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  • 1. Abou-Hamad, E.
    et al.
    Babaa, M. -R
    Bouhrara, M.
    Kim, Y.
    Saih, Y.
    Dennler, S.
    Mauri, F.
    Basset, J. -M
    Goze-Bac, C.
    Wågberg, Thomas
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Structural properties of carbon nanotubes derived from (13)C NMR2011Inngår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 84, nr 16, s. 165417-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We present a detailed experimental and theoretical study on how structural properties of carbon nanotubes can be derived from 13C NMR investigations. Magic angle spinning solid state NMR experiments have been performed on single-and multiwalled carbon nanotubes with diameters in the range from 0.7 to 100 nm and with number of walls from 1 to 90. We provide models on how diameter and the number of nanotube walls influence NMR linewidth and line position. Both models are supported by theoretical calculations. Increasing the diameter D, from the smallest investigated nanotube, which in our study corresponds to the inner nanotube of a double-walled tube to the largest studied diameter, corresponding to large multiwalled nanotubes, leads to a 23.5 ppm diamagnetic shift of the isotropic NMR line position d. We show that the isotropic line follows the relation d = 18.3/D + 102.5 ppm, where D is the diameter of the tube and NMR line position d is relative to tetramethylsilane. The relation asymptotically tends to approach the line position expected in graphene. A characteristic broadening of the line shape is observed with the increasing number of walls. This feature can be rationalized by an isotropic shift distribution originating from different diamagnetic shielding of the encapsulated nanotubes together with a heterogeneity of the samples. Based on our results, NMR is shown to be a nondestructive spectroscopic method that can be used as a complementary method to, for example, transmission electron microscopy to obtain structural information for carbon nanotubes, especially bulk samples.

  • 2. Abou-Hamad, E.
    et al.
    Kim, Y.
    Bouhrara, M.
    Saih, Y.
    Wågberg, Thomas
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Luzzi, D. E.
    Goze-Bac, C.
    NMR strategies to study the local magnetic properties of carbon nanotubes2012Inngår i: Physica. B, Condensed matter, ISSN 0921-4526, E-ISSN 1873-2135, Vol. 407, nr 4, s. 740-742Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The local magnetic properties of the one dimensional inner space of the nanotubes are investigated using C-13 nuclear magnetic resonance spectroscopy of encapsulated fullerene molecules inside single walled carbon nanotubes. Isotope engineering and magnetically purified nanotubes have been advantageously used on our study to discriminate between the different diamagnetic and paramagnetic shifts of the resonances. Ring currents originating from the pi electrons circulating on the nanotube, are found to actively screen the applied magnetic field by -36.9 ppm. Defects and holes in the nanotube walls cancel this screening locally. What is interesting, that at high magnetic fields, the modifications of the NMR resonances of the molecules from free to encapsulated can be exploited to determine some structural characteristics of the surrounding nanotubes, never observed experimentally. (C) 2011 Elsevier B.V. All rights reserved.

  • 3.
    Abou-Hamad, Edy
    et al.
    Universite Montpellier II.
    Kim, Y
    University of Pennsylvania.
    Talyzin, Alexandr
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Fysik.
    Goze-Bac, Christophe
    Universite Montpellier II.
    Luzzi, David
    University of Pennsylvania.
    Rubio, Angelo
    University of Basque Country.
    Wågberg, Thomas
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Fysik.
    Hydrogenation of C-60 in Peapods: Physical Chemistry in Nano Vessels2009Inngår i: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 113, nr 20, s. 8583-8587Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Hydrogenation of C-60 molecules inside SWNT was achieved by direct reaction with hydrogen gas at elevated pressure and temperature. Evidence for the C-60 hydrogenation in peapods is provided by isotopic engineering with specific enrichment of encapsulated species and high resolution C-13 and H-1 NMR spectroscopy with the observation of characteristic diamagnetic and paramagnetic shifts of the NMR lines and the appearance of sp(3) carbon resonances. We estimate that approximately 78% of the C-60 molecules inside SWNTs are hydrogenated to an average degree of 14 hydrogen atoms per C-60 molecule. As a consequence, the rotational dynamics of the encapsulated C60Hx molecules is clearly hindered. Our successful hydrogenation experiments open completely new roads to understand and control confined chemical reactions at the nano scale

