag(2) mode and resemble analogous changes accompanying the photopolymerization of C60 fullerene. The intensity of new bands exhibits exponential growth with increasing exposure time. The photopolymer yield depends on both the laser radiation power and external pressure. The Ag(2) mode splitting under irradiation can be related to the formation of photo-oligomers with various numbers of intermolecular covalent bonds per C60 molecule

  15. Phase transitions and photoinduced transformations at high pressure in the molecular donor-acceptor fullerene complex {Cd(dedtc)2}2 · C60

    Meletov, K. P.; Konarev, D. V.; Tolstikova, A. O.

    2015-06-01

    The Raman spectra of crystals of C60 fullerene-cadmium diethyldithiocarbamate molecular donor-acceptor complexes {Cd(dedtc)2}2 · C60 were measured at pressures of up to 17 GPa, and the crystal lattice parameters of these complexes were determined at pressures of up to 6 GPa. An increase in pressure up to ˜2 GPa leads to changes in the Raman spectra, which are manifested by splitting of the intramolecular H g (1)- H g (8) phonon modes and by softening of the A g (2) mode of the C60 molecule. A further increase in pressure up to 17 GPa does not induce significant new changes to the Raman spectra, while a decrease is accompanied by the reverse transformation at a pressure of about 2 GPa. The pressure dependence of the lattice parameters also exhibits a reversible feature at 2 GPa related to a jumplike decrease in compressibility. All these data are indicative of a phase transition in the vicinity of 2 GPa related to the formation of covalent bonds between C60 molecules and, probably, the appearance of C120 dimers in fullerene layers. It was also found that, in the pressure interval from 2 to 6.3 GPa, the Raman spectra of complexes exhibit photoinduced transformations under prolonged exposure to laser radiation with a wavelength of λ = 532 nm and power density up to 5000 W/cm2. These changes are manifested by splitting and softening of the A g (2) mode and resemble analogous changes accompanying the photopolymerization of C60 fullerene. The intensity of new bands exhibits exponential growth with increasing exposure time. The photopolymer yield depends on both the laser radiation power and external pressure. The A g (2) mode splitting under irradiation can be related to the formation of photo-oligomers with various numbers of intermolecular covalent bonds per C60 molecule.

  16. High pressure experimental water loop

    A high pressure experimental water loop has been made for studying the detection and evolution of cladding failure in a pressurized reactor. The loop has been designed for a maximum temperature of 360 deg. C, a maximum of 160 kg/cm2 and flow rates up to 5 m3/h. The entire loop consists of several parts: a main circuit with a canned rotor circulation pump, steam pressurizer, heating tubes, two hydro-cyclones (one de-gasser and one decanter) and one tubular heat exchanger; a continuous purification loop, connected in parallel, comprising pressure reducing valves and resin pots which also allow studies of the stability of resins under pressure, temperature and radiation; following the gas separator is a gas loop for studying the recombination of the radiolytic gases in the steam phase. The preceding circuits, as well as others, return to a low pressure storage circuit. The cold water of the low pressure storage flask is continuously reintroduced into the high pressure main circuit by means of a return pump at a maximum head of 160 kg /cm2, and adjusted to the pressurizer level. This loop is also a testing bench for the tight high pressure apparatus. The circulating pump and the connecting flanges (Oak Ridge type) are water-tight. The feed pump and the pressure reducing valves are not; the un-tight ones have a system of leak recovery. To permanently check the tightness the circuit has been fitted with a leak detection system (similar to the HRT one). (author)

  17. Phase transitions and photoinduced transformations at high pressure in the molecular donor-acceptor fullerene complex (Cd(dedtc){sub 2}){sub 2} · C{sub 60}

    Meletov, K. P., E-mail: mele@issp.ac.ru [Russian Academy of Sciences, Institute of Solid State Physics (Russian Federation); Konarev, D. V. [Russian Academy of Sciences, Institute of Problems of Chemical Physics (Russian Federation); Tolstikova, A. O. [Russian Academy of Sciences, Institute of Solid State Physics (Russian Federation)

