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Sample records for accompanying high-pressure phase

  1. Shearing instabilities accompanying high-pressure phase transformations and the mechanics of deep earthquakes

    PubMed Central

    Green, Harry W.

    2007-01-01

    Deep earthquakes have been a paradox since their discovery in the 1920s. The combined increase of pressure and temperature with depth precludes brittle failure or frictional sliding beyond a few tens of kilometers, yet earthquakes occur continually in subduction zones to ≈700 km. The expected healing effects of pressure and temperature and growing amounts of seismic and experimental data suggest that earthquakes at depth probably represent self-organized failure analogous to, but different from, brittle failure. The only high-pressure shearing instabilities identified by experiment require generation in situ of a small fraction of very weak material differing significantly in density from the parent material. This “fluid” spontaneously forms mode I microcracks or microanticracks that self-organize via the elastic strain fields at their tips, leading to shear failure. Growing evidence suggests that the great majority of subduction zone earthquakes shallower than 400 km are initiated by breakdown of hydrous phases and that deeper ones probably initiate as a shearing instability associated with breakdown of metastable olivine to its higher-pressure polymorphs. In either case, fault propagation could be enhanced by shear heating, just as is sometimes the case with frictional sliding in the crust. Extensive seismological interrogation of the region of the Tonga subduction zone in the southwest Pacific Ocean provides evidence suggesting significant metastable olivine, with implication for its presence in other regions of deep seismicity. If metastable olivine is confirmed, either current thermal models of subducting slabs are too warm or published kinetics of olivine breakdown reactions are too fast. PMID:17468397

  2. High-pressure phase transitions of strontianite

    NASA Astrophysics Data System (ADS)

    Speziale, S.; Biedermann, N.; Reichmann, H. J.; Koch-Mueller, M.; Heide, G.

    2015-12-01

    Strontianite (SrCO3) is isostructural to aragonite, a major high-pressure polymorph of calcite. Thus it is a material of interest to investigate the high-pressure phase behavior of aragonite-group minerals. SrCO3 is a common component of natural carbonates and knowing its physical properties at high pressures is necessary to properly model the thermodynamic properties of complex carbonates, which are major crustal minerals but are also present in the deep Earth [Brenker et al., 2007] and control carbon cycling in the Earth's mantle. The few available high-pressure studies of SrCO3 disagree regarding both pressure stability and structure of the post-aragonite phase [Lin & Liu, 1997; Ono et al., 2005; Wang et al. 2015]. To clarify such controversies we investigated the high-pressure behavior of synthetic SrCO3 by Raman spectroscopy. Using a diamond anvil cell we compressed single-crystals or powder of strontianite (synthesized at 4 GPa and 1273 K for 24h in a multi anvil apparatus), and measured Raman scattering up to 78 GPa. SrCO3 presents a complex high-pressure behavior. We observe mode softening above 20 GPa and a phase transition at 25 - 26.9 GPa, which we interpret due to the CO3 groups rotation, in agreement with Lin & Liu [1997]. The lattice modes in the high-pressure phase show dramatic changes which may indicate a change from 9-fold coordinated Sr to a 12-fold-coordination [Ono, 2007]. Our results confirm that the high-pressure phase of strontianite is compatible with Pmmn symmetry. References Brenker, F.E. et al. (2007) Earth and Planet. Sci. Lett., 260, 1; Lin, C.-C. & Liu, L.-G. (1997) J. Phys. Chem. Solids, 58, 977; Ono, S. et al. (2005) Phys. Chem. Minerals, 32, 8; Ono, S. (2007) Phys. Chem. Minerals, 34, 215; Wang, M. et al. (2015) Phys Chem Minerals 42, 517.

  3. 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.

  4. Phase transitions at high pressure in tetracyanoethylene

    NASA Astrophysics Data System (ADS)

    Mukhopadhyay, R.; Deb, S. K.; Das, Amitabh; Chaplot, S. L.

    2009-11-01

    We report in situ x-ray diffraction studies in tetracyanoethylene (TCNE) at high pressure using diamond anvil cell (DAC) at Elettra synchrotron source, Trieste, Italy. Experiments were performed with both the polymorphic phases (monoclinic and cubic) of TCNE as the starting phase. While starting with monoclinic (the high temperature stable) TCNE, it was found that the Bragg peaks get broadened with increase of pressure and above 5 GPa only few broad peaks remained to be observed. On release of pressure from 6.4 GPa, when the sample started turning black, the diffraction pattern at ambient pressure corresponds to cubic, the other crystalline phase of TCNE. Results reconfirm the monoclinic to cubic transition at high pressure but via an intermediate 'disordered' phase. This settles a number of conflicting issues. TCNE represents only system, which undergoes transition from one crystalline to another crystalline phase via a 'disordered' metastable phase at high pressure. When the starting phase was cubic (the low temperature stable) no apparent phase transition was observed up to 10.8 GPa.

  5. Superconducting high-pressure phases of disilane.

    PubMed

    Jin, Xilian; Meng, Xing; He, Zhi; Ma, Yanming; Liu, Bingbing; Cui, Tian; Zou, Guangtian; Mao, Ho-Kwang

    2010-06-01

    High-pressure structures of disilane (Si(2)H(6)) are investigated extensively by means of first-principles density functional theory and a random structure-searching method. Three metallic structures with P-1, Pm-3m, and C2/c symmetries are found, which are more stable than those of XY(3)-type candidates under high pressure. Enthalpy calculations suggest a remarkably wide decomposition (Si and H(2)) pressure range below 135 GPa, above which three metallic structures are stable. Perturbative linear-response calculations for Pm-3m disilane at 275 GPa show a large electron-phonon coupling parameter lambda of 1.397 and the resulting superconducting critical temperature beyond the order of 10(2) K. PMID:20479272

  6. Superconducting high-pressure phases of disilane

    PubMed Central

    Jin, Xilian; Meng, Xing; He, Zhi; Ma, Yanming; Liu, Bingbing; Cui, Tian; Zou, Guangtian; Mao, Ho-kwang

    2010-01-01

    High-pressure structures of disilane (Si2H6) are investigated extensively by means of first-principles density functional theory and a random structure-searching method. Three metallic structures with P-1, Pm-3m, and C2/c symmetries are found, which are more stable than those of XY3-type candidates under high pressure. Enthalpy calculations suggest a remarkably wide decomposition (Si and H2) pressure range below 135 GPa, above which three metallic structures are stable. Perturbative linear-response calculations for Pm-3m disilane at 275 GPa show a large electron-phonon coupling parameter λ of 1.397 and the resulting superconducting critical temperature beyond the order of 102 K. PMID:20479272

  7. High pressure phase transitions in tetrahedrally coordinated semiconducting compounds

    NASA Technical Reports Server (NTRS)

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

    1978-01-01

    New experimental results are reported for structural transitions at high pressure in several III-V compounds and two II-VI compounds. These data, together with earlier results, are then compared with the predictions of model calculations of Van Vechten. Experimental transition pressures are often at variance with calculated values. However, his calculation assumes that the high pressure phase is metallic, with the beta-Sn structure. The present results show that several compounds assume an ionic NaCl structure at high pressure, while others have neither the beta-Sn nor NaCl structure.

  8. The high-pressure semiconducting phase of LiBC

    NASA Astrophysics Data System (ADS)

    Zhang, Meiguang

    2016-04-01

    A high-pressure hexagonal semiconducting phase (space group P63mc , 2f.u./cell) of LiBC stable above 108 GPa was predicted through first-principles calculations combined with unbiased swarm structure searching techniques. This new phase consisted of three-dimensional B-C networks which originate from the dramatic out-of-plane distortions of the graphene-like B-C sublattice in the low-pressure P63/mmc phase under compression. Contrary to the metallizations of LiBC under high pressure previously proposed, the resulting three-dimensional B-C framework lacks the system of π bonds with mobile electrons and has more localized electrons, as a result of the semiconducting nature of this high-pressure LiBC phase.

  9. 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.

  10. High pressure x-ray absorption studies of phase transitions

    SciTech Connect

    Tranquada, J.M.; Ingalls, R.; Crozier, E.D.

    1984-01-01

    High pressure generally changes all of the properties of substances, leading to phase transitions in many cases. This paper reviews how such phase changes reveal themselves in x-ray absorption spectra. Examples are given using the salts NaBr, RbCl, CuBr, and SnSe. (DLC)

  11. 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.

  12. High-pressure phase transitions in rubidium and caesium hydroxides.

    PubMed

    Hermann, Andreas

    2016-06-28

    A computational investigation of the high-pressure phase sequence of the heaviest alkali hydroxides, RbOH and CsOH, shows that the phase diagram of both compounds is richer than hitherto thought. First-principles calculations suggest, based on energetics and comparisons to experimental diffraction and spectroscopy signatures, that the high-pressure phase RbOH-VI, stable above 6 GPa in experiment, should be assigned the KOH-VI structure type, and features localised hydrogen-bonded (OH)4 units. Meanwhile, a new high-pressure phase CsOH-VII is predicted to be stable above 10 GPa in an isosymmetric phase transition that, like RbOH-VI, marks the transition from layered to three-dimensional network structures under increased compression. Both new phases highlight an unexpected flexibility of hydrogen bond network formation in a series of compounds that seemingly only vary in the cation size, and potential consequences for similar systems, such as water-carrying minerals, are discussed briefly. PMID:27271485

  13. 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.

  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. 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. PMID:27389226

  16. 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)

  17. 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.

  18. 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.

  19. High Pressure Deformation in Two-Phase Aggregates

    SciTech Connect

    Li,L.; Addad, A.; Weidner, D.; Long, H.; Chen, J.

    2007-01-01

    We investigate the rheological behavior of multi-phase aggregates at high pressure and high temperature. Using synchrotron X-ray radiation as the probing tool, we are able to quantify the stress state of individual phases within the aggregates. This method provides fundamental information in interpreting the behavior of two phase/multi-phase mixtures, which contribute to our understanding of the deformation process at deep earth conditions. We choose MgAl{sub 2}O{sub 4} spinel and MgO periclase as our model materials. Mixtures of various volume proportions were deformed in a multi-anvil high pressure deformation apparatus at pressure of 5 GPa and elevated temperatures. Stress is determined from X-ray diffraction, providing a measure of stress in each individual phase of the mixture in situ during the deformation. Macroscopic strain is determined from X-ray imaging. We compare the steady state strength of various mixtures at 1000 {sup o}C and 800 {sup o}C and at the strain rate in the range of 1.8 to 8.8 x 10{sup -5} s{sup -1}. Our data indicate that the weak phase (MgO) is responsible for most of the accumulated strains while the strong phase (spinel) is supporting most of the stress when the volume proportion is 75% spinel and 25% MgO. The intermediate compositions (40/60) are much weaker than either of the end members, while the grain sizes for the intermediate compositions (submicrons) are much smaller than the end members (5-10 {mu}m). We conclude that a change in flow mechanism resulting from these smaller grains is responsible for the low strength of the intermediate composition mixtures. This study demonstrates an approach of using synchrotron X-rays to study the deformation behaviors of multi-phase aggregates at high pressure and high temperature.

  20. 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.

  1. 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

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

    NASA Astrophysics Data System (ADS)

    Celebonovic, Vladan

    1992-09-01

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

  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. PMID:26388165

  4. New High-Pressure Phase in Fe2O3

    NASA Astrophysics Data System (ADS)

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

    2009-12-01

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

  5. 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.

  6. Phase transitions and hydrogen bonding in deuterated calcium hydroxide: High-pressure and high-temperature neutron diffraction measurements

    SciTech Connect

    Iizuka, Riko; Komatsu, Kazuki; Kagi, Hiroyuki; Nagai, Takaya; Sano-Furukawa, Asami; Hattori, Takanori; Gotou, Hirotada; Yagi, Takehiko

    2014-10-15

    In situ neutron diffraction measurements combined with the pulsed neutron source at the Japan Proton Accelerator Research Complex (J-PARC) were conducted on high-pressure polymorphs of deuterated portlandite (Ca(OD){sub 2}) using a Paris–Edinburgh cell and a multi-anvil press. The atomic positions including hydrogen for the unquenchable high-pressure phase at room temperature (phase II′) were first clarified. The bent hydrogen bonds under high pressure were consistent with results from Raman spectroscopy. The structure of the high-pressure and high-temperature phase (Phase II) was concordant with that observed previously by another group for a recovered sample. The observations elucidate the phase transition mechanism among the polymorphs, which involves the sliding of CaO polyhedral layers, position modulations of Ca atoms, and recombination of Ca–O bonds accompanied by the reorientation of hydrogen to form more stable hydrogen bonds. - Graphical abstract: Crystal structures of high-pressure polymorphs of Ca(OD){sub 2}, (a) at room temperature (phase II′) and (b) at high temperature (phase II), were obtained from in situ neutron diffraction measurements. - Highlights: • We measured in situ neutron diffraction of high-pressure polymorphs of Ca(OD){sub 2}. • Hydrogen positions of the high-pressure phase are first determined. • The obtained hydrogen bonds reasonably explain Raman peaks of OH stretching modes. • A phase transition mechanism among the polymorphs is proposed.

