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

International Nuclear Information System (INIS)

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

2010-01-01

We review high pressure phases of calcium which have obtained by recent experimental and first-principles studies. In this study, we investigated the face-centered cubic (fcc) structure, the body-centered cubic (bcc) structure, the simple cubic (sc) structure, a tetragonal P4 3 2 1 2 [Ishikawa T et al. 2008 Phys. Rev. B 77 020101(R)], an orthorhombic Cmca [Ishikawa T et al. 2008 Phys. Rev. B 77 020101(R)], an orthorhombic Cmcm [Teweldeberhan A M and Bonev S A 2008 Phys. Rev. B 78 140101(R)], an orthorhombic Pnma [Yao Y et al. 2008 Phys. Rev. B 78 054506] and a tetragonal I4/mcm [Arapan S et al. 2008 Proc. Natl. Acad. Sci. USA 105 20627]. We compared the enthalpies among the structures up to 200 GPa and theoretically determined the phase diagram of calcium. The sequence of the structural transitions is fcc (0- 3.5 GPa) → bcc (3.5 - 35.7 GPa) → Cmcm (35.7- 52GPa) → P4 3 2 1 2 (52-109 GPa) → Cmca (109-117.4GPa) → Pnma (117.4-134.6GPa) → I4mcm(134.6 GPa -). The sc phase is experimentally observed in the pressure range from 32 to 113 GPa but, in our calculation, there is no pressure region where the sc phase is the most stable. In addition, we found that the enthalpy of the hexagonal close-packed (hcp) structure is lower than that of I4/mcm above 495 GPa.

Integrated-fin gasket for palm cubic-anvil high pressure apparatus

Energy Technology Data Exchange (ETDEWEB)

Cheng, J.-G. [Institute for Solid State Physics, University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8581 (Japan); Beijing National Laboratory for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences, Beijing 100190 (China); Matsubayashi, K.; Nagasaki, S.; Hisada, A.; Hirayama, T.; Uwatoko, Y. [Institute for Solid State Physics, University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8581 (Japan); Hedo, M. [Faculty of Science, University of Ryukyus, Senbaru, Nishihara, Okinawa 903-0213 (Japan); Kagi, H. [Graduate School of Science, University of Tokyo, 7-3-1, Hongo Bunkyo-Ku, Tokyo 113-0033 (Japan)

2014-09-15

We described an integrated-fin gasket technique for the palm cubic-anvil apparatus specialized for the high-pressure and low-temperature measurements. By using such a gasket made from the semi-sintered MgO ceramics and the tungsten-carbide anvils of 2.5 mm square top, we successfully generate pressures over 16 GPa at both room and cryogenic temperatures down to 0.5 K. We observed a pressure self-increment for this specific configuration and further characterized the thermally induced pressure variation by monitoring the antiferromagnetic transition temperature of chromium up to 12 GPa. In addition to enlarge the pressure capacity, such a modified gasket also improves greatly the surviving rate of electrical leads hanging the sample inside a Teflon capsule filled with the liquid pressure-transmitting medium. These improvements should be attributed to the reduced extrusion of gasket materials during the initial compression.

Phase transition and water incorporation into Eu2Sn2O7 pyrochlore at high pressure

Science.gov (United States)

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

2016-04-01

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

High-temperature and high-pressure cubic zirconia anvil cell for Raman spectroscopy.

Science.gov (United States)

Chen, Jinyang; Zheng, Haifei; Xiao, Wansheng; Zeng, Yishan

2003-10-01

A simple and inexpensive cubic zirconia anvil cell has been developed for the performance of in situ Raman spectroscopy up to the conditions of 500 degrees C and 30 kbar pressure. The design and construction of this cell are fully described, as well as its applications for Raman spectroscopy. Molybdenum heater wires wrapped around ceramic tubes encircling two cubic zirconia anvils are used to heat samples, and the temperatures are measured and controlled by a Pt-PtRh thermocouple adhered near the sample chamber and an intelligent digital control apparatus. With this cell, Raman spectroscopic measurements have been satisfactorily performed on water at 6000 bar pressure to 455 degrees C and on ice of room temperature to 24 kbar, in which the determinations of pressures make use of changes of the A1 Raman modes of quartz and the shift of the sharpline (R-line) luminescence of ruby, respectively.

High-pressure synthesis of fully occupied tetragonal and cubic tungsten bronze oxides

Energy Technology Data Exchange (ETDEWEB)

Ikeuchi, Yuya; Takatsu, Hiroshi; Tassel, Cedric; Goto, Yoshihiro; Murakami, Taito; Kageyama, Hiroshi [Graduate School of Engineering, Kyoto University (Japan)

2017-05-15

A high-pressure reaction yielded the fully occupied tetragonal tungsten bronze K{sub 3}W{sub 5}O{sub 15} (K{sub 0.6}WO{sub 3}). The terminal phase shows an unusual transport property featuring slightly negative temperature-dependence in resistivity (dρ/dT<0) and a large Wilson ratio of R{sub W}=3.2. Such anomalous metallic behavior possibly arises from the low-dimensional electronic structure with a van Hove singularity at the Fermi level and/or from enhanced magnetic fluctuations by geometrical frustration of the tungsten sublattice. The asymmetric nature of the tetragonal tungsten bronze K{sub x}WO{sub 3}-K{sub 0.6-y}Ba{sub y}WO{sub 3} phase diagram implies that superconductivity for x≤0.45 originates from the lattice instability because of potassium deficiency. A cubic perovskite KWO{sub 3} phase was also identified as a line phase - in marked contrast to Na{sub x}WO{sub 3} and Li{sub x}WO{sub 3} with varying quantities of x (<1). This study presents a versatile method by which the solubility limit of tungsten bronze oxides can be extended. (copyright 2017 Wiley-VCH Verlag GmbH and Co. KGaA, Weinheim)

High pressure studies of YMn{sub 2} Laves phase and its deuterides

Energy Technology Data Exchange (ETDEWEB)

Sugiura, H.; Paul-Boncour, V.; Percheron-Guegan, A.; Marchuk, I.; Hirata, T.; Filipek, S.M.; Dorogova, M

2004-03-24

The C15 Laves phase intermetallic YMn{sub 2} and its deuterides containing 1.15, 2, 3.4 and 4 deuterium (D) atoms per formula unit (pfu) (the structure of YMn{sub 2}D{sub 4} is rhombohedral whereas other three deuterides preserve the cubic C15 structure) were compressed up to 31 GPa by using diamond anvil cell (DAC). Parameters of equation of state (EOS) were derived for all phases investigated. The discontinuous change of bulk modulus under high pressure has been revealed for all samples investigated. Two deuterides, YMn{sub 2}D{sub 1.15} and YMn{sub 2}D{sub 2}, decomposed reversibly under pressure into two phases: poor and enriched in deuterium.

Phase transformation of metastable cubic γ-phase in U-Mo alloys

International Nuclear Information System (INIS)

Sinha, V.P.; Hegde, P.V.; Prasad, G.J.; Dey, G.K.; Kamath, H.S.

2010-01-01

Over the past decade considerable efforts have been put by many fuel designers to develop low enriched uranium (LEU 235 ) base U-Mo alloy as a potential fuel for core conversion of existing research and test reactors which are running on high enriched uranium (HEU > 85%U 235 ) fuel and also for the upcoming new reactors. U-Mo alloy with minimum 8 wt% molybdenum shows excellent metastability with cubic γ-phase in cast condition. However, it is important to characterize the decomposition behaviour of metastable cubic γ-uranium in its equilibrium products for in reactor fuel performance point of view. The present paper describes the phase transformation behaviour of cubic γ-uranium phase in U-Mo alloys with three different molybdenum compositions (i.e. 8 wt%, 9 wt% and 10 wt%). U-Mo alloys were prepared in an induction melting furnace and characterized by X-ray diffraction (XRD) method for phase determination. Microstructures were developed for samples in as cast condition. The alloys were hot rolled in cubic γ-phase to break the cast structure and then they were aged at 500 o C for 68 h and 240 h, so that metastable cubic γ-uranium will undergo eutectoid decomposition to form equilibrium phases of orthorhombic α-uranium and body centered tetragonal U 2 Mo intermetallic compound. U-Mo alloy samples with different ageing history were then characterized by XRD for phase and development of microstructure.

High pressure orthorhombic structure of CuInSe2

International Nuclear Information System (INIS)

Bovornratanaraks, T; Saengsuwan, V; Yoodee, K; McMahon, M I; Hejny, C; Ruffolo, D

2010-01-01

The structural behaviour of CuInSe 2 under high pressure has been studied up to 53 GPa using angle-dispersive x-ray powder diffraction techniques. The previously reported structural phase transition from its ambient pressure tetragonal structure to a high pressure phase with a NaCl-like cubic structure at 7.6 GPa has been confirmed. On further compression, another structural phase transition is observed at 39 GPa. A full structural study of this high pressure phase has been carried out and the high pressure structure has been identified as orthorhombic with space group Cmcm and lattice parameters a = 4.867(8) A, b = 5.023(8) A and c = 4.980(3) A at 53.2(2) GPa. This phase transition behaviour is similar to those of analogous binary and trinary semiconductors, where the orthorhombic Cmcm structure can also be viewed as a distortion of the cubic NaCl-type structure.

Pressure-induced phase transitions in nanocrystalline ReO3

International Nuclear Information System (INIS)

Biswas, Kanishka; Muthu, D V S; Sood, A K; Kruger, M B; Chen, B; Rao, C N R

2007-01-01

Pressure-induced phase transitions in the nanocrystals of ReO 3 with an average diameter of ∼12 nm have been investigated in detail by using synchrotron x-ray diffraction and the results compared with the literature data of bulk samples of ReO 3 . The study shows that the ambient-pressure cubic I phase (space group Pm3-barm) transforms to a monoclinic phase (space group C 2/c), then to a rhombohedral I phase (space group R3-barc), and finally to another rhombohedral phase (rhombohedral II, space group R3-barc) with increasing pressure over the 0.0-20.3 GPa range. The cubic I to monoclinic transition is associated with the largest volume change (∼5%), indicative of a reconstructive transition. The transition pressures are generally lower than those known for bulk ReO 3 . The cubic II (Im3-bar) or tetragonal (P4/mbm) phases do not occur at lower pressures. The nanocrystals are found to be more compressible than bulk ReO 3 . On decompression to ambient pressure, the structure does not revert back to the cubic I structure

Phase transitions in solids under high pressure

CERN Document Server

Blank, Vladimir Davydovich

2013-01-01

Phase equilibria and kinetics of phase transformations under high pressureEquipment and methods for the study of phase transformations in solids at high pressuresPhase transformations of carbon and boron nitride at high pressure and deformation under pressurePhase transitions in Si and Ge at high pressure and deformation under pressurePolymorphic α-ω transformation in titanium, zirconium and zirconium-titanium alloys Phase transformations in iron and its alloys at high pressure Phase transformations in gallium and ceriumOn the possible polymorphic transformations in transition metals under pressurePressure-induced polymorphic transformations in АIBVII compoundsPhase transformations in AIIBVI and AIIIBV semiconductor compoundsEffect of pressure on the kinetics of phase transformations in iron alloysTransformations during deformation at high pressure Effects due to phase transformations at high pressureKinetics and hysteresis in high-temperature polymorphic transformations under pressureHysteresis and kineti...

Phase stability, electronic structure and equation of state of cubic TcN from first-principles calculations

International Nuclear Information System (INIS)

Song, T.; Ma, Q.; Sun, X.W.; Liu, Z.J.; Fu, Z.J.; Wei, X.P.; Wang, T.; Tian, J.H.

2016-01-01

The phase transition, electronic band structure, and equation of state (EOS) of cubic TcN are investigated by first-principles pseudopotential method based on density-functional theory. The calculated enthalpies show that TcN has a transformation between zincblende and rocksalt phases and the pressure determined by the relative enthalpy is 32 GPa. The calculated band structure indicates the metallic feature and it might make cubic TcN a better candidate for hard materials. Particular attention is paid to the predictions of volume, bulk modulus and its pressure derivative which play a central role in the formulation of approximate EOSs using the quasi-harmonic Debye model. - Highlights: • The phase transition pressure and electronic band structure for cubic TcN are determined. • Particular attention is paid to investigate the equation of state parameters for cubic TcN. • The thermodynamic properties up to 80 GPa and 3000 K are successfully predicted.

Instability of the layered orthorhombic post-perovskite phase of SrTiO3 and other candidate orthorhombic phases under pressure

Science.gov (United States)

Bhandari, Churna; Lambrecht, Walter R. L.

2018-06-01

While the tetragonal antiferro-electrically distorted (AFD) phase with space group I 4 / mcm is well known for SrTiO3 to occur below 105 K, there are also some hints in the literature of an orthorhombic phase, either at the lower temperature or at high pressure. A previously proposed orthorhombic layered structure of SrTiO3, known as the post-perovskite or CaIrO3 structure with space group Cmcm is shown to have significantly higher energy than the cubic or tetragonal phase and to have its minimum volume at larger volume than cubic perovskite. The Cmcm structure is thus ruled out. We also study an alternative Pnma phase obtained by two octahedral rotations about different axes. This phase is found to have slightly lower energy than the I 4 / mcm phase in spite of the fact that its parent, in-phase tilted P 4 / mbm phase is not found to occur. Our calculated enthalpies of formation show that the I 4 / mcm phase occurs at slightly higher volume than the cubic phase and has a negative transition pressure relative to the cubic phase, which suggests that it does not correspond to the high-pressure tetragonal phase. The enthalpy of the Pnma phase is almost indistinguishable from the I 4 / mcm phase. Alternative ferro-electric tetragonal and orthorhombic structures previously suggested in literature are discussed.

Effect of Hydrostatic Pressure on the Structural, Electronic and Optical Properties of SnS2 with a Cubic Structure: The DFT Approach

Science.gov (United States)

Bakhshayeshi, A.; Taghavi Mendi, R.; Majidiyan Sarmazdeh, M.

2018-02-01

Recently, a cubic structure of polymorphic SnS2 has been synthesized experimentally, which is stable at room temperature. In this paper, we calculated some structural, electronic and optical properties of the cubic SnS2 structure based on the full potential-linearized augmented plane waves method. We also studied the effect of hydrostatic pressure on the physical properties of the cubic SnS2 structure. Structural results show that the compressibility of the cubic SnS2 phase is greater than its trigonal phase and the compressibility decreases with increasing pressure. Investigations of the electronic properties indicate that pressure changes the density of states and the energy band gap increases with increasing pressure. The variation of energy band gap versus pressure is almost linear. We concluded that cubic SnS2 is a semiconductor with an indirect energy band gap, like its trigonal phase. The optical calculations revealed that the dielectric constant decreases with increasing pressure, and the width of the forbidden energy interval increases for electromagnetic wave propagation. Moreover, plasmonic energy and refractive index are changed with increasing pressure.

High pressure phase transformations revisited

Science.gov (United States)

Levitas, Valery I.

2018-04-01

High pressure phase transformations play an important role in the search for new materials and material synthesis, as well as in geophysics. However, they are poorly characterized, and phase transformation pressure and pressure hysteresis vary drastically in experiments of different researchers, with different pressure transmitting media, and with different material suppliers. Here we review the current state, challenges in studying phase transformations under high pressure, and the possible ways in overcoming the challenges. This field is critically compared with fields of phase transformations under normal pressure in steels and shape memory alloys, as well as plastic deformation of materials. The main reason for the above mentioned discrepancy is the lack of understanding that there is a fundamental difference between pressure-induced transformations under hydrostatic conditions, stress-induced transformations under nonhydrostatic conditions below yield, and strain-induced transformations during plastic flow. Each of these types of transformations has different mechanisms and requires a completely different thermodynamic and kinetic description and experimental characterization. In comparison with other fields the following challenges are indicated for high pressure phase transformation: (a) initial and evolving microstructure is not included in characterization of transformations; (b) continuum theory is poorly developed; (c) heterogeneous stress and strain fields in experiments are not determined, which leads to confusing material transformational properties with a system behavior. Some ways to advance the field of high pressure phase transformations are suggested. The key points are: (a) to take into account plastic deformations and microstructure evolution during transformations; (b) to formulate phase transformation criteria and kinetic equations in terms of stress and plastic strain tensors (instead of pressure alone); (c) to develop multiscale continuum

High pressure phase transformations revisited.

Science.gov (United States)

Levitas, Valery I

2018-04-25

High pressure phase transformations play an important role in the search for new materials and material synthesis, as well as in geophysics. However, they are poorly characterized, and phase transformation pressure and pressure hysteresis vary drastically in experiments of different researchers, with different pressure transmitting media, and with different material suppliers. Here we review the current state, challenges in studying phase transformations under high pressure, and the possible ways in overcoming the challenges. This field is critically compared with fields of phase transformations under normal pressure in steels and shape memory alloys, as well as plastic deformation of materials. The main reason for the above mentioned discrepancy is the lack of understanding that there is a fundamental difference between pressure-induced transformations under hydrostatic conditions, stress-induced transformations under nonhydrostatic conditions below yield, and strain-induced transformations during plastic flow. Each of these types of transformations has different mechanisms and requires a completely different thermodynamic and kinetic description and experimental characterization. In comparison with other fields the following challenges are indicated for high pressure phase transformation: (a) initial and evolving microstructure is not included in characterization of transformations; (b) continuum theory is poorly developed; (c) heterogeneous stress and strain fields in experiments are not determined, which leads to confusing material transformational properties with a system behavior. Some ways to advance the field of high pressure phase transformations are suggested. The key points are: (a) to take into account plastic deformations and microstructure evolution during transformations; (b) to formulate phase transformation criteria and kinetic equations in terms of stress and plastic strain tensors (instead of pressure alone); (c) to develop multiscale continuum

High-pressure U3O8 with the fluorite-type structure

International Nuclear Information System (INIS)

Zhang, F.X.; Lang, M.; Wang, J.W.; Li, W.X.; Sun, K.; Prakapenka, V.; Ewing, R.C.

2014-01-01

A new high-pressure phase of U 3 O 8 , which has a fluorite-type structure, forms at pressures greater than ∼8.1 GPa that was confirmed by in situ x-ray diffraction (XRD) measurements. The fluorite-type U 3 O 8 is stable at pressures at least up to ∼40 GPa and temperatures to 1700 K, and quenchable to ambient conditions. Based on the XRD analysis, there is a huge volume collapse (>20%) for U 3 O 8 during the phase transition and the quenched high-pressure phase is 28% denser than the initial orthorhombic phase at ambient conditions. The high-pressure phase has a very low compressibility comparing with the starting orthorhombic phase. - Graphical abstract: α-U 3 O 8 is in a layered structure with orthorhombic symmetry, at high pressures, it transformed to a fluorite-type cubic structure. There are a lot of defects in the cubic structure, and it is a new kind of hyperstoichiometric uranium oxide, which is stable at ambient conditions. - Highlights: • A new fluorite-type high-pressure phase was found in hyperstoichometric UO 2 +x (x∼0.8). • The new high-pressure structure is quenchable to ambient conditions. • Pressure driven phase transition in orthorhombic U 3 O 8 was first found

High-pressure Raman and optical absorption studies on lead pyroniobate (Pb2Nb2O7) and pressure-induced phase transitions

International Nuclear Information System (INIS)

Jayaraman, A.; Kourouklis, G.A.; Cooper, A.S.; Espinosa, G.P.

1990-01-01

High-pressure Raman scattering and optical absorption studies have been carried out on lead pyroniobate (Pb 2 Nb 2 O 7 ) up to 33 GPa, using a gasketed diamond anvil cell. The Raman study reveals the occurrence of two, possibly three, pressure-induced phase changes; a rather subtle change is indicated near 4.5 GPa. The transition near 13 GPa is attributed to a structural transition from the rhombohedral to the cubic pyrochlore structure. The third phase change occurs near 20 GPa. From the broad Raman feature that is observed at about 800 cm -1 , it is concluded that the system turns amorphous at pressures above 20 GPa. The amorphous phase recrystallizes to the original rhombohedral phase, on release of pressure. The broad Raman peaks of the recrystallized phase indicate a high degree of disorder in the material. Lead pyroniobate turns deep red near 30 GPa, from light yellow at ambient pressure. Semi quantitative absorption measurements show that the energy gap shifts red at a rate of 30 meV/GPa. This shift is attributed to the downward motion of the 5d (es) conduction band of Pb

Influence of a hydrostatic pressure on the diffusion in metals having a cubic structure

International Nuclear Information System (INIS)

Beyeler, M.

1969-01-01

In view of obtaining informations on the structure of vacancies. We have determined, by diffusion experiments under high pressure, the activation volumes for self diffusion in different face centered cubic metals: silver, gold, copper, aluminium and in body centered cubic uranium (gamma phase). Activation volumes for noble metals diffusion in aluminium have also been investigated. The experimental results on gold, silver and copper are in good agreement with most of the theoretical models. The estimated activation volume for gamma uranium seems to indicate a vacancy mechanism.The results on aluminium for both self and impurity diffusion agree quite well with Friedel's theoretical predictions [fr

Calculations of and evidence for chain packing stress in inverse lyotropic bicontinuous cubic phases.

Science.gov (United States)

Shearman, Gemma C; Khoo, Bee J; Motherwell, Mary-Lynn; Brakke, Kenneth A; Ces, Oscar; Conn, Charlotte E; Seddon, John M; Templer, Richard H

2007-06-19

Inverse bicontinuous cubic lyotropic phases are a complex solution to the dilemma faced by all self-assembled water-amphiphile systems: how to satisfy the incompatible requirements for uniform interfacial curvature and uniform molecular packing. The solution reached in this case is for the water-amphiphile interfaces to deform hyperbolically onto triply periodic minimal surfaces. We have previously suggested that although the molecular packing in these structures is rather uniform the relative phase behavior of the gyroid, double diamond, and primitive inverse bicontinuous cubic phases can be understood in terms of subtle differences in packing frustration. In this work, we have calculated the packing frustration for these cubics under the constraint that their interfaces have constant mean curvature. We find that the relative packing stress does indeed differ between phases. The gyroid cubic has the least packing stress, and at low water volume fraction, the primitive cubic has the greatest packing stress. However, at very high water volume fraction, the double diamond cubic becomes the structure with the greatest packing stress. We have tested the model in two ways. For a system with a double diamond cubic phase in excess water, the addition of a hydrophobe may release packing frustration and preferentially stabilize the primitive cubic, since this has previously been shown to have lower curvature elastic energy. We have confirmed this prediction by adding the long chain alkane tricosane to 1-monoolein in excess water. The model also predicts that if one were able to hydrate the double diamond cubic to high water volume fractions, one should destabilize the phase with respect to the primitive cubic. We have found that such highly swollen metastable bicontinuous cubic phases can be formed within onion vesicles. Data from monoelaidin in excess water display a well-defined transition, with the primitive cubic appearing above a water volume fraction of 0.75. Both of

High-pressure structural and elastic properties of Tl₂O₃

Energy Technology Data Exchange (ETDEWEB)

Gomis, O., E-mail: osgohi@fis.upv.es; Vilaplana, R. [Centro de Tecnologías Físicas, MALTA Consolider Team, Universitat Politècnica de València, 46022 València (Spain); Santamaría-Pérez, D. [Departamento de Física Aplicada-ICMUV, MALTA Consolider Team, Universidad de Valencia, Edificio de Investigación, C/Dr. Moliner 50, 46100 Burjassot (Spain); Earth Sciences Department, University College London, Gower Street, WC1E 6BT London (United Kingdom); Ruiz-Fuertes, J. [Departamento de Física Aplicada-ICMUV, MALTA Consolider Team, Universidad de Valencia, Edificio de Investigación, C/Dr. Moliner 50, 46100 Burjassot (Spain); Geowissenschaften, Goethe-Universität, Altenhöferallee 1, 60438 Frankfurt am Main (Germany); Sans, J. A.; Manjón, F. J.; Mollar, M. [Instituto de Diseño para la Fabricación y Producción Automatizada, MALTA Consolider Team, Universitat Politècnica de València, 46022 València (Spain); and others

2014-10-07

The structural properties of Thallium (III) oxide (Tl₂O₃) have been studied both experimentally and theoretically under compression at room temperature. X-ray powder diffraction measurements up to 37.7 GPa have been complemented with ab initio total-energy calculations. The equation of state of Tl₂O₃ has been determined and compared to related compounds. It has been found experimentally that Tl₂O₃ remains in its initial cubic bixbyite-type structure up to 22.0 GPa. At this pressure, the onset of amorphization is observed, being the sample fully amorphous at 25.2 GPa. The sample retains the amorphous state after pressure release. To understand the pressure-induced amorphization process, we have studied theoretically the possible high-pressure phases of Tl₂O₃. Although a phase transition is theoretically predicted at 5.8 GPa to the orthorhombic Rh₂O₂-II-type structure and at 24.2 GPa to the orthorhombic α-Gd₂S₃-type structure, neither of these phases were observed experimentally, probably due to the hindrance of the pressure-driven phase transitions at room temperature. The theoretical study of the elastic behavior of the cubic bixbyite-type structure at high-pressure shows that amorphization above 22 GPa at room temperature might be caused by the mechanical instability of the cubic bixbyite-type structure which is theoretically predicted above 23.5 GPa.

High pressure phases of uranium monophosphide studied by synchrotron X-ray diffraction

International Nuclear Information System (INIS)

Staun Olson, J.; Gerward, L.; Benedict, U.; Dabos, S.; Vogt, O.

1988-01-01

X-ray diffraction studies have been performed on UP powder for pressures up to 51 GPa using synchrotron radiation and a diamond anvil cell. At ambient pressure UP has the rocksalt structure. The bulk modulus has been determined to B 0 = 102(4) GPa and its pressure derivative to B 0 ' = 4.0(8). The cubic phase has been found to transform to a new phase, UP II, at about 10 GPa. UP II can be characterized by a rhombohedral Bravais lattice. UP II transforms to an orthorhombic phase, UP III, at 28 GPa. No volume change has been observed at the two transitions. The influence of the 5f electrons on the transformations is discussed. (orig.)

Thermal expansivity and bulk modulus of ZnO with NaCl-type cubic structure at high pressures and temperatures

International Nuclear Information System (INIS)

Sun Xiaowei; Liu Zijiang; Chen Qifeng; Chu Yandong; Wang Chengwei

2006-01-01

The thermal expansivity and bulk modulus of ZnO with NaCl-type cubic structure were estimated by using the constant temperature and pressure molecular dynamics technique with effective pair potentials which consist of the Coulomb, dispersion, and repulsion interaction at high pressures and temperatures. It is shown that the calculated thermodynamic parameters including linear thermal expansion coefficient, isothermal bulk modulus and its pressure derivative are in good agreement with the available experimental data and the latest theoretical results. At an extended pressure and temperature ranges, linear thermal expansion coefficient and isothermal bulk modus have also been predicted. The thermodynamic properties of ZnO with NaCl-type cubic structure are summarized in the pressure 0-150 GPa ranges and the temperature up to 3000 K

The effects of Na on high pressure phases of CuIn0.5Ga0.5Se2 from ab initio calculation

International Nuclear Information System (INIS)

Pluengphon, P; Bovornratanaraks, T; Pinsook, U; Vannarat, S

2012-01-01

The effects of Na atoms on high pressure structural phase transitions of CuIn 0.5 Ga 0.5 Se 2 (CIGS) were studied by an ab initio method using density functional theory. At ambient pressure, CIGS is known to have chalcopyrite (I 4-bar 2 d) structure. The high pressure phase transitions of CIGS were proposed to be the same as the order in the CuInSe 2 phase transitions which are I 4-bar 2 d→F m 3-bar m→C m c m structures. By using the mixture atoms method, the Na concentration in CIGS was studied at 0.1, 1.0 and 6.25%. The positive mixing enthalpy of Na at In/Ga sites (Na InGa ) is higher than that of Na at Cu sites (Na Cu ). It confirmed previous studies that Na preferably substitutes on the Cu sites more than the (In, Ga) sites. From the energy-volume curves, we found that the effect of the Na substitutes is to reduce the hardness of CIGS under high pressure. The most significant effects occur at 6.25% Na. We also found that the electronic density of states of CIGS near the valence band maximum is increased noticeably in the chalcopyrite phase. The band gap is close in the cubic and orthorhombic phases. Also, the Na Cu -Se bond length in the chalcopyrite phase is significantly reduced at 6.25% Na, compared with the pure Cu-Se bond length. Consequently, the energy band gap in this phase is wider than in pure CIGS, and the gap increased at the rate of 31 meV GPa -1 under pressure. The Na has a small effect on the transition pressure. The path of transformation from the cubic to orthorhombic phase was derived. The Cu-Se plane in the cubic phase displaced relatively parallel to the (In, Ga)-Se plane by 18% in order to transform to the Cmcm phase. The enthalpy barrier is 0.020 eV/atom, which is equivalent to a thermal energy of 248 K. We predicted that F m 3-bar m and Cmcm can coexist in some pressure range. (paper)

Phase transformations in chalkogenides of germanium subgroup elements and in alloys on their base at high pressures

International Nuclear Information System (INIS)

Skums, V.F.; Skoropanov, A.S.; Vecher, A.A.

1990-01-01

An attempt was made to systematize and analyze the available data on behaviour of chalkogenides of germanium subgroup elements and their alloys at high pressures, as applied to the problem of their use as reference materials for pressure determination. It is shown that phase transformations, accompanied by sharp change of electric resistance, are observed in chalkogenides of cubic and rhombohedral structures (lead, tin (SnTe) and germanium (GeTe)) under the effect of high pressures. It was established that electric resistance in the region of phase transformation (electric signal) depended on the type and concentration of current carriers: electric sigual grew with decrease of current carrier concentration; substances with p-type of conductivity were characterized by lower electric signal, as compared to substances with n-conductivety

Implementation of perturbed-chain statistical associating fluid theory (PC-SAFT), generalized (G)SAFT+cubic, and cubic-plus-association (CPA) for modeling thermophysical properties of selected 1-alkyl-3-methylimidazolium ionic liquids in a wide pressure range.

Science.gov (United States)

Polishuk, Ilya

2013-03-14

This study is the first comparative investigation of predicting the isochoric and the isobaric heat capacities, the isothermal and the isentropic compressibilities, the isobaric thermal expansibilities, the thermal pressure coefficients, and the sound velocities of ionic liquids by statistical associating fluid theory (SAFT) equation of state (EoS) models and cubic-plus-association (CPA). It is demonstrated that, taking into account the high uncertainty of the literature data (excluding sound velocities), the generalized for heavy compounds version of SAFT+Cubic (GSAFT+Cubic) appears as a robust estimator of the auxiliary thermodynamic properties under consideration. In the case of the ionic liquids the performance of PC-SAFT seems to be less accurate in comparison to ordinary compounds. In particular, PC-SAFT substantially overestimates heat capacities and underestimates the temperature and pressure dependencies of sound velocities and compressibilities. An undesired phenomenon of predicting high fictitious critical temperatures of ionic liquids by PC-SAFT should be noticed as well. CPA is the less accurate estimator of the liquid phase properties, but it is advantageous in modeling vapor pressures and vaporization enthalpies of ionic liquids. At the same time, the preliminary results indicate that the inaccuracies in predicting the deep vacuum vapor pressures of ionic liquids do not influence modeling of phase equilibria in their mixtures at much higher pressures.

Unusually large unit cell of lipid bicontinuous cubic phase: towards nature's length scales

Science.gov (United States)

Kim, Hojun; Leal, Cecilia

Lipid bicontinuous cubic phases are of great interest for drug delivery, protein crystallization, biosensing, and templates for directing hard material assembly. Structural modulations of lipid mesophases regarding phase identity and unit cell size are often necessary to augment loading and gain pore size control. One important example is the need for unit cells large enough to guide the crystallization of bigger proteins without distortion of the templating phase. In nature, bicontinuous cubic constructs achieve unit cell dimensions as high as 300 nm. However, the largest unit cell of lipid mesophases synthesized in the lab is an order of magnitude lower. In fact, it has been predicted theoretically that lipid bicontinuous cubic phases of unit cell dimensions exceeding 30 nm could not exist, as high membrane fluctuations would damp liquid crystalline order. Here we report non-equilibrium assembly methods of synthesizing metastable bicontinuous cubic phases with unit cell dimensions as high as 70 nm. The phases are stable for very long periods and become increasingly ordered as time goes by without changes to unit cell dimensions. We acknowledge the funding source as a NIH.

Crystalline and amorphous phases in carbon nitride films produced by intense high-pressure plasma

International Nuclear Information System (INIS)

Gurarie, V.N.; Orlov, A.V.; Bursill, L.A.; JuLin, P.; Nugent, K.W.; Chon, J.W.; Prawer, S.

1997-01-01

Carbon-nitride films are prepared using a high-intensity pulsed plasma deposition technique. A wide range of nitrogen pressure and discharge intensity are used to investigate their effect on the morphology, nitrogen content, structure, bonding, phase composition and mechanical characteristics of the CN films deposited. Increasing the nitrogen pressure from 0.1 atm to 10 atm results in an increase of nitrogen incorporation into CN films to maximum of 45 at %. Under the high-energy density deposition conditions which involve ablation of the quartz substrate the CN films are found to incorporate in excess of 60 at %N. Raman spectra of these films contain sharp peaks characteristic of a distinct crystalline CN phase. TEM diffraction patterns for the films deposited below 1 atm unambiguously show the presence of micron-sized crystals displaying a cubic symmetry. (authors)

XPS analysis for cubic boron nitride crystal synthesized under high pressure and high temperature using Li3N as catalysis

International Nuclear Information System (INIS)

Guo, Xiaofei; Xu, Bin; Zhang, Wen; Cai, Zhichao; Wen, Zhenxing

2014-01-01

Highlights: • The cBN was synthesized by Li 3 N as catalyst under high pressure and high temperature (HPHT). • The film coated on the as-grown cBN crystals was studied by XPS. • The electronic structure variation in the film was investigated. • The growth mechanism of cubic boron nitride crystal was analyzed briefly. - Abstract: Cubic boron nitride (cBN) single crystals are synthesized with lithium nitride (Li3N) as catalyst under high pressure and high temperature. The variation of electronic structures from boron nitride of different layers in coating film on the cBN single crystal has been investigated by X-ray photoelectron spectroscopy. Combining the atomic concentration analysis, it was shown that from the film/cBN crystal interface to the inner, the sp 2 fractions are decreasing, and the sp 3 fractions are increasing in the film at the same time. Moreover, by transmission electron microscopy, a lot of cBN microparticles are found in the interface. For there is no Li 3 N in the film, it is possible that Li 3 N first reacts with hexagonal boron nitride to produce Li 3 BN 2 during cBN crystals synthesis under high pressure and high temperature (HPHT). Boron and nitrogen atoms, required for cBN crystals growth, could come from the direct conversion from hexagonal boron nitride with the catalysis of Li 3 BN 2 under high pressure and high temperature, but not directly from the decomposition of Li 3 BN 2

High pressure synthesis of a hexagonal close-packed phase of the high-entropy alloy CrMnFeCoNi

Energy Technology Data Exchange (ETDEWEB)

Tracy, Cameron L.; Park, Sulgiye; Rittman, Dylan R.; Zinkle, Steven J.; Bei, Hongbin; Lang, Maik; Ewing, Rodney C.; Mao, Wendy L.

2017-05-25

High-entropy alloys, near-equiatomic solid solutions of five or more elements, represent a new strategy for the design of materials with properties superior to those of conventional alloys. However, their phase space remains constrained, with transition metal high-entropy alloys exhibiting only face- or body-centered cubic structures. Here, we report the high-pressure synthesis of a hexagonal close-packed phase of the prototypical high-entropy alloy CrMnFeCoNi. This martensitic transformation begins at 14 GPa and is attributed to suppression of the local magnetic moments, destabilizing the initial fcc structure. Similar to fcc-to-hcp transformations in Al and the noble gases, the transformation is sluggish, occurring over a range of >40 GPa. However, the behaviour of CrMnFeCoNi is unique in that the hcp phase is retained following decompression to ambient pressure, yielding metastable fcc-hcp mixtures. This demonstrates a means of tuning the structures and properties of high-entropy alloys in a manner not achievable by conventional processing techniques.

Electrostatic Effects in Phase Transitions of Biomembranes between Cubic Phases and Lamellar Liquid-Crystalline (Lα) phase

Science.gov (United States)

Masum, Shah Md.; Li, Shu Jie; Tamba, Yukihiro; Yamashita, Yuko; Yamazaki, Masahito

2004-04-01

Elucidation of the mechanisms of transitions between cubic phase and liquid-crystalline (Lα) phase, and between different IPMS cubic phases, are essential for understanding of dynamics of biomembranes and topological transformation of lipid membranes. Recently, we found that electrostatic interactions due to surface charges of lipid membranes induce transition between cubic phase and Lα phase, and between different IPMS cubic phases. As electrostatic interactions increase, the most stable phase of a monoolein (MO) membrane changes: Q224 ⇒ Q229 ⇒ Lα. We also found that a de novo designed peptide partitioning into electrically neutral lipid membrane changed the phase stability of the MO membranes. As peptide-1 concentration increased, the most stable phase of a MO membrane changes: Q224 ⇒ Q229 ⇒Lα. In both cases, the increase in the electrostatic repulsive interaction greatly reduced the absolute value of spontaneous curvature of the MO monolayer membrane. We also investigated factors such as poly (L-lysine) and osmotic stress to control structure and phase stability of DOPA/MO membranes. Based on these results, we discuss the mechanism of the effect of electrostatic interactions on the stability of cubic phase.

Non-spherical micelles in an oil-in-water cubic phase

DEFF Research Database (Denmark)

Leaver, M.; Rajagopalan, V.; Ulf, O.

2000-01-01

phase, both with and without SDS, was established by NMR self-diffusion. In addition H-2 NMR relaxation experiments have demonstrated that the micelles in the cubic phase are non-spherical, having grown and changed shape upon formation of the cubic phase from the micellar solution. Small angle...... associated with the micellar cubic phase, Pm3n and Fd3m. The micellar volumes calculated for these space groups are similar and are consistent with a change in micellar geometry from spherical to prolate.......The cubic phase formed between the microemulsion and hexagonal phases of the ternary pentaethylene glycol dodecyl ether (C12E5)-decane-water system and that doped with small amounts of sodium dodecylsulfate (SDS) have been investigated. The presence of discrete oil-swollen micelles in the cubic...

Effects of High Pressure on Internally Self-Assembled Lipid Nanoparticles

DEFF Research Database (Denmark)

Kulkarni, Chandrashekhar V; Yaghmur, Anan; Steinhart, Milos

2016-01-01

We present the first report on the effects of hydrostatic pressure on colloidally stabilized lipid nanoparticles enveloping inverse nonlamellar self-assemblies in their interiors. These internal self-assemblies were systematically tuned into bicontinuous cubic (Pn3m and Im3m), micellar cubic (Fd3...... the tolerance of lipid nanoparticles [cubosomes, hexosomes, micellar cubosomes, and emulsified microemulsions (EMEs)] for high pressures, confirming their robustness for various technological applications.......We present the first report on the effects of hydrostatic pressure on colloidally stabilized lipid nanoparticles enveloping inverse nonlamellar self-assemblies in their interiors. These internal self-assemblies were systematically tuned into bicontinuous cubic (Pn3m and Im3m), micellar cubic (Fd3m......), hexagonal (H2), and inverse micellar (L2) phases by regulating the lipid/oil ratio as the hydrostatic pressure was varied from atmospheric pressure to 1200 bar and back to atmospheric pressure. The effects of pressure on these lipid nanoparticles were compared with those on their equilibrium bulk...

Mixing and phase separation at supercritical and transcritical pressures

NARCIS (Netherlands)

Hickel, S.; Matheis, Jan

2017-01-01

We have developed a thermodynamically consistent and tuning-parameter-free two-phase model for Eulerian large-eddy simulations (LES) of liquid-fuel injection and mixing at high pressure. The model is based on cubic equations of state and vaporliquid equilibrium calculations. It can represent the

Application of the cubic-plus-association equation of state to mixtures with polar chemicals and high pressures

DEFF Research Database (Denmark)

Folas, Georgios; Kontogeorgis, Georgios; Michelsen, Michael Locht

2006-01-01

was given to low pressures and liquid-liquid equilibria. In this work, CPA is applied to two classes of mixtures containing polar chemicals for which high-pressure data are available: acetone-containing systems and dimethyl ether mixtures. They are of both scientific and industrial importance. Moreover, CPA......The cubic-plus-association (CPA) equation of state has been previously applied to vapor-liquid, liquid-liquid, and solid-liquid equilibria of mixtures containing associating compounds (water, alcohols, glycols, acids, amines). Although some high-pressure applications have been presented, emphasis...... to conventional models such as MHV2. Very good results are also obtained for multicomponent vapor-liquid-liquid equilibria for mixtures containing gases, water, and dimethyl ether. Finally, it is shown that high-pressure SLE can be predicted based on interaction parameters obtained from low-pressure SLE data....

High-pressure phase transitions of strontianite

Science.gov (United States)

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.

Observation of a New High-Pressure Solid Phase in Dynamically Compressed Aluminum

Science.gov (United States)

Polsin, D. N.

2017-10-01

Aluminum is ideal for testing theoretical first-principles calculations because of the relative simplicity of its atomic structure. Density functional theory (DFT) calculations predict that Al transforms from an ambient-pressure, face-centered-cubic (fcc) crystal to the hexagonal close-packed (hcp) and body-centered-cubic (bcc) structures as it is compressed. Laser-driven experiments performed at the University of Rochester's Laboratory for Laser Energetics and the National Ignition Facility (NIF) ramp compressed Al samples to pressures up to 540 GPa without melting. Nanosecond in-situ x-ray diffraction was used to directly measure the crystal structure at pressures where the solid-solid phase transformations of Al are predicted to occur. Laser velocimetry provided the pressure in the Al. Our results show clear evidence of the fcc-hcp and hpc-bcc transformations at 216 +/- 9 GPa and 321 +/- 12 GPa, respectively. This is the first experimental in-situ observation of the bcc phase in compressed Al and a confirmation of the fcc-hcp transition previously observed under static compression at 217 GPa. The observations indicate these solid-solid phase transitions occur on the order of tens of nanoseconds time scales. In the fcc-hcp transition we find the original texture of the sample is preserved; however, the hcp-bcc transition diminishes that texture producing a structure that is more polycrystalline. The importance of this dynamic is discussed. The NIF results are the first demonstration of x-ray diffraction measurements at two different pressures in a single laser shot. This material is based upon work supported by the Department of Energy National Nuclear Security Administration under Award Number DE-NA0001944.

Pressure-induced structural phase transformation and superconducting properties of titanium mononitride

Science.gov (United States)

Li, Qian; Guo, Yanan; Zhang, Miao; Ge, Xinlei

2018-03-01

In this work, we have systematically performed the first-principles structure search on titanium mononitride (TiN) within Crystal Structure AnaLYsis by Particle Swarm Optimization (CALYPSO) methodology at high pressures. Here, we have confirmed a phase transition from cubic rock-salt (fcc) phase to CsCl (bcc) phase of TiN at ∼348 GPa. Further simulations reveal that the bcc phase is dynamically stable, and could be synthesized experimentally in principle. The calculated elastic anisotropy decreases with the phase transformation from fcc to bcc structure under high pressures, and the material changes from ductile to brittle simultaneously. Moreover, we found that both structures are superconductive with the superconducting critical temperature of 2-12 K.

Pressure-induced phase transformation in ZrW2O8 - Compressibility and thermal expansion of the orthorhombic phase

International Nuclear Information System (INIS)

Hu, Z.; Jorgensen, J.D.; Teslic, S.; Short, S.; Argyriou, D.N.

1997-01-01

In situ neutron powder diffraction has been used to show that the application of hydrostatic pressure at room temperature produces a transformation of ZrW 2 O 8 from the cubic to an orthorhombic phase beginning at 2.1 kbar and completed by 3.1 kbar, with a 5% reduction in volume. After release of pressure, the orthorhombic phase is retained at room temperature. Its thermal expansion is negative below room temperature, but is positive above room temperature with a transformation back to the cubic phase at about 390 K. The WO 4 groups are found to play the dominant role in both phase transformations. The volume compressibilities of the cubic and orthorhombic phases are 1.38 x 10 -3 and 1.53 x 10 -3 kbar -1 , respectively. (orig.)

High pressure structural studies on nanophase praseodymium oxide

International Nuclear Information System (INIS)

Saranya, L.; Chandra Shekar, N.V.; Amirthapandian, S.; Hussain, Shamima; Arulraj, A.; Sahu, P. Ch.