    2015-06-15

    The Raman spectra of crystals of C{sub 60} fullerene-cadmium diethyldithiocarbamate molecular donor-acceptor complexes (Cd(dedtc){sub 2}){sub 2} · C{sub 60} were measured at pressures of up to 17 GPa, and the crystal lattice parameters of these complexes were determined at pressures of up to 6 GPa. An increase in pressure up to ∼2 GPa leads to changes in the Raman spectra, which are manifested by splitting of the intramolecular H{sub g}(1)-H{sub g}(8) phonon modes and by softening of the A{sub g}(2) mode of the C{sub 60} molecule. A further increase in pressure up to 17 GPa does not induce significant new changes to the Raman spectra, while a decrease is accompanied by the reverse transformation at a pressure of about 2 GPa. The pressure dependence of the lattice parameters also exhibits a reversible feature at 2 GPa related to a jumplike decrease in compressibility. All these data are indicative of a phase transition in the vicinity of 2 GPa related to the formation of covalent bonds between C{sub 60} molecules and, probably, the appearance of C{sub 120} dimers in fullerene layers. It was also found that, in the pressure interval from 2 to 6.3 GPa, the Raman spectra of complexes exhibit photoinduced transformations under prolonged exposure to laser radiation with a wavelength of λ = 532 nm and power density up to 5000 W/cm{sup 2}. These changes are manifested by splitting and softening of the A{sub g}(2) mode and resemble analogous changes accompanying the photopolymerization of C{sub 60} fullerene. The intensity of new bands exhibits exponential growth with increasing exposure time. The photopolymer yield depends on both the laser radiation power and external pressure. The A{sub g}(2) mode splitting under irradiation can be related to the formation of photo-oligomers with various numbers of intermolecular covalent bonds per C{sub 60} molecule.

  18. Prediction of incommensurate crystal structure in Ca at high pressure

    Arapan, Sergiu; Mao, Ho-kwang; Ahuja, Rajeev

    2008-01-01

    Ca shows an interesting high-pressure phase transformation sequence, but, despite similar physical properties at high pressure and affinity in the electronic structure with its neighbors in the periodic table, no complex phase has been identified for Ca so far. We predict an incommensurate high-pressure phase of Ca from first principle calculations and describe a procedure of estimating incommensurate structure parameters by means of electronic structure calculations for periodic crystals. Th...

  19. Theory of high pressure hydrogen, made simple

    Magdau, Ioan B; Ackland, Graeme J

    2015-01-01

    Phase I of hydrogen has several peculiarities. Despite having a close-packed crystal structure, it is less dense than either the low temperature Phase II or the liquid phase. At high pressure, it transforms into either phase III or IV, depending on the temperature. Moreover, spectroscopy suggests that the quantum rotor behaviour disappears with pressurisation, without any apparent phase transition. Here we present a simple thermodynamic model for this behaviour based on packing atoms and molecules and discuss the thermodynamics of the phase boundaries. We also report first principles molecular dynamics calculations for a more detailed look at the same phase transitions.

  20. Combined Theoretical and in Situ Scattering Strategies for Optimized Discovery and Recovery of High-Pressure Phases: A Case Study of the GaN-Nb2O5 System.

    Woerner, William R; Qian, Guang-Rui; Oganov, Artem R; Stephens, Peter W; Dharmagunawardhane, H A Naveen; Sinclair, Alexandra; Parise, John B

    2016-04-01

    The application of pressure in solid-state synthesis provides a route for the creation of new and exciting materials. However, the onerous nature of high-pressure techniques limits their utility in materials discovery. The systematic search for novel oxynitrides-semiconductors for photocatalytic overall water splitting-is a representative case where quench high-pressure synthesis is useful and necessary in order to obtain target compounds. We utilize state of the art crystal structure prediction theory (USPEX) and in situ synchrotron-based X-ray scattering to speed up the discovery and optimization of novel compounds using high-pressure synthesis. Using this approach, two novel oxynitride phases were discovered in the GaN-Nb2O5 system. The (Nb2O5)0.84:(NbO2)0.32:(GaN)0.82 rutile structured phase was formed at 1 GPa and 900 °C and gradually transformed to a α-PbO2-related structure above 2.8 GPa and 1000 °C. The low-pressure rutile type phase was found to have a direct optical band gap of 0.84 eV and an indirect gap of 0.51 eV. PMID:27002597

  1. Coexistence of weak ferromagnetism and ferroelectricity in the high pressure LiNbO{sub 3}-type phase of FeTiO{sub 3}.

    Varga, T.; Kumar, A.; Vlahos, E.; Denev, S.; Park, M.; Hong, S.; Sanehira, T.; Wang, Y.; Fennie, C. J.; Streiffer, S. K.; Ke, X.; Schiffer, P.; Gopalan, V.; Mitchell, J. F.; Pennsylvania State Univ.; Univ. of Chicago; Cornell Univ.

