Temperature-dependent phase transitions in zeptoliter volumes of a complex biological membrane

International Nuclear Information System (INIS)

Nikiforov, Maxim P; Jesse, Stephen; Kalinin, Sergei V; Hohlbauch, Sophia; Proksch, Roger; King, William P; Voitchovsky, Kislon; Contera, Sonia Antoranz

2011-01-01

Phase transitions in purple membrane have been a topic of debate for the past two decades. In this work we present studies of a reversible transition of purple membrane in the 50-60 deg. C range in zeptoliter volumes under different heating regimes (global heating and local heating). The temperature of the reversible phase transition is 52 ± 5 deg. C for both local and global heating, supporting the hypothesis that this transition is mainly due to a structural rearrangement of bR molecules and trimers. To achieve high resolution measurements of temperature-dependent phase transitions, a new scanning probe microscopy-based method was developed. We believe that our new technique can be extended to other biological systems and can contribute to the understanding of inhomogeneous phase transitions in complex systems.

On the high temperature phase transition in Ba(Zr0.20Ti0.80O3 ceramic

Directory of Open Access Journals (Sweden)

K. P. Chandra

2017-08-01

Full Text Available Temperature dependent X-ray diffraction (XRD and dielectric properties of perovskite Ba(Zr0.2Ti0.8O3 ceramic prepared using a standard solid-state reaction process is presented. Along with phase transitions at low temperature, a new phase transition at high temperature (873∘C at 20Hz, diffusive in character has been found where the lattice structure changes from monoclinic (space group: P2∕m to hexagonal (space group: P6∕mmm. This result places present ceramic in the list of potential candidate for intended high temperature applications. The AC conductivity data followed hopping type charge conduction and supports jump relaxation model. The experimental value of d33=98pC/N was found. The dependence of polarization and strain on electric field at room temperature suggested that lead-free Ba(Zr0.2Ti0.8O3 is a promising material for electrostrictive applications.

Martensitic phase transitions

International Nuclear Information System (INIS)

Petry, W.; Neuhaus, J.

1996-01-01

Many elements transform from a high temperature bcc phase to a more dense packed temperature phase. The great majority of these transitions are of 1st order, displacive and reconstructive. The lattice potentials which govern these martensitic transitions can be probed by inelastic neutron scattering, thereby answering fundamental questions like : Will the transition be announced by dynamical or static fluctuations? What are the trajectories for the displacements needed for the transformation? Does the vibrational entropy stabilize the high temperature phase? Are the unusual transport properties in these materials related to their ability to transform? (author) 17 figs., 1 tab., 46 refs

Martensitic phase transitions

Energy Technology Data Exchange (ETDEWEB)

Petry, W; Neuhaus, J [Techn. Universitaet Muenchen, Physik Department E13, Munich (Germany)

1996-11-01

Many elements transform from a high temperature bcc phase to a more dense packed temperature phase. The great majority of these transitions are of 1st order, displacive and reconstructive. The lattice potentials which govern these martensitic transitions can be probed by inelastic neutron scattering, thereby answering fundamental questions like : Will the transition be announced by dynamical or static fluctuations? What are the trajectories for the displacements needed for the transformation? Does the vibrational entropy stabilize the high temperature phase? Are the unusual transport properties in these materials related to their ability to transform? (author) 17 figs., 1 tab., 46 refs.

Quantum phase transitions

International Nuclear Information System (INIS)

Sachdev, S.

1999-01-01

Phase transitions are normally associated with changes of temperature but a new type of transition - caused by quantum fluctuations near absolute zero - is possible, and can tell us more about the properties of a wide range of systems in condensed-matter physics. Nature abounds with phase transitions. The boiling and freezing of water are everyday examples of phase transitions, as are more exotic processes such as superconductivity and superfluidity. The universe itself is thought to have passed through several phase transitions as the high-temperature plasma formed by the big bang cooled to form the world as we know it today. Phase transitions are traditionally classified as first or second order. In first-order transitions the two phases co-exist at the transition temperature - e.g. ice and water at 0 deg., or water and steam at 100 deg. In second-order transitions the two phases do not co-exist. In the last decade, attention has focused on phase transitions that are qualitatively different from the examples noted above: these are quantum phase transitions and they occur only at the absolute zero of temperature. The transition takes place at the ''quantum critical'' value of some other parameter such as pressure, composition or magnetic field strength. A quantum phase transition takes place when co-operative ordering of the system disappears, but this loss of order is driven solely by the quantum fluctuations demanded by Heisenberg's uncertainty principle. The physical properties of these quantum fluctuations are quite distinct from those of the thermal fluctuations responsible for traditional, finite-temperature phase transitions. In particular, the quantum system is described by a complex-valued wavefunction, and the dynamics of its phase near the quantum critical point requires novel theories that have no analogue in the traditional framework of phase transitions. In this article the author describes the history of quantum phase transitions. (UK)

Structural phase transitions at high-temperature in double perovskite Sr{sub 2}GdRuO{sub 6}

Energy Technology Data Exchange (ETDEWEB)

Triana, C.A.; Corredor, L.T.; Landinez Tellez, D.A. [Grupo de Fisica de Nuevos Materiales, Departamento de Fisica, Universidad Nacional de Colombia, A.A. 14490, Bogota D.C (Colombia); Roa-Rojas, J., E-mail: jroar@unal.edu.co [Grupo de Fisica de Nuevos Materiales, Departamento de Fisica, Universidad Nacional de Colombia, A.A. 14490, Bogota D.C (Colombia)

2012-08-15

The crystal structure evolution of the Sr{sub 2}GdRuO{sub 6} complex perovskite at high-temperature has been investigated over a wide temperature range between 298 K{<=}T{<=}1273 K. Powder X-ray diffraction measurements at room temperature and Rietveld analysis show that this compounds crystallizes in a monoclinic perovskite-type structure with P2{sub 1}/n (no. 14) space group and the 1:1 ordered arrangement of Ru{sup 5+} and Gd{sup 3+} cations over the six-coordinate M sites, with lattice parameters a=5.81032(8) A, b=5.82341(4) A, c=8.21939(7) A, V=278.11(6) A{sup 3} and angle {beta}=90.311(2){sup o}. The high-temperature analysis shows that this material suffers two-phase transitions. At 373 K it adopts a monoclinic perovskite structure with I2/m space group, and lattice parameters a=5.81383(2) A, b=5.82526(4) A, c=8.22486(1) A, V=278.56(2) A{sup 3} and angle {beta}=90.28(2){sup o}. Above of 773 K, it suffers a phase transition from monoclinic I2/m to tetragonal I4/m, with lattice parameters a=5.84779(1) A, c=8.27261(1) A, V=282.89(5) A{sup 3} and angle {beta}=90.02(9){sup o}. The high-temperature phase transition from monoclinic I2/m to tetragonal I4/m is characterized by strongly anisotropic displacements of the anions.

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)

Cosmological phase transitions

International Nuclear Information System (INIS)

Kolb, E.W.

1987-01-01

If the universe stated from conditions of high temperature and density, there should have been a series of phase transitions associated with spontaneous symmetry breaking. The cosmological phase transitions could have observable consequences in the present Universe. Some of the consequences including the formation of topological defects and cosmological inflation are reviewed here. One of the most important tools in building particle physics models is the use of spontaneous symmetry breaking (SSB). The proposal that there are underlying symmetries of nature that are not manifest in the vacuum is a crucial link in the unification of forces. Of particular interest for cosmology is the expectation that are the high temperatures of the big bang symmetries broken today will be restored, and that there are phase transitions to the broken state. The possibility that topological defects will be produced in the transition is the subject of this section. The possibility that the Universe will undergo inflation in a phase transition will be the subject of the next section. Before discussing the creation of topological defects in the phase transition, some general aspects of high-temperature restoration of symmetry and the development of the phase transition will be reviewed. 29 references, 1 figure, 1 table

Phase transition of a cobalt-free perovskite as a high-performance cathode for intermediate-temperature solid oxide fuel cells.

Science.gov (United States)

Jiang, Shanshan; Zhou, Wei; Niu, Yingjie; Zhu, Zhonghua; Shao, Zongping

2012-10-01

It is generally recognized that the phase transition of a perovskite may be detrimental to the connection between cathode and electrolyte. Moreover, certain phase transitions may induce the formation of poor electronic and ionic conducting phase(s), thereby lowering the electrochemical performance of the cathode. Here, we present a study on the phase transition of a cobalt-free perovskite (SrNb(0.1)Fe(0.9)O(3-δ), SNF) and evaluate its effect on the electrochemical performance of the fuel cell. SNF exists as a primitive perovskite structure with space group P4mm (99) at room temperature. As evidenced by in situ high-temperature X-ray diffraction measurements over the temperature range of 600 to 1000 °C, SNF undergoes a transformation to a tetragonal structure with a space group I4/m (87). This phase transition is accompanied by a moderate change in the volume, allowing a good cathode/electrolyte interface on thermal cycling. According to the electrochemical impedance spectroscopy evaluation, the I4/m phase exhibits positive effects on the cathode's performance, showing the highest oxygen reduction reaction activity of cobalt-free cathodes reported so far. This activity improvement is attributed to enhanced oxygen surface processes. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Highly tilted liquid crystalline materials possessing a direct phase transition from antiferroelectric to isotropic phase

Energy Technology Data Exchange (ETDEWEB)

Milewska, K.; Drzewiński, W. [Institute of Chemistry, Military University of Technology, 00-908 Warsaw (Poland); Czerwiński, M., E-mail: mczerwinski@wat.edu.pl [Institute of Chemistry, Military University of Technology, 00-908 Warsaw (Poland); Dąbrowski, R. [Institute of Chemistry, Military University of Technology, 00-908 Warsaw (Poland); Piecek, W. [Institute of Applied Physics, Military University of Technology, 00-908 Warsaw (Poland)

2016-03-01

Pure compounds and multicomponent mixtures with a broad temperature range of high tilted liquid crystalline antiferroelectric phase and a direct phase transition from antiferroelectric to isotropic phase, were obtained. X-ray diffraction analysis confirms these kinds of materials form a high tilted anticlinic phase, with a fixed layer spacing and very weak dependency upon temperature, after the transition from the isotropic phase. Due to this, not only pure orthoconic antiferroelectric liquid crystals but also those with a moderate tilt should generate a good dark state. Furthermore, due to the increased potential for forming anticlinic forces, such materials could minimize a commonly observed asymmetry of a rise and fall switching times at a surface stabilized geometry. - Highlights: • The new class of liquid crystalline materials with the direct SmC{sub A}*. • Iso phase transition were obtained. • Materials possess the layer spacing fixed and very weak dependent upon temperature. • Smectic layers without shrinkage are observed. • A good dark state can be generate in SSAFLC.

High-pressure phase transition in Ho2O3

International Nuclear Information System (INIS)

Lonappan, Dayana; Shekar, N.V. Chandra; Ravindran, T.R.; Sahu, P. Ch.

2010-01-01

High-pressure X-ray diffraction and Raman studies on holmium sesquioxide (Ho 2 O 3 ) have been carried out up to a pressure of ∼17 GPa in a diamond-anvil cell at room temperature. Holmium oxide, which has a cubic or bixbyite structure under ambient conditions, undergoes an irreversible structural phase transition at around 9.5 GPa. The high-pressure phase has been identified to be low symmetry monoclinic type. The two phases coexist to up to about 16 GPa, above which the parent phase disappears. The high-pressure laser-Raman studies have revealed that the prominent Raman band ∼370 cm -1 disappears around the similar transition pressure. The bulk modulus of the parent phase is reported.

Brane-antibrane systems at finite temperature and phase transition near the Hagedorn temperature

International Nuclear Information System (INIS)

Hotta, Kenji

2002-01-01

In order to study the thermodynamic properties of brane-antibrane systems, we compute the finite temperature effective potential of tachyon T in this system on the basis of boundary string field theory. At low temperature, the minimum of the potential shifts towards T=0 as the temperature increases. In the D9-anti-D9 case, the sign of the coefficient of vertical bar T vertical bar 2 term of the potential changes slightly below the Hagedorn temperature. This means that a phase transition occurs near the Hagedorn temperature. On the other hand, the coefficient is kept negative in the Dp-anti-Dp case with p≤8, and thus a phase transition does not occur. This leads us to the conclusion that only a D9-anti-D9 pair and no other (lower dimensional) brane-antibrane pairs are created near the Hagedorn temperature. We also discuss a phase transition in NS9B-anti-NS9B case as a model of the Hagedorn transition of closed strings. (author)

Evolution of low-temperature phases in a low-temperature structural transition of a La cuprate

International Nuclear Information System (INIS)

Inoue, Y.; Horibe, Y.; Koyama, Y.

1997-01-01

The microstructure produced by a low-temperature structural phase transition in La 1.5 Nd 0.4 Sr 0.1 CuO 4 has been examined by transmission electron microscopy with the help of imaging plates. The low-temperature transition was found to be proceeded not only by the growth of the Pccn/low-temperature-tetragonal phases nucleated along the twin boundary but also by the nucleation and growth of the phases in the interior of the low-temperature-orthorhombic domain. In addition, because the map of the octahedron tilt as an order parameter is not identical to that of the spontaneous strain accompanied by the transition, the microstructure below the transition is understood to be a very complex mixture of the low-temperature phases. copyright 1997 The American Physical Society

Finite temperature susy GUT phase transitions determined by radiative corrections

International Nuclear Information System (INIS)

Kripfganz, J.; Perlt, H.

1983-02-01

Studying the 2-loop perturbative contribution to the free energy of grand unified theories a sequence of phase transitions is found, with SU(3)xSU(2)xU(1) being the prefered low temperature phase. The transition temperatures are still within the weak coupling regime. (author)

Structural phase transition of BaZrO3 under high pressure

International Nuclear Information System (INIS)

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

2014-01-01

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

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.

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.

In Situ Observation of Gypsum-Anhydrite Transition at High Pressure and High Temperature

Institute of Scientific and Technical Information of China (English)

LIU Chuan-Jiang; ZHENG Hai-Fei

2012-01-01

An in-situ Raman spectroscopic study of gypsum-anhydrite transition under a saturated water condition at high pressure and high temperature is performed using a hydrothermal diamond anvil cell (HDAC).The experimental results show that gypsum dissolvs in water at ambient temperature and above 496 MPa.With increasing temperature,the anhydrite (CaSO4) phase precipitates at 250 320℃ in the pressure range of 1.0 1.5 GPa,indicating that under a saturated water condition,both stable conditions of pressure and temperature and high levels of Ca and SO4 ion concentrations in aqueous solution are essential for the formation of anhydrite.A linear relationship between the pressure and temperature for the precipitation of anhydrite is established as P(GPa) =0.0068T - 0.7126 (250℃≤T≤320℃).Anhydrite remained stable during rapid cooling of the sample chamber,showing that the gypsum-anhydrite transition involving both dissolution and precipitation processes is irreversible at high pressure and high temperature.%An in-situ Raman spectroscopic study of gypsum-anhydrite transition under a saturated water condition at high pressure and high temperature is performed using a hydrothermal diamond anvil cell (HDAC). The experimental results show that gypsum dissolvs in water at ambient temperature and above 496 Mpa. With increasing temperature, the anhydrite (CaSO4) phase precipitates at 250-320℃ in the pressure range of 1.0-1.5 Gpa, indicating that under a saturated water condition, both stable conditions of pressure and temperature and high levels of Ca and SO4 ion concentrations in aqueous solution are essential for the formation of anhydrite. A linear relationship between the pressure and temperature for the precipitation of anhydrite is established as P(Gpa) = 0.0068T - 0.7126 (250℃≤T≤320℃). Anhydrite remained stable during rapid cooling of the sample chamber, showing that the gypsum-anhydrite transition involving both dissolution and precipitation processes is

High-temperature superconducting phase in rare earth alloys

International Nuclear Information System (INIS)

Vedyaev, A.V.; Molodykh, O.Eh.; Savchenko, M.A.; Stefanovich, A.V.

1984-01-01

A possibility of high-temperature superconducting phase existence in rare e arth alloys with aluminium: TbAl-NdAl is predicted. Such a phase is shown t o exist at t approximately 40 k, however its existence is possible only in a nar row temperature range and it might be metastable. A possibility of a supercondu cting phase occurrence in spin glass is studied. It is shown that the first kin d phase transition to superconducting state may first occur under definite condi tions in the system. But the phase in question will be a low-temperature one be cause of rather inefficient elctron-phonon interaction. Further temperature dec rease would lead to an appearance of magnetic order and to disappearance of the superconductivity

CosmoTransitions: Computing cosmological phase transition temperatures and bubble profiles with multiple fields

Science.gov (United States)

Wainwright, Carroll L.

2012-09-01

I present a numerical package (CosmoTransitions) for analyzing finite-temperature cosmological phase transitions driven by single or multiple scalar fields. The package analyzes the different vacua of a theory to determine their critical temperatures (where the vacuum energy levels are degenerate), their supercooling temperatures, and the bubble wall profiles which separate the phases and describe their tunneling dynamics. I introduce a new method of path deformation to find the profiles of both thin- and thick-walled bubbles. CosmoTransitions is freely available for public use.Program summaryProgram Title: CosmoTransitionsCatalogue identifier: AEML_v1_0Program summary URL: http://cpc.cs.qub.ac.uk/summaries/AEML_v1_0.htmlProgram obtainable from: CPC Program Library, Queen's University, Belfast, N. IrelandLicensing provisions: Standard CPC licence, http://cpc.cs.qub.ac.uk/licence/licence.htmlNo. of lines in distributed program, including test data, etc.: 8775No. of bytes in distributed program, including test data, etc.: 621096Distribution format: tar.gzProgramming language: Python.Computer: Developed on a 2009 MacBook Pro. No computer-specific optimization was performed.Operating system: Designed and tested on Mac OS X 10.6.8. Compatible with any OS with Python installed.RAM: Approximately 50 MB, mostly for loading plotting packages.Classification: 1.9, 11.1.External routines: SciPy, NumPy, matplotLibNature of problem: I describe a program to analyze early-Universe finite-temperature phase transitions with multiple scalar fields. The goal is to analyze the phase structure of an input theory, determine the amount of supercooling at each phase transition, and find the bubble-wall profiles of the nucleated bubbles that drive the transitions.Solution method: To find the bubble-wall profile, the program assumes that tunneling happens along a fixed path in field space. This reduces the equations of motion to one dimension, which can then be solved using the overshoot

Possibility of high temperature superconducting phases in PdH

Science.gov (United States)

Tripodi, Paolo; Di Gioacchino, Daniele; Borelli, Rodolfo; Vinko, Jenny Darja

2003-05-01

Possible new superconducting phases with a high critical transition temperature (Tc) have been found in stable palladium-hydrogen (PdHx) samples for stoichiometric ratio x=H/Pd⩾1, in addition to the well-known low critical transition temperature (0⩽Tc⩽9) when x is in the range (0.75⩽x⩽1.00). Possible new measured superconducting phases with critical temperature in the range 51⩽Tc⩽295 K occur. This Tc varies considerably with every milli part of x when x exceeds unit. A superconducting critical current density Jc⩾6.1×104 A cm-2 has been measured at 77 K with HDC=0 T.

Low-temperature structural phase transition in deuterated and protonated lithium acetate dihydrate

Energy Technology Data Exchange (ETDEWEB)

Schroeder, F., E-mail: schroeder@kristall.uni-frankfurt.d [Goethe-Universitaet Frankfurt am Main, Institut fuer Geowissenschaften, Abt. Kristallographie, Altenhoeferallee 1, 60438 Frankfurt am Main (Germany); Winkler, B.; Haussuehl, E. [Goethe-Universitaet Frankfurt am Main, Institut fuer Geowissenschaften, Abt. Kristallographie, Altenhoeferallee 1, 60438 Frankfurt am Main (Germany); Cong, P.T.; Wolf, B. [Goethe-Universitaet Frankfurt am Main, Physikalisches Institut, Max-von-Laue-Strasse 1, 60438 Frankfurt am Main (Germany); Avalos-Borja, M. [Instituto Potosino de Investigacion Cientifica y Tecnologica, A.C. Camino a la Presa San Jose 2055, Col. Lomas 4 seccion CP 78216, San Luis Potosi (Mexico); Quilichini, M.; Hennion, B. [Laboratoire Leon Brillouin, CEN Saclay, 91191 Gif-sur-Yvette (France)

2010-08-15

Heat capacity measurements of protonated lithium acetate dihydrate show a structural phase transition at T = 12 K. This finding is in contrast to earlier work, where it was thought that only the deuterated compound undergoes a low temperature structural phase transition. This finding is confirmed by low temperature ultrasound spectroscopy, where the structural phase transition is associated with a velocity decrease of the ultrasonic waves, i.e. with an elastic softening. We compare the thermodynamic properties of the protonated and deuterated compounds and discuss two alternatives for the mechanism of the phase transition based on the thermal expansion measurements.

High-temperature phase transitions and domain structures of KLiSO{sub 4}. Studied by polarisation-optics, X-ray topography and liquid-crystal surface decoration

Energy Technology Data Exchange (ETDEWEB)

Scherf, Christian; Chung, Su Jin; Hahn, Theo; Klapper, Helmut [RWTH Aachen Univ. (Germany). Inst. fuer Kristallographie; Ivanov, Nicolay R. [Russian Academy of Sciences, Moscow (Russian Federation). Shubnikov Inst. of Crystallography

2017-07-01

The transitions between the room temperature phase III (space group P6{sub 3}) and the two high-temperature phases II (Pcmn) and I (P6{sub 3}/mmc) of KLiSO{sub 4} and the domain structures generated by them were investigated by high-temperature polarisation optics (birefringence) and room-temperature X-ray topography, optical activity and nematic-liquid-crystal (NLC) surface decoration. The transition from the polar hexagonal phase III into the centrosymmetric orthorhombic phase II at 708 K leads, due to the loss of the trigonal axis and the radial temperature gradient of the optical heating chamber used, to a roughly hexagonal arrangement of three sets of thin orthorhombic {110} lamelleae with angles of 60 (120 ) between them. The associated twin law ''reflection m{110}{sub orth}'' corresponds to the frequent growth twin m{10 anti 10}{sub hex} of phase III. The domains are easily ferroelastically switched. Upon further heating above 949 K into phase I (P6{sub 3}/mmc) all domains vanish. Upon cooling back into phase II the three domain states related by 60 (120 ) reflections m{110}{sub orth} re-appear, however (due to the higher thermal agitation at 949 K) with a completely different domain structure consisting of many small, irregularly arranged {110}{sub orth} domains. Particular attention is paid to the domain structure of the hexagonal room temperature phase III generated during the re-transition from the orthorhombic phase II. Curiously, from the expected three twin laws inversion anti 1, rotation 2 perpendicular to [001]{sub hex} and reflection m{10 anti 10}{sub hex} only the latter, which corresponds to the frequent growth twinning, has been found. Finally a short treatise of the structural relations of the KLiSO{sub 4} high-temperature polymorphs is given.

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)

Possibility of high temperature superconducting phases in PdH

Energy Technology Data Exchange (ETDEWEB)

Tripodi, Paolo; Di Gioacchino, Daniele; Borelli, Rodolfo; Vinko, Jenny Darja

2003-05-15

Possible new superconducting phases with a high critical transition temperature (T{sub c}) have been found in stable palladium-hydrogen (PdH{sub x}) samples for stoichiometric ratio x=H/Pd{>=}1, in addition to the well-known low critical transition temperature (0{<=}T{sub c}{<=}9) when x is in the range (0.75{<=}x{<=}1.00). Possible new measured superconducting phases with critical temperature in the range 51{<=}T{sub c}{<=}295 K occur. This T{sub c} varies considerably with every milli part of x when x exceeds unit. A superconducting critical current density J{sub c}{>=}6.1x10{sup 4} A cm{sup -2} has been measured at 77 K with H{sub DC}=0 T.

Nuclear matter at high density: Phase transitions, multiquark states, and supernova outbursts

International Nuclear Information System (INIS)

Krivoruchenko, M. I.; Nadyozhin, D. K.; Rasinkova, T. L.; Simonov, Yu. A.; Trusov, M. A.; Yudin, A. V.

2011-01-01

Phase transition from hadronic matter to quark-gluon matter is discussed for various regimes of temperature and baryon number density. For small and medium densities, the phase transition is accurately described in the framework of the Field Correlation Method, whereas at high density predictions are less certain and leave room for the phenomenological models. We study formation of multiquark states (MQS) at zero temperature and high density. Relevant MQS components of the nuclear matter can be described using a previously developed formalism of the quark compound bags (QCB). Partialwave analysis of nucleon-nucleon scattering indicates the existence of 6QS which manifest themselves as poles of P matrix. In the framework of the QCB model, we formulate a self-consistent system of coupled equations for the nucleon and 6QS propagators in nuclear matter and the G matrix. The approach provides a link between high-density nuclear matter with the MQS components and the cumulative effect observed in reactions on the nuclei, which requires the admixture of MQS in the wave functions of nuclei kinematically. 6QS determines the natural scale of the density for a possible phase transition into theMQS phase of nuclear matter. Such a phase transition can lead to dynamic instability of newly born protoneutron stars and dramatically affect the dynamics of supernovae. Numerical simulations show that the phase transition may be a good remedy for the triggering supernova explosions in the spherically symmetric supernovamodels. A specific signature of the phase transition is an additional neutrino peak in the neutrino light curve. For a Galactic core-collapse supernova, such a peak could be resolved by the present neutrino detectors. The possibility of extracting the parameters of the phase of transition from observation of the neutrino signal is discussed also.

Nuclear matter at high density: Phase transitions, multiquark states, and supernova outbursts

Energy Technology Data Exchange (ETDEWEB)

Krivoruchenko, M. I.; Nadyozhin, D. K.; Rasinkova, T. L.; Simonov, Yu. A.; Trusov, M. A., E-mail: trusov@itep.ru; Yudin, A. V. [Institute for Theoretical and Experimental Physics (Russian Federation)

2011-03-15

Phase transition from hadronic matter to quark-gluon matter is discussed for various regimes of temperature and baryon number density. For small and medium densities, the phase transition is accurately described in the framework of the Field Correlation Method, whereas at high density predictions are less certain and leave room for the phenomenological models. We study formation of multiquark states (MQS) at zero temperature and high density. Relevant MQS components of the nuclear matter can be described using a previously developed formalism of the quark compound bags (QCB). Partialwave analysis of nucleon-nucleon scattering indicates the existence of 6QS which manifest themselves as poles of P matrix. In the framework of the QCB model, we formulate a self-consistent system of coupled equations for the nucleon and 6QS propagators in nuclear matter and the G matrix. The approach provides a link between high-density nuclear matter with the MQS components and the cumulative effect observed in reactions on the nuclei, which requires the admixture of MQS in the wave functions of nuclei kinematically. 6QS determines the natural scale of the density for a possible phase transition into theMQS phase of nuclear matter. Such a phase transition can lead to dynamic instability of newly born protoneutron stars and dramatically affect the dynamics of supernovae. Numerical simulations show that the phase transition may be a good remedy for the triggering supernova explosions in the spherically symmetric supernovamodels. A specific signature of the phase transition is an additional neutrino peak in the neutrino light curve. For a Galactic core-collapse supernova, such a peak could be resolved by the present neutrino detectors. The possibility of extracting the parameters of the phase of transition from observation of the neutrino signal is discussed also.

Thermodynamic studies on the ferroelectric phase transition in neutron irradiated (LixK1-x)2SO4 crystals at high temperature

International Nuclear Information System (INIS)

Kassem, M.E.; El-Khatib, A.M.; Ammar, E.A.; Denton, M.M.

1989-05-01

Thermodynamic studies of (Li x K 1-x ) 2 SO 4 , LKS, mixed crystals have been made in the concentration range (x=0.1,0.2,...,x=0.5). The thermal behavior has been investigated by differential thermal analysis, DTA, and differential scanning calorimeter, DSC, in the vicinity of high temperature phases. Also, the effect of the mixed neutron field of fast and thermal neutrons (10% of the reactor neutron pile is fast neutrons) on the thermal properties of mixed crystals was studied. The results showed a change in the transition temperature Tc, as well as the value of specific heat Cp at transition temperature, due to the change of stoichiometric ratio and radiation doses. The change of enthalpy and entropy of mixed crystals have been estimated numerically. The obtained small values of ΔS/R is characteristic of incommensurate phase transition as previously confirmed by the results of neutron diffraction technique. (author). 16 refs, 5 figs, 1 tab

Phase transitions in surfactant monolayers

International Nuclear Information System (INIS)

Casson, B.D.

1998-01-01

Two-dimensional phase transitions have been studied in surfactant monolayers at the air/water interface by sum-frequency spectroscopy and ellipsometry. In equilibrium monolayers of medium-chain alcohols C n H 2n+1 OH (n = 9-14) a transition from a two-dimensional crystalline phase to a liquid was observed at temperatures above the bulk melting point. The small population of gauche defects in the solid phase increased only slightly at the phase transition. A model of the hydrocarbon chains as freely rotating rigid rods allowed the area per molecule and chain tilt in the liquid phase to be determined. The area per molecule, chain tilt and density of the liquid phase all increased with increasing chain length, but for each chain length the density was higher than in a bulk liquid hydrocarbon. In a monolayer of decanol adsorbed at the air/water interface a transition from a two-dimensional liquid to a gas was observed. A clear discontinuity in the coefficient of ellipticity as a function of temperature showed that the transition is first-order. This result suggests that liquid-gas phase transitions in surfactant monolayers may be more widespread than once thought. A solid-liquid phase transition has also been studied in mixed monolayers of dodecanol with an anionic surfactant (sodium dodecyl sulphate) and with a homologous series of cationic surfactants (alkyltrimethylammonium bromides: C n TABs, n = 12, 14, 16). The composition and structure of the mixed monolayers was studied above and below the phase transition. At low temperatures the mixed monolayers were as densely packed as a monolayer of pure dodecanol in its solid phase. At a fixed temperature the monolayers under-went a first-order phase transition to form a phase that was less dense and more conformationally disordered. The proportion of ionic surfactant in the mixed monolayer was greatest in the high temperature phase. As the chain length of the C n TAB increased the number of conformational defects

In Situ Observation of Gypsum-Anhydrite Transition at High Pressure and High Temperature

International Nuclear Information System (INIS)

Liu Chuan-Jiang; Zheng Hai-Fei

2012-01-01

An in-situ Raman spectroscopic study of gypsum-anhydrite transition under a saturated water condition at high pressure and high temperature is performed using a hydrothermal diamond anvil cell (HDAC). The experimental results show that gypsum dissolvs in water at ambient temperature and above 496 MPa. With increasing temperature, the anhydrite (CaSO 4 ) phase precipitates at 250–320°C in the pressure range of 1.0–1.5GPa, indicating that under a saturated water condition, both stable conditions of pressure and temperature and high levels of Ca and SO 4 ion concentrations in aqueous solution are essential for the formation of anhydrite. A linear relationship between the pressure and temperature for the precipitation of anhydrite is established as P(GPa) = 0.0068T−0.7126 (250°C≤T≤320°C). Anhydrite remained stable during rapid cooling of the sample chamber, showing that the gypsum-anhydrite transition involving both dissolution and precipitation processes is irreversible at high pressure and high temperature. (geophysics, astronomy, and astrophysics)

Quasi-dynamic pressure and temperature initiated βδ solid phase transitions in HMX

Science.gov (United States)

Zaug, Joseph M.; Farber, Daniel L.; Craig, Ian M.; Blosch, Laura L.; Shuh, David K.; Hansen, Donald W.; Aracne-Ruddle, Chantel M.

2000-04-01

The phase transformation of β-HMX (>0.5% RDX) to δ phase has been studied for over twenty years and more recently with an high-contrast optical second harmonic generation technique. Shock studies of the plastic binder composites of HMX have indicated that the transition is perhaps irreversible, a result that concurs with the static pressure results published by F. Goetz et al. [1] in 1978. However, the stability field favors the β polymorph over δ as pressure is increased (up to 5.4 GPa) along any thermodynamically reasonable isotherm. In this experiment, strict control of pressure and temperature is maintained while x-ray and optical diagnostics are applied to monitor the conformational dynamics of HMX. Unlike the temperature induced β→δ transition, the pressure induced is heterogeneous in nature. The 1 bar 25 °C δ→β transition is not immediate, occuring over tens of hours. Transition points and kinetics are path dependent and consequently this paper describes our work in progress.

High temperature phase equilibria and phase diagrams

CERN Document Server

Kuo, Chu-Kun; Yan, Dong-Sheng

2013-01-01

High temperature phase equilibria studies play an increasingly important role in materials science and engineering. It is especially significant in the research into the properties of the material and the ways in which they can be improved. This is achieved by observing equilibrium and by examining the phase relationships at high temperature. The study of high temperature phase diagrams of nonmetallic systems began in the early 1900s when silica and mineral systems containing silica were focussed upon. Since then technical ceramics emerged and more emphasis has been placed on high temperature

Transition temperature to the superconducting phase of QCD at high baryon density

International Nuclear Information System (INIS)

Brown, William E.; Liu, James T.; Ren, Hai-cang

2000-01-01

Recent interest in the study of color superconductivity has focused on the regime of high baryon density where perturbative QCD may be employed. Based on the dominant one-gluon-exchange interaction, both the transition temperature and zero temperature gap have been determined to leading order in the coupling g. While the leading non-BCS behavior T C ∼μg -5 e -κ/g is easily obtained, the pre-exponential factor has proved more difficult to evaluate. Focusing on the transition temperature, we present a perturbative derivation of this factor, exact to leading order in g. This approach is first motivated by the study of a toy model and involves working to second order in the perturbative expansion. We compare this result to the zero temperature gap. Additionally, we extend the analysis to the case of higher angular momentum for longitudinal and transverse quark pairing. (c) 2000 The American Physical Society

Low temperature phase transition of the stoichiometric Ln2NiO4 oxides

International Nuclear Information System (INIS)

Fernandez, F.; Saez-Puche, R.; Botto, I.L.; Baran, E.J.

1991-01-01

In this paper we will present a comparative study of the structural phase transition in Ln 2 NiO 4 oxides, by means of neutron diffraction and infrared(IR) spectroscopy. In the Ln 2 NiO 4 oxides (Ln=La, Pr and Nd), there is a low temperature structural phase transition from the orthorhombic symmetry to a tetragonal phase, of first order character. The IR spectra show, at low temperature, a splitting of the bands related with the stretching Ni-O, strongly correlated with the phase transformation. From the neutron data, the phase transition can be visualized as a sudden tilt of the nickel octahedra

A new manganese-based single-molecule magnet with a record-high antiferromagnetic phase transition temperature

International Nuclear Information System (INIS)

Cui Yan; Li Yan-Rong; Li Rui-Yuan; Wang Yun-Ping

2014-01-01

We perform both dc and ac magnetic measurements on the single crystal of Mn 3 O(Et-sao) 3 (ClO 4 )(MeOH) 3 single-molecule magnet (SMM) when the sample is preserved in air for different durations. We find that, during the oxidation process, the sample develops into another SMM with a smaller anisotropy energy barrier and a stronger antiferromagnetic intermolecular exchange interaction. The antiferromagnetic transition temperature observed at 6.65 K in the new SMM is record-high for the antiferromagnetic phase transition in all the known SMMs. Compared to the original SMM, the only apparent change for the new SMM is that each molecule has lost three methyl groups as revealed by four-circle x-ray diffraction (XRD), which is thought to be the origin of the stronger antiferromagnetic intermolecular exchange interaction

Possible higher order phase transition in large-N gauge theory at finite temperature

Energy Technology Data Exchange (ETDEWEB)

Nishimura, Hiromichi

2017-08-07

We analyze the phase structure of SU(¥) gauge theory at finite temperature using matrix models. Our basic assumption is that the effective potential is dominated by double-trace terms for the Polyakov loops. As a function of the temperature, a background field for the Polyakov loop, and a quartic coupling, it exhibits a universal structure: in the large portion of the parameter space, there is a continuous phase transition analogous to the third-order phase transition of Gross,Witten and Wadia, but the order of phase transition can be higher than third. We show that different confining potentials give rise to drastically different behavior of the eigenvalue density and the free energy. Therefore lattice simulations at large N could probe the order of phase transition and test our results. Critical

Transition conductivity study of high temperature superconductor compounds: the role of fluctuations

International Nuclear Information System (INIS)

Pagnon, V.

1991-04-01

This memory subject is the transition conductivity study of high temperature superconductors in corelation with their anisotropy. Systematic conductivity measurements were made on YBaCuO and BaSrCaCuO in relation with temperature from 4.2 K to 1200 K, and with a magnetic field up to 8 T in several directions. Oxygen order has an effect on the characteristics at YBaCuO transition conductivity. The activation energy for oxygen absorption is about 0.5eV. One method of analysis of the conductivity fluctuations about the transition temperature is proposed. Two separate rates are noticeable in YBaCuO compound. The 3 D fluctuations rate in the immediate neighbourghood of the transition lets place to the 2 D fluctuations rate at high temperature. Transitions temperatures governing each rate are different, that's incompatible with the formula proposed by Lawrence and Doniach. On the other hand, the analogy with quasi-2 D magnetic systems seems more relevant. A magnetic field application or a lowering of oxygen concentration removes the 3 D fluctuations rate. Non ohmic effects observed at the transition conductivity foot are analysis as a non-linear 2 D excitation manifestation of the supraconductive phase. Finally, by measurements on strontium doped YBaCuO crystals, we confirm a metal-insulator transition along the C-Axe when oxygen concentration reduces. This is connected with the specific heat jump. All these results uplighten the fundamental bidimensional character of high transition temperature superconductivity [fr

Luminous transmittance and phase transition temperature of VO 2 ...