  7. 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

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

    PubMed

    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 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. PMID:26315260

  9. New Phases of C60 Synthesized at High Pressure

    NASA Astrophysics Data System (ADS)

    Iwasa, Y.; Arima, T.; Fleming, R. M.; Siegrist, T.; Zhou, O.; Haddon, R. C.; Rothberg, L. J.; Lyons, K. B.; Carter, H. L., Jr.; Hebard, A. F.; Tycko, R.; Dabbagh, G.; Krajewski, J. J.; Thomas, G. A.; Yagi, T.

    1994-06-01

    The fullerene C60 can be converted into two different structures by high pressure and temperature. They are metastable and revert to pristine C60 on reheating to 300^circC at ambient pressure. For synthesis temperatures between 300^circ and 400^circC and pressures of 5 gigapascals, a nominal face-centered-cubic structure is produced with a lattice parameter a_o = 13.6 angstroms. When treated at 500^circ to 800^circC at the same pressure, C60 transforms into a rhombohedral structure with hexagonal lattice parameters of a_o = 9.22 angstroms and c_o = 24.6 angstroms. The intermolecular distance is small enough that a chemical bond can form, in accord with the reduced solubility of the pressure-induced phases. Infrared, Raman, and nuclear magnetic resonance studies show a drastic reduction of icosahedral symmetry, as might occur if the C60 molecules are linked.

  10. 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

  11. 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.

  12. 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.

  13. 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

  14. 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

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

    PubMed

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

    2014-07-22

    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

  16. 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.

  17. 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.

  18. 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.

  19. 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

  20. Theoretical studies of the high pressure phases in cerium

    SciTech Connect

    Wills, J.M.; Eriksson, O.; Boring, A.M. )

    1991-10-14

    We present full potential linear-muffin-tin-orbital calculations based on the local-density approximation, which reproduce the {ital T}=0 phase diagram of cerium (Ce), including the volumes and transition pressures for both the {alpha}{r arrow}{alpha}{prime}, and the {alpha}{prime}{r arrow}bct transitions. The {alpha}{r arrow}{alpha}{prime} transition is largely determined by a balance of two competing terms: a Madelung term and a 4{ital f} one-electron term. The {alpha}{prime}{r arrow}bct transition is driven by both 4{ital f} and 5{ital d} partial-wave contributions. This is the first successful, {ital ab} {ital initio} calculation of a crystallographic ({ital T}=0) phase diagram of an {ital f}-electron system.

  1. 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.

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

    SciTech Connect

    Yang, Xue; Li, Quanjun; Liu, Ran; Liu, Bo; Zhang, Huafang; Jiang, Shuqing; Zou, Bo; Cui, Tian; Liu, Bingbing; Liu, Jing

    2014-03-28

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

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

    NASA Astrophysics Data System (ADS)

    Szczȩśniak, D.; Zemła, T. P.

    2015-08-01

    Motivated by the ambiguous experimental data for the superconducting phase in silane (SiH4), which may originate from platinum hydride (PtH), we provide a theoretical study of the superconducting state in the latter alloy. The quantitative estimates of the thermodynamics of PtH at 100 GPa are given for a wide range of Coulomb pseudopotential values ({μ }*) within the Eliashberg formalism. The obtained critical temperature value ({T}{{C}}\\in < 12.94,20.01> for {μ }*\\in < 0.05,0.15> ) agrees well with the experimental TC for SiH4, which may be ascribed to PtH. Moreover, the calculated characteristic thermodynamic ratios exceed the predictions of the Bardeen-Cooper-Schrieffer theory, implying the occurrence of strong-coupling and retardation effects in PtH. We note that our results may be of high relevance for future theoretical and experimental studies on hydrides.

  4. High-pressure phase transition in Y3Fe5O12

    NASA Astrophysics Data System (ADS)

    Stan, C. V.; Wang, J.; Zouboulis, I. S.; Prakapenka, V.; Duffy, T. S.

    2015-10-01

    Yttrium iron garnet (YIG, Y3Fe5O12) was examined up to 74 GPa and 1800 K using synchrotron x-ray diffraction in a diamond anvil cell. At room temperature, YIG remained in the garnet phase until abrupt amorphization occurred at 51 GPa, consistent with earlier studies. Upon laser heating up to 1800 K, the material transformed to a single-phase orthorhombic GdFeO3-type perovskite of composition (Y0.75Fe0.25)FeO3. No evidence of decomposition of the sample was observed. Both the room-temperature amorphization and high-temperature transformation to the perovskite structure are consistent with the behaviour of other rare earth oxide garnets. The perovskite sample was compressed between 28-74 GPa with annealing to 1450-1650 K every 3-5 GPa. Between 46 and 50 GPa, a 6.8% volume discontinuity was observed without any accompanying change in the number or intensity of diffraction peaks. This is indicative of a high-spin to low-spin electronic transition in Fe3+, likely in the octahedrally coordinated B-site of the perovskite. The volume change of the inferred spin transition is consistent with those observed in other rare earth ferric iron perovskites at high pressures.

  5. High-pressure phase transition in Y3Fe5O12.

    PubMed

    Stan, C V; Wang, J; Zouboulis, I S; Prakapenka, V; Duffy, T S

    2015-10-14

    Yttrium iron garnet (YIG, Y3Fe5O12) was examined up to 74 GPa and 1800 K using synchrotron x-ray diffraction in a diamond anvil cell. At room temperature, YIG remained in the garnet phase until abrupt amorphization occurred at 51 GPa, consistent with earlier studies. Upon laser heating up to 1800 K, the material transformed to a single-phase orthorhombic GdFeO3-type perovskite of composition (Y(0.75)Fe(0.25))FeO3. No evidence of decomposition of the sample was observed. Both the room-temperature amorphization and high-temperature transformation to the perovskite structure are consistent with the behaviour of other rare earth oxide garnets. The perovskite sample was compressed between 28-74 GPa with annealing to 1450-1650 K every 3-5 GPa. Between 46 and 50 GPa, a 6.8% volume discontinuity was observed without any accompanying change in the number or intensity of diffraction peaks. This is indicative of a high-spin to low-spin electronic transition in Fe(3+), likely in the octahedrally coordinated B-site of the perovskite. The volume change of the inferred spin transition is consistent with those observed in other rare earth ferric iron perovskites at high pressures. PMID:26402583

  6. 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.

  7. 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.

  8. Experimental and Theoretical Studies on a High Pressure Monoclinic Phase of Ammonia Borane

    SciTech Connect

    Lin, Yu; Ma, Hongwei; Matthews, Charles Wesley; Kolb, Brian; Sinogeikin, Stanislav; Thonhauser, Timo; Mao, Wendy L.

    2012-03-15

    The effect of pressure on the structure of ammonia borane NH{sub 3}BH{sub 3} (AB) was investigated using a combination of high pressure X-ray diffraction (XRD) and density functional theory (DFT). In situ XRD was performed up to 15.0 GPa at room temperature in a diamond anvil cell, and two first-order phase transitions were observed at 1.6 and 12.9 GPa. The ambient pressure I4mm structure transformed into the high pressure Cmc2{sub 1} phase at 1.6 GPa, and then experienced a second-order isostructural phase transition at 5 GPa, and further developed into a monoclinic P2{sub 1} (Z = 4) phase at 12.9 GPa. The structure of the high pressure P2{sub 1} phase was solved by powder diffraction data and further optimized using DFT calculations. The high pressure phase transitions were found to be reversible upon releasing pressure. The behavior of the N-H {hor_ellipsis} H-B dihydrogen bonding framework, inter- and intramolecular interactions at high pressure was also investigated. The origin of the phase transition at 12.9 GPa is attributed to the reorganization of the dihydrogen bonding network and the change in the rotational dynamics of the NH{sub 3} and BH{sub 3} groups.

  9. Boron under Pressure: Phase Diagram and Novel High-Pressure Phase

    NASA Astrophysics Data System (ADS)

    Oganov, Artem R.

    Boron has a unique chemistry, responsible for remarkable complexities even in the pure element. I review some of the history of the discovery of this element, and recent surprises found in boron under pressure. I discuss the recent discovery of a new high-pressure phase, ?-B28, consisting of icosahedral B12 clusters and B2 pairs in a NaCl-type arrangement: (B2)δ+(B12)δ-, and displaying a significant charge transfer δ ~ 0.48. Boron is the only light element, for which the phase diagram has become clear only in the last couple of years, and this phase diagram is discussed here among other recent findings.

  10. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2011-07-01

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

  12. 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.

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

    NASA Astrophysics Data System (ADS)

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

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

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

    NASA Astrophysics Data System (ADS)

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

    2016-01-01

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

  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 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].

  17. Phase Behavior of Dipalmitoylphosphatidylglycerol Bilayer Membrane in Saline Water Under High Pressure

    NASA Astrophysics Data System (ADS)

    Tanaka, Saeko; Goto, Masaki; Tamai, Nobutake; Matsuki, Hitoshi

    The phase transitions of dipalmitoylphosphatidylglycerol (DPPG) bilayer membrane in the aqueous NaCl solution were observed by means of an optical method under atmospheric and high pressures. The temperature-pressure phase diagram of the DPPG bilayer showed that the phase behavior of the DPPG bilayer was similar to that of dipalmitoylphosphatidylcholine (DPPC) bilayer except for the interdigitated gel (LβI) phase. Comparing the phase diagram with the diagram obtained in a phosphate buffer, it turned out that the formation of the LβI phase is suppressed by the shielding effect of NaCl on the repulsive interaction among polar headgroups.

  18. 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.

  19. Structural Evidence for a Fast-Ion Transition in the High-Pressure Rocksalt Phase of Silver Iodide

    NASA Astrophysics Data System (ADS)

    Keen, D. A.; Hull, S.; Hayes, W.; Gardner, N. J. G.

    1996-12-01

    This Letter describes neutron diffraction measurements of the rocksalt structured phase of AgI at high pressure and temperature and the structural disorder which accompanies its high conductivity. In contrast to the first-order structural phase transition which results in fast-ionic α-AgI at ambient pressure, the fast-ionic behavior in rocksalt structured AgI occurs above a diffuse transition with a small anomaly in lattice parameter and a continuous increase in occupation of interstitial tetrahedral sites with increasing temperature. There are approximately 10 times more defects in the fast-ionic phase of rocksalt AgI than in isostructural AgBr at ambient pressure, 1 K below melting.

  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. 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.

  2. 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...

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

    NASA Astrophysics Data System (ADS)

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

    2013-09-01

    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.

  4. 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

  5. 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.

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

    DOE PAGESBeta

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

    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

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

    NASA Astrophysics Data System (ADS)

    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

    2015-07-01

    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.