    2009-01-01

    We report the magnetic and electrical characteristics of polycrystalline FeTiO{sub 3} synthesized at high pressure that is isostructural with acentric LiNbO{sub 3} (LBO). Piezoresponse force microscopy, optical second harmonic generation, and magnetometry demonstrate ferroelectricity at and below room temperature and weak ferromagnetism below {approx} 120 K. These results validate symmetry-based criteria and first-principles calculations of the coexistence of ferroelectricity and weak ferromagnetism in a series of transition metal titanates crystallizing in the LBO structure.

  2. Structural relaxation accompanied by photo-induced chromatic phase transition of polydiacetylenes with butylene-N-difluorophenyl carbamate side chains

    Maekawa, Yuuki; Sakamoto, Naoya; Kokado, Ryousuke; Kajimoto, Naoshi; Izumi, Yuuichiro [Department of Materials Science and Chemistry, Wakayama University, 930 Sakaedani, Wakayama (Japan); Itoh, Chihiro, E-mail: citoh@sys.wakayama-u.ac.jp [Department of Materials Science and Chemistry, Wakayama University, 930 Sakaedani, Wakayama (Japan)

    2013-01-15

    We have studied the phase transition of poly-5,7-dodecadiyne-1,12-diol bis[2,4-difluorophenyl carbamate] (PDA-2,4-DFPC) and poly-5,7-dodecadiyne-1,12-diol bis[3,4-difluorophenyl carbamate] (PDA-3,4-DFPC) by visible reflection spectroscopy and mid-infrared absorption spectroscopy. Both PDA-2,4-DFPC and PDA-3,4-DFPC show the reflection spectra characterized by a sharp peak at around 1.9 eV at room temperature. While PDA-3,4-DFPC shows thermochromic phase transition to the phase showing the reflection spectrum with a peak around 2.2 eV above 120 Degree-Sign C, PDA-2,4-DFPC shows no abrupt change of the reflection spectrum. However, PDA-2,4-DFPC shows drastic change of the reflection spectrum under 532-nm CW-laser excitation. Based on these results, we can draw the following two conclusions. First, the phase transition behavior of PDA can be controlled by modifying the side-chain structure. Second, we demonstrate that thermally inaccessible phase of PDA is induced by the photo-excitation. By measuring mid-infrared absorption of PDAs, we elucidated that conformational change of side chains is accompanied with the phase transition. Based on the results, we discussed the role of the side chain in the phase transition. - Highlights: Black-Right-Pointing-Pointer We have synthesized polydiacetylene (PDA) with difluorophenyl carbamate side chain. Black-Right-Pointing-Pointer PDAs show distinct phase transition (PT) depending on the side-chain structure. Black-Right-Pointing-Pointer PDA with 3,4-difluorophenyl carbamate shows PT by thermal stimulation. Black-Right-Pointing-Pointer However, PDA with 2,4-difluorophenyl carbamate shows PT only under photo-excitation.

  3. Psychosocial Accompaniment

    Mary Watkins

    2015-01-01

    This essay advocates for a paradigm shift in psychology toward the activity and ethics of accompaniment. Accompaniment requires a reorientation of the subjectivity, interpersonal practices, and critical understanding of the accompanier so that (s)he can stand alongside others who desire listening, witnessing, advocacy, space to develop critical inquiry and research, and joint imagination and action to address desired and needed changes. The idea of “accompaniment” emerged in liberation theolo...

  4. Study of ceramics sintering under high pressures

    A systematic study was made on high pressure sintering of ceramics in order to obtain materials with controlled microstructure, which are not accessible by conventional methods. Some aspects with particular interest were: to achieve very low porosity, with fine grains; to produce dispersed metastable and denser phases which can act as toughening agents; the study of new possibilities for toughening enhancement. (author)

  5. High pressure engineering and technology

    This book contains 10 papers. Some of the titles are: Control of vibration in high pressure piping systems; Hazards and safeguards of high pressure hydraulic fatigue testing; Load, stress and fatigue analysis of threaded end closures; Application of fatigue crack growth to an isostatic press; and Time dependent failure in high strength steels for autoclave service

  6. Flow regime transition to wavy dispersed flow for high-pressure steam/water two-phase flow in horizontal pipe

    A wavy-dispersed flow regime was observed between slug and annular-dispersed flow regimes in TPTF high-pressure steam/water horizontal pipe experiments, employing the video probe visual observation. The onset of entrainment was identified to cause slug to wavy-dispersed flow transition. The wavy-dispersed flow regime extended towards lower gas flow rates as pressure was increased. Furthermore, it was found that the gas-liquid relative velocity for the onset of entrainment decreases significantly, resulting in decrease in the minimum void fraction. Consequently, the slug flow regime was found to disappear for pressures above 8.6 MPa, as observed in the previous TPTF experiments. Applicability of available models and correlations on the onset of entrainment was assessed against the TPTF data. Steen-Wallis parameter correlated the data well when the superficial gas velocity term in this parameter is replaced by the gas-liquid relative velocity. (author)