  • 4.
    Abou-Hamad, Edy
    et al.
    Universite Montpellier 2, France.
    Kim, Y.
    University of Pennsylvania, Philadelphia.
    Wågberg, Thomas
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Boesch, D.
    University of California at Berkeley, and Materials Sciences Division, Lawrence Berkeley National Laboratory.
    Aloni, S.
    University of California at Berkeley, and Materials Sciences Division, Lawrence Berkeley National Laboratory.
    Zettl, Alex
    University of California at Berkeley, and Materials Sciences Division, Lawrence Berkeley National Laboratory.
    Rubio, Angelo
    Universidad del Pas Vasco UPV/EHU.
    Luzzi, David E.
    University of Pennsylvania, Philadelphia.
    Goze-Bac, Christophe
    CNRS Universit Montpellier 2.
    Molecular dynamics and phase transition in one-dimensional crystal of C60 encapsulated inside single wall carbon nanotubes2009Inngår i: ACS Nano, ISSN 1936-0851, E-ISSN 1936-086X, Vol. 3, nr 12, s. 3878-3883Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    One-dimensional crystals of 25% 13C-enriched C60 encapsulated inside highly magnetically purified SWNTs were investigated by following the temperature dependence of the 13C NMR line shapes and the relaxation rates from 300 K down to 5 K. High-resolution MAS techniques reveal that 32% of the encapsulated molecules, so-called the C60α, are blocked at room temperature and 68%, labeled C60β, are shown to reversly undergo molecular reorientational dynamics. Contrary to previous NMR studies, spin−lattice relaxation time reveals a phase transition at 100 K associated with the changes in the nature of the C60β dynamics. Above the transition, the C60β exhibits continuous rotational diffusion; below the transition, C60β executes uniaxial hindered rotations most likely along the nanotubes axis and freeze out below 25 K. The associated activation energies of these two dynamical regimes are measured to be 6 times lower than in fcc-C60, suggesting a quiet smooth orientational dependence of the interaction between C60β molecules and the inner surface of the nanotubes.

  • 5.
    ABUDULIMU, ABASI
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Effectof Growth Time, Growth Temperature and Light  on Growth Mechanism of C60 nanorods2013Independent thesis Advanced level (degree of Master (Two Years)), 10 poäng / 15 hpOppgave
    Abstract [en]

    In this thesis work C60 nanorods were produced by Liquid-Liquid Interfacial Precipitation method (LLIP) assisted with 10 s of weak sonication. Ethanol and m-dichlorobenzene were used as poor and good solvents of C60, respectively. Five different temperatures, 4, 10, 20, 30, 40 and 50                         , were chosen as growth temperatures of different samples to investigate the effect of temperature on the grown structures. Different samples were prepared in the dark and under the light with various growth time to determine the effect of light and growth time on growth of C60 nanorods. The characterization of the grown C60 nanorods were conducted by transmission electron microscopy (TEM) and x-ray diffraction (XRD). The result of characterization indicated that the sonication introduced smaller C60 nanostructures; light irradiation and temperature increase (till 40 C0) during the growth time resulted in nanorods with smaller diameter, whereas the long growth time lead to the increase of the diameter of C60 nanorods. The as-grown C60 nanorods synthesized at different conditions possess an hcp crystal structure.    