  8. A new, layered monoclinic phase of Co3O4 at high pressure.

    PubMed

    Kaewmaraya, Thanayut; Luo, Wei; Yang, Xiao; Panigrahi, Puspamitra; Ahuja, Rajeev

    2015-08-14

    We present the crystal structures and electronic properties of a Co3O4 spinel under high pressure. Co3O4 undergoes a first-order transition from a cubic (CB) Fd3̄m to a lower-symmetry monoclinic (MC) P21/c phase at 35 GPa, occurring after the local high-spin to low-spin phase transition. The high-pressure phase exhibits the octahedral coordination of Co(II) and Co(III), whereas the CB phase contains the fourfold coordination of Co(II) and the sixfold coordination of Co(III). The CB-to-MC transition is attributed to the charge-transfer between the di- and trivalent cations via the enhanced 3d-3d interactions. PMID:26166770

  9. Theoretical and experimental evidence for the post-cotunnite phase transition in zirconia at high pressure

    NASA Astrophysics Data System (ADS)

    Nishio-Hamane, Daisuke; Dekura, Haruhiko; Seto, Yusuke; Yagi, Takehiko

    2015-05-01

    A post-cotunnite phase transition in zirconia (ZrO2) at high pressure was investigated by synchrotron X-ray diffraction measurements and ab initio calculations based on density functional theory. This study successfully demonstrated a cotunnite- to Fe2P-type phase transition. Static enthalpy difference (Δ H) calculations predicted the appearance of the Fe2P phase at 124 GPa (LDA) and 143 GPa (GGA), and experimental trials demonstrated the coexistence of the Fe2P and cotunnite phases at 175 GPa after heating to 3,000 K. Both phases were quenchable to ambient conditions. The volume of the Fe2P phase was slightly less (~Δ 0.6 %) than that of the cotunnite phase over the experimental pressure range, indicating that the Fe2P phase is the higher pressure phase. The coexistence of both phases in this study may be attributed to the slow kinetics of the phase transition resulting from the close structural relationship of the two phases. An Fe2P-type structural model can be derived by applying a simple operation to the cotunnite-type structure, consisting of a 1/2 shift of several zirconium arrangements parallel to the b-axis of the cotunnite-type unit cell. It is concluded that the high-pressure cotunnite-to-Fe2P phase transition may be a common trend in many dioxides.

  10. 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.

  11. 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.

  12. Synthesis, lattice dynamics, and mechanical properties of a high-pressure scheelite phase of RVO4.

    PubMed

    Huang, Zuocai; Zhang, Lei; Pan, Wei

    2012-11-01

    High-pressure scheelite phases of RVO(4) (R = Y, Sm, Gd, Yb, Lu) compounds were prepared by high pressure (up to 25 GPa) from zircon RVO(4) compounds. Raman spectra of these scheelite phases of RVO(4) were determined and discussed in detail. Mechanical properties, including bulk, shear, Young's modulus, B/G and Poisson's ratios, of the scheelite phase of RVO(4) were measured by an ultrasonic method and compared with the results calculated by density functional theory. The calculated lattice parameters and mechanical properties are in good agreement with the experimental results. The radius and states of the 4f orbital of R show distinct effects on the mechanical properties. PMID:23075278

  13. Structural Phase Transitions in AuIn2 at High Pressure

    NASA Astrophysics Data System (ADS)

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

    2007-12-01

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

  14. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2015-11-01

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

  16. Structural Phase Transitions and Metallized Phenomena in Arsenic Telluride under High Pressure.

    PubMed

    Zhao, Jinggeng; Yang, Liuxiang; Yu, Zhenhai; Wang, Yong; Li, Chunyu; Yang, Ke; Liu, Zhiguo; Wang, Yi

    2016-04-18

    In this study, first-principle calculations, in situ angle-dispersive X-ray diffraction, and in situ electrical resistance measurements were performed on arsenic telluride (As2Te3) under high pressure. Structural phase transitions and metallized phenomena were observed from the calculated and experimental results. Upon compression, α-As2Te3 transforms into phases α' and α″ at ∼5.09 and ∼13.2 GPa, respectively, with two isostructural phase transitions. From 13.2 GPa, As2Te3 starts to transform into phase γ, with one first-order monoclinic to monoclinic crystal structural phase transition. According to the first-principle calculations and electrical resistance measurements, the structural phase transitions in the compression process induce the transformation from an insulator (phase α) across a semimetal (phase α') into a metal (phases α″ and γ). The evolution of the structure and transport property upon compression on As2Te3 is helpful for understanding the properties of other A2B3-type compounds under high pressure. PMID:27035163

  17. 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.

  18. 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. PMID:26732344

  19. 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.

  20. 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.

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

    PubMed

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

    2016-04-13

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

  2. Phase transition of CaSi2 at high pressures and high temperatures

    NASA Astrophysics Data System (ADS)

    Imai, Motoharu

    2001-03-01

    We have studied a pressure effect on alkaline-earth-metal disilicides because their structures have characteristic Si configurations. In situ x-ray diffraction measurements of BaSi2 showed that the structure changes from orthorhombic to cubic, then to trigonal with increasing pressure. The cubic and the trigonal structures are the same as those of SrSi2 and CaSi2 at ambient conditions, respectively. Thus, the structures that appear at high pressure are the same as those at ambient conditions of the other alkaline-earth-metal disilicides with a smaller atomic number metal. This structural sequence is different from those known in elements and the other AB_2-type compounds such as dioxides of 14 group elements. For better understanding of the structural sequence, pressure experiments are necessary for the other alkaline-earth-metal disilicides. In this study, a pressure-temperature phase diagram of CaSi2 is investigated by in situ x-ray diffraction measurements at pressures up to 10.6 GPa and temperatures from 290 to 1300 K. The in situ observation revealed that CaSi2 has a low-temperature, high-pressure phase with a trigonal structure, and a high-temperature, high-pressure phase with a tetragonal structure. The results will be discussed in comparison with the results of BaSi_2. [1] M. Imai et al., Phys. Rev. B58, 11922 (1998).

  3. 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.

  4. 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.

  5. 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.

  6. Structural phase transitions in Bi2Se3 under high pressure

    DOE PAGESBeta

    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 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

  7. 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

  8. 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

    2015-01-01

    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

  9. 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. PMID:24050356

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

    PubMed

    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

  11. High pressure structural, electronic, and optical properties of polymorphic InVO4 phases

    NASA Astrophysics Data System (ADS)

    Mondal, S.; Appalakondaiah, S.; Vaitheeswaran, G.

    2016-02-01

    In the present work, we report a detailed density functional theory calculation on polymorphic InVO4 phases by means of projector augmented wave method. The computed first-order structural phase transformation from orthorhombic (Cmcm) to monoclinic (P2/c) structure is found to occur around 5.6 GPa along with a large volume collapse of 16.6%, which is consistent with previously reported experimental data. This transformation also leads to an increase in the coordination number of vanadium atom from 4 to 6. The computed equilibrium and high pressure structural properties of both InVO4 phases, including unit cell parameters, equation of state, and bulk moduli, are in good agreement with the available experimental data. In addition, compressibility is found to be highly anisotropic and the b-axis being more compressible than the other for both the structures. Electronic band structures for both the phases were calculated, and the band gaps for orthorhombic and monoclinic InVO4 are found to be 4.02 and 1.67 eV, respectively, within the Tran-Blaha Modified Becke-Johnson potential as implemented in linearized augmented planewave method. We further examined the optical properties such as dielectric function, refractive index, and absorption spectra for both the structures. From the implications of these results, it can be proposed that the high pressure InVO4 phase can be more useful than orthorhombic phase for photo catalytic applications.

  12. 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.

  13. 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

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

    DOE PAGESBeta

    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

  15. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2016-04-01

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

  17. 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.

  18. Modeling the warm-up phase of a high-pressure-lamps lighting network

    SciTech Connect

    Stambouli, M.; Charrada, K. ); Costache, C.; Damelincourt, J.J. . Centre de Physique des Plasmas et de leurs Applications)

    1999-06-01

    This work presents a study of the dynamic regime of a lamp-network interaction corresponding to the warm-up phase of a high-pressure mercury discharge lamp. The lamp's behavior is described by a variable pressure model using the local thermodynamic equilibrium (LTE) concept. Indeed, this model covers the most interesting phase of the network dynamic regime, where discharge lamps appreciably impose their nonlinearity. The authors first analyze the electrical behavior of the discharge lamp in a single phase circuit, taking into account the ballast saturation. Then a micronetwork is studied and they show the influence of the discharge's evolution on currents in phases and neutral conductors. Finally, from the results of the physical model, they set up a simple parametric modeling which reproduces the electrical behavior of the lamp during its warm-up phase. Such an approach can be useful for electrical engineers working on the discharge supply circuits at industrial frequency (50--60 Hz).

  19. Five-dimensional visualization of phase transition in BiNiO3 under high pressure

    PubMed Central

    Liu, Yijin; Wang, Junyue; Azuma, Masaki; Mao, Wendy L.; Yang, Wenge

    2014-01-01

    Colossal negative thermal expansion was recently discovered in BiNiO3 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. PMID:24753622

  20. 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

  1. a Quantum Monte Carlo Study of the High Pressure Phases of Solid Hydrogen

    NASA Astrophysics Data System (ADS)

    Natoli, Vincent Dominic

    1994-01-01

    Variational and Diffusion Monte Carlo are powerful computational methods which can afford accurate estimates of the ground state properties of quantum many-body problems. We have applied these Monte Carlo methods to the high pressure phases of solid hydrogen to elucidate those parts of the phase diagram where experimental results are inconclusive or lacking. The method allows us to treat both electrons and protons as quantum particles by incorporating them in the trial wavefunction and avoids the Born-Oppenheimer and harmonic approximations. Our trial wavefunction uses single-body solutions from a mean-field calculation coupled with standard pair potential terms to achieve the most accurate results to date. Equally accurate results were realized for calculations in the disparate insulating molecular and metallic atomic regime. We performed a study of the possible ground state structures of the atomic metallic phase of hydrogen which identifies a new family of low energy atomic structures. Another study was done on the molecular phase over the range of pressures (40-180GPa) where recent experiments have observed spectral discontinuities and other interesting new phenomena. Particular attention was directed to determining the equation of state and orientational ordering. We find that molecular hydrogen adopts a lower symmetry insulating structure over a wide range of pressure. The results of the atomic and molecular studies are combined to draw conclusions about the molecular-atomic transition and other details about the high pressure phase diagram.

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

    PubMed

    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

  3. The behaviors of anatase and TiO2(B) phase coexisting nanosheets under high pressure

    NASA Astrophysics Data System (ADS)

    Huang, Yanwei; Li, Wentao; Ren, Xiangting; Yu, Zhenhai; Samanta, Sudeshna; Yan, Shuai; Zhang, Jun; Wang, Lin

    2016-03-01

    High pressure behaviors of anatase TiO2 and TiO2(B) coexisting nanosheets were investigated using in situ synchrotron X-ray diffraction and Raman Spectroscopy. The X-ray diffraction revealed that upon compression an α-PbO2 phase appeared at 11.4 GPa, and then the baddeleyite phase appeared at 23.6 GPa. Upon decompression the anatase phase still existed obviously and TiO2(B) phase almost cannot be observed. The Raman spectrum at ambient pressure presented the typical curve of anatase TiO2, however the pressure dependence for compression and decompression did not show the common phase transion from anatase to α-PbO2 or to baddeleyite. This is different from high pressure behaviors of other TiO2 nanostructures and could be attributed to the existence of small amount of TiO2(B) at the starting materials. The pressure relationship of the Raman frequencies shift slope indicated the coexistence nanosheet has high incompressibility compared with other TiO2 nanomaterials and corresponding bulks.

  4. Phase transition induced strain in ZnO under high pressure

    DOE PAGESBeta

    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 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

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

    NASA Astrophysics Data System (ADS)

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

    2015-11-01

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

  6. 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.

  7. 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.

  8. 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.

  9. Anomalous phase transition of InN nanowires under high pressure

    NASA Astrophysics Data System (ADS)

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

    2015-09-01

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

  10. 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.

  11. Synthesis and equation of state of high pressure phase of chromium-bearing spinel

    NASA Astrophysics Data System (ADS)

    Shieh, S. R.; Khan, T.; Prescher, C.; Prakapenka, V.; MI, Z.

    2015-12-01

    Chromium-bearing spinel (Mg,Fe)Cr2O4 can be found in the Earth's crust, upper mantle, and even in meteorites. Mantle derived chromium-bearing spinel suggests that its high pressure phase may be existing at deep mantle but however its high pressure elastic property is not well understood yet. In situ synchrotron X-ray diffraction studies of magnesiochromite and chromite using the laser-heated diamond anvil cell were performed at GSECARS, Advanced Photon Source, to explore their high pressure phases and elastic property. Our results on magnesiochromite showed dissociation of MgCr2O4 to Cr2O3+MgO at ~15 GPa and to modified Ludwigite (mLd)-type Mg2Cr2O5+Cr2O3 below and above ~1500 K, respectively. At above 20 GPa, only a single phase CaTi2O4-type structure of MgCr2O4 was observed at 1400-2000 K. Pressure-volume data of CaTi2O4 type structure of MgCr2O4 fitted to Birch-Murnaghan equation of state yield zero-pressure volume (V0) = 264.4(8) Å3, bulk modulus (K0) = 185.4(4) GPa, and pressure derivative (K0') = 4; and mLd-type Mg2Cr2O5 yields: V0 = 338.9(8) Å3, K0 = 186.5(6) GPa, K0' = 4. For CaTi2O4 type structure of natural chromite, our fitted P-V data show V0 = 261(1) Å3, K0 = 175.4(2) GPa, and K0' = 4.