African Journals Online (AJOL)

The phase transition temperature (τc) of the films was obtained from both the transmittance and sheet resistance against temperature curves. A change in sheet resistance of 2 to 3 orders of magnitude was observed for both undoped and Ce-doped VO2 films. Comparison between undoped and doped VO2 films revealed ...

Spin crossover and Mott—Hubbard transition under high pressure and high temperature in the low mantle of the Earth

Science.gov (United States)

Ovchinnikov, S. G.; Ovchinnikova, T. M.; Plotkin, V. V.; Dyad'kov, P. G.

2015-11-01

Effect of high pressure induced spin crossover on the magnetic, electronic and structural properties of the minerals forming the Earth's low mantle is discussed. The low temperature P, T phase diagram of ferropericlase has the quantum phase transition point Pc = 56 GPa at T = 0 confirmed recently by the synchrotron Mössbauer spectroscopy. The LDA+GTB calculated phase diagram describes the experimental data. Its extension to the high temperature resulted earlier in prediction of the metallic properties of the Earth's mantle at the depth 1400 km insulator transition and compare them with the experimental seismic and geomagnetic field data.

Phase transitions modern applications

CERN Document Server

Gitterman, Moshe

2014-01-01

This book provides a comprehensive review of the theory of phase transitions and its modern applications, based on the five pillars of the modern theory of phase transitions i.e. the Ising model, mean field, scaling, renormalization group and universality. This expanded second edition includes, along with a description of vortices and high temperature superconductivity, a discussion of phase transitions in chemical reaction and moving systems. The book covers a close connection between phase transitions and small world phenomena as well as scale-free systems such as the stock market and the Internet. Readership: Scientists working in different fields of physics, chemistry, biology and economics as well as teaching material for undergraduate and graduate courses.

Finite temperature susy GUT phase transitions determined by radiative corrections

International Nuclear Information System (INIS)

Kripfganz, J.; Perlt, H.

1983-01-01

Studying the 2-loop perturbative contribution to the free energy of supersymmetric grand unified theories, SU(3)xSU(2)xU(1) is found to be the prefered low temperature phase. The transition temperature is still within the weak coupling regime. (author)

Structural evolution of calcite at high temperatures: Phase V unveiled

Science.gov (United States)

Ishizawa, Nobuo; Setoguchi, Hayato; Yanagisawa, Kazumichi

2013-01-01

The calcite form of calcium carbonate CaCO3 undergoes a reversible phase transition between Rc and Rm at ~1240 K under a CO2 atmosphere of ~0.4 MPa. The joint probability density function obtained from the single-crystal X-ray diffraction data revealed that the oxygen triangles of the CO3 group in the high temperature form (Phase V) do not sit still at specified positions in the space group Rm, but migrate along the undulated circular orbital about carbon. The present study also shows how the room temperature form (Phase I) develops into Phase V through an intermediate form (Phase IV) in the temperature range between ~985 K and ~1240 K. PMID:24084871

PHASE TRANSITION OF CaFeO2.5 AT HIGH TEMPERATURE

Directory of Open Access Journals (Sweden)

T Labii

2011-12-01

Full Text Available The numerous studies conducted on the structure of CaFeO2.5 showed that the material undergoes a series of transformations based on temperature. The first one appears around 700 K and indicates the evolution of the phasemagnetic material to a paramagnetic phase. At about 970 K the structure of CaFeO2.5 changes from rhombohedral to centered structure. Finally, around 1180 K it undergoes the transition to a structure that has been described as incommensurate modulated structure. We have observed the behavior of the material beyond this temperature by dilatometry, DSC and TGA. The tests conducted on a single crystal CaFeO2.5 confirm the changes already observed.For the first time there was a dilatometric anomaly (confirmed by DSC and TGA at 1310 K. This anomaly appears only in the crystallographic direction b which should probably be a  commensurate transformation of the material.

Reversible temperature regulation of electrical and thermal conductivity using liquid–solid phase transitions

Science.gov (United States)

Zheng, Ruiting; Gao, Jinwei; Wang, Jianjian; Chen, Gang

2011-01-01

Reversible temperature tuning of electrical and thermal conductivities of materials is of interest for many applications, including seasonal regulation of building temperature, thermal storage and sensors. Here we introduce a general strategy to achieve large contrasts in electrical and thermal conductivities using first-order phase transitions in percolated composite materials. Internal stress generated during a phase transition modulates the electrical and thermal contact resistances, leading to large contrasts in the electrical and thermal conductivities at the phase transition temperature. With graphite/hexadecane suspensions, the electrical conductivity changes 2 orders of magnitude and the thermal conductivity varies up to 3.2 times near 18 °C. The generality of the approach is also demonstrated in other materials such as graphite/water and carbon nanotube/hexadecane suspensions. PMID:21505445

Reversible temperature regulation of electrical and thermal conductivity using liquid-solid phase transitions.

Science.gov (United States)

Zheng, Ruiting; Gao, Jinwei; Wang, Jianjian; Chen, Gang

2011-01-01

Reversible temperature tuning of electrical and thermal conductivities of materials is of interest for many applications, including seasonal regulation of building temperature, thermal storage and sensors. Here we introduce a general strategy to achieve large contrasts in electrical and thermal conductivities using first-order phase transitions in percolated composite materials. Internal stress generated during a phase transition modulates the electrical and thermal contact resistances, leading to large contrasts in the electrical and thermal conductivities at the phase transition temperature. With graphite/hexadecane suspensions, the electrical conductivity changes 2 orders of magnitude and the thermal conductivity varies up to 3.2 times near 18 °C. The generality of the approach is also demonstrated in other materials such as graphite/water and carbon nanotube/hexadecane suspensions.

High-temperature entropy of anionic model for the phase transition in SnCl2.2H2O

International Nuclear Information System (INIS)

Freitas, L.C. de; Salinas, S.R.

1975-01-01

The basic model of the phase transition in the hydrogen-bonded layered crystal SnCl 2 .2H 2 O to account for the presence of ionic defects is modified. It is easy to obtain a series expansion for the high-temperature entropy of the ionic model in terms of closed subgraphs, with vertices of degree two, of the original three-coordinated 4-8 lattice. High-temperature entropy of the ionic model is shown to be identical to the residual entropy of a simple antiferromagnetic Ising model in a 3-4-8 lattice. This latter model can be solved exact by a set of transformations which lead to a well studied Ising model in a Union Jack lattice [pt

Oxygen order-disorder phase transition in PrBaCo2O5.48 at high temperature

International Nuclear Information System (INIS)

Streule, S.; Podlesnyak, A.; Pomjakushina, E.; Conder, K.; Sheptyakov, D.; Medarde, M.; Mesot, J.

2006-01-01

We have investigated the PrBaCo 2 O 5.48 compound by means of neutron powder diffraction at temperatures 300K OD =776K, which we associate with an oxygen order-disorder transition: the well-known room temperature ordered crystal structure, in which slabs of CoO 6 octahedra and CoO 5 pyramids interleave (Pmmm symmetry) gets lost at temperatures T>T OD , resulting in a statistical distribution of octahedra and pyramids in the sample. The new phase can be described by the tetragonal P4/mmm space group. The transition is caused by displacement of apical oxygen ions and is an indication that ionic conductivity, which has been observed in 3D cobaltites, may also exist in layered cobaltites

Reconstructive structural phase transitions in dense Mg

International Nuclear Information System (INIS)

Yao Yansun; Klug, Dennis D

2012-01-01

The question raised recently about whether the high-pressure phase transitions of Mg follow a hexagonal close-packed (hcp) → body centered cubic (bcc) or hcp → double hexagonal close-packed (dhcp) → bcc sequence at room temperature is examined by the use of first principles density functional methods. Enthalpy calculations show that the bcc structure replaces the hcp structure to become the most stable structure near 48 GPa, whereas the dhcp structure is never the most stable structure in the pressure range of interest. The characterized phase-transition mechanisms indicate that the hcp → dhcp transition is also associated with a higher enthalpy barrier. At room temperature, the structural sequence hcp → bcc is therefore more energetically favorable for Mg. The same conclusion is also reached from the simulations of the phase transitions using metadynamics methods. At room temperature, the metadynamics simulations predict the onset of a hcp → bcc transition at 40 GPa and the transition becomes more prominent upon further compression. At high temperatures, the metadynamics simulations reveal a structural fluctuation among the hcp, dhcp, and bcc structures at 15 GPa. With increasing pressure, the structural evolution at high temperatures becomes more unambiguous and eventually settles to a bcc structure once sufficient pressure is applied. (paper)

Topological Phase Transitions in Zinc-Blende Semimetals Driven Exclusively by Electronic Temperature

Science.gov (United States)

Trushin, Egor; Görling, Andreas

2018-04-01

We show that electronic phase transitions in zinc-blende semimetals with quadratic band touching (QBT) at the center of the Brillouin zone, like GaBi, InBi, or HgTe, can occur exclusively due to a change of the electronic temperature without the need to involve structural transformations or electron-phonon coupling. The commonly used Kohn-Sham density-functional methods based on local and semilocal density functionals employing the local density approximation (LDA) or generalized gradient approximations (GGAs), however, are not capable of describing such phenomena because they lack an intrinsic temperature dependence and account for temperature only via the occupation of bands, which essentially leads only to a shift of the Fermi level without changing the shape or topology of bands. Kohn-Sham methods using the exact temperature-dependent exchange potential, not to be confused with the Hartree-Fock exchange potential, on the other hand, describe such phase transitions. A simple modeling of correlation effects can be achieved by screening of the exchange. In the considered zinc-blende compounds the QBT is unstable at low temperatures and a transition to electronic states without QBT takes place. In the case of HgTe and GaBi Weyl points of type I and type II, respectively, emerge during the transitions. This demonstrates that Kohn-Sham methods can describe such topological phase transitions provided they are based on functionals more accurate than those within the LDA or GGA. Moreover, the electronic temperature is identified as a handle to tune topological materials.

High transition temperature superconducting integrated circuit

International Nuclear Information System (INIS)

DiIorio, M.S.

1985-01-01

This thesis describes the design and fabrication of the first superconducting integrated circuit capable of operating at over 10K. The primary component of the circuit is a dc SQUID (Superconducting QUantum Interference Device) which is extremely sensitive to magnetic fields. The dc SQUID consists of two superconductor-normal metal-superconductor (SNS) Josephson microbridges that are fabricated using a novel step-edge process which permits the use of high transition temperature superconductors. By utilizing electron-beam lithography in conjunction with ion-beam etching, very small microbridges can be produced. Such microbridges lead to high performance dc SQUIDs with products of the critical current and normal resistance reaching 1 mV at 4.2 K. These SQUIDs have been extensively characterized, and exhibit excellent electrical characteristics over a wide temperature range. In order to couple electrical signals into the SQUID in a practical fashion, a planar input coil was integrated for efficient coupling. A process was developed to incorporate the technologically important high transition temperature superconducting materials, Nb-Sn and Nb-Ge, using integrated circuit techniques. The primary obstacles were presented by the metallurgical idiosyncrasies of the various materials, such as the need to deposit the superconductors at elevated temperatures, 800-900 0 C, in order to achieve a high transition temperature

Competing magnetic interactions and low temperature magnetic phase transitions in composite multiferroics

International Nuclear Information System (INIS)

Borkar, Hitesh; Singh, V N; Kumar, Ashok; Choudhary, R J; Tomar, M; Gupta, Vinay

2015-01-01

Novel magnetic properties and magnetic interactions in composite multiferroic oxides Pb[(Zr 0.52 Ti 0.48 ) 0.60 (Fe 0.67 W 0.33 ) .40 ]O 3 ] 0.80 –[CoFe 2 O 4 ] 0.20 (PZTFW–CFO) have been studied from 50 to 1000 Oe field cooled (FC) and zero field cooled (ZFC) probing conditions, and over a wide range of temperatures (4–350 K). Crystal structure analysis, surface morphology, and high resolution transmission electron microscopy images revealed the presence of two distinct phases, where micro- and nano-size spinel CFO were embedded in tetragonal PZTFW matrix and applied a significant built-in compressive strain (∼0.4–0.8%). Three distinct magnetic phase transitions were observed with the subtle effect of CFO magnetic phase on PZTFW magnetic phase transitions below the blocking temperature (T B ). Temperature dependence magnetic property m(T) shows a clear evidence of spin freezing in magnetic order with lowering in thermal vibration. Chemical inhomogeneity and confinement of nanoscale ferrimagnetic phase in paramagnetic/antiferromagnetic matrix restrict the long range interaction of spin which in turn develop a giant spin frustration. A large divergence in the FC and ZFC data and broad hump in ZFC data near 200 (±10) K were observed which suggests that large magnetic anisotropy and short range order magnetic dipoles lead to the development of superparamagnetic states in composite. (paper)

Search for the first-order liquid-to-liquid phase transition in low-temperature confined water by neutron scattering

Science.gov (United States)

Chen, Sow-Hsin; Wang, Zhe; Kolesnikov, Alexander I.; Zhang, Yang; Liu, Kao-Hsiang

2013-02-01

It has been conjectured that a 1st order liquid-to-liquid (L-L) phase transition (LLPT) between high density liquid (HDL) and low density liquid (LDL) in supercooled water may exist, as a thermodynamic extension to the liquid phase of the 1st order transition established between the two bulk solid phases of amorphous ice, the high density amorphous ice (HDA) and the low density amorphous ice (LDA). In this paper, we first recall our previous attempts to establish the existence of the 1st order L-L phase transition through the use of two neutron scattering techniques: a constant Q elastic diffraction study of isobaric temperature scan of the D2O density, namely, the equation of state (EOS) measurements. A pronounced density hysteresis phenomenon in the temperature scan of the density above P = 1500 bar is observed which gives a plausible evidence of crossing the 1st order L-L phase transition line above this pressure; an incoherent quasi-elastic scattering measurements of temperature-dependence of the α-relaxation time of H2O at a series of pressures, namely, the study of the Fragile-to-Strong dynamic crossover (FSC) phenomenon as a function of pressure which we interpreted as the results of crossing the Widom line in the one-phase region. In this new experiment, we used incoherent inelastic neutron scattering (INS) to measure the density of states (DOS) of H atoms in H2O molecules in confined water as function of temperature and pressure, through which we may be able to follow the emergence of the LDL and HDL phases at supercooled temperature and high pressures. We here report for the first time the differences of librational and translational DOSs between the hypothetical HDL and LDL phases, which are similar to the corresponding differences between the well-established HDA and LDA ices. This is plausible evidence that the HDL and LDL phases are the thermodynamic extensions of the corresponding amorphous solid water HDA and LDA ices.

A low membrane lipid phase transition temperature is associated with a high cryotolerance of Lactobacillus delbrueckii subspecies bulgaricus CFL1.

Science.gov (United States)

Gautier, J; Passot, S; Pénicaud, C; Guillemin, H; Cenard, S; Lieben, P; Fonseca, F

2013-09-01

The mechanisms of cellular damage that lactic acid bacteria incur during freeze-thaw processes have not been elucidated to date. Fourier transform infrared spectroscopy was used to investigate in situ the lipid phase transition behavior of the membrane of Lactobacillus delbrueckii ssp. bulgaricus CFL1 cells during the freeze-thaw process. Our objective was to relate the lipid membrane behavior to membrane integrity losses during freezing and to cell-freezing resistance. Cells were produced by using 2 different culture media: de Man, Rogosa, and Sharpe (MRS) broth (complex medium) or mild whey-based medium (minimal medium commonly used in the dairy industry), to obtain different membrane lipid compositions corresponding to different recovery rates of cell viability and functionality after freezing. The lipid membrane behavior studied by Fourier transform infrared spectroscopy was found to be different according to the cell lipid composition and cryotolerance. Freeze-resistant cells, exhibiting a higher content of unsaturated and cyclic fatty acids, presented a lower lipid phase transition temperature (Ts) during freezing (Ts=-8°C), occurring within the same temperature range as the ice nucleation, than freeze-sensitive cells (Ts=+22°C). A subzero value of lipid phase transition allowed the maintenance of the cell membrane in a relatively fluid state during freezing, thus facilitating water flux from the cell and the concomitant volume reduction following ice formation in the extracellular medium. In addition, the lipid phase transition of freeze-resistant cells occurred within a short temperature range, which could be ascribed to a reduced number of fatty acids, representing more than 80% of the total. This short lipid phase transition could be associated with a limited phenomenon of lateral phase separation and membrane permeabilization. This work highlights that membrane phase transitions occurring during freeze-thawing play a fundamental role in the

Non-linear thermal evolution of the crystal structure and phase transitions of LaFeO3 investigated by high temperature X-ray diffraction

International Nuclear Information System (INIS)

Selbach, Sverre M.; Tolchard, Julian R.; Fossdal, Anita; Grande, Tor

2012-01-01

The crystal structure, anisotropic thermal expansion and structural phase transition of the perovskite LaFeO 3 has been studied by high-temperature X-ray diffraction from room temperature to 1533 K. The structural evolution of the orthorhombic phase with space group Pbnm and the rhombohedral phase with R3 ¯ c structure of LaFeO 3 is reported in terms of lattice parameters, thermal expansion coefficients, atomic positions, octahedral rotations and polyhedral volumes. Non-linear lattice expansion across the antiferromagnetic to paramagnetic transition of LaFeO 3 at T N =735 K was compared to the corresponding behavior of the ferroelectric antiferromagnet BiFeO 3 to gain insight to the magnetoelectric coupling in BiFeO 3 , which is also multiferroic. The first order phase transition of LaFeO 3 from Pbnm to R3 ¯ c was observed at 1228±9 K, and a subsequent transition to Pm3 ¯ m was extrapolated to occur at 2140±30 K. The stability of the Pbnm and R3 ¯ c polymorphs of LaFeO 3 is discussed in terms of the competing enthalpy and entropy of the two crystal polymorphs and the thermal evolution of the polyhedral volume ratio V A /V B . - Graphical abstract: Aniostropic thermal evolution of the lattice parameters and phase transition of LaFeO 3 . Highlights: ► The crystal structure of LaFeO 3 is studied by HTXRD from RT to 1533 K. ► A non-linear expansion across the Néel temperature is observed for LaFeO 3 . ► The ratio V A /V B is used to rationalize the thermal evolution of the structure.

Low temperature phase transition and crystal structure of CsMgPO{sub 4}

Energy Technology Data Exchange (ETDEWEB)

Orlova, Maria, E-mail: maria.p.orlova@gmail.com [Institute of Mineralogy and Petrography, University of Innsbruck, Innrain 52, Innsbruck 6020 (Austria); Khainakov, Sergey [Departamento de Química Física y Analítica, Universidad de Oviedo—CINN, 33006 Oviedo (Spain); Servicios Científico Técnicos, Universidad de Oviedo, 33006 Oviedo (Spain); Michailov, Dmitriy [Department of Chemistry, University of Nizhny Novgorod, 23 Gagarin av., Nizhny Novgorod 603950 (Russian Federation); Perfler, Lukas [Institute of Mineralogy and Petrography, University of Innsbruck, Innrain 52, Innsbruck 6020 (Austria); Langes, Christoph [Institute of Pharmacy, University of Innsbruck, Innrain 52, Innsbruck 6020 (Austria); Kahlenberg, Volker [Institute of Mineralogy and Petrography, University of Innsbruck, Innrain 52, Innsbruck 6020 (Austria); Orlova, Albina [Department of Chemistry, University of Nizhny Novgorod, 23 Gagarin av., Nizhny Novgorod 603950 (Russian Federation)

2015-01-15

CsMgPO{sub 4} doped with radioisotopes is a promising compound for usage as a radioactive medical source. However, a low temperature phase transition at temperatures close to ambient conditions (∼−40 °C) was observed. Information about such kind of structural changes is important in order to understand whether it can cause any problem for medical use of this compound. The phase transition has been investigated in detail using synchrotron powder diffraction, Raman spectroscopy and DFT calculations. The structure undergoes a transformation from an orthorhombic modification, space group Pnma (RT phase) to a monoclinic polymorph, space group P2{sub 1}/n (LT phase). New LT modification adopts similar to RT but slightly distorted unit cell: a=9.58199(2) Å, b=8.95501(1) Å, c=5.50344(2) Å, β=90.68583(1)°, V=472.198(3) Å{sup 3}. CsMgPO{sub 4} belongs to the group of framework compounds and is made up of strictly alternating MgO{sub 4}- and PO{sub 4}-tetrahedra sharing vertices. The cesium counter cations are located in the resulting channel-like cavities. Upon the transformation a combined tilting of the tetrahedra is observed. A comparison with other phase transitions in ABW-type framework compounds is given. - Graphical abstract: Structural behavior of β-tridymite-type phosphate CsMgPO{sub 4}, considered as potential chemical form for radioactive Cs-source has been studied at near ambient temperatures. A phase transition at (∼−40 °C) has been found and investigated. It has been established that the known orthorhombic RT modification, space group Pnma, adopts a monoclinic cell with space group P2{sub 1}/n at low temperatures. In this paper, we present results of structural analysis of changes accompanying this phase transition and discuss its possible impact on the application properties. - Highlights: • β-Tridymite type phosphate CsMgPO{sub 4} undergoes so called translationengleiche phase transition of index 2 at −40 °C. • The structure

'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

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%

Thermodynamics of phase transitions

International Nuclear Information System (INIS)

Cofta, H.

1972-01-01

The phenomenology of the phase transitions has been considered. The definitions of thermodynamic functions and parameters, as well as those of the phase transitions, are given and some of the relations between those quantities are discussed. The phase transitions classification proposed by Ehrenfest has been described. The most important features of phase transitions are discussed using the selected physical examples including the critical behaviour of ferromagnetic materials at the Curie temperature and antiferromagnetic materials at the Neel temperature. Some aspects of the Ehrenfest's equations, that have been derived, for the interfacial lines and surfaces are considered as well as the role the notion of interfaces. (S.B.)

Photoinduced charge transfer phase transition in cesium manganese hexacyanoferrate

International Nuclear Information System (INIS)

Matsuda, Tomoyuki; Tokoro, Hiroko; Hashimoto, Kazuhito; Ohkoshi, Shin-ichi

2007-01-01

Cesium manganese hexacyanoferrate, Cs 1.51 Mn[Fe(CN) 6 ], shows a thermal phase transition between Mn II -NC-Fe III [high-temperature (HT) phase] and Mn III -NC-Fe II [low-temperature (LT) phase] with phase transition temperatures of 170 K (HT→LT) and 230 K (LT→HT). The LT phase shows ferromagnetism with Curie temperature of 7 K and coercive field of 60 Oe. Irradiating with 532 nm laser light converts the LT phase into the photoinduced (PI) phase, which does not have spontaneous magnetization. The electronic state of the PI phase corresponds to that of the HT phase and the relaxation temperature from the PI to the LT phase is observed at 90 K

The crystal structure and the phase transitions of pyridinium trifluoromethanesulfonate

International Nuclear Information System (INIS)

Jesariew, Dominik; Ilczyszyn, Maria M; Pietraszko, Adam

2014-01-01

The calorimetric and optical studies and the structural properties of pyridinium trifluoromethanesulfonate (abbreviated as PyHOTf) are reported. A sequence of four fully reversible solid–solid phase transitions, at 223.0, 309.0, 359.9 and 394.3 K, has been discovered. The phase transition sequence was confirmed by x-ray diffraction data. The crystal structures of three phases (V, IV and III) have been determined from the single crystal x-ray diffraction data. Structural properties of the high temperature phases are characterized using powder x-ray diffraction data measured in the 290–425 K temperature range. The structural changes triggered by the temperature change are discussed in relation to the phase transitions. Two low temperature phases (V and IV) belong to the P4 3 2 1 2 space group of the tetragonal system. The intermediate phases (III and II) are monoclinic and the prototype high temperature phase (I) is a pseudo-cubic (tetragonal) one. The low temperature phases (V and IV) are well ordered. The crystal structure of intermediate (III and II) and prototype (I) phases are characterized by high disorder of the pyridinium cations and triflate anions. (papers)

Temperature and baryon-chemical-potential-dependent bag pressure for a deconfining phase transition

International Nuclear Information System (INIS)

Patra, B.K.; Singh, C.P.

1996-01-01

We explore the consequences of a bag model developed by Leonidov et al. for the deconfining phase transition in which the bag pressure is made to depend on the temperature and baryon chemical potential in order to ensure the entropy and baryon number conservation at the phase boundary together with the Gibbs construction for an equilibrium phase transition. We show that the bag pressure thus obtained yields an anomalous increasing behavior with the increasing baryon chemical potential at a fixed temperature which defies a physical interpretation. We demonstrate that the inclusion of the perturbative interactions in the QGP phase removes this difficulty. Further consequences of the modified bag pressure are discussed. copyright 1996 The American Physical Society

Phase transitions in (NH4)2MoO2F4 crystal

Science.gov (United States)

Krylov, Alexander; Laptash, Natalia; Vtyurin, Alexander; Krylova, Svetlana

2016-11-01

The mechanisms of temperature and high pressure phase transitions have been studied by Raman spectroscopy. Room temperature (295 K) experiments under high hydrostatic pressure up to 3.6 GPa for (NH4)2 MoO2 F4 have been carried out. Experimental data indicates a phase transition into a new high-pressure phase for (NH4)2 MoO2 F4 at 1.2 GPa. This phase transition is related to the ordering anion octahedron groups [MoO2 F4]2- and is not associated with ammonium group. Raman spectra of small non-oriented crystals ranging from 10 to 350 K have been observed. The experiment shows anion groups [MoO2 F4]2- and ammonium in high temperature phase are disordered. The phase transition at T1 = 269.8 K is of the first-order, close to the tricritical point. The first temperature phase transition is related to the ordering anion octahedron groups [MoO2 F4]2-. Second phase transitions T2 = 180 K are associated with the ordering of ammonium. The data presented within this study demonstrate that 2D correlation analysis combined with traditional Raman spectroscopy are powerful tool to study phase transitions in the crystals.

Phase transition temperatures of 405-725 K in superfluid ultra-dense hydrogen clusters on metal surfaces

International Nuclear Information System (INIS)

Holmlid, Leif; Kotzias, Bernhard

2016-01-01

Ultra-dense hydrogen H(0) with its typical H-H bond distance of 2.3 pm is superfluid at room temperature as expected for quantum fluids. It also shows a Meissner effect at room temperature, which indicates that a transition point to a non-superfluid state should exist above room temperature. This transition point is given by a disappearance of the superfluid long-chain clusters H_2_N(0). This transition point is now measured for several metal carrier surfaces at 405 - 725 K, using both ultra-dense protium p(0) and deuterium D(0). Clusters of ordinary Rydberg matter H(l) as well as small symmetric clusters H_4(0) and H_3(0) (which do not give a superfluid or superconductive phase) all still exist on the surface at high temperature. This shows directly that desorption or diffusion processes do not remove the long superfluid H_2_N(0) clusters. The two ultra-dense forms p(0) and D(0) have different transition temperatures under otherwise identical conditions. The transition point for p(0) is higher in temperature, which is unexpected.

Phase transitions in K-doped MoO{sub 2}

Energy Technology Data Exchange (ETDEWEB)

Alves, L. M. S., E-mail: leandro-fisico@hotmail.com; Lima, B. S. de; Santos, C. A. M. dos [Departamento de Engenharia de Materiais, Escola de Engenharia de Lorena-USP, Lorena, São Paulo 12602-810 (Brazil); Rebello, A.; Masunaga, S. H.; Neumeier, J. J. [Department of Physics, Montana State University, P.O. Box 173840, Bozeman, Montana 59717-3840 (United States); Leão, J. B. [NIST Center for Neutron Research, National Institute of Standards and Technology, 100 Bureau Dr. MS 6102, Gaithersburg, Maryland 20899-6102 (United States)

2014-05-28

K{sub 0.05}MoO{sub 2} has been studied by x-ray and neutron diffractometry, electrical resistivity, magnetization, heat capacity, and thermal expansion measurements. The compound displays two phase transitions, a first-order phase transition near room temperature and a second-order transition near 54 K. Below the transition at 54 K, a weak magnetic anomaly is observed and the electrical resistivity is well described by a power-law temperature dependence with exponent near 0.5. The phase transitions in the K-doped MoO{sub 2} compound have been discussed for the first time using neutron diffraction, high resolution thermal expansion, and heat capacity measurements as a function of temperature.

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)

Live cell plasma membranes do not exhibit a miscibility phase transition over a wide range of temperatures.

Science.gov (United States)

Lee, Il-Hyung; Saha, Suvrajit; Polley, Anirban; Huang, Hector; Mayor, Satyajit; Rao, Madan; Groves, Jay T

2015-03-26

Lipid/cholesterol mixtures derived from cell membranes as well as their synthetic reconstitutions exhibit well-defined miscibility phase transitions and critical phenomena near physiological temperatures. This suggests that lipid/cholesterol-mediated phase separation plays a role in the organization of live cell membranes. However, macroscopic lipid-phase separation is not generally observed in cell membranes, and the degree to which properties of isolated lipid mixtures are preserved in the cell membrane remain unknown. A fundamental property of phase transitions is that the variation of tagged particle diffusion with temperature exhibits an abrupt change as the system passes through the transition, even when the two phases are distributed in a nanometer-scale emulsion. We support this using a variety of Monte Carlo and atomistic simulations on model lipid membrane systems. However, temperature-dependent fluorescence correlation spectroscopy of labeled lipids and membrane-anchored proteins in live cell membranes shows a consistently smooth increase in the diffusion coefficient as a function of temperature. We find no evidence of a discrete miscibility phase transition throughout a wide range of temperatures: 14-37 °C. This contrasts the behavior of giant plasma membrane vesicles (GPMVs) blebbed from the same cells, which do exhibit phase transitions and macroscopic phase separation. Fluorescence lifetime analysis of a DiI probe in both cases reveals a significant environmental difference between the live cell and the GPMV. Taken together, these data suggest the live cell membrane may avoid the miscibility phase transition inherent to its lipid constituents by actively regulating physical parameters, such as tension, in the membrane.

Low temperature electroweak phase transition in the Standard Model with hidden scale invariance

Directory of Open Access Journals (Sweden)

Suntharan Arunasalam

2018-01-01

Full Text Available We discuss a cosmological phase transition within the Standard Model which incorporates spontaneously broken scale invariance as a low-energy theory. In addition to the Standard Model fields, the minimal model involves a light dilaton, which acquires a large vacuum expectation value (VEV through the mechanism of dimensional transmutation. Under the assumption of the cancellation of the vacuum energy, the dilaton develops a very small mass at 2-loop order. As a result, a flat direction is present in the classical dilaton-Higgs potential at zero temperature while the quantum potential admits two (almost degenerate local minima with unbroken and broken electroweak symmetry. We found that the cosmological electroweak phase transition in this model can only be triggered by a QCD chiral symmetry breaking phase transition at low temperatures, T≲132 MeV. Furthermore, unlike the standard case, the universe settles into the chiral symmetry breaking vacuum via a first-order phase transition which gives rise to a stochastic gravitational background with a peak frequency ∼10−8 Hz as well as triggers the production of approximately solar mass primordial black holes. The observation of these signatures of cosmological phase transitions together with the detection of a light dilaton would provide a strong hint of the fundamental role of scale invariance in particle physics.

Windows open for highly tunable magnetostructural phase transitions

KAUST Repository

Li, Y.

2016-07-18

An attempt was made to tailor the magnetostructural transitions over a wide temperature range under the principle of isostructural alloying. A series of wide Curie-temperature windows (CTWs) with a maximal width of 377 K between 69 and 446 K were established in the Mn1− yCoyNiGe1− xSix system. Throughout the CTWs, the magnetic-field-induced metamagnetic behavior and giant magnetocaloric effects are obtained. The (Mn,Co)Ni(Ge,Si) system shows great potential as multifunctional phase-transition materials that work in a wide range covering liquid-nitrogen and above water-boiling temperatures. Moreover, general understanding of isostructural alloying and CTWs constructed in (Mn,Co)Ni(Ge,Si) as well as (Mn,Fe)Ni(Ge,Si) is provided.

Ferroelectric InMnO{sub 3}: Growth of single crystals, structure and high-temperature phase transitions

Energy Technology Data Exchange (ETDEWEB)

Bekheet, Maged F., E-mail: maged.bekheet@ceramics.tu-berlin.de [Fachbereich Material‐ und Geowissenschaften, Technische Universität Darmstadt, Alarich-Weiss-Straße 2, 64287 Darmstadt (Germany); Fachgebiet Keramische Werkstoffe / Chair of Advanced Ceramic Materials, Institut für Werkstoffwissenschaften und -technologien, Technische Universität Berlin, Hardenbergstraße 40, 10623 Berlin (Germany); Svoboda, Ingrid; Liu, Na [Fachbereich Material‐ und Geowissenschaften, Technische Universität Darmstadt, Alarich-Weiss-Straße 2, 64287 Darmstadt (Germany); Bayarjargal, Lkhamsuren [Institut für Geowissenschaften, Goethe-Universität, Altenhöferallee 1, d-60438 Frankfurt a.M. (Germany); Irran, Elisabeth [Institut für Chemie, Technische Universität Berlin, Straße des 17, Juni 135, 10623 Berlin (Germany); Dietz, Christian; Stark, Robert W.; Riedel, Ralf [Fachbereich Material‐ und Geowissenschaften, Technische Universität Darmstadt, Alarich-Weiss-Straße 2, 64287 Darmstadt (Germany); Gurlo, Aleksander [Fachgebiet Keramische Werkstoffe / Chair of Advanced Ceramic Materials, Institut für Werkstoffwissenschaften und -technologien, Technische Universität Berlin, Hardenbergstraße 40, 10623 Berlin (Germany)

2016-09-15

To understand the origin of the ferroelectricity in InMnO{sub 3}, single crystals with average size of 1 mm were grown in PbF{sub 2} flux at 950 °C. The results of single crystal X-ray diffraction, second harmonic generation and piezoresponse force microscopy studies of high-quality InMnO{sub 3} single crystals reveal that the room-temperature state in this material is ferroelectric with P6{sub 3}cm symmetry. The polar InMnO{sub 3} specimen undergoes a reversible phase transition from non-centrosymmetric P6{sub 3}cm structure to a centrosymmetric P6{sub 3}/mmc structure at 700 °C as confirmed by the in situ high-temperature Raman spectroscopic and synchrotron X-ray diffraction experiments. - Graphical abstract: Piezoresponse fore microscopy (PFM) studies of high quality InMnO{sub 3} single crystal revealed that the room-temperature state of this material is ferroelectric with a clear cloverleaf pattern corresponding to six antiphase ferroelectric domains with alternating polarization ±P{sub z}. Display Omitted - Highlights: • InMnO{sub 3} single crystals with average size of 1 mm were grown in PbF{sub 2} flux at 950 °C. • The room-temperature state of InMnO{sub 3} is ferroelectric with polar P6{sub 3}cm structure. • PolarInMnO{sub 3} reversibly transforms to a centrosymmetric P6{sub 3}/mmc structure above 700 °C.

Comparing two tetraalkylammonium ionic liquids. II. Phase transitions

Energy Technology Data Exchange (ETDEWEB)

Lima, Thamires A.; Paschoal, Vitor H.; Faria, Luiz F. O.; Ribeiro, Mauro C. C., E-mail: mccribei@iq.usp.br [Laboratório de Espectroscopia Molecular, Departamento de Química Fundamental, Instituto de Química, Universidade de São Paulo, CP 26077, CEP 05513-970 São Paulo, SP (Brazil); Ferreira, Fabio F.; Costa, Fanny N. [Centro de Ciências Naturais e Humanas, Universidade Federal do ABC, Santo André, SP (Brazil); Giles, Carlos [Depto. de Física da Matéria Condensada, Instituto de Física Gleb Wataghin, Universidade Estadual de Campinas, 13083-859 Campinas, SP (Brazil)

2016-06-14

Phase transitions of the ionic liquids n-butyl-trimethylammonium bis(trifluoromethanesulfonyl)imide, [N{sub 1114}][NTf{sub 2}], and methyl-tributylammonium bis(trifluoromethanesulfonyl)imide, [N{sub 1444}][NTf{sub 2}], were investigated by differential scanning calorimetry (DSC), X-ray diffraction (XRD) measurements, and Raman spectroscopy. XRD and Raman spectra were obtained as a function of temperature at atmospheric pressure, and also under high pressure at room temperature using a diamond anvil cell (DAC). [N{sub 1444}][NTf{sub 2}] experiences glass transition at low temperature, whereas [N{sub 1114}][NTf{sub 2}] crystallizes or not depending on the cooling rate. Both the ionic liquids exhibit glass transition under high pressure. XRD and low-frequency Raman spectra provide a consistent physical picture of structural ordering-disordering accompanying the thermal events of crystallization, glass transition, cold crystallization, pre-melting, and melting. Raman spectra in the high-frequency range of some specific cation and anion normal modes reveal conformational changes of the molecular structures along phase transitions.