    Fulltekst (pdf)
    Effect of Growth Time, Growth Temperature and Light on Growth Mechanism of C60 nanorods
  • 6.
    Adranno, Brando
    et al.
    Department of Materials and Environmental Chemistry, Stockholm University, Svante Arrhenius väg 16C, SE-10691 Stockholm, Sweden.
    Renier, Olivier
    Department of Materials and Environmental Chemistry, Stockholm University, Svante Arrhenius väg 16C, SE-10691 Stockholm, Sweden.
    Bousrez, Guillaume
    Department of Materials and Environmental Chemistry, Stockholm University, Svante Arrhenius väg 16C, SE-10691 Stockholm, Sweden.
    Paterlini, Veronica
    Department of Materials and Environmental Chemistry, Stockholm University, Svante Arrhenius väg 16C, SE-10691 Stockholm, Sweden.
    Baryshnikov, Glib V.
    Department of Science and Technology, Laboratory of Organic Electronics, Linköping University, SE-60174 Norrköping, Sweden.
    Smetana, Volodymyr
    Department of Materials and Environmental Chemistry, Stockholm University, Svante Arrhenius väg 16C, SE-10691 Stockholm, Sweden.
    Tang, Shi
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Ågren, Hans
    Department of Physics and Astronomy, Uppsala University, Box 516, SE-751 20 Uppsala, Sweden.
    Metlen, Andreas
    The QUILL Research Centre and School of Chemistry and Chemical Engineering The Queen’s University of Belfast Belfast, Northern Ireland BT9 5AG, UK.
    Edman, Ludvig
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Anja-Verena, Mudring
    Department of Materials and Environmental Chemistry, Stockholm University, Svante Arrhenius väg 16C, SE-10691 Stockholm, Sweden; Intelligent Advanced Materials (iAM), Department of Biological and Chemical Engineering and iNANO, Aarhus University, 8000 Aarhus C, Denmark.
    Rogers, Robin D.
    Department of Materials and Environmental Chemistry, Stockholm University, Svante Arrhenius väg 16C, SE-10691 Stockholm, Sweden; The QUILL Research Centre and School of Chemistry and Chemical Engineering The Queen’s University of Belfast Belfast, Northern Ireland BT9 5AG, UK.
    The 8-hydroxyquinolinium cation as a lead structure for efficient color-tunable ionic small molecule emitting materials2023Inngår i: Advanced Photonics Research, ISSN 2699-9293, Vol. 4, nr 3, artikkel-id 2200279Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Albeit tris(8-hydroxyquinolinato) aluminum (Alq3) and its derivatives are prominent emitter materials for organic lighting devices, and the optical transitions occur among ligand-centered states, the use of metal-free 8-hydroxyquinoline is impractical as it suffers from strong nonradiative quenching, mainly through fast proton transfer. Herein, it is shown that the problem of rapid proton exchange and vibration quenching of light emission can be overcome not only by complexation, but also by organization of the 8-hydroxyquinolinium cations into a solid rigid network with appropriate counter-anions (here bis(trifluoromethanesulfonyl)imide). The resulting structure is stiffened by secondary bonding interactions such as pi-stacking and hydrogen bonds, which efficiently block rapid proton transfer quenching and reduce vibrational deactivation. Additionally, the optical properties are tuned through methyl substitution from deep blue (455 nm) to blue-green (488 nm). Time-dependent density functional theory (TDFT) calculations reveal the emission to occur from which an unexpectedly long-lived S-1 level, unusual for organic fluorophores. All compounds show comparable, even superior photoluminescence compared to Alq3 and related materials, both as solids and thin films with quantum yields (QYs) up to 40-50%. In addition, all compounds show appreciable thermal stability with decomposition temperatures above 310 °C.

    Fulltekst (pdf)
    fulltext
  • 7. Ajuria, Jon
    et al.
    Arnaiz, Maria
    Botas, Cristina
    Carriazo, Daniel
    Mysyk, Roman
    Rojo, Teofilo
    Talyzin, Alexandr V.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Goikolea, Eider
    Graphene-based lithium ion capacitor with high gravimetric energy and power densities2017Inngår i: Journal of Power Sources, ISSN 0378-7753, E-ISSN 1873-2755, Vol. 363, s. 422-427Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Hybrid capacitor configurations are now of increasing interest to overcome the current energy limitations of supercapacitors. In this work, we report a lithium ion capacitor (LIC) entirely based on graphene. On the one hand, the negative-battery-type- electrode consists of a self-standing, binder-free 3D macroporous foam formed by reduced graphene oxide and decorated with tin oxide nanoparticles (SnO2-rGO). On the other hand, the positive-capacitor-type- electrode is based on a thermally expanded and physically activated reduced graphene oxide (a-TEGO). For comparison purposes, a symmetric electrical double layer capacitor (EDLC) using the same activated graphene in 1.5 M Et4NBE4/ACN electrolyte is also assembled. Built in 1 M LiPF6 EC:DMC, the graphene-based LIC shows an outstanding, 10-fold increase in energy density with respect to its EDLC counterpart at low discharge rates (up to 200 Wh kg(-1)). Furthermore, it is still capable to deliver double the energy in the high power region, within a discharge time of few seconds.