  12. Crystal lattice and band structure of the intermediate high-pressure phase of PbSe.

    PubMed

    Streltsov, S V; Manakov, A Yu; Vokhmyanin, A P; Ovsyannikov, S V; Shchennikov, V V

    2009-09-23

    In the present paper the results of fitting synchrotron diffraction data are obtained for the intermediate high-pressure phase (9.5 GPa) of the lead selenide based compound Pb(1-x)Sn(x)Se (x = 0.125)-an optoelectronic as well as a thermoelectric material-for two types of lattice symmetries Pnma (space group #62) and Cmcm (space group #63). Both lattice parameters and positions of atoms for the above mentioned structures have been used in calculations of the electron structure of high-pressure phases. The main difference between the electronic properties for Cmcm and Pnma structures established in electronic structure calculations is that in the first one the PbSe compound was found to be a metal, while in the second a small semiconductor gap (E(G) = 0.12 eV) was obtained. Moreover, the forces in the Cmcm structure are an order of magnitude larger than those calculated for the Pnma lattice. In the optimized, Pnma structure within a generalized gradient approximation (GGA), the band gap increases up to E(G) = 0.27 eV. The result coincides with the data on thermoelectric power and electrical resistance data pointing to a semiconductor gap of ∼0.2 eV at ∼9.5 GPa. Thus, the Pmna type of lattice seems to be a preferable version for the intermediate phase compared with the Cmcm one. PMID:21832372

  13. High pressure phase transformation in thorium carbide: A first principle study

    NASA Astrophysics Data System (ADS)

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

    2013-06-01

    First principles calculations using full potential linearized augmented plane wave (FP-LAPW) method have been carried out to analyze structural, electronic and elastic properties of ThC under hydrostatic compression. Our calculations carried out within the generalized gradient approximation (GGA) predict a structural phase transition from rocksalt type (B1) phase to CsCl type cubic (B2) structure at ˜ 45 GPa. The same transition is predicted to occur at ˜ 35 GPa by the calculations performed within local density approximation (LDA). Various physical quantities such as equilibrium volume, bulk modulus, pressure derivative of bulk modulus and elastic constants determined for both the phases at zero pressure are compared with data available in literature. We find that at zero pressure the B2 structure is unstable elastically also. However, it emerges as elastically stable structure before it stabilizes energetically at high pressure. Further, the activation barrier between these structures has been calculated at various pressures.

  14. Structural Stability and Phase Transitions in K8Si46 Clathrate under High Pressure

    NASA Astrophysics Data System (ADS)

    Tse, John S.; Desgreniers, Serge; Li, Zhi-Qiang; Ferguson, Michael R.; Kawazoe, Yoshiyuki

    2002-10-01

    The structural stability of type-I K8Si46 clathrate has been investigated at high pressure by synchrotron x-ray diffraction. In contrast to that observed in the Na-doped structure-II analogue [

    A. San-Miguel et al., Phys. Rev. Lett. 83, 5290 (1999)
    ], no phase separation into the β-Sn Si structure was identified at 11 GPa. Instead, K8Si46 is found to undergo a transition to an isostructural positional disordered phase at around 15 GPa. Ab initio phonon band structure calculations reveal a novel phenomenon of phonon instabilities of K atoms in the large cavities is responsible for this transition. Above 32 GPa, the new structure transforms into an amorphous phase.

  15. 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.

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

    SciTech Connect

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

    2008-10-24

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

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

    NASA Astrophysics Data System (ADS)

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

    2014-05-01

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

  18. 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. PMID:23802968

  19. 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.

  20. 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.

  1. Effect of high pressure on the formation of ordered phases in Ta-C systems

    SciTech Connect

    Markhasev, B.I.; Dzhamarov, S.S.; Geshko, E.I.; Klyugvant, V.V.; Pilipovskii, Y.L.; Shamatov, Y.M.

    1985-03-01

    This paper considers the effect of pressure on the completion of the transformations TaC /SUB x/ Ta/sub 4/C/sub 3/ and TaC /SUB x/ Ta/sub 2/C. The data show that in the samples with C/Ta = 0.68 and 0.71, the applied pressure substantially increases the diffraction peak heights of the ordered phases, Ta/sub 4/C/sub 3/ and Ta/sub 2/C. In samples with C/Ta = 0.76, high pressure does not generally increase the intensities of the diffracted peaks of Ta/sub 4/C/sub 3/ and Ta/sub 2/C, however the equilibrium between them is displaced to the side of increased Ta/sub 2/C content. In one of the samples a complete disappearance of the disordered TaC /SUB x/ is not observed. It is concluded that high pressure ( about7GPa) promotes the transition of nonstoichiometric TaC /SUB x/ into ordered Ta/sub 4/C/sub 3/ and Ta/sub 2/C as well as broadens the existence region of the latter. A complete transformation of TaC /SUB x/ into the ordered phase does not occur even at pressures up to about 9 GPa.

  2. Liquidus Phases of the Richardson H5 Chondrite at High Pressures and Temperatures

    NASA Technical Reports Server (NTRS)

    Channon, M.; Garber, J.; Danielson, L. R.; Righter, K.

    2007-01-01

    Part of early mantle evolution may include a magma ocean, where core formation began before the proto-Earth reached half of its present radius. Temperatures were high and bombardment and accretion were still occurring, suggesting that the proto-Earth consisted of a core and an at least partially liquid mantle, the magma ocean. As the Earth accreted, pressure near the core increased and the magma ocean decreased in volume and became shallower as it began to cool and solidify. As crystals settled, or floated, the composition of the magma ocean could change significantly and begin to crystallize different minerals from the residual liquid. Therefore, the mantle may be stratified following the P-T phase diagram for the bulk silicate Earth. To understand mantle evolution, it is necessary to know liquidus phase relations at high pressures and temperatures. In order to model the evolution of the magma ocean, high pressure and temperature experiments have been conducted to simulate the crystallization process using a range of materials that most likely resemble the bulk composition of the early Earth.

  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.

    2013-06-12

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

    NASA Astrophysics Data System (ADS)

    Azadi, Sam; Foulkes, Matthew

    2015-03-01

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

  6. Elasticity and phase transitions of stishovite and sodium chloride at high pressure

    NASA Astrophysics Data System (ADS)

    Lakshtanov, Dmitry Leonidovich

    2007-12-01

    Knowledge of elastic properties of the phases constituting the Earth's mantle are of extreme importance for determination of Earth's chemical composition, the distribution of phases and the processes that result in such distribution. Data on elasticity of these constituent phases are critical not only for interpreting seismic observations, but are also essential for geochemical and geodynamical modeling. This dissertation is mainly devoted to determination of the elasticity and stability of stishovite, the high-pressure silica polymorph, as a major constituent of the MORB layer of subducting lithospheric slabs. These thin (˜10km thick) layers subducted into the Earth mantle create regions of thermal, compositional and, hence, rheological heterogeneity. Being a key component of the mantle convection system, subducting slabs may counteract compositional stratification of the Earth by acting to remix differentiated lithospheric material. In addition, there has recently been great interest in subducting slabs as possible carriers of volatiles - mainly water - back to the lower mantle. Stishovite is likely the primary water-bearing phase. The elastic properties and thermodynamic stability of water-bearing stishovite, and the effect of other impurities on these properties, is the main focus of this work. An important related issue I addressed is the establishment of a self-consistent (absolute) equation of state for the B2 phase of sodium chloride (NaCl). NaCl is a commonly-used pressure transmitting medium in high-pressure devices. Accurate knowledge of the NaCl equation of state therefore reduces errors in pressure determination resulting from the use of the secondary pressure calibrants. In order to perform these tasks I used Brillouin scattering and Raman spectroscopy, combined with synchrotron x-ray diffraction at standard conditions, and at high pressures and temperatures in the diamond anvil cell. Experiments were performed in Merrill-Bassett and piston

  7. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2009-07-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2016-04-01

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

  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. 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.

  12. 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.

  13. Decomposition of the ω-phase in the equiatomic TiZr alloy under high pressure

    NASA Astrophysics Data System (ADS)

    Bashkin, I. O.; Shestakov, V. V.; Sakharov, M. K.; Ponyatovsky, E. G.

    2008-07-01

    The phase decomposition phenomenon is found in the hexagonal ω-phase of the Ti—Zr system under high pressure. The ω → ω1 + ω2 decomposition of the equiatomic TiZr alloy occurred due to long thermobaric treatment at P = 5.5±0.6 GPa and T = 710±30 K. The chemical compositions of the ω1- and ω2-phases recovered to ambient conditions were estimated from the X-ray data to be around Ti20Zr80 and Ti83Zr17. The experimental data were used to calculate the mixing energy and the top of the decomposition curve in the isobaric T-C diagram of this system. We find that the equilibrium T-C phase diagram of the Ti-Zr system at pressures above ~8 GPa is of the eutectoid type with the high-temperature β-phase and the low-temperature ω1- and ω2-phases.

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

    NASA Astrophysics Data System (ADS)

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

    2013-06-01

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

  15. 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.

  16. 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)

  17. Electronic structure of low-pressure and high-pressure phases of silicon disulfide

    NASA Astrophysics Data System (ADS)

    Bletskan, D. I.; Vakulchak, V. V.; Glukhov, K. E.

    2014-07-01

    Self-consistent density functional theory calculations of band spectra, densities of states as well as the spatial distribution of valence electron charge density were carried out for the low-pressure α-phase and the high-pressure β-phase of SiS2. Group-theoretical analysis performed for both phases enabled the symmetry of wave functions in a number of high-symmetry points of the Brillouin zone as well as the structure of valence band representations to be found. Based on the calculations of the band structure, the orthorhombic α-phase of SiS2 was determined to be an indirect-gap semiconductor with the band gap E gi = 2.44 eV (T 1 → X 8 transition), while the β-phase was shown to be direct gap with E gd = 2.95 eV (Г 3 → Г 2 transition). The calculated energy distribution of the total density of states in the valence band of α-SiS2 qualitatively and quantitatively correlates with the main experimental features of the X-ray photoelectron spectrum.

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

    NASA Astrophysics Data System (ADS)

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

    2014-08-01

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

  19. High-pressure phase transitions in ordered and disordered Bi2Te2Se.

    PubMed

    Nielsen, M B; Parisiades, P; Madsen, S R; Bremholm, M

    2015-08-21

    We report studies of pressure-induced phase transitions of ordered and disordered ternary tetradymite-like Bi2Te2Se by synchrotron powder X-ray diffraction (PXRD) in diamond anvil cells (DACs) for pressures up to 59 and 49 GPa, respectively. The first sample (SB) was prepared from a single crystal with ordered Se/Te sites while the second sample (Q) was prepared from a quenched melt resulting in disordered Se/Te. This allows for an investigation of the effect of disorder on the phase transitions and the equation of states (EoS) of the tetradymite-like α phase. Fitting of a third order Birch-Murnaghan EoS to the α phases yielded bulk moduli K0 of 34.5(10) and 38.3(17) GPa and K' of 6.2(3) and 5.0(5) for the SB and Q samples, respectively. An electronic topological transition (ETT) was identified in both samples at pressures of 4.4 and 3.1 GPa, respectively. This was followed by a transition near 11 GPa to a phase that is isostructural with the β phase of Bi2Te3. The Se/Te ordering only affects the transition pressure to a small extent. A cubic phase that resembles the δ phase observed in high-pressure studies of Bi2Te3 appears at 17-20 GPa, but the ternary composition leads to a more complex structure. The presence of a low angle diffraction peak in the δ phase demonstrates that the true structure is not simply body-centred cubic. In this way the samples resemble Bi2Se3 where Bi and Se show a high degree of ordering, but the proposed structure of δ-Bi2Se3 also does not fully describe the data for δ-Bi2Te2Se. PMID:26169469

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

    SciTech Connect

    Yoo, C; Evans, W; Cynn, H

    2004-03-30

    This study is for in-situ investigation of chemical bonding and molecular structure of low z-elements and simple molecular solids at high pressures and temperatures using 3rd-generation synchrotron x-ray diffraction. To understand the contribution of the empty d-electron orbital of Mg in relation to the formation of molecular solids like MgO, which is one of the important Earth lower mantle materials and MgB{sub 2}, which has recently been the focus of intense superconducting material research, we have performed double-sided laser heating experiments using a diamond anvil cell (DAC). Understanding the structural stability and the formation of the above Mg-compounds requires studying Mg itself as well as the relevant compounds. BL10XU at the Spring-8 was used to study phase stability and make accurate equation of state (EOS) determinations of Mg coupled with external heating and the double-sided laser heating technique. Monochromatic x-ray at 30 keV (0.4135 {angstrom}) was focused to about 40 {micro}m at the sample and the diffracted x-ray were recorded using a high-resolution image plate (3000 x 3000 pixels with a 0.1 mm resolution per pixel). EOS parameters for hcp and bcc Mg were determined by fitting to a Birch-Murnaghan equation. An isothermal compression of Mg at 300 K up to 100 GPa provides EOS parameters (B{sub 0}, B{sub 0}{prime}, and V{sub 0}) comparable for both hcp and bcc phases, which is similar to the cases for hcp and fcc phases measured in cobalt and xenon. Similar EOS parameters for both low and high pressure phases with a very small or no measurable volume discontinuity at the phase transition pressure suggests that the hcp-bcc structural transition of Mg may be driven by a stacking fault due to a shear instability as seen in xenon and cobalt. Compared to the recent estimation determined using a large volume press [1], our B{sub 0} is smaller by more than 10% suggesting that the difference may be due to non-hydrostatic conditions. The phase

  1. 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.