Molecular dynamics simulation of the rotational order-disorder phase transition in calcite

International Nuclear Information System (INIS)

Kawano, Jun; Miyake, Akira; Shimobayashi, Norimasa; Kitamura, Masao

2009-01-01

Molecular dynamics (MD) simulation of calcite was carried out with the interatomic potential model based on ab initio calculations to elucidate the phase relations for calcite polymorphs and the mechanism of the rotational order-disorder transition of calcite at high temperature at the atomic scale. From runs of MD calculations with increasing temperature within a pressure range of 1 atm and 2 GPa, the transition of calcite with R3-barc symmetry into a high-temperature phase with R3-barm symmetry was reproduced. In the high-temperature R3-barm phase, CO 3 groups vibrate with large amplitudes either around the original positions in the R3-barc structure or around other positions rotated ± 60 deg., and their positions change continuously with time. Moreover, contrary to the suggestion of previous investigators, the motion of CO 3 groups is not two-dimensional. At 1 atm, the transition between R3-barc and R3-barm is first order in character. Upon increasing temperature at high pressure, however, first a first-order isosymmetric phase transition between the R3-barc phases occurs, which corresponds to the start of ± 120 deg. flipping of CO 3 groups. Then, at higher temperatures, the transition of R3-barc to R3-barm phases happens, which can be considered second order. This set of two types of transitions at elevated pressure can be characterized by the appearance of an 'intermediate' R3-barc phase between the stable region of calcite and the high-temperature R3-barm phase, which may correspond to the CaCO 3 -IV phase.

Phase transition in SO(3) gauge theory

International Nuclear Information System (INIS)

Datta, Saumen; Gavai, Rajiv V.

1998-01-01

The phase transition in SO(3) lattice gauge theory is investigated by Monte Carlo techniques with a view (i) to understand the relationship between the bulk transition and the deconfinement transition, and (ii) to resolve the current ambiguity about the nature of the high temperature phase. By introduction of a magnetic field, it was shown that the +ve and -ve values of a > correspond to the same phase. Studies on different sized lattices lead to the conclusion that in SO(3), there is only one transition, which is deconfining in nature. (author)

Non-equilibrium phase transition

International Nuclear Information System (INIS)

Mottola, E.; Cooper, F.M.; Bishop, A.R.; Habib, S.; Kluger, Y.; Jensen, N.G.

1998-01-01

This is the final report of a one-year, Laboratory Directed Research and Development (LDRD) project at the Los Alamos National Laboratory (LANL). Non-equilibrium phase transitions play a central role in a very broad range of scientific areas, ranging from nuclear, particle, and astrophysics to condensed matter physics and the material and biological sciences. The aim of this project was to explore the path to a deeper and more fundamental understanding of the common physical principles underlying the complex real time dynamics of phase transitions. The main emphasis was on the development of general theoretical tools to deal with non-equilibrium processes, and of numerical methods robust enough to capture the time-evolving structures that occur in actual experimental situations. Specific applications to Laboratory multidivisional efforts in relativistic heavy-ion physics (transition to a new phase of nuclear matter consisting of a quark-gluon plasma) and layered high-temperature superconductors (critical currents and flux flow at the National High Magnetic Field Laboratory) were undertaken

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.

Phase transition temperatures of 405-725 K in superfluid ultra-dense hydrogen clusters on metal surfaces

Energy Technology Data Exchange (ETDEWEB)

Holmlid, Leif, E-mail: holmlid@chem.gu.se [Atmospheric Science, Department of Chemistry, University of Gothenburg, SE-412 96 Göteborg (Sweden); Kotzias, Bernhard [Airbus DS, Department Mechanical Engineering, D28199 Bremen (Germany)

2016-04-15

Ultra-dense hydrogen H(0) with its typical H-H bond distance of 2.3 pm is superfluid at room temperature as expected for quantum fluids. It also shows a Meissner effect at room temperature, which indicates that a transition point to a non-superfluid state should exist above room temperature. This transition point is given by a disappearance of the superfluid long-chain clusters H{sub 2N}(0). This transition point is now measured for several metal carrier surfaces at 405 - 725 K, using both ultra-dense protium p(0) and deuterium D(0). Clusters of ordinary Rydberg matter H(l) as well as small symmetric clusters H{sub 4}(0) and H{sub 3}(0) (which do not give a superfluid or superconductive phase) all still exist on the surface at high temperature. This shows directly that desorption or diffusion processes do not remove the long superfluid H{sub 2N}(0) clusters. The two ultra-dense forms p(0) and D(0) have different transition temperatures under otherwise identical conditions. The transition point for p(0) is higher in temperature, which is unexpected.

Alternative methods of determining phase transition temperatures of phospholipids that constitute liposomes on the example of DPPC and DMPC

Energy Technology Data Exchange (ETDEWEB)

Pentak, Danuta, E-mail: danuta.pentak@us.edu.pl

2014-05-01

Highlights: • New phase transition for DMPC was found. • FT-IR method is an important addition to the DSC studies. • The proposed method for determining the T{sub C} give very consistent results. - Abstract: In this work, alternatives to differential scanning calorimetry (DSC) as a method of determining the main phospholipid phase transition temperature are presented. The bilayer phase transitions from the ripple gel phase (P{sub β{sup ′}}) to the liquid-crystal phase (L{sub α}) of 1,2-dipalmitoyl-sn-glycerol-3-phosphocholine (DPPC) and 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) were studied by differential scanning calorimetry (DSC), Fourier transform infrared (FT-IR), nuclear magnetic resonance (NMR), and electron paramagnetic resonance (EPR) methods. In this work, two correlations between the DSC and FT-IR methods, and NMR and EPR methods are shown. The proposed methods allow for determining the T{sub C} temperature with a high degree of accuracy. Furthermore, a comparison of results obtained using the DSC and FT-IR methods allowed for an observation of a new DMPC phase transition. The liposomes analyzed in this work were obtained by the modified reverse-phase evaporation method (mREV)

Temperature-dependent Raman and ultraviolet photoelectron spectroscopy studies on phase transition behavior of VO{sub 2} films with M1 and M2 phases

Energy Technology Data Exchange (ETDEWEB)

Okimura, Kunio, E-mail: okifn@keyaki.cc.u-tokai.ac.jp; Hanis Azhan, Nurul [Graduate School of Engineering, Tokai University, Hiratsuka 259-1292 (Japan); Hajiri, Tetsuya [UVSOR Facility, Institute for Molecular Science, Okazaki 444-8585 (Japan); Graduate School of Engineering, Nagoya University, Nagoya 464-8603 (Japan); Kimura, Shin-ichi [UVSOR Facility, Institute for Molecular Science, Okazaki 444-8585 (Japan); Graduate School of Frontier Biosciences, Osaka University, Suita 565-0871 (Japan); Zaghrioui, Mustapha; Sakai, Joe [GREMAN, UMR 7347 CNRS, Université François Rabelais de Tours, Parc de Grandmont, 37200 Tours (France)

2014-04-21

Structural and electronic phase transitions behavior of two polycrystalline VO{sub 2} films, one with pure M1 phase and the other with pure M2 phase at room temperature, were investigated by temperature-controlled Raman spectroscopy and ultraviolet photoelectron spectroscopy (UPS). We observed characteristic transient dynamics in which the Raman modes at 195 cm{sup −1} (V-V vibration) and 616 cm{sup −1} (V-O vibration) showed remarkable hardening along the temperature in M1 phase film, indicating the rearrangements of V-V pairs and VO{sub 6} octahedra. It was also shown that the M1 Raman mode frequency approached those of invariant M2 peaks before entering rutile phase. In UPS spectra with high energy resolution of 0.03 eV for the M2 phase film, narrower V{sub 3d} band was observed together with smaller gap compared to those of M1 phase film, supporting the nature of Mott insulator of M2 phase even in the polycrystalline film. Cooperative behavior of lattice rearrangements and electronic phase transition was suggested for M1 phase film.

Neutron-Diffraction Study of the Phase Transition in Stannous Chloride Dihydrate

DEFF Research Database (Denmark)

Youngblood, R.; Kjems, Jørgen

1979-01-01

of the system does not change. We present neutron-diffraction results which show that the temperature dependence of the hydrogen-site occupancies is also highly symmetric around the phase-transition temperature. These results are discussed in terms of a lattice statistical model which was proposed and solved......The order-disorder phase transition in two-dimensional hydrogen-bonded layers of water molecules in SnCl2·2D2O is remarkable in several respects. It has been shown that the peak in the specific heat is highly symmetric around the phase-transition temperature, and that the crystallographic symmetry...

Transition conductivity study of high temperature superconductor compounds: the role of fluctuations; Etude de la transition resistive sur des composes supraconducteurs a haute temperature critique le role des fluctuations

Energy Technology Data Exchange (ETDEWEB)

Pagnon, V

1991-04-01

This memory subject is the transition conductivity study of high temperature superconductors in corelation with their anisotropy. Systematic conductivity measurements were made on YBaCuO and BaSrCaCuO in relation with temperature from 4.2 K to 1200 K, and with a magnetic field up to 8 T in several directions. Oxygen order has an effect on the characteristics at YBaCuO transition conductivity. The activation energy for oxygen absorption is about 0.5eV. One method of analysis of the conductivity fluctuations about the transition temperature is proposed. Two separate rates are noticeable in YBaCuO compound. The 3 D fluctuations rate in the immediate neighbourghood of the transition lets place to the 2 D fluctuations rate at high temperature. Transitions temperatures governing each rate are different, that`s incompatible with the formula proposed by Lawrence and Doniach. On the other hand, the analogy with quasi-2 D magnetic systems seems more relevant. A magnetic field application or a lowering of oxygen concentration removes the 3 D fluctuations rate. Non ohmic effects observed at the transition conductivity foot are analysis as a non-linear 2 D excitation manifestation of the supraconductive phase. Finally, by measurements on strontium doped YBaCuO crystals, we confirm a metal-insulator transition along the C-Axe when oxygen concentration reduces. This is connected with the specific heat jump. All these results uplighten the fundamental bidimensional character of high transition temperature superconductivity.

Liquid-gas phase transition in asymmetric nuclear matter at finite temperature

Science.gov (United States)

Maruyama, Toshiki; Tatsumi, Toshitaka; Chiba, Satoshi

2010-03-01

Liquid-gas phase transition is discussed in warm asymmetric nuclear matter. Some peculiar features are figured out from the viewpoint of the basic thermodynamics about the phase equilibrium. We treat the mixed phase of the binary system based on the Gibbs conditions. When the Coulomb interaction is included, the mixed phase is no more uniform and the sequence of the pasta structures appears. Comparing the results with those given by the simple bulk calculation without the Coulomb interaction, we extract specific features of the pasta structures at finite temperature.

Liquid-gas phase transition in asymmetric nuclear matter at finite temperature

International Nuclear Information System (INIS)

Maruyama, Toshiki; Tatsumi, Toshitaka; Chiba, Satoshi

2010-01-01

Liquid-gas phase transition is discussed in warm asymmetric nuclear matter. Some peculiar features are figured out from the viewpoint of the basic thermodynamics about the phase equilibrium. We treat the mixed phase of the binary system based on the Gibbs conditions. When the Coulomb interaction is included, the mixed phase is no more uniform and the sequence of the pasta structures appears. Comparing the results with those given by the simple bulk calculation without the Coulomb interaction, we extract specific features of the pasta structures at finite temperature.

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

Holography and the Electroweak Phase Transition

CERN Document Server

Creminelli, Paolo; Rattazzi, Riccardo; Creminelli, Paolo; Nicolis, Alberto; Rattazzi, Riccardo

2002-01-01

We study through holography the compact Randall-Sundrum (RS) model at finite temperature. In the presence of radius stabilization, the system is described at low enough temperature by the RS solution. At high temperature it is described by the AdS-Schwarzshild solution with an event horizon replacing the TeV brane. We calculate the transition temperature T_c between the two phases and we find it to be somewhat smaller than the TeV scale. Assuming that the Universe starts out at T >> T_c and cools down by expansion, we study the rate of the transition to the RS phase. We find that the transition is too slow and the Universe ends up in an old inflation scenario unless tight bounds are satisfied by the model parameters. In particular we find that the AdS curvature must be comparable to the 5D Planck mass and that the radius stabilization mechanism must lead to a sizeable distortion of the basic RS metric.

Displacive phase transition at the 5/3 monolayer of Pb on Ge(001)

Science.gov (United States)

Cvetko, D.; Ratto, F.; Cossaro, A.; Bavdek, G.; Morgante, A.; Floreano, L.

2005-07-01

At a coverage of 5/3 monolayer (ML), Pb adsorbed on Ge(001) forms a ground phase displaying a ((21)/(06)) symmetry. This phase undergoes two reversible phase transitions ((21)/(06))↔((21)/(03))↔(2×1) at the critical temperatures Tc1˜178K and Tc2˜375K , respectively. We investigated the behavior of the relevant order parameters at the critical temperatures by means of He and in-plane x-ray diffraction (HAS and XRD, respectively). Both phase transitions at the critical temperature put in evidence a clear order-disorder behavior, in agreement with the universality class expected for the corresponding symmetry group transformation. The low-temperature transition yields the critical exponent of the two-dimensional (2-D) Ising universality class, whereas the three-state Potts’ critical exponents are found for the high-temperature transition. By out-of-plane XRD measurements, the low-temperature phase transition is observed to be accompanied by a static surface distortion at room temperature. A complementary HAS study of the temperature evolution of the surface charge corrugation reveals that the complete ((21)/(06))↔((21)/(03)) transition is of the displacive type. On the contrary, the high-temperature phase transition does not show any change of the surface corrugation up to its irreversible decomposition, thus pointing to a pure order-disorder character.

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)

Eigenstate Phase Transitions

Science.gov (United States)

Zhao, Bo

Phase transitions are one of the most exciting physical phenomena ever discovered. The understanding of phase transitions has long been of interest. Recently eigenstate phase transitions have been discovered and studied; they are drastically different from traditional thermal phase transitions. In eigenstate phase transitions, a sharp change is exhibited in properties of the many-body eigenstates of the Hamiltonian of a quantum system, but not the thermal equilibrium properties of the same system. In this thesis, we study two different types of eigenstate phase transitions. The first is the eigenstate phase transition within the ferromagnetic phase of an infinite-range spin model. By studying the interplay of the eigenstate thermalization hypothesis and Ising symmetry breaking, we find two eigenstate phase transitions within the ferromagnetic phase: In the lowest-temperature phase the magnetization can macroscopically oscillate by quantum tunneling between up and down. The relaxation of the magnetization is always overdamped in the remainder of the ferromagnetic phase, which is further divided into phases where the system thermally activates itself over the barrier between the up and down states, and where it quantum tunnels. The second is the many-body localization phase transition. The eigenstates on one side of the transition obey the eigenstate thermalization hypothesis; the eigenstates on the other side are many-body localized, and thus thermal equilibrium need not be achieved for an initial state even after evolving for an arbitrary long time. We study this many-body localization phase transition in the strong disorder renormalization group framework. After setting up a set of coarse-graining rules for a general one dimensional chain, we get a simple "toy model'' and obtain an almost purely analytical solution to the infinite-randomness critical fixed point renormalization group equation. We also get an estimate of the correlation length critical exponent nu

Phase transition temperatures of Sn-Zn-Al system and their comparison with calculated phase diagrams

Czech Academy of Sciences Publication Activity Database

Smetana, B.; Zlá, S.; Kroupa, Aleš; Žaludová, M.; Drápala, J.; Burkovič, R.; Petlák, D.

2012-01-01

Roč. 110, č. 1 (2012), s. 369-378 ISSN 1388-6150 R&D Projects: GA MŠk(CZ) OC08053 Institutional support: RVO:68081723 Keywords : Sn-Zn-Al system * DTA * phase transition temperatures Subject RIV: BJ - Thermodynamics Impact factor: 1.982, year: 2012

Substrate effects on photoluminescence and low temperature phase transition of methylammonium lead iodide hybrid perovskite thin films

Science.gov (United States)

Shojaee, S. A.; Harriman, T. A.; Han, G. S.; Lee, J.-K.; Lucca, D. A.

2017-07-01

We examine the effects of substrates on the low temperature photoluminescence (PL) spectra and phase transition in methylammonium lead iodide hybrid perovskite (CH3NH3PbI3) thin films. Structural characterization at room temperature with X-ray diffraction (XRD), scanning electron microscopy (SEM), and Raman spectroscopy indicated that while the chemical structure of films deposited on glass and quartz was similar, the glass substrate induced strain in the perovskite films and suppressed the grain growth. The luminescence response and phase transition of the perovskite thin films were studied by PL spectroscopy. The induced strain was found to affect both the room temperature and low temperature PL spectra of the hybrid perovskite films. In addition, it was found that the effects of the glass substrate inhibited a tetragonal to orthorhombic phase transition such that it occurred at lower temperatures.

Phase Transition Control for High Performance Ruddlesden-Popper Perovskite Solar Cells

KAUST Repository

Zhang, Xu; Munir, Rahim; Xu, Zhuo; Liu, Yucheng; Tsai, Hsinhan; Nie, Wanyi; Li, Jianbo; Niu, Tianqi; Smilgies, Detlef-M.; Kanatzidis, Mercouri G.; Mohite, Aditya D.; Zhao, Kui; Amassian, Aram; Liu, Shengzhong Frank

2018-01-01

Ruddlesden-Popper reduced-dimensional hybrid perovskite (RDP) semiconductors have attracted significant attention recently due to their promising stability and excellent optoelectronic properties. Here, the RDP crystallization mechanism in real time from liquid precursors to the solid film is investigated, and how the phase transition kinetics influences phase purity, quantum well orientation, and photovoltaic performance is revealed. An important template-induced nucleation and growth of the desired (BA)(MA)PbI phase, which is achieved only via direct crystallization without formation of intermediate phases, is observed. As such, the thermodynamically preferred perpendicular crystal orientation and high phase purity are obtained. At low temperature, the formation of intermediate phases, including PbI crystals and solvate complexes, slows down intercalation of ions and increases nucleation barrier, leading to formation of multiple RDP phases and orientation randomness. These insights enable to obtain high quality (BA)(MA)PbI films with preferentially perpendicular quantum well orientation, high phase purity, smooth film surface, and improved optoelectronic properties. The resulting devices exhibit high power conversion efficiency of 12.17%. This work should help guide the perovskite community to better control Ruddlesden-Popper perovskite structure and further improve optoelectronic and solar cell devices.

Phase Transition Control for High Performance Ruddlesden-Popper Perovskite Solar Cells

KAUST Repository

Zhang, Xu

2018-04-03

Ruddlesden-Popper reduced-dimensional hybrid perovskite (RDP) semiconductors have attracted significant attention recently due to their promising stability and excellent optoelectronic properties. Here, the RDP crystallization mechanism in real time from liquid precursors to the solid film is investigated, and how the phase transition kinetics influences phase purity, quantum well orientation, and photovoltaic performance is revealed. An important template-induced nucleation and growth of the desired (BA)(MA)PbI phase, which is achieved only via direct crystallization without formation of intermediate phases, is observed. As such, the thermodynamically preferred perpendicular crystal orientation and high phase purity are obtained. At low temperature, the formation of intermediate phases, including PbI crystals and solvate complexes, slows down intercalation of ions and increases nucleation barrier, leading to formation of multiple RDP phases and orientation randomness. These insights enable to obtain high quality (BA)(MA)PbI films with preferentially perpendicular quantum well orientation, high phase purity, smooth film surface, and improved optoelectronic properties. The resulting devices exhibit high power conversion efficiency of 12.17%. This work should help guide the perovskite community to better control Ruddlesden-Popper perovskite structure and further improve optoelectronic and solar cell devices.

Reduction in L10 phase transition temperature of PLD grown FePt thin by pre-annealing pulse laser exposure

International Nuclear Information System (INIS)

Wang, Y.; Rawat, R.S.; Bisht, A.

2013-01-01

A pre-annealing atmospheric pulsed laser exposure was applied to decrease the phase transition (from chemically disordered A1 phase to chemically ordered L1 0 phase) temperature of FePt nano-particles on a Si (100) substrate. Different pre-annealing laser energy densities of 0.024 and 0.079 J/cm2 were utilized to expose the pulsed laser deposition (PLD) FePt thin film samples under atmospheric conditions. Subsequently, FePt thin film samples were annealed at different temperatures of 300 and 400 ºC to observe the influence of laser exposure on the phase transition temperature. The phase transition temperature was decreased from conventional 600 ºC to 400 ºC by one shot pre-annealing atmospheric pulsed laser exposure. (author)

Displacive phase transition at the 5/3 monolayer of Pb on Ge(001)

International Nuclear Information System (INIS)

Cvetko, D.; Ratto, F.; Cossaro, A.; Floreano, L.; Bavdek, G.; Morgante, A.

2005-01-01

At a coverage of 5/3 monolayer (ML), Pb adsorbed on Ge(001) forms a ground phase displaying a ((2 1/0 6)) symmetry. This phase undergoes two reversible phase transitions ((2 1/0 6))↔((2 1/0 3))↔(2x1) at the critical temperatures T c 1 ∼178 K and T c 2 ∼375 K, respectively. We investigated the behavior of the relevant order parameters at the critical temperatures by means of He and in-plane x-ray diffraction (HAS and XRD, respectively). Both phase transitions at the critical temperature put in evidence a clear order-disorder behavior, in agreement with the universality class expected for the corresponding symmetry group transformation. The low-temperature transition yields the critical exponent of the two-dimensional (2-D) Ising universality class, whereas the three-state Potts' critical exponents are found for the high-temperature transition. By out-of-plane XRD measurements, the low-temperature phase transition is observed to be accompanied by a static surface distortion at room temperature. A complementary HAS study of the temperature evolution of the surface charge corrugation reveals that the complete ((2 1/0 6))↔((2 1/0 3)) transition is of the displacive type. On the contrary, the high-temperature phase transition does not show any change of the surface corrugation up to its irreversible decomposition, thus pointing to a pure order-disorder character

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.

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.

Relaxation theory of spin-3/2 Ising system near phase transition temperatures

International Nuclear Information System (INIS)

Canko, Osman; Keskin, Mustafa

2010-01-01

Dynamics of a spin-3/2 Ising system Hamiltonian with bilinear and biquadratic nearest-neighbour exchange interactions is studied by a simple method in which the statistical equilibrium theory is combined with the Onsager's theory of irreversible thermodynamics. First, the equilibrium behaviour of the model in the molecular-field approximation is given briefly in order to obtain the phase transition temperatures, i.e. the first- and second-order and the tricritical points. Then, the Onsager theory is applied to the model and the kinetic or rate equations are obtained. By solving these equations three relaxation times are calculated and their behaviours are examined for temperatures near the phase transition points. Moreover, the z dynamic critical exponent is calculated and compared with the z values obtained for different systems experimentally and theoretically, and they are found to be in good agrement. (general)

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.

Critical Line of the Deconfinement Phase Transitions

Science.gov (United States)

Gorenstein, Mark I.

Phase diagram of strongly interacting matter is discussed within the exactly solvable statistical model of the quark-gluon bags. The model predicts two phases of matter: the hadron gas at a low temperature T and baryonic chemical potential μ B , and the quark-gluon gas at a high T and/or μ B . The nature of the phase transition depends on a form of the bag massvolume spectrum (its pre-exponential factor), which is expected to change with the μ B /T ratio. It is therefore likely that the line of the 1 st order transition at a high μ B/T ratio is followed by the line of the 2 nd order phase transition at an intermediate μ B/T, and then by the lines of "higher order transitions" at a low μ B /T. This talk is based on a recent paper (Gorenstein, Gaździcki, and Greiner, 2005).

Nucleation and temperature-driven phase transitions of silicene superstructures on Ag(1 1 1)

International Nuclear Information System (INIS)

Grazianetti, C; Chiappe, D; Cinquanta, E; Fanciulli, M; Molle, A

2015-01-01

Silicene grown on Ag(1 1 1) is characterized by several critical parameters. Among them, the substrate temperature plays a key role in determining the morphology during growth. However, an unexpected important role is also equally played by the post-deposition annealing temperature which determines the self-organization of silicene domains even in the submonolayer coverage regime and consecutive transitions between silicene with different periodicity. These temperature-driven phase transitions can be exploited to select the desired majority silicene phase, thus allowing for the manipulation of silicene properties. (paper)

Phonon renormalization at small q values in the high-temperature phase of CsCuCl sub 3

CERN Document Server

Foerster, U; Schotte, U; Stuhr, U

1997-01-01

The hexagonal perovskite CsCuCl sub 3 exhibits a structural phase transition from a dynamically disordered high-temperature phase to an ordered low-temperature phase due to the cooperative Jahn-Teller effect. The lattice dynamics of the high-temperature phase has been studied by inelastic neutron scattering experiments. The investigations concentrated on small wave vectors q, where for the first time renormalized phonons at q=0.02-0.05 A sup - sup 1 could be observed. The measurements confirm the predictions of a theoretical approach based on the coupling between dynamic reorientation processes and acoustic lattice waves (pseudo-spin phonon coupling). (author)

Investigation of the Influence of Sucrose and Cholesterol on the Phase Transition Temperature of nanoliposomal formulation besides using particle size Reduction Techniques (Ultrasonication/High Pressure Homogenization

Directory of Open Access Journals (Sweden)

Z Malaei-Balasi

2017-05-01

Full Text Available Introduction: The successful application of nanoliposoms as an effective drug delivery system depends on their stability in the medium. In this article, influence of additive materials such as cholesterol and sucrose besides two natural and synthesized phospholipids have been investigated. Methods: In the present study, designing and synthesis of nanoliposomal formulations were prepared using thin film method. This liposomal suspension was downsized by two methods, the high-pressure homogenizer and ultrasound to form small unilamellar vesicles. The size distributions, zeta potentials and phase transition temperature of formulations were all determined by a zetasizer and differential scanning calorimetry(DSC. In addition, the contribution of nanoliposomal formulation has been investigated by HPLC and FTIR methods. Results: Results of the DSC measurments indicated that incorporation of unsaturated phospholipid (SOY PC may cause phase separation with partial miscibility in the liposome bilayer containing of DPPG. The optimal nanoliposomal formulation was composed of (DPPC: CHOL: mPEG2000-DSPE with the mole percents equal to (83:15:2, respectively. In addition, sucrose has been used in the formulation with a total amounts six times greater than that of the lipids. The properties of optimized nanoliposome have been shown as the size average 104nm, zeta potential 8.04mv and phase transition temperature of lipid less than 37°C which were stable enough to be utilized for loading and releasing bioactives in body temperature. Conclusion: Finally the produced nanoliposomes were stable vesicles in the proper size, phase transition temperature and surface charge without any aggregation and fusion.

Magnetodynamical resonance near the low-temperature phase transition in ErFeO3

International Nuclear Information System (INIS)

Dan'shin, N.K.; Kovtun, N.M.; Sdvizhkov, M.A.

1986-01-01

Magnetodynamical resonance (MDR) near low-temperature phase transition (PT) in erbium ortoferrite is investigated. At temperature below 4K (PT temperature) pt can be induced by a magnetic field. It is revealed that PT is accompained by partialsoftening of one of the magnetic resonance MR) branches. Besides MR soft mode resonance absorption was observed. This absorption is shown to be related to the excitation in a sample of dielectric resonance (DR). Essential differences of MDR near PT in ErFeO 3 are as follows: interaction between MR abd DR at PT takes place under softening of all interacting models; ErFeO 3 is characterized by a high value of permittivity epslon and by considerable anisotropy epsilon and magnetic permeability

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.

Temperature anomalies of shock and isentropic waves of quark-hadron phase transition

Science.gov (United States)

Konyukhov, A. V.; Iosilevskiy, I. L.; Levashov, P. R.; Likhachev, A. P.

2018-01-01

In this work, we consider a phenomenological equation of state, which combinesstatistical description for hadron gas and a bag-model-based approach for the quark-gluon plasma. The equation of state is based on the excluded volume method in its thermodynamically consistent variant from Satarov et al [2009 Phys. At. Nucl. 72 1390]. The characteristic shape of the Taub adiabats and isentropes in the phase diagram is affected by the anomalous pressure-temperature dependence along the curve of phase equilibrium. The adiabats have kink points at the boundary of the two-phase region, inside which the temperature decreases with compression. Thermodynamic properties of matter observed in the quark-hadron phase transition region lead to hydrodynamic anomalies (in particular, to the appearance of composite compression and rarefaction waves). On the basis of relativistic hydrodynamics equations we investigate and discuss the structure and anomalous temperature behavior in these waves.

Effect of In-situ Cure on Measurement of Glass Transition Temperatures in High-temperature Thermosetting Polymers

Science.gov (United States)

2015-01-01

TEMPERATURES IN HIGH-TEMPERATURE THERMOSETTING POLYMERS 5a. CONTRACT NUMBER In-House 5b. GRANT NUMBER 5c. PROGRAM ELEMENT NUMBER 6. AUTHOR(S...illustrated the difficulties inherent in measurement of the glass transition temperature of this high-temperature thermosetting polymer via dynamic...copyright protection in the United States. EFFECT OF IN-SITU CURE ON MEASUREMENT OF GLASS TRANSITION TEMPERATURES IN HIGH-TEMPERATURE THERMOSETTING

Low-temperature structural phase transition in synthetic libethenite Cu2PO4OH

International Nuclear Information System (INIS)

Belik, Alexei A.; Naumov, Pance; Kim, Jungeun; Tsuda, Shunsuke

2011-01-01

Low-temperature structural properties of the synthetic mineral libethenite Cu 2 PO 4 OH were investigated by single-crystal X-ray diffraction, synchrotron X-ray powder diffraction, specific heat measurements, and Raman spectroscopy. A second-order structural phase transition from the Pnnm symmetry (a=8.0553(8) A, b=8.3750(9) A, c=5.8818(6) A at 180 K) to the P2 1 /n symmetry (a=8.0545(8) A, b=8.3622(9) A, c=5.8755(6) A, β=90.0012(15) at 120 K) was found at 160 K during cooling. At 120 K, the monoclinic angle is 90.0012(15) from single crystal X-ray data vs 90.083(1) from powder X-ray diffraction data. The P2 1 /n-to-Pnnm transition may be a general feature of the adamite-type compounds, M 2 XO 4 OH. - Graphical Abstract: Fragments of experimental synchrotron X-ray powder diffraction patterns of Cu 2 PO 4 OH between 100 and 280 K. Arrows show additional reflections that appear below 160 K in the monoclinic P2 1 /n phase. Highlights: → A low-temperature phase transition was found in the mineral libethenite Cu 2 PO 4 OH. → No magnetic anomalies and weak specific heat anomalies are detected. → Phase transition is of the second order. → Libethenite may exemplify a general feature of the adamite-type compounds.

Phase Transition Control for High Performance Ruddlesden-Popper Perovskite Solar Cells.

Science.gov (United States)

Zhang, Xu; Munir, Rahim; Xu, Zhuo; Liu, Yucheng; Tsai, Hsinhan; Nie, Wanyi; Li, Jianbo; Niu, Tianqi; Smilgies, Detlef-M; Kanatzidis, Mercouri G; Mohite, Aditya D; Zhao, Kui; Amassian, Aram; Liu, Shengzhong Frank

2018-05-01

Ruddlesden-Popper reduced-dimensional hybrid perovskite (RDP) semiconductors have attracted significant attention recently due to their promising stability and excellent optoelectronic properties. Here, the RDP crystallization mechanism in real time from liquid precursors to the solid film is investigated, and how the phase transition kinetics influences phase purity, quantum well orientation, and photovoltaic performance is revealed. An important template-induced nucleation and growth of the desired (BA) 2 (MA) 3 Pb 4 I 13 phase, which is achieved only via direct crystallization without formation of intermediate phases, is observed. As such, the thermodynamically preferred perpendicular crystal orientation and high phase purity are obtained. At low temperature, the formation of intermediate phases, including PbI 2 crystals and solvate complexes, slows down intercalation of ions and increases nucleation barrier, leading to formation of multiple RDP phases and orientation randomness. These insights enable to obtain high quality (BA) 2 (MA) 3 Pb 4 I 13 films with preferentially perpendicular quantum well orientation, high phase purity, smooth film surface, and improved optoelectronic properties. The resulting devices exhibit high power conversion efficiency of 12.17%. This work should help guide the perovskite community to better control Ruddlesden-Popper perovskite structure and further improve optoelectronic and solar cell devices. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Phase Transformation and Shape Memory Effect of Ti-Pd-Pt-Zr High-Temperature Shape Memory Alloys

Science.gov (United States)

Yamabe-Mitarai, Yoko; Takebe, Wataru; Shimojo, Masayuki

2017-12-01

To understand the potential of high-temperature shape memory alloys, we have investigated the phase transformation and shape memory effect of Ti-(50 - x)Pt- xPd-5Zr alloys ( x = 0, 5, and 15 at.%), which present the B2 structure in the austenite phase and B19 structure in the martensite phase. Their phase transformation temperatures are very high; A f and M f of Ti-50Pt are 1066 and 1012 °C, respectively. By adding Zr and Pd, the phase transition temperatures decrease, ranging between 804 and 994 °C for A f and 590 and 865 °C for M f. Even at the high phase transformation temperature, a maximum recovery ratio of 70% was obtained for one cycle in a thermal cyclic test. A work output of 1.2 J/cm3 was also obtained. The recovery ratio obtained by the thermal cyclic test was less than 70% because the recovery strain was training effect was also investigated.

Effect of the Temperature, External Magnetic Field, and Transport Current on Electrical Properties, Vortex Structure Evolution Processes, and Phase Transitions in Subsystems of Superconducting Grains and "Weak Links" of Granular Two-Level High-Temperature Superconductor YBa2Cu3O7-δ

Science.gov (United States)

Derevyanko, V. V.; Sukhareva, T. V.; Finkel', V. A.

2018-03-01

The temperature dependences of the resistivity of granular high-temperature superconductor YBa2Cu3O7-δ ρ( T) are measured at various transverse external magnetic fields 0 ≤ H ext ≤ 100 Oe in the temperature range from the resistivity onset temperature T ρ = 0 to the superconducting transition critical temperature T c at the transport current density from 50 to 2000 mA/cm2. The effect of the external magnetic field and transport current density on the kinetics of phase transitions in both subsystems of granular two-level HTSC ( T = T c2J, T c1g, T c ) is determined. The feasibility of the topological phase transition, i.e., the Berezinsky-Kosterlitz-Thouless transition, in the Josephson medium at T c2J < T BKT < T c1g "in transport current" is established, and its feasibility conditions are studied.

Fluorinated epoxy resins with high glass transition temperatures

Science.gov (United States)

Griffith, James R.

1991-01-01

Easily processed liquid resins of low dielectric constants and high glass transition temperatures are useful for the manufacture of certain composite electronic boards. That combination of properties is difficult to acquire when dielectric constants are below 2.5, glass transition temperatures are above 200 C and processability is of conventional practicality. A recently issued patent (US 4,981,941 of 1 Jan. 1991) teaches practical materials and is the culmination of 23 years of research and effort and 15 patents owned by the Navy in the field of fluorinated resins of several classes. In addition to high fluorine content, practical utility was emphasized.

A phase transition close to room temperature in BiFeO{sub 3} thin films

Energy Technology Data Exchange (ETDEWEB)

Kreisel, J; Jadhav, P; Chaix-Pluchery, O [Laboratoire des Materiaux et du Genie Physique, Grenoble INP, CNRS, Minatec, 3, parvis Louis Neel, 38016 Grenoble (France); Varela, M [Departamento Fisica Aplicada i Optica, Universitat de Barcelona, Carrer MartI i Franques 1. 08028 Campus UAB, Bellaterra 08193 (Spain); Dix, N; Sanchez, F; Fontcuberta, J, E-mail: jens.kreisel@grenoble-inp.fr [Institut de Ciencia de Materials de Barcelona (ICMAB-CSIC), Campus UAB, Bellaterra 08193 (Spain)

2011-08-31

BiFeO{sub 3} (BFO) multiferroic oxide has a complex phase diagram that can be mapped by using appropriately substrate-induced strain in epitaxial films. By using Raman spectroscopy, we conclusively show that films of the so-called supertetragonal T-BFO phase, stabilized under compressive strain, display a reversible temperature-induced phase transition at about 100 deg. C, and thus close to room temperature. (fast track communication)

Predicting a new phase (T'') of two-dimensional transition metal di-chalcogenides and strain-controlled topological phase transition

Science.gov (United States)

Ma, Fengxian; Gao, Guoping; Jiao, Yalong; Gu, Yuantong; Bilic, Ante; Zhang, Haijun; Chen, Zhongfang; Du, Aijun

2016-02-01

Single layered transition metal dichalcogenides have attracted tremendous research interest due to their structural phase diversities. By using a global optimization approach, we have discovered a new phase of transition metal dichalcogenides (labelled as T''), which is confirmed to be energetically, dynamically and kinetically stable by our first-principles calculations. The new T'' MoS2 phase exhibits an intrinsic quantum spin Hall (QSH) effect with a nontrivial gap as large as 0.42 eV, suggesting that a two-dimensional (2D) topological insulator can be achieved at room temperature. Most interestingly, there is a topological phase transition simply driven by a small tensile strain of up to 2%. Furthermore, all the known MX2 (M = Mo or W; X = S, Se or Te) monolayers in the new T'' phase unambiguously display similar band topologies and strain controlled topological phase transitions. Our findings greatly enrich the 2D families of transition metal dichalcogenides and offer a feasible way to control the electronic states of 2D topological insulators for the fabrication of high-speed spintronics devices.Single layered transition metal dichalcogenides have attracted tremendous research interest due to their structural phase diversities. By using a global optimization approach, we have discovered a new phase of transition metal dichalcogenides (labelled as T''), which is confirmed to be energetically, dynamically and kinetically stable by our first-principles calculations. The new T'' MoS2 phase exhibits an intrinsic quantum spin Hall (QSH) effect with a nontrivial gap as large as 0.42 eV, suggesting that a two-dimensional (2D) topological insulator can be achieved at room temperature. Most interestingly, there is a topological phase transition simply driven by a small tensile strain of up to 2%. Furthermore, all the known MX2 (M = Mo or W; X = S, Se or Te) monolayers in the new T'' phase unambiguously display similar band topologies and strain controlled topological

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)

Phase transition of aragonite in abalone nacre

Science.gov (United States)

An, Yuanlin; Liu, Zhiming; Wu, Wenjian

2013-04-01

Nacre is composed of about 95 vol.% aragonite and 5 vol.% biopolymer and famous for its "brick and mortar" microstructure. The phase transition temperature of aragonite in nacre is lower than the pure aragonite. In situ XRD was used to identify the phase transition temperature from aragonite to calcite in nacre, based on the analysis of TG-DSC of fresh nacre and demineralized nacre. The results indicate that the microstructure and biopolymer are the two main factors that influence the phase transition temperature of aragonite in nacre.

