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Sample records for accompanying high-pressure phase

  1. Carbon in iron phases under high pressure

    NASA Astrophysics Data System (ADS)

    Huang, L.; Skorodumova, N. V.; Belonoshko, A. B.; Johansson, B.; Ahuja, R.

    2005-11-01

    The influence of carbon impurities on the properties of iron phases (bcc, hcp, dhcp, fcc) has been studied using the first-principles projector augmented-wave (PAW) method for a wide pressure range. It is shown that the presence of ~6 at. % of interstitial carbon has a little effect on the calculated structural sequence of the iron phases under high pressure. The bcc -> hcp transition both for pure iron and iron containing carbon takes place around 9 GPa. According to the enthalpies comparison, the solubility of carbon into the iron solid is decreased by high pressure. The coexistence of iron carbide (Fe3C) + pure hcp Fe is most stable phase at high pressure compared with other phases. Based on the analysis of the pressure-density dependences for Fe3C and hcp Fe, we suggest that there might be some fraction of iron carbide present in the core.

  2. Strength coupling in mixed phases under high pressure

    NASA Astrophysics Data System (ADS)

    Yan, Xiaozhi; Dong, Haini; Sun, Guangai; Ren, Xiangting; He, Duanwei; Yang, Wenge

    2016-10-01

    The strength of a material can be altered by temperature, pressure, grain size, and orientation distributions. At the microscale, neighboring grains often play important roles in the elastic and plastic deformation process. By applying high pressure to a mixture of germanium and gold powder in the vicinity of the germanium phase transition pressure, we found that the deformation behavior of gold largely correlates with that of the surrounding germanium. The deviatoric strain and compressibility of Au behaves anomalously when Ge undergoes a diamond to β-tin structure transition, accompanying a large volume and strength drop. The results demonstrate that the intrinsic strength of a mixed phase could be largely controlled by the other surrounding phase, which is fundamentally important in understanding the deformation mechanism of multiphase materials, especially when one phase undergoes dramatic changes in strength under high pressure conditions.

  3. High-pressure behavior of hydrous phases

    NASA Astrophysics Data System (ADS)

    Mookherjee, M.; Tsuchiya, J.; Hermann, A.; Speziale, S.

    2016-12-01

    One of the most distinguishing features of the Earth is its surface water, which is a crucial component in making it a habitable planet. How this water is partitioned among the various reservoirs within the Earth's interior is of considerable interest to the Solid Earth Sciences community. In convergent plate margins such as subduction zone, the hydrous phases in the subducting slabs deliver water into the Earth's interior. Upon reaching greater depths, depending on the limits of their thermodynamic stability, the hydrous phases dehydrate, releasing water. A fraction of water is released back into the hydrosphere through arc volcanism. Recent estimates show that the worldwide flux of water from subducting slabs amounts to about one ocean mass over the age of the Earth. The water in the Earth's interior is stored in several distinct forms: as aqueous fluids; hydrous silicate melts; nominally anhydrous phases; grain boundaries, and various hydrous phases. Among these multiple hosts, hydrous phases are particularly important because they influence solid earth processes in the crust and mantle. The thermodynamic stability of hydrous phases dictates how efficiently they transport and store water in the Earth's interior. Their presence severely affects the onset of melting. Hydrous phases that are likely to be stable at higher pressures are often not recorded in natural samples. It is possible that these hydrous phases are not sampled by melts that arise from depths that are shallower than where high-pressure hydrous phases may occur. It is also possible that these hydrous phases do not survive exhumation. In addition, many hydrous phases might have limited thermal stability. High-pressure experiments and first-principles simulations based on density functional theory (DFT) have been crucial in enhancing our understanding of hydrous phases that are likely to be present in the Earth's mantle and subduction zones. In this study, we present DFT results and compare them with

  4. High-pressure phase transition in ZnSe

    NASA Astrophysics Data System (ADS)

    Köfferlein, M.; Karzel, H.; Potzel, W.; Schiessl, W.; Steiner, M.; Kalvius, G. M.; Mitchell, D. W.; Das, T. P.

    1994-12-01

    A high-pressure Mössbauer spectrometer for the 93.3-keV resonance in67Zn and an X-ray diffractometer of the Guinier type are used to investigate67ZnSe powder at high external pressures. At ˜ 13 GPa, a phase transition from the zinc blende to the fcc (NaCl) structure is observed. The transition is accompanied by a 15.2% decrease of the volume of the unit cell. The Lamb-Mössbauer factor (LMF) increases from f=0.53% at ambient pressure to f=1.07% at 6.1 GPa. It then decreases to f=0.91% as the pressure is further increased to 8.2 GPa. This behavior is investigated by lattice-dynamical calculations using an 11-parameter rigid-ion model. The decrease of the LMF at high pressures is caused by the softening of the TA phonon modes, which occurs already far below the phase transition. The s-electron density ρ(0) at the67Zn nucleus increases with reduced volume. The change of ρ(0) as well as theoretical Hartree-Fock cluster calculations show that covalency of bonding 4s/4p states of Zn and Se plays an essential role and determines the isomer shift.

  5. High pressure phase transitions in lawsonite at simultaneous high pressure and temperature: A single crystal study

    NASA Astrophysics Data System (ADS)

    O'Bannon, E. F., III; Vennari, C.; Beavers, C. C. G.; Williams, Q. C.

    2015-12-01

    Lawsonite (CaAl2Si2O7(OH)2.H2O) is a hydrous mineral with a high overall water content of ~11.5 wt.%. It is a significant carrier of water in subduction zones to depths greater than ~150 km. The structure of lawsonite has been extensively studied under room temperature, high-pressure conditions. However, simultaneous high-pressure and high-temperature experiments are scarce. We have conducted synchrotron-based simultaneous high-pressure and temperature single crystal experiments on lawsonite up to a maximum pressure of 8.4 GPa at ambient and high temperatures. We used a natural sample of lawsonite from Valley Ford, California (Sonoma County). At room pressure and temperature lawsonite crystallizes in the orthorhombic system with Cmcm symmetry. Room temperature compression indicates that lawsonite remains in the orthorhombic Cmcm space group up to ~9.0 GPa. Our 5.0 GPa crystal structure is similar to the room pressure structure, and shows almost isotropic compression of the crystallographic axes. Unit cell parameters at 5.0 GPa are a- 5.7835(10), b- 8.694(2), and c- 13.009(3). Single-crystal measurements at simultaneous high-pressure and temperature (e.g., >8.0 GPa and ~100 oC) can be indexed to a monoclinic P-centered unit cell. Interestingly, a modest temperature increase of ~100 oC appears to initiate the orthorhombic to monoclinic phase transition at ~0.6-2.4 GPa lower than room temperature compression studies have shown. There is no evidence of dehydration or H atom disorder under these conditions. This suggests that the orthorhombic to monoclinic transition could be kinetically impeded at 298 K, and that monoclinic lawsonite could be the dominant water carrier through much of the depth range of upper mantle subduction processes.

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

    SciTech Connect

    Durandurdu, Murat

    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.

  7. Experimental methods for phase equilibria at high pressures.

    PubMed

    Dohrn, Ralf; Fonseca, José M S; Peper, Stephanie

    2012-01-01

    Knowledge of high-pressure phase equilibria is crucial in many fields, e.g., for the design and optimization of high-pressure chemical and separation processes, carbon capture and storage, hydrate formation, applications of ionic liquids, and geological processes. This review presents the variety of methods to measure phase equilibria at high pressures and, following a classification, discusses the measurement principles, advantages, challenges, and error sources. Examples of application areas are given. A detailed knowledge and understanding of the different methods is fundamental not only for choosing the most suitable method for a certain task but also for the evaluation of experimental data. The discrepancy between the (sometimes low) true accuracy of published experimental data and the (high) accuracy claimed by authors is addressed. Some essential requirements for the generation of valuable experimental results are summarized.

  8. Collision condition indicted by High Pressure Phases in a Chondrite

    NASA Astrophysics Data System (ADS)

    Kato, Y.; Sekine, T.; Kayama, M.; Miyahara, M.; Yamaguchi, A.

    2012-12-01

    It has been generally recognized that there were many collisions during planetary accretion. Chondrites include the materials at the time of formation of the solar system. It is essential to unravel the shock history in meteorites and the parent planet in order to understand such collisional processes. In this study, we investigate a thin section of ordinary chondrite Y-790729 classified as L6 in which high-pressure minerals are found in the about 620-μm-wide shock vein. The mineralogical and chemical features give us detailed information to constrain the shock conditions. We have tried to constrain the P-T condition from the viewpoints of the mineral assemblage and cathodoluminescense (CL) spectroscopy. Y-790729 consists mostly of olivine and pyroxene and has shock veins. To identify high pressure phases, we used an optical microscope, a scanning electron microscope (SEM), micro Raman spectroscopy, and electron probe micro analyzer (EPMA). In addition, scanning electron microscopy-cathodoluminescence (SEM-CL) analysis, detectable shock-induced defect centers, was used to characterize the shock metamorphism in feldspar minerals. The presence of shock vein, maskelynite, and high pressure phases confirms shock record. 7 high pressure phases of ringwoodite, high-pressure clinoenstatite (HPC), majorite, merrillite, lingunite, high-pressure chromite and akimotoite were found in this section. All of them exist only in a shock vein, but maskelynite occurs everywhere in the section. From these observations, it is obvious that the shock vein experienced the high pressure and high temperature generated by shock wave. If some of the high pressure minerals are equilibrated, the P-T condition can be estimated. Based on the equilibrium phase diagram of MgSiO3 polymorphs (Presnall. 1995), the P-T conditions for crystallization of majorite, HPC and akimotoite is about 17 GPa and 1600 oC, because the compositions of the three phases are close to MgSiO3. It is consistent with the

  9. High pressure phase transformation in iron under fast compression

    SciTech Connect

    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.

  10. Theoretical Predictions of Phase Transitions at Ultra-high Pressures

    NASA Astrophysics Data System (ADS)

    Boates, Brian

    2013-06-01

    We present ab initio calculations of the high-pressure phase diagrams of important planetary materials such as CO2, MgSiO3, and MgO. For CO2, we predict a series of distinct liquid phases over a wide pressure (P) and temperature (T) range, including a first-order transition to a dense polymer liquid. We have computed finite-temperature free energies of liquid and solid CO2 phases to determine the melting curve beyond existing measurements and investigate possible phase separation transitions. The interaction of these phase boundaries with the mantle geotherm will also be discussed. Furthermore, we find evidence for a vast pressure-temperature regime where molten MgSiO3 decomposes into liquid SiO2 and solid MgO, with a volume change of approximately 1.2 percent. The demixing transition is driven by the crystallization of MgO ? the reaction only occurs below the high-pressure MgO melting curve. The predicted transition pressure at 10,000 K is in close proximity to an anomaly reported in recent laser-driven shock experiments of MgSiO3. We also present new results for the high-pressure melting curve of MgO and its B1-B2 solid phase transition, with a triple point near 364 GPa and 12,000 K.

  11. Computation of temperature induced phase transitions at high pressure

    NASA Astrophysics Data System (ADS)

    Belonoshko, Anatoly

    2014-03-01

    Phase transitions at high pressure and temperature is perhaps one of the most controversial topics in high pressure science. There is a number of theoretical methods developed recently to address this problem. Unfortunately, none of them is fully satisfactory, considering stringent requirements to accuracy of the computed free energies of the involved phases. This, in part, explains the variety of the suggested methods. The experimental data is rather controversial as well, probably because the experiments at extreme conditions are difficult. I will provide overview of the theoretical methods that are applied for the computation and simulation of T-induced phase transitions. Both liquid-solid and solid-solid transitions will be covered. Possible sources of the disagreement between theoretical methods as well as between theory and experiment will be illustrated by examples. Insight from simulations will be used to suggest alternative explanations of experimental data. The optimal, at present, method to compute the transitions will be suggested.

  12. Theoretical investigation of high pressure phases of carbon dioxide

    PubMed

    Holm; Ahuja; Belonoshko; Johansson

    2000-08-07

    The recent discovery of a new solid phase of carbon dioxide ( CO2-V) has made it apparent that the properties of this vital chemical species are drastically altered under high pressure conditions. The reported transition at around 40 GPa from the Cmca phase ( CO2-III), which is a molecular solid, into the novel phase, which was observed to be quartzlike, clearly suggests a dramatic change of the chemical, electronic, and structural properties. We here present a theoretical analysis of the implications of this metamorphosis. At even higher pressures, we predict the existence of a very hard phase of the stishovite type.

  13. Elasticity of methane hydrate phases at high pressure.

    PubMed

    Beam, Jennifer; Yang, Jing; Liu, Jin; Liu, Chujie; Lin, Jung-Fu

    2016-04-21

    Determination of the full elastic constants (cij) of methane hydrates (MHs) at extreme pressure-temperature environments is essential to our understanding of the elastic, thermodynamic, and mechanical properties of methane in MH reservoirs on Earth and icy satellites in the solar system. Here, we have investigated the elastic properties of singe-crystal cubic MH-sI, hexagonal MH-II, and orthorhombic MH-III phases at high pressures in a diamond anvil cell. Brillouin light scattering measurements, together with complimentary equation of state (pressure-density) results from X-ray diffraction and methane site occupancies in MH from Raman spectroscopy, were used to derive elastic constants of MH-sI, MH-II, and MH-III phases at high pressures. Analysis of the elastic constants for MH-sI and MH-II showed intriguing similarities and differences between the phases' compressional wave velocity anisotropy and shear wave velocity anisotropy. Our results show that these high-pressure MH phases can exhibit distinct elastic, thermodynamic, and mechanical properties at relevant environments of their respective natural reservoirs. These results provide new insight into the determination of how much methane exists in MH reservoirs on Earth and on icy satellites elsewhere in the solar system and put constraints on the pressure and temperature conditions of their environment.

  14. Elasticity of methane hydrate phases at high pressure

    NASA Astrophysics Data System (ADS)

    Beam, Jennifer; Yang, Jing; Liu, Jin; Liu, Chujie; Lin, Jung-Fu

    2016-04-01

    Determination of the full elastic constants (cij) of methane hydrates (MHs) at extreme pressure-temperature environments is essential to our understanding of the elastic, thermodynamic, and mechanical properties of methane in MH reservoirs on Earth and icy satellites in the solar system. Here, we have investigated the elastic properties of singe-crystal cubic MH-sI, hexagonal MH-II, and orthorhombic MH-III phases at high pressures in a diamond anvil cell. Brillouin light scattering measurements, together with complimentary equation of state (pressure-density) results from X-ray diffraction and methane site occupancies in MH from Raman spectroscopy, were used to derive elastic constants of MH-sI, MH-II, and MH-III phases at high pressures. Analysis of the elastic constants for MH-sI and MH-II showed intriguing similarities and differences between the phases' compressional wave velocity anisotropy and shear wave velocity anisotropy. Our results show that these high-pressure MH phases can exhibit distinct elastic, thermodynamic, and mechanical properties at relevant environments of their respective natural reservoirs. These results provide new insight into the determination of how much methane exists in MH reservoirs on Earth and on icy satellites elsewhere in the solar system and put constraints on the pressure and temperature conditions of their environment.

  15. High pressure phase transition in Pr-monopnictides

    SciTech Connect

    Raypuria, Gajendra Singh E-mail: gsraypuria@gmail.com; Gupta, Dinesh Chandra

    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.

  16. Phase transition of La- chalcogenides under high pressure

    SciTech Connect

    Gupta, Dinesh Chandra; Raypuria, Gajendra Singh

    2014-04-24

    The lanthanum 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.

  17. High pressure structural phase transitions of PbPo

    NASA Astrophysics Data System (ADS)

    Bencherif, Y.; Boukra, A.; Zaoui, A.; Ferhat, M.

    2012-09-01

    First-principles calculations have been performed to investigate the high pressure phase transitions and dynamical properties of the less known lead polonium compound. The calculated ground state parameters for the NaCl phase show good agreement with the experimental data. The obtained results show that the intermediate phase transition for this compound is the orthorhombic Pnma phase. The PbPo undergoes from the rocksalt to Pnma phase at 4.20 GPa. Further structural phase transition from intermediate to CsCl phase has been found at 8.5 GPa. In addition, phonon dispersion spectra were derived from linear-response to density functional theory. In particular, we show that the dynamical properties of PbPo exhibit some peculiar features compared to other III-V compounds. Finally, thermodynamics properties have been also addressed from quasiharmonic approximation.

  18. The phase diagram of high-pressure superionic ice

    NASA Astrophysics Data System (ADS)

    Sun, Jiming; Clark, Bryan K.; Torquato, Salvatore; Car, Roberto

    2015-08-01

    Superionic ice is a special group of ice phases at high temperature and pressure, which may exist in ice-rich planets and exoplanets. In superionic ice liquid hydrogen coexists with a crystalline oxygen sublattice. At high pressures, the properties of superionic ice are largely unknown. Here we report evidence that from 280 GPa to 1.3 TPa, there are several competing phases within the close-packed oxygen sublattice. At even higher pressure, the close-packed structure of the oxygen sublattice becomes unstable to a new unusual superionic phase in which the oxygen sublattice takes the P21/c symmetry. We also discover that higher pressure phases have lower transition temperatures. The diffusive hydrogen in the P21/c superionic phase shows strong anisotropic behaviour and forms a quasi-two-dimensional liquid. The ionic conductivity changes abruptly in the solid to close-packed superionic phase transition, but continuously in the solid to P21/c superionic phase transition.

  19. High Pressure Phase Transformations in Heavy Rare Earth Metals and Connections to Actinide Crystal Structures

    SciTech Connect

    Vohra, Yogesh K.; Sangala, Bagvanth Reddy; Stemshorn, Andrew K.; Hope, Kevin M.

    2008-07-01

    High-pressure studies have been performed on heavy rare earth metals Terbium (Tb) to 155 GPa and Holmium (Ho) to 134 GPa in a diamond anvil cell at room temperature. The following crystal structure sequence was observed in both metals hcp {yields} Sm-type {yields} dhcp {yields} distorted fcc (hR-24) {yields} monoclinic (C2/m) with increasing pressure. The last transformation to a low symmetry monoclinic phase is accompanied by a volume collapse of 5 % for Tb at 51 GPa and a volume collapse of 3 % for Ho at 103 GPa. This volume collapse under high pressure is reminiscent of f-shell delocalization in light rare earth metal Cerium (Ce), Praseodymium (Pr), and heavy actinide metals Americium (Am) and Curium (Cm). The orthorhombic Pnma phase that has been reported in Am and Cm after f-shell delocalization is not observed in heavy rare earth metals under high pressures. (authors)

  20. High Pressure Materials Research: Novel Extended Phases of Molecular Triatomics

    SciTech Connect

    Yoo, C

    2004-05-26

    Application of high pressure significantly alters the interatomic distance and thus the nature of intermolecular interaction, chemical bonding, molecular configuration, crystal structure, and stability of solid [1]. With modern advances in high-pressure technologies [2], it is feasible to achieve a large (often up to a several-fold) compression of lattice, at which condition material can be easily forced into a new physical and chemical configuration [3]. The high-pressure thus offers enhanced opportunities to discover new phases, both stable and metastable ones, and to tune exotic properties in a wide-range of atomistic length scale, substantially greater than (often being several orders of) those achieved by other thermal (varying temperatures) and chemical (varying composition or making alloys) means. Simple molecular solids like H{sub 2}, C, CO{sub 2}, N{sub 2}, O{sub 2}, H{sub 2}O, CO, NH{sub 3}, and CH{sub 4} are bounded by strong covalent intramolecular bonds, yet relatively weak intermolecular bonds of van der Waals and/or hydrogen bonds. The weak intermolecular bonds make these solids highly compressible (i.e., low bulk moduli typically less than 10 GPa), while the strong covalent bonds make them chemically inert at least initially at low pressures. Carbon-carbon single bonds, carbon-oxygen double bonds and nitrogen-nitrogen triple bonds, for example, are among the strongest. These molecular forms are, thus, often considered to remain stable in an extended region of high pressures and high temperatures. High stabilities of these covalent molecules are also the basis of which their mixtures are often presumed to be the major detonation products of energetic materials as well as the major constituents of giant planets. However, their physical/chemical stabilities are not truly understood at those extreme pressure-temperature conditions. In fact, an increasing amount of experimental evidences contradict the assumed stability of these materials at high

  1. High pressure ferroelastic phase transition in SrTiO₃.

    PubMed

    Salje, E K H; Guennou, M; Bouvier, P; Carpenter, M A; Kreisel, J

    2011-07-13

    High pressure measurements of the ferroelastic phase transition of SrTiO₃ (Guennou et al 2010 Phys. Rev. B 81 054115) showed a linear pressure dependence of the transition temperature between the cubic and tetragonal phase. Furthermore, the pressure induced transition becomes second order while the temperature dependent transition is near a tricritical point. The phase transition mechanism is characterized by the elongation and tilt of the TiO₆ octahedra in the tetragonal phase, which leads to strongly nonlinear couplings between the structural order parameter, the volume strain and the applied pressure. The phase diagram is derived from the Clausius-Clapeyron relationship and is directly related to a pressure dependent Landau potential. The nonlinearities of the pressure dependent strains lead to an increase of the fourth order Landau coefficient with increasing pressure and, hence, to a tricritical-second order crossover. This behaviour is reminiscent of the doping related crossover in isostructural KMnF₃.

  2. Phase separation of lanthanum hydride under high pressure

    NASA Astrophysics Data System (ADS)

    Machida, A.; Watanuki, T.; Kawana, D.; Aoki, K.

    2011-02-01

    Structural change of lanthanum dihydride LaH2.3, which has a face-centered-cubic (fcc) metal lattice with tetrahedral interstitial sites fully occupied with hydrogen atoms and partially occupied octahedral sites, has been investigated at high pressures up to 20 GPa at ambient temperature by synchrotron radiation x-ray diffraction. Additional Bragg reflections appear just on higher angle sides of the original ones at ~11 GPa and their peak intensities increase gradually on further compression. The coexistence state of two fcc metal lattices thus observed above 11 GPa is interpreted in terms of phase separation or disproportionation reaction from the dihydride toward a solid solution and trihydride states, in both of which the octahedral interstitial sites are partially occupied with hydrogen atoms. A gradual distortion from the cubic to a tetragonal lattice is observed prior to the phase separation. The coexistence phase goes back to the dihydride fcc phase via the lattice distorted phase with decreasing pressure.

  3. A novel phase of beryllium fluoride at high pressure.

    PubMed

    Rakitin, Maksim S; Oganov, Artem R; Niu, Haiyang; Esfahani, M Mahdi Davari; Zhou, Xiang-Feng; Qian, Guang-Rui; Solozhenko, Vladimir L

    2015-10-21

    A previously unknown thermodynamically stable high-pressure phase of BeF2 has been predicted using the evolutionary algorithm USPEX. This phase occurs in the pressure range 18-27 GPa. Its structure has C2/c space group symmetry and contains 18 atoms in the primitive unit cell. Given the analogy between BeF2 and SiO2, silica phases have been investigated as well, but the new phase has not been observed to be thermodynamically stable for this system. However, it is found to be metastable and to have comparable energy to the known metastable phases of SiO2, suggesting a possibility of its synthesis.

  4. Molecular to atomic phase transition in hydrogen under high pressure.

    PubMed

    McMinis, Jeremy; Clay, Raymond C; Lee, Donghwa; Morales, Miguel A

    2015-03-13

    The metallization of high-pressure hydrogen, together with the associated molecular to atomic transition, is one of the most important problems in the field of high-pressure physics. It is also currently a matter of intense debate due to the existence of conflicting experimental reports on the observation of metallic hydrogen on a diamond-anvil cell. Theoretical calculations have typically relied on a mean-field description of electronic correlation through density functional theory, a theory with well-known limitations in the description of metal-insulator transitions. In fact, the predictions of the pressure-driven dissociation of molecules in high-pressure hydrogen by density functional theory is strongly affected by the chosen exchange-correlation functional. In this Letter, we use quantum Monte Carlo calculations to study the molecular to atomic transition in hydrogen. We obtain a transition pressure of 447(3) GPa, in excellent agreement with the best experimental estimate of the transition 450 GPa based on an extrapolation to zero band gap from experimental measurements. Additionally, we find that C2/c is stable almost up to the molecular to atomic transition, in contrast to previous density functional theory (DFT) and DFT+quantum Monte Carlo studies which predict large stability regimes for intermediary molecular phases.

  5. High-pressure Raman spectroscopy of phase change materials

    SciTech Connect

    Hsieh, Wen-Pin Mao, Wendy L.; Zalden, Peter; Wuttig, Matthias; Lindenberg, Aaron M.

    2013-11-04

    We used high-pressure Raman spectroscopy to study the evolution of vibrational frequencies of the phase change materials (PCMs) Ge{sub 2}Sb{sub 2}Te{sub 5}, GeSb{sub 2}Te{sub 4}, and SnSb{sub 2}Te{sub 4}. We found that the critical pressure for triggering amorphization in the PCMs decreases with increasing vacancy concentration, demonstrating that the presence of vacancies, rather than differences in the atomic covalent radii, is crucial for pressure-induced amorphization in PCMs. Compared to the as-deposited amorphous phase, the pressure-induced amorphous phase has a similar vibrational spectrum but requires much lower laser power to transform into the crystalline phase, suggesting different kinetics of crystallization, which may have implications for applications of PCMs in non-volatile data storage.

  6. Phase relations of iron alloys at high pressure (Invited)

    NASA Astrophysics Data System (ADS)

    Kuwayama, Y.; Hirose, K.; Sata, N.; Ohishi, Y.

    2009-12-01

    The Earth's core is believed to be composed of iron-nickel alloy with a small amount of one or more light elements (such as H, C, O, Si and S). Phase relations and crystal structures of iron alloys at high pressures are essential for understanding the seismic observations and the nature of the solid inner core. For recent years, we have developed experimental techniques of the high P-T generation using a laser-heated diamond-anvil cell (LH-DAC) and studied the phase relations of various iron alloys at high pressure and high temperature. For example, phase relations of iron and iron-nickel alloys were investigated up to 300 GPa and 2000 K (Kuwayama et al. EPSL, 2008). Iron-silicon alloys and iron-sulfur alloys were also studied up to more than 200 GPa, based on in-situ x-ray diffraction measurements along with chemical analysis of the quenched samples using a field-emission electron microprobe (FE-EPMA)(Kuwayama et al. PCM, 2009). In this talk, I will present recent experimental results on iron alloys and discuss the structure and composition of the Earth's inner core.

  7. High-pressure phase transition observed in barium hydride

    NASA Astrophysics Data System (ADS)

    Smith, Jesse S.; Desgreniers, Serge; Tse, John S.; Klug, Dennis D.

    2007-08-01

    The pressure-dependent structural and vibrational properties of barium hydride have been studied up to 22 GPa at room temperature by means of powder x-ray diffraction, Raman spectroscopy, and first-principles calculations. At ambient conditions, BaH2 crystallizes in the cotunnite structure (Pnma). A reversible, first-order structural phase transition is observed at 1.6 GPa. The high-pressure phase can be indexed by a hexagonal unit cell with a proposed Ni2In structure (P63/mmc), with the Ba and H atoms in special positions. The experimental volume compression of the high-pressure phase yields an isothermal bulk modulus B0=24(1) GPa (B0' fixed at 4.13). This compares favorably with the results of the first-principles calculations, which reproduce the first-order nature of the transition. The relevance of these results is discussed in the contexts of metal hydrides in particular and ionic AX2(A =metal) compounds in general.

  8. Structural Phase Transition of ThC Under High Pressure.

    PubMed

    Yu, Cun; Lin, Jun; Huai, Ping; Guo, Yongliang; Ke, Xuezhi; Yu, Xiaohe; Yang, Ke; Li, Nana; Yang, Wenge; Sun, Baoxing; Xie, Ruobing; Xu, Hongjie

    2017-03-07

    Thorium monocarbide (ThC) as a potential fuel for next generation nuclear reactor has been subjected to its structural stability investigation under high pressure, and so far no one reported the observation of structure phase transition induced by pressure. Here, utilizing the synchrotron X-ray diffraction technique, we for the first time, experimentally revealed the phase transition of ThC from B1 to P4/nmm at pressure of ~58 GPa at ambient temperature. A volume collapse of 10.2% was estimated during the phase transition. A modulus of 147 GPa for ThC at ambient pressure was obtained and the stoichiometry was attributed to the discrepancy of this value to the previous reports.

  9. The phase diagram of high-pressure superionic ice

    PubMed Central

    Sun, Jiming; Clark, Bryan K.; Torquato, Salvatore; Car, Roberto

    2015-01-01

    Superionic ice is a special group of ice phases at high temperature and pressure, which may exist in ice-rich planets and exoplanets. In superionic ice liquid hydrogen coexists with a crystalline oxygen sublattice. At high pressures, the properties of superionic ice are largely unknown. Here we report evidence that from 280 GPa to 1.3 TPa, there are several competing phases within the close-packed oxygen sublattice. At even higher pressure, the close-packed structure of the oxygen sublattice becomes unstable to a new unusual superionic phase in which the oxygen sublattice takes the P21/c symmetry. We also discover that higher pressure phases have lower transition temperatures. The diffusive hydrogen in the P21/c superionic phase shows strong anisotropic behaviour and forms a quasi-two-dimensional liquid. The ionic conductivity changes abruptly in the solid to close-packed superionic phase transition, but continuously in the solid to P21/c superionic phase transition. PMID:26315260

  10. The phase diagram of high-pressure superionic ice.

    PubMed

    Sun, Jiming; Clark, Bryan K; Torquato, Salvatore; Car, Roberto

    2015-08-28

    Superionic ice is a special group of ice phases at high temperature and pressure, which may exist in ice-rich planets and exoplanets. In superionic ice liquid hydrogen coexists with a crystalline oxygen sublattice. At high pressures, the properties of superionic ice are largely unknown. Here we report evidence that from 280 GPa to 1.3 TPa, there are several competing phases within the close-packed oxygen sublattice. At even higher pressure, the close-packed structure of the oxygen sublattice becomes unstable to a new unusual superionic phase in which the oxygen sublattice takes the P2(1)/c symmetry. We also discover that higher pressure phases have lower transition temperatures. The diffusive hydrogen in the P2(1)/c superionic phase shows strong anisotropic behaviour and forms a quasi-two-dimensional liquid. The ionic conductivity changes abruptly in the solid to close-packed superionic phase transition, but continuously in the solid to P2(1)/c superionic phase transition.

  11. Superhard Semiconducting Optically Transparent High Pressure Phase of Boron

    SciTech Connect

    Zarechnaya, E.Yu.; Dubrovinsky, L.; Dubrovinskaia, N.; Filinchuk, Y.; Chernyshov, D.; Dmitriev, V.; Miyajima, N.; Goresy, A. El; Braun, H.F.; Van Smaalen, S.; Kantor, I.; Kantor, A.; Prakapenka, V.; Hanfland, M.; Mikhaylushkin, A.S.; Abrikosov, I.A.; Simak, S.I.

    2009-05-21

    An orthorhombic (space group Pnnm) boron phase was synthesized at pressures above 9 GPa and high temperature, and it was demonstrated to be stable at least up to 30 GPa. The structure, determined by single-crystal x-ray diffraction, consists of B{sub 12} icosahedra and B{sub 2} dumbbells. The charge density distribution obtained from experimental data and ab initio calculations suggests covalent chemical bonding in this phase. Strong covalent interatomic interactions explain the low compressibility value (bulk modulus is K{sub 300} = 227 GPa) and high hardness of high-pressure boron (Vickers hardness H{sub v} = 58 GPa), after diamond the second hardest elemental material.

  12. Phase changes of CO2 hydrate under high pressure and low temperature.

    PubMed

    Hirai, Hisako; Komatsu, Kazuki; Honda, Mizuho; Kawamura, Taro; Yamamoto, Yoshitaka; Yagi, Takehiko

    2010-09-28

    High pressure and low temperature experiments with CO(2) hydrate were performed using diamond anvil cells and a helium-refrigeration cryostat in the pressure and temperature range of 0.2-3.0 GPa and 280-80 K, respectively. In situ x-ray diffractometry revealed that the phase boundary between CO(2) hydrate and water+CO(2) extended below the 280 K reported previously, toward a higher pressure and low temperature region. The results also showed the existence of a new high pressure phase above approximately 0.6 GPa and below 1.0 GPa at which the hydrate decomposed to dry ice and ice VI. In addition, in the lower temperature region of structure I, a small and abrupt lattice expansion was observed at approximately 210 K with decreasing temperature under fixed pressures. The expansion was accompanied by a release of water content from the sI structure as ice Ih, which indicates an increased cage occupancy. A similar lattice expansion was also described in another clathrate, SiO(2) clathrate, under high pressure. Such expansion with increasing cage occupancy might be a common manner to stabilize the clathrate structures under high pressure and low temperature.

  13. High Pressure Materials Research: Novel Extended Phases of Molecular Triatomics

    SciTech Connect

    Yoo, Choong-Shik

    2006-01-27

    Application of high pressure significantly alters the interatomic distance and thus the nature of intermolecular interaction, chemical bonding, molecular configuration, crystal structure, and stability of solid. With modern advances in high-pressure technologies, it is feasible to achieve a large (often up to a several-fold) compression of lattice, at which condition material can be easily forced into a new physical and chemical configuration. The high-pressure thus offers enhanced opportunities to discover new phases, both stable and metastable ones, and to tune exotic properties in a wide-range of atomistic length scale, substantially greater than (often being several orders of) those achieved by other thermal (varing temperatures) and chemical (varying composition or making alloys) means. Simple molecular solids like H{sub 2}, C, CO{sub 2}, N{sub 2}, O{sub 2}, H{sub 2}O, CO, NH{sub 3}, and CH{sub 4} are bounded by strong covalent intramolecular bonds, yet relatively weak intermolecular bonds of van der Waals and/or hydrogen bonds. The weak intermolecular bonds make these solids highly compressible (i.e., low bulk moduli typically less than 10 GPa), while the strong covalent bonds make them chemically inert at least initially at low pressures. Carboncarbon single bonds, carbon-oxygen double bonds and nitrogen-nitrogen triple bonds, for example, are among the strongest. These molecular forms are, thus, often considered to remain stable in an extended region of high pressures and high temperatures. High stabilities of these covalent molecules are also the basis of which their mixtures are often presumed to be the major detonation products of energetic materials as well as the major constituents of giant planets. However, their physical/chemical stabilities are not truly understood at those extreme pressure-temperature conditions. In fact, an increasing amount of experimental evidences contradict the assumed stability of these materials at high pressures and

  14. High-pressure behavior of fcc phase FeHx

    NASA Astrophysics Data System (ADS)

    Thompson, E. C.; Chidester, B.; Fischer, R. A.; Prakapenka, V.; Bi, W.; Alp, E. E.; Campbell, A. J.

    2015-12-01

    Earth's core is composed of iron with the inclusion of light elements to compensate for the difference between seismically obtained densities and the density of pure Fe at relevant pressure and temperature conditions. As the most abundant and lightest element in the solar system, hydrogen is a plausible contributor to this core density deficit. Nearly stoichiometric iron hydride (FeHx) has been shown to result from the reaction of Fe and hydrous silicates, and is stable up to at least 80 GPa [1]. Iron hydride formation at Earth's surface is unlikely because the equilibrium hydrogen solubility in iron at atmospheric conditions is prohibitively low, yet as hydrogen solubility increases with pressure, so does the likelihood of FeHx formation within the Earth's interior [2]. Recent experimental and ab initio attempts disagree on the equation of state parameters needed to describe the compressional behavior of FeHx [3-5]. The work presented here combines synchrotron x-ray diffraction of laser-heated diamond anvil cell compressed samples with high-pressure, ambient temperature nuclear resonant inelastic scattering (NRIXS) and synchrotron Mössbauer spectroscopy (SMS) to better constrain the behavior of the fcc phase of FeHx at elevated pressures and temperatures. By pairing P-V-T data for iron hydride with the sound velocity information available through high-pressure NRIXS studies, we can better understand the degree to which hydrogen may contribute to the density deficit of Earth's iron core. [1] Antonov et al. (1998) J. Alloys Compd. 264, 214-222 [2] Fukai and Akimoto (1983) Proc. Japan Acad. 59, 158-162 [3] Pépin et al. (2014) Phys. Rev. Lett. 265504, 1-5 [4] Hirao (2004) Geophys. Res. Lett. 31, L06616 [5] Badding et al. (1991) Science. 253, 421-424

  15. Fully Consistent Finite-Strain Landau Theory for High-Pressure Phase Transitions

    NASA Astrophysics Data System (ADS)

    Tröster, A.; Schranz, W.; Karsai, F.; Blaha, P.

    2014-07-01

    Landau theory (LT) is an indispensable cornerstone in the thermodynamic description of phase transitions. As with structural transitions, most applications require one to consistently take into account the role of strain. If temperature drives the transition, the relevant strains are, as a rule, small enough to be treated as infinitesimal, and therefore one can get away with linearized elasticity theory. However, for transitions driven by high pressure, strains may become so large that it is absolutely mandatory to treat them as finite and deal with the nonlinear nature of the accompanying elastic energy. In this paper, we explain how to set up and apply what is, in fact, the only possible consistent Landau theory of high-pressure phase transitions that systematically allows us to take these geometrical and physical nonlinearities into account. We also show how to incorporate available information on the pressure dependence of elastic constants taken from experiment or simulation. We apply our new theory to the example of the high-pressure cubic-tetragonal phase transition in strontium titanate, a model perovskite that has played a central role in the development of the theory of structural phase transitions. Armed with pressure-dependent elastic constants calculated by density-functional theory, we give an accurate description of recent high-precision experimental data and predict a number of elastic transition anomalies accessible to experiments.

  16. High-pressure polymeric phases of carbon dioxide.

    PubMed

    Sun, Jian; Klug, Dennis D; Martonák, Roman; Montoya, Javier Antonio; Lee, Mal-Soon; Scandolo, Sandro; Tosatti, Erio

    2009-04-14

    Understanding the structural transformations of solid CO(2) from a molecular solid characterized by weak intermolecular bonding to a 3-dimensional network solid at high pressure has challenged researchers for the past decade. We employ the recently developed metadynamics method combined with ab initio calculations to provide fundamental insight into recent experimental reports on carbon dioxide in the 60-80 GPa pressure region. Pressure-induced polymeric phases and their transformation mechanisms are found. Metadynamics simulations starting from the CO(2)-II (P4(2)/mnm) at 60 GPa and 600 K proceed via an intermediate, partially polymerized phase, and finally yield a fully tetrahedral, layered structure (P-4m2). Based on the agreement between calculated and experimental Raman and X-ray patterns, the recently identified phase VI [Iota V, et al. (2007) Sixfold coordinated carbon dioxide VI. Nature Mat 6:34-38], assumed to be disordered stishovite-like, is instead interpreted as the result of an incomplete transformation of the molecular phase into a final layered structure. In addition, an alpha-cristobalite-like structure (P4(1)2(1)2), is predicted to be formed from CO(2)-III (Cmca) via an intermediate Pbca structure at 80 GPa and low temperatures (<300 K). Defects in the crystals are frequently observed in the calculations at 300 K whereas at 500 to 700 K, CO(2)-III transforms to an amorphous form, consistent with experiment [Santoro M, et al. (2006) Amorphous silica-like carbon dioxide. Nature 441:857-860], but the simulation yields additional structural details for this disordered solid.

  17. High-pressure polymeric phases of carbon dioxide

    PubMed Central

    Sun, Jian; Klug, Dennis D.; Martoňák, Roman; Montoya, Javier Antonio; Lee, Mal-Soon; Scandolo, Sandro; Tosatti, Erio

    2009-01-01

    Understanding the structural transformations of solid CO2 from a molecular solid characterized by weak intermolecular bonding to a 3-dimensional network solid at high pressure has challenged researchers for the past decade. We employ the recently developed metadynamics method combined with ab initio calculations to provide fundamental insight into recent experimental reports on carbon dioxide in the 60–80 GPa pressure region. Pressure-induced polymeric phases and their transformation mechanisms are found. Metadynamics simulations starting from the CO2-II (P42/mnm) at 60 GPa and 600 K proceed via an intermediate, partially polymerized phase, and finally yield a fully tetrahedral, layered structure (P-4m2). Based on the agreement between calculated and experimental Raman and X-ray patterns, the recently identified phase VI [Iota V, et al. (2007) Sixfold coordinated carbon dioxide VI. Nature Mat 6:34–38], assumed to be disordered stishovite-like, is instead interpreted as the result of an incomplete transformation of the molecular phase into a final layered structure. In addition, an α-cristobalite-like structure (P41212), is predicted to be formed from CO2-III (Cmca) via an intermediate Pbca structure at 80 GPa and low temperatures (<300 K). Defects in the crystals are frequently observed in the calculations at 300 K whereas at 500 to 700 K, CO2-III transforms to an amorphous form, consistent with experiment [Santoro M, et al. (2006) Amorphous silica-like carbon dioxide. Nature 441:857–860], but the simulation yields additional structural details for this disordered solid. PMID:19332796

  18. High pressure effects on isotropic Nd2Fe14B magnet accompanying change in coercive field

    NASA Astrophysics Data System (ADS)

    Mito, M.; Goto, H.; Nagai, K.; Tsuruta, K.; Deguchi, H.; Tajiri, T.; Konishi, K.

    2015-10-01

    We investigated the effects of hydrostatic pressure on an isotropic Nd2Fe14B magnet (the exact chemical formula is Nd2.0Fe14.1B) consisting of nanocrystals, with the size of approximately 30 nm, by magnetization measurements at pressures (P's) up to 9.3 GPa and structural analyses up to 4.3 GPa. Magnetization curves were measured by using a miniature diamond anvil cell made of Ti alloy with spatially uniform magnetization. The initial value of coercive field Hc at 300 K is 840 kA/m (=10.6 kOe), and Hc initially increases to approximately 1180 kA/m (=15.0 kOe) almost linearly against the pressure. The increase in Hc, however, saturates at around P = 3 GPa. The change in Hc is understood by the decrease in the saturation magnetization Ms within the framework of the constant anisotropy of the single domain phase. The crystalline strain increases for P < 1 GPa. Afterward, the crystalline size (D) starts to decrease with increasing pressure, and the reduction tends to saturate at above approximately 3 GPa. Furthermore, the change in Ms is actually related with both the change in strain and that in D. The data on the temperature dependence of Hc at P = 0, 6.6, and 9.3 GPa exhibit pressure-induced suppression of the Curie temperature. The maximum energy product decreases with increasing pressure over the whole temperature range.

  19. High pressure studies on extended phases of CO2

    NASA Astrophysics Data System (ADS)

    Montoya, Javier A.; Lee, Mal-Soon; Scandolo, Sandro

    2010-03-01

    Recent findings have shown that the chemistry of CO2 at high pressure and temperature is richer than previously thought and that the activation of the C=O bond that can give origin to different forms of non-molecular CO2. Such findings may have important implications for the understanding of the Earth's deep carbon cycle and CO2 sequestration technologies. First principles simulations of CO2's electronic properties under different pressure and temperature conditions can constrain the thermodynamic phase diagram of CO2 and explore P-T conditions necessary for the C=O bond activation. We have shown that at about 50 GPa molecular CO2 can transform to a metastable amorphous form characterized by an almost equal proportion of three- and four-fold coordinated carbon atoms [1], while higher carbon coordination does not take place up to at least 900 GPa [2-3]. We have also found that doping with transition metals can reduce the activation barrier and transition pressure for the C=O bond activation in CO2 [4]. Our results suggest that pressure can radically alter the oxidation chemistry of carbon. [1] J. A. Montoya et al., PRL 100, 163002 (2008) [2] J. Sun et al., PNAS 106, 6077 (2009) [3] M-S. Lee, J. A. Montoya and S. Scandolo, PRB 79, 144102 (2009) [4] J. A. Montoya, R. Rousseau, and S. Scandolo, unpublished.

  20. Structural phase transitions of sodium nitride at high pressure

    NASA Astrophysics Data System (ADS)

    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.

  1. Dense superconducting phases of copper-bismuth at high pressure

    NASA Astrophysics Data System (ADS)

    Amsler, Maximilian; Wolverton, Chris

    2017-08-01

    Although copper and bismuth do not form any compounds at ambient conditions, two intermetallics, CuBi and Cu11Bi7 , were recently synthesized at high pressures. Here we report on the discovery of additional copper-bismuth phases at elevated pressures with high densities from ab initio calculations. In particular, a Cu2Bi compound is found to be thermodynamically stable at pressures above 59 GPa, crystallizing in the cubic Laves structure. In strong contrast to Cu11Bi7 and CuBi, cubic Cu2Bi does not exhibit any voids or channels. Since the bismuth lone pairs in cubic Cu2Bi are stereochemically inactive, the constituent elements can be closely packed and a high density of 10.52 g/cm3 at 0 GPa is achieved. The moderate electron-phonon coupling of λ =0.68 leads to a superconducting temperature of 2 K, which exceeds the values observed both in Cu11Bi7 and CuBi, as well as in elemental Cu and Bi.

  2. Phase transitions in Sc{sub 2}(WO{sub 4}){sub 3} under high pressure

    SciTech Connect

    Garg, Nandini; Murli, Chitra; Sharma, Surinder M.; Tyagi, A.K.

    2005-08-01

    High-pressure x-ray diffraction and Raman scattering studies on scandium tungstate [Sc{sub 2}(WO{sub 4}){sub 3}] show that it transforms to a monoclinic phase at {approx}0.6{+-}0.3 GPa. The high-pressure phase has P2{sub 1}/a symmetry and is related to the initial orthorhombic phase through cell doubling along the c axis. The compound undergoes another phase transition at {approx}1.6 GPa, accompanied by a volume reduction of {approx}8%. At {approx}6.5 GPa, the diffraction pattern and Raman spectra of Sc{sub 2}(WO{sub 4}){sub 3} indicate the emergence of a disordered crystalline state which evolves into an amorphous phase beyond {approx}14 GPa. The structural changes are found to be reversible up to {approx}1.6 GPa. However, transformation to the amorphous state is found to be irreversible, though our results suggest some structural relaxation on release of pressure.

  3. High-pressure phase behavior of SrCO3: an experimental and computational Raman scattering study

    NASA Astrophysics Data System (ADS)

    Biedermann, Nicole; Speziale, Sergio; Winkler, Björn; Reichmann, Hans Josef; Koch-Müller, Monika; Heide, Gerhard

    2017-05-01

    The high-pressure phase behavior of strontianite (SrCO3) was both experimentally and theoretically investigated by Raman spectroscopy up to 78 GPa in a diamond anvil cell and density functional theory-based calculations. Our study shows a phase transition between 23.7 and 26.8 GPa during compression from space group Pmcn to post-aragonite SrCO3, which is accompanied by significant changes in the vibrational spectrum. The excellent agreement between the observed and computed Raman frequencies and intensities implies that the high-pressure polymorph has space group Pmmn and contributes to resolving an existing disagreement concerning the correct space group symmetry of this high-pressure polymorph. It is shown that the transition pressure from the aragonite to a post-aragonite phase increases linearly with decreasing cation radius for (Ca, Sr, Ba, Pb) carbonates.

  4. High-pressure phase behavior of SrCO3: an experimental and computational Raman scattering study

    NASA Astrophysics Data System (ADS)

    Biedermann, Nicole; Speziale, Sergio; Winkler, Björn; Reichmann, Hans Josef; Koch-Müller, Monika; Heide, Gerhard

    2016-11-01

    The high-pressure phase behavior of strontianite (SrCO3) was both experimentally and theoretically investigated by Raman spectroscopy up to 78 GPa in a diamond anvil cell and density functional theory-based calculations. Our study shows a phase transition between 23.7 and 26.8 GPa during compression from space group Pmcn to post-aragonite SrCO3, which is accompanied by significant changes in the vibrational spectrum. The excellent agreement between the observed and computed Raman frequencies and intensities implies that the high-pressure polymorph has space group Pmmn and contributes to resolving an existing disagreement concerning the correct space group symmetry of this high-pressure polymorph. It is shown that the transition pressure from the aragonite to a post-aragonite phase increases linearly with decreasing cation radius for (Ca, Sr, Ba, Pb) carbonates.

  5. High-pressure phase transition in {gamma}-hexanitrohexaazaisowurtzitane

    SciTech Connect

    Russell, T.P.; Miller, P.J.; Piermarini, G.J.; Block, S.

    1992-06-25

    FTIR, EDXD, and PLM; data for a new high-pressure polymorph, {zeta}-HNIW, which is formed from {gamma}-HNIW at 0.7 +/- 0.05 GPa and room temperature. The {gamma}-{zeta} transformation is rapid and reversible in single crystals in a hydrostatic pressure transmitting medium, but the {zeta} form could not be retrieved to ambient conditions. 12 refs., 6 figs., 2 tabs.

  6. High-pressure phase equilibria with compressed gases.

    PubMed

    Ren, Wei; Scurto, Aaron M

    2007-12-01

    An apparatus is described that is capable of determining high-pressure vapor-liquid equilibrium, liquid-liquid equilibrium, solid-liquid-vapor equilibrium, vapor-liquid-liquid equilibrium, and mixture critical points and transitions. The device is capable of temperatures to 150 degrees C and pressures to 300 bars (higher with slight modifications). The construction and operation are described in detail and do not require the use of mercury. This method requires very low sample volumes and no analytical equipment nor system-specific calibration. The apparatus was verified by comparison with literature data for the decane-CO(2) mixture and CO(2)-ionic liquid [1-hexyl-3-methyl-imidazolium bis(trifyl)imide)] systems. The experimental data have excellent agreement with the literature data that used different experimental methods. A rigorous error analysis of the system is also presented.

  7. High-pressure chemistry of molecular solids: evidences for novel extended phases of carbon dioxide

    SciTech Connect

    Yoo, C S

    1999-07-22

    At high pressures and temperatures, many molecular solids become unstable and transform into denser extended phases. Recently, we have discovered evidences for two novel extended phases of carbon dioxide at high pressures and temperatures: (1) an ionic form of dimeric CO,, C02+C03*- at 8-13 GPa and above 2000 K [I] and (2) a polymeric phase CO,-V above 35 GPa and 1800 K [2,3]. These extended phases can be quenched at room temperature at low pressures, from which their molecular and crystal structures have been determined. These transitions occur to soften highly repulsive intermolecular potentials via delocalization of electrons at high pressures and temperatures. Based on these and other previous results, we conjecture that three fundamental mechanisms of high-pressure chemistry are ionization, polymerization, and metallization, occurring in high-density molecular solids and fluids. [carbon dioxide, polymeric COZ, ionic CO, dimer, high-pressure chemistry, electron delocalization

  8. PHASE EQUILIBRIUM STUDIES OF GERMANIUM AND SILICON AT HIGH PRESSURES.

    DTIC Science & Technology

    phase Ge-IV with the body centered cubic structure . The triple point between Ge-I (diamond structure), Ge-III (body centered tetragonal) and Ge-IV (body...Another new phase with the simple cubic structure has been detected for the first time although its relations to the other polymorphs of germanium has

  9. Collective spin 1 singlet phase in high-pressure oxygen

    PubMed Central

    Crespo, Yanier; Fabrizio, Michele; Scandolo, Sandro; Tosatti, Erio

    2014-01-01

    Oxygen, one of the most common and important elements in nature, has an exceedingly well-explored phase diagram under pressure, up to and beyond 100 GPa. At low temperatures, the low-pressure antiferromagnetic phases below 8 GPa where O2 molecules have spin S = 1 are followed by the broad apparently nonmagnetic ε phase from about 8 to 96 GPa. In this phase, which is our focus, molecules group structurally together to form quartets while switching, as believed by most, to spin S = 0. Here we present theoretical results strongly connecting with existing vibrational and optical evidence, showing that this is true only above 20 GPa, whereas the S = 1 molecular state survives up to about 20 GPa. The ε phase thus breaks up into two: a spinless ε0 (20−96 GPa), and another ε1 (8−20 GPa) where the molecules have S = 1 but possess only short-range antiferromagnetic correlations. A local spin liquid-like singlet ground state akin to some earlier proposals, and whose optical signature we identify in existing data, is proposed for this phase. Our proposed phase diagram thus has a first-order phase transition just above 20 GPa, extending at finite temperature and most likely terminating into a crossover with a critical point near 30 GPa and 200 K. PMID:25002513

  10. Phase transition of solid bismuth under high pressure

    NASA Astrophysics Data System (ADS)

    Chen, Hai-Yan; Xiang, Shi-Kai; Yan, Xiao-Zhen; Zheng, Li-Rong; Zhang, Yi; Liu, Sheng-Gang; Bi, Yan

    2016-10-01

    As a widely used pressure calibrator, the structural phase transitions of bismuth from phase I, to phase II, to phase III, and then to phase V with increasing pressure at 300 K have been widely confirmed. However, there are different structural versions for phase III, most of which are determined by x-ray diffraction (XRD) technology. Using x-ray absorption fine structure (XAFS) measurements combined with ab initio calculations, we show that the proposed incommensurate composite structure of bismuth of the three configurations is the best option. An abnormal continuous increase of the nearest-neighbor distance of phase III with elevated pressure is also observed. The electronic structure transformation from semimetal to metal is responsible for the complex behavior of structure transformation. Project supported by the National Natural Science Foundation of China (Grant Nos. 10904133, 11304294, 11274281, 11404006, and U1230201), the Development Foundation of China Academy of Engineering Physics (Grant Nos. 2015B0101004, 2013B0401062, and 2012A0101001), the Research Foundation of the Laboratory of Shock Wave and Detonation, China (Grant No. 9140C670201140C67282).

  11. New Phase Transition of Solid Bromine under High Pressure

    SciTech Connect

    San-Miguel, A.; Libotte, H.; Gaspard, J.-P.; Gauthier, M.; Aquilanti, G.; Pascarelli, S.

    2007-07-06

    Solid bromine has been studied by x-ray absorption spectroscopy experiments up to a maximum pressure of 75 GPa. The data analysis of the extended fine structure reveals that the intramolecular distance first increases, reaching its maximum value at 25{+-}5 GPa. From this value the intramolecular distance abruptly begins to decrease evidencing a nonpreviously observed phase transformation taking place at 25{+-}5 GPa. A maximum variation of 0.08 A ring is observed at 65{+-}5 GPa where again a phase transition occurs. This last transformation could correspond with the recently observed change to an incommensurate modulated phase. We discuss the possible generalization of the observed new phase transition at 25{+-}5 GPa to the case of the other halogens.

  12. Phase diagram of Mo at high pressure and temperature

    SciTech Connect

    Ross, M

    2008-10-01

    We report values of the Poisson Ratios for shock compressed Mo, calculated from the sound speed measurements, which provide evidence that the 210 GPa ({approx}4100K) transition cannot be a bcc-hcp transition, as originally proposed. Instead, we find the transition is from the bcc to a noncrystalline phase. For pressures above 210 GPa, the Poisson Ratio increases steadily with increasing temperature, approaching the liquid value of 0.5 at 390 GPa({approx}10,000K), suggesting the presence of a noncrystalline solid-liquid mixture. Free energy model calculations were used to show that the low melting slope of Mo, and the phase diagram, can be explained by the presence of local liquid structures. A new phase diagram is proposed for Mo that is constrained by the experimental evidence.

  13. High pressure phase transition and elastic properties of americium telluride

    NASA Astrophysics Data System (ADS)

    Aynyas, Mahendra; Rukmangad, Aditi; Arya, B. S.; Sanyal, S. P.

    2013-06-01

    The structural and elastic properties of Americium Telluride (AmTe) have been investigated by using a modified inter-ionic potential theory (MIPT). This theory is capable of explaining first order phase transition with a crystallographic change NaCl to CsCl structure for this compound. The values of optimized lattice constant, phase transition pressure, zero pressure bulk modulus and second order elastic constants (C11, C44) agree well with their corresponding experimental data. Debye temperature (θD) is also calculated for this compound for the first time.

  14. Hydrogen Disorder and Elasticity of Phase D at High Pressures

    NASA Astrophysics Data System (ADS)

    Kiefer, B.; Li, L.

    2007-12-01

    One of the major goals of Earth's sciences is to develop models for the evolution of our planet. This goal is directly linked to our understanding of the dynamics within the Earth's interior. It has long been recognized that small amounts of volatiles such as hydrogen can have a disproportionately large effect on viscosity. This implies less resistance to convection and shorter overturn times. Thus knowing the abundance of hydrogen and its distribution in the mantle has important implications for the evolution of our planet. However, one of the remaining question is provide observables that may aid constraining the presence of volatiles. Phase D, MgSi2O6H2, is of particular interest since it is the only hydrogen bearing phase whose stability field extends into the lower mantle. Thus, phase D is a prime candidate for hydrogen transport into the lower mantle along subduction zones. In order to investigate the elasticity of phase D, we performed static (0 K) first-principle calculations. All calculations were performed with a plane-wave basis-set using GGA-PAW potentials. We find that long H-H bonds are energetically favorable which is likely due to H-H repulsion. The equation of state of the energetically most favorable structures are consistent with previous and experimental and theoretical studies of Phase D. Our preliminary results show that hydrogen bond symmetrization occurs in the pressure range of 40-50 GPa in agreement with previous theoretical studies. The elastic constant tensors of the relevant hydrogen distributions agree to within ~0.5% at least up 70 GPa. We also find that the largest change in elasticity with hydrogen symmetrization is an increase of C33 by ~ 10%. The induced changes of compressional and shear wave speeds are similar, ~ 1% at 40 GPa. The predicted azimuthal and polarization anisotropies of shear waves decrease by only ~ 1% with symmetrization. In contrast, the azimuthal P-wave anisotropy decreases from ~ 18% to ~ 7% with hydrogen bond

  15. Superconducting high-pressure phases composed of hydrogen and iodine

    DOE PAGES

    Shamp, Andrew; Zurek, Eva

    2015-09-25

    Evolutionary structure searches predict three new phases of iodine polyhydrides stable under pressure. Insulating P1-H5I, consisting of zigzag chains of (HI) δ+ and H 2 molecules, is stable between 30-90 GPa. Cmcm-H2I and P6/mmm-H4I are found on the 100, 150 and 200 GPa convex hulls. These two phases are good metals, even at 1 atm, because they consist of monoatomic lattices of iodine. At 100 GPa the superconducting transition temperature, Tc, of H2I and H4I are estimated to be 7.8 and 17.5 K, respectively. Lastly, the increase in Tc relative to elemental iodine results from a larger ωlog from themore » light mass of hydrogen, and an enhanced from modes containing H/I and H/H vibrations.« less

  16. High pressure phase transition in group III nitrides compounds

    NASA Astrophysics Data System (ADS)

    Soni, Shubhangi; Verma, S.; Kaurav, Netram; Choudhary, K. K.

    2016-05-01

    Using an effective interionic interaction potential (EIOP), the pressure induced structural phase transformation from ZnS-type (B3) to NaCl-type (B1) structure in group III Post-Transition Metal Nitrides [TMN; TM=Ga and Tl] were investigated. The long range Coulomb, van der Waals (vdW) interaction and the short-range repulsive interaction upto second-neighbor ions within the Hafemeister and Flygare approach with modified ionic charge are properly incorporated in the EIOP. The vdW coefficients are computed following the Slater-Kirkwood variational method, as both the ions are polarizable. The estimated value of the phase transition pressure (Pt) and the magnitude of the discontinuity in volume at the transition pressure are consistent as compared to the reported data.

  17. High pressure partially ionic phase of water ice.

    PubMed

    Wang, Yanchao; Liu, Hanyu; Lv, Jian; Zhu, Li; Wang, Hui; Ma, Yanming

    2011-11-29

    Water ice dissociates into a superionic solid at high temperature (>2,000 K) and pressure, where oxygen forms the lattice, but hydrogen diffuses completely. At low temperature, however, the dissociation into an ionic ice of hydronium (H(3)O)(+) hydroxide (OH)(-) is not expected because of the extremely high energy cost (~1.5 eV) of proton transfer between H(2)O molecules. Here we show the pressure-induced formation of a partially ionic phase (monoclinic P2(1) structure) consisting of coupled alternate layers of (OH)(δ-) and (H(3)O)(δ+) (δ=0.62) in water ice predicted by particle-swarm optimization structural search at zero temperature and pressures of >14 Mbar. The occurrence of this ionic phase follows the break-up of the typical O-H covalently bonded tetrahedrons in the hydrogen symmetric atomic phases and is originated from the volume reduction favourable for a denser structure packing.

  18. Rheology of phase A at high pressure and high temperature

    NASA Astrophysics Data System (ADS)

    Hilairet, N.; Amiguet, E.; Wang, Y.; Merkel, S.

    2013-12-01

    Subduction zones are locations where a tectonic plate slides and bends under another one. Materials there undergo large and heterogeneous deformations and stresses which are released through seismicity, occasionally. Thus plasticity of minerals filling faults and shear zones is a critical parameter for understanding the stress balance of whole subduction zones. We present a deformation study on a hexagonal hydrous phase that can exist in shear zones within subducting slabs, phase A, after dehydration of serpentine into pyroxene + phase A. Pure phase A samples were synthesized at 11 GPa and ca. 1100K, in the multi-anvil facility in Clermont-Ferrand, France, with N. Bolfan and D. Andrault. Three samples were deformed at 11 GPa confining pressure, and 673K or 973K, using a D-DIA apparatus [1] at 13B-MD at GSE-CARS, APS, in uniaxial shortening up to -0.24 strain and at 5.10-5 s-1. Lattice strains (a proxy for macro-stress), texture and strain were measured in-situ, using synchrotron radiation. Results from lattice strain and texture analysis show a decrease in flow stress and a change in deformation mechanisms with temperature, coherent with the findings in transmission electron microscopy on samples recovered in relaxation experiments from [2]. The slip systems involved during deformation were further analyzed using Visco-Plastic Self-Consistent (VPSC) simulations [3]. The model inputs were known slip systems for hexagonal materials, including the ones observed by [2], with tunable strengths, the strain rate, final strain, and either a random texture or the starting experimental texture. The final experimental textures could be reproduced. The slip systems that had to be activated for matching the experimental texture confirm the observations by [2]: at 673K, the most active slip systems are prismatic and pyramidal, with the requirement of a smaller activity on the basal system, and at 973K the basal system is the main slip system activated. [1] Wang et al, Review for

  19. Superconducting high-pressure phases composed of hydrogen and iodine

    SciTech Connect

    Shamp, Andrew; Zurek, Eva

    2015-09-25

    Evolutionary structure searches predict three new phases of iodine polyhydrides stable under pressure. Insulating P1-H5I, consisting of zigzag chains of (HI) δ+ and H 2 molecules, is stable between 30-90 GPa. Cmcm-H2I and P6/mmm-H4I are found on the 100, 150 and 200 GPa convex hulls. These two phases are good metals, even at 1 atm, because they consist of monoatomic lattices of iodine. At 100 GPa the superconducting transition temperature, Tc, of H2I and H4I are estimated to be 7.8 and 17.5 K, respectively. Lastly, the increase in Tc relative to elemental iodine results from a larger ωlog from the light mass of hydrogen, and an enhanced from modes containing H/I and H/H vibrations.

  20. High-pressure synthesis of a pentazolate salt [High-pressure synthesis of condensed-phase pentazolate

    DOE PAGES

    Steele, Brad A.; Stavrou, Elissaios; Crowhurst, Jonathan C.; ...

    2016-12-06

    The pentazolates, the last all-nitrogen members of the azole series, have been notoriously elusive for the last hundred years despite enormous efforts to make these compounds in either gas or condensed phases. Here, we report a successful synthesis of a solid state compound consisting of isolated pentazolate anions N5–, which is achieved by compressing and laser heating cesium azide (CsN3) mixed with N2 cryogenic liquid in a diamond anvil cell. The experiment was guided by theory, which predicted the transformation of the mixture at high pressures to a new compound, cesium pentazolate salt (CsN5). Electron transfer from Cs atoms tomore » N5 rings enables both aromaticity in the pentazolates as well as ionic bonding in the CsN5 crystal. As a result, this work provides critical insight into the role of extreme conditions in exploring unusual bonding routes that ultimately lead to the formation of novel high nitrogen content species.« less

  1. High-pressure synthesis of a pentazolate salt [High-pressure synthesis of condensed-phase pentazolate

    SciTech Connect

    Steele, Brad A.; Stavrou, Elissaios; Crowhurst, Jonathan C.; Zaug, Joseph M.; Prakapenka, Vitali B.; Oleynik, Ivan I.

    2016-12-06

    The pentazolates, the last all-nitrogen members of the azole series, have been notoriously elusive for the last hundred years despite enormous efforts to make these compounds in either gas or condensed phases. Here, we report a successful synthesis of a solid state compound consisting of isolated pentazolate anions N5, which is achieved by compressing and laser heating cesium azide (CsN3) mixed with N2 cryogenic liquid in a diamond anvil cell. The experiment was guided by theory, which predicted the transformation of the mixture at high pressures to a new compound, cesium pentazolate salt (CsN5). Electron transfer from Cs atoms to N5 rings enables both aromaticity in the pentazolates as well as ionic bonding in the CsN5 crystal. As a result, this work provides critical insight into the role of extreme conditions in exploring unusual bonding routes that ultimately lead to the formation of novel high nitrogen content species.

  2. Transformation of Hume-Rothery phases under the action of high pressure torsion

    NASA Astrophysics Data System (ADS)

    Straumal, B. B.; Kilmametov, A. R.; Kucheev, Yu. O.; Kolesnikova, K. I.; Korneva, A.; Zieba, P.; Baretzky, B.