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

    SciTech Connect

    Araoud, Z.; Ben Ahmed, R.; Bouaoun, M.; Ben El Hadj Rhouma, M.; Charrada, K.; Zissis, G.

    2008-09-15

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

  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. 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.

  5. 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.

  6. Equation of state and phase transition of antigorite under high pressure and high temperature

    NASA Astrophysics Data System (ADS)

    Yang, Cuiping; Inoue, Toru; Yamada, Akihiro; Kikegawa, Takumi; Ando, Jun-ichi

    2014-03-01

    The equation of state of natural antigorite has been determined up to ∼10 GPa and 500 °C by in situ X-ray diffraction in a cubic type multi-anvil apparatus, MAX80, located at the Photon Factory-Advanced Ring at the High Energy Accelerator Research Organization (KEK), and the temperature dependence of the bulk modulus was determined for the first time by high pressure and high temperature X-ray diffraction based on a series of direct measurements. No dehydration occurred during the entire experimental process, and no significant deviatoric stress was observed after heating. The room temperature P-V data below 7 GPa have been fit to the Birch-Murnaghan equation of state, yielding V0,300 K = 366.9(7) Å3, K0, 300 K = 65.2(31) GPa, and the pressure derivative K‧ fixed to 6.1. The high pressure phase transition was observed through volume softening behavior at around 7 GPa, and the dP/dT slope seems to be flat or slightly positive, which is consistent with the recent report by Bezacier et al. (2013). The high temperature Birch-Murnaghan equation of state was used to fit the P-V-T data below 7 GPa. Since the present experimental data was obtained by energy dispersive X-ray diffraction at high pressure and high temperature, the resolution was slightly lower than that obtained by the angle dispersive X-ray method. So the bulk modulus K0, 300 K and the pressure derivative K‧ were fixed to 62.9 GPa and 6.1, respectively, which was obtained by single crystal X-ray diffraction in a diamond anvil cell by means of the angle dispersive method (Nestola et al., 2010) during fitting. From the fitting, we obtained V0, 300 K = 367.3(2) Å3, dK/dT = -0.0265(41) GPa/K, thermal expansion α0 = 3.92(50) × 10-5/K. The temperature dependence of the bulk modulus was larger than the value calculated empirically (Holland and Powell, 1998). The thermal expansion of antigorite is larger than the results from the previous study. The compression of antigorite is very anisotropic along

  7. 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.

  8. 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.

  9. Structural Phase Transitions in High-Pressure Wurtzite to Rocksalt Phase in GaN and SiC

    SciTech Connect

    Xiao, H. Y.; Gao, Fei; Wang, Lumin M.; Zu, Xiaotao T.; Zhang, Yanwen; Weber, William J.

    2008-06-16

    Ab initio molecular dynamics simulations are employed to study the atomistic mechanisms and pathways of high-pressure phase transformation in GaN and SiC. Our simulations bring a fundamental level of understanding of the wurtzite to rocksalt phase transformation that undergoes inhomogeneous displacements via a tetragonal atomic configuration, and suggest that the transition path may be independent of the presence of d electrons on the cation in GaN. The discrepancies between experimental and theoretical studies of transition paths are discussed.

  10. High pressure-temperature phase diagram and equation of state of titanium

    NASA Astrophysics Data System (ADS)

    Dewaele, Agnès; Stutzmann, Vincent; Bouchet, Johann; Bottin, François; Occelli, Florent; Mezouar, Mohamed

    2015-04-01

    The high pressure-temperature behavior of titanium has been studied with x-ray diffraction in resistively heated and laser-heated diamond anvil cells up to 200 GPa and ˜3500 K. The stability fields of α -Ti ,ω -Ti ,β -Ti ,γ -Ti , and δ -Ti have been determined in this range. γ -Ti and δ -Ti , which had been evidenced earlier under nonhydrostatic compression, are also observed in helium pressure transmitting medium. Equation-of-state parameters are proposed for α -Ti and ω -Ti at 300 K, and β -Ti at high temperature. The stability fields of the α ,ω ,γ , and δ phases are also studied using the projector-augmented wave method based on density-functional theory. Using the relevant core radius to avoid overlapping between atomic spheres, and relaxing cells and atomic positions, we show that all those phases have a stability domain at 0 K. We explain why γ -Ti and δ -Ti were calculated to be unstable in earlier works. In addition, a new phase, called δ'-Ti, which is a distortion of δ -Ti , is predicted to form between 80 and 120 GPa and below ≃200 K.

  11. 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.

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

    NASA Astrophysics Data System (ADS)

    Xiong, Yan; Kiran, Erdogan

    1998-03-01

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

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

    PubMed

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

    2009-12-14

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

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

    NASA Astrophysics Data System (ADS)

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

    2016-07-01

    The Hugoniot data for TeO2 single crystals were obtained for pressures up to ∼85 GPa along both the <100> (a-axis) and <001> (c-axis) directions using a velocity interferometer system for any reflector and inclined-mirror method combined with a powder gun or two-stage light gas gun. The Hugoniot-elastic limit of TeO2 was determined to be 3.3–4.3 GPa along the c-axes. The shock velocity (U s) versus particle velocity (U p) relation for TeO2 shows a kink around U p = 1.0 km s‑1, which suggests a phase transition completes at ∼26 ± 2 GPa. The Hugoniot relations of the low and high pressure phase are given by U s = 3.13(5) + 1.10(6)U p for U p < 1.0 km s‑1 and U s = 2.73(9) + 1.49(5)U p for U p > 1.0 km s‑1, respectively. First-principles geometry optimizations based on the generalized gradient approximation after Perdew, Burke and Ernzerhof method were also performed on TeO2. It suggested that a continuous structure distortion occurs up to 22 GPa, and the lattice parameters b and c abruptly increase and decrease at 22 GPa, respectively, indicating a first-order phase transition to the cotunnite structure phase. The equation of state of the cotunnite phase TeO2 is discussed based on the experimental and simulation results.

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

    PubMed

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

    2016-03-01

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

  16. 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. PMID:25086753

  17. 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

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

    PubMed

    Faria, Luiz F O; Ribeiro, Mauro C C

    2015-11-01

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

  19. 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.

  20. 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. PMID:24355938

  1. The novel phase transition of NaBi(WO{sub 4}){sub 2} under high pressure

    SciTech Connect

    Ma, Chunli; Cui, Hang; Li, Fangfei; Wang, Jingshu; Wu, Xiaoxin; Zhang, Jian; Zhou, Qiang; Liu, Jinghe; Cui, Qiliang

    2013-04-15

    The Raman and synchrotron angle-dispersive X-ray diffraction studies have been performed on NaBi(WO{sub 4}){sub 2} under high pressure up to 30.7 and 36.2 GPa, respectively, at room temperature. With pressure increases to ∼7.0 GPa, the structure of NaBi(WO{sub 4}){sub 2} begins to transform from tetragonal (I4{sub 1}/a) into monoclinic (P2/m), and the phase transition completes around 13 GPa. With pressure higher than 29.0 GPa, the NaBi(WO{sub 4}){sub 2} turns into amorphous state. The random arrangement of Na{sup +} and Bi{sup 3+} in short-range ordered scheelite NaBi(WO{sub 4}){sub 2} results in the tetragonal to monoclinic phase transition, which is different from that observed in AWO{sub 4} tungstates and AMoO{sub 4} molybdates (A=Ca, Sr, Ba, Pb, Eu, Cd). - Graphical abstract: The NaBi(WO{sub 4}){sub 2} transforms from tetragonal into monoclinic, which starts around 7 GPa and completes at about 13 GPa. With pressure higher than 29 GPa, the NaBi(WO{sub 4}){sub 2} turns into amorphous state. Highlights: ► Raman and X-ray diffraction studies performed on NaBi(WO{sub 4}){sub 2} up to 30.7 and 36.2 GPa, respectively. ► The tetragonal (I4{sub 1}/a) into monoclinic (P2/m) phase transition is determined. ► With pressure higher than 29 GPa, the NaBi(WO{sub 4}){sub 2} ultimately turns into amorphous state. ► The ambient pressure bulk modulus and volume of tetragonal and monoclinic phases are obtained.

  2. 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.

  3. Crystal structure of a high-pressure/high-temperature phase of alumina by in situ X-ray diffraction.

    PubMed

    Lin, Jung-Fu; Degtyareva, Olga; Prewitt, Charles T; Dera, Przemyslaw; Sata, Nagayoshi; Gregoryanz, Eugene; Mao, Ho-Kwang; Hemley, Russell J

    2004-06-01

    Alumina (alpha-Al(2)O(3)) has been widely used as a pressure calibrant in static high-pressure experiments and as a window material in dynamic shock-wave experiments; it is also a model material in ceramic science. So understanding its high-pressure stability and physical properties is crucial for interpreting such experimental data, and for testing theoretical calculations. Here we report an in situ X-ray diffraction study of alumina (doped with Cr(3+)) up to 136 GPa and 2,350 K. We observe a phase transformation that occurs above 96 GPa and at high temperatures. Rietveld full-profile refinements show that the high-pressure phase has the Rh(2)O(3) (II) (Pbcn) structure, consistent with theoretical predictions. This phase is structurally related to corundum, but the AlO(6) polyhedra are highly distorted, with the interatomic bond lengths ranging from 1.690 to 1.847 A at 113 GPa. Ruby luminescence spectra from Cr(3+) impurities within the quenched samples under ambient conditions show significant red shifts and broadening, consistent with the different local environments of chromium atoms in the high-pressure structure inferred from diffraction. Our results suggest that the ruby pressure scale needs to be re-examined in the high-pressure phase, and that shock-wave experiments using sapphire windows need to be re-evaluated. PMID:15146173

  4. Anomalous compression and new high-pressure phases of vanadium sesquioxide, V2O3

    NASA Astrophysics Data System (ADS)

    Ovsyannikov, Sergey V.; Trots, Dmytro M.; Kurnosov, Alexander V.; Morgenroth, Wolfgang; Liermann, Hanns-Peter; Dubrovinsky, Leonid

    2013-09-01

    We report results of a powder x-ray diffraction (XRD) study of vanadium sesquioxide, V2O3, under pressurization in a neon pressure-transmitting medium up to 57 GPa. We have established a bulk modulus value for corundum-type V2O3 of B0 = 150 GPa at B‧ = 4. This bulk modulus value is the lowest among those known for the corundum-type-structured oxides, e.g. Al2O3, α-Fe2O3, Cr2O3, Ti2O3, and α-Ga2O3. We have proposed that this might be related to the difference in the electronic band structures: at room temperature V2O3 is metallic, but the above corundum-structured sesquioxides are semiconducting or insulating. Around ˜21-27 and ˜50 GPa we registered changes in the XRD patterns that might be addressed to phase transitions. These transitions were sluggish upon room-temperature compression, and hence we additionally facilitated them by the laser heating of one sample. We have refined the XRD patterns of only the first high-pressure phase in an orthorhombic lattice of a Rh2O3(II)-type. Our findings significantly extend the knowledge of the P-T phase diagram of V2O3 and advance the understanding of its properties. We speculate that the elastic properties of V2O3 can be closely linked to its electronic band structure and, consequently, we propose that slightly doped V2O3 (e.g. with Cr) could be a potential candidate for systems in which the bulk modulus value may be remarkably switched by moderate pressure or temperature.