Theory of high-T sub c superconductivity based on the fermion-condensation quantum phase transition

CERN Document Server

Amusia, M Ya; Shaginyan, V R

2001-01-01

A theory of high temperature superconductivity based on the combination of the fermion-condensation quantum phase transition and the conventional theory of superconductivity is presented. This theory describes maximum values of the superconducting gap which can be as big as DELTA sub 1 approx 0.1 epsilon sub F , with epsilon sub F being the Fermi level. It is shown that the critical temperature 2T sub c approx = DELTA sub 1. If there exists the pseudogap above T sub c then 2T* approx = DELTA sub 1 , and T* is the temperature at which the pseudogap vanished. A discontinuity in the specific heat at T sub c is calculated. The transition from conventional superconductors to high-T sub c ones as a function of the doping level is investigated

Dynamics of the α-β phase transitions in quartz and cristobalite as observed by in-situ high temperature 29Si and 17O NMR

Science.gov (United States)

Spearing, Dane R.; Farnan, Ian; Stebbins, Jonathan F.

1992-12-01

Relaxation times (T1) and lineshapes were examined as a function of temperature through the α-β transition for 29Si in a single crystal of amethyst, and for 29Si and 17O in cristobalite powders. For single crystal quartz, the three 29Si peaks observed at room temperature, representing each of the three differently oriented SiO4 tetrahedra in the unit cell, coalesce with increasing temperature such that at the α-β transition only one peak is observed. 29Si T1's decrease with increasing temperature up to the transition, above which they remain constant. Although these results are not uniquely interpretable, hopping between the Dauphiné twin related configurations, α1 and α2, may be the fluctuations responsible for both effects. This exchange becomes observable up to 150° C below the transition, and persists above the transition, resulting in β-quartz being a time and space average of α1 and α2. 29Si T1's for isotopically enriched powdered cristobalite show much the same behavior as observed for quartz. In addition, 17O T1's decrease slowly up to the α-β transition at which point there is an abrupt 1.5 order of magnitude drop. Fitting of static powder 17O spectra for cristobalite gives an asymmetry parameter (η) of 0.125 at room T, which decreases to <0.040 at the transition temperature. The electric field gradient (EFG) and chemical shift anisotropy (CSA), however, remain the same, suggesting that the decrease in η is caused by a dynamical rotation of the tetrahedra below the transition. Thus, the mechanisms of the α-β phase transitions in quartz and cristobalite are similar: there appears to be some fluctuation of the tetrahedra between twin-related orientations below the transition temperature, and the β-phase is characterized by a dynamical average of the twin domains on a unit cell scale.

Physical Properties of Phase Pure 4C Pyrrhotite (Fe7S8) during its Low Temperature Besnus Transition

Science.gov (United States)

Volk, M.; Feinberg, J. M.; McCalla, E.; Leighton, C.; Voigt, B.

2017-12-01

Of all magnetic minerals that play a role in recording terrestrial and extraterrestrial magnetic fields, the low temperature phase transition of monoclinic Fe7S8 is the least well understood. At room temperature an array of ordered vacancies gives rise to ferrimagnetism in pyrrhotite. The mineral's physical properties change dramatically at ≈30 K during what is known as the Besnus transition. The mechanism driving these changes, however, is not fully understood. Several explanations have been proposed, including changes in crystalline anisotropy, a transformation of the crystal symmetry, and magnetic interactions within in a two-phase (4C/5C*) system among them. To better understand the transition we studied magnetic, electric and structural properties as well as the heat capacity of a large, phase pure monoclinic crystal (Fe6.8±0.1S8). The single-phase sample shows a clear peak at 32 K in the heat capacity associated with a second order phase transition. Zero field cooling of 2.5 T saturating isothermal remanent magnetizations acquired at 300 and 20 K, as well electrical conductivity exhibit sudden changes between 30-33 K. Susceptibility shows a secondary peak within the same temperature interval. These phenomena can be related to the peak in heat capacity, indicating that the changes are related to the phase transition. In-field measurements show that the magnetic and electric transitions are mildly field dependent. Repeated measurements on different instruments show that the transition temperature for susceptibility is 1 K higher when measured parallel to the crystallographic c-axis as compared to within the c-plane. Similar trends could be found in magnetoresistivity, which is negative (≈ -2%) in the c-plane and larger and positive (≈ 5%) along the c-axis. While this comprehensive data set is not able to unambiguously explain the mechanism driving the transition, it indicates the coupling of structural and magnetocrystalline properties and suggests that

High-pressure phase transition and phase diagram of gallium arsenide

Science.gov (United States)

Besson, J. M.; Itié, J. P.; Polian, A.; Weill, G.; Mansot, J. L.; Gonzalez, J.

1991-09-01

Under hydrostatic pressure, cubic GaAs-I undergoes phase transitions to at least two orthorhombic structures. The initial phase transition to GaAs-II has been investigated by optical-transmittance measurements, Raman scattering, and x-ray absorption. The structure of pressurized samples, which are retrieved at ambient, has been studied by x-ray diffraction and high-resolution diffraction microscopy. Various criteria that define the domain of stability of GaAs-I are examined, such as the occurrence of crystalline defects, the local variation in atomic coordination number, or the actual change in crystal structure. These are shown not to occur at the same pressure at 300 K, the latter being observable only several GPa above the actual thermodynamic instability pressure of GaAs-I. Comparison of the evolution of these parameters on increasing and decreasing pressure locates the thermodynamic transition region GaAs-I-->GaAs-II at 12+/-1.5 GPa and at 300 K that is lower than generally reported. The use of thermodynamic relations around the triple point, and of regularities in the properties of isoelectronic and isostructural III-V compounds, yields a phase diagram for GaAs which is consistent with this value.

Pressure-dependence of the phase transitions and thermal expansion in zirconium and hafnium pyrovanadate

Energy Technology Data Exchange (ETDEWEB)

Gallington, Leighanne C.; Hester, Brett R.; Kaplan, Benjamin S. [School of Chemistry and Biochemistry, Georgia Institute of Technology, Atlanta, GA 30332‐0400 (United States); Wilkinson, Angus P., E-mail: angus.wilkinson@chemistry.gatech.edu [School of Chemistry and Biochemistry, Georgia Institute of Technology, Atlanta, GA 30332‐0400 (United States); School of Materials Science and Engineering, Georgia Institute of Technology, Atlanta, GA 30332‐0245 (United States)

2017-05-15

Low or negative thermal expansion (NTE) has been previously observed in members of the ZrP{sub 2}O{sub 7} family at temperatures higher than their order-disorder phase transitions. The thermoelastic properties and phase behavior of the low temperature superstructure and high temperature negative thermal expansion phases of ZrV{sub 2}O{sub 7} and HfV{sub 2}O{sub 7} were explored via in situ variable temperature/pressure powder x-ray diffraction measurements. The phase transition temperatures of ZrV{sub 2}O{sub 7} and HfV{sub 2}O{sub 7} exhibited a very strong dependence on pressure (∼700 K GPa), with moderate compression suppressing the formation of their NTE phases below 513 K. Compression also reduced the magnitude of the coefficients of thermal expansion in both the positive and negative thermal expansion phases. Additionally, the high temperature NTE phase of ZrV{sub 2}O{sub 7} was found to be twice as stiff as the low temperature positive thermal expansion superstructure (24 and 12 GPa respectively). - Graphical abstract: The temperature at which ZrV{sub 2}O{sub 7} transforms to a phase displaying negative thermal expansion is strongly pressure dependent. The high temperature form of ZrV{sub 2}O{sub 7} is elastically stiffer than the low temperature form. - Highlights: • The order-disorder phase transition temperatures in ZrV{sub 2}O{sub 7} and HfV{sub 2}O{sub 7} are strongly pressure dependent (∼700 K.GPa). • The high temperature (disordered) phase of ZrV{sub 2}O{sub 7} is much stiffer than the ambient temperature (ordered) phase. • Compression reduces the magnitude of the negative thermal expansion in the high temperature phase of ZrV{sub 2}O{sub 7}.

The quantum phase-transitions of water

Science.gov (United States)

Fillaux, François

2017-08-01

It is shown that hexagonal ices and steam are macroscopically quantum condensates, with continuous spacetime-translation symmetry, whereas liquid water is a quantum fluid with broken time-translation symmetry. Fusion and vaporization are quantum phase-transitions. The heat capacities, the latent heats, the phase-transition temperatures, the critical temperature, the molar volume expansion of ice relative to water, as well as neutron scattering data and dielectric measurements are explained. The phase-transition mechanisms along with the key role of quantum interferences and that of Hartley-Shannon's entropy are enlightened. The notions of chemical bond and force-field are questioned.

Anharmonic behavior and structural phase transition in Yb2O3

Directory of Open Access Journals (Sweden)

Sugandha Dogra Pandey

2013-12-01

Full Text Available The investigation of structural phase transition and anharmonic behavior of Yb2O3 has been carried out by high-pressure and temperature dependent Raman scattering studies respectively. In situ Raman studies under high pressure were carried out in a diamond anvil cell at room temperature which indicate a structural transition from cubic to hexagonal phase at and above 20.6 GPa. In the decompression cycle, Yb2O3 retained its high pressure phase. We have observed a Stark line in the Raman spectra at 337.5 cm−1 which arises from the electronic transition between 2F5/2 and 2F7/2 multiplates of Yb3+ (4f13 levels. These were followed by temperature dependent Raman studies in the range of 80–440 K, which show an unusual mode hardening with increasing temperature. The hardening of the most dominant mode (Tg + Ag was analyzed in light of the theory of anharmonic phonon-phonon interaction and thermal expansion of the lattice. Using the mode Grüneisen parameter obtained from high pressure Raman measurements; we have calculated total anharmonicity of the Tg + Ag mode from the temperature dependent Raman data.

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.

Tunable Crystal-to-Crystal Phase Transition in a Cadmium Halide Chain Polymer

Directory of Open Access Journals (Sweden)

Ulli Englert

2011-07-01

Full Text Available The chain polymer [{Cd(μ-X2py2}1∞] (X = Cl, Br; py = pyridine undergoes a fully reversible phase transition between a monoclinic low-temperature and an orthorhombic high-temperature phase. The transformation can be directly monitored in single crystals and can be confirmed for the bulk by powder diffraction. The transition temperature can be adjusted by tuning the composition of the mixed-halide phase: Transition temperatures between 175 K up to the decomposition of the material at ca. 350 K are accessible. Elemental analysis, ion chromatography and site occupancy refinements from single-crystal X-ray diffraction agree with respect to the stoichiometric composition of the samples.

Lowering of L10 phase transition temperature of FePt thin films by single shot H+ ion exposure using plasma focus device

International Nuclear Information System (INIS)

Pan, Z.Y.; Lin, J.J.; Zhang, T.; Karamat, S.; Tan, T.L.; Lee, P.; Springham, S.V.; Ramanujan, R.V.; Rawat, R.S.

2009-01-01

FePt thin films are exposed to pulsed energetic H + ion beam from plasma focus. In irradiated films, the phase transition from the low K u disordered face-centered-cubic structure to high K u ordered face-centered-tetragonal phase was achieved at 400 deg. C with the order parameter S ranging from 0.73 to 0.83, high coercivity of about 5356 kA/m, high negative nucleation field of about 7700 kA/m and high squareness ratio ranging from 0.73 to 0.79. The advantage of using plasma focus device is that it can lower phase transition temperature and significantly enhance the magnetic properties by a pulsed single shot exposure

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.

Phase transition of the nucleon-antinucleon plasma at different ratios

International Nuclear Information System (INIS)

Delfino, A.; Jansen, M.; Timoteo, V. S.

2008-01-01

We investigate phase transitions for the Walecka model at very high temperatures. As is well known, depending on the parametrization of this model and for the particular case of a zero chemical potential (μ), a first-order phase transition is possible [J. Theis, G. Graebner, G. Buchwald, J. A. Maruhn, W. Greiner, H. Stocker, and J. Polonyi, Phys. Rev. D 28, 2286 (1983)]. We investigate this model for the case in which μ≠0. It turns out that, in this situation, phases with different values of antinucleon-nucleon ratios and net baryon densities may coexist. We present the temperature versus antinucleon-nucleon ratio as well as the temperature versus the net baryon density for the coexistence region. The temperature versus chemical potential phase diagram is also presented

Phase competition and anomalous thermal evolution in high-temperature superconductors

Science.gov (United States)

Yu, Zuo-Dong; Zhou, Yuan; Yin, Wei-Guo; Lin, Hai-Qing; Gong, Chang-De

2017-07-01

The interplay of competing orders is relevant to high-temperature superconductivity known to emerge upon suppression of a parent antiferromagnetic order typically via charge doping. How such interplay evolves at low temperature—in particular at what doping level the zero-temperature quantum critical point (QCP) is located—is still elusive because it is masked by the superconducting state. The QCP had long been believed to follow a smooth extrapolation of the characteristic temperature T* for the strange normal state well above the superconducting transition temperature. However, recently the T* within the superconducting dome was reported to unexpectedly exhibit back-bending likely in the cuprate Bi2Sr2CaCu2O8 +δ . Here we show that the original and revised phase diagrams can be understood in terms of weak and moderate competitions, respectively, between superconductivity and a pseudogap state such as d -density or spin-density wave, based on both Ginzburg-Landau theory and the realistic t -t'-t''-J -V model for the cuprates. We further found that the calculated temperature and doping-level dependence of the quasiparticle spectral gap and Raman response qualitatively agrees with the experiments. In particular, the T* back-bending can provide a simple explanation of the observed anomalous two-step thermal evolution dominated by the superconducting gap and the pseudogap, respectively. Our results imply that the revised phase diagram is likely to take place in high-temperature superconductors.

Magnetic properties of Gd5(Si1.5Ge2.5) near the temperature and magnetic field induced first order phase transition

International Nuclear Information System (INIS)

Levin, E.M.; Gschneidner, K.A.; Pecharsky, V.K.

2001-01-01

The temperature (from 5 to 300 K) and DC magnetic field (from 0 to 90 kOe) dependencies of the DC magnetization and magnetic susceptibility, and the temperature (from 5 to 350 K) dependency of the AC magnetic susceptibility of Gd 5 (Si 1.5 Ge 2.5 ) have been studied. The temperature and/or magnetic field induced magnetic phase transition in Gd 5 (Si 1.5 Ge 2.5 ) is a first order ferromagnet-paramagnet transition. The temperature of the magnetic transition in low AC magnetic field is 206 and 217 K for cooling and heating, respectively. The DC magnetic field increases the transition temperature by ∼0.36 K/kOe indicating that the paramagnetic phase can be reversibly transformed into the ferromagnetic phase. When the magnetic field is removed, the ferromagnetic phase transforms into the paramagnetic phase showing a large remanence-free hysteresis. The magnetic phase diagram based on the isothermal magnetic field dependence of the DC magnetization at various temperatures for Gd 5 (Si 1.5 Ge 2.5 ) is proposed. The magnetic field dependence of the magnetization in the vicinity of the first order phase transition shows evidence for the formation of a magnetically heterogeneous system in the volume of Gd 5 (Si 1.5 Ge 2.5 ) specimen where the magnetically ordered (ferromagnetic) and disordered (paramagnetic) phases co-exist

Dielectric behavior and phase transition in [111]-oriented PIN–PMN–PT single crystals under dc bias

Directory of Open Access Journals (Sweden)

Yuhui Wan

2014-01-01

Full Text Available Temperature and electric field dependences of the dielectric behavior and phase transition for [111]-oriented 0.23PIN–0.52PMN–0.25PT (PIN-PMN–0.25PT and 0.24PIN–0.43PMN–0.33PT (PIN–PMN–0.33PT single crystals were investigated over a temperature range from -100°C to 250°C using field-heating (FH dielectric measurements. The transition phenomenon from ferroelectric microdomain to macrodomain was found in rhombohedra (R phase region in the single crystals under dc bias. This transition temperature Tf of micro-to-macrodomain is sensitive to dc bias and move quickly to lower temperature with increasing dc bias. The phase transition temperatures in the two single crystals shift toward high temperature and the dielectric permittivities at the phase transition temperature decrease with increasing dc bias. Especially, the phase transition peaks are gradually broad in PIN–PMN–0.33PT single crystal with the increasing dc bias. Effects of dc bias on the dielectric behavior and phase transition in PIN–PMN–PT single crystals are discussed.

Phenomenology of cosmic phase transitions

International Nuclear Information System (INIS)

Kaempfer, B.; Lukacs, B.; Paal, G.

1989-11-01

The evolution of the cosmic matter from Planck temperature to the atomic combination temperature is considered from a phenomenological point of view. Particular emphasis is devoted to the sequence of cosmic phase transitions. The inflationary era at the temperature of the order of the grand unification energy scale and the quantum chromodynamic confinement transition are dealt with in detail. (author) 131 refs.; 26 figs

Solid-solid phase transitions in Fe nanowires induced by axial strain

International Nuclear Information System (INIS)

Sandoval, Luis; Urbassek, Herbert M

2009-01-01

By means of classical molecular-dynamics simulations we investigate the solid-solid phase transition from a bcc to a close-packed crystal structure in cylindrical iron nanowires, induced by axial strain. The interatomic potential employed has been shown to be capable of describing the martensite-austenite phase transition in iron. We study the stress versus strain curves for different temperatures and show that for a range of temperatures it is possible to induce a solid-solid phase transition by axial strain before the elasticity is lost; these transition temperatures are below the bulk transition temperature. The two phases have different (non-linear) elastic behavior: the bcc phase softens, while the close-packed phase stiffens with temperature. We also consider the reversibility of the transformation in the elastic regimes, and the role of the strain rate on the critical strain necessary for phase transition.

Phase transitions and steady-state microstructures in a two-temperature lattice-gas model with mobile active impurities

DEFF Research Database (Denmark)

Henriksen, Jonas Rosager; Sabra, Mads Christian; Mouritsen, Ole G.

2000-01-01

The nonequilibrium, steady-state phase transitions and the structure of the different phases of a two-dimensional system with two thermodynamic temperatures are studied via a simple lattice-gas model with mobile active impurities ("hot/cold spots'') whose activity is controlled by an external drive...... on the temperatures, microstructured phases of both lamellar and droplet symmetry arise, described by a length scale that is determined by the characteristic temperature controlling the diffusive motion of the active impurities....

Electroweak phase transitions

International Nuclear Information System (INIS)

Anderson, G.W.

1991-01-01

An analytic treatment of the one Higgs doublet, electroweak phase transition is given. The phase transition is first order, occurs by the nucleation of thin walled bubbles and completes at a temperature where the order parameter, left-angle φ right-angle T is significantly smaller than it is when the origin becomes absolutely unstable. The rate of anomalous baryon number violation is an exponentially function of left-angle φ right-angle T . In very minimal extensions of the standard model it is quite easy to increase left-angle φ right-angle T so that anomalous baryon number violation is suppressed after completion of the phase transition. Hence baryogenesis at the electroweak phase transition is tenable in minimal of the standard model. In some cases additional phase transitions are possible. For a light Higgs boson, when the top quark mass is sufficiently large, the state where the Higgs field has a vacuum expectation value left-angle φ right-angle = 246 GeV is not the true minimum of the Higgs potential. When this is the case, and when the top quark mass exceeds some critical value, thermal fluctuations in the early universe would have rendered the state left-angle φ right-angle = 246 GeV unstable. The requirement that the state left-angle φ right-angle = 246 GeV is sufficiently long lived constrains the masses of the Higgs boson and the top quark. Finally, we consider whether local phase transitions can be induced by heavy particles which act as seeds for deformations in the scalar field

Fermion condensation quantum phase transition versus conventional quantum phase transitions

International Nuclear Information System (INIS)

Shaginyan, V.R.; Han, J.G.; Lee, J.

2004-01-01

The main features of fermion condensation quantum phase transition (FCQPT), which are distinctive in several aspects from that of conventional quantum phase transition (CQPT), are considered. We show that in contrast to CQPT, whose physics in quantum critical region is dominated by thermal and quantum fluctuations and characterized by the absence of quasiparticles, the physics of a Fermi system near FCQPT or undergone FCQPT is controlled by the system of quasiparticles resembling the Landau quasiparticles. Contrary to the Landau quasiparticles, the effective mass of these quasiparticles strongly depends on the temperature, magnetic fields, density, etc. This system of quasiparticles having general properties determines the universal behavior of the Fermi system in question. As a result, the universal behavior persists up to relatively high temperatures comparatively to the case when such a behavior is determined by CQPT. We analyze striking recent measurements of specific heat, charge and heat transport used to study the nature of magnetic field-induced QCP in heavy-fermion metal CeCoIn 5 and show that the observed facts are in good agreement with our scenario based on FCQPT and certainly seem to rule out the critical fluctuations related with CQPT. Our general consideration suggests that FCQPT and the emergence of novel quasiparticles near and behind FCQPT and resembling the Landau quasiparticles are distinctive features intrinsic to strongly correlated substances

Ge(001)-(<2 1>, <0 3>)-Pb(<2 1>, <0 6>)↔Pb: Low-temperature two-dimensional phase transition

DEFF Research Database (Denmark)

Bunk, Oliver; Nielsen, Martin Meedom; Zeysing, J.H.

2001-01-01

The Ge(001)-((2 1)(0 3))-Pb surface reconstruction with a lead coverage of 5/3 monolayer is on the borderline between the low-coverage covalently-bonded and high-coverage metallic lead overlayers. This gives rise to an unusual low-temperature phase transition with concomitant changes in the bonding...

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

Hadronization during quark-gluon plasma phase transition

International Nuclear Information System (INIS)

Mohanty, A.K.; Kataria, S.K.

1996-01-01

The hadron multiplicity distributions and factorial moments are studied in the framework of Landau theory of phase transitions. The factorial moments show a scaling law with a scaling exponent ν which characterizes the intermittency properties of the hadron phase for T c (or T t ) where T c (or T t ) is the transition temperature for second (or first) order transition. The scaling exponent ν is weakly dependent on the free energy parameters as well as on temperature. It is shown that ν remains practically constant in the hadron phase for which T c or T t whether the transition is second order or first order of second kind where the free energy expansion includes cubic term. This universality in the scaling exponent is also maintained above T c over a wide range of temperature even if the transition is strongly first order of first kind where the free energy expansion has only even order coefficients, except around the critical temperature T t where T t approx-gt T c . Therefore, the scaling exponent ν is rather more universal and only indicates the presence of a possible phase transition. It is further shown that the hadron multiplicity distribution is quite sensitive to the free energy parameters. The study of hadron multiplicity distribution at various resolution or bin size reveals more information about the dynamics of the phase transition. The calculated hadron multiplicity distributions are also compared with the negative binomial distribution, often used to explain the experimental multiplicity distributions. copyright 1996 The American Physical Society

Infrared properties of the organic semiconductor MEM(TCNQ)2 in its high-temperature phase

DEFF Research Database (Denmark)

Yartsev, V. M.; Jacobsen, Claus Schelde

1981-01-01

The infrared spectrum of N-methyl-N-ethylmorpholinium tetra-cyanoquinodimethane, MEM(TCNQ)2, at temperatures above the phase transition at T=335 K is reported. The oscillator strength associated with chargetransfer processes is shifted down in frequency as compared to the room-temperature phase. ...

Monitoring of temperature-mediated phase transitions of adipose tissue by combined optical coherence tomography and Abbe refractometry.

Science.gov (United States)

Yanina, Irina Y; Popov, Alexey P; Bykov, Alexander V; Meglinski, Igor V; Tuchin, Valery V

2018-01-01

Observation of temperature-mediated phase transitions between lipid components of the adipose tissues has been performed by combined use of the Abbe refractometry and optical coherence tomography. The phase transitions of the lipid components were clearly observed in the range of temperatures from 24°C to 60°C, and assessed by quantitatively monitoring the changes of the refractive index of 1- to 2-mm-thick porcine fat tissue slices. The developed approach has a great potential as an alternative method for obtaining accurate information on the processes occurring during thermal lipolysis. (2018) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE).

Magnetic phase transitions and large magnetic entropy change with a wide temperature span in HoZn

Energy Technology Data Exchange (ETDEWEB)

Li, Lingwei, E-mail: wei0396@hotmail.com [Key Laboratory of Electromagnetic Processing of Materials (Ministry of Education), Northeastern University, Shenyang 110819 (China); Institut für Anorganische und Analytische Chemie, Universität Münster, Corrensstrasse 30, D-48149 Münster (Germany); Yuan, Ye [Helmholtz-Zentrum Dresden-Rossendorf (HZDR), Institute of Ion Beam Physics and Materials Research, P.O. Box 510119, 01314 Dresden (Germany); Zhang, Yikun [Key Laboratory of Electromagnetic Processing of Materials (Ministry of Education), Northeastern University, Shenyang 110819 (China); Pöttgen, Rainer [Institut für Anorganische und Analytische Chemie, Universität Münster, Corrensstrasse 30, D-48149 Münster (Germany); Zhou, Shengqiang [Helmholtz-Zentrum Dresden-Rossendorf (HZDR), Institute of Ion Beam Physics and Materials Research, P.O. Box 510119, 01314 Dresden (Germany)

2015-09-15

Highlights: • Magnetic phase transitions and magnetocaloric effect in HoZn were studied. • The critical properties of HoZn were systematically investigated. • The obtained critical exponents are satisfied with scaling theory. • A large reversible magnetocaloric effect in HoZn was observed. • HoZn could be a promising candidate for magnetic refrigeration. - Abstract: CsCl-type HoZn undergoes two successive magnetic phase transitions: (i) paramagnetic to ferromagnetic (FM) at T{sub C} ∼ 72 K and (ii) a spin reorientation (SR) at T{sub SR} ∼ 26 K. Magnetization and modified Arrott plots indicate that HoZn undergoes a second-order magnetic phase transition around T{sub C}. The obtained critical exponents have some small deviations from the mean-field theory, indicating a short range or a local magnetic interaction which is properly related to the coexistence of FM and SR transitions at low temperature. Two successive magnetic transitions in HoZn induce one broad pronounced peak together with a shoulder in the temperature dependence of the magnetic entropy change −ΔS{sub M}(T) curves, resulting in a wide temperature range with a large relative cooling power (RCP). For a field change of 0–7 T, the maximum value of −ΔS{sub M} is 15.2 J/kg K around T{sub C} with a large RCP value of 1124 J/kg. The large reversible magnetocaloric effect (MCE) and RC indicate that HoZn is a good candidate for active magnetic refrigeration.

Structural, magnetic and superconducting phase transitions in CaFe2As2 under ambient and applied pressure

International Nuclear Information System (INIS)

Canfield, P.C.; Bud'ko, S.L.; Ni, N.; Kreyssig, A.; Goldman, A.I.; McQueeney, R.J.; Torikachvili, M.S.; Argyriou, D.N.; Luke, G.; Yu, W.

2009-01-01

At ambient pressure CaFe 2 As 2 has been found to undergo a first order phase transition from a high temperature, tetragonal phase to a low-temperature orthorhombic/antiferromagnetic phase upon cooling through T ∼ 170 K. With the application of pressure this phase transition is rapidly suppressed and by ∼0.35 GPa it is replaced by a first order phase transition to a low-temperature collapsed tetragonal, non-magnetic phase. Further application of pressure leads to an increase of the tetragonal to collapsed tetragonal phase transition temperature, with it crossing room temperature by ∼1.7 GPa. Given the exceptionally large and anisotropic change in unit cell dimensions associated with the collapsed tetragonal phase, the state of the pressure medium (liquid or solid) at the transition temperature has profound effects on the low-temperature state of the sample. For He-gas cells the pressure is as close to hydrostatic as possible and the transitions are sharp and the sample appears to be single phase at low temperatures. For liquid media cells at temperatures below media freezing, the CaFe 2 As 2 transforms when it is encased by a frozen media and enters into a low-temperature multi-crystallographic-phase state, leading to what appears to be a strain stabilized superconducting state at low temperatures.

Phase transitions in huddling emperor penguins

Science.gov (United States)

Richter, S.; Gerum, R.; Winterl, A.; Houstin, A.; Seifert, M.; Peschel, J.; Fabry, B.; Le Bohec, C.; Zitterbart, D. P.

2018-05-01

Emperor penguins (Aptenodytes forsteri) are highly adapted to the harsh conditions of the Antarctic winter: they are able to fast for up to 134 days during breeding. To conserve energy, emperor penguins form tight groups (huddles), which is key for their reproductive success. The effect of different meteorological factors on the huddling behaviour, however, is not well understood. Using time-lapse image recordings of an emperor penguin colony, we show that huddling can be described as a phase transition from a fluid to a solid state. We use the colony density as order parameter, and an apparent temperature that is perceived by the penguins as the thermodynamic variable. We approximate the apparent temperature as a linear combination of four meteorological parameters: ambient temperature, wind speed, global radiation and relative humidity. We find a wind chill factor of  ‑2.9 , a humidity chill factor of  ‑0.5 rel. humidity, and a solar radiation heating factor of 0.3 . In the absence of wind, humidity and solar radiation, the phase transition temperature (50% huddling probability) is  ‑48.2 °C for the investigated time period (May 2014). We propose that higher phase transition temperatures indicate a shrinking thermal insulation and thus can serve as a proxy for lower energy reserves of the colony, integrating pre-breeding foraging success at sea and energy expenditure at land due to environmental conditions. As current global change is predicted to have strong detrimental effects on emperor penguins within the next decades, our approach may thus contribute towards an urgently needed long-term monitoring system for assessing colony health.

Phase transitions of sodium niobate powder and ceramics, prepared by solid state synthesis

Science.gov (United States)

Koruza, J.; Tellier, J.; Malič, B.; Bobnar, V.; Kosec, M.

2010-12-01

Phase transitions of sodium niobate, prepared by the solid state synthesis method, were examined using dielectric measurements, differential scanning calorimetry, and high temperature x-ray diffraction, in order to contribute to the clarification of its structural behavior below 400 °C. Four phase transitions were detected in the ceramic sample using dielectric measurements and differential scanning calorimetry and the obtained temperatures were in a good agreement with previous reports for the transitions of the P polymorph. The anomaly observed by dielectric measurements in the vicinity of 150 °C was frequency dependent and could be related to the dynamics of the ferroelectric nanoregions. The phase transitions of the as-synthesized NaNbO3 powder were investigated using differential scanning calorimetry and high temperature x-ray diffraction. The results show the existence of the Q polymorph at room temperature, not previously reported for the powder, which undergoes a transition to the R polymorph upon heating through a temperature region between 265 and 326.5 °C. This transition is mainly related to the displacement of Na into a more symmetric position and a minor change in the tilting system. The structures at room temperature, 250, 300, and 420 °C were refined by the Rietveld method and the evolution of the tilting system of the octahedral network and cationic displacement are reported.

Phase transitions of sodium niobate powder and ceramics, prepared by solid state synthesis

International Nuclear Information System (INIS)

Koruza, J.; Tellier, J.; Malic, B.; Bobnar, V.; Kosec, M.

2010-01-01

Phase transitions of sodium niobate, prepared by the solid state synthesis method, were examined using dielectric measurements, differential scanning calorimetry, and high temperature x-ray diffraction, in order to contribute to the clarification of its structural behavior below 400 deg. C. Four phase transitions were detected in the ceramic sample using dielectric measurements and differential scanning calorimetry and the obtained temperatures were in a good agreement with previous reports for the transitions of the P polymorph. The anomaly observed by dielectric measurements in the vicinity of 150 deg. C was frequency dependent and could be related to the dynamics of the ferroelectric nanoregions. The phase transitions of the as-synthesized NaNbO 3 powder were investigated using differential scanning calorimetry and high temperature x-ray diffraction. The results show the existence of the Q polymorph at room temperature, not previously reported for the powder, which undergoes a transition to the R polymorph upon heating through a temperature region between 265 and 326.5 deg. C. This transition is mainly related to the displacement of Na into a more symmetric position and a minor change in the tilting system. The structures at room temperature, 250, 300, and 420 deg. C were refined by the Rietveld method and the evolution of the tilting system of the octahedral network and cationic displacement are reported.

Infield X-ray diffraction studies of field and temperature driven structural phase transition in Nd{sub 0.49}Sr{sub 0.51}MnO{sub 3+δ}

Energy Technology Data Exchange (ETDEWEB)

Shahee, Aga, E-mail: agashahee@gmail.com [UGC-DAE Consortium for Scientific Research, University Campus, Khandwa Road, Indore 452001 (India); Department of Physics, IIT Bombay, Powai, Mumbai 400076 (India); Sharma, Shivani; Singh, K.; Lalla, N.P. [UGC-DAE Consortium for Scientific Research, University Campus, Khandwa Road, Indore 452001 (India)

2017-07-15

Highlights: • Temperature and magnetic field driven coupled magneto-structural phase transition in Nd{sub 0.49}Sr{sub 0.51}MnO{sub 3+δ}. • Microscopic evidence of strong spin-charge-lattice coupling. • Iso-thermal magnetic field driven structure phase transition. • Field-driven structural phase transition origin of observed 1st order type CMR effect. - Abstract: Comprehensive X-ray diffraction (XRD) studies have been performed at different temperature (T) (4.2–300 K) and magnetic field (H) (0–8 T) to understand the evolution of crystal structure of Nd{sub 0.49}Sr{sub 0.51}MnO{sub 3+δ} (NSMO) under non ambient conditions. The T dependent XRD results show the abrupt change in the lattice parameters without any change in lattice symmetry at ∼200 K, which is associated with the first order structural phase transition from ferromagnetic to antiferromagnetic phase. This phase transition is strongly H dependent and shifted to lower temperature (∼150 K) on the application of 8 T field with phase coexistence (high temperature phase ∼18%), even down to 4.2 K. Isothermal XRD results at 150 K under different H clearly illustrate the H induced first order structural phase transition. The critical H at which this phase transformation starts is ∼1 T, with rapid growth above 4 T with hysteretic nature during increasing and decreasing H. These results are supported with the resistivity and magnetoresistance results and affirm the strong spin-lattice coupling in NSMO. Our detail studies reveal the structural correlations to the observed colossal magnetoresistance and magnetocaloric effect in this material.

About the dynamics of structural phase transitions

International Nuclear Information System (INIS)

Medeiros, J.T.N.

1975-01-01

The dynamics of structural phase transitions with a fourth order interaction between the soft phonon fields is studied in the 1/n approximation, using many body methods at finite temperatures. Two limits are considered: high transition temperature T sub(c) (classical limit) and T sub(c) = 0 (quantum limit). The dynamical contribution to the critical coefficient eta of the correlation function is calculated in these limits. It is found that there is no dynamical contribution to eta in the classical limit, whereas in the quantum limit eta is non-zero only for dimensions of the system d [pt

Low temperature phase of the trigonal RbIn(MoO4)2 crystal

Science.gov (United States)

Zapart, W.; Zapart, M. B.; Schranz, W.; Reinecker, M.

2013-02-01

The present article is devoted to a new low-temperature phase transition found at about T pt = 84 K in the layered RbIn(MoO4)2 crystal. This phase transition is well proved by dynamical mechanical analysis through anomalies in the temperature behaviour of both real and imaginary parts of the Young's modulus. From the polarizing microscope observations it was found that below T pt the ferroelastic phase disappears. This transition has also been seen through strong changes in the shape of the electron paramagnetic resonance lines. EPR studies, performed in the liquid nitrogen temperature, yield evidence of strong rebuilding of the crystal unit cell in comparison with that of the high temperature paraelastic phase.