2014-01-01

The phase stability of nanocrystalline Pr 2 O 3 has been investigated under pressure by in-situ high pressure X-ray diffraction using Mao-Bell type diamond anvil cell. The ambient structure and phase of the praseodymium oxide have been resolved unambiguously using x-ray diffraction, SEM and TEM techniques. Under the action of pressure the cubic phase of the system is retained up to 15 GPa. This is unusual as other isostructural rare earth oxides show structural transformations even at lower pressures. From the best fit to the P–V data with the Murnaghan equation of state yields a bulk modulus of 171 GPa

High pressure structural studies on nanophase praseodymium oxide

Energy Technology Data Exchange (ETDEWEB)

Saranya, L. [Jamal Mohamed College, Tiruchirapalli 620020, Tamil Nadu (India); Chandra Shekar, N.V., E-mail: chandru@igcar.gov.in [Condensed Matter Physics Division, Materials Science Group, Indira Gandhi Centre for Atomic Research, Kalpakkam 603102, Tamil Nadu (India); Amirthapandian, S. [Materials Physics Division, Materials Science Group, Indira Gandhi Centre for Atomic Research, Kalpakkam 603102, Tamil Nadu (India); Hussain, Shamima [UGC-DAE-CSR node, Kokilamedu 603103, Tamil Nadu (India); Arulraj, A.; Sahu, P. Ch. [Condensed Matter Physics Division, Materials Science Group, Indira Gandhi Centre for Atomic Research, Kalpakkam 603102, Tamil Nadu (India)

2014-09-15

The phase stability of nanocrystalline Pr{sub 2}O{sub 3} has been investigated under pressure by in-situ high pressure X-ray diffraction using Mao-Bell type diamond anvil cell. The ambient structure and phase of the praseodymium oxide have been resolved unambiguously using x-ray diffraction, SEM and TEM techniques. Under the action of pressure the cubic phase of the system is retained up to 15 GPa. This is unusual as other isostructural rare earth oxides show structural transformations even at lower pressures. From the best fit to the P–V data with the Murnaghan equation of state yields a bulk modulus of 171 GPa.

Hardness and thermal stability of cubic silicon nitride

DEFF Research Database (Denmark)

Jiang, Jianzhong; Kragh, Flemming; Frost, D. J.

2001-01-01

The hardness and thermal stability of cubic spinel silicon nitride (c-Si3N4), synthesized under high-pressure and high-temperature conditions, have been studied by microindentation measurements, and x-ray powder diffraction and scanning electron microscopy, respectively The phase at ambient...

On the mechanical stability of the body-centered cubic phase and the emergence of a metastable cI16 phase in classical hard sphere solids

Science.gov (United States)

Warshavsky, Vadim B.; Ford, David M.; Monson, Peter A.

2018-01-01

The stability of the body-centered cubic (bcc) solid phase of classical hard spheres is of intrinsic interest and is also relevant to the development of perturbation theories for bcc solids of other model systems. Using canonical ensemble Monte Carlo, we simulated systems initialized in a perfect bcc lattice at various densities in the solid region. We observed that the systems rapidly evolved into one of four structures that then persisted for the duration of the simulation. Remarkably, one of these structures was identified as cI16, a cubic crystalline structure with 16 particles in the unit cell, which has recently been observed experimentally in lithium and sodium solids at high pressures. The other three structures do not exhibit crystalline order but are characterized by common patterns in the radial distribution function and bond-orientational order parameter distribution; we refer to them as bcc-di, with i ranging from 1 to 3. We found similar outcomes when employing any of the three single occupancy cell (SOC) restrictions commonly used in the literature. We also ran long constant-pressure simulations with box shape fluctuations initiated from bcc and cI16 initial configurations. At lower pressures, all the systems evolved to defective face-centered cubic (fcc) or hexagonal close-packed (hcp) structures. At higher pressures, most of the systems initiated as bcc evolved to cI16 with some evolving to defective fcc/hcp. High pressure systems initiated from cI16 remained in that structure. We computed the chemical potential of cI16 using the Einstein crystal reference method and found that it is higher than that of fcc by ˜0.5kT-2.5kT over the pressure range studied, with the difference increasing with pressure. We find that the undistorted bcc solid, even with constant-volume and SOC restrictions applied, is so mechanically unstable that it is unsuitable for consideration as a metastable phase or as a reference system for studying bcc phases of other systems

Interaction of dispersed cubic phases with blood components

DEFF Research Database (Denmark)

Bode, J C; Kuntsche, Judith; Funari, S S

2013-01-01

The interaction of aqueous nanoparticle dispersions, e.g. based on monoolein/poloxamer 407, with blood components is an important topic concerning especially the parenteral way of administration. Therefore, the influence of human and porcine plasma on dispersed cubic phases was investigated. Part...... activity of cubic phases based on monoolein and poloxamer 188, on soy phosphatidylcholine, glycerol dioleate and polysorbate 80 or the parenteral fat emulsion Lipofundin MCT 20%....

Pressure and high-Tc superconductivity in sulfur hydrides.

Science.gov (United States)

Gor'kov, Lev P; Kresin, Vladimir Z

2016-05-11

The paper discusses fundamentals of record-TC superconductivity discovered under high pressure in sulfur hydride. The rapid increase of TC with pressure in the vicinity of Pcr ≈ 123GPa is interpreted as the fingerprint of a first-order structural transition. Based on the cubic symmetry of the high-TC phase, it is argued that the lower-TC phase has a different periodicity, possibly related to an instability with a commensurate structural vector. In addition to the acoustic branches, the phonon spectrum of H3S contains hydrogen modes with much higher frequencies. Because of the complex spectrum, usual methods of calculating TC are here inapplicable. A modified approach is formulated and shown to provide realistic values for TC and to determine the relative contributions of optical and acoustic branches. The isotope effect (change of TC upon Deuterium for Hydrogen substitution) originates from high frequency phonons and differs in the two phases. The decrease of TC following its maximum in the high-TC phase is a sign of intermixing with pairing at hole-like pockets which arise in the energy spectrum of the cubic phase at the structural transition. On-pockets pairing leads to the appearance of a second gap and is remarkable for its non-adiabatic regime: hydrogen mode frequencies are comparable to the Fermi energy.

Spectra and energy levels of Eu{sup 3+} in cubic phase Gd{sub 2}O{sub 3}

Energy Technology Data Exchange (ETDEWEB)

Smith, Eric R. [Kratos Defense and Security Solutions, Inc., 5030 Bradford Dr., Huntsville, AL 35805 (United States); Gruber, John B. [Department of Physics and Astronomy, University of Texas at San Antonio, San Antonio, TX 78249-0697 (United States); Wellenius, Patrick; Muth, John F. [Department of Electrical and Computer Engineering, NC State University, Raleigh, NC 27606 (United States); Everitt, Henry O. [Department of Physics, Duke University, Durham, NC 27708 (United States); Army Aviation and Missile RD and E Center, Redstone Arsenal, AL 35898 (United States)

2010-07-15

In pulsed laser deposition of the sesquioxide semiconductor Gd{sub 2}O{sub 3}, adjusting the chamber oxygen pressure controls the crystalline structure of the host. This technique was used to deposit thin films of nominally 1.6% by weight europium-doped, cubic phase Gd{sub 2}O{sub 3} using 50 mTorr of oxygen. Structural measurements using high-resolution transmission electron microscopy and selected area electron diffraction confirm the films were polycrystalline, cubic phase Eu:Gd{sub 2}O{sub 3}. The spectroscopic assignment of emission lines to specific radiative transitions within the trivalent Eu ion is confirmed by theoretical analysis of the appropriate crystal field Hamiltonian. Detailed crystal-field splittings are presented for the {sup 5}D{sub J=0-2} and {sup 7}F{sub J=0-5} multiplet manifolds of Eu{sup 3+} in this host material. (Abstract Copyright [2010], Wiley Periodicals, Inc.)

Microstructure and spectroscopy studies on cubic boron nitride synthesized under high-pressure conditions

International Nuclear Information System (INIS)

Nistor, L C; Nistor, S V; Dinca, G; Georgeoni, P; Landuyt, J van; Manfredotti, C; Vittone, E

2002-01-01

High-resolution electron microscopy (HREM) studies of the microstructure and specific defects in hexagonal boron nitride (h-BN) precursors and cubic boron nitride (c-BN) crystals made under high-pressure high-temperature conditions revealed the presence of half-nanotubes at the edges of the h-BN particles. Their sp 3 bonding tendency could strongly influence the nucleation rates of c-BN. The atomic resolution at extended dislocations was insufficient to allow us to determine the stacking fault energy in the c-BN crystals. Its mean value of 191 pm, 15 mJ m -2 is of the same order of magnitude as that of diamond. High-frequency (94 GHz) electron paramagnetic resonance studies on c-BN single crystals have produced new data on the D1 centres associated with the boron species. Ion-beam-induced luminescence measurements have indicated that c-BN is a very interesting luminescent material, which is characterized by four luminescence bands and exhibits a better resistance to ionizing radiation than CVD diamond

Path Dependency of High Pressure Phase Transformations

Science.gov (United States)

Cerreta, Ellen

2017-06-01

At high pressures titanium and zirconium are known to undergo a phase transformation from the hexagonal close packed (HCP), alpha-phase to the simple-hexagonal, omega-phase. Under conditions of shock loading, the high-pressure omega-phase can be retained upon release. It has been shown that temperature, peak shock stress, and texture can influence the transformation. Moreover, under these same loading conditions, plastic processes of slip and twinning are also affected by similar differences in the loading path. To understand this path dependency, in-situ velocimetry measurements along with post-mortem metallographic and neutron diffraction characterization of soft recovered specimens have been utilized to qualitatively understand the kinetics of transformation, quantify volume fraction of retained omega-phase and characterize the shocked alpha and omega-phases. Together the work described here can be utilized to map the non-equilibrium phase diagram for these metals and lend insight into the partitioning of plastic processes between phases during high pressure transformation. In collaboration with: Frank Addesssio, Curt Bronkhorst, Donald Brown, David Jones, Turab Lookman, Benjamin Morrow, Carl Trujillo, Los Alamos National Lab.; Juan Pablo Escobedo-Diaz, University of New South Wales; Paulo Rigg, Washington State University.

Effect of electrostatic interactions on phase stability of cubic phases of biomembranes.

Science.gov (United States)

Li, Shu Jie; Masum, Shah Md; Yamashita, Yuko; Tamba, Yukihiro; Yamazaki, Masahito

2002-06-01

We investigated effect of electrostatic interactions due to surfacecharges on structures and stability of cubic phases of monoolein (MO)membrane using the small-angle X-ray scattering method. Firstly, wechanged the surface charge density of the membrane by usingdioleoylphosphatidic acid (DOPA). As increasing DOPA concentration in themembrane at 30 wt % lipid concentration, a Q(224) to Q(229) phasetransition occurred at 0.6 mol % DOPA, and at and above 25 mol %, DOPA/MOmembranes were in the L(α) phase. NaCl in the bulk phase reduced theeffect of DOPA. These results indicate that as the electrostaticinteractions increase, the most stable phase changes as follows: Q(224)⇒ Q(229) ⇒ L(α). The increase in DOPAconcentration reduced the absolute value of spontaneous curvature of themembrane, | H(0) |. Secondly, we changed the surface charge of themembrane by adding a de novo designed peptide, which has netpositive charges and a binding site on the electrically neutral membraneinterface. The peptide-1 (WLFLLKKK) induced a Q(224) to Q(229)phase transition in the MO membrane at low peptide concentration. As NaClconcentration increases, the MO/peptide-1 membrane changed from Q(229)to Q(224) phase. The increase in peptide-1 concentration reduced |H(0) |. Based on these results, the stability of the cubic phases and themechanism of phase transition between cubic phase and L(α) phase arediscussed.

Chamber with punches made from polycrystal cubic boron nitrides for Moessbauer study at high hydrostatic pressure

International Nuclear Information System (INIS)

Kapitanov, E.V.; Yakovlev, E.N.

1978-01-01

The design of a high hydrostatic pressure chamber with polycrystallic boron nitride dies weakly absorbing gamma radiation with energies of more than 14 keV is described. The use of this material permits to investigate single- and polycrystal bodies using the Moessbauer effect when the geometry of the experiment remains unchanged and the hydrostatic pressure is up to 70 kbar. The basic units of the chamber are a teflon capsule placed in a container made of a pressed boron and epoxide resin mixture, electric inputs and a die of polycrystal cubic boron nitride. The pressure is transferred to the sample tested through a liquid (petrol or the 4 to 1 mixture of methanole and ethanole) which does not become solid at a pressure below 37 kbar. Basic dimensions of the chamber are given and the dependence of the pressure in the capsule on the force applied to the chamber is also presented

Superconducting and Structural Transitions in the β-Pyrochlore Oxide KOs2O6 under High Pressure

Science.gov (United States)

Ogusu, Hiroki; Takeshita, Nao; Izawa, Koichi; Yamaura, Jun-ichi; Ohishi, Yasuo; Tsutsui, Satoshi; Okamoto, Yoshihiko; Hiroi, Zenji

2010-11-01

Rattling-induced superconductivity in the β-pyrochlore oxide KOs2O6 is investigated under high pressure up to 5 GPa. Resistivity measurements in a high-quality single crystal reveal a gradual decrease in the superconducting transition temperature Tc from 9.7 K at 1.0 GPa to 6.5 K at 3.5 GPa, followed by a sudden drop to 3.3 K at 3.6 GPa. Powder X-ray diffraction experiments show a structural transition from cubic to monoclinic or triclinic at a similar pressure. The sudden drop in Tc is ascribed to this structural transition, by which an enhancement in Tc due to a strong electron-rattler interaction present in the low-pressure cubic phase is abrogated as the rattling of the K ion is completely suppressed or weakened in the high-pressure phase of reduced symmetry. In addition, we find two anomalies in the temperature dependence of resistivity in the low-pressure phase, which may be due to subtle changes in rattling vibration.

Low-pH-induced transformation of bilayer membrane into bicontinuous cubic phase in dioleoylphosphatidylserine/monoolein membranes.

Science.gov (United States)

Okamoto, Yoshihide; Masum, Shah Md; Miyazawa, Haruna; Yamazaki, Masahito

2008-04-01

Cubic biomembranes, nonbilayer membranes with connections in three-dimensional space that have a cubic symmetry, have been observed in various cells. Interconversion between the bilayer liquid-crystalline (L(alpha)) phase and cubic phases attracted much attention in terms of both biological and physicochemical aspects. Herein we report the pH effect on the phase and structure of dioleoylphosphatidylserine (DOPS)/monoolein (MO) membranes under a physiological ion concentration condition, which was revealed by small-angle X-ray scattering (SAXS) measurement. At neutral pH, DOPS/MO membranes containing high concentrations of DOPS were in the L(alpha) phase. First, the pH effect on the phase and structure of the multilamellar vesicles (MLVs) of the DOPS/MO membranes preformed at neutral pH was investigated by adding various low-pH buffers into the MLV suspension. For 20%-DOPS/80%-MO MLVs, at and below pH 2.9, a transition from the L(alpha) to cubic (Q(224)) phase occurred within 1 h. This phase transition was reversible; a subsequent increase in pH to a neutral one in the membrane suspension transformed the cubic phase into the original L(alpha) phase. Second, we found that a decrease in pH transformed large unilamellar vesicles of DOPS/MO membranes into the cubic phase under similar conditions. We have proposed the mechanism of the low-pH-induced phase transition and also made a quantitative analysis on the critical pH of the phase transition. This finding is the first demonstration that a change in pH can induce a reversible phase transition between the L(alpha) and cubic phases of lipid membranes within 1 h.

Correlation of phase equilibria for water + hydrocarbon systems at high temperatures and pressures by cubic equation of state

Energy Technology Data Exchange (ETDEWEB)

Haruki, Masashi; Yahiro, Yukihito; Higashi, Hidenori; Iwai, Yoshio; Arai, Yasuhiko [Kyushu University, FUkuoka (Japan). Graduate School of Engineering

1999-08-01

A modified-Soave-Redlich-Kwong (MSRK) equation of state with an exponent-type mixing rule for the energy parameter and a conventional rule for the size parameter is applied to correlate the phase equilibria for four binary mixtures of water + hydrocarbon (benzene, hexane, decane, and dodecane) systems at high temperatures and pressures. It is noted that good correlation results are obtained by using the mixing rules with interaction parameters between unlike molecules. (author)

High pressure structural phase transitions of TiO2 nanomaterials

International Nuclear Information System (INIS)

Li Quan-Jun; Liu Bing-Bing

2016-01-01

Recently, the high pressure study on the TiO 2 nanomaterials has attracted considerable attention due to the typical crystal structure and the fascinating properties of TiO 2 with nanoscale sizes. In this paper, we briefly review the recent progress in the high pressure phase transitions of TiO 2 nanomaterials. We discuss the size effects and morphology effects on the high pressure phase transitions of TiO 2 nanomaterials with different particle sizes, morphologies, and microstructures. Several typical pressure-induced structural phase transitions in TiO 2 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 TiO 2 -B nanoribbons. Various TiO 2 nanostructural materials with high pressure structures are prepared successfully by high pressure treatment of the corresponding crystal nanomaterials, such as amorphous TiO 2 nanoribbons, α -PbO 2 -type TiO 2 nanowires, nanosheets, and nanoporous materials. These studies suggest that the high pressure phase transitions of TiO 2 nanomaterials depend on the nanosize, morphology, interface energy, and microstructure. The diversity of high pressure behaviors of TiO 2 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. (topical review)

High-pressure phase transitions of deep earth materials

International Nuclear Information System (INIS)

Hirose, Kei

2009-01-01

Recent developments in synchrotron XRD measurements combined with laser-heated diamond-anvil cell (LHDAC) techniques have enabled us to search for a novel phase transition at extremely high pressure and temperature. A phase transition from MgSiO 3 perovskite to post-perovskite was discovered through a drastic change in XRD patterns above 120 GPa and 2500 K, corresponding to the condition in the lowermost mantle (Murakami et al., 2004; Oganov and Ono, 2004). A pressure-induced phase transformation from ABO 3 -type perovskite to any denser structures was not known at that time. This new MgSiO 3 polymorph called post-perovskite has an orthorhombic symmetry (space group: Cmcm) with a sheet-stacking structure. The Mg site in post-perovskite is smaller than that in perovskite, which results in a volume reduction by 1.0-1.5% from perovskite structure. The electrical conductivity of post-perovskite is higher by three orders of magnitude than that of perovskite at similar pressure range (Ohta et al., 2008). This is likely due to a shorter Fe-Fe distance in post-perovskite structure, while conduction mechanism is yet to be further examined. Phase transition boundary between perovskite and post-perovskite has been determined in a wide temperature range up to 4400 K at 170 GPa (Tateno et al., 2008). Phase relations of Fe alloys have been also studied at core pressures (>135 GPa), although the generation of high temperature is more difficult at higher pressures. A new high-pressure B2 phase of B2 phase of FeS was recently discovered above 180 GPa (Sata et al., 2008). The Fe-Ni alloys have a wide pressure-temperature stability field of fcc phase at the core pressure range, depending on the Ni content (Kuwayama et al., 2008). (author)

High pressure phases of terbium: Possibility of a thcp phase

International Nuclear Information System (INIS)

Staun Olsen, J.; Steenstrup, S.; Gerward, L.

1985-01-01

High pressure phases of trivalent Tb studied by energy dispersive X-ray diffraction with synchrotron radiation exhibits the closed packed sequence (hcp -> Sm -> dhcp -> fcc) typical of the trivalent rare earth metals. Furthermore, a phase consistent with a triple hexagonal closed packed (thcp) structure was observed in a narrow pressure range around 30 GPa. (orig.)

Diamonds: powerful tools for high-pressure physics

International Nuclear Information System (INIS)

Anon.

1983-01-01

Diamond-anvil high-pressure studies have progressed to the point where they complement shock-wave studies. Because they operate at static high pressure, they permit time-consuming procedures, such as x-ray diffraction measurements for determining crystal structure. The sample material is completely recoverable and the method is adaptable to minute advantage when dealing with rare or hazardous materials. One of our goals in investigating the high-pressure behavior of iridium was to test the theoretical prediction that iridium would exhibit a phase transformation from the face-centered cubic crystal structure at about 9 GPa. Our finding that no such transformation takes place even at pressures up to 30 GPa will need to be taken into account by physicsts working to improve solid-state theory

Microstructure and spectroscopy studies on cubic boron nitride synthesized under high-pressure conditions

Energy Technology Data Exchange (ETDEWEB)

Nistor, L C [National Institute for Materials Physics, Bucharest (Romania); Nistor, S V [National Institute for Materials Physics, Bucharest (Romania); Dinca, G [Dacia Synthetic Diamonds Factory, Bucharest (Romania); Georgeoni, P [Dacia Synthetic Diamonds Factory, Bucharest (Romania); Landuyt, J van [University of Antwerpen - RUCA, EMAT, Antwerpen (Belgium); Manfredotti, C [Experimental Physics Department, University of Turin, Turin (Italy); Vittone, E [Experimental Physics Department, University of Turin, Turin (Italy)

2002-11-11

High-resolution electron microscopy (HREM) studies of the microstructure and specific defects in hexagonal boron nitride (h-BN) precursors and cubic boron nitride (c-BN) crystals made under high-pressure high-temperature conditions revealed the presence of half-nanotubes at the edges of the h-BN particles. Their sp{sup 3} bonding tendency could strongly influence the nucleation rates of c-BN. The atomic resolution at extended dislocations was insufficient to allow us to determine the stacking fault energy in the c-BN crystals. Its mean value of 191 pm, 15 mJ m{sup -2} is of the same order of magnitude as that of diamond. High-frequency (94 GHz) electron paramagnetic resonance studies on c-BN single crystals have produced new data on the D1 centres associated with the boron species. Ion-beam-induced luminescence measurements have indicated that c-BN is a very interesting luminescent material, which is characterized by four luminescence bands and exhibits a better resistance to ionizing radiation than CVD diamond.

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

Science.gov (United States)

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.

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

International Nuclear Information System (INIS)

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. (paper)

Solid gas reaction phase diagram under high gas pressure

International Nuclear Information System (INIS)

Ishizaki, K.

1992-01-01

This paper reports that to evaluate which are the stable phases under high gas pressure conditions, a solid-gas reaction phase diagram under high gas pressure (HIP phase diagram) has been proposed by the author. The variables of the diagram are temperature, reactant gas partial pressure and total gas pressure. Up to the present time the diagrams have been constructed using isobaric conditions. In this work, the stable phases for a real HIP process were evaluated assuming an isochoric condition. To understand the effect of the total gas pressure on stability is of primary importance. Two possibilities were considered and evaluated, those are: the total gas pressure acts as an independent variable, or it only affects the fugacity values. The results of this work indicate that the total gas pressure acts as an independent variable, and in turn also affects the fugacity values

Electrochemical properties and diffusion of a redox active surfactant incorporated in bicontinuous cubic and lamellar phase

International Nuclear Information System (INIS)

Kostela, J.; Elmgren, M.; Almgren, M.

2005-01-01

The objective of this study was to investigate the electrochemical behaviour of the divalent redox active surfactant, N-cetyl-N'-methylviologen (CMV), in bicontinuous cubic and lamellar phases. The liquid crystalline phases were prepared from the system glycerolmonooleate (GMO)-water (and brine)-cationic surfactant. A comparison of the phase behaviour of GMO with the monovalent cetyltrimethylammonium bromide (CTAB) and the divalent CMV surfactant showed that the surfactants gave about the same effect at the same surface charge density. The electrochemical measurements were made with a mixture of CTAB and CMV as the surfactant. Cyclic voltammetry was used to study the electrochemistry of CMV incorporated in the cubic and lamellar phases that were spread on a gold electrode. The E 0 -values in the cubic samples were more negative (-0.55 V versus SCE) than in the lamellar samples (-0.53 V versus SCE). This can be explained by the higher charge density in the lamellar phase. The diffusion coefficients were also measured in the cubic phase. The mass transport is slowed down about fifty times in the cubic phase compared to in the pure electrolyte. The concentration dependence on the diffusion coefficient was also investigated. No electron hopping could be observed, which suggest that diffusional movement of the redox probe is the main source of charge transport. By placing the samples on a conducting glass slide, spectroelectrochemical investigations were performed. In the lamellar phase strong dimerization was detected at high concentration of viologen, but much less in the cubic phase

Electrochemical properties and diffusion of a redox active surfactant incorporated in bicontinuous cubic and lamellar phase

Energy Technology Data Exchange (ETDEWEB)

Kostela, J. [Uppsala University, Department of Physical Chemistry, Box 579, S-75123 Uppsala (Sweden)]. E-mail: johan.kostela@fki.uu.se; Elmgren, M. [Uppsala University, Department of Physical Chemistry, Box 579, S-75123 Uppsala (Sweden); Almgren, M. [Uppsala University, Department of Physical Chemistry, Box 579, S-75123 Uppsala (Sweden)

2005-05-30

The objective of this study was to investigate the electrochemical behaviour of the divalent redox active surfactant, N-cetyl-N'-methylviologen (CMV), in bicontinuous cubic and lamellar phases. The liquid crystalline phases were prepared from the system glycerolmonooleate (GMO)-water (and brine)-cationic surfactant. A comparison of the phase behaviour of GMO with the monovalent cetyltrimethylammonium bromide (CTAB) and the divalent CMV surfactant showed that the surfactants gave about the same effect at the same surface charge density. The electrochemical measurements were made with a mixture of CTAB and CMV as the surfactant. Cyclic voltammetry was used to study the electrochemistry of CMV incorporated in the cubic and lamellar phases that were spread on a gold electrode. The E {sup 0}-values in the cubic samples were more negative (-0.55 V versus SCE) than in the lamellar samples (-0.53 V versus SCE). This can be explained by the higher charge density in the lamellar phase. The diffusion coefficients were also measured in the cubic phase. The mass transport is slowed down about fifty times in the cubic phase compared to in the pure electrolyte. The concentration dependence on the diffusion coefficient was also investigated. No electron hopping could be observed, which suggest that diffusional movement of the redox probe is the main source of charge transport. By placing the samples on a conducting glass slide, spectroelectrochemical investigations were performed. In the lamellar phase strong dimerization was detected at high concentration of viologen, but much less in the cubic phase.

A viscosity measurement during the high pressure phase transition in triolein

International Nuclear Information System (INIS)

Siegoczynski, R M; Rostocki, A J; Kielczynski, P; Szalewski, M

2008-01-01

The high-pressure properties of triolein, a subject of extensive research at the Faculty of Physics of Warsaw University of Technology (WUT) have been enhanced by the results of viscosity measurement within the pressure range up to 0.8 GPa. For the measurement the authors have adopted a new ultrasonic method based on Bleustein-Gulyaev waves, successfully developed earlier for the low pressures in the Section of Acoustoelectronics of the Institute of Fundamental Technological Research. The measurements have shown: 1. Exponential rise of viscosity with pressure up to 0.5 GPa. 2. Extraordinary increment of viscosity at constant pressure during phase transition. 3. Further exponential rise of viscosity with pressure of the high-pressure phase of triolein. 4. The pressure exponents of the viscosity of both phases were different (the high-pressure phase had much smaller exponent). 5. The decomposition of the high pressure phase due to the slow decompression have shown very large hysteresis of viscosity on pressure dependence

Cationic Phospholipids Forming Cubic Phases: Lipoplex Structure and Transfection Efficiency

Energy Technology Data Exchange (ETDEWEB)

Koynova, Rumiana; Wang, Li; MacDonald, Robert C. (NWU)

2008-10-29

The transfection activity and the phase behavior of two novel cationic O-alkyl-phosphatidylcholines, 1,2-dioleoyl-sn-glycero-3-hexylphosphocholine (C6-DOPC) and 1,2-dierucoyl-sn-glycero-3-ethylphosphocholine (di22:1-EPC), have been examined with the aim of more completely understanding the mechanism of lipid-mediated DNA delivery. Both lipids form cubic phases: C6-DOPC in the entire temperature range from -10 to 90 C, while di22:1-EPC exhibits an irreversible lamellar-cubic transition between 50 and 70 C on heating. The lipoplexes formed by C6-DOPC arrange into hexagonal phase, while the lipoplexes of di22:1-EPC are lamellar. Both lipids exhibit lower transfection activity than the lamellar-forming 1,2-dioleoyl-sn-glycero-3-ethylphosphocholine (EDOPC). Thus, for the studied cationic phospholipid-DNA systems, the lipoplex phase state is a factor that does not seem to correlate with transfection activity. The parameter that exhibits better correlation with the transfection activity within the present data set is the phase state of the lipid dispersion prior to the addition of DNA. Thus, the lamellar lipid dispersion (EDOPC) produces more efficient lipoplexes than the dispersion with coexisting lamellar and cubic aggregates (diC22:1-EPC), which is even more efficient than the purely cubic dispersions (C6-DOPC; diC22:1-EPC after heating). It could be inferred from these data and from previous research that cubic phase lipid aggregates are unlikely to be beneficial to transfection. The lack of correlation between the phase state of lipoplexes and their transfection activity observed within the present data set does not mean that lipid phase state is generally unimportant for lipofection: a viewpoint now emerging from our previous studies is that the critical factor in lipid-mediated transfection is the structural evolution of lipoplexes within the cell, upon interacting and mixing with cellular lipids.

Cationic phospholipids forming cubic phases: lipoplex structure and transfection efficiency.

Science.gov (United States)

Koynova, Rumiana; Wang, Li; Macdonald, Robert C

2008-01-01

The transfection activity and the phase behavior of two novel cationic O-alkyl-phosphatidylcholines, 1,2-dioleoyl- sn-glycero-3-hexylphosphocholine (C6-DOPC) and 1,2-dierucoyl- sn-glycero-3-ethylphosphocholine (di22:1-EPC), have been examined with the aim of more completely understanding the mechanism of lipid-mediated DNA delivery. Both lipids form cubic phases: C6-DOPC in the entire temperature range from -10 to 90 degrees C, while di22:1-EPC exhibits an irreversible lamellar-cubic transition between 50 and 70 degrees C on heating. The lipoplexes formed by C6-DOPC arrange into hexagonal phase, while the lipoplexes of di22:1-EPC are lamellar. Both lipids exhibit lower transfection activity than the lamellar-forming 1,2-dioleoyl- sn-glycero-3-ethylphosphocholine (EDOPC). Thus, for the studied cationic phospholipid-DNA systems, the lipoplex phase state is a factor that does not seem to correlate with transfection activity. The parameter that exhibits better correlation with the transfection activity within the present data set is the phase state of the lipid dispersion prior to the addition of DNA. Thus, the lamellar lipid dispersion (EDOPC) produces more efficient lipoplexes than the dispersion with coexisting lamellar and cubic aggregates (diC22:1-EPC), which is even more efficient than the purely cubic dispersions (C6-DOPC; diC22:1-EPC after heating). It could be inferred from these data and from previous research that cubic phase lipid aggregates are unlikely to be beneficial to transfection. The lack of correlation between the phase state of lipoplexes and their transfection activity observed within the present data set does not mean that lipid phase state is generally unimportant for lipofection: a viewpoint now emerging from our previous studies is that the critical factor in lipid-mediated transfection is the structural evolution of lipoplexes within the cell, upon interacting and mixing with cellular lipids.

A ₂ TiO ₅ (A = Dy, Gd, Er, Yb) at High Pressure

Energy Technology Data Exchange (ETDEWEB)

Park, Sulgiye [Department of Geological Science, Stanford University, Stanford, California 94305, United States; Rittman, Dylan R. [Department of Geological Science, Stanford University, Stanford, California 94305, United States; Tracy, Cameron L. [Department of Geological Science, Stanford University, Stanford, California 94305, United States; Chapman, Karena W. [X-ray Science Division, Advanced Photon; Zhang, Fuxiang [Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, United States; Park, Changyong [HPCAT, Carnegie Institution of Washington, Argonne, Illinois 60439, United States; Tkachev, Sergey N. [Center for Advanced Radiation Sources, University of Chicago, Chicago, Illinois 60637, United States; O’Quinn, Eric [Department of Nuclear Engineering, University of Tennessee, Knoxville, Tennessee 37996, United States; Shamblin, Jacob [Department of Nuclear Engineering, University of Tennessee, Knoxville, Tennessee 37996, United States; Lang, Maik [Department of Nuclear Engineering, University of Tennessee, Knoxville, Tennessee 37996, United States; Mao, Wendy L. [Department of Geological Science, Stanford University, Stanford, California 94305, United States; Stanford; amp, Energy Sciences, SLAC National Accelerator Laboratory, Menlo Park, California 94025, United States; Ewing, Rodney C. [Department of Geological Science, Stanford University, Stanford, California 94305, United States

2018-02-07

The structural evolution of lanthanide A2TiO5 (A = Dy, Gd, Yb, and Er) at high pressure is investigated using synchrotron X-ray diffraction. The effects of A-site cation size and of the initial structure are systematically examined by varying the composition of the isostructural lanthanide titanates, and the structure of dysprosium titanate polymorphs (orthorhombic, hexagonal and cubic), respectively. All samples undergo irreversible high pressure phase transformations, but with different onset pressures depending on the initial structure. While individual phase exhibits different phase transformation histories, all samples commonly experience a sluggish transformation to a defect cotunnite-like (Pnma) phase for a certain pressure range. Orthorhombic Dy2TiO5 and Gd2TiO5 form P21am at pressures below 9 GPa and Pnma above 13 GPa. Pyrochlore-type Dy2TiO5 and Er2TiO5 as well as defect-fluorite-type Yb2TiO5 form Pnma at ~ 21 GPa, followed by Im-3m. Hexagonal Dy2TiO5 forms Pnma directly, although a small amount of remnants of hexagonal Dy2TiO5 is observed even at the highest pressure (~ 55 GPa) reached, indicating a kinetic limitations in the hexagonal Dy2TiO5 phase transformations at high pressure. Decompression of these materials leads to different metastable phases. Most interestingly, a high pressure cubic X-type phase (Im-3m) is confirmed using highresolution transmission electron microscopy on recovered pyrochlore-type Er2TiO5. The kinetic constraints on this metastable phase yield a mixture of both the X-type phase and amorphous domains upon pressure release. This is the first observation of an X-type phase for an A2BO5 composition at high pressure.

Effect of boron oxide on the cubic-to-monoclinic phase transition in yttria-stabilized zirconia

International Nuclear Information System (INIS)

Florio, D.Z. de; Muccillo, R.

2004-01-01

Specimens of yttria fully stabilized zirconia with different amounts of boron oxide have been studied by X-ray diffraction at room temperature and at higher temperatures up to 1250 deg. C. A boron oxide-assisted cubic-to-monoclinic phase transformation was determined in the temperature range 800-1250 deg. C. In situ high temperature X-ray diffraction experiments gave evidences of the dependence of the phase transformation on the heating rate. The possibility of tuning the cubic-monoclinic phase ratio by suitable addition of boron oxide before pressing and sintering is proposed

Moessbauer study of phase transitions under high hydrostatic pressures. 1

International Nuclear Information System (INIS)

Kapitanov, E.V.; Yakovlev, E.N.

1979-01-01

Experimental results of the hydrostatic pressure influence on Moessbauer spectrum parameters are obtained over the pressure range including the area of structural phase transition. A linear increase of the Moessbauer effect probability (recoilless fraction) is accompanied by a linear decrease of the electron density at tin nuclei within the pressure range foregoing the phase transition. The electric resistance and the recoilless fraction of the new phase of Mg 2 Sn are lower, but the electron density at tin nuclei is greater than the initial phase ones. Hydrostatic conditions allow to fix clearly the diphasic transition area and to determine the influence of the pressure on the Moessbauer line position and on the recoilless fraction of the high pressure phase. The phase transition heat Q = 415 cal mol -1 is calculated using recoilless fractions of the high and low pressure phases at 25 kbar. The present results are qualitatively and quantitatively different from the results, obtained at nonhydrostatic conditions. (author)

Stress-Induced Cubic-to-Hexagonal Phase Transformation in Perovskite Nanothin Films.

Science.gov (United States)

Cao, Shi-Gu; Li, Yunsong; Wu, Hong-Hui; Wang, Jie; Huang, Baoling; Zhang, Tong-Yi

2017-08-09

The strong coupling between crystal structure and mechanical deformation can stabilize low-symmetry phases from high-symmetry phases or induce novel phase transformation in oxide thin films. Stress-induced structural phase transformation in oxide thin films has drawn more and more attention due to its significant influence on the functionalities of the materials. Here, we discovered experimentally a novel stress-induced cubic-to-hexagonal phase transformation in the perovskite nanothin films of barium titanate (BaTiO 3 ) with a special thermomechanical treatment (TMT), where BaTiO 3 nanothin films under various stresses are annealed at temperature of 575 °C. Both high-resolution transmission electron microscopy and Raman spectroscopy show a higher density of hexagonal phase in the perovskite thin film under higher tensile stress. Both X-ray photoelectron spectroscopy and electron energy loss spectroscopy does not detect any change in the valence state of Ti atoms, thereby excluding the mechanism of oxygen vacancy induced cubic-to-hexagonal (c-to-h) phase transformation. First-principles calculations show that the c-to-h phase transformation can be completed by lattice shear at elevated temperature, which is consistent with the experimental observation. The applied bending plus the residual tensile stress produces shear stress in the nanothin film. The thermal energy at the elevated temperature assists the shear stress to overcome the energy barriers during the c-to-h phase transformation. The stress-induced phase transformation in perovskite nanothin films with TMT provides materials scientists and engineers a novel approach to tailor nano/microstructures and properties of ferroelectric materials.

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

International Nuclear Information System (INIS)

Gerward, L.; Staun Olsen, J.; Benedict, U.

1986-01-01

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

High-pressure Raman spectroscopy of phase change materials

Energy Technology Data Exchange (ETDEWEB)

Hsieh, Wen-Pin, E-mail: wphsieh@stanford.edu; Mao, Wendy L. [SLAC National Accelerator Laboratory, Stanford Institute for Materials and Energy Sciences, Menlo Park, California 94025 (United States); Department of Geological and Environmental Sciences, Stanford University, Stanford, California 94305 (United States); Zalden, Peter [SLAC National Accelerator Laboratory, Stanford Institute for Materials and Energy Sciences, Menlo Park, California 94025 (United States); Wuttig, Matthias [I. Physikalisches Institut (IA), RWTH Aachen University, 52056 Aachen (Germany); JARA – Fundamentals of Future Information Technology, RWTH Aachen University, 52056 Aachen (Germany); Lindenberg, Aaron M. [SLAC National Accelerator Laboratory, Stanford Institute for Materials and Energy Sciences, Menlo Park, California 94025 (United States); Department of Materials Science and Engineering, Stanford University, Stanford, California 94305 (United States); SLAC National Accelerator Laboratory, PULSE Institute, Menlo Park, California 94025 (United States)

2013-11-04

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

Method for estimating critical properties of heavy compounds suitable for cubic equations of state and its application to the prediction of vapor pressures

DEFF Research Database (Denmark)

Kontogeorgis, Georgios; Ioannis, Smirlis; Iakovos, Yakoumis

1997-01-01

S. The proposed scheme employs a recent group-contribution method (Constantinou et al. Fluid Phase Equilib. 1995, 103 (1), 11) for estimating the acentric factor. The two critical properties are estimated via a generalized correlation for the ratio T-c/P-c (with the van der Waals surface area) and the cubic Eo...... pressures for several nonpolar and slightly polar heavy compounds with very satisfactory results, essentially independent of the experimental point used. Furthermore, the method yields critical properties for heavy alkanes (N-c > 20) and other compounds which are in very good agreement with recent available......Cubic equations of state (EoS) are often used for correlating and predicting phase equilibria. Before extending any EoS to mixtures, reliable vapor-pressure prediction is essential. This requires experimental, if possible, critical temperatures T-c, pressures P-c, and acentric factor omega...

T- P Phase Diagram of Nitrogen at High Pressures

Science.gov (United States)

Algul, G.; Enginer, Y.; Yurtseven, H.

2018-05-01

By employing a mean field model, calculation of the T- P phase diagram of molecular nitrogen is performed at high pressures up to 200 GPa. Experimental data from the literature are used to fit a quadratic function in T and P, describing the phase line equations which have been derived using the mean field model studied here for N 2, and the fitted parameters are determined. Our model study gives that the observed T- P phase diagram can be described satisfactorily for the first-order transitions between the phases at low as well as high pressures in nitrogen. Some thermodynamic quantities can also be predicted as functions of temperature and pressure from the mean field model studied here and they can be compared with the experimental data.

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

Science.gov (United States)

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.

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

International Nuclear Information System (INIS)

Edalati, Kaveh; Emami, Hoda; Staykov, Aleksandar; Smith, David J.; Akiba, Etsuo; Horita, Zenji

2015-01-01

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

High-Pressure Design of Advanced BN-Based Materials

Directory of Open Access Journals (Sweden)

Oleksandr O. Kurakevych

2016-10-01

Full Text Available The aim of the present review is to highlight the state of the art in high-pressure design of new advanced materials based on boron nitride. Recent experimental achievements on the governing phase transformation, nanostructuring and chemical synthesis in the systems containing boron nitride at high pressures and high temperatures are presented. All these developments allowed discovering new materials, e.g., ultrahard nanocrystalline cubic boron nitride (nano-cBN with hardness comparable to diamond, and superhard boron subnitride B13N2. Thermodynamic and kinetic aspects of high-pressure synthesis are described based on the data obtained by in situ and ex situ methods. Mechanical and thermal properties (hardness, thermoelastic equations of state, etc. are discussed. New synthetic perspectives, combining both soft chemistry and extreme pressure–temperature conditions are considered.

Phase stability limit of c-BN under hydrostatic and non-hydrostatic pressure conditions

International Nuclear Information System (INIS)

Xiao, Jianwei; Du, Jinglian; Wen, Bin; Zhang, Xiangyi; Melnik, Roderick; Kawazoe, Yoshiyuki

2014-01-01

Phase stability limit of cubic boron nitride (c-BN) has been investigated by the crystal structure search technique. It indicated that this limit is ∼1000 GPa at hydrostatic pressure condition. Above this pressure, c-BN turns into a metastable phase with respect to rocksalt type boron nitride (rs-BN). However, rs-BN cannot be retained at 0 GPa owing to its instability at pressure below 250 GPa. For non-hydrostatic pressure conditions, the phase stability limit of c-BN is substantially lower than that under hydrostatic pressure conditions and it is also dramatically different for other pressure mode

Microstructures define melting of molybdenum at high pressures

Science.gov (United States)

Hrubiak, Rostislav; Meng, Yue; Shen, Guoyin

2017-03-01

High-pressure melting anchors the phase diagram of a material, revealing the effect of pressure on the breakdown of the ordering of atoms in the solid. An important case is molybdenum, which has long been speculated to undergo an exceptionally steep increase in melting temperature when compressed. On the other hand, previous experiments showed nearly constant melting temperature as a function of pressure, in large discrepancy with theoretical expectations. Here we report a high-slope melting curve in molybdenum by synchrotron X-ray diffraction analysis of crystalline microstructures, generated by heating and subsequently rapidly quenching samples in a laser-heated diamond anvil cell. Distinct microstructural changes, observed at pressures up to 130 gigapascals, appear exclusively after melting, thus offering a reliable melting criterion. In addition, our study reveals a previously unsuspected transition in molybdenum at high pressure and high temperature, which yields highly textured body-centred cubic nanograins above a transition temperature.

High-pressure phase transformations of fluorite-type dioxides

International Nuclear Information System (INIS)

Lin-Gun Liu

1980-01-01

Phase transformations in six fluorite-type dioxides ('TbO 2 ', PbO 2 , 'PrO 2 ', CeO 2 , UO 2 and ThO 2 in the order of increasing cation size, where the quotation marks indicate non-stoichiometric materials) have been investigated in the diamond-anvil press coupled with laser heating. Together with earlier work, the results show that the post-fluorite phase transformations of these dioxides fall into two groups. The smaller cation group (HfO 2 , ZrO 2 and 'TbO 2 ') transforms to a cotunnite or a distorted cotunnite-type structure at pressures in the vicinity of 100 kbar and at about 1000 0 C. The larger cation group (from PbO 2 to ThO 2 ) is believed to transform to a different type of orthorhombic modification at high pressures. It is plausible that this high-pressure phase may possess a Ni 2 Si-related structure, as was observed in ThO 2 and 'PrO 2 ' at pressures greater than 150 and 200 kbar, respectively. (orig./ME)

High-pressure phase transitions - Examples of classical predictability

Science.gov (United States)

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.

Kinetics and mechanism of transitions involving the lamellar, cubic, inverted hexagonal, and fluid isotropic phases of hydrated monoacylglycerides monitored by time-resolved X-ray diffraction

International Nuclear Information System (INIS)

Caffrey, M.