    2014-11-01

    It has been revealed experimentally that high-pressure torsion induces phase transformations of certain Hume-Rothery phases (electron compounds) to others. High-pressure torsion induces the ξ → δ + ɛ reaction in copper-tin alloys with the appearance of the δ + ɛ phase mixture as after long-term annealing in the temperature range T eff = 350-589°C. The mass transfer rate driven by high-pressure torsion is 14-18 orders of magnitude higher than the rate of conventional thermal diffusion at the processing temperature T HPT. This phenomenon can be explained by an increased concentration of defects (in particular, vacancies) in the steady state under high-pressure torsion, which is equivalent to an increase in the temperature.

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

    NASA Astrophysics Data System (ADS)

    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.

  4. High pressure structural phase transitions of TiO2 nanomaterials

    NASA Astrophysics Data System (ADS)

    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.

  5. Laser-driven formation of a high-pressure phase in amorphous silica.

    PubMed

    Salleo, Alberto; Taylor, Seth T; Martin, Michael C; Panero, Wendy R; Jeanloz, Raymond; Sands, Timothy; Génin, François Y

    2003-12-01

    Because of its simple composition, vast availability in pure form and ease of processing, vitreous silica is often used as a model to study the physics of amorphous solids. Research in amorphous silica is also motivated by its ubiquity in modern technology, a prominent example being as bulk material in transmissive and diffractive optics for high-power laser applications such as inertial confinement fusion (ICF). In these applications, stability under high-fluence laser irradiation is a key requirement, with optical breakdown occurring when the fluence of the beam is higher than the laser-induced damage threshold (LIDT) of the material. The optical strength of polished fused silica transmissive optics is limited by their surface LIDT. Surface optical breakdown is accompanied by densification, formation of point defects, cratering, material ejection, melting and cracking. Through a combination of electron diffraction and infrared reflectance measurements we show here that synthetic vitreous silica transforms partially into a defective form of the high-pressure stishovite phase under high-intensity (GW cm(-2)) laser irradiation. This phase transformation offers one suitable mechanism by which laser-induced damage grows catastrophically once initiated, thereby dramatically shortening the service lifetime of optics used for high-power photonics.

  6. Structural phase transitions of SrF2 at high pressure

    NASA Astrophysics Data System (ADS)

    Wang, J. S.; Ma, C. L.; Zhou, D.; Xu, Y. S.; Zhang, M. Z.; Gao, W.; Zhu, H. Y.; Cui, Q. L.

    2012-02-01

    The high-pressure behavior of SrF2 has been investigated by angle-dispersive synchrotron X-ray powder diffraction measurement up to 50.3 GPa at room temperature. Two phase transformations were observed at 6.8 and 29.5 GPa, and the two high pressure phases were identified as orthorhombic (Pnma) phase and hexagonal (P63/mmc) phase by Rietveld refinement. Upon decompression, retransformation was observed and the sample recovered under ambient conditions consisted of a mixture of cubic phase and orthorhombic phase. The compressing characteristics of SrF2 as the pressure increases were discussed, indicating higher incompressibility of SrF2 under high pressure.

  7. First-principles investigation of iron pentacarbonyl molecular solid phases at high pressure

    NASA Astrophysics Data System (ADS)

    Cong, Kien Nguyen; Steele, Brad A.; Landerville, Aaron C.; Oleynik, Ivan I.

    2017-01-01

    The polymeric phases of carbon monoxide (p-CO), an extended non-molecular solid, represent a new class of low-Z energetic materials. The presence of transition metal ions is believed to stabilize polymeric carbon monoxide (p-CO) at ambient conditions. Since p-CO forms at high pressures, it becomes important to investigate the high-pressure behavior of one of the potential precursors, iron pentacarbonyl Fe(CO)5. In this work, a first-principles evolutionary structure search method is used to determine the crystal phases of Fe(CO)5 at high pressure. The calculations predict the crystal structure of Phase I in agreement with experiment. Moreover, the previously unidentified crystal structure of Phase II is found. The calculated pressure-dependent Raman spectra are used to demonstrate that the changes in Raman spectra as a function of pressure observed in recent experiment can be explained without invoking a phase transition to a new phase III.

  8. 77 FR 3281 - High Pressure Steel Cylinders From China; Scheduling of the Final Phase of Countervailing Duty...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2012-01-23

    ...-1188 (Final)] High Pressure Steel Cylinders From China; Scheduling of the Final Phase of Countervailing... high pressure steel cylinders, provided for in subheading 7311.00.00 of the Harmonized Tariff Schedule... compressed or liquefied gas (``high pressure steel cylinders''). High pressure steel cylinders are...

  9. The new phase of HgF2 at high pressure

    NASA Astrophysics Data System (ADS)

    Wang, Xiaoli; Li, Jianfu

    2013-05-01

    Mercury halides form an amazing number of solid phases and remarkably only the crystal structure of HgF2 at high pressure is not established. We here report a stabilization HgF2 high-pressure phase predicted by the density functional structural searches, which adopts the Pnma symmetric structure (12 atoms/cell, α-PbCl2-type, or cotunnite). The phase transition from the ambient conditions phase Fm-3m (phase I) to the Pnma phase (phase II) was confirmed at 4.7 GPa. The calculated equation of state suggests that this is a first-order phase transition. At this phase transition, the coordination number of Hg2+ increases from eight to nine, similar to the phase transition sequence of CaF2. Furthermore, a thorough CALYPSO structural search up to 100 GPa cannot find any other structure that is more stable than the Pnma structure.

  10. Phase H: A new high pressure phase of dense hydrous magnesium silicates in the lower mantle

    NASA Astrophysics Data System (ADS)

    Tsuchiya, J.; Tsuchiya, T.; Nishi, M.; Mookherjee, M.

    2014-12-01

    It has been believed that water is carried into the deep Earth's interior by hydrous minerals such as the dense hydrous magnesium silicates (DHMSs) in the descending cold plate. Recently, the new high pressure phase of DHMSs is theoretically predicted (Tsuchiya 2013) and experimentally confirmed in lower mantle pressure conditions above ~45 GPa (Nishi et al. 2014). This phase has MgSiO4H2 chemical composition and named as phase H. At the lower mantle pressure conditions, Al and H-bearing SiO2, δ-AlOOH, ɛ-FeOOH and phase H may be the potential hydrous phases in the subducting slabs. Interestingly, the crystal structure of these hydrous phases are almost same and have CaCl2 type structure. This suggests that these hydrous phases may be able to make the wide range of solid solution. Some experimental studies already reported that Al preferentially partitioned into phase H and the stability of phase H drastically increased by incorporation of Al (Nishi et al. 2014, Ohira et al. 2014). The density of subducted MORB is reported to be denser than that of pyrolite in the lower mantle. Therefore, there is a possibility that phase H containing Al and Fe in subducted MORB survive down to the bottom of lower mantle and the melting of phase H at the core mantle boundary may contribute to the cause of ultra-low velocity zones. In this study, we report the effects of Al and Fe on the stability of phase H, elasticity and seismic anisotropy of this new hydrous mineral using first principles calculation techniques and discuss the possible effects of this hydrous phase at the bottom of lower mantle.

  11. Structural phase transitions in Zn(CN){sub 2} under high pressures

    SciTech Connect

    Poswal, H.K. Tyagi, A.K.; Lausi, Andrea; Deb, S.K.; Sharma, Surinder M.

    2009-01-15

    High pressure behavior of zinc cyanide (Zn(CN){sub 2}) has been investigated with the help of synchrotron-based X-ray diffraction measurements. Our studies reveal that under pressure this compound undergoes phase transformations and the structures of the new phases depend on whether the pressure is hydrostatic or not. Under hydrostatic conditions, Zn(CN){sub 2} transforms from cubic to orthorhombic to cubic-II to amorphous phases. In contrast, the non-hydrostatic pressure conditions drive the ambient cubic phase to a partially disordered crystalline phase, which eventually evolves to a substantially disordered phase. The final disordered phase in the latter case is distinct from the amorphous phase observed under the hydrostatic pressures. - Graphical abstract: High pressure X-ray diffraction investigations on Zn(CN){sub 2} show three phase transformations i.e., cubic{yields}orthorhombic{yields}cubic-II{yields}amorphous. However, the results strongly depend upon the nature of stress.

  12. Crystal Structure of High-Pressure Phases V and VI of Potassium Dihydrogen Phosphate

    NASA Astrophysics Data System (ADS)

    Nakamoto, Yuki; Sakata, Masafumi; Fujihisa, Hiroshi; Shimizu, Katsuya; Deguchi, Kiyoshi

    2012-06-01

    Potassium dihydrogen phosphate KH2PO4 is the most typical hydrogen-bonded ferroelectric. The P--T phase diagram and the existence of high-pressure phases V and VI have already been reported. However, their crystal structures remain unknown. We performed a powder x-ray diffraction experiment under high pressure using synchrotron radiation and analyzed the structures from the obtained data. The structures of phases V and VI were determined to be orthorhombic C2221 and triclinic P\\bar{1}. Their hydrogen positions were predicted by a density functional theory calculation.

  13. Pressure and Temperature effects on the High Pressure Phase Transformation in Zirconium

    SciTech Connect

    Escobedo-Diaz, Juan P.; Cerreta, Ellen K.; Brown, Donald W.; Trujillo, Carl P.; Rigg, Paulo A.; Bronkhorst, Curt A.; Addessio, Francis L.; Lookman, Turab

    2012-06-20

    At high pressure zirconium is known to undergo a phase transformation from the hexagonal close packed (HCP) alpha phase ({alpha}) to the simple hexagonal omega phase ({omega}). Under conditions of shock loading, the high-pressure omega phase is retained upon release. However, the hysteresis in this transformation is not well represented by equilibrium phase diagrams. For this reason, the influence of peak shock pressure and temperature on the retention of omega phase in Zr is explored in this study. In situ VISAR 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, morphology of the shocked alpha and omega phases, and qualitatively understand the kinetics of this transformation. This understanding of the role of peak shock stress will be utilized to address physics to be encoded in our present macro-scale models.

  14. REVIEWS OF TOPICAL PROBLEMS: Properties of high pressure phases in metal-hydrogen systems

    NASA Astrophysics Data System (ADS)

    Ponyatovskiĭ, E. G.; Antonov, Vladimir E.; Belash, I. T.

    1982-08-01

    The development of high-pressure technology has in recent years permitted obtaining extensive new information on the properties of hydrides of group VI-VIII transition metals. In this review, the experimental procedures for compressing macroscopic quantities of hydrogen to record high pressures, phase transitions, and structures of new high-pressure phases in Me-H systems are briefly described. Special attention is devoted to the magnetic properties of solid solutions of hydrogen in 3d metals and their alloys, whose study has yielded definite conclusions concerning the effect of hydrogen on the band structure and exchange interaction in these materials. The role of structural instabilities in the formation of superconducting properties of hydrogen solutions in 4d metal alloys based on palladium is examined.

  15. Vibrational Spectroscopy at High Pressure in CF4: Implications to the Phase Diagram

    SciTech Connect

    Lorenzana, H E; Magnus, J L; Evans, W J; Hemmi, N

    2000-08-15

    The molecular analogue of methane, CF{sub 4} is the most fundamental saturated perfluorocarbon, exhibiting complex optical behavior that is highly unusual for such a simple molecular system. We present Raman measurements in solid CF{sub 4} over a wide range in pressure from 1.6 to over 30 GPa at room temperature. The Raman spectra exhibit polarization-dependent intensity variations and history-dependent absence or presence of high pressure modes. Our results compellingly demonstrate that previously identified phase transitions in CF{sub 4} based on Raman signatures need to be reconsidered. Though our data suggest possible new high-pressure transitions, we do not identify new phases because of spectral complexity. Finally, we used the measured longitudinal and transverse optical mode splitting to estimate the dipole moment derivative at high pressures and find it close to that of gaseous CF{sub 4}.

  16. High-pressure phase of brucite stable at Earth's mantle transition zone and lower mantle conditions

    NASA Astrophysics Data System (ADS)

    Hermann, Andreas; Mookherjee, Mainak

    2016-12-01

    We investigate the high-pressure phase diagram of the hydrous mineral brucite, Mg(OH)2, using structure search algorithms and ab initio simulations. We predict a high-pressure phase stable at pressure and temperature conditions found in cold subducting slabs in Earth’s mantle transition zone and lower mantle. This prediction implies that brucite can play a much more important role in water transport and storage in Earth’s interior than hitherto thought. The predicted high-pressure phase, stable in calculations between 20 and 35 GPa and up to 800 K, features MgO6 octahedral units arranged in the anatase–TiO2 structure. Our findings suggest that brucite will transform from a layered to a compact 3D network structure before eventual decomposition into periclase and ice. We show that the high-pressure phase has unique spectroscopic fingerprints that should allow for straightforward detection in experiments. The phase also has distinct elastic properties that might make its direct detection in the deep Earth possible with geophysical methods.

  17. High-pressure phase transitions of solid HF, HCl, and HBr: An ab initio evolutionary study

    NASA Astrophysics Data System (ADS)

    Zhang, Lijun; Wang, Yanchao; Zhang, Xinxin; Ma, Yanming

    2010-07-01

    Using ab initio evolutionary methodology for structure predictions, we investigated the high-pressure phase diagram for solid-state HF, HCl, and HBr at zero temperature. The ambient-pressure chain-type Cmc21 structure and sequent high-pressure symmetric hydrogen-bonded Cmcm structure were successfully reproduced by structural simulations with the only known information of chemical compositions. We have also presented insight into the underlying mechanism of hydrogen-bond symmetrization at the Cmc21→Cmcm transformation, by analysis of electron localization functions, potential wells, and zone-center phonons with pressure. At higher pressures, it was predicted that HF transforms from the Cmcm phase to another chain-type Pnma structure at ˜143GPa while the post- Cmcm phase of HCl and HBr adopts an intriguing triclinic P1¯ structure at above 108 GPa and 59 GPa, respectively, which consists of nearly planar squares resembling the ambient phase of HI. The newly predicted high-pressure phases of these halides all contain symmetric hydrogen bonds and satisfy lattice dynamical stability. As for the earlier proposed dissociation of HBr, we found that this can only occur at rather high pressures (above 120 GPa) with the formation of monatomic Br and solid H2 .

  18. High-pressure phase transitions of ScPO[subscript 4] and YPO[subscript 4

    SciTech Connect

    Zhang, F.X.; Wang, J.W.; Lang, M.; Zhang, J.M.; Ewing, R.C.; Boatner, L.A.

    2010-01-12

    ScPO{sub 4} and YPO{sub 4} with the tetragonal zircon-structure were studied at room temperature and pressures up to -50 GPa. Pressure-induced phase transitions to the sheelite structure occur at 30 GPa for ScPO{sub 4} and 16.3 GPa for YPO{sub 4}, respectively. In addition to the scheelite-type high-pressure phase, an intermediate phase with the monoclinic monazite-type structure formed during the phase transition process of YPO{sub 4}. The high-pressure phases of ScPO{sub 4} and YPO{sub 4} are not quenchable on pressure release. The pressure dependence of the total energy of the different phases was calculated using density-functional method, and the results confirm the experimentally observed phase relations under pressure. Structural parameters and compressibility of each phase were determined by refinement of the x-ray diffraction patterns. The high-pressure phase of ScPO{sub 4} has a very large bulk modulus [376(8) GPa].

  19. Phase transition induced strain in ZnO under high pressure

    NASA Astrophysics Data System (ADS)

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

    2016-05-01

    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.

  20. High pressure phase transitions in scheelite structured fluoride: ErLiF{sub 4}

    SciTech Connect

    Garg, Nandini; Mishra, A.K.; Poswal, H.K.; Tyagi, A.K.; Sharma, Surinder M

    2015-09-15

    Our synchrotron based angle dispersive x-ray diffraction studies on scheelite structured ErLiF{sub 4} 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 LiF{sub 4} tetrahedra, the compressibility of LnLiF{sub 4} (Ln=Eu–Lu) kind of scheelites is more affected by the LnF{sub 8} dodecahedra than the LiF{sub 4} tetrahedra. - Graphical abstract: Volume per formula unit of the scheelite and high pressure phases of ErLiF{sub 4} as a function of pressure. - Highlights: • ErLiF{sub 4} transforms to fergusonite and P2/c phase at high pressure. • Polyhedra of LnF{sub 8} affects compressibility of LnLiF{sub 4} (Ln=Eu–Lu) more than LiF{sub 4}. • Amorphization pressure varies inversely in LnLiF{sub 4} with ionic size of Ln cation. • In ErLiF{sub 4}a/c ratio reduces with pressure in contrast to reported increase in YLiF{sub 4}.

  1. ANALYSIS OF SELECTED PYRETHROID PESTICIDES USING REVERSE PHASE HIGH PRESSURE LIQUID CHROMATOGRAPHY/UV

    EPA Science Inventory

    This research was conducted in cooperation with EPA Region 4 in Athens, GA to develop a method to analyze selected pyrethroid pesticides using Reverse Phase-High Pressure Liquid Chromatography (HPLC). This HPLC method will aid researchers in separating and identifying these py...

  2. Phase transitions in delafossite CuLaO{sub 2} at high pressures

    SciTech Connect

    Salke, Nilesh P.; Rao, Rekha Gupta, M. K.; Mittal, R.; Garg, Alka B.; Achary, S. N.; Tyagi, A. K.

    2014-04-07

    Structural stability of a transparent conducting oxide CuLaO{sub 2} 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 3{sup rd} order Birch-Murnaghan equation of state, zero pressure bulk modulus of CuLaO{sub 2} is determined to be 154(25) GPa. The vibrational properties in the ambient delafossite phase of CuLaO{sub 2} are investigated using ab-initio calculations of phonon frequencies to complement the Raman spectroscopic measurements. Temperature dependence of the Raman modes of CuLaO{sub 2} is investigated to estimate the anharmonicity of Raman modes.

  3. Separation of bacterial ubiquinones by reverse-phase high-pressure liquid chromatography.

    PubMed Central

    Moss, C W; Guerrant, G O

    1983-01-01

    A procedure was developed for the separation of ubiquinones by high-pressure liquid chromatography on a reverse-phase C18 column. Ubiquinones Q6 through Q14 were resolved in 20 min and were distinguished from menaquinones by comparing UV spectra at 248 and 275 nm. PMID:6885985

  4. ANALYSIS OF SELECTED PYRETHROID PESTICIDES USING REVERSE PHASE HIGH PRESSURE LIQUID CHROMATOGRAPHY/UV

    EPA Science Inventory

    This research was conducted in cooperation with EPA Region 4 in Athens, GA to develop a method to analyze selected pyrethroid pesticides using Reverse Phase-High Pressure Liquid Chromatography (HPLC). This HPLC method will aid researchers in separating and identifying these py...

  5. Phase field simulations of plastic strain-induced phase transformations under high pressure and large shear

    NASA Astrophysics Data System (ADS)

    Javanbakht, Mahdi; Levitas, Valery I.

    2016-12-01

    Pressure and shear strain-induced phase transformations (PTs) in a nanograined bicrystal at the evolving dislocations pile-up have been studied utilizing a phase field approach (PFA). The complete system of PFA equations for coupled martensitic PT, dislocation evolution, and mechanics at large strains is presented and solved using the finite element method (FEM). The nucleation pressure for the high-pressure phase (HPP) under hydrostatic conditions near a single dislocation was determined to be 15.9 GPa. Under shear, a dislocation pile-up that appears in the left grain creates strong stress concentration near its tip and significantly increases the local thermodynamic driving force for PT, which causes nucleation of HPP even at zero pressure. At pressures of 1.59 and 5 GPa and shear, a major part of a grain transforms to HPP. When dislocations are considered in the transforming grain as well, they relax stresses and lead to a slightly smaller stationary HPP region than without dislocations. However, they strongly suppress nucleation of HPP and require larger shear. Unexpectedly, the stationary HPP morphology is governed by the simplest thermodynamic equilibrium conditions, which do not contain contributions from plasticity and surface energy. These equilibrium conditions are fulfilled either for the majority of points of phase interfaces or (approximately) in terms of stresses averaged over the HPP region or for the entire grain, despite the strong heterogeneity of stress fields. The major part of the driving force for PT in the stationary state is due to deviatoric stresses rather than pressure. While the least number of dislocations in a pile-up to nucleate HPP linearly decreases with increasing applied pressure, the least corresponding shear strain depends on pressure nonmonotonously. Surprisingly, the ratio of kinetic coefficients for PT and dislocations affect the stationary solution and the nanostructure. Consequently, there are multiple stationary solutions

  6. High Pressure Phase-Transformation Induced Texture Evolution and Strengthening in Zirconium Metal: Experiment and Modeling

    PubMed Central

    Yu, Xiaohui; Zhang, Ruifeng; Weldon, David; Vogel, Sven C.; Zhang, Jianzhong; Brown, Donald W.; Wang, Yanbin; Reiche, Helmut M.; Wang, Shanmin; Du, Shiyu; Jin, Changqing; Zhao, Yusheng

    2015-01-01

    We studied the phase-transition induced texture changes and strengthening mechanism for zirconium metal under quasi-hydrostatic compression and uni-axial deformation under confined high pressure using the deformation-DIA (D-DIA) apparatus. It is shown that the experimentally obtained texture for ω-phase Zr can be qualitatively described by combining a subset of orientation variants previously proposed in two different models. The determined flow stress for the high-pressure ω-phase is 0.5–1.2 GPa, more than three times higher than that of the α-phase. Using first-principles calculations, we investigated the mechanical and electronic properties of the two Zr polymorphs. We find that the observed strengthening can be attributed to the relatively strong directional bonding in the ω phase, which significantly increases its shear plastic resistance over the α-phase Zr. The present findings provide an alternate route for Zr metal strengthening by high-pressure phase transformation. PMID:26218405

  7. High pressure phase-transformation induced texture evolution and strengthening in zirconium metal: Experiment and modeling

    SciTech Connect

    Yu, Xiaohui; Zhang, Ruifeng; Weldon, David; Vogel, Sven C.; Zhang, Jianzhong; Brown, Donald W.; Wang, Yanbin; Reiche, Helmut M.; Wang, Shanmin; Du, Shiyu; Jin, Changqing; Zhao, Yusheng

    2015-07-28

    We studied the phase-transition induced texture changes and strengthening mechanism for zirconium metal under quasi-hydrostatic compression and uni-axial deformation under confined high pressure using the deformation-DIA (D-DIA) apparatus. It is shown that the experimentally obtained texture for ω-phase Zr can be qualitatively described by combining a subset of orientation variants previously proposed in two different models. The determined flow stress for the high-pressure ω-phase is 0.5–1.2 GPa, more than three times higher than that of the α-phase. Using first-principles calculations, we investigated the mechanical and electronic properties of the two Zr polymorphs. We find that the observed strengthening can be attributed to the relatively strong directional bonding in the ω phase, which significantly increases its shear plastic resistance over the α-phase Zr. The present findings provide an alternate route for Zr metal strengthening by high-pressure phase transformation.

  8. Phase changes of filled ice Ih methane hydrate under low temperature and high pressure.

    PubMed

    Tanaka, Takehiko; Hirai, Hisako; Matsuoka, Takahiro; Ohishi, Yasuo; Yagi, Takehiko; Ohtake, Michika; Yamamoto, Yoshitaka; Nakano, Satoshi; Irifune, Tetsuo

    2013-09-14

    Low-temperature and high-pressure experiments were performed with filled ice Ih structure of methane hydrate under 2.0-77.0 GPa and 30-300 K using diamond anvil cells and a helium-refrigeration cryostat. In situ X-ray diffractometry revealed distinct changes in the compressibility of the axial ratios of the host framework with pressure. Raman spectroscopy showed a split in the C-H vibration modes of the guest methane molecules, which was previously explained by the orientational ordering of the guest molecules. The pressure and temperature conditions at the split of the vibration modes agreed well with those of the compressibility change. The results indicate the following: (i) the orientational ordering of the guest methane molecules from an orientationally disordered state occurred at high pressures and low temperatures; and (ii) this guest ordering led to anisotropic contraction in the host framework. Such guest orientational ordering and subsequent anisotropic contraction of the host framework were similar to that reported previously for filled ice Ic hydrogen hydrate. Since phases with different guest-ordering manners were regarded as different phases, existing regions of the guest disordered-phase and the guest ordered-phase were roughly estimated by the X-ray study. In addition, above the pressure of the guest-ordered phase, another high-pressure phase developed in the low-temperature region. The deuterated-water host samples were also examined, and the influence of isotopic effects on guest ordering and phase transformation was observed.

  9. High pressure phase-transformation induced texture evolution and strengthening in zirconium metal: Experiment and modeling

    DOE PAGES

    Yu, Xiaohui; Zhang, Ruifeng; Weldon, David; ...

    2015-07-28

    We studied the phase-transition induced texture changes and strengthening mechanism for zirconium metal under quasi-hydrostatic compression and uni-axial deformation under confined high pressure using the deformation-DIA (D-DIA) apparatus. It is shown that the experimentally obtained texture for ω-phase Zr can be qualitatively described by combining a subset of orientation variants previously proposed in two different models. The determined flow stress for the high-pressure ω-phase is 0.5–1.2 GPa, more than three times higher than that of the α-phase. Using first-principles calculations, we investigated the mechanical and electronic properties of the two Zr polymorphs. We find that the observed strengthening can bemore » attributed to the relatively strong directional bonding in the ω phase, which significantly increases its shear plastic resistance over the α-phase Zr. The present findings provide an alternate route for Zr metal strengthening by high-pressure phase transformation.« less

  10. Disorder-order phase transition at high pressure in ammonium fluoride

    NASA Astrophysics Data System (ADS)

    Bellin, Christophe; Mafety, Adrien; Narayana, Chandrabhas; Giura, Paola; Rousse, Gwenaelle; Itié, Jean-Paul; Polian, Alain; Saitta, A. Marco; Shukla, Abhay

    2017-09-01

    Solid NH4F displays intriguing parallels with ice despite its apparently ionic character. Here we investigate its phase diagram in low-temperature and high-pressure regions using Raman spectroscopy, x-ray diffraction, and ab initio structure search calculations. We focus on the high-pressure cubic phase which resembles that found in ice under pressure and is also the ambient pressure phase of other ammonium halides. We detect a disorder-order transition above 10 GPa, recalling those found both in other ammonium halides and in ice. The transition reveals itself in the pressure dependence of several Raman modes as well as through the progressive splitting of lattice and bending modes of the cubic phase at low temperatures. An in-depth analysis of the Raman modes and their evolution is made.

  11. Single-crystal elasticity of natural Fe-bearing orthoenstatite across a high-pressure phase transition

    NASA Astrophysics Data System (ADS)

    Zhang, Jin S.; Bass, Jay D.

    2016-08-01

    Sound velocities and elastic moduli have been measured on Fe-bearing orthoenstatite (OEN) single crystals up to 12 GPa by Brillouin spectroscopy. The ambient adiabatic bulk modulus (Ks0) and shear modulus (G0) are determined to be 113(1) GPa and 75.9(7) GPa, respectively. A fourth-order finite strain fit to the data yields pressure derivatives of Ks0' = 8.8(1), Ks0″ = -0.68(6), G0' = 2.9(1), and G0″ = -0.40(2). These values are significantly higher than those for other major mantle minerals up to 10.5 GPa but lower than some previous measurements on OEN. A pronounced increase of shear anisotropy was observed at a pressure of 12.06(9) GPa, coinciding with a phase transition from orthoenstatite to a recently discovered high-pressure phase with space group P21/c. A high-pressure phase transition in OEN is unlikely to be the cause of the X discontinuity in the 250-325 km depth range. Rather, a change in seismic anisotropy would be expected to accompany the orthoenstatite-to-P21/c phase transition in the upper mantle at greater depths.

  12. High-pressure Raman scattering of CaWO₄ up to 46.3 GPa: evidence of a new high-pressure phase.

    PubMed

    Botella, Pablo; Lacomba-Perales, Raúl; Errandonea, Daniel; Polian, Alain; Rodríguez-Hernández, Placida; Muñoz, Alfonso

    2014-09-15

    The high-pressure behavior of CaWO4 was analyzed at room temperature by Raman spectroscopy. Pressure was generated using a diamond-anvil cell and Ne as pressure-transmitting medium. The pressure range of previous studies has been extended from 23.4 to 46.3 GPa. The experiments reveal the existence of two reversible phase transitions. The first one occurs from the tetragonal scheelite structure to the monoclinic fergusonite structure and is observed at 10 GPa. The onset of a previously unknown second transition is found at 33.4 GPa. The two high-pressure phases coexist up to 39.4 GPa. The Raman spectra measured for the low-pressure phase and the first high-pressure phase are consistent with previous studies in the pressure range where comparison is possible. The pressure dependence of all the Raman-active modes is reported for different phases. We also report total-energy and lattice-dynamics calculations, which determine the occurrence of two phase transitions in the pressure range covered by the experiments. The first transition is in full agreement with experiments (scheelite-to-fergusonite). According to calculations, the second-highest pressure phase has an orthorhombic structure (space group Cmca). Details of this structure, its Raman modes, and its electronic band structure are given. The reliability of the reported results is supported by the consistency between the theoretical and experimental values obtained for transition pressures, phonon frequencies, and phonon pressure coefficients.

  13. Revealing an unusual transparent phase of superhard iron tetraboride under high pressure

    PubMed Central

    Kotmool, Komsilp; Kaewmaraya, Thanayut; Chakraborty, Sudip; Anversa, Jonas; Bovornratanaraks, Thiti; Luo, Wei; Gou, Huiyang; Piquini, Paulo Cesar; Kang, Tae Won; Mao, Ho-kwang; Ahuja, Rajeev

    2014-01-01

    First principles–based electronic structure calculations of superhard iron tetraboride (FeB4) under high pressure have been undertaken in this study. Starting with a “conventional” superconducting phase of this material under high pressure leads to an unexpected phase transition toward a semiconducting one. This transition occurred at 53.7 GPa, and this pressure acts as a demarcation between two distinct crystal symmetries, metallic orthorhombic and semiconducting tetragonal phases, with Pnnm and I41/acd space groups, respectively. In this work, the electron–phonon coupling-derived superconducting Tc has been determined up to 60 GPa and along with optical band gap variation with increasing pressure up to 300 GPa. The dynamic stability has been confirmed by phonon dispersion calculations throughout this study. PMID:25404295

  14. High pressure Raman scattering study on the phase stability of LuVO{sub 4}

    SciTech Connect

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

    2009-07-15

    High pressure Raman spectroscopic investigations have been carried out on rare earth orthovanadate LuVO{sub 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 reversible fergusonite transition. Pressure dependencies of the Raman active modes in the zircon and the scheelite phases are reported. - Graphical abstract: Study of scheelite-fergusonite transition in RVO{sub 4} by Raman spectroscopy is rare. Here we report Raman spectroscopic investigations of LuVO{sub 4} at high pressure to obtain insight into nature of post-scheelite phases.

  15. Magnetic and structural phase transitions in erbium at low temperatures and high pressures

    SciTech Connect

    Thomas, Sarah A.; Tsoi, Georgiy M.; Wenger, Lowell E.; Vohra, Yogesh K.

    2012-02-07

    Electrical resistance and crystal structure measurements have been carried out on polycrystalline erbium (Er) at temperatures down to 10 K and pressures up to 20 GPa. An abrupt change in the slope of the resistance is observed with decreasing temperature below 84 K, which is associated with the c-axis modulated (CAM) antiferromagnetic (AFM) ordering of the Er moments. With increasing pressure the temperature of the resistance slope change and the corresponding AFM ordering temperature decrease until vanishing above 10.6 GPa. The disappearance of the slope change in the resistance occurs at similar pressures where the hcp structural phase of Er is transformed to a nine-layer {alpha}-Sm structural phase, as confirmed by our high-pressure synchrotron x-ray diffraction studies. These results suggest that the disappearance in the AFM ordering of Er moments is strongly correlated to the structural phase transition at high pressures and low temperatures.

  16. Phase transition and water incorporation into Eu2Sn2O7 pyrochlore at high pressure

    NASA Astrophysics Data System (ADS)

    Zhang, F. X.; Lang, M.; Ewing, R. C.

    2016-04-01

    Structural changes of europium stannate pyrochlore, Eu2Sn2O7, have been investigated at high pressures with in situ Raman spectroscopy, photoluminescence (PL), and synchrotron X-ray diffraction (XRD) techniques. The XRD measurements suggest that a pressure-induced phase transition starts at 34.4 GPa. The PL spectrum from Eu3+ cations also suggests a phase transition above 36 GPa. XRD analysis shows that the unit cell of the cubic phase deviates from the equation of state at pressures above 23.8 GPa. This is due to the incorporation of water from the pressure medium in the structure at high pressures, which is confirmed by optical spectroscopy measurements.

  17. Phase equilibria in fluid mixtures at high pressures: The He-CH4 system

    NASA Technical Reports Server (NTRS)

    Streett, W. B.; Erickson, A. L.; Hill, J. L. E.

    1972-01-01

    An experimental study of phase equilibria in the He-CH4 system was carried out over the temperature range 95 to 290 K and at pressures to 10,000 atm. The experimental results consist of equilibrium phase composition for twenty-eight isotherms in the region of coexistence of two fluid phases, together with the pressure-temperature trace of the three-phase boundary at which a CH4-rich solid phase is in equilibrium with the two fluid phases. The system exhibits a fluid-fluid phase separation which persists to temperatures and pressures beyond the range of this experiment. These results, together with those recently obtained for other binary systems, provide information about the form of phase diagrams for binary gas mixtures in the region of pressure induced phase transitions at high pressures. These findings are relevant to problems of deep atmosphere and interior structures in the outer planets.

  18. Phase stability of {epsilon} and {gamma} HNIW (CL-20) at high-pressure and temperature

    SciTech Connect

    Gump, Jared C.; Stoltz, Chad A.; Peiris, Suhithi M.

    2007-12-12

    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 ({alpha}, {beta}, {gamma}, {epsilon}, {zeta}). 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.

  19. Phase Stability of Epsilon and Gamma Hniw (CL-20) at High-Pressure and Temperature

    NASA Astrophysics Data System (ADS)

    Gump, Jared C.; Stoltz, Chad A.; Peiris, Suhithi M.

    2007-12-01

    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, ɛ, 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 °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 °C then underwent a transition to the gamma phase above 125 °C and then thermal decomposition occurred above 150 °C. Upon compression, the gamma phase underwent a phase transition at both ambient temperature and 140 °C. Pressure—volume data for the epsilon and gamma phase at ambient temperature and the epsilon phase at 75 °C were fit to the Birch-Murnaghan formalism to obtain isothermal equations of state.

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

    PubMed

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

    2016-01-27

    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.

  1. Superconductivity in room-temperature stable electride and high-pressure phases of alkali metals.

    PubMed

    Hosono, Hideo; Kim, Sung-Wng; Matsuishi, Satoru; Tanaka, Shigeki; Miyake, Atsushi; Kagayama, Tomoko; Shimizu, Katsuya

    2015-03-13

    S-band metals such as alkali and alkaline earth metals do not undergo a superconducting transition (SCT) at ambient pressure, but their high-pressure phases do. By contrast, room-temperature stable electride [Ca(24)Al(28)O(64)](4+)⋅4e(-) (C12A7:e(-)) in which anionic electrons in the crystallographic sub-nanometer-size cages have high s-character exhibits SCT at 0.2-0.4 K at ambient pressure. In this paper, we report that crystal and electronic structures of C12A7:e(-) are close to those of the high-pressure superconducting phase of alkali and alkaline earth metals and the SCT of both materials is induced when electron nature at Fermi energy (EF) switches from s- to sd-hybridized state. © 2015 The Author(s) Published by the Royal Society. All rights reserved.

  2. Phase transition and metallization of FeO at high pressures and temperatures

    SciTech Connect

    Fischer, Rebecca A.; Campbell, Andrew J.; Lord, Oliver T.; Shofner, Gregory A.; Dera, Przemyslaw; Prakapenka, Vitali B.

    2012-05-10

    Wuestite, Fe{sub 1-x}O, is an important component in the mineralogy of Earth's lower mantle and may also be a component of the core. Therefore its high pressure-temperature behavior, including its electronic structure, is essential to understanding the nature and evolution of Earth's deep interior. We performed X-ray diffraction and radiometric measurements on wuestite in a laser-heated diamond anvil cell, finding an insulator-metal transition at high pressures and temperatures. Our data show a negative slope for this apparently isostructural phase boundary, which is characterized by a volume decrease and emissivity increase. The metallic phase of FeO is stable at conditions of the lower mantle and core, which has implications for the high P-T character of Fe-O bonds, magnetic field propagation, and lower mantle conductivity.

  3. Phase transition and thermodynamic properties of beryllium telluride under high pressure

    NASA Astrophysics Data System (ADS)

    Guo, Zhi-Cheng; Luo, Fen; Zhang, Xiu-Lu; Liu, Cheng-An; Cai, Ling-Cang

    2015-04-01

    A theoretical investigation on structural, dynamical, phase diagram and thermodynamic properties of beryllium telluride (BeTe) under high pressure and temperature is presented in the framework of density functional theory. The calculated structural parameters of BeTe in both zinc blende (ZB) and nickel arsenide (NiAs) structures are in reasonable agreement with available experimental data and previous theoretical work. The phonon dispersion relations, dielectric tensor and Born effective charge are investigated within the density functional perturbation theory (DFPT). The investigation of the phase diagram indicated that the NiAs structure BeTe becomes stable at high pressure and temperature. Based on the quasiharmonic Debye model, the pressure and temperature dependences of bulk modulus, Grüneisen parameter, Debye temperature, specific heat and thermal expansion coefficient are all successfully obtained. We hope that the theoretical results reported here can give more insight into the structural and thermodynamic properties of other semiconductors at high temperature and pressure.

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

    NASA Astrophysics Data System (ADS)

    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.

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

    SciTech Connect

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

    2016-01-06

    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. As a result, 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.

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

    DOE PAGES

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

    2016-01-06

    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. As a result, this new data is combined with previous ambientmore » temperature high-pressure Raman and X- ray diffraction data to create the first HPHT phase diagram of paracetamol.« less

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

    NASA Astrophysics Data System (ADS)

    Ma, Y. M.; Zhou, Q.; He, Z.; Li, F. F.; Yang, K. F.; Cui, Q. L.; Zou, G. T.

    2007-10-01

    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.

  8. Role of relativity in high-pressure phase transitions of thallium.

    PubMed

    Kotmool, Komsilp; Chakraborty, Sudip; Bovornratanaraks, Thiti; Ahuja, Rajeev

    2017-02-20

    We demonstrate the relativistic effects in high-pressure phase transitions of heavy element thallium. The known first phase transition from h.c.p. to f.c.c. is initially investigated by various relativistic levels and exchange-correlation functionals as implemented in FPLO method, as well as scalar relativistic scheme within PAW formalism. The electronic structure calculations are interpreted from the perspective of energetic stability and electronic density of states. The full relativistic scheme (FR) within L(S)DA performs to be the scheme that resembles mostly with experimental results with a transition pressure of 3 GPa. The s-p hybridization and the valence-core overlapping of 6s and 5d states are the primary reasons behind the f.c.c. phase occurrence. A recent proposed phase, i.e., a body-centered tetragonal (b.c.t.) phase, is confirmed with a small distortion from the f.c.c. phase. We have also predicted a reversible b.c.t. → f.c.c. phase transition at 800 GPa. This finding has been suggested that almost all the III-A elements (Ga, In and Tl) exhibit the b.c.t. → f.c.c. phase transition at extremely high pressure.

  9. Role of relativity in high-pressure phase transitions of thallium

    PubMed Central

    Kotmool, Komsilp; Chakraborty, Sudip; Bovornratanaraks, Thiti; Ahuja, Rajeev

    2017-01-01

    We demonstrate the relativistic effects in high-pressure phase transitions of heavy element thallium. The known first phase transition from h.c.p. to f.c.c. is initially investigated by various relativistic levels and exchange-correlation functionals as implemented in FPLO method, as well as scalar relativistic scheme within PAW formalism. The electronic structure calculations are interpreted from the perspective of energetic stability and electronic density of states. The full relativistic scheme (FR) within L(S)DA performs to be the scheme that resembles mostly with experimental results with a transition pressure of 3 GPa. The s-p hybridization and the valence-core overlapping of 6s and 5d states are the primary reasons behind the f.c.c. phase occurrence. A recent proposed phase, i.e., a body-centered tetragonal (b.c.t.) phase, is confirmed with a small distortion from the f.c.c. phase. We have also predicted a reversible b.c.t. → f.c.c. phase transition at 800 GPa. This finding has been suggested that almost all the III-A elements (Ga, In and Tl) exhibit the b.c.t. → f.c.c. phase transition at extremely high pressure. PMID:28216669

  10. Role of relativity in high-pressure phase transitions of thallium

    NASA Astrophysics Data System (ADS)

    Kotmool, Komsilp; Chakraborty, Sudip; Bovornratanaraks, Thiti; Ahuja, Rajeev

    2017-02-01

    We demonstrate the relativistic effects in high-pressure phase transitions of heavy element thallium. The known first phase transition from h.c.p. to f.c.c. is initially investigated by various relativistic levels and exchange-correlation functionals as implemented in FPLO method, as well as scalar relativistic scheme within PAW formalism. The electronic structure calculations are interpreted from the perspective of energetic stability and electronic density of states. The full relativistic scheme (FR) within L(S)DA performs to be the scheme that resembles mostly with experimental results with a transition pressure of 3 GPa. The s-p hybridization and the valence-core overlapping of 6s and 5d states are the primary reasons behind the f.c.c. phase occurrence. A recent proposed phase, i.e., a body-centered tetragonal (b.c.t.) phase, is confirmed with a small distortion from the f.c.c. phase. We have also predicted a reversible b.c.t. → f.c.c. phase transition at 800 GPa. This finding has been suggested that almost all the III-A elements (Ga, In and Tl) exhibit the b.c.t. → f.c.c. phase transition at extremely high pressure.

  11. High-Pressure Phase Transition in Cs 2KMnF 6

    NASA Astrophysics Data System (ADS)

    Xu, Y.; Söderberg, K.; Norrestam, R.

    2000-09-01

    The stability of the cubic high-temperature (HT) form of Cs2KMnF6, with an elpasolite structure, is studied at elevated pressures. The present study shows that the HT form of Cs2KMnF6 undergoes a pressure-induced phase transition at 40 kbar to a more ordered high-pressure (HP) phase of lower symmetry. The space group symmetry of the HP phase, I4/mmm, is the same as that observed for the low-temperature (LT) phase. High-pressure studies performed on the LT phase indicated no transitions up to 50 kbar and gave compressibility features similar to those obtained for the HP phase. Single-crystal X-ray diffraction data for the HP phase were collected at 44 kbar. Refining nine structural parameters against 69 independent significant reflections gave a linear R value of 0.072 (wR=0.086). The values of the positional parameters are in agreement with those observed for the LT phase under ambient conditions. The transition characteristics for the HT form depend on the crystal quality and/or the pressure transmitting media used. With liquid argon, loaded into the pressure cell at low temperature and ambient pressure, the transition pressure became 30 kbar. With methanol:ethanol:water, loaded under ambient conditions, the transition was observed at 40 kbar.

  12. Phase equilibria in molecular hydrogen-helium mixtures at high pressures

    NASA Technical Reports Server (NTRS)

    Streett, W. B.

    1973-01-01

    Experiments on phase behavior in hydrogen-helium mixtures have been carried out at pressures up to 9.3 kilobars, at temperatures from 26 to 100 K. Two distinct fluid phases are shown to exist at supercritical temperatures and high pressures. Both the trend of the experimental results and an analysis based on the van der Waals theory of mixtures suggest that this fluid-fluid phase separation persists at temperatures and pressures beyond the range of these experiments, perhaps even to the limits of stability of the molecular phases. The results confirm earlier predictions concerning the form of the hydrogen-helium phase diagram in the region of pressure-induced solidification of the molecular phases at supercritical temperatures. The implications of this phase diagram for planetary interiors are discussed.

  13. Structural stability and phase transition of Bi2Te3 under high pressure and low temperature

    NASA Astrophysics Data System (ADS)

    Zhang, J. L.; Zhang, S. J.; Zhu, J. L.; Liu, Q. Q.; Wang, X. C.; Jin, C. Q.; Yu, J. C.

    2017-09-01

    Structural stability and phase transition of topological insulator Bi2Te3 were studied via angle-dispersive synchrotron radiation X-ray diffraction under high pressure and low temperature condition. The results manifest that the R-3m phase (phase I) is stable at 8 K over the pressure range up to 10 GPa and phase transition occurs between 8 K and 45 K at 8 GPa. According to the Birch-Murnaghan equation of state, the bulk modulus at ambient pressure B0 was estimated to be 45 ± 3 GPa with the assumption of B0‧ = 4. The structural robustness of phase I at 8 K suggests that the superconductivity below 10 GPa is related to phase I. Topological properties of superconducting Bi2Te3 phase under pressure were discussed.

  14. Pyroxenes and olivines: Structural implications of shock-wave data for high pressure phases

    NASA Technical Reports Server (NTRS)

    Jeanloz, R.; Ahrens, T. J.

    1975-01-01

    The nature of the shock-induced, high-pressure phases of olivine and pyroxene rocks is examined in the light of data for the densities of a new class of perovskite-related silicate structures. Also examined are some new Hugoniot and release adiabat data for bronzite. Reexamining available shock data for magnesian pyroxenes and olivines leads to the conclusion that they define a mixed phase (or disequilibrium) region to about the 100 GPa range, related to the kinetics of phase transformation in these silicates. By recognizing this point, certain discrepancies in previous interpretations of shock data can be explained. A set of theoretical Hugonoits for pyroxene and olivine stoichiometry, perovskite-bearing assemblages was constructed based on their properties deduced from high-pressure work, showing that the shock data is compatible with transformations to perovskites in the 45-7GPa region. Finally, the shock data indicate very similar properties for olivine and pyroxene at high pressures making them both equally likely candidates for the lower mantle.

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

    NASA Astrophysics Data System (ADS)

    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.

  16. Phase transformation of Ho[subscript 2]O[subscript 3] at high pressure

    SciTech Connect

    Jiang, Sheng; Liu, Jing; Li, Xiaodong; Bai, Ligang; Xiao, Wansheng; Zhang, Yufeng; Lin, Chuanlong; Li, Yanchun; Tang, Lingyun

    2012-01-20

    The structural stability of cubic Ho{sub 2}O{sub 3} under high pressure has been investigated by angle-dispersive x-ray diffraction (ADXD) in a diamond anvil cell up to 63.0 GPa at room temperature. The diffraction data reveal two structural transformations on compression. The structural transformation from a cubic to a monoclinic structure starts at 8.9 GPa and is complete at 16.3 GPa with an {approx}8.1% volume collapse. A hexagonal phase begins to appear at {approx}14.8 GPa and becomes dominant at 26.4 GPa. This high-pressure hexagonal phase with a small amount of retained monoclinic phase is stable up to the highest pressure of 63.0 GPa in this study. After release of pressure, the hexagonal phase transforms to a monoclinic structure. A third-order Birch-Murnaghan fit yields zero pressure bulk moduli (B{sub 0}) of 206(3), 200(7) and 204(19) GPa and their pressure derivatives (B'{sub 0}) of 4.8(4), 2.1(4), 3.8(5) for the cubic, monoclinic and hexagonal phases, respectively. Comparing with other rare-earth sesquioxides, it is suggested that the transition pressure from cubic to monoclinic phase, as well as the bulk modulus of the cubic phase, increases with the decreasing of the cation radius of rare-earth sesquioxides.

  17. Structural phase transitions in Bi2Se3 under high pressure

    DOE PAGES

    Yu, Zhenhai; Gu, Genda; Wang, Lin; ...

    2015-11-02

    Raman spectroscopy and angle dispersive X-ray diffraction (XRD) experiments of bismuth selenide (Bi2Se3) have been carried out to pressures of 35.6 and 81.2 GPa, respectively, to explore its pressure-induced phase transformation. The experiments indicate that a progressive structural evolution occurs from an ambient rhombohedra phase (Space group (SG): R-3m) to monoclinic phase (SG: C2/m) and eventually to a high pressure body-centered tetragonal phase (SG: I4/mmm). Evidenced by our XRD data up to 81.2 GPa, the Bi2Se3 crystallizes into body-centered tetragonal structures rather than the recently reported disordered body-centered cubic (BCC) phase. Furthermore, first principles theoretical calculations favor the viewpoint thatmore » the I4/mmm phase Bi2Se3 can be stabilized under high pressure (>30 GPa). Remarkably, the Raman spectra of Bi2Se3 from this work (two independent runs) are still Raman active up to ~35 GPa. Furthermore, it is worthy to note that the disordered BCC phase at 27.8 GPa is not observed here. The remarkable difference in atomic radii of Bi and Se in Bi2Se3 may explain why Bi2Se3 shows different structural behavior than isocompounds Bi2Te3 and Sb2Te3.« less

  18. Structural phase transitions in Bi2Se3 under high pressure

    PubMed Central

    Yu, Zhenhai; Wang, Lin; Hu, Qingyang; Zhao, Jinggeng; Yan, Shuai; Yang, Ke; Sinogeikin, Stanislav; Gu, Genda; Mao, Ho-kwang

    2015-01-01

    Raman spectroscopy and angle dispersive X-ray diffraction (XRD) experiments of bismuth selenide (Bi2Se3) have been carried out to pressures of 35.6 and 81.2 GPa, respectively, to explore its pressure-induced phase transformation. The experiments indicate that a progressive structural evolution occurs from an ambient rhombohedra phase (Space group (SG): R-3m) to monoclinic phase (SG: C2/m) and eventually to a high pressure body-centered tetragonal phase (SG: I4/mmm). Evidenced by our XRD data up to 81.2 GPa, the Bi2Se3 crystallizes into body-centered tetragonal structures rather than the recently reported disordered body-centered cubic (BCC) phase. Furthermore, first principles theoretical calculations favor the viewpoint that the I4/mmm phase Bi2Se3 can be stabilized under high pressure (>30 GPa). Remarkably, the Raman spectra of Bi2Se3 from this work (two independent runs) are still Raman active up to ~35 GPa. It is worthy to note that the disordered BCC phase at 27.8 GPa is not observed here. The remarkable difference in atomic radii of Bi and Se in Bi2Se3 may explain why Bi2Se3 shows different structural behavior than isocompounds Bi2Te3 and Sb2Te3. PMID:26522818

  19. Structural phase transitions in Bi2Se3 under high pressure

    NASA Astrophysics Data System (ADS)

    Yu, Zhenhai; Wang, Lin; Hu, Qingyang; Zhao, Jinggeng; Yan, Shuai; Yang, Ke; Sinogeikin, Stanislav; Gu, Genda; Mao, Ho-Kwang

    2015-11-01

    Raman spectroscopy and angle dispersive X-ray diffraction (XRD) experiments of bismuth selenide (Bi2Se3) have been carried out to pressures of 35.6 and 81.2 GPa, respectively, to explore its pressure-induced phase transformation. The experiments indicate that a progressive structural evolution occurs from an ambient rhombohedra phase (Space group (SG): R-3m) to monoclinic phase (SG: C2/m) and eventually to a high pressure body-centered tetragonal phase (SG: I4/mmm). Evidenced by our XRD data up to 81.2 GPa, the Bi2Se3 crystallizes into body-centered tetragonal structures rather than the recently reported disordered body-centered cubic (BCC) phase. Furthermore, first principles theoretical calculations favor the viewpoint that the I4/mmm phase Bi2Se3 can be stabilized under high pressure (>30 GPa). Remarkably, the Raman spectra of Bi2Se3 from this work (two independent runs) are still Raman active up to ~35 GPa. It is worthy to note that the disordered BCC phase at 27.8 GPa is not observed here. The remarkable difference in atomic radii of Bi and Se in Bi2Se3 may explain why Bi2Se3 shows different structural behavior than isocompounds Bi2Te3 and Sb2Te3.

  20. Structural phase transitions in Bi2Se3 under high pressure.

    PubMed

    Yu, Zhenhai; Wang, Lin; Hu, Qingyang; Zhao, Jinggeng; Yan, Shuai; Yang, Ke; Sinogeikin, Stanislav; Gu, Genda; Mao, Ho-kwang

    2015-11-02

    Raman spectroscopy and angle dispersive X-ray diffraction (XRD) experiments of bismuth selenide (Bi2Se3) have been carried out to pressures of 35.6 and 81.2 GPa, respectively, to explore its pressure-induced phase transformation. The experiments indicate that a progressive structural evolution occurs from an ambient rhombohedra phase (Space group (SG): R-3m) to monoclinic phase (SG: C2/m) and eventually to a high pressure body-centered tetragonal phase (SG: I4/mmm). Evidenced by our XRD data up to 81.2 GPa, the Bi2Se3 crystallizes into body-centered tetragonal structures rather than the recently reported disordered body-centered cubic (BCC) phase. Furthermore, first principles theoretical calculations favor the viewpoint that the I4/mmm phase Bi2Se3 can be stabilized under high pressure (>30 GPa). Remarkably, the Raman spectra of Bi2Se3 from this work (two independent runs) are still Raman active up to ~35 GPa. It is worthy to note that the disordered BCC phase at 27.8 GPa is not observed here. The remarkable difference in atomic radii of Bi and Se in Bi2Se3 may explain why Bi2Se3 shows different structural behavior than isocompounds Bi2Te3 and Sb2Te3.

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

    PubMed Central

    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

    NASA Astrophysics Data System (ADS)

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

    2016-03-01

    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.

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

    SciTech Connect

    Zhang, Jin S.; Dera, Przemyslaw; Bass, Jay D.

    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. High-pressure phases of a hydrogen-rich compound: Tetramethylgermane

    NASA Astrophysics Data System (ADS)

    Qin, Zhen-Xing; Zhang, Chao; Tang, Ling-Yun; Zhong, Guo-Hua; Lin, Hai-Qing; Chen, Xiao-Jia

    2012-11-01

    The vibrational and structural properties of a hydrogen-rich group IVa hydride, Ge(CH3)4, are studied by combining Raman spectroscopy and synchrotron x-ray diffraction measurements at room temperature and at pressures up to 30.2 GPa. Both techniques allow the obtaining of complementary information on the high-pressure behaviors and yield consistent phase transitions at 1.4 GPa for the liquid to solid and 3.0, 5.4, and 20.3 GPa for the solid to solid. The four high-pressure solid phases are identified to have the cubic, orthorhombic, monoclinic, and monoclinic crystal structures with space groups of Pa-3 for phase I, Pnma for phase II, P21/c for phase III, and P21 for phase IV, respectively. These transitions are suggested to result from the changes in the inter- and intramolecular bonding of this compound. The softening of some Raman modes on CH3 groups and their sudden disappearance indicate that Ge(CH3)4 might be an ideal compound to realize metallization and even high-temperature superconductivity at modest static pressure for laboratory capability.

  5. Effect of high pressure homogenization on aqueous phase solvent extraction of lipids from Nannochloris Oculata microalgae

    DOE PAGES

    Samarasinghe, Nalin; Fernando, Sandun; Faulkner, William B.

    2012-12-01

    The ability to extract lipids from high-moisture Nannochloris Oculata algal biomass disrupted with high pressure homogenization was investigated. During the first phase, the effect of high pressure homogenization (system pressure and number of passes) on disrupting aqueous algae (of different concentrations and degree of stress) was investigated. Secondly, the effect of degree of cell wall disruption on the amount of lipids extracted with three solvents, namely: hexane, dichloromethane and chloroform, were compared. Studies reveled that high pressure homogenization is effective on cell disruption while the amount of system pressure being the most significant factor affecting the degree of cell breakage.more » Although the number of passes had some impact, the level of disruption seemed to level-off after a certain number of passes. The study revealed that slightly polar solvents (such as chloroform and dichloromethane) performed better in aqueous-phase lipid extractions as compared to hexane. Also, it was revealed that it was not necessary to disrupt the algal cells completely to achieve appreciable levels of lipid yields. In fact, conditions that exerted only 20% of the cells to completely disrupt, allowed sufficient damage to liberate most of the lipids contained in the remainder of the cells.« less

  6. Effect of high pressure homogenization on aqueous phase solvent extraction of lipids from Nannochloris Oculata microalgae

    SciTech Connect

    Samarasinghe, Nalin; Fernando, Sandun; Faulkner, William B.

    2012-12-01

    The ability to extract lipids from high-moisture Nannochloris Oculata algal biomass disrupted with high pressure homogenization was investigated. During the first phase, the effect of high pressure homogenization (system pressure and number of passes) on disrupting aqueous algae (of different concentrations and degree of stress) was investigated. Secondly, the effect of degree of cell wall disruption on the amount of lipids extracted with three solvents, namely: hexane, dichloromethane and chloroform, were compared. Studies reveled that high pressure homogenization is effective on cell disruption while the amount of system pressure being the most significant factor affecting the degree of cell breakage. Although the number of passes had some impact, the level of disruption seemed to level-off after a certain number of passes. The study revealed that slightly polar solvents (such as chloroform and dichloromethane) performed better in aqueous-phase lipid extractions as compared to hexane. Also, it was revealed that it was not necessary to disrupt the algal cells completely to achieve appreciable levels of lipid yields. In fact, conditions that exerted only 20% of the cells to completely disrupt, allowed sufficient damage to liberate most of the lipids contained in the remainder of the cells.

  7. High-pressure phase transition and equation of state of CsI

    NASA Technical Reports Server (NTRS)

    Mao, H. K.; Hemley, R. J.; Chen, L. C.; Shu, J. F.; Wu, Y.

    1990-01-01

    Stuructural properties of CsI at high pressure have been investigated by the use of synchrotron X-ray-diffraction techniques with the diamond-anvil cell at 300 K. The results indicate that the material undergoes a continuous distortion from B2 to an hcp-like phase, which is stable to at least 302 GPa. The intermediate orthorhombic phase is geometrically different from previous assignments and about 10 percent denser. With the new structure, the p-V results of static pressure experiments, shock-wave studies, and theoretical calculations are now in good agreement.

  8. Computation of Space Shuttle high-pressure cryogenic turbopump ball bearing two-phase coolant flow

    NASA Technical Reports Server (NTRS)

    Chen, Yen-Sen

    1990-01-01

    A homogeneous two-phase fluid flow model, implemented in a three-dimensional Navier-Stokes solver using computational fluid dynamics methodology is described. The application of the model to the analysis of the pump-end bearing coolant flow of the high-pressure oxygen turbopump of the Space Shuttle main engine is studied. Results indicate large boiling zones and hot spots near the ball/race contact points. The extent of the phase change of the liquid oxygen coolant flow due to the frictional and viscous heat fluxes near the contact areas has been investigated for the given inlet conditions of the coolant.

  9. Computation of Space Shuttle high-pressure cryogenic turbopump ball bearing two-phase coolant flow

    NASA Technical Reports Server (NTRS)

    Chen, Yen-Sen

    1990-01-01

    A homogeneous two-phase fluid flow model, implemented in a three-dimensional Navier-Stokes solver using computational fluid dynamics methodology is described. The application of the model to the analysis of the pump-end bearing coolant flow of the high-pressure oxygen turbopump of the Space Shuttle main engine is studied. Results indicate large boiling zones and hot spots near the ball/race contact points. The extent of the phase change of the liquid oxygen coolant flow due to the frictional and viscous heat fluxes near the contact areas has been investigated for the given inlet conditions of the coolant.

  10. Phase Transitions in Solids Stimulated by Simultaneous Exposure to High Pressure and Relativistic Heavy Ions

    SciTech Connect

    Glasmacher, Ulrich A.; Lang, Maik; Neumann, Reinhard; Schardt, Dieter; Trautmann, Christina; Keppler, Hans; Langenhorst, Falko; Wagner, Guenther A.

    2006-05-19

    In many solids, heavy ions of high kinetic energy (MeV-GeV) produce long cylindrical damage trails with diameters of order 10 nm. Up to now, no information was available how solids cope with the simultaneous exposure to these energetic projectiles and to high pressure. We report the first experiments where relativistic uranium and gold ions from the SIS heavy-ion synchrotron at GSI were injected through several mm of diamond into solid samples pressurized up to 14 GPa in a diamond anvil cell. In synthetic graphite and natural zircon, the combination of pressure and ion beams triggered drastic structural changes not caused by the applied pressure or the ions alone. The modifications comprise long-range amorphization of graphite rather than individual track formation, and in the case of zircon the decomposition into nanocrystals and nucleation of the high-pressure phase reidite.

  11. Light-induced phase transition in AlD3 at high pressure

    NASA Astrophysics Data System (ADS)

    Besedin, Stanislav P.; Jephcoat, Andrew P.; Irodova, Alla V.

    2011-09-01

    Trivalent aluminum hydride in the rhombohedral α phase (R3¯c space group) was studied at high pressures in a diamond-anvil cell by means of Raman scattering, x-ray diffraction, observation of optical transmission, and the density functional simulations. At P≈53 GPa the heavier isotope AlD3 undergoes a first-order structural phase transition which was found to be stimulated by the laser irradiation used for the Raman-scattering measurements. In the new high-pressure phase Al atoms form a lattice with a monoclinic unit cell (P21/c space group) over which a superstructure is developed when pressure is varied. The superstructure is formed by regular displacements of the Al atoms with the period over three unit cells; the propagation vector is k2=((1)/(3)(1)/(3)(1)/(3)). The undistorted P21/c lattice itself appears as superstructure over the rhombohedral R3¯c one resulting from the displacive structure transformation with the propagation vector k1=((1)/(2)0(1)/(2)). The band gap as given by the density functional calculations and evidenced from the sample transparency behavior at high pressures remains greater than the laser photon energy used (Eph=2.41 eV). That indicates that bond weakening/breaking due to electron excitation across the band gap is not the cause of the phase transition. A likely mechanism of the light action is that structure transformation is driven by phonons, which are excited due to strong electron-phonon coupling in the α phase.

  12. Phase transition induced strain in ZnO under high pressure

    SciTech Connect

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

    2016-05-13

    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. Ultimately, these findings are of fundamental importance to understanding the mechanism of phase transition and the properties of materials under pressure.

  13. Phase transition induced strain in ZnO under high pressure

    DOE PAGES

    Yan, Xiaozhi; Dong, Haini; Li, Yanchun; ...

    2016-05-13

    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 strengthmore » 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. Ultimately, these findings are of fundamental importance to understanding the mechanism of phase transition and the properties of materials under pressure.« less

  14. Phase transition induced strain in ZnO under high pressure

    PubMed Central

    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

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

    PubMed Central

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

    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 ternary systems (gas-liquid-liquid) are the specific examples discussed herein. For instance, the ternary THF-Water-CO2 system was studied at 25 and 40 °C and is described herein. Of key importance, this technique does not require sampling. Circumventing the possible disturbance of the system equilibrium upon sampling, inherent measurement errors, and technical difficulties of physically sampling under pressure is a significant benefit of this technique. Perhaps as important, the sapphire cell also enables the direct visual observation of the phase behavior. In fact, as the CO2 pressure is increased, the homogeneous THF-Water solution phase splits at about 2 MPa. With this technique, it was possible to easily and clearly observe the cloud point and determine the composition of the newly formed phases as a function of pressure. The data acquired with the sapphire cell technique can be used for many applications. In our case, we measured swelling and composition for tunable solvents, like gas-expanded liquids, gas-expanded ionic liquids and Organic Aqueous Tunable Systems (OATS)1-4. For the latest system, OATS, the high-pressure sapphire cell enabled the study of (1) phase behavior as a function of pressure and temperature, (2) composition of each phase (gas-liquid-liquid) as a function of pressure and temperature and (3) catalyst partitioning in the two liquid phases as a function of pressure and composition. Finally, the sapphire cell is an especially effective tool to gather

  16. High-pressure sapphire cell for phase equilibria measurements of CO2/organic/water systems.

    PubMed

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

    2014-01-24

    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 ternary systems (gas-liquid-liquid) are the specific examples discussed herein. For instance, the ternary THF-Water-CO2 system was studied at 25 and 40 °C and is described herein. Of key importance, this technique does not require sampling. Circumventing the possible disturbance of the system equilibrium upon sampling, inherent measurement errors, and technical difficulties of physically sampling under pressure is a significant benefit of this technique. Perhaps as important, the sapphire cell also enables the direct visual observation of the phase behavior. In fact, as the CO2 pressure is increased, the homogeneous THF-Water solution phase splits at about 2 MPa. With this technique, it was possible to easily and clearly observe the cloud point and determine the composition of the newly formed phases as a function of pressure. The data acquired with the sapphire cell technique can be used for many applications. In our case, we measured swelling and composition for tunable solvents, like gas-expanded liquids, gas-expanded ionic liquids and Organic Aqueous Tunable Systems (OATS)(1-4). For the latest system, OATS, the high-pressure sapphire cell enabled the study of (1) phase behavior as a function of pressure and temperature, (2) composition of each phase (gas-liquid-liquid) as a function of pressure and temperature and (3) catalyst partitioning in the two liquid phases as a function of pressure and composition. Finally, the sapphire cell is an especially effective tool to gather

  17. On the Concordance of Static High Pressure Phase Transformation Data on Minerals With Shock Wave Data

    NASA Astrophysics Data System (ADS)

    de Carli, P. S.; El Goresy, A.; Xie, Z.; Sharp, T. G.