Structural Phase Transition Nomenclature, Report of an IUCr Working Group on Phase Transition Nomenclature

NARCIS (Netherlands)

Toleddano, J.C.; Glazer, A.M.; Hahn, Th.; Parthe, E.; Roth, R.S.; Berry, R.S.; Metselaar, R.; Abrahams, S.C.

1998-01-01

A compact and intuitive nomenclature is recommended for naming each phase formed by a given material in a sequence of phase transitions as a function of temperature and/or pressure. The most commonly used label for each phase in a sequence, such as [alpha], [beta], ..., I, II, ... etc., is included

Two-phase coexistence in the monovalent-to-divalent phase transition of dineopentylbiferrocene-fluorotetracyanoquinodimethane [npBifc-(F1TCNQ)3], charge-transfer salt

International Nuclear Information System (INIS)

Uruichi, Mikio; Yue, Yue; Yakushi, Kyuya; Mochida, Tomoyuki

2007-01-01

We present experimental findings showing that for npBifc-(F 1 TCNQ) 3 , two phases coexist over a wide temperature interval of 100-150 K near the monovalent-to-divalent phase transition temperature. Macroscopic domains of the high-temperature (monovalent) and low-temperature (divalent) phases were detected in the transition temperature region using X-ray diffraction and micro-Raman spectroscopy techniques. The volume fraction of the two domains continuously varied depending upon the temperature. A considerably large volume difference was found between the monovalent and divalent phases. The effect of volumetric strain due to this volume difference is discussed to understand this inhomogeneous state. (author)

Phase transition study in strongly correlated VO{sub 2} based sensing systems

Energy Technology Data Exchange (ETDEWEB)

Simo, A., E-mail: alinesimo.aline@gmail.com [UNESCO-UNISA Africa Chair in Nanoscience’s/Nanotechnology, College of Graduate Studies, University of South Africa, Muckleneuk ridge, P.O. Box 392, Pretoria (South Africa); Nanosciences African Network (NANOAFNET), iThemba LABS-National Research Foundation, 1 Old Faure road, Somerset West 7129, P.O. Box 722, Somerset West, Western Cape Province (South Africa); Kaviyarasu, K. [UNESCO-UNISA Africa Chair in Nanoscience’s/Nanotechnology, College of Graduate Studies, University of South Africa, Muckleneuk ridge, P.O. Box 392, Pretoria (South Africa); Nanosciences African Network (NANOAFNET), iThemba LABS-National Research Foundation, 1 Old Faure road, Somerset West 7129, P.O. Box 722, Somerset West, Western Cape Province (South Africa); Mwakikunga, B. [Council for Scientific and Industrial Research, P.O. Box 395, Pretoria 0001 (South Africa); Madjoe, R. [Physics Department, University of Western Cape, 7535 Belville Cape Town (South Africa); Gibaud, A. [Laboratoire de Physique de l’Etat Condensé, Université du Maine Faculte des sciences, UPRESA 6087, 72085, Le Mans Cedex 9 (France); Maaza, M. [UNESCO-UNISA Africa Chair in Nanoscience’s/Nanotechnology, College of Graduate Studies, University of South Africa, Muckleneuk ridge, P.O. Box 392, Pretoria (South Africa); Nanosciences African Network (NANOAFNET), iThemba LABS-National Research Foundation, 1 Old Faure road, Somerset West 7129, P.O. Box 722, Somerset West, Western Cape Province (South Africa)

2017-04-15

Highlights: • At 230 °C for about 48 h to prepare successfully VO{sub 2} nanobelts. • 1D shows good sensing performance due to the large active surface of the material. • The good selectivity of methanol compared to acetone and isopropanol. • VOC compounds was observed at room temperature. - Abstract: Intermediate phase monoclinic M2 was observed by inducing in situ X-ray thermo diffraction on VO{sub 2} (M) nanoplatelets. The solid-solid phase transition occurs at around 65 °C assisted with the percolative transition metal-insulator. The existence of an intermediate crystalline phase with room temperature insulator phase and high temperature metallic phase across MIT in VO{sub 2} could be of relevance to understand structural contributions to the phase transition dynamics. In addition, pellet of VO{sub 2} nanostructures have shown to present good sensing properties to various alcohols vapors at room temperature and good selectivity of methanol with 5.54% sensitivity and limit detection below 5 ppm, compared to isopropanol 3.2% and acetone 2.4% respectively.

Oxygen vacancies dependent phase transition of Y{sub 2}O{sub 3} films

Energy Technology Data Exchange (ETDEWEB)

Yu, Pengfei; Zhang, Kan [Department of Materials Science, State Key Laboratory of Superhard Materials, and Key Laboratory of Automobile Materials, MOE, Jilin University, Changchun 130012 (China); Huang, Hao [Titanium Alloys Lab. Beijing Institute of Aeronautical Materials, Beijing 81-15 100095 (China); Wen, Mao, E-mail: Wenmao225@jlu.edu.cn [Department of Materials Science, State Key Laboratory of Superhard Materials, and Key Laboratory of Automobile Materials, MOE, Jilin University, Changchun 130012 (China); Li, Quan; Zhang, Wei; Hu, Chaoquan [Department of Materials Science, State Key Laboratory of Superhard Materials, and Key Laboratory of Automobile Materials, MOE, Jilin University, Changchun 130012 (China); Zheng, Weitao, E-mail: WTZheng@jlu.edu.cn [Department of Materials Science, State Key Laboratory of Automotive Simulation and Control and Key Laboratory of Automobile Materials, MOE, Jilin University, Changchun 130012 (China)

2017-07-15

Highlights: • Oxygen vacancies for Y{sub 2}O{sub 3} films increase monotonously with increasing T{sub s}. • Oxygen vacancies can promote the nucleation of monoclinic phase. • That monoclinic phase with oxygen deficiency is not thermodynamic stable at high temperature. • Phase transition from monoclinic to oxygen defective occurs at high concentrations of oxygen vacancies. • High hardness just appears in Y{sub 2}O{sub 3} films with mixed phase configurations. - Abstract: Y{sub 2}O{sub 3} films have great application potential in high-temperature metal matrix composite and nuclear engineering, used as interface diffusion and reaction barrier coating owing to their excellent thermal and chemical stability, high melting point and extremely negative Gibbs formation energy, and thus their structural and mechanical properties at elevated temperature are especially important. Oxygen vacancies exist commonly in yttrium oxide (Y{sub 2}O{sub 3}) thin films and act strongly on the phase structure and properties, but oxygen vacancies dependent phase transition at elevated temperature has not been well explored yet. Y{sub 2}O{sub 3} thin films with different oxygen vacancy concentrations have been achieved by reactive sputtering through varying substrate temperature (T{sub s}), in which oxygen vacancies increase monotonously with increasing T{sub s}. For as-deposited Y{sub 2}O{sub 3} films, oxygen vacancies present at high T{sub s} can promote the nucleation of monoclinic phase, meanwhile, high T{sub s} can induce the instability of monoclinic phase. Thus their competition results in forming mixed phases of cubic and monoclinic at high T{sub s}. During vacuum annealing at 1000 °C, a critical oxygen vacancy concentration is observed, below which phase transition from monoclinic to cubic takes place, and above which phase transfer from monoclinic to the oxygen defective phase (ICDD file no. 39-1063), accompanying by stress reversal from compressive to tensile and

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.

High temperature series expansions with a multiple-exchange Hamiltonian for the bcc and hcp phases of solid 3He

International Nuclear Information System (INIS)

Roger, M.; Suaudeau, E.; Bernier, M.E.R.

1987-08-01

High temperature series expansions with a multiple-exchange Hamiltonian are performed to fourth order in arbitrary magnetic field for both phases of solid 3 He. The susceptibility series are analysed with Pade approximants and compared with recent experimental results. For the hcp phase we estimate the ferromagnetic ordering temperature from susceptibility series and discuss the influence of four-particle exchange in lowering the transition

Rubberlike Dynamics in Sulphur above the λ-Transition Temperature

International Nuclear Information System (INIS)

Monaco, G.; Crapanzano, L.; Crichton, W.; Mezouar, M.; Verbeni, R.; Bellissent, R.; Fioretto, D.; Scarponi, F.

2005-01-01

The high-frequency acoustic dynamics of sulfur across the liquid-liquid, λ transition has been studied using inelastic x-ray scattering. The combination of these high-frequency data with lower frequency, literature data indicates that liquid sulfur develops, in the high-temperature, polymeric solution phase, some characteristic features of a rubber. In particular, entanglement coupling among polymeric chains plays a relevant role in the dynamics of this liquid phase

The high temperature orthorhombic ⇄ hexagonal phase transformation of FeMnP

Science.gov (United States)

Chenevier, B.; Soubeyroux, J. L.; Bacmann, M.; Fruchart, D.; Fruchart, R.

1987-10-01

The compound FeMnP has the hexagonal Fe 2P structure above 1473K. The metal atoms are disordered. The disorder rate decreases with temperature and at 1413K a transition Hex → Orth. takes place. The low temperature phase is of Co 2P type. A simple transition model is proposed based on the displacement of phosphorus chains along the shortest axis of the structure. The thermal evolution of the orthorhombic cell parameters evidences the strong anisotropy of the bondings.

Order-disorder phase transition in ZrV2Dsub(3.6)

International Nuclear Information System (INIS)

Didisheim, J.-J.; Yvon, K.; Tissot, P.

1981-01-01

The deuterated C15-type Laves phase ZrV 2 Dsub(3.6) undergoes a structural phase transition near room temperature (T of the order of 325 K). In the cubic high-temperature phase the deuterium atoms are disordered over two types of tetrahedral interstices, the centres of which are 1.3 A apart. In the tetragonal low-temperature phase the D atoms are ordered and occupy only the energetically more favourable interstices. The tetragonal structure is isotypic with the low-temperature phase of HfV 2 D 4 . The shortest D-D distance is 2.1 A. (author)

Phase Transition and Thermodynamics of Ruthenium Diboride via First-Principles Calculations

International Nuclear Information System (INIS)

Fen, Luo; Yan, Cheng; Xiang-Rong, Chen; Guang-Fu, Ji

2009-01-01

The pressure induced phase transitions of RuB 2 from the OsB 2 -type structure to the ReB 2 -type structure are investigated by first-principles calculations based on the plane-wave basis set with the generalized gradient approximation for exchange and correlation. It is found that the phase transition occurs at 18.6 GPa. We predict the phase transition from the OsB 2 -type RuB 2 to the ReB 2 -type RuB 2 at high temperatures for the first time. The dependences of the heat capacity, thermal expansion coefficient, and the Grüneisen parameter on pressure and temperature for OsB 2 -type RuB 2 and ReB 2 -type RuB 2 are also investigated

Martensitic phase transitions in Co-0.85 at % Fe

International Nuclear Information System (INIS)

Prem, M.

1997-12-01

Co-0.85at%Fe shows the two martensitic phase transitions hcp-dhcp and dhcp-fcc. The lattice dynamics of Co-0.85at%Fe was investigated by the means of inelastic neutron scattering at a series of temperatures up to 750K in order to understand the two martensitic phase transitions of this system. In all of the measured phonon branches anomalies were neither found near the hcp-dhcp phase transition nor going through the dhcp-fcc transition. Lattice-parameter scans were performed through the whole temperature range. Diffuse neutron scattering revealed a lattice parameter shift between the dhcp and fcc phase of ∼0.4 % measured at the same temperature. This was possible because the system shows a wide temperature hysteresis at the two phase transitions. In the temperature region of coexistence of dhcp and fcc phase diffuse satellites arose near the (111)fcc Bragg peak (which is equivalent to the (00.2)dhcp peak). Their intensity varied in accordance to the volume fraction of the phases but vanished on changing wavelength. The elastic measurements were performed at the Austrian triple axis spectrometer VALSE located at the Laboratoire Leon Brillouin (LLB) in Saclay (F); the inelastic measurements were performed at the spectrometers IN3 and INS of the Institute Laue Langevin (ILL) in Grenoble (F). (author)

Antiferrodistortive phase transitions and ground state of PZT ceramics

International Nuclear Information System (INIS)

Pandey, Dhananjai

2013-01-01

The ground state of the technologically important Pb(Zr x Ti (1-x) )O 3 , commonly known as PZT, ceramics is currently under intense debate. The phase diagram of this material shows a morphotropic phase boundary (MPB) for x∼0.52 at 300K, across which a composition induced structural phase transition occurs leading to maximization of the piezoelectric properties. In search for the true ground state of the PZT in the MPB region, Beatrix Noheda and coworkers first discovered a phase transition from tetragonal (space group P4mm) to an M A type monoclinic phase (space group Cm) at low temperatures for x=0.52. Soon afterwards, we discovered yet another low temperature phase transition for the same composition in which the M A type (Cm) monoclinic phase transforms to another monoclinic phase with Cc space group. We have shown that the Cm to Cc phase transition is an antiferrodistortive (AFD) transition involving tilting of oxygen octahedra leading to unit cell doubling and causing appearance of superlattice reflections which are observable in the electron and neutron diffraction patterns only and not in the XRD patterns, as a result of which Noheda and coworkers missed the Cc phase in their synchrotron XRD studies at low temperatures. Our findings were confirmed by leading groups using neutron, TEM, Raman and high pressure diffraction studies. The first principles calculations also confirmed that the true ground state of PZT in the MPB region has Cc space group. However, in the last couple of years, the Cc space group of the ground state has become controversial with an alternative proposal of R3c as the space group of the ground state phase which is proposed to coexist with the metastable Cm phase. In order to resolve this controversy, we recently revisited the issue using pure PZT and 6% Sr 2+ substituted PZT, the latter samples show larger tilt angle on account of the reduction in the average cationic radius at the Pb 2+ site. Using high wavelength neutrons and high

Anelasticity maps for acoustic dissipation associated with phase transitions in minerals

Science.gov (United States)

Carpenter, Michael A.; Zhang, Zhiying

2011-07-01

Acoustic dissipation due to structural phase transitions in minerals could give rise to large seismic attenuation effects superimposed on the high temperature background contribution from dislocations and grain boundaries in the Earth. In addition to the possibility of a sharp peak actually at a transition point for both compressional and shear waves, significant attenuation might arise over wider temperature intervals due to the mobility of transformation twins or other defects associated with the transition. Attenuation due to structural phase transitions in quartz, pyroxenes, perovskites, stishovite and hollandite, or to spin state transitions of Fe2+ in magnesiowüstite and perovskite and the hcp/bcc transition in iron-nickel (Fe-Ni) alloy, are reviewed from this perspective. To these can be added possible loss behaviour associated with reconstructive transitions which might occur by a ledge mechanism on topotactic interfaces (orthopyroxene/clinopyroxene, olivine/spinel and perovskite/postperovskite), with impurities (Snoek effect) or with mobility of protons. There are experimental difficulties associated with measuring dissipation effects in situ at simultaneous high pressures and temperatures, so reliance is currently placed on investigation of analogue phases such as LaCoO3 for spin-state behaviour and LaAlO3 for the dynamics of ferroelastic twin walls. Similarly, it is not possible to measure loss dynamics simultaneously at the low stresses and low frequencies that pertain in seismic waves, so reliance must be placed on combining different techniques, such as dynamic mechanical analysis (low frequency, relatively high stress) and resonant ultrasound spectroscopy (high frequency, low stress), to extrapolate acoustic loss behaviour over wide frequency, temperature and stress intervals. In this context 'anelasticity maps' provide a convenient means of representing different loss mechanisms. Contouring of the inverse mechanical quality factor, Q-1, can be

Determination of phase transitions in a lyotropic liquid crystal by Positron Annihilation technique

International Nuclear Information System (INIS)

Castillo V, V.M.

1994-01-01

Positron annihilation technique was used to determine the phase transitions in a lyotropic liquid crystal, as a function of temperature. Seven different concentrations of the surfactant cetyldimethylethylammonium bromide, were studied. The liquid crystal studied consisted of a binary system, formed by the surfactant and water. Positron annihilation technique has a very high sensitivity toward changes in the microestructure, in condensed matter, this is useful in order to detect the temperatures at which phase transitions occur and the number of these, in a liquid crystalline system. Thus, phase transitions are related with changes occurred in the ortho-positronium parameters: lifetime (τ 3 ) and intensity of formation (I 3 ). Six different kinds of phases were detected in the system studied in a temperature range of 35 to 140 Centigrade degrees, those phases were: hexagonal, hexagonal-lamellae, lamellae, lamellae-cubic, nematic and anisotropic. Using optical microscopic the textures of these phases were assigned. (Author)

Thermodynamic study of the A-B phase transition in superfluid 3He: Phase diagram and consequences

International Nuclear Information System (INIS)

Hahn, I.

1993-01-01

The authors have measured the A-B phase transition temperature of superfluid 3 He at pressures from zero to 29 bars, and in all magnetic fields up to the high field limit of the B phase (0.59 Tesla). This work is the first precision measurement of the A-B phase transition over the entire phase diagram (P, T, B). Measurements at low magnetic fields can be related to microscopic interactions in liquid 3 He. The results show that all current microscopic models of normal liquid 3 He are incomplete. Also, the results suggest the possibility that the conventional identification of the order parameter of superfluid 3 He-A is incorrect. The measurements at high magnetic fields can be related through thermodynamic identities to quantities which are immeasurable directly, such as the molar volume changes at the A-B phase transition, and the specific heat of the A-phase of superfluid 3 He in the limit T → 0. The authors detect the phase transition by monitoring the attenuation of zero around traversing a 4-mm path in the superfluid. Because thermometry is so crucial to the success of the measurements, the authors elected to use two independent thermometers. The authors use a pulsed NMR measurement of the susceptibility of Pt nuclei, which varies as 1/T, to guarantee linearity of the temperature scale. In order to achieve the high resolution required by the experiment, the authors also use an LCMN thermometer driven by a unique digital bridge which the authors constructed

Dynamic phase transition in the kinetic spin-32 Blume-Capel model: Phase diagrams in the temperature and crystal-field interaction plane

International Nuclear Information System (INIS)

Keskin, Mustafa; Canko, Osman; Deviren, Bayram

2007-01-01

We analyze, within a mean-field approach, the stationary states of the kinetic spin-32 Blume-Capel (BC) model by the Glauber-type stochastic dynamics and subject to a time-dependent oscillating external magnetic field. The dynamic phase transition (DPT) points are obtained by investigating the behavior of the dynamic magnetization as a function of temperature and as well as calculating the Liapunov exponent. Phase diagrams are constructed in the temperature and crystal-field interaction plane. We find five fundamental types of phase diagrams for the different values of the reduced magnetic field amplitude parameter (h) in which they present a disordered, two ordered phases and the coexistences phase regions. The phase diagrams also exhibit a dynamic double-critical end point for 0 5.06

Is the Freeze Drying Method Effect on the Phase Transition Temperature ofβ/β́́ Lithium Zirconium Phosphate?

Directory of Open Access Journals (Sweden)

S. M. Seyedahmadian

2014-07-01

Full Text Available Spherical granules of the superionic conductor β/β́ LiZr2(PO43 in the range of sub 100 nm sizewere synthesizedvia freeze drying methodand fully reviewed in all aspects. Samples were characterized by the X-ray diffractometry (XRD, the Thermal analysis (TG, DSC, theFourier Transform Infra-Red Spectroscopy (FTIR and the Scanning Electron Microscopy (SEM.Their structuredepends largely on the method of synthesis, thermaltreatment, and conditions of storing samples. Degree of Crystallinity and phase purity in different annealing time were tested. The synthesize temperature does not exceed 873 K in any step of the synthesis.The low temperature phases (β with the Pbna space group and β́ with the P21/n space group were preparedat optimum condition. By the Differential Scanning Calorimetry it was shown the phase transition from β↔β́ occurred at about 567-597 K. The temperature of annealing the phosphate and calcination time is not very effective to phase transition temperature.

Phase transitions in dense matter

Science.gov (United States)

Dexheimer, Veronica; Hempel, Matthias; Iosilevskiy, Igor; Schramm, Stefan

2017-11-01

As the density of matter increases, atomic nuclei disintegrate into nucleons and, eventually, the nucleons themselves disintegrate into quarks. The phase transitions (PT's) between these phases can vary from steep first order to smooth crossovers, depending on certain conditions. First-order PT's with more than one globally conserved charge, so-called non-congruent PT's, have characteristic differences compared to congruent PT's. In this conference proceeding we discuss the non-congruence of the quark deconfinement PT at high densities and/or temperatures relevant for heavy-ion collisions, neutron stars, proto-neutron stars, supernova explosions, and compact-star mergers.

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.

Electronic properties and phase transitions in low-dimensional semiconductors

International Nuclear Information System (INIS)

Panich, A M

2008-01-01

We present the first review of the current state of the literature on electronic properties and phase transitions in TlX and TlMX 2 (M = Ga, In; X = Se, S, Te) compounds. These chalcogenides belong to a family of the low-dimensional semiconductors possessing chain or layered structure. They are of significant interest because of their highly anisotropic properties, semi- and photoconductivity, nonlinear effects in their I-V characteristics (including a region of negative differential resistance), switching and memory effects, second harmonic optical generation, relaxor behavior and potential applications for optoelectronic devices. We review the crystal structure of TlX and TlMX 2 compounds, their transport properties under ambient conditions, experimental and theoretical studies of the electronic structure, transport properties and semiconductor-metal phase transitions under high pressure, and sequences of temperature-induced structural phase transitions with intermediate incommensurate states. The electronic nature of the ferroelectric phase transitions in the above-mentioned compounds, as well as relaxor behavior, nanodomains and possible occurrence of quantum dots in doped and irradiated crystals is discussed. (topical review)

High pressure antiferrodistortive phase transition in mixed crystals of EuTiO{sub 3} and SrTiO{sub 3}

Energy Technology Data Exchange (ETDEWEB)

Parisiades, Paraskevas, E-mail: paraskevas.parisiadis@univ-paris-diderot.fr [Laboratoire Matériaux et Phénoménes Quantiques (UMR 7162 CNRS), Université Paris Diderot-Paris 7, Paris Cedex 13 (France); ID27 Beamline, European Synchrotron Radiation Facility, 71 Avenue des Martyrs, 38000 Grenoble (France); Saltarelli, Francesco [Sapienza University of Rome, Physics Dept., Piazzale Aldo Moro 5, 00185 Roma (Italy); Liarokapis, Efthymios [Department of Physics, National Technical University of Athens, GR-15780 Athens (Greece); Köhler, Jürgen; Bussmann-Holder, Annette [Max-Planck-Institute for Solid State Research, Heisenbergstrasse 1, D-70569 Stuttgart (Germany)

2016-06-15

We report a detailed high pressure study on Eu{sub 1−x}Sr{sub x}TiO{sub 3} polycrystalline samples using synchrotron x-ray diffraction. We have observed a second-order antiferrodistortive phase transition for all doping levels which corresponds to the transition that has been previously explored as a function of temperature. The analysis of the compression mechanism by calculating the lattice parameters, spontaneous strains and tilt angles of the TiO{sub 6} octahedra leads to a high pressure phase diagram for Eu{sub 1−x}Sr{sub x}TiO{sub 3}.

Luminescence detection of phase transitions in crystals and nanoparticle inclusions

International Nuclear Information System (INIS)

Townsend, P. D.; Yang, B.; Wang, Y.

2008-01-01

Luminescence measurements are extremely sensitive to variations in structural environment and thus have the potential to probe distortions of fluorescence sites. Changes can be monitored via luminescence efficiency, emission spectra or excited state lifetimes and these factors are influenced by the local neighbourhood around the emission site, and therefore by structure, composition, pressure and temperature. A rarely exploited approach for condensed matter has been to use the changes in luminescence responses during heating or cooling of a material to provide a rapid survey to detect the presence of phase transitions. One can often differentiate between bulk and surface effects by contrasting results from radioluminescence for bulk responses, and cathodoluminescence or photoluminescence for surface effects. One expects that discontinuous changes in optical parameters occur during temperature changes through phase transitions of insulating materials. In practice, optical signals also exist from surface states of fullerenes and high temperature superconductors etc which identify the presence of structural or superconducting transitions. Numerous examples are cited which match standard documented transitions. Interestingly many examples show the host signals are strongly sensitive to impurity phase transitions from inclusions such as nanoparticles of water, N 2 , O 2 or CO 2 . Recent luminescence data reveal many examples of new transitions, hysteresis and irreversible changes. The signals equally respond to relaxations of a structure and surprisingly indicate that in some materials, such as SrTiO 3 or ZnO, ion implantation of the surface triggers relaxations and phase changes throughout the bulk of the material. Luminescence routes to detect phase transitions are powerful tools but have a tiny literature and so the subject is ideal for rapid exploitation and development. (Author)

Critical bubbles and fluctuations at the electroweak phase transition

CERN Document Server

Kripfganz, J; Schmidt, M G

1995-01-01

We discuss the critical bubbles of the electroweak phase transition using an effective high-temperature 3-dimensional action for the Higgs field \\varphi. The separate integration of gauge and Goldstone boson degrees of freedom is conveniently described in the 't Hooft-Feynman covariant background gauge. The effective dimensionless gauge coupling g_3(T)^2 in the broken phase is well behaved throughout the phase transition. However, the behavior of the one-loop Z(\\varphi) factors of the Higgs and gauge kinetic terms signalizes the breakdown of the derivative expansion and of the perturbative expansion for a range of small \\varphi values increasing with the Higgs mass m_H. Taking a functional S_z[\\varphi] with constant Z(\\varphi)=z instead of the full non-local effective action in some neighborhood of the saddlepoint we are calculating the critical bubbles for several temperatures. The fluctuation determinant is calculated to high accuracy using a variant of the heat kernel method. It gives a strong suppression ...

Multiple phase transitions and magnetoresistance of HoFe{sub 4}Ge{sub 2}

Energy Technology Data Exchange (ETDEWEB)

Liu, J., E-mail: liujing@iastate.edu; Pecharsky, V.K.; Gschneidner, K.A.

2015-05-15

Highlights: • Three magnetic transitions at T{sub N} = 51 K, T{sub f1} = 42 K, and T{sub f2} = 15 K. • Kinetically arrested phase below a freezing point of ∼11 K. • First-order metamagnetic transition at critical field ∼22 kOe below 35 K. • A large magnetoresistance of ∼30% at a field change of 30 kOe near 15 K. - Abstract: A systematic study of the structural, magnetic, heat capacity, electrical resistivity and magnetoresistance properties of HoFe{sub 4}Ge{sub 2} has been performed. The temperature dependencies of the magnetization and heat capacity show three magnetic transitions at T{sub N} = 51 K, T{sub f1} = 42 K, and T{sub f2} = 15 K. The high temperature transition is antiferromagnetic ordering and the two low temperature phase transitions are due to rearrangements of the magnetic structure. A kinetically arrested phase is observed below a freezing point of ∼11 K. Below 35 K, the behavior of the isothermal magnetization reflects a first-order metamagnetic phase transition. Multiple phase transitions are also manifested in the electrical resistivity behavior. For a field change of 30 kOe, a large magnetoresistance of ∼30% is observed near T{sub f2} (15 K)

Chiral ward-Takahashi identities at finite temperature and chiral phase transition in (2+1) dimensional chiral Gross-Neveu model

International Nuclear Information System (INIS)

Shen Kun; Qiu Zhongping

1993-01-01

Chiral Ward-Takahashi identities at finite temperature are derived in (2+1) dimensional chiral Gross-Neveu model. In terms of these identities, fermion mass generation and the mass spectra of bound states are investigate at finite temperature. Taking the fermion mass as an order parameter, the authors discuss the phase structure and chiral phase transition and obtain the critical temperature

The MSSM Electroweak Phase Transition on the Lattice

CERN Document Server

Laine, Mikko

1998-01-01

We study the MSSM finite temperature electroweak phase transition with lattice Monte Carlo simulations, for a large Higgs mass (m_H ~ 95 GeV) and light stop masses (m_tR ~ 150...160 GeV). We employ a 3d effective field theory approach, where the degrees of freedom appearing in the action are the SU(2) and SU(3) gauge fields, the weakly interacting Higgs doublet, and the strongly interacting stop triplet. We determine the phase diagram, the critical temperatures, the scalar field expectation values, the latent heat, the interface tension and the correlation lengths at the phase transition points. Extrapolating the results to the infinite volume and continuum limits, we find that the transition is stronger than indicated by 2-loop perturbation theory, guaranteeing that the MSSM phase transition is strong enough for baryogenesis in this regime. We also study the possibility of a two-stage phase transition, in which the stop field gets an expectation value in an intermediate phase. We find that a two-stage transi...

Theory of high-T{sub C} superconductivity: transition temperature

Energy Technology Data Exchange (ETDEWEB)

Harshman, Dale R [Physikon Research Corporation, Lynden, WA 98264 (United States); Fiory, Anthony T [Department of Physics, New Jersey Institute of Technology, Newark, NJ 07102 (United States); Dow, John D, E-mail: drh@physikon.net [Department of Physics, Arizona State University, Tempe, AZ 85287 (United States)

2011-07-27

It is demonstrated that the transition temperature (T{sub C}) of high-T{sub C} superconductors is determined by their layered crystal structure, bond lengths, valency properties of the ions, and Coulomb coupling between electronic bands in adjacent, spatially separated layers. Analysis of 31 high-T{sub C} materials (cuprates, ruthenates, ruthenocuprates, iron pnictides, organics) yields the universal relationship for optimal compounds, k{sub B}T{sub C0} ={beta}/{iota}{zeta}, where {iota} is related to the mean spacing between interacting charges in the layers, {zeta} is the distance between interacting electronic layers, {beta} is a universal constant and T{sub C0} is the optimal transition temperature (determined to within an uncertainty of {+-} 1.4 K by this relationship). Non-optimum compounds, in which sample degradation is evident, e.g. by broadened superconducting transitions and diminished Meissner fractions, typically exhibit reduced T{sub C} < T{sub C0}. It is shown that T{sub C0} may be obtained from an average of the Coulomb interaction forces between the two layers.

Phase Transition Control for High-Performance Blade-Coated Perovskite Solar Cells

KAUST Repository

Li, Jianbo

2018-05-07

Summary Here, we have identified that the key issue for rational transitioning from spin-coating to blade-coating processes of perovskite films arises from whether intermediate phases participate in the phase transition. In situ characterizations were carried out to provide a comprehensive picture of structural evolution and crystal growth mechanisms. These findings present opportunities for designing an effective process for blade-coating perovskite film: a large-grained dense perovskite film with high crystal quality and photophysical properties can be obtained only via direct crystallization for both spin-coating and blade-coating processes. As a result, the blade-coated MAPbI3 films deliver excellent charge-collection efficiency at both short circuit and open circuit, and photovoltaic properties with efficiencies of 18.74% (0.09 cm2) and 17.06% (1 cm2) in planar solar cells. The significant advances in understanding how the phase transition links spin-coating and blade-coating processes should provide a path toward high-performance printed perovskite devices.

Phase change based cooling for high burst mode heat loads with temperature regulation above the phase change temperature

Science.gov (United States)

The United States of America as represented by the United States Department of Energy

2009-12-15

An apparatus and method for transferring thermal energy from a heat load is disclosed. In particular, use of a phase change material and specific flow designs enables cooling with temperature regulation well above the fusion temperature of the phase change material for medium and high heat loads from devices operated intermittently (in burst mode). Exemplary heat loads include burst mode lasers and laser diodes, flight avionics, and high power space instruments. Thermal energy is transferred from the heat load to liquid phase change material from a phase change material reservoir. The liquid phase change material is split into two flows. Thermal energy is transferred from the first flow via a phase change material heat sink. The second flow bypasses the phase change material heat sink and joins with liquid phase change material exiting from the phase change material heat sink. The combined liquid phase change material is returned to the liquid phase change material reservoir. The ratio of bypass flow to flow into the phase change material heat sink can be varied to adjust the temperature of the liquid phase change material returned to the liquid phase change material reservoir. Varying the flowrate and temperature of the liquid phase change material presented to the heat load determines the magnitude of thermal energy transferred from the heat load.

Phase transition to QGP matter : confined vs deconfined matter

CERN Multimedia

Maire, Antonin

2015-01-01

Simplified phase diagram of the nuclear phase transition, from the regular hadronic matter to the QGP phase. The sketch is meant to describe the transition foreseen along the temperature axis, at low baryochemical potential, µB.

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

Dynamic phase transition in the kinetic spin-1 Blume-Capel model: Phase diagrams in the temperature and crystal-field interaction plane

International Nuclear Information System (INIS)

Keskin, M.; Canko, O.; Temizer, U.

2007-01-01

Within a mean-field approach, the stationary states of the kinetic spin-1 Blume-Capel model in the presence of a time-dependent oscillating external magnetic field is studied. The Glauber-type stochastic dynamics is used to describe the time evolution of the system and obtain the mean-field dynamic equation of motion. The dynamic phase-transition points are calculated and phase diagrams are presented in the temperature and crystal-field interaction plane. According to the values of the magnetic field amplitude, three fundamental types of phase diagrams are found: One exhibits a dynamic tricritical point, while the other two exhibit a dynamic zero-temperature critical point

Extracellular ice phase transitions in insects.

Science.gov (United States)

Hawes, T C

2014-01-01

At temperatures below their temperature of crystallization (Tc), the extracellular body fluids of insects undergo a phase transition from liquid to solid. Insects that survive the transition to equilibrium (complete freezing of the body fluids) are designated as freeze tolerant. Although this phenomenon has been reported and described in many Insecta, current nomenclature and theory does not clearly delineate between the process of transition (freezing) and the final solid phase itself (the frozen state). Thus freeze tolerant insects are currently, by convention, described in terms of the temperature at which the crystallization of their body fluids is initiated, Tc. In fact, the correct descriptor for insects that tolerate freezing is the temperature of equilibrium freezing, Tef. The process of freezing is itself a separate physical event with unique physiological stresses that are associated with ice growth. Correspondingly there are a number of insects whose physiological cryo-limits are very specifically delineated by this transitional envelope. The distinction also has considerable significance for our understanding of insect cryobiology: firstly, because the ability to manage endogenous ice growth is a fundamental segregator of cryotype; and secondly, because our understanding of internal ice management is still largely nascent.

Determination of thermal diffusivity at low temperature using the two-beam phase-lag photoacoustic method with observation of phase-transitions

International Nuclear Information System (INIS)

Jorge, M.P.P.

1992-01-01

This study consists of the determination of thermal diffusivity int he temperature range from 77 K to 300 K by the two-beam phase-lag photoacoustic method. Room temperature measurements of NTD (neutron transmutation doping) silicon suggest that the doping process does not affect its thermal properties. For the superconductor Y Ba 2 Cu 3 O 7 - x it has been verified that the sample density affects its thermal diffusivity. The validity of the experimental method on the Li K SO 4 crystal has been examined by using the thermal diffusivity of a Li F crystal and an Y 2 O 3 ceramic, at room temperature. The behavior of the thermal diffusivity as a function of the temperature for the Li K SO 4 crystal shows two anomalies which correspond at phase-transitions of this crystal in the studied temperature range. (author)

Macroscopic phase separation in high-temperature superconductors

Science.gov (United States)

Wen, Hai-Hu

2000-01-01

High-temperature superconductivity is recovered by introducing extra holes to the Cu-O planes, which initially are insulating with antiferromagnetism. In this paper I present data to show the macroscopic electronic phase separation that is caused by either mobile doping or electronic instability in the overdoped region. My results clearly demonstrate that the electronic inhomogeneity is probably a general feature of high-temperature superconductors. PMID:11027323

The Structural Phase Transition in Octaflournaphtalene

DEFF Research Database (Denmark)

Mackenzie, Gordon A.; Arthur, J. W.; Pawley, G. S.

1977-01-01

The phase transition in octafluoronaphthalene has been investigated by Raman scattering and neutron powder diffraction. The weight of the experimental evidence points to a unit cell doubling in the a direction, but with no change in space group symmetry. Lattice dynamics calculations support...... this evidence and indicate that the mechanism of the phase transition may well be the instability of a zone boundary acoustic mode of librational character. The structure of the low-temperature phase has been refined and the Raman spectra of the upper and lower phases are reported....

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...

Phase transformation in multiferroic Bi5Ti3FeO15 ceramics by temperature-dependent ellipsometric and Raman spectra: An interband electronic transition evidence

Science.gov (United States)

Jiang, P. P.; Duan, Z. H.; Xu, L. P.; Zhang, X. L.; Li, Y. W.; Hu, Z. G.; Chu, J. H.

2014-02-01

Thermal evolution and an intermediate phase between ferroelectric orthorhombic and paraelectric tetragonal phase of multiferroic Bi5Ti3FeO15 ceramic have been investigated by temperature-dependent spectroscopic ellipsometry and Raman scattering. Dielectric functions and interband transitions extracted from the standard critical-point model show two dramatic anomalies in the temperature range of 200-873 K. It was found that the anomalous temperature dependence of electronic transition energies and Raman mode frequencies around 800 K can be ascribed to intermediate phase transformation. Moreover, the disappearance of electronic transition around 3 eV at 590 K is associated with the conductive property.

Phase transition over gauge group center and quark confinement in QCD

International Nuclear Information System (INIS)

Khokhlachev, S.B.; Makeenko, Yu.N.