1987-01-01

A study of the dynamics and mechanism of the various thermotropic phase transitions undergone by the hydrated monoacylglycerides monoolein and monoelaidin, in the temperature range of 20-120 0 C and from 0 to 5 M NaCl, has been undertaken. Measurements were made by using time-resolved X-ray diffraction at the Cornell High-Energy Synchrotron Source. The lamellar chain order/disorder, lamellar/cubic (body centered, space group No.8), cubic (body centered, No.8)/cubic (primitive No.4), cubic (body centered, No.12)/cubic (primitive, No.4), cubic (primitive, No.4)/fluid isotropic, cubic (body centered, No.12)/inverted hexagonal, cubic (primitive, No.4)/inverted hexagonal, and hexagonal/fluid isotropic transitions were examined under active heating and passive cooling by using a jump in temperature to effect phase transformation. All of the transitions with the exception of the cubic (body centered, No.8)/cubic (primitive, No.4) and the cubic (body centered, No.12)/cubic (primitive, No.4) cooling transitions were found (1) to be repeatable, (2) to be reversible, and (3) to have an upper bound on the transit time (time required to complete the transition) of ≤ 3s. In addition to the time-resolved measurements, data were obtained on the stability of the various phases in the temperature range of 20-120 0 C and from 0 to 5 M NaCl. In the case of fully hydrated monoolein, high salt strongly favors the hexagonal over the cubic (body centered, No.8) phase and slightly elevates the hexagonal/fluid isotropic transition temperature. With fully hydrated monoelaidin, the hexagonal phase which is not observed in the absence of salt becomes the dominant phase at high salt concentration

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

Science.gov (United States)

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

2014-04-25

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

High pressure phase transition in Pr-monopnictides

Energy Technology Data Exchange (ETDEWEB)

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

2015-06-24

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

High-pressure structure of Pb-based relaxor ferroelectrics

Energy Technology Data Exchange (ETDEWEB)

Maier, Bernd J.; Mihailova, Boriana; Paulmann, Carsten; Welsch, Anna-Maria; Bismayer, Ulrich [Mineralogisch-Petrographisches Institut, Universitaet Hamburg (Germany); Angel, Ross J. [Crystallography Laboratory, Virgina Tech, Blacksburg (United States); Marshall, William G. [ISIS Neutron Facility, STFC Rutherford Appleton Laboratory, Chilton, Didcot, Oxon (United Kingdom); Engel, Jens M. [Institut fuer Werkstoffwissenschaft, Technische Universitaet Dresden (Germany); Gospodinov, Marin [Institute of Solid State Physics, Bulgarian Academy of Sciences, Sofia (Bulgaria); Petrova, Dimitrina [Institute of Solid State Physics, Bulgarian Academy of Sciences, Sofia (Bulgaria); South-West University Neofit Rilski, Blagoevgrad (Bulgaria)

2010-07-01

The pressure-induced phase transitions that occur in the perovskite-type relaxor ferroelectric PbSc{sub 0.5}Ta{sub 0.5}O{sub 3} (PST) and Pb{sub 0.78}Ba{sub 0.22}Sc{sub 0.5}Ta{sub 0.5}O{sub 3} (PST-Ba) were studied with combined neutron powder diffraction and single-crystal X-ray diffraction. An increase in the intensities of h,k,l=all odd reflections is observed while the intensity of h,h,h peaks, h=2n+1, does not change with pressure, indicating a glide-plane pseudo-symmetry of the structural distortion along the left angle 111 right angle cubic directions. Rietveld refinement to the neutron powder data shows that the high-pressure phase has either R anti 3c or R anti 3 symmetry, depending on whether the presence of 1:1 octahedral cation ordering is neglected or taken into account, and comprises anti-phase octahedral tilts of type a{sup -}a{sup -}a{sup -} that continuously evolve with pressure.

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

International Nuclear Information System (INIS)

Mokhtari, Ali

2009-01-01

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.

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

Energy Technology Data Exchange (ETDEWEB)

Mokhtari, Ali [Simulation Laboratory, Department of Physics, Faculty of Science, Shahrekord University, PB 115, Shahrekord (Iran, Islamic Republic of)], E-mail: mokhtari@sci.sku.ac.ir

2009-07-08

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.

Magnetic phase diagram of Ce2Fe17 under high pressures in high magnetic fields

International Nuclear Information System (INIS)

Ishikawa, Fumihiro; Goto, Tsuneaki; Fujii, Hironobu

2003-01-01

The magnetization of Ce 2 Fe 17 was precisely measured under high pressures up to 1.2 GPa in magnetic fields up to 18 T. The magnetic phase diagram in the B-T plane is determined at 0, 0.3, 0.4, 0.6, 0.9 and 1.2 GPa. At 0 GPa, five magnetic phases exist and the application of high pressure produces two additional magnetic phases. The shape of the phase diagram changes drastically with increasing pressure

High-pressure phases of uranium monophosphide studied by synchrotron x-ray diffraction

DEFF Research Database (Denmark)

Olsen, J. Staun; Gerward, Leif; Benedict, U.

1988-01-01

X-ray diffraction studies have been performed on UP powder for pressures up to 51 GPa using synchrotron radiation and a diamond-anvil cell. At ambient pressure UP has the rocksalt structure. The bulk modulus has been determined to B0=102(4) GPa and its pressure derivative to B0’=4.0(8). The cubic...

Curvature and bottlenecks control molecular transport in inverse bicontinuous cubic phases

Science.gov (United States)

Assenza, Salvatore; Mezzenga, Raffaele

2018-02-01

We perform a simulation study of the diffusion of small solutes in the confined domains imposed by inverse bicontinuous cubic phases for the primitive, diamond, and gyroid symmetries common to many lipid/water mesophase systems employed in experiments. For large diffusing domains, the long-time diffusion coefficient shows universal features when the size of the confining domain is renormalized by the Gaussian curvature of the triply periodic minimal surface. When bottlenecks are widely present, they become the most relevant factor for transport, regardless of the connectivity of the cubic phase.

High pressure structural phase transition of neodymium mono pnictides

International Nuclear Information System (INIS)

Pagare, Gitanjali; Ojha, P.; Sanyal, S.P.; Aynyas, Mahendra

2007-01-01

We have investigated theoretically the high-pressure structural phase transition of two neodymium mono NdX (X=As, Sb) using an interionic potential theory with necessary modification to include the effect of Coulomb screening by the delocalized f electrons of Nd ion. These compounds exhibits first order crystallographic phase transition from their NaCl (B 1 ) phase to body centered tetragonal (BCT) at 27 GPa and 15.3 GPa respectively. We also calculated the Nd-Nd distance as a function of pressure. (author)

Cubic martensite in high carbon steel

Science.gov (United States)

Chen, Yulin; Xiao, Wenlong; Jiao, Kun; Ping, Dehai; Xu, Huibin; Zhao, Xinqing; Wang, Yunzhi

2018-05-01

A distinguished structural characteristic of martensite in Fe-C steels is its tetragonality originating from carbon atoms occupying only one set of the three available octahedral interstitial sites in the body-centered-cubic (bcc) Fe lattice. Such a body-centered-tetragonal (bct) structure is believed to be thermodynamically stable because of elastic interactions between the interstitial carbon atoms. For such phase stability, however, there has been a lack of direct experimental evidence despite extensive studies of phase transformations in steels over one century. In this Rapid Communication, we report that the martensite formed in a high carbon Fe-8Ni-1.26C (wt%) steel at room temperature induced by applied stress/strain has actually a bcc rather than a bct crystal structure. This finding not only challenges the existing theories on the stability of bcc vs bct martensite in high carbon steels, but also provides insights into the mechanism for martensitic transformation in ferrous alloys.

Variable-temperature single-crystal X-ray diffraction study of tetragonal and cubic perovskite-type barium titanate phases.

Science.gov (United States)

Nakatani, Tomotaka; Yoshiasa, Akira; Nakatsuka, Akihiko; Hiratoko, Tatsuya; Mashimo, Tsutomu; Okube, Maki; Sasaki, Satoshi

2016-02-01

A variable-temperature single-crystal X-ray diffraction study of a synthetic BaTiO3 perovskite has been performed over the temperature range 298-778 K. A transition from a tetragonal (P4mm) to a cubic (Pm3m) phase has been revealed near 413 K. In the non-centrosymmetric P4mm symmetry group, both Ti and O atoms are displaced along the c-axis in opposite directions with regard to the Ba position fixed at the origin, so that Ti(4+) and Ba(2+) cations occupy off-center positions in the TiO6 and BaO12 polyhedra, respectively. Smooth temperature-dependent changes of the atomic coordinates become discontinuous with the phase transition. Our observations imply that the cations remain off-center even in the high-temperature cubic phase. The temperature dependence of the mean-square displacements of Ti in the cubic phase includes a significant static component which means that Ti atoms are statistically distributed in the off-center positions.

Plasma deposition of cubic boron nitride films from non-toxic material at low temperatures

International Nuclear Information System (INIS)

Karim, M.Z.; Cameron, D.C.; Murphy, M.J.; Hashmi, M.S.J.

1991-01-01

Boron nitride has become the focus of a considerable amount of interest because of its properties which relate closely to those of carbon. In particular, the cubic nitride phase has extreme hardness and very high thermal conductivity similar to the properties of diamond. The conventional methods of synthesis use the highly toxic and inflammable gas diborane (B 2 H 6 ) as the reactant material. A study has been made of the deposition of thin films of boron nitride (BN) using non-toxic material by the plasma-assisted chemical vapour deposition technique. The source material was borane-ammonia (BH 3 -NH 3 ) which is a crystalline solid at room temperature with a high vapour pressure. The BH 3 -NH 3 vapour was decomposed in a 13.56 MHz nitrogen plasma coupled either inductively or capacitively with the system. The composition of the films was assessed by measuring their IR absorption when deposited on silicon and KBr substrates. The hexagonal (graphitic) and cubic (diamond-like) allotropes can be distinguished by their characteristic absorption bands which occur at 1365 and 780 cm -1 (hexagonal) and 1070 cm -1 (cubic). We have deposited BN films consisting of a mixture of hexagonal and cubic phases; the relative content of the cubic phase was found to be directly dependent on r.f. power and substrate bias. (orig.)

Negative pressure driven phase transformation in Sr doped SmCoO₃.

Science.gov (United States)

Arshad Farhan, M; Javed Akhtar, M

2010-02-24

Atomistic computer simulation techniques based on energy minimization procedures are utilized for the structural investigation of perovskite-type SmCoO(3). A reliable potential model is derived which reproduces both cubic as well as orthorhombic phases of SmCoO(3). We observe a negative chemical pressure induced structural phase transformation from distorted perovskite (orthorhombic) to perfect perovskite (cubic) due to the substitution of Sr(2 + ) at the Sm(3 + ) sites. However, external hydrostatic pressure shows isotropic compression and no pressure-induced structural transformation is observed up to 100 GPa. To maintain the electroneutrality of the system, charge compensation is through oxygen vacancies which results in the brownmillerite-type structure. A defect model is proposed, which is consistent with experimental results. The solution energies for divalent and trivalent cations are also calculated. These results show that the cations having ionic radii less than 0.75 Å will occupy the Co sites and those with ionic radii larger than 0.75 Å will substitute at the Sm sites.

Influence of strontium on the cubic to ordered hexagonal phase

Indian Academy of Sciences (India)

... Refresher Courses · Symposia · Live Streaming. Home; Journals; Bulletin of Materials Science; Volume 23; Issue 6. Influence of strontium on the cubic to ordered hexagonal phase transformation in barium magnesium niobate. M Thirumal A K Ganguli. Phase Transitions Volume 23 Issue 6 December 2000 pp 495-498 ...

Superconductivity in the unconventional high pressure phase bismuth-III

Energy Technology Data Exchange (ETDEWEB)

Semeniuk, Konstantin; Brown, Philip; Vasiljkovic, Aleksandar; Grosche, Malte [University of Cambridge (United Kingdom)

2015-07-01

One of the most surprising developments in high pressure research was the realisation that many elements assume very unexpected high pressure structures, described in terms of extremely large or even infinite unit cells. Elemental bismuth, which has been known to undergo a series of pressure induced structural transitions between 25 kbar and 80 kbar, is an interesting example: the intermediate pressure Bi-III phase has a complex 'host-guest' structure consisting of two incommensurate sublattices. Since the unit cell is infinitely large, the description of electronic and lattice excitations is problematic. Apart from its metallic character and the observation of superconductivity at low temperature, little is known about the electronic structure in this phase. We investigate the electrical resistivity within the metallic Bi-III phase under high hydrostatic pressure and in applied magnetic field using a piston cylinder cell. Superconductivity is observed below 7.1 K, and we extract the temperature dependence of the upper critical field, which exceeds 2 T at low temperature. The normal state resistivity exhibits an approximately linear temperature dependence. This could be attributed to strong scattering from low-lying excitations, as caused by an unusually soft phonon spectrum. The results suggest that strong coupling superconductivity arises within the host-guest structure of Bi-III out of an unusual electronic state.

The phase space of the focused cubic Schroedinger equation: A numerical study

Energy Technology Data Exchange (ETDEWEB)

Burlakov, Yuri O. [Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)

1998-05-01

In a paper of 1988 [41] on statistical mechanics of the nonlinear Schroedinger equation, it was observed that a Gibbs canonical ensemble associated with the nonlinear Schroedinger equation exhibits behavior reminiscent of a phase transition in classical statistical mechanics. The existence of a phase transition in the canonical ensemble of the nonlinear Schroedinger equation would be very interesting and would have important implications for the role of this equation in modeling physical phenomena; it would also have an important bearing on the theory of weak solutions of nonlinear wave equations. The cubic Schroedinger equation, as will be shown later, is equivalent to the self-induction approximation for vortices, which is a widely used equation of motion for a thin vortex filament in classical and superfluid mechanics. The existence of a phase transition in such a system would be very interesting and actually very surprising for the following reasons: in classical fluid mechanics it is believed that the turbulent regime is dominated by strong vortex stretching, while the vortex system described by the cubic Schroedinger equation does not allow for stretching. In superfluid mechanics the self-induction approximation and its modifications have been used to describe the motion of thin superfluid vortices, which exhibit a phase transition; however, more recently some authors concluded that these equations do not adequately describe superfluid turbulence, and the absence of a phase transition in the cubic Schroedinger equation would strengthen their argument. The self-induction approximation for vortices takes into account only very localized interactions, and the existence of a phase transition in such a simplified system would be very unexpected. In this thesis the authors present a numerical study of the phase transition type phenomena observed in [41]; in particular, they find that these phenomena are strongly related to the splitting of the phase space into

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

International Nuclear Information System (INIS)

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

2014-01-01

Colossal negative thermal expansion was recently discovered in BiNiO 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

Nature of phase transitions in crystalline and amorphous GeTe-Sb2Te3 phase change materials.

Science.gov (United States)

Kalkan, B; Sen, S; Clark, S M

2011-09-28

The thermodynamic nature of phase stabilities and transformations are investigated in crystalline and amorphous Ge(1)Sb(2)Te(4) (GST124) phase change materials as a function of pressure and temperature using high-resolution synchrotron x-ray diffraction in a diamond anvil cell. The phase transformation sequences upon compression, for cubic and hexagonal GST124 phases are found to be: cubic → amorphous → orthorhombic → bcc and hexagonal → orthorhombic → bcc. The Clapeyron slopes for melting of the hexagonal and bcc phases are negative and positive, respectively, resulting in a pressure dependent minimum in the liquidus. When taken together, the phase equilibria relations are consistent with the presence of polyamorphism in this system with the as-deposited amorphous GST phase being the low entropy low-density amorphous phase and the laser melt-quenched and high-pressure amorphized GST being the high entropy high-density amorphous phase. The metastable phase boundary between these two polyamorphic phases is expected to have a negative Clapeyron slope. © 2011 American Institute of Physics

Study on flow regimes of high-pressure and dense-phase pneumatic conveying

International Nuclear Information System (INIS)

Lu Peng; Chen Xiaoping; Liang Cai; Pu Wenhao; Zhou Yun; Xu Pan; Zhao Changsui

2009-01-01

High-pressure and dense-phase pneumatic conveying of pulverized coal is a key technology in the field of large-scale entrained bed coal gasification. Flow regime plays an important role in two-phase flow because it affects not only flow behavior and safety operation, but also the reliability of practical processes. Few references and experiences in high-pressure and dense-phase conveying are available, especially for the flow regimes. And because of the high stickiness and electrostatic attraction of pulverized coal to the pipe wall, it is very difficult to make out the flow regimes in the conveying pipe by visualization method. Thus quartz powder was chosen as the conveyed material to study the flow regime. High-speed digital video camera was employed to photograph the flow patterns. Experiments were conducted on a pilot scale experimental setup at the pressure up to 3.6MPa. With the decrease in superficial gas velocity, three distinguishable flow regimes were observed: stratified flow, dune flow and plug flow. The characteristics of pressure traces acquired by high frequency response pressure transmitter and their EMD (Empirical Mode Decomposition) characteristics were correlated strongly with the flow regimes. Combining high-speed photography and pressure signal analysis together can make the recognition of flow patterns in the high-pressure and dense-phase pneumatic conveying system more accurate. The present work will lead to better understanding of the flow regime transition under high-pressure.

High-pressure modifications of CaZn2, SrZn2, SrAl2, and BaAl2: Implications for Laves phase structural trends

International Nuclear Information System (INIS)

Kal, Subhadeep; Stoyanov, Emil; Belieres, Jean-Philippe; Groy, Thomas L.; Norrestam, Rolf; Haeussermann, Ulrich

2008-01-01

High-pressure forms of intermetallic compounds with the composition CaZn 2 , SrZn 2 , SrAl 2 , and BaAl 2 were synthesized from CeCu 2 -type precursors (CaZn 2 , SrZn 2 , SrAl 2 ) and Ba 21 Al 40 by multi-anvil techniques and investigated by X-ray powder diffraction (SrAl 2 and BaAl 2 ), X-ray single-crystal diffraction (CaZn 2 ), and electron microscopy (SrZn 2 ). Their structures correspond to that of Laves phases. Whereas the dialuminides crystallize in the cubic MgCu 2 (C15) structure, the dizincides adopt the hexagonal MgZn 2 (C14) structure. This trend is in agreement with the structural relationship displayed by sp bonded Laves phase systems at ambient conditions. - Graphical abstract: CeCu 2 -type polar intermetallics can be transformed to Laves phases upon simultaneous application of pressure and temperature. The observed structures are controlled by the valence electron concentration

Phase diagram and equation of state of TiH2 at high pressures and high temperatures

International Nuclear Information System (INIS)

Endo, Naruki; Saitoh, Hiroyuki; Machida, Akihiko; Katayama, Yoshinori; Aoki, Katsutoshi

2013-01-01

Highlights: ► We determined the phase diagram of TiH 2 at high pressures and high temperatures. ► Compression induced stain inhibited the phase transition from the bct to fcc phase. ► The phase boundary was appropriately determined using a sample with heat treatment. ► The high temperature Birch–Murnaghan equation of state of fcc TiH 2 was firstly determined. - Abstract: We determined the phase diagram and the equation of state (EoS) of TiH 2 at high pressures up to 8.7 GPa and high temperatures up to 600 °C by in situ synchrotron radiation X-ray diffraction measurements. Compression induced strain inhibited the phase transition from the low-temperature bct phase to the high-temperature fcc phase, making the phase diagram difficult to determine. However, heating around 600 °C relieved the strain, and the phase boundary between the bct and fcc phases was elucidated. The phase transition temperature at ambient pressure increased from around room temperature to 200 °C at 8.7 GPa. The high temperature Birch–Murnaghan EoS was determined for the fcc phase. With the pressure derivative of the bulk modulus K′ 0 = 4.0, the following parameters were obtained: ambient bulk modulus K 0 = 97.7 ± 0.2 GPa, ambient unit cell of the fcc phase V 0 = 88.57 ± 0.02 Å 3 , temperature derivative of the bulk modulus at constant pressure (∂K/∂T) P = −0.01 ± 0.02, and volumetric thermal expansivity α = a + bT with a = 2.62 ± 1.4 × 10 −5 and b = 5.5 ± 4.5 × 10 −8 . K 0 of fcc TiH 2 was close to those for pure Ti and bct TiH 2 reported in previous studies.

Lattice vibrations and cubic to tetragonal phase transition in ZrO2

International Nuclear Information System (INIS)

Negita, K.

1989-01-01

On the basis of analyses of phonon modes in ZrO 2 , it is suggested that condensation of a phonon X 2 - at the cubic Brillouin zone boundary X point, (0, 0, 2 π/a), is associated with the cubic to tetragonal phase transition in ZrO 2 . Free energy consideration shows that spontaneous volume and shear strains, e Alg = (e 1 +e 2 +e 3 ) and e Eg = (2e 3 - e 1 - e 2 )/ Λ3, are induced in the tetragonal phase as a result of indirect couplings of the X 2 - mode to homogeneous elastic strains; the tetragonal phase is improper ferroelastic

Pressure-temperature phase behavior of mixtures of natural sphingomyelin and ceramide extracts.

Science.gov (United States)

Barriga, Hanna M G; Parsons, Edward S; McCarthy, Nicola L C; Ces, Oscar; Seddon, John M; Law, Robert V; Brooks, Nicholas J

2015-03-31

Ceramides are a group of sphingolipids that act as highly important signaling molecules in a variety of cellular processes including differentiation and apoptosis. The predominant in vivo synthetic pathway for ceramide formation is via sphingomyelinase catalyzed hydrolysis of sphingomyelin. The biochemistry of this essential pathway has been studied in detail; however, there is currently a lack of information on the structural behavior of sphingomyelin- and ceramide-rich model membrane systems, which is essential for developing a bottom-up understanding of ceramide signaling and platform formation. We have studied the lyotropic phase behavior of sphingomyelin-ceramide mixtures in excess water as a function of temperature (30-70 °C) and pressure (1-200 MPa) by small- and wide-angle X-ray scattering. At low ceramide concentrations the mixtures form the ripple gel phase (P(β)') below the gel transition temperature for sphingomyelin, and this observation has been confirmed by atomic force microscopy. Formation of the ripple gel phase can also be induced at higher temperatures via the application of hydrostatic pressure. At high ceramide concentration an inverse hexagonal phase (HII) is formed coexisting with a cubic phase.

Phase transition of La- chalcogenides under high pressure

Energy Technology Data Exchange (ETDEWEB)

Gupta, Dinesh Chandra [Condensed Matter Theory Group, School of Studies in Physics, Jiwaji University, Gwalior - 474 011 (India); Raypuria, Gajendra Singh, E-mail: gsraypuria@gmail.com [Department of Physics, Govt. K.R.G. P.G. Autonomous College, Gwalior - 474 001 (India)

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.

Compressibility of the high-pressure rocksalt phase of ZnO

DEFF Research Database (Denmark)

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

1998-01-01

We report the results of a combined experimental and theoretical investigation on the stability and the volume behavior under hydrostatic pressure of the rocksalt (B1) phase of ZnO. Synchrotron-radiation x-ray powder-diffraction data are obtained from 0 to 30 GPa. Static simulations of the ZnO B1...... phase are performed using the ab initio perturbed ion method and the local and nonlocal approximations to the density-functional theory. After the pressure induced transition from the wurtzite phase, we have found that a large fraction of the B1 high-pressure phase is retained when pressure is released....... The metastability of this ZnO polymorph is confirmed through the theoretical evaluation of the Hessian eigenvalues of a nine-parameter potential energy surface. This allows us to treat the experimental and theoretical pressure-volume data on an equal basis. In both cases, we have obtained values of the bulk modulus...

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

Science.gov (United States)

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

2017-02-20

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

High pressure apparatus for neutron scattering at low temperature

International Nuclear Information System (INIS)

Munakata, Koji; Uwatoko, Yoshiya; Aso, Naofumi

2010-01-01

Effects of pressure on the physical properties are very important for understanding highly correlated electron systems, in which pressure-induced attractive phenomena such as superconductivity and magnetically ordered non-Fermi liquid have been observed. Up to now, many scientists have developed a lot of high pressure apparatus for each purpose. The characteristic features of various materials and pressure transmitting media for use of high pressure apparatus are reported. Then, two kinds of clamp type high-pressure cell designed for low-temperature neutron diffraction measurements are shown; one is a piston cylinder type high-pressure cell which can be attached to the dilution refrigerator, and the other one is a newly-developed cubic anvil type high-pressure cell which can generate pressure above 7GPa. We also introduce the results of magnetic neutron scattering under pressure on a pressure-induced superconducting ferromagnet UGe 2 in use of the piston cylinder type clamp cell, and those on an iron arsenide superconductor SrFe 2 As 2 in use of the cubic anvil type clamp cell. (author)

Structure and phase transition of BiFeO3 cubic micro-particles prepared by hydrothermal method

International Nuclear Information System (INIS)

Zhou, Jian-Ping; Yang, Ruo-Lin; Xiao, Rui-Juan; Chen, Xiao-Ming; Deng, Chao-Yong

2012-01-01

Graphical abstract: Bismuth ferrite (BiFeO 3 ) cubic micro-particles with smooth surfaces were synthesized. BiFeO 3 has a hexagonal perovskite structure with a space group R3c below 370 °C and rhombohedral perovskite structure with a space group R3m below 755 °C, undergoes a phase transition in the temperature range of 755–817 °C to a cubic structure, then decompose to liquid and Fe 2 O 3 above 939 °C. Highlights: ► BiFeO 3 micro-particles with smooth surface were synthesized by hydrothermal method. ► BiFeO 3 enjoys hexagonal structure with well element ratio and chemical valence. ► BiFeO 3 transition from rhombohedral phase to cubic phase lasts 60 °C. -- Abstract: Single-phase bismuth ferrite (BiFeO 3 ) powders were synthesized with a hydrothermal method by controlling the experimental conditions carefully. The powder structure, morphology and composition were characterized by using X-ray diffraction (XRD), scanning electron microscopy, transmission electron microscope, Raman measurement and X-ray photoelectron spectroscopy. The particles change from irregular agglomerations to regular cubes with increasing KOH concentration. The large BiFeO 3 cubic particles enjoy much smooth surfaces with well-matched element ratio (Bi:Fe:O = 1:1:3) and chemical valence (Bi 3+ , Fe 3+ and O 2− ). The high temperature XRD and differential scanning calorimetry show that BiFeO 3 powders have a hexagonal perovskite structure with a space group R3c below 370 °C and a rhombohedral structure with a space group R3m below 755 °C. BiFeO 3 undergoes a phase transition in the temperature range of 755–817 °C from rhombohedral structure to a cubic phase, then decomposes to liquid and Fe 2 O 3 above 939 °C.

Experimental and computational study on the phase stability of Al-containing cubic transition metal nitrides

International Nuclear Information System (INIS)

Rovere, Florian; Mayrhofer, Paul H; Music, Denis; Ershov, Sergey; Baben, Moritz to; Schneider, Jochen M; Fuss, Hans-Gerd

2010-01-01

The phase stability of Al-containing cubic transition metal (TM) nitrides, where Al substitutes for TM (i.e. TM 1-x Al x N), is studied as a function of the TM valence electron concentration (VEC). X-ray diffraction and thermal analyses data of magnetron sputtered Ti 1-x Al x N, V 1-x Al x N and Cr 1-x Al x N films indicate increasing phase stability of cubic TM 1-x Al x N at larger Al contents and higher temperatures with increasing TM VEC. These experimental findings can be understood based on first principle investigations of ternary cubic TM 1-x Al x N with TM = Sc, Ti, V, Cr, Y, Zr and Nb where the TM VEC and the lattice strain are systematically varied. However, our experimental data indicate that, in addition to the decomposition energetics (cubic TM 1-x Al x N → cubic TMN + hexagonal AlN), future stability models have to include nitrogen release as one of the mechanisms that critically determine the overall phase stability of TM 1-x Al x N.

High-pressure phase transition and properties of spinel ZnMn2O4

DEFF Research Database (Denmark)

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

1999-01-01

to normal pressure. The c/a ratio reduces from 1.62 to 1.10 above P-c and remains nearly pressure independent in the high-pressure phase. The transition is attributed to the changes in electron configuration of the Mn3+ ions. According to the crystal field theory, the e(g) electron of octahedrally......-pressure behavior of ZnMn2O4 was investigated up to 52 GPa using the energy-dispersive x-ray diffraction technique and synchrotron radiation. The structural first-order phase transition from the body-centered to primitive-tetragonal cell takes place at P-c = 23 GPa. The high-pressure phase is metastable down...... coordinated Mn3+ is either in the d(z)(2) orbital or in the d(x2-y2). In the first configuration the MnO6 octahedron will be elongated and this is the case at normal pressure, while the second configuration gives the flattened octahedron. In the high-pressure phase some proportion of the e(g) electrons...

Phase formation in the (1-y)BiFeO{sub 3}-yBiScO{sub 3} system under ambient and high pressure

Energy Technology Data Exchange (ETDEWEB)

Salak, A.N., E-mail: salak@ua.pt [Department of Materials and Ceramic Engineering and CICECO – Aveiro Institute of Materials, University of Aveiro, 3810-193 Aveiro (Portugal); Khalyavin, D.D., E-mail: dmitry.khalyavin@stfc.ac.uk [ISIS Facility, Rutherford Appleton Laboratory, Chilton, OX11 0QX Didcot (United Kingdom); Pushkarev, A.V.; Radyush, Yu.V.; Olekhnovich, N.M. [Scientific-Practical Materials Research Centre of NAS of Belarus, P. Brovka Street, 19, 220072 Minsk (Belarus); Shilin, A.D.; Rubanik, V.V. [Institute of Technical Acoustics of NAS of Belarus, Lyudnikov Avenue, 13, 210023 Vitebsk (Belarus)

2017-03-15

Formation and thermal stability of perovskite phases in the BiFe{sub 1-y}Sc{sub y}O{sub 3} system (0≤y≤0.70) were studied. When the iron-to-scandium substitution rate does not exceed about 15 at%, the single-phase perovskite ceramics with the rhombohedral R3c symmetry (as that of the parent compound, BiFeO{sub 3}) can be prepared from the stoichiometric mixture of the respective oxides at ambient pressure. Thermal treatment of the oxide mixtures with a higher content of scandium results in formation of two main phases, namely a BiFeO{sub 3}-like R3c phase and a cubic (I23) sillenite-type phase based on γ-Bi{sub 2}O{sub 3}. Single-phase perovskite ceramics of the BiFe{sub 1-y}Sc{sub y}O{sub 3} composition were synthesized under high pressure from the thermally treated oxide mixtures. When y is between 0 and 0.25 the high-pressure prepared phase is the rhombohedral R3c with the √2a{sub p}×√2a{sub p}×2√3a{sub p} superstructure (a{sub p} ~ 4 Å is the pseudocubic perovskite unit-cell parameter). The orthorhombic Pnma phase (√2a{sub p}×4a{sub p}×2√2a{sub p}) was obtained in the range of 0.30≤y≤0.60, while the monoclinic C2/c phase (√6a{sub p}×√2a{sub p}×√6a{sub p}) is formed when y=0.70. The normalized unit-cell volume drops at the crossover from the rhombohedral to the orthorhombic composition range. The perovskite BiFe{sub 1-y}Sc{sub y}O{sub 3} phases prepared under high pressure are metastable regardless of their symmetry. At ambient pressure, the phases with the compositions in the ranges of 0.20≤y≤0.25, 0.30≤y<0.50 and 0.50≤y≤0.70 start to decompose above 970, 920 and 870 K, respectively. - Graphical abstract: Formation of perovskite phases in the BiFe{sub 1-y}Sc{sub y}O{sub 3} system when y≥0.15 requires application of pressure of several GPa. The phases formed under high pressure: R3c (0.20≤y≤0.25), Pnma (0.30≤y≤0.60) and C2/c (y≥0.70) are metastable. - Highlights: • Maximal Fe-to-Sc substitution rate in Bi

Superconductivity of divalent Chevrel phases at very high pressures

International Nuclear Information System (INIS)

Yao, Y.S.; Guertin, R.P.; Hinks, D.G.; Jorgensen, J.; Capone II, D.W.

1988-01-01

The electrical resistivity and the superconducting transition temperatures were examined for three representative divalent Chevrel phase systems, SnMo 6 S 8 , EuMo 6 S 8 , and BaMo 6 S 8 , as a function of hydrostatic pressure to 2 GPa and in quasihydrostatic pressures to 10 GPa. In all systems, T/sub c/ is depressed to 0 K for sufficiently large pressures. For the Sn- and Eu-based systems, both highly purified samples and samples with controlled oxygen content were used. In an oxygenated SnMo 6 S 8 sample (less than 3% O 2 substituted for the S atoms) the pressure threshold and maximum T/sub c/ are 40% lower than in the pure sample, but for P>3.5 GPa the T/sub c/-P phase diagrams nearly coincide, with T/sub c/ reaching zero at an extrapolated pressure of about 12 GPa. In pure EuMo 6 S 8 , superconductivity appears only above a threshold pressure of about 1 GPa and is depressed to 0 K above 4.5 GPa. In an oxygenated sample the maximum T/sub c/ and the threshold pressure are depressed, and above about 3.5 GPa the T/sub c/-P phase diagrams coincide, as in the Sn-based system, although T/sub c/ is then rapidly depressed to 0 K at about 4.5 GPa. In a highly purified BaMo 6 S 8 sample superconductivity appears above about 2 GPa and is depressed to 0 K at extrapolated pressures above 12 GPa. A full transition to the zero-resistance superconducting state is observed in BaMo 6 S 8 . The data are discussed in terms of a model linking the rhombohedral-to-triclinic structural transition, the superconducting transition temperature, and the role of pressure in suppressing the structural transition

Electron spin transition causing structure transformations of earth's interiors under high pressure

Science.gov (United States)

Yamanaka, T.; Kyono, A.; Kharlamova, S.; Alp, E.; Bi, W.; Mao, H.

2012-12-01

To elucidate the correlation between structure transitions and spin state is one of the crucial problems for understanding the geophysical properties of earth interiors under high pressure. High-pressure studies of iron bearing spinels attract extensive attention in order to understand strong electronic correlation such as the charge transfer, electron hopping, electron high-low spin transition, Jahn-Teller distortion and charge disproponation in the lower mantle or subduction zone [1]. Experiment Structure transitions of Fe3-xSixO4, Fe3-xTixO4 Fe3-xCrxO4 spinel solid solution have been investigated at high pressure up to 60 GPa by single crystal and powder diffraction studies using synchrotron radiation with diamond anvil cell. X-ray emission experiment (XES) at high pressure proved the spin transition of Fe-Kβ from high spin (HS) to intermediate spin state (IS) or low spin state (LS). Mössbauer experiment and Raman spectra study have been also conducted for deformation analysis of Fe site and confirmation of the configuration change of Fe atoms. Jahn-Teller effect A cubic-to-tetragonal transition under pressure was induced by Jahn-Teller effect of IVFe2+ (3d6) in the tetrahedral site of Fe2TiO4 and FeCr2O4, providing the transformation from 43m (Td) to 42m (D2d). Tetragonal phase is formed by the degeneracy of e orbital of Fe2+ ion. Their c/a ratios are c/adisordered in the M2 site. At pressures above 53 GPa, Fe2TiO4 structure further transforms to Pmma. This structure change results in the order-disorder transition [2]. New structure of Fe2SiO4 The spin transition exerts an influence to Fe2SiO4 spinel structure and triggers two distinct curves of the lattice constant in the spinel phase. The reversible structure transition from cubic to pseudo-rhombohedral phase was observed at about 45 GPa. This transition is induced by the 20% shrinkage of ionic radius of VIFe2+at the low sin state. Laser heating experiment at 1500 K has confirmed the decomposition from the

Diamond cubic phase of monoolein and water as an amphiphilic matrix for electrophoresis of oligonucleotides.

Science.gov (United States)

Carlsson, Nils; Winge, Ann-Sofie; Engström, Sven; Akerman, Björn

2005-10-06

We used a cubic liquid crystal formed by the nonionic monoglyceride monoolein and water as a porous matrix for the electrophoresis of oligonucleotides. The diamond cubic phase is thermodynamically stable when in contact with a water-rich phase, which we exploit to run the electrophoresis in the useful submarine mode. Oligonucleotides are separated according to size and secondary structure by migration through the space-filling aqueous nanometer pores of the regular liquid crystal, but the comparatively slow migration means the cubic phase will not be a replacement for the conventional DNA gels. However, our demonstration that the cubic phase can be used in submarine electrophoresis opens up the possibility for a new matrix for electrophoresis of amphiphilic molecules. From this perspective, the results on the oligonucleotides show that water-soluble particles of nanometer size, typical for the hydrophilic parts of membrane-bound proteins, may be a useful separation motif. A charged contamination in the commercial sample of monoolein, most likely oleic acid that arises from its hydrolysis, restricts useful buffer conditions to a pH below 5.6.

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

Energy Technology Data Exchange (ETDEWEB)

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

2015-11-05

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

Phase transformations in cerium and thorium metals at ultra high pressures

International Nuclear Information System (INIS)

Vohra, Y.K.

1991-01-01

This paper reports on the role of pressure variable in phase transformation which has not been fully exploited in metallic elements and their alloys. The static compression of over 50% in volume can readily be obtained in most metals and this tremendous change in inter-atomic distances can lead to the formation of new exotic crystal structures. The pressure-induced electron transfer amongst existing electronic energy bands and the occupation of new bands are the driving forces in a rich variety of phase transformations. The modern high pressure diamond anvil cell techniques can produce calibrated static pressures of over 300 to 400 GPa range and this technology, when interfaced with the synchrotron radiation sources, can yield rapid structural information (1-3). These capabilities have given new impetus for investigation of phase transformations in metallic systems at extreme conditions of temperatures and pressures and in establishing phase boundaries at high pressures and high temperatures. Cerium (Ce) and thorium (Th) metals occupy special positions in the periodic table at the beginning of the 4-f lanthanide and 5-f, actinide series, respectively. Ce has one electron in the localized 4-f shell, apart from the three valence electrons. Th metal, on the other hand, has four valence electrons and an unoccupied 5-f band above the Fermi-energy at ambient conditions. In view of the unoccupied 5-f band, Th metal is normally regarded as a tetravalent transition metal like Ti, Zr, and Hf and its bonding and other electronic properties can be explained within the tetravalent transition metal framework. However, the application of ultra-high pressures causes the delocalization of the 4-f shell in Ce and it is believed that Ce above 0.8 GPa pressure is a 4-f band metal

Nanosize stabilization of cubic and tetragonal phases in reactive plasma synthesized zirconia powders

Energy Technology Data Exchange (ETDEWEB)

Jayakumar, S., E-mail: sjayakumar.physics@gmail.com [Research and Development Centre, Bharathiar University, Coimbatore 641 014 (India); Department of Physics, Pollachi Institute of Engineering and Technology, Pollachi 642 205 (India); Ananthapadmanabhan, P.V.; Thiyagarajan, T.K. [Laser and Plasma Technology Division, BARC, Trombay, Mumbai 400 085 (India); Perumal, K. [Vision for Wisdom, Temple of Consciousness, Aliyar 642 101 (India); Mishra, S.C. [Department of Metallurgical and Materials Engg, National Institute of Technology, Rourkela 769 008 (India); Suresh, G. [Department of Physics, Park College of Engineering and Technology, Coimbatore 641 659 (India); Su, L.T.; Tok, A.I.Y. [School of Materials Science and Engg, Nanyang Technological University, 50 Nanyang Avenue, Singapore 639 798 (Singapore)

2013-06-15

Pure zirconium oxide powders with particle size 2–33 nm are synthesized by reactive plasma processing. Transmission electron microscopy investigation of these particles revealed size dependent behavior for their phase stabilization. The monoclinic phase is found to be stable when particle size is ≥20 nm; Tetragonal is found to be stabilized in the range of 7–20 nm and as the particle size decreases to 6 nm and less, the cubic phase is stabilized. - Highlights: ► Direct conversion of micron-sized zirconium hydride powder to single crystal ZrO{sub 2} nanopowder. ► Size dependent stabilization of cubic, tetragonal and monoclinic phases in the reactive plasma synthesized ZrO{sub 2} nanopowder. ► Transmission electron microscopic investigation to identify particles of different sizes and their corresponding phase structure.

Origin of the pressure-dependent Tc valley in superconducting simple cubic phosphorus

Science.gov (United States)

Wu, Xianxin; Jeschke, Harald O.; Di Sante, Domenico; von Rohr, Fabian O.; Cava, Robert J.; Thomale, Ronny

2018-03-01

Motivated by recent experiments, we investigate the pressure-dependent electronic structure and electron-phonon (e-ph) coupling for simple cubic phosphorus by performing first-principles calculations within the full potential linearized augmented plane-wave method. As a function of increasing pressure, our calculations show a valley feature in Tc, followed by an eventual decrease for higher pressures. We demonstrate that this Tc valley at low pressures is due to two nearby Lifshitz transitions, as we analyze the band-resolved contributions to the e-ph coupling. Below the first Lifshitz transition, the phonon hardening and shrinking of the γ Fermi surface with s -orbital character results in a decreased Tc with increasing pressure. After the second Lifshitz transition, the appearance of δ Fermi surfaces with 3 d -orbital character generate strong e-ph interband couplings in α δ and β δ channels, and hence lead to an increase of Tc. For higher pressures, the phonon hardening finally dominates, and Tc decreases again. Our study reveals that the intriguing Tc valley discovered in experiment can be attributed to Lifshitz transitions, while the plateau of Tc detected at intermediate pressures appears to be beyond the scope of our analysis. This strongly suggests that aside from e-ph coupling, electronic correlations along with plasmonic contributions may be relevant for simple cubic phosphorus. Our findings hint at the notion that increasing pressure can shift the low-energy orbital weight towards d character, and as such even trigger an enhanced importance of orbital-selective electronic correlations despite an increase of the overall bandwidth.

Structure and phase transition of BiFeO{sub 3} cubic micro-particles prepared by hydrothermal method

Energy Technology Data Exchange (ETDEWEB)

Zhou, Jian-Ping, E-mail: zhoujp@snnu.edu.cn [College of Physics and Information Technology, Shaanxi Normal University, Xi’an 710062 (China); Yang, Ruo-Lin; Xiao, Rui-Juan; Chen, Xiao-Ming [College of Physics and Information Technology, Shaanxi Normal University, Xi’an 710062 (China); Deng, Chao-Yong [Department of Electronic Science, Guizhou University, Guizhou Guiyang 550025 (China)

2012-11-15

Graphical abstract: Bismuth ferrite (BiFeO{sub 3}) cubic micro-particles with smooth surfaces were synthesized. BiFeO{sub 3} has a hexagonal perovskite structure with a space group R3c below 370 °C and rhombohedral perovskite structure with a space group R3m below 755 °C, undergoes a phase transition in the temperature range of 755–817 °C to a cubic structure, then decompose to liquid and Fe{sub 2}O{sub 3} above 939 °C. Highlights: ► BiFeO{sub 3} micro-particles with smooth surface were synthesized by hydrothermal method. ► BiFeO{sub 3} enjoys hexagonal structure with well element ratio and chemical valence. ► BiFeO{sub 3} transition from rhombohedral phase to cubic phase lasts 60 °C. -- Abstract: Single-phase bismuth ferrite (BiFeO{sub 3}) powders were synthesized with a hydrothermal method by controlling the experimental conditions carefully. The powder structure, morphology and composition were characterized by using X-ray diffraction (XRD), scanning electron microscopy, transmission electron microscope, Raman measurement and X-ray photoelectron spectroscopy. The particles change from irregular agglomerations to regular cubes with increasing KOH concentration. The large BiFeO{sub 3} cubic particles enjoy much smooth surfaces with well-matched element ratio (Bi:Fe:O = 1:1:3) and chemical valence (Bi{sup 3+}, Fe{sup 3+} and O{sup 2−}). The high temperature XRD and differential scanning calorimetry show that BiFeO{sub 3} powders have a hexagonal perovskite structure with a space group R3c below 370 °C and a rhombohedral structure with a space group R3m below 755 °C. BiFeO{sub 3} undergoes a phase transition in the temperature range of 755–817 °C from rhombohedral structure to a cubic phase, then decomposes to liquid and Fe{sub 2}O{sub 3} above 939 °C.

High-pressure phase diagrams of liquid CO2 and N2

Science.gov (United States)

Boates, Brian; Bonev, Stanimir

2011-06-01

The phase diagrams of liquid CO2 and N2 have been investigated using first-principles theory. Both materials exhibit transitions to conducting liquids at high temperatures (T) and relatively modest pressures (P). Furthermore, both liquids undergo polymerization phase transitions at pressures comparable to their solid counterparts. The liquid phase diagrams have been divided into several regimes through a detailed analysis of changes in bonding, as well as structural and electronic properties for pressures and temperatures up to 200 GPa and 10 000 K, respectively. Similarities and differences between the high- P and T behavior of these fluids will be discussed. Calculations of the Hugoniot are in excellent agreement with available experimental data. Work supported by NSERC, LLNL, and the Killam Trusts. Prepared by LLNL under Contract DE-AC52-07NA27344.