    2006-12-01

    . In other samples, constrained to the same pressure range, long-duration (> 0.1 s) shock pressures are inferred from constant high-pressure mineralogy across wide (>1mm) veins and diaplectic glass is found throughout the meteorite. Evidence for kinetic effects may also be inferred from studies of samples from large impact craters. Pressure estimates based on shock recovery experiments imply post-shock temperatures that are too high for the survival of metastable high-pressure phases, such as stishovite, present in the samples. Release adiabat measurements on quartz also account for the presence of coesite in association with stishovite and diaplectic glass. Release wave velocitie slow below about 7 GPa, providing a relatively long period for the growth of coesite in its stability field from shock heated silica. Studies of high-pressure phases of olivine and pyroxene in meteorites are also concordant with both static high pressure data and inferences from Hugoniot and release measurements. These phases are not found in microsecond duration shock recovery experiments. Finally experiments on the shock synthesis of diamond are in complete accord with evidence for shock synthesized diamond in large impact craters and with static high pressure data on the direct uncatalyzed transition of graphite to diamond.

  18. Successive disorder to disorder phase transitions in ionic liquid [HMIM][BF4] under high pressure

    NASA Astrophysics Data System (ADS)

    Zhu, Xiang; Yuan, Chaosheng; Li, Haining; Zhu, Pinwen; Su, Lei; Yang, Kun; Wu, Jie; Yang, Guoqiang; Liu, Jing

    2016-02-01

    In situ high-pressure Raman spectroscopy and synchrotron X-ray diffraction have been employed to investigate the phase behavior of ionic liquid, 1-hexyl-3-methylimidazolium tetrafluoroborate ([HMIM][BF4]) under high pressure up to 20 GPa at room temperature. With increasing pressure, some characteristic bands of [HMIM][BF4] disappear, and some characteristic bands of [HMIM][BF4] display non-monotonic pressure-induced frequency shift and non-monotonic variation of full width at half-maximum. Two successive phase transitions at ˜1.7 GPa and 7.3 GPa have been corroborated by the results above. The glass transition pressure (Pg) of [HMIM][BF4] at ˜7.3 GPa has been obtained by ruby R1 line broadening measurements and analysis of synchrotron X-ray diffraction patterns, and its glass transition mechanism is also analyzed in detail. These facts are suggestive of two successive disorder to disorder phase transitions induced by compression, that is, [HMIM][BF4] serves as a superpressurized glass under the pressure above 7.3 GPa, which is similar to the glassy state at low temperature, and a compression-induced liquid to liquid phase transition in [HMIM][BF4] occurs at ˜1.7 GPa. Besides, the conformational equilibrium of the GAAA conformer and AAAA conformer was converted easily in liquid [HMIM][BF4], while it was difficult to be influenced in glassy state.

  19. Electronic structure, phase transition, and elastic properties of ScC under high pressure

    NASA Astrophysics Data System (ADS)

    Zhao, Yu-Xin; Zhu, Jun; Hao, Yan-Jun; Li, Zi-Yuan; Chen, Long-Qing; Ji, Guang-Fu

    2015-12-01

    The structural properties and the phase transition for scandium carbide (ScC) have been studied in NaCl (B1), CsCl (B2), ZB (B3), WZ (B4), NiAs (B81), WC (B h ), and Pmmn structures by using the pseudopotential plane-wave method in the framework of the density functional theory. Our theoretical results show that the most stable structure is the B1 phase, contrary to the result of Rahim et al. The phase transitions B1 → Pmmn and Pmmn → B2 are predicted at 83.7 and 109.7 GPa, respectively. At the same time, we find that the B3, B4, B81, and B h phases are not stable over the whole pressure range considered. In particular, the elastic constants of Pmmn-ScC under high pressure are obtained successfully. The effects of pressure on the elastic properties of B1-ScC and Pmmn-ScC are also predicted. The Debye temperatures Θ and the sound velocities of these two structures are estimated from the elastic constants, and by analyzing G/ B, the brittle-ductile behavior of ScC is assessed. In addition, the density of states of B1-ScC at high pressures is also discussed.

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

    NASA Astrophysics Data System (ADS)

    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.

  1. High pressure-induced distortion in face-centered cubic phase of thallium

    NASA Astrophysics Data System (ADS)

    Kotmool, Komsilp; Li, Bing; Chakraborty, Sudip; Bovornratanaraks, Thiti; Luo, Wei; Mao, Ho-kwang; Ahuja, Rajeev

    2016-10-01

    The complex and unusual high-pressure phase transition of III-A (i.e. Al, Ga, and In) metals have been investigated in the last several decades because of their interesting periodic table position between the elements having metallic and covalent bonding. Our present first principles-based electronic structure calculations and experimental investigation have revealed the unusual distortion in face-centered cubic (f.c.c.) phase of the heavy element thallium (Tl) induced by the high pressure. We have predicted body-centered tetragonal (b.c.t) phase at 83 GPa using an evolutionary algorithm coupled with ab initio calculations, and this prediction has been confirmed with a slightly distorted parameter (2 × a - c)/c lowered by 1% using an angle-dispersive X-ray diffraction technique. The density functional theory (DFT)-based calculations suggest that s-p mixing states and the valence-core overlapping of 6s and 5d states play the most important roles for the phase transitions along the pathway h.c.p→b.c.t.

  2. High-pressure structural phase transitions in chromium-doped BaFe2As2

    SciTech Connect

    Uhoya, Walter; Brill, Joseph W.; Montgomery, Jeffrey M; Samudrala, G K; Tsoi, Georgiy; Vohra, Y. K.; Weir, S. T.; Safa-Sefat, Athena

    2012-01-01

    We report on the results from high pressure x-ray powder diffraction and electrical resistance measurements for hole doped BaFe{sub 2-x}Cr{sub x}As{sub 2} (x = 0, 0.05, 0.15, 0.4, 0.61) up to 81 GPa and down to 10 K using a synchrotron source and diamond anvil cell (DAC). At ambient temperature, an isostructural phase transition from a tetragonal (T) phase (I4/mmm) to a collapsed tetragonal (CT) phase is observed at 17 GPa. This transition is found to be dependent on ambient pressure unit cell volume and is slightly shifted to higher pressure upon increase in the Cr-doping. Unlike BaFe{sub 2}As{sub 2} which superconduct under high pressure, we have not detected any evidence of pressure induced superconductivity in chromium doped samples in the pressure and temperature range of this study. The measured equation of state parameters are presented for both the tetragonal and collapsed tetragonal phases for x = 0.05, 0.15, 0.40 and 0.61.

  3. High pressure-induced distortion in face-centered cubic phase of thallium

    PubMed Central

    Kotmool, Komsilp; Li, Bing; Chakraborty, Sudip; Bovornratanaraks, Thiti; Luo, Wei; Mao, Ho-kwang; Ahuja, Rajeev

    2016-01-01

    The complex and unusual high-pressure phase transition of III-A (i.e. Al, Ga, and In) metals have been investigated in the last several decades because of their interesting periodic table position between the elements having metallic and covalent bonding. Our present first principles-based electronic structure calculations and experimental investigation have revealed the unusual distortion in face-centered cubic (f.c.c.) phase of the heavy element thallium (Tl) induced by the high pressure. We have predicted body-centered tetragonal (b.c.t) phase at 83 GPa using an evolutionary algorithm coupled with ab initio calculations, and this prediction has been confirmed with a slightly distorted parameter (2 × a − c)/c lowered by 1% using an angle-dispersive X-ray diffraction technique. The density functional theory (DFT)-based calculations suggest that s–p mixing states and the valence-core overlapping of 6s and 5d states play the most important roles for the phase transitions along the pathway h.c.p→f.c.c.→b.c.t. PMID:27655891

  4. High pressure-induced distortion in face-centered cubic phase of thallium.

    PubMed

    Kotmool, Komsilp; Li, Bing; Chakraborty, Sudip; Bovornratanaraks, Thiti; Luo, Wei; Mao, Ho-Kwang; Ahuja, Rajeev

    2016-10-04

    The complex and unusual high-pressure phase transition of III-A (i.e. Al, Ga, and In) metals have been investigated in the last several decades because of their interesting periodic table position between the elements having metallic and covalent bonding. Our present first principles-based electronic structure calculations and experimental investigation have revealed the unusual distortion in face-centered cubic (f.c.c.) phase of the heavy element thallium (Tl) induced by the high pressure. We have predicted body-centered tetragonal (b.c.t) phase at 83 GPa using an evolutionary algorithm coupled with ab initio calculations, and this prediction has been confirmed with a slightly distorted parameter ([Formula: see text] × a - c)/c lowered by 1% using an angle-dispersive X-ray diffraction technique. The density functional theory (DFT)-based calculations suggest that s-p mixing states and the valence-core overlapping of 6s and 5d states play the most important roles for the phase transitions along the pathway h.c.p[Formula: see text]f.c.c.[Formula: see text]b.c.t.

  5. On the high-pressure phase stability and elastic properties of β-titanium alloys.

    PubMed

    Smith, D; Joris, O P J; Sankaran, A; Weekes, H E; Bull, D J; Prior, T J; Dye, D; Errandonea, D; Proctor, J E

    2017-04-20

    We have studied the compressibility and stability of different β-titanium alloys at high pressure, including binary Ti-Mo, Ti-24Nb-4Zr-8Sn (Ti2448) and Ti-36Nb-2Ta-0.3O (gum metal). We observed stability of the β phase in these alloys to 40 GPa, well into the ω phase region in the P-T diagram of pure titanium. Gum metal was pressurised above 70 GPa and forms a phase with a crystal structure similar to the η phase of pure Ti. The bulk moduli determined for the different alloys range from 97  ±  3 GPa (Ti2448) to 124  ±  6 GPa (Ti-16.8Mo-0.13O).

  6. Nuclear quantum and electronic exchange-correlation effects on the high pressure phase diagram of lithium

    NASA Astrophysics Data System (ADS)

    Clay, Raymond; Morales, Miguel; Bonev, Stanimir

    Lithium at ambient conditions is the simplest alkali metal and exhibits textbook nearly-free electron character. However, increased core/valence electron overlap under compression leads to surprisingly complex behavior. Dense lithium is known to posses a maximum in the melting line, a metal to semiconductor phase transition around 80GPa, reemergent metallicity around 120GPa, and low coordination solid and liquid phases. In addition to its complex electronic structure at high pressure, the atomic mass of lithium is low enough that nuclear quantum effects could have a nontrivial impact on its phase diagram. Through a combination of density functional theory based path-integral and classical molecular dynamics simulations, we have investigated the impact of both nuclear quantum effects and anharmonicity on the melting line and solid phase boundaries. Additionally, we have determined the robustness of previously predicted tetrahedral clustering in the dense liquid to the inclusion of nuclear quantum effects and approximate treatment of electronic exchange-correlation effects.

  7. On the high-pressure phase stability and elastic properties of β-titanium alloys

    NASA Astrophysics Data System (ADS)

    Smith, D.; Joris, O. P. J.; Sankaran, A.; Weekes, H. E.; Bull, D. J.; Prior, T. J.; Dye, D.; Errandonea, D.; Proctor, J. E.

    2017-04-01

    We have studied the compressibility and stability of different β-titanium alloys at high pressure, including binary Ti-Mo, Ti-24Nb-4Zr-8Sn (Ti2448) and Ti-36Nb-2Ta-0.3O (gum metal). We observed stability of the β phase in these alloys to 40 GPa, well into the ω phase region in the P-T diagram of pure titanium. Gum metal was pressurised above 70 GPa and forms a phase with a crystal structure similar to the η phase of pure Ti. The bulk moduli determined for the different alloys range from 97  ±  3 GPa (Ti2448) to 124  ±  6 GPa (Ti-16.8Mo-0.13O).

  8. Superconductivity in metastable phases of phosphorus-hydride compounds under high pressure

    NASA Astrophysics Data System (ADS)

    Flores Livas, Jose; Amsler, Maximilian; Sanna, Antonio; Heil, Christoph; Boeri, Lilia; Profeta, Gianni; Wolverton, Crhis; Goedecker, Stefan; Gross, E. K. U.

    Recently, compressed phosphine was reported to metallize at pressures above 45 GPa, reaching a superconducting transition temperature (Tc) of 100 K at 200 GPa. However, neither the exact composition nor the crystal structure of the superconducting phase have been conclusively determined. In this work the phase diagram of PHn (n = 1 , 2 , 3 , 4 , 5 , 6) was extensively explored by means of ab initio crystal structure prediction methods. The results do not support the existence of thermodynamically stable PHn compounds, which exhibit a tendency for elemental decomposition at high pressure even when vibrational contributions to the free energies are taken into account. Although the lowest energy phases of PH1 , 2 , 3 display Tc's comparable to experiments, it remains questionable if the measured values of Tc can be fully attributed to a phase-pure compound of PHn. This work was done within the NCCR MARVEL project.

  9. High-Pressure Measurements of Hydrogen Phase IV Using Synchrotron Infrared Spectroscopy

    NASA Astrophysics Data System (ADS)

    Zha, Chang-sheng; Liu, Zhenxian; Ahart, Muhtar; Boehler, Reinhard; Hemley, Russell J.

    2013-05-01

    Phase IV of dense solid hydrogen has been identified by its infrared spectrum using high-pressure synchrotron radiation techniques. The spectrum exhibits a sharp vibron band at higher frequency and lower intensity than that for phase III, indicating the stability of molecular H2 with decreased intermolecular interactions and charge transfer between molecules. A low-frequency vibron having a strong negative pressure shift indicative of strongly interacting molecules is also observed. The character of the spectrum is consistent with an anisotropic, mixed layer structure related to those recently predicted theoretically. Phase IV was found to be stable from 220 GPa (300 K) to at least 340 GPa (near 200 K), with the I-III-IV triple point located. Infrared transmission observed to the lowest photon energies measured places constraints on the electronic properties of the phase.

  10. Observation of a high-pressure cinnabar phase in CdTe

    NASA Astrophysics Data System (ADS)

    Nelmes, R. J.; McMahon, M. I.; Wright, N. G.; Allan, D. R.

    1993-07-01

    Angle-dispersive powder-diffraction techniques with an image-plate area detector and synchrotron radiation have been used to reexamine the high-pressure behavior of cadmium telluride. We find that the well-known structural phase transition at ~3.5 GPa from the zinc-blende to NaCl structure actually involves two closely spaced transitions-zinc blende to cinnabar, and cinnabar to NaCl. This is the example of the cinnabar structure outside the mercury chalcogenides. The Cd and Te atoms are site ordered, and the coordination of the structure is closer to fourfold than is found in HgS cinnabar.

  11. First-principles Study of High-pressure Phases of AlN

    NASA Astrophysics Data System (ADS)

    Louhibi-Fasla, S.; Achour, H.; Kefif, K.; Ghalem, Y.

    We report study of high-pressure phases of AlN compound, using a recent version of the full potential linear muffin-tin orbitals method (FPLMTO) which enables an accurate treatment of the interstitial regions. The Exchange-correlation has been accounted for within LDA using the exchange-correlation potential calculated by Perdew et al. Calculations are given for lattice parameters, bulk modulus and its first derivatives in the wurtzite, zinc-blende, rock-salt, CsCl, NiAs, βSn, the Cinnabar and the hexagonal structures. The results of these calculations are compared with the available theoretical and experimental data.

  12. Reverse phase high pressure liquid chromatography for the separation of peptide hormone diastereoisomers.

    PubMed

    Larsen, B; Viswanatha, V; Chang, S Y; Hruby, V J

    1978-05-01

    Diastereoisomers of specifically labeled oxytocin derivatives were resolved using reverse phase high pressure liquid chromatography. The peptides [1-hemi-DL-[alpha-2H]cystine]oxytocin, [6-hemi-DL-[alpha-2H]cystine]oxytocin, [2-DL-[alpha-2H]tyrosine]oxytocin and[8-DL-[2-13C]leucine]oxytocin were readily separated using the conditions described. The diastereoisomers of the oxytocin analog [3-DL-[2-13C]leucine]oxytocin also demonstrated baseline resolution under the same conditions. The procedure offers the investigator a rapid method for screening synthetic oxytocin peptides for undesirable diastereoisomeric by-products.

  13. Reverse phase ion pair high pressure liquid chromatographic determination of ethylenediaminetetraacetic acid in crabmeat and mayonnaise.

    PubMed

    Perfetti, G A; Warner, C R

    1979-09-01

    A method is described for the determination of ethylenediaminetetraacetic acid (EDTA) in crabmeat and mayonnaise. EDTA is extracted from the food sample with water and converted to its copper chelate, which is then quantitated by reverse phase ion pair high pressure liquid chromatography with ultraviolet detection. Maximum sensitivity is obtained with detection at about 254 nm; higher wavelengths may be used for enhanced specificity. Cleanup procedures for crabmeat and mayonnaise were improved by using a radiotracer method. Analyses of crabmeat and mayonnaise samples spiked at 3 different levels showed greater than 90% recovery of EDTA.

  14. Superconductivity of high-pressure phases of S and Se to 230 GPa

    NASA Astrophysics Data System (ADS)

    Struzhkin, Viktor; Gregoryanz, Eugene; Timofeev, Yuri; Eremets, Mikhail; Mao, Ho-Kwang; Hemley, Russell

    2000-03-01

    We have investigated in detail the superconducting state of sulfur in its β-Po phase from 160 to 230 GPa. The superconducting Tc is close to 17 K from 160 to 200 GPa, and drops to 15 K at 230 GPa. Similar behavior was predicted recently [1] from ab initio LDA calculations. The high value of Tc in the β-Po phase is consistent with electon-phonon coupling mechanism with reasonably strong electron-phonon coupling (λ=0.76), and with the standard value of the Morel-Anderson pseudopotential μ^*=0.11 [1]. Our measurements in Se at high pressures indicate superconductivity from 17 to 23 GPa, which apparently has not been previously reported. We relate this behavior to the occurence of new metastable phase in Se which can be observed on decompression from 30 GPa at low temperatures. The results for Tc in Se at higher pressures will be also presented. We will also discuss the similiarities in high-pressure induced superconductivity of chalcogen family members: S, Se, and Te. ^1 Sven P. Rudin and Amy Y. Liu, Phys. Rev. Lett. 83, 3049 (1999).

  15. Phase transformations in amorphous fullerite C60 under high pressure and high temperature

    NASA Astrophysics Data System (ADS)

    Borisova, P. A.; Blanter, M. S.; Brazhkin, V. V.; Somenkov, V. A.; Filonenko, V. P.

    2015-08-01

    First phase transformations of amorphous fullerite C60 at high temperatures (up to 1800 K) and high pressures (up to 8 GPa) have been investigated and compared with the previous studies on the crystalline fullerite. The study was conducted using neutron diffraction and Raman spectroscopy. The amorphous fullerite was obtained by ball-milling. We have shown that under thermobaric treatment no crystallization of amorphous fullerite into С60 molecular modification is observed, and it transforms into amorphous-like or crystalline graphite. A kinetic diagram of phase transformation of amorphous fullerite in temperature-pressure coordinates was constructed for the first time. Unlike in crystalline fullerite, no crystalline polymerized phases were formed under thermobaric treatment on amorphous fullerite. We found that amorphous fullerite turned out to be less resistant to thermobaric treatment, and amorphous-like or crystalline graphite were formed at lower temperatures than in crystalline fullerite.

  16. Equation of state and phase diagram of ammonia at high pressures from ab initio simulations.

    PubMed

    Bethkenhagen, Mandy; French, Martin; Redmer, Ronald

    2013-06-21

    We present an equation of state as well as a phase diagram of ammonia at high pressures and high temperatures derived from ab initio molecular dynamics simulations. The predicted phases of ammonia are characterized by analyzing diffusion coefficients and structural properties. Both the phase diagram and the subsequently computed Hugoniot curves are compared to experimental results. Furthermore, we discuss two methods that allow us to take into account nuclear quantum effects, which are of considerable importance in molecular fluids. Our data cover pressures up to 330 GPa and a temperature range from 500 K to 10,000 K. This regime is of great interest for interior models of the giant planets Uranus and Neptune, which contain, besides water and methane, significant amounts of ammonia.

  17. Shear wave measurements in shock-induced, high-pressure phases

    SciTech Connect

    Aidun, J.B.

    1993-01-01

    Structural phase transformations under shock loading are of considerable interest for understanding the response of solids under nonhydrostatic stresses and at high strain-rates. Examining shock-induced transformations from continuum level measurements is fundamentally constrained by the inability to directly identify microscopic processes, and also by the limited number of material properties that can be directly measured. ne latter limitation can be reduced by measuring both shear and compression waves using Lagrangian gauges in combined, compression and shear loading. The shear wave serves as an important, real-time probe of the shocked state and unloading response. Using results from a recent study of CaCO[sub 3], the unique information obtained from the shear wave speed and the detailed structure of the shear wave are shown to be useful for distinguishing the effects of phase transformations from yielding, as well as in characterizing the high-pressure phases and the yielding process under shock loading.

  18. Shear wave measurements in shock-induced, high-pressure phases

    SciTech Connect

    Aidun, J.B.

    1993-07-01

    Structural phase transformations under shock loading are of considerable interest for understanding the response of solids under nonhydrostatic stresses and at high strain-rates. Examining shock-induced transformations from continuum level measurements is fundamentally constrained by the inability to directly identify microscopic processes, and also by the limited number of material properties that can be directly measured. ne latter limitation can be reduced by measuring both shear and compression waves using Lagrangian gauges in combined, compression and shear loading. The shear wave serves as an important, real-time probe of the shocked state and unloading response. Using results from a recent study of CaCO{sub 3}, the unique information obtained from the shear wave speed and the detailed structure of the shear wave are shown to be useful for distinguishing the effects of phase transformations from yielding, as well as in characterizing the high-pressure phases and the yielding process under shock loading.

  19. Modeling high-pressure and high-temperature phase changes in bulk carbon

    SciTech Connect

    Glosi, J N; Ree, F H

    1999-07-01

    The phase diagram of carbon is not experimentally well known at high pressure and/or high temperature. We have determined the phase diagram of carbon by means of Monte Carlo and molecular dynamics simulations methods using the Brenner bond order potential. The melting line of diamond was found to have a positive slope with the graphite-diamond-liquid triple point in agreement with an estimated value based on experiment. The present calculation predicts a first-order phase transition in liquid carbon terminated by a critical point and by a triple point on the graphite melting line. The low-density liquid is predominantly sp bonded with little sp{sup 3} character. The high-density liquid is mostly sp{sup 3} bonded with little sp character.

  20. Hybrid functional study rationalizes the simple cubic phase of calcium at high pressures.

    PubMed

    Liu, Hanyu; Cui, Wenwen; Ma, Yanming

    2012-11-14

    Simple cubic (SC) phase has been long experimentally determined as the high-pressure phase III of elemental calcium (Ca) since 1984. However, recent density functional calculations within semi-local approximation showed that this SC phase is structurally unstable by exhibiting severely imaginary phonons, and is energetically unstable with respect to a theoretical body-centered tetragonal I4(1)/amd structure over the pressure range of phase III. These calculations generated extensive debates on the validity of SC phase. Here we have re-examined the SC structure by performing more precise density functional calculations within hybrid functionals of Heyd-Scuseria-Erhzerhof and PBE0. Our calculations were able to rationalize fundamentally the phase stability of SC structure over all other known phases by evidence of its actual energetic stability above 33 GPa and its intrinsically dynamical stability without showing any imaginary phonons in the entire pressure range studied. We further established that the long-thought theoretical I4(1)/amd structure remains stable in a narrow pressure range before entering SC phase and is actually the structure of experimental Ca-III(') synthesized recently at low temperature 14 K as supported by the excellent agreement between our simulated x-ray diffraction patterns and the experimental data. Our results shed strong light on the crucial role played by the precise electron exchange energy in a proper description of the potential energy of Ca.

  1. High Pressure Behaviors of FeOOH and Fe-bearing Phase H

    NASA Astrophysics Data System (ADS)

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

    2016-12-01

    Surface water can be brought into the Earth's interior by the subduction of cold oceanic plates. Although, most of water is released by decompositions of phyllosilicates at shallower depth in the subducting plates, it has been suggested that small portion of water is carried into the deeper part of the Earth's interior by the taking the form of the dense hydrous magnesium silicates. It is important to clarify the high pressure and temperature behaviors of such hydrous phases, since trace amount of water can change the physical properties of mantle minerals significantly. At the lower mantle pressure conditions, Al and H-bearing SiO2, δ-AlOOH, ɛ-FeOOH and phase H may be the relevant hydrous phases in the subducting slabs. Interestingly, the crystal structure of these hydrous phases are almost same and have CaCl2 type structure. This suggests that these hydrous phases may potentially be able to make the wide range of solid solution. Some experimental studies already reported that Al preferentially partitioned into phase H and the stability of phase H drastically increased by incorporation of Al (Nishi et al. 2014, Ohira et al. 2014). The density of subducted MORB is reported to be denser than that of pyrolite in the lower mantle (e.g. Kawai et al. 2009). Therefore, there is a possibility that phase H containing Al and Fe in subducted MORB survive down to the bottom of lower mantle and the melting of phase H at the core mantle boundary may contribute to the cause of ultra-low velocity zones. In this study, we further extends our exploration of these hydrous phases, such as the spin transition of Fe in phase H and ɛ-FeOOH, and the possibility of further structural transition using first principles calculation techniques by determining the Hubbard U parameter in an internally consistent scheme (Cococcioni & de Gironcoli 2005). The calculated results are compared with the high pressure x-ray diffraction study using diamond anvil cell apparatus. We discuss the possible

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

    SciTech Connect

    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.

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

    SciTech Connect

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

    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.

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

    NASA Astrophysics Data System (ADS)

    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.

  5. [Raman characterization of rutile phase transitions under high-pressure and high-temperature].

    PubMed

    Xiao, Wan-Sheng; Zhang, Hong; Tan, Da-Yong; Weng, Ke-Nan; Li, Yan-Chun; Luo, Chong-Ju; Liu, Jing; Xie, Hong-Sen

    2007-07-01

    The pressure-induced phase transition of rutile-structured TiO2 was investigated by in-situ Raman spectrum method in a laser-heated diamond anvil cell (DAC). The experiment was conducted at 35 GPa under quasihydrostatic conditions using argon as medium. At room temperature, the rutile-type TiO2 begins to transform to baddeleyite-type phase at 13.4 GPa and completes at 21 GPa, and this new high-pressure structure retains up to 35 GPa, the upmost pressure used in this study. At the pressure of 29.4 GPa the sample of baddeleyite-type TiO2 was heated by an YAG laser to about 1 000-1500 degrees C, and then the baddeleyite phase transformed to a Pbca phase. The Pbca phase was heated again at 35.0 GPa and it was still stable. The sample then began to be decompressed, and the Pbca phase of TiO2 transformed to baddeleyite structure at 26.3 GPa, which stayed stable to 11.4 GPa. The formation of Pbca phase from baddeleyite phase needs the condition of high temperature, it transforms back to badde-leyite structure completely at pressure of a little below that on its formation, which suggests the boundary of the two phases can be determined at about 28 GPa. At 7. 6 GPa, and the Raman spectrum shows the characteristics of the mixture of two phases of baddeleyite-type and alpha-PbO2-type, which indicates that the baddeleyite phase transforms to alpha-PbO2 phase at about 7 GPa. The alpha-PbO2-type TiO2 is metastable under ambient condition.

  6. Phase transitions, mechanical properties and electronic structures of novel boron phases under high-pressure: A first-principles study

    PubMed Central

    Fan, Changzeng; Li, Jian; Wang, Limin

    2014-01-01

    We have explored the mechanical properties, electronic structures and phase transition behaviors of three designed new phases for element boron from ambient condition to high-pressure of 120 GPa including (1) a C2/c symmetric structure (m-B16); (2) a symmetric structure (c-B56) and (3) a Pmna symmetric structure (o-B24). The calculation of the elastic constants and phonon dispersions shows that the phases are of mechanical and dynamic stability. The m-B16 phase is found to transform into another new phase (the o-B16 phase) when pressure exceeds 68 GPa. This might offer a new synthesis strategy for o-B16 from the metastable m-B16 at low temperature under high pressure, bypassing the thermodynamically stable γ-B28. The enthalpies of the c-B56 and o-B24 phases are observed to increase with pressure. The hardness of m-B16 and o-B16 is calculated to be about 56 GPa and 61 GPa, approaching to the highest value of 61 GPa recorded for α-Ga-B among all available Boron phases. The electronic structures and bonding characters are analyzed according to the difference charge-density and crystal orbital Hamilton population (COHP), revealing the metallic nature of the three phases. PMID:25345910

  7. Structural phase transition in CaH{sub 2} at high pressures

    SciTech Connect

    Tse, J. S.; Klug, D. D.; Desgreniers, S.; Smith, J. S.; Flacau, R.; Liu, Z.; Hu, J.; Chen, N.; Jiang, D. T.

    2007-04-01

    The structural and vibrational properties of CaH{sub 2} have been examined up to 30 GPa at room temperature. Under ambient conditions, CaH{sub 2} has a Pnma (cotunnite-type) structure. A structural phase transformation was observed around 15 GPa and completed at 20 GPa. The high pressure structure is identified as hexagonal P6{sub 3}/mmc. First-principles calculations reproduced the first-order nature of the transition. Since P6{sub 3}/mmc is a supergroup of Pnma the structural change can be traced back to gradual displacements of the hydrogen atoms from the 4c positions in the cotunnite structure to the special 2a and 2d positions in the hexagonal structure. The observed phase transition pressure is much lower than that predicted for MgH{sub 2}.

  8. The role of correlations in the high-pressure phase of FeSe.

    PubMed

    Naghavi, S Shahab; Chadov, Stanislav; Felser, Claudia

    2011-05-25

    This study addresses the structural and electronic properties of the NiAs- and MnP-type phases dominating in FeSe at high pressures. The analysis is performed using first-principle band structure calculations within the framework of the B3LYP hybrid exchange-correlation functional. Based on the volume-pressure relation deduced from the available experimental data, we optimize the form and internal coordinates of the unit cell, which agree reasonably well with experiment. In particular, the present calculations resolve the structural NiAs-MnP phase transition which occurs at about 10 GPa. Both structures are found to be semiconducting at low pressures and metallizing at about 80-90 GPa. Using the complementary LDA + U approach the semiconducting state can be explained as the result of the strong local correlations within the Fe d-shell.

  9. Observations of a high-pressure phase creation in oleic acid

    NASA Astrophysics Data System (ADS)

    Kościesza, R.; Kulisiewicz, L.; Delgado, A.

    2010-03-01

    Oleic acid is one of the unsaturated fatty acids which frequently appears in food products such as edible fats and oils. A molecule of oleic acid possesses a double carbon bond, C=C, which is responsible for a transition to a new phase when pressure is applied. This work presents the results of optical observations of such a transition. The observations were made in two cases, the first being static p-T conditions under 60 MPa at 20°C and the other the dynamic application of the pressure up to 350 MPa. The obtained visualization reveals differences in the creation of the phase and in its further appearance. Some crystal forms may be recognized. These results tend to be of interest for food engineers due to increasing interest in high-pressure food preservation among nutritionists and medical scientists concerned with fatty acids.

  10. Phase stability and magnetic behavior of hexagonal phase of N2-O2 system with kagome lattice under high pressure and low temperature

    NASA Astrophysics Data System (ADS)

    Akahama, Y.; Ishihara, D.; Yamashita, H.; Fujihisa, H.; Hirao, N.; Ohishi, Y.

    2016-08-01

    The pressure-temperature (P -T ) phase diagram of N2-O2 mixture with a composition of N2-48 mol % O2 has been investigated using x-ray diffraction and the phase stability of a hexagonal phase (space group: P 6 /mmm), with the kagome lattice examined under high-pressure and low-temperature conditions. While the phase appears as a low-temperature phase of the cubic phase (P m 3 n ) with the structure of γ -O2 or δ -N2 and is stable in a wide range of pressures and temperatures, it transforms to lower symmetry monoclinic or orthorhombic phases at lower temperature, accompanied with a distortion of the kagome lattice. Based on Rietveld refinements, the monoclinic and orthorhombic phases are found to be in the P 21/a and Cmmm space groups, respectively. In magnetization measurements, a magnetic transition is observed with a relatively large drop of magnetization, corresponding to the cubic-to-hexagonal phase transition. This suggests that the hexagonal phase has a certain magnetic ordered state that arises from the molecular magnetic moment of O2.

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

    NASA Astrophysics Data System (ADS)

    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.

  12. High pressure phase transition and variation of elastic constants of diluted magnetic semiconductors

    NASA Astrophysics Data System (ADS)

    Varshney, Dinesh; Sharma, P.; Kaurav, N.; Shah, S.; Singh, R. K.

    2004-11-01

    A theoretical study of the high-pressure phase transition and elastic behavior in diluted magnetic semiconductors Zn0.83Mn0.17Se, using a three-body interaction (TBI) potential caused by the electron-shell deformation of the overlapping ions is carried out. The estimated values of phase transition pressure and the vast volume discontinuity in pressure-volume (PV) phase diagram indicate the structural phase transition from zincblende (B3) to rock salt (B1). The variation of second-order elastic constants with pressure resembles that observed in some binary semiconductors. The inconsistency in the deduced value of pressure derivative of second order elastic constant with the available data is attributed to the fact that we derive expressions neglecting thermal effects and assuming the overlap repulsion significant only up to nearest neighbors. The vdW interaction is effective in obtaining the thermodynamical parameters such as Debye temperature, Gruneisen parameter, thermal expansion coefficient, compressibility as well phase stability in diluted magnetic semiconductors. It is revealed that TBI model has a promise to predict the phase transition pressure and the pressure variation of elastic constants of other semiconductors as well.

  13. High-pressure structural phase transitions in CuWO[subscript 4

    SciTech Connect

    Ruiz-Fuertes, J.; Errandonea, D.; Lacomba-Perales, R.; Segura, A.; González, J.; Rodríguez, F.; Manjón, F.J.; Ray, S.; Rodríguez-Hernández, P.; Muñoz, A.; Zhu, Zh.; Tu, C.Y.

    2010-07-23

    We study the effects of pressure on the structural, vibrational, and magnetic behavior of cuproscheelite. We performed powder x-ray diffraction and Raman spectroscopy experiments up to 27 GPa as well as ab initio total-energy and lattice-dynamics calculations. Experiments provide evidence that a structural phase transition takes place at 10 GPa from the low-pressure triclinic phase (P1{sup -}) to a monoclinic wolframite-type structure (P2/c). Calculations confirmed this finding and indicate that the phase transformation involves a change in the magnetic order. In addition, the equation of state for the triclinic phase is determined: V{sub 0} = 132.8(2) {angstrom}{sup 3}, B{sub 0} = 139(6) GPa, and B{prime}{sub 0} = 4. Furthermore, experiments under different stress conditions show that nonhydrostatic stresses induce a second phase transition at 17 GPa and reduce the compressibility of CuWO{sub 4}, B{sub 0} = 171(6) GPa. The pressure dependence of all Raman modes of the triclinic and high-pressure phases is also reported and discussed.

  14. High-pressure phases of Mg2Si from first principles

    NASA Astrophysics Data System (ADS)

    Huan, Tran Doan; Tuoc, Vu Ngoc; Le, Nam Ba; Minh, Nguyen Viet; Woods, Lilia M.

    2016-03-01

    First-principles calculations are presented to resolve the possible pressure-dependent phases of Mg2Si . Although previous reports show that Mg2Si is characterized by the cubic antifluorite F m 3 ¯m structure at low pressures, the situation at higher pressures is less clear with many contradicting results. Here we utilize several methods to examine the stability, electron, phonon, and transport properties of this material as a function of pressure and temperature. We find that Mg2Si is thermodynamically stable at low and high pressures. Between 6 and 24 GPa, Mg2Si can transform into Mg9Si5 , a defected compound, and vice versa, without energy cost. Perhaps this result is related to the aforementioned inconsistency in the structures reported for Mg2Si within this pressure range. Focusing solely on Mg2Si , we find a new monoclinic C 2 /m structure of Mg2Si , which is stable at high pressures within thermodynamical considerations. The calculated electrical conductivity and Seebeck coefficient taking into account results from the electronic structure calculations help us understand better how transport can be affected in this material by modulating pressure and temperature.

  15. Crystal growth, complex phase diagram and high pressure studies of layer compound PdBi2

    NASA Astrophysics Data System (ADS)

    Zhao, Kui; Zhu, Xiyu; Lv, Bing; Xue, Yuyi; Chu, Paul

    2013-03-01

    Among the different Pd-Bi Alloys, β-PdBi2, which is crystallized in a layered tetragonal (I4/mmm) structure, has been identified as a superconductor with transition temperature at ~ 5.4K. Band structure calculation indicates that the interlayer Bi-Bi bonds are weak but not negligible, which implies the 3D bonding character of this compound. In order to enhance or weaken the interlayer bonding and ultimately increase the Tc in this system, high pressure measurement, isovalent chemical substitution of Bi with Sb, and chemical intercalation using transition metal Cu and alkali metal Na, are applied to the system. Meanwhile, aliovalent chemical substitution on the Bi site by Pb is also carried out. The magnetic, electrical, and calorimetric properties of these compounds are determined at ambient pressure and compared. The detailed high pressure results and the complete phase diagram of chemical substitution and intercalation will be presented and discussed. Work in Houston is supported in part by US AFOSR, the State of Texas, T. L. L. Temple Foundation and John and Rebecca Moores Endowment.

  16. Phase-modulated dispersion interferometry for electron-density determination of high-pressure plasma

    NASA Astrophysics Data System (ADS)

    Urabe, Keiichiro; Akiyama, Tsuyoshi; Terashima, Kazuo

    2014-10-01

    Phase-modulated dispersion interferometry (PMDI) is a laser interferometry technique that was first developed for measurement of electron density in large fusion reactors. PMDI can eliminate the effect of nondispersive components in the refractive-index variation on the measured signals; therefore, it is mostly free from vibration of optical devices during the measurement. Also, configuration of the laser beam axis in PMDI is simpler than that in heterodyne interferometry. In this paper, we demonstrate the potential of PMDI for the diagnostics of low-temperature plasmas generated at high pressures. Most of the variation of the refractive index induced by the variation of gas density was eliminated by signal processing, and it contributed to accurate electron-density determination in high-pressure plasmas. The measurement results for a pulsed-dc microdischarge in an atmospheric-pressure helium gas flow revealed that the electron density in the microdischarge was in the range between 4 ×1013 and 1 . 4 ×1014 cm-3, and our PMDI system had a temporal resolution of 110 μs and a sensitivity of the line-integrated electron density of 7 ×1011 cm-2 respectively. This work is supported in part by MEXT of Japan, JSPS, and NIFS.

  17. Exploring the Phase Diagram SiO2-CO2 at High Pressures and Temperatures

    NASA Astrophysics Data System (ADS)

    Kavner, A.

    2015-12-01

    CO2 is an important volatile system relevant for planetary sciences and fundamental chemistry. Molecular CO2 has doubly bonded O=C=O units but high pressure-high temperature (HP-HT) studies have recently shown its transformation into a three-dimensional network of corner-linked [CO4] units analogous to the silica mineral polymorphs, through intermediate non-molecular phases. Here, we report P-V-T data on CO2-IV ice from time-of-flight neutron diffraction experiments, which allow determining the compressibility and thermal expansivity of this intermediate molecular-to-non-molecular phase.1 Aditionally, we have explored the SiO2-CO2 phase diagram and the potential formation of silicon carbonate compounds. New data obtained by laser-heating diamond-anvil experiments in CO2-filled microporous silica polymorphs will be shown. In particular, these HP-HT experiments explore the existence of potential CO2/SiO2 compounds with tetrahedrally-coordinated C/Si atoms by oxygens, which are predicted to be stable (or metastable) by state-of-the-art ab initio simulations.2,3 These theoretical predictions were supported by a recent study that reports the formation of a cristobalite-type Si0.4C0.6O2 solid solution at high-pressures and temperatures, which can be retained as a metastable solid down to ambient conditions.4 Entirely new families of structures could exist based on [CO4]4- units in various degrees of polymerisation, giving rise to a range of chain, sheet and framework solids like those found in silicate chemistry. References[1] S. Palaich et al., Am. Mineral. Submitted (2015) [2] A. Morales-Garcia et al., Theor. Chem. Acc. 132, 1308 (2013) [3] R. Zhou et al., Phys. Rev. X, 4, 011030 (2014) [4] M. Santoro et al. Nature Commun. 5, 3761 (2014)

  18. High-pressure phase behavior of binary mixtures of octacosane and carbon dioxide

    SciTech Connect

    McHugh, M.A.; Seckner, A.J.; Yogan, T.J.

    1984-11-01

    The high-pressure fluid phase behavior of binary mixtures of octacosane and CO/sub 2/ is experimentally investigated. Solubilities of octacosane in supercritical CO/sub 2/ and mixture molar volumes are determined for isotherms of 34.7, 45.4, 50.2, and 52.0/sup 0/C over a range of pressures from 80 to 325 atm. The solubility data are obtained by two different experimental techniques. The pressure-temperature projection of the two branches of the three-phase solid-liquid-gas freezing point depression curve is also determined. The octacosane-CO/sub 2/ LCEP is determined as 32.2/sup 0/ C and 72.6 atm. The UCEP, which is at a pressure greater than 650 atm, could not be determined due to the pressure limitation of the experimental apparatus. Phase diagram constructions are used qualitatively to explain the observed phase behavior and to provide information on the expected phase behavior of the octacosane-CO/sub 2/ system at pressures higher than those experimentally investigated.

  19. New high-pressure phases of MoSe2 and MoTe2

    NASA Astrophysics Data System (ADS)

    Kohulák, Oto; MartoÅák, Roman

    2017-02-01

    Three Mo-based transition-metal dichalcogenides MoS2,MoSe2, and MoTe2 share at ambient conditions the same structure 2 Hc , consisting of layers where Mo atoms are surrounded by six chalcogen atoms in trigonal prism coordination. The knowledge of their high-pressure behavior is, however, limited, particularly in case of MoSe2 and MoTe2. The latter materials do not undergo a layer-sliding transition 2 Hc→ 2 Ha known in MoS2 and currently no other stable phase aside from 2 Hc is known in these systems at room temperature. Employing evolutionary crystal structure prediction in combination with ab initio calculations, we study the zero-temperature phase diagram of both materials up to Mbar pressures. We find a tetragonal phase with space group P4/mmm, previously predicted in MoS2, to become stable in MoSe2 at 118 GPa. In MoTe2, we predict at 50 GPa a transition to a new layered tetragonal structure with space group I4/mmm, similar to CaC2, where Mo atoms are surrounded by eight Te atoms. The phase is metallic already at the transition pressure and becomes a good metal beyond 1 Mbar. We discuss chemical trends in the family of Mo-based transition-metal dichalcogenides and suggest that MoTe2 likely offers the easiest route towards the post-2 H phases.

  20. High pressure phase transitions in the rare earth metal erbium to 151 GPa.

    PubMed

    Samudrala, Gopi K; Thomas, Sarah A; Montgomery, Jeffrey M; Vohra, Yogesh K

    2011-08-10

    High pressure x-ray diffraction studies have been performed on the heavy rare earth metal erbium (Er) in a diamond anvil cell at room temperature to a pressure of 151 GPa and Er has been compressed to 40% of its initial volume. The rare earth crystal structure sequence hcp → Sm type → dhcp → distorted fcc (hcp: hexagonal close packed; fcc: face centered cubic; dhcp: double hcp) is observed in Er below 58 GPa. We have carried out Rietveld refinement of crystal structures in the pressure range between 58 GPa and 151 GPa. We have examined various crystal structures that have been proposed for the distorted fcc (dfcc) phase and the post-dfcc phase in rare earth metals. We find that the hexagonal hR 24 structure is the best fit between 58 and 118 GPa. Above 118 GPa, a structural transformation from hR 24 phase to a monoclinic C 2/m phase is observed with a volume change of - 1.9%. We have also established a clear trend for the pressure at which a post-dfcc phase is formed in rare earth metals and show that there is a monotonic increase in this pressure with the filling of 4f shell.

  1. Phase transitions in Group III-V and II-VI semiconductors at high pressure

    NASA Technical Reports Server (NTRS)

    Yu, S. C.; Liu, C. Y.; Spain, I. L.; Skelton, E. F.

    1979-01-01

    The structures and transition pressures of Group III-V and II-VI semiconductors and of a pseudobinary system (Ga/x/In/1-x/Sb) have been investigated. Results indicate that GaP, InSb, GaSb, GaAs and possible AlP assume Metallic structures at high pressures; a tetragonal, beta-Sn-like structure is adopted by only InSb and GaSb. The rocksalt phase is preferred in InP, InAs, AlSb, ZnO and ZnS. The model of Van Vechten (1973) gives transition pressures which are in good agreement with measured values, but must be refined to account for the occurrence of the ionic rocksalt structure in some compounds. In addition, discrepancies between the theoretical scaling values for volume changes at the semiconductor-to-metal transitions are observed.

  2. The Effect of High Pressure on Phase Relationships and Some Properties of Ti and Its alloys.

    DTIC Science & Technology

    1981-05-01

    I AD- AlGA 828 TECHNION - ISRAEL INST OF TECH HAIFA DEPT OF MATERIA-ETC F/6 11/6 THE EFFECT OF HIGH PRESSURE ON PHASE RELATIONSHIPS AND SOME PRO-ETCIU...Il1 l -. om i rws. Inif ialiv the slit ronc e orrel-ated displacemnents apvear aild resuilt lrn thle Jiilrai er itr Ldii 1u, W~ hen driving forces for...i, es u r ie ei s I ie i i’a’ ~ at i, ’o n tie ’ iIr. p. f’,1 u I ’d I ) It I I-l d- J-I 1,*. " ’ILI :i1~ 1ii I sI ’ Lai -49 3.2. Experimental

  3. Isotope effect in the superconducting high-pressure simple cubic phase of calcium from first principles

    NASA Astrophysics Data System (ADS)

    Errea, Ion; Rousseau, Bruno; Bergara, Aitor

    2012-06-01

    It has been recently shown [I. Errea, B. Rousseau, and A. Bergara, Phys. Rev. Lett. 106, 165501 (2011)] that the phonons of the high-pressure simple cubic phase of calcium are stabilized by strong quantum anharmonic effects. This was obtained by a fully ab initio implementation of the self-consistent harmonic approximation including explicitly anharmonic coefficients up to fourth order. The renormalized anharmonic phonons make possible to estimate the superconducting transition temperature in this system, and a sharp agreement with experiments is found. In this work, this analysis is extended in order to study the effect of anharmonicity in the isotope effect. According to our calculations, despite the huge anharmonicity in the system, the isotope coefficient is predicted to be 0.45, close to the 0.5 value expected for a harmonic BCS superconductor.

  4. Structural characterization of a new high-pressure phase of GaAsO4.

    PubMed

    Santamaría-Pérez, David; Haines, Julien; Amador, Ulises; Morán, Emilio; Vegas, Angel

    2006-12-01

    As in SiO2 which, at high pressures, undergoes the alpha-quartz-->stishovite transition, GaAsO4 transforms into a dirutile structure at 9 GPa and 1173 K. In 2002, a new GaAsO4 polymorph was found by quenching the compound from 6 GPa and 1273 K to ambient conditions. The powder diagram was indexed on the basis of a hexagonal cell (a=8.2033, c=4.3941 A, V=256.08 A3), but the structure did not correspond to any known structure of other AXO4 compounds. We report here the ab initio crystal structure determination of this hexagonal polymorph from powder data. The new phase is isostructural to beta-MnSb2O6 and it can be described as a lacunary derivative of NiAs with half the octahedral sites being vacant, but it also contains fragments of the rutile-like structure.

  5. Study on objective functions for the slow shot phase in high-pressure die casting

    NASA Astrophysics Data System (ADS)

    Frings, Markus; Behr, Marek; Elgeti, Stefanie

    2016-10-01

    High-pressure die casting is an important process in the field of aluminum processing. Especially during the slow shot phase, the process parameters immensely influence the cast part quality. At the current state of the art, the appropriate process parameters are identified based on running-in trials and significant experience. To translate this experience into a mathematical framework is the aim of this work. The idea is to shift the running-in trials to the computer—now in the form of a numerical optimization. In view of the optimization, this paper presents a selection of objective functions. These are assessed with the respect to (1) their suitability as an overall quality measure of the casting process and (2) the extent to which they reflect the goals of the casting process.

  6. Persistence of Jahn Teller distortion in high pressure metallic phase of LaMnO3

    SciTech Connect

    Baldini, Maria; Struzhkin, Viktor V.; Goncharov, Alexander F.; Postorino, P.; Mao, Wendy L.

    2011-02-11

    High pressure, low temperature Raman measurements performed on LaMnO{sub 3} up to 34 GPa provide the first experimental evidence for the persistence of the Jahn-Teller distortion over the entire stability range of the insulating phase. This result resolves the ongoing debate about the nature of the pressure driven insulator to metal transition (IMT), demonstrating that LaMnO{sub 3} is not a classical Mott insulator. The formation of domains of distorted and regular octahedra, observed from 3 to 34 GPa, sheds new light on the mechanism behind the IMT suggesting that LaMnO{sub 3} becomes metallic when the fraction of undistorted octahedra domains increases beyond a critical threshold.

  7. High pressure induced phase transition and superdiffusion in anomalous fluid confined in flexible nanopores

    SciTech Connect

    Bordin, José Rafael; Krott, Leandro B. Barbosa, Marcia C.

    2014-10-14

    The behavior of a confined spherical symmetric anomalous fluid under high external pressure was studied with Molecular Dynamics simulations. The fluid is modeled by a core-softened potential with two characteristic length scales, which in bulk reproduces the dynamical, thermodynamical, and structural anomalous behavior observed for water and other anomalous fluids. Our findings show that this system has a superdiffusion regime for sufficient high pressure and low temperature. As well, our results indicate that this superdiffusive regime is strongly related with the fluid structural properties and the superdiffusion to diffusion transition is a first order phase transition. We show how the simulation time and statistics are important to obtain the correct dynamical behavior of the confined fluid. Our results are discussed on the basis of the two length scales.

  8. Melting and Phase Relations in the FeO-FeS System at High Pressure

    NASA Astrophysics Data System (ADS)

    Campbell, A. J.; Reaman, D. M.; Fischer, R. A.; Chidester, B.; Myers, G.; Heinz, D. L.; Prakapenka, V.

    2013-12-01

    Terrestrial planetary cores, like that of the Earth, are composed of iron alloys with light elements such as O, S, Si, and/or C, and therefore the phase relations of these iron-rich systems are essential to understanding the structure, composition, and evolution of planetary cores. Binary Fe-X phase diagrams are largely established up to approximately Earth's core-mantle boundary pressures at least, but the relevant ternary and higher order phase equilibria are less well understood. Here we present phase relations, including melting, on the FeO-FeS join to better constrain the Fe-FeO-FeS system that may be important to planetary cores, including Earth's. We performed synchrotron X-ray diffraction experiments to monitor the phases present in FeO:FeS mixtures up to 60 GPa and >2500 K. A basic result is that FeO and FeS do coexist at high pressures and temperatures, with no evidence of a new phase forming between the two. At pressures near 46 GPa the eutectic composition lies on the FeS-rich side of this binary, as indicated by the loss of FeS diffraction and persistence of FeO diffraction in a 1:1 FeO:FeS mixture. Melting in the FeO-FeS binary at high pressures occurs at temperatures within ~100-200 K of the FeS melting curve [1]. Building upon earlier work on the structural (e.g., [1,2]) and binary melting (e.g., [3,4]) behavior in the Fe-FeS and Fe-FeO systems, these results help define the ternary Fe-FeO-FeS system under P,T conditions relevant to terrestrial planetary cores. In particular, the P,T conditions of the Martian core are covered by this study, and the FeO-FeS system may be especially relevant there because of its high mantle FeO content and its low core density, suggesting a relatively high sulfur content. [1] Reaman et al., AGU Fall Meeting 2012. [2] Fischer et al., Geophys. Res. Lett. 38, L24301, 2011. [3] Campbell et al., Phys. Earth Planet. Int. 162, 119-128, 2007. [4] Seagle et al., Earth Planet. Sci. Lett. 265, 655-665, 2008.

  9. High-pressure phases of group-II difluorides: Polymorphism and superionicity

    NASA Astrophysics Data System (ADS)

    Nelson, Joseph R.; Needs, Richard J.; Pickard, Chris J.

    2017-02-01

    We investigate the high-pressure behavior of beryllium, magnesium, and calcium difluorides using ab initio random structure searching and density functional theory (DFT) calculations, over the pressure range 0 -70 GPa. Beryllium fluoride exhibits extensive polymorphism at low pressures, and we find two new phases for this compound—the silica moganite and CaCl2 structures—which are stable over the wide pressure range 12 -57 GPa. For magnesium fluoride, our searching results show that the orthorhombic "O-I" TiO2 structure (P b c a ,Z =8 ) is stable for this compound between 40 and 44 GPa. Our searches find no new phases at the static-lattice level for calcium difluoride between 0 and 70 GPa; however, a phase with P 6 ¯2 m symmetry is close to stability over this pressure range, and our calculations predict that this phase is stabilized at high temperature. The P 6 ¯2 m structure exhibits an unstable phonon mode at large volumes which may signal a transition to a superionic state at high temperatures. The group-II difluorides are isoelectronic to a number of other AB2-type compounds such as SiO2 and TiO2, and we discuss our results in light of these similarities.

  10. Chromatographic behaviour of synthetic high pressure high temperature diamond in aqueous normal phase chromatography.

    PubMed

    Peristyy, Anton; Paull, Brett; Nesterenko, Pavel N

    2016-10-28

    The chromatographic properties of high pressure high temperature synthesised diamond (HPHT) are investigated under the conditions of hydrophilic interaction liquid chromatography (HILIC). A 50×4.6mm ID stainless steel column packed with HPHT particles of mean diameter 1.6μm and specific surface area 5.1m(2)g(-1) is used. According to the results of acid-base titration with NaOH the purified HPHT batch contains 4.59μeqg(-1) of protogenic, mainly carboxyl- and hydroxyl-, groups, which make this polar adsorbent suitable for use as a stationary phase in HILIC. The retention behaviour of several classes of polar compounds including benzoic and benzenesulfonic acids, nitro- and chlorophenols, various organic bases, and quaternary ammonium compounds are studied using acetonitrile and methanol based mobile phases containing 5-30v/v% of water. The effects of the buffer pH and concentration, column temperature and organic solvent content on retention of model compounds are also investigated. It is shown that both pH and acetonitrile/methanol ratio in the mobile phase can be used to vary the separation selectivity. Molecular adsorption mechanism (related to aqueous normal phase mode), rather than partitioning is established to be responsible for the retention.

  11. Superconductivity in metastable phases of phosphorus-hydride compounds under high pressure

    NASA Astrophysics Data System (ADS)

    Flores-Livas, José A.; Amsler, Maximilian; Heil, Christoph; Sanna, Antonio; Boeri, Lilia; Profeta, Gianni; Wolverton, Chris; Goedecker, Stefan; Gross, E. K. U.

    2016-01-01

    Hydrogen-rich compounds have been extensively studied both theoretically and experimentally in the quest for novel high-temperature superconductors. Reports on sulfur hydride attaining metallicity under pressure and exhibiting superconductivity at temperatures as high as 200 K have spurred an intense search for room-temperature superconductors in hydride materials. Recently, compressed phosphine was reported to metallize at pressures above 45 GPa, reaching a superconducting transition temperature (TC) of 100 K at 200 GPa. However, neither the exact composition nor the crystal structure of the superconducting phase have been conclusively determined. In this work, the phase diagram of PHn (n =1 ,2 ,3 ,4 ,5 ,6 ) was extensively explored by means of ab initio crystal structure predictions using the minima hopping method (MHM). The results do not support the existence of thermodynamically stable PHn compounds, which exhibit a tendency for elemental decomposition at high pressure even when vibrational contributions to the free energies are taken into account. Although the lowest energy phases of PH1 ,2 ,3 display TC's comparable to experiments, it remains uncertain if the measured values of TC can be fully attributed to a phase-pure compound of PHn.

  12. An ab initio molecular dynamics study of iron phases at high pressure and temperature

    NASA Astrophysics Data System (ADS)

    Belonoshko, A. B.; Arapan, S.; Rosengren, A.

    2011-12-01

    The crystal structure of iron, the major component of the Earth’s inner core (IC), is unknown for the IC high pressure (P; 3.3-3.6 Mbar) and temperature (T; 5000-7000 K). There is mounting evidence that the hexagonal close-packed (hcp) phase of iron, stable at the high P of the IC and a low T, might be unstable under the IC conditions due to the impact of high T and impurities. Experiments at the IC P and T are difficult and do not provide a conclusive answer as regards the iron stability at the pressure of the IC and temperatures close to the iron melting curve. Recent theory provides contradictory results regarding the nature of the stable Fe phase. We investigated the possibility of body-centered cubic (bcc) phase stabilization at the P and T in the vicinity of the Fe melting curve by using ab initio molecular dynamics. Thermodynamic calculations, relying on the model of uncorrelated harmonic oscillators, provide nearly identical free energies within the error bars of our calculations. However, direct simulation of iron crystallization demonstrates that liquid iron freezes in the bcc structure at the P of the IC and T = 6000 K. All attempts to grow the hcp phase from the liquid failed. The mechanism of bcc stabilization is explained. This resolves most of the earlier confusion.

  13. Atomic ordering in cubic bismuth telluride alloy phases at high pressure

    NASA Astrophysics Data System (ADS)

    Loa, I.; Bos, J.-W. G.; Downie, R. A.; Syassen, K.

    2016-06-01

    Pressure-induced transitions from ordered intermetallic phases to substitutional alloys to semi-ordered phases were studied in a series of bismuth tellurides. By using angle-dispersive x-ray diffraction, the compounds Bi4Te5 , BiTe, and Bi2Te were observed to form alloys with the disordered body-centered cubic (bcc) crystal structure upon compression to above 14-19 GPa at room temperature. The BiTe and Bi2Te alloys and the previously discovered high-pressure alloys of Bi2Te3 and Bi4Te3 were all found to show atomic ordering after gentle annealing at very moderate temperatures of ˜100 ∘C . Upon annealing, BiTe transforms from bcc to the B2 (CsCl) crystal-structure type, and the other phases adopt semi-disordered variants thereof, featuring substitutional disorder on one of the two crystallographic sites. The transition pressures and atomic volumes of the alloy phases show systematic variations across the BimTen series including the end members Bi and Te. First-principles calculations were performed to characterize the electronic structure and chemical bonding properties of B2-type BiTe and to identify the driving forces of the ordering transition. The calculated Fermi surface of B2-type BiTe has an intricate structure and is predicted to undergo three topological changes between 20 and 60 GPa.

  14. Inelastic neutron scattering, lattice dynamics, and high-pressure phase stability of zircon-structured lanthanide orthophosphates

    SciTech Connect

    Bose, Preyoshi P.; Mittal, R; Chaplot, S L; Loong, C. K.; Boatner, Lynn A

    2010-01-01

    Inelastic neutron-scattering experiments and lattice-dynamical calculations are reported on a series of rareearth orthophosphates RPO4 R=Tm, Er, Ho, and Tb. The experimental phonon spectra for the compounds are in good agreement with our model calculations. The lattice-dynamical model is found useful for the calculation of various thermodynamic properties such as the lattice specific heat, thermal expansion, and equation of state of these compounds. The RPO4 compounds are known to transform to the scheelite body-centered tetragonal, I41 /a or monoclinic phase P21 /n at high pressures. Our calculations show that while the scheelite phase stabilizes at high pressure due to its lower volume, the monoclinic phase may occur as an intermediate phase depending on the ionic size of the R atom. The latter phase is stabilized at higher temperature at high pressure due to its high vibrational entropy. A pressure-temperature phase diagram is proposed.

  15. The high-pressure phase of lawsonite: A single crystal study of a key mantle hydrous phase

    NASA Astrophysics Data System (ADS)

    O'Bannon, Earl; Beavers, Christine M.; Kunz, Martin; Williams, Quentin

    2017-08-01

    Lawsonite CaAl2Si2O7(OH)2·H2O is an important water carrier in subducting oceanic crusts and the primary hydrous phase in basalt at depths greater than 80 km. We have conducted high-pressure synchrotron single-crystal X-ray diffraction experiments on natural lawsonite at room temperature up to 10.0 GPa to study its high-pressure polymorphism. We find that lawsonite remains orthorhombic with Cmcm symmetry up to 9.3 GPa and shows nearly isotropic compression. Above 9.3 GPa, lawsonite becomes monoclinic with P21/m symmetry. Across the phase transition, the Ca polyhedron becomes markedly distorted, and the average positions of the H2O molecules and hydroxyls change. The changes observed in the H-atom positions under compression are different than the low-temperature changes in this material. We resolve for the first time the H-bonding configuration of the high-pressure monoclinic phase of lawsonite. A bond valence approach is deployed to determine that the phase transition from orthorhombic to monoclinic is primarily driven by the Si2O7 groups, and in particular their bridging oxygen atoms (O1). The changes in the structure strongly indicate that entropy increases across the symmetry-lowering transition and hence that the slope of the phase transition is negative. Monoclinic lawsonite is thus stable under the pressure and temperature conditions that exist in the Earth and is likely to be a major water carrier in colder, deep subducted slabs. Monoclinic lawsonite also likely has enhanced electrical conductivity along its c axis due to its dynamically disordered hydrogen atoms.

  16. Phase transformations in a Cu−Cr alloy induced by high pressure torsion

    SciTech Connect

    Korneva, Anna; Straumal, Boris; Kilmametov, Askar; Chulist, Robert; Straumal, Piotr; Zięba, Paweł

    2016-04-15

    Phase transformations induced by high pressure torsion (HPT) at room temperature in two samples of the Cu-0.86 at.% Cr alloy, pre-annealed at 550 °C and 1000 °C, were studied in order to obtain two different initial states for the HPT procedure. Observation of microstructure of the samples before HPT revealed that the sample annealed at 550 °C contained two types of Cr precipitates in the Cu matrix: large particles (size about 500 nm) and small ones (size about 70 nm). The sample annealed at 1000 °C showed only a little fraction of Cr precipitates (size about 2 μm). The subsequent HPT process resulted in the partial dissolution of Cr precipitates in the first sample and dissolution of Cr precipitates with simultaneous decomposition of the supersaturated solid solution in another. However, the resulting microstructure of the samples after HPT was very similar from the standpoint of grain size, phase composition, texture analysis and hardness measurements. - Highlights: • Cu−Cr alloy with two different initial states was deformed by HPT. • Phase transformations in the deformed materials were studied. • SEM, TEM and X-ray diffraction techniques were used for microstructure analysis. • HPT leads to formation the same microstructure independent of the initial state.

  17. Phase transition of iron doped MgO under high pressure by first-principles study

    NASA Astrophysics Data System (ADS)

    Yang, K. S.; Li, S. L.; Zhang, J.; Zeng, Z.; Qin, X. Y.; Zhou, X. M.

    2015-07-01

    The (Mg, Fe)O solid solution is one of the major lower mantle minerals, and studying its properties and structures under high pressure is a fundamental step toward understanding Earth's deep interior. Here within the framework of density functional theory, we first discuss the relationship between the total energy and iron doped positions of (Mg, Fe)O, and find that the doped iron favors to be dispersive. Then the pressure-induced phase transitions of (Mg, Fe)O from NaCl-type (B1) to CsCl-type (B2) are probed. It is found that the phase transition pressure of (Mg, Fe)O decreases with damped oscillation, as the increase of iron concentration. This phenomenon is essentially determined by the iron concentration as well as iron doped positions. The electronic structures of MgO and (Mg0.75Fe0.25)O at 436 GPa are calculated, and the results show that the doped irons play a crucial role in the metallicity of (Mg0.75Fe0.25)O. Our results are in agreement with the experimental counterparts. This study would provide some useful information for understanding the behavior of pressure-induced phase transition and geoscience.

  18. Phase transition of iron doped MgO under high pressure by first-principles study

    NASA Astrophysics Data System (ADS)

    Yang, K. S.; Li, S. L.; Zhang, J.; Zeng, Z.; Qin, X. Y.; Zhou, X. M.

    2014-07-01

    The (Mg, Fe)O solid solution is one of the major lower mantle minerals, and studying its properties and structures under high pressure is a fundamental step toward understanding Earth's deep interior. Here within the framework of density functional theory, we first discuss the relationship between the total energy and iron doped positions of (Mg, Fe)O, and find that the doped iron favors to be dispersive. Then the pressure-induced phase transitions of (Mg, Fe)O from NaCl-type (B1) to CsCl-type (B2) are probed. It is found that the phase transition pressure of (Mg, Fe)O decreases with damped oscillation, as the increase of iron concentration. This phenomenon is essentially determined by the iron concentration as well as iron doped positions. The electronic structures of MgO and (Mg0.75Fe0.25)O at 436 GPa are calculated, and the results show that the doped irons play a crucial role in the metallicity of (Mg0.75Fe0.25)O. Our results are in agreement with the experimental counterparts. This study would provide some useful information for understanding the behavior of pressure-induced phase transition and geoscience.