  • 8. Aksenova, N.A.
    et al.
    Isakina, A.P.
    Prokhvatilov, A.I.
    Strzhemechny, M.A.
    Soldatov, Alexander V.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Sundqvist, Bertil
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Structure studies of C60 polymerized at low pressures1997Inngår i: Fullerenes: Recent Advances in the Chemistry and Physics of Fullerenes and Related Materials, vol. 5, Pennington, NJ: The Electrochemical Society , 1997, s. 687-694Konferansepaper (Fagfellevurdert)
    Abstract [en]

    The structure and lattice properties of a polymerized C60 sample were investigated by X-ray powder diffraction over the range from liquid-nitrogen to room temperature. The aim of these studies was to establish the effect of low-pressure compression (up to 1.1 GPa) on the phase composition of the sample, to determine the structure of the phases involved, to obtain the variation of the lattice parameters with temperature, to observe eventual phase transformation in polymerized C60, and to elucidate the evolution of the orientational order with varying temperature. Analysis of the room-temperature diffraction patterns indicates that the sample contained at least two major phases, namely rhombohedral and and tetragonal with the polymerization array close to two-dimensional. Our data obtained on samples annealed at 300 C in the air allow us to conclude that polymerized C60 converts to a mixture of the fcc structure plus a new phase, presumably C60O.

  • 9.
    Albinsson, I.
    et al.
    Department of Physics, Chalmers University of Technology, Gothenburg, Sweden.
    Jacobsson, Per
    Department of Physics, Chalmers University of Technology, Gothenburg, Sweden.
    Mellander, Bengt-Erik
    Department of Physics, Chalmers University of Technology, Gothenburg, Sweden.
    Stevens, James R.
    Department of Physics, Chalmers University of Technology, Gothenburg, Sweden.
    Ion association effects and ionic conduction in polyalkalene modified polydimethylsiloxanes1992Inngår i: Solid State Ionics, ISSN 0167-2738, E-ISSN 1872-7689, Vol. 53-56, nr Part 2, s. 1044-1053Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Poly (ethylene oxide) and poly (propylene oxide) modified poly (dimethyl siloxane) (PDMS) have been complexed with LiCF3SO3, NaCF3SO3 and KCF3SO3. In order to study ion association in these systems, the nondegenerate symmetric stretch (A1, SO3) Raman modes have been studied as a function of temperature at several different salt concentrations. Ionic conductivity has also been measured. For the poly (ethylene oxide) modified PDMS (PEO-PDMS), ether oxygen to metal ratios ranged from 12500:1 to 9:1. Changing the cation from Li+ to Na+ to K+ increases the conductivity of the complex. Plots of the molar conductivity versus salt concentration show that the characteristic shape and the region of increase in the molar conductivity is influenced most by the fraction of “free” ions which increases with increasing salt concentration. Charged triplets and contact ion-pairs are also present at the higher salt concentrations; the number of triplets increases with concentration and temperature. Non-VTF behaviour is observed. For the poly (propylene oxide) modified PDMS (PPO-PDMS) (with excess PPO), phase separation is observed when these triflate salts are complexed in. These solutions above and below the boundary layer have been studied by Raman spectroscopy revealing that the upper region is siloxane rich. The formation of the boundary layer is attributed to an increasing difference in surface tension between the PPO/salt/PPO-PDMS complexes and the separate PPO, PPO-PDMS components. The boundary layer moves up with increase in salt concentration. There is evidence of “free” ions, contact-ion pairs, triplets and aggregates. Values of conductivity of 2.2×10−6 and 1.6×10−5 S/cm are quoted for 293 K and 8 mol% LiCF3SO3 in respectively PPO-PDMS/PPO and PEO-PDMS/PEO. Both are better conductors than the corresponding 8 mol% PPG4000/LiCF3SO3 complex.

  • 10. Aleksandrovskii, A. N.
    et al.
    Dolbin, A.V.
    Esel'son, V.B.
    Gavrilko, V.G.
    Manzhelii, V.G.
    Udovidchenko, B.G.
    Bakai, A.S.
    Gadd, G.E.
    Moricca, S.
    Sundqvist, Bertil
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Low-temperature thermal expansion of pure and inert gas-doped fullerite C602003Inngår i: Fizika Nizkikh Temperatur (Kharkov), ISSN 0132-6414 (Print) 1816-0328 (On-line), Vol. 29, nr 4, s. 432-442Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The low temperature (2–24 K) thermal expansion of pure (single-crystal and polycrystalline) C60 and polycrystalline C60 intercalated with He, Ne, Ar, and Kr has been investigated using the high-resolution capacitance dilatometer. The investigation of the time dependence of the sample length variations deltaL(t) on heating by deltaT shows that the thermal expansion is determined by the sum of positive and negative contributions, which have different relaxation times. The negative thermal expansion usually prevails at helium temperatures. The positive expansion is connected with the phonon thermalization of the system. The negative expansion is caused by reorientation of the C60 molecules. It is assumed that the reorientation is of a quantum character. The inert gas impurities affect the reorientation of the C60 molecules very strongly, especially at liquid helium temperatures. A temperature hysteresis of the thermal expansion coefficient of Kr– and He–C60 solutions has been revealed. The hysteresis is attributed to orientational polyamorphous transformation in these systems.