1979-01-01

A lattice gauge model with the phase transition corresponding to spontaneous breakdown of the group center symmetry is considered. It is shown that the phase diagram, obtained in multicolor case, separates the high and low-temperature phases with confined and nonconfined quarks. The possibility of the Lorentz-invariant continuum limit in the phase with permanently confined quarks is confirmed

Quarks-bags phase transition in quantum chromodynamics

International Nuclear Information System (INIS)

Gorenshtejn, M.I.

1981-01-01

Phase transitions in the quark-gluon plasma are considered at finite temperatures and chemical potentials. A phenomenological account for a complicated structure of the QCD vacuum results in the necessity to use the formalism of isobaric ensembles to describe the system. The phase transition curve separating the regions of the quark-gluon plasma and the hadronic bag phase in the μT plane is calculated [ru

Li-ion batteries: Phase transition

International Nuclear Information System (INIS)

Hou Peiyu; Zhang Yantao; Zhang Lianqi; Chu Geng; Gao Jian

2016-01-01

Progress in the research on phase transitions during Li + extraction/insertion processes in typical battery materials is summarized as examples to illustrate the significance of understanding phase transition phenomena in Li-ion batteries. Physical phenomena such as phase transitions (and resultant phase diagrams) are often observed in Li-ion battery research and already play an important role in promoting Li-ion battery technology. For example, the phase transitions during Li + insertion/extraction are highly relevant to the thermodynamics and kinetics of Li-ion batteries, and even physical characteristics such as specific energy, power density, volume variation, and safety-related properties. (topical review)

Neutron diffraction study of high temperature phase of K2SeO4

International Nuclear Information System (INIS)

Iwata, Yutaka; Koyano, Nobumitsu; Shibuya, Iwao; Hidaka, Masanori; Okazaki, Atsushi.

1984-01-01

The crystal structure of high-temperature phase of K 2 SeO 4 has been determined by means of single crystal neutron diffraction. The space group is P6 3 /mmc of hexagonal system with two formula units per unit cell. The structure is characterized by an averaged dispositions of SeO 4 tetrahedra with one of its Se-O bonds pointing parallel and antiparallel to the hexagonal c-axis in addition to the split distribution of potassium atoms. Heavily distorted distribution of oxygen atoms in SeO 4 is observed in Fourier maps corrersponding to split positions and reorientational motion of tetrahedra. This disordered arrangement is found to have close relation with the room temperature orthorhombic structure. The hexagonal-orthorhombic phase transition of K 2 SeO 4 at 472 0 C is grouped to an order-disorder type. (author)

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

Surface phase transitions in cu-based solid solutions

Science.gov (United States)

Zhevnenko, S. N.; Chernyshikhin, S. V.

2017-11-01

We have measured surface energy in two-component Cu-based systems in H2 + Ar gas atmosphere. The experiments on solid Cu [Ag] and Cu [Co] solutions show presence of phase transitions on the surfaces. Isotherms of the surface energy have singularities (the minimum in the case of copper solid solutions with silver and the maximum in the case of solid solutions with cobalt). In both cases, the surface phase transitions cause deficiency of surface miscibility: formation of a monolayer (multilayer) (Cu-Ag) or of nanoscale particles (Cu-Co). At the same time, according to the volume phase diagrams, the concentration and temperature of the surface phase transitions correspond to the solid solution within the volume. The method permits determining the rate of diffusional creep in addition to the surface energy. The temperature and concentration dependence of the solid solutions' viscosity coefficient supports the fact of the surface phase transitions and provides insights into the diffusion properties of the transforming surfaces.

Quantum phase transitions of strongly correlated electron systems

International Nuclear Information System (INIS)

Imada, Masatoshi

1998-01-01

Interacting electrons in solids undergo various quantum phase transitions driven by quantum fluctuations. The quantum transitions take place at zero temperature by changing a parameter to control quantum fluctuations rather than thermal fluctuations. In contrast to classical phase transitions driven by thermal fluctuations, the quantum transitions have many different features where quantum dynamics introduces a source of intrinsic fluctuations tightly connected with spatial correlations and they have been a subject of recent intensive studies as we see below. Interacting electron systems cannot be fully understood without deep analyses of the quantum phase transitions themselves, because they are widely seen and play essential roles in many phenomena. Typical and important examples of the quantum phase transitions include metal-insulator transitions, (2, 3, 4, 5, 6, 7, 8, 9) metal-superconductor transitions, superconductor-insulator transitions, magnetic transitions to antiferromagnetic or ferromagnetic phases in metals as well as in Mott insulators, and charge ordering transitions. Here, we focus on three different types of transitions

Insight into structural phase transitions from the decoupled anharmonic mode approximation.

Science.gov (United States)

Adams, Donat J; Passerone, Daniele

2016-08-03

We develop a formalism (decoupled anharmonic mode approximation, DAMA) that allows calculation of the vibrational free energy using density functional theory even for materials which exhibit negative curvature of the potential energy surface with respect to atomic displacements. We investigate vibrational modes beyond the harmonic approximation and approximate the potential energy surface with the superposition of the accurate potential along each normal mode. We show that the free energy can stabilize crystal structures at finite temperatures which appear dynamically unstable at T  =  0. The DAMA formalism is computationally fast because it avoids statistical sampling through molecular dynamics calculations, and is in principle completely ab initio. It is free of statistical uncertainties and independent of model parameters, but can give insight into the mechanism of a structural phase transition. We apply the formalism to the perovskite cryolite, and investigate the temperature-driven phase transition from the P21/n to the Immm space group. We calculate a phase transition temperature between 710 and 950 K, in fair agreement with the experimental value of 885 K. This can be related to the underestimation of the interaction of the vibrational states. We also calculate the main axes of the thermal ellipsoid and can explain the experimentally observed increase of its volume for the fluorine by 200-300% throughout the phase transition. Our calculations suggest the appearance of tunneling states in the high temperature phase. The convergence of the vibrational DOS and of the critical temperature with respect of reciprocal space sampling is investigated using the polarizable-ion model.

First order electroweak phase transition

International Nuclear Information System (INIS)

Buchmueller, W.; Fodor, Z.

1993-01-01

In this work, the authors have studied the phase transition in the SU(2)gauge theory at finite temperature. The authors' improved perturbative approach does not suffer from the infrared problems appearing in the ordinary loop expansion. The authors have calculated the effective potential up to cubic terms in the couplings. The higher order terms suggest that the method is reliable for Higgs masses smaller than 80 GeV. The authors have obtained a non-vanishing magnetic mass which further weakens the transitions. By use of Langer's theory of metastability, the authors have calculated the nucleation rate for critical bubbles and have discussed some cosmological consequences. For m H <80 GeV the phase transition is first order and proceeds via bubble nucleation and growth. The thin wall approximation is only marginally applicable. Since the phase transition is quite weak SM baryogenesis is unlikely. 8 refs., 5 figs

Evidence for plasma phase transition in high pressure hydrogen from ab-initio simulations

Energy Technology Data Exchange (ETDEWEB)

Morales, M; Pierleoni, C; Schwegler, E; Ceperley, D

2010-02-08

We have performed a detailed study of molecular dissociation in liquid hydrogen using both Born-Oppenheimer molecular dynamics with Density Functional Theory and Coupled Electron-Ion Monte Carlo simulations. We observe a range of densities where (dP/d{rho}){sub T} = 0 that coincides with sharp discontinuities in the electronic conductivity, which is clear evidence of the plasma phase transition for temperatures 600K {le} T {le} 1500K. Both levels of theory exhibit the transition, although Quantum Monte Carlo predicts higher transition pressures. Based on the temperature dependence of the discontinuity in the electronic conductivity, we estimate the critical point of the transition at temperatures slightly below 2000 K. We examine the influence of proton zero point motion by using Path Integral Molecular Dynamics with Density Functional Theory; the main effect is to shift the transition to lower pressures. Furthermore, we calculate the melting curve of molecular hydrogen up to pressures of 200 GPa, finding a reentrant melting line in good agreement with previous calculations. The melting line crosses the metalization line at 700 K and 220 GPa using density functional energetics and at 550 K and 290 GPa using Quantum Monte Carlo energetics.

Phase transitions in field theory

International Nuclear Information System (INIS)

Carvalho, C.A.A. de; Bollini, C.G.; Giambiagi, J.J.

1984-01-01

By means of an example for which the effective potential is explicitly calculable (up to the one loop approximation), it is discussed how a phase transition takes place as the temperature is increased and pass from spontaneously broken symmetry to a phase in which the symmetry is restored. (Author) [pt

Predicting glass-to-glass and liquid-to-liquid phase transitions in supercooled water using classical nucleation theory

Science.gov (United States)

Tournier, Robert F.

2018-01-01

Glass-to-glass and liquid-to-liquid phase transitions are observed in bulk and confined water, with or without applied pressure. They result from the competition of two liquid phases separated by an enthalpy difference depending on temperature. The classical nucleation equation of these phases is completed by this quantity existing at all temperatures, a pressure contribution, and an enthalpy excess. This equation leads to two homogeneous nucleation temperatures in each liquid phase; the first one (Tn- below Tm) being the formation temperature of an "ordered" liquid phase and the second one corresponding to the overheating temperature (Tn+ above Tm). Thermodynamic properties, double glass transition temperatures, sharp enthalpy and volume changes are predicted in agreement with experimental results. The first-order transition line at TLL = 0.833 × Tm between fragile and strong liquids joins two critical points. Glass phase above Tg becomes "ordered" liquid phase disappearing at TLL at low pressure and at Tn+ = 1.302 × Tm at high pressure.

High temperature interdiffusion and phase equilibria in U-Mo

International Nuclear Information System (INIS)

Lundberg, L.B.

1988-01-01

Experimental data for interdiffusion and phase equilibria in the U-Mo system have been obtained over the temperature range 1400 to 1525 K as a fallout from compatibility experiments in which UO 2 was decomposed by lithium in closed molybdenum capsules. Composition-position, x-ray diffraction and microstructural data from the interdiffusion zones indicate that the intermediate phase U 2 Mo is found in this temperature range, contrary to the currently accepted equilibrium U-Mo phase diagram. The U-Mo interdiffusion data are in good agreement with published values. Inclusion of the U 2 Mo phase in a theoretical correlation of interdiffusion and phase equilibria data using Darken's equation indicate that high temperature interdiffusion of uranium and molybdenum follows the usual thermodynamic rules. Significant changes in the value of the thermodynamic based Darken factor near the U 2 Mo phase boundary on the high uranium side are indicated from both the new and published interdiffusion data. 9 refs., 10 figs., 3 tabs

Summary of workshop on high temperature materials based on Laves phases

Energy Technology Data Exchange (ETDEWEB)

NONE

1996-08-01

The Offices of Fossil Energy and Basic Energy Sciences of the Department of Energy jointly sponsored the Workshop on High Temperature Materials Based on Laves Phases in conjunction with the Tenth Annual Conference on Fossil Energy Materials held at the Radisson Summit Hill Hotel in Knoxville, Tennessee on May 14-16, 1996. The objective of this workshop was to review the current status and to address critical issues in the development of new-generation high-temperature structural materials based on Laves phases. The one-day workshop included two sessions of overview presentations and a session of discussion on critical scientific and technological issues. The Laves phases represent an abundant class of intermetallic alloys with possible high-temperature structural applications. Laves phases form at or near the AB{sub 2} composition, and there are over 360 binary Laves phases. The ability of these alloys to dissolve considerable amounts of ternary alloying additions provides over 900 combined binary and ternary Laves phases. Many Laves phases have unique properties which make them attractive for high-temperature structural use. At half their homologous temperature, they retain >0.85 of their ambient yield strength, which is higher than all other intermetallics. Many of the Laves phases also have high melting temperatures, excellent creep properties, reasonably low densities, and for alloys containing Cr, Al, Si or Be, good oxidation resistance. Despite these useful properties, the tendency for low-temperature brittleness has limited the potential application of this large class of alloys.

Synchrotron radiation topography studies of the phase transition in LaGaO 3 crystals

Science.gov (United States)

Yao, G.-D.; Dudley, M.; Wang, Y.; Liu, X.; Liebermann, R. C.

1991-05-01

An investigation of the orthorhombic to rhombohedral phase transformation occurring at 145°C in lanthanum gallate has been conducted using white beam synchrotron X-ray topography (WBSXRT). The existence of the first order transition was confirmed by differential thermal analysis and X-ray diffractometer powder analysis. Subsequent to this, synchrotron white beam Laue patterns were recorded in situ as a function of temperature, during the transition. Before the transition point was reached, (112) orth type reflection twinning was found to be dominant although a small amount of (110) orth type twinning was also observed in the same crystal. Beyond the transition point, not only did the structural change become evident but also reflection twinning on the (110) rhom planes was observed. The scale of this twinning became finer as the temperature was increased beyond the transition temperature. The twinning observed in both the low and high temperature phases gives rise to deformation of the (011) rhom surface plane which creates problems for the potential use of this material as a substrate for growing high Tc superconducting epitaxial layers.

Synchrotron radiation topography studies of the phase transition in LaGaO3 crystals

International Nuclear Information System (INIS)

Yao, G.D.; Dudley, M.; Wang, Y.; Liu, X.; Liebermann, R.C.

1991-01-01

An investigation of the orthorhombic to rhombohedral phase transformation occurring at 145degC in lanthanum gallate has been conducted using white beam synchrotron X-ray topography (WBSXRT). The existence of the first order transition was confirmed by differential thermal analysis and X-ray diffractometer powder analysis. Subsequent to this, synchrotron white beam Laue patterns were recorded in situ as a function of temperature, during the transition. Before the transition point was reached, (112) orth type reflection twinning was found to be dominant although a small amount of (110) orth type twinning was also observed in the same crystal. Beyond the transition point, not only did the structural change become evident but also reflection twinning on the (110) rhom planes was observed. The scale of this twinning became finer as the temperature was increased beyond the transition temperature. The twinning observed in both the low and high temperature phases gives rise to deformation of the (011) rhom surface plane which creates problems for the potential use of this material as a substrate for growing high Tc superconducting epitaxial layers. (orig.)

QCD phase transition at real chemical potential with canonical approach

Energy Technology Data Exchange (ETDEWEB)

Nakamura, Atsushi [RCNP, Osaka University,Osaka, 567-0047 (Japan); Nishina Center, RIKEN,Wako, Saitama 351-0198 (Japan); School of Biomedicine, Far Eastern Federal University,Vladivostok, 690950 (Russian Federation); Oka, Shotaro [Institute of Theoretical Physics, Department of Physics, Rikkyo University,Toshima-ku, Tokyo 171-8501 (Japan); Taniguchi, Yusuke [Graduate School of Pure and Applied Sciences, University of Tsukuba,Tsukuba, Ibaraki 305-8571 (Japan)

2016-02-08

We study the finite density phase transition in the lattice QCD at real chemical potential. We adopt a canonical approach and the canonical partition function is constructed for N{sub f}=2 QCD. After derivation of the canonical partition function we calculate observables like the pressure, the quark number density, its second cumulant and the chiral condensate as a function of the real chemical potential. We covered a wide range of temperature region starting from the confining low to the deconfining high temperature; 0.65T{sub c}≤T≤3.62T{sub c}. We observe a possible signal of the deconfinement and the chiral restoration phase transition at real chemical potential below T{sub c} starting from the confining phase. We give also the convergence range of the fugacity expansion.

Magnetic dipole self-organization of charge carriers in high-temperature superconductors and kinetics of phase transformation

CERN Document Server

Voronov, A V; Shuvalov, V V

2001-01-01

The phenomenological model, describing the magnetic dipole self-organization of charge carriers (formation of so-called stripe-structures and energy gap in the states spectrum), is designed for interpreting the data on the nonstationary nonlinear spectroscopy of the high-temperature superconductors. It is shown that after fast heating of the superconducting sample the kinetics of the subsequent phase transition depends on the initial temperature T. The destruction of the stripe-structures at low overheating T* < T < T sub m approx = (1.4-1.5)T*, whereby T sub c and T* approx = T sub c are the temperatures of transition into the superconducting state and formation of the stripe-structures occurs slowly (the times above 10 sup - sup 9 s) in spite of practically instantaneous disappearance of the superconductivity

Optical study of phase transitions in single-crystalline RuP

Science.gov (United States)

Chen, R. Y.; Shi, Y. G.; Zheng, P.; Wang, L.; Dong, T.; Wang, N. L.

2015-03-01

RuP single crystals of MnP-type orthorhombic structure were synthesized by the Sn flux method. Temperature-dependent x-ray diffraction measurements reveal that the compound experiences two structural phase transitions, which are further confirmed by enormous anomalies shown in temperature-dependent resistivity and magnetic susceptibility. Particularly, the resistivity drops monotonically upon temperature cooling below the second transition, indicating that the material shows metallic behavior, in sharp contrast with the insulating ground state of polycrystalline samples. Optical conductivity measurements were also performed in order to unravel the mechanism of these two transitions. The measurement revealed a sudden reconstruction of band structure over a broad energy scale and a significant removal of conducting carriers below the first phase transition, while a charge-density-wave-like energy gap opens below the second phase transition.

Phase transformation in multiferroic Bi5Ti3FeO15 ceramics by temperature-dependent ellipsometric and Raman spectra: An interband electronic transition evidence

International Nuclear Information System (INIS)

Jiang, P. P.; Duan, Z. H.; Xu, L. P.; Zhang, X. L.; Li, Y. W.; Hu, Z. G.; Chu, J. H.

2014-01-01

Thermal evolution and an intermediate phase between ferroelectric orthorhombic and paraelectric tetragonal phase of multiferroic Bi 5 Ti 3 FeO 15 ceramic have been investigated by temperature-dependent spectroscopic ellipsometry and Raman scattering. Dielectric functions and interband transitions extracted from the standard critical-point model show two dramatic anomalies in the temperature range of 200–873 K. It was found that the anomalous temperature dependence of electronic transition energies and Raman mode frequencies around 800 K can be ascribed to intermediate phase transformation. Moreover, the disappearance of electronic transition around 3 eV at 590 K is associated with the conductive property

Photo-induced charge-transfer phase transition of rubidium manganese hexacyanoferrate in ferromagnetic and paramagnetic states

International Nuclear Information System (INIS)

Tokoro, Hiroko; Hashimoto, Kazuhito; Ohkoshi, Shin-ichi

2007-01-01

A charge transfer phase transition with thermal hysteresis loop is observed in a series of rubidium manganese hexacyanoferrates, RbMn[Fe(China) 6 ] (1), Rb 0.88 Mn[Fe(China) 6 ] 0.96 .0.6H 2 O (2), and Rb 0.97 Mn[Fe(China) 6 ] 0.99 .0.2H 2 O (3). This phase transition is accompanied by a structural change from cubic (F4-bar 3m) to tetragonal (I4-bar m2). Its high-temperature (HT) and low-temperature (LT) phases are composed of Mn II (S=2/5)NC-Fe III (S=1/2) and Mn III (S=2)-NC-Fe II (S=0), respectively. The phase transition is caused by a metal-to-metal charge transfer from Mn II to Fe III and a Jahn-Teller distortion of the produced Mn III ion. At the ferromagnetic state in LT phase of 2, the photo-induced phase transition is observed, i.e., magnetization is quenched by the irradiation with only one shot of laser pulse. This phenomenon is caused by a photo-induced phase transition from the LT phase to the HT phase. In 3, optical switching between LT and HT phases at room temperature in paramagnetic region is observed

T-p phase diagrams and the barocaloric effect in materials with successive phase transitions

Science.gov (United States)

Gorev, M. V.; Bogdanov, E. V.; Flerov, I. N.

2017-09-01

An analysis of the extensive and intensive barocaloric effect (BCE) at successive structural phase transitions in some complex fluorides and oxyfluorides was performed. The high sensitivity of these compounds to a change in the chemical pressure allows one to vary the succession and parameters of the transformations (temperature, entropy, baric coefficient) over a wide range and obtain optimal values of the BCE. A comparison of different types of schematic T-p phase diagrams with the complicated T( p) dependences observed experimentally shows that in some ranges of temperature and pressure the BCE in compounds undergoing successive transformations can be increased due to a summation of caloric effects associated with distinct phase transitions. The maximum values of the extensive and intensive BCE in complex fluorides and oxyfluorides can be realized at rather low pressure (0.1-0.3 GPa). In a narrow temperature range around the triple points conversion from conventional BCE to inverse BCE is observed, which is followed by a gigantic change of both \\vertΔ S_BCE\\vert and \\vertΔ T_AD\\vert .

Structure determination at room temperature and phase transition ...

Indian Academy of Sciences (India)

Unknown

Solid State and Structural Chemistry Unit, Indian Institute of Science, Bangalore 560 012, India. MS received 9 May 2002 ... exhibit a ferroelectric–paraelectric phase transition at ele- ..... The pattern decomposition and peak extraction methods ...

A quaternary lead based perovskite structured materials with diffuse phase transition behavior

International Nuclear Information System (INIS)

Puli, Venkata Sreenivas; Martínez, R.; Kumar, Ashok; Scott, J.F.; Katiyar, Ram S.

2011-01-01

Graphical abstract: (a) Curie–Weiss plot for the inverse of the relative dielectric permittivity and (b) log (1/ε − 1/ε m ) as function of log (T − T m ) for ceramics at 1 kHz. Highlights: ► Retaining phase pure structure with quaternary complex stoichiometric compositions. ► P–E loops with good saturation polarization (P s ∼ 30.7 μC/cm 2 ). ► Diffused relaxor phase transition behavior with γ estimated is ∼1.65. -- Abstract: A lead based quaternary compound composed of 0.25(PbZr 0.52 Ti 0.48 O 3 ) + 0.25(PbFe 0.5 Ta 0.5 O 3 ) + 0.25 (PbF 0.67 W 0.33 O 3 ) + 0.25(PbFe 0.5 Nb 0.5 O 3 ) – (PZT–PFT–PFW–PFN) was synthesized by conventional solid-state reaction techniques. It showed moderate high dielectric constant, low dielectric loss, and two diffuse phase transitions, one below the room temperature ∼261 K and other above ∼410 K. X-ray diffraction (XRD) patterns revealed a tetragonal crystal structure at room temperature where as scanning electron micrograph (SEM) indicates inhomogeneous surface with an average grain size of 500 nm–3 μm. Well saturated ferroelectric hysteresis loops with good saturation polarization (spontaneous polarization, P s ∼ 30.68 μC/cm 2 ) were observed. Temperature-dependent ac conductivity displayed low conductivity with kink in spectra near the phase transition. In continuing search for developing new ferroelectric materials, in the present study we report stoichiometric compositions of complex perovskite ceramic materials: (PZT–PFT–PFW–PFN) with diffuse phase transition behavior. The crystal structure, dielectric properties, and ferroelectric properties were characterized by XRD, SEM, dielectric spectroscopy, and polarization. 1/ε versus (T) plots revealed diffuse relaxor phase transition (DPT) behavior. The compositional variation on the phase transition temperature, dielectric constant, and ferroelectric to paraelectric phase transitions are discussed.

A quaternary lead based perovskite structured materials with diffuse phase transition behavior

Energy Technology Data Exchange (ETDEWEB)

Puli, Venkata Sreenivas, E-mail: pvsri123@gmail.com [Department of Physics and Institute for Functional Nano Materials, University of Puerto Rico, San Juan, PR 00936 (United States); Martinez, R.; Kumar, Ashok [Department of Physics and Institute for Functional Nano Materials, University of Puerto Rico, San Juan, PR 00936 (United States); Scott, J.F. [Department of Physics and Institute for Functional Nano Materials, University of Puerto Rico, San Juan, PR 00936 (United States); Cavendish Laboratory, Dept. Physics, University of Cambridge, Cambridge CB0 3HE (United Kingdom); Katiyar, Ram S., E-mail: rkatiyar@uprrp.edu [Department of Physics and Institute for Functional Nano Materials, University of Puerto Rico, San Juan, PR 00936 (United States)

2011-12-15

Graphical abstract: (a) Curie-Weiss plot for the inverse of the relative dielectric permittivity and (b) log (1/{epsilon} - 1/{epsilon}{sub m}) as function of log (T - T{sub m}) for ceramics at 1 kHz. Highlights: Black-Right-Pointing-Pointer Retaining phase pure structure with quaternary complex stoichiometric compositions. Black-Right-Pointing-Pointer P-E loops with good saturation polarization (P{sub s} {approx} 30.7 {mu}C/cm{sup 2}). Black-Right-Pointing-Pointer Diffused relaxor phase transition behavior with {gamma} estimated is {approx}1.65. -- Abstract: A lead based quaternary compound composed of 0.25(PbZr{sub 0.52}Ti{sub 0.48}O{sub 3}) + 0.25(PbFe{sub 0.5}Ta{sub 0.5}O{sub 3}) + 0.25 (PbF{sub 0.67}W{sub 0.33}O{sub 3}) + 0.25(PbFe{sub 0.5}Nb{sub 0.5}O{sub 3}) - (PZT-PFT-PFW-PFN) was synthesized by conventional solid-state reaction techniques. It showed moderate high dielectric constant, low dielectric loss, and two diffuse phase transitions, one below the room temperature {approx}261 K and other above {approx}410 K. X-ray diffraction (XRD) patterns revealed a tetragonal crystal structure at room temperature where as scanning electron micrograph (SEM) indicates inhomogeneous surface with an average grain size of 500 nm-3 {mu}m. Well saturated ferroelectric hysteresis loops with good saturation polarization (spontaneous polarization, P{sub s} {approx} 30.68 {mu}C/cm{sup 2}) were observed. Temperature-dependent ac conductivity displayed low conductivity with kink in spectra near the phase transition. In continuing search for developing new ferroelectric materials, in the present study we report stoichiometric compositions of complex perovskite ceramic materials: (PZT-PFT-PFW-PFN) with diffuse phase transition behavior. The crystal structure, dielectric properties, and ferroelectric properties were characterized by XRD, SEM, dielectric spectroscopy, and polarization. 1/{epsilon} versus (T) plots revealed diffuse relaxor phase transition (DPT) behavior. The

Isostructural magnetic phase transition and magnetocaloric effect in Ising antiferromagnet

International Nuclear Information System (INIS)

Lavanov, G.Yu; Kalita, V.M.; Loktev, V.M.

2014-01-01

It is shown that the external magnetic field induced isostructural I st order magnetic phase transition between antiferromagnetic phases with different antiferromagnetic vector values is associated with entropy. It is found, that depending on temperature the entropy jump and the related heat release change their sign at this transition point. In the low-temperature region of metamagnetic I st order phase tensition the entropy jump is positive, and in the triple point region this jump for isostructural magnetic transition is negative

Dynamic phase transition in the kinetic spin-32 Blume-Capel model: Phase diagrams in the temperature and crystal-field interaction plane

Energy Technology Data Exchange (ETDEWEB)

Keskin, Mustafa [Department of Physics, Erciyes University, 38039 Kayseri (Turkey)]. E-mail: keskin@erciyes.edu.tr; Canko, Osman [Department of Physics, Erciyes University, 38039 Kayseri (Turkey); Deviren, Bayram [Department of Physics, Erciyes University, 38039 Kayseri (Turkey)

2007-06-15

We analyze, within a mean-field approach, the stationary states of the kinetic spin-32 Blume-Capel (BC) model by the Glauber-type stochastic dynamics and subject to a time-dependent oscillating external magnetic field. The dynamic phase transition (DPT) points are obtained by investigating the behavior of the dynamic magnetization as a function of temperature and as well as calculating the Liapunov exponent. Phase diagrams are constructed in the temperature and crystal-field interaction plane. We find five fundamental types of phase diagrams for the different values of the reduced magnetic field amplitude parameter (h) in which they present a disordered, two ordered phases and the coexistences phase regions. The phase diagrams also exhibit a dynamic double-critical end point for 05.06.

Specific heat and electric conductivity of zirconium alloy with 2,5 mass% niobium in the range of phase transitions

International Nuclear Information System (INIS)

Roshchupkin, V.V.; Pokrasin, M.A.; Chernov, A.I.; Semashko, N.A.

1996-01-01

Experimental investigation of specific heat and electric resistance of zirconium alloy with 2.5 mass% niobium in the range of phase transitions was conducted, using adiabatic calorimeter of original design, characterized by high sensitivity, efficiency and high accuracy. It was revealed that temperature dependence of specific heat was characterized by anomalous growth at 590 deg C, related with (α+β Nb )→(α+β Zr )-transition, and at 810 deg -related with (α+β Zr )→β Zr - transition. Temperature dependence of electric resistance was specific in the region of α+β Zr →β Zr phase transition. It was established that revealed anomalies were connected with high oxygen absorption at high temperatures. 11 refs., 1 fig., 1 tab

Two cloud-point phenomena in tetrabutylammonium perfluorooctanoate aqueous solutions: anomalous temperature-induced phase and structure transitions.

Science.gov (United States)

Yan, Peng; Huang, Jin; Lu, Run-Chao; Jin, Chen; Xiao, Jin-Xin; Chen, Yong-Ming

2005-03-24

This paper reported the phase behavior and aggregate structure of tetrabutylammonium perfluorooctanoate (TBPFO), determined by differential scanning calorimeter, electrical conductivity, static/dynamic light scattering, and rheology methods. We found that above a certain concentration the TBPFO solution showed anomalous temperature-dependent phase behavior and structure transitions. Such an ionic surfactant solution exhibits two cloud points. When the temperature was increased, the solution turned from a homogeneous-phase to a liquid-liquid two-phase system, then to another homogeneous-phase, and finally to another liquid-liquid two-phase system. In the first homogeneous-phase region, the aggregates of TBPFO were rodlike micelles and the solution was Newtonian fluid. While in the second homogeneous-phase region, the aggregates of TBPFO were large wormlike micelles, and the solution behaved as pseudoplastic fluid that also exhibited viscoelastic behavior. We thought that the first cloud point might be caused by the "bridge" effect of the tetrabutylammonium counterion between the micelles and the second one by the formation of the micellar network.

Thermodynamic phase transition of a black hole in rainbow gravity

Directory of Open Access Journals (Sweden)

Zhong-Wen Feng

2017-09-01

Full Text Available In this letter, using the rainbow functions that were proposed by Magueijo and Smolin, we investigate the thermodynamics and the phase transition of rainbow Schwarzschild black hole. First, we calculate the rainbow gravity corrected Hawking temperature. From this modification, we then derive the local temperature, free energy, and other thermodynamic quantities in an isothermal cavity. Finally, we analyze the critical behavior, thermodynamic stability, and phase transition of the rainbow Schwarzschild black hole. The results show that the rainbow gravity can stop the Hawking radiation in the final stages of black holes' evolution and lead to the remnants of black holes. Furthermore, one can observe that the rainbow Schwarzschild black hole has one first-order phase transition, two second-order phase transitions, and three Hawking–Page-type phase transitions in the framework of rainbow gravity theory.

The deconfinement phase transition, hadronization and the NJL model

International Nuclear Information System (INIS)

Raha, Sibaji

2000-01-01

One of the confident predictions of QCD is that at sufficiently high temperature and/or density, hadronic matter should undergo a thermodynamic phase transition to a color deconfined state of matter-popularly called the Quark-Gluon Plasma (QGP). In low energy effective theories of Quantum Chromodynamics (QCD), one usually talks of the chiral transition for which a well defined order parameter exists. We investigate the dissociation of pions and kaons in a medium of hot quark matter described by the Nambu-Jona Lasinio (NJL) model. The decay widths of pion and kaon are found to be large but finite at temperature much higher than the critical temperature for the chiral (or deconfinement) transition, the kaon decay width being much larger. Thus pions and even kaons (with a lower density compared to pions) may coexist with quarks and gluons at such high temperatures. On the basis of such premises, we investigate the process of hadronization in quark-gluon plasma with special emphasis on whether such processes shed any light on acceptable low energy effective theories of QCD

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).

Raman spectroscopic study of calcite III to aragonite transformation under high pressure and high temperature

Science.gov (United States)

Liu, Chuanjiang; Zheng, Haifei; Wang, Duojun

2017-10-01

In our study, a series of Raman experiments on the phase transition of calcite at high pressure and high temperature were investigated using a hydrothermal diamond anvil cell and Raman spectroscopy technique. It was found that calcite I transformed to calcite II and calcite III at pressures of 1.62 and 2.12 GPa and room temperature. With increasing temperature, the phase transition of calcite III to aragonite occurred. Aragonite was retained upon slowly cooling of the system, indicating that the transition of calcite III to aragonite was irreversible. Based on the available data, the phase boundary between calcite III and aragonite was determined by the following relation: P(GPa) = 0.013 × T(°C) + 1.22 (100°C ≤ T ≤ 170°C). It showed that the transition pressure linearly rose with increasing temperature. A better understanding of the stability of calcite III and aragonite is of great importance to further explore the thermodynamic behavior of carbonates and carbon cycling in the mantle.

Two-phase regime in the magnetic field-temperature phase diagram of a type-II superconductor

International Nuclear Information System (INIS)

Adams, L.L.A.; Halterman, Klaus; Valls, Oriol T.; Goldman, A.M.

2004-01-01

The magnetic field and temperature dependencies of the magnetic moments of superconducting crystals of V 3 Si have been studied. In a constant magnetic field and at temperatures somewhat below the superconducting transition temperature, the moments are hysteretic in temperature. However, the magnetic moment-magnetic field isotherms are reversible and exhibit features that formally resemble the pressure-volume isotherms of the liquid-gas transition. This suggests the existence of a first-order phase transition, a two-phase regime, and a critical point in the superconducting phase diagram. The two phases are disordered vortex configurations with the same magnetization, but with different vortex densities. The entropy change, determined from the data using the Clausius-Clapeyron equation, is consistent with estimates based on the difference in the vortex densities of the two phases

Two-phase regime in the magnetic field-temperature phase diagram of a type-II superconductor

Energy Technology Data Exchange (ETDEWEB)

Adams, L.L.A.; Halterman, Klaus; Valls, Oriol T.; Goldman, A.M

2004-01-01

The magnetic field and temperature dependencies of the magnetic moments of superconducting crystals of V{sub 3}Si have been studied. In a constant magnetic field and at temperatures somewhat below the superconducting transition temperature, the moments are hysteretic in temperature. However, the magnetic moment-magnetic field isotherms are reversible and exhibit features that formally resemble the pressure-volume isotherms of the liquid-gas transition. This suggests the existence of a first-order phase transition, a two-phase regime, and a critical point in the superconducting phase diagram. The two phases are disordered vortex configurations with the same magnetization, but with different vortex densities. The entropy change, determined from the data using the Clausius-Clapeyron equation, is consistent with estimates based on the difference in the vortex densities of the two phases.

Temperature-induced phase transition in hydrogels of interpenetrating networks poly(N-isopropylmethacrylamide)/poly(N-isopropylacrylamide)

Czech Academy of Sciences Publication Activity Database

Šťastná, J.; Hanyková, L.; Sedláková, Zdeňka; Valentová, H.; Spěváček, Jiří

2013-01-01

Roč. 291, č. 10 (2013), s. 2409-2417 ISSN 0303-402X R&D Projects: GA ČR GA202/09/1281 Institutional support: RVO:61389013 Keywords : temperature-induced volume phase transition * poly (N-isopropylmethacrylamide) poly (Nisopropylacrylamide) interpenetrating network * 1H NMR spectroscopy Subject RIV: CD - Macromolecular Chemistry Impact factor: 2.410, year: 2013

Shear induced phase transitions induced in edible fats

Science.gov (United States)

Mazzanti, Gianfranco; Welch, Sarah E.; Marangoni, Alejandro G.; Sirota, Eric B.; Idziak, Stefan H. J.

2003-03-01

The food industry crystallizes fats under different conditions of temperature and shear to obtain products with desired crystalline phases. Milk fat, palm oil, cocoa butter and chocolate were crystallized from the melt in a temperature controlled Couette cell. Synchrotron x-ray diffraction studies were conducted to examine the role of shear on the phase transitions seen in edible fats. The shear forces on the crystals induced acceleration of the alpha to beta-prime phase transition with increasing shear rate in milk fat and palm oil. The increase was slow at low shear rates and became very strong above 360 s-1. In cocoa butter the acceleration between beta-prime-III and beta-V phase transition increased until a maximum of at 360 s-1, and then decreased, showing competition between enhanced heat transfer and viscous heat generation.

Phase transitions in ternary caesium lead bromide

Czech Academy of Sciences Publication Activity Database

Rodová, Miroslava; Brožek, J.; Knížek, Karel; Nitsch, Karel

2003-01-01

Roč. 71, - (2003), s. 667-673 ISSN 1388-6150 R&D Projects: GA AV ČR IAA2010926; GA ČR GA203/02/0436 Institutional research plan: CEZ:AV0Z1010914 Keywords : DSC * high temperature X-ray diffraction * phase transitions * CsPbBr 3 * thermal expansion coefficient * TMA Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 1.094, year: 2003

Phase Transition to an Opaque Plasma in a Sonoluminescing Bubble

Science.gov (United States)

Kappus, Brian; Khalid, Shahzad; Chakravarty, Avik; Putterman, Seth

2011-06-01

Time-resolved spectrum measurements of a sonoluminescing Xe bubble reveal a transition from transparency to an opaque Planck blackbody. As the temperature is <10000K and the density is below liquid density, the photon scattering length is 10 000 times too large to explain its opacity. We resolve this issue with a model that reduces the ionization potential. According to this model, sonoluminescence originates in a new phase of matter with high ionization. Analysis of line emission from Xe* also yields evidence of phase segregation for this first-order transition inside a bubble.