  19. Serpentines, talc, chlorites, and their high-pressure phase transitions: a Raman spectroscopic study

    NASA Astrophysics Data System (ADS)

    Reynard, Bruno; Bezacier, Lucile; Caracas, Razvan

    2015-09-01

    Raman spectra of magnesian phyllosilicates belonging to the serpentine, talc, and chlorite groups have been obtained at ambient conditions, and at high pressures and up to 200 °C in order to study high-pressure transformations in the 10 GPa range. The complex and distinct Raman spectra of these minerals allow straightforward identification, which may otherwise be difficult from optical microscopy. High-pressure measurements are in good agreement with DFT calculations for talc and lizardite. Pressure-induced displacive modifications are identified in lizardite and antigorite serpentines, and in chlorite at ~4, 7 and 8 GPa, respectively, while talc shows no transition up to ~11 GPa. At high temperature, the high-pressure distortions of serpentines shift to higher pressures. Given the stability limits of these minerals, and the natural range of P-T conditions, none of the high-pressure distortions observed at high pressure are likely to occur at depth in the Earth.

  20. Kinematics and thermodynamics of a growing rim of high-pressure phase

    NASA Astrophysics Data System (ADS)

    Morris, S. J. S.

    2014-03-01

    We have reanalysed the problem of growth of a dense product rim on a sphere of parent phase. To decouple the problem of calculating deformation from rheology, we assume spherical symmetry, and incompressible phases. Within the product, the radial deviatoric strain and its time-derivative prove to be of opposite sign: strain is compressive, but the strain rate is tensile. Further, the radial deviatoric strain in the new product adjacent to the interface is invariant in time. Propagation of the phase interface is determined by a competition between two mechanisms: as an element of material is transformed, its shear strain energy is increased; and the core pressure performs work compressing it. For elastic phases, this competition results in metastability. Within a certain pressure range, either phase can occur alone, but the two phases can not coexist. Because this result is inconsistent with experiments by Kawazoe et al. (2010) in which a rim of high-pressure phase (wadsleyite) coexists with a central core of low-pressure phase (olivine), we then incorporate plastic flow. Assuming perfect plasticity, we show that for a given applied pressure exceeding the coexistence pressure, a rim of product can now nucleate if the excess pressure Δp exceeds a critical value depending on yield stress. Increasing Δp above this value allows product to grow into the parent phase. There are now two possibilities, depending on the value of Δp. Growth may eventually cease to produce a state in which the product rim is in equilibrium with a parent core; or growth may follow a more complicated path: within a range of excess pressures, the growth rate can decrease strongly from its initial value to produce a quasi-equilibrium state, before increasing again to a rate similar to that at which transformation began. We interpret these results to mean that if Δp is increased slowly in a series of experiments with constant yield stress, the sample passes through a series of equilibria until

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

    PubMed

    Faria, Luiz F O; Ribeiro, Mauro C C

    2015-11-05

    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 .

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

    SciTech Connect

    Li, Chunyu E-mail: yanhao@hpstar.ac.cn; Ke, Feng; Yu, Zhenhai; Chen, Zhiqiang; Yan, Hao E-mail: yanhao@hpstar.ac.cn; Hu, Qingyang; Zhao, Jinggeng

    2016-04-07

    Here, we report comprehensive studies on the high-pressure structural and electrical transport properties of the layered transition metal chalcogenide (Cr{sub 2}S{sub 3}) up to 36.3 GPa. A structural phase transition was observed in the rhombohedral Cr{sub 2}S{sub 3} 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 Cr{sub 2}S{sub 3} based applications under extreme conditions.

  3. Incommensurate atomic density waves in the high-pressure IVb phase of barium.

    PubMed

    Arakcheeva, Alla; Bykov, Maxim; Bykova, Elena; Dubrovinsky, Leonid; Pattison, Phil; Dmitriev, Vladimir; Chapuis, Gervais

    2017-03-01

    The host-guest structures of elements at high pressure discovered a decade ago still leave many open questions due to the lack of precise models based on full exploitation of the diffraction data. This concerns in particular Ba IV, which is stable in the range 12-45 GPa. With the example of phase Ba IVb, which is characterized here for the first time, a systematic analysis is presented of possible host-guest structure models based on high-quality single-crystal diffraction data obtained with synchrotron radiation at six different pressures between 16.5 and 19.6 GPa. It is shown that a new incommensurately modulated (IM) structure model better fits the experimental data. Unlike the composite models which are commonly reported for the Ba IV phases, the IM model reveals a density wave and its pressure-dependent evolution. The crucial role played by the selected model in the interpretation of structure evolution under pressure is discussed. The findings give a new experimental basis for a better understanding of the nature of host-guest structures.

  4. Structures of the metallic and superconducting high pressure phases of solid CS2

    PubMed Central

    Zarifi, Niloofar; Liu, Hanyu; Tse, John S.

    2015-01-01

    First principles structural prediction and molecular dynamics (MD) calculations have been performed to examine the structures responsible for the recently reported metallic and superconducting phases of highly compressed CS2. The low pressure experimental molecular crystal structure was found to be metastable and transformed into a disordered structure above 10 GPa. At 60 GPa, the predicted low energy structures show molecular CS2 is separated into C and S dominant regions. A crystalline structure with the P21/m symmetry was found to be most stable from 60 to 120 GPa. The structure is formed from alternate layers of hexagonal C rings and S 2D-square-nets linked by C-S bonds. A non-crystalline structure with similar features structure is also predicted by MD calculations. Electron-phonon coupling calculations show this crystalline phase is superconductive. Contrary to the suggestions made from the experiments, no magnetism was found in all predicted low enthalpy high pressure structures. Moreover, the theoretical results do not support the proposal on the existence of hypervalent 6-coordinated carbon at 120 GPa. PMID:25982346

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

    SciTech Connect

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

    2016-04-07

    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.

  6. Incommensurate atomic density waves in the high-pressure IVb phase of barium

    PubMed Central

    Arakcheeva, Alla; Bykov, Maxim; Bykova, Elena; Dubrovinsky, Leonid; Pattison, Phil; Dmitriev, Vladimir; Chapuis, Gervais

    2017-01-01

    The host–guest structures of elements at high pressure discovered a decade ago still leave many open questions due to the lack of precise models based on full exploitation of the diffraction data. This concerns in particular Ba IV, which is stable in the range 12–45 GPa. With the example of phase Ba IVb, which is characterized here for the first time, a systematic analysis is presented of possible host–guest structure models based on high-quality single-crystal diffraction data obtained with synchrotron radiation at six different pressures between 16.5 and 19.6 GPa. It is shown that a new incommensurately modulated (IM) structure model better fits the experimental data. Unlike the composite models which are commonly reported for the Ba IV phases, the IM model reveals a density wave and its pressure-dependent evolution. The crucial role played by the selected model in the interpretation of structure evolution under pressure is discussed. The findings give a new experimental basis for a better understanding of the nature of host–guest structures. PMID:28250954

  7. Structures of the metallic and superconducting high pressure phases of solid CS2.

    PubMed

    Zarifi, Niloofar; Liu, Hanyu; Tse, John S

    2015-05-18

    First principles structural prediction and molecular dynamics (MD) calculations have been performed to examine the structures responsible for the recently reported metallic and superconducting phases of highly compressed CS2. The low pressure experimental molecular crystal structure was found to be metastable and transformed into a disordered structure above 10 GPa. At 60 GPa, the predicted low energy structures show molecular CS2 is separated into C and S dominant regions. A crystalline structure with the P21/m symmetry was found to be most stable from 60 to 120 GPa. The structure is formed from alternate layers of hexagonal C rings and S 2D-square-nets linked by C-S bonds. A non-crystalline structure with similar features structure is also predicted by MD calculations. Electron-phonon coupling calculations show this crystalline phase is superconductive. Contrary to the suggestions made from the experiments, no magnetism was found in all predicted low enthalpy high pressure structures. Moreover, the theoretical results do not support the proposal on the existence of hypervalent 6-coordinated carbon at 120 GPa.

  8. Titanium-scaffolded organic-monolithic stationary phases for ultra-high-pressure liquid chromatography.

    PubMed

    Vonk, Rudy J; Vaast, Axel; Eeltink, Sebastiaan; Schoenmakers, Peter J

    2014-09-12

    Organic-polymer monoliths with overall dimensions larger than one millimetre are prone to rupture - either within the monolith itself or between the monoliths and the containing wall - due to the inevitable shrinkage accompanying the formation of a cross-linked polymeric network. This problem has been addressed by creating titanium-scaffolded poly(styrene-co-divinylbenzene) (S-co-DVB) monoliths. Titanium-scaffolded monoliths were successfully used in liquid chromatography at very high pressures (up to 80MPa) and using gradients spanning the full range of water-acetonitrile compositions (0 to 100%). The kinetic-performance of (50-mm long) titanium-scaffolded monoliths was compared to that of similar monolith created in 1-mm i.d. glass-lined tubing at pressures up to 50MPa. The peak capacities obtained with the titanium-scaffolded column was about 30% lower. An increased Eddy-diffusion, due to the pillar-structure, and a decreased permeability are thought to be the main reasons for this reduced kinetic-performance. No decrease in performance was observed when the titanium-scaffolded columns were operated at pressures of 80MPa for up to 12h. The column-to-column repeatability (n=5) was acceptable in terms of observed peak widths at half heights (RSD ca. 10%) The run-to-run repeatability (n=135) in terms of retention times and peak widths at half height were found to be good. Titanium-scaffolded columns coupled in series up to a combined length of (200mm) were used for the analyses of a complex Escherichia coli protein sample. Our experiments demonstrate that columns based on titanium-scaffolded organic-polymer monolith can be operated under strenuous conditions without loss in performance. The titanium-scaffolded approach makes it feasible to create organic-polymer monoliths in wide-bore columns with accurate temperature control.

  9. Review of high pressure phases of calcium by first-principles calculations

    NASA Astrophysics Data System (ADS)

    Ishikawa, T.; Nagara, H.; Suzuki, N.; Tsuchiya, J.; Tsuchiya, T.

    2010-03-01

    We review high pressure phases of calcium which have obtained by recent experimental and first-principles studies. In this study, we investigated the face-centered cubic (fcc) structure, the body-centered cubic (bcc) structure, the simple cubic (sc) structure, a tetragonal P43212 [Ishikawa T et al. 2008 Phys. Rev. B 77 020101(R)], an orthorhombic Cmca [Ishikawa T et al. 2008 Phys. Rev. B 77 020101(R)], an orthorhombic Cmcm [Teweldeberhan A M and Bonev S A 2008 Phys. Rev. B 78 140101(R)], an orthorhombic Pnma [Yao Y et al. 2008 Phys. Rev. B 78 054506] and a tetragonal I4/mcm(00) [Arapan S et al. 2008 Proc. Natl. Acad. Sci. USA 105 20627]. We compared the enthalpies among the structures up to 200 GPa and theoretically determined the phase diagram of calcium. The sequence of the structural transitions is fcc (0- 3.5 GPa) → bcc (3.5 - 35.7 GPa) → Cmcm (35.7- 52GPa) → P43212 (52-109 GPa) → Cmca (109-117.4GPa) → Pnma (117.4-134.6GPa) → I4/mcm(00) (134.6 GPa -). The sc phase is experimentally observed in the pressure range from 32 to 113 GPa but, in our calculation, there is no pressure region where the sc phase is the most stable. In addition, we found that the enthalpy of the hexagonal close-packed (hcp) structure is lower than that of I4/mcm(00) above 495 GPa.

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

    PubMed

    Alnemrat, S; Hooper, J P; Vasiliev, I; Kiefer, B

    2014-01-29

    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 A(3)/atom, K0 = 177.72 GPa; hcp: V0 = 10.525 A(3)/atom, K0 = 295.16 GPa; and fcc: V0 = 10.682 A(3)/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.

  11. Investigation of high pressure phase transition and electronic properties of Lutetium Nitride

    NASA Astrophysics Data System (ADS)

    Singh, Sanjay Kumar; Verma, U. P.

    2015-09-01

    In the present manuscript we have investigated the structural, electronic and phase transition properties of the heaviest lanthanide lutetium nitride (LuN) compound using an ab initio calculations based on the density functional theory with Perdrew, Burke and Ernzerhof generalized gradient approximation (PBE-GGA) and Engel-Vosko(EV)-GGA as implemented in WIEN2k code. The basic ground state properties viz., lattice constants (a), bulk modulus (B0) and its pressure derivative (B0’) and total energy (E0) are calculated. The calculated values of lattice constant is 4.76 Å which is in good agreement with experimental value a= 4.76 A and other theoretical value. The relative stabilities of LuN at high pressures in the NaCl (B1), CsCl (B2), zinc blende (B3) and body centred tetragonal (BCT) structures are analysed. At compressed volumes, this compound is found to favour the CsCl phase rather the body centred tetragonal phase and zinc blende as observed in other lanthanum pnictides, which has been predicted by the total energy minimization. Under compression LuN undergoes a transition from NaCl to CsCl type structure at around 250.81 GPa with a volume collapse of 3.75%. To see the effect of functional we have also computed the band structure in B1 and B2 structure. Obtained result on band structure shows that LuN are semimetal by GGA while depicts semiconducting behaviour by EV-GGA. It shows metallic nature in B2 phase.

  12. A Novel High-Density Phase and Amorphization of Nitrogen-Rich 1H-Tetrazole (CH2N4) under High Pressure

    PubMed Central

    Li, Wenbo; Huang, Xiaoli; Bao, Kuo; Zhao, Zhonglong; Huang, Yanping; Wang, Lu; Wu, Gang; Zhou, Bo; Duan, Defang; Li, Fangfei; Zhou, Qiang; Liu, Bingbing; Cui, Tian

    2017-01-01

    The high-pressure behaviors of nitrogen-rich 1H-tetrazole (CH2N4) have been investigated by in situ synchrotron X-ray diffraction (XRD) and Raman scattering up to 75 GPa. A first crystalline-to-crystalline phase transition is observed and identified above ~3 GPa with a large volume collapse (∼18% at 4.4 GPa) from phase I to phase II. The new phase II forms a dimer-like structure, belonging to P1 space group. Then, a crystalline-to-amorphous phase transition takes place over a large pressure range of 13.8 to 50 GPa, which is accompanied by an interphase region approaching paracrystalline state. When decompression from 75 GPa to ambient conditions, the final product keeps an irreversible amorphous state. Our ultraviolet (UV) absorption spectrum suggests the final product exhibits an increase in molecular conjugation. PMID:28218236

  13. A Novel High-Density Phase and Amorphization of Nitrogen-Rich 1H-Tetrazole (CH2N4) under High Pressure

    NASA Astrophysics Data System (ADS)

    Li, Wenbo; Huang, Xiaoli; Bao, Kuo; Zhao, Zhonglong; Huang, Yanping; Wang, Lu; Wu, Gang; Zhou, Bo; Duan, Defang; Li, Fangfei; Zhou, Qiang; Liu, Bingbing; Cui, Tian

    2017-02-01

    The high-pressure behaviors of nitrogen-rich 1H-tetrazole (CH2N4) have been investigated by in situ synchrotron X-ray diffraction (XRD) and Raman scattering up to 75 GPa. A first crystalline-to-crystalline phase transition is observed and identified above ~3 GPa with a large volume collapse (∼18% at 4.4 GPa) from phase I to phase II. The new phase II forms a dimer-like structure, belonging to P1 space group. Then, a crystalline-to-amorphous phase transition takes place over a large pressure range of 13.8 to 50 GPa, which is accompanied by an interphase region approaching paracrystalline state. When decompression from 75 GPa to ambient conditions, the final product keeps an irreversible amorphous state. Our ultraviolet (UV) absorption spectrum suggests the final product exhibits an increase in molecular conjugation.

  14. The High-Pressure Monoclinic Lawsonite Phase: The Primary Carrier of Water from Subducted Crust to the Deep Mantle

    NASA Astrophysics Data System (ADS)

    O'Bannon, E. F., III; Williams, Q.; Beavers, C.

    2016-12-01

    Lawsonite (CaAl2Si2O7(OH)2.H2O) is the primary subduction zone mineral that carries water within subducted oceanic crust to depths of greater than 80 km. The structure of lawsonite has been extensively studied under room temperature, high-pressure conditions using spectroscopic and X-ray diffraction techniques, as well as under room pressure and varying temperature conditions. Simultaneous high-pressure and temperature measurements on lawsonite to pressures and temperatures approaching its maximum stability are limited to a few multianvil synchrotron based powder diffraction studies. The initially orthorhombic lawsonite has been observed to undergo a phase transition near 9 GPa; however, the high-pressure monoclinic structure of lawsonite has only been reported from non-hydrostatic powder diffraction experiments. We conducted simultaneous high pressure and temperature single-crystal synchrotron based x-ray diffraction experiments on natural lawsonite under hydrostatic conditions. At room pressure and temperature, lawsonite crystallizes with Cmcm symmetry. We solved the structure of the high-pressure phase of lawsonite at 9.7 GPa as monoclinic with P21/m symmetry. The volume change from the low-pressure phase is negligible. Our simultaneous high-pressure and temperature measurements indicate that the orthorhombic to monoclinic transition occurs at nearly 1 GPa lower pressure when heated to temperatures of only 120 0C. There is no evidence of dehydration under these conditions, and the H2O molecule does not change its orientation across this transition. From our single-crystal data, the OH groups in lawsonite may become disordered across this high-pressure transition. The Si and Al sites do not become more distorted under compression or through the phase transition, but the Ca site shows a dramatic increase in its distortion across the high-pressure transition. Our results suggest that the bound water molecule in the high-pressure form of lawsonite is largely

  15. Elastic Softening of Peridotite Due to the Presence of Melt Phases at High Pressure

    SciTech Connect

    Li, L.; Wang, L; Vaughan, M

    2008-01-01

    Here we report an observation of softening of Young's modulus of a sample of KLB-1 peridotite as a metallic Ni melt intruded into it at 2.5 GPa and about 1500 C. A uniaxial oscillation of stress was applied to the sample with frequency of 0.01-0.02 Hz and an amplitude up to 500 MPa. The Young's modulus is measured as the amplitude ratio between the sample and a reference material, while the attenuation is determined by the phase angle delays. The Ni intrusion was captured by in situ X-ray radiography. A planar intrusion occurred gradually, but advanced only during the extension; eventually, the Ni melt dissected the sample on a plane normal to the extension axis. Accompanied softening of Young's modulus was observed after the Ni intrusion was completed. This study suggests that percolation of a liquid metallic phase is possible within a partially melted mantle rock in the presence of a differential stress field.

  16. The high-pressure stability of zoisite and phase relationships of zoisite-bearing assemblages

    NASA Astrophysics Data System (ADS)

    Poli, S.; Schmidt, M. W.

    The fluid-absent reaction 12 zoisite=3 lawsonite+7 grossular+8 kyanite+1 coesite was experimentally reversed in the model system CaO-Al2O3-SiO2-H2O (CASH) using a multi-anvil apparatus. The upper pressure stability limit for zoisite was found to extend to 5.0GPa at 700°C and to 6.6GPa at 950°C. Additional experiments both in the H2O-SiO2-saturated and in the H2O-Al2O3-saturated portions of CASH provide further constraints on high pressure phase relationships of lawsonite, zoisite, grossular, kyanite, coesite, and an aqueous fluid. Consistency of the present experiments with the H2O-saturated breakdown of lawsonite is demonstrated by thermodynamic analysis using linear programming techniques. Two sets of data consistent with databases of Berman (1988) and Holland and Powell (1990) were retrieved combining experimental phase relationships, calorimetric constraints, and recently measured elastic properties of solid phases. The best fits result in Gf,1,298∘,zoisite=-6,499,400 J and S1,298∘,zoisite=302 J/K, and Gf,1,298∘,lawsonite=-4,514,600 J and S1,298∘,lawsonite=220 J/K for the dataset of Holland and Powell, and Gf,1,298∘,zoisite=-6,492,120 J and S1,298∘,zoisite=304 J/K, and Gf,1,298∘,lawsonite=-4,513,000 J and S1,298∘,lawsonite= 218 J/K for the dataset of Berman. Examples of the usage of zoisite as a geohygrometer and as a geobarometer in rocks metamorphosed at eclogite facies conditions are worked, profiting from the thermodynamic properties retrieved here.

  17. In Situ Determination of the NiAs Phase of FeO at High Pressure and Temperature.

    PubMed

    Fei, Y; Mao, H K

    1994-12-09

    In situ synchrotron x-ray diffraction measurements of FeO at high pressures and high temperatures revealed that the high-pressure phase of FeO has the NiAs structure (B8). The lattice parameters of this NiAs phase at 96 gigapascals and 800 kelvin are a = 2.574(2) angstroms and c = 5.172(4) angstroms (the number in parentheses is the error in the last digit). Metallic behavior of the high-pressure phase is consistent with a covalently and metallically bonded NiAs structure of FeO. Transition to the NiAs structure of FeO would enhance oxygen solubility in molten iron. This transition thus provides a physiochemical basis for the incorporation of oxygen into the Earth's core.

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

    NASA Astrophysics Data System (ADS)

    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.

  19. High pressure phase equilibrium in the system Fe-Mg-Si-O

    SciTech Connect

    Saxena, S.K.; Fei, Y.

    1985-01-01

    Recent experimental data on high pressure synthesis of minerals in the Fe-Mg-Si-O system permit the establishment of a thermochemical-thermophysical data set with which phase equilibrium for the earth's mantle can be computed. The results indicate that low pressure (<200 Kbar) silicates (Mg-Fe) spinel and stishovite react to form (Mg-Fe) perovskite and (Mg-Fe) wuestite starting at a pressure close to 200 Kbar. The iron content of perovskite increases with depth a corresponding iron depletion in wuestite. Between 1000 and 1100 Kbar, both minerals begin to lose iron rapidly with pressure. Metal Fe with almost pure Mg-perovskite, MgO and oxygen becomes stable above 1200 Kbar, which pressure corresponds closely to the core-mantle boundary. This is a general feature over a range of temperatures and compositions. Conclusions are a) the present state of the earth is a consequence of thermochemical equilibrium which could have established over a range of post-accretionary temperatures, and b) the oxygen released in the equilibrium reaction could be available as a light element in the core. These results have a very important influence on trace element geochemical models of the mantle and therefore, on models of petrogenetic evolution of the earth.

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

    NASA Astrophysics Data System (ADS)

    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.

  1. Extraction of Lipids from Chlorella saccharophila Using High-Pressure Homogenization Followed by Three Phase Partitioning.

    PubMed

    Mulchandani, Ketan; Kar, Jayaranjan R; Singhal, Rekha S

    2015-07-01

    Commercial exploitation of microalgae for biofuel and food ingredients is hindered due to laborious extraction protocols and use of hazardous chemicals. Production of lipids in the microalga grown in modified BG11 medium was evaluated to arrive at the appropriate harvesting conditions. The use of three phase partitioning (TPP) as a green approach for extraction of lipids from Chlorella saccharophila was investigated. Cells disrupted by probe sonication were used for separation of lipids by TPP. The TPP-optimized conditions of 30 % ammonium sulfate, using slurry/t-butanol of 1:0.75 for 60 min at 25 to 35 °C, showed a lipid recovery of 69.05 ± 3.12 % (w/w) as against 100 % (w/w) by using chloroform-methanol extraction. Subsequently, parameters of high-pressure homogenization for cell disruption were optimized for maximum recovery of lipids by TPP. A final recovery of 89.91 ± 3.69 % (w/w) lipids was obtained along with ∼1.26 % w/w carotenoids of dry biomass in the t-butanol layer and protein content of ∼12 % w/w of dry biomass in the middle protein layer due to ammonium sulfate precipitation, after performing TPP under the optimized conditions.

  2. Electron band structure of the high pressure cubic phase of AlH3

    NASA Astrophysics Data System (ADS)

    Shi, Hongliang; Zarifi, Niliffar; Yim, Wai-Leung; Tse, J. S.

    2012-07-01

    The electronic band structure of the cubic Pm3n phase of AlH3 stable above 100 GPa is examined with semi-local, Tran-Blaha modified Becke-Johnson local density approximation (TB-mBJLDA), screened hybrid density functionals and GW methods. The shift of the conduction band to higher energy with increasing pressure is predicted by all methods. However, there are significant differences in detail band structure. In the pressure range from 90 to160 GPa, semi-local, hybrid functional and TB-mBJLDA calculations predicted that AlH3 is a poor metal. In comparison, GW calculations show a gap opening at 160 GPa and AlH3 becomes a small gap semi-conductor. From the trends of the calculated band shifts, it can be concluded that the favourable conditions leading to the nesting of Fermi surfaces predicted by semi-local calculation have disappeared if the exchange term is included. The results highlight the importance of the correction to the exchange energy on the band structure of hydrogen dominant dense metal hydrides at high pressure hydrides and may help to rationalize the absence of superconductivity in AlH3 from experimental measurements.

  3. High-pressure displacive phase transition of a natural Mg-rich pigeonite

    NASA Astrophysics Data System (ADS)

    Alvaro, Matteo; Nestola, Fabrizio; Cámara, Fernando; Domeneghetti, M. Chiara; Tazzoli, Vittorio

    2011-05-01

    A high-pressure single-crystal X-ray diffraction study has been carried out on a P21/ c natural Mg-rich pigeonite sample with composition ca. Wo6En76Fs18 using a diamond anvil-cell. The unit-cell parameters were determined at 14 different pressures to 7.14 GPa. The sudden disappearance of the b-type reflections ( h + k = odd) and a strong discontinuity (about 2.8%) in the unit-cell volume indicated a first-order P21/ c- C2/ c phase transition between 4.66 and 4.88 GPa. The P( V) data of the P21/ c phase were fitted to 4.66 GPa by a third-order Birch-Murnaghan equation of state (BM3 EoS), whereas the limited number of experimental data collected within the C2/ c phase between 4.88 and 7.14 GPa were fitted using the same equation of state but with K' constrained to the value obtained for the P21/ c fitting. The equation of state coefficients are V 0 = 424.66(6) Å3, K T0 = 104(2) GPa and K' = 8(1) for the P21/ c phase, and V 0 = 423.6(1) Å3, K T0 = 112.4(8) GPa, and K' fixed to 8(1) for the C2/ c phase. The axial moduli for a, b, and c for the P21/ c phase were obtained using also a BM3-EoS, while for the C2/ c phase only a linear calculation could be performed, and therefore the same approach was applied for comparison also to the P21/ c phase. In general the C2/ c phase exhibits axial compressibilities ( β c > β a >> β b) lower than those of the P21/ c phase ( β b > β c ≈ β a; similar to those found in previous studies in clinopyroxenes and orthopyroxenes). The lower compressibility of the C2/ c phase compared with that of the P21/ c could be ascribed to the greater stiffness along the b direction. A previously published relationship between P c and M2 average cation radius (i.r.) has been updated using all the literature data on P21/ c clinopyroxene containing large cations at M2 site and our new data. The following weighted regression was obtained: P c (GPa) = 26(4) - 28(5) × i.r (Å), R 2 = 0.97. This improved equation can be used to predict the

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

    SciTech Connect

    Xiong, Lun Liu, Jing; Bai, Ligang; Li, Xiaodong; Lin, Chuanlong; Lin, Jung-Fu

    2014-12-28

    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 K{sub 0} = 36(1) GPa with its pressure derivate K{sub 0}′ = 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 K{sub 0}′ fixed at 4, the derived K{sub 0} 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.

  5. High-pressure phase transition of alkali metal-transition metal deuteride Li2PdD2

    NASA Astrophysics Data System (ADS)

    Yao, Yansun; Stavrou, Elissaios; Goncharov, Alexander F.; Majumdar, Arnab; Wang, Hui; Prakapenka, Vitali B.; Epshteyn, Albert; Purdy, Andrew P.

    2017-06-01

    A combined theoretical and experimental study of lithium palladium deuteride (Li2PdD2) subjected to pressures up to 50 GPa reveals one structural phase transition near 10 GPa, detected by synchrotron powder x-ray diffraction, and metadynamics simulations. The ambient-pressure tetragonal phase of Li2PdD2 transforms into a monoclinic C2/m phase that is distinct from all known structures of alkali metal-transition metal hydrides/deuterides. The structure of the high-pressure phase was characterized using ab initio computational techniques and from refinement of the powder x-ray diffraction data. In the high-pressure phase, the PdD2 complexes lose molecular integrity and are fused to extended [PdD2]∞ chains. The discovered phase transition and new structure are relevant to the possible hydrogen storage application of Li2PdD2 and alkali metal-transition metal hydrides in general.

  6. High-pressure phase transition of alkali metal-transition metal deuteride Li2PdD2.

    PubMed

    Yao, Yansun; Stavrou, Elissaios; Goncharov, Alexander F; Majumdar, Arnab; Wang, Hui; Prakapenka, Vitali B; Epshteyn, Albert; Purdy, Andrew P

    2017-06-21

    A combined theoretical and experimental study of lithium palladium deuteride (Li2PdD2) subjected to pressures up to 50 GPa reveals one structural phase transition near 10 GPa, detected by synchrotron powder x-ray diffraction, and metadynamics simulations. The ambient-pressure tetragonal phase of Li2PdD2 transforms into a monoclinic C2/m phase that is distinct from all known structures of alkali metal-transition metal hydrides/deuterides. The structure of the high-pressure phase was characterized using ab initio computational techniques and from refinement of the powder x-ray diffraction data. In the high-pressure phase, the PdD2 complexes lose molecular integrity and are fused to extended [PdD2]∞ chains. The discovered phase transition and new structure are relevant to the possible hydrogen storage application of Li2PdD2 and alkali metal-transition metal hydrides in general.

  7. Structure and compressibility of the high-pressure molecular phase II of carbon dioxide

    NASA Astrophysics Data System (ADS)

    Datchi, Frédéric; Mallick, Bidyut; Salamat, Ashkan; Rousse, Gwenaëlle; Ninet, Sandra; Garbarino, Gaston; Bouvier, Pierre; Mezouar, Mohamed

    2014-04-01

    The structure and equation of state of the crystalline molecular phase II of carbon dioxide have been investigated at room temperature from 15.5 to 57.5 GPa using synchrotron x-ray diffraction methods. The CO2 samples were embedded in neon pressure medium in order to provide quasihydrostatic conditions. The x-ray diffraction patterns of phase II are best described by a tetragonal structure, with space group P42/mnm and 2 molecules per unit cell, in accordance with a previous study [Yoo et al., Phys. Rev. B 65, 104103 (2002), 10.1103/PhysRevB.65.104103]. There is however a large (15%) difference in the intramolecular C=O bond length between the present study, 1.14(3) Å, and the latter work (1.329-1.366 Å). The present value is similar to that of the free molecule and is in very good agreement with predictions based on density functional theory. The compressibility of CO2-II determined here also disagrees with the previous study: our value for the zero-pressure bulk modulus, B0=8.5(3) GPa [with B0'=(∂B/∂P)0=6.29], is 15.5 times smaller. These findings oppose the view that CO2-II is an intermediate state between the low-pressure molecular phases and the high-pressure nonmolecular forms, consistent with our previous results for phase IV [Datchi et al., Phys. Rev. Lett. 103, 185701 (2009), 10.1103/PhysRevLett.103.185701]. The x-ray diffraction patterns of CO2-II above 15 GPa indicate the presence of a large orthorhombic microstrain. Carrying out density functional theory calculations of the elastic tensor and stress-strain relation, we interpret this as due to the softness of the crystal against deviatoric stress in the [110] and symmetry-related directions. Unlike the other dioxides of the group-14 elements, there is however no mechanical or dynamical instability of the P42/mnm structure in CO2 up to 57.5 GPa at 295 K, and therefore no symmetry lowering to Pnnm.

  8. Phase transformation in hexagonal ErMnO3 under high pressure

    NASA Astrophysics Data System (ADS)

    Lin, Chuanlong; Liu, Jing; Li, Xiaodong; Li, Yanchun; Chu, Shenqi; Xiong, Lun; Li, Rui

    2012-12-01

    The pressure-induced phase transition of the hexagonal manganite ErMnO3 has been investigated using the synchrotron x-ray diffraction technique up to 57.6 GPa in a diamond anvil cell. The hexagonal structure exhibits anisotropic compression behavior. The bulk modulus (B0) is 168(3) GPa with B0' = 4.0 (fixed). At room temperature, ErMnO3 undergoes a hexagonal-to-orthorhombic phase transition at ˜20.2 GPa, but coexists with the orthorhombic phase up to the highest pressure of 57.6 GPa. When laser-heated to 1500-2000 K, the hexagonal ErMnO3 transforms to a denser orthorhombic perovskite structure completely at ˜17 GPa, accompanied by ˜11% volume reduction. The distortion and tilts of the octahedra MnO6 in the orthorhombic structure decrease with increasing pressure. The bulk modulus of the orthorhombic structure is 214(4) GPa with B0' = 4.0 (fixed), larger than that of the hexagonal structure. The orthorhombic structure ErMnO3 is stable at least up to ˜45 GPa and can be quenched.

  9. Volumetric and Optical Studies of High Pressure Phases of MgSO4-H2O with Applications to Europa

    NASA Astrophysics Data System (ADS)

    Dougherty, A. J.; Hogenboom, D. L.; Kargel, J. S.

    2007-03-01

    We use optical images of high-pressure phases of the MgSO4-H2O system, coupled with measurements of pressure, temperature, and volume changes, to report eutectic transitions for pressures up to 200 MPa, with implications for modeling Europa's ocean.

  10. Stability of the fergusonite phase in GdNbO4 by high pressure XRD and Raman experiments

    NASA Astrophysics Data System (ADS)

    Pellicer-Porres, J.; Garg, A. B.; Vázquez-Socorro, D.; Martínez-García, D.; Popescu, C.; Errandonea, D.

    2017-07-01

    We describe the results of high pressure x-ray diffraction and Raman measurements on gadolinium orthoniobate. The ambient pressure monoclinic fergusonite phase remains stable in a remarkable large pressure range. There is no significative evolution of the monoclinic distortion up to 25 GPa, the maximum pressure achieved. Instead, the anisotropic compressibility is associated to the stiffness of NbO4 tetrahedra in respect to the GdO8 polyhedra. The high pressure evolution of external modes parallels the wavenumber dependence on ionic radius along the lanthanide series. The chemical pressure analogy is attributed to the compression of GdO8 polyhedra. There is no evidence of any phonon softening.

  11. Effect of pressure on the selectivity of polymeric C18 and C30 stationary phases in reversed-phase liquid chromatography. Increased separation of isomeric fatty acid methyl esters, triacylglycerols, and tocopherols at high pressure.

    PubMed

    Okusa, Kensuke; Iwasaki, Yuki; Kuroda, Ikuma; Miwa, Shohei; Ohira, Masayoshi; Nagai, Toshiharu; Mizobe, Hoyo; Gotoh, Naohiro; Ikegami, Tohru; McCalley, David V; Tanaka, Nobuo

    2014-04-25

    A high-density, polymeric C18 stationary phase (Inertsil ODS-P) or a polymeric C30 phase (Inertsil C30) provided improved resolution of the isomeric fatty acids (FAs), FA methyl esters (FAMEs), triacylglycerols (TAGs), and tocopherols with an increase in pressure of 20-70MPa in reversed-phase HPLC. With respect to isomeric C18 FAMEs with one cis-double bond, ODS-P phase was effective for recognizing the position of a double bond among petroselinic (methyl 6Z-octadecenoate), oleic (methyl 9Z-octadecenoate), and cis-vaccenic (methyl 11Z-octadecenoate), especially at high pressure, but the differentiation between oleic and cis-vaccenic was not achieved by C30 phase regardless of the pressure. A monomeric C18 phase (InertSustain C18) was not effective for recognizing the position of the double bond in monounsaturated FAME, while the separation of cis- and trans-isomers was achieved by any of the stationary phases. The ODS-P and C30 phases provided increased separation for TAGs and β- and γ-tocopherols at high pressure. The transfer of FA, FAME, or TAG molecules from the mobile phase to the ODS-P stationary phase was accompanied by large volume reduction (-30∼-90mL/mol) resulting in a large increase in retention (up to 100% for an increase of 50MPa) and improved isomer separation at high pressure. For some isomer pairs, the ODS-P and C30 provided the opposite elution order, and in each case higher pressure improved the separation. The two stationary phases showed selectivity for the isomers having rigid structures, but only the ODS-P was effective for differentiating the position of a double bond in monounsaturated FAMEs. The results indicate that the improved isomer separation was provided by the increased dispersion interactions between the solute and the binding site of the stationary phase at high pressure.

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

    SciTech Connect

    Yan, Xiaozhi; Ren, Xiangting; He, Duanwei E-mail: yangwg@hpstar.ac.cn; Chen, Bin; Yang, Wenge E-mail: yangwg@hpstar.ac.cn

    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.

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

    PubMed Central

    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

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

    PubMed

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

    2014-04-25

    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.

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

    NASA Astrophysics Data System (ADS)

    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.

  16. In Situ Observations of Thermoreversible Gelation and Phase Separation of Agarose and Methylcellulose Solutions under High Pressure.

    PubMed

    Kometani, Noritsugu; Tanabe, Masahiro; Su, Lei; Yang, Kun; Nishinari, Katsuyoshi

    2015-06-04

    Thermoreversible sol-gel transitions of agarose and methylcellulose (MC) aqueous solutions on isobaric cooling or heating under high pressure up to 400 MPa have been investigated by in situ observations of optical transmittance and falling-ball experiments. For agarose, which undergoes the gelation on cooling, the application of pressure caused a gradual rise in the cloud-point temperature over the whole pressure range examined, which is almost consistent with the pressure dependence of gelling temperature estimated by falling-ball experiments, suggesting that agarose gel is stabilized by compression and that the gelation occurs nearly in parallel with phase separation under ambient and high-pressure conditions. For MC, which undergoes the gelation on heating, the cloud-point temperature showed a slight rise with an initial elevation of pressure up to ∼150 MPa, whereas it showed a marked depression above 200 MPa. In contrast, the gelling temperature of MC, which is nearly identical to the cloud-point temperature at ambient pressure, showed a monotonous rise with increasing pressure up to 350 MPa, which means that MC undergoes phase separation prior to gelation on heating under high pressure above 200 MPa. Similar results were obtained for the melting process of MC gel on cooling. The unique behavior of the sol-gel transition of MC under high pressure has been interpreted in terms of the destruction of hydrophobic hydration by compression.

  17. Li-Ion Conductivity and Phase Stability of Ca-Doped LiBH4 under High Pressure.

    PubMed

    Mezaki, Takeya; Kuronuma, Yota; Oikawa, Itaru; Kamegawa, Atsunori; Takamura, Hitoshi

    2016-10-17

    The effect of Ca doping on the Li-ion conductivity and phase stability of the rock-salt-type LiBH4 phase emerging under high pressures in the range of gigapascals has been investigated. In situ electrochemical measurements under high pressure were performed using a cubic-anvil-type apparatus. Ca doping drastically enhanced the ionic conductivity of the rock-salt-type phase: the ionic conductivity of undoped and 5 mol %Ca-doped LiBH4 was 2.2 × 10(-4) and 1.4 × 10(-2) S·cm(-1) under 4.0 GPa at 220 °C, respectively. The activation volume of LiBH4-5 mol %Ca(BH4)2, at 3.2 cm(3)·mol(-1), was comparable to that of other fast ionic conductors, such as lithium titanate and NASICONs. Moreover, Ca-doped LiBH4 showed lithium plating-stripping behavior in a cyclic voltammogram. These results indicate that the conductivity enhancement by Ca doping can be attributed to the formation of a LiBH4-Ca(BH4)2 solid solution; however, the solid solution decomposed into the orthorhombic LiBH4 phase and the orthorhombic Ca(BH4)2 phase after unloading the high pressure.

  18. Thermodynamics of the ferromagnetic phase transition in nearly half metallic CoS2 at high pressures

    SciTech Connect

    Elkin, F. S.; Zibrov, I. P.; Novikov, A. P.; Khasanov, S. S.; Sidorov, V. A.; Petrova, A. E.; Lograsso, Thomas A.; Thompson, J. D.; Stishov, S. M.

    2013-12-06

    The volume change and heat capacity at the ferromagnetic phase transition in COS2 were measured at high pressures using X-rays generated by the Argonne synchrotron light source and by ac-calorimetry, respectively. The transition entropy, calculated on the basis of these experimental data, drops along the transition line due to quantum degradation, as required by Nernst's law. The volume change increases strongly along the transition line, which is explained by specifics of the compressibility difference of coexisting phases that results from nearly half metallic nature of the ferromagnetic phase of COS2. (C) 2013 Elsevier Ltd. All rights reserved.

  19. First principles prediction of a new high pressure phase of dense hydrous magnesium silicates in the lower mantle

    NASA Astrophysics Data System (ADS)

    Tsuchiya, J.

    2013-12-01

    The global circulation of water in the earth is important to investigate the evolution history and dynamics of the earth, since the physical properties (e.g. atomic diffusivity, melting temperature, electrical conductivity and seismic velocities) of the constituent minerals are considerably changed by the presence of water. It has been reported that water is carried into the deep Earth's interior by hydrous minerals such as the dense hydrous magnesium silicates (DHMSs) in the descending cold plate. However, high pressure behavior of DHMSs, especially the stability of phase D which is the highest pressure phase of DHMSs has not been clarified so far. In this study, I explored the possibility of further phase transition and dissociation of phase D into the hydrous or anhydrous minerals. As a result, the new phase which has lower enthalpy than phase D has been found above about 40 GPa. Therefore, there is a possibility that this new phase in subducting slab takes over water and carries into the deeper part of earth's lower mantle. The detail of the structure and the high pressure-temperature phase boundary determined by quasi-harmonic approximation will be shown and the possible geophysical implications will also be discussed at the presentation. Research supported in part by special coordination funds for promoting science and technology (Supporting Young Researchers with Fixed-term Appointments) and Grants-In-Aid for Scientific Research from the Japan Society for the Promotion of Science (Nos. 21740380, 20103005, and 24740357).

  20. Development and testing of a high-pressure downhole pump for jet-assist drilling. Topical report, Phase II

    SciTech Connect

    1997-10-01

    The goal of jet-assisted drilling is to increase the rate of penetration (ROP) in deeper gas and oil wells, where the rocks become harder and more difficult to drill. Increasing the ROP can result in fewer drilling days, and therefore, lower drilling cost. In late 1993, FlowDril and the Gas Research Institute (GRI) began a three-year development of a down hole pump (DHP{reg_sign}) capable of producing 30,000 psi out pressure to provide the high-pressure flow for high-pressure jet-assist of the drill bit. The U.S. Department of Energy (DOE) through its Morgantown, WV (DOE-Morgantown) field office, joined with GRI and FlowDril to develop and test a second prototype designed for drilling in 7-7/8 inch holes. This project, {open_quotes}Development and Testing of a High-Pressure Down Hole Pump for Jet-Assist Drilling,{close_quotes} is for the development and testing of the second prototype. It was planned in two phases. Phase I included an update of a market analysis, a design, fabrication, and an initial laboratory test of the second prototype. Phase II is continued iterative laboratory and field developmental testing. This report summarizes the results of Phase II. In the downhole pump approach shown in the following figure, conventional drill pipe and drill collars are used, with the DHP as the last component of the bottom hole assembly next to the bit. The DHP is a reciprocating double ended, intensifier style positive displacement, high-pressure pump. The drive fluid and the high-pressure output fluid are both derived from the same source, the abrasive drilling mud pumped downhole through the drill string. Approximately seven percent of the stream is pressurized to 30,000 psi and directed through a high-pressure nozzle on the drill bit to produce the high speed jet and assist the mechanical action of the bit to make it drill faster.

  1. Observation of an Ultrahard Phase of Graphite Quenched from High-pressure

    DTIC Science & Technology

    2011-02-01

    Buga, S. G.; Serebryanaya, N. R.; Denisov , V . N.; Dubitsky, G. A.; Ivley, A. N.; Mavrin, B. N.; Popov, M. Yu . Ultrahard and Superhard Carbon...Gatti, C.; Ma, Y.; Ma, Y.; Glass, C. W.; Liu, Z.; Yu , T.; Kurakevych, O. O.; Solozhenko, V . L. Ionic High-pressure Form of Elemental Boron. Nature...Prescribed by ANSI Std. Z39.18 iii Contents List of Figures iv  List of Tables iv  Acknowledgments v   1.  Introduction 1  2.  Experimental

  2. Phase segregation in MgxZn1-xO probed by optical absorption and photoluminescence at high pressure

    NASA Astrophysics Data System (ADS)

    Marín-Borrás, V.; Ruiz-Fuertes, J.; Segura, A.; Muñoz-Sanjosé, V.

    2017-09-01

    The appearance of segregated wurtzite MgxZn1-xO with low Mg content in thin films with x > 0.3 affected by phase separation cannot be reliably probed with crystallographic techniques owing to its embedded nanocrystalline configuration. Here, we show a high-pressure approach which exploits the distinctive behaviors under pressure of wurtzite MgxZn1-xO thin films with different Mg contents to unveil phase segregation for x > 0.3. By using ambient conditions, photoluminescence (PL), and with optical absorption and PL under high pressure for x = 0.3, we show that the appearance of a segregated wurtzite phase with a magnesium content of x ˜ 0.1 is inherent to the wurtzite and rock-salt phase separation. We also show that the presence of segregated wurtzite phase in oversaturated thin films phase is responsible for the low-energy absorption tail observed above x = 0.3 in our MgxZn1-xO thin films. Our study has also allowed us to extend the concentration dependence of the pressure coefficient of the band gap from the previous limit of x = 0.13 to x ≈ 0.3 obtaining dEg/dP = 29 meV/GPa for wurtzite with x ≈ 0.3 and 25 meV/GPa for the segregated x ≈ 0.09 wurtzite phase.

  3. Entropic phase transitions and accompanying anomalous thermodynamics of matter

    NASA Astrophysics Data System (ADS)

    Iosilevskiy, I. L.

    2015-11-01

    Thermodynamic consequences of subdivision for all first-order phase transitions (PT) into enthalpy- and entropy-driven ones (H-PT and S-PT), proposed previously [arXiv:1403.8053], are under discussions. Key-value for proposed discrimination is main benefit (decreasing) in enthalpy or (nega)entropy in spontaneous phase decomposition, i.e. the sign of latent heat of PT and consequent slope of its P(T)-dependence. The main driving mechanism for many isostructural S-PT is the decay (delocalization) of some kind of bound complexes, e.g. atoms, molecules etc. Thermodynamic features of H-PT and S-PT differ significantly. Entropic PT are always the part of more general thermodynamic anomaly—domain where great number of usually positive second cross derivatives (e.g. Grüneisen parameter, thermal pressure coefficient etc.) became negative simultaneously. This domain is restricted (in the case of isostructural S-PT) by remarkable bound, where all mentioned second derivatives are equal to zero. Isostructural S-PT has more complicated topology of stable, metastable and unstable states and their boundaries—binodals and spinodals in comparison with ordinary enthalpic PTs. Two new thermodynamic objects accompany isostructural S-PT: (i) appearance of third (additional) region of metastable states with positive compressibility, isolated from the regions of stable states; (ii) appearance of new additional spinodal, topped with a new singular point, separating metastable and unstable states. These additional spinodal and singular point obey to relation (∂P/∂V)T = ∞. All thermodynamic anomalies of entropic PTs correspond to conclusive and transparent geometrical feature of such PTs: multilayered structure of thermodynamic surfaces for temperature, entropy and internal energy as pressure- density functions U(P, V), S(P, V) and T(P, V).

  4. Ionic and superionic phases in ammonia dihydrate N H3.2 H2O under high pressure

    NASA Astrophysics Data System (ADS)

    Jiang, Xue; Wu, Xue; Zheng, Zhaoyang; Huang, Yingying; Zhao, Jijun

    2017-04-01

    Water and ammonia have long been seen as the main species of extraterrestrial space, especially on solar giants, moons, comets, and numerous extrasolar planets. The phases formed by their admixtures under temperature and pressure conditions of the giant planets are important for understanding many observable properties (gravitational moments, atmospheric composition, and magnetic field). Here we employ a Monte Carlo packing algorithm combined with first-principles calculations to search the low-energy crystal structures of ammonia dihydrate (ADH). At high pressure above 11.81 GPa, we predict an unusual ionic phase (tetragonal, I 41c d ) consisting of three alternating layers of H2O ,NH4+ , and O H- . The occurrence of ionic phase is attributed to the NH4+ and O H- electrostatic interaction induced volume reduction, which lowers the energy barrier of molecular to ionic phase transition. Analysis of proton transfer under pressure further supports the transformation mechanism between molecular and ionic phase. According to the mobility of hydrogen atoms from ab initio molecular dynamics, this ionic crystal will transform into a superionic phase under high temperature and high pressure. The existence of ionic or superionic ADH may have important implications for understanding the interiors of Neptune, Uranus, and many extrasolar planets.

  5. Theoretical Study of the High-Pressure Isosymmetric Phase Transition in Lead Fluoride, PbF2

    NASA Astrophysics Data System (ADS)

    Dutta, R.; Stan, C. V.; White, C.; Duffy, T. S.

    2016-12-01

    Under compression many AX2 compounds including the alkaline earth fluorides follow a canonical transition sequence from the fluorite-type (Coordination Number, CN = 8) to the cotunnite-type (CN = 9) to the Ni2In-type phase (CN = 11). Lead fluoride is instead reported to undergo an unusual isosymmetric phase transition from the cotunnite phase to a "Co2Si-like" phase (9-fold coordination) at 10 GPa1. Previous theoretical calculations2 have reported that the Ni2In-type structure should be stable, but this phase has not been observed experimentally. In our previous experimental study, we examined the high-pressure behavior of PbF2 using in-situ synchrotron x-ray diffraction to 70 GPa. Here we use theoretical density functional theory calculations to better understand the high-pressure behavior of this material. The calculated lattice parameters display highly anomalous trends from 9-21 GPa, consistent with experiments. Experimental evidence for a transition to a Co2Si-like phase was based solely on lattice parameter systematics. Here we use electron density calculations, to directly show that the high-pressure phase is Co2Si-type. Our calculations also reveal the detailed atomic rearrangements associated with the development of an extra Pb-F bond in the high-pressure phase. At P > 9 GPa, both the lead and fluorine ions begin to reorient themselves as an additional fluorine atom, initially outside the 9-fold coordination polyhedron of cotunnite, approaches it. The transition regime from 9 to 21 GPa is marked by continuous atomic movements leading to anomalous behavior of the lattice parameters and compressibilities. At P 21 GPa, the transformation to the Co2Si-type structure is completed with an increase in the coordination number from 9 to 10. References1Haines, J. M. Léger, and O. Schulte, Phys. Rev. B 57, 7551 (1998). 2A. Costales, M. A. Blanco, R. Pandey, and J. M. Recio, Phys. Rev. B 61, 11359 (2000). 3W. Jeitschko, Acta Crystallogr. Sect. B 24, 930 (1968).

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

    NASA Astrophysics Data System (ADS)

    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

  7. Melting and phase relations in the Fe-C-S-O system at high pressure and temperature

    NASA Astrophysics Data System (ADS)

    Fei, Yingwei

    2010-05-01

    The physical state of the core (liquid outer core and solid inner core) could provide tight constraint on the core temperature if melting temperature of core materials is precisely determined at high pressure. On the other hand, the density of the Earth's core is significantly lower than that of pure iron measured experimentally at high pressure and temperature. The density deficit in the core (both liquid outer core and solid inner core) provides inside into the chemistry of the core, suggesting that the core must contain several weight percent of one or more light elements (lighter than iron) in addition to Fe-Ni alloy. Sulfur (S), carbon (C), and oxygen (O) are the prominent candidates among the proposed light elements, because of their high solar abundance and strong chemical affinity for Fe. Determining the effect of pressure on melting relations in the Fe-S, Fe-C, and Fe-O binary systems and multi-component system is crucial for understanding the chemistry, temperature, and evolution of planetary cores. There has been significant progress in determining the melting relations in the system Fe-FeS at high pressure, using multi-anvil apparatus and laser-heating diamond-anvil cell. These studies have revealed new iron-sulfur compounds (Fe3S2, Fe2S, and Fe3S) stable at high pressures, change of melting relations, and pressure effect on eutectic temperature and composition. The behaviors of the Fe-C and Fe-O systems have also been experimentally investigated recently. Experimental data in the Fe-C-S-O system at high pressure have just emerged. In parallel, there are high-quality data on density measurements of solid and liquid phases at high pressure and temperature. In this study, I present recent advances in experimental techniques and melting relations in the Fe-C-S-O system. The emphasis will be on the need to develop thermodynamic models by synthesis of thermochemical, thermophysical, and phase equilibrium data. The systematic approach provides a better

  8. Series of Phase Transitions in Cesium Azide Under High Pressure Studied by in situ X-ray Diffraction

    SciTech Connect

    D Hou; F Zhang; C Ji; T Hannon; H Zhu; J Wu; Y Ma

    2011-12-31

    In situ x-ray diffraction measurements of cesium azide (CsN{sub 3}) were performed at high pressures of up to 55.4 GPa at room temperature. Three phase transitions were revealed as follows: tetragonal (I4/mcm, Phase II) {yields} monoclinic (C2/m, Phase III) {yields} monoclinic (P2{sub 1}/m or P2{sub 1}, Phase IV) {yields} triclinic (P1 or P1{sup -}, Phase V), at 0.5, 4.4, and 15.4 GPa, respectively. During the II-III phase transition, CsN{sub 3} keeps its layered structure and the azide anions rotate obviously. The compressibility of Phase II is dominated by the repulsions between azide anions. The deformation of unit cell is isotropic in Phases II and IV and anisotropic in Phase III. With increasing pressures, the monoclinic angle increases in Phase III and then becomes stable in Phase IV. The bulk moduli of Phases II, III, IV, and V are determined to be 18 {+-} 4, 20 {+-} 1, 27 {+-} 1 and 34 {+-} 1 GPa, respectively. The ionic character of alkali azides is found to play a key role in their pressure-induced phase transitions.

  9. Five-dimensional visualization of phase transition in BiNiO{sub 3} under high pressure

    SciTech Connect

    Liu, Yijin E-mail: wyang@ciw.edu; Wang, Junyue; Yang, Wenge E-mail: wyang@ciw.edu; Azuma, Masaki; Mao, Wendy L.

    2014-01-27

    Colossal negative thermal expansion was recently discovered in BiNiO{sub 3} associated with a low density to high density phase transition under high pressure. The varying proportion of co-existing phases plays a key role in the macroscopic behavior of this material. Here, we utilize a recently developed X-ray Absorption Near Edge Spectroscopy Tomography method and resolve the mixture of high/low pressure phases as a function of pressure at tens of nanometer resolution taking advantage of the charge transfer during the transition. This five-dimensional (X, Y, Z, energy, and pressure) visualization of the phase boundary provides a high resolution method to study the interface dynamics of high/low pressure phase.

  10. High-pressure phase diagram, structural transitions, and persistent nonmetallicity of BaBiO3: Theory and experiment

    NASA Astrophysics Data System (ADS)

    MartoÅák, Roman; Ceresoli, Davide; Kagayama, Tomoko; Matsuda, Yusuke; Yamada, Yuh; Tosatti, Erio

    2017-07-01

    BaBiO3 is a mixed-valence perovskite, which escapes the metallic state through a Bi valence (and Bi-O bond) disproportionation or CDW distortion, resulting in a semiconductor with a gap of 0.8 eV at zero pressure. The evolution of structural and electronic properties at high pressure is, however, largely unknown. Pressure, one might have hoped, could reduce the disproportionation, making the two Bi ions equivalent and bringing the system closer to metallicity or even to superconductivity, such as is attained at ambient pressure upon metal doping. We address the high-pressure phase diagram of pristine BaBiO3 by ab initio DFT calculations based on GGA and hybrid functionals in combination with crystal structure prediction methods based on evolutionary algorithms, molecular dynamics, and metadynamics. The calculated phase diagram from 0 to 50 GPa indicates that pristine BaBiO3 resists metallization under pressure, undergoing instead at room temperature structural phase transitions from monoclinic I2/m to nearly tetragonal P-1 at 7 GPa, possibly to monoclinic C2/m at 27 GPa, and to triclinic P1 at 43 GPa. Remarkably, all these phases sustain and in fact increase the inequivalence of two Bi neighboring sites and of their Bi-O bonds and, in all cases except semimetallic C2/m, the associated insulating character. We then present high-pressure resistivity data, which generally corroborate these results, and show that the insulating character persists at least up to 80 GPa, suggesting that the C2/m phase is probably an artifact of the small computational cell.

  11. Structural and magnetic phase transitions in gadolinium under high pressures and low temperatures

    DOE PAGES

    Samudrala, Gopi K.; Tsoi, Georgiy M.; Weir, Samuel T.; ...

    2014-11-07

    High pressure structural transition studies have been carried out on rare earth metal gadolinium in a diamond anvil cell at room temperature to 169 GPa. Gadolinium has been compressed to 38% of its initial volume at this pressure. With increasing pressure, a crystal structure sequence of hcp → Smtype→ dhcp → fcc → dfcc → monoclinic has been observed in our studies on gadolinium. The measured equation of state of gadolinium is presented to 169 GPa at ambient temperature. Magnetic ordering temperature of gadolinium has been studied using designer diamond anvils to a pressure of 25 GP and a temperaturemore » of 10 K. The magnetic ordering temperature has been determined from the four-point electrical resistivity measurements carried out on gadolinium. Furthermore, our experiments show that the magnetic transition temperature decreases with increasing pressure to 19 GPa and then increases when gadolinium is subjected to higher pressures.« less

  12. Structural and magnetic phase transitions in gadolinium under high pressures and low temperatures

    SciTech Connect

    Samudrala, Gopi K.; Tsoi, Georgiy M.; Weir, Samuel T.; Vohra, Yogesh K.

    2014-11-07

    High pressure structural transition studies have been carried out on rare earth metal gadolinium in a diamond anvil cell at room temperature to 169 GPa. Gadolinium has been compressed to 38% of its initial volume at this pressure. With increasing pressure, a crystal structure sequence of hcp → Smtype→ dhcp → fcc → dfcc → monoclinic has been observed in our studies on gadolinium. The measured equation of state of gadolinium is presented to 169 GPa at ambient temperature. Magnetic ordering temperature of gadolinium has been studied using designer diamond anvils to a pressure of 25 GP and a temperature of 10 K. The magnetic ordering temperature has been determined from the four-point electrical resistivity measurements carried out on gadolinium. Furthermore, our experiments show that the magnetic transition temperature decreases with increasing pressure to 19 GPa and then increases when gadolinium is subjected to higher pressures.

  13. Quantitative analysis of vitamin D3 in a feed using normal phase high pressure liquid chromatography.

    PubMed

    Cohen, H; Lapointe, M

    1979-09-01

    A procedure is described for the separation and quantification of Vitamin D3 from different feeds and premixes. The study was conducted, first using a liquid partition step as a preliminary clean-up after extraction, then chromatography on activated Silica gel 60 before final analysis on a high pressure liquid chromatograph (HPLC) using a LiChrosorb NH2 (10 mu) column and a variable wavelength UV detector set at 264 nm. Total analysis on the HPLC was achieved in fifteen minutes. The detector response curve for an authentic D3 standard was linear using peak areas with a minimum detectable amount being 5 ng. The overall percent recovery of D3 in feeds was 94.4 +/- 2.4%. The minimum detectable amount of D3 in animal feeds was found to be in the region of 2,000 I.U./kg.

  14. Theoretical calculations of phase transitions and optical properties of solid iodine under high pressures

    NASA Astrophysics Data System (ADS)

    San, Xiaojiao; Wang, Liancheng; Ma, Yanming; Liu, Zhiming; Cui, Tian; Liu, Bingbing; Zou, Guangtian

    2008-04-01

    The structural stability and optical properties of solid iodine under pressure have been studied using the ab initio pseudopotential plane-wave method. The dependence of lattice parameters on pressure indicates that the first structural phase transition from phase I to phase V occurs at about 20 GPa. From the pressure dependence of our elastic constants for solid iodine in phase I, it is found that the first structural transformation from molecular phase I to the intermediate phase V occurs at about 20 GPa due to the softening of the elastic constant C44, which is very close to the transition pressure of 20 GPa obtained by geometry optimizations and 23.2 GPa obtained by experimental measurements. The optimized structure for phase V is a face-centered orthorhombic (fco) phase with equal interatomic distances d1 = d2 = d3, but this fco structure is mechanically unstable, with shear elastic stiffness coefficient C44<0. To understand the modulated phase V, we use a periodic crystal structure to mimic the incommensurate phase V and obtain some quantitative information. In our calculation, the modulated phase is thermodynamically and mechanically stable. It is believed that phase V is not a monatomic phase but an intermediate state between a molecular and a monatomic state.

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

    NASA Astrophysics Data System (ADS)

    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

  16. Density-functional approach to the valence change in SmS: Normal and high-pressure phases

    NASA Astrophysics Data System (ADS)

    Schumann, R.; Richter, M.; Steinbeck, L.; Eschrig, H.

    1995-09-01

    The electronic structure of SmS in dependence of the lattice constant is calculated by means of density-functional theory. The local-density approximation (LDA) to the exchange and correlation potential is employed. The 4f electrons, however, are treated in three different ways, viz., (i) as localized core states, (ii) as extended band states, and (iii) as self-interaction corrected (SIC) band states. While the experimentally observed Sm valency of normal state SmS (black phase) cannot be described by methods (i) and (ii) the SIC calculations are consistent with the measured value. For pressures above 30 kbar, method (ii) agrees well with the observed Sm valency, whereas methods (i) and (iii) fail. Therefore we conclude that the phase transition in SmS is very similar to the α-γ transition in Ce metal. The SIC band structure shows the splitting between the occupied and empty 4f states due to the large on-site electron correlation. The Fermi level ɛF is situated in the gap between the S 3p states and the Sm band states mainly of 5d character. In the high-pressure phase the 4f states presumably become delocalized, resulting in vanishing self-interaction corrections. Therefore the uncorrected LDA results are appropriate for the high-pressure phase.

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

    PubMed Central

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

    2016-01-01

    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 mm3. A robust polarization-preserving effect is also observed, raising the possibility of advanced optical technological applications. PMID:27574703

  18. High-pressure structural phase transitions in chromium-doped BaFe[subscript 2]As[subscript 2

    SciTech Connect

    Uhoya, W.O.; Montgomery, J.M.; Samudrala, G.K.; Tsoi, G.M.; Vohra, Y.K.; Weir, S.T.; Sefat, A.S.

    2012-10-23

    We report on the results from high pressure x-ray powder diffraction and electrical resistance measurements for hole doped BaFe{sub 2-x}Cr{sub x}As{sub 2} (x = 0, 0.05, 0.15, 0.4, 0.61) up to 81 GPa and down to 10 K using a synchrotron source and diamond anvil cell (DAC). At ambient temperature, an isostructural phase transition from a tetragonal (T) phase (I4/mmm) to a collapsed tetragonal (CT) phase is observed at 17 GPa. This transition is found to be dependent on ambient pressure unit cell volume and is slightly shifted to higher pressure upon increase in the Cr-doping. Unlike BaFe{sub 2}As{sub 2} which superconduct under high pressure, we have not detected any evidence of pressure induced superconductivity in chromium doped samples in the pressure and temperature range of this study. The measured equation of state parameters are presented for both the tetragonal and collapsed tetragonal phases for x = 0.05, 0.15, 0.40 and 0.61.

  19. Optical properties of the high-pressure phases of SnO(2): first-principles calculation.

    PubMed

    Li, Yanlu; Fan, Weiliu; Sun, Honggang; Cheng, Xiufeng; Li, Pan; Zhao, Xian; Hao, Jingcheng; Jiang, Minhua

    2010-01-21

    We present a detailed investigation on the optical properties, including dielectric function, reflectivity, absorption, refractive index, and electron energy-loss spectrum, of the high-pressure phase SnO(2) in the rutile, pyrite, fluorite, and cotunnite structures by using the density functional theory (DFT) plane-wave pseudopotential method. The results indicate that with the increasing of pressure the band gaps become larger, the density of states are broader, so the curves of optical properties have a little blue shift. Except that the fluorite phase has some metallic properties, the other three phases exhibit excellent dielectric behavior. Interestingly, the fluorite and cotunnite SnO(2) phases always have some special characteristics, such as higher plasma frequency, which need further fundamental and application research.

  20. Liquid water-ice I phase diagrams under high pressure: sodium chloride and sucrose models for food systems.

    PubMed

    Guignon, Bérengère; Otero, Laura; Molina-García, Antonio D; Sanz, Pedro D

    2005-01-01

    The knowledge of high pressure and low temperature phase diagrams of aqueous systems is required in fields such as food sciences, biology, cryo-microscopy and geology, to reduce processing costs, improve treatments results or advance in physical phenomena understanding. The phase transition curve between liquid water and ice I for sucrose and sodium chloride solutions has been obtained for concentrations ranging from 16% to 36% and from 1.63% to 16.09% (w/w), respectively. An accurate experimental method, based on the pressurization of an ice-solution mixture, adequate to build the entire phase transition curve at constant concentration, has been developed. Simon-like equations have been used to empirically describe the phase transition curves, so that they allow easy data interpolation.

  1. Phase equilibria in fluid mixtures at high pressures - The He-CH4 system.

    NASA Technical Reports Server (NTRS)

    Streett, W. B.; Erickson, A. L.; Hill, J. L. E.

    1972-01-01

    An experimental study of phase equilibria in the He-CH4 system has been carried out over the temperature range 95 to 290 K and at pressures to 10,000 atm. The experimental results consist of equilibrium phase composition for twenty-eight isotherms in the region of coexistence of two fluid phases, together with the pressure-temperature trace of the three-phase boundary at which a CH4-rich solid phase is in equilibrium with the two fluid phases. The system exhibits a fluid-fluid phase separation which persists to temperatures and pressures beyond the range of this experiment. These findings are relevant to problems of deep atmosphere and interior structures in the outer planets.-

  2. High-temperature and high-pressure phase transitions in uranium

    NASA Astrophysics Data System (ADS)

    Bouchet, J.; Bottin, F.