  • 11. Aleksandrovskii, A. N.
    et al.
    Esel'son, V.B.
    Manzhelii, Vadim Grigorovich
    Udovidchenko, B.G.
    Soldatov, Alexander
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Sundqvist, Bertil
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Negative thermal expansion of fullerite C60 at helium temperatures1997Inngår i: Low temperature physics (Woodbury, N.Y., Print), ISSN 1063-777X, E-ISSN 1090-6517, Vol. 23, nr 11, s. 943-946Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The thermal expansion of fullerite C60 has been measured in the temperature range 2–9 K. A compacted fullerite sample with a diameter of about 6 mm and height of 2.4 mm was used. It was found that at temperatures below ~ 3.4 K the linear thermal expansion coefficient becomes negative. At temperatures above 5 K our results are in good agreement with the available literature data. A qualitative explanation of the results is proposed

  • 12. Aleksandrovskii, A. N.
    et al.
    Esel'son, V.B.
    Manzhelii, V.G.
    Udovidchenko, B.G.
    Soldatov, Alexander
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Sundqvist, Bertil
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Thermal expansion of single-crystal fullerite C60 at helium temperatures2000Inngår i: Low temperature physics (Woodbury, N.Y., Print), ISSN 1063-777X, E-ISSN 1090-6517, Vol. 26, nr 1, s. 75-80Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The thermal expansion of single-crystal fullerite C60 has been studied in the range of liquid-helium temperatures (2–10 K). At temperatures below ~4.5 K the thermal expansion of fullerite C60 becomes negative, in agreement with the previous results on polycrystalline materials. A qualitative explanation of the results is proposed.

  • 13. Aleksandrovskii, A. N.
    et al.
    Gavrilko, V.G.
    Esel'son, V.B.
    Manzhelii, V. G.
    Udovidchenko, B.G.
    Maletskiy, V.P.
    Sundqvist, Bertil
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Effect of argon on the thermal expansion of fullerite C60 at helium temperatures2001Inngår i: Low temperature physics (Woodbury, N.Y., Print), ISSN 1063-777X, E-ISSN 1090-6517, Vol. 27, nr 3, s. 245-246Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The linear thermal expansion of compacted Ar-doped fullerite C60(ArxC60) is investigated at 2–12 K using a dilatometric method. The thermal expansion of ArxC60 is also studied after partial desaturation of argon from fullerite. It is revealed that argon doping resulted in a considerable change of the temperature dependence of the thermal expansion of fullerite. An explanation of the observed effects is proposed.

  • 14. Aleksandrovskii, A.N.
    et al.
    Bakai, A.S.
    Cassidy, D.
    Dolbin, A.V.
    Esel'son, V.B.
    Gadd, G.E.
    Gavrilko, V.G.
    Manzhelii, V.G.
    Moricca, S.
    Sundqvist, Bertil
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Fysik.
    On the polyamorphism of fullerite-based orientational glasses.2005Inngår i: Low Temperature Physics, ISSN 1063-777X, Vol. 31, nr 5, s. 429-444Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The dilatometric investigation in the temperature range of 2–28 K shows that a first-order

    polyamorphous transition occurs in the orientational glasses based on C60 doped with H2, D2 and

    Xe. A polyamorphous transition was also detected in C60 doped with Kr and He. It is observed that

    the hysteresis of thermal expansion caused by the polyamorphous transition (and, hence, the transition

    temperature) is essentially dependent on the type of doping gas. Both positive and negative

    contributions to the thermal expansion were observed in the low-temperature phase of the glasses.