Theory of relaxation phenomena in a spin-3/2 Ising system near the second-order phase transition temperature

International Nuclear Information System (INIS)

Keskin, Mustafa; Canko, Osman

2005-01-01

The relaxation behavior of the spin-3/2 Ising model Hamiltonian with bilinear and biquadratic interactions near the second-order phase transition temperature or critical temperature is studied by means of the Onsager's theory of irreversible thermodynamics or the Onsager reciprocity theorem (ORT). First, we give the equilibrium case briefly within the molecular-field approximation in order to study the relaxation behavior by using the ORT. Then, the ORT is applied to the model and the kinetic equations are obtained. By solving these equations, three relaxation times are calculated and examined for temperatures near the second-order phase transition temperature. It is found that one of the relaxation times goes to infinity near the critical temperature on either side, the second relaxation time makes a cusp at the critical temperature and third one behaves very differently in which it terminates at the critical temperature while approaching it, then showing a 'flatness' property and then decreases. We also study the influences of the Onsager rate coefficients on the relaxation times. The behavior of these relaxation times is discussed and compared with the spin-1/2 and spin-1 Ising systems

Crystal structure across the β to α phase transition in thermoelectric Cu2−xSe

Directory of Open Access Journals (Sweden)

Espen Eikeland

2017-07-01

Full Text Available The crystal structure uniquely imparts the specific properties of a material, and thus provides the starting point for any quantitative understanding of thermoelectric properties. Cu2−xSe is an intensely studied high performing, non-toxic and cheap thermoelectric material, and here for the first time, the average structure of β-Cu2−xSe is reported based on analysis of multi-temperature single-crystal X-ray diffraction data. It consists of Se–Cu layers with additional copper between every alternate layer. The structural changes during the peculiar zT enhancing phase transition mainly consist of changes in the inter-layer distance coupled with subtle Cu migration. Just prior to the transition the structure exhibits strong negative thermal expansion due to the reordering of Cu atoms, when approached from low temperatures. The phase transition is fully reversible and group–subgroup symmetry relations are derived that relate the low-temperature β-phase to the high-temperature α-phase. Weak superstructure reflections are observed and a possible Cu ordering is proposed. The structural rearrangement may have a significant impact on the band structure and the Cu rearrangement may also be linked to an entropy increase. Both factors potentially contribute to the extraordinary zT enhancement across the phase transition.

Quasi-phases and pseudo-transitions in one-dimensional models with nearest neighbor interactions

Science.gov (United States)

de Souza, S. M.; Rojas, Onofre

2018-01-01

There are some particular one-dimensional models, such as the Ising-Heisenberg spin models with a variety of chain structures, which exhibit unexpected behaviors quite similar to the first and second order phase transition, which could be confused naively with an authentic phase transition. Through the analysis of the first derivative of free energy, such as entropy, magnetization, and internal energy, a "sudden" jump that closely resembles a first-order phase transition at finite temperature occurs. However, by analyzing the second derivative of free energy, such as specific heat and magnetic susceptibility at finite temperature, it behaves quite similarly to a second-order phase transition exhibiting an astonishingly sharp and fine peak. The correlation length also confirms the evidence of this pseudo-transition temperature, where a sharp peak occurs at the pseudo-critical temperature. We also present the necessary conditions for the emergence of these quasi-phases and pseudo-transitions.

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 and temperature induced structural and elastic properties of lutetium chalcogenides

Science.gov (United States)

Shriya, S.; Kinge, R.; Khenata, R.; Varshney, Dinesh

2018-04-01

The high-pressure structural phase transition and pressure as well temperature induced elastic properties of rock salt to CsCl structures in semiconducting LuX (X = S, Se, and Te) chalcogenides compound have been performed using effective interionic interaction potential with emphasis on charge transfer interactions and covalent contribution. Estimated values of phase transition pressure and the volume discontinuity in pressure-volume phase diagram indicate the structural phase transition from ZnS to NaCl structure. From the investigations of elastic constants the pressure (temperature) dependent volume collapse/expansion, melting temperature TM, Hardness (HV), and young modulus (E) the LuX lattice infers mechanical stiffening, and thermal softening.

Influence of lattice distortion on phase transition properties of polycrystalline VO{sub 2} thin film

Energy Technology Data Exchange (ETDEWEB)

Lin, Tiegui [State Key Laboratory of Advanced Welding and Joining, Harbin Institute of Technology, Harbin 150001 (China); Wang, Langping, E-mail: aplpwang@hit.edu.cn [State Key Laboratory of Advanced Welding and Joining, Harbin Institute of Technology, Harbin 150001 (China); Wang, Xiaofeng; Zhang, Yufen [State Key Laboratory of Advanced Welding and Joining, Harbin Institute of Technology, Harbin 150001 (China); Yu, Yonghao, E-mail: yhyu@hit.edu.cn [Academy of Fundamental and Interdisciplinary Science, Harbin Institute of Technology, Harbin 150001 (China)

2016-08-30

Highlights: • Polycrystalline VO{sub 2} thin films were fabricated by high power impulse magnetron sputtering. • The reported lowest phase transition temperature for undoped polycrystalline VO{sub 2} thin film was reduced to 32 °C by this research. • XRD patterns at varied temperatures revealed that the main structual change was a gradual shift in interplanar spacing with temperature. - Abstract: In this work, high power impulse magnetron sputtering was used to control the lattice distortion in polycrystalline VO{sub 2} thin film. SEM images revealed that all the VO{sub 2} thin films had crystallite sizes of below 20 nm, and similar configurations. UV–vis-near IR transmittance spectra measured at different temperatures showed that most of the as-deposited films had a typical metal–insulator transition. Four-point probe resistivity results showed that the transition temperature of the films varied from 54.5 to 32 °C. The X-ray diffraction (XRD) patterns of the as-deposited films revealed that most were polycrystalline monoclinic VO{sub 2}. The XRD results also confirmed that the lattice distortions in the as-deposited films were different, and the transition temperature decreased with the difference between the interplanar spacing of the as-deposited thin film and standard rutile VO{sub 2}. Furthermore, a room temperature rutile VO{sub 2} thin film was successfully synthesized when this difference was small enough. Additionally, XRD patterns measured at varied temperatures revealed that the phase transition process of the polycrystalline VO{sub 2} thin film was a coordinative deformation between grains with different orientations. The main structural change during the phase transition was a gradual shift in interplanar spacing with temperature.

Open volume defects and magnetic phase transition in Fe{sub 60}Al{sub 40} transition metal aluminide

Energy Technology Data Exchange (ETDEWEB)

Liedke, M. O., E-mail: m.liedke@hzdr.de; Anwand, W.; Butterling, M.; Wagner, A. [Institute of Radiation Physics, Helmholtz-Zentrum Dresden - Rossendorf, Bautzner Landstraße 400, 01328 Dresden (Germany); Bali, R.; Cornelius, S.; Potzger, K. [Institute of Ion Beam Physics and Materials Research, Helmholtz-Zentrum Dresden - Rossendorf, Bautzner Landstraße 400, 01328 Dresden (Germany); Trinh, T. T. [Institute of Radiation Physics, Helmholtz-Zentrum Dresden - Rossendorf, Bautzner Landstraße 400, 01328 Dresden (Germany); Technical University Dresden, Helmholtzstr. 10, 01609 Dresden (Germany); Salamon, S.; Walecki, D.; Smekhova, A.; Wende, H. [Faculty of Physics and Center for Nanointegration Duisburg-Essen (CENIDE), University of Duisburg-Essen, Lotharstraße 1, 47048 Duisburg (Germany)

2015-04-28

Magnetic phase transition in the Fe{sub 60}Al{sub 40} transition metal aluminide from the ferromagnetic disordered A2-phase to the paramagnetic ordered B2-phase as a function of annealing up to 1000 °C has been investigated by means of magneto-optical and spectroscopy techniques, i.e., Kerr effect, positron annihilation, and Mössbauer spectroscopy. The positron annihilation spectroscopy has been performed in-situ sequentially after each annealing step at the Apparatus for In-situ Defect Analysis that is a unique tool combining positron annihilation spectroscopy with temperature treatment, material evaporation, ion irradiation, and sheet resistance measurement techniques. The overall goal was to investigate the importance of the open volume defects onto the magnetic phase transition. No evidence of variation in the vacancy concentration in matching the magnetic phase transition temperature range (400–600 °C) has been found, whereas higher temperatures showed an increase in the vacancy concentration.

Molecular dynamics simulations of nucleation and phase transitions in molecular clusters of hexafluorides

International Nuclear Information System (INIS)

Xu, S.

1993-01-01

Molecular dynamics simulations of nucleation and phase transitions in TeF 6 and SeF 6 clusters containing 100-350 molecules were carried out. Simulations successfully reproduced the crystalline structures observed in electron diffraction studies of large clusters (containing about 10 4 molecules) of the same materials. When the clusters were cooled, they spontaneously underwent the same bcc the monoclinic phase transition in simulations as in experiment, despite the million-fold difference in the time scales involved. Other transitions observed included melting and freezing. Several new techniques based on molecular translation and orientation were introduced to identify different condensed phases, to study nucleation and phase transitions, and to define characteristic temperatures of transitions. The solid-state transition temperatures decreased with cluster size in the same way as did the melting temperature, in that the depression of transition temperature was inversely proportional to the cluster radius. Rotational melting temperatures, as inferred from the rotational diffusion of molecules, coincided with those of the solid-state transition. Nucleation in liquid-solid and bcc-monoclinic transitions started in the interior of clusters on cooling, and at the surface on heating. Transition temperatures on cooling were always lower than those on heating due to the barriers to nucleation. Linear growth rates of nuclei in freezing were an order of magnitude lower than those in the bcc-monoclinic transition. Revealing evidence about the molecular behavior associated with phase changes was found. Simulations showed the formation of the actual transition complexes along the transition pathway, i.e., the critical nuclei of the new phase. These nuclei, consisting of a few dozen molecules, were distinguishable in the midst of the surrounding matter

Magnetic Phase Transitions of CeSb. I

DEFF Research Database (Denmark)

Fischer, Pernille Hertz; Lebech, Bente; Meier, G.

1978-01-01

The magnetic ordering of the anomalous antiferromagnet CeSb, which has a NaCl crystal structure, was determined in zero applied magnetic field by means of neutron diffraction investigations of single crystals and powder. Below the Neel temperature TN of (16.1+or-0.1)K, there exist six partially...... a first-order phase transition at TN. At approximately TN/2 there is a first-order phase transition to a FCC type IA low-temperature configuration. The unusual magnetic properties of CeSb, which result from anisotropic exchange and crystalline electric field effects, resemble those of certain actinide Na...

Phase stability and elastic properties of Tan+1AlCn (n = 1-3) at high pressure and elevated temperature

International Nuclear Information System (INIS)

Music, Denis; Emmerlich, Jens; Schneider, Jochen M

2007-01-01

We have studied the electronic structure of Ta n+1 AlC n (space group P6 3 /mmc,n = 1-3) under uniform compression from 0 to 60 GPa and at temperatures from 0 to 1500 K using ab initio calculations. These phases can be characterized by alternating layers of high and low electron density and are referred to as nanolaminates. At 0 K we observe similar compressibilities in both the a and c directions for all phases investigated. This is unusual for nanolaminates. Based on the density of states analysis, we propose that these similar compressibilities may be caused by an increase in Ta-Al and Ta-Ta bonding strength as well as a stronger long-range interaction between TaC-TaC layers. No evidence of a phase transition is observed as the pressure is increased to 60 GPa. However, as the temperature is increased to approximately 1000 K without applying pressure, a first-order phase transition occurs in Ta 3 AlC 2 . These results are relevant for applications of Ta n+1 AlC n at elevated temperature and pressure

Thermal study of monovalent-divalent phase transition in npBifc-F1TCNQ System

International Nuclear Information System (INIS)

Sato, Michiko; Nishio, Yutaka; Kajita, Koji; Mochida, Tomoyuki

2009-01-01

In a new molecular solid composed of di-neopentyl-biferrocene (npBifc) and fluorotetracyanoquinodimethane (F 1 TCNQ) 3 , Mochida reported the discovery of a reversible valence transfer that can be regarded as an 'ionic(I)-ionic(II)' phase transfer between the monovalent state (D + A - ) and the divalent state (D 2+ A 2- ). We have studied thermo-dynamical properties of this transformation for this complex using the differential thermal analyses (DTA). We observed a broad excess specific heat with multi-peaks attributed to micro-domain structure over the corresponding temperature range (100-150K) accompanied by temperature hysteresis of 7K. The transition entropy (ΔS) was determined to be 22 ± 2 J/mol-K and almost satisfied a Clausius-Clapeyron relation. These experimental results provide an experimental confirmation of the first order phase transition for the monovalent-divalent transfer. At the transition, we observe that the electronic degrees of freedom remained constant values, while large entropy absorbed crossing from low temperature phase to high temperature one is contributed by the lattice one. We finally estimated the internal energy and concluded that delicate energy valance between Madelung, ionization and affinity energies enable this system to exhibit a temperature induce monovalent-divalent phase transition.

Behavior of the antiferromagnetic phase transition near the fermion condensation quantum phase transition in YbRh{sub 2}Si{sub 2}

Energy Technology Data Exchange (ETDEWEB)

Shaginyan, V.R., E-mail: vrshag@thd.pnpi.spb.r [Petersburg Nuclear Physics Institute, RAS, Gatchina 188300 (Russian Federation); Racah Institute of Physics, Hebrew University, Jerusalem 91904 (Israel); Amusia, M.Ya. [Racah Institute of Physics, Hebrew University, Jerusalem 91904 (Israel); Popov, K.G. [Komi Science Center, Ural Division, RAS, Syktyvkar 167982 (Russian Federation)

2010-01-11

Low-temperature specific-heat measurements on YbRh{sub 2}Si{sub 2} at the second order antiferromagnetic (AF) phase transition reveal a sharp peak at T{sub N}=72 mK. The corresponding critical exponent alpha turns out to be alpha=0.38, which differs significantly from that obtained within the framework of the fluctuation theory of second order phase transitions based on the scale invariance, where alphaapprox =0.1. We show that under the application of magnetic field the curve of the second order AF phase transitions passes into a curve of the first order ones at the tricritical point leading to a violation of the critical universality of the fluctuation theory. This change of the phase transition is generated by the fermion condensation quantum phase transition. Near the tricritical point the Landau theory of second order phase transitions is applicable and gives alphaapprox =1/2. We demonstrate that this value of alpha is in good agreement with the specific-heat measurements.

Phase transitions in the hard-core Bose-Fermi-Hubbard model at non-zero temperatures in the heavy-fermion limit

Energy Technology Data Exchange (ETDEWEB)

Stasyuk, I.V.; Krasnov, V.O., E-mail: krasnoff@icmp.lviv.ua

2017-04-15

Phase transitions at non-zero temperatures in ultracold Bose- and Fermi-particles mixture in optical lattices using the Bose-Fermi-Hubbard model in the mean field and hard-core boson approximations are investigated. The case of infinitely small fermion transfer and the repulsive on-site boson-fermion interaction is considered. The possibility of change of order (from the 2nd to the 1st one) of the phase transition to the superfluid phase in the regime of fixed values of the chemical potentials of Bose- and Fermi-particles is established. The relevant phase diagrams determining the conditions at which such a change takes place, are built.

Decomposition of silicon carbide at high pressures and temperatures

Energy Technology Data Exchange (ETDEWEB)

Daviau, Kierstin; Lee, Kanani K. M.

2017-11-01

We measure the onset of decomposition of silicon carbide, SiC, to silicon and carbon (e.g., diamond) at high pressures and high temperatures in a laser-heated diamond-anvil cell. We identify decomposition through x-ray diffraction and multiwavelength imaging radiometry coupled with electron microscopy analyses on quenched samples. We find that B3 SiC (also known as 3C or zinc blende SiC) decomposes at high pressures and high temperatures, following a phase boundary with a negative slope. The high-pressure decomposition temperatures measured are considerably lower than those at ambient, with our measurements indicating that SiC begins to decompose at ~ 2000 K at 60 GPa as compared to ~ 2800 K at ambient pressure. Once B3 SiC transitions to the high-pressure B1 (rocksalt) structure, we no longer observe decomposition, despite heating to temperatures in excess of ~ 3200 K. The temperature of decomposition and the nature of the decomposition phase boundary appear to be strongly influenced by the pressure-induced phase transitions to higher-density structures in SiC, silicon, and carbon. The decomposition of SiC at high pressure and temperature has implications for the stability of naturally forming moissanite on Earth and in carbon-rich exoplanets.

Isothermal phase transition and the transition temperature limitation in the lead-free (1-x)Bi0.5Na0.5TiO3-xBaTiO3 system

International Nuclear Information System (INIS)

Zhang, Dawei; Yao, Yonggang; Fang, Minxia; Luo, Zhengdong; Zhang, Lixue; Li, Linglong; Cui, Jian; Zhou, Zhijian; Bian, Jihong; Ren, Xiaobing; Yang, Yaodong

2016-01-01

Most ferroelectric transitions occur ultrafast and are time independent. However, here in (1-x) (Bi 0.5 Na 0.5 )TiO 3 -xBaTiO 3 , we have found a ferroelectric phase transition induced solely by increasing waiting time at certain temperatures (isothermal phase transition). Through cooling, a unique metastable state between a relaxor ferroelectric and a ferroelectric is unveiled, which in essence is initially a short-range ordered glassy state and then can evolve into a long-range ordered ferroelectric state through the isothermal process. It is also found that these isothermal ferroelectric transitions only occur within a specific temperature region with different waiting time needed. These features of isothermal phase transition can be understood by Landau theory analysis with the consideration of random defects as a competition between the thermodynamically favored long-range ordered state and the kinetically frustrated short-range ordered glassy state from random defects. This study offers a precise experimental as well as a phenomenological interpretation on the isothermal ferroelectric transition, which may help to further clarify the intricate structure-property relationship in this important lead-free piezoelectric material and other related systems.

The finite temperature QCD phase transition and the thermodynamic equation of state. An investigation employing lattice QCD with Nf=2 twisted mass quarks

International Nuclear Information System (INIS)

Burger, Florian

2012-01-01

In this thesis we report about an investigation of the finite temperature crossover/phase transition of quantum chromodynamics and the evaluation of the thermodynamic equation of state. To this end the lattice method and the Wilson twisted mass discretisation of the quark action are used. This formulation is known to have an automatic improvement of lattice artifacts and thus an improved continuum limit behaviour. This work presents first robust results using this action for the non-vanishing temperature case. We investigate the chiral limit of the two flavour phase transition with several small values of the pion mass in order to address the open question of the order of the transition in the limit of vanishing quark mass. For the currently simulated pion masses in the range of 300 to 700 MeV we present evidence that the finite temperature transition is a crossover transition rather than a genuine phase transition. The chiral limit is investigated by comparing the scaling of the observed crossover temperature with the mass including several possible scenarios. Complementary to this approach the chiral condensate as the order parameter for the spontaneous breaking of chiral symmetry is analysed in comparison with the O(4) universal scaling function which characterises a second order transition. With respect to thermodynamics the equation of state is obtained from the trace anomaly employing the temperature integral method which provides the pressure and energy density in the crossover region. The continuum limit of the trace anomaly is studied by considering several values of N τ and the tree-level correction technique.

Phase transitions

CERN Document Server

Sole, Ricard V; Solé, Ricard V; Solé, Ricard V; Sol, Ricard V; Solé, Ricard V

2011-01-01

Phase transitions--changes between different states of organization in a complex system--have long helped to explain physics concepts, such as why water freezes into a solid or boils to become a gas. How might phase transitions shed light on important problems in biological and ecological complex systems? Exploring the origins and implications of sudden changes in nature and society, Phase Transitions examines different dynamical behaviors in a broad range of complex systems. Using a compelling set of examples, from gene networks and ant colonies to human language and the degradation of diverse ecosystems, the book illustrates the power of simple models to reveal how phase transitions occur. Introductory chapters provide the critical concepts and the simplest mathematical techniques required to study phase transitions. In a series of example-driven chapters, Ricard Solé shows how such concepts and techniques can be applied to the analysis and prediction of complex system behavior, including the origins of ...

Can Holstein-Kondo lattice model be used as a candidate for the theory of high transition temperature superconductors

Directory of Open Access Journals (Sweden)

R Nourafkan

2009-08-01

Full Text Available   It is a common knowledge that the formation of electron pairs is a necessary ingredient of any theoretical work describing superconductivity. Thus, finding the mechanism of the formation of the electron pairs is of utmost importance. There are some experiments on high transition temperature superconductors which support the electron-phonon (e-ph interactions as the pairing mechanism (ARPES, and there are others which support the spin fluctuations as their pairing mechanism (tunneling spectroscopy. In this paper, we introduce the Holstein-Kondo lattice model (H-KLM which incorporates the e-ph as well as the Kondo exchange interaction. We have used the dynamical mean field theory (DMFT to describe heavy fermion semiconductors and have employed the exact-diagonalization technique to obtain our results. The phase diagram of these systems in the parameter space of the e-ph coupling, g, and the Kondo exchange coupling, J, show that the system can be found in the Kondo insulating phase, metallic phase or the bi-polaronic phase. It is shown that these systems develop both spin gap and a charge gap, which are different and possess energies in the range of 1-100 meV. In view of the fact that both spin excitation energies and phonon energies lie in this range, we expect our work on H-KLM opens a way to formalize the theory of the high transition temperature superconductors .

The influence of phase transitions in phosphatidylethanolamine models on the activity of violaxanthin de-epoxidase.

Science.gov (United States)

Vieler, Astrid; Scheidt, Holger A; Schmidt, Peter; Montag, Cindy; Nowoisky, Janine F; Lohr, Martin; Wilhelm, Christian; Huster, Daniel; Goss, Reimund

2008-04-01

In the present study, the influence of the phospholipid phase state on the activity of the xanthophyll cycle enzyme violaxanthin de-epoxidase (VDE) was analyzed using different phosphatidylethanolamine species as model lipids. By using (31)P NMR spectroscopy, differential scanning calorimetry and temperature dependent enzyme assays, VDE activity could directly be related to the lipid structures the protein is associated with. Our results show that the gel (L beta) to liquid-crystalline (L alpha) phase transition in these single lipid component systems strongly enhances both the solubilization of the xanthophyll cycle pigment violaxanthin in the membrane and the activity of the VDE. This phase transition has a significantly stronger impact on VDE activity than the transition from the L alpha to the inverted hexagonal (HII) phase. Especially at higher temperatures we found increased VDE reaction rates in the presence of the L alpha phase compared to those in the presence of HII phase forming lipids. Our data furthermore imply that the HII phase is better suited to maintain high VDE activities at lower temperatures.

Spin Crossover and the Magnetic P- T Phase Diagram of Hematite at High Hydrostatic Pressures and Cryogenic Temperatures

Science.gov (United States)

Gavriliuk, A. G.; Struzhkin, V. V.; Mironovich, A. A.; Lyubutin, I. S.; Troyan, I. A.; Chow, P.; Xiao, Y.

2018-02-01

The magnetic properties of the α-Fe2O3 hematite at a high hydrostatic pressure have been studied by synchrotron Mössbauer spectroscopy (nuclear forward scattering (NFS)) on iron nuclei. Time-domain NFS spectra of hematite have been measured in a diamond anvil cell in the pressure range of 0-72 GPa and the temperature range of 36-300 K in order to study the magnetic properties at a phase transition near a critical pressure of 50 GPa. In addition, Raman spectra at room temperature have been studied in the pressure range of 0-77 GPa. Neon has been used as a pressure-transmitting medium. The appearance of an intermediate electronic state has been revealed at a pressure of 48 GPa. This state is probably related to the spin crossover in Fe3+ ions at their transition from the high-spin state (HS, S = 5/2) to a low-spin one (LS, S = 1/2). It has been found that the transient pressure range of the HS-LS crossover is extended from 48 to 55 GPa and is almost independent of the temperature. This surprising result differs fundamentally from other cases of the spin crossover in Fe3+ ions observed in other crystals based on iron oxides. The transition region of spin crossover appears because of thermal fluctuations between HS and LS states in the critical pressure range and is significantly narrowed at cooling because of the suppression of thermal excitations. The magnetic P- T phase diagram of α-Fe2O3 at high pressures and low temperatures in the spin crossover region has been constructed according to the results of measurements.

Entropy and baryon number conservation in the deconfinement phase transition

International Nuclear Information System (INIS)

Leonidov, A.; Redlich, K.; Satz, H.; Suhonen, E.; Weber, G.

1994-01-01

The conservation of entropy and baryon number in the deconfinement phase transition is studied in the framework of the bag model. In the standard construction of the equilibrium phase transition from a quark-gluon plasma into a hadron gas a subsequent dilution and reheating of the system on the phase boundary is necessary to preserve the entropy and baryon number conservation. We propose modifying the bag pressure to depend explicitly on temperature and baryon chemical potential. It is shown that this modification is sufficient to construct a model in agreement with the Gibbs equilibrium criteria for a phase transition, while simultaneously assuring entropy and baryon number conservation on the phase boundary. Within this model the quark-gluon plasma hadronizes at a fixed temperature and chemical potential

High-field magnetic phase transitions and spin excitations in magnetoelectric LiNiPO4

DEFF Research Database (Denmark)

Toft-Petersen, Rasmus; Jensen, Jens; Jensen, Thomas Bagger Stibius

2011-01-01

The magnetically ordered phases and spin dynamics of magnetoelectric LiNiPO4 have been studied in fields up to 17.3 T along the c axis. Using neutron diffraction, we show that a previously proposed linearly polarized incommensurate (IC) structure exists only for temperatures just below the Neel...... temperature T-N. The ordered IC structure at the lowest temperatures is shown instead to be an elliptically polarized canted spiral for fields larger than 12 T. The transition between the two IC phases is of second order and takes place about 2 K below T-N. For mu H-0 > 16 T and temperatures below 10 K......, the spiral structure is found to lock in to a period of five crystallographic unit cells along the b axis. Based on the neutron-diffraction data, combined with detailed magnetization measurements along all three crystallographic axes, we establish the magnetic phase diagrams for fields up to 17.3 T along c...

Experimental study of the magnetic phase transition in the MnSi itinerant helimagnet

International Nuclear Information System (INIS)

Stishov, S. M.; Petrova, A. E.; Khasanov, S.; Panova, G. Kh.; Shikov, A. A.; Lashley, J. C.; Wu, D.; Lograsso, T. A.

2008-01-01

Magnetic susceptibility, heat capacity, thermal expansion, and resistivity of a high-quality single crystal of MnSi were carefully studied at ambient pressure. The calculated change in magnetic entropy in the temperature range 0-30 K is less than 0.1R, a low value that emphasizes the itinerant nature of magnetism in MnSi. A linear temperature term dominates the behavior of the thermal expansion coefficient in the range 30-150 K, which correlates to a large enhancement of the linear electronic term in the heat capacity. A surprising similarity between variation of the heat capacity, the thermal expansion coefficient, and the temperature derivative of resistivity through the phase transition in MnSi is observed. Specific forms of the heat capacity, thermal expansion coefficient, and temperature derivative of resistivity at the phase transition to a helical magnetic state near 29 K are interpreted as a combination of sharp first-order features and broad peaks or shallow valleys of yet unknown origin. The appearance of these broad satellites probably hints at a frustrated magnetic state in MnSi slightly above the transition temperature. Present experimental findings bring the current views on the phase diagram of MnSi into question

Thermophysical data for various transition metals at high temperatures obtained by a submicrosecond-pulse-heating method

International Nuclear Information System (INIS)

Seydel, U.; Bauhof, H.; Fucke, W.; Wadle, H.

1979-01-01

Thermophysical data for several transition metals are reported including enthalpies, electric resistivities, and specific volumes at the melting transition, and volume expansion coefficients and heat capacities in the liquid phase. Values for the critical temperatures, pressures, and volumes are given for molybdenum and tungsten. All data have been obtained by a submicrosecond-pulse-heating method. (author)

Tuning of cu doping on phase transition and high-field phase diagram of Nd{sub 0.5}Sr{sub 0.5}Mn{sub 1−x}Cu{sub x}O{sub 3}

Energy Technology Data Exchange (ETDEWEB)

Shang, C. [Wuhan National High Magnetic Field Center, Huazhong University of Science and Technology, Wuhan 430074 (China); School of Physics, Huazhong University of Science and Technology, Wuhan 430074 (China); Xia, Z.C., E-mail: xia9020@hust.edu.cn [Wuhan National High Magnetic Field Center, Huazhong University of Science and Technology, Wuhan 430074 (China); Wei, M.; Jin, Z.; Chen, B.R.; Shi, L.R. [Wuhan National High Magnetic Field Center, Huazhong University of Science and Technology, Wuhan 430074 (China); School of Physics, Huazhong University of Science and Technology, Wuhan 430074 (China); Ouyang, Z.W. [Wuhan National High Magnetic Field Center, Huazhong University of Science and Technology, Wuhan 430074 (China); Huang, S.; Xiao, G.L. [Wuhan National High Magnetic Field Center, Huazhong University of Science and Technology, Wuhan 430074 (China); School of Physics, Huazhong University of Science and Technology, Wuhan 430074 (China)

2016-10-15

Pulsed high magnetic fields up to 52 T have been used in the systematic investigation of the magnetic properties of manganites Nd{sub 0.5}Sr{sub 0.5}Mn{sub 1−x}Cu{sub x}O{sub 3} (0≤x≤0.15). The Cu-doping dependent first-order metamagnetic transitions are observed below the charge ordering temperature, which is ascribed to both Cu-doping and field-induced collapse of the charge ordering with antiferromagnetic phase. Based on the magnetization and electrical transport measurements, a three-dimensional phase diagram with coordinate axis of temperature, magnetic field, and doping level has been obtained, in which the critical fields of the metamagnetic transitions increase with the increase in Cu content and decrease with increasing temperature. The experimental results confirm that Mn-site substitution with Cu destroys the Mn{sup 3+}–O{sup 2−}–Mn{sup 4+} bridges and weakens the double exchange interaction between Mn{sup 3+} and Mn{sup 4+} ions, which shows an obvious tuning effect on the metamagnetic transition under the external magnetic field. - Highlights: • Tuning effect of Cu-doping on the properties of Nd{sub 0.5}Sr{sub 0.5}Mn{sub 1−x}Cu{sub x}O{sub 3} was studied. • First-order metamagnetic transition was observed under high magnetic fields. • A phase diagram with temperature, magnetic field and doping level was obtained. • Cu-doping weakens the ferromagnetic coupling in Nd{sub 0.5}Sr{sub 0.5}Mn{sub 1−x}Cu{sub x}O{sub 3}.

Quantum phase transition with dissipative frustration

Science.gov (United States)

Maile, D.; Andergassen, S.; Belzig, W.; Rastelli, G.

2018-04-01

We study the quantum phase transition of the one-dimensional phase model in the presence of dissipative frustration, provided by an interaction of the system with the environment through two noncommuting operators. Such a model can be realized in Josephson junction chains with shunt resistances and resistances between the chain and the ground. Using a self-consistent harmonic approximation, we determine the phase diagram at zero temperature which exhibits a quantum phase transition between an ordered phase, corresponding to the superconducting state, and a disordered phase, corresponding to the insulating state with localized superconducting charge. Interestingly, we find that the critical line separating the two phases has a nonmonotonic behavior as a function of the dissipative coupling strength. This result is a consequence of the frustration between (i) one dissipative coupling that quenches the quantum phase fluctuations favoring the ordered phase and (ii) one that quenches the quantum momentum (charge) fluctuations leading to a vanishing phase coherence. Moreover, within the self-consistent harmonic approximation, we analyze the dissipation induced crossover between a first and second order phase transition, showing that quantum frustration increases the range in which the phase transition is second order. The nonmonotonic behavior is reflected also in the purity of the system that quantifies the degree of correlation between the system and the environment, and in the logarithmic negativity as an entanglement measure that encodes the internal quantum correlations in the chain.

Spatial heterogeneity in liquid–liquid phase transition

International Nuclear Information System (INIS)

Duan Yun-Rui; Li Tao; Wu Wei-Kang; Li Jie; Zhou Xu-Yan; Liu Si-Da; Li Hui

2017-01-01

Molecular dynamics simulations are performed to investigate the liquid–liquid phase transition (LLPT) and the spatial heterogeneity in Al–Pb monotectic alloys. The results reveal that homogeneous liquid Al–Pb alloy undergoes an LLPT, separating into Al-rich and Pb-rich domains, which is quite different from the isocompositional liquid water with a transition between low-density liquid (LDL) and high-density liquid (HDL). With spatial heterogeneity becoming large, LLPT takes place correspondingly. The relationship between the cooling rate, relaxation temperature and percentage of Al and the spatial heterogeneity is also reported. This study may throw light on the relationship between the structure heterogeneity and LLPT, which provides novel strategies to control the microstructures in the fabrication of the material with high performance. (paper)

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.

Dual QCD and phase transition in early universe

International Nuclear Information System (INIS)

Ranjan, Akhilesh; Raina, P.K.; Nandan, Hemwati

2009-01-01

The quantum chromodynamics (QCD) vacuum with condensed monopoles/ dyons (i.e., a dual Ginzburg- Landau (DGL) type model of QCD or dual QCD) has been quite successful to describe the large-distance behavior of QCD vacuum. Further, such DGL theory of QCD at finite temperature is also found to be useful in studying the phase transition process as believed to occur in early universe. In the present article, we have used the DGL theory of QCD with dyons to study the hadronisation in early universe. The effective potential at finite temperature is calculated. The notions of the phase transition in the background of the dyonically condensed QCD vacuum has been investigated by calculating the critical temperature in view of the temperature dependent couplings

Synchrotron radiation topography studies of the phase transition in LaGaO sub 3 crystals

Energy Technology Data Exchange (ETDEWEB)

Yao, G.D.; Dudley, M. (Dept. of Materials Science and Engineering, SUNY at Stony Brook, NY (USA)); Wang, Y.; Liu, X.; Liebermann, R.C. (Dept. of Earth and Space Sciences, SUNY at Stony Brook, NY (USA))

1991-05-01

An investigation of the orthorhombic to rhombohedral phase transformation occurring at 145degC in lanthanum gallate has been conducted using white beam synchrotron X-ray topography (WBSXRT). The existence of the first order transition was confirmed by differential thermal analysis and X-ray diffractometer powder analysis. Subsequent to this, synchrotron white beam Laue patterns were recorded in situ as a function of temperature, during the transition. Before the transition point was reached, (112){sub orth} type reflection twinning was found to be dominant although a small amount of (110){sub orth} type twinning was also observed in the same crystal. Beyond the transition point, not only did the structural change become evident but also reflection twinning on the (110){sub rhom} planes was observed. The scale of this twinning became finer as the temperature was increased beyond the transition temperature. The twinning observed in both the low and high temperature phases gives rise to deformation of the (011){sub rhom} surface plane which creates problems for the potential use of this material as a substrate for growing high Tc superconducting epitaxial layers. (orig.).

Interplay of the Glass Transition and the Liquid-Liquid Phase Transition in Water

Science.gov (United States)

Giovambattista, Nicolas; Loerting, Thomas; Lukanov, Boris R.; Starr, Francis W.

2012-01-01

Water has multiple glassy states, often called amorphous ices. Low-density (LDA) and high-density (HDA) amorphous ice are separated by a dramatic, first-order like phase transition. It has been argued that the LDA-HDA transformation connects to a first-order liquid-liquid phase transition (LLPT) above the glass transition temperature Tg. Direct experimental evidence of the LLPT is challenging to obtain, since the LLPT occurs at conditions where water rapidly crystallizes. In this work, we explore the implications of a LLPT on the pressure dependence of Tg(P) for LDA and HDA by performing computer simulations of two water models – one with a LLPT, and one without. In the absence of a LLPT, Tg(P) for all glasses nearly coincide. When there is a LLPT, different glasses exhibit dramatically different Tg(P) which are directly linked with the LLPT. Available experimental data for Tg(P) are only consistent with the scenario including a LLPT. PMID:22550566

Thermal study of monovalent-divalent phase transition in npBifc-F{sub 1}TCNQ System

Energy Technology Data Exchange (ETDEWEB)

Sato, Michiko; Nishio, Yutaka; Kajita, Koji [Department of Physics, Faculty of Science, Toho University, Miyama 2-2-1, Funabashi, Chiba, 274-8510 (Japan); Mochida, Tomoyuki, E-mail: nishio@ph.sci.toho-u.ac.j [Department of Chemistry, Faculty of Science, Kobe University, Rokkodai, Nada, Kobe 657-8501 (Japan)

2009-03-01

In a new molecular solid composed of di-neopentyl-biferrocene (npBifc) and fluorotetracyanoquinodimethane (F{sub 1}TCNQ){sub 3}, Mochida reported the discovery of a reversible valence transfer that can be regarded as an 'ionic(I)-ionic(II)' phase transfer between the monovalent state (D{sup +}A{sup -}) and the divalent state (D{sup 2+}A{sup 2-}). We have studied thermo-dynamical properties of this transformation for this complex using the differential thermal analyses (DTA). We observed a broad excess specific heat with multi-peaks attributed to micro-domain structure over the corresponding temperature range (100-150K) accompanied by temperature hysteresis of 7K. The transition entropy (DELTAS) was determined to be 22 +- 2 J/mol-K and almost satisfied a Clausius-Clapeyron relation. These experimental results provide an experimental confirmation of the first order phase transition for the monovalent-divalent transfer. At the transition, we observe that the electronic degrees of freedom remained constant values, while large entropy absorbed crossing from low temperature phase to high temperature one is contributed by the lattice one. We finally estimated the internal energy and concluded that delicate energy valance between Madelung, ionization and affinity energies enable this system to exhibit a temperature induce monovalent-divalent phase transition.