  7. Infrared spectroscopic and modeling studies of H{sub 2}/CH{sub 4} microwave plasma gas phase from low to high pressure and power

    Rond, C., E-mail: rond@lspm.cnrs.fr; Lombardi, G.; Gicquel, A. [LSPM CNRS UPR 3407 Université Paris 13, 99 Avenue J.-B. Clément, 93430 Villetaneuse (France); Hamann, S.; Röpcke, J. [INP Greifswald, Felix-Hausdorff-Str. 2, 17489 Greifswald (Germany); Wartel, M. [GREMI UMR 7344, CNRS/Université d' Orléans, site de Bourges, rue G. Berger, 18000 Bourges (France)

    2014-09-07

    InfraRed Tunable Diode Laser Absorption Spectroscopy technique has been implemented in a H{sub 2}/CH{sub 4} Micro-Wave (MW frequency f = 2.45 GHz) plasma reactor dedicated to diamond deposition under high pressure and high power conditions. Parametric studies such as a function of MW power, pressure, and admixtures of methane have been carried out on a wide range of experimental conditions: the pressure up to 270 mbar and the MW power up to 4 kW. These conditions allow high purity Chemical Vapor Deposition diamond deposition at high growth rates. Line integrated absorption measurements have been performed in order to monitor hydrocarbon species, i.e., CH{sub 3}, CH{sub 4}, C{sub 2}H{sub 2}, C{sub 2}H{sub 4}, and C{sub 2}H{sub 6}. The densities of the stable detected species were found to vary in the range of 10{sup 12}–10{sup 17} molecules cm{sup −3}, while the methyl radical CH{sub 3} (precursor of diamond growth under these conditions) measured into the plasma bulk was found up to 10{sup 14} molecules cm{sup −3}. The experimental densities have been compared to those provided by 1D-radial thermochemical model for low power and low pressure conditions (up to 100 mbar/2 kW). These densities have been axially integrated. Experimental measurements under high pressure and power conditions confirm a strong increase of the degree of dissociation of the precursor, CH{sub 4}, associated to an increase of the C{sub 2}H{sub 2} density, the most abundant reaction product in the plasma.

  8. Infrared spectroscopic and modeling studies of H2/CH4 microwave plasma gas phase from low to high pressure and power

    InfraRed Tunable Diode Laser Absorption Spectroscopy technique has been implemented in a H2/CH4 Micro-Wave (MW frequency f = 2.45 GHz) plasma reactor dedicated to diamond deposition under high pressure and high power conditions. Parametric studies such as a function of MW power, pressure, and admixtures of methane have been carried out on a wide range of experimental conditions: the pressure up to 270 mbar and the MW power up to 4 kW. These conditions allow high purity Chemical Vapor Deposition diamond deposition at high growth rates. Line integrated absorption measurements have been performed in order to monitor hydrocarbon species, i.e., CH3, CH4, C2H2, C2H4, and C2H6. The densities of the stable detected species were found to vary in the range of 1012–1017 molecules cm−3, while the methyl radical CH3 (precursor of diamond growth under these conditions) measured into the plasma bulk was found up to 1014 molecules cm−3. The experimental densities have been compared to those provided by 1D-radial thermochemical model for low power and low pressure conditions (up to 100 mbar/2 kW). These densities have been axially integrated. Experimental measurements under high pressure and power conditions confirm a strong increase of the degree of dissociation of the precursor, CH4, associated to an increase of the C2H2 density, the most abundant reaction product in the plasma

  9. High pressure diffraction at ISIS

    The development of the high pressure diffraction programme at ISIS is reviewed. Along with general accounts of the technique and the pressure cells used, examples of science carried out in this field are given. (author)

  10. On the room-temperature phase diagram of high pressure hydrogen: an ab initio molecular dynamics perspective and a diffusion Monte Carlo study.

    Chen, J; Ren, X.; Li, X Z; Alfè, D.; Wang, E

    2014-01-01

    The finite-temperature phase diagram of hydrogen in the region of phase IV and its neighborhood was studied using the ab initio molecular dynamics (MD) and the ab initio path-integral molecular dynamics (PIMD). The electronic structures were analyzed using the density-functional theory (DFT), the random-phase approximation, and the diffusion Monte Carlo (DMC) methods. Taking the state-of-the-art DMC results as benchmark, comparisons of the energy differences between structures generated from ...