Phase martensitic transformation study in mechanically alloyed Ti{sub 50}Ni{sub 25}Fe{sub 25} alloy via high pressure

Energy Technology Data Exchange (ETDEWEB)

Lima, Joao Cardoso de; Ferreira, Ailton da Silva, E-mail: joao.cardoso.lima@ufsc.br [Universidade Federal de Santa Catarina (UFSC), Florianopolis (Brazil); Rovani, Pablo Roberto; Pereira, Altair Soria [Universidade Federal do Rio Grande do Sul (UFRGS), Porto Alegre (Brazil)

2016-07-01

Full text: Alloys based on titanium and nickel with shape memory effect (SME) have been widely investigated due to potential use in different areas of science and technology, such as electronics, medicine, and space.1 Among them, the superalloys Ti-Ni-Fe show high corrosion resistance and good mechanical properties even at high temperatures that make them suitable for use in applications such as power plant components that work under aggressive conditions. At room temperature, the TiNi alloy has a monoclinic (B19'), known as the martensitic phase. With increasing temperature, the B19' phase transforms into a trigonal/hexagonal (B19) phase, known as the R- or pre martensitic phase, which, in its turn, transforms into a cubic (B2) structure, known as the austenitic phase. On cooling to room temperature, the reverse B2→B19→B19' phase transformations are observed. Since the B19↔B19' transformation occurs at a temperature low enough to inhibit diffusion-controlled processes, it belongs to a class of diffusionless phase transformations known as martensitic transformations. For this study, a Ti{sub 50}Ni{sub 25}Fe{sub 25} (B2) alloy was prepared by mechanical alloying, and the effects of high pressures up to 18 GPa will be presented. The structural changes with increasing pressure were followed by recording in situ angle-dispersive X-ray diffraction (ADXRD) diffractograms, in transmission geometry, using a long fine focus Mo X-ray tube and an imaging plate detector. The obtained results were already reported in Ref [1]. (1) A. S. Ferreira, P. R. Rovani, J. C. de Lima, A. S. Pereira, J. Appl. Phys. 117 (2015). (author)

Phase transition of solid bismuth under high pressure

International Nuclear Information System (INIS)

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

2016-01-01

As a widely used pressure calibrator, the structural phase transitions of bismuth from phase I, to phase II, to phase III, and then to phase V with increasing pressure at 300 K have been widely confirmed. However, there are different structural versions for phase III, most of which are determined by x-ray diffraction (XRD) technology. Using x-ray absorption fine structure (XAFS) measurements combined with ab initio calculations, we show that the proposed incommensurate composite structure of bismuth of the three configurations is the best option. An abnormal continuous increase of the nearest-neighbor distance of phase III with elevated pressure is also observed. The electronic structure transformation from semimetal to metal is responsible for the complex behavior of structure transformation. (paper)

Auger electron spectroscopy analysis for growth interface of cubic boron nitride single crystals synthesized under high pressure and high temperature

Science.gov (United States)

Lv, Meizhe; Xu, Bin; Cai, Lichao; Guo, Xiaofei; Yuan, Xingdong

2018-05-01

After rapid cooling, cubic boron nitride (c-BN) single crystals synthesized under high pressure and high temperature (HPHT) are wrapped in the white film powders which are defined as growth interface. In order to make clear that the transition mechanism of c-BN single crystals, the variation of B and N atomic hybrid states in the growth interface is analyzed with the help of auger electron spectroscopy in the Li-based system. It is found that the sp2 fractions of B and N atoms decreases, and their sp3 fractions increases from the outer to the inner in the growth interface. In addition, Lithium nitride (Li3N) are not found in the growth interface by X-ray diffraction (XRD) experiment. It is suggested that lithium boron nitride (Li3BN2) is produced by the reaction of hexagonal boron nitride (h-BN) and Li3N at the first step, and then B and N atoms transform from sp2 into sp3 state with the catalysis of Li3BN2 in c-BN single crystals synthesis process.

The influence of high hydrostatic pressure on lattice parameters of a single crystal of BaTiO3

International Nuclear Information System (INIS)

Malinowski, M.; Lukaszewicz, K.; Asbrink, S.

1986-01-01

The lattice parameters of a single crystal of BaTiO 3 have been measured under high hydrostatic pressure up to 5 GPa using a diamond-anvil high-pressure cell of a new design. The lattice becomes cubic at 2.08(8) GPa and stays cubic at higher pressures. The pressure dependence of the tetragonal-cubic transition temperature is estimated to be -46 K GPa -1 . (orig.)

A theoretical study of pressure-induced phase transitions and electronic band structure of anti-A-sesquioxide type γ-Be3N2

International Nuclear Information System (INIS)

Paliwal, Uttam; Joshi, Kunj Bihari

2011-01-01

Structural parameters and electronic band structure of anti-A-sesquioxide (aAs) type γ-Be 3 N 2 are presented following the first-principles linear combination of atomic orbitals method within the framework of a posteriori density-functional theory implemented in the CRYSTAL code. Pressure-induced phase transitions among the four polymorphs α, β, cubic-γ and aAs-γ of Be 3 N 2 are examined. Enthalpy-pressure curves do not show the possibility of pressure-induced structural phase transition to the cubic-γ phase. However, α → aAs-γ and β → aAs-γ structural phase transitions are observed at 139 GPa and 93 GPa, respectively. Band structure calculations predict that aAs-γ Be 3 N 2 is an indirect semiconductor with 4.73 eV bandgap at L point. Variation of bandgap with pressure and deformation potentials are studied for the α, β and aAs-γ polymorphs. Pressure-dependent band structure calculations reveal that, within the low-pressure limit, bandgaps of β and aAs-γ increase with pressure unlike α-Be 3 N 2 .

Pressure response of vacancy ordered maghemite (γ-Fe2O3) and high pressure transformed hematite (α-Fe2O3)

Science.gov (United States)

Hearne, Giovanni; Pischedda, Vittoria

2012-03-01

Combined XRD and Mössbauer effect spectroscopy studies to high pressures of ˜30 GPa of vacancy ordered maghemite are presented. The vacancy ordered superstructure is robust and remains intact up to the pressure-induced onset transition to hematite at 13-16 GPa. The pressure transformed hematite is shown to be crystallographically textured, unlike the randomised low pressure maghemite phase. This arises out of a pressure or stress instigated topotactic transformation of the cubic-spinel to hexagonal-corundum structure. The textured sample permits us to obtain information on the spin reorientation behavior of the pressure transformed hematite in compression and decompression sequences. Spin reorientation is restricted to ˜15° over wide pressure ranges, attributable to the effect of entrapped vacancies in the high pressure structure. Thus there are structural and magnetic peculiarities specific to pressure transformed hematite not evident in pressurized hematite starting material. These are triggered by the maghemite→hematite transformation.

Rapid hydrothermal route to synthesize cubic-phase gadolinium oxide nanorods

International Nuclear Information System (INIS)

Hazarika, Samiran; Paul, Nibedita; Mohanta, Dambarudhar

2014-01-01

An inexpensive fabrication route and growth mechanism is being reported for obtaining quality gadolinium oxide ( Gd 2 O 3 ) nanoscale rods. The elongated nanoscale systems, as produced via a hydrothermal process, were characterized by X-ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM), optical absorption spectroscopy, photoluminescence (PL) spectroscopy, Raman spectroscopy and magnetic hysteresis measurements. XRD patterns of the nanorods, as-prepared from independent precursors of different pH, depict a cubic crystal phase and an average crystallite size of 5-6.5 nm. As revealed from HRTEM micrographs, diameter of the nanorods prepared at pH = 13.3 (∼7 nm) was much smaller than the rods prepared at pH = 10.8 (∼19 nm). However, the aspect ratio was more than double in the former case than the latter case. PL response was found to be dominated by defect mediated emissions, whereas Raman spectrum of a given specimen (pH = 10.8) has revealed characteristic F g + A g modes of cubic phase of Gd 2 O 3 nanorods, apart from other independent modes. Furthermore, M ∼ H plot of the nanorod system (pH = 10.8) exhibited slight departure from the ideal superparamagnetic behaviour, with low remanence and coercive field values. The exploitation of one-dimensional Gd 2 O 3 nanorods have immense potential in the production of advanced contrast agents, smart drives and also in making novel ferrofluids of technological relevance. (author)

Recent progress in high-pressure studies on organic conductors

Directory of Open Access Journals (Sweden)

Syuma Yasuzuka and Keizo Murata

2009-01-01

Full Text Available Recent high-pressure studies of organic conductors and superconductors are reviewed. The discovery of the highest Tc superconductivity among organics under high pressure has triggered the further progress of the high-pressure research. Owing to this finding, various organic conductors with the strong electron correlation were investigated under high pressures. This review includes the pressure techniques using the cubic anvil apparatus, as well as high-pressure studies of the organic conductors up to 10 GPa showing extraordinary temperature and pressure dependent transport phenomena.

Multi-component vapor-liquid equilibrium model for LES of high-pressure fuel injection and application to ECN Spray A

NARCIS (Netherlands)

Matheis, Jan; Hickel, S.

2018-01-01

We present and evaluate a two-phase model for Eulerian large-eddy simulations (LES) of liquid-fuel injection and mixing at high pressure. The model is based on cubic equations of state and vapor-liquid equilibrium calculations and can represent the coexistence of supercritical states and

Anomalous phase transition of InN nanowires under high pressure

International Nuclear Information System (INIS)

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

2015-01-01

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. (paper)

Structural and electronic properties of high pressure phases of lead chalcogenides

Science.gov (United States)

Petersen, John; Scolfaro, Luisa; Myers, Thomas

2012-10-01

Lead chalcogenides, most notably PbTe and PbSe, have become an active area of research due to their thermoelectric properties. The high figure of merit (ZT) of these materials has brought much attention to them, due to their ability to convert waste heat into electricity. Variation in synthesis conditions gives rise to a need for analysis of structural and thermoelectric properties of these materials at different pressures. In addition to the NaCl structure at ambient conditions, lead chalcogenides have a dynamic orthorhombic (Pnma) intermediate phase and a higher pressure yet stable CsCl phase. By altering the lattice constant, we simulate the application of external pressure; this has notable effects on ground state total energy, band gap, and structural phase. Using the General Gradient Approximation (GGA) in Density Functional Theory (DFT), we calculate the phase transition pressures by finding the differences in enthalpy from total energy calculations. For each phase, elastic constants, bulk modulus, shear modulus, Young's modulus, and hardness are calculated, using two different approaches. In addition to structural properties, we analyze the band structure and density of states at varying pressures, paying special note to thermoelectric implications.

High-pressure boron hydride phases

International Nuclear Information System (INIS)

Barbee, T.W. III; McMahan, A.K.; Klepeis, J.E.; van Schilfgaarde, M.

1997-01-01

The stability of boron-hydrogen compounds (boranes) under pressure is studied from a theoretical point of view using total-energy methods. We find that the molecular forms of boranes known to be stable at ambient pressure become unstable at high pressure, while structures with extended networks of bonds or metallic bonding are energetically favored at high pressures. If such structures are metastable on return to ambient pressure, they would be energetic as well as dense hydrogen storage media. An AlH 3 -like structure of BH 3 is particularly interesting in that it may be accessible by high-pressure diamond anvil experiments, and should exhibit both second-order structural and metal-insulator transitions at lower pressures. copyright 1997 The American Physical Society

The pseudo-binary mercury chalcogenide alloy HgSe sub 0 sub . sub 7 S sub 0 sub . sub 3 at high pressure: a mechanism for the zinc blende to cinnabar reconstructive phase transition

CERN Document Server

Kozlenko, D P; Ehm, L; Hull, S; Savenko, B N; Shchennikov, V V; Voronin, V I

2003-01-01

The structure of the pseudo-binary mercury chalcogenide alloy HgSe sub 0 sub . sub 7 S sub 0 sub . sub 3 has been studied by x-ray and neutron powder diffraction at pressures up to 8.5 GPa. A phase transition from the cubic zinc blende structure to the hexagonal cinnabar structure was observed at P approx 1 GPa. A phenomenological model of this reconstructive phase transition based on a displacement mechanism is proposed. Analysis of the geometrical relationship between the zinc blende and the cinnabar phases has shown that the possible order parameter for the zinc blende-cinnabar structural transformation is the spontaneous strain e sub 4. This assignment agrees with the previously observed high pressure behaviour of the elastic constants of some mercury chalcogenides.

High pressure Moessbauer spectroscopy with nuclear resonant forward scattering of synchrotron radiation

Energy Technology Data Exchange (ETDEWEB)

Nasu, Saburo [Osaka Univ., Toyonaka (Japan). Faculty of Engineering Science

1996-04-01

The first observation of the pressure-induced transition from the antiferromagnetic to the ferromagnetic SrFeO{sub 3} was succeeded by measuring Moessbauer spectroscopy under high pressure produced by the diamond anvil cell (DAC). Sample is a polycrystal powder of antiferromagnetic SrFe0{sub 3} with the Neel temperature T{sub N}=140 K, the cubic system and perovskite type crystal. The average pressures used were 44 GPa and 74 GPa (300 K). SrFeO{sub 3} is paramagnetic material at 300 K, but the Neel temperature increases more than 300 K under high pressure and the quantized axis turns to the external magnetic field, so that we take it as it means the system displaying the phase transition to the ferromagnet. By the method, we can practice the measurement at low and high temperature under the external magnetic field by using the polarized light source. (S.Y.)

Cubic phase control of ultrashort laser pulses

International Nuclear Information System (INIS)

Mecseki, K.; Erdelyi, M.; Kovacs, A.P.; Szabo, G.

2006-01-01

Complete test of publication follows. The temporal shape of an ultrashort laser pulse may change upon propagating through a linear dispersive medium having a phase shift ψω. The change can be characterized by the Taylor-coefficients of the phase shift which are calculated around the central frequency ω 0 of the pulse. Measurements and independent control of the group delay dispersion (GDD, ψ'(ω 0 )) and the third order dispersion (TOD, ψ'(ω 0 )) are important in several research fields, particularly in the generation of ultrashort laser pulses by chirped pulse amplification (CPA) and pulse shaping for molecular control. The GDD and the TOD of an ideal pulse compressor are equal to the negative of the corresponding dispersion coefficients of the medium. However, in the case of prism-pair and grating-pair compressor is different from the ratio of the coefficients of the medium to be compensated for. Therefore it is necessary to develop so-called cubic compressors that are able to control the TOD of the pulse, yet, do not affect the GDD. In this paper a new cubic compressor setup is investigated theoretically and experimentally, which resembles the set-up proposed by White, however, we control the GDD and the TOD by the position of a birefringent, semi-cylinder crystal place around the focal point of an achromatic lens. For the evaluation of the phase shift introduced by the proposed cubic compressor, a ray tracing program was written. The program allows optimizing the compressor parameters, such as the radius of the crystal, magnification of the lens etc. Calcite was applied because it is a strong birefringent material. Calculations showed that there is a trajectory, along which shifting the crystal the TOD can be tuned independently of the GDD. The value of the TOD changed in a relatively wide range between -3.15 x 10 5 fs 3 and -1.67 x 10 5 fs 3 . Although the defocus also affects the angular dispersion of the pulse leaving the compressor, if does not exceed

Performance of Cubic Eos At High Pressures Performance des équations d'état cubiques à hautes pressions

Directory of Open Access Journals (Sweden)

Stamataki S.

2006-12-01

Full Text Available This paper presents an evaluation of the performance of cubic equations of state in the prediction of the phase behavior of hyperbaric mixtures. It points out a number of problems that should be resolved in a cooperative way. Items related to EoS parameter definitions such as interaction coefficients, critical properties of hydrocarbon compounds and volume translation are investigated. VLE experimental data, isothermal flash compositional and volumetric data up to 4000 bar as well as PVT data up to 2000 bar for binary mixtures and synthetic multicomponent systems have been considered in this study. Correlation and prediction results are presented with the translated and modified Peng-Robinson (t-mPR EoS. It is shown that serious problems are encountered at high pressure, when extrapolated interaction coefficients are used. Prediction of saturation pressures of gas condensates is more satisfactory when binary interaction parameters are obtained from high pressure dew point correlations. Compositional and volumetric predictions are remarkable under the assumption that definition of the EoS parameters is based on high pressure VLE binary data. Contradictory results are obtained with different methods for estimating the critical properties of high molecular weight hydrocarbons. Generalized expressions for the volume translation appear to be very efficient even at very high temperatures and pressures (up to 2000 bar. Cet article présente une évaluation des performances des équations d'états (EoS cubiques pour la prévision des comportements de phases des mélanges hyperbares. Il met en évidence un certain nombre de problèmes auxquels il devrait être répondu d'une manière coopérative. Les points relatifs à la définition des paramètres des EoS, tels que les coefficients d'interaction, les propriétés critiques des composants hydrocarbonés et la translation de volume sont examinés. Plusieurs types d'informations ont été pris en compte

High-pressure phases of CuI studied by 129I-Moessbauer spectroscopy

International Nuclear Information System (INIS)

Kaindl, G.; Nowik, I.; Frank, K.H.

1992-01-01

The results of an 129 I-Moessbauer study of the high-pressure phases of CuI at 4.2 K and for external pressures up to 71 kbar are reported. The isomer shift S and the electric quadrupole interaction E q are found to undergo large discontinuities at the crystallographic phase-transition pressures of ≅18 kbar from zinc-blende to rhombohedral structure and at ≅46 kbar from rhombohedral to tetragonal. The pressure coefficients of these hyperfine parameters are significantly different for the three phases (zinc-blende; rhombohedral; tetragonal): dS/dP=-3.3; =+1.5; =+2.5x10 -3 mm/s/kbar. These results cannot be explained in terms of a simple molecular-orbital picture; instead, they reflect pressure-induced variations of the halogen-p/metal-d hybridization in the valence bands of the various phases of CuI. (orig.)

Method for calculating solid-solid phase transitions at high temperature: An application to N2O

International Nuclear Information System (INIS)

Kuchta, B.; Etters, R.D.

1992-01-01

Two similar techniques for calculating solid-solid phase transitions at high temperatures are developed, where the contribution of the entropy may be a decisive factor. They utilize an artificial reversible path from one phase to another by application of a control parameter. Thermodynamic averages are calculated using constant-volume and constant-pressure Monte Carlo techniques. An application to N 2 O at room temperature shows that the cubic Pa3 to orthorhombic Cmca transition occurs near 4.9-GPa pressure, very close to the value calculated at very low temperatures. These results support experimental evidence that the transition pressure is virtually independent of temperature

Structural, electronic and elastic properties of the cubic CaTiO3 under pressure: A DFT study

Directory of Open Access Journals (Sweden)

Saad Tariq

2015-07-01

Full Text Available Using highly accurate FP-LAPW method with GGA approximation structural, electronic and elastic properties of cubic CaTiO3 have been calculated from 0-120 GPa range of pressure. It is observed that lattice constant, bond length and anisotropy factor decrease with increase in pressure. Also the brittle nature and indirect band-gap of the compound become ductile and direct band-gap respectively at 120 GPa. Moduli of elasticity, density of the material, Debye temperature and wave elastic wave velocities increase with increase in pressure. Spin dependent DOS’s plots show invariant anti-ferromagnetic nature of the compound under pressure. Our calculated results are in good agreement with available theoretical and experimental results.

Terbium oxide at high pressures

International Nuclear Information System (INIS)

Dogra, Sugandha; Sharma, Nita Dilawar; Singh, Jasveer; Bandhyopadhyay, A.K.

2011-01-01

In this work we report the behaviour of terbium oxide at high pressures. The as received sample was characterized at ambient by X-ray diffraction and Raman spectroscopy. The X-ray diffraction showed the sample to be predominantly cubic Tb 4 O 7 , although a few peaks also match closely with Tb 2 O 3 . In fact in a recent study done on the same sample, the sample has been shown to be a mixture of Tb 4 O 7 and Tb 2 O 3 . The sample was subjected to high pressures using a Mao-Bell type diamond anvil cell upto a pressure of about 42 GPa with ruby as pressure monitor

Triclinic-cubic phase transition and negative expansion in the actinide IV (Th, U, Np, Pu) diphosphates

International Nuclear Information System (INIS)

Wallez, Gilles; Bregiroux, Damien; Raison, Philippe E.; Bykov, Denis; Konings, Rudy J.M.; Dacheux, Nicolas; Clavier, Nicolas; Delevoye, Laurent; Popa, Karin; Fitch, Andrew N.

2012-01-01

The AnP 2 O 7 diphosphates (An = Th, U, Np, Pu) have been synthesized by various routes depending on the stability of the An(IV) cation and its suitability for the unusual octahedral environment. Synchrotron and X-ray diffraction, thermal analysis, Raman spectroscopy, and 31 P nuclear magnetic resonance reveal them as a new family of diphosphates which probably includes the recently studied CeP 2 O 7 . Although they adopt at high temperature the same cubic archetypal cell as the other known MP 2 O 7 diphosphates, they differ by a very faint triclinic distortion at room temperature that results from an ordering of the P 2 O 7 units, as shown using high-resolution synchrotron diffraction for UP 2 O 7 . The uncommon triclinic-cubic phase transition is first order, and its temperature is very sensitive to the ionic radius of An(IV). The conflicting effects which control the thermal variations of the P-O-P angle are responsible for a strong expansion of the cell followed by a contraction at higher temperature. This inversion of expansion occurs at a temperature significantly higher than the phase transition, at variance with the parent compounds with smaller Mn(IV) cations in which the two phenomena coincide. As shown by various approaches, the P-O-b-P linkage remains bent in the cubic form. (authors)

MgB2 and Mg1-xAlxB2 single crystals: high pressure growth and physical properties

International Nuclear Information System (INIS)

Karpinski, J.; Kazakov, S.M.; Jun, J.; Zhigadlo, N.D.; Angst, M.; Puzniak, R.; Wisniewski, A.

2004-01-01

Single crystals of MgB 2 have been grown with a high pressure cubic anvil technique. They grow via the peritectic decomposition of the MgNB 9 ternary nitride. The crystals are of a size up to 2 x 1 x 0.1 mm 3 with a weight up to 230 μg. Typically they have transition temperatures between 38 and 38.6 K with a width of 0.3-0.5 K. Investigations of the P-T phase diagram prove that the MgB 2 phase is stable at least up to 2190 deg. C at high hydrostatic pressure in the presence of Mg vapor under high pressure. Substitution of aluminum for magnesium in single crystals leads to stepwise decrease of T c . This indicates a possible appearance of superstructures or phases with different T c 's. The upper critical field decreases with Al doping

Nonsymmorphic cubic Dirac point and crossed nodal rings across the ferroelectric phase transition in LiOsO3

Science.gov (United States)

Yu, Wing Chi; Zhou, Xiaoting; Chuang, Feng-Chuan; Yang, Shengyuan A.; Lin, Hsin; Bansil, Arun

2018-05-01

Crystalline symmetries can generate exotic band-crossing features, which can lead to unconventional fermionic excitations with interesting physical properties. We show how a cubic Dirac point—a fourfold-degenerate band-crossing point with cubic dispersion in a plane and a linear dispersion in the third direction—can be stabilized through the presence of a nonsymmorphic glide mirror symmetry in the space group of the crystal. Notably, the cubic Dirac point in our case appears on a threefold axis, even though it has been believed previously that such a point can only appear on a sixfold axis. We show that a cubic Dirac point involving a threefold axis can be realized close to the Fermi level in the nonferroelectric phase of LiOsO3. Upon lowering temperature, LiOsO3 has been shown experimentally to undergo a structural phase transition from the nonferroelectric phase to the ferroelectric phase with spontaneously broken inversion symmetry. Remarkably, we find that the broken symmetry transforms the cubic Dirac point into three mutually crossed nodal rings. There also exist several linear Dirac points in the low-energy band structure of LiOsO3, each of which is transformed into a single nodal ring across the phase transition.

Visualization of membrane protein crystals in lipid cubic phase using X-ray imaging

International Nuclear Information System (INIS)

Warren, Anna J.; Armour, Wes; Axford, Danny; Basham, Mark; Connolley, Thomas; Hall, David R.; Horrell, Sam; McAuley, Katherine E.; Mykhaylyk, Vitaliy; Wagner, Armin; Evans, Gwyndaf

2013-01-01

A comparison of X-ray diffraction and radiographic techniques for the location and characterization of protein crystals is demonstrated on membrane protein crystals mounted within lipid cubic phase material. The focus in macromolecular crystallography is moving towards even more challenging target proteins that often crystallize on much smaller scales and are frequently mounted in opaque or highly refractive materials. It is therefore essential that X-ray beamline technology develops in parallel to accommodate such difficult samples. In this paper, the use of X-ray microradiography and microtomography is reported as a tool for crystal visualization, location and characterization on the macromolecular crystallography beamlines at the Diamond Light Source. The technique is particularly useful for microcrystals and for crystals mounted in opaque materials such as lipid cubic phase. X-ray diffraction raster scanning can be used in combination with radiography to allow informed decision-making at the beamline prior to diffraction data collection. It is demonstrated that the X-ray dose required for a full tomography measurement is similar to that for a diffraction grid-scan, but for sample location and shape estimation alone just a few radiographic projections may be required

Visualization of membrane protein crystals in lipid cubic phase using X-ray imaging

Energy Technology Data Exchange (ETDEWEB)

Warren, Anna J. [Diamond Light Source, Harwell Science and Innovation Campus, Didcot OX11 0DE (United Kingdom); Armour, Wes [Diamond Light Source, Harwell Science and Innovation Campus, Didcot OX11 0DE (United Kingdom); Oxford e-Research Centre, 7 Keble Road, Oxford OX1 3QG (United Kingdom); Axford, Danny; Basham, Mark; Connolley, Thomas; Hall, David R. [Diamond Light Source, Harwell Science and Innovation Campus, Didcot OX11 0DE (United Kingdom); Horrell, Sam [Diamond Light Source, Harwell Science and Innovation Campus, Didcot OX11 0DE (United Kingdom); University of Liverpool, Liverpool L69 3BX (United Kingdom); McAuley, Katherine E.; Mykhaylyk, Vitaliy; Wagner, Armin; Evans, Gwyndaf, E-mail: gwyndaf.evans@diamond.ac.uk [Diamond Light Source, Harwell Science and Innovation Campus, Didcot OX11 0DE (United Kingdom)

2013-07-01

A comparison of X-ray diffraction and radiographic techniques for the location and characterization of protein crystals is demonstrated on membrane protein crystals mounted within lipid cubic phase material. The focus in macromolecular crystallography is moving towards even more challenging target proteins that often crystallize on much smaller scales and are frequently mounted in opaque or highly refractive materials. It is therefore essential that X-ray beamline technology develops in parallel to accommodate such difficult samples. In this paper, the use of X-ray microradiography and microtomography is reported as a tool for crystal visualization, location and characterization on the macromolecular crystallography beamlines at the Diamond Light Source. The technique is particularly useful for microcrystals and for crystals mounted in opaque materials such as lipid cubic phase. X-ray diffraction raster scanning can be used in combination with radiography to allow informed decision-making at the beamline prior to diffraction data collection. It is demonstrated that the X-ray dose required for a full tomography measurement is similar to that for a diffraction grid-scan, but for sample location and shape estimation alone just a few radiographic projections may be required.

High pressure Raman scattering study on the phase stability of LuVO4

International Nuclear Information System (INIS)

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

2009-01-01

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. - Graphical abstract: Study of scheelite-fergusonite transition in RVO 4 by Raman spectroscopy is rare. Here we report Raman spectroscopic investigations of LuVO 4 at high pressure to obtain insight into nature of post-scheelite phases.

Magnetic and Structural Phase Transitions in Thulium under High Pressures and Low Temperatures

Energy Technology Data Exchange (ETDEWEB)

Vohra, Yogesh K.; Tsoi, Georgiy M.; Samudrala, Gopi K. [UAB

2017-10-01

The nature of 4f electrons in many rare earth metals and compounds may be broadly characterized as being either "localized" or "itinerant", and is held responsible for a wide range of physical and chemical properties. The pressure variable has a very dramatic effect on the electronic structure of rare earth metals which in turn drives a sequence of structural and magnetic transitions. We have carried out four-probe electrical resistance measurements on rare earth metal Thulium (Tm) under high pressures to 33 GPa and low temperatures to 10 K to monitor the magnetic ordering transition. These studies are complemented by angle dispersive x-ray diffraction studies to monitor crystallographic phase transitions at high pressures and low temperatures. We observe an abrupt increase in magnetic ordering temperature in Tm at a pressure of 17 GPa on phase transition from ambient pressure hcp-phase to α-Sm phase transition. In addition, measured equation of state (EOS) at low temperatures show anomalously low thermal expansion coefficients likely linked to magnetic transitions.

/sup 87/Rb NMR study at the cubic to tetragonal phase transition in RbCaF/sub 3/

Energy Technology Data Exchange (ETDEWEB)

Bulou, A [Angers Univ., 72 - Le Mans (France). Centre Universitaire; Theveneau, H; Trokiner, A; Papon, P [Ecole Superieure de Physique et Chimie Industrielles, 75 - Paris (France)

1979-07-01

The /sup 87/Rb nuclear magnetic resonance spectrum, in perovskite single crystal of RbCaF/sub 3/, is studied above and below the cubic-to-tetragonal phase transition occurring at 198 K. In the high-temperature cubic phase, the temperature dependence of the resonance line amplitude deviates from the Curie law and this can be attributed to the existence of tetragonal domains. In the low temperature tetragonal phase, a second-order quadrupole shift of the central line is observed, from which the CaF/sub 6/ tilt angle (order parameter) is derived. The order parameter temperature dependence is described by a power law with a cross over from exponent 0.5 to exponent 0.32 at 150 K. The tilt angle PHI is compared to the values obtained from X-ray and neutron powder diffraction data.

Magnetic phase diagram of UNi2Si2 under magnetic field and high-pressure

International Nuclear Information System (INIS)

Honda, F.; Oomi, G.; Svoboda, P.; Syshchenko, A.; Sechovsky, V.; Khmelevski, S.; Divis, M.; Andreev, A.V.; Takeshita, N.; Mori, N.; Menovsky, A.A.

2001-01-01

Measurements of electrical resistance under high pressure and neutron diffraction in high-magnetic field of single crystalline UNi 2 Si 2 have been performed. We have found the analogy between the p-T and B-T magnetic phase diagrams. It is also found that the propagation vector q Z of incommensurate antiferromagnetic phase decreases with increasing magnetic field. A new pronounced pressure-induced incommensurate-commensurate magnetic phase transition has been detected

A popular metastable omega phase in body-centered cubic steels

Energy Technology Data Exchange (ETDEWEB)

Ping, D.H., E-mail: ping.de-hai@nims.go.jp [National Institute for Materials Science, Sengen 1-2-1, Tsukuba 305-0047 (Japan); Geng, W.T., E-mail: geng@ustb.edu.cn [School of Materials Science and Engineering, University of Science and Technology Beijing, Beijing 100083 (China)

2013-05-15

Steel remains to be one of the most common structural materials in the world as human civilization advances from the Iron Age to the ongoing Silicon Age. Our knowledge of its microstructure evolution and structure–performance relationship is nevertheless still incomplete. We report the observation and characterization of a long ignored metastable phase formed in steels with body-centered cubic (bcc) structure using both transmission electron microscopy and density functional theory calculations. This ω phase has a hexagonal structure and coherent interface with the matrix: a{sub ω} = √2 × a{sub bcc} and c{sub ω} = √3/2 × a{sub bcc}. It is 3.6% smaller in volume and 0.18 eV higher in energy than bcc-Fe, with atoms in alternating close- and loose-packed layers couple anti-ferromagnetically. Carbon plays a crucial role in promoting bcc to ω transformation. At a concentration higher than 4 at.% they tend to segregate from the bcc matrix to the ω-phase; at about 14 at.%, they can induce bcc to ω transformation; and finally at 25 at.%, they stabilize the ω phase as ω-Fe{sub 3}C. The ω phase in bcc Fe can serve as sinks for vacancies, H, and He atoms, leading to improved resistance of martensitic steels to irradiation damage. - Highlights: ► A long-ignored metastable ω phase in body-centered cubic (bcc) steel. ► The ω phase has hexagonal structure with lattice parameters a{sub ω} = √2 × a{sub bcc} and c{sub ω} = √3/2 × a{sub bcc}. ► Carbon enrichment is found to play a crucial role on the bcc-to-ω phase transformation. ► The ω phase is strongly related to the martensitic transformation and twinning structure. ► The ω phase in bcc Fe can serve as sinks for vacancies, H, and He atoms.

High pressure phase transitions in Europous oxide

International Nuclear Information System (INIS)

Kremser, D.T.

1982-01-01

The pressure-volume relationship for EuO was investigated to 630 kilobars at room temperature with a diamond-anvil, high-pressure cell. Volumes were determined by x-ray diffraction; pressures were determined by the ruby R 1 fluorescence method. The preferred interpretation involves normal compression behavior for EuO, initially in the B1 (NaCl-type) structure, to about 280 kilobars. Between approx. =280 and approx. =350 kilobars a region of anomalous compressibility in which the volume drops continuously by approximately 2% is observed. A second-order electronic transition is proposed with the 6s band overlapping with the 4f levels, thereby reducing the volume of EuO without changing the structure. This is not a semiconductor-to-metal transition. In reflected light, this transition is correlated with a subtle and continuous change in color from brown-black to a light brown. The collapsed B1 phase (postelectronic transition) is stable between approx. =350 and approx. =400 kilobars. At about 400 kilobars the collapsed B1 structure transforms to the B2 (CsCl-type) structure, with a zero pressure-volume change of approximately 12 +/- 1.5%

Structural, electronic and elastic properties of the cubic CaTiO{sub 3} under pressure: A DFT study

Energy Technology Data Exchange (ETDEWEB)

Tariq, Saad, E-mail: saadigi@hotmail.com; Ahmed, Afaq; Tariq, Samar [Centre of Excellence in Solid State Physics, University of Punjab, Lahore, 54000 (Pakistan); Saad, Saher [Centre for High Energy Physics, University of the Punjab, Lahore (Pakistan)

2015-07-15

Using highly accurate FP-LAPW method with GGA approximation structural, electronic and elastic properties of cubic CaTiO{sub 3} have been calculated from 0-120 GPa range of pressure. It is observed that lattice constant, bond length and anisotropy factor decrease with increase in pressure. Also the brittle nature and indirect band-gap of the compound become ductile and direct band-gap respectively at 120 GPa. Moduli of elasticity, density of the material, Debye temperature and wave elastic wave velocities increase with increase in pressure. Spin dependent DOS’s plots show invariant anti-ferromagnetic nature of the compound under pressure. Our calculated results are in good agreement with available theoretical and experimental results.

Dynamic High Pressure Study of Chemistry and Physics of Molecular Materials

Science.gov (United States)

Jezowski, Sebastian Ryszard

Both temperature and pressure control and influence the packing of molecules in crystalline phases. Our molecular simulations indicate that at ambient pressure, the cubic polymorph of tetracyanoethylene, TCNE, is the energetically stable form up to ˜ 160 K. The observed transition from the cubic to the monoclinic polymorph occurs however only at temperatures above ˜ 318 K due to the large transition barrier. The temperature-induced phase transition in TCNE studied with high-resolution IR spectroscopy is explained in terms of the increased vibrational entropy in the crystals of the monoclinic polymorph. Based upon the inverted design of the Merril-Bassett Diamond Anvil Cell, an improved, second generation dynamic Diamond Anvil Cell was developed. Based on the fluorescence of ruby crystals, we were able to demonstrate that the pressure variation range can be further increased at least up to 7 kbar and that the dynamic pressure compression of up to 1400 GPa/s can be achieved. A new class of mechanophoric system, bis-anthracene, BA, and its photoisomer, PI, is shown to respond reversibly to a mild, static pressure induced by a Diamond Anvil Cell as well as to shear deformation based on absorption spectroscopic measurements. The forward reaction occurs upon illumination with light while the back-reaction may be accelerated upon heating or mechanical stress, coupled to a rehybridization on four equivalent carbon atoms. It is an intriguing result as high pressure stabilizes the photodimerized species in related systems. Our molecular volume simulations ruled out significant differences in the volumes between bis-anthracene and its photoisomer. Kinetic absorption measurements at several different pressures reveal a negative volume of activation in the exothermic back-reaction at room temperature. Through a series of temperature-dependent kinetic measurements it is shown that the barrier of activation for the back-reaction is reduced by more than an order of magnitude at

Lipidic cubic phase serial millisecond crystallography using synchrotron radiation

Directory of Open Access Journals (Sweden)

Przemyslaw Nogly

2015-03-01

Full Text Available Lipidic cubic phases (LCPs have emerged as successful matrixes for the crystallization of membrane proteins. Moreover, the viscous LCP also provides a highly effective delivery medium for serial femtosecond crystallography (SFX at X-ray free-electron lasers (XFELs. Here, the adaptation of this technology to perform serial millisecond crystallography (SMX at more widely available synchrotron microfocus beamlines is described. Compared with conventional microcrystallography, LCP-SMX eliminates the need for difficult handling of individual crystals and allows for data collection at room temperature. The technology is demonstrated by solving a structure of the light-driven proton-pump bacteriorhodopsin (bR at a resolution of 2.4 Å. The room-temperature structure of bR is very similar to previous cryogenic structures but shows small yet distinct differences in the retinal ligand and proton-transfer pathway.

Shock-Assisted Superficial Hexagonal-to-Cubic Phase Transition in GaN/Sapphire Interface Induced by Using Ultra-violet Laser Lift-Of Techniques

International Nuclear Information System (INIS)

Wei-Hua, Chen; Xiao-Dong, Hu; Xiang-Ning, Kang; Xu-Rong, Zhou; Xiao-Min, Zhang; Tong-Jun, Yu; Zhi-Jian, Yang; Ke, Xu; Guo-Yi, Zhang; Xu-Dong, Shan; Li-Ping, You

2009-01-01

Ultra-violet (KrF excimer laser, λ = 248 nm) laser lift-of (LLO) techniques have been operated to the GaN/sapphire structure to separate GaN from the sapphire substrate. Hexagonal to cubic phase transformation induced by the ultra-violet laser lift-of (UV-LLO) has been characterized by micro-Raman spectroscopy, micro-photoluminescence, along with high-resolution transmission electron microscopy (HRTEM). HRTEM indicates that UV-LLO induced phase transition takes place above the LLO interface, without phase transition under the LLO interface. The formed cubic GaN often exists as nanocrystal grains attaching on the bulk hexagonal GaN. The half-loop-cluster-like UV-LLO interface indicates that the LLO-induced shock waves has generated and played an assistant role in the decomposition of the hexagonal GaN and in the formation of cubic GaN grains at the LLO surface

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

Science.gov (United States)

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

Photoluminescence studies of cubic phase GaN grown by molecular beam epitaxy on (001) silicon covered with SiC layer

International Nuclear Information System (INIS)

Godlewski, M.; Ivanov, V.Yu.; Bergman, J.P.; Monemar, B.; Barski, A.; Langer, R.

1997-01-01

In this work we evaluate optical properties of cubic phase GaN epilayers grown on top of (001) silicon substrate prepared by new process. Prior to the growth Si substrate was annealed at 1300-1400 o C in propane. The so-prepared substrate is covered within a thin (∼ 4 nm) SiC wafer, which allowed a successful growth of good morphological quality cubic phase GaN epilayers. The present results confirm recent suggestion on smaller ionization energies of acceptors in cubic phase GaN epilayers. (author)

Oxygen-Rich Lithium Oxide Phases Formed at High Pressure for Potential Lithium-Air Battery Electrode.

Science.gov (United States)

Yang, Wenge; Kim, Duck Young; Yang, Liuxiang; Li, Nana; Tang, Lingyun; Amine, Khalil; Mao, Ho-Kwang

2017-09-01

The lithium-air battery has great potential of achieving specific energy density comparable to that of gasoline. Several lithium oxide phases involved in the charge-discharge process greatly affect the overall performance of lithium-air batteries. One of the key issues is linked to the environmental oxygen-rich conditions during battery cycling. Here, the theoretical prediction and experimental confirmation of new stable oxygen-rich lithium oxides under high pressure conditions are reported. Three new high pressure oxide phases that form at high temperature and pressure are identified: Li 2 O 3 , LiO 2 , and LiO 4 . The LiO 2 and LiO 4 consist of a lithium layer sandwiched by an oxygen ring structure inherited from high pressure ε-O 8 phase, while Li 2 O 3 inherits the local arrangements from ambient LiO 2 and Li 2 O 2 phases. These novel lithium oxides beyond the ambient Li 2 O, Li 2 O 2 , and LiO 2 phases show great potential in improving battery design and performance in large battery applications under extreme conditions.

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

Science.gov (United States)

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

2017-06-01

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

Electronic structure and high pressure phase transition in LaSb and CeSb

International Nuclear Information System (INIS)

Mathi Jaya, S.; Sanyal, S.P.

1992-09-01

The electronic structure and high pressure structural phase transition in cerium and lanthanum antimonides have been investigated using the tight binding LMTO method. The calculation of total energy reveals that the simple tetragonal structure is found to be stable at high pressures for both the compounds. In the case of LaSb, the calculated value of the equilibrium cell volume and the cell volume at which phase transition occurs are found to have a fairly good agreement with the experimental results. However, in the case of CeSb, the agreement is not as good as in LaSb. We also predicted the most favoured c/a value in the high pressure phase (simple tetragonal) for these compounds. Further we present the calculated results on the electronic structure of these systems at the equilibrium as well as at the reduced cell volumes. (author). 8 refs, 11 figs, 1 tab

A new high-pressure phase of Fe2SiO4 and the relationship between spin and structural transitions

Science.gov (United States)

Yamanaka, T.; Kyono, A.; Nakamoto, Y.; Kharlamova, S. A.; Struzhkin, V. V.; Gramsch, S.; Mao, H.; Hemley, R. J.

2013-12-01

Structure transformation of Fe2SiO4 Angle-dispersive powder x-ray diffraction was carried out at beam line 16-BMD APS. Structure of a new high-pressure phase of I-Fe2SiO4 spinel was determined by Rietveld profile fitting of x-ray diffraction data up to 64GPa at ambient temperature. A structural transition from the cubic spinel to the new structure was observed at 34GPa. Diffraction patterns taken at 44.6GPa and 54.6GPa indicate a two-phase mixture of spinel and new high-pressure phase. Reversible transition from I-Fe2SiO4 to spinel was confirmed. Laser heating experiment at 1500K proved the decomposition of Fe2SiO4 spinel to two oxides of FeO and SiO2. Spin transition X-ray emission measurements of Fe2SiO4 were carried out up to 65GPa at ambient temperature at beam line 16-IDD APS. The spin transition exerts an influence to Fe2SiO4 spinel structure and triggers two distinct curves of the lattice constant in the spinel phase. Although the compression curve of the spinel is discontinuous at approximately 20 GPa, Fe Kβ emission measurements show that the transition from a high spin (HS) to an intermediate spin (IS) state begins at 17GPa in the spinel phase. The IS electronic state is gradually enhanced with pressure, which results in an isostructural phase transition. HS-to-LS transition of iron bearing spinels starts from 15.6GPa in Fe3O4 and 19.6GPa in Fe2TiO4. The transition is more capable due to Fe2+ in the octahedral site. The extremely shortened octahedral bonds result in a distortion of 6-fold cation site. New structure of Fe2SiO4 Monte Carlo method was applied to find candidates for the high-pressure phase using the diffraction intensities with fixed lattice constants determined by DICVOL. Rietveld profile fitting was then performed using the initial model. The new structure is a body centered orthorhombic phase (I-Fe2SiO4) with space group Imma and Z=4, with two crystallographically distinct FeO6 octahedra. Silicon exists in six-fold coordination in I-Fe2Si

Self diffusion and spectral modifications of a membrane protein, the Rubrivivax gelatinosus LH2 complex, incorporated into a monoolein cubic phase.

OpenAIRE

Tsapis, N; Reiss-Husson, F; Ober, R; Genest, M; Hodges, R S; Urbach, W

2001-01-01

The light-harvesting complex LH2 from a purple bacterium, Rubrivivax gelatinosus, has been incorporated into the Q230 cubic phase of monoolein. We measured the self-diffusion of LH2 in detergent solution and in the cubic phase by fluorescence recovery after photobleaching. We investigated also the absorption and fluorescence properties of this oligomeric membrane protein in the cubic phase, in comparison with its beta-octyl glucoside solution. In these experiments, native LH2 and LH2 labeled ...

Metastable phase transformation and hcp-ω transformation pathways in Ti and Zr under high hydrostatic pressures

International Nuclear Information System (INIS)

Gao, Lei; Ding, Xiangdong; Sun, Jun; Lookman, Turab; Salje, E. K. H.

2016-01-01

The energy landscape of Zr at high hydrostatic pressure suggests that its transformation behavior is strongly pressure dependent. This is in contrast to the known transition mechanism in Ti, which is essentially independent of hydrostatic pressure. Generalized solid-state nudged elastic band calculations at constant pressure shows that α-Zr transforms like Ti only at the lowest pressure inside the stability field of ω-phase. Different pathways apply at higher pressures where the energy landscape contains several high barriers so that metastable states are expected, including the appearance of a transient bcc phase at ca. 23 GPa. The global driving force for the hcp-ω transition increases strongly with increasing pressure and reaches 23.7 meV/atom at 23 GPa. Much of this energy relates to the excess volume of the hcp phase compared with its ω phase.

Metastable phase transformation and hcp-ω transformation pathways in Ti and Zr under high hydrostatic pressures

Energy Technology Data Exchange (ETDEWEB)

Gao, Lei; Ding, Xiangdong, E-mail: dingxd@mail.xjtu.edu.cn, E-mail: ekhard@esc.cam.ac.uk; Sun, Jun [State Key Laboratory for Mechanical Behavior of Materials, Xi' an Jiaotong University, Xi' an 710049 (China); Lookman, Turab [Theoretical Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States); Salje, E. K. H., E-mail: dingxd@mail.xjtu.edu.cn, E-mail: ekhard@esc.cam.ac.uk [State Key Laboratory for Mechanical Behavior of Materials, Xi' an Jiaotong University, Xi' an 710049 (China); Department of Earth Sciences, University of Cambridge, Cambridge CB2 3EQ (United Kingdom)

2016-07-18

The energy landscape of Zr at high hydrostatic pressure suggests that its transformation behavior is strongly pressure dependent. This is in contrast to the known transition mechanism in Ti, which is essentially independent of hydrostatic pressure. Generalized solid-state nudged elastic band calculations at constant pressure shows that α-Zr transforms like Ti only at the lowest pressure inside the stability field of ω-phase. Different pathways apply at higher pressures where the energy landscape contains several high barriers so that metastable states are expected, including the appearance of a transient bcc phase at ca. 23 GPa. The global driving force for the hcp-ω transition increases strongly with increasing pressure and reaches 23.7 meV/atom at 23 GPa. Much of this energy relates to the excess volume of the hcp phase compared with its ω phase.