  5. The behaviour of peptides on reverse-phase supports during high-pressure liquid chromatography.

    PubMed Central

    Wilson, K J; Honegger, A; Stötzel, R P; Hughes, G J

    1981-01-01

    High-pressure ('performance') liquid chromatography has been used to investigate the reverse-phase chromatographic behaviour of peptides, ranging in length from 2 to 65 amino acid residues, which have originated from primary-sequence determinations or solution/solid-phase syntheses. By using a pyridine/formate-pyridine/acetate/propan-1-ol buffer system, as previously described [Hughes, Winterhalter & Wilson (1979) FEBS Lett. 108, 81-86], the influence of various experimental parameters were examined. (a) Peptide retention was observed to be temperature-independent between 25 and 55 degrees C. (b) The dependence of chromatographic retention on pH decreases with increasing peptide hydrophobicity. (c) Chromatographic results from C8- and C18-chain-length, as well as from 5 micrometers- and 10 micrometers-particle-size, supports were comparable. (d) The hydrophobic strength of the organic solvent in the mobile phase was observed to decrease: propan-1-ol approximately equal to propan-2-ol greater than acetonitrile much greater than methanol. (e) When gradient rates (% of buffer B/unit time) were systematically decreased, peptide retention decreased in a hyperbolic manner. Comparisons of the peptides chromatographed with respect to their measured retention properties and calculated hydrophobicities were performed by computer analysis. Deviation of peptide chromatographic behaviour was observed to be essentially independent of hydrophobicity, chain length and charge. On the basis of the measured retention properties of the chromatographed peptides, hydrophobic constants for the various amino acid side chains were determined and compared with similar constants available from the literature. PMID:7337711

  6. Phase transition of SrSi2 at high pressures and high temperatures

    NASA Astrophysics Data System (ADS)

    Imai, Motoharu; Hirano, Toshiyuki

    2000-03-01

    We have studied pressure effect on alkaline-earth-metal disilicides because their structures have characteristic Si configurations. In situ x-ray diffraction measurements of BaSi2 showed that the structure changes from orthorhombic to cubic, then to trigonal with increasing pressure. The cubic and the trigonal structures are the same as those of SrSi2 and CaSi2 at ambient conditions, respectively. Thus, the structures that appear at high pressure are the same as those at ambient conditions of the other alkaline-earth-metal disilicides with a smaller atomic number metal[1]. This structural sequence is different from those known in elements and the other AB_2-type compounds such as dioxides of 14 group elements. For better understanding of the structural sequence, pressure experiments are necessary for the other alkaline-earth-metal disilicides. In this study, a pressure-temperature phase diagram of SrSi2 is investigated by in-situ x-ray diffraction measurements at pressures up to 5.3 GPa and temperatures from 290 to 1300 K. When heated at constant pressures above 3.5 GPa, the structure changes from the cubic to a tetragonal one, the α-ThSi2 -type structure. The results will be discussed in comparison with the results of BaSi_2. [1] M. Imai et al., Phys. Rev. B58, 11922 (1998).

  7. 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.

  8. 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. PMID:25969157

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

    PubMed

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

    2016-05-14

    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. PMID:27179475

  10. 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.

  11. 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.

  12. High-pressure phase relations and thermodynamic properties of CaAl 4Si 2O 11 CAS phase

    NASA Astrophysics Data System (ADS)

    Akaogi, M.; Haraguchi, M.; Yaguchi, M.; Kojitani, H.

    2009-03-01

    Phase relations in CaAl4Si2O11 were examined at 12-23 GPa and 1000-1800 °C by multianvil experiments. A three-phase mixture of grossular, kyanite and corundum is stable below about 13 GPa at 1000-1800 °C. At higher pressure and at temperature below about 1200 °C, a mixture of grossular, stishovite and corundum is stable, indicating the decomposition of kyanite. Above about 1200 °C, CaAl4Si2O11 CAS phase is stable at pressure higher than about 13 GPa. The triple point is placed at 14.7 GPa and 1280 °C. The equilibrium boundary of formation of CAS phase from the mixture of grossular, kyanite and corundum has a small negative slope, and that from the mixture of grossular, stishovite and corundum has a strongly negative slope, while the decomposition boundary of kyanite has a small positive slope. Enthalpies of the transitions were measured by high-temperature drop-solution calorimetry. The enthalpy of formation of CaAl4Si2O11 CAS phase from the mixture of grossular, kyanite and corundum was 139.5 ± 15.6 kJ/mol, and that from the mixture of grossular, stishovite and corundum was 94.2 ± 15.4 kJ/mol. The transition boundaries calculated using the measured enthalpy data were consistent with those determined by the high-pressure experiments. The boundaries in this study are placed about 3 GPa higher in pressure and about 200 °C lower in temperature than those by Zhai and Ito [Zhai, S., Ito, E., 2008. Phase relations of CaAl4Si2O11 at high-pressure and high-temperature with implications for subducted continental crust into the deep mantle. Phys. Earth Planet. Inter. 167, 161-167]. Combining the thermodynamic data measured in this study with those in the literature, dissociation boundary of CAS phase into a mixture of Ca-perovskite, corundum and stishovite and that of grossular into Ca-perovskite plus corundum were calculated to further constrain the stability field of CAS phase. The result suggests that the stability of CAS phase would be limited at the bottom of

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

    NASA Astrophysics Data System (ADS)

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

    2012-12-01

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

  14. Coupled phase transformations and plastic flows under torsion at high pressure in rotational diamond anvil cell: Effect of contact sliding

    NASA Astrophysics Data System (ADS)

    Feng, Biao; Levitas, Valery I.

    2013-12-01

    A three-dimensional large-sliding contact model coupled with strain-induced phase transformations (PTs) and plastic flow in a disk-like sample under torsion at high pressure in rotational diamond anvil cell (RDAC) is formulated and studied. Coulomb and plastic friction are combined and take into account variable parameters due to PT. Results are obtained for weaker, equal-strength, and stronger high pressure phases, and for three values of the kinetic coefficient in a strain-controlled kinetic equation and friction coefficient. All drawbacks typical of problem with cohesion are overcome, including eliminating mesh-dependent shear band and artificial plastic zones. Contact sliding intensifies radial plastic flow, which leads to larger reduction in sample thickness. Larger plastic strain and increased pressure in the central region lead to intensification of PT. However, the effect of the reduction in the friction coefficient on PT kinetics is nonmonotonous. Sliding increases away from the center and with growing rotation and is weakly dependent on the kinetic coefficient. Also, cyclic back and forth torsion is studied and compared to unidirectional torsion. Multiple experimental phenomena, e.g., pressure self-multiplication effect, steps (plateaus) at pressure distribution, flow to the center of a sample, and oscillatory pressure distribution for weaker high-pressure phase, are reproduced and interpreted. Reverse PT in high pressure phase that flowed to the low pressure region is revealed. Possible misinterpretation of experimental PT pressure is found. Obtained results represent essential progress toward understanding of strain-induced PTs under compression and shear in RDAC and may be used for designing experiments for synthesis of new high pressure phases and reduction in PT pressure for known phases, as well as for determination of PT kinetics from experiments.

  15. High-pressure phase transitions in BiFeO3: hydrostatic versus non-hydrostatic conditions

    NASA Astrophysics Data System (ADS)

    Guennou, Mael; Bouvier, Pierre; Haumont, Raphaël; Garbarino, Gaston; Kreisel, Jens

    2011-05-01

    We report high pressure X-ray diffraction experiments on BiFeO3 (BFO) single crystals in diamond-anvil cells up to 14 GPa. Two data sets are compared, one in hydrostatic conditions, with helium used as a pressure-transmitting medium (PTM), and the other in non-hydrostatic conditions, with silicon oil as a PTM. It is shown that the crystal undergoes different phase transitions in the two cases, highlighting the high sensitivity of BFO to non-hydrostatic stress. Consequences for the interpretation of high pressure structural studies are discussed.

  16. 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.

  17. 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

    2014-01-01

    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

  18. Droplet entrainment correlation for high pressure annular two-phase flow

    SciTech Connect

    Lopez de Betodano, M.A.; Jan, Cheng-Shiun; Beus, S.G.

    1996-01-01

    The amount of entrainment in annular flow is essential to predict the point of dryout. Most of the entrainment correlations available in the literature are obtained from air-water low pressure data. However many important industrial applications involve high pressure annular flows. There are very few correlations applicable in this range and they are solely based on empirical data fits. Comparing the low pressure entrainment data of Cousins and Hewitt (1968) and the high pressure data of Keeys et. al. (1970) and Wurtz (1978) with existing correlations, the agreement at high pressure is generally poor, except for the empirical correlation of Nigmatulin and Krushenok (1989) which depends on a Weber number that includes the droplet concentration. We propose a new semi-mechanistic entrainment correlation for fully developed annular flow conditions: E = (0.9642)/(1 + (3836/We{sub C})). It is developed based on the droplet continuity equation and the entrainment rate model of Dallman et. al. (1979). This model is then modified to introduce a Weber number that includes the droplet concentration, We{sub C}. This Weber number is shown to scale the available high and low pressure air-water and steam-water data better than the other definitions. Because the new correlation is based on a model of entrainment rate it may be used as a starting point in the development of a correlation for this process applicable to high pressure water-steam annular flows. A correlation is suggested pending validation with high pressure entrainment rate data. 12 refs., 11 figs.

  19. 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

    2015-06-01

    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. PMID:25984597

  20. 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.

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

    NASA Astrophysics Data System (ADS)

    Hirai, H.; Tanaka, T.; Matsuoka, T.; Ohishi, Y.; Yagi, T.; Ohtake, M.; Yamamoto, Y.

    2014-05-01

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

  2. In situ characterization of formation and growth of high-pressure phases in single-crystal silicon during nanoindentation

    NASA Astrophysics Data System (ADS)

    Huang, Hu; Yan, Jiwang

    2016-04-01

    Pressure-induced intermediate phases of silicon exhibit unique characteristics in mechanics, chemistry, optics, and electrics. Clarifying the formation and growth processes of these new phases is essential for the preparation and application of them. For in situ characterization of the formation and growth of high-pressure phases in single-crystal silicon, a quantitative parameter, namely displacement change of indenter (Δ h) during the unloading holding process in nanoindentation, was proposed. Nanoindentation experiments under various unloading holding loads and loading/unloading rates were performed to investigate their effects on Δ h. Results indicate that Δ h varies significantly before and after the occurrence of pop-out; for the same maximum indentation load, it tends to increase with the decrease in the holding load and to increase with the increase in the loading/unloading rate. Thus, the value of Δ h can be regarded as an indicator that reflects the formation and growth processes of the high-pressure phases. Using Δ h, the initial position for the nucleation of the high-pressure phases, their growth, and their correlation to the loading/unloading rate were predictable.

  3. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2014-03-01

    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.

  5. Monoclinic phase of boron nitride appearing during the hexagonal cubic phase transition at high pressure and high temperature

    NASA Astrophysics Data System (ADS)

    Horiuchi, Shigeo; He, Lian-Long; Onoda, Mitsuko; Akaishi, Minoru

    1996-01-01

    Fine structures appearing on the phase transition from h (hexagonal) to c (cubic) boron nitride under high pressure (7.7 GPa) and high temperature (1800-2150 °C) are examined by high-resolution transmission electron microscopy. A prominent contraction of the interplanar spacing between sp2 sheets from 3.33 to 3.10 Å in so-called ``compressed h-BN'' is attributable to a monoclinic lattice distortion of the residual h-BN, which originates from the difference in the compressibility as well as the thermal expansion between adjoining h- and c-BN grains. The parameters of the monoclinic unit cell are am=4.33, bm=2.50, cm=3.1-3.3 Å, and β=92-95°. Thin plates of h-BN are often folded and the folding also causes the monoclinic structure. The sheet sequence of r (rhombohedral)-BN locally appears when the strong volume shrinkage occurs due to the formation of a c-BN grain. Nanoscale twins appear in resulting c-BN grains, as long as they are small, and w (wurzite)-BN is sometimes included in them.