Scratching the surface of ice: Interfacial phase transitions and their kinetic implications

Science.gov (United States)

Limmer, David

The surface structure of ice maintains a high degree of disorder down to surprisingly low temperatures. This is due to a number of underlying interfacial phase transitions that are associated with incremental changes in broken symmetry relative to the bulk crystal. In this talk I summarize recent work attempting to establish the nature and locations of these different phase transitions as well as how they depend on external conditions and nonequilibrium driving. The implications of this surface disorder is discussed in the context of simple kinetic processes that occur at these interfaces. Recent experimental work on the roughening transition is highlighted.

Magnetic Phase Transitions of CeSb. II: Effects of Applied Magnetic Fields

DEFF Research Database (Denmark)

Meier, G.; Fischer, P.; Hälg, W.

1978-01-01

For pt.I see ibid., vol.11, p.345 (1978). The metamagnetic phase transition and the associated phase diagram of the anomalous antiferromagnet CeSb were determined in a neutron diffraction study of the magnetic ordering of CeSb single crystals in applied magnetic fields parallel to the (001...... magnetic fields. The observed magnetic structures do not correspond to the stable configurations expected from the molecular field theory of the face-centred cubic lattice. The change from a first-order transition at the Neel temperature in zero field to second-order transition at high fields points...

Effect of In-Situ Cure on Measurement of Glass Transition Temperatures in High-Temperature Thermosetting Polymers (Briefing Charts)

Science.gov (United States)

2015-05-20

TEMPERATURES IN HIGH-TEMPERATURE THERMOSETTING POLYMERS 5a. CONTRACT NUMBER In-House 5b. GRANT NUMBER 5c. PROGRAM ELEMENT NUMBER 6. AUTHOR(S) 5d...temperature thermosetting polymer via dynamic mechanical analysis alone. These difficulties result from the residual cure of samples heated beyond their...98) Prescribed by ANSI Std. 239.18 Effect of In-Situ Cure on Measurement of Glass Transition Temperatures in High-Temperature Thermosetting

Variable-temperature Microwave Impedance Microscope with Light Stimulation for Research on Photo-induced Phase Transitions

Science.gov (United States)

2017-07-24

SECURITY CLASSIFICATION OF: The DURIP program "Variable-temperature Microwave Impedance Microscope with Light Stimulation for Research on Photo... Stimulation for Research on Photo- induced Phase Transitions The views, opinions and/or findings contained in this report are those of the author(s) and should...reporting burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing instructions

Thermoelectric power and phase transitions in lanthanides under pressure up to 20 GPa

International Nuclear Information System (INIS)

Ovsyannikov, Sergey V.; Shchennikov, Vladimir V.; Goshchitskii, Boris N.

2007-01-01

Pressure dependencies of thermopower S of rare-earth metals (Ce and Pr) in a pressure P range of 0-20 GPa and at room temperature are reported. A non-monotonic behaviour of S(P) has been established both at pressure-induced phase transitions: fcc → modified fcc → monoclinic → tetragonal lattice for Ce, and double hexagonal close packed (dhcp) → fcc → modified fcc → monoclinic for Pr. S kept a positive sign for the all high-pressure phases mentioned. Simultaneous measurements of sample contraction have revealed anomalies in the vicinity of the transitions in qualitative agreement with diffraction volumetric data published before. The S(P) dependencies were analysed on the basis of the known results of electronic structure calculation for the Ce and Pr phases. An advantage was demonstrated of the thermopower method in the study of phase transitions and electronic structure of high-pressure phases

Transition Temperatures of Thermotropic Liquid Crystals from the Local Binary Gray Level Cooccurrence Matrix

Directory of Open Access Journals (Sweden)

S. Sreehari Sastry

2012-01-01

Full Text Available This paper presents a method which combines the statistical analysis with texture structural analysis called Local Binary Gray Level Cooccurrence Matrix (LBGLCM to investigate the phase transition temperatures of thermotropic p,n-alkyloxy benzoic acid (nOBA, n=4,6,8,10 and 12 liquid crystals. Textures of the homeotropically aligned liquid crystal compounds are recorded as a function of temperature using polarizing optical microscope attached to the hot stage and high resolution camera. In this method, second-order statistical parameters (contrast, energy, homogeneity, and correlation are extracted from the LBGLCM of the textures. The changes associatedwiththe values of extracted parameters as a function of temperature are a helpful process to identify the phases and phase transition temperatures of the samples. Results obtained from this method have validity and are in good agreement with the literature.

Pressure-induced phase transitions in Zr-rich PbZr{sub 1-x}Ti{sub x}O{sub 3} ceramics

Energy Technology Data Exchange (ETDEWEB)

Souza Filho, A.G. [Departamento de Fisica, Universidade Federal do Ceara, Fortaleza, Ceara (Brazil)]. E-mail: agsf@fisica.ufc.br; Faria, J.L.B.; Freire, P.T.C.; Ayala, A.P.; Sasaki, J.M.; Melo, F.E.A.; Mendes Filho, J. [Departamento de Fisica, Universidade Federal do Ceara, Fortaleza, Ceara (Brazil); Araujo, E.B. [Departamento de Fisica e Quimica, Universidade Estadual de Sao Paulo, Campus de Ilha Solteira, Ilha Solteira, SP (Brazil); Eiras, J.A. [Departamento de Fisica, Universidade Federal de Sao Carlos, Sao Carlos, SP (Brazil)

2001-08-20

A Raman study of structural changes in the Zr-rich PbZr{sub 1-x}Ti{sub x}O{sub 3} (PZT) system under hydrostatic pressures up to 5.0 GPa is presented. We observe that externally applied pressure induces several phase transitions in PZT ceramics among phases with orthorhombic (A{sub O}), rhombohedral low-temperature (R{sub LT}), and rhombohedral high-temperature (R{sub HT}) symmetries (all found in PZT at ambient pressure and room temperature). Each of the compositions investigated (0.02{<=}x{<=}0.14) exhibits a high-pressure phase with orthorhombic (O{sub I'}) symmetry. We further report a detailed study of the pressure dependence of Raman frequencies to elucidate the phase transitions and to provide a set of pressure coefficients for the high-pressure phases. (author)

Novel phase transitions in B-site doped manganites

International Nuclear Information System (INIS)

Popovic, Z.V.; Cantarero, A.; Thijssen, W.H.A.; Paunovic, N.; Dohcevic-Mitrovic, Z.; Sapina, F.

2005-01-01

We have examined the infrared reflectivity and the electrical resistivity of La 1- x [Sr(Ba)] x Mn 1- z [Cu(Zn)] z O 3 samples in ferromagnetic metallic and insulator regime. Several phase transitions are observed, the most obvious being the transition from a ferromagnetic metallic to a ferromagnetic insulator phase that is related to the formation of short-range orbitally ordered domains. The temperature T 1 of the phase transition is dependent on doping concentration and for optimally doped samples (∼32% of Mn 4+ ions) we have found T 1 ∼0.93 T C

Inorganic Nanostructured High-Temperature Magnet Wires, Phase I

Data.gov (United States)

National Aeronautics and Space Administration — This project will develop a high-temperature tolerant electrically-insulating coating for magnet wires. The Phase I program will result in a flexible, inorganic...

Effect of borojo (Borojoa patinoi Cuatrecasas) three-phase composition and gum arabic on the glass transition temperature.

Science.gov (United States)

Rodríguez-Bernal, Jenny M; Tello, Edisson; Flores-Andrade, Enrique; Perea-Flores, Maria de Jesús; Vallejo-Cardona, Alba A; Gutiérrez-López, Gustavo F; Quintanilla-Carvajal, Maria X

2016-02-01

The search for natural, novel, high-quality, stable food ingredients is an ongoing practice in the food industry. Pulp of borojo (Borojoa patinoi Cuatrecasas), which is a fruit of the Colombian Pacific region, can be separated into three phases: liquid (LP), medium (MP) and solid (SP) phases. The objective of this work was to evaluate the effect of the three-phase composition and gum arabic on their glass transitions temperatures (T(g)). The best mixture, LP-MP, MP-SP and LP-SP and gum arabic (GA) was identified by response surface methodology. When adding GA to SP borojo phase in a 1:1 proportion, the resulting T(g) of the mixture was 132.27 °C whereas Tg for GA and SP-phase were 154.89 °C and 79.86 °C respectively, which supported this combination as attractive from a processing perspective and supports an industrial advantage of using borojo as food ingredient. Phases were characterized by high-performance liquid chromatography, Fourier transform infrared spectroscopy, confocal laser scanning microscopy and mass spectrometry. Low molecular weight compounds such as fructose for MP lowered T(g) whereas the presence of lignin increased T(g) of the mixtures as with the SP. The addition of GA significantly increased T(g) of borojo phases so leading to propose them as novel food processing materials. © 2015 Society of Chemical Industry.

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

International Nuclear Information System (INIS)

Zhang Bin; Liang Yongcheng; Sun Huiyu

2007-01-01

Nanographite sheets under high compressive stresses at ambient temperature have been investigated through molecular dynamics simulations using the Tersoff-Brenner potential. Nanographite undergoes a soft to hard phase transition at a certain compressive stress, about 15 GPa. With increasing compressions, the bonding structures of nanographite are changed, interlayer sp 3 -bonds are formed, and nanographite transforms into a superhard carbon phase (SCP). Further compressions lead to the instabilities of the SCP. Although the detailed lattice structure of the SCP remains elusive, its compressive strength can approach 150 GPa, comparable to that of diamond. The maximum failure stresses of nanographite sheets are sensitive to the inter-and intra-layer interstices. Our results may explain paradoxical experimental results in the available literature

Thermal properties and phase transition in the fluoride, (NH4)3SnF7

International Nuclear Information System (INIS)

Kartashev, A.V.; Gorev, M.V.; Bogdanov, E.V.; Flerov, I.N.; Laptash, N.M.

2016-01-01

Calorimetric, dilatometric and differential thermal analysis studies were performed on (NH 4 ) 3 SnF 7 for a wide range of temperatures and pressures. Large entropy (δS 0 =22 J/mol K) and elastic deformation (δ(ΔV/V) 0 =0.89%) jumps have proven that the Pa-3↔Pm-3m phase transition is a strong first order structural transformation. A total entropy change of ΔS 0 =32.5 J/mol K is characteristic for the order–disorder phase transition, and is equal to the sum of entropy changes in the related material, (NH 4 ) 3 TiF 7 , undergoing transformation between the two cubic phases through the intermediate phases. Hydrostatic pressure decreases the stability of the high temperature Pm-3m phase in (NH 4 ) 3 SnF 7 , contrary to (NH 4 ) 3 TiF 7 , characterised by a negative baric coefficient. The effect of experimental conditions on the chemical stability of (NH 4 ) 3 SnF 7 was observed. - Graphical abstract: Strong first order structural transformation Pa-3↔Pm-3m in (NH 4 ) 3 SnF 7 is associated with very large total entropy change of ΔS 0 =32.5 J/mol K characteristic for the ordering processes and equal to the sum of entropy changes in the related (NH 4 ) 3 TiF 7 undergoing transformation between the same two cubic phases through the intermediate phases. - Highlights: • (NH 4 ) 3 SnF 7 undergoes strong first order Pa-3↔Pm-3m phase transition. • Anomalous behaviour of ΔC p and ΔV/V exists far below phase transition temperature. • Structural distortions are accompanied by huge total entropy change ΔS≈Rln50. • High pressure strongly increases the stability of Pa-3 phase in (NH 4 ) 3 SnF 7 . • Entropy of the Pa-3↔Pm-3m phase transition does not depend on pressure.

Phase transitions in the urea/n-nonadecane system by calorimetric techniques

International Nuclear Information System (INIS)

Lopez-Echarri, A; Ruiz-Larrea, I; Fraile-RodrIguez, A; Diaz-Hernandez, J; Breczewski, T; Bocanegra, E H

2007-01-01

A calorimetric study of urea/n-nonadecane, CO(NH 2 ) 2 /C 19 H 40 , and the deuterated derivatives, CO(ND 2 ) 2 /C 19 D 40 and CO(NH 2 ) 2 /C 19 D 40 , around the structural phase transition temperature is presented. For this purpose differential scanning (DSC), temperature-modulated (AC) and adiabatic calorimetry have been used and the obtained results are compared. Leaving apart the noticeable peak associated with the main phase transition at 158.5, 149.4 and 154 K respectively, small anomalies of the specific heat are found at lower temperatures and their corresponding entropic and enthalpic changes are reported. Heating and cooling experiments show the influence of the temperature rate and the thermal history on the detailed profile of the specific heat traces. The presence of thermal hysteresis and latent heat as a way to characterize the order of the phase transitions is discussed. Finally, a tentative approach to the urea and the alkyl chain contributions to the specific heat and their influence on the phase transition mechanisms is presented

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...

Hawking–Page phase transition in new massive gravity

Directory of Open Access Journals (Sweden)

Shao-Jun Zhang

2015-07-01

Full Text Available We consider Hawking–Page phase transition between the BTZ black hole with M≥0 and the thermal soliton with M=−1 in new massive gravity. By comparing the on-shell free energies, we can see that there exists a critical temperature. The thermal soliton is more probable than the black hole below the critical temperature while the black hole is more probable than the thermal soliton above the critical temperature. By consistently constructing the off-shell free energies taking into account the conical singularity, we show that there exist infinite non-equilibrium states connecting the BTZ black hole and the thermal soliton, so that they provide a picture of continuous evolution of the phase transition.

Ring diagrams and phase transitions

International Nuclear Information System (INIS)

Takahashi, K.

1986-01-01

Ring diagrams at finite temperatures carry most infrared-singular parts among Feynman diagrams. Their effect to effective potentials are in general so significant that one must incorporate them as well as 1-loop diagrams. The author expresses these circumstances in some examples of supercooled phase transitions

Dynamic phase transitions and dynamic phase diagrams of the Ising model on the Shastry-Sutherland lattice

Energy Technology Data Exchange (ETDEWEB)

Deviren, Şeyma Akkaya, E-mail: sadeviren@nevsehir.edu.tr [Department of Science Education, Education Faculty, Nevsehir Hacı Bektaş Veli University, 50300 Nevşehir (Turkey); Deviren, Bayram [Department of Physics, Nevsehir Hacı Bektaş Veli University, 50300 Nevsehir (Turkey)

2016-03-15

The dynamic phase transitions and dynamic phase diagrams are studied, within a mean-field approach, in the kinetic Ising model on the Shastry-Sutherland lattice under the presence of a time varying (sinusoidal) magnetic field by using the Glauber-type stochastic dynamics. The time-dependence behavior of order parameters and the behavior of average order parameters in a period, which is also called the dynamic order parameters, as a function of temperature, are investigated. Temperature dependence of the dynamic magnetizations, hysteresis loop areas and correlations are investigated in order to characterize the nature (first- or second-order) of the dynamic phase transitions as well as to obtain the dynamic phase transition temperatures. We present the dynamic phase diagrams in the magnetic field amplitude and temperature plane. The phase diagrams exhibit a dynamic tricritical point and reentrant phenomena. The phase diagrams also contain paramagnetic (P), Néel (N), Collinear (C) phases, two coexistence or mixed regions, (N+C) and (N+P), which strongly depend on interaction parameters. - Highlights: • Dynamic magnetization properties of spin-1/2 Ising model on SSL are investigated. • Dynamic magnetization, hysteresis loop area, and correlation have been calculated. • The dynamic phase diagrams are constructed in (T/|J|, h/|J|) plane. • The phase diagrams exhibit a dynamic tricritical point and reentrant phenomena.

Combined effect of dopant and electron beam-irradiation on phase transition in lithium potassium sulphate[Lithium potassium sulphate; Phase transition; Impurity effect; Thermal properties

Energy Technology Data Exchange (ETDEWEB)

Kassem, M.E.; Gaafar, M.; Abdel Gawad, M.M.H.; El-Muraikhi, M.; Ragab, I.M

2004-02-01

Thermodynamic studies of polycrystalline ruthenium (Ru) doped LiKSO{sub 4} have been made for different concentrations of Ru in the range 0%, 0.1%, 0.2%, 0.5%, 1%, 2%, 3% by weight. The thermal behaviour has been investigated using a differential scanning calorimeter in the vicinity of high temperature phases. From this, the effect of electron beam-irradiation on the thermal properties of these polycrystalline samples has been studied. The results showed a change in the transition temperature T{sub c}, as well as the value of specific heat C{sub P{sub max}} at the transition temperature due to the change in Ru content and irradiation energies. The change of enthalpy and entropy of the polycrystalline have been estimated numerically.

High Temperature Fiberoptic Thermal Imaging System, Phase I

Data.gov (United States)

National Aeronautics and Space Administration — The proposed Phase 1 program will fabricate and demonstrate a small diameter single fiber endoscope that can perform high temperature thermal imaging in a jet engine...

Cosmological phase transitions

International Nuclear Information System (INIS)

Kolb, E.W.

1993-10-01

If modern ideas about the role of spontaneous symmetry breaking in fundamental physics are correct, then the Universe should have undergone a series of phase transitions early in its history. The study of cosmological phase transitions has become an important aspect of early-Universe cosmology. In this lecture I review some very recent work on three aspects of phase transitions: the electroweak transition, texture, and axions

Phase transformation in multiferroic Bi{sub 5}Ti{sub 3}FeO{sub 15} ceramics by temperature-dependent ellipsometric and Raman spectra: An interband electronic transition evidence

Energy Technology Data Exchange (ETDEWEB)

Jiang, P. P.; Duan, Z. H.; Xu, L. P.; Zhang, X. L.; Li, Y. W.; Hu, Z. G., E-mail: zghu@ee.ecnu.edu.cn; Chu, J. H. [Key Laboratory of Polar Materials and Devices, Ministry of Education, Department of Electronic Engineering, East China Normal University, Shanghai 200241 (China)

2014-02-28

Thermal evolution and an intermediate phase between ferroelectric orthorhombic and paraelectric tetragonal phase of multiferroic Bi{sub 5}Ti{sub 3}FeO{sub 15} ceramic have been investigated by temperature-dependent spectroscopic ellipsometry and Raman scattering. Dielectric functions and interband transitions extracted from the standard critical-point model show two dramatic anomalies in the temperature range of 200–873 K. It was found that the anomalous temperature dependence of electronic transition energies and Raman mode frequencies around 800 K can be ascribed to intermediate phase transformation. Moreover, the disappearance of electronic transition around 3 eV at 590 K is associated with the conductive property.

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

Quantum percolation phase transition and magnetoelectric dipole glass in hexagonal ferrites

Science.gov (United States)

Rowley, S. E.; Vojta, T.; Jones, A. T.; Guo, W.; Oliveira, J.; Morrison, F. D.; Lindfield, N.; Baggio Saitovitch, E.; Watts, B. E.; Scott, J. F.

2017-07-01

Hexagonal ferrites not only have enormous commercial impact (£2 billion/year in sales) due to applications that include ultrahigh-density memories, credit-card stripes, magnetic bar codes, small motors, and low-loss microwave devices, they also have fascinating magnetic and ferroelectric quantum properties at low temperatures. Here we report the results of tuning the magnetic ordering temperature in PbF e12 -xG axO19 to zero by chemical substitution x . The phase transition boundary is found to vary as TN˜(1-x /xc ) 2 /3 with xc very close to the calculated spin percolation threshold, which we determine by Monte Carlo simulations, indicating that the zero-temperature phase transition is geometrically driven. We find that this produces a form of compositionally tuned, insulating, ferrimagnetic quantum criticality. Close to the zero-temperature phase transition, we observe the emergence of an electric dipole glass induced by magnetoelectric coupling. The strong frequency behavior of the glass freezing temperature Tm has a Vogel-Fulcher dependence with Tm finite, or suppressed below zero in the zero-frequency limit, depending on composition x . These quantum-mechanical properties, along with the multiplicity of low-lying modes near the zero-temperature phase transition, are likely to greatly extend applications of hexaferrites into the realm of quantum and cryogenic technologies.

Ferroelastoelectric phase transition in (NH4)2CuCl4·2H2O single crystal

International Nuclear Information System (INIS)

Tylczyński, Zbigniew; Wiesner, Maciej

2015-01-01

The (NH 4 ) 2 CuCl 4 ·2H 2 O crystal exhibits anomalous thermal, piezoelectric, dielectric and elastic properties in the vicinity of the ferroelastoelectric phase transition at T C  = 200 K. Macroscopic order parameter is the h 36 component of the spontaneous piezoelectric tensor connecting polarisation P 3 and strain η 6 . The temperature change in h 36 component was proportional to (T C  − T) α , where α = 0.58 ± 0.05. Close to T C changes in dielectric permittivity were negligible. High value of ac conductivity in the high-temperature phase results from protons jumping between disordered ions NH 4 + and between molecules of crystallisation water. Only longitudinal ultrasonic waves exhibited an abrupt change upon the phase transition. The relaxation time of the order parameter was determined from anomalous changes in attenuation of the longitudinal waves. - Highlights: • Low-temperature phase shows higher-order ferroicity: ferroelastoelectricity. • Temperature change of spontaneous piezoelectricity was studied in the ordered phase. • Dispersion of complex dielectric constant was investigated in wide temperature range. • At high-temperature phase ac conductivity is caused by proton jumps. • Anomalies of ultrasonic waves at T C were analysed using phenomenological theory

Modified T-history method for measuring thermophysical properties of phase change materials at high temperature

Science.gov (United States)

Omaraa, Ehsan; Saman, Wasim; Bruno, Frank; Liu, Ming

2017-06-01

Latent heat storage using phase change materials (PCMs) can be used to store large amounts of energy in a narrow temperature difference during phase transition. The thermophysical properties of PCMs such as latent heat, specific heat and melting and solidification temperature need to be defined at high precision for the design and estimating the cost of latent heat storage systems. The existing laboratory standard methods, such as differential thermal analysis (DTA) and differential scanning calorimetry (DSC), use a small sample size (1-10 mg) to measure thermophysical properties, which makes these methods suitable for homogeneous elements. In addition, this small amount of sample has different thermophysical properties when compared with the bulk sample and may have limitations for evaluating the properties of mixtures. To avoid the drawbacks in existing methods, the temperature - history (T-history) method can be used with bulk quantities of PCM salt mixtures to characterize PCMs. This paper presents a modified T-history setup, which was designed and built at the University of South Australia to measure the melting point, heat of fusion, specific heat, degree of supercooling and phase separation of salt mixtures for a temperature range between 200 °C and 400 °C. Sodium Nitrate (NaNO3) was used to verify the accuracy of the new setup.

Non-equilibrium effects in high temperature chemical reactions

Science.gov (United States)

Johnson, Richard E.

1987-01-01

Reaction rate data were collected for chemical reactions occurring at high temperatures during reentry of space vehicles. The principle of detailed balancing is used in modeling kinetics of chemical reactions at high temperatures. Although this principle does not hold for certain transient or incubation times in the initial phase of the reaction, it does seem to be valid for the rates of internal energy transitions that occur within molecules and atoms. That is, for every rate of transition within the internal energy states of atoms or molecules, there is an inverse rate that is related through an equilibrium expression involving the energy difference of the transition.

Energetics of a hexagonal-lamellar-hexagonal-phase transition sequence in dioleoylphosphatidylethanolamine membranes

International Nuclear Information System (INIS)

Gawrisch, K.; Parsegian, V.A.; Hajduk, D.A.; Tate, M.W.; Gruner, S.M.; Fuller, N.L.; Rand, R.P.

1992-01-01

The phase diagram of DOPE/water dispersions was investigated by NMR and X-ray diffraction in the water concentration range from 2 to 20 water molecules per lipid and in the temperature range from -5 to +50C. At temperature above 22C, the dispersions form an inverse (H II ) phase at all water concentrations. Below 25C, an H II phase occurs at high water concentrations, an L α phase is formed at intermediate water concentrations, and finally the system switches back to an H II phase at low water concentrations. The enthalpy of the L α -H II -phase transition is +0.3 kcal/mol as measured by differential scanning calorimetry. Using 31 P and 2 H NMR and X-ray diffraction. The authors measured the trapped water volumes in H II and L α phases as a function of osmotic pressure. The change of the H II -phase free energy as a function of hydration was calculated by integrating the osmotic pressure vs trapped water volume curve. The phase diagram calculated on the basis of the known enthalpy of transition and the osmotic pressure vs water volume curves is in good agreement with the measured one. The H II -L α -H II double-phase transition at temperatures below 22C can be shown to be a consequence of (1) the greater degree of hydration of the H II phase in excess water and (2) the relative sensitivities with which the lamellar and hexagonal phases dehydrate with increasing osmotic pressure. These results demonstrate the usefulness of osmotic stress measurements to understand lipid-phase diagrams

Phase transition and electrical properties of strontium orthovanadate

International Nuclear Information System (INIS)

Pati, Biswajit; Choudhary, R.N.P.; Das, Piyush R.

2013-01-01

Highlights: •Highly crystallized Sr 3 V 2 O 8 ceramic has a structural and micro-structural stability. •The low values of ε r and tan δ make this material useful for microwave applications. •The material exhibits good ferroelectric properties suitable for memory devices. •The dielectric relaxation is of non Debye-type and ac conductivity obeys Jonscher power law. •The small value of dc activation energy suggests the conduction initiates with a small energy. -- Abstract: The current research work reports the study of phase transition and transport mechanism in lead-free strontium orthovanadate (Sr 3 V 2 O 8 ), prepared using a high-temperature solid-state reaction technique. Preliminary X-rays diffraction studies exhibit the formation of a single-phase compound in the trigonal crystal system. Study of microstructure of gold-coated pellet by scanning electron microscopy (SEM) shows well-defined and homogeneous grains in the morphology. Detailed studies of dielectric parameters (ε r and tan δ) of the compound as a function of temperature at some selected frequencies reveal their independence for a wide range of temperatures. An anomaly in relative permittivity (ε r ) suggests the existence of a ferroelectric–paraelectric phase transition of diffuse-type in the material that confirms through the detailed studies of its electric polarization. Detailed studies of impedance and related parameters exhibit that the electrical properties of the material are strongly dependent on temperature, and bear a good correlation with its microstructure (i.e., bulk, grain boundary, etc.). The decrease in value of bulk resistance on increasing temperature suggests the negative temperature co-efficient of resistance (NTCR) behavior of the material. Studies of electric modulus indicate the presence of hopping conduction mechanism in the system with non-exponential type of conductivity relaxation. The nature of variation of dc conductivity with temperature confirms the

Structural phase transitions in BaMo6S8: Evidence for an incommensurate phase

International Nuclear Information System (INIS)

Jorgensen, J.D.; Hinks, D.G.; Hatch, D.M.; Putnam, R.M.

1986-01-01

The structure of BaMo 6 S 8 has been studied over the temperature range 19 K to 573 K by time-of-flight neutron powder diffraction. Below 175 K the data can be suitably refined in a triclinic, P1, cell with volume equal to the rhombohedral, R3, cell common to most Chevrel-phase structures. At temperatures immediately above 175 K, the rhombohedral, R3, Bragg peaks are broadened by satellite reflections which appear to be identical to those recently observed at low temperature in PbMo 6 S 8 and SnMo 6 S 8 . An abrupt change in the sign of the temperature dependence of the hexagonal c axis (∂c/∂T) signals the transition to an undistorted rhombohedral, R3, structure at temperatures above about 350 K. An extended Landau theory determines both continuous and discontinuous transitions from R3 induced by a single order parameter. Analysis of the order parameters inducing commensurate transitions imposes symmetry restrictions on the atomic displacements in the lower symmetry phases. The assumption of an R3 commensurate phase is not consistent with the bond lengths obtained for the distortions to the P1 (or P1) phase for any of the possible cells preserving order parameters. Thus the phase immediately above 175 K cannot be a commensurate R3 structure. This is consistent with experimental evidence. 25 refs., 11 figs., 8 tabs

A perturbative RS I cosmological phase transition

Energy Technology Data Exchange (ETDEWEB)

Bunk, Don [Skidmore College, Department of Physics, Saratoga Springs, NY (United States); Hubisz, Jay [Syracuse University, Department of Physics, Syracuse, NY (United States); Jain, Bithika [Korea Institute for Advanced Study, School of Physics, Seoul (Korea, Republic of)

2018-01-15

We identify a class of Randall-Sundrum type models with a successful first order cosmological phase transition during which a 5D dual of approximate conformal symmetry is spontaneously broken. Our focus is on soft-wall models that naturally realize a light radion/dilaton and suppressed dynamical contribution to the cosmological constant. We discuss phenomenology of the phase transition after developing a theoretical and numerical analysis of these models both at zero and finite temperature. We demonstrate a model with a TeV-Planck hierarchy and with a successful cosmological phase transition where the UV value of the curvature corresponds, via AdS/CFT, to an N of 20, where 5D gravity is expected to be firmly in the perturbative regime. (orig.)

Phase transitions in nuclear matter

International Nuclear Information System (INIS)

Glendenning, N.K.

1984-11-01

The rather general circumstances under which a phase transition in hadronic matter at finite temperature to an abnormal phase in which baryon effective masses become small and in which copious baryon-antibaryon pairs appear is emphasized. A preview is also given of a soliton model of dense matter, in which at a density of about seven times nuclear density, matter ceases to be a color insulator and becomes increasingly color conducting. 22 references

Diffusionless phase transitions and related structures in oxides

International Nuclear Information System (INIS)

Boulesteix, C.

1992-01-01

The relative importance of oxides in the field of materials science has been spectacularly increasing during the last twenty years. First the study of ferroelectrics kept the attention of scientists. Nevertheless this domain is far from being worked out and a lot of new results and of new fields of interest were recently discovered. Other ferroic oxides, especially ferroelastics, have also been the subject of a very great number of new results. In these cases the properties of oxides are at room temperature very tightly related to the phase transition that is generally occurring a few hundred of degrees above this room temperature. In many other cases also properties of oxides can be related to the existence of a phase transition or to a rather similar phenomenon. This book has been specially devoted to the study of the properties of oxides which are in some way related to the existence of a phase transition. The first chapters are focussed on general considerations: the first one is devoted to a general study of phase transitions, the second one to the twinning phenomenon which is of special interest for many oxides. Chapters 3 and 4 are focussed on ferroelectric and ferroelastic materials. These four chapters consitute the first part of the book. Chapters 5 to 8 are devoted to the study of oxides of special interest which have some of their properties related to a phase transition or to a rather similar phenomenon: rare earth oxides, oxides with a diffuse phase transition, zirconia and alumina systems, tungsten oxides and their relatives. These four chapters constitute the second part of the book. (orig.)

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

Spatially resolved quantitative mapping of thermomechanical properties and phase transition temperatures using scanning probe microscopy

Science.gov (United States)

Jesse, Stephen; Kalinin, Sergei V; Nikiforov, Maxim P

2013-07-09

An approach for the thermomechanical characterization of phase transitions in polymeric materials (polyethyleneterephthalate) by band excitation acoustic force microscopy is developed. This methodology allows the independent measurement of resonance frequency, Q factor, and oscillation amplitude of a tip-surface contact area as a function of tip temperature, from which the thermal evolution of tip-surface spring constant and mechanical dissipation can be extracted. A heating protocol maintained a constant tip-surface contact area and constant contact force, thereby allowing for reproducible measurements and quantitative extraction of material properties including temperature dependence of indentation-based elastic and loss moduli.

Zpif's law in the liquid gas phase transition of nuclei

International Nuclear Information System (INIS)

Ma, Y.G.

1999-01-01

Zpif's law in the field of linguistics is tested in the nuclear disassembly within the framework of isospin dependent lattice gas model. It is found that the average cluster charge (or mass) of rank n in the charge (or mass) list shows exactly inversely to its rank, i.e., there exists Zpif's law, at the phase transition temperature. This novel criterion shall be helpful to search the nuclear liquid gas phase transition experimentally and theoretically. In addition, the finite size scaling of the effective phase transition temperature at which the Zpif's law appears is studied for several systems with different mass and the critical exponents of ν and β are tentatively extracted. (orig.)

Surface charge sensing by altering the phase transition in VO2

Science.gov (United States)

Kumar, S.; Esfandyarpour, R.; Davis, R.; Nishi, Y.

2014-08-01

Detection of surface charges has various applications in medicine, electronics, biotechnology, etc. The source of surface charge induction may range from simple charge-polarized molecules like water to complicated proteins. It was recently discovered that surface charge accumulation can alter the temperature at which VO2 undergoes a Mott transition. Here, we deposited polar molecules onto the surface of two-terminal thin-film VO2 lateral devices and monitored the joule-heating-driven Mott transition, or conductance switching. We observed that the power required to induce the conductance switching reduced upon treatment with polar molecules and, using in-situ blackbody-emission direct measurement of local temperature, we show that this reduction in power was accompanied by reduction in the Mott transition temperature. Further evidence suggested that this effect has specificity to the nature of the species used to induce surface charges. Using x-ray absorption spectroscopy, we also show that there is no detectable change in oxidation state of vanadium or structural phase in the bulk of the 40 nm VO2 thin-film even as the phase transition temperature is reduced by up to 20 K by the polar molecules. The ability to alter the phase transition parameters by depositing polar molecules suggests a potential application in sensing surface charges of different origins and this set of results also highlights interesting aspects of the phase transition in VO2.

Novel phase transitions in B-site doped manganites

Energy Technology Data Exchange (ETDEWEB)

Popovic, Z.V. [Institute of Physics, P.O. Box 68, 11080 Belgrade/Zemun (Serbia and Montenegro)]. E-mail: zoran.popovic@phy.bg.ac.yu; Cantarero, A. [Materials Science Institute, University of Valencia, P.O. Box 22085, 46071 Valencia (Spain); Thijssen, W.H.A. [Kamerlingh Onnes Laboratorium, Leiden University, Postbus 9504, 2300 RA Leiden (Netherlands); Paunovic, N. [Institute of Physics, P.O. Box 68, 11080 Belgrade/Zemun (Serbia and Montenegro); Dohcevic-Mitrovic, Z. [Institute of Physics, P.O. Box 68, 11080 Belgrade/Zemun (Serbia and Montenegro); Sapina, F. [Materials Science Institute, University of Valencia, P.O. Box 22085, 46071 Valencia (Spain)

2005-04-30

We have examined the infrared reflectivity and the electrical resistivity of La{sub 1-} {sub x} [Sr(Ba)] {sub x} Mn{sub 1-} {sub z} [Cu(Zn)] {sub z} O{sub 3} samples in ferromagnetic metallic and insulator regime. Several phase transitions are observed, the most obvious being the transition from a ferromagnetic metallic to a ferromagnetic insulator phase that is related to the formation of short-range orbitally ordered domains. The temperature T {sub 1} of the phase transition is dependent on doping concentration and for optimally doped samples ({approx}32% of Mn{sup 4+} ions) we have found T {sub 1}{approx}0.93 T {sub C}.

Phase transition in a modified square Josephson-junction array

CERN Document Server

Han, J

1999-01-01

We study the phase transition in a modified square proximity-coupled Josephson-junction array with small superconducting islands at the center of each plaquette. We find that the modified square array undergoes a Kosterlitz-Thouless-Berezinskii-like phase transition, but at a lower temperature than the simple square array with the same single-junction critical current. The IV characteristics, as well as the phase transition, resemble qualitatively those of a disordered simple square array. The effects of the presence of the center islands in the modified square array are discussed.

Phase stability of TiH{sub 2} under high pressure and temperatures

Energy Technology Data Exchange (ETDEWEB)

Selva Vennila, R.; Durygin, A.; Saxena, S.K. [Center for Study of Matter at Extreme Conditions (CeSMEC), Florida International University, VH-150, University Park, Miami, FL 33199 (United States); Merlini, Marco [European Synchrotron Radiation Facility (ESRF), Grenoble 38043 (France); Wang, Zhongwu [Cornell High Energy Synchrotron Source (CHESS), Wilson Laboratory, Cornell University, Ithaca, NY 14853 (United States)

2008-11-15

Phase stability of titanium hydride (TiH{sub 2}) was studied at high pressure-high temperature conditions using synchrotron radiation under non-hydrostatic conditions. Resistive heating method was used to heat the sample to a maximum temperature of 873 K in a diamond anvil cell (DAC) under pressure up to 12 GPa. Pressure-temperature behavior was studied by varying the temperature upto 823 K in steps of 50 K with pressure variations within 3 GPa. Structural phase transformation from tetragonal (I4/mmm) to cubic (Fm-3 m) was observed with increase in temperature. Tetragonal phase was found to be stabilized when the sample was subjected to pressure and temperature cycle. (author)

Tunneling anisotropic magnetoresistance driven by magnetic phase transition.

Science.gov (United States)