Epitaxial growth of high purity cubic InN films on MgO substrates using HfN buffer layers by pulsed laser deposition

International Nuclear Information System (INIS)

Ohba, R.; Ohta, J.; Shimomoto, K.; Fujii, T.; Okamoto, K.; Aoyama, A.; Nakano, T.; Kobayashi, A.; Fujioka, H.; Oshima, M.

2009-01-01

Cubic InN films have been grown on MgO substrates with HfN buffer layers by pulsed laser deposition (PLD). It has been found that the use of HfN (100) buffer layers allows us to grow cubic InN (100) films with an in-plane epitaxial relationship of [001] InN //[001] HfN //[001] MgO . X-ray diffraction and electron back-scattered diffraction measurements have revealed that the phase purity of the cubic InN films was as high as 99%, which can be attributed to the use of HfN buffer layers and the enhanced surface migration of the film precursors by the use of PLD. - Graphical abstract: Cubic InN films have been grown on MgO substrates with HfN buffer layers by pulsed laser deposition (PLD). It has been revealed that the phase purity of the cubic InN films was as high as 99 %, which can be attributed to the use of HfN buffer layers and the enhanced surface migration of the film precursors by the use of PLD.

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

CERN Document Server

Ahuja, R

2002-01-01

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

Pressure-induced phase transformation of HfO2

International Nuclear Information System (INIS)

Arashi, H.

1992-01-01

This paper reports on the pressure dependence of the Raman spectra of HfO 2 that was measured by a micro-Raman technique using a single-crystal specimen in the pressure range from 0 to 10 GPa at room temperature. The symmetry assignment of Raman bands of the monoclinic phase was experimentally accomplished from the polarization measurements for the single crystal. With increased pressure, a phase transformation for the monoclinic phase took place at 4.3 ± 0.3 GPa. Nineteen Raman bands were observed for the high-pressure phase. The spectral structure of the Raman bands for the high-pressure phase was similar with those reported previously for ZrO 2 . The space group for the high pressure phase of HfO 2 was determined as Pbcm, which was the same as that of the high-pressure phase for ZrO 2 on the basis of the number and the spectral structure of the Raman bands

Anomalous plastic flow of cerium near the isomorphic phase transformations under high hydrostatic pressure

International Nuclear Information System (INIS)

Witczak, Z.; Goncharova, V.A.

1999-01-01

Compression tests have been carried out on cerium specimens at room temperature (0.27 T m ) under high hydrostatic pressures up to 1.2 GPa. A strong increase of the yield strength was observed for both isomorphic γ and α phases at pressures approaching the γ ↔ α isomorphic phase transformations. That increase was in good agreement with the theory of dislocations when the dependence of elastic properties and a lattice parameter of cerium on pressure was applied to calculate the effect of pressure on the yield stress controlled by the edge dislocations. An anomalous strong decrease of the yield stress was observed in both γ and α phases in the vicinity of both γ ↔ α phase transformations. That phenomenon was explained as an effect of pressure induced new phase atoms through spreading the cores of edge dislocations. A complete disappearance of work hardening in both γ and α phases was also observed in the wide range of pressures. The influence of hydrostatic pressure on the energy of grain boundaries of both phases was considered to be responsible for that property. The ratio of the grain boundary energy to the Peierls energy is suggested to be a criterion of the work hardening ability of f.c.c. polycrystals

High-pressure phase equilibria in the (carbon dioxide + 1-hexanol) system

International Nuclear Information System (INIS)

Secuianu, Catinca; Feroiu, Viorel; Geana, Dan

2010-01-01

(Vapour + liquid) equilibria (VLE) and (vapour + liquid + liquid) equilibria (VLLE) data for the (carbon dioxide + 1-hexanol) system were measured at (293.15, 303.15, 313.15, 333.15, and 353.15) K. Phase behaviour measurements were made in a high-pressure visual cell with variable volume, based on the static-analytic method. The pressure range under investigation was between (0.6 and 14.49) MPa. The Soave-Redlich-Kwong (SRK) equation of state (EOS) with classical van der Waals mixing rules (two-parameters conventional mixing rule, 2PCMR), was used in a semi-predictive approach, in order to represent the complex phase behaviour (critical curve, LLV line, isothermal VLE, LLE, and VLLE) of the system. The topology of phase behaviour is reasonably well predicted.

Effect of shear on cubic phases in gels of a diblock copolymer

DEFF Research Database (Denmark)

Hamley, I.W.; Pople, J.A.; Fairclough, J.P.A.

1998-01-01

The effect of shear on the orientation of cubic micellar phases formed by a poly(oxyethylene)poly(oxybutylene) diblock copolymer in aqueous solution has been investigated using small-angle x-ray scattering (SAXS) and small-angle neutron scattering (SANS). SAXS was performed on samples oriented in...

Plastic fluctuations in empty crystals formed by cubic wireframe particles

Science.gov (United States)

McBride, John M.; Avendaño, Carlos

2018-05-01

We present a computer simulation study of the phase behavior of colloidal hard cubic frames, i.e., particles with nonconvex cubic wireframe geometry interacting purely by excluded volume. Despite the propensity of cubic wireframe particles to form cubic phases akin to their convex counterparts, these particles exhibit unusual plastic fluctuations in which a random and dynamic fraction of particles rotate around their lattice positions in the crystal lattice while the remainder of the particles remains fully ordered. We argue that this unexpected effect stems from the nonconvex geometry of the particles in which the faces of a particle can be penetrated by the vertices of the nearest neighbors even at high number densities.

Synthesis of Cubic Phase-Co Microspheres by Mechanical Solid-State Reaction-Thermal Decomposition and Research on Its Growth Kinetics

Directory of Open Access Journals (Sweden)

Ying Deng

2016-01-01

Full Text Available Cubic phase cobalt (Co, which can be used as a key component for composite materials given its excellent ductility and internal structure, is not easy to obtain at room temperature. In this study, oxalic acid and cobalt nitrate are used as raw materials to synthesize the cobalt oxalate precursor, which has a stable structure with a five-membered chelate ring. Cobalt oxalate microspheres, having a high internal energy content, were prepared by using mechanical solid-state reaction in the presence of a surfactant, which can produce spherical micelles. The thermal decomposition of the precursor was carried out by maintaining it in a nitrogen atmosphere at 450°C for 3 h. At the end of the procedure, 100 nm cubic phase-Co microspheres, stable at room temperature, were obtained. Isothermal and nonisothermal kinetic mechanisms of cobalt grain growth were investigated. The cubic-Co grain growth activation energy, Q, was calculated in this study to be 71.47 kJ/mol. The required reaction temperature was low, making the production process simple and suitable for industrial applications.

Plastic crystal phases of simple water models

International Nuclear Information System (INIS)

Aragones, J. L.; Vega, C.

2009-01-01

We report the appearance of two plastic crystal phases of water at high pressure and temperature using computer simulations. In one of them the oxygen atoms form a body centered cubic structure (bcc) and in the other they form a face centered cubic structure (fcc). In both cases the water molecules were able to rotate almost freely. We have found that the bcc plastic crystal transformed into a fcc plastic crystal via a Martensitic phase transition when heated at constant pressure. We have performed the characterization and localization in the phase diagram of these plastic crystal phases for the SPC/E, TIP4P, and TIP4P/2005 water potential models. For TIP4P/2005 model free energy calculations were carried out for the bcc plastic crystal and fcc plastic crystal using a new method (which is a slight variation of the Einstein crystal method) proposed for these types of solid. The initial coexistence points for the SPC/E and TIP4P models were obtained using Hamiltonian Gibbs–Duhem integration. For all of these models these two plastic crystal phases appear in the high pressure and temperature region of the phase diagram. It would be of interest to study if such plastic crystal phases do indeed exist for real water. This would shed some light on the question of whether these models can describe satisfactorily the high pressure part of the phase diagram of water, and if not, where and why they fail.

Efficient Reservoir Simulation with Cubic Plus Association and Cross-Association Equation of State for Multicomponent Three-Phase Compressible Flow with Applications in CO2 Storage and Methane Leakage

Science.gov (United States)

Moortgat, J.

2017-12-01

We present novel simulation tools to model multiphase multicomponent flow and transport in porous media for mixtures that contain non-polar hydrocarbons, self-associating polar water, and cross-associating molecules like methane, ethane, unsaturated hydrocarbons, CO2 and H2S. Such mixtures often occur when CO2 is injected and stored in saline aquifers, or when methane is leaking into groundwater. To accurately predict the species transfer between aqueous, gaseous and oleic phases, and the subsequent change in phase properties, the self- and cross-associating behavior of molecules needs to be taken into account, particularly at the typical temperatures and pressures in deep formations. The Cubic-Plus-Association equation-of-state (EOS) has been demonstrated to be highly accurate for such problems but its excessive computational cost has prevented widespread use in reservoir simulators. We discuss the thermodynamical framework and develop sophisticated numerical algorithms that allow reservoir simulations with efficiencies comparable to a simple cubic EOS. This approach improves our predictive powers for highly nonlinear fluid behavior related to geological carbon sequestration, such as density driven flow and natural convection (solubility trapping), evaporation of water into the CO2-rich gas phase, and competitive dissolution-evaporation when CO2 is injected in, e.g., methane saturated aquifers. Several examples demonstrate the accuracy and robustness of this EOS framework for complex applications.

Plasma synthesis and HPHT consolidation of BN nanoparticles, nanospheres, and nanotubes to produce nanocrystalline cubic boron nitride

Science.gov (United States)

Stout, Christopher

Plasma methods offer a variety of advantages to nanomaterials synthesis. The process is robust, allowing varying particle sizes and phases to be generated simply by modifying key parameters. The work here demonstrates a novel approach to nanopowder synthesis using inductively-coupled plasma to decompose precursor, which are then quenched to produce a variety of boron nitride (BN)-phase nanoparticles, including cubic phase, along with short-range-order nanospheres (e.g., nano-onions) and BN nanotubes. Cubic BN (c-BN) powders can be generated through direct deposition onto a chilled substrate. The extremely-high pyrolysis temperatures afforded by the equilibrium plasma offer a unique particle growth environment, accommodating long deposition times while exposing resulting powders to temperatures in excess of 5000K without any additional particle nucleation and growth. Such conditions can yield short-range ordered amorphous BN structures in the form of 20nm diameter nanospheres. Finally, when introducing a rapid-quenching counter-flow gas against the plasma jet, high aspect ratio nanotubes are synthesized, which are collected on substrate situated radially. The benefits of these morphologies are also evident in high-pressure/high-temperature consolidation experiments, where nanoparticle phases can offer a favorable conversion route to super-hard c-BN while maintaining nanocrystallinity. Experiments using these morphologies are shown to begin to yield c-BN conversion at conditions as low as 2.0 GPa and 1500°C when using micron sized c-BN seeding to create localized regions of high pressures due to Hertzian forces acting on the nanoparticles.

Formation of cubic phases from large unilamellar vesicles of dioleoylphosphatidylglycerol/monoolein membranes induced by low concentrations of Ca2+.

Science.gov (United States)

Awad, Tarek S; Okamoto, Yoshihide; Masum, Shah Md; Yamazaki, Masahito

2005-12-06

We developed a new method for the transformation of large unilamellar vesicles (LUVs) into the cubic phase. We found that the addition of low concentrations of Ca(2+) to suspensions of multilamellar vesicles (MLVs) of membranes of monoolein (MO) and dioleoylphosphatidylglycerol (DOPG) mixtures (DOPG/MO) changed their L(alpha) phase to the cubic phases. For instance, the addition of 15-25 mM Ca(2+) to 30%-DOPG/70%-MO-MLVs induced the Q(229) phase, whereas the addition of > or =28 mM Ca(2+) induced the Q(224) phase. LUVs of DOPG/MO membranes containing > or =25 mol % DOPG were prepared easily. Low concentrations of Ca(2+) transformed these LUVs in excess buffer into the Q(224) or the Q(229) phase, depending on the Ca(2+) concentration. For example, 15 and 50 mM Ca(2+) induced the Q(224) and Q(229) phase in the 30%-DOPG/70%-MO-LUVs at 25 degrees C, respectively. This finding is the first demonstration of transformation of LUVs of lipid membranes into the cubic phase under excess water condition.

Equation of state, phase stability, and phase transformations of uranium-6 wt. % niobium under high pressure and temperature

Science.gov (United States)

Zhang, Jianzhong; Vogel, Sven; Brown, Donald; Clausen, Bjorn; Hackenberg, Robert

2018-05-01

In-situ time-of-flight neutron diffraction experiments were conducted on the uranium-niobium alloy with 6 wt. % Nb (U-6Nb) at pressures up to 4.7 GPa and temperatures up to 1073 K. Upon static compression at room temperature, the monoclinic structure of U-6Nb (α″ U-6Nb) remains stable up to the highest experimental pressure. Based on the pressure-volume measurements at room temperature, the least-squares fit using the finite-strain equation of state (EOS) yields an isothermal bulk modulus of B0 = 127 ± 2 GPa for the α″-phase of U-6Nb. The calculated zero-pressure bulk sound speed from this EOS is 2.706 ± 0.022 km/s, which is in good agreement with the linear extrapolation of the previous Hugoniot data above 12 GPa for α″ U-6Nb, indicating that the dynamic response under those shock-loading conditions is consistent with the stabilization of the initial monoclinic phase of U-6Nb. Upon heating at ambient and high pressures, the metastable α″ U-6Nb exhibits complex transformation paths leading to the diffusional phase decomposition, which are sensitive to applied pressure, stress state, and temperature-time path. These findings provide new insight into the behavior of atypical systems such as U-Nb and suggest that the different U-Nb phases are separated by rather small energies and hence highly sensitive to compositional, thermal, and mechanical perturbations.

Neutron powder diffraction under high pressure at J-PARC

International Nuclear Information System (INIS)

Utsumi, Wataru; Kagi, Hiroyuki; Komatsu, Kazuki; Arima, Hiroshi; Nagai, Takaya; Okuchi, Takuo; Kamiyama, Takashi; Uwatoko, Yoshiya; Matsubayashi, Kazuyuki; Yagi, Takehiko

2009-01-01

It is expected that high-pressure material science and the investigation of the Earth's interior will progress greatly using the high-flux pulse neutrons of J-PARC. In this article, we introduce our plans for in situ neutron powder diffraction experiments under high pressure at J-PARC. The use of three different types of high-pressure devices is planned; a Paris-Edinburgh cell, a new opposed-anvil cell with a nano-polycrystalline diamond, and a cubic anvil high-pressure apparatus. These devices will be brought to the neutron powder diffraction beamlines to conduct a 'day-one' high-pressure experiment. For the next stage of research, we propose construction of a dedicated beamline for high-pressure material science. Its conceptual designs are also introduced here.

High-pressure BaCrO_3 polytypes and the 5H–BaCrO_2_._8 phase

International Nuclear Information System (INIS)

Arévalo-López, Angel M.; Paul Attfield, J.

2015-01-01

Polytypism of BaCrO_3 perovskites has been investigated at 900–1100 °C and pressures up to 22 GPa. Hexagonal 5H, 4H, and 6H perovskites are observed with increasing pressure, and the cubic 3C perovskite (a=3.99503(1) Å) is observed in bulk form for the first time at 19–22 GPa. An oxygen-deficient material with limiting composition 5H–BaCrO_2_._8 is synthesised at 1200 °C under ambient pressure. This contains double tetrahedral Cr"4"+ layers and orders antiferromagnetically below 260 K with a (0 0 1/2) magnetic structure. - Graphical abstract: Hexagonal 5H, 4H, and 6H perovskites polytypes of BaCrO_3 are observed with increasing pressure and the cubic 3C perovskite is stabilised in bulk form for the first time at 19–22 GPa. Oxygen-deficient 5H–BaCrO_2_._8 synthesised at ambient pressure contains double tetrahedral Cr"4"+ layers and orders antiferromagnetically below 260 K with a (0 0 1/2) magnetic structure.

Neutron diffraction study of structural transformations in ternary systems of HgSe sub 1 sub - sub x S sub x mercury chalcogenides at high pressure

CERN Document Server

Voronin, V I; Berger, I F; Glazkov, V P; Kozlenko, D P; Savenko, B N; Tikhomirov, S V

2001-01-01

The structure of the ternary systems of the HgSe sub 1 sub - sub x S sub x mercury chalcogenides is studied at high pressures up to 35 kbar. It is established that by increase in the pressure in the HgSe sub 1 sub - sub x S sub x there takes place the transition from the sphalerite type cubic structure to the cinnabar type hexagonal structure, which is accompanied by the jump-like change in the elementary cell volume and interatomic distances. The parameters of the elementary cell and positional parameters of the Hg and Se/S for the hexagonal phase of high pressure are determined. The existence of the two-phase state in the area of the phase transformation is determined

Different phases of a system of hard rods on three dimensional cubic lattice

Science.gov (United States)

Vigneshwar, N.; Dhar, Deepak; Rajesh, R.

2017-11-01

We study the different phases of a system of monodispersed hard rods of length k on a cubic lattice, using an efficient cluster algorithm able to simulate densities close to the fully-packed limit. For k≤slant 4 , the system is disordered at all densities. For k=5, 6 , we find a single density-driven transition, from a disordered phase to high density layered-disordered phase, in which the density of rods of one orientation is strongly suppressed, breaking the system into weakly coupled layers. Within a layer, the system is disordered. For k ≥slant 7 , three density-driven transitions are observed numerically: isotropic to nematic to layered-nematic to layered-disordered. In the layered-nematic phase, the system breaks up into layers, with nematic order in each layer, but very weak correlation between the ordering directions of different layers. We argue that the layered-nematic phase is a finite-size effect, and in the thermodynamic limit, the nematic phase will have higher entropy per site. We expect the systems of rods in four and higher dimensions will have a qualitatively similar phase diagram.

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

International Nuclear Information System (INIS)

Cerreta, E K; Addessio, F L; Bronkhorst, C A; Brown, D W; Escobedo, J P; Fensin, S J; Gray, G T III; Lookman, T; Rigg, P A; Trujillo, C P

2014-01-01

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

Reactor for tracking catalyst nanoparticles in liquid at high temperature under a high-pressure gas phase with X-ray absorption spectroscopy.

Science.gov (United States)

Nguyen, Luan; Tao, Franklin Feng

2018-02-01

Structure of catalyst nanoparticles dispersed in liquid phase at high temperature under gas phase of reactant(s) at higher pressure (≥5 bars) is important for fundamental understanding of catalytic reactions performed on these catalyst nanoparticles. Most structural characterizations of a catalyst performing catalysis in liquid at high temperature under gas phase at high pressure were performed in an ex situ condition in terms of characterizations before or after catalysis since, from technical point of view, access to the catalyst nanoparticles during catalysis in liquid phase at high temperature under high pressure reactant gas is challenging. Here we designed a reactor which allows us to perform structural characterization using X-ray absorption spectroscopy including X-ray absorption near edge structure spectroscopy and extended X-ray absorption fine structure spectroscopy to study catalyst nanoparticles under harsh catalysis conditions in terms of liquid up to 350 °C under gas phase with a pressure up to 50 bars. This reactor remains nanoparticles of a catalyst homogeneously dispersed in liquid during catalysis and X-ray absorption spectroscopy characterization.

Theoretical investigations of the bulk modulus in the tetra-cubic transition of PbTiO3 material

Directory of Open Access Journals (Sweden)

Renan A. P. Ribeiro

2014-01-01

Full Text Available Resulting from ion displacement in a solid under pressure, piezoelectricity is an electrical polarization that can be observed in perovskite-type electronic ceramics, such as PbTiO3, which present cubic and tetragonal symmetries at different pressures. The transition between these crystalline phases is determined theoretically through the bulk modulus from the relationship between material energy and volume. However, the change in the material molecular structure is responsible for the piezoelectric effect. In this study, density functional theory calculations using the Becke 3-Parameter-Lee-Yang-Parr hybrid functional were employed to investigate the structure and properties associated with the transition state of the tetragonal-cubic phase change in PbTiO3 material.

High-pressure Raman investigations of phase transformations in pentaerythritol (C(CH sub 2 OH) sub 4)

CERN Document Server

Bhattacharya, T

2002-01-01

Our high-pressure Raman scattering experiments on pentaerythritol (C(CH sub 2 OH) sub 4) show that this compound undergoes at least three phase transformations up to 25 GPa. Splitting of various modes at approx 6.3, approx 8.2 and 10 GPa suggests that these phase transformations result in lowering of crystalline symmetry. A very small discontinuous change in slope of most of the Raman-active modes is observed at 0.3 GPa. However, no other signature of a phase transition was observed at this pressure. The observed correlation of the pressures for the onset of the two phase transformations with the limiting values of the distances between various non-bonded atoms in the parent phase suggests that the molecular rearrangements across the phase transformations are not very drastic. In addition, our earlier Fourier transform infrared and present Raman investigations indicate that high-pressure compression leads to increase in strength of the hydrogen bond present in this compound.

Enzymatic biofuel cell based on electrodes modified with lipid liquid-crystalline cubic phases

Science.gov (United States)

Nazaruk, Ewa; Smoliński, Sławomir; Swatko-Ossor, Marta; Ginalska, Grażyna; Fiedurek, Jan; Rogalski, Jerzy; Bilewicz, Renata

Two glassy carbon electrodes modified with enzymes embedded in lyotropic liquid-crystalline cubic phase were used for the biofuel cell construction. The monoolein liquid-crystalline film allowed to avoid separators in the biofuel cell. Glucose and oxygen as fuels, and glucose oxidase and laccase as anode and cathode biocatalysts, respectively were used. The biofuel cell parameters were examined in McIlvaine buffer, pH 7 solution containing 15 mM of glucose and saturated with dioxygen. A series of mediators were tested taking into account their formal potentials, stability in the cubic phase and efficiency of mediation. Most stable was the biofuel cell based on tetrathiafulvalene (TTF) and 2,2‧-azino-bis(3-ethylbenzothiazoline-6-sulfonate) (ABTS) as anode and cathode mediators, respectively. The open-circuit voltage was equal to 450 ± 40 mV. The power densities and current densities were measured for all the systems studied.

Polymorphism of a lipid extract from Pseudomonas fluorescens: Structure analysis of a hexagonal phase and of a novel cubic phase of extinction symbol Fd--

International Nuclear Information System (INIS)

Mariani, P.; Rivas, E.; Delacroix, H.; Luzzati, V.

1990-01-01

The phase diagram of the Pseudomonas fluorescens lipid extract is unusual, in the sense that it displays a cubic phase straddled by a hexagonal phase. The hexagonal phase was studied over an extended concentration range, and the reflections were phased on the assumption that the structure contains circular cylinders of known radius. The cubic phase, whose extinction symbol is Fd--, was analyzed by reference to space group No. 227 (Fd3m). The phases of the reflections were determined by using a novel pattern recognition approach, based upon the notion that the average fourth power of the electron density contrast 4 > is dependent on chemical composition but not on physical structure, provided that the function Δr(r) satisfies the constraints = 0 and 2 > = 1. The authors analyzed two cubic samples of different composition: for each of them they generated all the phase combinations compatible with the X-ray scattering data and they searched for those whose 4 > best agrees with the hexagonal phase. They concluded that the chemical composition of the phases being compared must be identical, that the X-ray scattering data should not be truncated artificially, and that the apodization must be mild so that the curvature takes a value intermediate between those corresponding to the raw data of the two phases. The structure may be visualized as a 3D generalization of the lipid monolayer. The structure, moreover, does not belong to the class of the infinite periodic surfaces without intersections

High-pressure pyrolysis study of C sub 3 N sub 6 H sub 6 : a route to preparing bulk C sub 3 N sub 4

CERN Document Server

Ma, H A; Chen, L X; Zhu, P W; Guo, W L; Guo, X B; Wang, Y D; Li, S Q; Zou Guang Tian; Zhang, G; Bex, P

2002-01-01

In order to prepare bulk C sub 3 N sub 4 , high-pressure pyrolysis of melamine (C sub 3 N sub 6 H sub 6) at different temperatures was carried out. The products were characterized by C, N, H element analysis, Fourier transform infrared spectroscopy, x-ray photoelectron spectroscopy, and x-ray diffractometry. The results of the analysis reveal that graphitic phase C sub 3 N sub 4 has been synthesized. It provides a novel route to synthesis of the theoretical superhard cubic C sub 3 N sub 4 and other C sub 3 N sub 4 phases from organic compounds by a high-pressure and high-temperature method.

The influence of high pressure and high temperature on the structure of ZrO sub 2 nanosolids

CERN Document Server

Xu Da Peng; LiuShue; Wang Quan Yong; Su Wen Hui

2002-01-01

Using nanoparticles of ZrO sub 2 (disordered structure) prepared by the method of precipitation as starting materials, ZrO sub 2 nanosolids have been synthesized under different pressures and at different temperatures. The x-ray diffraction results show that the crystallization temperature of the nanoparticles and the temperature at which the structural cubic-monoclinic transformation occurs are obviously reduced for the nanosolids synthesized under high pressure. X-ray photoelectron spectroscopy and EPR measurements indicate that there are some Zr sup 3 sup + ions in nanosolids. With increasing pressure, the number of Zr sup 3 sup + ions in the nanosolids essentially does not vary, and yet the content of oxygen ions with unsaturated bonds and dangling bonds in the interfacial region gradually decreases. The effect of synthesis pressure on the structure and interface states is mainly due to the decrease of the interatomic distance and the increasing interdiffusion of atoms in the interface phase.

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

Energy Technology Data Exchange (ETDEWEB)

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.

Electronic, ductile, phase transition and mechanical properties of Lu-monopnictides under high pressures.

Science.gov (United States)

Gupta, Dinesh C; Bhat, Idris Hamid

2013-12-01

The structural, elastic and electronic properties of lutatium-pnictides (LuN, LuP, LuAs, LuSb, and LuBi) were analyzed by using full-potential linearized augmented plane wave within generalized gradient approximation in the stable rock-salt structure (B1 phase) with space group Fm-3m and high-pressure CsCl structure (B2 phase) with space group Pm-3m. Hubbard-U and spin-orbit coupling were included to predict correctly the semiconducting band gap of LuN. Under compression, these materials undergo first-order structural transitions from B1 to B2 phases at 241, 98, 56.82, 25.2 and 32.3 GPa, respectively. The computed elastic properties show that LuBi is ductile by nature. The electronic structure calculations show that LuN is semiconductor at ambient conditions with an indirect band gap of 1.55 eV while other Lu-pnictides are metallic. It was observed that LuN shows metallization at high pressures. The structural properties, viz, equilibrium lattice constant, bulk modulus and its pressure derivative, transition pressure, equation of state, volume collapse, band gap and elastic moduli, show good agreement with available data.

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

Science.gov (United States)

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

2013-06-01

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

Phase boundary between cubic B1 and rhombohedral structures in (Mg,Fe)O magnesiowüstite determined by in situ X-ray diffraction measurements

Science.gov (United States)

Dymshits, Anna M.; Litasov, Konstantin D.; Shatskiy, Anton; Chanyshev, Artem D.; Podborodnikov, Ivan V.; Higo, Yuji

2018-01-01

The phase relations and equation of state of (Mg0.08Fe0.92)O magnesiowüstite (Mw92) have been studied using the Kawai-type high-pressure apparatus coupled with synchrotron radiation. To determine the phase boundary between the NaCl-type cubic (B1) and rhombohedral ( rB1) structures in Mw92, in situ X-ray observations were carried out at pressures of 0-35 GPa and temperatures of 300-1473 K. Au and MgO were used as the internal pressure markers and metallic Fe as oxygen fugacity buffer. The phase boundary between B1 and rB1 structures was described by a linear equation P (GPa) = 1.6 + 0.033 × T (K). The Clapeyron slope (d P/d T) determined in this study is close to that obtained at pressures above 70 GPa but steeper than that obtained for FeO. An addition of MgO to FeO structure expands the stability field of the rB1 phase to lower pressures and higher temperatures. Thus, the rB1 phase may be stabilized with respect to the B1 phase at a lower pressures. The pressure-volume-temperature equation of state of B1-Mw92 was determined up to 30 GPa and 1473 K. Fitting the hydrostatic compression data up to 30 GPa with the Birch-Murnaghan equation of state (EoS) yielded: unit cell volume ( V 0, T0), 79.23 ± 4 Å3; bulk modulus ( K 0, T0), 183 ± 4 GPa; its pressure derivative ( K' T ), 4.1 ± 0.4; (∂ K 0, T /∂ T) = -0.029 ± 0.005 GPa K‒1; a = 3.70 ± 0.27 × 10-5 K-1 and b = 0.47 ± 0.49 × 10-8 K-2, where α0, T = a + bT is the volumetric thermal expansion coefficient. The obtained bulk modulus of Mw92 is very close to the value expected for stoichiometric iron-rich (Mg,Fe)O. This result confirms the idea that the bulk modulus of (Mg,Fe)O is greatly affected by the actual defect structure, caused by either Mg2+ or vacancies.

Phase stability and microstructures of high entropy alloys ion irradiated to high doses

Energy Technology Data Exchange (ETDEWEB)

Xia, Songqin [State Key Laboratory for Advanced Metals and Materials, University of Science and Technology Beijing, Beijing, 100083 (China); Gao, Michael C. [National Energy Technology Laboratory, 1450 Queen Ave SW, Albany, OR, 97321 (United States); AECOM, P.O. Box 1959, Albany, OR, 97321 (United States); Yang, Tengfei [State Key Laboratory of Nuclear Physics and Technology, Center for Applied Physics and Technology, Peking University, Beijing, 100871 (China); Liaw, Peter K. [Department of Materials Science and Engineering, The University of Tennessee, Knoxville, TN, 37996 (United States); Zhang, Yong, E-mail: drzhangy@ustb.edu.cn [State Key Laboratory for Advanced Metals and Materials, University of Science and Technology Beijing, Beijing, 100083 (China)

2016-11-15

The microstructures of Al{sub x}CoCrFeNi (x = 0.1, 0.75 and 1.5 in molar ratio) high entropy alloys (HEAs) irradiated at room temperature with 3 MeV Au ions at the highest fluence of 105, 91, and 81 displacement per atom, respectively, were studied. Transmission electron microscopy (TEM) and high-resolution TEM (HRTEM) analyses show that the initial microstructures and phase composition of all three alloys are retained after ion irradiation and no phase decomposition is observed. Furthermore, it is demonstrated that the disordered face-centered cubic (FCC) and disordered body-centered cubic (BCC) phases show much less defect cluster formation and structural damage than the NiAl-type ordered B2 phase. This effect is explained by higher entropy of mixing, higher defect formation/migration energies, substantially lower thermal conductivity, and higher atomic level stress in the disordered phases.

Structural Phase Transition and Compressibility of CaF2 Nanocrystals under High Pressure

Directory of Open Access Journals (Sweden)

Jingshu Wang

2018-05-01

Full Text Available The structural phase transition and compressibility of CaF2 nanocrystals with size of 23 nm under high pressure were investigated by synchrotron X-ray diffraction measurement. A pressure-induced fluorite to α-PbCl2-type phase transition starts at 9.5 GPa and completes at 20.2 GPa. The phase-transition pressure is lower than that of 8 nm CaF2 nanocrystals and closer to bulk CaF2. Upon decompression, the fluorite and α-PbCl2-type structure co-exist at the ambient pressure. The bulk modulus B0 of the 23 nm CaF2 nanocrystals for the fluorite and α-PbCl2-type phase are 103(2 and 78(2 GPa, which are both larger than those of the bulk CaF2. The CaF2 nanocrystals exhibit obviously higher incompressibility compare to bulk CaF2. Further analysis demonstrates that the defect effect in our CaF2 nanocrystals plays a dominant role in the structural stability.

Kinetic boundaries and phase transformations of ice i at high pressure

Science.gov (United States)

Wang, Yu; Zhang, Huichao; Yang, Xue; Jiang, Shuqing; Goncharov, Alexander F.

2018-01-01

Raman spectroscopy in diamond anvil cells has been employed to study phase boundaries and transformation kinetics of H2O ice at high pressures up to 16 GPa and temperatures down to 15 K. Ice i formed at nearly isobaric cooling of liquid water transforms on compression to high-density amorphous (HDA) ice at 1.1-3 GPa at 15-100 K and then crystallizes in ice vii with the frozen-in disorder (ice vii') which remains stable up to 14.1 GPa at 80 K and 15.9 GPa at 100 K. Unexpectedly, on decompression of ice vii', it transforms to ice viii in its domain of metastability, and then it relaxes into low-density amorphous (LDA) ice on a subsequent pressure release and warming up. On compression of ice i at 150-170 K, ice ix is crystallized and no HDA ice is found; further compression of ice ix results in the sequential phase transitions to stable ices vi and viii. Cooling ice i to 210 K at 0.3 GPa transforms it to a stable ice ii. Our extensive investigations provide previously missing information on the phase diagram of water, especially on the kinetic paths that result in formation of phases which otherwise are not accessible; these results are keys for understanding the phase relations including the formation of metastable phases. Our observations inform on the ice modifications that can occur naturally in planetary environments and are not accessible for direct observations.

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

Science.gov (United States)

2012-01-23

...)] High Pressure Steel Cylinders From China; Scheduling of the Final Phase of Countervailing Duty and... retarded, by reason of subsidized and less-than-fair-value imports from China of high pressure steel... (``high pressure steel cylinders''). High pressure steel cylinders are fabricated of chrome alloy steel...

Tetragonal-cubic phase boundary in nanocrystalline ZrO2-Y2O3 solid solutions synthesized by gel-combustion

International Nuclear Information System (INIS)

Fabregas, Ismael O.; Craievich, Aldo F.; Fantini, Marcia C.A.; Millen, Ricardo P.; Temperini, Marcia L.A.; Lamas, Diego G.

2011-01-01

Research highlights: → Gel-combustion synthesis yields compositionally homogeneous, single-phased ZrO 2 -Y 2 O 3 nanopowders, that exhibit the presence at room temperature of three different phases depending on Y 2 O 3 content, namely two tetragonal forms (t' and t'') and the cubic phase. → Phase identification can be achieved by synchrotron XPD (SXPD) and Raman spectroscopy since the tetragonal forms and the cubic phase can be distinguished by these techniques. → The crystallographic features of ZrO 2 -Y 2 O 3 nanopowders were determined by SXPD. They are similar to those reported by Yashima and coworkers for compositionally homogeneous materials containing larger (micro)crystals. However, the lattice parameters are slightly different and the axial ratios c/a of our t' samples are smaller than those reported by these authors. → Compositional t'/t'' and t''/cubic phase boundaries are located at (9 ± 1) and (10.5 ± 0.5) mol% Y 2 O 3 , respectively. → For the whole series of nanocrystalline ZrO 2 -Y 2 O 3 solid solutions studied in the present work, no evidences of the presence of a mixture of phases - as reported by Yashima and coworkers for microcrystalline solid solutions - were detected. - Abstract: By means of synchrotron X-ray powder diffraction (SXPD) and Raman spectroscopy, we have detected, in a series of nanocrystalline and compositionally homogeneous ZrO 2 -Y 2 O 3 solid solutions, the presence at room temperature of three different phases depending on Y 2 O 3 content, namely two tetragonal forms and the cubic phase. The studied materials, with average crystallite sizes within the range 7-10 nm, were synthesized by a nitrate-citrate gel-combustion process. The crystal structure of these phases was also investigated by SXPD. The results presented here indicate that the studied nanocrystalline ZrO 2 -Y 2 O 3 solid solutions exhibit the same phases reported in the literature for compositionally homogeneous materials containing larger (micro

Some elements go cubic under pressure

Czech Academy of Sciences Publication Activity Database

Legut, Dominik

2007-01-01

Roč. 60, č. 10 (2007), s. 17-17 ISSN 0031-9228 Institutional research plan: CEZ:AV0Z20410507 Keywords : ab initio * polonium * cubic structure Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 5.133, year: 2007

Formation of ice XII at low temperatures and high pressures

International Nuclear Information System (INIS)

Schober, H.; Koza, M.; Toelle, A.; Fujara, F.

1999-01-01

Complete text of publication follows. Solid water features a large variety of crystalline as well as two amorphous phases. The versatility of water's behavior has been reinforced recently by the identification of still another form of crystalline ice [1]. Ice XII was obtained by cooling liquid water to 260 K at a pressure of 5.5 kbar. Ice XII could be produced in a completely different region of water's phase diagram [2]. Using a. piston-cylinder apparatus ice XII was formed during the production of high-density amorphous ice (HDA) at 77 K as described previously [3]. The amount of crystalline ice XII contamination within the HDA sample varies in a so far unpredictable way with both extremes, i.e. pure HDA as well as pure ice XII. realized. Our results indicate that water's phase diagram needs modification in the region assigned to HDA. Ice XII is characterized as well as its transition towards cubic ice by elastic and inelastic neutron scattering. (author)

Numerical modeling and investigation of two-phase reactive flow in a high-low pressure chambers system

International Nuclear Information System (INIS)

Cheng, Cheng; Zhang, Xiaobing

2016-01-01

Highlights: • A novel two-dimensional two-phase flow model is established for the high-low pressure chambers system. • A strong packing of particles is observed at the projectile base and will cause the pressure to rise faster. • Different length–diameter ratios can affect the flow behavior through the vent-holes obviously. • The muzzle velocity decreases with the length–diameter ratio of the high-pressure chamber. - Abstract: A high-low pressure chambers system is proposed to meet the demands of low launch acceleration for informative equipment in many special fields such as Aeronautics, Astronautics and Weaponry. A two-dimensional two-phase flow numerical model is established to describe the complex physical process based on a modified two-fluid theory, which takes into account gas production, interphase drag, intergranular stress, and heat transfer between two phases. In order to reduce the computational cost, the parameters in the high-pressure chamber at the instant the vent-holes open are calculated by the zero-dimensional model as the initial conditions for the two-phase flow simulation in the high-low pressure chambers system. The simulation results reveal good agreement with the experiments and the launch acceleration of a projectile can be improved by this system. The propellant particles can be tracked clearly in both chambers and a strong packing of particles at the base of projectile will cause the pressure to rise faster than at other areas both in the axis and radial directions. The length–diameter ratio of the high-pressure chamber (a typical multi-dimensional parameter) is investigated. Different length–diameter ratios can affect the maximum pressure drop and the loss of total pressure impulse through the vent-hole, then the muzzle velocity and the launch acceleration of projectiles can be influenced directly. This article puts forward a new prediction tool for the understanding and design of transient processes in high-low pressure

Cubic colloids : Synthesis, functionalization and applications

NARCIS (Netherlands)

Castillo, S.I.R.

2015-01-01

This thesis is a study on cubic colloids: micron-sized cubic particles with rounded corners (cubic superballs). Owing to their shape, particle packing for cubes is more efficient than for spheres and results in fascinating phase and packing behavior. For our cubes, the particle volume fraction when

Orientation selection process during the early stage of cubic dendrite growth: A phase-field crystal study

International Nuclear Information System (INIS)

Tang Sai; Wang Zhijun; Guo Yaolin; Wang Jincheng; Yu Yanmei; Zhou Yaohe

2012-01-01

Using the phase-field crystal model, we investigate the orientation selection of the cubic dendrite growth at the atomic scale. Our simulation results reproduce how a face-centered cubic (fcc) octahedral nucleus and a body-centered cubic (bcc) truncated-rhombic dodecahedral nucleus choose the preferred growth direction and then evolve into the dendrite pattern. The interface energy anisotropy inherent in the fcc crystal structure leads to the fastest growth velocity in the 〈1 0 0〉 directions. New { 1 1 1} atomic layers prefer to nucleate at positions near the tips of the fcc octahedron, which leads to the directed growth of the fcc dendrite tips in the 〈1 0 0〉 directions. A similar orientation selection process is also found during the early stage of bcc dendrite growth. The orientation selection regime obtained by phase-field crystal simulation is helpful for understanding the orientation selection processes of real dendrite growth.

New pathway for the formation of metallic cubic phase Ge-Sb-Te compounds induced by an electric current.

Science.gov (United States)

Park, Yong-Jin; Cho, Ju-Young; Jeong, Min-Woo; Na, Sekwon; Joo, Young-Chang

2016-02-23

The novel discovery of a current-induced transition from insulator to metal in the crystalline phase of Ge2Sb2Te5 and GeSb4Te7 have been studied by means of a model using line-patterned samples. The resistivity of cubic phase Ge-Sb-Te compound was reduced by an electrical current (~1 MA/cm(2)), and the final resistivity was determined based on the stress current density, regardless of the initial resistivity and temperature, which indicates that the conductivity of Ge-Sb-Te compound can be modulated by an electrical current. The minimum resistivity of Ge-Sb-Te materials can be achieved at high kinetic rates by applying an electrical current, and the material properties change from insulating to metallic behavior without a phase transition. The current-induced metal transition is more effective in GeSb4Te7 than Ge2Sb2Te5, which depends on the intrinsic vacancy of materials. Electromigration, which is the migration of atoms induced by a momentum transfer from charge carriers, can easily promote the rearrangement of vacancies in the cubic phase of Ge-Sb-Te compound. This behavior differs significantly from thermal annealing, which accompanies a phase transition to the hexagonal phase. This result suggests a new pathway for modulating the electrical conductivity and material properties of chalcogenide materials by applying an electrical current.

High-pressure phases of Weyl semimetals NbP, NbAs, TaP, and TaAs

Science.gov (United States)

Guo, ZhaoPeng; Lu, PengChao; Chen, Tong; Wu, JueFei; Sun, Jian; Xing, DingYu

2018-03-01

In this study, we used the crystal structure search method and first-principles calculations to systematically explore the highpressure phase diagrams of the TaAs family (NbP, NbAs, TaP, and TaAs). Our calculation results show that NbAs and TaAs have similar phase diagrams, the same structural phase transition sequence I41 md→ P6¯ m2→ P21/ c→ Pm3¯ m, and slightly different transition pressures. The phase transition sequence of NbP and TaP differs somewhat from that of NbAs and TaAs, in which new structures emerge, such as the Cmcm structure in NbP and the Pmmn structure in TaP. Interestingly, we found that in the electronic structure of the high-pressure phase P6¯ m2-NbAs, there are coexistingWeyl points and triple degenerate points, similar to those found in high-pressure P6¯ m2-TaAs.

A Structural Study of the Pseudo-Binary Mercury Chalcogenide Alloy HgSe_{0.7}S_{0.3} at High Pressure

CERN Document Server

Kozlenko, D P; Ehm, L; Knorr, K; Hull, S; Shchennikov, V V; Voronin, V I

2002-01-01

The structure of the pseudo-binary mercury chalcogenide alloy HgSe_{0.7}S_{0.3} has been studied by means of X-ray and neutron powder diffraction at pressure up to 8.5 GPa. A phase transition from the cubic zinc blende structure to the hexagonal cinnabar structure was observed at P{\\sim}1 GPa. The obtained structural parameters were used for the analysis of the geometrical relationship between the zinc blende and the cinnabar phases. The zinc blende-cinnabar phase transition is discussed in the framework of Landau theory of the phase transitions. It was found that the possible order parameter for the structural transformation is the spontaneous strain e_{4}. This assignment agrees with previously observed high pressure behaviour of the elastic constants of other mercury chalcogenides.

A structural study of the pseudo-binary mercury chalcogenide alloy HgSe0.7S0.3 at high pressure

International Nuclear Information System (INIS)

Kozlenko, D.P.; Savenko, B.N.; Ehm, L.; Knorr, K.; Hull, S.; Shchennikov, V.V.; Voronin, V.I.

2002-01-01

The structure of the pseudo-binary mercury chalcogenide alloy HgSe 0.7 S 0.3 has been studied by means of X-ray and neutron powder diffraction at pressure up to 8.5 GPa. A phase transition from the cubic zinc blende structure to the hexagonal cinnabar structure was observed at P∼1 GPa. The obtained structural parameters were used for the analysis of the geometrical relationship between the zinc blende and the cinnabar phases. The zinc blende-cinnabar phase transition is discussed in the framework of the Landau theory of phase transitions. It was found that the possible order parameter for the structural transformation is the spontaneous strain e 4 . This assignment agrees with previously observed high pressure behaviour of the elastic constants of other mercury chalcogenides

Germination of vegetable seeds exposed to very high pressure

International Nuclear Information System (INIS)

Mori, Y; Yokota, S; Ono, F

2012-01-01

Effects of high hydrostatic pressure were investigated on vegetable seeds in the GPa range to examine the potentialities of breed improvement by high-pressure processing. Specimens of several seeds of broccoli (Brassica oleracea var. italica), Turnip leaf (Brassica rapa var. perviridis) and Potherb Mustard (Brassica rapa var. nipposinica) were put in a teflon capsule with liquid high pressure medium, fluorinate, and inserted into a pyrophillite cube. By using a cubic anvil press a hydrostatic pressure of 5.5 GP a was applied to these seeds for 15 minutes. After being brought back to ambient pressure, they were seeded on humid soil in a plant pot. Many of these vegetable seeds began to germinate within 6 days after seeded.

Germination of vegetable seeds exposed to very high pressure

Science.gov (United States)

Mori, Y.; Yokota, S.; Ono, F.