  6. 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

  7. 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

  8. 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.

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

    DOE PAGESBeta

    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 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

  10. 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.

  11. 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

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

    PubMed

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

    2016-08-01

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

  13. 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

  14. High-pressure phases of SiO2 made in air by Fedoseev-Derjaguin laser process

    NASA Astrophysics Data System (ADS)

    Alam, M.; DebRoy, T.; Roy, R.; Breval, E.

    1988-10-01

    Exposure of a falling stream of 1 μm average size α-quartz particles to a continuous wave or pulsed CO2 laser beam in air resulted in the formation of a complete series of high-pressure phases of silica: coesite, stishovite, and apparently even denser forms with α-PbO2 and Fe2N structures. Since the laser exposure technique works with the carbon black to diamond transition, the technique is confirmed as a simple and generally applicable means to achieve the same effects as exposure to several hundred kilobars pressure.

  15. The natural high-pressure phase of cubic CdSe in impact glass from Zhamanshin crater

    NASA Astrophysics Data System (ADS)

    Kartashov, P. M.; Gornostaeva, T. A.; Mokhov, A. V.; Bogatikov, O. A.

    2016-04-01

    A CdSe high-pressure polymorph of the NaCl structural type of a 0 = 0.549 nm and Fm-3m space group was discovered in nature for the first time. Its composition is within range of CdSe-CdSe1- x where x = 0.2 apfu. The phase was discovered as abundant nanosize inclusions in irgizite-type condensate glass separated from the sample of impact rock of the Zhamanshin crater (Central Kazakhstan). The treated mineral was presumably formed within a gas-plasma cloud at the moment of impact.

  16. High-pressure structural phase transition in MnWO4

    NASA Astrophysics Data System (ADS)

    Ruiz-Fuertes, J.; Friedrich, A.; Gomis, O.; Errandonea, D.; Morgenroth, W.; Sans, J. A.; Santamaría-Pérez, D.

    2015-03-01

    The pressure-induced phase transition of the multiferroic manganese tungstate MnWO4 is studied on single crystals using synchrotron x-ray diffraction and Raman spectroscopy. We observe the monoclinic P 2 /c to triclinic P 1 ¯ phase transition at 20.1 GPa and get insight on the phase transition mechanism from the appearance of tilted triclinic domains. Selective Raman spectroscopy experiments with single crystals have shown that the onset of the phase transition occurs 5 GPa below the previously reported pressure obtained from experiments performed with powder samples.

  17. 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.

  18. Pressure-induced transformations in PrVO4 and SmVO4 and isolation of high-pressure metastable phases.

    PubMed

    Errandonea, Daniel; Achary, S Nagabhusan; Pellicer-Porres, Julio; Tyagi, Avesh K

    2013-05-01

    Zircon-type PrVO4 and SmVO4 have been studied by high-pressure Raman spectroscopy up to 17 GPa. The occurrence of phase transitions has been detected when compression exceeds 6 GPa. The transformations are not reversible. Raman spectra of the high-pressure phases show similarities with those expected for a monazite-type phase in PrVO4 and a scheelite-type phase in SmVO4.The high-pressure phases have been also synthesized using a large-volume press and recovered at ambient conditions. X-ray diffraction measurements of the metastable products recovered after decompression confirms the monazite (PrVO4) and scheelite (SmVO4) structures of the high-pressure phases. Based upon optical properties of the reported new polymorphs, novel applications for rare-earth vanadates are proposed, including photocatalytic hydrogen production. PMID:23600563

  19. 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.

  20. Structural phase transitions in EuFe[subscript 2]As[subscript 2] superconductor at low temperatures and high pressures

    SciTech Connect

    Uhoya, Walter O.; Tsoi, Georgiy M.; Vohra, Yogesh K.; McGuire, Michael A.; Sefat, Athena S.

    2011-09-20

    The crystal structure of EuFe{sub 2}As{sub 2} has been studied up to a pressure of 35 GPa and down to a temperature of 8 K using temperature dependent x-ray diffraction in a diamond anvil cell at a synchrotron source. At 4.3 GPa, we have detected a structural phase transition from a high temperature tetragonal phase with I4/mmm space group to a low temperature orthorhombic phase with Fmmm space group around 120 K. With the application of pressure at a low temperature of 10 K, the orthorhombic phase is suppressed and a phase change to a collapsed tetragonal phase with I4/mmm space group is observed at 11 GPa. This collapsed tetragonal phase is similar to the one observed at ambient temperature and pressure above 8.5 GPa. We have shown that the collapsed tetragonal phase of EuFe{sub 2}As{sub 2} has the same pressure-volume (P-V) equation of state at ambient temperature and at 10 K, implying that the high pressure phase of EuFe{sub 2}As{sub 2} has a negligible thermal expansion coefficient.

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

    NASA Astrophysics Data System (ADS)

    Dzhavadov, Leonid N.; Ryzhov, Valentin N.

    2016-06-01

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

  2. 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.

  3. Phase Transition of ZnxMn1-xS Dilute Magnetic Semiconductor Nanoparticles under Ultra-high Pressure

    SciTech Connect

    Z Zong; Y Ma; T Hu; Q Cui; M Zhang; G Zou

    2011-12-31

    The high-pressure behavior of different doping content of ZnS nanocrystals has been investigated using angle-dispersive synchrotron X-ray powder diffraction up to 45.1 GPa. A phase transformation from the zinc-blende(ZB) to the rock-salt (RS) structure is observed at pressures of about 17.7 and 18.3 GPa at room temperature, corresponding to the Mn{sup 2+} ion mole percent content solutions 0.85% and 1.26%, respectively. The obtained results indicate that the Mn{sup 2+} doping could obviously enhance the phase transition pressure of ZnS nanocrystal. The elevation of phase transition pressure could origin from the higher surface energy induced by ion doping.

  4. 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.

  5. 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.

  6. 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.

  7. 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.

  8. 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.

  9. Spectroscopic Study of the Effects of Pressure Media on High-Pressure Phase Transitions in Natrolite

    SciTech Connect

    D Liu; W Lei; Z Liu; Y Lee

    2011-12-31

    Structural phase transitions in natrolite have been investigated as a function of pressure and different hydrostatic media using micro-Raman scattering and synchrotron infrared (IR) spectroscopy. Natrolite undergoes two reversible phase transitions at 0.86 and 1.53 GPa under pure water pressure medium. These phase transitions are characterized by the changes in the vibrational frequencies of four- and eight-membered rings related to the variations in the bridging T-O-T angles and the geometry of the elliptical eight-ring channels under pressure. Concomitant to the changes in the framework vibrational modes, the number of the O-H stretching vibrational modes of natrolite changes as a result of the rearrangements of the hydrogen bonds in the channels caused by a successive increase in the hydration level under hydrostatic pressure. Similar phase transitions were also observed at relatively higher pressures (1.13 and 1.59 GPa) under alcohol-water pressure medium. Furthermore, no phase transition was found up to 2.52 GPa if a lower volume ratio of the alcohol-water to natrolite was employed. This indicates that the water content in the pressure media plays a crucial role in triggering the pressure-induced phase transitions in natrolite. In addition, the average of the mode Grueneisen parameters is calculated to be about 0.6, while the thermodynamic Grueneisen parameter is found to be 1.33. This might be attributed to the contrast in the rigidity between the TO{sub 4} tetrahedral primary building units and other flexible secondary building units in the natrolite framework upon compression and subsequent water insertion.

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

    NASA Astrophysics Data System (ADS)

    Dias, Ranga; Yoo, Choong-Shik

    2012-02-01

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

  11. 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

  12. 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.

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

    PubMed

    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

  14. Ice phases under ambient and high pressure: Insights from density functional theory

    NASA Astrophysics Data System (ADS)

    Fang, Yuan; Xiao, Bing; Tao, Jianmin; Sun, Jianwei; Perdew, John P.

    2013-06-01

    Water is common and plays a crucial role in biological, chemical, and physical processes, but its crystalline or ice state has a complicated structure. In this work, we study the lattice mismatch challenge for ice nucleation on silver iodide, the sublimation energy for different ice phases, and the structural phase-transition pressures of ice, with various density functionals. Our calculations show that the recently developed meta-generalized gradient approximation made simple (MGGA_MS) yields a lattice mismatch (3%) of hexagonal ice (ice Ih) with β-AgI in good agreement with experiment (2%), significantly better than the Perdew-Burke-Ernzerhof (PBE) GGA mismatch (6%). MGGA_MS is a computationally efficient semilocal functional that incorporates intermediate-range van der Waals (vdW) interaction, which, overall, performs well for ice and may be expected to improve upon PBE for liquid water. While MGGA_MS predicts the most realistic volumes and volume changes in the phase transitions of ice Ih to trigonal ice (ice II) and tetragonal ice (ice VIII), a more accurate description of some other properties of the higher-pressure phases (ice II and ice VIII) is provided by some functionals that include long-range vdW corrections (e.g., revised Tao-Perdew-Staroverov-Scuseria+vdW for sublimation energy and optB88-vdW for transition pressure).

  15. High Pressure Dielectric Studies of a Substance with the Smectic A1 Phase

    NASA Astrophysics Data System (ADS)

    Urban, Stanisław; Würflinger, Albert

    1999-09-01

    The results of dielectric studies of 5-n-hexyl-2-(4'-isothiocyanato)-l,3-dioxane (6DBT) in the smectic A, phase at pressures up to 150 MPa and temperatures up to 340 K are presented. The low frequen-cy relaxation time τ|| (p, T) yields the activation volume Δ# V|| = RT(∂|| In τ||/p)T and activation enthalpy Δ# H|| = R(∂In τ||/∂T-1)p. The calculated values of these parameters are compared with those ob-tained recently for n-octyl-cyanobiphenyl (8CB) forming the smectic Ad phase. In the case of 6DBT both these quantities are practically constant, whereas those for 8CB decrease, when going away from the phase transitions isotropic -smectic A1 (6DBT) or nematic -smectic Ad (8CB). These differences support our earlier conclusion that increase of pressure leads to a breaking of the antiparallel associa-tions of cyanobiphenyl molecules in the smectic as well as in the nematic phases.

  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. 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

  19. 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.

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

    SciTech Connect

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

    2014-04-24

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

  1. 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

  2. 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. PMID:24985659

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

    NASA Astrophysics Data System (ADS)

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

    2004-08-01

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

  4. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2016-02-01

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

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

    PubMed

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

    2016-02-01

    Single-crystal B4.3C boron carbide is investigated through the pressure-dependence and inter-relation of atomic distances, optical properties and Raman-active phonons up to ~70 GPa. The anomalous pressure evolution of the gap width to higher energies is striking. This is obtained from observations of transparency, which most rapidly increases around 55 GPa. Full visible optical transparency is approached at pressures of  >60 GPa indicating that the band gap reaches ~3.5 eV; at high pressure, boron carbide is a wide-gap semiconductor. The reason is that the high concentration of structural defects controlling the electronic properties of boron carbide at ambient conditions initially decreases and finally vanishes at high pressures. The structural parameters and Raman-active phonons indicate a pressure-dependent phase transition in single-crystal (nat)B4.3C boron carbide near 40 GPa, likely related to structural changes in the C-B-C chains, while the basic icosahedral structure appears to be less affected. PMID:26751337

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

    PubMed

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

    2016-01-28

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

  8. 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.

  9. 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.

  10. 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

  11. High pressure study of the zinc phosphide semiconductor compound in two different phases

    NASA Astrophysics Data System (ADS)

    Mokhtari, Ali

    2009-07-01

    Electronic and structural properties of the zinc phosphide semiconductor compound are calculated at hydrostatic pressure using the full-potential all-electron linearized augmented plane wave plus local orbital (FP-LAPW+lo) method in both cubic and tetragonal phases. The exchange-correlation potential is treated by the generalized gradient approximation within the scheme of Perdew, Burke and Ernzerhof, GGA96 (1996 Phys. Rev. Lett. 77 3865). Also, the Engel and Vosko GGA formalism, EV-GGA (Engel and Vosko 1993 Phys. Rev. B 47 13164), is used to improve the band-gap results. Internal parameters are optimized by relaxing the atomic positions in the force directions using the Hellman-Feynman approach. The lattice constants, internal parameters, bulk modulus, cohesive energy and band structures have been calculated and compared to the available experimental and theoretical results. The structural calculations predict that the stable phase is tetragonal. The effects of hydrostatic pressure on the behavior of band parameters such as band-gap, valence bandwidths and internal gaps (the energy gap between different parts of the valence bands) are studied using both GGA96 and EV-GGA.