    2017-02-01

    The phase diagram of uranium has been explored up to 100 GPa and 2000 K by means of ab initio molecular dynamics (AIMD) simulations. The lattice dynamics and energetics of the stable phases observed experimentally in this range of pressure and temperature are studied in this work. The phonon spectra of the α and γ phases are shown to evolve strongly as a function of temperature, unveiling the huge anharmonic effects present in this material. If the elastics constants and the bulk and shear moduli of the γ phase do not disclose any temperature effects, the shear modulus of the α phase decreases strongly as a function of temperature. Using the pressure- and temperature-dependent vibrational density of states and the Gibbs free energy of these two structures, we found a line transition between the α and γ phases which slightly underestimates the experimental one. Coherently with experiments, the bct structure is never found stable between 0 and 100 GPa.

  3. The Phase Transition of Zn0.854Cu0.146O Under High Pressure

    SciTech Connect

    Y Jin; J Zhang; P Zhu; W Gao; Q Cui

    2011-12-31

    Pressure induced phase transition of hexagonal Zn{sub 0.854}Cu{sub 0.146}O is studied by using synchrotron angle dispersive X-ray diffraction (ADXRD) up to 43.1 GPa at room temperature. A structural transformation from a hexagonal phase to a cubic phase is observed, which starts at 10.2 GPa and finishes at about 16.5 GPa. The phase transition leads to a volume collapse of 17% at 10.2 GPa. The cubic phase of Zn{sub 0.854}Cu{sub 0.146}O remains stable up to the highest experiment pressure. The pressure-volume data are fitted with the Birch-Murnaghan equation of state. The bulk modulus obtained upon compression from the fitting are 175(2) and 259(6) GPa for the hexagonal and cubic phases, respectively.

  4. Magnetoresistance of the high-pressure ferromagnetic phases (GaSb)2M (M=Cr,Mn)

    NASA Astrophysics Data System (ADS)

    Pronin, A. A.; Kondrin, M. V.; Gizatullin, V. R.; Sazanova, O. A.; Lyapin, A. G.; Popova, S. V.; Ivanov, V. Y.

    2014-08-01

    For the first time magnetoresistance of the ferromagnetic high-pressure phases (GaSb)2M (M=Cr,Mn) has been measured in a wide range of temperature and magnetic field. It was found that the magnetic field dependencies of resistivity of both systems contain several contributions, including relatively smaller s-d exchange (Yosida-type) components in low fields and a quadratic positive term (PMR) in the low temperature region. The magnitude of the predominated negative term (NMR), which can be attributed to the quantum corrections effects, demonstrates a peak in the vicinity of Curie temperature.

  5. Structural phase transitions in Bi2Se3 under high pressure

    SciTech Connect

    Yu, Zhenhai; Gu, Genda; Wang, Lin; Hu, Qingyang; Zhao, Jinggeng; Yan, Shuai; Yang, Ke; Sinogeikin, Stanislav; Mao, Ho -kwang

    2015-11-02

    Raman spectroscopy and angle dispersive X-ray diffraction (XRD) experiments of bismuth selenide (Bi2Se3) have been carried out to pressures of 35.6 and 81.2 GPa, respectively, to explore its pressure-induced phase transformation. The experiments indicate that a progressive structural evolution occurs from an ambient rhombohedra phase (Space group (SG): R-3m) to monoclinic phase (SG: C2/m) and eventually to a high pressure body-centered tetragonal phase (SG: I4/mmm). Evidenced by our XRD data up to 81.2 GPa, the Bi2Se3 crystallizes into body-centered tetragonal structures rather than the recently reported disordered body-centered cubic (BCC) phase. Furthermore, first principles theoretical calculations favor the viewpoint that the I4/mmm phase Bi2Se3 can be stabilized under high pressure (>30 GPa). Remarkably, the Raman spectra of Bi2Se3 from this work (two independent runs) are still Raman active up to ~35 GPa. Furthermore, it is worthy to note that the disordered BCC phase at 27.8 GPa is not observed here. The remarkable difference in atomic radii of Bi and Se in Bi2Se3 may explain why Bi2Se3 shows different structural behavior than isocompounds Bi2Te3 and Sb2Te3.

  6. Real-Time Optical Monitoring of Flow Kinetics and Gas Phase Reactions Under High-Pressure OMCVD Conditions

    NASA Technical Reports Server (NTRS)

    Dietz, N.; McCall, S.; Bachmann, K. J.

    2001-01-01

    This contribution addresses the real-time optical characterization of gas flow and gas phase reactions as they play a crucial role for chemical vapor phase depositions utilizing elevated and high pressure chemical vapor deposition (HPCVD) conditions. The objectives of these experiments are to validate on the basis of results on real-time optical diagnostics process models simulation codes, and provide input parameter sets needed for analysis and control of chemical vapor deposition at elevated pressures. Access to microgravity is required to retain high pressure conditions of laminar flow, which is essential for successful acquisition and interpretation of the optical data. In this contribution, we describe the design and construction of the HPCVD system, which include access ports for various optical methods of real-time process monitoring and to analyze the initial stages of heteroepitaxy and steady-state growth in the different pressure ranges. To analyze the onset of turbulence, provisions are made for implementation of experimental methods for in-situ characterization of the nature of flow. This knowledge will be the basis for the design definition of experiments under microgravity, where gas flow conditions, gas phase and surface chemistry, might be analyzed by remote controlled real-time diagnostics tools, developed in this research project.

  7. Real-Time Optical Monitoring of Flow Kinetics and Gas Phase Reactions Under High-Pressure OMCVD Conditions

    NASA Technical Reports Server (NTRS)

    Dietz, N.; McCall, S.; Bachmann, K. J.

    2001-01-01

    This contribution addresses the real-time optical characterization of gas flow and gas phase reactions as they play a crucial role for chemical vapor phase depositions utilizing elevated and high pressure chemical vapor deposition (HPCVD) conditions. The objectives of these experiments are to validate on the basis of results on real-time optical diagnostics process models simulation codes, and provide input parameter sets needed for analysis and control of chemical vapor deposition at elevated pressures. Access to microgravity is required to retain high pressure conditions of laminar flow, which is essential for successful acquisition and interpretation of the optical data. In this contribution, we describe the design and construction of the HPCVD system, which include access ports for various optical methods of real-time process monitoring and to analyze the initial stages of heteroepitaxy and steady-state growth in the different pressure ranges. To analyze the onset of turbulence, provisions are made for implementation of experimental methods for in-situ characterization of the nature of flow. This knowledge will be the basis for the design definition of experiments under microgravity, where gas flow conditions, gas phase and surface chemistry, might be analyzed by remote controlled real-time diagnostics tools, developed in this research project.

  8. Phase relationships in Fe-Ni alloys at high pressures and temperatures

    NASA Technical Reports Server (NTRS)

    Huang, Eugene; Bassett, William A.; Weathers, Maura S.

    1988-01-01

    Diffusionless phase transformations in Fe-Ni alloys with up to 35 wt pct Ni were studied using resistance-heated diamond anvil cells and synchrotron radiation. At temperatures up to 600 C and pressures up to 25 GPa, Fe-35 percent Ni showed only the face-centered cubic (fcc) phase while Fe-25 percent Ni and Fe-10 percent Ni showed the body-centered cubic (bcc) and hexagonal close-packed (hcp) phases in addition to the fcc phase. The phase relationships of these solid phases are topologically similar to those of pure iron. The triple point becomes lower in temperature, and the slope (dT/dP) of the fcc/hcp boundary decreased as Ni-content increases in the alloys. From these results it is inferred that Fe-Ni alloys in the earth's inner core might exist as two phases, fcc and hcp. The existence of these two phases could have played an important role in the separation of the inner and outer core.

  9. Phase relationships in Fe-Ni alloys at high pressures and temperatures

    NASA Technical Reports Server (NTRS)

    Huang, Eugene; Bassett, William A.; Weathers, Maura S.

    1988-01-01

    Diffusionless phase transformations in Fe-Ni alloys with up to 35 wt pct Ni were studied using resistance-heated diamond anvil cells and synchrotron radiation. At temperatures up to 600 C and pressures up to 25 GPa, Fe-35 percent Ni showed only the face-centered cubic (fcc) phase while Fe-25 percent Ni and Fe-10 percent Ni showed the body-centered cubic (bcc) and hexagonal close-packed (hcp) phases in addition to the fcc phase. The phase relationships of these solid phases are topologically similar to those of pure iron. The triple point becomes lower in temperature, and the slope (dT/dP) of the fcc/hcp boundary decreased as Ni-content increases in the alloys. From these results it is inferred that Fe-Ni alloys in the earth's inner core might exist as two phases, fcc and hcp. The existence of these two phases could have played an important role in the separation of the inner and outer core.

  10. Phase diagram of ammonium perchlorate: Raman spectroscopic constrains at high pressures and temperatures

    NASA Astrophysics Data System (ADS)

    Dunuwille, Mihindra; Yoo, Choong-Shik

    2016-06-01

    We present the pressure-temperature (PT) induced physical and chemical transformations in ammonium perchlorates (APs) up to 50 GPa and 450 °C, using diamond anvil cells and confocal micro-Raman spectroscopy, which provide new constraints for the phase diagram of AP. The results show spectral evidences for three new polymorphs (III, IV, and VI) of AP, in addition to two previously known phases (I and II), at various PT conditions with varying degrees of hydrogen bonding and lack of strong spectral evidence for previously known high-temperature cubic phase (phase V). Upon further heating, AP chemically decomposes to N2, N2O, and H2O. The present phase diagram is, therefore, in sharp contrast to the previous one, underscoring a rich polymorphism, a large stability field for solids, and a replacement of the melt with a decomposition line.

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

    SciTech Connect

    Popov, D. Park, C.; Kenney-Benson, C.; Shen, G.

    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.

  12. A two-dimensional modeling of the warm-up phase of a high-pressure mercury discharge lamp

    SciTech Connect

    Araoud, Z.; Ben Ahmed, R.; Ben Hamida, M. B.; Charrada, K.; Franke, St.; Stambouli, M.; Zissis, G.

    2010-06-15

    The main objective of this work is to provide a better understanding of the warm-up phase of high-intensity discharge lamps. As an example of application, we chose the high-pressure mercury lamp. Based on two-dimensional fluid model parameters, such as the electric current, the length and the diameter of the burner are modified and the effect of the convective transport is studied. This allows us to obtain a thorough understanding of the physics of these lamps in their transitory phase. The simulation of the warm-up phase is a must for the proper predictions of the lamp behavior and can be conducted by solving the energy balance, momentum, and Laplace's equations for the plasma, using the frame of the local thermodynamic equilibrium coupled with the energy balance of the wall.

  13. High Pressure-Temperature Phase Diagram of 1,1-diamino-2,2-dinitroethylene

    NASA Astrophysics Data System (ADS)

    Bishop, Matthew; Chellappa, Raja; Liu, Zhenxian; Preston, Daniel; Sandstrom, Mary; Dattelbaum, Dana; Vohra, Yogesh; Velisavljevic, Nenad

    2013-06-01

    1,1-diamino-2,2-dinitroethelyne (FOX-7) is a less sensitive energetic material with performance comparable to commonly used secondary explosives such as RDX and HMX. At ambient pressure, FOX-7 exhibits complex polymorphism with at least three structurally distinct phases (α, β, and γ) . In this study, we have investigated the high P-T stability of FOX-7 polymorphs using synchrotron mid-infrared (MIR) spectroscopy. At ambient pressure, our MIR spectra confirmed the known α --> β (110 °C) and β --> γ (160 °C) phase transitions; as well as, indicated an additional phase transition, γ --> δ (210°C), with the δ phase being stable up to 250 °C prior to melt/decomposition. In situ MIR spectra obtained during isobaric heating at 0.9 GPa revealed that the α --> β transition occurs at 180 °C, while β --> β + δ phase transition shifted to 300 °C with suppression of γ phase. Decomposition was observed above 325 °C. Based on multiple high P-T measurements, we have established the first high P-T phase diagram of FOX-7. This work was, in part, supported by the US DOE under contract No. DE-AC52-06NA25396 and Science Campaign 2 Program. MB acknowledges additional support from the NSF BD program. Use of NSLS (DE-AC02-98CH10886) beamline U2A (COMPRES, No.EAR01-35554, CDAC).

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

    PubMed

    Montgomery, Jeffrey M; Samudrala, Gopi K; Tsoi, Georgiy M; Vohra, Yogesh K

    2011-04-20

    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/V₀ = 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.

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

    SciTech Connect

    Ming, L. C.; Zinin, P. V.; Sharma, S. K.

    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.

  16. In situ observations of a high-pressure phase of H2O ice

    USGS Publications Warehouse

    Chou, I.-Ming; Blank, J.G.; Goncharov, A.F.; Mao, Ho-kwang; Hemley, R.J.

    1998-01-01

    A previously unknown solid phase of H2O has been identified by its peculiar growth patterns, distinct pressure-temperature melting relations, and vibrational Raman spectra. Morphologies of ice crystals and their pressure-temperature melting relations were directly observed in a hydrothermal diamond-anvil cell for H2O bulk densities between 1203 and 1257 kilograms per cubic meter at temperatures between -10??and 50??C. Under these conditions, four different ice forms were observed to melt: two stable phases, ice V and ice VI, and two metastable phases, ice IV and the new ice phase. The Raman spectra and crystal morphology are consistent with a disordered anisotropic structure with some similarities to ice VI.

  17. Residuum upgrading by high pressure slurry phase technology: Technical, economic and environmental aspects

    SciTech Connect

    Kretschmar, K.; Wenzel, F.

    1994-12-31

    The technology of petroleum residue upgrading in slurry-phase reactors under high hydrogen partial pressure is based on the Bergius-Pier technology for coal liquefaction commercialized in Germany since the mid-1930`s. The paper describes the principle of slurry phase hydrogenation (SPH), reactivity and yield distribution in SPH, the operating pressure of SPH, integrated hydrotreating, processing of liquid and solid wastes, and economics of conversion projects.

  18. Gapped excitations in the high-pressure antiferromagnetic phase of URu2Si2

    DOE PAGES

    Williams, Travis J.; Oak Ridge National Lab.; Barath, Harini; ...

    2017-05-31

    Here, we report a neutron scattering study of the magnetic excitation spectrum in each of the three temperature and pressure driven phases of URu2Si2. We also found qualitatively similar excitations throughout the (H0L) scattering plane in the hidden order and large moment phases, with no changes in the hbar-omega-widths of the excitations at the Sigma = (1.407,0,0) and Z = (1,0,0) points, within our experimental resolution. There is, however, an increase in the gap at the Sigma point and an increase in the first moment of both excitations. At 8 meV where the Q-dependence of magnetic scattering in the hiddenmore » order phase is extended in Q-space, the excitations in the large moment phase are sharper. Furthermore, the expanded Q-hbar-omega coverage of this study suggest more complete nesting within the antiferromagnetic phase, an important property for future theoretical predictions of a hidden order parameter.« less

  19. An extended high pressure-temperature phase diagram of NaBH4.

    PubMed

    George, Lyci; Drozd, Vadym; Couvy, Helene; Chen, Jiuhua; Saxena, Surendra K

    2009-08-21

    We have studied the structural stability of NaBH(4) under pressures up to 17 GPa and temperatures up to 673 K in a diamond anvil cell and formed an extended high P-T phase diagram using combined synchrotron x-ray diffraction and Raman spectroscopy. Even though few reports on phase diagram of NaBH(4) are found in current literature, up to our knowledge this is the first experimental work using diamond anvil cell in a wide pressure/temperature range. Bulk modulus, its temperature dependence, and thermal expansion coefficient for the ambient cubic phase of NaBH(4) are found to be 18.76(1) GPa, -0.0131 GPa K(-1), and 12.5x10(-5)+23.2x10(-8) T/K, respectively. We have also carried out Raman spectroscopic studies at room temperature up to 30 GPa to reinvestigate the phase transitions observed for NaBH(4). A comparative symmetry analysis also has been carried out for different phases of NaBH(4).

  20. Structural phase stability in group IV metals under static high pressure

    SciTech Connect

    Velisavljevic, Nenad; Chesnut, Garry N; Dattelbaum, Dana M; Vohra, Yogesh K; Stemshorn, Andrew

    2009-01-01

    In group IV metals (Ti, Zr, and Hf) room temperature compression leads to a martensitic transformation from a ductile {alpha} to a brittle {omega} phase. {alpha} {yields} {omega} phase boundary decreases to lower pressure at high temperature and can limit the use of group IV metals in industrial applications. There is a large discrepancy in the transition pressure reported in literature, with some of the variation attributed to experimental conditions (i.e. hydrostatic vs. non-hydrostatic). Shear deformation in non-hydrostatic experiments drives {alpha} {yields} {omega} transition and decreases transition pressure. Impurities can also aid or suppress {alpha} {yields} {omega} transition. By performing x-ray diffraction experiments on samples in a diamond anvil cell we show that interstitial impurities, such as C, N, and O can obstruct {alpha} {yields} {omega} transition and stabilize {alpha} phase to higher pressure. We also show that reduction in grain size can also influence {alpha} {yields} {omega} phase boundary and help stabilize {alpha} phase to higher pressure under non-hydrostatic conditions.

  1. Hyperbaric reservoir fluids: High-pressure phase behavior of asymmetric methane + n-alkane systems

    NASA Astrophysics Data System (ADS)

    Flöten, E.; de Loos, Th. W.; de Swaan Arons, J.

    1995-01-01

    In this paper, experimental three-phase equilibrium (solid n-alkane + liquid + vapor) data for binary methane + n-alkane systems are presented. For the binary system methane + tetracosane, the three-phase curve was determined based on two phase equilibrium measurements in a composition range from x c24 = 0.0027 to x c24 = 1.0. The second critical endpoint of this system was found at p = (1114.7 ± 0.5) M Pa. T = (322.6 ± 0.25) K, and a mole fraction of tetracosane in the critical fluidphase of x c24 = 0.0415 ± 0.0015. The second critical endpoint occurs where solid tetracosane is in equilibrium with a critical fluid phase ( S c24 + L = V). For the binary systems of methane with the n-alkanes tetradecane, triacontane, tetracontane, and pentacontane, only the coordinates of the second critical endpoints were measured. The second critical endpoint temperature is found close to the atmospheric melting point temperature of the n-alkane. The pressures at the second critical endpoints do not exceed 200 MPa. Based on these experimental data and data from the literature, correlations for the pressure. temperature, and fluid phase composition at the second critical endpoint of binary methane + n-alkane systems with n-alkanes between octane and pentacontane were developed.

  2. Phase Diagram and Physical Properties of H[subscript 2]O at High Pressures and temperatures: Applications to Planetary Interiors

    SciTech Connect

    Lin, Jung-Fu; Schwegler, Eric; Yoo, Choong-Shik

    2007-02-22

    Here we discuss the phase diagram and physical properties of H{sub 2}O under pressure-temperature conditions relevant to planetary interiors. Recent studies show that the melting curve of H{sub 2}O increases rapidly above a recently discovered triple point at approximately 35 to 47 GPa and 1000 K, indicating a large increase in {Delta}V/{Delta}S (volume versus entropy change) and associated changes in the physical properties of H{sub 2}O at high pressures and temperatures. Existence of the triple point is thought to be associated with the formation of a superionic phase, dynamically-disordered ice VII, or extension of the ice VII-ice X phase boundary; although the precise pressure and temperature of the triple point, curvature of the melting line, and nature of the solid-solid transition below the triple point all remain to be further explored. The steep increase in the melting curve of H{sub 2}O at high pressures and temperatures has important implications on our understanding of planetary interiors. Depending on its curvature, the melting line of H{sub 2}O may intersect the isentropes of Neptune and Uranus as well as the geotherm of Earth's lower mantle. Furthermore, if the triple point is due to the occurrence of the theoretically predicted superionic phase, besides leading to significant ionic conductivity, fast proton diffusion would cause enhanced chemical reactivity and formation of complex compounds in these planets. For example, reaction of H{sub 2}O with iron and other metals to form metal hydrides such as FeH{sub x} could provide a mechanism for incorporation of hydrogen as a light element into Earth's core. The equation of state of water is also presented as it pertains to the properties of hydrous fluid and melt phases in the mantle.

  3. Synthesis of dense BC[subscript x] phases under high-pressure and high-temperature

    SciTech Connect

    Ming, L.C.; Zinin, P.V.; Liu, X.R.; Nakamoto, Y.; Jia, R.

    2010-05-24

    We synthesized a new phase from the B-C system, cubic BC{sub 4} (c-BC{sub 4}), by direct transformation from graphitic phases at a pressure of 44 GPa and a temperature 2020 K in a laser-heated diamond anvil cell (DAC). Both x-ray diffraction and Raman spectroscopy confirm the presence of cubic BC{sub 4} from the sample recovered at ambient conditions. The zero-pressure lattice parameter of the c-BC{sub 4} calculated from diffraction peaks was found to be 3.587 {angstrom}. The composition of the new phase is determined from electron microprobe (EMP) measurements. The value of the C/B ratio is around 4 (3.91 {+-} 0.26).

  4. Phase diagram and decomposition of 1,1-diamino-2,2-dinitroethene single crystals at high pressures and temperatures

    SciTech Connect

    Dreger, Zbigniew A.; Tao, Yuchuan; Gupta, Yogendra M.

    2016-05-10

    The high pressure-high temperature (HP-HT) phase diagram and decomposition of FOX-7, central to understanding its stability and reactivity, were determined using optical spectroscopy and imaging measurements in hydrostatically compressed and heated single crystals. Boundaries between various FOX-7 phases (α, α’, β, γ, and ε) and melting/decomposition curves were established up to 10 GPa and 750 K. Main findings are: (i) a triple point is observed between α, β, and γ phases ~ 0.6 GPa and ~ 535 K, (ii) previously suggested δ phase is not a new phase but is partly decomposed γ phase, (iii) the α-α’ transition takes place along an isobar, whereas the α’-ε transition pressure decreases with increasing temperature, and (iv) melting/decomposition temperatures increase rapidly with pressure, with an increase in the slope at the onset of the α’-ε transition. Our results differ from the recently reported HP-HT phase diagram for nonhydrostatically compressed polycrystalline FOX-7. In addition, the observed interplay between melting and decomposition suggests the suppression of melting with pressure. Our FTIR measurements at different pressures to 3.5 GPa showed similar decomposition products, suggesting similar decomposition pathways irrespective of the pressure. Lastly, the present results provide new insights into the structural and chemical stability of an important insensitive high explosive (IHE) crystal under well-defined HP-HT conditions.

  5. Phase diagram and decomposition of 1,1-diamino-2,2-dinitroethene single crystals at high pressures and temperatures

    DOE PAGES

    Dreger, Zbigniew A.; Tao, Yuchuan; Gupta, Yogendra M.

    2016-05-10

    The high pressure-high temperature (HP-HT) phase diagram and decomposition of FOX-7, central to understanding its stability and reactivity, were determined using optical spectroscopy and imaging measurements in hydrostatically compressed and heated single crystals. Boundaries between various FOX-7 phases (α, α’, β, γ, and ε) and melting/decomposition curves were established up to 10 GPa and 750 K. Main findings are: (i) a triple point is observed between α, β, and γ phases ~ 0.6 GPa and ~ 535 K, (ii) previously suggested δ phase is not a new phase but is partly decomposed γ phase, (iii) the α-α’ transition takes placemore » along an isobar, whereas the α’-ε transition pressure decreases with increasing temperature, and (iv) melting/decomposition temperatures increase rapidly with pressure, with an increase in the slope at the onset of the α’-ε transition. Our results differ from the recently reported HP-HT phase diagram for nonhydrostatically compressed polycrystalline FOX-7. In addition, the observed interplay between melting and decomposition suggests the suppression of melting with pressure. Our FTIR measurements at different pressures to 3.5 GPa showed similar decomposition products, suggesting similar decomposition pathways irrespective of the pressure. Lastly, the present results provide new insights into the structural and chemical stability of an important insensitive high explosive (IHE) crystal under well-defined HP-HT conditions.« less

  6. Stability of rhombohedral phases in vanadium at high-pressure and high-temperature: first-principles investigations

    PubMed Central

    Wang, Yi X.; Wu, Q.; Chen, Xiang R.; Geng, Hua Y.

    2016-01-01

    The pressure-induced transition of vanadium from BCC to rhombohedral structures is unique and intriguing among transition metals. In this work, the stability of these phases is revisited by using density functional theory. At finite temperatures, a novel transition of rhombohedral phases back to BCC phase induced by thermal electrons is discovered. This reentrant transition is found not driven by phonons, instead it is the electronic entropy that stabilizes the latter phase, which is totally out of expectation. Parallel to this transition, we find a peculiar and strong increase of the shear modulus C44 with increasing temperature. It is counter-intuitive in the sense that it suggests an unusual harding mechanism of vanadium by temperature. With these stability analyses, the high-pressure and finite-temperature phase diagram of vanadium is proposed. Furthermore, the dependence of the stability of RH phases on the Fermi energy and chemical environment is investigated. The results demonstrate that the position of the Fermi level has a significant impact on the phase stability, and follows the band-filling argument. Besides the Fermi surface nesting, we find that the localization/delocalization of the d orbitals also contributes to the instability of rhombohedral distortions in vanadium. PMID:27581551

  7. Stability of rhombohedral phases in vanadium at high-pressure and high-temperature: first-principles investigations

    NASA Astrophysics Data System (ADS)

    Wang, Yi X.; Wu, Q.; Chen, Xiang R.; Geng, Hua Y.

    2016-09-01

    The pressure-induced transition of vanadium from BCC to rhombohedral structures is unique and intriguing among transition metals. In this work, the stability of these phases is revisited by using density functional theory. At finite temperatures, a novel transition of rhombohedral phases back to BCC phase induced by thermal electrons is discovered. This reentrant transition is found not driven by phonons, instead it is the electronic entropy that stabilizes the latter phase, which is totally out of expectation. Parallel to this transition, we find a peculiar and strong increase of the shear modulus C44 with increasing temperature. It is counter-intuitive in the sense that it suggests an unusual harding mechanism of vanadium by temperature. With these stability analyses, the high-pressure and finite-temperature phase diagram of vanadium is proposed. Furthermore, the dependence of the stability of RH phases on the Fermi energy and chemical environment is investigated. The results demonstrate that the position of the Fermi level has a significant impact on the phase stability, and follows the band-filling argument. Besides the Fermi surface nesting, we find that the localization/delocalization of the d orbitals also contributes to the instability of rhombohedral distortions in vanadium.

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

    NASA Astrophysics Data System (ADS)

    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.

  9. Phase diagram and decomposition of 1,1-diamino-2,2-dinitroethene single crystals at high pressures and temperatures

    SciTech Connect

    Dreger, Zbigniew A.; Tao, Yuchuan; Gupta, Yogendra M.

    2016-05-10

    The high pressure-high temperature (HP-HT) phase diagram and decomposition of FOX-7, central to understanding its stability and reactivity, were determined using optical spectroscopy and imaging measurements in hydrostatically compressed and heated single crystals. Boundaries between various FOX-7 phases (α, α’, β, γ, and ε) and melting/decomposition curves were established up to 10 GPa and 750 K. Main findings are: (i) a triple point is observed between α, β, and γ phases ~ 0.6 GPa and ~ 535 K, (ii) previously suggested δ phase is not a new phase but is partly decomposed γ phase, (iii) the α-α’ transition takes place along an isobar, whereas the α’-ε transition pressure decreases with increasing temperature, and (iv) melting/decomposition temperatures increase rapidly with pressure, with an increase in the slope at the onset of the α’-ε transition. Our results differ from the recently reported HP-HT phase diagram for nonhydrostatically compressed polycrystalline FOX-7. In addition, the observed interplay between melting and decomposition suggests the suppression of melting with pressure. Our FTIR measurements at different pressures to 3.5 GPa showed similar decomposition products, suggesting similar decomposition pathways irrespective of the pressure. Lastly, the present results provide new insights into the structural and chemical stability of an important insensitive high explosive (IHE) crystal under well-defined HP-HT conditions.

  10. Beryl-II, a high-pressure phase of beryl: Raman and luminescence spectroscopy to 16.4 GPa

    NASA Astrophysics Data System (ADS)

    O'Bannon, Earl; Williams, Quentin

    2016-10-01

    The Raman and Cr3+ and V2+ luminescence spectra of beryl and emerald have been characterized up to 15.0 and 16.4 GPa, respectively. The Raman spectra show that an E 1g symmetry mode at 138 cm-1 shifts negatively by -4.57 (±0.55) cm-1/GPa, and an extrapolation of the pressure dependence of this mode indicates that a soft-mode transition should occur near 12 GPa. Such a transition is in accord with prior theoretical results. Dramatic changes in Raman mode intensities and positions occur between 11.2 and 15.0 GPa. These changes are indicative of a phase transition that primarily involves tilting and mild distortion of the Si6O18 rings. New Raman modes are not observed in the high-pressure phase, which indicates that the local bonding environment is not altered dramatically across the transition (e.g., changes in coordination do not occur). Both sharp line and broadband luminescence are observed for both Cr3+ and V2+ in emerald under compression to 16.4 GPa. The R-lines of both Cr3+ and V2+ shift to lower energy (longer wavelength) under compression. Both R-lines of Cr3+ split at ~13.7 GPa, and the V2+ R1 slope changes at this pressure and shifts more rapidly up to ~16.4 GPa. The Cr3+ R-line splitting and FWHM show more complex behavior, but also shift in behavior at ~13.7 GPa. These changes in the pressure dependency of the Cr3+ and V2+ R-lines and the changes in R-line splitting and FWHM at ~13.7 GPa further demonstrate that a phase transition occurs at this pressure, in good agreement with our Raman results. The high-pressure phase of beryl appears to have two Al sites that become more regular under compression. Hysteresis is not observed in our Raman or luminescence spectra on decompression, suggesting that this transition is second order in nature: The occurrence of a second-order transition near this pressure is also in accord with prior theoretical results. We speculate that the high-pressure phase (beryl-II) might be a mildly modulated structure, and/or that

  11. Stabilization of tetragonal phase in LaN under high pressure via Peierls distortion

    NASA Astrophysics Data System (ADS)

    Mukherjee, D.; Sahoo, B. D.; Joshi, K. D.; Gupta, Satish C.

    2013-08-01

    First-principles calculations have been carried out using the full potential linearized augmented plane wave method to analyze the structural stability of LaN under hydrostatic compression. Our calculations suggest that the rocksalt-type (B1) phase will transform to a primitive tetragonal structure (HP-LaN) having space group symmetry P4/nmm at a pressure of ∼25.8 GPa as compared to the experimental value of 22.8 GPa [Schneider SB, Baumann D, Salamat A, Schnick W, J Appl Phys. 2012;111:093503-1-6]. Additionally, we predict that the HP-LaN structure will further transform to CsCl type (B2) structure at ∼169 GPa. Analysis of band structures of HP-LaN and B2 phases suggests that the low symmetry HP-LaN phase, which can be viewed as a distortion of the B2 structure also, could be stabilized at lower pressure due to total energy lowering caused by Peierls distortion. The elastic moduli of B1 phase as a function of hydrostatic compression have also been calculated. The examination of behavior of elastic moduli as a function of pressure indicates that though the C44 modulus decreases monotonically with increasing pressure, it softens completely at a pressure much beyond the B1 to HP-LaN transition pressure.

  12. Structural and Phase State of Fractured Rotor of High-Pressure Steam Turbine

    NASA Astrophysics Data System (ADS)

    Smirnov, A. N.; Ababkov, N. V.; Kozlov, E. V.; Koneva, N. A.; Popova, N. A.

    2016-03-01

    The structural and phase state of the metal of a fractured rotor of a steam turbine is studied with the use of modern methods of physical research. The metal is shown to contain gradient structures. The cause of the failure of the rotor is established. The gradient structures are determined by the developed method of acoustic scanning.

  13. Molecular dynamics for Raman modes of high pressure phases of hydrogen

    NASA Astrophysics Data System (ADS)

    Magdau, Ioan-Bogdan; Ackland, Graeme

    2013-06-01

    We present ab initio molecular dynamics (MD) calculations of hydrogen at high temperature. We calculated the Raman spectra for phases III and IV and make direct comparison of Raman vibrons with experiment. The MD structures are sensitive to initial conditions and system size, but experimental comparison provides excellent discrimination between structures found, and enables us to explain some of the existing anomalies in the literature. Structures observed for pressure-temperature conditions of phase IV are based on layers of ordered molecules and layers of either static or freely rotating hexagonal trimers, however only two are consistent with experiment. The high temperature phase IV is a hexagonal structure with alternate layers of freely rotating hydrogen molecules, and hexagonal trimers. The low temperature phase III is similar to the C2/c structure previously proposed. These structures are qualitatively different from previous work which introduced spurious features through finite size effects. The MD properly accounts for anharmonic effects and gives much better agreement with Raman data than lattice dynamics calculation.

  14. Monte Carlo simulations of high-pressure phase equilibria of CO2-H2O mixtures.

    PubMed

    Liu, Yang; Panagiotopoulos, Athanassios Z; Debenedetti, Pablo G

    2011-05-26

    Histogram-reweighting grand canonical Monte Carlo simulations were used to obtain the phase behavior of CO(2)-H(2)O mixtures over a broad temperature and pressure range (50 °C ≤ T ≤ 350 °C, 0 ≤ P ≤ 1000 bar). We performed a comprehensive test of several existing water (SPC, TIP4P, TIP4P2005, and exponential-6) and carbon dioxide (EPM2, TraPPE, and exponential-6) models using conventional Lorentz-Berthelot combining rules for the unlike-pair parameters. None of the models we studied reproduce adequately experimental data over the entire temperature and pressure range, but critical assessments were made on the range of T and P where particular model pairs perform better. Away from the critical region (T ≤ 250 °C), the exponential-6 model combination yields the best predictions for the CO(2)-rich phase, whereas the TraPPE/TIP4P2005 model combination provides the most accurate coexistence composition and pressure for the H(2)O-rich phase. Near the critical region (250 °C < T ≤ 350 °C), the critical points are not accurately estimated by any of the models studied, but the exponential-6 models are able to qualitatively capture the critical loci and the shape of the phase envelopes. Local improvements can be achieved at specific temperatures by introducing modification factors to the Lorentz-Berthelot combining rules, but the modified combining rule is still not able to achieve global improvements over the entire temperature and pressure range. Our work points to the challenge and importance of improving current atomistic models so as to accurately predict the phase behavior of this important binary mixture.

  15. Neutron diffraction and electrical transport studies on the incommensurate magnetic phase transition in holmium at high pressures.

    PubMed

    Thomas, Sarah A; Uhoya, Walter O; Tsoi, Georgiy M; Wenger, Lowell E; Vohra, Yogesh K; Chesnut, Gary N; Weir, Samuel T; Tulk, Christopher A; dos Santos, Antonio M

    2012-05-30

    Neutron diffraction and electrical transport measurements have been made on the heavy rare earth metal holmium at high pressures and low temperatures in order to elucidate its transition from a paramagnetic (PM) to a helical antiferromagnetic (AFM) ordered phase as a function of pressure. The electrical resistance measurements show a change in the resistance slope as the temperature is lowered through the antiferromagnetic Néel temperature. The temperature of this antiferromagnetic transition decreases from approximately 122 K at ambient pressure at a rate of -4.9 K GPa(-1) up to a pressure of 9 GPa, whereupon the PM-to-AFM transition vanishes for higher pressures. Neutron diffraction measurements as a function of pressure at 89 and 110 K confirm the incommensurate nature of the phase transition associated with the antiferromagnetic ordering of the magnetic moments in a helical arrangement and that the ordering occurs at similar pressures as determined from the resistance results for these temperatures.

  16. Neutron diffraction and electrical transport studies on the incommensurate magnetic phase transition in holmium at high pressures

    SciTech Connect

    Thomas, Sarah; Uhoya, Walter; Tsoi, Georgiy; Wenger, Lowell E; Vohra, Yogesh; Chesnut, Gary Neal; Weir, S. T.; Tulk, Christopher A; Moreira Dos Santos, Antonio F

    2012-01-01

    Neutron diffraction and electrical transport measurements have been made on the heavy rare earth metal holmium at high pressures and low temperatures in order to elucidate its transition from a paramagnetic (PM) to a helical antiferromagnetic (AFM) ordered phase as a function of pressure. The electrical resistance measurements show a change in the resistance slope as the temperature is lowered through the antiferromagnetic Neel temperature. The temperature of this antiferromagnetic transition decreases from approximately 122 K at ambient pressure at a rate of -4.9 K GPa(-1) up to a pressure of 9 GPa, whereupon the PM-to-AFM transition vanishes for higher pressures. Neutron diffraction measurements as a function of pressure at 89 and 110 K confirm the incommensurate nature of the phase transition associated with the antiferromagnetic ordering of the magnetic moments in a helical arrangement and that the ordering occurs at similar pressures as determined from the resistance results for these temperatures.

  17. Some aspects of two-phase flow, heat transfer and dynamic instabilities in medium and high pressure steam generators

    NASA Astrophysics Data System (ADS)

    Unal, H. C.

    1981-03-01

    Experimental data for void fraction, incipient point of boiling, initial point of net vapor generation, bubble dynamics, dryout, two-phase flow pressure drop and density-wave oscillations were obtained in long, sodium heated steam generator tubes of different geometries for a wide range of operating conditions and at medium and high pressures. These data and data from literature taken in sodium and electrically heated steam generator tubes were correlated. Aspects of two-phase flow, heat transfer and density-wave oscillations in these steam generators disclosed include the distribution factor in small- and medium-size diameter steam generator tubes, the characteristic of the transitions at the incipient point of boiling and initial point of net vapor generation, bubble growth during subcooled nucleate flow boiling, the importance of the equivalent length for dryout in non-uniformly heated steam generator tubes and the mechanisms of density-wave oscillations in once-through steam generator tubes.

  18. Stable high-pressure phases in the H-S system determined by chemically reacting hydrogen and sulfur

    NASA Astrophysics Data System (ADS)

    Goncharov, Alexander F.; Lobanov, Sergey S.; Prakapenka, Vitali B.; Greenberg, Eran

    2017-04-01

    Synchrotron x-ray diffraction and Raman spectroscopy have been used to study the chemical reactions of molecular hydrogen (H2) with sulfur (S) at high pressures. We find theoretically predicted Cccm and I m 3 ¯m H3S to be the reaction products at 50 and 140 GPa, respectively. I m 3 ¯m H3S is a stable crystalline phase above 140 GPa and it transforms to R 3 m H3S on pressure release below 140 GPa. The latter phase is (meta)stable down to at least 70 GPa where it transforms to Cccm H3S upon annealing (T <1300 K) to overcome the kinetic hindrance. Cccm H3S has an extended structure with symmetric hydrogen bonds at 50 GPa, and upon decompression it experiences a transformation to a molecular mixed H2S -H2 structure below 40 GPa without any apparent change in the crystal symmetry.

  19. The origin of low velocity layers in subduction zones: elasticity of hydrous phases at high pressures and temperatures

    NASA Astrophysics Data System (ADS)

    Mookherjee, M.; Chantel, J.; Frost, D. J.

    2012-12-01

    A 5-10 km thick low velocity layer (LVL) at the top of the subducting slab has been seismically detected in many subduction zone settings. The LVL may persist up to a depth of 250 km. The shear wave velocity of the LVL could be 10 % slower than the surrounding mantle. Based on thermal profile of the subducting slabs it is hard to relate the LVL with partial melting or pore fluids. We have undertaken experimental and theoretical studies to constrain the pressure and temperature dependence of elasticity of eclogitic rocks formed from hydrated oceanic crust. In particular, we focus on hydrous phases such as lawsonite [CaAl2Si2O7(OH)2.H2O]. Our study shows that lawsonite has unusual shear modulus at high pressure and temperatures relevant at 250 km depths. Formation of hydrous phases such as lawsonite at the expense of garnet additionally lowers the seismic velocities.

  20. First principles simulation of a superionic phase of hydrogen fluoride (HF) at high pressures and temperatures

    SciTech Connect

    Goldman, N; Fried, L E

    2006-04-10

    The authors have conducted Ab initio molecular dynamics simulations of hydrogen fluoride (HF) at pressures of 5-66 GPa along the 900 K isotherm. They predict a superionic phase at 33 GPa, where the fluorine atoms are fixed in a bcc lattice while the hydrogen atoms diffuse rapidly with a diffusion constant of between 2 x 10{sup -5} and 5 x 10{sup -5} cm{sup 2}/s. They find that a transformation from asymmetric to symmetric hydrogen bonding occurs in HF at 66 GPa and 900 K. With superionic HF they have discovered a model system where symmetric hydrogen bonding occurs at experimentally achievable conditions. Given previous results on superionic H{sub 2}O[1,2,3] and NH{sub 3}[1], they conclude that high P,T superionic phases of electronegative element hydrides could be common.

  1. High-pressure superconducting phase diagram of 6Li: Isotope effects in dense lithium

    PubMed Central

    Schaeffer, Anne Marie; Temple, Scott R.; Bishop, Jasmine K.; Deemyad, Shanti

    2015-01-01

    We measured the superconducting transition temperature of 6Li between 16 and 26 GPa, and report the lightest system to exhibit superconductivity to date. The superconducting phase diagram of 6Li is compared with that of 7Li through simultaneous measurement in a diamond anvil cell (DAC). Below 21 GPa, Li exhibits a direct (the superconducting coefficient, α, Tc∝M−α, is positive), but unusually large isotope effect, whereas between 21 and 26 GPa, lithium shows an inverse superconducting isotope effect. The unusual dependence of the superconducting phase diagram of lithium on its atomic mass opens up the question of whether the lattice quantum dynamic effects dominate the low-temperature properties of dense lithium. PMID:25538300

  2. Effects of 3 GPa High Pressure Treatment on the β1 → α + β2 Phase Transition Dynamics of TC4 Titanium Alloy

    NASA Astrophysics Data System (ADS)

    Wang, Hai-Yan; Chen, Yan; Liu, Jian-Hua; Wang, Wen-Kui

    2013-03-01

    The temperature, duration, activation energy, and Avrami exponent of the solid phase transformation β1 → α + β2 of TC4 titanium alloy treated at 3 GPa in a cooling process are calculated by means of differential scanning calorimetric curves. Then the effects of high pressure on the β1 → α + β2 phase transformation dynamics of TC4 alloy in a cooling process are investigated. The results show that 3 GPa high pressure treatment can increase the activation energy of the TC4 alloy. The beginning time, end time, and duration of the β1 → α + β2 phase transition of the 3 GPa high pressure treated TC4 alloy at the cooling rate of 10°C/min are increased by 2.90°C, 7.78°C and -29.28 s respectively. It is known that 3 GPa high pressure treatment has little effect on the phase transition mechanism.

  3. Superconductivity and crystal structure of high-pressure phases in V-Ru-H system

    NASA Astrophysics Data System (ADS)

    Animonov, V. Ye.; Belash, I. T.; Ponyatovskiy, Ye. G.; Rashchupkin, V. I.; Romanenko, I. M.

    1987-10-01

    In the search for materials which, upon hydrogenation, form phase with higher superconductor transition temperature, V-Ru alloys were selected for study. Specimens were produced by mixing electrolytic powder of each metal into three batches with 10, 18, 33 atom percent. respectively, compacting the mixtures under a pressure of 20 kbar at room temperature, and then sintering them in an induction furnace in an argon atmosphere. The compacts were annealed at 1200 C in vacuum (10 to the -6 torr) for 24 h then cooled in the furnace. The specimens of three alloys, now containing 10, 18.5., 34+0.4 atom percent Ru, respectively, were hydrogenated in an H2 atmosphere at 300 C under pressures up to 70 kbar for 24 h and then quenched under pressure to about -180 C. The hydrogen content was then determined accurately within 5 percent, from the amount of H2 evolving during thermal decomposition at 500 C. The superconducting transition temperature was measured by the inductive method. The results reveal formation of a phase with the atomic hydrogen-to-metal ratio H:Me approx = 1 and an f.c.c. metal sublattice in the V sub 90 Ru sub 10-H alloy, only this phase being superconductive at temperatures T greater than or = 2K with a 0.3 K wide transition range.

  4. Low-temperature and high-pressure phase transitions in ferroelectric dabcoHBF4

    NASA Astrophysics Data System (ADS)

    Szafranski, Marek

    2004-09-01

    NH--N hydrogen bonded ferroelectric dabcoHBF4, [C6H13N2]+·BF4-, has been studied by dielectric spectroscopy, differential thermal analysis and pyroelectric charge measurement investigations in the low-temperature range between 12 and 300 K, and at elevated hydrostatic pressures up to 1 GPa. The p-T phase diagram has been determined and described. In addition to the known first-order phase transitions at 378 and 153 K, two new structural transitions of continuous type have been revealed, i.e., the transition at 37 K and the pressure-induced one occurring above the triple point situated at 80 MPa and 165 K. Both of these transitions have essentially displacive character and a mechanism related to distortions of the hydrogen bonded polycationic chains, preserving polar properties of the crystal. The possible order-disorder contribution to the transition at 153 K between the ferroelectric phases II and III is discussed in relation to the conformational properties of the dabco cation.

  5. Phase Equilibria of the Carbon Dioxide + 1-Decanol System at High Pressures.

    PubMed

    Ioniţă, Simona; Feroiu, Viorel; Geană, Dan

    2013-11-14

    In this work experimental vapor-liquid equilibrium (VLE) data and three-phase vapor-liquid-liquid equilibrium (VLLE) data are presented for the carbon dioxide + 1-decanol system. The VLE data were measured at five temperatures, (303.2, 308.2, 323.2, 333.2, and 343.2) K, and pressures up to 16 MPa. The VLLE data cover pressure-temperature (P-T) values from 289 K and 5 MPa to the upper critical end point (UCEP). We have used two models to represent the complex fluid phase behavior (P-T critical curve, VLLE line, and VLE isotherms) of the carbon dioxide + 1-decanol system: the cubic general equation of state (GEOS) and Peng-Robinson (PR) equation in conjunction with van der Waals two parameters conventional mixing rules (2PCMR). A correlation method involving temperature-dependent interaction parameters and a semipredictive approach with independent temperature interaction parameters have been used. Comparisons with experimental data reported in this work and available in the literature indicate that the topology of fluid phase behavior is satisfactorily given by the semipredictive procedure both for the critical line and in subcritical region, considering the relative simple used cubic equations of state.

  6. Phase Behavior of Three PBX Elastomers in High-Pressure Chlorodifluoromethane

    NASA Astrophysics Data System (ADS)

    Lee, Byung-Chul

    2017-10-01

    The phase equilibrium behavior data are presented for three kinds of commercial polymer-bonded explosive (PBX) elastomers in chlorodifluoromethane (HCFC22). Levapren^{{registered }} ethylene- co-vinyl acetate (LP-EVA), HyTemp^{{registered }} alkyl acrylate copolymer (HT-ACM), and Viton^{{registered }} fluoroelastomer (VT-FE) were used as the PBX elastomers. For each elastomer + HCFC22 system, the cloud point (CP) and/or bubble point (BP) pressures were measured while varying the temperature and elastomer composition using a phase equilibrium apparatus fitted with a variable-volume view cell. The elastomers examined in this study indicated a lower critical solution temperature phase behavior in the HCFC22 solvent. LP-EVA showed the CPs at temperatures of 323 K to 343 K and at pressures of 3 MPa to 10 MPa, whereas HT-ACM showed the CPs at conditions between 338 K and 363 K and between 4 MPa and 12 MPa. For the LP-EVA and HT-ACM elastomers, the BP behavior was observed at temperatures below about 323 K. For the VT-FE + HCFC22 system, only the CP behavior was observed at temperatures between 323 K and 353 K and at pressures between 6 MPa and 21 MPa. As the elastomer composition increased, the CP pressure increased, reached a maximum value at a specific elastomer composition, and then remained almost constant.

  7. Enhanced superconductivity in the high pressure phase of SnAs studied from first principles

    NASA Astrophysics Data System (ADS)

    Sreenivasa Reddy, P. V.; Kanchana, V.; Millichamp, T. E.; Vaitheeswaran, G.; Dugdale, S. B.

    2017-01-01

    First principles calculations are performed using density functional theory and density functional perturbation theory for SnAs. Total energy calculations show the first order phase transition from an NaCl structure to a CsCl one at around 37 GPa, which is also confirmed from enthalpy calculations and agrees well with experimental work. Calculations of the phonon structure and hence the electron-phonon coupling, λep, and superconducting transition temperature, Tc, across the phase diagram are performed. These calculations give an ambient pressure Tc, in the NaCl structure, of 3.08 K, in good agreement with experiment whilst at the transition pressure, in the CsCl structure, a drastically increased value of Tc = 12.2 K is found. Calculations also show a dramatic increase in the electronic density of states at this pressure. The lowest energy acoustic phonon branch in each structure also demonstrates some softening effects. Electronic structure calculations of the Fermi surface in both phases are presented for the first time as well as further calculations of the generalised susceptibility with the inclusion of matrix elements. These calculations indicate that the softening is not derived from Fermi surface nesting and it is concluded to be due to a wavevector-dependent enhancement of the electron-phonon coupling.

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

    NASA Astrophysics Data System (ADS)

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

    2014-06-01

    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.

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

    SciTech Connect

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

    2016-04-07

    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 the 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. Additionally, the unit cell volumes of each phase deviate from the expected thermal expansion behavior just before each transition is observed from the diffraction data. 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.

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

    PubMed

    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.

  11. New investigations on shock-wave synthesized high-pressure phases in the system Si-Al-O-N

    NASA Astrophysics Data System (ADS)

    Schlothauer, T.; Greif, A.; Keller, K.; Schwarz, M. R.; Kroke, E.; Heide, G.

    2012-12-01

    The shock-wave synthesis of nanostructured high-pressure phases at a gram-scale permits the analysis of spinel type nitrides with different chemical composition using methods not suitable for microgram amounts of material. Methods with a significant mass loss through the analytical process like TG-MS or FT-IR or bulk methods at the g-scale like 29Si-MAS-NMR or neutron diffraction were used. The synthesis of pure high-pressure modifications (gamma-phases) of different SiAlON-compounds using amorphous H-bearing precursors at pressures of 30-40 GPa is a necessary prerequisite for precise determinations of crystal chemical features. Etching with HF is a well-known method to purify the high-pressure nitrides (Sekine 2002). The etched parts were analyzed by neutron diffraction, TG-MS, and carrier gas hot extraction (CGHE). Volatile elements like H2 and Cl2, as well as non-stoichiometric oxygen and nitrogen, and NOx, H2O are enriched in the disordered rims. This degassing process ends at temperatures of approximately 600°C, while the spinel structure remains well preserved up to 1300°C. Under these conditions the gamma-phases stay unchanged under air, argon and vacuum. Furthermore chlorine, an important impurity of the H-bearing precursors neither influences the synthesized products nor the synthesis process itself. IR-spectroscopy of gamma-Si3(O,N)4 shows that peak shifts of octahedral lattice vibrations (≈ 680 cm-1) and both tetrahedral vibrations (ny3 and ny4) (Jeanloz 1980, Preudhomme & Tarte 1971) to higher frequencies with decreasing oxygen content occur. This effect is also visible in samples contaminated with impurities of low pressure modifications. The more complex structure of gamma-SiAlON and the simultaneously exchange of the cation- and the anion-positions prevents the appearance of this important feature. Yet to be synthesized pure gamma-SiAlON using similar H-bearing precursors is necessary to resolve its structure. Sekine, T., H. He, T. Kobayashi, K

  12. Structure and elasticity of phase-pi, Al3Si2O7(OH)3 at high-Pressure

    NASA Astrophysics Data System (ADS)

    Liu, S.; Mookherjee, M.; Hermann, A.; Wunder, B.

    2016-12-01

    Phase-pi is a hydrous aluminosilicate (Al3Si2O7(OH)3) mineral that is likely to be stabilized in subducted sedimentary rocks. It is capable of transporting water into the deep Earth. The mineralogy of subducted sediments can be modeled within the ternary system with Al2O3-SiO2-H2O (ASH) as end member components. Hydrous phases that are stable in the ASH ternary system includes gibbsite (Al(OH)3), diaspore (AlOOH), kaolinite (Al2Si2O5(OH)4), topaz-OH (Al2SiO4(OH)2), phase Egg (AlSiO3(OH)), and phase-Pi (Al3Si2O7(OH)3). Among these various phases almost nothing is known about the high-pressure behavior of phase-Pi. High-pressure phase relations have shown that phase-Pi is stable between 2 and 7 GPa (Wunder et al., 1993). Here we report the crystal structure and elasticity as a function of pressure. We find that the pressure volume results from the first principles simulation could be described by a finite strain fit with volume, V0, bulk modulus, K0, and its pressure derivative at zero pressure, K0' as 310.3 Å3, 133 GPa, and 3.6, respectively. At zero pressure, the full elastic stiffness tensor shows significant anisotropy with the diagonal principal components- C11, C22, and C33 being 235.0 (7.2), 291.5 (6.2), 265.6 (4.6) GPa respectively, the diagonal shear C44, C55, and C66 being 86.0 (1.8), 92.4 (3.3), and 87.2 (1.2) GPa respectively, and the off-diagonal stiffness C12, C13, C14, C15, C16, C23, C24, C25, C26, C34, C35, C36, C45, C46, and C56 being 73.4 (3.7), 77.8 (3.1), 6.2 (0.2), -29.6 (1.2), 14.6 (-0.2), 60.6 (3.2), 17.3 (-0.2), 2.4 (0.5), 1.3 (0.02), -12.8 (-0.3), -14.7 (0.6), 5.5 (0.1), 3.3 (-0.4), 1.0 (0.3), and 3.3 (-0.3) GPa respectively. The numbers in the brackets represent the pressure derivatives of the components of full elastic stiffness tensor, i.e., dCij/dP. Upon compression, hydrogen bonding in phase-pi diversifies, with some hydrogen bonds weakening and others strengthening. The latter eventually undergo symmetrization at pressure greater (> 40

  13. High-pressure phase transitions and compressibility of wolframite-type tungstates

    NASA Astrophysics Data System (ADS)

    Ruiz-Fuertes, J.; López-Moreno, S.; Errandonea, D.; Pellicer-Porres, J.; Lacomba-Perales, R.; Segura, A.; Rodríguez-Hernández, P.; Muñoz, A.; Romero, A. H.; González, J.

    2010-04-01

    This paper reports an investigation on the phase diagram and compressibility of wolframite-type tungstates by means of x-ray powder diffraction and absorption in a diamond-anvil cell and ab initio calculations. X-ray diffraction experiments show that monoclinic wolframite-type MgWO4 suffers at least two phase transitions, the first one being to a triclinic polymorph with a structure similar to that of CuWO4 and FeMoO4-II. The onset of each transition is detected at 17.1 and 31 GPa. In ZnWO4 the onset of the monoclinic-triclinic transition has been also found at 16.7 GPa. This transition does not involve any change in the atomic coordination as confirmed by x-ray absorption measurements. These findings are supported by density-functional theory calculations, which predict the occurrence of additional transitions upon further compression. Calculations have been also performed for wolframite-type MnWO4, which is found to have an antiferromagnetic configuration. In addition, our study reveals details of the local-atomic compression in MgWO4 and ZnWO4. In particular, below the transition pressure the ZnO6 and equivalent polyhedra tend to become more regular, whereas, the WO6 octahedra remain almost unchanged. Fitting the pressure-volume data we obtained the equation of state for the low-pressure phase of MgWO4 and ZnWO4. These and previous results on MnWO4 and CdWO4 are compared with the calculations. The compressibility of wolframite-type tungstates is also systematically discussed. Finally Raman spectroscopy measurements and lattice dynamics calculations are presented for MgWO4.

  14. High pressure structural phase transition of osmium nitride (OsN)

    NASA Astrophysics Data System (ADS)

    Sarwan, Madhu; Abdul Shukoor, V.; Dubey, Ritu; Singh, Sadhna

    2015-05-01

    The structural phase transition and relative volume change of OsN compound has been investigated by means of interaction potential model (IPM) which consists of Coulomb interaction, three-body interaction (TBI), van der Waal interaction (vdW) and short range overlap repulsive interactions up to second neighbor ions. It is found that the OsN transforms from zinc-blende structure (B3) to rock-salt structure (B1) at 87.0 GPa. The second order elastic constants are also investigated. These results are compared with available results.

  15. The separation of glutathione transferase subunits by using reverse-phase high-pressure liquid chromatography.

    PubMed Central

    Ostlund Farrants, A K; Meyer, D J; Coles, B; Southan, C; Aitken, A; Johnson, P J; Ketterer, B

    1987-01-01

    A simple method is described for the separation and quantification of the subunits of GSH transferases present in rat tissue extracts. This method, involving GSH-agarose affinity chromatography followed by reverse-phase h.p.l.c., is rapid and sufficiently sensitive to measure 5 micrograms of each subunit in a mixture. Examples are given of its application to extracts of rat kidney, adrenal, testicular interstitial cells and seminiferous tubules. The analysis of seminiferous tubules indicates that the technique may be of value for the identification of novel subunits. Preliminary separations of subunits from human GSH transferases are also described. PMID:3663168

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

    NASA Astrophysics Data System (ADS)

    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.

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

    SciTech Connect

    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.

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

    PubMed

    Bouibes, A; Zaoui, A

    2015-07-23

    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.

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

    PubMed Central

    Bouibes, A.; 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, 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. PMID:26202342

  20. Phase relations in Fe-Ni-C system at high pressures and temperatures

    SciTech Connect

    Narygina, O; Dubrovinsky, L S; Miyajima, N; McCammon, C A; Kantor, I Yu; Mezouar, M; Prakapenka, V B; Dubrovinskaia, N A; Dmitriev, V

    2012-10-23

    We performed comparative study of phase relations in Fe1-x Nix (0.10 ≤ x ≤ 0.22 atomic fraction) and Fe0.90Ni0.10-x Cx (0.1 ≤ x ≤ 0.5 atomic fraction) systems at pressures to 45 GPa and temperatures to 2,600 K using laser-heated diamond anvil cell and large-volume press (LVP) techniques. We show that laser heating of Fe,Ni alloys in DAC even to relatively low temperatures can lead to the contamination of the sample with the carbon coming from diamond anvils, which results in the decomposition of the alloy into iron- and nickel-rich phases. Based on the results of LVP experiments with Fe-Ni-C system (at pressures up to 20 GPa and temperatures to 2,300 K) we demonstrate decrease of carbon solubility in Fe,Ni alloy with pressure.

  1. Phase relations in the system diopside-jadeite at high pressures and high temperatures

    NASA Astrophysics Data System (ADS)

    Liu, Lin-Gun

    1980-05-01

    Phase behaviour in the system diopside-jadeite (CaMgSi 2O 6sbnd NaAlSi 2O 6) have been investigated in the pressure region 100-300 kbar at about 1000°C in a diamond-anvil press coupled with laser heating. The omphacite solid solution extends from 30 to at least 200 kbar for the entire system. Omphacites, ranging in composition from pure diopside to more than 40 mole % jadeite, transform to diopside (II) at pressures greater than 230 kbar. Diopside (II), which probably possesses a perovskite-type structure, cannot be preserved when experiments are quenched to ambient conditions. Jadeite-rich omphacites were found to decompose into an assemblage of NaAlSiO 4(CaFe 2O 4-type structure) + stishovite + diopside (II) (?) at pressures greater than about 260 kbar. These results suggest that an eclogitic model mantle would not display the 400-km seismic discontinuity. Moreover, sodium in the transition zone and lower mantle would most likely be accommodated in phases of omphacite and diopside (II).

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

    NASA Astrophysics Data System (ADS)

    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.

  3. Elasticity of single-crystal superhydrous phase B at simultaneous high pressure-temperature conditions

    NASA Astrophysics Data System (ADS)

    Li, Xinyang; Mao, Zhu; Sun, Ningyu; Liao, Yifan; Zhai, Shuangmeng; Wang, Yi; Ni, Huaiwei; Wang, Jingyun; Tkachev, Sergey N.; Lin, Jung-Fu

    2016-08-01

    We investigated the combined effect of pressure and temperature on the elasticity of single-crystal superhydrous phase B (Shy-B) using Brillouin scattering and X-ray diffraction up to 12 GPa and 700 K. Using the obtained elasticity, we modeled the anisotropy of Shy-B along slab geotherms, showing that Shy-B has a low anisotropy and cannot be the major cause of the observed anisotropy in the region. Modeled velocities of Shy-B show that Shy-B will be shown as positive velocity anomalies at the bottom transition zone. Once Shy-B is transported to the topmost lower mantle, it will exhibit a seismic signature of lower velocities than topmost lower mantle. We speculate that an accumulation of hydrous phases, such as Shy-B, at the topmost lower mantle with a weight percentage of ~17-26% in the peridotite layer as subduction progresses could help explain the observed 2-3% low shear velocity anomalies in the region.

  4. A theoretical study of MgH2 ambient and high-pressure phases using NQCC parameters

    NASA Astrophysics Data System (ADS)

    Rafiee, Marjan A.

    2014-12-01

    Quadrupolar parameters of nuclei can be used as a tool to understand the electronic structure of the compounds. Magnesium hydride (MgH2) is a potential hydrogen storage material due to its outstanding hydrogen capacity, however, its high thermodynamic stability is unfavorable for dehydrogenation processes. Understanding the bonding nature of Mg and H is essential for improving its dehydrogenation performance. In this work the charge density distribution in MgH2 is studied. For this purpose, using calculated NQCCs of hydrogen atoms, the electronic structure of α-MgH2 with several high pressure forms of MgH2 were compared. The results show that in the high pressure phases (β, γ, and δ) some hydrogens have very small NQCC and therefore these hydrogens form weaker bond with Mg. In other words, easier condition for dehydrogenation in pressure-induced forms is expected. The electric field gradient (EFG) at the site of quadrupolar nuclei were calculated to obtain NQCC parameters using Gaussian 03 at B3LYP/6-31G level of theory. The selected level and basis set give the rather acceptable qualitative NQCCs of hydrogen atoms.

  5. New high-pressure phase of Fe3S predicted from first-principles calculation

    NASA Astrophysics Data System (ADS)

    Ishikawa, T.; Tsuchiya, T.

    2010-12-01

    It has long been recognized that the Earth's outer core must contain a significant amount of light elements, candidates for which have included hydrogen, carbon, silicon, sulfur and oxygen. High-P,T experiments (Jephcoat and Olson, 1987; Mao et al., 1998; Fiquet et al., 2001;Uchida et al., 2001) extended this argument to the inner core on the basis of the equation of state analysis of the hexagonal-closed-pack (hcp) form of pure iron, which concluded that it still has 4-5% excess density compared to the inner core values, although significant extrapolations were usually applied. At present, one of the most popular light-element candidates is sulfur. Therefore, it is crucial to determine the melting behavior of the Fe-FeS binary under core conditions, before models of core formation can be developed. The Fe-FeS binary was known to form a eutectic at low pressures (Usselman, 1975). Sherman (1995), however, suggested the stabilization of an intermediate iron sulfide compound Fe3S with AuCu3 form theoretically, and then Fei et al. (1997) found in the high-P,T experiments that Fe3S2 forms over 14 GPa, and Fe3S and Fe2S further form over 21 GPa (Fei et al., 2000). Fe3S, which is the most iron-rich sulfide compound known to exist, has a tetragonal cell isostructural with the Fe3P structure (space group No.82, Z = 8) and no phase transition has so far been identified up to 80 GPa (Seagle et al., 2006) and even at over 200 GPa (Kuwayama private comm.). These are supportive of an ab initio investigation (Martin et al., 2004), which found that the Fe3P structure is the most stable among fcc, LaF3, YF3 and Fe3P postulations. In this study, we explored higher-pressure phases of Fe3S using first-principles calculations. Comparing enthalpies among candidate structures, we found a new structure which is more stable than the Fe3P structure at the inner core pressures. In our presentation, we will make a detailed report with respect to the new stable structure and discuss phase

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

    SciTech Connect

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

    2016-04-07

    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.

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

    SciTech Connect

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

    2016-04-07

    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 8GPa and 600K. 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 0–10GPa and 300–650K

  8. Characterization of the high-pressure structures and phase transformations in SnO2. A density functional theory study.

    PubMed

    Gracia, L; Beltrán, A; Andrés, J

    2007-06-14

    Theoretical investigations concerning the high-pressure polymorphs, the equations of state, and the phase transitions of SnO2 have been performed using density functional theory at the B3LYP level. Total energy calculations and geometry optimizations have been carried out for all phases involved, and the following sequence of structural transitions from the rutile-type (P42/mnm) driven by pressure has been obtained (the transition pressure is in parentheses): --> CaCl2-type, Pnnm (12 GPa) --> alpha-PbO2-type, Pbcn (17 GPa) --> pyrite-type, Pa (17 GPa) --> ZrO2-type orthorhombic phase I, Pbca (18 GPa) --> fluorite-type, Fmm (24 GPa) --> cotunnite-type orthorhombic phase II, Pnam (33 GPa). The highest bulk modulus values, calculated by fitting pressure-volume data to the second-order Birch-Murnaghan equation of state, correspond to the cubic pyrite and the fluorite-type phases with values of 293 and 322 GPa, respectively.

  9. Study of Raman Spectroscopy on Phase Relations of CaCO3 at High Temperature and High Pressure

    NASA Astrophysics Data System (ADS)

    Li, M.; Zheng, H.; Duan, T.