2012-07-01

Effects of high hydrostatic pressure were investigated on vegetable seeds in the GPa range to examine the potentialities of breed improvement by high-pressure processing. Specimens of several seeds of broccoli (Brassica oleracea var. italica), Turnip leaf (Brassica rapa var. perviridis) and Potherb Mustard (Brassica rapa var. nipposinica) were put in a teflon capsule with liquid high pressure medium, fluorinate, and inserted into a pyrophillite cube. By using a cubic anvil press a hydrostatic pressure of 5.5 GP a was applied to these seeds for 15 minutes. After being brought back to ambient pressure, they were seeded on humid soil in a plant pot. Many of these vegetable seeds began to germinate within 6 days after seeded.

Pressure-induced phase transitions and templating effect in three-dimensional organic-inorganic hybrid perovskites

Science.gov (United States)

Lee, Yongjae; Mitzi, David; Barnes, Paris; Vogt, Thomas

2003-07-01

Pressure-induced structural changes of conducting halide perovskites (CH3NH3)SnI3, (CH3NH3)0.5(NH2CH=NH2)0.5SnI3, and (NH2CH=NH2)SnI3, have been investigated using synchrotron x-ray powder diffraction. In contrast to low-temperature structural changes, no evidence of an increased ordering of the organic cations was observed under pressure. Instead, increase in pressure results first in a ReO3-type doubling of the primitive cubic unit cell, followed by a symmetry distortion, and a subsequent amorphization above 4 GPa. This process is reversible and points towards a pressure-induced templating role of the organic cation. Bulk compressions are continuous across the phase boundaries. The compressibilities identify these hybrids as the most compressible perovskite system ever reported. However, the Sn-I bond compressibility in (CH3NH3)SnI3 shows a discontinuity within the supercell phase. This is possibly due to an electronic localization.

Structural insights into the cubic-hexagonal phase transition kinetics of monoolein modulated by sucrose solutions.

Science.gov (United States)

Reese, Caleb W; Strango, Zachariah I; Dell, Zachary R; Tristram-Nagle, Stephanie; Harper, Paul E

2015-04-14

Using DSC (differential scanning calorimetry), we measure the kinetics of the cubic-HII phase transition of monoolein in bulk sucrose solutions. We find that the transition temperature is dramatically lowered, with each 1 mol kg(-1) of sucrose concentration dropping the transition by 20 °C. The kinetics of this transition also slow greatly with increasing sucrose concentration. For low sucrose concentrations, the kinetics are asymmetric, with the cooling (HII-cubic) transition taking twice as long as the heating (cubic-HII) transition. This asymmetry in transition times is reduced for higher sucrose concentrations. The cooling transition exhibits Avrami exponents in the range of 2 to 2.5 and the heating transition shows Avrami exponents ranging from 1 to 3. A classical Avrami interpretation would be that these processes occur via a one or two dimensional pathway with variable nucleation rates. A non-classical perspective would suggest that these exponents reflect the time dependence of pore formation (cooling) and destruction (heating). New density measurements of monoolein show that the currently accepted value is about 5% too low; this has substantial implications for electron density modeling. Structural calculations indicate that the head group area and lipid length in the cubic-HII transition shrink by about 12% and 4% respectively; this reduction is practically the same as that seen in a lipid with a very different molecular structure (rac-di-12:0 β-GlcDAG) that makes the same transition. Thermodynamic considerations suggest there is a hydration shell about one water molecule thick in front of the lipid head groups in both the cubic and HII phases.

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

Energy Technology Data Exchange (ETDEWEB)

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

2012-09-15

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

First-principles calculations of the elastic constants of the cubic, orthorhombic and hexagonal phases of BaF{sub 2}

Energy Technology Data Exchange (ETDEWEB)

Nyawere, P.W.O., E-mail: otienop98@yahoo.ca [Computational Materials Science Group, Department of Physics, University of Eldoret, P.O. Box 1125-30100 Eldoret (Kenya); Department of Computing, Kabarak University, P.O. - Private Bag - 20157 Kabarak (Kenya); The Abdus Salam International Centre for Theoretical Physics, Trieste (Italy); Makau, N.W., E-mail: wanimak@yahoo.com [Computational Materials Science Group, Department of Physics, University of Eldoret, P.O. Box 1125-30100 Eldoret (Kenya); Amolo, G.O., E-mail: georgeamolo862@gmail.com [Computational Materials Science Group, Department of Physics, University of Eldoret, P.O. Box 1125-30100 Eldoret (Kenya)

2014-02-01

All the elastic constants of cubic, orthorhombic and hexagonal phases of BaF{sub 2} have been calculated using first principles methods. We have employed density-functional theory within generalized gradient approximation (GGA) using a plane-wave pseudopotentials method and a plane-wave basis set. The calculated elastic constant values for a cubic phase compare well with recent theoretical and experimental calculations. The bulk modulus derived from the elastic constant calculations of orthorhombic phase of BaF{sub 2} is 94.5 GPa and those of hexagonal phase is 161 GPa. These values are in good agreement with experimental data available. Stability of these phases of BaF{sub 2} is also estimated in different crystallographic directions.

Pressure-induced anomalous phase transitions and colossal enhancement of piezoelectricity in PbTiO3.

Science.gov (United States)

Wu, Zhigang; Cohen, Ronald E

2005-07-15

We find an unexpected tetragonal-to-monoclinic-to-rhombohedral-to-cubic phase transition sequence induced by pressure, and a morphotropic phase boundary in a pure compound using first-principles calculations. Huge dielectric and piezoelectric coupling constants occur in the transition regions, comparable to those observed in the new complex single-crystal solid-solution piezoelectrics such as Pb(Mg(1/3)Nb(2/3))O3-PbTiO3, which are expected to revolutionize electromechanical applications. Our results show that morphotropic phase boundaries and giant piezoelectric effects do not require intrinsic disorder, and open the possibility of studying this effect in simple systems.

Phenomenological Equations Relating Various Critical Anomalies above a Cubic-to-Tetragonal Phase Transition Point

Science.gov (United States)

Hamano, Katsumi; Hirotsu, Shunsuke

1980-01-01

Phenomenological equations are derived which interrelate the anomalies in various thermodynamic quantities above the transition point of a cubic-to-tetragonal phase transition caused by an instability of a triply degenerate soft mode. The anomalous part of the Gibbs free energy is assumed to be a simple sum of the three parts which represent the contributions from the three fluctuation components. A cylindrical approximation is adopted to each of the three contributions by taking into account the symmetry of the fluctuations. The theory predicts that the adiabatic elastic compliances, s11s, s12s, and also s11s-s12s should exhibit anomalies proportional to the anomaly in the specific heat at constant pressure. This is in marked contrast with the result of the generalized Pippard equations derived by Garland, and by Janovec. The new equations are successfully tested for KMnF3, CsPbCl3, and CsPbBr3. The β-γ transition of NH4Br is also discussed.

Unraveling Crystalline Structure of High-Pressure Phase of Silicon Carbonate

Directory of Open Access Journals (Sweden)

Rulong Zhou

2014-03-01

Full Text Available Although CO_{2} and SiO_{2} both belong to group-IV oxides, they exhibit remarkably different bonding characteristics and phase behavior at ambient conditions. At room temperature, CO_{2} is a gas, whereas SiO_{2} is a covalent solid with rich polymorphs. A recent successful synthesis of the silicon-carbonate solid from the reaction between CO_{2} and SiO_{2} under high pressure [M. Santoro et al., Proc. Natl. Acad. Sci. U.S.A. 108, 7689 (2011] has resolved a long-standing puzzle regarding whether a Si_{x}C_{1−x}O_{2} compound between CO_{2} and SiO_{2} exists in nature. Nevertheless, the detailed atomic structure of the Si_{x}C_{1−x}O_{2} crystal is still unknown. Here, we report an extensive search for the high-pressure crystalline structures of the Si_{x}C_{1−x}O_{2} compound with various stoichiometric ratios (SiO_{2}:CO_{2} using an evolutionary algorithm. Based on the low-enthalpy structures obtained for each given stoichiometric ratio, several generic structural features and bonding characteristics of Si and C in the high-pressure phases are identified. The computed formation enthalpies show that the SiC_{2}O_{6} compound with a multislab three-dimensional (3D structure is energetically the most favorable at 20 GPa. Hence, a stable crystalline structure of the elusive Si_{x}C_{1−x}O_{2} compound under high pressure is predicted and awaiting future experimental confirmation. The SiC_{2}O_{6} crystal is an insulator with elastic constants comparable to typical hard solids, and it possesses nearly isotropic tensile strength as well as extremely low shear strength in the 2D plane, suggesting that the multislab 3D crystal is a promising solid lubricant. These valuable mechanical and electronic properties endow the SiC_{2}O_{6} crystal for potential applications in tribology and nanoelectronic devices, or as a stable solid-state form for CO_{2} sequestration.

Phase diagrams of the Fe-rich part of the Fe-W system under high pressure

International Nuclear Information System (INIS)

Yamane, T.; Kang, Y.S.; Minamino, Y.; Araki, H.; Hiraki, A.; Miyamoto, Y.

1995-01-01

Phase diagrams of the Fe-rich part of the Fe-W system under high pressure (1.2 and 2.2 GPa) were established by a reaction-diffusion method and calculated with thermodynamic and volumetric data. When high pressure is applied, the γ region extends and the α region contracts. As a result of increasing pressure, eutectoid and peritectoid reactions appear. (orig.)

ISAR Imaging of Ship Targets Based on an Integrated Cubic Phase Bilinear Autocorrelation Function

Directory of Open Access Journals (Sweden)

Jibin Zheng

2017-03-01

Full Text Available For inverse synthetic aperture radar (ISAR imaging of a ship target moving with ocean waves, the image constructed with the standard range-Doppler (RD technique is blurred and the range-instantaneous-Doppler (RID technique has to be used to improve the image quality. In this paper, azimuth echoes in a range cell of the ship target are modeled as noisy multicomponent cubic phase signals (CPSs after the motion compensation and a RID ISAR imaging algorithm is proposed based on the integrated cubic phase bilinear autocorrelation function (ICPBAF. The ICPBAF is bilinear and based on the two-dimensionally coherent energy accumulation. Compared to five other estimation algorithms, the ICPBAF can acquire higher cross term suppression and anti-noise performance with a reasonable computational cost. Through simulations and analyses with the synthetic model and real radar data, we verify the effectiveness of the ICPBAF and corresponding RID ISAR imaging algorithm.

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

Science.gov (United States)

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

2014-04-25

A high-density, polymeric C18 stationary phase (Inertsil ODS-P) or a polymeric C30 phase (Inertsil C30) provided improved resolution of the isomeric fatty acids (FAs), FA methyl esters (FAMEs), triacylglycerols (TAGs), and tocopherols with an increase in pressure of 20-70MPa in reversed-phase HPLC. With respect to isomeric C18 FAMEs with one cis-double bond, ODS-P phase was effective for recognizing the position of a double bond among petroselinic (methyl 6Z-octadecenoate), oleic (methyl 9Z-octadecenoate), and cis-vaccenic (methyl 11Z-octadecenoate), especially at high pressure, but the differentiation between oleic and cis-vaccenic was not achieved by C30 phase regardless of the pressure. A monomeric C18 phase (InertSustain C18) was not effective for recognizing the position of the double bond in monounsaturated FAME, while the separation of cis- and trans-isomers was achieved by any of the stationary phases. The ODS-P and C30 phases provided increased separation for TAGs and β- and γ-tocopherols at high pressure. The transfer of FA, FAME, or TAG molecules from the mobile phase to the ODS-P stationary phase was accompanied by large volume reduction (-30∼-90mL/mol) resulting in a large increase in retention (up to 100% for an increase of 50MPa) and improved isomer separation at high pressure. For some isomer pairs, the ODS-P and C30 provided the opposite elution order, and in each case higher pressure improved the separation. The two stationary phases showed selectivity for the isomers having rigid structures, but only the ODS-P was effective for differentiating the position of a double bond in monounsaturated FAMEs. The results indicate that the improved isomer separation was provided by the increased dispersion interactions between the solute and the binding site of the stationary phase at high pressure. Copyright © 2014 Elsevier B.V. All rights reserved.

Phase transition of intermetallic TbPt at high temperature and high pressure

Science.gov (United States)

Qin, Fei; Wu, Xiang; Yang, Ke; Qin, Shan

2018-04-01

Here we present synchrotron-based x-ray diffraction experiments combined with diamond anvil cell and laser heating techniques on the intermetallic rare earth compound TbPt (Pnma and Z  =  4) up to 32.5 GPa and ~1800 K. The lattice parameters of TbPt exhibit continuous compression behavior up to 18.2 GPa without any evidence of phase transformation. Pressure-volume data were fitted to a third-order Birch-Murnaghan equation of state with V 0  =  175.5(2) Å3, {{K}{{T0}}}   =  110(5) GPa and K{{T0}}\\prime   =  3.8(7). TbPt exhibits anisotropic compression with β a   >  β b   >  β c and the ratio of axial compressibility is 2.50:1.26:1.00. A new monoclinic phase of TbPt assigned to the Pc or P2/c space group was observed at 32.5 GPa after laser heating at ~1800 K. This new phase is stable at high pressure and presented a quenchable property on decompression to ambient conditions. The pressure-volume relationship is well described by the second-order Birch-Murnaghan equation of state, which yields V 0  =  672(4) Å3, {{K}{{T0}}}   =  123(6) GPa, which is about ~14% more compressible than the orthorhombic TbPt. Our results provide more information on the structure and elastic property view, and thus a better understanding of the physical properties related to magnetic structure in some intermetallic rare earth alloys.

Bulk moduli and high pressure phases of ThX compounds. Pt. 2

International Nuclear Information System (INIS)

Staun Olsen, J.; Gerward, L.; Benedict, U.; Luo, H.; Vogt, O.

1989-01-01

The high-pressure crystal structures of the members of the ThX series, where X = S, Se and Te, have been studied using synchrotron X-ray diffraction in the pressure range up to about 60 GPa. A distorted fcc structure is observed for ThS above 20 GPa. These transforms to the CsCl structure at 15 GPa. has the CsCl structure already at atmospheric pressure and no further phase transition has been observed. A log-log plot of bulk modulus versus specific volume gives a straight line with slope -1.85. (orig.)

Numerical Simulation of Sloshing Phenomena in Cubic Tank with Multiple Baffles

Directory of Open Access Journals (Sweden)

Mi-An Xue

2012-01-01

Full Text Available A two-phase fluid flow model solving Navier-Stokes equations was employed in this paper to investigate liquid sloshing phenomena in cubic tank with horizontal baffle, perforated vertical baffle, and their combinatorial configurations under the harmonic motion excitation. Laboratory experiment of liquid sloshing in cubic tank with perforated vertical baffle was carried out to validate the present numerical model. Fairly good agreements were obtained from the comparisons between the present numerical results and the present experimental data, available numerical data. Liquid sloshing in cubic tank with multiple baffles was investigated numerically in detail under different external excitation frequencies. Power spectrum of the time series of free surface elevation was presented with the aid of fast Fourier transform technique. The dynamic impact pressures acting on the normal and parallel sidewalls were discussed in detail.

High-pressure studies of a ThMn sub 1 sub 2 -type actinide compound: UFe sub 5 Al sub 7

CERN Document Server

Halevy, I; Kimmel, G; Atzmony, U; Pereira, L C J; Goncalves, A P; Schäfer, W

2002-01-01

The ternary inter-metallic compound, UFe sub 5 Al sub 7 , crystallize in a tetragonal ThMn sub 1 sub 2 type structure. In the as-cast samples a residual phase of FeAl (approx 2% wt) was identified in the grain boundaries. The amount of the residual cubic phase of FeAl was determined by Rietveld analysis and reduced by the annealing process. UFe sub 5 Al sub 7 maintains the tetragonal symmetry as a function of pressure, while FeAl keeps the cubic structure as was determined by the Rietveld analysis. The volume-pressure curve calculated from the x-ray analysis is V/V sub 0 = 0.87 for UFe sub 5 Al sub 7 at 26.0 GPa.

Pressure response of vacancy ordered maghemite (γ-Fe2O3) and high pressure transformed hematite (α-Fe2O3)

International Nuclear Information System (INIS)

Hearne, Giovanni; Pischedda, Vittoria

2012-01-01

Combined XRD and Mössbauer effect spectroscopy studies to high pressures of ∼30 GPa of vacancy ordered maghemite are presented. The vacancy ordered superstructure is robust and remains intact up to the pressure-induced onset transition to hematite at 13–16 GPa. The pressure transformed hematite is shown to be crystallographically textured, unlike the randomised low pressure maghemite phase. This arises out of a pressure or stress instigated topotactic transformation of the cubic-spinel to hexagonal-corundum structure. The textured sample permits us to obtain information on the spin reorientation behavior of the pressure transformed hematite in compression and decompression sequences. Spin reorientation is restricted to ∼15° over wide pressure ranges, attributable to the effect of entrapped vacancies in the high pressure structure. Thus there are structural and magnetic peculiarities specific to pressure transformed hematite not evident in pressurized hematite starting material. These are triggered by the maghemite→hematite transformation. - Graphical abstract: Pressure instigated topotactic transformation of vacancy ordered γ-Fe 2 O 3 →α-Fe 2 O 3 . There is restricted spin (B hf ) reorientation in the new pressure transformed hematite due to entrapped vacancies. The change in direction of V zz signifies a distortion of the FeO 6 octahedral local environment. Highlights: ► Robust vacancy ordered superstructure in maghemite to high pressures. ► Pressure instigated topotactic transformation to hematite and subsequent texture. ► Defect trapping in the pressure transformed hematite. ► Entrapped defects restricts spin reorientation in pressure transformed hematite. ► Contrasting behavior with pressurized hematite starting material.

First principles study of the structural and electronic properties of double perovskite Ba2YTaO6 in cubic and tetragonal phases

International Nuclear Information System (INIS)

Deluque Toro, C.E.; Rodríguez M, Jairo Arbey; Landínez Téllez, D.A.; Moreno Salazar, N.O.; Roa-Rojas, J.

2014-01-01

The Ba 2 YTaO 6 double perovskite presents a transition from cubic (Fm−3m) to tetragonal structure (I4/m) at high temperature. In this work, we present a detailed study of the structural and electronic properties of the double perovskite Ba 2 YTaO 6 in space group Fm−3m and I4/m. Calculations were made with the Full-Potential Linear Augmented Plane Wave method (FP-LAPW) within the framework of the Density Functional Theory (DFT) with exchange and correlation effects in the Generalized Gradient (GGA) and Local Density (LDA) approximations. From the minimization of energy as a function of volume and the fitting of the Murnaghan equation some structural characteristics were determined as, for example, total energy, lattice parameter (a=8.50 Å in cubic phase and a=5.985 Å and c=8.576 Å in tetragonal), bulk modulus (135.6 GPa in cubic phase and 134.1 GPa in tetragonal phase) and its derivative. The study of the electronic characteristics was performed from the analysis of the electronic density of states (DOS). We find a non-metallic behavior for this with a direct band gap of approximately 3.5 eV and we found that the Ba 2 YTaO 6 (I4/m) phase is the most stable one. © 2013 Elsevier Science. All rights reserved

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

Science.gov (United States)

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.

Multiple pathways in pressure-induced phase transition of coesite

Science.gov (United States)

Liu, Wei; Wu, Xuebang; Liu, Changsong; Miranda, Caetano R.; Scandolo, Sandro

2017-01-01

High-pressure single-crystal X-ray diffraction method with precise control of hydrostatic conditions, typically with helium or neon as the pressure-transmitting medium, has significantly changed our view on what happens with low-density silica phases under pressure. Coesite is a prototype material for pressure-induced amorphization. However, it was found to transform into a high-pressure octahedral (HPO) phase, or coesite-II and coesite-III. Given that the pressure is believed to be hydrostatic in two recent experiments, the different transformation pathways are striking. Based on molecular dynamic simulations with an ab initio parameterized potential, we reproduced all of the above experiments in three transformation pathways, including the one leading to an HPO phase. This octahedral phase has an oxygen hcp sublattice featuring 2 × 2 zigzag octahedral edge-sharing chains, however with some broken points (i.e., point defects). It transforms into α-PbO2 phase when it is relaxed under further compression. We show that the HPO phase forms through a continuous rearrangement of the oxygen sublattice toward hcp arrangement. The high-pressure amorphous phases can be described by an fcc and hcp sublattice mixture. PMID:29162690

Superconducting phases of phosphorus hydride under pressure. Stabilization by mobile molecular hydrogen

Energy Technology Data Exchange (ETDEWEB)

Bi, Tiange; Miller, Daniel P.; Shamp, Andrew; Zurek, Eva [Department of Chemistry, State University of New York, Buffalo, NY (United States)

2017-08-14

At 80 GPa, phases with the PH{sub 2} stoichiometry, which are composed of simple cubic like phosphorus layers capped with hydrogen atoms and layers of H{sub 2} molecules, are predicted to be important species contributing to the recently observed superconductivity in compressed phosphine. The electron-phonon coupling in these phases results from the motions of the phosphorus atoms and the hydrogen atoms bound to them. The role of the mobile H{sub 2} layers is to decrease the Coulomb repulsion between the negatively charged hydrogen atoms capping the phosphorus layers. An insulating PH{sub 5} phase, the structure and bonding of which is reminiscent of diborane, is also predicted to be metastable at this pressure. (copyright 2017 Wiley-VCH Verlag GmbH and Co. KGaA, Weinheim)

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

International Nuclear Information System (INIS)

Zhilyaev, A.P.; Sabirov, I.; Gonzalez-Doncel, G.; Molina-Aldareguia, J.; Srinivasarao, B.; Perez-Prado, M.T.

2011-01-01

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

Study of SmS properties in the low pressure phase (black phase)

International Nuclear Information System (INIS)

Bordier, G.

1986-01-01

SmS was studied for the transition from low pressure phase (black phase) to high pressure phase with an intermediate valence. But the study of the black phase is very rich. The variations of electron transport properties with pressure at low temperature show a semi-metal phase located, in the pressure-temperature diagram in the black phase for pressure over 4 kbars, corresponding to the phase B'of the doping-temperature diagram. Electron spin resonance shows a lack of sulfur and nearby this defect a samarium ion, magnetically coupled with the matrix, presents a divalent trivalent transition. Resonance lines are broadened with temperature. Conductivity relaxations occur at low pressure and low temperature by trapping a conduction electron, by magnetic exchange giving a bounded magnetic polaron. The relaxation time at null magnetic field is activated. An approximation of trapping barrier and critical field corresponding the maximum magnetoresistance is given by a model [fr

Structural phase transitions in Iron - based superconductors BaFe2-xCrxAs2 under high pressure

International Nuclear Information System (INIS)

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

2011-01-01

Pure BaFe 2 As 2 with the ThCr 2 Si 2 -type crystal structure under ambient conditions is known to superconduct under high pressure and undergo an isostructural phase transition from tetragonal to collapsed tetragonal phase which is accompanied by anomalous compressibility effects. Presently, there is no reported work on the crystal structure on any of the chemically doped 122- iron based superconductors under high pressure. We have carried out the electrical resistance measurements and high pressure X-ray diffraction studies on Chromium doped samples of BaFe 2-x Cr x As 2 (x = 0, 0.05, 0.15, 0.4, 0.61) to a pressure of 75 GPa and a temperature of 10K using a synchrotron source and designer diamond anvils, so as to investigate the influence of chemical doping and high pressure on crystal structure and superconductivity

Structural Phase Transitions of Mg(BH4)2 under Pressure

International Nuclear Information System (INIS)

George, L.; Drozd, V.; Saxena, S.; Bardaji, E.; Fichtner, M.

2009-01-01

The structural stability of Mg(BH4)2, a promising hydrogen storage material, under pressure has been investigated in a diamond anvil cell up to 22 GPa with combined synchrotron X-ray diffraction and Raman spectroscopy. The analyses show a structural phase transition around 2.5 GPa and again around 14.4 GPa. An ambient-pressure phase of Mg(BH4)2 has a hexagonal structure (space group P61, a = 10.047(3) A, c = 36.34(1) A, and V = 3176(1) A3 at 0.2 GPa), which agrees well with early reports. The structure of high-pressure phase is found to be different from reported theoretical predictions; it also does not match the high-temperature phase. The high-pressure polymorph of Mg(BH4)2 is found to be stable on decompression, similar to the case of the high-temperature phase. Raman spectroscopic study shows a similarity in high-pressure behavior of as-prepared Mg(BH4)2 and its high-temperature phase.

Phases of Ca from first principles

International Nuclear Information System (INIS)

Qiu, S L; Marcus, P M

2009-01-01

Structures and properties of many of the phases of Ca under pressure are calculated from first principles by a systematic procedure that minimizes total energy E with respect to structure under the constraint of constant volume V. The minima of E are followed on successive sweeps of lattice parameters for 11 of 14 Bravais symmetries for one-atom-per-cell structures. The structures include the four orthorhombic phases. Also included are the hexagonal close-packed and cubic diamond phases with two atoms per primitive cell. No uniquely orthorhombic phases are found; all one-atom orthorhombic phases over a mega-bar pressure range are identical to higher-symmetry phases. The simple cubic phase is shown to be stable where it is the ground state. The number of distinct one-atom phases reduces to five plus the two two-atom phases. For each of these phases the Gibbs free energy at pressure p, G(p), is calculated for a non-vibrating lattice; the functions G(p) give the ground state at each p, the relative stabilities of all phases and the thermodynamic phase transition pressures for all phase transitions over a several-megabar range.

Study on effect of cubic- and tetragonal phased BaTiO{sub 3} on the electrical and thermal properties of polymeric nanocomposites

Energy Technology Data Exchange (ETDEWEB)

Thanki, A.A.; Goyal, R.K., E-mail: rkgoyal72@yahoo.co.in

2016-11-01

Polymer matrix nanocomposites based on polycarbonate (PC) and nanosized-cubic/tetragonal phases of barium titanate (BaTiO{sub 3}) were fabricated using a solution method followed by hot pressing. The content of both cubic- and tetragonal phased BaTiO{sub 3} was varied from 0 to 50 wt%. For a given weight fraction, the dielectric constant of the nanocomposites containing tetragonal BaTiO{sub 3} is more than those of cubic BaTiO{sub 3} filled nanocomposites. Moreover, cubic BaTiO{sub 3}/PC nanocomposites showed significantly lower dissipation factor than those of tetragonal BaTiO{sub 3}/PC nanocomposites. The dielectric constant of the nanocomposites was found to be frequency-independent. The microhardness of the nanocomposites increased with increase in the BaTiO{sub 3} content (both cubic- and tetragonal-phased) compared to the pure matrix. Scanning electron microscopy showed better dispersion and good interaction of the tetragonal BaTiO{sub 3} nanoparticles in the matrix. The addition of cubic BaTiO{sub 3} nanoparticles significantly reduced the thermal stability of the nanocomposites compared to matrix while the addition of tetragonal BaTiO{sub 3} nanoparticles decreased it slightly. The glass transition temperature of the cubic BaTiO{sub 3}/PC nanocomposites decreased significantly, whereas it reduced slightly for the tetragonal BaTiO{sub 3}/PC nanocomposites. - Highlights: • The effect of cubic-BaTiO{sub 3} and tetragonal-BaTiO{sub 3} nanoparticles were studied. • Cubic-BaTiO{sub 3} nanoparticles showed better microhardness. • Tetragonal-BaTiO{sub 3} nanoparticles showed better dielectric and thermal properties. • Frequency independent dielectric constants of the nanocomposites were observed.

Structural phase transition and elastic properties of AnAs (An= Th, U, Np, Pu) compounds at high pressure

International Nuclear Information System (INIS)

Aynyas, Mahendra; Arya, B.S.; Srivastava, Vipul; Sanyal, Sankar P.

2006-01-01

The high pressure behavior and pressure induced structural phase transition of mono arsenides (AnAs; An = Th, U, Np, Pu) have been investigated by using a three body interaction potential (TBI). This method has been found quite satisfactory in the case of other Rare-Earth compounds. The calculated compression curves of mono-arsenides obtained so have been compared with high pressure X-ray diffraction work. The theoretically predicted phase transition pressure and other structural properties for these compounds agree reasonably well with the measured values. (author)

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

Science.gov (United States)

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

2006-05-01

Laser Raman Spectroscopy was used to study phase relations between calcite I, calcite II and aragonite at high pressure and high temperature. The experiment was performed in an externally heated Basselt type diamond anvil cell (DAC). Natural calcite (calcite I) was used as starting mineral. The sample and a small chip of quartz were loaded in a cavity (300 μm in diameter and 250 μm in depth) in a rhenium gasket. The Na2CO3 aqueous solution of 1mol/L was also loaded as a pressure medium to yield hydrostatic pressure. The whole assembly was pressurized first and then heated stepwise to 400°C. Pressure and temperature in the chamber were determined by the shift of Raman band at 464 cm-1 of quartz and by NiCr-NiSi thermocouple, respectively. The Raman spectra were measured by a Renishaw 1000 spetrometer with 50 mW of 514.5nm argon-ion laser as the excitation light source. The slit width was 50 μm and the corresponding resolution was ±1 cm-1. From the experiments, we observed the phase transitions between calcite I and calcite II, calcite I and aragonite, calcite II and aragonite, respectively. Our data showed a negative slope for the boundary between calcite I and calcite II, which was similar to Bridgman's result, although Hess et al. gave a positive slope. The boundary with a negative slope for calcite II and aragonite was also defined, which had never been done before. And all these data can yield a more complete phase diagram of CaCO3 than the studies of Hess et al. and Suito et al.Reference:Bridgeman P. W.(1939) Journal: American Journal of Science, Vol. 237, p. 7-18Bassett W. A. et al. (1993) Journal: Review of Scientific Instruments, Vol. 64, p. 2340-2345Suito K. et al. (2001) Journal: American Mineralogist, Vol. 86, p. 997- 1002Hess N. J. et al. (1991) In A. K. Singh, Ed., Recent Trends in High Pressure Research; Proc. X IIIth AIRAPT International Conference on High Pressure Science and Technology, p. 236-241. Oxford & IBH Publishing Co. Pvt, Ltd., New

THERMODYNAMIC PARAMETERS OF LEAD SULFIDE CRYSTALS IN THE CUBIC PHASE

Directory of Open Access Journals (Sweden)

T. O. Parashchuk

2016-07-01

Full Text Available Geometric and thermodynamic parameters of cubic PbS crystals were obtained using the computer calculations of the thermodynamic parameters within density functional theory method DFT. Cluster models for the calculation based on the analysis of the crystal and electronic structure. Temperature dependence of energy ΔE and enthalpy ΔH, Gibbs free energy ΔG, heat capacity at constant pressure CP and constant volume CV, entropy ΔS were determined on the basis of ab initio calculations of the crystal structure of molecular clusters. Analytical expressions of temperature dependences of thermodynamic parameters which were approximated with quantum-chemical calculation points have been presented. Experimental results compared with theoretically calculated data.

High-pressure fluid-phase equilibria: Experimental methods and systems investigated (2000-2004)

DEFF Research Database (Denmark)

Dohrn, Ralf; Peper, Stephanie; Fonseca, José

2010-01-01

As a part of a series of reviews, a compilation of systems for which high-pressure phase-equilibrium data were published between 2000 and 2004 is given. Vapor-liquid equilibria, liquid-liquid equilibria, vapor-liquid-liquid equilibria,solid-liquid equilibria, solid-vapor equilibria, solid-vapor-l...

Clean Grain Boundary Found in C14/Body-Center-Cubic Multi-Phase Metal Hydride Alloys

Directory of Open Access Journals (Sweden)

Hao-Ting Shen

2016-06-01

Full Text Available The grain boundaries of three Laves phase-related body-center-cubic (bcc solid-solution, metal hydride (MH alloys with different phase abundances were closely examined by scanning electron microscopy (SEM, transmission electron microscopy (TEM, and more importantly, electron backscatter diffraction (EBSD techniques. By using EBSD, we were able to identify the alignment of the crystallographic orientations of the three major phases in the alloys (C14, bcc, and B2 structures. This finding confirms the presence of crystallographically sharp interfaces between neighboring phases, which is a basic assumption for synergetic effects in a multi-phase MH system.

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

Science.gov (United States)

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.

Modeling vapor liquid equilibrium of ionic liquids + gas binary systems at high pressure with cubic equations of state

Directory of Open Access Journals (Sweden)

A. C. D. Freitas

2013-03-01

Full Text Available Ionic liquids (IL have been described as novel environmentally benign solvents because of their remarkable characteristics. Numerous applications of these solvents continue to grow at an exponential rate. In this work, high pressure vapor liquid equilibria for 17 different IL + gas binary systems were modeled at different temperatures with Peng-Robinson (PR and Soave-Redlich-Kwong (SRK equations of state, combined with the van der Waals mixing rule with two binary interaction parameters (vdW-2. The experimental data were taken from the literature. The optimum binary interaction parameters were estimated by minimization of an objective function based on the average absolute relative deviation of liquid and vapor phases, using the modified Simplex algorithm. The solubilities of all gases studied in this work decrease as the temperature increases and increase with increasing pressure. The correlated results were highly satisfactory, with average absolute relative deviations of 2.10% and 2.25% for PR-vdW-2 and SRK-vdW-2, respectively.

High dose effects in neutron irradiated face-centered cubic metals

International Nuclear Information System (INIS)

Garner, F.A.; Toloczko, M.B.

1993-06-01

During neutron irradiation, most face-centered cubic metals and alloys develop saturation or quasi-steady state microstructures. This, in turn, leads to saturation levels in mechanical properties and quasi-steady state rates of swelling and creep deformation. Swelling initially plays only a small role in determining these saturation states, but as swelling rises to higher levels, it exerts strong feedback on the microstructure and its response to environmental variables. The influence of swelling, either directly or indirectly via second order mechanisms, such as elemental segregation to void surfaces, eventually causes major changes, not only in irradiation creep and mechanical properties, but also on swelling itself. The feedback effects of swelling on irradiation creep are particularly complex and lead to problems in applying creep data derived from highly pressurized creep tubes to low stress situations, such as fuel pins in liquid metal reactors

High-pressure fluid phase equilibria phenomenology and computation

CERN Document Server

Deiters, Ulrich K

2012-01-01

The book begins with an overview of the phase diagrams of fluid mixtures (fluid = liquid, gas, or supercritical state), which can show an astonishing variety when elevated pressures are taken into account; phenomena like retrograde condensation (single and double) and azeotropy (normal and double) are discussed. It then gives an introduction into the relevant thermodynamic equations for fluid mixtures, including some that are rarely found in modern textbooks, and shows how they can they be used to compute phase diagrams and related properties. This chapter gives a consistent and axiomatic approach to fluid thermodynamics; it avoids using activity coefficients. Further chapters are dedicated to solid-fluid phase equilibria and global phase diagrams (systematic search for phase diagram classes). The appendix contains numerical algorithms needed for the computations. The book thus enables the reader to create or improve computer programs for the calculation of fluid phase diagrams. introduces phase diagram class...

New High Pressure Phase of CaCO3: Implication for the Deep Diamond Formation

Science.gov (United States)

Mao, Z.; Li, X.; Zhang, Z.; Lin, J. F.; Ni, H.; Prakapenka, V.

2017-12-01

Surface carbon can be transported to the Earth's deep interior through sinking subduction slabs. Carbonates, including CaCO3, MgCO3 and MgCa(CO3)2, are important carbon carriers for the deep carbon cycle. Experimental studies on the phase stability of carbonates with coexisting mantle minerals at relevant pressure and temperature conditions are thus important for understanding the deep carbon cycle. In particular, recent petrological studies have revealed the evidence for the transportation of CaCO3 to the depth at least of the top lower mantle by analyzing the diamond inclusions. Yet the phase stability of CaCO3 at relevant pressure and temperature conditions of the top lower mantle is still unclear. Previous single-crystal study has shown that CaCO3 transforms from the CaCO3-III structure to CaCO3-VI at 15 GPa and 300 K. The CaCO3-VI is stable at least up to 40 GPa at 300 K. At high temperatures, CaCO3 in the aragonite structure will directly transform into the post-aragonite structure at 40 GPa. However, a recent theoretical study predicted a new phase of CaCO3 with a space group of P21/c between 32 and 48 GPa which is different from previous experimental results. In this study, we have investigated the phase stability of CaCO3 at high pressure-temperature conditions using synchrotron X-ray diffraction in laser-heated diamond anvil cells. We report the discovery of a new phase of CaCO3 at relevant pressure-temperature conditions of the top lower mantle which is consistent with previous theoretical predictions. This new phase is an important carrier for the transportation of carbon to the Earth's lower mantle and crucial for growing deep diamonds in the region.

Hydrostatic-pressure studies of confined transitions in cubic Zn1-xCdxSe/ZnSe strained-layer quantum wells

International Nuclear Information System (INIS)

Thomas, R.J.; Chandrasekhar, H.R.; Chandrasekhar, M.; Samarth, N.; Luo, H.; Furdyna, J.

1992-01-01

Photoluminescence spectra of cubic Zn 0.82 Cd 0.18 Se quantum wells of widths 30, 60, and 200 A are studied as a function of hydrostatic pressure (0--60 kbar) at 80 K. The pressure coefficients of heavy-hole excitons are found to decrease with increasing well width. The photoluminescence energies of the ZnSe barrier and cap layers are also observed to shift as a function of hydrostatic pressure, providing a measure of the pressure coefficient of the direct gap in this material

High-pressure torsion of hafnium

International Nuclear Information System (INIS)

Edalati, Kaveh; Horita, Zenji; Mine, Yoji

2010-01-01

Pure Hf (99.99%) is processed by high-pressure torsion (HPT) under pressures of 4 and 30 GPa to form an ultrafine-grained structure with a gain size of ∼180 nm. X-ray diffraction analysis shows that, unlike Ti and Zr, no ω phase formation is detected after HPT processing even under a pressure of 30 GPa. A hydride formation is detected after straining at the pressure of 4 GPa. The hydride phase decomposes either by application of a higher pressure as 30 GPa or by unloading for prolong time after HPT processing. Microhardness, tensile and bending tests show that a high hardness (360 Hv) and an appreciable ductility (8%) as well as high tensile and bending strength (1.15 and 2.75 GPa, respectively) are achieved following the high-pressure torsion.

High pressure X-ray studies

International Nuclear Information System (INIS)

Sikka, S.K.

1981-01-01

High pressure research has already led to new insights in the physical properties of materials and at times to the synthesis of new ones. In all this, X-ray diffraction has been a valuable diagnostic experimental tool. In particular, X-rays in high pressure field have been used (a) for crystallographic identification of high pressure polymorphs and (b) for study of the effect of pressure on lattice parameters and volume under isothermal conditions. The results in the area (a) are reviewed. The techniques of applying high pressures are described. These include both static and dynamic shockwave X-ray apparatus. To illustrate the effect of pressure, some of the pressure induced phase transitions in pure metals are described. It has been found that there is a clear trend for elements in any group of the periodic table to adopt similar structures at high pressures. These studies have enabled to construct generalized phase diagrams for many groups. In the case of alloys, the high pressure work done on Ti-V alloys is presented. (author)

Tetragonal-cubic phase boundary in nanocrystalline ZrO{sub 2}-Y{sub 2}O{sub 3} solid solutions synthesized by gel-combustion

Energy Technology Data Exchange (ETDEWEB)

Fabregas, Ismael O. [CINSO (Centro de Investigaciones en Solidos), CITEFA-CONICET, J.B. de La Salle 4397, 1603 Villa Martelli, Pcia. de Buenos Aires (Argentina); Craievich, Aldo F.; Fantini, Marcia C.A. [Instituto de Fisica, Universidade de Sao Paulo, Travessa R da Rua do Matao, No. 187, Cidade Universitaria, 05508-900 Sao Paulo (Brazil); Millen, Ricardo P.; Temperini, Marcia L.A. [Instituto de Quimica, Universidade de Sao Paulo, Avenida Prof. Lineu Prestes 748, Cidade Universitaria, 05508-900 Sao Paulo (Brazil); Lamas, Diego G., E-mail: dlamas@uncoma.edu.ar [CINSO (Centro de Investigaciones en Solidos), CITEFA-CONICET, J.B. de La Salle 4397, 1603 Villa Martelli, Pcia. de Buenos Aires (Argentina); Laboratorio de Caracterizacion de Materiales, Facultad de Ingenieria, Universidad Nacional del Comahue, Buenos Aires 1400, (8300) Neuquen Capital, Prov. de Neuquen (Argentina)

2011-04-21

Research highlights: > Gel-combustion synthesis yields compositionally homogeneous, single-phased ZrO{sub 2}-Y{sub 2}O{sub 3} nanopowders, that exhibit the presence at room temperature of three different phases depending on Y{sub 2}O{sub 3} content, namely two tetragonal forms (t' and t'') and the cubic phase. > Phase identification can be achieved by synchrotron XPD (SXPD) and Raman spectroscopy since the tetragonal forms and the cubic phase can be distinguished by these techniques. > The crystallographic features of ZrO{sub 2}-Y{sub 2}O{sub 3} nanopowders were determined by SXPD. They are similar to those reported by Yashima and coworkers for compositionally homogeneous materials containing larger (micro)crystals. However, the lattice parameters are slightly different and the axial ratios c/a of our t' samples are smaller than those reported by these authors. > Compositional t'/t'' and t''/cubic phase boundaries are located at (9 {+-} 1) and (10.5 {+-} 0.5) mol% Y{sub 2}O{sub 3}, respectively. > For the whole series of nanocrystalline ZrO{sub 2}-Y{sub 2}O{sub 3} solid solutions studied in the present work, no evidences of the presence of a mixture of phases - as reported by Yashima and coworkers for microcrystalline solid solutions - were detected. - Abstract: By means of synchrotron X-ray powder diffraction (SXPD) and Raman spectroscopy, we have detected, in a series of nanocrystalline and compositionally homogeneous ZrO{sub 2}-Y{sub 2}O{sub 3} solid solutions, the presence at room temperature of three different phases depending on Y{sub 2}O{sub 3} content, namely two tetragonal forms and the cubic phase. The studied materials, with average crystallite sizes within the range 7-10 nm, were synthesized by a nitrate-citrate gel-combustion process. The crystal structure of these phases was also investigated by SXPD. The results presented here indicate that the studied nanocrystalline ZrO{sub 2}-Y{sub 2}O{sub 3} solid

Cubic to tetragonal phase transition of Tm3+ doped nanocrystals in oxyfluoride glass ceramics

International Nuclear Information System (INIS)

Li, Yiming; Fu, Yuting; Shi, Yahui; Zhang, Xiaoyu; Yu, Hua; Zhao, Lijuan

2016-01-01

Tm 3+ ions doped β-PbF 2 nanocrystals in oxyfluoride glass ceramics with different doping concentrations and thermal temperatures are prepared by a traditional melt-quenching and thermal treatment method to investigate the structure and the phase transition of Tm 3+ doped nanocrystals. The structures are characterized by X-ray diffraction Rietveld analysis and confirmed with numerical simulation. The phase transitions are proved further by the emission spectra. Both of the doping concentration and thermal temperature can induce an O h to D 4h site symmetry distortion and a cubic to tetragonal phase transition. The luminescence of Tm 3+ doped nanocrystals at 800 nm was modulated by the phase transition of the surrounding crystal field

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

International Nuclear Information System (INIS)

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

2014-01-01

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.

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

International Nuclear Information System (INIS)

Ohwada, K.; Fujii, Y.; Takesue, N.; Isobe, M.; Ueda, Y.; Nakao, H.; Wakabayashi, Y.; Murakami, Y.; Ito, K.; Amemiya, Y.

2001-01-01

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

Formation of metastable cubic phase in Ce{sub 100−x}Al{sub x} (x=45, 50) alloys and their thermal and magnetic properties

Energy Technology Data Exchange (ETDEWEB)

Idzikowski, Bogdan, E-mail: idzi@ifmpan.poznan.pl [Institute of Molecular Physics, Polish Academy of Sciences, M. Smoluchowskiego 17, 60-179 Poznań (Poland); Centre for Advanced Materials and Smart Structures, Polish Academy of Sciences, Okólna 2, 50-422 Wrocław (Poland); Śniadecki, Zbigniew [Institute of Molecular Physics, Polish Academy of Sciences, M. Smoluchowskiego 17, 60-179 Poznań (Poland); Centre for Advanced Materials and Smart Structures, Polish Academy of Sciences, Okólna 2, 50-422 Wrocław (Poland); Puźniak, Roman [Institute of Physics, Polish Academy of Sciences, Aleja Lotników 32/46, 02-668 Warszawa (Poland); Kaczorowski, Dariusz [Institute of Low Temperature and Structure Research, Polish Academy of Sciences, P.O. Box 1410, 50-950 Wrocław (Poland); Centre for Advanced Materials and Smart Structures, Polish Academy of Sciences, Okólna 2, 50-422 Wrocław (Poland)

2017-01-01

Ce{sub 100−x}Al{sub x} (x=45 and 50) alloys were synthesized by rapid quenching technique in the form of ribbons composed of nanocrystalline phase of CeAl with the ClCs-type structure (Pm-3m space group) embedded in an amorphous matrix. The cubic CeAl phase is known as metastable with random distribution of Ce and Al atoms in the unit cell. The crystalline volume fraction is about 7.5% in Ce{sub 55}Al{sub 45} and 3% in Ce{sub 50}Al{sub 50}. The alloy Ce{sub 55}Al{sub 45} shows better thermal stability than Ce{sub 50}Al{sub 50}, indicated by higher effective activation energy and higher crystallization temperature. Small off-stoichiometry in Ce{sub 55}Al{sub 45} results in degrading the glass forming ability and promotes formation of the cubic CeAl phase, as confirmed by magnetic measurements. In both alloys, the Ce ions are in stable trivalent state and order magnetically near 20 K. Another magnetic phase transition close to 10 K was found for Ce{sub 50}Al{sub 50} and was attributed to the presence of the well-known stable orthorhombic CeAl phase. To the best of our knowledge, the magnetic behavior of the CeAl cubic phase is reported here for the first time. - Highlights: • Synthesis of metastable cubic CeAl phase by rapid quenching. • The Ce ions in Ce{sub 55}Al{sub 45} and Ce{sub 50}Al{sub 50} are in stable trivalent state. • Magnetic transition near 10 K connected with the orthorhombic CeAl phase. • Phase transition at about 20 K originates from the cubic CeAl phase.