  12. Hot pressing of polycrystals of high-pressure phases of mantle minerals in multi-anvil apparatus

    NASA Astrophysics Data System (ADS)

    Gwanmesia, Gabriel D.; Li, Baosheng; Liebermann, Robert C.

    1993-06-01

    In the 1960s, E. Schreiber and his colleagues pioneered the use of hot-pressed polycrystalline aggregates for studies of the pressure and temperature dependence of the elastic wave velocities in minerals. We have extended this work to the high-pressure polymorphs of mantle minerals by developing techniques to fabricate large polycrystalline specimens in a 2000-ton uniaxial split-sphere apparatus. A new cell assembly has been developed to extend this capability to pressures of 20 GPa and temperatures of 1700°C. Key elements in the new experimental design include: a telescopic LaCrO3 for T>1200°C; Toshiba Tungaloy grade F tungsten carbide anvils; and the use of homogeneous glasses or seeded powder mixtures as starting material to enhance reactivity and maximize densities. Cell temperatures are linearly related to electrical power to 1700°C and uniform throughout the 3 mm specimens. Pressure calibrations at 25°C and 1700°C are identical to 15 GPa. Cylindrical specimens of the beta and spinel phases of Mg2SiO4, stishovite (SiO2-rutile), and majorite-pyrope garnets have been synthesized within their stability fields in runs of 1 4 hr duration and recovered at ambient conditions by simultaneously decompressing and cooling along a computer-controlled P-T path designed to preserve the high-pressure phase and to relax intergranualar stress in the polycrystalline aggregate. These specimens are single-phased, fine-grained (<5 micron), free of microcracks and preferred orientation, and have bulk densities greater than 99% of X-ray density. The successful fabrication of these high-quality polycrystalline specimens has made possible experiments to determine the pressure dependence of acoustic velocities in the ultrasonics laboratory of S. M. Rigden and I. Jackson at the Australian National University.

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

    NASA Astrophysics Data System (ADS)

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

    2016-04-01

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

  14. Phase transformations and metallization of magnesium oxide at high pressure and temperature.

    PubMed

    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. PMID:23180773

  15. Determination of vitamin E in animal feeds by normal phase high pressure liquid chromatography.

    PubMed

    Cohen, H; Lapointe, M R

    1980-11-01

    A simple and rapid quantitative method for the determination of vitamin E in animal feeds is described. The method involves direct extraction with a mixture of isooctane--1,4-dioxane (80 + 20) followed by saponification. Additional purification was achieved by using a silica gel Sep-Pak. Elution time for vitamin E alcohol was 7.98 min (standard deviation (SD) 0.06) using a Partisil-10 PAC column and an isocratic mobile phase of hexane--dichloromethane--isopropanol (70 + 30 + 0.2) with a flow rate of 1 mL/min, and detection at 292 nm and 0.01 AUFS by a variable UV monitor. The average recovery of vitamin E was 96.64% (SD 5.19) in 4 different animal feeds. The method compared favorably with the official AOAC method. The minimum detectable amount of vitamin E in an animal feed is 10 IU/kg. PMID:7451386

  16. 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.

  17. 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.

  18. 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.

  19. Theoretical predictions of novel superconducting phases of BaGe3 stable at atmospheric and high pressures.

    PubMed

    Zurek, Eva; Yao, Yansun

    2015-03-16

    A series of new superconducting binary silicides and germanides have recently been synthesized under high-pressure high-temperature conditions. A representative member of this group, BaGe3, was theoretically investigated using evolutionary structure searches coupled with structural analogies in the pressure range from 1 atm to 250 GPa, where three new phases were discovered. At 1 atm, in addition to the synthesized P63/mmc phase, we predicted two new phases, I4/mmm and Amm2, to be dynamically stable. The Amm2 structure comprises Ge clusters and triangular prisms intercalated with Ba and Ge atoms, a unique structural motif unknown to this group. The I4/mmm structure has been previously synthesized in binary silicides and is calculated to be thermodynamically stable in BaGe3 between 15.6 and 35.4 GPa. Above 35.4 GPa, two new phases of P6̅m2 and R3̅m symmetry become the global minima and remain so up to the highest pressure considered. These two phases have very similar enthalpies, and both feature layers of double Kagome nets of Ge intercalated with Ba-Ge layers. The predicted phases are suggested to be metallic with itinerant electrons and to be potentially superconducting from the considerable electron-phonon coupling strength. Density functional perturbation calculations combined with the Allen-Dynes-modified McMillan formula were used to estimate the superconducting critical temperatures (Tc) for these new phases, which, with slight pressure variations, are comparable to the experimental Tc measured for the P63/mmc phase. PMID:25731906

  20. 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

    2014-11-01

    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. PMID:26278751

  1. 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.

  2. 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).

  3. High pressure synthesis of a new phase of YbAg2: Structure, valence of Yb and properties

    DOE PAGESBeta

    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; et al

    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).

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

    DOE PAGESBeta

    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 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

  5. [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. PMID:22512172

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

    NASA Astrophysics Data System (ADS)

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

    2015-04-01

    The compressional behaviour of (triclinic) pyrophyllite-1 Tc was investigated by means of in situ synchrotron single-crystal diffraction up to 6.2 GPa (at room temperature) using a diamond anvil cell. Its thermal behaviour was investigated by in situ synchrotron powder diffraction up to 923 K (at room pressure) with a furnace. No evidence of phase transition has been observed within the pressure range investigated. The α angle decreases whereas the β and γ angles increase with P, with the following linear trends: α( P) = α 0 - 0.203(9)·Δ P, β( P) = β 0 + 0.126(8)·Δ P, and γ( P) = γ 0 + 0.109(5)·Δ P (angles in ° and P in GPa). P- V data fits with isothermal Murnaghan and third-order Birch-Murnaghan Equations of State yield: K T0 = 47(3) GPa and K' = 6.6(14) for the M-EoS fit, K T0 = 47(4) GPa and K' = 7.3(19) for a III-BM-EoS fit, with the following anisotropic compressional scheme: β a : β b : β c = 1.06:1:4.00. The evolution of the "Eulerian finite strain" versus "normalized stress" leads to: Fe(0) = 47(3) GPa as intercept value and regression line slope with K' = 7.1(18). A drastic and irreversible change of the thermal behaviour of pyrophyllite-1 Tc was observed at 700 < T < 850 K, likely ascribable to the first stage of the T-induced de-hydroxylation. Between 298 and 700 K, the α angle shows a slight decrease whereas the β and γ angles tend to be unaffected in response to the applied temperature; all the unit-cell edges show a monotonic increase. The axial and volume thermal expansion coefficients of pyrophyllite were modelled between 298 and 773 K following the equation α V( T) = α 0(1 - 10 T -1/2), with α V298 K = 2.2(2) × 10-5 K-1 [with V 0 = 424.2(1) Å3 and α 0 = 5.5(3) × 10-5 K-1] and thermal anisotropic scheme α a : α b : α c = 1.20:1:2.72. By linear regression, we obtained: V( T)/ V 0 = 1 + α 0V· T = 1 + 3.1(2) × 10-5 ( T - T 0). The thermal behaviour of talc-1 Tc was investigated by in situ synchrotron powder

  7. Seismic velocities and anisotropy in subducting slabs: Constrains from high pressure Brillouin scattering studies on hydrous phases

    NASA Astrophysics Data System (ADS)

    Sanchez-Valle, C.

    2009-05-01

    Water transported and released into the upper mantle via subduction of oceanic lithosphere has a profound effect on the physical and mechanical properties of mantle materials and may trigger earthquakes and partial melting. The identification of water storage sites in the slab is therefore necessary to constrain H2O recycling through subduction zones and the effect that its circulation on a global scale has on the dynamics of the Earth's interior. As seismology represents the preferred method to detect hydration, knowledge of the sound velocities and elastic properties of candidate hydrous minerals are essential to interpret the seismic velocity structure and anisotropy of subducted plates. Dense hydrous magnesium silicates (DHMS) are recognized as important host for H2O in the slab, but their elastic properties under the appropriate pressure-temperature conditions are still poorly constrained. Here I present recent high-pressure Brillouin spectroscopy measurements to determine the sound velocities and single-crystal elastic properties of Fe-bearing phase A (phA) and phase E (phE), two DHMS that may transport water into the upper mantle and transition zone. Measurements were performed on samples compressed up to 16.5(2) GPa in the diamond-anvil cell. The results provide new insights into the behavior of hydrous minerals under subduction conditions and the possibility of identifying hydration through seismic observations. In both cases, the shear properties of the materials are important factors in the conclusions reached. The compressional (VP) and shear (VS) wave velocities of phA and phE are significantly lower than those of other phases in slab peridotite with whom they coexist. The new data is used with existing thermoelastic data to compute the density and seismic velocity structure of harzburgitic subducted slabs with various degrees of hydration at pressures corresponding to the upper mantle and transition zone. The results suggest that the seismic

  8. Influence of external effects on the electrical properties of high pressure perovskite-like phases CaCu3Ti4-xVxO12

    NASA Astrophysics Data System (ADS)

    Melnikova, N. V.; Ustinova, I. S.; Kadyrova, N. I.; Mirzorakhimov, A. A.; Zaynulin, Yu G.; Babushkin, A. N.

    2015-11-01

    Samples of high pressure perovskite-like phases CaCu3Ti4-xVxO12, x = 0.1, 0.2, 0.3, 0.4 and 0.5 were synthesized at high-pressure and high-temperature conditions in a toroid-type high-pressure chamber. Their electrical properties were studied by impedance spectroscopy in the frequency range from 1 Hz to 30 MHz at temperatures of 300 to 600 K and at pressures of 10 to 30 GPa.

  9. Ab initio investigation of phase stability of Y2Ti2O7 and Y2Zr2O7 under high pressure

    SciTech Connect

    Xiao, Haiyan Y.; Gao, Fei; Weber, William J.

    2009-12-31

    The phase stabilities of Y2Ti2O7 and Y2Zr2O7 under high pressure were investigated by ab initio methods. Pyrochlore-structured Y2Ti2O7 and defect-fluorite Y2Zr2O7 exhibit different responses to high pressure. Both the defect-fluorite and defect-cotunnite structures are energetically more stable at high pressure in Y2Ti2O7, but comparison with experimental results suggest that only the transformation to the defect-fluorite structure is kinetically favored. For Y2Zr2O7, the defect-fluorite phase should undergo a structural transformation to the defect-cotunnite state under high pressure.

  10. High-pressure and high-temperature phase diagram for Fe0.9Ni0.1-H alloy

    NASA Astrophysics Data System (ADS)

    Shibazaki, Yuki; Terasaki, Hidenori; Ohtani, Eiji; Tateyama, Ryuji; Nishida, Keisuke; Funakoshi, Ken-ichi; Higo, Yuji

    2014-03-01

    Planetary cores are considered to consist of an iron-nickel (Fe-Ni) alloy and light elements and hydrogen is one of plausible light elements in the core. Here we have performed in situ X-ray diffraction experiments on an Fe0.9Ni0.1-H system up to 15.1 GPa and 1673 K, and investigated the effect of Ni on phase relations of FeHx under high pressure and high temperature. The experimental system in the present work was oversaturated with hydrogen. We found a face-center-cubic (fcc) phase (with hydrogen concentration up to x∼1) and a body-center-cubic (bcc) phase (x < 0.1) as stable phases. The partial melting was observed below 6 GPa. We could not observe a double-hexagonal-close-packed (dhcp) phase because of limitations in pressure and temperature conditions. The stability field of each phase of Fe0.9Ni0.1Hx was almost same as that of FeHx. The solidus of Fe0.9Ni0.1Hx was 500-700 K lower than the melting curve of Fe and its liquidus was 400-600 K lower than that of Fe in the pressure range of this study. Both the solidus and liquidus of Fe0.9Ni0.1Hx were depressed at around 3.5 GPa, as was the solidus of FeHx. The hydrogen contents in fcc-Fe0.9Ni0.1Hx just below solidus were slightly lower than those of fcc-FeHx, which suggests that nickel is likely to prevent dissolution of hydrogen into iron. Due to the lower hydrogen solubilities in Fe0.9Ni0.1 compared to Fe, the solidus of Fe0.9Ni0.1Hx is about 100-150 K higher than that of FeHx.