    2006-05-01

    Laser Raman Spectroscopy was used to study phase relations between calcite I, calcite II and aragonite at high pressure and high temperature. The experiment was performed in an externally heated Basselt type diamond anvil cell (DAC). Natural calcite (calcite I) was used as starting mineral. The sample and a small chip of quartz were loaded in a cavity (300 μm in diameter and 250 μm in depth) in a rhenium gasket. The Na2CO3 aqueous solution of 1mol/L was also loaded as a pressure medium to yield hydrostatic pressure. The whole assembly was pressurized first and then heated stepwise to 400°C. Pressure and temperature in the chamber were determined by the shift of Raman band at 464 cm-1 of quartz and by NiCr-NiSi thermocouple, respectively. The Raman spectra were measured by a Renishaw 1000 spetrometer with 50 mW of 514.5nm argon-ion laser as the excitation light source. The slit width was 50 μm and the corresponding resolution was ±1 cm-1. From the experiments, we observed the phase transitions between calcite I and calcite II, calcite I and aragonite, calcite II and aragonite, respectively. Our data showed a negative slope for the boundary between calcite I and calcite II, which was similar to Bridgman's result, although Hess et al. gave a positive slope. The boundary with a negative slope for calcite II and aragonite was also defined, which had never been done before. And all these data can yield a more complete phase diagram of CaCO3 than the studies of Hess et al. and Suito et al.Reference:Bridgeman P. W.(1939) Journal: American Journal of Science, Vol. 237, p. 7-18Bassett W. A. et al. (1993) Journal: Review of Scientific Instruments, Vol. 64, p. 2340-2345Suito K. et al. (2001) Journal: American Mineralogist, Vol. 86, p. 997- 1002Hess N. J. et al. (1991) In A. K. Singh, Ed., Recent Trends in High Pressure Research; Proc. X IIIth AIRAPT International Conference on High Pressure Science and Technology, p. 236-241. Oxford & IBH Publishing Co. Pvt, Ltd., New

  10. Benzene under high pressure: A story of molecular crystals transforming to saturated networks, with a possible intermediate metallic phase

    SciTech Connect

    Wen, Xiao-Dong; Hoffmann, Roald; Ashcroft, N. W.

    2011-01-01

    In a theoretical study, benzene is compressed up to 300 GPa. The transformations found between molecular phases generally match the experimental findings in the moderate pressure regime (<20 GPa): phase I (Pbca) is found to be stable up to 4 GPa, while phase II (P43212) is preferred in a narrow pressure range of 4–7 GPa. Phase III (P21/c) is at lowest enthalpy at higher pressures. Above 50 GPa, phase V (P21 at 0 GPa; P21/c at high pressure) comes into play, slightly more stable than phase III in the range of 50–80 GP, but unstable to rearrangement to a saturated, four-coordinate (at C), one-dimensional polymer. Actually, throughout the entire pressure range, crystals of graphane possess lower enthalpy than molecular benzene structures; a simple thermochemical argument is given for why this is so. In several of the benzene phases there nevertheless are substantial barriers to rearranging the molecules to a saturated polymer, especially at low temperatures. Even at room temperature these barriers should allow one to study the effect of pressure on the metastable molecular phases. Molecular phase III (P21/c) is one such; it remains metastable to higher pressures up to ~200 GPa, at which point it too rearranges spontaneously to a saturated, tetracoordinate CH polymer. At 300 K the isomerization transition occurs at a lower pressure. Nevertheless, there may be a narrow region of pressure, between P = 180 and 200 GPa, where one could find a metallic, molecular benzene state. We explore several lower dimensional models for such a metallic benzene. We also probe the possible first steps in a localized, nucleated benzene polymerization by studying the dimerization of benzene molecules. Several new (C6H6)2 dimers are predicted.

  11. Seismic signature of ultra-high pressure hydrous phases in subduction zones and constrains on water recycling

    NASA Astrophysics Data System (ADS)

    Rosa, A. D.; Sanchez-Valle, C.

    2012-12-01

    Seismic anomalies in deep slabs including low velocity zones and seismic anisotropies have often been attributed to the presence of hydrated regions. Superhydrous phase B and phase D which can respectively contain up to 5.8 wt.% and 10 wt.% of water are considered as important water carriers in cold slabs. Phase equilibrium studies have also shown that these phases can represent up to 50 vol.% in water saturated peridotites [1]. Recent Brillouin scattering experiments performed at ambient conditions have revealed the potential for both phases to be responsible for the observed negative velocity anomalies [2]. In addition, due to their layered structure both phases may easily align in a stress field and therefore significantly contribute to observed seismic anisotropies. The detailed knowledge of their seismic properties at high pressure is therefore essential to infer the hydration state of deep subducted slabs. Here, we report the single-crystal elastic properties of superhydrous phase B (chemical composition Mg10.4Si3.1H2.7O18) using Brillouin scattering in the diamond anvil cell. The results on the elasticity studies are combined with previous plasticity studies on phase D [3] and most plausible slip systems of superhydrous B to evaluate the velocity contrast between hydrous and anhydrous peridotites and the contribution of these phases to seismic anisotropy in deep subducted slabs. The results will be discussed in the light of seismic observations to draw a better picture of water recycling via subduction beyond 410 km depth. [1] Iwamori, H. (2004), Earth Planet. Sc. Lett. 227, 57-71. [2] Rosa, A.D., C. Sanchez-Valle and S. Ghosh (2012) Geophys. Res. Lett., 39, L06304. [3] Rosa A.D., et al. (2011) Abstract DI44A-03 Fall AGU Meeting 2011.

  12. Flash flow pyrolysis: mimicking flash vacuum pyrolysis in a high-temperature/high-pressure liquid-phase microreactor environment.

    PubMed

    Cantillo, David; Sheibani, Hassan; Kappe, C Oliver

    2012-03-02

    Flash vacuum pyrolysis (FVP) is a gas-phase continuous-flow technique where a substrate is sublimed through a hot quartz tube under high vacuum at temperatures of 400-1100 °C. Thermal activation occurs mainly by molecule-wall collisions with contact times in the region of milliseconds. As a preparative method, FVP is used mainly to induce intramolecular high-temperature transformations leading to products that cannot easily be obtained by other methods. It is demonstrated herein that liquid-phase high-temperature/high-pressure (high-T/p) microreactor conditions (160-350 °C, 90-180 bar) employing near- or supercritical fluids as reaction media can mimic the results obtained using preparative gas-phase FVP protocols. The high-T/p liquid-phase "flash flow pyrolysis" (FFP) technique was applied to the thermolysis of Meldrum's acid derivatives, pyrrole-2,3-diones, and pyrrole-2-carboxylic esters, producing the expected target heterocycles in high yields with residence times between 10 s and 10 min. The exact control over flow rate (and thus residence time) using the liquid-phase FFP method allows a tuning of reaction selectivities not easily achievable using FVP. Since the solution-phase FFP method does not require the substrate to be volatile any more--a major limitation in classical FVP--the transformations become readily scalable, allowing higher productivities and space-time yields compared with gas-phase protocols. Differential scanning calorimetry measurements and extensive DFT calculations provided essential information on pyrolysis energy barriers and the involved reaction mechanisms. A correlation between computed activation energies and experimental gas-phase FVP (molecule-wall collisions) and liquid-phase FFP (molecule-molecule collisions) pyrolysis temperatures was derived.

  13. Phase diagram for ammonia-water mixtures at high pressures - Implications for icy satellites

    NASA Technical Reports Server (NTRS)

    Cynn, H. C.; Boone, S.; Koumvakalis, A.; Nicol, M.; Stevenson, D. J.

    1989-01-01

    The (NH3)x(H2O)1-x phase diagram for X from 0 to 0.50 has been reexamined at temperatures from 125 K to 400 K and at pressures from 6.0 GPa using diamond anvil cells, and the implications of the findings for icy satellites are addressed. Titan is likely to have a thicker NH3-H2O ocean than previously suspected, because the stability field of NH3-H2O is found to be smaller than previously supposed. The implications for methane and ammonia volcanism on Titan are briefly discussed. The experimentally observed reactivity between the liquid and iron may also have implications for planetary and satellite evolution.

  14. Phase Transformations and Metallization of Magnesium Oxide at High Pressure and Temperature

    NASA Astrophysics Data System (ADS)

    McWilliams, R. Stewart; Spaulding, Dylan K.; Eggert, Jon H.; Celliers, Peter M.; Hicks, Damien G.; Smith, Raymond F.; Collins, Gilbert W.; Jeanloz, Raymond

    2012-12-01

    Magnesium oxide (MgO) is representative of the rocky materials comprising the mantles of terrestrial planets, such that its properties at high temperatures and pressures reflect the nature of planetary interiors. Shock-compression experiments on MgO to pressures of 1.4 terapascals (TPa) reveal a sequence of two phase transformations: from B1 (sodium chloride) to B2 (cesium chloride) crystal structures above 0.36 TPa, and from electrically insulating solid to metallic liquid above 0.60 TPa. The transitions exhibit large latent heats that are likely to affect the structure and evolution of super-Earths. Together with data on other oxide liquids, we conclude that magmas deep inside terrestrial planets can be electrically conductive, enabling magnetic field-producing dynamo action within oxide-rich regions and blurring the distinction between planetary mantles and cores.

  15. Isolation and determination of deoxynivalenol by reversed-phase high-pressure liquid chromatography

    PubMed Central

    Gupta, Vikas Kumar; Chattopadhyay, Pronobesh; Kalita, Mohan Ch; Chaurasia, Asshwani Kumar; Gogoi, Hemanta Kumar; Singh, Lokendra

    2011-01-01

    Deoxynivalenol (DON) is a mycotoxin produced by food contamination. It is a pharmacologically active compound that acts on the serotonin receptor, leading to several neuroendocrine and hematological disorders. In this article we describe a simple, accurate, and sensitive method for the quantification of DON. DON was quantified using a Phenomenex® ODS analytical C18 column (150 mm × 46 mm, 5 μm) with a mobile phase composed of mixture of water-acetonitrile-methanol (5:4:1, v/v/v) at a flow rate of 1.5 ml/min and at 254 nm in an ultraviolet (UV) detector The method has been validated with isolated samples of DON and provides a tool for the control of substandard and counterfeit commercial food products. PMID:23781426

  16. Phase diagram for ammonia-water mixtures at high pressures - Implications for icy satellites

    NASA Technical Reports Server (NTRS)

    Cynn, H. C.; Boone, S.; Koumvakalis, A.; Nicol, M.; Stevenson, D. J.

    1989-01-01

    The (NH3)x(H2O)1-x phase diagram for X from 0 to 0.50 has been reexamined at temperatures from 125 K to 400 K and at pressures from 6.0 GPa using diamond anvil cells, and the implications of the findings for icy satellites are addressed. Titan is likely to have a thicker NH3-H2O ocean than previously suspected, because the stability field of NH3-H2O is found to be smaller than previously supposed. The implications for methane and ammonia volcanism on Titan are briefly discussed. The experimentally observed reactivity between the liquid and iron may also have implications for planetary and satellite evolution.

  17. Laser-driven formation of a high-pressure phase in amorphous silica

    SciTech Connect

    Salleo, Alberto; Taylor, Seth T.; Martin, Michael C.; Panero, Wendy R.; Jeanloz, Raymond; Genin, Francois Y.; Sands, Timothy

    2002-05-31

    A combination of electron diffraction and infrared reflectance measurements shows that synthetic silica transforms partially into stishovite under high-intensity (GW/cm2) laser irradiation, probably by the formation of a dense ionized plasma above the silica surface. During the transformation the silicon coordination changes from four-fold to six-fold and the silicon-oxygen bond changes from mostly covalent to mostly ionic, such that optical properties of the transformed material differ significantly from those of the original glass. This phase transformation offers one suitable mechanism by which laser-induced damage grows catastrophically once initiated, thereby dramatically shortening the service lifetime of optics used for high-power photonics applications such as inertial confinement fusion.

  18. High-pressure and high-temperature stability and equation of state of superhydrous phase B

    NASA Astrophysics Data System (ADS)

    Inoue, Toru; Ueda, Takayuki; Higo, Yuji; Yamada, Akihiro; Irifune, Tetsuo; Funakoshi, Ken-ichi

    We have determined the stability and P-V-T equation of state of superhydrous phase B, Mg10Si3O18H4 (hereafter referred to as Shy-B) by in situ X-ray diffraction measurements at SPring-8 at pressure between 13 and 23 GPa and temperatures up to 1400°C. High temperature X-ray diffraction measurements using a conventional X-ray source were also conducted to determine the thermal expansion coefficient at atmospheric pressure. Shy-B was found to melt incongruently into assemblies of wadsleyite (β) + liquid, or ringwoodite (γ) + liquid, depending on pressure at temperatures of 1000-1250°C. The isothermal bulk modulus (KT0) and temperature derivative (dK/dT) of Shy-B are 132(1) GPa and -2.5(1)×10-2 GPa/K, respectively, when we adopted an equation of state of Au proposed by Anderson et al. [1989] and also assumed its pressure derivative is 5.8 proposed by Crichton et al. [1999], while the thermal expansion coefficient (α0) is 37.6(1)×10-6 K-1. Phase relations imply that Shy-B may be stable in relatively low temperature regions of the mantle transition zone, such as within older subducted slabs, but not in the surrounding mantle. The density difference between model subducted hydrous slabs and the surrounding mantle was calculated at 20 GPa as functions of water content and temperature in the slab using the present results, which demonstrates that the Shy-B bearing slabs with H2O contents of 0.5 wt%, 1.0 wt % and 1.5 wt% are denser than the surrounding mantle at temperatures below 1200°C, 900°C and 600°C, respectively. This implies that the possible penetration of a hydrous slab into the deeper mantle depends critically on the water content and temperature profile of the slab.

  19. High pressure phase transformations in yttrium and scandium: Relation to rare earths and actinides crystal structures

    NASA Astrophysics Data System (ADS)

    Grosshans, W. A.; Vohra, Y. K.; Holzapfel, W. B.

    1982-10-01

    The phase transformations in the 4d transition metal yttrium (Y) and the 3d transition metal scandium (Sc) have been studied under pressures up to 45 GPa by energy dispersive X-ray diffraction. The metal Y shows the complete rare earth crystal structure sequence i.e. hcp→Sm-type→dhcp→fcc with increasing pressure. This establishes experimentally the similarity of Y with heavy lanthanides, and that the rare earth crystal structure sequence is driven by s→d transfer without any significant contribution from 4f electrons. The metal Sc does not undergo the rare earth crystal structure sequence with pressure but shows above 20 GPa β-Neptunium (Np) structure (tetragonal, 4 atoms/cell). This structure remains stable up to the highest pressure of 45 GPa. The occurence of the high temperature β-Np structure in trivalent Sc combined with large thermal expansions of Np and plutonium (Pu) suggest that itinerant 5f electrons become localized at high temperature in Np and Pu close to melting. This Mott transition with temperature is similar to the one observed between Pu and americium (Am).

  20. Collapsed tetragonal phase in SrCo2As2 under high pressure

    NASA Astrophysics Data System (ADS)

    Jayasekara, W. T.; Ueland, B. G.; Kreyssig, A.; Pandey, Abhishek; Sangeetha, N. S.; Fabbris, G.; Feng, Yejun; Haskel, D.; Johnston, D. C.; Goldman, A. I.

    2015-03-01

    SrCo2As2 possesses the same tetragonal ThCr2Si2 structure as the AFe2As2 (A = Ca, Sr, Ba) family of high-temperature superconductors but does not manifest magnetic order or superconductivity down to a temperature of 1.8 K. Nevertheless, inelastic neutron scattering data show the presence of magnetic fluctuations peaked at a wavevector of (1/2 1/2 1), which corresponds to the stripe antiferromagnetic propagation vector found for AFe2As2. Here, we present evidence from high-energy x-ray diffraction experiments which show that SrCo2As2 undergoes a transition to a collapsed-tetragonal phase characterized by a 10% reduction of the c-lattice parameter for an applied pressure of 5 GPa at 7 K. This fascinating result opens another path for studying the role of magnetic ordering, spin fluctuations, and magnetoelastic coupling in the development of superconductivity in the Fe-pnictides and related materials. - Work at Ames Laboratory was supported by US DOE, Office of Basic Energy Sciences, Division of Materials Sciences and Engineering under Contract No. DE-AC02-07CH11358. This research used resources of the Advanced Photon Source, a US DOE, Office of Science User Facility.

  1. Synthesis, conductivity and high-pressure phase transition of amorphous boron carbon nitride

    NASA Astrophysics Data System (ADS)

    Bai, Suo Zhu; Yao, Bin; Xing, Guo Zhong; Zhang, Ke; Su, Wen-Hui

    2007-06-01

    Amorphous BCN was prepared by chemical solid-state reaction between boracic acid (H 3BO 3) and melamine (C 3N 6H 6) in mass ratios of H 3BO 3 to C 3N 6H 6 of 1:2-1:4 and heat treatment at 1273 K under 10 -3 Pa. The amorphous B sbnd C sbnd N behave insulating property below 890 K, but semiconductor conductivity above 890 K and show different conductivity-temperature relationships in temperature ranges of 913-963 and 963-1083 K. The conductive activation energy was calculated to be 0.26-0.34 eV at 913-963 K and 1.02-1.10 eV at 963-1083 K, implying that the conduction mechanisms are different in the different temperature ranges. Annealed for 40 min at 1473 K under 4.0 GPa, the amorphous BCN with the chemical composition B 0.48C 0.29N 0.23 was prepared in the mass ratio of 1:3 crystallizes into single-phase hexagonal (h-BCN) compound with lattice constants of a=0.2506 nm and c=0.6652 nm. Raman scattering peaks were observed at 1330, 1364,1584 and 1617 cm -1 in the Raman spectrum (RS) of h-BCN, of which the peaks located at 1330 and 1617 cm -1 are assigned to characteristic peaks of the h-BCN.

  2. Experimental study on pressure drop of bends in dense phase pneumatic conveying under high pressure

    NASA Astrophysics Data System (ADS)

    Yuan, Gaoyang; Liang, Cai; Chen, Xiaoping; Xu, Pan; Xu, Guiling; Shen, Liu

    2014-04-01

    The transport test using nitrogen as conveying gas are carried out at high operating pressure up to 4MPa in the experimental equipment for dense phase pneumatic conveying. The transport powders in the experiment are anthracite coal and petroleum coke. The pressure drop characteristics in bends are acquired with the different transport powder. The experimental results show that under the similar mass flow, the pressure drop of vertical upward bend is greater than the horizontal bend and the horizontal bend is greater than the vertical downward bend at the same superficial gas velocity, while there is a best superficial gas velocity minimizes the pressure drop of the bend. Under the similar mass flow rate and the similar particle size, the pressure drop of the bend with the petroleum coke is greater than the pressure drop with the anthracite coal as the same superficial gas velocity. According to Barth's additional pressure drop method, the pressure drop fitting formulas of the vertical upward bend, the horizontal bend and the vertical downward bend are obtained, and the predicted results are in accordance with that of the experiments.

  3. Synthesis, structural characterization and high pressure phase transitions of monolithium hydronium sulfate

    NASA Astrophysics Data System (ADS)

    Banerjee, Debasis; Plonka, Anna M.; Kim, Sun Jin; Xu, Wenqian; Parise, John B.

    2013-01-01

    A three dimensional lithium hydronium sulfate LiSO4·H3O [1], [space group Pna21a=8.7785(12) Å, b=9.1297(12) Å, c=5.2799(7) Å, V=423.16(10) Å3] was synthesized via solvothermal methods using 1,5-naphthalenedisulfonic acid (1,5-NSA) as the source of sulfate ions. The structure of [1], determined by single crystal X-ray diffraction techniques, consists of corner sharing LiO4 and SO4 tetrahedra, forming an anionic 3-D open framework that is charge balanced by hydronium ions positioned within channels running along [001] and forming strong H-bonding with the framework oxygen atoms. Compound [1] undergoes two reversible phase transitions, involving reorientation of SO42- ions at pressures of approximately 2.5 and 5 GPa at room temperature, as evident from characteristic discontinuous frequency drops in the ν1 mode of the Raman spectra. Additionally, compound [1] forms dense β-lithium sulfate at 300 °C, as evident from temperature dependent powder XRD and combined reversible TGA-DSC experiments.

  4. Evidence for plasma phase transition in high pressure hydrogen from ab-initio simulations

    SciTech Connect

    Morales, M; Pierleoni, C; Schwegler, E; Ceperley, D

    2010-02-08

    We have performed a detailed study of molecular dissociation in liquid hydrogen using both Born-Oppenheimer molecular dynamics with Density Functional Theory and Coupled Electron-Ion Monte Carlo simulations. We observe a range of densities where (dP/d{rho}){sub T} = 0 that coincides with sharp discontinuities in the electronic conductivity, which is clear evidence of the plasma phase transition for temperatures 600K {le} T {le} 1500K. Both levels of theory exhibit the transition, although Quantum Monte Carlo predicts higher transition pressures. Based on the temperature dependence of the discontinuity in the electronic conductivity, we estimate the critical point of the transition at temperatures slightly below 2000 K. We examine the influence of proton zero point motion by using Path Integral Molecular Dynamics with Density Functional Theory; the main effect is to shift the transition to lower pressures. Furthermore, we calculate the melting curve of molecular hydrogen up to pressures of 200 GPa, finding a reentrant melting line in good agreement with previous calculations. The melting line crosses the metalization line at 700 K and 220 GPa using density functional energetics and at 550 K and 290 GPa using Quantum Monte Carlo energetics.

  5. High pressure synthesis of a new phase of YbAg2: Structure, valence of Yb and properties

    DOE PAGES

    Tsvyashchenko, A. V.; Menushenkov, A. P.; Sidorov, V. A.; ...

    2015-08-05

    The new phase of YbAg2 was obtained using high-pressure and high-temperature reaction. YbAg2 crystallizes in the MgZn2 structure (the space group P63/mmc space group, No 194) with a = 5.68153(3) Å and c = 9.31995(7) Å and the unit cell volume V = 260.54(3) Å3. The XANES analysis showed that the valence state of Yb is +2.8. The low-temperature dependences of the electrical resistivity and magnetic susceptibility can be adequately described by a T2 term that supports the Fermi-liquid picture. Furthermore, the Kadowaki–Woods relation gives a low value of the degeneracy (N = 2).

  6. High pressure synthesis of a new phase of YbAg2: Structure, valence of Yb and properties

    SciTech Connect

    Tsvyashchenko, A. V.; Menushenkov, A. P.; Sidorov, V. A.; Petrova, A. E.; Fomicheva, L. N.; Chernysheva, O. V.; Lebed, Yu. B.; Axenov, S. N.; Bud’ko, S. L.; Sun, Liling; Zhao, Zhongxian

    2015-08-05

    The new phase of YbAg2 was obtained using high-pressure and high-temperature reaction. YbAg2 crystallizes in the MgZn2 structure (the space group P63/mmc space group, No 194) with a = 5.68153(3) Å and c = 9.31995(7) Å and the unit cell volume V = 260.54(3) Å3. The XANES analysis showed that the valence state of Yb is +2.8. The low-temperature dependences of the electrical resistivity and magnetic susceptibility can be adequately described by a T2 term that supports the Fermi-liquid picture. Furthermore, the Kadowaki–Woods relation gives a low value of the degeneracy (N = 2).

  7. Zinc-blende to rock-salt structural phase transition of BP and BAs under high pressure

    NASA Astrophysics Data System (ADS)

    Sarwan, Madhu; Bhardwaj, Purvee; Singh, Sadhna

    2013-11-01

    In the present paper, we have investigated the pressure induced phase transition and thermophysical properties of BP and BAs by means of modified interaction potential model (MIPM). The MIPM consists of Coulomb interaction, three-body interaction (TBI) modified by taking covalency effect, van-der Waal interaction (vdW), short range overlap repulsive interaction and zero point energy effect. These compounds crystallize in zinc-blende (ZB) structure at ambient condition and transform to rock-salt (RS) structure at pressures 111 and 93 GPa and their equation of state show volume collapse of 14% and 4% respectively for BP and BAs. The second order elastic constants have also been computed at zero and high pressures. Our results are in good agreement with the experimental results. The mechanical and thermophysical properties in ZB structure are also predicted.

  8. Connecting the Water Phase Diagram to the Metastable Domain: High-Pressure Studies in the Supercooled Regime.

    PubMed

    Fanetti, Samuele; Pagliai, Marco; Citroni, Margherita; Lapini, Andrea; Scandolo, Sandro; Righini, Roberto; Bini, Roberto

    2014-11-06

    Pressure is extremely efficient to tune intermolecular interactions, allowing the study of the mechanisms regulating, at the molecular level, the structure and dynamics of condensed phases. Among the simplest molecules, water represents in many respects a mystery despite its primary role in ruling most of the biological, physical, and chemical processes occurring in nature. Here we report a careful characterization of the dynamic regime change associated with low-density and high-density forms of liquid water by measuring the line shape of the OD stretching mode of HOD in liquid water along different isotherms as a function of pressure. Remarkably, the high-pressure studies have been here extended down to 240 K, well inside the supercooled regime. Supported by molecular dynamics simulations, a correlation among amorphous and crystalline solids and the two different liquid water forms is attempted to provide a unified picture of the metastable and thermodynamic regimes of water.

  9. High pressure structural phase transition and elastic properties of Ga1-xInxAs semiconducting compounds

    NASA Astrophysics Data System (ADS)

    Varshney, D.; Joshi, G.

    2009-08-01

    The present paper addresses the high-pressure phase transformation and mechanical properties of Ga1-xInxAs (x = 0.25, 0.5 and 0.75) by formulating an effective interionic interaction potential. This potential consists of the long-range Coulomb and charge transfer caused by the deformation of the electron shells of the overlapping ions and the Hafemeister and Flygare type short-range overlap repulsion extended upto the second neighbor ions and the van der Waals (vdW) interaction. The estimated values of phase transition pressure and the vast volume discontinuity in pressure-volume ( PV) phase diagram indicate the structural phase transition from zinc blende (B3) to rock salt (B1). The equation of state curves plotted between V (P)/ V (0) and pressure are for both the zincblende (B3) and rocksalt (B1) structures. Further, the variations of the second and third order elastic constants with pressure have followed a systematic trend, which are almost identical to those exhibited by the observed data measured for other compounds of this family.

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

    DOE PAGES

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

    2016-04-07

    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 8GPa and 600K. 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 phasemore » 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 0–10GPa and 300–650K« less

  11. Ambient-temperature high-pressure-induced ferroelectric phase transition in CaMnTi2O6

    NASA Astrophysics Data System (ADS)

    Ruiz-Fuertes, J.; Bernert, T.; Zimmer, D.; Schrodt, N.; Koch-Müller, M.; Winkler, B.; Bayarjargal, L.; Popescu, C.; MacLeod, S.; Glazyrin, K.

    2017-09-01

    The ferroelectric to paraelectric phase transition of multiferroic CaMnTi2O6 has been investigated at high pressures and ambient temperature by second-harmonic generation (SHG), Raman spectroscopy, and powder and single-crystal x-ray diffraction. We have found that CaMnTi2O6 undergoes a pressure-induced structural phase transition (P 42m c →P 42/n m c ) at ˜7 GPa to the same paraelectric structure found at ambient pressure and Tc=630 K . The continuous linear decrease of the SHG intensity that disappears at 7 GPa and the existence of a Raman active mode at 244 cm-1 that first softens up to 7 GPa and then hardens with pressure are used to discuss the nature of the phase transition of CaMnTi2O6 , for which a d Tc/d P =-48 K/GPa has been found. Neither a volume contraction nor a change in the normalized pressure on the Eulerian strain is observed across the phase transition with all the unit-cell volume data following a second-order Birch-Murnaghan equation of state with a bulk modulus of B0=182.95 (2 ) GPa .

  12. First principles prediction of a new high-pressure phase and transport properties of Mg2Si

    NASA Astrophysics Data System (ADS)

    Kessair, S.; Arbouche, O.; Amara, K.; Benallou, Y.; Azzaz, Y.; Zemouli, M.; Bekki, M.; Ameri, M.; Bouazza, B. S.

    2016-12-01

    We have investigated the structural properties of seven different structure types of Mg2Si which include the cubic CaF2, orthorhombic PbCl2, hexagonal Ni2In, tetragonal Al2Cu, Laves phase (cubic MgCu2), hexagonal MgZn2 and dihexagonal MgNi2 type of structures, using a full potential linearized augmented plane wave method as implemented in WIEN2k within the framework of density functional theory. The exchange-correlation potential is treated by the new form of generalized gradient approximation (GGA-PBEsol). In total energy calculations it is clearly seen that cubic CaF2-type structure is stable at ambient conditions, and it undergoes a first-order phase transition to orthorhombic PbCl2-type, then to the hexagonal Ni2In-type structure and finally to the cubic Laves phase MgCu2-type. A new structure type is predicted to be stable at high pressure. Moreover, we intend to combine the electronic structure calculations performed by mean of generalized gradient approximation and modified Becke-Johnson potential with Boltzmann transport theory as incorporated in BoltzTraP code to interpret and predict the thermoelectric performance of each stable phase as a function of the chemical potential at various temperatures. We find a high thermoelectric thermopower values in cubic CaF2-type structure that could promise an excellent candidate for potential thermoelectric applications.

  13. Hydrogen bond symmetrization and superconducting phase of HBr and HCl under high pressure: An ab initio study.

    PubMed

    Duan, Defang; Tian, Fubo; He, Zhi; Meng, Xing; Wang, Liancheng; Chen, Changbo; Zhao, Xiusong; Liu, Bingbing; Cui, Tian

    2010-08-21

    Ab initio calculations are performed to probe the hydrogen bonding, structural, and superconducting behaviors of HBr and HCl under high pressure. The calculated results show that the hydrogen bond symmetrization (Cmc2(1)-->Cmcm transition) of HBr and HCl occurs at 25 and 40 GPa, respectively, which can be attributed to the symmetry stretching A(1) mode softening. After hydrogen bond symmetrization, a pressure-induced soft transverse acoustic phonon mode of Cmcm phase is identified and a unique metallic phase with monoclinic structure of P2(1)/m (4 molecules/cell) for both compounds is revealed by ab initio phonon calculations. This phase preserves the symmetric hydrogen bond and is stable in the pressure range from 134 to 196 GPa for HBr and above 233 GPa for HCl, while HBr is predicted to decompose into Br(2)+H(2) above 196 GPa. Perturbative linear-response calculations predict that the phase P2(1)/m is a superconductor with T(c) of 27-34 K for HBr at 160 GPa and 9-14 K for HCl at 280 GPa.

  14. [In situ experimental study of phase transition of calcite by Raman spectroscopy at high temperature and high pressure].

    PubMed

    Liu, Chuan-jiang; Zheng, Hai-fei

    2012-02-01

    The phase transitions of calcite at high temperature and high pressure were investigated by using hydrothermal diamond anvil cell combined with Raman spectroscopy. The result showed that the Raman peak of 155 cm(-1) disappeared, the peak of 1 087 cm(-1) splited into 1083 and 1 090 cm(-1) peaks and the peak of 282 cm(-1) abruptly reduced to 231 cm(-1) at ambient temperature when the system pressure increased to 1 666 and 2 127 MPa respectively, which proved that calcite transformed to calcite-II and calcite-III. In the heating process at the initial pressure of 2 761 MPa and below 171 degrees C, there was no change in Raman characteristic peaks of calcite-III. As the temperature increased to 171 degrees C, the color of calcite crystal became opaque completely and the symmetric stretching vibration peak of 1 087 cm(-1), in-plane bending vibration peak of 713 cm(-1) and lattice vibration peaks of 155 and 282 cm(-1) began to mutate, showing that the calcite-III transformed to a new phase of calcium carbonate at the moment. When the temperature dropped to room temperature, this new phase remained stable all along. It also indicated that the process of phase transformation from calcite to the new phase of calcium carbonate was irreversible. The equation of phase transition between calcite-III and new phase of calcium carbonate can be determined by P(MPa) = 9.09T x (degrees C) +1 880. The slopes of the Raman peak (v1 087) of symmetrical stretching vibration depending on pressure and temperature are dv/dP = 5.1 (cm(-1) x GPa(-1)) and dv/dT = -0.055 3(cm(-1) x degrees C(-1)), respectively.

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

    DOE PAGES

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

    2016-04-07

    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 scanmore » 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 the 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. Additionally, the unit cell volumes of each phase deviate from the expected thermal expansion behavior just before each transition is observed from the diffraction data. 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.« less

  16. High-pressure behavior of 10 Å phase (Mg3Si4O10(OH)2.H2O)

    NASA Astrophysics Data System (ADS)

    Mookherjee, M.; Kalvan, E.; Hermann, A.

    2016-12-01

    Layered hydrous phases such as serpentine (Mg3Si2O5(OH)4), talc (Mg3Si4O10(OH)2), chlorite (Mg5Al(Si3Al)O10(OH)8), and 10 Å phase (Mg3Si4O10(OH)2.xH2O, where x=1,2) play important roles in transporting water into the Earth's interior. Using first principles simulations, we investigate the high-pressure behavior of 10 Å phase. In particular, we investigate the crystal structure of 10 Å phase and how it evolves upon compression. The predicted lattice parameters from the first principles simulations are in good agreement with the previous x-ray diffraction studies. The energy vs. volume results can be expressed in terms of a Birch-Murnaghan finite strain fit, with parameters, V0, K0 and K0' being 525.7 Å3, 32.1 GPa, and 17.4 respectively. The predicted V0 is greater than that of the experimentally determined value by 5.4 %. This discrepancy is often typical for the density functional theory calculations based on Genaralized Gradient Approximations (GGA). We are exploring the elasticity of 10 Å phase and how it varies as a function of pressure. The layered hydrous silicates such as serpentine, chlorite, and talc are often assicated with significant elastic anisotropy and are often responsible for the large delay times observed in certain subduction zones. We will accurately constrain the sound wave velocity and elastic anisotropy of 10 Å phase to gain insight into the degree of shallow mantle hydration and explain geophysical observations pertaining to subduction zones. Acknowledgements: The research is supported by NSF EAR 1639552, 1634422.

  17. Combined high-pressure and high-temperature vibrational studies of dolomite: phase diagram and evidence of a new distorted modification

    NASA Astrophysics Data System (ADS)

    Efthimiopoulos, I.; Jahn, S.; Kuras, A.; Schade, U.; Koch-Müller, M.

    2017-02-01

    A combined high-pressure mid-infrared absorption and Raman spectroscopy study on a natural CaMg0.98Fe0.02(CO3)2 dolomite sample was performed both at ambient and high temperatures. A pressure-temperature phase diagram was constructed for all the reported dolomite ambient- and high-pressure polymorphs. In addition, a local distortion of the ambient-pressure dolomite structure was identified close to 11 GPa, just before the transition toward the first known high-pressure phase. All the Clausius-Clapeyron slopes are found to be positive with similar magnitudes. Complementary first-principles calculations suggest a metastable nature of the high-pressure dolomite polymorphs. Finally, theoretical spectroscopy is used to interpret and discuss the observed changes in the measured vibrational spectra.

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

    NASA Astrophysics Data System (ADS)

    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.

  19. Theoretical investigation of the high pressure structure, lattice dynamics, phase transition, and thermal equation of state of titanium metal

    NASA Astrophysics Data System (ADS)

    Hu, Cui-E.; Zeng, Zhao-Yi; Zhang, Lin; Chen, Xiang-Rong; Cai, Ling-Cang; Alfè, Dario

    2010-05-01

    We report a detailed first-principles calculation to investigate the structures, elastic constants, and phase transition of Ti. The axial ratios of both α-Ti and ω-Ti are nearly constant under hydrostatic compression, which confirms the latest experimental results. From the high pressure elastic constants, we find that the α-Ti is unstable when the applied pressures are larger than 24.2 GPa, but the ω-Ti is mechanically stable at all range of calculated pressure. The calculated phonon dispersion curves agree well with experiments. Under compression, we captured a large softening around Γ point of α-Ti. When the pressure is raised to 35.9 GPa, the frequencies around the Γ point along Γ-M-K and Γ-A in transverse acoustical branches become imaginary, indicating a structural instability. Within quasiharmonic approximation, we obtained the full phase diagram and accurate thermal equations of state of Ti. The phase transition ω-Ti→α-Ti→β-Ti at zero pressure occurs at 146 K and 1143 K, respectively. The predicted triple point is at 9.78 GPa, 931 K, which is close to the experimental data. Our thermal equations of state confirm the available experimental results and are extended to a wider pressure and temperature range.

  20. High-pressure phases of cordierite from single-crystal X-ray diffraction to 15 GPa

    DOE PAGES

    Finkelstein, Gregory J.; Dera, Przemyslaw K.; Duffy, Thomas S.

    2015-08-14

    High-pressure single-crystal X-ray diffraction experiments were conducted on natural cordierite crystals with composition Mg1.907(18)Fe0.127(6)Al4.01(2)Si4.96(3)Na0.026(3)O18.12(9) using a synchrotron X-ray source. The samples were compressed at 300 K in a diamond anvil cell to a maximum pressure of 15.22(15) GPa with a neon pressure-transmitting medium and a gold pressure calibrant. We observed a recently described orthorhombic to triclinic transition, as well as a further transition to a second triclinic phase. We solved and refined both new triclinic hases in space group P1, and designate them cordierite II and III. The structures of cordierite II and III were refined at 7.52(3) GPa atmore » 15.22(15) GPa, respectively. The lattice parameters at these pressures are a = 15.567(3) Å, b = 9.6235(4) Å, c = 9.0658(6) Å, α = 89.963(5)°, β = 86.252(10)°, and γ = 90.974(8)° for cordierite II, and a = 8.5191(19) Å, b = 8.2448(3) Å, c = 9.1627(4) Å, α = 85.672(4)°, β = 85.986(7)°, and γ = 70.839(10)° for cordierite III. Across the phase transitions there is a significant reduction in the length of the a-axis (~2 Å per phase transition), whereas both the b- and c-axis remain largely unchanged. Cordierite II has four- and five-coordinated Si and Al, while cordierite III has four-, five-, and six-coordinated Si, four- and five-coordinated Al, and five- and six-coordinated Mg. The sequence of high-pressure phases shows increasing polymerization of coordination polyhedra. These results, together with other recent studies, suggest that mixed 4-, 5-, and 6-fold coordination states may occur more commonly in silicate structures compressed at 300 K than previously recognized.« less

  1. High-pressure phases of cordierite from single-crystal X-ray diffraction to 15 GPa

    SciTech Connect

    Finkelstein, Gregory J.; Dera, Przemyslaw K.; Duffy, Thomas S.

    2015-08-14

    High-pressure single-crystal X-ray diffraction experiments were conducted on natural cordierite crystals with composition Mg1.907(18)Fe0.127(6)Al4.01(2)Si4.96(3)Na0.026(3)O18.12(9) using a synchrotron X-ray source. The samples were compressed at 300 K in a diamond anvil cell to a maximum pressure of 15.22(15) GPa with a neon pressure-transmitting medium and a gold pressure calibrant. We observed a recently described orthorhombic to triclinic transition, as well as a further transition to a second triclinic phase. We solved and refined both new triclinic hases in space group P1, and designate them cordierite II and III. The structures of cordierite II and III were refined at 7.52(3) GPa at 15.22(15) GPa, respectively. The lattice parameters at these pressures are a = 15.567(3) Å, b = 9.6235(4) Å, c = 9.0658(6) Å, α = 89.963(5)°, β = 86.252(10)°, and γ = 90.974(8)° for cordierite II, and a = 8.5191(19) Å, b = 8.2448(3) Å, c = 9.1627(4) Å, α = 85.672(4)°, β = 85.986(7)°, and γ = 70.839(10)° for cordierite III. Across the phase transitions there is a significant reduction in the length of the a-axis (~2 Å per phase transition), whereas both the b- and c-axis remain largely unchanged. Cordierite II has four- and five-coordinated Si and Al, while cordierite III has four-, five-, and six-coordinated Si, four- and five-coordinated Al, and five- and six-coordinated Mg. The sequence of high-pressure phases shows increasing polymerization of coordination polyhedra. These results, together with other recent studies, suggest that mixed 4-, 5-, and 6-fold coordination states may occur more commonly in silicate structures compressed at 300 K than previously recognized.

  2. Structures of two intermediate phases between the B1 and B2 phases of PbS under high pressure

    SciTech Connect

    Li, Yanchun E-mail: liuj@ihep.ac.cn; Lin, Chuanlong; Li, Xiaodong; Liu, Jing E-mail: liuj@ihep.ac.cn; Xu, Jian; Li, Gong

    2014-12-15

    The structural transitions of PbS were investigated at pressures up to 50 GPa using synchrotron powder and single crystal X-ray diffraction (XRD) methods in diamond anvil cells. We found two intermediate phases between the B1 phase under atmospheric pressure and the B2 phase at 21.1 GPa, which is different to previous reports. The structures of these two intermediate phases were indexed as B27 and B33, respectively. Their structural parameters were investigated using density functional theory (DFT) calculations. Our results provide a new insight into understanding the transition pathway between the B1 and B2 phases in PbS.

  3. Separation and quantitation of free fatty acids and fatty acid methyl esters by reverse phase high pressure liquid chromatography.

    PubMed

    Aveldano, M I; VanRollins, M; Horrocks, L A

    1983-01-01

    Reverse phase high pressure liquid chromatography (HPLC) on octadecylsilyl columns separates mixtures of either free fatty acids or fatty acid methyl esters prepared from mammalian tissue phospholipids. Acetonitrile-water mixtures are used for the elution of esters. Aqueous phosphoric acid is substituted for water for the separation of the free acids. Unsaturated compounds are detected and quantitated by their absorption at 192 nm. Saturates are detected better at 205 nm. The order of elution of fatty acids in complex mixtures varies as a function of acetonitrile concentration. At any given concentration, some compounds overlap. However, by varying the solvent strength, any fatty acid of interest can be resolved including many geometrical and positional isomers. Methyl esters prefractionated according to unsaturation by argentation thin-layer chromatography (TLC) are rapidly and completely separated by elution with CH3CN alone. Argentation TLC-reverse phase HPLC can be used as an analytical as well as a preparative procedure. Octylsilyl columns are used for rapid resolution and improved detection of minor or low ultraviolet-absorbing components in the fractions. For example, monoenoic fatty acids with up to 32 carbons have been detected in bovine brain glycerophospholipids. Specific radioactivities of 3H- and 14C-labeled fatty acids and the distribution of radioactivity among acyl groups from complex lipids are measured. The method is not recommended for complete compositional analysis, but is useful for determinations of specific radioactivities during studies on turnover and metabolic conversions of labeled fatty acids.

  4. High-Efficiency, Ultra-High Pressure Electrolysis With Direct Linkage to PV Arrays - Phase II SBIR Final Report

    SciTech Connect

    Martin A Shimko

    2009-08-08

    In this Phase II SBIR, Avalence LLC met all proposed objectives. Because the original Phase III partner pulled out of the project, several alternative sites/partners were used to achieve the goals. The on-site operation and PV measurements were performed on a smaller unit at General Motors proving grounds in Milford, MI. The actual equipment targeted for AC Transit will be delivered to Robins Air Force Base in September of 2009 to support the fueling of a fuel cell powered fork lift and 'Bobcat'. In addition the Transit Agency Site Requirements and Constraints were performed for the Greater New Haven Transit District (GNHTD) for the Hamden, CT Public Works building that will be the site for a similar fueling station to be delivered in the Spring of 2010. The Detailed Design Package was also based on the Design for the GNHTD unit. The work on this project successfuly demonstrated the potential of Avalence's high pressure technology to address the need for renewably produced hydrogen fuel for transportation applications. Several follow-on projects in a numerber of related applications are now underway as a result of this SBIR project.

  5. Lattice dynamics and pressure-induced phase transitions in Bi2W2O9 : High-pressure Raman study

    NASA Astrophysics Data System (ADS)

    Maczka, M.; Paraguassu, W.; Freire, P. T. C.; Souza Filho, A. G.; Mendes Filho, J.; Hanuza, J.

    2010-03-01

    Lattice dynamics calculations and high-pressure Raman scattering study of Bi2W2O9 , which is an m=2 member of the cation-deficient bismuth layered Aurivillius family of compounds, are presented. These studies showed the onset of two reversible second-order phase transitions near 2.8 and 4.8 GPa. The pressure dependence of Raman bands provides strong evidence that the first phase transition involves the loss of the WO6 tilt mode around pseudotetragonal axis. The second transition is likely related to some shift of the W atoms and/or tilting of the WO6 octahedra plus shift of the Bi atoms or the whole Bi2O2 layers. In contrast to the m=1 cation-deficient bismuth layered compounds, Bi2WO6 and Bi2MoO6 , no soft-mode behavior was observed for Bi2W2O9 and the transition at 4.8 GPa leads to symmetry lowering.

  6. Radiation-induced solid-state polymerization in an acrylamide-water system: The effect of phase transformations of metastable high-pressure ice VIII

    SciTech Connect

    Kiryukhin, D.P.; Barkalov, I.M.; Barkalov, O.I.

    1995-07-01

    A drastic suppression of the chain post polymerization process in the quenched high-pressure phase of an acrylamide-water eutectic mixture was observed upon warming of the samples irradiated with {gamma}-rays at 77 K. This effect is explained by dispersion of the samples in the temperature region of the transition of the quenched high-pressure phase into the equilibrium phase ({approximately}150K). The size of the resulting microcrystals of monomer was estimated to be approximately 0.1 {mu}m.

  7. Melting phase relations in MgO-FeO-SiO2 ternary system at high pressure

    NASA Astrophysics Data System (ADS)

    Morishita, A.; Nomura, R.; Hirose, K.

    2014-12-01

    Seismological observations show that the presence of a small fraction of partial melt at the base of the mantle. The knowledge of chemical composition of such partial melt is key to understand its buoyancy and stability in the lowermost mantle. Recent melting experiments performed in the deep lower mantle conditions demonstrated that 1) MgSiO3-rich perovskite (bridgemanite) is the first phase to crystallize from melts with a wide range of (Mg + Fe)/ Si ratios in the middle to deep lower mantle and 2) iron is preferentially partitioned into melt rather than solid [Nomura et al., 2011 Nature; Tateno et al., 2014 JGR], suggesting that melts evolves towards a FeO-rich / SiO2-poor composition upon crystallization. Here we carried out melting experiments under both shallow and deep lower mantle pressures using a laser-heated diamond-anvil cell (DAC), in order to determine melting phase equilibria in the MgO-FeO-SiO2 ternary system. Several different starting materials were used. After heating at high pressure, sample was recovered from a DAC, and then examined with dual beam scanning microprobe (FIB + FE-SEM) (Versa 3DTM, FEI) and field-emission-type electron probe microanalyzer (FE-EPMA) (JXA-8530F, JEOL). On the basis of X-ray maps and quantitative point-analyses, quenched partial melt with non-stoichiometric composition was found at the center of the sample (the hottest part) and surrounded by a liquidus phase. The partial melts were sometimes in direct contact with more than one solid phases such as bridgemanite + ferropericlase or bridgemanite + stishovite, which can tightly constrain the locations of cotectic lines. These results imply that eutectic melt is strongly enriched in FeO in the MgO-FeO-SiO2 ternary system in a wide range of lower mantle pressures.

  8. Equations of State and Phase Transformation of Depleted Uranium DU-238 by High Pressure-Temperature Diffraction Studies

    SciTech Connect

    Zhao,Y.; Zhang, J.; Brown, D.; Korzekwa, D.; Hixson, R.

    2007-01-01

    We have conducted in situ high-pressure diffraction experiments on depleted uranium (DU-238) at pressures up to 8.5 GPa and temperatures up to 1123 K. From the pressure (P)-volume (V)-temperature (T) measurements, thermoelastic parameters were derived for a-uranium based on a modified high-T Birch-Murnaghan equation of state and a thermal-pressure approach. With the pressure derivative of the bulk modulus K0' fixed at 4.0, we obtained ambient bulk modulus K0=117(2) GPa, temperature derivative of bulk modulus at constant pressure ({partial_derivative}K/{partial_derivative}T)P=-3.4(4)x10-2 GPa/K and at constant volume ({partial_derivative}K/{partial_derivative}T)v=-1.1(6)x10-2 GPa/K, volumetric thermal expansivity aT=a+bT, with a=1.2({+-}0.4)x10-5 K-1 and b=8.0({+-}0.7)x10-8 K-2, and the pressure derivative of thermal expansion ({partial_derivative}a/{partial_derivative}P)T=-2.5(5)x10-6 GPa-1 K-1. Within the experimental errors, the ambient bulk modulus and volumetric thermal expansion derived from this work are in good agreement with previous experimental results, whereas all other thermoelastic parameters represent the first determinations for the a phase of uranium. We also studied the a- phase transformation and obtained a phase boundary described by T (in K)=1032+7.4P (in GPa). Although the -phase uranium cannot be pressure quenched to ambient conditions, it was observed to be stable upon cooling from 1123 to 300 K at pressures of 7-8 GPa. These observations indicate that pressure, in addition to the commonly utilized alloying techniques, provides an alternative route for stabilizing the {gamma}-uranium at room temperature.

  9. Investigation of Fe-FeS phase diagram and liquid structure at high pressure and high temperature

    NASA Astrophysics Data System (ADS)

    Morard, G.; Sanloup, C.; Fiquet, G.; Mezouar, M.; Andrault, D.; Guignot, N.

    2007-12-01

    Sulfur is believed to be an alloying light element in iron-rich planetary cores such as those of the Earth and Mars 1, 2. Recent studies have suggested that Mars, like the Earth, could have a liquid metallic outer core together with a solid inner core 3. Hence, it is important to investigate the evolution of the Fe-FeS phase diagram and of the structural properties of the liquid Fe-FeS alloys in respect to pressure, temperature and sulphur content. A new cell assembly has been developed to heat samples to more than 1300 K at 17 GPa using the Paris Edinburgh Press4. This allows us to conduct detailed structural investigations of the Fe-FeS eutectic liquid by in situ X-ray diffraction5 . Analysis of these data highlights an increase of the liquid compacity with increasing pressure. We also show that the eutectic liquid structure is closer to that of FeSi, explaining the closure of the miscibility gap in the Fe-S-Si system 6. The evolution of the Fe-FeS eutectic liquid structure at high pressure could have significant effect on extrapolated wave speed of metallic Fe-FeS alloy at core pressures. We have used a double-sided laser-heated diamond-anvil cell 7 to study the Fe-FeS phase diagram up to 65 GPa and 2500 K8. We used laser heated diamond anvil cell coupled with synchrotron radiation and confirm a S- solubility below 4 at% (2.3 %wt) up to 65 GPa. The eutectic temperatures present a uniform increase, with a rate of ~15K/GPa, up to 65 GPa and 2200 K. Finally, we present new constraints on the phase diagram evolution to very high pressures which provide unambiguous evidence for an upper limit of 4-8 %wt for the inner core S- content. Therefore, sulphur is not favoured to be the major light element in the Earth's core. 1. Allegre, C. J., Poirier, J. P., Humler, E. & Hofmann, A. W. The chemical composition of the Earth. Earth Planet. Sc. Lett. 134, 515-526 (1995). 2. Sohl, F. & Spohn, T. The interior structure of Mars : Implications from SNC meteorites. J. Geophys. Res

  10. The 10Å phase: a high-pressure expandable sheet silicate stable during subduction of hydrated lithosphere

    NASA Astrophysics Data System (ADS)

    Fumagalli, Patrizia; Stixrude, Lars; Poli, Stefano; Snyder, Don

    2001-03-01

    H 2O storage and release in deep subducting lithosphere is controlled by complex reaction suites involving a variety of hydrous phases. As a result of its relatively large thermal stability and intermediate composition, the 10Å phase (Mg 3Si 4O 10(OH) 2· nH 2O) has been regarded as a relevant H 2O reservoir in a wide range of rock compositions and mineral assemblages. High-pressure syntheses of the 10Å phase were carried out at 6.7 GPa and 650°C under fluid-saturated conditions in a Walker-type multi-anvil apparatus, from 5 min to 430 h. X-ray powder diffraction of large platy hexagonal crystals of the 10Å phase (up to 100 μm) were indexed on the basis of a trioctahedral-type structure. Long-term run products (>110 h) reveal sensitivity of the 10Å phase to treatment with acetone leading to the appearance of diffractions at greater d-spacings (10.2-11.6 Å) with respect to the basal peak of the 10Å phase (9.64-10.07 Å). This swelling behavior is strongly related to synthesis run duration. The Raman spectrum of the 10Å phase at frequencies less than 800 cm -1 shows a strong similarity to talc. In the Si-O stretching region (800-1100 cm -1), the 10Å phase exhibits three modes (909, 992 and 1058 cm -1), as compared to two in talc. The bending mode of water (ν 2) is found at 1593 cm -1. In the OH stretching region, peaks at 3593, 3622 and 3668 cm -1 were observed. The acetone treated sample shows a C-H stretching mode at 2923 cm -1 while the double bond CO signal is absent. The swelling behavior of the 10Å phase is interpreted as due to intercalation of acetone with pre-existing interlayer water. The efficiency of this process is dependent on the amount of the interlayer water which in turn depends on run duration. The relation between the response to acetone treatment and run duration is therefore interpreted as a time-dependent hydration of the 10Å phase. The fractions transformed from non-expandable to expandable fractions was fitted to the Avrami

  11. Timing and conditions of high-pressure metamorphism in the western Grenville Province: Constraints from accessory mineral composition and phase equilibrium modeling

    NASA Astrophysics Data System (ADS)

    Marsh, Jeffrey H.; Culshaw, Nicholas G.

    2014-07-01

    Previous geochronological analyses of high pressure (HP) metamorphic rocks in the western Grenville Province, Ontario, Canada have yielded precise U-Pb zircon ages; however, uncertainty has remained as to whether these ages represent the timing of HP metamorphism or the granulite/amphibolite facies overprint accompanying exhumation to a hot middle orogenic crust. Detailed study of these HP rocks, involving garnet, rutile, and zircon trace element analysis, phase equilibrium modeling, and zircon U-Pb geochronology, has yielded much improved constraints on the timing and conditions of HP metamorphism. Zircon from five of the six HP samples yield anchored discordia upper intercept and 207Pb/206Pb weighted average ages between 1097 and 1085 Ma, and typically have trace element compositions consistent with growth in a garnet-rich, plagioclase-poor eclogite-type assemblage (i.e. no negative Eu anomaly and flat HREE trends). Titanium-in-zircon and Zr-in-rutile thermometry indicates that the range of zircon crystallization temperatures for most samples (643-767 °C) is close to that of rutile inclusions in garnet (668-753 °C) and matrix rutile (690-772 °C). Phase relations in a pseudosection calculated for the sample that best preserves the HP assemblage indicate that: (1) the stability field for the inclusions observed in garnet and kyanite is between 11.5 < P < 14 kbar and 600 < T < 700 °C, and (2) zircon and rutile crystallization temperatures intersect the inferred HP assemblage field (Grt + Cpx + Ky + Rt + Hbl + Qtz) and garnet and kyanite modal isopleths at P > ~ 15 kbar, indicating that the ca. 1090 Ma zircon ages date metamorphism at eclogite facies conditions. Thus, the deep burial of mafic lower crust that resulted in HP metamorphism in the western CGB occurred just prior to the main "Ottawan" phase of continental collision in the western Grenville Province (ca. 1080-1040 Ma).

  12. Phase relations and sound velocity measurements of iron-sulfur systems at high pressure: implications for the Earth's inner core

    NASA Astrophysics Data System (ADS)

    Ohtani, E.; Kamada, S.; Sakai, T.; Terasaki, H.; Shibazaki, Y.; Sakamaki, T.; Takahashi, S.; Sakairi, T.; Fukui, H.; Baron, A. Q.

    2012-12-01

    The sound velocity is one of the most important physical properties which can be assessed by seismology. In spite of its importance, the technical difficulty provides limitation of the measurements under the core conditions. Here we show the results of measurements of the sound velocity of hcp-iron, Fe3S, and FeH by the inelastic X-ray scattering (IXS) method using DAC at high pressure and temperature. Inelastic X-ray scattering spectra were taken at BL35XU, Spring-8. We made the measurements of hcp-iron at pressures up to 180 GPa at room temperature, which is the highest pressure for the IXS measurement. Sound velocity measurements at high pressure and temperature were made up to 91 GPa at 700 K, and to 62 GPa and 1000 K using the external heating diamond anvil cell. The present results revealed that there is almost no temperature effect on the sound velocity of hcp-Fe at least up to 1000 K. We also measured the sound velocity and density of Fe3S up to 85 GPa at room temperature, and clarified the effect of sulfur and hydrogen on the sound velocity of iron at high pressure. Phase relations of the Fe-S (Kamada et al., 2010; 2012) and Fe-S-O systems (Terasaki et al., 2011) were studied up to the core pressures based on the laser heated diamond anvil cell combined with the in situ synchrotron X-ray diffraction at SPring-8. Fe3S dissolves first at the solidus before melting of FeO and metallic iron alloy at the liquidus of the systems up to 180 GPa. The maximum solubility of sulfur in hcp-iron approaches to about 7.5 at % at 86 GPa and 8 at % at 123 GPa, and it does not increase so much at higher pressures. The temperature at ICB based on the extrapolation of the liquidus and solidus temperatures of the outer core composition in the Fe-S-O is about 4360-5630 K assuming that the outer core composition is Fe75O5S20 in the atomic ratio. The temperature at the core-mantle boundary will be 3340-4300 K by the adiabatic decompression from the temperature at the inner core

  13. Pressure-induced structural phase transition, elastic and thermodynamic properties of ReC under high pressure

    NASA Astrophysics Data System (ADS)

    Lei, Hui-Ru; Zhu, Jun; Hao, Yan-Jun; Zhang, Lin; Zhao, Yu-Xin; Zhan, Guo-Fu

    2015-10-01

    The pressure-induced structural phase transition of rhenium monocarbon (ReC) is investigated via the projector augmented wave (PAW) method with the generalized gradient approximation (GGA). Using the first-principles calculations, the equilibrium structural parameters of ReC in rocksalt (NaCl), cesium chloride (CsCl), zinc blende (ZB), wurtzite (WZ), nickel arsenide (NiAs) and tungsten carbide (WC) types are successfully obtained, and the results are well consistent with other theoretical data. It is firstly noted that WC-ReC translates into CsCl-ReC at 510.50 GPa by analyzing the enthalpy difference versus pressure. From the calculated elastic constants, the aggregate elastic modulus (B, G, E), the Poisson's ratio (σ) and the Debye temperature ΘD of WC-type are also derived. It is observed that all the data of WC-ReC obtained increase monotonically with increasing pressure. Meanwhile, the thermodynamic properties of WC-ReC under high temperature and high pressure are investigated applying nonempirical Debye model in the quasi-harmonic approximation.

  14. Phase stability and incompressibility of tungsten boride (WB) researched by in-situ high pressure x-ray diffraction

    NASA Astrophysics Data System (ADS)

    Fan, Cong; Liu, Chenji; Peng, Fang; Tan, Ning; Tang, Mingjun; Zhang, Qiang; Wang, Qiming; Li, Fengjiao; Wang, Jianghua; Chen, Ying; Liang, Hao; Guan, Shixue; Yang, Ke; Liu, Jing

    2017-09-01

    The binary tungsten boride, WB, has potential industrial applications as it not only has a high melting point but is generally harder and less compressible than the pure metals. Here, the physical and mechanical properties (phase stability, bulk modulus and compressibility) of WB were investigated by in situ high-pressure x-ray diffraction and theoretical calculations. Its crystal structure still remains stable even at the highest pressure of 63.7 GPa and room temperature for the diamond-anvil cell experiments. The pressure-volume (P-V) data were fitted using the Birch-Murnaghan EOS and the Vinet EOS to obtain the isothermal bulk modulus, K0 = 452 (4) GPa and 451(3) GPa and its pressure derivative, K0‧ = 4 (fixed) in the two sets of experiments with two different pressure transmitting mediums (PTMs), respectively. The excellent bulk modulus (K0) is attributed to the high valence electron density of W atom, the layered and chain-like crystal structure of WB and the strong chemical bonds formed by W and B atoms. Besides, anisotropic compression behavior of the unit-cell axes (a- and c-axes) of WB is manifested by experimental observations and theoretical calculations. This remarkably elastic property is closely related to the strongly directional bonding between W and B atoms.

  15. A theoretical study of high-pressure-induced phases of LiAlH4 using calculated NQCC parameters

    NASA Astrophysics Data System (ADS)

    Rafiee, Marjan A.

    2016-12-01

    Quadrupolar parameters of nuclei can be used as a tool to understand the electronic structure of compounds. Lithium alanate (LiAlH4) is a potential hydrogen storage material because of its high capacity of 10.5 wt % H2. However, the drawbacks of its dehydrogenation process are the relatively high temperatures and the slow dehydrogenation kinetics; furthermore, its reversibility is rather poor. Understanding the bonding nature of Al and H is essential for improving its dehydrogenation performance. In this work the charge density distribution in LiAlH4 is studied. Thus using calculated nuclear quadrupole coupling constants of hydrogens (2H-NQCCs), the electronic structure of α-LiAlH4 with high pressure forms of LiAlH4, (β- and γ-LiAlH4) were compared. The results show that easier condition for dehydrogenation is expected in β-LiAlH4. Comparison of calculated dehydrogenation enthalpies of LiAlH4 phases verifies this prediction. The electric field gradient (EFG) of quadrupolar nuclei were calculated to obtain NQCC parameters. All calculations performed using Gaussian 03 at B3LYP/6-31G* level of theory.

  16. Determination of β-Carotene in Supplements and Raw Materials by Reversed-Phase High Pressure Liquid Chromatography

    PubMed Central

    Szpylka, John; DeVries, Jonathan W.; Bhandari, S.; Bui, M.H.; Ji, D.; Konings, E.; Lewis, R.; Maas, P.; Parish, H.; Post, B.; Schierle, J.; Sullivan, D.; Taylor, A.; Wang, J.; Ware, G.; Woollard, D.; Wu, T.

    2008-01-01

    Twelve laboratories representing 4 countries participated in an interlaboratory study conducted to determine all-trans-β-carotene and total β-carotene in dietary supplements and raw materials. Thirteen samples were sent as blind duplicates to the collaborators. Results obtained from 11 laboratories are reported. For products composed as softgels and tablets that were analyzed for total β-carotene, the reproducibility relative standard deviation (RSDR) ranged from 3.35 to 23.09% and the HorRat values ranged from 1.06 to 3.72. For these products analyzed for trans β-carotene, the reproducibility relative standard deviation (RSDR) ranged from 4.28 to 22.76% and the HorRat values ranged from 0.92 to 3.37. The RSDr and HorRat values in the analysis of a beadlet raw material were substantial and it is believed that the variability within the material itself introduced significant variation in subsampling. The method uses high pressure liquid chromatography (LC) in the reversed-phase mode with visible light absorbance for detection and quantitation. If high levels of α-carotenes are present, a second LC system is used for additional separation and quantitation of the carotene species. It is recommended that the method be adopted as an AOAC Official Method. PMID:16385976

  17. Electronic, mechanical, phase transition, and thermo-physical properties of TMC (TM = V, Nb, and Ta): high pressure ab initio study

    NASA Astrophysics Data System (ADS)

    Chauhan, Mamta; Gupta, Dinesh C.

    2015-12-01

    The structural, electronic, mechanical, phase transition, and thermo-physical properties of refractory carbides, viz. VC, NbC, and TaC have been computed in stable B1 and high pressure B2 phases by means of two different ab initio calculations using pseudo- and full-potential schemes. These materials have mixed covalent-, metallic-, and ionic-type bonding. The calculations of elastic constants show the mechanical stability of these materials in B1 phase only. The brittle nature and anisotropy is observed in these materials in B1 phase. Non-central forces are present in both the phases. Elastic wave velocities and Debye temperature have also been calculated. The present results on structural, phase transition, elastic, and other properties are in reasonably good agreement with the available experimental and theoretical data. The calculations in high pressure phase need experimental verification.

  18. High pressure antiferrodistortive phase transition in mixed crystals of EuTiO{sub 3} and SrTiO{sub 3}

    SciTech Connect

    Parisiades, Paraskevas; Saltarelli, Francesco; Liarokapis, Efthymios; Köhler, Jürgen; Bussmann-Holder, Annette

    2016-06-15

    We report a detailed high pressure study on Eu{sub 1−x}Sr{sub x}TiO{sub 3} polycrystalline samples using synchrotron x-ray diffraction. We have observed a second-order antiferrodistortive phase transition for all doping levels which corresponds to the transition that has been previously explored as a function of temperature. The analysis of the compression mechanism by calculating the lattice parameters, spontaneous strains and tilt angles of the TiO{sub 6} octahedra leads to a high pressure phase diagram for Eu{sub 1−x}Sr{sub x}TiO{sub 3}.

  19. Magnetic phase transition of high-pressure phase (VO)2P2O7 studied by high-field ESR measurements

    NASA Astrophysics Data System (ADS)

    Hiraka, K.; Nagasaka, Y.; Kunimoto, T.; Inagaki, Y.; Okubo, S.; Ohta, H.; Saito, T.; Azuma, M.; Takano, M.

    2004-05-01

    The high-pressure phase of (VO)2P2O7 (HP-VOPO) is a S=1/2 Heisenberg antiferromagnetic alternating chain compound with one spin gap. The high-field ESR measurements of the HP-VOPO single crystal have been performed using the pulsed magnetic field up to 30T. Small anomaly is observed in ESR mode for both a- and b-axis. The linewidth became broad around Bc=20T when the field is applied along the a- and b-axis. The magnetic state of HP-VOPO above Bc will be discussed.