Application of neural networks to prediction of phase transport characteristics in high-pressure two-phase turbulent bubbly flows

International Nuclear Information System (INIS)

Yang, A.-S.; Kuo, T.-C.; Ling, P.-H.

2003-01-01

The phase transport phenomenon of the high-pressure two-phase turbulent bubbly flow involves complicated interfacial interactions of the mass, momentum, and energy transfer processes between phases, revealing that an enormous effort is required in characterizing the liquid-gas flow behavior. Nonetheless, the instantaneous information of bubbly flow properties is often desired for many industrial applications. This investigation aims to demonstrate the successful use of neural networks in the real-time determination of two-phase flow properties at elevated pressures. Three back-propagation neural networks, trained with the simulation results of a comprehensive theoretical model, are established to predict the transport characteristics (specifically the distributions of void-fraction and axial liquid-gas velocities) of upward turbulent bubbly pipe flows at pressures covering 3.5-7.0 MPa. Comparisons of the predictions with the test target vectors indicate that the averaged root-mean-squared (RMS) error for each one of three back-propagation neural networks is within 4.59%. In addition, this study appraises the effects of different network parameters, including the number of hidden nodes, the type of transfer function, the number of training pairs, the learning rate-increasing ratio, the learning rate-decreasing ratio, and the momentum value, on the training quality of neural networks.

High-temperature superconducting phase of HBr under pressure predicted by first-principles calculations

Science.gov (United States)

Gu, Qinyan; Lu, Pengchao; Xia, Kang; Sun, Jian; Xing, Dingyu

2017-08-01

The high pressure phases of HBr are explored with an ab initio crystal structure search. By taking into account the contribution of zero-point energy (ZPE), we find that the P 4 /n m m phase of HBr is thermodynamically stable in the pressure range from 150 to 200 GPa. The superconducting critical temperature (Tc) of P 4 /n m m HBr is evaluated to be around 73 K at 170 GPa, which is the highest record so far among binary halogen hydrides. Its Tc can be further raised to around 95K under 170 GPa if half of the bromine atoms in the P 4 /n m m HBr are substituted by the lighter chlorine atoms. Our study shows that, in addition to lower mass, higher coordination number, shorter bonds, and more highly symmetric environment for the hydrogen atoms are important factors to enhance the superconductivity in hydrides.

High pressure stability of the monosilicides of cobalt and the platinum group elements

International Nuclear Information System (INIS)

Hernandez, J.A.; Vočadlo, L.; Wood, I.G.

2015-01-01

Highlights: • We model the high-pressure phases of cobalt- and platinum-group-monosilicides. • CoSi, RuSi, OsSi transform with pressure from the ε-FeSi to the CsCl structure. • RhSi and IrSi transform with pressure from the MnP structure to the ε-FeSi structure. • PdSi and PtSi transform with pressure from the MnP structure to the CuTi structure. - Abstract: The high pressure stability of CoSi, RuSi, RhSi, PdSi, OsSi, IrSi and PtSi was investigated by static first-principles calculations up to 300 GPa at 0 K. As found experimentally, at atmospheric pressure, CoSi, RuSi and OsSi were found to adopt the cubic ε-FeSi structure (P2 1 3) whereas RhSi, PdSi, IrSi and PtSi were found to adopt the orthorhombic MnP (Pnma) structure. At high pressure, CoSi, RuSi and OsSi show a phase transition to the CsCl structure (Pm3 ¯ m) structure at 270 GPa, 7 GPa and 6 GPa respectively. RhSi and IrSi were found to transform to an ε-FeSi structure at 10 GPa and 25 GPa. For PdSi and PtSi, a transformation from the MnP structure to the tetragonal CuTi structure (P4/nmm) occurs at 13 GPa and 20 GPa. The pressure dependence of the electronic density of states reveals that RuSi and OsSi are semiconductors in the ε-FeSi structure and become metallic in the CsCl structure. RhSi and IrSi are metals in the MnP structure and become semimetals in their high pressure ε-FeSi form. CoSi in the ε-FeSi configuration is a semimetal. PdSi and PtSi remain metallic throughout up to 300 GPa

Electrical resistance, superconductivity and phase transformations of Rb and Cs under high pressure

International Nuclear Information System (INIS)

Ullrich, K.

1980-01-01

Four lead electrical resistance measurements were performed on Rb under pressures up to 210 kbar for temperatures in the range 0.05 K to 300 K. Pressure was applied using a Bridgman-anvil-configuration with dense sintered diamond in the highly stressed tip regions of the Carboloy pistons. The sample cell was pressurized at room temperature by a mechanical press connected to the mixing chamber of a 3 He- 4 He-cryostat. The pressure remained essentially constant during cooling. Discontinuous changes in resistance at pressures of 70 and 140 kbar indicate two phase transitions and confirm the results of other authors. The resistance of Rb increases after a minimum at 20 kbar by about two orders of magnitude. (orig.) [de

Microscopic insight into properties and electronic instabilities of impurities in cubic and lower symmetry insulators: the influence of pressure

International Nuclear Information System (INIS)

Moreno, M; Barriuso, M T; Aramburu, J A; GarcIa-Fernandez, P; GarcIa-Lastra, J M

2006-01-01

This article reviews the microscopic origin of properties due to transition-metal (TM) impurities, M, in insulator materials. Particular attention is paid to the influence of pressure upon impurity properties. Basic concepts such as the electronic localization in an MX N complex, the electrostatic potential, V R , arising from the rest of the lattice ions or the elastic coupling of the complex to the host lattice are initially exposed. The dependence of optical and magnetic parameters on the impurity-ligand distance, R, in cubic lattices is discussed in a first step. Emphasis is put on the actual origin of the R dependence of 10Dq. Examples revealing that laws for strict cubic symmetry cannot in general be transferred to lower symmetries are later given. This relevant fact is shown to come from allowed hybridizations like nd-(n+1)s as well as the influence of V R . As a salient feature the different colour in ruby and emerald is stressed to arise from distinct V R potentials in Al 2 O 3 and Be 3 Si 6 Al 2 O 18 . The last part of this review deals with electronic instabilities. The phenomena associated with the Jahn-Teller (JT) effect in cubic lattices, the origin of the energy barrier among equivalent minima and the existence of coherent tunnelling in systems like MgO:Cu 2+ are discussed. An increase of elastic coupling is pointed out to favour a transition from an elongated to a compressed equilibrium conformation. Interestingly the equilibrium geometry of JT ions in non-cubic lattices is shown to be controlled by mechanisms different to those in cubic systems, V R playing again a key role. The relevance of first principles calculations for clarifying the subtle mechanisms behind off-centre instabilities is also pointed out. Examples concern monovalent and divalent TM impurities in lattices with the CaF 2 structure. The instability due to the transition from the ground to an excited state is finally considered. For complexes with significant elastic coupling

Microscopic insight into properties and electronic instabilities of impurities in cubic and lower symmetry insulators: the influence of pressure.

Science.gov (United States)

Moreno, M; Barriuso, M T; Aramburu, J A; García-Fernández, P; García-Lastra, J M

2006-05-03

This article reviews the microscopic origin of properties due to transition-metal (TM) impurities, M, in insulator materials. Particular attention is paid to the influence of pressure upon impurity properties. Basic concepts such as the electronic localization in an MX(N) complex, the electrostatic potential, V(R), arising from the rest of the lattice ions or the elastic coupling of the complex to the host lattice are initially exposed. The dependence of optical and magnetic parameters on the impurity-ligand distance, R, in cubic lattices is discussed in a first step. Emphasis is put on the actual origin of the R dependence of 10Dq. Examples revealing that laws for strict cubic symmetry cannot in general be transferred to lower symmetries are later given. This relevant fact is shown to come from allowed hybridizations like nd-(n+1)s as well as the influence of V(R). As a salient feature the different colour in ruby and emerald is stressed to arise from distinct V(R) potentials in Al(2)O(3) and Be(3)Si(6)Al(2)O(18). The last part of this review deals with electronic instabilities. The phenomena associated with the Jahn-Teller (JT) effect in cubic lattices, the origin of the energy barrier among equivalent minima and the existence of coherent tunnelling in systems like MgO:Cu(2+) are discussed. An increase of elastic coupling is pointed out to favour a transition from an elongated to a compressed equilibrium conformation. Interestingly the equilibrium geometry of JT ions in non-cubic lattices is shown to be controlled by mechanisms different to those in cubic systems, V(R) playing again a key role. The relevance of first principles calculations for clarifying the subtle mechanisms behind off-centre instabilities is also pointed out. Examples concern monovalent and divalent TM impurities in lattices with the CaF(2) structure. The instability due to the transition from the ground to an excited state is finally considered. For complexes with significant elastic coupling

Thermodynamics of face-centered-cubic silicon nucleation at the nanoscale from laser ablation

International Nuclear Information System (INIS)

Hu Shengliang; Li Wuhong; Liu Wei; Dong Yingge; Cao Shirui; Yang Jinlong

2011-01-01

The thermodynamic nucleation and the phase transition of the face-centered-cubic structure of Si (fcc-Si) on the nanoscale are performed by taking the effect of nanosize-induced additional pressure on the fcc-Si formation under the conditions generated by laser ablation in liquid into account. The thermodynamic analyses showed that the formation of fcc-Si nanocrystals with sizes of 2-6 nm would take place prior to that of large fcc-Si nanocrystals, and the phase transition probability from diamond-like structure Si (d-Si) to fcc-Si is rather high, up to 10 -3 -10 -2 , under the conditions created by laser ablation of an Si target in water. These theoretical results suggest that laser ablation in liquid would be an effective industrial route to prepare ultrasmall fcc-Si nanocrystals.

First principles study of LiAlO2: new dense monoclinic phase under high pressure

Science.gov (United States)

Liu, Guangtao; Liu, Hanyu

2018-03-01

In this work, we have systematically explored the crystal structures of LiAlO2 at high pressures using crystal structure prediction method in combination with the density functional theory calculations. Besides the reported α, β, γ, δ and ɛ-phases, here we propose a new monoclinic ζ-LiAlO2 (C2/m) structure, which becomes thermodynamically and dynamically stable above 27 GPa. It is found that the cation coordination number increases from 4 to 6 under compression. Consisting of the compact {LiO6} and {AlO6} octahedrons, the newly-discovered ζ-phase possesses a very high density. Further electronic calculations show that LiAlO2 is still an insulator up to 60 GPa, and its bandgap increases upon compression. The present study advances our understanding on the crystal structures and high-pressure phase transitions of LiAlO2 that may trigger applications in multiple areas of industry and provoke more related basic science research.

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

Science.gov (United States)

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

2015-06-04

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

Exchange of Na+ and K+ between water vapor and feldspar phases at high temperature and low vapor pressure

Science.gov (United States)

Fournier, R.O.

1976-01-01

In order to determine whether gas (steam) containing a small amount of dissolved alkali chloride is effective in promoting base exchange of Na+ and K+ among alkali feldspars and coexisting brine or brine plus solid salt, experiments were carried out at 400-700??C and steam densities ranging down to less than 0.05. For bulk compositions rich in potassium, the low pressure results are close to previous high-pressure results in composition of the fluid and coexisting solid phase. However, when the bulk composition is more sodic, alkali feldspars are relatively richer in potassium at low pressure than at high pressure. This behaviour corresponds to enrichment of potassium in the gas phase relative to coexisting brine and precipitation of solid NaCl when the brine plus gas composition becomes moderately sodic. The gas phase is very effective in promoting base exchange between coexisting alkali feldspars at high temperature and low water pressure. This suggests that those igneous rocks which contain coexisting alkali feldspars out of chemical equilibrium either remained very dry during the high-temperature part of their cooling history or that the pore fluid was a gas containing very little potassium relative to sodium. ?? 1976.

Low-pH-Induced Lamellar to Bicontinuous Primitive Cubic Phase Transition in Dioleoylphosphatidylserine/Monoolein Membranes.

Science.gov (United States)

Oka, Toshihiko; Hasan, Moynul; Islam, Md Zahidul; Moniruzzaman, Md; Yamazaki, Masahito

2017-10-31

Electrostatic interactions (EIs) play important roles in the structure and stability of inverse bicontinuous cubic (Q II ) phases of lipid membranes. We examined the effect of pH on the phase of dioleoylphosphatidylserine (DOPS)/monoolein (MO) membranes at low ionic strengths using small-angle X-ray scattering (SAXS). We found that the phase transitions from lamellar liquid-crystalline (L α ) to primitive cubic (Q II P ) phases in DOPS/MO (2/8 molar ratio) membranes occurred in buffers containing 50 mM NaCl at and below the final pH of 2.75 as the pH of the membrane suspension was decreased from a neutral value. The kinetic pathway of this transition was revealed using time-resolved SAXS with a stopped-flow apparatus. The first step is a rapid transition from the L α phase to the hexagonal II (H II ) phase, and the second step is a slow transition from the H II phase to the Q II P phase. We determined the rate constants of the first step, k 1 , and of the second step, k 2 , by analyzing the time course of SAXS intensities quantitatively. The k 1 value increased with temperature. The analysis of this result provided the values of its apparent activation energy, which were constant over temperature but increased with pH. This can be explained by an EI effect on the free energy of the transition state. In contrast, the k 2 value decreased with temperature, indicating that the true activation energy increased with temperature. These experimental results were analyzed using the theory of the activation energy of phase transitions of lipid membranes when the free energy of the transition state depends on temperature. On the basis of these results, we discussed the mechanism of this phase transition.

Phase mapping of aging process in InN nanostructures: oxygen incorporation and the role of the zinc blende phase

International Nuclear Information System (INIS)

Gonzalez, D; Lozano, J G; Herrera, M; Morales, F M; GarcIa, R; Ruffenach, S; Briot, O

2010-01-01

Uncapped InN nanostructures undergo a deleterious natural aging process at ambient conditions by oxygen incorporation. The phases involved in this process and their localization is mapped by transmission electron microscopy (TEM)-related techniques. The parent wurtzite InN (InN-w) phase disappears from the surface and gradually forms a highly textured cubic layer that completely wraps up a InN-w nucleus which still remains from the original single-crystalline quantum dots. The good reticular relationships between the different crystals generate low misfit strains and explain the apparent easiness for phase transformations at room temperature and pressure conditions, but also disable the classical methods to identify phases and grains from TEM images. The application of the geometrical phase algorithm in order to form numerical moire mappings and RGB multilayered image reconstructions allows us to discern among the different phases and grains formed inside these nanostructures. Samples aged for shorter times reveal the presence of metastable InN:O zinc blende (zb) volumes, which act as the intermediate phase between the initial InN-w and the most stable cubic In 2 O 3 end phase. These cubic phases are highly twinned with a proportion of 50:50 between both orientations. We suggest that the existence of the intermediate InN:O-zb phase should be seriously considered to understand the reason for the widely scattered reported fundamental properties of thought to be InN-w, as its bandgap or superconductivity.

Growth of cubic InN on r-plane sapphire

International Nuclear Information System (INIS)

Cimalla, V.; Pezoldt, J.; Ecke, G.; Kosiba, R.; Ambacher, O.; Spiess, L.; Teichert, G.; Lu, H.; Schaff, W.J.

2003-01-01

InN has been grown directly on r-plane sapphire substrates by plasma-enhanced molecular-beam epitaxy. X-ray diffraction investigations have shown that the InN layers consist of a predominant zinc blende (cubic) structure along with a fraction of the wurtzite (hexagonal) phase which content increases with proceeding growth. The lattice constant for zinc blende InN was found to be a=4.986 A. For this unusual growth of a metastable cubic phase on a noncubic substrate an epitaxial relationship was proposed where the metastable zinc blende phase grows directly on the r-plane sapphire while the wurtzite phase arises as the special case of twinning in the cubic structure

Shear induced phase transition in PbO under high pressure

International Nuclear Information System (INIS)

Giefers, Hubertus; Porsch, Felix

2007-01-01

We have studied the structural behavior of lead monoxide (PbO) as a function of pressure via angular dispersive X-ray diffraction employing two different pressure transmitting media that were quasi-hydrostatic (N 2 ) and non-hydrostatic (MgO), respectively. Besides litharge (α-PbO) and massicot (β-PbO), which are both stable at ambient pressure, there is an orthorhombic γ-PbO phase which appears upon application of pressure to α-PbO. We have found that the orthorhombic γ-PbO phase is favored by shear stress under non-hydrostatic conditions. α-PbO shows strong anisotropy in compressibility. The a-axis is rather incompressible with a linear stiffness coefficient of K a0 =540(30) GPa whereas the c-axis stiffness is K c0 =25(1) GPa. The bulk modulus of α-PbO is K 0 =23.1(3) GPa and its derivative K 0 ' =7.0(3)

Neutron diffraction study of structural changes in ammonium halides ND4Br and ND4Cl under high pressure

International Nuclear Information System (INIS)

Balagurov, A.M.; Kozlenko, D.P.; Savenko, B.N.; Glazkov, V.P.; Somenkov, V.A.

1997-01-01

Structural changes in ammonium halides ND 4 Br and ND 4 Cl at pressures up to 45 kbar and up to 35 kbar, respectively, have been studied with the DN-12 diffractometer at the IBR-2 pulsed reactor. For both systems, the equation of state and the position parameter of deuterium atoms as functions of pressure were obtained. The obtained equations of state are nearly the same as the ones for the nondeuterated systems NH 4 Br and NH 4 Cl obtained by the piston displacement technique. It was found that the order - disorder phase transition from the phase in which the ammonium tetrahedra are randomly oriented (CsCl-type cubic structure, space group Pm3m) into the phase in which the ammonium tetrahedra are oriented in parallel (CsCl-type cubic structure, space group P4 bar 3m), occurs at equal critical value of the position parameter u=0.153 ± 0.002 in both systems. It appears to be valid for all of the ammonium halides, and, possibly, for other similar compounds. (author)

Sound velocities of the 23 Å phase at high pressure and implications for seismic velocities in subducted slabs

Science.gov (United States)

Cai, N.; Chen, T.; Qi, X.; Inoue, T.; Li, B.

2017-12-01

Dense hydrous phases are believed to play an important role in transporting water back into the deep interior of the Earth. Recently, a new Al-bearing hydrous Mg-silicate, named the 23 Å phase (ideal composition Mg12Al2Si4O16(OH)14), was reported (Cai et al., 2015), which could be a very important hydrous phase in subducting slabs. Here for the first time we report the measurements of the compressional and shear wave velocities of the 23 Å phase under applied pressures up to 14 GPa and room temperature, using a bulk sample with a grain size of less than 20 μm and density of 2.947 g/cm3. The acoustic measurements were conducted in a 1000-ton uniaxial split-cylinder multi-anvil apparatus using ultrasonic interferometry techniques (Li et al., 1996). The pressures were determined in situ by using an alumina buffer rod as the pressure marker (Wang et al., 2015). A dual-mode piezoelectric transducer enabled us to measure P and S wave travel times simultaneously, which in turn allowed a precise determination of the sound velocities and elastic bulk and shear moduli at high pressures. A fit to the acoustic data using finite strain analysis combined with a Hashin-Shtrikman (HS) bounds calculation yields: Ks0 = 113.3 GPa, G0 = 42.8 GPa, and K' = 3.8, G' = 1.9 for the bulk and shear moduli and their pressure derivatives. The velocities (especially for S wave) of this 23 Å phase (ambient Vp = 7.53 km/s, Vs = 3.72 km/s) are lower than those of phase A, olivine, pyrope, etc., while the Vp/Vs ratio (from 2.02 to 1.94, decreasing with increasing pressure) is quite high. These results suggest that a hydrous assemblage containing 23 Å phase should be distinguishable from a dry one at high pressure and temperature conditions relevant to Al-bearing subducted slabs.

High-Pressure Geophysical Properties of Fcc Phase FeHX

Science.gov (United States)

Thompson, E. C.; Davis, A. H.; Bi, W.; Zhao, J.; Alp, E. E.; Zhang, D.; Greenberg, E.; Prakapenka, V. B.; Campbell, A. J.

2018-01-01

Face centered cubic (fcc) FeHX was synthesized at pressures of 18-68 GPa and temperatures exceeding 1,500 K. Thermally quenched samples were evaluated using synchrotron X-ray diffraction (XRD) and nuclear resonant inelastic X-ray scattering (NRIXS) to determine sample composition and sound velocities to 82 GPa. To aid in the interpretation of nonideal (X ≠ 1) stoichiometries, two equations of state for fcc FeHX were developed, combining an empirical equation of state for iron with two distinct synthetic compression curves for interstitial hydrogen. Matching the density deficit of the Earth's core using these equations of state requires 0.8-1.1 wt % hydrogen at the core-mantle boundary and 0.2-0.3 wt % hydrogen at the interface of the inner and outer cores. Furthermore, a comparison of Preliminary Reference Earth Model (PREM) to a Birch's law extrapolation of our experimental results suggests that an iron alloy containing ˜0.8-1.3 wt % hydrogen could reproduce both the density and compressional velocity (VP) of the Earth's outer core.

Design and test of a new high pressure phase equlibrium apparatus for highly corrosive mixtures of importance for natural gas

NARCIS (Netherlands)

Mota Martinez, M.; Samdani, S.; Berrouk, A.S.; Alves da Rocha, M.A.; Elhseinat, E.Y.; Banat, F.; Kroon, M.C.; Peters, C.J.

2015-01-01

A new static analytical apparatus for high-pressure phase equilibrium measurements has been designed and built. The new apparatus enables the measurement of vapor–liquid and liquid–liquid equilibria, which can operate at temperatures ranging from 225 K to 475 K and pressures up to 20 MPa. It is

Dynamism or Disorder at High Pressures?

Science.gov (United States)

Angel, R. J.; Bismayer, U.; Marshall, W. G.

2002-12-01

Phase transitions in minerals at elevated temperatures typically involve dynamics as a natural consequence of the increase in thermal energy available to the system. Classic examples include quartz, cristobalite, and carbonates in which the high-temperature, high symmetry phase is dynamically disordered. This disorder has important thermodynamic consequences, including displacement and curvature of phase boundaries (e.g. calcite-aragonite). In other minerals such as clinopyroxenes and anorthite feldspar, the dynamic behaviour is restricted to the neighbourhood of the phase transition. The fundamental question is whether increasing pressure generally suppresses such dynamic behaviour (as in anorthite; Angel, 1988), or not. In the latter case it must be included in thermodynamic models of high-pressure phase equilibria and seismological modelling of the mantle; the potential dynamics and softening in stishovite may provide the critical observational constraint on the presence or otherwise of free silica in the lower mantle. We have continued to use the lead phosphate as a prototype ferroelastic in which to understand dynamic behaviour, simply because its dynamics and transition behaviour is far better characterised than any mineral. Furthermore, the phase transition is at a pressure where experimental difficulties do not dominate the experimental results. Our previous neutron diffraction study (Angel et al., 2001) revealed that some disorder, either dynamic or static, is retained in the high-symmetry, high-pressure phase just above the phase transition. New neutron diffraction data on the pure material now suggests that this disorder slowly decreases with increasing pressure until at twice the transition pressure it is ordered. Further data for doped material provides insights into the nature of this disorder. Angel (1988) Amer. Mineral. 73:1114. Angel et al (2001) J PhysC 13: 5353.

Phase Behavior of Three PBX Elastomers in High-Pressure Chlorodifluoromethane

Science.gov (United States)

Lee, Byung-Chul

2017-10-01

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

High pressure study of high-temperature superconductors

Energy Technology Data Exchange (ETDEWEB)

Souliou, Sofia-Michaela

2014-09-29

The current thesis studies experimentally the effect of high external pressure on high-T{sub c} superconductors. The structure and lattice dynamics of several members of the high-T{sub c} cuprate and Fe-based superconductors families were investigated by means of Raman spectroscopy and X-ray diffraction under well-controlled, hydrostatic high pressure and low temperature conditions. The lattice dynamics of the high-T{sub c} superconductor YBa{sub 2}Cu{sub 3}O{sub 6+x} have been investigated systematically by Raman spectroscopy as a function of doping (x = 0.95, 0.75, 0.60, 0.55, and 0.45) and external pressure. Under ambient pressure conditions, in addition to the Raman modes expected from group theory, we observe new Raman active phonons upon cooling the underdoped samples, at temperatures well above the superconducting transition temperature. The doping dependence and the onset temperatures of the new Raman features suggest that they are associated with the incommensurate charge density wave (CDW) state recently discovered in underdoped cuprates using synchrotron X-ray scattering techniques. Under high pressure conditions (from 2 to 12 GPa), our Raman measurements on highly ordered underdoped YBa{sub 2}Cu{sub 3}O{sub 6.55} samples do not show any of the new Raman phonons seen at ambient pressure. High pressure and low temperature Raman measurements have been performed on the underdoped superconductor YBa{sub 2}Cu{sub 4}O{sub 8}. A clear renormalization of some of the Raman phonons is seen below T{sub c} as a result of the changes in the phonon self-energy upon the opening of the superconducting gap, with the most prominent one being that of the B{sub 1g}-like buckling phonon mode. The amplitude of this renormalization strongly increases with pressure, resembling the effect of hole doping in YBa{sub 2}Cu{sub 3}O{sub 6+x}. At ∝ 10 GPa, the system undergoes a reversible pressure-induced structural phase transition to a non-centrosymmmetric structure (space group

High pressure study of high-temperature superconductors

International Nuclear Information System (INIS)

Souliou, Sofia-Michaela

2014-01-01

The current thesis studies experimentally the effect of high external pressure on high-T c superconductors. The structure and lattice dynamics of several members of the high-T c cuprate and Fe-based superconductors families were investigated by means of Raman spectroscopy and X-ray diffraction under well-controlled, hydrostatic high pressure and low temperature conditions. The lattice dynamics of the high-T c superconductor YBa 2 Cu 3 O 6+x have been investigated systematically by Raman spectroscopy as a function of doping (x = 0.95, 0.75, 0.60, 0.55, and 0.45) and external pressure. Under ambient pressure conditions, in addition to the Raman modes expected from group theory, we observe new Raman active phonons upon cooling the underdoped samples, at temperatures well above the superconducting transition temperature. The doping dependence and the onset temperatures of the new Raman features suggest that they are associated with the incommensurate charge density wave (CDW) state recently discovered in underdoped cuprates using synchrotron X-ray scattering techniques. Under high pressure conditions (from 2 to 12 GPa), our Raman measurements on highly ordered underdoped YBa 2 Cu 3 O 6.55 samples do not show any of the new Raman phonons seen at ambient pressure. High pressure and low temperature Raman measurements have been performed on the underdoped superconductor YBa 2 Cu 4 O 8 . A clear renormalization of some of the Raman phonons is seen below T c as a result of the changes in the phonon self-energy upon the opening of the superconducting gap, with the most prominent one being that of the B 1g -like buckling phonon mode. The amplitude of this renormalization strongly increases with pressure, resembling the effect of hole doping in YBa 2 Cu 3 O 6+x . At ∝ 10 GPa, the system undergoes a reversible pressure-induced structural phase transition to a non-centrosymmmetric structure (space group Imm2). The structural transition is clearly reflected in the high pressure

A reduction method for phase equilibrium calculations with cubic equations of state

Directory of Open Access Journals (Sweden)

D. V. Nichita

2006-09-01

Full Text Available In this work we propose a new reduction method for phase equilibrium calculations using a general form of cubic equations of state (CEOS. The energy term in the CEOS is a quadratic form, which is diagonalized by applying a linear transformation. The number of the reduction parameters is related to the rank of the matrix C with elements (1-Cij, where Cij denotes the binary interaction parameters (BIPs. The dimensionality of the problem depends only on the number of reduction parameters, and is independent of the number of components in the mixture.

Collapse of the magnetic moment under pressure of AFe{sub 2} (A=Y, Zr, Lu and Hf) in the cubic Laves phase

Energy Technology Data Exchange (ETDEWEB)

Zhang, Wenxu, E-mail: xwzhang@uestc.edu.cn; Zhang, Wanli

2016-04-15

The electronic structures of four Laves phase iron compounds (e.g. YFe{sub 2}, ZrFe{sub 2}, LuFe{sub 2} and HfFe{sub 2}) have been calculated with a state-of-the-art full potential electronic structure code. Our theoretical work predicted that the magnetic moments collapse under hydrostatic pressure. This feature is found to be universal in these materials. Its electronic origin is provided by the sharp peaks in the density of states near the Fermi level. It is shown that a first order quantum phase transition can be expected under pressure in Y(Zr, or Lu)Fe{sub 2}, while a second order one in HfFe{sub 2}. The bonding characteristics are discussed to elucidate the equilibrium lattice constant variation. The large spontaneous volume magnetostriction gives one of the most important characteristics of these compounds. Invar anomalies in these compounds can be partly explained by the current work when the fast continuous magnetic moment decrease with the decrease of the lattice constant was properly considered. This work may be as a first insight into the rich world of quantum phase transition and Invar mechanism in these Laves phase compounds. - Highlights: • Magnetic moment of YFe{sub 2}, ZrFe{sub 2}, LuFe{sub 2} and HfFe{sub 2} collapses under pressure. • The transition in Y(Zr or Lu) Fe{sub 2} under pressure is first order. • The transition in HfFe{sub 2} under pressure is second order. • The Invar effects in the compounds can be put into the magnetostriction model.

First principles study of the structural and electronic properties of double perovskite Ba{sub 2}YTaO{sub 6} in cubic and tetragonal phases

Energy Technology Data Exchange (ETDEWEB)

Deluque Toro, C.E., E-mail: deluquetoro@gmail.com [Grupo de Nuevos Materiales, Universidad Popular del Cesar, Valledupar (Colombia); Rodríguez M, Jairo Arbey [Grupo de Estudios de Materiales—GEMA, Departamento de Física, Universidad Nacional de Colombia, AA 5997 Bogotá DC (Colombia); Landínez Téllez, D.A. [Grupo de Física de Nuevos Materiales, Departamento de Física, Universidad Nacional de Colombia, AA 5997 Bogotá DC (Colombia); Moreno Salazar, N.O. [Departamento de Física, Universidade Federal de Sergipe (Brazil); Roa-Rojas, J. [Grupo de Física de Nuevos Materiales, Departamento de Física, Universidad Nacional de Colombia, AA 5997 Bogotá DC (Colombia)

2014-12-15

The Ba{sub 2}YTaO{sub 6} double perovskite presents a transition from cubic (Fm−3m) to tetragonal structure (I4/m) at high temperature. In this work, we present a detailed study of the structural and electronic properties of the double perovskite Ba{sub 2}YTaO{sub 6} in space group Fm−3m and I4/m. Calculations were made with the Full-Potential Linear Augmented Plane Wave method (FP-LAPW) within the framework of the Density Functional Theory (DFT) with exchange and correlation effects in the Generalized Gradient (GGA) and Local Density (LDA) approximations. From the minimization of energy as a function of volume and the fitting of the Murnaghan equation some structural characteristics were determined as, for example, total energy, lattice parameter (a=8.50 Å in cubic phase and a=5.985 Å and c=8.576 Å in tetragonal), bulk modulus (135.6 GPa in cubic phase and 134.1 GPa in tetragonal phase) and its derivative. The study of the electronic characteristics was performed from the analysis of the electronic density of states (DOS). We find a non-metallic behavior for this with a direct band gap of approximately 3.5 eV and we found that the Ba{sub 2}YTaO{sub 6} (I4/m) phase is the most stable one. {sup ©} 2013 Elsevier Science. All rights reserved.

Formation of soft magnetic high entropy amorphous alloys composites containing in situ solid solution phase

Science.gov (United States)

Wei, Ran; Sun, Huan; Chen, Chen; Tao, Juan; Li, Fushan

2018-03-01

Fe-Co-Ni-Si-B high entropy amorphous alloys composites (HEAACs), which containing high entropy solid solution phase in amorphous matrix, show good soft magnetic properties and bending ductility even in optimal annealed state, were successfully developed by melt spinning method. The crystallization phase of the HEAACs is solid solution phase with body centered cubic (BCC) structure instead of brittle intermetallic phase. In addition, the BCC phase can transformed into face centered cubic (FCC) phase with temperature rise. Accordingly, Fe-Co-Ni-Si-B high entropy alloys (HEAs) with FCC structure and a small amount of BCC phase was prepared by copper mold casting method. The HEAs exhibit high yield strength (about 1200 MPa) and good plastic strain (about 18%). Meanwhile, soft magnetic characteristics of the HEAs are largely reserved from HEAACs. This work provides a new strategy to overcome the annealing induced brittleness of amorphous alloys and design new advanced materials with excellent comprehensive properties.

Highly Aminated Mesoporous Silica Nanoparticles with Cubic Pore Structure

KAUST Repository

Suteewong, Teeraporn; Sai, Hiroaki; Cohen, Roy; Wang, Suntao; Bradbury, Michelle; Baird, Barbara; Gruner, Sol M.; Wiesner, Ulrich

2011-01-01

Mesoporous silica with cubic symmetry has attracted interest from researchers for some time. Here, we present the room temperature synthesis of mesoporous silica nanoparticles possessing cubic Pm3n symmetry with very high molar ratios (>50%) of 3-aminopropyl triethoxysilane. The synthesis is robust allowing, for example, co-condensation of organic dyes without loss of structure. By means of pore expander molecules, the pore size can be enlarged from 2.7 to 5 nm, while particle size decreases. Adding pore expander and co-condensing fluorescent dyes in the same synthesis reduces average particle size further down to 100 nm. After PEGylation, such fluorescent aminated mesoporous silica nanoparticles are spontaneously taken up by cells as demonstrated by fluorescence microscopy.

Highly Aminated Mesoporous Silica Nanoparticles with Cubic Pore Structure

KAUST Repository

Suteewong, Teeraporn

2011-01-19

Mesoporous silica with cubic symmetry has attracted interest from researchers for some time. Here, we present the room temperature synthesis of mesoporous silica nanoparticles possessing cubic Pm3n symmetry with very high molar ratios (>50%) of 3-aminopropyl triethoxysilane. The synthesis is robust allowing, for example, co-condensation of organic dyes without loss of structure. By means of pore expander molecules, the pore size can be enlarged from 2.7 to 5 nm, while particle size decreases. Adding pore expander and co-condensing fluorescent dyes in the same synthesis reduces average particle size further down to 100 nm. After PEGylation, such fluorescent aminated mesoporous silica nanoparticles are spontaneously taken up by cells as demonstrated by fluorescence microscopy.

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

Energy Technology Data Exchange (ETDEWEB)

Meducin, F.

2001-10-01

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

High-pressure phase transition in silicon carbide under shock loading using ultrafast x-ray diffraction

Science.gov (United States)

Tracy, S. J.; Smith, R. F.; Wicks, J. K.; Fratanduono, D. E.; Gleason, A. E.; Bolme, C.; Speziale, S.; Appel, K.; Prakapenka, V. B.; Fernandez Panella, A.; Lee, H. J.; MacKinnon, A.; Eggert, J.; Duffy, T. S.

2017-12-01

The behavior of silicon carbide (SiC) under shock loading was investigated through a series of time-resolved pump-probe x-ray diffraction (XRD) measurements. SiC is found at impact sites and has been put forward as a possible constituent in the proposed class of extra-solar planets known as carbon planets. Previous studies have used wave profile measurements to identify a phase transition under shock loading near 1 Mbar, but crystal structure information was not obtained. We have carried out an in situ XRD study of shock-compressed SiC using the Matter in Extreme Conditions instrument of the Linac Coherent Light Source. The femtosecond time resolution of the x-ray free electron laser allows for the determination of time-dependent atomic arrangements during shock loading and release. Two high-powered lasers were used to generate ablation-driven compression waves in the samples. Time scans were performed using the same drive conditions and nominally identical targets. For each shot in a scan, XRD data was collected at a different probe time after the shock had entered the SiC. Probe times extended up to 40 ns after release. Scans were carried out for peak pressures of 120 and 185 GPa. Our results demonstrate that SiC transforms directly from the ambient tetrahedrally-coordinated phase to the octahedral B1 structure on the nanosecond timescale of laser-drive experiments and reverts to the tetrahedrally coordinated ambient phase within nanoseconds of release. The data collected at 120 GPa exhibit diffraction peaks from both compressed ambient phase and transformed B1 phase, while the data at 185 GPa show a complete transformation to the B1 phase. Densities determined from XRD peaks are in agreement with an extrapolation of previous continuum data as well as theoretical predictions. Additionally, a high degree of texture was retained in both the high-pressure phase as well as on back transformation. Two-dimensional fits to the XRD data reveal details of the

Microscopic insight into properties and electronic instabilities of impurities in cubic and lower symmetry insulators: the influence of pressure

Energy Technology Data Exchange (ETDEWEB)

Moreno, M [Departamento de Ciencias de la Tierra y Fisica de la Materia Condensada, Universidad de Cantabria, 39005 Santander (Spain); Barriuso, M T [Departamento de Fisica Moderna, Universidad de Cantabria, 39005 Santander (Spain); Aramburu, J A [Departamento de Ciencias de la Tierra y Fisica de la Materia Condensada, Universidad de Cantabria, 39005 Santander (Spain); GarcIa-Fernandez, P [Departamento de Ciencias de la Tierra y Fisica de la Materia Condensada, Universidad de Cantabria, 39005 Santander (Spain); GarcIa-Lastra, J M [Departamento de Fisica Moderna, Universidad de Cantabria, 39005 Santander (Spain)

2006-05-03

This article reviews the microscopic origin of properties due to transition-metal (TM) impurities, M, in insulator materials. Particular attention is paid to the influence of pressure upon impurity properties. Basic concepts such as the electronic localization in an MX{sub N} complex, the electrostatic potential, V{sub R}, arising from the rest of the lattice ions or the elastic coupling of the complex to the host lattice are initially exposed. The dependence of optical and magnetic parameters on the impurity-ligand distance, R, in cubic lattices is discussed in a first step. Emphasis is put on the actual origin of the R dependence of 10Dq. Examples revealing that laws for strict cubic symmetry cannot in general be transferred to lower symmetries are later given. This relevant fact is shown to come from allowed hybridizations like nd-(n+1)s as well as the influence of V{sub R}. As a salient feature the different colour in ruby and emerald is stressed to arise from distinct V{sub R} potentials in Al{sub 2}O{sub 3} and Be{sub 3}Si{sub 6}Al{sub 2}O{sub 18}. The last part of this review deals with electronic instabilities. The phenomena associated with the Jahn-Teller (JT) effect in cubic lattices, the origin of the energy barrier among equivalent minima and the existence of coherent tunnelling in systems like MgO:Cu{sup 2+} are discussed. An increase of elastic coupling is pointed out to favour a transition from an elongated to a compressed equilibrium conformation. Interestingly the equilibrium geometry of JT ions in non-cubic lattices is shown to be controlled by mechanisms different to those in cubic systems, V{sub R} playing again a key role. The relevance of first principles calculations for clarifying the subtle mechanisms behind off-centre instabilities is also pointed out. Examples concern monovalent and divalent TM impurities in lattices with the CaF{sub 2} structure. The instability due to the transition from the ground to an excited state is finally

Equilibrium triple point pressure and pressure-temperature phase diagram of polyethylene

NARCIS (Netherlands)

Hikosaka, M.; Tsukijima, K.; Rastogi, S.; Keller, A.

1992-01-01

The equil. triple point and pressure and temp. phase diagrams of polyethylene were obtained by in situ optical microscopic and x-ray observations of the melting temp. of hexagonal and orthorhombic isolated extended-chain single crystals at high pressure. The melting temps. of extended-chain crystals

A structural study of the pseudo-binary mercury chalcogenide alloy HgSe sub 0 sub . sub 7 S sub 0 sub . sub 3 at high pressure

CERN Document Server

Kozlenko, D P; Hull, S; Knorr, K; Savenko, B N; Shchennikov, V V; Voronin, V I

2002-01-01

The structure of the pseudo-binary mercury chalcogenide alloy HgSe sub 0 sub . sub 7 S sub 0 sub . sub 3 has been studied by means of X-ray and neutron powder diffraction at pressure up to 8.5 GPa. A phase transition from the cubic zinc blende structure to the hexagonal cinnabar structure was observed at P approx 1 GPa. The obtained structural parameters were used for the analysis of the geometrical relationship between the zinc blende and the cinnabar phases. The zinc blende-cinnabar phase transition is discussed in the framework of the Landau theory of phase transitions. It was found that the possible order parameter for the structural transformation is the spontaneous strain e sub 4. This assignment agrees with previously observed high pressure behaviour of the elastic constants of other mercury chalcogenides

Phase portraits of cubic polynomial vector fields of Lotka-Volterra type having a rational first integral of degree 2

International Nuclear Information System (INIS)

Cairo, Laurent; Llibre, Jaume

2007-01-01

We classify all the global phase portraits of the cubic polynomial vector fields of Lotka-Volterra type having a rational first integral of degree 2. For such vector fields there are exactly 28 different global phase portraits in the Poincare disc up to a reversal of sense of all orbits

Application of high-pressure techniques: stabilization and oxidation-state control of novel superconductive and related multi-layered copper oxides

International Nuclear Information System (INIS)

Yamauchi, H.; Karppinen, M.

2000-01-01

Copper oxide superconductors possess multi-layered structures with a layer sequence of -CuO 2 -(Q-CuO 2 ) n-1 -AO-(MO 1±δ ) m -AO- or -CuO 2 -B-(O 2 -B) s-1 -CuO 2 -AO-(MO 1±δ ) m -AO- along the elongated c axis. Based on this layer sequence, the known copper oxide structures are categorized as members of the homologous series, M m A r Q n-1 Cu n O m+r+2 +n ±δ (M-mr(n-1)n ; category A) or M m A 2k B s Cu 1+k O m +4k +2s±δ (M-m(2k)s (1+k ); category B). Stabilization of such structures especially in the case of high values of the n /s parameter, i.e. the higher members of the homologous series, has been demonstrated to be apparently promoted under high pressures and/or strongly oxidizing conditions. Consequently, techniques for applying both high oxygen gas pressures (10-2000 atm) and ultra-high solid-medium pressures (2-8 GPa) have been advantageously utilized in synthesizing various superconductive copper oxide phases. Especially the ultra-high solid-medium pressure synthesis carried out in the so-called cubic-anvil/belt-type apparatus has proven to be extremely successful in synthesizing novel superconductive phases. In order to achieve high partial pressures of oxygen in the solid-medium environment, 'external' oxygen-generating oxides such as KClO 4 , KClO 3 and Ag 2 O 2 are commonly added to the precursor mixtures. It is emphasized that in some cases it is possible to utilize 'internal' oxidizing agents alone, i.e. highly oxidized precursors such as BaCuO 2+δ and Ba 2 Cu 3 O 5+δ containing metal constituents common with the desired copper oxide phase only. In the present paper, the potential and applications of high-pressure techniques in synthesizing multi-layered copper oxides and related structures are reviewed and discussed with emphasis on the important 'historical' discoveries of novel phases and the present status of controlled production of high-quality samples of such phases. (author)

Phase behavior for the poly(alkyl methacrylate)+supercritical CO2+DME mixture at high pressures

International Nuclear Information System (INIS)

Choi, Yong-Seok; Chio, Sang-Won; Byun, Hun-Soo

2016-01-01

The phase behavior curves of binary and ternary system were measured for poly(alkyl methacrylate) in supercritical CO 2 , as well as for the poly(alkyl methacrylate)+dimethyl ether (DME) (or 1-butene) in CO 2 . The solubility curves are reported for the poly(alkyl methacrylate)+DME in supercritical CO 2 at temperature from (300 to 465) K and a pressure from (3.66 to 248) MPa. Also, The high-pressure static-type apparatus of cloud-point curve was tested by comparing the measured phase behavior data of the poly(methyl methacrylate) [PMMA]+CO 2 +20.0 and 30.4 wt% methyl methacrylate (MMA) system with literature data of 10.4, 28.8 and 48.4 wt% MMA concentration. The phase behavior data for the poly(alkyl methacrylate)+CO 2 +DME mixture were measured in changes of the pressure-temperature (p, T) slope and with DME concentrations. Also, the cloud-point pressure for the poly(alkyl methacrylate)+1- butene solution containing supercritical CO 2 shows from upper critical solution temperature (UCST) region to lower critical solution temperature (LCST) region at concentration range from (0.0 to 95) wt% 1-butene at below 455 K and at below 245MPa.

G-phase precipitation in austenitic stainless steel deformed by high pressure torsion

International Nuclear Information System (INIS)

Shuro, I.; Kuo, H.H.; Sasaki, T.; Hono, K.; Todaka, Y.; Umemoto, M.