  20. High-pressure structural configuration and phase transition in celsian, BaAl2Si2O8

    NASA Astrophysics Data System (ADS)

    Curetti, Nadia; Benna, Piera; Bruno, Emiliano

    2017-03-01

    In situ high-pressure X-ray diffraction study was performed on celsian (Cls97Or3) from Jakobsberg, Sweden. A single crystal of celsian was loaded in an ETH-type diamond anvil cell, and unit-cell parameters were measured at 20 different pressures up to 6.0 GPa at room T. The evolution of the unit-cell parameters and volume as a function of pressure shows a discontinuity at P 5.7 GPa indicating a displacive first-order phase transition. The P- V data were fitted by a second-order Birch-Murnaghan EoS only up to 2.55 GPa, because at higher pressures a slight change in the compressional behavior of the unit-cell volume is observed, indicating a pre-transition volume softening. The resulting EoS coefficients are V 0 = 1461.4(1) Å3 and K T0 = 88.1(6) GPa. A second crystal of celsian was loaded in the DAC cell, and single-crystal in situ H P X-ray diffraction was performed at P = 0.0001, 2.1, 4.2, 5.5, 5.9, 6.5 and 7.8 GPa. The data collections between 0 and 5.5 GPa show only a- and b-type reflections confirming the I2/ c space group. The appearance of c and d-type reflections at 5.9, 6.5 and 7.8 GPa, the analysis of the systematic absence and the structural refinements define the H P phase transition as an I2/ c- P21/ c transition. The most significant changes with compression in celsian are the deformation in the Ba polyhedra and the variation in the T-O-T angles.

  1. High-pressure structural configuration and phase transition in celsian, BaAl2Si2O8

    NASA Astrophysics Data System (ADS)

    Curetti, Nadia; Benna, Piera; Bruno, Emiliano

    2016-10-01

    In situ high-pressure X-ray diffraction study was performed on celsian (Cls97Or3) from Jakobsberg, Sweden. A single crystal of celsian was loaded in an ETH-type diamond anvil cell, and unit-cell parameters were measured at 20 different pressures up to 6.0 GPa at room T. The evolution of the unit-cell parameters and volume as a function of pressure shows a discontinuity at P ~ 5.7 GPa indicating a displacive first-order phase transition. The P-V data were fitted by a second-order Birch-Murnaghan EoS only up to 2.55 GPa, because at higher pressures a slight change in the compressional behavior of the unit-cell volume is observed, indicating a pre-transition volume softening. The resulting EoS coefficients are V 0 = 1461.4(1) Å3 and K T0 = 88.1(6) GPa. A second crystal of celsian was loaded in the DAC cell, and single-crystal in situ HP X-ray diffraction was performed at P = 0.0001, 2.1, 4.2, 5.5, 5.9, 6.5 and 7.8 GPa. The data collections between 0 and 5.5 GPa show only a- and b-type reflections confirming the I2/c space group. The appearance of c and d-type reflections at 5.9, 6.5 and 7.8 GPa, the analysis of the systematic absence and the structural refinements define the HP phase transition as an I2/c-P21/c transition. The most significant changes with compression in celsian are the deformation in the Ba polyhedra and the variation in the T-O-T angles.

  2. High pressure effect on the main transition from the ripple gel P'beta phase to the liquid crystal (Lalpha) phase in dipalmitoylphosphatidylcholine. Microcalorimetric study.

    PubMed

    Potekhin, S A; Senin, A A; Abdurakhmanov, N N; Khusainova, R S

    2008-11-01

    Scanning microcalorimetry has been used to study the high pressure effect on the main transition from the ripple gel P'(beta) phase to the liquid crystal (L(alpha)) phase in DPPC (dipalmitoylphosphatidylcholine). It has been demonstrated that an increase of the pressure by 200 MPa shifts the transition to higher temperatures by 36.4 degrees. The pressure increase does not affect the cooperativity of transition but reduces noticeably its enthalpy. The changes of the molar partial volume, isothermal compressibility as well as volume thermal expansibility during transition in DPPC suspension have been estimated. It has been shown that monovalent ions (Na(+), Cl(-)) in solution slightly affect the main thermodynamic parameters of the transition. Calcium ions significantly decrease distinction in compressibility and thermal expansibility between liquid-crystal and ripple gel phases of lipid suspension, which in its turn reflects less difference in their volume fluctuations.

  3. Recognition and measurement gas-liquid two-phase flow in a vertical concentric annulus at high pressures

    NASA Astrophysics Data System (ADS)

    Li, Hao; Sun, Baojiang; Guo, Yanli; Gao, Yonghai; Zhao, Xinxin

    2017-08-01

    The air-water flow characteristics under pressure in the range of 1-6 MPa in a vertical annulus were evaluated in this report. Time-resolved bubble rising velocity and void fraction were also measured using an electrical void fraction meter. The results showed that the pressure has remarkable effect on the density, bubble size and rise velocity of the gas. Four flow patterns (bubble, cap-bubble, cap-slug, and churn) were also observed instead of Taylor bubble at high pressure. Additionally, the transition process from bubble to cap-bubble was investigated at atmospheric and high pressures, respectively. The results revealed that the flow regime transition criteria for atmospheric pressure do not work at high pressure, hence a new flow regime transition model for annular flow channel geometry was developed to predict the flow regime transition, which thereafter exhibited high accuracy at high pressure condition.

  4. Effects of gasket on coupled plastic flow and strain-induced phase transformations under high pressure and large torsion in a rotational diamond anvil cell

    NASA Astrophysics Data System (ADS)

    Feng, Biao; Levitas, Valery I.

    2016-01-01

    Combined plastic flow and strain-induced phase transformations (PTs) under high pressure in a sample within a gasket subjected to three dimensional compression and torsion in a rotational diamond anvil cell (RDAC) are studied using a finite element approach. The results are obtained for the weaker, equal-strength, and stronger high-pressure phases in comparison with low-pressure phases. It is found that, due to the strong gasket, the pressure in the sample is relatively homogenous and the geometry of the transformed zones is mostly determined by heterogeneity in plastic flow. For the equal-strength phases, the PT rate is higher than for the weaker and stronger high-pressure phases. For the weaker high-pressure phase, transformation softening induces material instability and leads to strain and PT localization. For the stronger high-pressure phase, the PT is suppressed by strain hardening during PT. The effect of the kinetic parameter k that scales the PT rate in the strain-controlled kinetic equation is also examined. In comparison with a traditional diamond anvil cell without torsion, the PT progress is much faster in RDAC under the same maximum pressure in the sample. Finally, the gasket size and strength effects are discussed. For a shorter and weaker gasket, faster plastic flow in radial and thickness directions leads to faster PT kinetics in comparison with a longer and stronger gasket. The rates of PT and plastic flows are not very sensitive to the modest change in a gasket thickness. Multiple experimental results are reproduced and interpreted. Obtained results allow one to design the desired pressure-plastic strain loading program in the experiments for searching new phases, reducing PT pressure by plastic shear, extracting kinetic properties from experiments with heterogeneous fields, and controlling homogeneity of all fields and kinetics of PTs.

  5. CH3OH in High-Pressure Phases of H2O: Implications for Ice-Rich Planets

    NASA Astrophysics Data System (ADS)

    Aarestad, B.; Frank, M. R.; Scott, H. P.; Maglio, S.; Prakapenka, V.

    2007-12-01

    A significant body of research exists on the structure, lattice parameters, and density of high-pressure ice polymorphs, namely Ice VI and Ice VII, as these ices may make up a considerable part of the interior of large icy satellites and select extra solar planets; though most research thus far has been constrained to the pure H2O system. Salty subsurface oceans are also believed to exist within some of these icy bodies which may have prolonged interaction with the Ice VII phase present, incorporating foreign ions or molecules into the lattice of high-pressure ices. Recent research concerning the effects that charged ions have on Ice VII has shown that the presence of these ions notably affects the structure, increasing the Ice VII molar density at any given pressure relative to pure Ice VII (Frank et al., 2006, PEPI, 155, 152-162). This study focused on the incorporation of CH3OH into Ice VII to determine if the change in density was predominantly a result of charge-induced partial ordering of the hydrogen in Ice VII (as outlined in Frank et al., 2006) or if it was controlled solely by the addition of large foreign molecules into the lattice structure. Solutions of 1.60, 5.00 and 10.0 mol% CH3OH in H2O were loaded into a diamond anvil cell. The experiments were performed at GSECARS 13-BM-D at the Advanced Photon Source at Argonne National Laboratory. The unit cell parameters were measured using monochromatic X-ray radiation, 0.3344 Å, and a MAR 345 online imaging system. Powder diffraction patterns were collected in ~1 GPa increments up to ~31, ~48, and ~35 GPa, respectively. The volume-pressure relations (at 300 K) were used to determine an equation of state (EOS) for select compositions in the CH3OH - H2O system. Diffraction data indicate that the unit cell volume of Ice VII formed from a 1.60 mol% CH3OH aqueous solution did not deviate significantly from that of Ice VII formed from pure H2O. Conversely, the volumes of Ice VII formed from 5.00 and 10.0 mol

  6. The phase diagram of water at high pressures as obtained by computer simulations of the TIP4P/2005 model: the appearance of a plastic crystal phase.

    PubMed

    Aragones, J L; Conde, M M; Noya, E G; Vega, C

    2009-01-21

    In this work the high pressure region of the phase diagram of water has been studied by computer simulation by using the TIP4P/2005 model of water. Free energy calculations were performed for ices VII and VIII and for the fluid phase to determine the melting curve of these ices. In addition, molecular dynamics simulations were performed at high temperatures (440 K) observing the spontaneous freezing of the liquid into a solid phase at pressures of about 80,000 bar. The analysis of the structure obtained lead to the conclusion that a plastic crystal phase was formed. In the plastic crystal phase the oxygen atoms were arranged forming a body center cubic structure, as in ice VII, but the water molecules were able to rotate almost freely. Free energy calculations were performed for this new phase, and it was found that for TIP4P/2005 this plastic crystal phase is thermodynamically stable with respect to ices VII and VIII for temperatures higher than about 400 K, although the precise value depends on the pressure. By using Gibbs-Duhem simulations, all coexistence lines were determined, and the phase diagram of the TIP4P/2005 model was obtained, including ices VIII and VII and the new plastic crystal phase. The TIP4P/2005 model is able to describe qualitatively the phase diagram of water. It would be of interest to study if such a plastic crystal phase does indeed exist for real water. The nearly spherical shape of water makes possible the formation of a plastic crystal phase at high temperatures. The formation of a plastic crystal phase at high temperatures (with a bcc arrangements of oxygen atoms) is fast from a kinetic point of view occurring in about 2 ns. This is in contrast to the nucleation of ice Ih which requires simulations of the order of hundreds of ns.

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

    NASA Astrophysics Data System (ADS)

    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

  8. Volumetric and Optical Studies of High-Pressure Phases of MgSO4-H2O with Applications to Europa and Mars

    NASA Astrophysics Data System (ADS)

    Hogenboom, D. L.; Dougherty, A. J.; Kargel, J. S.; Mushi, S. E.

    2005-03-01

    Optical imaging of high-pressure phases of the MgSO4-H2O system while measuring the volume change of the sample near the eutectic transition provides new insight into the metastability of this system with consequences for modeling Europa's ocean.

  9. High Pressure Biomass Gasification

    SciTech Connect

    Agrawal, Pradeep K

    2016-07-29

    According to the Billion Ton Report, the U.S. has a large supply of biomass available that can supplement fossil fuels for producing chemicals and transportation fuels. Agricultural waste, forest residue, and energy crops offer potential benefits: renewable feedstock, zero to low CO2 emissions depending on the specific source, and domestic supply availability. Biomass can be converted into chemicals and fuels using one of several approaches: (i) biological platform converts corn into ethanol by using depolymerization of cellulose to form sugars followed by fermentation, (ii) low-temperature pyrolysis to obtain bio-oils which must be treated to reduce oxygen content via HDO hydrodeoxygenation), and (iii) high temperature pyrolysis to produce syngas (CO + H2). This last approach consists of producing syngas using the thermal platform which can be used to produce a variety of chemicals and fuels. The goal of this project was to develop an improved understanding of the gasification of biomass at high pressure conditions and how various gasification parameters might affect the gasification behavior. Since most downstream applications of synags conversion (e.g., alcohol synthesis, Fischer-Tropsch synthesis etc) involve utilizing high pressure catalytic processes, there is an interest in carrying out the biomass gasification at high pressure which can potentially reduce the gasifier size and subsequent downstream cleaning processes. It is traditionally accepted that high pressure should increase the gasification rates (kinetic effect). There is also precedence from coal gasification literature from the 1970s that high pressure gasification would be a beneficial route to consider. Traditional approach of using thermogravimetric analyzer (TGA) or high-pressure themogravimetric analyzer (PTGA) worked well in understanding the gasification kinetics of coal gasification which was useful in designing high pressure coal gasification processes. However

  10. Ammonia-water mixtures at high pressures - Melting curves of ammonia dihydrate and ammonia monohydrate and a revised high-pressure phase diagram for the water-rich region. [in primordial solar system ices

    NASA Technical Reports Server (NTRS)

    Boone, S.; Nicol, M. F.

    1991-01-01

    The phase relations of some mixtures of ammonia and water are investigated to create a phase diagram in pressure-temperature-composition space relevant to the geophysical study of bodies in the outer solar system. The mixtures of NH3(x)H2O(1-x), where x is greater than 0.30 but less than 0.51, are examined at pressures and temperatures ranging from 0-6.5 GPa and 125-400 K, respectively. The ruby luminescence technique monitors the pressure and a diamond-anvil cell compresses the samples, and the phases are identified by means of normal- and polarized-light optical microscopy. The melting curve for NH3H2O(2) is described by the equation T = 176 + 60P - 8.5P squared for the ranges of 0.06-1.4 GPa and 179-243 K. The equation for NH3H2O is T = 194 + 37P - P squared, which represents a minor correction of a previous description by Johnson et al. (1985). Observed phase transitions are consistent with the high-pressure stability limit of NH3H2O(2), and the transition boundary is found to be linear.

  11. Ammonia-water mixtures at high pressures - Melting curves of ammonia dihydrate and ammonia monohydrate and a revised high-pressure phase diagram for the water-rich region. [in primordial solar system ices

    NASA Technical Reports Server (NTRS)

    Boone, S.; Nicol, M. F.

    1991-01-01

    The phase relations of some mixtures of ammonia and water are investigated to create a phase diagram in pressure-temperature-composition space relevant to the geophysical study of bodies in the outer solar system. The mixtures of NH3(x)H2O(1-x), where x is greater than 0.30 but less than 0.51, are examined at pressures and temperatures ranging from 0-6.5 GPa and 125-400 K, respectively. The ruby luminescence technique monitors the pressure and a diamond-anvil cell compresses the samples, and the phases are identified by means of normal- and polarized-light optical microscopy. The melting curve for NH3H2O(2) is described by the equation T = 176 + 60P - 8.5P squared for the ranges of 0.06-1.4 GPa and 179-243 K. The equation for NH3H2O is T = 194 + 37P - P squared, which represents a minor correction of a previous description by Johnson et al. (1985). Observed phase transitions are consistent with the high-pressure stability limit of NH3H2O(2), and the transition boundary is found to be linear.

  12. High-Temperature Phase Transitions in CsH2PO4 Under Ambient and High-Pressure Conditions: A Synchrotron X-ray Diffraction Study

    SciTech Connect

    Botez,C.; Hermosillo, J.; Zhang, J.; Qian, J.; Zhao, Y.; Majzlan, J.; Chianelli, R.; Pantea, C.

    2007-01-01

    To clarify the microscopic origin of the temperature-induced three-order-of-magnitude jump in the proton conductivity of CsH2PO4 (superprotonic behavior), we have investigated its crystal structure modifications within the 25-300 C temperature range under both ambient- and high-pressure conditions using synchrotron x-ray diffraction. Our high-pressure data show no indication of the thermal decomposition/polymerization at the crystal surface recently proposed as the origin of the enhanced proton conductivity. Instead, we found direct evidence that the superprotonic behavior of the title material is associated with a polymorphic structural transition to a high-temperature cubic phase. Our results are in excellent agreement with previous high-pressure ac impedance measurements.

  13. High-Pressure Vibrational Spectroscopy.

    NASA Astrophysics Data System (ADS)

    Pogson, Mark

    1987-09-01

    Available from UMI in association with The British Library. Requires signed TDF. The study of solids at high pressure and variable temperature enables development of accurate interatomic potential functions over wide ranges of interatomic distances. A review of the main models used in the determination of these potentials is given in Chapter one. A discussion of phonon frequency as a variable physical parameter reflecting the interatomic potential is given. A high pressure Raman study of inorganic salts of the types MSCN, (M = K,Rb,Cs & NH_4^+ ) and MNO_2, (M = K,Na) has been completed. The studies have revealed two new phases in KNO_2 and one new phase in NaNO _2 at high pressure. The accurate phonon shift data have enabled the determination of the pure and biphasic stability regions of the phases of KNO _2. A discussion of the B1, B2 relationship of univalent nitrites is also given. In the series of thiocyanates studied new phases have been found in all four materials. In both the potassium and rubidium salts two new phases have been detected, and in the ceasium salt one new phase has been detected, all at high pressure, from accurate phonon shift data. These transitions are discussed in terms of second-order mechanisms with space groups suggested for all phases, based on Landau's theory of second-order phase transitions. In the ammonium salt one new phase has been detected. This new phase transition has been interpreted as a second-order transition. The series of molecular crystals CH_3 HgX, (X = Cl,Br & I) has been studied at high pressure and at variable temperature. In Chapter five, their phase behaviour at high pressure is detailed along with the pressure dependencies of their phonon frequencies. In the chloride and the bromide two new phases have been detected. In the bromide one has been detected at high temperature and one at high pressure, and latter being interpreted as the stopping of the methyl rotation. In the chloride one phase has been found at

  14. High pressure synthesis gas fermentation

    SciTech Connect

    Not Available

    1992-01-01

    The construction of the high pressure gas phase fermentation system has been completed. Photographs of the various components of the system are presented, along with an operating procedure for the equipment.

  15. High pressure homogenization and two-phased anaerobic digestion for enhanced biogas conversion from municipal waste sludge.

    PubMed

    Wahidunnabi, Abdullahil K; Eskicioglu, Cigdem

    2014-12-01

    This study compared advanced anaerobic digestion combining two-phased anaerobic digestion (2PAD) with high pressure homogenization (HPH) pretreatment to conventional anaerobic digestion of municipal sludge at laboratory scale. The study began with examination of thickened waste activated sludge (TWAS) solubilization due to HPH pretreatment at different pressure (0-12,000 psi) and chemical dose (0.009-0.036 g NaOH/g total solids). Homogenizing pressure was found as the most significant factor (p-value < 0.05) for increasing solubilization of particulate chemical oxygen demand (COD) and biopolymers in TWAS. Based on the preliminary results, a pretreatment with chemical dose of 0.009 g NaOH/g total solids and pressure of 12,000 psi was selected for digester studies. Upon acclimation of anaerobic inocula to pretreatments, a total number of twelve lab-scale digesters were operated under scenarios including single-stage (control), 2PAD, and HPH coupled with 2PAD (HPH + 2PAD) at sludge retention times (SRTs) of 20, 14 and 7 days. Between mesophilic and thermophilic temperatures, mesophilic digestion was found to benefit more from pretreatments. Relative (to control) improvements in methane yield and volatile solids (VS) removals increased noticeably as SRT was shortened from 20 to 14 and 7 days. HPH + 2PAD system was found to achieve the maximum methane production (0.61-1.32 L CH4/Ldigester-d) and VS removals (43-64%). Thermophilic control, 2PAD and HPH + 2PAD systems resulted in significant pathogen removals meeting Class A biosolids requirements according to Organic Matter Recycling Regulations (OMRR) of British Columbia (BC) at 20 d SRT. Energy analysis indicated that all the digestion scenarios attained positive energy balance with 2PAD system operated at 20 d SRT producing the maximum net energy of 4.76 GJ/tonne CODadded.

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

    SciTech Connect

    Prilliman, Stephen Gerald

    2003-01-01

    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 (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

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

    SciTech Connect

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

    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.

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

    PubMed

    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.

  19. In situ observation of multiple phase transitions in low-melting ionic liquid [BMIM][BF4] under high pressure up to 30 GPa.

    PubMed

    Su, Lei; Zhu, Xiang; Wang, Zheng; Cheng, Xuerui; Wang, Yongqiang; Yuan, Chaosheng; Chen, Zhenping; Ma, Chunli; Li, Fangfei; Zhou, Qiang; Cui, Qiliang

    2012-02-23

    In situ characterization of phase transitions and direct microscopic observations of a low-melting ionic liquid, 1-butyl-3-methyl imidazolium tetrafluoroborate ([BMIM][BF(4)]), has been performed in detail by Raman spectroscopy. Compression of [BMIM][BF(4)] was measured under hydrostatic pressure up to ~30.0 GPa at room temperature by using a high-pressure diamond anvil cell. With pressure increasing, the characteristic bands of [BMIM][BF(4)] displayed nonmonotonic pressure-induced frequency shifts, and it is found to undergo four successive phase transitions at around 2.25, 6.10, 14.00, and 21.26 GPa. Especially, above a pressure of 21.26 GPa, luminescence of the sample occurs, which is connected with the most significant phase transition at around this pressure. It was indicated that the structure change under high pressure might be associated with a conformational change in the butyl chain. Upon releasing pressure, the spectrum was not recovered under a pressure up to 1.16 GPa, thereby indicating that this high-pressure phase remains stable over a large pressure range between 30 and 1.16 GPa in low-melting ionic liquid [BMIM][BF(4)]. Although the sample was kept under the normal pressure for 24 h, the spectrum was recovered, and it showed that the phase transition of [BMIM][BF(4)] was reversible. In other words, such a low-melting ionic liquid [BMIM][BF(4)] remains stable even after being treated under so a high pressure of up to 30 GPa. © 2012 American Chemical Society

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

    SciTech Connect

    Ono, Shigeaki; Kikegawa, Takumi

    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.

  1. Crystal structure, equation of state, and elasticity of hydrous aluminosilicate phase, topaz-OH (Al2SiO4(OH)2) at high pressures

    NASA Astrophysics Data System (ADS)

    Mookherjee, Mainak; Tsuchiya, Jun; Hariharan, Anant

    2016-02-01

    We examined the equation of state and high-pressure elasticity of the hydrous aluminosilicate mineral topaz-OH (Al2SiO4(OH)2) using first principles simulation. Topaz-OH is a hydrous phase in the Al2O3-SiO2-H2O (ASH) ternary system, which is relevant for the mineral phase relations in the hydrated sedimentary layer of subducting slabs. Based on recent neutron diffraction experiments, it is known that the protons in the topaz-OH exhibit positional disorder with half occupancy over two distinct crystallographic sites. In order to adequately depict the proton environment in the topaz-OH, we examined five crystal structure models with distinct configuration for the protons in topaz-OH. Upon full geometry optimization we find two distinct space group, an orthorhombic Pbnm and a monoclinic P21/c for topaz-OH. The topaz-OH with the monoclinic P21/c space group has a lower energy compared to the orthorhombic Pbmn space group symmetry. The pressure-volume results for the monoclinic topaz-OH is well represented by a third order Birch-Murnaghan formulation, with V0mon = 348.63 (±0.04) Å3, K0mon = 164.7 (±0.04) GPa, and K0mon = 4.24 (±0.05). The pressure-volume results for the orthorhombic topaz-OH is well represented by a third order Birch-Murnaghan formulation, with V0orth = 352.47 (±0.04) Å3, K0orth = 166.4 (±0.06) GPa, and K0orth = 4.03 (±0.04). While the bulk moduli are very similar for both the monoclinic and orthorhombic topaz-OH, the shear elastic constants and the shear moduli are very sensitive to the position of the proton, orientation of the O-H dipole, and the space group symmetry. The S-wave anisotropy for the orthorhombic and monoclinic topaz-OH are also quite distinct. In the hydrated sedimentary layer of subducting slabs, transformation of a mineral assemblage consisting of coesite (SiO2) and diaspore (AlOOH) to topaz-OH (Al2SiO4(OH)2) is likely to be accompanied by an increase in density, compressional velocity, and shear wave velocity. However

  2. Metallization in the molten and solid state and phase diagrams of the GeSe2 and GeS2 under high pressure

    NASA Astrophysics Data System (ADS)

    Brazhkin, V. V.; Bychkov, E.; Kondrin, M. V.

    2014-12-01

    We found that under high pressure, the GeSe2 and GeS2 melts pass into the metallic state. In the vicinity of the melting curves, their metallization begins at 3.5 and 7 GPa, respectively. The position of the semiconductor-metal transition line on the phase diagram for GeSe2 liquid is established. The GeS2-II and GeSe2-III high-pressure crystalline modifications are semiconductors, whereas the GeSe2-III modification at pressures exceeding 3.5-4 GPa is a metal (σ ≈ 103 Ω-1 cm-1). The ( P, T) phase diagrams for these compounds are constructed in the pressure range up to 10 GPa. Metallization during the GeSe2-II-GeSe2-III transition is evidently responsible for the small jump of entropy and the corresponding almost vertical slope of the transition line.

  3. High pressure synthesis of a hexagonal close-packed phase of the high-entropy alloy CrMnFeCoNi

    DOE PAGES

    Tracy, Cameron L.; Park, Sulgiye; Rittman, Dylan R.; ...

    2017-05-25

    High pressure x-ray diffraction measurements reveal that the face-centered cubic (fcc) high-entropy alloy CrMnFeCoNi transforms martensitically to a hexagonal close-packed (hcp) phase at ~14 GPa. We attribute this to suppression of the local magnetic moments, destabilizing the fcc phase. Similar to fcc-to-hcp transformations in Al and the noble gases, this transformation is sluggish, occurring over a range of >40 GPa. But, the behavior of CrMnFeCoNi is unique in that the hcp phase is retained following decompression to ambient pressure, yielding metastable fcc-hcp mixtures.

  4. New design of fiber-optic reflectometer for determining the phase boundary of multicomponent fluid mixtures at high pressures and high temperatures

    NASA Astrophysics Data System (ADS)

    Wu, Weize; Ke, Jie; Poliakoff, Martyn

    2006-02-01

    A dynamic synthetic method based on an optic fiber sensor has been developed to measure phase boundaries of multicomponent fluid at high temperatures >300°C and pressures >30MPa. The breakthrough has been the design of the equilibrium cell containing the optic fiber, which gives highly reproducible signals for the phase transition. We demonstrate that this method can clearly distinguish between dew points and bubble points in the phase transitions of mixtures. Overall, the method is characterized by speed, simplicity, high pressures, and high temperatures.

  5. Development of a laser-induced plasma probe to measure gas phase plasma signals at high pressures and temperatures

    NASA Astrophysics Data System (ADS)

    Gounder, J. D.; Kutne, P.; Meier, W.

    2012-08-01

    The ability of laser induced breakdown spectroscopy (LIBS) technique for on line simultaneous measurement of elemental concentrations has led to its application in a wide number of processes. The simplicity of the technique allows its application to harsh environments such as present in boilers, furnaces and gasifiers. This paper presents the design of a probe using a custom optic which transforms a round beam into a ring (Donut) beam, which is used for forming a plasma in an atmosphere of nitrogen at high pressure (20 bar) and temperature (200 °C). The LIBS experiments were performed using a high pressure cell to characterize and test the effectiveness of the donut beam transmitted through the LIBS probe and collect plasma signal in back scatter mode. The first tests used the second harmonic of a Nd:YAG laser, pulse width 7 ns, to form a plasma in nitrogen gas at five different pressures (1, 5, 10, 15 and 20 bar) and three different gas temperatures (25, 100 and 200 °C). The uniqueness of this probe is the custom made optic used for reshaping the round laser beam into a ring (Donut) shaped laser beam, which is fed into the probe and focused to form a plasma at the measurement point. The plasma signal is collected and collimated using the laser focusing lens and is reflected from the laser beam axis onto an achromatic lens by a high reflection mirror mounted in the center section of the donut laser beam. The effect of gas pressure and temperature on N(I) lines in the high pressure cell experiment shows that the line intensity decreases with pressure and increases with temperature. Mean plasma temperature was calculated using the ratios of N(I) line intensities ranging from 7400 K to 8900 K at 1 bar and 2400 K to 3200 K at 20 bar for the three different gas temperatures. The results show that as a proof of principle the donut beam optics in combination with the LIBS probe can be used for performing extensive LIBS measurements in well controlled laboratory

  6. 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

    NASA Astrophysics Data System (ADS)

    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.

  7. SINGLE CRYSTAL DIFFRACTION OF SIDERITE UP TO 54 GPA AND HIGH PRESSURE-HIGH TEMPERATURE PHASES IN THE Fe-C-O SYSTEM (Invited)

    NASA Astrophysics Data System (ADS)

    Lavina, B.; Dera, P. K.; Downs, R. T.

    2009-12-01

    Phases in the Fe-C-O system are of interest for the deep carbon cycle, they might play an important role in buffering the mantle fO2. Carbon is also common in the fluid phases that greatly influence the Earth’s processes. The study of the high pressure behavior of siderite and of the phases synthesized after laser heating offers a good opportunity to illustrate the advantages and importance of single crystal diffraction in the high pressure science. The structure of siderite, FeCO3, has been refined up to 54 GPa across the spin pairing transition. Splitting of the diffraction peaks at the transition pressure provides unequivocal evidence of the sharpness of the spin crossover and of the absence of any intermediate volume and therefore of an intermediate spin state at ambient temperature. Diffraction intensities were collected in about 30 minutes at a bending magnet station (HPCAT, APS) and in about one minute at an insertion device station (GSECARS, APS). The quality of the refinement is unvaried in the investigated range, and the results obtained from the two different radiation and detectors are consistent. The refinements provide an accurate and robust determination of the dependence of bond distances and angles with pressure. Subtle structural rearrangements associated with the collapse of the octahedral cation size will be discussed. In situ laser heating is a very powerful method to study minerals at the actual P-T of the Earth’s deep interior. Overcoming the kinetic barriers required for bond breaking and atom diffusion, high pressure-high temperature phases may be synthesized. The analysis of high-pressure phases is very challenging. Diffraction patterns are usually of moderate quality and resolution, furthermore in addition to the sample, the pattern contains the contribution of other phases such as those used to insulate the anvils, to provide a pressure medium and a pressure marker. In several cases after laser heating, we observed phase transitions

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

    NASA Astrophysics Data System (ADS)

    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.

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

    PubMed

    Kanno, H; Kajiwara, K; Miyata, K

    2010-05-21

    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 T(H) (homogeneous ice nucleation temperature) and T(m) (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 T(H) 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 P(c2)= approximately 200 MPa and at T(c2)<-100 degrees C (P(c2): pressure of SCP, T(c2): temperature of SCP). The presence of two T(H) peaks for DMSO solutions (R=15, 12, and 10) suggests that phase separation occurs in aqueous DMSO solution (Rhigh pressures and low temperatures (<-90 degrees C). The pressure dependence of the two T(H) 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.

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

    NASA Astrophysics Data System (ADS)

    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.

  11. Predicted Suppression of the Superconducting Transition of New High-Pressure Yttrium Phases with Increasing Pressure from First-Principles Calculations

    NASA Astrophysics Data System (ADS)

    Chen, Yue; Hu, Qing-Miao; Yang, Rui

    2012-10-01

    Structure searches for new high-pressure phases of Y metal have been performed by using evolutionary algorithms in conjunction with a first-principles, pseudopotential plane-wave method based on density functional theory. The oF16-Fddd and hP3-P3121 phases are predicted to be energetically favorable at pressures over 97 GPa. These two phases are shown to be dynamically stable by computing their phonon dispersions. We thus propose that oF16-Fddd and hP3-P3121 are the most probable crystal structures Y may take in the 97-206 GPa range. The superconducting critical temperatures (Tc) of the new phases are estimated using the Allen-Dynes formula. The Tc is predicted to decrease with increasing pressure over about 100 GPa, in sharp contrast to its observed monotonic increase under lower pressure. The electronic origins of the stabilities of the proposed high-pressure phases have also been investigated.

  12. Phase transitions in I2O5 at high pressures: Raman and X-ray diffraction studies

    NASA Astrophysics Data System (ADS)

    Kim, Minseob; Yoo, Choong-Shik

    2016-03-01

    We have studied the pressure-induced phase transitions of I2O5 in diamond anvil cells using optical spectroscopy and X-ray diffraction. X-ray and Raman data indicate that the linear structure of phase I isostructurally transforms into a stacking layer structure of phase II at 5 GPa and, then, into an amorphous network of phase III at 15 GPa. Phase III further transforms into amorphous solid at 23 GPa, which can be recovered at ambient condition. Anisotropic van der Waals interaction between lone pairs of iodines and neighboring molecules drives to the observed phase change with increasing of iodine coordination number.

  13. Phase formation in the (1-y)BiFeO3-yBiScO3 system under ambient and high pressure

    NASA Astrophysics Data System (ADS)

    Salak, A. N.; Khalyavin, D. D.; Pushkarev, A. V.; Radyush, Yu. V.; Olekhnovich, N. M.; Shilin, A. D.; Rubanik, V. V.

    2017-03-01

    Formation and thermal stability of perovskite phases in the BiFe1-yScyO3 system (0≤y≤0.70) were studied. When the iron-to-scandium substitution rate does not exceed about 15 at%, the single-phase perovskite ceramics with the rhombohedral R3c symmetry (as that of the parent compound, BiFeO3) can be prepared from the stoichiometric mixture of the respective oxides at ambient pressure. Thermal treatment of the oxide mixtures with a higher content of scandium results in formation of two main phases, namely a BiFeO3-like R3c phase and a cubic (I23) sillenite-type phase based on γ-Bi2O3. Single-phase perovskite ceramics of the BiFe1-yScyO3 composition were synthesized under high pressure from the thermally treated oxide mixtures. When y is between 0 and 0.25 the high-pressure prepared phase is the rhombohedral R3c with the √2ap×√2ap×2√3ap superstructure (ap 4 Å is the pseudocubic perovskite unit-cell parameter). The orthorhombic Pnma phase (√2ap×4ap×2√2ap) was obtained in the range of 0.30≤y≤0.60, while the monoclinic C2/c phase (√6ap×√2ap×√6ap) is formed when y=0.70. The normalized unit-cell volume drops at the crossover from the rhombohedral to the orthorhombic composition range. The perovskite BiFe1-yScyO3 phases prepared under high pressure are metastable regardless of their symmetry. At ambient pressure, the phases with the compositions in the ranges of 0.20≤y≤0.25, 0.30≤y<0.50 and 0.50≤y≤0.70 start to decompose above 970, 920 and 870 K, respectively.

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

    NASA Astrophysics Data System (ADS)

    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.

  15. The effects of Na on high pressure phases of CuIn(0.5)Ga(0.5)Se(2) from ab initio calculation.

    PubMed

    Pluengphon, P; Bovornratanaraks, T; Vannarat, S; Pinsook, U

    2012-03-07

    The effects of Na atoms on high pressure structural phase transitions of CuIn(0.5)Ga(0.5)Se(2) (CIGS) were studied by an ab initio method using density functional theory. At ambient pressure, CIGS is known to have chalcopyrite (I42d) structure. The high pressure phase transitions of CIGS were proposed to be the same as the order in the CuInSe(2) phase transitions which are I42d → Fm3m → Cmcm structures. By using the mixture atoms method, the Na concentration in CIGS was studied at 0.1, 1.0 and 6.25%. The positive mixing enthalpy of Na at In/Ga sites (Na(InGa)) is higher than that of Na at Cu sites (Na(Cu)). It confirmed previous studies that Na preferably substitutes on the Cu sites more than the (In, Ga) sites. From the energy-volume curves, we found that the effect of the Na substitutes is to reduce the hardness of CIGS under high pressure. The most significant effects occur at 6.25% Na. We also found that the electronic density of states of CIGS near the valence band maximum is increased noticeably in the chalcopyrite phase. The band gap is close in the cubic and orthorhombic phases. Also, the Na(Cu)-Se bond length in the chalcopyrite phase is significantly reduced at 6.25% Na, compared with the pure Cu-Se bond length. Consequently, the energy band gap in this phase is wider than in pure CIGS, and the gap increased at the rate of 31 meV GPa(-1) under pressure. The Na has a small effect on the transition pressure. The path of transformation from the cubic to orthorhombic phase was derived. The Cu-Se plane in the cubic phase displaced relatively parallel to the (In, Ga)-Se plane by 18% in order to transform to the Cmcm phase. The enthalpy barrier is 0.020 eV/atom, which is equivalent to a thermal energy of 248 K. We predicted that Fm3m and Cmcm can coexist in some pressure range.

  16. Theoretical study of high-pressure phase stability of NaZr2(PO4)3 via elastic constants and equation of state

    NASA Astrophysics Data System (ADS)

    Chinnappan, Ravi; Panigrahi, B. K.

    2017-03-01

    Phase stability of NaZr_2(PO_4)_3 has been studied through density functional theory calculations of elastic constants, equation of state and enthalpies. The changes in elastic constants as a function of pressure show that the ambient rhombohedral (Rbar{3}c) NaZr_2(PO_4)_3 becomes unstable above 8 GPa and this instability is driven by a softening of C_{44} elastic constant through one of the Born stability criteria. High-pressure equation-of-state and enthalpy calculations further show that the ambient rhombohedral (Rbar{3}c) structure transforms first into another rhombohedral ( R3) phase and subsequently to LiZr_2(PO_4)_3-type orthorhombic phase at pressures above 6 and 8 GPa respectively which are in agreement with a recent x-ray diffraction study. Analysis of interatomic distances show that LiZr_2(PO_4)_3-type orthorhombic structure allows for shorter Na-O and Zr-P bonds at high pressures which appears to enable strong bonding and stability. Calculated formation enthalpy and bulk modulus of the ambient phase of NaZr_2(PO_4)_3 are found to be in reasonable agreement with the respective experimental values.

  17. Physical properties and phase diagram of the magnetic compound Cr{sub 0.26}NbS{sub 1.74} at high pressures

    SciTech Connect

    Sidorov, V. A.; Petrova, A. E.; Pinyagin, A. N.; Kolesnikov, N. N.; Khasanov, S. S.; Stishov, S. M.

    2016-06-15

    We report the results of a study of magnetic, electrical, and thermodynamic properties of a single crystal of the magnetic compound Cr{sub 0.26}NbS{sub 1.74} at ambient and high pressures. Results of the measurements of magnetization as a function of temperature reveal the existence of a ferromagnetic phase transition in Cr{sub 0.26}NbS{sub 1.74}. The effective number of Bohr magnetons per Cr atom in the paramagnetic phase of Cr{sub 0.26}NbS{sub 1.74} is µ{sub eff} ≈ 4.6µB, which matches the literature data for Cr1/3NbS2. Similarly, the effective number of Bohr magnetons per Cr atom in the saturation fields is rather close in both substances and corresponds to the number of magnetons in the Cr{sup +3} ion. In contrast to the stoichiometric compound, Cr{sub 0.26}NbS{sub 1.74} does not show a metamagnetic transition, that indicates the lack of a magnetic soliton. A high-pressure phase diagram of the compound reveals the quantum phase transition at T = 0 and P ≈ 4.2 GPa and the triple point situated at T ≈ 20 K and P ≈ 4.2 GPa.

  18. Quasi-hydrostatic X-ray powder diffraction study of the low- and high-pressure phases of CaWO4 up to 28 GPa

    NASA Astrophysics Data System (ADS)

    Vilaplana, R.; Lacomba-Perales, R.; Gomis, O.; Errandonea, D.; Meng, Y.

    2014-10-01

    We have studied CaWO4 under compression using Ne as pressure-transmitting medium at room temperature by means of synchrotron X-ray powder diffraction. We have found that CaWO4 beyond 8.8 GPa transforms from its low-pressure tetragonal structure (scheelite) into a monoclinic structure (fergusonite). The high-pressure phase remains stable up to 28 GPa and the low-pressure phase is totally recovered after full decompression. The pressure dependence of the unit-cell parameters, as well as the pressure-volume equation of state, has been determined for both phases. Compared with previous studies, we found in our quasi-hydrostatic experiments a different behavior for the unit-cell parameters of the fergusonite phase and a different transition pressure. These facts suggest that deviatoric stresses influence on the high-pressure structural behavior of CaWO4 as previously found in related compounds. The reported experiments also provide information on the pressure dependence of interatomic bond distances, shedding light on the transition mechanisms.

  19. Phonon density of states of single-crystal SrF e2A s2 across the collapsed phase transition at high pressure

    NASA Astrophysics Data System (ADS)

    Wang, Y. Q.; Lu, P. C.; Wu, J. J.; Liu, J.; Wang, X. C.; Zhao, J. Y.; Bi, W.; Alp, E. E.; Park, C. Y.; Popov, D.; Jin, C. Q.; Sun, J.; Lin, J. F.

    2016-07-01

    To help our understanding of the structural and superconducting transitions in ferropnictides, partial phonon density of states (PDOS) of iron in a single-crystal SrF e2A s2 pnictide have been investigated from both out-of-plane and in-plane polarizations with respect to the basal plane of the crystal structure using nuclear resonant inelastic x-ray scattering in a high-pressure diamond anvil cell at ambient temperature. The partial PDOS of iron in the pnictide crystal changes dramatically at approximately 8 GPa, which can be associated with the tetragonal (T) to collapsed tetragonal (CT) isostructural transition as evidenced in high-pressure x-ray diffraction measurements and theoretical calculations. Across the T-CT phase transition, analysis of the PDOS spectra shows a rapid stiffening of the optical phonon modes and a dramatic increase of the Lamb-Mössbauer factor (fLM) and mean force constant which can be associated with the rapid decrease of the c axis and the anomalous expansion of the a axis. Theoretically calculated Fe partial PDOS and lattice parameters of SrF e2A s2 further reveal the strong correlation between the lattice parameters and phonons. Our results show that the T-CT transition can induce significant changes in the vibrational, elastic, and thermodynamic properties of SrF e2A s2 single crystal at high pressure.

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

    SciTech Connect

    Sorb, Y.A. Sornadurai, D.

    2015-05-15

    The PbFX (X = Cl{sup –}or Br{sup –}) 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 (P2{sub 1}/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{sup –}, Br{sup –}or I{sup –}). PbFCl has a larger structural stability range compared to BaFCl and is attributed to the large anisotropic coordination of the Pb{sup 2+} and Cl{sup –}ions.

  1. High-pressure synthesis and superconductivity of the Laves phase compound Ca(Al,Si)2 composed of truncated tetrahedral cages Ca@(Al,Si))12.

    PubMed

    Tanaka, Masashi; Zhang, Shuai; Inumaru, Kei; Yamanaka, Shoji

    2013-05-20

    The Zintl compound CaAl2Si2 peritectically decomposes to a new ternary cubic Laves phase Ca(Al,Si)2 and an Al-Si eutectic at temperatures above 750 °C under a pressure of 13 GPa. The ternary Laves phase compound can also be prepared as solid solutions Ca(Al(1-x)Si(x))2 (0.35 ≤ x ≤ 0.75) directly from the ternary mixtures under high-pressure and high-temperature conditions. The cubic Laves phase structure can be regarded as a type of clathrate compound composed of face-sharing truncated tetrahedral cages with Ca atoms at the center, Ca@(Al,Si)12. The compound with a stoichiometric composition CaAlSi exhibits superconductivity with a transition temperature of 2.6 K. This is the first superconducting Laves phase compound composed solely of commonly found elements.

  2. The particle image velocimetry method in the study of the dynamics of phase transitions induced by high pressures in triolein and oleic acid

    NASA Astrophysics Data System (ADS)

    Tefelski, D. B.; Kulisiewicz, L.; Wierschem, A.; Delgado, A.; Rostocki, A. J.; Siegoczyński, R. M.

    2011-03-01

    Particle image velocimetry (PIV) is an optical measurement method capable of providing visualisation of velocity field of particle flow in fluids. After analysis of data acquired in the form of an image sequence, it is possible to retrieve information about flow parameters as mean values of velocity, vorticity, shear and normal strain. This paper presents the results of high pressure experiments using this method applied to triolein and oleic acid samples in their phase transition region. A high pressure optical chamber, He-Ne laser and light-sheet optics together with a digital camera and image acquisition computer allow us to study the motion of particles in high pressure conditions. The set-up was similar to that presented in Özmutlu et al. [Momentum and energy transfer during phase change of water under high hydrostatic pressure, Innov. Food Sci. Emerg. Technol. 7(3) (2006), pp. 161-168] and Kulisiewicz et al. [Visualization of pressure-shift freezing and thawing of concentrated aqueous sucrose solutions, High Press. Res. 27(2) (2007), pp. 291-297]. The analysis of phase transition dynamics in triolein and oleic acid is an extension to the work presented in Tefelski et al. [The investigation of the dynamics of the phase transformation in triolein and oleic acid under pressure, J. Phys.: Conf. Ser. 121(142004) (2008), pp. 1-6]. Oleic acid is a monounsaturated fatty acid and has a bent rod shape. Triolein is a triglyceride and has a "chair"-like shape. It is the base particle of many vegetable oils, especially olive oil. Triolein consists of three chains of oleic acid bound by a glycerol part. Information obtained by the study of phase transitions dynamics is important for food science and food technology processes which involve high pressure treatment. The PIV method shows differences in the solidification process of both substances in time, the existence of inhomogeneities (layers of different densities in the observed flow) and allows us to calculate the

  3. Chromium at High Pressure

    NASA Astrophysics Data System (ADS)

    Jaramillo, Rafael

    2012-02-01

    Chromium has long served as the archetype of spin density wave magnetism. Recently, Jaramillo and collaborators have shown that Cr also serves as an archetype of magnetic quantum criticality. Using a combination of x-ray diffraction and electrical transport measurements at high pressures and cryogenic temperatures in a diamond anvil cell, they have demonstrated that the N'eel transition (TN) can be continuously suppressed to zero, with no sign of a concurrent structural transition. The order parameter undergoes a broad regime of exponential suppression, consistent with the weak coupling paradigm, before deviating from a BCS-like ground state within a narrow but accessible quantum critical regime. The quantum criticality is characterized by mean field scaling of TN and non mean field scaling of the transport coefficients, which points to a fluctuation-induced reconstruction of the critical Fermi surface. A comparison between pressure and chemical doping as means to suppress TN sheds light on different routes to the quantum critical point and the relevance of Fermi surface nesting and disorder at this quantum phase transition. The work by Jaramillo et al. is broadly relevant to the study of magnetic quantum criticality in a physically pure and theoretically tractable system that balances elements of weak and strong coupling. [4pt] [1] R. Jaramillo, Y. Feng, J. Wang & T. F. Rosenbaum. Signatures of quantum criticality in pure Cr at high pressure. Proc. Natl. Acad. Sci. USA 107, 13631 (2010). [0pt] [2] R. Jaramillo, Y. Feng, J. C. Lang, Z. Islam, G. Srajer, P. B. Littlewood, D. B. McWhan & T. F. Rosenbaum. Breakdown of the Bardeen-Cooper-Schrieffer ground state at a quantum phase transition. Nature 459, 405 (2009).

  4. In situ imaging of the dynamics of photo-induced structural phase transition at high pressures by picosecond acoustic interferometry

    NASA Astrophysics Data System (ADS)

    Kuriakose, Maju; Chigarev, Nikolay; Raetz, Samuel; Bulou, Alain; Tournat, Vincent; Zerr, Andreas; Gusev, Vitalyi E.

    2017-05-01

    Picosecond acoustic interferometry is used to monitor in time the motion of the phase transition boundary between two water ice phases, VII and VI, coexisting at a pressure of 2.15 GPa when compressed in a diamond anvil cell at room temperature. By analyzing the time-domain Brillouin scattering signals accumulated for a single incidence direction of probe laser pulses, it is possible to access ratios of sound velocity values and of the refractive indices of the involved phases, and to distinguish between the structural phase transition and a recrystallization process. Two-dimensional spatial imaging of the phase transition dynamics indicates that it is initiated by the pump and probe laser pulses, preferentially at the diamond/ice interface. This method should find applications in three-dimensional monitoring with nanometer spatial resolution of the temporal dynamics of low-contrast material inhomogeneities caused by phase transitions or chemical reactions in optically transparent media.

  5. Initial phases of explosion earthquakes accompanying Vulcanian eruptions at Lokon-Empung volcano, Indonesia

    NASA Astrophysics Data System (ADS)

    Yamada, Taishi; Aoyama, Hiroshi; Nishimura, Takeshi; Yakiwara, Hiroshi; Nakamichi, Haruhisa; Oikawa, Jun; Iguchi, Masato; Hendrasto, Muhamad; Suparman, Yasa

    2016-11-01

    We examine the initial phases of explosion earthquakes accompanying Vulcanian eruptions at Lokon-Empung volcano in Indonesia to reveal the triggering process of explosive eruptions. In 2012-2013, 56 Vulcanian eruptions at Lokon-Empung were observed by our temporary observation network being comprised of four broadband seismometers and two infrasound microphones at 1.6-6.8 km from the active vent. The seismic records of each explosion earthquake share almost the same waveform characteristics of initial phases, consisting of a small compressional onset (P phase) and a subsequent large dilatational phase (D phase). Particle orbits of both phases show straight motion from beneath the active vent, which suggests that these phases are composed of a longitudinal body wave. For each explosion, the origin times of the P phase precedes 0.8-2.5 s before the occurrence of an explosion at the vent that are detected by infrasound data. Since the signal-to-noise ratio of the P phase is insufficient for a quantitative analysis, we analyze the D phase dominating the initial phases. Our analysis for the signals of 0.2-1.0 Hz shows the D phase are well explained by a cylindrical contraction source with a half-cosine shaped time function located at 1.0-1.3 km depth beneath the active vent. We also recognize that some explosions are followed by a prominent tremor that coincides with continuous ash emission (ET). The seismic amplitudes and intensity of the D phase of events in ET are larger than the explosions without accompanying tremor (EX). The frequency distribution of the time interval from the previous eruption is also different in the events in ET and EX. The implosion source in the initial phases of explosion earthquakes at several km beneath the active vent has been reported at Sakurajima volcano. Since our result shows considerable agreement with the previous works at Sakurajima, both Lokon-Empung and Sakurajima may share similar initial processes of Vulcanian eruptions.

  6. High-pressure phase diagram and equation of state of solid helium from single-crystal X-ray diffraction to 23.3 GPa

    NASA Technical Reports Server (NTRS)

    Mao, H. K.; Hemley, R. J.; Jephcoat, A. P.; Finger, L. W.; Wu, Y.

    1988-01-01

    Single-crystal X-ray diffraction measurements have been performed on solid He-4 from 15.6 to 23.3 GPa at 300 K with synchrotron radiation. The diffraction patterns demonstrate that the structure of the solid is hexagonal close packed over this pressure-temperature range, contrary to both the interpretation of high-pressure optical studies and to theoretical predictions. The solid is more compressible than is indicated by equations of state calculated with recently determined helium pair potentials. The results suggest that a significant revision of current views of the phase diagram and energetics of dense solid helium is in order.

  7. Large-aperture variable-volume view cell for the determination of phase-equilibria in high pressure systems and supercritical fluids

    NASA Astrophysics Data System (ADS)

    Licence, Peter; Dellar, Martin P.; Wilson, Richard G. M.; Fields, Peter A.; Litchfield, David; Woods, Helen M.; Poliakoff, Martyn; Howdle, Steven M.

    2004-10-01

    A high-pressure, variable-volume view cell incorporating a custom engineered, optically transparent sapphire piston is described. The view cell has an unbroken field of vision that enables the entire sample volume to be observed at all times. When lit from the rear of the cell, a near perfect view of any physical transition or change in state is available to the experimenter. The system has been shown to be particularly suitable for the determination of phase equilibria and cloud point measurements in supercritical fluid systems and has been rated for experiments up to 400 bar, 200 °C.

  8. High-pressure phase diagram and equation of state of solid helium from single-crystal X-ray diffraction to 23.3 GPa

    NASA Technical Reports Server (NTRS)

    Mao, H. K.; Hemley, R. J.; Jephcoat, A. P.; Finger, L. W.; Wu, Y.

    1988-01-01

    Single-crystal X-ray diffraction measurements have been performed on solid He-4 from 15.6 to 23.3 GPa at 300 K with synchrotron radiation. The diffraction patterns demonstrate that the structure of the solid is hexagonal close packed over this pressure-temperature range, contrary to both the interpretation of high-pressure optical studies and to theoretical predictions. The solid is more compressible than is indicated by equations of state calculated with recently determined helium pair potentials. The results suggest that a significant revision of current views of the phase diagram and energetics of dense solid helium is in order.

  9. Quantum simulation of thermally-driven phase transition and oxygen K-edge x-ray absorption of high-pressure ice

    PubMed Central

    Kang, Dongdong; Dai, Jiayu; Sun, Huayang; Hou, Yong; Yuan, Jianmin

    2013-01-01

    The structure and phase transition of high-pressure ice are of long-standing interest and challenge, and there is still a huge gap between theoretical and experimental understanding. The quantum nature of protons such as delocalization, quantum tunneling and zero-point motion is crucial to the comprehension of the properties of high-pressure ice. Here we investigated the temperature-induced phase transition and oxygen K-edge x-ray absorption spectra of ice VII, VIII and X using ab initio path-integral molecular dynamics simulations. The tremendous difference between experiments and the previous theoretical predictions is closed for the phase diagram of ice below 300 K at pressures up to 110 GPa. Proton tunneling assists the proton-ordered ice VIII to transform into proton-disordered ice VII where only thermal activated proton-transfer cannot occur. The oxygen K edge with its shift is sensitive to the order-disorder transition, and therefore can be applied to diagnose the dynamics of ice structures. PMID:24253589

  10. Quantum simulation of thermally-driven phase transition and oxygen K-edge x-ray absorption of high-pressure ice.

    PubMed

    Kang, Dongdong; Dai, Jiayu; Sun, Huayang; Hou, Yong; Yuan, Jianmin

    2013-11-20

    The structure and phase transition of high-pressure ice are of long-standing interest and challenge, and there is still a huge gap between theoretical and experimental understanding. The quantum nature of protons such as delocalization, quantum tunneling and zero-point motion is crucial to the comprehension of the properties of high-pressure ice. Here we investigated the temperature-induced phase transition and oxygen K-edge x-ray absorption spectra of ice VII, VIII and X using ab initio path-integral molecular dynamics simulations. The tremendous difference between experiments and the previous theoretical predictions is closed for the phase diagram of ice below 300 K at pressures up to 110 GPa. Proton tunneling assists the proton-ordered ice VIII to transform into proton-disordered ice VII where only thermal activated proton-transfer cannot occur. The oxygen K edge with its shift is sensitive to the order-disorder transition, and therefore can be applied to diagnose the dynamics of ice structures.

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

    NASA Astrophysics Data System (ADS)

    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).

  12. Theoretical calculations of high-pressure phases of NiF2: An ab initio constant-pressure study

    NASA Astrophysics Data System (ADS)

    Kürkçü, Cihan; Merdan, Ziya; Öztürk, Hülya

    2016-12-01

    We have studied the structural properties of the antiferromagnetic NiF2 tetragonal structure with P42/ mnm symmetry using density functional theory (DFT) under rapid hydrostatic pressure up to 400 GPa. For the exchange correlation energy we used the local density approximation (LDA) of Ceperley and Alder (CA). Two phase transformations are successfully observed through the simulations. The structures of XF2-type compounds crystallize in rutile-type structure. NiF2 undergoes phase transformations from the tetragonal rutile-type structure with space group P42/ mnm to orthorhombic CaCl2-type structure with space group Pnnm and from this orthorhombic phase to monoclinic structure with space group C2/ m at 152 GPa and 360 GPa, respectively. These phase changes are also studied by total energy and enthalpy calculations. According to these calculations, we perdict these phase transformations at about 1.85 and 30 GPa.

  13. Order-disorder phase transition and dissociation of hydrogen sulfide under high pressure: Ab initio molecular dynamics study

    NASA Astrophysics Data System (ADS)

    Wang, Liancheng; Tian, Fubo; Feng, Wanxiang; Chen, Changbo; He, Zhi; Ma, Yanming; Cui, Tian; Liu, Bingbing; Zou, Guangtian

    2010-04-01

    The structural and dynamical properties of phase IV and V of hydrogen sulfide were investigated by means of extensive ab initio molecular dynamics simulations. Starting from an experimental proposal for the structure of phase IV, an Ibca symmetry with a stable hydrogen bonding network is found at 15 GPa and 100 K. Molecular dynamics simulations at increasing temperature and at the pressure of 15 GPa suggest that phase IV will transform to a proton disordered structure at 15 GPa and 350 K. The newfound structure has a hexagonal lattice of P63/mmc symmetry, which is believed to be the remaining crystalline structure of phase V. The high mobility of protons in phase V is believed to be the key point to the dissociation and decomposition of hydrogen sulfide.

  14. High-pressure differential thermal analysis (DTA) of the phase behaviors of didodecyl-dimethylammoniumbromide (DDAB) and ditetradecyl-dimethylammoniumbromide (DTAB)

    NASA Astrophysics Data System (ADS)

    Hamann, F.; Reuter, John; Wuerflinger, A.; Godlewska, Malgorzata; Dynarowicz, Patrycja

    1998-01-01

    Dialkyldimethylammonium halides are known for their applications as commercial detergents and for their membrane-mimetic properties. They display both thermotropic and lyotropic liquid crystalline properties. In this work we establish the T(p)-phase diagrams of two representatives, namely didodecyl- and ditetradecyl-ammonium bromides. The transitions between crystal, smectic Ii and smectic I phases were recorded using a high-pressure differential thermal analysis device. For both compounds the stable range of smectic II phase is pressure-limited, resulting in a triple point crystal/smectic II/smectic I. Enthalpy changes at ambient pressure have been determined with the aid of a commercial heat flux differential scanning calorimeter. Volume changes were calculated from the slopes of the transitions lines, employing the Clausius Clapeyron equation.

  15. Steam-water two-phase flow in large diameter vertical piping at high pressures and temperatures

    SciTech Connect

    Hasanein, H.A.; Kawaji, Masahiro; Chan, A.M.C.; Yoshioka, Yuzuru

    1996-08-01

    No information on steam/water two-phase flow behavior in large diameter pipes (10 inch or larger) at elevated pressures is available in the open literature. However, there are many applications, in the nuclear, chemical and petroleum industries among others where two-phase flows in large diameter pipes at elevated pressures and temperatures are encountered routinely or under accident scenarios. Experimental data on steam-water two-phase flow in a large diameter (20 inch, 50.08 cm I.D.) vertical pipe at elevated pressures and temperatures (2.8 MPa/230 C--6.4 MPa/280 C) have been obtained. Void fraction, two-phase mass flux, phase and velocity distributions as well as pressure drop along the test pipe have been measured using the Ontario Hydro Technologies (OHT) Pump Test Loop. The void fraction distributions were found to be axially symmetric and nearly flat over a wide range of two-phase flow conditions. The two-phase flow regime could be inferred from the dynamic void fluctuations data. For the 280 C tests, the flow was found to be relatively stable with bubbly flow at low average void fractions and churn turbulent or wispy-annular flow at higher void fractions. At 230 C, the flow became rather oscillatory and slugging was suspected at relatively low voids. It has also been found that the average void fractions in the test section can be determined reasonably accurately using the axial pressure drop data.

  16. The High Pressure Nervous Syndrome and Other High Pressure Effects.

    DTIC Science & Technology

    Many of the problems of exposing man to a high pressure environment depend overtly on the properties of gases in the gaseous phase--such as the...or to changes in pressure. These are the subject of this chapter. The distinction is an arbitrary one, since both hyperbaric arthralgia and the high

  17. Publisher's Note: High-temperature superconductivity stabilized by electron-hole interband coupling in collapsed tetragonal phase of KFe2As2 under high pressure [Phys. Rev. B 91 , 060508(R) (2015)

    DOE PAGES

    Nakajima, Yasuyuki; Wang, Renxiong; Metz, Tristin; ...

    2015-03-09

    Here, we report a high-pressure study of simultaneous low-temperature electrical resistivity and Hall effect measurements on high quality single-crystalline KFe2As2 using designer diamond anvil cell techniques with applied pressures up to 33 GPa. In the low pressure regime, we show that the superconducting transition temperature Tc finds a maximum onset value of 7 K near 2 GPa, in contrast to previous reports that find a minimum Tc and reversal of pressure dependence at this pressure. Upon applying higher pressures, this Tc is diminished until a sudden drastic enhancement occurs coincident with a first-order structural phase transition into a collapsed tetragonalmore » phase. The appearance of a distinct superconducting phase above 13 GPa is also accompanied by a sudden reversal of dominant charge carrier sign, from hole- to electron-like, which agrees with our band calculations predicting the emergence of an electron pocket and diminishment of hole pockets upon Fermi surface reconstruction. Our results suggest the high-temperature superconducting phase in KFe2As2 is substantially enhanced by the presence of nested electron and hole pockets, providing the key ingredient of high-Tc superconductivity in iron pnictide superconductors.« less

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

    SciTech Connect

    Wu, Yan.

    1990-11-01

    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.

  19. The effect of morphology and confinement on the high-pressure phase transition in ZnO nanostructure

    SciTech Connect

    Kotmool, Komsilp; Bovornratanaraks, Thiti; Chakraborty, Sudip; Ahuja, Rajeev

    2015-03-21

    The transition pressure (P{sub t}) of the B4-to-B1 phase transformation of zinc oxide nanoparticle (n-ZnO) structures was investigated in terms of their size and morphology. Nanorods, nanopencils, nanopyramids, nanowires, and nanotubes of the B4 phase in various sizes were directly built up by accounting for the atomic basis of the core and surface regions. The previously proposed transformation path was performed for constructing shapes and sizes compatible with B1 phases. Using systematic density functional theory, the surfaces were cleaved from the optimized crystal structures at different pressures in both the B4 and B1 phases. A method for calculating the surface energy at different pressures is proposed using an asymmetric slab model. Using the proposed model, the transition pressure of n-ZnO structures was found to significantly depend on their morphology and size, which is in good agreement with the available experimental reports.

  20. High pressure cosmochemistry applied to major planetary interiors: Experimental studies. [phase diagram for the ammonia water system

    NASA Technical Reports Server (NTRS)

    Nicol, M. F.; Johnson, M.; Schwake, A.

    1983-01-01

    Progress is reported in the development of the P-T-X diagram for 0 less than or = X less than or = 0.50 and in the development of techniques for measuring adiabats of phases of NH3-H2O. The partial phase diagram is presented, investigations of the compositions of ammonia ices are described, and methods for obtaining the infrared spectra of ices are discussed.

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

    NASA Astrophysics Data System (ADS)

    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.

  2. High-temperature high-pressure phases of lithium from electron force field (eFF) quantum electron dynamics simulations

    PubMed Central

    Kim, Hyungjun; Su, Julius T.; Goddard, William A.

    2011-01-01

    We recently developed the electron force field (eFF) method for practical nonadiabatic electron dynamics simulations of materials under extreme conditions and showed that it gave an excellent description of the shock thermodynamics of hydrogen from molecules to atoms to plasma, as well as the electron dynamics of the Auger decay in diamondoids following core electron ionization. Here we apply eFF to the shock thermodynamics of lithium metal, where we find two distinct consecutive phase changes that manifest themselves as a kink in the shock Hugoniot, previously observed experimentally, but not explained. Analyzing the atomic distribution functions, we establish that the first phase transition corresponds to (i) an fcc-to-cI16 phase transition that was observed previously in diamond anvil cell experiments at low temperature and (ii) a second phase transition that corresponds to the formation of a new amorphous phase (amor) of lithium that is distinct from normal molten lithium. The amorphous phase has enhanced valence electron-nucleus interactions due to localization of electrons into interstitial locations, along with a random connectivity distribution function. This indicates that eFF can characterize and compute the relative stability of states of matter under extreme conditions (e.g., warm dense matter). PMID:21873210

  3. Experimental study and thermodynamic calculations of phase relations in the Fe-C system at high pressure

    NASA Astrophysics Data System (ADS)

    Fei, Yingwei; Brosh, Eli

    2014-12-01

    We have conducted a series of melting experiments in the Fe-C system at pressures up to 25 GPa in the temperature range of 1473-2073 K. The results define the phase relations at several pressures, including the eutectic temperature and composition as a function of pressure, carbon partitioning between solid iron and liquid, and change of melting relations involving iron carbides. In order to interpolate and extrapolate the phase relations over a wide pressure and temperature range, we have established a comprehensive thermodynamic model in the Fe-C binary system. The calculated phase diagrams at pressures of 5, 10, and 20 GPa reproduce the experimental data, including the solubility of carbon in solid iron and the effect of pressure on the eutectic temperature and composition. The formation of Fe7C3 at pressures above 5 GPa is correctly modeled and the change of phase relations in the Fe-C system between 5 and 10 GPa is captured in the model. The model provides predictions of the phase relations at 136 GPa and 330 GPa, based on existing knowledge of the thermochemistry of the system at lower pressure. The calculated phase relations can be used to understand the role of carbon during inner core crystallization, predicting carbon distribution between the inner and outer cores and mineralogy of the solid inner core.