2012-01-01

Highlights: ► Using TEM and APT analyses, G-phase precipitation was observed in HPTed SUS304 with no trace of spinodal decomposition. ► G-phase precipitation occurred much shorter time than previous studies probably due to the elimination of prior SD and enhanced diffusion by severe plastic deformation. ► G-phase composition is a function of aging time. ► Tensile tests showed that in SUS304 embrittlement occurs solely due to G-phase precipitation. - Abstract: G phase an intermetallic silicide has been observed in martensite of precipitation hardened stainless steels and in the ferrite of dual (austenite and ferrite) phase stainless steels. In both cases, before G-phase precipitates, the matrix composition changes due to spinodal decomposition and solute partitioning between ferrite and austenite. Thus in the present study, single bcc phase and high Ni content stainless steel, was selected to study G-phase precipitation expecting elimination of the interference from spinodal decomposition and solute partitioning. Fe–18Cr–8Ni (SUS304) austenitic stainless steel samples were deformed at room temperature by high pressure torsion to obtain 100% volume fraction of deformation induced martensite (α′). HPT deformation was chosen due to its ability to induce high strength by grain refinement and also attain 100% α′ at room temperature. After annealing at 400 °C for 500 h, G-phase precipitation was observed in the fully martensitic matrix without spinodal decomposition. Crystallographic analysis of annealed samples using high resolution transmission electron microscopy (HRTEM) and energy dispersive spectroscopy (EDS) detected a Mn–Ni–Si rich G-phase with fcc crystal structure with lattice parameter of 1.16 nm. The value of lattice parameter corresponds well with previously reported values. Chemical analysis by atom probe tomography (APT) showed G-phase of composition Mn 21 Ni 50 Si 24 Fe 4 Cr. Tensile tests showed that G-phase precipitation leads to

G-phase precipitation in austenitic stainless steel deformed by high pressure torsion

Energy Technology Data Exchange (ETDEWEB)

Shuro, I., E-mail: innoshuro@martens.me.tut.ac.jp [Functional Materials Engineering, Toyohashi University of Technology, 1-1, Toyohashi, Aichi 441-8580 (Japan); Kuo, H.H. [Functional Materials Engineering, Toyohashi University of Technology, 1-1, Toyohashi, Aichi 441-8580 (Japan); Sasaki, T.; Hono, K. [National Institute for Materials Sciences, Sengen 1-2-1, Tsukuba 305-0047 (Japan); Todaka, Y.; Umemoto, M. [Functional Materials Engineering, Toyohashi University of Technology, 1-1, Toyohashi, Aichi 441-8580 (Japan)

2012-08-30

Highlights: Black-Right-Pointing-Pointer Using TEM and APT analyses, G-phase precipitation was observed in HPTed SUS304 with no trace of spinodal decomposition. Black-Right-Pointing-Pointer G-phase precipitation occurred much shorter time than previous studies probably due to the elimination of prior SD and enhanced diffusion by severe plastic deformation. Black-Right-Pointing-Pointer G-phase composition is a function of aging time. Black-Right-Pointing-Pointer Tensile tests showed that in SUS304 embrittlement occurs solely due to G-phase precipitation. - Abstract: G phase an intermetallic silicide has been observed in martensite of precipitation hardened stainless steels and in the ferrite of dual (austenite and ferrite) phase stainless steels. In both cases, before G-phase precipitates, the matrix composition changes due to spinodal decomposition and solute partitioning between ferrite and austenite. Thus in the present study, single bcc phase and high Ni content stainless steel, was selected to study G-phase precipitation expecting elimination of the interference from spinodal decomposition and solute partitioning. Fe-18Cr-8Ni (SUS304) austenitic stainless steel samples were deformed at room temperature by high pressure torsion to obtain 100% volume fraction of deformation induced martensite ({alpha} Prime ). HPT deformation was chosen due to its ability to induce high strength by grain refinement and also attain 100% {alpha} Prime at room temperature. After annealing at 400 Degree-Sign C for 500 h, G-phase precipitation was observed in the fully martensitic matrix without spinodal decomposition. Crystallographic analysis of annealed samples using high resolution transmission electron microscopy (HRTEM) and energy dispersive spectroscopy (EDS) detected a Mn-Ni-Si rich G-phase with fcc crystal structure with lattice parameter of 1.16 nm. The value of lattice parameter corresponds well with previously reported values. Chemical analysis by atom probe tomography

Single-phase highly densified SrBi{sub 2}Ta{sub 2}O{sub 9} compacts produced by high-pressure sintering

Energy Technology Data Exchange (ETDEWEB)

Pereira, Altair Soria; Souza, Ricson Rocha de; Sousa, Vania Caldas de, E-mail: altair@if.ufrgs.br [Universidade Federal do Rio Grande do Sul (UFRGS), Porto Alegre (Brazil)

2016-07-01

Full text: The development of high-performance lead-free piezoelectric ceramics is an important scientific and technological challenge, as environmental and health issues have imposed restrictions to the use of lead zirconate titanates, the most employed material in ferroelectric devices [1]. Strontium bismuth tantalate (SBT),SrBi{sub 2}Ta{sub 2}O{sub 9}, is an interesting alternative ferroelectric material as its polarization can be modified at low voltages and it shows limited polarization switching fatigue. However, the production of highly densified single-phase bulk SBT by conventional sintering procedures is strongly compromised by stoichiometric changes due to bismuth loss. In this work, high-pressure sintering has been exploited as an alternative procedure to obtain SBT highly-densified single-phase compacts. Using toroidal-type high-pressure chambers, samples were produced by reaction sintering of BiTaO{sub 4} and SrCO{sub 3} powders, mixed in the stoichiometric ratio corresponding to SrBi{sub 2}Ta{sub 2}O{sub 9}, at pressures of 2.5 GPa and 7.7 GPa, and temperatures up to 1250°C, during 10 min. X-ray diffraction and scanning electron microscopy associated to energy-dispersive X-ray spectroscopy were used to follow the phase composition and the microstructure evolution as a function of the processing conditions. A single-phase SBT compact, with a relative density of 93% and a homogeneous microstructure, was produced by sintering at 2.5 GPa/900°C [2]. References: [1] K. Panda, J. Mater. Sci. 44, 5049-5062 (2009). [2] Ricson R.Souza, Rejane K. Kirchner, Jose R. Jurado, Altair S. Pereira, Vania C. Sousa. Journal of Solid State Chemistry 233, 259-268 (2016). (author)

Pressure response of vacancy ordered maghemite ({gamma}-Fe{sub 2}O{sub 3}) and high pressure transformed hematite ({alpha}-Fe{sub 2}O{sub 3})

Energy Technology Data Exchange (ETDEWEB)

Hearne, Giovanni, E-mail: grhearne@uj.ac.za [Department of Physics, University of Johannesburg, PO Box 524, Auckland Park, 2006 Johannesburg (South Africa); Pischedda, Vittoria, E-mail: Vittoria.Pischedda@univ-lyon1.fr [Laboratoire de Physique de la Matiere Condensee et Nanostructures, University Lyon 1 and CNRS, 69622 Villeurbanne Cedex (France)

2012-03-15

Combined XRD and Moessbauer effect spectroscopy studies to high pressures of {approx}30 GPa of vacancy ordered maghemite are presented. The vacancy ordered superstructure is robust and remains intact up to the pressure-induced onset transition to hematite at 13-16 GPa. The pressure transformed hematite is shown to be crystallographically textured, unlike the randomised low pressure maghemite phase. This arises out of a pressure or stress instigated topotactic transformation of the cubic-spinel to hexagonal-corundum structure. The textured sample permits us to obtain information on the spin reorientation behavior of the pressure transformed hematite in compression and decompression sequences. Spin reorientation is restricted to {approx}15 Degree-Sign over wide pressure ranges, attributable to the effect of entrapped vacancies in the high pressure structure. Thus there are structural and magnetic peculiarities specific to pressure transformed hematite not evident in pressurized hematite starting material. These are triggered by the maghemite{yields}hematite transformation. - Graphical abstract: Pressure instigated topotactic transformation of vacancy ordered {gamma}-Fe{sub 2}O{sub 3}{yields}{alpha}-Fe{sub 2}O{sub 3}. There is restricted spin (B{sub hf}) reorientation in the new pressure transformed hematite due to entrapped vacancies. The change in direction of V{sub zz} signifies a distortion of the FeO{sub 6} octahedral local environment. Highlights: Black-Right-Pointing-Pointer Robust vacancy ordered superstructure in maghemite to high pressures. Black-Right-Pointing-Pointer Pressure instigated topotactic transformation to hematite and subsequent texture. Black-Right-Pointing-Pointer Defect trapping in the pressure transformed hematite. Black-Right-Pointing-Pointer Entrapped defects restricts spin reorientation in pressure transformed hematite. Black-Right-Pointing-Pointer Contrasting behavior with pressurized hematite starting material.

Second-order phase transition at high-pressure in GeS crystal

Energy Technology Data Exchange (ETDEWEB)

Hashimzade, F.M.; Huseinova, D.A.; Jahangirli, Z.A.; Mehdiyev, B.H., E-mail: bachschi@yahoo.de

2014-12-01

In this paper we give a theoretical proof of the existence of a second-order structural phase transition in the GeS at a pressure of 35.4 GPa. We use the plane-wave pseudopotential approach to the density functional theory in the local density approximation. The evidence of the phase transition is the abrupt change in the bulk modulus as the volume of the unit cell of the crystal changes continuously. We show that the phase transition is caused by the softening of the low-frequency fully symmetric interlayer mode with increasing pressure. As a result, phase transition of a displacement type takes place with the change of translational symmetry of the crystal from the simple orthorhombic to the base-centered orthorhombic (P{sub bnm}(D{sub 2h}{sup 16})→C{sub mcm}(D{sub 2h}{sup 17}))

Phase behaviour measurements for the system (carbon dioxide + biodiesel + ethanol) at high pressures

International Nuclear Information System (INIS)

Araújo, Odilon A.S.; Silva, Fabiano R.; Ramos, Luiz P.; Lenzi, Marcelo K.; Ndiaye, Papa M.; Corazza, Marcos L.

2012-01-01

Graphical abstract: Comparison between ethyl and methyl esters in a pressure-composition of {CO 2 (1) + biodiesel(2)} at 303.15 K (triangles), 323.15 K (squares) and 343.15 K (circles). Open symbols are ethyl biodiesel (this work) and closed symbols are methyl biodiesel data by Pinto et al. Highlights: ► We measured phase behaviour for the system involving {CO 2 + biodiesel + ethanol}. ► The saturation pressures were obtained using a variable-volume view cell. ► The experimental data were modelled using PR-vdW2 and PR-WS equations of state. - Abstract: This work reports phase equilibrium measurements for binary system {CO 2 (1) + biodiesel(2)} and ternary system {CO 2 (1) + biodiesel(2) + ethanol(3)}. The biodiesel (ethyl esters) used in this work was produced from soybean oil, purified and characterised following the standard specification for subsequent use. Nowadays, great interest in biodiesel production processes at supercritical and/or pressurised solvents is observed, such as, non-catalytic supercritical biodiesel production and enzyme-catalyzed biodiesel production, besides the supercritical CO 2 can be an interesting alternative to glycerol separation in the biodiesel purification step. Towards this, the main goal of this work is to study the phase behaviour at high pressure for the binary and ternary systems involving CO 2 , biodiesel and ethanol. Experiments were carried out in a high pressure variable-volume view cell with operating temperatures ranging from (303.15 to 343.15) K and pressures up to 25 MPa. The CO 2 molar fraction ranged from 0.4213 to 0.9855 for the system {CO 2 (1) + biodiesel(2)}, 0.4263 to 0.9781 for the system {CO 2 (1) + biodiesel(2) + ethanol(3)} with a biodiesel to ethanol molar ratio of (1:3), and 0.4317 to 0.9787 for the system {CO 2 (1) + biodiesel(2) + ethanol(3)} with a biodiesel to ethanol molar ratio of (1:8). For the systems investigated, vapour–liquid (VL), liquid–liquid (LL) and vapour–liquid–liquid (VLL

High Pressure EVA Glove (HPEG), Phase I

Data.gov (United States)

National Aeronautics and Space Administration — Final Frontier Design's (FFD) High Pressure EVA Glove (HPEG) is a game changing technology enabling future exploration class space missions. The high operating...

Computational study of Ca, Sr and Ba under pressure

International Nuclear Information System (INIS)

Jona, F; Marcus, P M

2006-01-01

A first-principles procedure for the calculation of equilibrium properties of crystals under hydrostatic pressure is applied to Ca, Sr and Ba. The procedure is based on minimizing the Gibbs free energy G (at zero temperature) with respect to the structure at a given pressure p, and hence does not require the equation of state to fix the pressure. The calculated lattice constants of Ca, Sr and Ba are shown to be generally closer to measured values than previous calculations using other procedures. In particular for Ba, where careful and extensive pressure data are available, the calculated lattice parameters fit measurements to about 1% in three different phases, both cubic and hexagonal. Rigid-lattice transition pressures between phases which come directly from the crossing of G(p) curves are not close to measured transition pressures. One reason is the need to include zero-point energy (ZPE) of vibration in G. The ZPE of cubic phases is calculated with a generalized Debye approximation and applied to Ca and Sr, where it produces significant shifts in transition pressures. An extensive tabulation is given of structural parameters and elastic constants from the literature, including both theoretical and experimental results

Computational study of Ca, Sr and Ba under pressure

Energy Technology Data Exchange (ETDEWEB)

Jona, F; Marcus, P M [Department of Materials Science and Engineering, State University of New York, Stony Brook, NY 11794-2275 (United States)

2006-05-17

A first-principles procedure for the calculation of equilibrium properties of crystals under hydrostatic pressure is applied to Ca, Sr and Ba. The procedure is based on minimizing the Gibbs free energy G (at zero temperature) with respect to the structure at a given pressure p, and hence does not require the equation of state to fix the pressure. The calculated lattice constants of Ca, Sr and Ba are shown to be generally closer to measured values than previous calculations using other procedures. In particular for Ba, where careful and extensive pressure data are available, the calculated lattice parameters fit measurements to about 1% in three different phases, both cubic and hexagonal. Rigid-lattice transition pressures between phases which come directly from the crossing of G(p) curves are not close to measured transition pressures. One reason is the need to include zero-point energy (ZPE) of vibration in G. The ZPE of cubic phases is calculated with a generalized Debye approximation and applied to Ca and Sr, where it produces significant shifts in transition pressures. An extensive tabulation is given of structural parameters and elastic constants from the literature, including both theoretical and experimental results.

High-pressure behavior of CaMo O4

Science.gov (United States)

Panchal, V.; Garg, N.; Poswal, H. K.; Errandonea, D.; Rodríguez-Hernández, P.; Muñoz, A.; Cavalli, E.

2017-09-01

We report a high-pressure study of tetragonal scheelite-type CaMo O4 up to 29 GPa. In order to characterize its high-pressure behavior, we have combined Raman and optical-absorption measurements with density functional theory calculations. We have found evidence of a pressure-induced phase transition near 15 GPa. Experiments and calculations agree in assigning the high-pressure phase to a monoclinic fergusonite-type structure. The reported results are consistent with previous powder x-ray-diffraction experiments, but are in contradiction with the conclusions obtained from earlier Raman measurements, which support the existence of more than one phase transition in the pressure range covered by our studies. The observed scheelite-fergusonite transition induces significant changes in the electronic band gap and phonon spectrum of CaMo O4 . We have determined the pressure evolution of the band gap for the low- and high-pressure phases as well as the frequencies and pressure dependencies of the Raman-active and infrared-active modes. In addition, based on calculations of the phonon dispersion of the scheelite phase, carried out at a pressure higher than the transition pressure, we propose a possible mechanism for the reported phase transition. Furthermore, from the calculations we determined the pressure dependence of the unit-cell parameters and atomic positions of the different phases and their room-temperature equations of state. These results are compared with previous experiments showing a very good agreement. Finally, information on bond compressibility is reported and correlated with the macroscopic compressibility of CaMo O4 . The reported results are of interest for the many technological applications of this oxide.

Second-order phase transition in PbO and SnO at high pressure: Implications for the litharge-massicot phase transformation

Science.gov (United States)

Adams, David M.; Christy, Andrew G.; Haines, Julian; Clark, Simon M.

1992-11-01

We have studied the structural behavior of PbO at high pressure by powder neturon diffraction in a McWhan cell, and by energy-dispersive powder x-ray diffraction and Raman spectroscopy in a diamond anvil cell. A phase (γ-PbO) occurs at room temperature between ~0.7 and ~2.5 GPa pressure, between the stability fields of litharge (phase is related to litharge by a reversible second-order transition. We infer that this is associated with the collapse of the eu acoustic mode. Unit-cell data at 1.6 GPa are Pm21n, a=4.027(3) Å, b=3.950(3) Å, c=4.767(4) Å, and Z=2. The pressure evolution of the spontaneous strain follows a simple Landau model. There are four distinct solid-state transformation paths between litharge and massicot that maintain the known topotactic relationship between the phases, maintain the translational symmetry common to both, and make use of continuous transitions between group-subgroup related structural intermediates. Both the γ phase and the modulated low-temperature phase of PbO are closely related to one step on one of these paths. Although there is evidence to suggest that the intermediate states do have a transient existence, several paths appear to be utilized. A transition to a γ-like phase also occurs in SnO, at 2.5 GPa, although there is no evidence of a massicotlike polymorph of this compound. The orthorhombic phase is stable to at least 7.5 GPa.

Pressure-induced phase transitions in acentric BaHf(BO{sub 3}){sub 2}

Energy Technology Data Exchange (ETDEWEB)

Mączka, Mirosław, E-mail: m.maczka@int.pan.wroc.pl [Institute of Low Temperature and Structure Research, Polish Academy of Sciences, P.O. Box 1410, 50-950 Wrocław 2 (Poland); Szymborska-Małek, Katarzyna [Institute of Low Temperature and Structure Research, Polish Academy of Sciences, P.O. Box 1410, 50-950 Wrocław 2 (Poland); Sousa Pinheiro, Gardenia de [Departamento de Física, Universidade Federal do Piauí, Teresina, PI 64049-550 (Brazil); Cavalcante Freire, Paulo Tarso [Departamento de Fisica, Universidade Federal do Ceara, Fortaleza CE-60455-970 (Brazil); Majchrowski, Andrzej [Institute of Applied Physics, Military University of Technology, 2 Kaliskiego Street, 00-908 Warszawa (Poland)

2015-08-15

High-pressure Raman scattering studies revealed that BaHf(BO{sub 3}){sub 2} is more compressible than calcite-type orthoborates and calcite, aragonite or dolomite carbonates. It undergoes a first-order reversible pressure-induced phase transition in the 3.9–4.4 GPa pressure range. Second structural change is observed at 9.2 GPa. The intermediate phase is most likely trigonal. However, Raman results suggest increase in the number of distinct BO{sub 3} groups from two in the ambient pressure phase to at least three in the intermediate phase. This intermediate phase is also strongly compressible and strong pressure dependence of the lattice modes proves that the main changes under pressure occur within the layers built from BaO{sub 6} and HfO{sub 6} octahedra. The second phase transition leads most likely to lowering of the trigonal symmetry, as evidenced by significant increase of the number of observed bands. The pressure coefficients of the Raman bands of the high-pressure phase are relatively small, suggesting more dense arrangement of the metal–oxygen polyhedra and BO{sub 3} groups in this phase. It is worth noting that the high-pressure phase was not reached in the second compression experiment up to 10 GPa. This behavior can be most likely attributed to worse hydrostatic conditions of the first experiment. - Graphical abstract: Raman spectra of BaHf(BO{sub 3}){sub 2} recorded at different pressures during compression showing onset of pressure-induced phase transitions. - Highlights: • High-pressure Raman spectra were measured for BaHf(BO{sub 3}){sub 2.} • BaHf(BO{sub 3}){sub 2} undergoes a reversible first-order phase transition at 3.9–4.4 GPa into a trigonal phase. • The intermediate trigonal phase is strongly compressible second structural transformation is observed at 9.2 GPa under non-perfect hydrostatic conditions.

TOPICAL REVIEW: Microscopic insight into properties and electronic instabilities of impurities in cubic and lower symmetry insulators: the influence of pressure

Science.gov (United States)

Moreno, M.; Barriuso, M. T.; Aramburu, J. A.; García-Fernández, P.; García-Lastra, J. M.

2006-05-01

This article reviews the microscopic origin of properties due to transition-metal (TM) impurities, M, in insulator materials. Particular attention is paid to the influence of pressure upon impurity properties. Basic concepts such as the electronic localization in an MXN complex, the electrostatic potential, VR, arising from the rest of the lattice ions or the elastic coupling of the complex to the host lattice are initially exposed. The dependence of optical and magnetic parameters on the impurity-ligand distance, R, in cubic lattices is discussed in a first step. Emphasis is put on the actual origin of the R dependence of 10Dq. Examples revealing that laws for strict cubic symmetry cannot in general be transferred to lower symmetries are later given. This relevant fact is shown to come from allowed hybridizations like nd-(n+1)s as well as the influence of VR. As a salient feature the different colour in ruby and emerald is stressed to arise from distinct VR potentials in Al2O3 and Be3Si6Al2O18. The last part of this review deals with electronic instabilities. The phenomena associated with the Jahn-Teller (JT) effect in cubic lattices, the origin of the energy barrier among equivalent minima and the existence of coherent tunnelling in systems like MgO:Cu2+ are discussed. An increase of elastic coupling is pointed out to favour a transition from an elongated to a compressed equilibrium conformation. Interestingly the equilibrium geometry of JT ions in non-cubic lattices is shown to be controlled by mechanisms different to those in cubic systems, VR playing again a key role. The relevance of first principles calculations for clarifying the subtle mechanisms behind off-centre instabilities is also pointed out. Examples concern monovalent and divalent TM impurities in lattices with the CaF2 structure. The instability due to the transition from the ground to an excited state is finally considered. For complexes with significant elastic coupling vibrational frequencies

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

Energy Technology Data Exchange (ETDEWEB)

Li, Chunyu, E-mail: licy@hpstar.ac.cn, E-mail: yanhao@hpstar.ac.cn; Ke, Feng; Yu, Zhenhai; Chen, Zhiqiang; Yan, Hao, E-mail: licy@hpstar.ac.cn, E-mail: yanhao@hpstar.ac.cn [Center for High Pressure Science and Technology Advanced Research, Shanghai 201203 (China); Hu, Qingyang [Center for High Pressure Science and Technology Advanced Research, Shanghai 201203 (China); Geophysical Laboratory, Carnegie Institution of Washington, Washington, DC 20015 (United States); Zhao, Jinggeng [Natural Science Research Center, Academy of Fundamental and Interdisciplinary Sciences, Harbin Institute of Technology, Harbin 150080 (China)

2016-04-07

Here, we report comprehensive studies on the high-pressure structural and electrical transport properties of the layered transition metal chalcogenide (Cr{sub 2}S{sub 3}) up to 36.3 GPa. A structural phase transition was observed in the rhombohedral Cr{sub 2}S{sub 3} near 16.5 GPa by the synchrotron angle dispersive X-ray diffraction measurement using a diamond anvil cell. Through in situ resistance measurement, the electric resistance value was detected to decrease by an order of three over the pressure range of 7–15 GPa coincided with the structural phase transition. Measurements on the temperature dependence of resistivity indicate that it is a semiconductor-to-metal transition in nature. The results were also confirmed by the electronic energy band calculations. Above results may shed a light on optimizing the performance of Cr{sub 2}S{sub 3} based applications under extreme conditions.

High pressure and high temperature EXAFS and diffraction study of AgI

International Nuclear Information System (INIS)

Yoshiasa, Akira; Arima, Hiroshi; Fukui, Hiroshi; Okube, Maki; Katayama, Yoshinori; Ohtaka, Osamu

2009-01-01

We have determined the precise P-T phase diagram of AgI by in-situ high-pressure high-temperature synchrotron experiments. X-ray diffraction and XAFS measurements were performed up to 6.0 GPa and 1100 K using a multi-anvil high-pressure device and synchrotron radiation from SPring-8. In the disordered rock-salt phase, Ag ions occupy both octahedral and tetrahedral sites and twenty percent of Ag ions occupy the tetrahedral site as a maximum value at 2 GPa. From the viewpoint of the local structure analyses, some sudden changes are recognized near broad phase transition point. Analysis of EXAFS Debye-Waller factor is useful because the force constant can be decided directly even at high pressure and high temperature. Pressure influences greatly the effective potential and anharmonicity decreases with increasing pressure. (author)

Effect of Internal Pressure and Temperature on Phase Transitions in Perovskite Oxides: The Case of the Solid Oxide Fuel Cell Cathode Materials of the La2-xSrxCoTiO6 Series.

Science.gov (United States)

Gómez-Pérez, Alejandro; Hoelzel, Markus; Muñoz-Noval, Álvaro; García-Alvarado, Flaviano; Amador, Ulises

2016-12-19

The symmetry of the room-temperature (RT) structure of title compounds La 2-x Sr x CoTiO 6-δ changes with x, from P2 1 /n (0 ≤ x ≤ 0.2) to Pnma (0.3 ≤ x ≤ 0.5) and to R3̅c (0.6 ≤ x ≤ 1). For x = 1 the three pseudocubic cell parameters become very close suggesting a transition to a cubic structure for higher Sr contents. Similar phase transitions were expected to occur on heating, paralleling the effect of internal pressure induced by substitution of La 3+ by Sr 2+ . However, only some of these aforementioned transitions have been thermally induced. The symmetry-adapted modes formalism is used in the structural refinements and fitting of neutron diffraction data recorded from RT to 1273 K. Thus, for x = 1, the out-of-phase tilting of the BO 6 octahedra vanishes progressively on heating, and a cubic structure with Pm3̅m symmetry is found at 1073 K. For lower Sr contents this transition is predicted to occur far above the temperature limit of common experimental setups. The analysis of the evolution of the perovskite tolerance factor, t-factor, with both Sr content and temperature indicates that temperature has a limited ability to release structural stress and thus to enable transitions to more symmetric phases. This is particularly true when compared to the effect of internal pressure induced by substitution of La by Sr. The existence of phase transitions in materials for solid oxide fuel cells that are usually exposed to heating-cooling cycles may have a detrimental effect. This work suggests strategies to stabilize the high-symmetry high-temperature phase of perovskite oxides through internal-pressure chemically induced.

High-pressure phase equilibrium data for systems with carbon dioxide, α-humulene and trans-caryophyllene

International Nuclear Information System (INIS)

Michielin, Eliane M.Z.; Rosso, Sibele R.; Franceschi, Elton; Borges, Gustavo R.; Corazza, Marcos L.; Oliveira, J. Vladimir; Ferreira, Sandra R.S.

2009-01-01

The aim of this work is to report phase equilibrium data for the binary systems (CO 2 + α-humulene) and (CO 2 + trans-caryophyllene), and for the ternary system (CO 2 + α-humulene + trans-caryophyllene). Results from literature show that α-humulene and trans-caryophyllene are the main compounds responsible for the anti-inflammatory and anti-allergic characteristics attributed to the medicinal plant Cordia verbenacea D.C., hence giving importance to the phase behaviour investigation performed in this work. Phase equilibrium experiments were performed in a high-pressure, variable-volume view cell over the temperature range of T = (303 to 343) K and pressures up to 20 MPa. (Liquid + liquid) and (vapour + liquid + liquid) equilibrium were observed at T = 303 K, while (vapour + liquid) phase transitions were verified to occur from T = (313 to 343) K, for all systems studied. Thermodynamic modelling was performed using the Peng-Robinson equation of state and the classical quadratic mixing rules, with a satisfactory agreement between experimental and calculated values

Structural stability, dynamical stability, thermoelectric properties, and elastic properties of GeTe at high pressure

Science.gov (United States)

Kagdada, Hardik L.; Jha, Prafulla K.; Śpiewak, Piotr; Kurzydłowski, Krzysztof J.

2018-04-01

The stability of GeTe in rhombohedral (R 3 m ), face centred cubic (F m 3 m ), and simple cubic (P m 3 m ) phases has been studied using density functional perturbation theory. The rhombohedral phase of GeTe is dynamically stable at 0 GPa, while F m 3 m and P m 3 m phases are stable at 3.1 and 33 GPa, respectively. The pressure-dependent phonon modes are observed in F m 3 m and P m 3 m phases at Γ and M points, respectively. The electronic and the thermoelectric properties have been investigated for the stable phases of GeTe. The electronic band gap for rhombohedral and F m 3 m phases of GeTe has been observed as 0.66 and 0.17 eV, respectively, while the P m 3 m phase shows metallic behavior. We have used the Boltzmann transport equation under a rigid band approximation and constant relaxation time approximation as implemented in boltztrap code for the calculation of thermoelectric properties of GeTe. The metallic behavior of P m 3 m phase gives a very low value of Seebeck coefficient compared to the other two phases as a function of temperature and the chemical potential μ. It is observed that the rhombohedral phase of GeTe exhibits higher thermoelectric performance. Due to the metallic nature of P m 3 m phase, negligible thermoelectric performance is observed compared to R 3 m and F m 3 m -GeTe. The calculated lattice thermal conductivities are low for F m 3 m -GeTe and high for R 3 m -GeTe. At the relatively higher temperature of 1350 K, the figure of merit ZT is found to be 0.7 for rhombohedral GeTe. The elastic constants satisfy the Born stability criteria for all three phases. The rhombohedral and F m 3 m phases exhibits brittleness and the P m 3 m phase shows ductile nature.

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

DEFF Research Database (Denmark)

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

2012-01-01

A new apparatus for the study of high-pressure phase equilibria at low temperatures using an analytical method was designed, assembled and tested. The apparatus was specially developed for the study of multi-phase equilibria in systems containing hydrocarbons, water and hydrate inhibitors, at tem...

Ab initio study of mechanical and thermo-acoustic properties of tough ceramics: applications to HfO2 in its cubic and orthorhombic phase

International Nuclear Information System (INIS)

Ponce, C A; Casali, R A; Caravaca, M A

2008-01-01

By means of the ab initio all-electron new full-potential linear-muffin-tin orbitals method, calculations were made for elastic constants C 11 , C 12 and C 44 for Si, ZrO 2 and HfO 2 in their cubic phase, and constants C 11 , C 22 , C 33 , C 12 , C 13 , C 23 , C 44 , C 55 and C 66 for HfO 2 in its orthorhombic phase. Using the Voigt and Reuss theory, estimations were made for polycrystals of their bulk, shear and Young moduli, and Poisson coefficients. The speed of elastic wave propagations and Debye temperatures were estimated for polycrystals built from Si and the above mentioned compounds. The semicore 4f 14 electrons should be included in the valence set of Hf atom in this all-electron approach if accurate results for elastic properties under pressures are looked for

Tolerance of budding yeast Saccharomyces cerevisiae to ultra high pressure

Science.gov (United States)

Shibata, M.; Torigoe, M.; Matsumoto, Y.; Yamamoto, M.; Takizawa, N.; Hada, Y.; Mori, Y.; Takarabe, K.; Ono, F.

2014-05-01

Our studies on the tolerance of plants and animals against very high pressure of several GPa have been extended to a smaller sized fungus, the budding yeast Saccharomyces cerevisiae. Several pieces of budding yeast (dry yeast) were sealed in a small teflon capsule with a liquid pressure medium fluorinate, and exposed to 7.5 GPa by using a cubic anvil press. The pressure was kept constant for various duration of time from 2 to 24 h. After the pressure was released, the specimens were brought out from the teflon capsule, and they were cultivated on a potato dextrose agar. It was found that the budding yeast exposed to 7.5 GPa for up to 6 h showed multiplication. However, those exposed to 7.5 GPa for longer than 12 h were found dead. The high pressure tolerance of budding yeast is a little weaker than that of tardigrades.

Group theoretical treatment of the low-temperature phase transition of the Cd6Ca 1/1-cubic approximant

International Nuclear Information System (INIS)

Tamura, R.; Shibata, K.; Nishimoto, K.; Takeuchi, S.; Edagawa, K.; Saitoh, K.; Isobe, M.; Ueda, Y.

2005-01-01

An antiparallel orientational transition is reported for an intermetallic compound, i.e., Cd 6 Ca crystal, which is a 1/1-1/1-1/1 crystalline approximant to the icosahedral quasicrystal Cd 5.7 Ca. A group theoretical analysis based on the Landau theory predicts that the space group of the low-temperature phase is either C2/c or C2/m, in good agreement with the observations. Accordingly, two types of orientational orderings of Cd 4 tetrahedra, which are located in the center of icosahedral clusters, may occur below 100 K: In both cases, the Cd 4 tetrahedra are orientationally ordered in an antiparallel fashion along the [110] direction of the high temperature body-centered-cubic phase. Such a transition in a metal is reminiscent of orientational transitions in molecular solids

Structure evolution upon chemical and physical pressure in (Sr{sub 1−x}Ba{sub x}){sub 2}FeSbO{sub 6}

Energy Technology Data Exchange (ETDEWEB)

Tiittanen, T.; Karppinen, M., E-mail: maarit.karppinen@aalto.fi

2017-02-15

Here we demonstrate the gradual structural transformation from the monoclinic I2/m to tetragonal I4/m, cubic Fm-3m and hexagonal P6{sub 3}/mmc structure upon the isovalent larger-for-smaller A-site cation substitution in the B-site ordered double-perovskite system (Sr{sub 1−x}Ba{sub x}){sub 2}FeSbO{sub 6}. This is the same transformation sequence previously observed up to Fm-3m upon heating the parent Sr{sub 2}FeSbO{sub 6} phase to high temperatures. High-pressure treatment, on the other hand, transforms the hexagonal P6{sub 3}/mmc structure of the other end member Ba{sub 2}FeSbO{sub 6} back to the cubic Fm-3m structure. Hence we may conclude that chemical pressure, physical pressure and decreasing temperature all work towards the same direction in the (Sr{sub 1−x}Ba{sub x}){sub 2}FeSbO{sub 6} system. Also shown is that with increasing Ba-for-Sr substitution level, i.e. with decreasing chemical pressure effect, the degree-of-order among the B-site cations, Fe and Sb, decreases. - Graphical abstract: In the (Sr{sub 1−x}Ba{sub x}){sub 2}FeSbO{sub 6} double-perovskite system the gradual structural transformation from the monoclinic I2/m to tetragonal I4/m, cubic Fm-3m and hexagonal P6{sub 3}/mmc structure is seen upon the isovalent larger-for-smaller A-site cation substitution. High-pressure treatment under 4 GPa extends stability of the cubic Fm-3m structure within a wider substitution range of x. - Highlights: • Gradual structural transitions upon A-cation substitution in (Sr{sub 1−x}Ba{sub x}){sub 2}FeSbO{sub 6.} • With increasing x structure changes from I2/m to I4/m, Fm-3m and P6{sub 3}/mmc. • Degree of B-site order decreases with increasing x and A-site cation radius. • High-pressure treatment extends cubic Fm-3m phase stability for wider x range. • High-pressure treatment affects bond lengths mostly around the A-cation.

Changing the cubic ferrimagnetic domain structure in temperature region of spin flip transition

International Nuclear Information System (INIS)

Djuraev, D.R.; Niyazov, L.N.; Saidov, K.S.; Sokolov, B.Yu.

2011-01-01

The transformation of cubic ferrimagnetic Tb 0.2 Y 2.8 Fe 5 O 12 domain structure has been studied by magneto optic method in the temperature region of spontaneous spin flip phase transition (SPT). It has been found that SPT occurs in a finite temperature interval where the coexistence of low- and high- temperature magnetic phase domains has observed. A character of domain structure evolution in temperature region of spin flip essentially depends on the presence of mechanical stresses in crystal. Interpretation of experimental results has been carried out within the framework of SPT theory for a cubic crystal. (authors)

Visualization of membrane protein crystals in lipid cubic phase using X-ray imaging.

Science.gov (United States)

Warren, Anna J; Armour, Wes; Axford, Danny; Basham, Mark; Connolley, Thomas; Hall, David R; Horrell, Sam; McAuley, Katherine E; Mykhaylyk, Vitaliy; Wagner, Armin; Evans, Gwyndaf

2013-07-01

The focus in macromolecular crystallography is moving towards even more challenging target proteins that often crystallize on much smaller scales and are frequently mounted in opaque or highly refractive materials. It is therefore essential that X-ray beamline technology develops in parallel to accommodate such difficult samples. In this paper, the use of X-ray microradiography and microtomography is reported as a tool for crystal visualization, location and characterization on the macromolecular crystallography beamlines at the Diamond Light Source. The technique is particularly useful for microcrystals and for crystals mounted in opaque materials such as lipid cubic phase. X-ray diffraction raster scanning can be used in combination with radiography to allow informed decision-making at the beamline prior to diffraction data collection. It is demonstrated that the X-ray dose required for a full tomography measurement is similar to that for a diffraction grid-scan, but for sample location and shape estimation alone just a few radiographic projections may be required.

New lipid family that forms inverted cubic phases in equilibrium with excess water: molecular structure-aqueous phase structure relationship for lipids with 5,9,13,17-tetramethyloctadecyl and 5,9,13,17-tetramethyloctadecanoyl chains.

Science.gov (United States)

Yamashita, Jun; Shiono, Manzo; Hato, Masakatsu

2008-10-02

With a view to discovering a new family of lipids that form inverted cubic phases, the aqueous phase behavior of a series of lipids with isoprenoid-type hydrophobic chains has been examined over a temperature range from -40 to 65 degrees C by using optical microscopy, DSC (differential scanning calorimetry), and SAXS (small-angle X-ray scattering) techniques. The lipids examined are those with 5,9,13,17-tetramethyloctadecyl and 5,9,13,17-tetramethyloctadecanoyl chains linked to a series of headgroups, that is, erythritol, pentaerythritol, xylose, and glucose. All of the lipid/water systems displayed a "water + liquid crystalline phase" two-phase coexistence state when sufficiently diluted. The aqueous phase structures of the most diluted liquid crystalline phases in equilibrium with excess water depend both on the lipid molecular structure and on the temperature. Given an isoprenoid chain, the preferred phase consistently follows a phase sequence of an H II (an inverted hexagonal phase) to a Q II (an inverted bicontinuous cubic phase) to an L alpha (a lamellar phase) as A* (cross-section area of the headgroup) increases. For a given lipid/water system, the phase sequence observed as the temperature increases is L alpha to Q II to H II. The present study allowed us to find four cubic phase-forming lipid species, PEOC 18+4 [mono- O-(5,9,13,17-tetramethyloctadecyl)pentaerythritol], beta-XylOC 18+4 [1- O-(5,9,13,17-tetramethyloctadecyl)-beta- d-xylopyranoside], EROCOC 17+4 [1- O-(5,9,13,17-tetramethyloctadecanoyl)erythritol], and PEOCOC 17+4 [mono- O-(5,9,13,17-tetramethyloctadecanoyl)pentaerythritol]. The values of T K (hydrated solid-liquid crystalline phase transition temperature) of the cubic phase-forming lipids are all below 0 degrees C. Quantitative analyses of the lipid molecular structure-aqueous phase structure relationship in terms of the experimentally evaluated "surfactant parameter" allow us to rationally select an optimum combination of hydrophilic

Two-phase materials for high-temperature service

CSIR Research Space (South Africa)

Nabarro, FRN

2000-09-01

Full Text Available load is carried by the g phase, which is a ductile material; at high temperatures the g phase is weak, and 0966-9795/00/$ - see front matter #2000 Elsevier Science Ltd. All rights reserved. PII: S0966-9795(00)00030-3 Intermetallics 8 (2000) 979?985 www...-temperature phase of ZrO2 containing 4.5 mol% per cent Y2O3 has the cubic ?uorite structure. A 980 F.R.N. Nabarro / Intermetallics 8 (2000) 979?985 face-centred cube of Zr atoms, with 4 Zr atoms in the unit cell, contains a simple cube of 8 O-atoms. On cooling...

Enhanced lithium-ion storage performance by structural phase transition from two-dimensional rhombohedral Fe_2O_3 to cubic Fe_3O_4

International Nuclear Information System (INIS)

Ren, Yurong; Wang, Jiawei; Huang, Xiaobing; Ding, Jianning

2016-01-01

Highlights: • The rhombohedral Fe_2O_3 transforms to the cubic Fe_3O_4 via a calcination treatment. • Phase structure of anodes has great influences on their electrochemical performances. • Fe_3O_4/reduced graphene oxide shows a high capacity of 825.3 mAh g"−"1 at 50 mA g"−"1. - Abstract: The electrochemical performance of a material varies with its structural phase transition. It is found that the rhombohedral Fe_2O_3 can transform to the cubic Fe_3O_4 via a calcination treatment in a nitrogen atmosphere, and lithium-ion storage performances of Fe_3O_4 get an obvious improvement due to its structural advantages. On the basis of data calculated by X-ray diffraction, the larger unit cell volume as well as the higher void fraction of cubic Fe_3O_4 provides lithium-ions with more transport channels for Li ions diffusion and storage without serious volume change, and thus the cubic Fe_3O_4 delivers an excellent reversible capacity of 921.1 mAh g"−"1 after 15 cycles at the current density of 50 mA g"−"1, which is much higher than 328.3 mAh g"−"1 for the rhombohedral Fe_2O_3. To further enhance the structural stability of electrodes, reduced graphene oxide is introduced. The Fe_3O_4/reduced graphene oxide show an excellent specific capacity of 825.3 mAh g"−"1 after 40 cycles and impressive rate performance of 600 mAh g"−"1 at the current density of 400 mA g"−"1, which are much higher than that of Fe_3O_4 (417 and 300 mAh g"−"1), Fe_2O_3 (137.4 and 95 mAh g"−"1) and Fe_2O_3/reduced graphene oxide (390.1 and 480 mAh g"−"1). These results demonstrate that the structural phase transition and reduced graphene oxide of Fe_3O_4/reduced graphene oxide composites offer unique characteristics suitable for high-performance energy storage application.

Cubic-to-Tetragonal Phase Transitions in Ag-Cu Nano rods

International Nuclear Information System (INIS)

Delogu, F.; Mascia, M.

2012-01-01

Molecular dynamics simulations have been used to investigate the structural behavior of nano rods with square cross section. The nano rods consist of pure Ag and Cu phases or of three Ag and Cu domains in the sequence Ag-Cu-Ag or Cu-Ag-Cu. Ag and Cu domains are separated by coherent interfaces. Depending on the side length and the size of individual domains, Ag and Cu can undergo a transition from the usual face-centered cubic structure to a body-centered tetragonal one. Such transition can involve the whole nano rod, or only the Ag domains. In the latter case, the transition is accompanied by a loss of coherency at the Ag-Cu interfaces, with a consequent release of elastic energy. The observed behaviors are connected with the stresses developed at the nano rod surfaces.

High pressure study of water-salt systems, phase equilibria, partitioning, thermodynic properties and implication for large icy worlds hydrospheres.

Science.gov (United States)

Journaux, B.; Brown, J. M.; Abramson, E.; Petitgirard, S.; Pakhomova, A.; Boffa Ballaran, T.; Collings, I.

2017-12-01

Water salt systems are predicted to be present in deep hydrosphere inside water-rich planetary bodies, following water/rock chemical interaction during early differentiation stages or later hydrothermal activity. Unfortunately the current knowledge of the thermodynamic and physical properties of aqueous salt mixtures at high pressure and high temperature is still insufficient to allow realistic modeling of the chemical or dynamic of thick planetary hydrospheres. Recent experimental results have shown that the presence of solutes, and more particularly salts, in equilibrium with high pressure ices have large effects on the stability fields, buoyancy and chemistry of all the phases present at these extreme conditions. Effects currently being investigated by our research group also covers ice melting curve depressions that depend on the salt species and incorporation of solutes inside the crystallographic lattice of high pressure ices. Both of these could have very important implication at the planetary scale, enabling thicker/deeper liquid oceans, and allowing chemical transportation through the high pressure ice layer in large icy worlds. We will present the latest results obtained in-situ using diamond anvil cell, coupled with Synchrotron X-Ray diffraction, Raman Spectroscopy and optical observations, allowing to probe the crystallographic structure, equations of state, partitioning and phase boundary of high pressure ice VI and VII in equilibrium with Na-Mg-SO4-Cl ionic species at high pressures (1-10 GPa). The difference in melting behavior depending on the dissolved salt species was characterized, suggesting differences in ionic speciation at liquidus conditions. The solidus P-T conditions were also measured as well as an increase of lattice volumes interpreted as an outcome of ionic incorporation in HP ice during incongruent crystallization. The measured phase diagrams, lattice volumes and important salt incorporations suggest a more complex picture of the

Pressure Induced Phase Transformations in Ceramics

Energy Technology Data Exchange (ETDEWEB)

Reimanis, Ivar [Colorado School of Mines, Golden, CO (United States); Cioabanu, Cristian [Colorado School of Mines, Golden, CO (United States)

2017-10-15

epsilon-eucryptite and show that the transformation nucleation is related to the motion of the tetrahedral units making up the structure. It was revealed that the conduction of Li ions through the structure is also dictated by the tetrahedral unit arrangement and how their positions change with temperature. The critical pressure to obtain the high pressure phase of eucryptite was shown to depend on the grain size. The structure of the high pressure phase was determined with a combination of atomistic modeling and in situ x-ray diffraction experiments.