  4. The effects of growth temperature and growth phase on the inactivation of Listeria monocytogenes in whole milk subject to high pressure processing.

    PubMed

    Hayman, Melinda M; Anantheswaran, Ramaswamy C; Knabel, Stephen J

    2007-04-10

    The aim of this study was to explore the effect of a wide range of growth temperatures, growth phases and plating media on the inactivation of Listeria monocytogenes by high pressure processing (HPP). In part one, L. monocytogenes was grown to mid-stationary phase at 4, 15, 25, 35 or 43 degrees C, inoculated into whole UHT milk at approximately 10(7) CFU/ml and high pressure processed at 400 MPa at room temperature (20-25 degrees C). Afterward, the HPP milk was plated on Tryptic Soy Yeast Extract Agar (TSYEA) and Modified Oxford Agar (MOX) to determine the degree of injury. For part two, cells were grown to mid-exponential, late-exponential or mid-stationary phase at 15 or 43 degrees C and processed in the same way. Time to reach a 5-log reduction was determined and data were analysed by ANOVA. The results from part one showed that both growth temperature and plating medium had a significant effect (P < 0.001) on the inactivation of stationary phase L. monocytogenes by HPP. Tukey's pairwise comparisons revealed that the effects of all temperatures, except 35 and 43 degrees C, were significantly different (P < 0.05). Cells grown at 15 degrees C were most sensitive to HPP, followed by cells grown at 4, 25 or 35 degrees C, with cells grown at 43 degrees C appearing to be the most resistant. Inactivation of cells grown at 4, 15 or 25 degrees C followed first order kinetics, whereas cells grown at 35 or 43 degrees C displayed non-linear inactivation kinetics due to tailing. In part two, both growth phase and plating medium had significant effects on the inactivation (P < or = 0.001) of L. monocytogenes by HPP. Cells grown at 15 degrees C to mid-stationary phase were the most pressure-resistant when tested on both media, and were significantly more resistant (P < 0.05) than cells grown at the same temperature to the other two phases of growth. There was no significant difference between mid- and late-exponential phase cells grown at 15 degrees C. When cells were grown at

  5. High-pressure mineral phases of olivine (Mg2SiO4) formed by pre-compression followed by laser-driven hypervelocity shock impact

    NASA Astrophysics Data System (ADS)

    Turner, A. A.; Tschauner, O. D.; Zaug, J. M.; Stavrou, E.; Armstrong, M.

    2016-12-01

    Understanding high-pressure phase transitions of olivine is a growing sphere of interest for Geoscientists, as olivine is an abundant mineral in the upper mantle of the Earth as well as pre-shocked meteorites. Knowledge of extreme condition olivine chemistry will provide insight into the process of shock metamorphism, which alters the composition and texture of materials during bolide impact and under extreme terrestrial conditions. The intention of investigating olivine under high pressures is to determine under what conditions the silicate spinel Ringwoodite (γ-Mg2SiO4), a high-pressure phase of olivine, is synthesized in shock-metamorphosed meteorites and to explore the nature of olivine beyond the phase boundary of Ringwoodite. Queries posed for these experiments focus primarily on what possible phases form as the result of compressing olivine to pressures above the 40 GPa, the likelihood of those phases to be conserved upon shock release, and what retrograde transformation products could possibly be generated from olivine under such pressures. Two independent endmember specimens (forsterite) of single crystal olivine (Mg2SiO4) were coated with 2.5 µm of aluminum and pre-compressed to 25 and 35 GPa, respectively in a diamond anvil cell. Lithium fluoride served as the pressure-transmitting medium. The specimens were then exposed to a laser-driven hypervelocity shock impact (400 picosecond duration) in order to investigate what phases if any form under more extreme pressures and dynamic stress states. The addition of laser-driven hypervelocity shock added 18 GPa of pressure to the pre-compressed samples, for a total of 43 and 53 GPa, respectively. From the analysis of the x-ray diffraction (XRD) measurements, it was determined that the olivine underwent a reduction of silicon and oxidation of the aluminum coating. These are fascinating observations revealed from a combined static and shock compression experiment. This work was performed under the auspices of

  6. ``Cs-tetra-ferri-annite:`` High-pressure and high-temperature behavior of a potential nuclear waste disposal phase

    SciTech Connect

    Comodi, P.; Zanazzi, P.F.; Weiss, Z.; Rieder, M.; Drabek, M.

    1999-03-01

    Structure deformations induced by pressure and temperature in synthetic Cs-tetra-ferri-annite 1M [Cs{sub 1.78}(Fe{sup 2+}{sub 5.93}Fe{sup 3+}{sub 0.07})(Si{sub 6.15}Fe{sup 3+}{sub 1.80}Al{sub 0.05})O{sub 20}(OH){sub 4}], space group C2/m, were analyzed to investigate the capability of the mica structure to store the radiogenic isotopes {sup 135}Cs and {sup 137}Cs. Cs-tetra-ferri-annite is not a mineral name, but for the sake of brevity is used here to designate a synthetic analog of the mineral tetra-ferri-annite. The bulk modulus and its pressure derivative determined by fitting the unit-cell volumes between 0 a/nd 47 kbar to a third-order Birch-Murnaghan equation of state are K{sub 0} = 257(8) kbar and K{prime}{sub 0} = 21(1), respectively. Between 23 C and 582 C, the a and b lattice parameters remain essentially unchanged, but the thermal expansion coefficient of the c axis is {alpha}{sub c} = 3.12(9) {times} 10{sup {minus}5} {degree}C{sup {minus}1}. High pressure (P) and high temperature (T) produce limited internal strain in the structure. The tetrahedral rotation angle, {alpha}, is very small and does not change significantly throughout the P and T range investigated. Above 450 C in air, Cs-tetra-ferri-annite underwent an oxidation of octahedral iron in the M2cis site, balanced by the loss of H and shown by a decrease of the unit-cell volume. Independent isobaric data on thermal expansion and isothermal compressibility data define the geometric equation of state for Cs-tetra-ferri-annite. On the whole, the data confirm that the structure of Cs-tetra-ferri-annite may be a suitable candidate for the storage of large ions, such as Cs in the interlayer and should be considered as a potential Synroc component.

  7. A new high-pressure phase of Fe2SiO4 and the relationship between spin and structural transitions

    NASA Astrophysics Data System (ADS)

    Yamanaka, T.; Kyono, A.; Nakamoto, Y.; Kharlamova, S. A.; Struzhkin, V. V.; Gramsch, S.; Mao, H.; Hemley, R. J.

    2013-12-01

    Structure transformation of Fe2SiO4 Angle-dispersive powder x-ray diffraction was carried out at beam line 16-BMD APS. Structure of a new high-pressure phase of I-Fe2SiO4 spinel was determined by Rietveld profile fitting of x-ray diffraction data up to 64GPa at ambient temperature. A structural transition from the cubic spinel to the new structure was observed at 34GPa. Diffraction patterns taken at 44.6GPa and 54.6GPa indicate a two-phase mixture of spinel and new high-pressure phase. Reversible transition from I-Fe2SiO4 to spinel was confirmed. Laser heating experiment at 1500K proved the decomposition of Fe2SiO4 spinel to two oxides of FeO and SiO2. Spin transition X-ray emission measurements of Fe2SiO4 were carried out up to 65GPa at ambient temperature at beam line 16-IDD APS. The spin transition exerts an influence to Fe2SiO4 spinel structure and triggers two distinct curves of the lattice constant in the spinel phase. Although the compression curve of the spinel is discontinuous at approximately 20 GPa, Fe Kβ emission measurements show that the transition from a high spin (HS) to an intermediate spin (IS) state begins at 17GPa in the spinel phase. The IS electronic state is gradually enhanced with pressure, which results in an isostructural phase transition. HS-to-LS transition of iron bearing spinels starts from 15.6GPa in Fe3O4 and 19.6GPa in Fe2TiO4. The transition is more capable due to Fe2+ in the octahedral site. The extremely shortened octahedral bonds result in a distortion of 6-fold cation site. New structure of Fe2SiO4 Monte Carlo method was applied to find candidates for the high-pressure phase using the diffraction intensities with fixed lattice constants determined by DICVOL. Rietveld profile fitting was then performed using the initial model. The new structure is a body centered orthorhombic phase (I-Fe2SiO4) with space group Imma and Z=4, with two crystallographically distinct FeO6 octahedra. Silicon exists in six-fold coordination in I-Fe2Si

  8. Molecular interactions in crystalline dibromomethane and diiodomethane, and the stabilities of their high-pressure and low-temperature phases.

    PubMed

    Podsiadło, Marcin; Dziubek, Kamil; Szafrański, Marek; Katrusiak, Andrzej

    2006-12-01

    Dibromomethane, CH2Br2, and diiodomethane, CH2I2, have been in situ pressure-crystallized in a diamond-anvil cell and their structures determined by single-crystal X-ray diffraction at 0.61 and 0.16 GPa, respectively. The pressure-frozen CH2Br2 crystal is isostructural with its C2/c phase obtained by cooling. CH2I2 is known to form several phases at low temperature, one of which is isostructural with CH2Br2. However, pressure freezing leads to the polar Fmm2 phase. The formation of the polar CH2I2 structure at 0.16 GPa has been rationalized by the electrostatic and anisotropic van der Waals interactions of the I atoms. No ferroelectric behaviour of the Fmm2 polar phase II of CH2I2 has been determined. The diffraction, calorimetric and dielectric constant studies reveal considerable temperature hysteresis of transformations between the CH2I2 phases, as well as metastable regions strongly dependent on the sample shape and history.

  9. Identification of high-pressure phases III and IV in hydrogen: Simulating Raman spectra using molecular dynamics

    NASA Astrophysics Data System (ADS)

    Magdău, Ioan B.; Ackland, Graeme J.

    2013-05-01

    We present a technique for extracting Raman intensities from ab initio molecular dynamics (MD) simulations at high temperature. The method is applied to the highly anharmonic case of dense hydrogen up to 500 K for pressures ranging from 180 to 300 GPa. On heating or pressurizing we find first-order phase transitions under the experimental conditions of the phase III-IV boundary. At even higher pressures, close to 350 GPa, we find a second phase transformation to the previously proposed Cmca-4. Our method enables, for the first time, a direct comparison of Raman vibrons between theory and experiment at finite temperature. This turns out to provide excellent discrimination between subtly different structures found in MD. We find candidate structures whose Raman spectra are in good agreement with experiment. The new phase obtained in high-temperature simulations adopts a dynamic, simple hexagonal structure with three layer types: freely rotating hydrogen molecules, static hexagonal trimers, and rotating hexagonal trimers. We show that previously calculated structures for phase IV are inconsistent with experiment, and their appearance in simulation is due to finite-size effects.

  10. High pressure phases in NWA 8711, a shock melted L6 chondrite from Northwest Africa: a combined Raman and EMPA study.

    NASA Astrophysics Data System (ADS)

    Moggi Cecchi, V.; Pratesi, G.; Caporali, S.; Zoppi, M.

    We report the occurrence of two coexisting high-pressure assemblages in shock-induced black veins of NWA 8711, an L6 chondrite recently found in Northwest Africa. The main phases of the host rock are olivine, enstatite, diopside, plagioclase, iron-nickel alloy and troilite. The presence of typical shock metamorphic features both in olivine and pyroxene, as well as of maskelynite and melt veins point to a shock stage S6. Two coexisting distinct assemblages were observed in the shock-melted areas: (1) a very fine-grained intergrowth of silicate phases sprinkled with fine-grained metal and troilite blebs and (2) a coarser-grained polycrystalline aggregate consisting of ringwoodite crystals. EMPA analyses were performed on both the chondritic matrix and on individual grains of the shock-melted area to characterize their mineralogical composition. EMPA analyses on the coarse-grained area suggested the presence of shock-generated ringwoodite and low-Ca majorite. These data are confirmed by Micro-Raman point analyses. The analyses performed on the fine-grained portion of the veins allowed to determine the presence of a majorite-pyrope solid solution. According to literature data the majorite-pyrope solid solution suggests a crystallization from a shock-melted chondritic matrix under high pressures and temperatures. Ringwoodite and low-Ca majorite were instead formed by solid state transformation of olivine and low-Ca pyroxene originally present in the meteorite.

  11. Shear-driven instability in zirconium at high pressure and temperature and its relationship to phase-boundary behaviors

    NASA Astrophysics Data System (ADS)

    Jacobsen, M. K.; Velisavljevic, N.; Kono, Y.; Park, C.; Kenney-Benson, C.

    2017-04-01

    Evidence in support of a shear driven anomaly in zirconium at elevated temperatures and pressures has been determined through the combined use of ultrasonic, diffractive, and radiographic techniques. Implications that these have on the phase diagram are explored through thermoacoustic parameters associated with the elasticity and thermal characteristics. In particular, our results illustrate a deviating phase boundary between the α and ω phases, referred to as a kink, at elevated temperatures and pressures. Further, pair distribution studies of this material at more extreme temperatures and pressures illustrate the scale on which diffusion takes place in this material. Possible interpretation of these can be made through inspection of shear-driven anomalies in other systems.

  12. X-ray diffraction and Raman study of DL-alanine at high pressure: revision of phase transitions.

    PubMed

    Tumanov, Nikolay A; Boldyreva, Elena V

    2012-08-01

    The effect of pressure on DL-alanine has been studied by X-ray powder diffraction (up to 8.3 GPa), single-crystal X-ray diffraction and Raman spectroscopy (up to ~6 GPa). No structural phase transitions have been observed. At ~1.5-2 GPa, cell parameters b and c become accidentally equal to each other, but the space-group symmetry does not change. There is no phase transition between 1.7 and 2.3 GPa, contrary to what has been reported earlier [Belo et al. (2010). Vibr. Spectrosc. 54, 107-111]. The presence of the second phase transition, which was claimed to appear within the pressure range from 6.0 to 7.3 GPa (Belo et al., 2010), is also argued. The changes in the Raman spectra have been shown to be continuous in all the pressure ranges studied.

  13. Shear-driven instability in zirconium at high pressure and temperature and its relationship to phase-boundary behaviors

    DOE PAGES

    Jacobsen, Matthew K.; Velisavljevic, Nenad; Kono, Yoshio; ...

    2017-04-05

    Evidence in support of a shear driven anomaly in zirconium at elevated temperatures and pressures has been determined through the combined use of ultrasonic, diffractive, and radiographic techniques. Implications that these have on the phase diagram are explored through thermoacoustic parameters associated with the elasticity and thermal characteristics. In particular, our results illustrate a deviating phase boundary between the α and ω phases, referred to as a kink, at elevated temperatures and pressures. Furthermore, pair distribution studies of this material at more extreme temperatures and pressures illustrate the scale on which diffusion takes place in this material. Possible interpretation ofmore » these can be made through inspection of shear-driven anomalies in other systems.« less

  14. High Pressure-Temperature Phase Diagram of 1,1-Diamino-2,2-dinitroethylene (FOX-7).

    PubMed

    Bishop, Matthew M; Velisavljevic, Nenad; Chellappa, Raja; Vohra, Yogesh K

    2015-09-17

    The pressure-temperature (P-T) phase diagram of 1,1-diamino-2,2-dinitroethylene (FOX-7) was determined by in situ synchrotron infrared radiation spectroscopy with the resistively heated diamond anvil cell (DAC) technique. The stability of high-P-T FOX-7 polymorphs is established from ambient pressure up to 10 GPa and temperatures until decomposition. The phase diagram indicates two near isobaric phase boundaries at ∼2 GPa (α → I) and ∼5 GPa (I → II) that persists from 25 °C until the onset of decomposition at ∼300 °C. In addition, the ambient pressure, high-temperature α → β phase transition (∼111 °C) lies along a steep boundary (∼100 °C/GPa) with a α-β-δ triple point at ∼1 GPa and 300 °C. A 0.9 GPa isobaric temperature ramping measurement indicates a limited stability range for the γ-phase between 0.5 and 0.9 GPa and 180 and 260 °C, terminating in a β-γ-δ triple point. With increasing pressure, the δ-phase exhibited a small negative dT/dP slope (up to ∼0.2 GPa) before turning over to a positive 70 °C/GPa slope, at higher pressures. The decomposition boundary (∼55 °C/GPa) was identified through the emergence of spectroscopic signatures of the characteristic decomposition products as well as trapped inclusions within the solid KBr pressure media.

  15. Elasticity of single-crystal NAL phase at high pressure: A potential source of the seismic anisotropy in the lower mantle

    NASA Astrophysics Data System (ADS)

    Wu, Ye; Yang, Jing; Wu, Xiang; Song, Maoshuang; Yoshino, Takashi; Zhai, Shuangmeng; Qin, Shan; Huang, Haijun; Lin, Jung-Fu

    2016-08-01

    The new hexagonal aluminous phase, named the NAL phase, is expected to be stable at depths of <1200 km in subducted slabs and believed to constitute 10~30 wt% of subducted mid-ocean ridge basalt together with the CaFe2O4-type aluminous phase. Here elasticity of the single-crystal NAL phase is investigated using Brillouin light scattering coupled with diamond anvil cells up to 20 GPa at room temperature. Analysis of the results shows that the substitution of iron lowers the shear modulus of the NAL phase by ~5% (~6 GPa) but does not significantly affect the adiabatic bulk modulus. The NAL phase exhibits high-velocity anisotropies with AVP = 14.7% and AVS = 15.12% for the Fe-bearing phase at ambient conditions. The high AVS of the NAL phase mainly results from the high anisotropy of the faster VS1 (13.9~15.8%), while the slower VS2 appears almost isotropic (0.1~2.8%) at ambient and high pressures. The AVP and AVS of the NAL phase decrease with increasing pressure but still have large values with AVP = 11.4% and AVS = 14.12% for the Fe-bearing sample at 20.4 GPa. The extrapolated AVP and AVS of the Fe-free and Fe-bearing NAL phases at 40 GPa are larger than those of bridgmanite at the same pressure. Together with its spin transition of iron and structural transition to the CF phase, the presence of the NAL phase with high-velocity anisotropies may contribute to the observed seismic anisotropy around subducted slabs in the uppermost lower mantle.

  16. Lattice-dynamical studies of Ti in the hcp- and ω -phase by Raman scattering at high-pressure

    NASA Astrophysics Data System (ADS)

    Olijnyk, H.; Nakano, S.; Jephcoat, A. P.; Takemura, K.

    2006-09-01

    Ti metal was investigated by Raman spectroscopy for pressures up to 46GPa . The E2g mode of the hcp phase shows no softening on approaching the transition to the ω phase, which contrasts the behavior of its heavier homologue Zr, however, it exhibits an anomalously low mode Grüneisen parameter. It is shown that this unusual behavior is also reflected in the pressure response of elastic modulus C44 . At ambient conditions the contributions to the temperature shift of this mode due to thermal expansion are one order of magnitude smaller than the explicit contribution. The E2g mode of the ω phase exhibits a positive frequency shift with an ambient pressure mode Grüneisen parameter γ≈2 , slightly higher than that of Zr, becoming smaller under compression. Predictions of a recent first principles calculation [Rudin , Phys. Rev. B 69, 094117 (2004)], limited to normal pressure and in quite good agreement with experimental data for hcp Ti, underestimate the frequency of the E2g mode of the ω phase by 17%.

  17. Equilibrium and Stability of a Rim of High--Pressure Phase on an Elastic Sphere subject to External Pressure

    NASA Astrophysics Data System (ADS)

    Morris, S.

    2012-12-01

    : In their study of the kinetics of the α-β transformation in olivine, Kubo et al. (1998) report that a rim of β phase formed on the sample and grew into the α phase core, but that growth ceased creating a stable rim. The phases are then in thermodynamic equilibrium across the rim-core interface, even though the applied pressure exceeds the pressure at which the phases would coexist in a common hydrostatic state. In the observed equilibrium, deviatoric stresses must exist within the phases; their presence means that the equilibrium can only be described by a model coupling interfacial conditions to the mechanics of the bulk phases. Existing models (a) incorrectly describe the strain within the rim, and (b) incorrectly account for the effect of strain energy on the thermodynamics. The underlying errors are conceptual, not algebraic. To illustrate items (a) and (b), I simplify by assuming the individual phases to be incompressible. Because models in which the phases are allowed to be compressible must correctly describe the incompressible case, this simple model provides a test of more complex ones. The model sample is a sphere subject at its surface to a constant pressure; the sphere consists initially of pure α phase. The displacement u is purely radial; the phase interface propagates inwards. Because u is determined purely by mass conservation, its calculation is elementary. Within the dense rim, the deviatoric radial strain proves to be negative, but the corresponding strain--rate is positive. I will explain how these two statements are consistent. So far, only kinematics has been used, but to determine stresses, a constitutive equation must be assumed. The significance of the italicized words now emerges. In the extremes in which radial deviatoric stress is assumed to depend either on deviatoric strain alone or on deviatoric strain-rate alone, the sign of the deviatoric stress is different. This has implications for the pressure field within the sample

  18. Can high pressure I-II transitions in semiconductors be affected by plastic flow and nanocrystal precipitation in phase I?

    NASA Astrophysics Data System (ADS)

    Weinstein, B. A.; Lindberg, G. P.

    Pressure-Raman spectroscopy in ZnSe and ZnTe single crystals reveals that Se and Te nano-crystals (NCs) precipitate in these II-VI hosts for pressures far below their I-II phase transitions. The inclusions are evident from the appearance and negative pressure-shift of the A1 Raman peaks of Se and Te (trigonal phase). The Se and Te NCs nucleate at dislocations and grain boundaries that arise from pressure-induced plastic flow. This produces chemical and structural inhomogeneities in the zincblende phase of the host. At substantially higher pressures, the I-II transition proceeds in the presence of these inhomogenities. This can affect the transition's onset pressure Pt and width ΔPt, and the occurrence of metastable phases along the transition path. Precipitation models in metals show that nucleation of inclusions depends on the Peierls stress τp and a parameter α related to the net free energy gained on nucleation. For favorable values of τp and α, NC precipitation at pressures below the I-II transition could occur in other compounds. We propose criteria to judge whether this is likely based on the observed ranges of τp in the hosts, and estimates of α derived from the cohesive energy densities of the NC materials. One finds trends that can serve as a useful guide, both to test the proposed criteria, and to decide when closer scrutiny of phase transition experiments is warranted, e.g., in powders where high dislocation densities are initially created

  19. Evidence for a High-Pressure Phase Transition of ε-2,4,6,8,10,12-hexanitrohexaazaisowurtzitane (CL-20) Using Vibrational Spectroscopy

    SciTech Connect

    Ciezak, J.; Jenkins, T; Liu, Z

    2007-01-01

    The high-pressure response of {epsilon}-2,4,6,8,10,12-hexanitrohexaazaisowurtizane (CL-20) has been examined to 27 GPa in diamond anvil cells using vibrational spectroscopy. The results reveal evidence of an {epsilon}{yields}{Upsilon} pressure-induced phase transition between 4.1 and 6.4 GPa and suggest the existence of a {Upsilon}{yields}{zeta} transition near 18.7 GPa. Several Raman and infrared frequencies were found to decrease in intensity as the phase boundaries are approached. An anomalous intensity increase was noted in the C-N-C infrared mode that is believed to result from an increase in the Raman cross-section due to a stronger interlayer coupling under pressure.

  20. Magnetocaloric effect in a dual-phase coupled LaFe11Si2 crystal prepared by a modified high-pressure zone-melting technique

    NASA Astrophysics Data System (ADS)

    Feng, Shutong; Fang, Yue; Zhai, Qijie; Luo, Zhiping; Zheng, Hongxing

    2016-10-01

    A modified high-pressure optical zone-melting technique was adopted to grow a rare-earth-based LaFe11Si2 crystal in the present work. Dual-phase coupled microstructure was obtained where aligned α(Fe) phase distributed in the La(Fe,Si)13 matrix. Magnetic measurements showed that the produced crystal underwent a second-order magnetic transition in the vicinity of 250 K. Under a magnetic field change of 30 kOe, the refrigeration capacity (RC) of the produced crystal reached up to 162 J/kg. It was confirmed that zone-melting crystal growth technique is an effective approach to strikingly enhance the magnetocaloric effect of La-Fe-Si refrigeration materials.

  1. High pressure synthesis gas fermentation

    SciTech Connect

    Not Available

    1991-01-01

    Construction of the high pressure gas phase fermentation system is nearing completion. All non-explosion proof components will be housed separately in a gas-monitored plexiglas cabinet. A gas-monitoring system has been designed to ensure the safety of the operations in case of small or large accidental gas releases. Preliminary experiments investigating the effects of high pressure on Clostridium 1jungdahlii have shown that growth and CO uptake are not negatively affected and CO uptake by an increased total pressure of 100 psig at a syngas partial pressure of 10 psig.

  2. Nanomaterials under high-pressure.

    PubMed

    San-Miguel, Alfonso

    2006-10-01

    The use of high-pressure for the study and elaboration of homogeneous nanostructures is critically reviewed. Size effects, the interaction between nanostructures and guest species or the interaction of the nanosystem with the pressure transmitting medium are emphasized. Phase diagrams and the possibilities opened by the combination of pressure and temperature for the elaboration of new nanomaterials is underlined through the examination of three different systems: nanocrystals, nano-cage materials which include fullerites and group-14 clathrates, and single wall nanotubes. This tutorial review is addressed to scientist seeking an introduction or a panoramic view of the study of nanomaterials under high-pressure.

  3. Equation of state modeling of the phase equilibria of ionic liquid mixtures at low and high pressure.

    PubMed

    Karakatsani, Eirini K; Economou, Ioannis G; Kroon, Maaike C; Bermejo, Maria D; Peters, Cor J; Witkamp, Geert-Jan

    2008-10-28

    Accurate design of processes based on ionic liquids (ILs) requires knowledge of the phase behavior of the systems involved. In this work, the truncated perturbed chain polar statistical associating fluid theory (tPC-PSAFT) is used to correlate the phase behavior of binary and ternary IL mixtures. Both non-polar and polar solvents are examined, while methyl imidazolium ILs are used in all cases. tPC-PSAFT accounts explicitly for weak dispersion interactions, highly directive polar interactions between permanent dipolar and quadrupolar molecules and association between hydrogen bonding molecules. For mixtures of non-polar solvents, tPC-PSAFT predicts accurately the binary mixture data. For the case of polar solvents, a binary interaction parameter is fitted to the experimental data and the agreement between experiment and correlation is very good in all cases.

  4. Reverse-phase high pressure liquid chromatographic analysis of harpagoside, scorodioside and verbascoside from Scrophularia scorodonia: quantitative determination of harpagoside.

    PubMed

    Díaz, A; Fernández, L; Ollivier, E; Martín, T; Villaescusa, L; Balansard, G

    1998-02-01

    A reversed-phase high performance liquid chromatographic method has been developed for the determination of the main compounds (harpagoside, scorodioside, and verbascoside) from different samples of Scrophularia scorodonia. The chromatographic method has been validated and applied for quantitative determination of harpagoside. The results show the highest levels of harpagoside in the leaf extract. The purity and identity of peaks were controlled by diode-array detection and comparison with standards.

  5. Kinetics of the wurtzite-to-rock-salt phase transformation in ZnO at high pressure.

    PubMed

    Solozhenko, Vladimir L; Kurakevych, Oleksandr O; Sokolov, Petr S; Baranov, Andrey N

    2011-05-05

    Kinetics of the wurtzite-to-rock-salt transformation in ZnO has been studied in the 5-7 GPa pressure range at temperatures below the activation of diffusion processes. The detailed analysis of non-isothermal experimental data using the general evolution equation describing the kinetics of direct phase transformations in solids allowed us to study the kinetic particularities of both nucleation and growth of the rock-salt phase in parent wurtzite ZnO. The main rate-limiting processes are thermally activated nucleation (E(N) = 383 kJ mol(-1) at 6.9 GPa) and thermally nonactivated (most probably quasi-martensitic) growth (k(G) = 0.833 min(-1) at 6.9 GPa). The high impact of thermal deactivation of nucleation places has been evidenced in the case of slow heating, which indirectly indicates that the rs-ZnO nucleation places are mainly produced by pressure-induced stresses in the parent phase.

  6. In situ Phase Transition Study of Nano- and Coarse-Grained TiO2 Under High Pressure/Temperature Conditions

    SciTech Connect

    Wang,Y.; Zhao, Y.; Zhang, J.; Xu, h.; Wang, L.; Luo, S.; Daemen, L.

    2008-01-01

    A comparative phase transition study of nanocrystalline and micro-TiO2 has been conducted under high pressure-temperature (P-T) conditions using energy-dispersive synchrotron x-ray diffraction (XRD). Our study reveals that on compression at room temperature, the micro-tetragonal anatase-type TiO2 started to transform to the orthorhombic columbite-type TiO2 near 1.6 GPa. In contrast, we did not observe this phase transition in nano-anatase at pressures of up to 8.5 GPa. At 8.5 GPa, by applying moderate heat, both samples were transformed completely to columbite-type TiO2 almost simultaneously, indicating that heat treatment could significantly expedite this phase transition. These columbite-type TiO2 phases were quenchable because after cooling them to room temperature and decompressing them to 2.0 GPa, the XRD patterns displayed no changes in comparison with those collected at 8.6 GPa and 1270 K. At 2 GPa, we heated the specimens again, and the rutile-type TiO2 started to emerge around 970 K. This phase was also quenchable after cooling and releasing pressure to ambient conditions. The grain size effects on the phase transition were discussed based on the kinetics mechanism. This study should be of considerable interest to the fields of materials science and condensed matter.

  7. Low temperature and high pressure thermoelastic and crystallographic properties of SrZrO3 perovskite in the Pbnm phase

    NASA Astrophysics Data System (ADS)

    Knight, Kevin S.; Bull, Craig L.

    2016-12-01

    The thermoelastic and structural properties of SrZrO3 perovskite in the Pnma (Pbnm) phase have been studied using neutron powder diffraction at 82 temperatures between 11 K and 406 K at ambient pressure, and at sixteen pressures between 0.07 and 6.7 GPa at ambient temperature. The bulk modulus, derived by fitting the equation of state to a second order Birch-Murnaghan equation-of-state, 157(5) GPa, is in excellent agreement with that deduced in a recent resonant ultrasound investigation. Experimental axial compressional moduli are in agreement with those calculated from the elastic stiffness coefficients derived by ab-initio calculation, although the experimental bulk modulus is significantly softer than that calculated. Following low temperature saturation for temperatures less than 40 K, the unit cell monotonically increases with a predicted high temperature limit in the volume expansivity of ∼2.65 × 10-5 K-1. Axial linear thermal expansion coefficients are found to be in the order αb < αc < αa for all temperatures greater than 20 K with the b axis indicating a weak, low temperature negative expansion coefficient at low temperatures. The thermoelastic properties of SrZrO3 can be approximated by a two-term Debye model for the phonon density of states with Debye temperatures of 238(4) K and 713(6) K derived in a self-consistent manner by simultaneously fitting the isochoric heat capacity and the unit cell volume. Atomic displacement parameters have been fitted to a modified Debye model in which the zero-point term is an additional refinable variable and shows the cations and anions have well separated Debye temperatures, mirroring the need for two Debye-like distributions in the vibrational density of states. The temperature dependence of the crystal structure is presented in terms of the amplitudes of the seven symmetry-adapted basis vectors of the aristotype phase that are consistent with space group Pbnm, thus permitting a direct measure of the order

  8. Paramagnetic defects as probes for the study of ferroelastic phase transition in lithium niobate and lithium tantalate under high pressure

    NASA Astrophysics Data System (ADS)

    Malovichko, G.; Grachev, V.; Andreev, V.; Nachal'Naya, T.

    It was found by optical polarization microscopy and the EPR study that lithium niobate and tantalate crystals undergo irreversible lattice changes under anisotropic hydrostatic compression. Regions having different cell orientations were registered. The observed changes were explained in terms of "strain switching" of ferroelastic domains. Possible sequence of phase transitions in these crystals (Pm3m<->R (3) over bar3 c<->R 3 c) and the symmetry of the condensed soft modes ( R-25 and Gamma(15) , correspondingly) were obtained by the analysis of the Gibbs free energy under external pressure.

  9. High-pressure systems for gas-phase free continuous incubation of enriched marine microbial communities performing anaerobic oxidation of methane.

    PubMed

    Deusner, Christian; Meyer, Volker; Ferdelman, Timothy G

    2010-02-15

    Novel high-pressure biotechnical systems that were developed and applied for the study of anaerobic oxidation of methane (AOM) are described. The systems, referred to as high-pressure continuous incubation system (HP-CI system) and high-pressure manifold-incubation system (HP-MI system), allow for batch, fed-batch, and continuous gas-phase free incubation at high concentrations of dissolved methane and were designed to meet specific demands for studying environmental regulation and kinetics as well as for enriching microbial biomass in long-term incubation. Anoxic medium is saturated with methane in the first technical stage, and the saturated medium is supplied for biomass incubation in the second stage. Methane can be provided in continuous operation up to 20 MPa and the incubation systems can be operated during constant supply of gas-enriched medium at a hydrostatic pressure up to 45 MPa. To validate the suitability of the high-pressure systems, we present data from continuous and fed-batch incubation of highly active samples prepared from microbial mats from the Black Sea collected at a water depth of 213 m. In continuous operation in the HP-CI system initial methane-dependent sulfide production was enhanced 10- to 15-fold after increasing the methane partial pressure from near ambient pressure of 0.2 to 10.0 MPa at a hydrostatic pressure of 16.0 MPa in the incubation stage. With a hydraulic retention time of 14 h a stable effluent sulfide concentration was reached within less than 3 days and a continuing increase of the volumetric AOM rate from 1.2 to 1.7 mmol L(-1) day(-1) was observed over 14 days. In fed-batch incubation the AOM rate increased from 1.5 to 2.7 and 3.6 mmol L(-1) day(-1) when the concentration of aqueous methane was stepwise increased from 5 to 15 mmol L(-1) and 45 mmol L(-1). A methane partial pressure of 6 MPa and a hydrostatic pressure of 12 MPa in manifold fed-batch incubation in the HP-MI system yielded a sixfold increase in the

  10. Quantum Monte Carlo computations of phase stability, equations of state, and elasticity of high-pressure silica.

    PubMed

    Driver, K P; Cohen, R E; Wu, Zhigang; Militzer, B; Ríos, P López; Towler, M D; Needs, R J; Wilkins, J W

    2010-05-25

    Silica (SiO(2)) is an abundant component of the Earth whose crystalline polymorphs play key roles in its structure and dynamics. First principle density functional theory (DFT) methods have often been used to accurately predict properties of silicates, but fundamental failures occur. Such failures occur even in silica, the simplest silicate, and understanding pure silica is a prerequisite to understanding the rocky part of the Earth. Here, we study silica with quantum Monte Carlo (QMC), which until now was not computationally possible for such complex materials, and find that QMC overcomes the failures of DFT. QMC is a benchmark method that does not rely on density functionals but rather explicitly treats the electrons and their interactions via a stochastic solution of Schrödinger's equation. Using ground-state QMC plus phonons within the quasiharmonic approximation of density functional perturbation theory, we obtain the thermal pressure and equations of state of silica phases up to Earth's core-mantle boundary. Our results provide the best constrained equations of state and phase boundaries available for silica. QMC indicates a transition to the dense alpha-PbO(2) structure above the core-insulating D" layer, but the absence of a seismic signature suggests the transition does not contribute significantly to global seismic discontinuities in the lower mantle. However, the transition could still provide seismic signals from deeply subducted oceanic crust. We also find an accurate shear elastic constant for stishovite and its geophysically important softening with pressure.

  11. Quantum Monte Carlo computations of phase stability, equations of state, and elasticity of high-pressure silica

    PubMed Central

    Driver, K. P.; Cohen, R. E.; Wu, Zhigang; Militzer, B.; Ríos, P. López; Towler, M. D.; Needs, R. J.; Wilkins, J. W.

    2010-01-01

    Silica (SiO2) is an abundant component of the Earth whose crystalline polymorphs play key roles in its structure and dynamics. First principle density functional theory (DFT) methods have often been used to accurately predict properties of silicates, but fundamental failures occur. Such failures occur even in silica, the simplest silicate, and understanding pure silica is a prerequisite to understanding the rocky part of the Earth. Here, we study silica with quantum Monte Carlo (QMC), which until now was not computationally possible for such complex materials, and find that QMC overcomes the failures of DFT. QMC is a benchmark method that does not rely on density functionals but rather explicitly treats the electrons and their interactions via a stochastic solution of Schrödinger’s equation. Using ground-state QMC plus phonons within the quasiharmonic approximation of density functional perturbation theory, we obtain the thermal pressure and equations of state of silica phases up to Earth’s core–mantle boundary. Our results provide the best constrained equations of state and phase boundaries available for silica. QMC indicates a transition to the dense α-PbO2 structure above the core-insulating D” layer, but the absence of a seismic signature suggests the transition does not contribute significantly to global seismic discontinuities in the lower mantle. However, the transition could still provide seismic signals from deeply subducted oceanic crust. We also find an accurate shear elastic constant for stishovite and its geophysically important softening with pressure. PMID:20457932

  12. Effects of gate insulator using high pressure annealing on the characteristics of solid phase crystallized polycrystalline silicon thin-film transistors

    NASA Astrophysics Data System (ADS)

    Kim, Moojin; Jin, GuangHai

    2009-04-01

    The oxidizing ambient was built using high pressure H2O vapor at 550 °C. For the solid phase crystallization (SPC) polycrystalline silicon (poly-Si) that is annealed for 1 h at 2 MPa, the oxide thickness is about 150 Å. The oxide layer is approximately 90 Å above the original surface of the poly-Si and 60 Å below the original surface. The oxide layer is used as the first gate insulator layer of thin-film transistors (TFTs). The heating at 550 °C with 2 MPa H2O vapor increased the carrier mobility from 17.6 cm2/V s of the conventional SPC process to 30.4 cm2/V s, and it reduced the absolute value of the threshold voltage (Vth) from 4.13 to 3.62 V. The subthreshold swing also decreased from 0.72 to 0.60 V/decade. This improvement is attributed mainly to the reduction in defect density at the oxide/poly-Si interface and in the poly-Si film by the high pressure annealing (HPA) process. Since the realization of excellent performance at the oxide/poly-Si interface and in poly-Si depends on the defect density, the poly-Si having the thermal oxide formed by a combined process of SPC and HPA may be well suited for fabrication of poly-Si TFTs for flat panel displays such as active matrix organic light emitting diodes.

  13. High-pressure Powder X-ray Diffraction Study of Cu5Si and Pressure-driven Isostructural Phase Transition

    SciTech Connect

    Li, C.; Yu, Z.; Liu, H.; Lu, T.

    2012-12-03

    The structural behaviour of Cu5Si under high-pressure (HP) has been studied by angular dispersive X-ray diffraction up to 49.9 GPa. The experimental results suggest that a pressure-induced isostructural phase transition occurs around 13.5 GPa as revealed by a discontinuity in volume as a function of pressure. The lattice parameter decreases with the pressure increasing for both low-pressure (LP) and HP phases of Cu5Si. However, a plot of the lattice parameter vs. pressure shows the existence of a plateau between 11.7 and 15.3 GPa. The bulk moduli, derived from the fitting of Birch–Murnaghan equation of state, are 150(2) GPa and 210(3) GPa for the LP phase and the HP phase of Cu5Si, respectively. A change in the electronic state of the copper is assumed to govern the observed structural phase transition.

  14. High-pressure single-crystal X-ray diffraction study on Super Fluorous Phase B up to 7.4 GPa

    NASA Astrophysics Data System (ADS)

    Kuribayashi, T.; Kojitani, H.; Nagase, T.; Akaogi, M.; Mao, H.; Hemley, R.; Kudoh, Y.

    2008-12-01

    Super hydrous phase B (SUP-B), Mg10Si3O14(OH)4, is known as one of dense hydrous magnesium silicate minerals (DHMS). Also, super fluorous phase B (sup-B-F), Mg10Si3O14F4, was firstly synthesized by Hazen et al. (1997). In the crystal structure of SUP-B-F, F replaces OH in sup-B structure. Therefore, differences of behavior between SUP-B-F and SUP-B under high-pressure conditions directory reflect the effect of hydrogen bonding. In this study, to clarify the behavior of SUP-B-F under high-pressure condition, SUP-B-F was synthesized at 21 GPa and 1400°C conditions using the Kawai type multi anvil apparatus installed in Gakushu-in University. Using a synthesized single-crystal (0.04 × 0.04 × 0.03 mm3), high-pressure single-crystal X-ray diffraction measurements were conducted up to 7.4 GPa with synchrotron radiation. Lattice constants were determined at several pressure points up to 7.4 GPa. The isothermal bulk modulus of SUP-B-F, calculated from the Birch-Murnaghan Equation of State, was 154(2) GPa with a pressure derivative K'=4 (assuming). This value is significantly larger than that of super hydrous phase B (142.8(5) GPa with K"f=5.7 by Crichton et al., 1999). The X-ray reflection intensity data set was collected at 5.0 GPa using the four-circle diffractometer installed at the beam line BL-10A in Photon Factory, Japan. 198 reflections were used for structure refinement (the number of measured reflections is 786). After Lorentz- polarization correction and background reduction were applied for all intensity data, the crystallographic equivalent reflections (Orthorhombic, Pnnm) were averaged. Structure refinement results were R=5.0% and wR2=13.1%, respectively.

  15. Structure determination of the high-pressure phases of topological insulator Bi2Se3 using experiments and calculations

    NASA Astrophysics Data System (ADS)

    Cheng, Hu; Zhang, Junran; Li, Yanchun; Li, Gong; Li, Xiaodong

    2017-06-01

    The pressure-induced phase transition of bismuth selenide (Bi2Se3) was investigated by combining theoretical calculations with synchrotron powder X-ray diffraction measurements up to 57.4 GPa. We demonstrated that the ambient-pressure rhombohedral Bi2Se3 crystallized into a monoclinic structure with the space group C2/m at 9.1 GPa, and eventually to a body-centered tetragonal structure with the space group I4/mmm at about 27.2 GPa. This behavior was different from the transformation sequences of Bi2Te3 and Sb2Te3. The stabilities of five structures of Bi2Se3 were studied by density functional theory calculations. Furthermore, an unusual irreversible relaxation process was observed. We attempted to make clear the unusual structural behavior of Bi2Se3 occurring in the compression process and the relaxation process.

  16. High-pressure phase transition makes B 4.3 C boron carbide a wide-gap semiconductor

    SciTech Connect

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

    2016-01-11

    Single-crystal B4.3C boron carbide is investigated concerning the pressure-dependence of optical properties and of Raman-active phonons up to ~70 GPa. The high concentration of structural defects determining the electronic properties of boron carbide at ambient conditions initially decrease and finally vanish with pressure increasing. We obtain this immediately from transparency photos, allowing to estimate the pressure-dependent variation of the absorption edge rapidly increasing around 55 GPa. Glass-like transparency at pressures exceeding 60 GPa indicate that the width of the band exceeds ~3.1 eV thus making boron carbide a wide-gap semiconductor. Furthermore, the spectra of Raman–active phonons indicate a pressure-dependent phase transition in single-crystal natB4.3C boron carbide near 35 GPa., particularly related to structural changes in connection with the C-B-C chains, while the basic icosahedral structure remains largely unaffected.

  17. The high-pressure phase diagram of Fe(0.94)O - A possible constituent of the earth's core

    NASA Technical Reports Server (NTRS)

    Knittle, Elise; Jeanloz, Raymond

    1991-01-01

    Electrical resistivity measurements to pressures of 83 GPa and temperatures ranging from 300 K to 4300 K confirm the presence of both crystalline and liquid metallic phases of FeO at pressures above 60-70 GPa and temperatures above 1000 K. By experimentally determinig the melting temperature of FeO to 100 GPa and of a model-core composition at 83 GPa, it is found that the solid-melt equilibria can be described by complete solid solution across the Fe-FeO system at pressures above 70 GPa. The results indicate that oxygen is a viable and likely candidate for the major light alloying element of the earth's liquid outer core. The data suggest that the temperature at the core-mantle boundary is close to 4800 K and that heat lost out of the core accounts for more than 20 percent of the heat flux observed at the surface.

  18. Probing high-pressure phase transitions in Ti-based perovskite-type ferroelectrics using visible resonance Raman spectroscopy.

    PubMed

    Fraysse, Guillaume; Rouquette, Jérôme; Haines, Julien; Bornand, Véronique; Papet, Philippe; Pereira, Altaïr Soria

    2012-12-03

    We report unprecedented dramatic changes in the 647.1 nm Raman signal of PbZr(0.6)Ti(0.4)O(3) occurring in the same pressure ranges as the critical pressures of the antiferrodistortive and ferroelectric-paraelectric phase transitions. This huge decrease in intensity of both the Raman modes and the background, observed for both pressure transmitting media used (glycerol or 4:1 methanol ethanol mixture), is shown to originate from the two-step loss of a resonance Raman effect and the concomitant fluorescence. Changes in the local titanium environment (first with the onset of octahedral tilting and then with the removal of polar cation displacements) alter the electronic band structure and modify the resonance conditions. Furthermore, the optimal resonance conditions are found to be particularly narrow, as shown by the fluorescence spectrum of PbZr(0.6)Ti(0.4)O(3) at atmospheric pressure characterized by the presence of a very well-defined sharp peak (fwhm = 8 nm) centered around 647.1 nm. These results thus demonstrate that visible resonance Raman spectroscopy can be used as a quick and efficient technique for probing phase transitions in PbZr(1-x)Ti(x)O(3) (PZT) and other technologically important perovskite-type materials such as PMN-xPT, PZN-xPT relaxors, lead free piezoelectrics, and ferroelectric nanopowders. This technique appears also a good alternative to UV Raman spectroscopy for probing the polar order at the nanoscale in ultrathinfilms and superlattices.

  19. High-pressure single-crystal elasticity study of CO{sub 2} across phase I-III transition

    SciTech Connect

    Zhang, Jin S. Bass, Jay D.; Shieh, Sean R.; Dera, Przemyslaw; Prakapenka, Vitali

    2014-04-07

    Sound velocities and elastic moduli of solid single-crystal CO{sub 2} were measured at pressures up to 11.7(3) GPa by Brillouin spectroscopy. The aggregate adiabatic bulk modulus (K{sub S}), shear modulus (G), and their pressure derivatives for CO{sub 2} Phase I are K{sub S0} = 3.4(6) GPa, G{sub 0} = 1.8(2) GPa, (dK{sub S}/dP){sub 0} = 7.8(3), (dG/dP){sub 0} = 2.5(1), (d{sup 2}K{sub S}/dP{sup 2}){sub 0} = −0.23(3) GPa{sup −1}, and (d{sup 2}G/dP{sup 2}){sub 0} = −0.10(1) GPa{sup −1}. A small increase of elastic properties was observed between 9.8(1) and 10.5(3) GPa, in agreement with the CO{sub 2} I-III transition pressure determined from previous x-ray diffraction experiments. Above the transition pressure P{sub T}, we observed a mixture dominated by CO{sub 2}-I, with minor CO{sub 2}-III. The CO{sub 2}-I + III mixture shows slightly increased sound velocities compared to pure CO{sub 2}-I. Elastic anisotropy calculated from the single-crystal elasticity tensor exhibits a decrease with pressure beginning at 7.9(1) GPa, which is lower than P{sub T}. Our results coincide with recent X-ray Raman observations, suggesting that a pressure-induced electronic transition is related to local structural and optical changes.

  20. Evidence of iso-structural phase transition in high pressure Raman spectroscopic studies of CaCu3Ti4O12

    NASA Astrophysics Data System (ADS)

    Tyagi, Shekhar; Sharma, Gaurav; Sathe, V. G.

    2017-02-01

    High pressure Raman spectroscopic studies on Polycrystalline CaCu3Ti4O12 and SrCu3Ti4O12 compounds are carried out in order to validate the theoretical predictions of a structural transformation near 3-4 GPa and an insulator to metal transition above 7 GPa [S. B. Fagan et al., Phys. Rev. B 72, 014106 (2005)]. Our studies showed normal hardening and broadening of peaks with increasing pressure up to 20 GPa besides a discontinuity between 8 and 9 GPa which is attributed to an isostructural phase transition. The Ag(1) peak occurring at 442 cm-1 showed asymmetric Fano lineshape and the lineshape parameter 'q' shows an increase with increasing pressure. This is completely against the theoretical predictions of an insulator to metal transition above 7 GPa.

  1. High pressure-high temperature phase diagram of an energetic crystal: Dihydroxylammonium 5,5'-bistetrazole-1,1'-diolate (TKX-50)

    DOE PAGES

    Dreger, Z. A.; Breshike, C. J.; Gupta, Y. M.

    2017-05-08

    Raman spectroscopy was used to examine the high pressure-high temperature structural and chemical stability of an insensitive, high-performance energetic crystal – dihydroxylammonium 5,5'-bistetrazole-1,1'-diolate (TKX-50). The phase diagram was determined over 8 GPa and (293-760) K. Under isobaric heating, the melting/decomposition of TKX-50 is preceded by a transformation to two consecutive high-temperature intermediates; a lower-temperature intermediate – diammonium 5,5’-bistetrazole-1,1'-diolate, and a higher-temperature intermediate – dihydroxylammonium 5,5'-bistetrazolate and/or diammonium 5,5'-bistetrazolate. Pressure strongly increases the transition temperatures for these transformations and subsequent decomposition. As a result, significant increase in the chemical stability of TKX-50 and intermediates with pressure was attributed to a suppressionmore » of hydrogen-transfer.« less

  2. Phase transition of synthetic zinc ferrite spinel (ZnFe2O4) at high pressure, from synchrotron X-ray powder diffraction

    NASA Astrophysics Data System (ADS)

    Levy, D.; Pavese, A.; Hanfland, M.

    Synthetic Zn-ferrite (ideally ZnFe2O4; mineral name: franklinite) was studied up to 37GPa, by X-ray powder diffraction at ESRF (Grenoble, France), on the ID9 beamline; high pressure was achieved by means of a DAC. The P-V equation of state of franklinite was investigated using the Birch-Murnaghan function, and the elastic properties thus inferred [K0=166.4(+/-3.0) GPa K0'=9.3(+/-0.6) K0''=-0.22GPa-1] are compared with earlier determinations for MgAl-spinel and magnetite. The structural behaviour of Zn-ferrite as a function of pressure was studied by Rietveld refinements, and interpreted in the light of a phase transition from spinel to either CaTi2O4- or MnFe2O4-like structure; this transformation occurs above 24GPa.

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

    NASA Technical Reports Server (NTRS)

    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).

  4. Thermodynamic data of the high-pressure phase Mg5Al5Si6O21(OH)7 (Mg-sursassite)

    NASA Astrophysics Data System (ADS)

    Grevel, K.-D.; Navrotsky, A.; Kahl, W. A.; Fasshauer, D. W.; Majzlan, J.

    Calorimetric and P-V-T data for the high-pressure phase Mg5Al5Si6O21(OH)7 (Mg-sursassite) have been obtained. The enthalpy of drop solution of three different samples was measured by high-temperature oxide melt calorimetry in two laboratories (UC Davis, California, and Ruhr University Bochum, Germany) using lead borate (2PbO.B2O3) at T=700∘C as solvent. The resulting values were used to calculate the enthalpy of formation from different thermodynamic datasets; they range from -221.1 to -259.4kJmol-1 (formation from the oxides) respectively -13892.2 to -13927.9kJmol-1 (formation from the elements). The heat capacity of Mg5Al5Si6O21(OH)7 has been measured from T=50 ∘C to T=500 ∘C by differential scanning calorimetry in step-scanning mode. A Berman and Brown (1985)-type four-term equation represents the heat capacity over the entire temperature range to within the experimental uncertainty: CP (Mg-sursassite) =(1571.104 -10560.89×T-0.5-26217890.0 ×T-2+1798861000.0×T-3) J K-1 mol-1 (T in K). The PVT behaviour of Mg-sursassite has been determined under high pressures and high temperatures up to 8GPa and 800∘C using a MAX 80 cubic anvil high-pressure apparatus. The samples were mixed with Vaseline to ensure hydrostatic pressure-transmitting conditions, NaCl served as an internal standard for pressure calibration. By fitting a Birch-Murnaghan EOS to the data, the bulk modulus was determined as 116.0+/-1.3GPa, (K'=4), VT,0=446.49 3 exp[∫(0.33+/-0.05) × 10-4 + (0.65+/-0.85)×10-8T dT], (KT/T)P=-0.011+/- 0.004GPaK-1. The thermodynamic data obtained for Mg-sursassite are consistent with phase equilibrium data reported recently (Fockenberg 1998); the best agreement was obtained with ΔfH0298 (Mg-sursassite)= -13901.33kJmol-1, and S0298 (Mg-sursassite)= 614.61JK-1mol-1.

  5. Crystal structure of the high-pressure phase of the oxonitridosilicate chloride Ce4[Si4O(3 + x)N(7 - x)]Cl(1 - x)O(x), x approximately = 0.2.

    PubMed

    Friedrich, Alexandra; Haussühl, Eiken; Morgenroth, Wolfgang; Lieb, Alexandra; Winkler, Björn; Knorr, Karsten; Schnick, Wolfgang

    2006-04-01

    The structural compression mechanism of Ce4[Si4O(3 + x)N(7 - x)]Cl(1 - x)O(x), x approximately = 0.2, was investigated by in situ single-crystal synchrotron X-ray diffraction at pressures of 3.0, 8.5 and 8.6 GPa using the diamond-anvil cell technique. On increasing pressure the low-pressure cubic structure first undergoes only minor structural changes. Between 8.5 and 8.6 GPa a first-order phase transition occurs, accompanied by a change of the single-crystal colour from light orange to dark red. The main structural mechanisms, leading to a volume reduction of about 5% at the phase transition, are an increase in and a rearrangement of the Ce coordination, the loss of the Ce2, Ce3 split position, and a bending of some of the inter-polyhedral Si-N-Si angles in the arrangement of the corner-sharing Si tetrahedra. The latter is responsible for the short c axis of the orthorhombic high-pressure structure compared with the cell parameter of the cubic low-pressure structure.

  6. Phase relation of C-Mg-Fe-Si-O system under various oxygen fugacity conditions at high pressure and high temperature

    NASA Astrophysics Data System (ADS)

    Takahashi, S.; Ohtani, E.; Terasaki, H.; Ito, Y.; Shibazaki, Y.; Ishii, M.; Funakoshi, K.; Higo, Y.

    2010-12-01

    Many exoplanets have been found recently based on the spectroscopic observation. A carbon-rich circumstellar gas was reported to exist around “beta-Pictoris”, which has an exoplanet (Roberge et al., 2006). In such gas, carbon-enriched planet, “carbon-planet” may be formed. Carbon-bearing phase, such as carbide, carbonate, graphite and diamond are likely to compose the carbon-planet interior. Therefore, it is important to investigate phase relations of carbon-rich systems under high pressure conditions. In this study, C-enriched Mg-Si-Fe-O-C system was investigated at high pressure and temperature in order to understand the internal structure of the carbon-planet. Phase relations were studied based on 2 series of experiments; (I)textural observation and chemical analysis of the recovered sample from 4 GPa and 1873K and (II)in situ X-ray diffraction experiments under high pressure and temperature. For the starting materials, we used several different mineral assemblages, as shown below: (i) MgCO3 + Fe + Si + C, (ii) (Mg1.8,Fe0.2)SiO4 + Fe + SiO2 + C, (iii) (Mg1.8,Fe0.2)SiO4 + Fe + Si + C, (iv) MgO + Fe + SiO2 + C, (v) MgO + Fe + Si + C. Oxygen fugacity (fO2) of the sample vaies dependign on these assembleges due to different O amount in the starting materials. The sample was enclosed in graphite or MgO capsule. MgO capsule enables us to estimate fO2 in the sample based on the FeO content of the capsule contacting with the samples. Chemical analyses of the recovered samples were performed using electron microprobe. In situ X-ray diffraction experiments were conducted at 4 GPa and up to 1873 K at BL04B1 beamline, SPring-8 synchrotron facility. Different mineral assemblages and their compositions were observed in the recovered samples depending on the redox condition of the sample. The compositions of metallic melt phases changes from Fe-C composition (C = 6.9~8.2 wt.%) in oxidizing conditions (ΔIW = -2.4 ~ -1.7) to Fe-Si composition (Si = 18 wt.%) in the more

  7. Anomaly in neural phase coherence accompanies reduced sensorimotor integration in adults who stutter.

    PubMed

    Sengupta, Ranit; Shah, Shalin; Gore, Katie; Loucks, Torrey; Nasir, Sazzad M

    2016-12-01

    Despite advances in our understanding of the human speech system, the neurophysiological basis of stuttering remains largely unknown. Here, it is hypothesized that the speech of adults who stutter (AWS) is susceptible to disruptions in sensorimotor integration caused by neural miscommunication within the speech motor system. Human speech unfolds over rapid timescales and relies on a distributed system of brain regions working in a parallel and synchronized manner, and a breakdown in neural communication between the putative brain regions could increase susceptibility to dysfluency. Using a speech motor adaptation paradigm under altered auditory feedback with simultaneous recording of EEG, the oscillatory cortical dynamics was investigated in stuttering and fluent adults (FA). Auditory feedback perturbation involved the shifting of the formant frequencies of the target vowel sound. Reduced adaptation in response to the feedback error was observed in AWS and was accompanied by differences in EEG spectral powers and anomalies in phase coherence evolving over the course of speech motor training. It is understood that phase coherence possibly captures neural communication within speech motor networks. Thus, the phase coherence network of the two groups exhibited differences involving the EEG frequency bands. These findings in anomalous neural synchrony provide novel evidence for compromised neuronal communication at short time scales within the speech motor network of AWS.

  8. Elastic behaviour and high-pressure phase transition of the P21/n LiAlGe2O6pyroxene

    NASA Astrophysics Data System (ADS)

    Artac, Andreas; Miletich-Pawliczek, Ronald; Nestola, Fabrizio; Redhammer, Günther J.; Secco, Luciano

    2014-05-01

    In a recent work by Redhammer et al. (2012), investigating a synthetic pyroxene sample with composition LiAlGe2O6, a new space group for the big family of pyroxenes has been surprisingly discovered renewing the interest for Li-bearing pyroxene compounds. Actually, the authors of that work intended to investigate the effect of the Si-Ge substitution on the high-pressure behaviour and possibly on the phase transition with respect to spodumene, LiAlSi2O6, investigated by Arlt and Angel in 2000. Spodumene in fact, not only shows a strong first order phase transition at 3.19 GPa from C2/c to P21/c but the low symmetry C2/c shows the greatest bulk modulus never found in pyroxenes (i.e. 144.2 GPa with the first pressure derivative fixed to 4). Redhammer et al. (2012) discovered that substituting Si for Ge in the spodumene structure the effect is dramatic in terms of symmetry change at room conditions with the Ge-spodumene showing a P21/n space group, first discovery of such symmetry in the big family of pyroxene. In this work we loaded one crystal of LiAlGe2O6 in a diamond-anvil cell and investigated the elastic behaviour and its possible high-pressure phase transition by single-crystal X-ray diffraction. In detail, we measured the unit-cell parameters using a Huber four-circle diffractometer equipped with a point detector up to about 9 GPa. The crystal structure was measured at different pressures loading simultaneously two fragments of the same crystal with a different orientation in the same diamond-anvil cell in order to cover a wider portion of the reciprocal space. The intensity data were measured on a STADI IV four-circle diffractometer equipped with a CCD using a diamond-backing plate cell, which gives better structural results with respect to a beryllium backing plate one (i.e. Periotto et al. 2011). The first important result of our work is that we found at about 5.2 GPa a very strong first-order phase transformation from P21/n to P21/c and this is the first

  9. Dynamic mechanical behavior and high pressure phase stability of a zirconium-based bulk metallic glass and its composite with tungsten

    NASA Astrophysics Data System (ADS)

    Martin, Morgana

    2008-10-01

    The research involved performing controlled impact experiments on BMG composites consisting of amorphous Zr57Nb5Cu 15:4Ni12:6Al10 (LM106 or Vitreloy106) with crystalline tungsten reinforcement particles. Monolithic LM106 was also examined to aid in the understanding of the composite. The mechanical behavior of the composite was investigated over a range of strain rates (10-3 s -1 to 106 s-1), stress states (compression, compression-shear, tension), and temperatures (RT to 600°C) to determine the dependence of mechanical properties and deformation and failure modes (i.e., homogeneous deformation vs. inhomogeneous shear banding) on these parameters. Mechanical testing in the quasi-static to intermediate strain-rate regimes was performed using an Instron, Drop Weight Tower, and Split Hopkinson Pressure Bar, respectively. High-strain-rate mechanical properties of the BMG-matrix composite and monolithic BMG were investigated using dynamic compression (reverse Taylor) and dynamic tension (spall) impact experiments performed using a gas gun instrumented with velocity interferometry and high-speed digital photography. These experiments provided information about dynamic strength and deformation modes, and allowed for validation of constitutive models via comparison of experimental and simulated transient deformation profiles and free surface velocity traces. Hugoniot equation of state measurements were performed on the monolithic BMG to investigate the high pressure phase stability of the glass and the possible implications of a high pressure phase transformation on mechanical properties. Specimens were recovered for post-impact microstructural and thermal analysis to gain information about the mechanisms of dynamic deformation and fracture, and to examine for possible shock-induced phase transformations of the amorphous phase. For the composite, mechanical testing revealed positive strain-rate sensitivity of its yield stress and negative strain-rate sensitivity of its

  10. In Situ Observation of High-Pressure Phase Transitions in SiO2 Under Shock Loading Using Time Resolved X-Ray Diffraction

    NASA Astrophysics Data System (ADS)

    Tracy, S. J.; Turneaure, S.; Duffy, T. S.

    2016-12-01

    Quartz is one of the most abundant minerals in Earth's crust and serves as an archetype for silicate minerals generally. The shock metamorphism of silica is important for understanding and interpreting meteorite impact events. Shock compression of quartz is characterized by a phase transition occurring over a broad mixed-phase region ( 10-40 GPa). Despite decades of study, the nature of this transformation and the structure of the high-pressure phase remain poorly understood. In situ x-ray diffraction data on shock-compressed SiO2 was collected at the Dynamic Compression Sector at the Advanced Photon Source. The behavior both single crystal alpha-quartz and fused silica was investigated under dynamic loading through a series real-time synchrotron x-ray diffraction measurements during peak stresses up to 65 GPa. A two-stage light gas gun was used to accelerate LiF flyer plates that impacted the SiO2 samples resulting in a propagating step-like increase in pressure and temperature behind the shock front. Four consecutive x-ray frames, separated by 153 ns, were collected during the transient loading and unloading. These measurements allow for the determination of time-dependent atomic arrangements, demonstrating that both amorphous silica as well as crystalline alpha-quartz transform to stishovite above 36 GPa. These measurements reveal important information about the role of kinetics as well texture development and potential defect structures in the transformed material.

  11. High-pressure vapor-phase hydrodeoxygenation of lignin-derived oxygenates to hydrocarbons by a PtMo bimetallic catalyst: Product selectivity, reaction pathway, and structural characterization

    SciTech Connect

    Yohe, Sara L.; Choudhari, Harshavardhan J.; Mehta, Dhairya D.; Dietrich, Paul J.; Detwiler, Michael D.; Akatay, Cem M.; Stach, Eric A.; Miller, Jeffrey T.; Delgass, W. Nicholas; Agrawal, Rakesh; Ribeiro, Fabio H.

    2016-12-01

    High-pressure, vapor-phase, hydrodeoxygenation (HDO) reactions of dihydroeugenol (2-methoxy-4-propylphenol), as well as other phenolic, lignin-derived compounds, were investigated over a bimetallic platinum and molybdenum catalyst supported on multi-walled carbon nanotubes (5%Pt2.5%Mo/MWCNT). Hydrocarbons were obtained in 100% yield from dihydroeugenol, including 98% yield of the hydrocarbon propylcyclohexane. The final hydrocarbon distribution was shown to be a strong function of hydrogen partial pressure. Kinetic analysis showed three main dihydroeugenol reaction pathways: HDO, hydrogenation, and alkylation. The major pathway occurred via Pt catalyzed hydrogenation of the aromatic ring and methoxy group cleavage to form 4-propylcyclohexanol, then Mo catalyzed removal of the hydroxyl group by dehydration to form propylcyclohexene, followed by hydrogenation of propylcyclohexene on either the Pt or Mo to form the propylcyclohexane. Transalkylation by the methoxy group occurred as a minor side reaction. Catalyst characterization techniques including chemisorption, scanning transmission electron microscopy, X-ray absorption spectroscopy, and X-ray photoelectron spectroscopy were employed to characterize the catalyst structure. Catalyst components identified were Pt particles, bimetallic PtMo particles, a Mo carbide-like phase, and Mo oxide phases.

  12. High pressure synthesis of a hexagonal close-packed phase of the high-entropy alloy CrMnFeCoNi

    NASA Astrophysics Data System (ADS)

    Tracy, Cameron L.; Park, Sulgiye; Rittman, Dylan R.; Zinkle, Steven J.; Bei, Hongbin; Lang, Maik; Ewing, Rodney C.; Mao, Wendy L.

    2017-05-01

    High-entropy alloys, near-equiatomic solid solutions of five or more elements, represent a new strategy for the design of materials with properties superior to those of conventional alloys. However, their phase space remains constrained, with transition metal high-entropy alloys exhibiting only face- or body-centered cubic structures. Here, we report the high-pressure synthesis of a hexagonal close-packed phase of the prototypical high-entropy alloy CrMnFeCoNi. This martensitic tra