    The relaxation time of the negative contribution occurs to be much longer than that of the positive

    contribution. The positive contribution is found to be due to phonon and libron modes, whilst the

    negative contribution is attributed to tunneling states of the C60 molecules. The characteristic

    time of the phase transformation from the low-T phase to the high-T phase has been found for the

    C60–H2 system at 12 K. A theoretical model is proposed to interpret these observed phenomena.

    The theoretical model proposed, includes a consideration of the nature of polyamorphism in

    glasses, as well as the thermodynamics and kinetics of the transition. A model of noninteracting

    tunneling states is used to explain the negative contribution to the thermal expansion. The experimental

    data obtained is considered within the framework of the theoretical model. From the theoretical

    model the order of magnitude of the polyamorphous transition temperature has been estimated.

    It is found that the late stage of the polyamorphous transformation is described well by the

    Kolmogorov law with an exponent of n = 1. At this stage of the transformation, the two-dimensional

    phase boundary moves along the normal, and the nucleation is not important.

  • 15. Aleksandrovskii, A.N.
    et al.
    Gavrilko, V.G.
    Esel'son, V.B.
    Manzhelii, V. G.
    Udovidchenko, B.G.
    Maletskiy, V.P.
    Sundqvist, Bertil
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Thermal expansion of fullerite C60 alloyed with argon and neon2001Inngår i: Low temperature physics (Woodbury, N.Y., Print), ISSN 1063-777X, E-ISSN 1090-6517, Vol. 27, nr 12, s. 1033-1036Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The linear thermal expansion of compacted fullerite C60 alloyed with argon (ArxC60) and neon (NexC60) are investigated by a dilatometric method. The experimental temperature is 2–12 K. In the same temperature interval the thermal expansion of ArxC60 and NexC60 are examined after partial desaturation of the gases from fullerite. It is found that Ar and Ne alloying affects the temperature dependence of the thermal expansion coefficient of C60 quite appreciably. The libration and translation contributions to the thermal expansion of pure C60 are separated. The experimental results on the thermal expansion are used to obtain the Debye temperature of pure C60. The effects observed are tentatively interpreted.

  • 16.
    Al-Hayali, Asifa
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Characterization of ion-irradiation-induced defects in graphite by Raman and Atomic Force Microscopy2013Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
    Abstract [en]

    Graphite is an interesting prototype material for ion implantation studies because of the anisotropy in its physical and structural properties; In particular, due to the layered nature of the graphite lattice, the processes of amorphization and recrystallization (graphitization) of the implanted region are conceptually different from that observed in commonly studied materials. Since ion implantation provides a controlled method for the introduction of lattice defects which can be subsequently annealed, this technique provides fundamental information on the unique crystalline regrowth (graphitization)process of this highly anisotropic material. The structure of ion‐irradiated HOPG has also been studied, and drawing inspiration from this, the crystallite size is fundamental in these novel properties in carbon. The bombarded graphite (with H+ and He ions), diamagnetic graphite, were performed using a Renishaw Raman microscope with a 514.5 nm Ar‐ion laser. The work includes the following parts:

    1. Raman spectroscopy (measurements, spectra treatment with Origin and LabFit program, interpretation based on available literature).

    2. Atomic force microscopy, interpretation with the SPIP software.

    3. TRIM software simulation ion tracks in the sample.

  • 17.
    Alm, Ove
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Andersson, Per
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Bäckström, Gunnar
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    A multiple coaxial wire for pressure calibration1974Inngår i: Review of Scientific Instruments, ISSN 0034-6748, E-ISSN 1089-7623, Vol. 45, nr 4, s. 594-595Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A single wire containing several metals suitable for pressure calibration has been produced by extrusion. Coaxial combinations of Ce-Bi-TI and Ce-Bi-Ba have been prepared by the procedure described.

  • 18.
    Alm, Ove
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Andersson, Per
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Bäckström, Gunnar
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Thermal and mechanical properties of textile-fibre-reinforced Bakelite under pressure1975Inngår i: High Temperatures-High Pressures, ISSN 0018-1544, E-ISSN 1472-3441, Vol. 7, nr 5, s. 549-550Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The thermal conductivity of textile-fibre-reinforced Bakelite has been determined up to 1 GPa by the transient hot-wire method. Plates of the material have also been tested for mechanical strength.

  • 19.
    Alm, Ove
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Bäckström, Gunnar
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Thermal conductivity of KCl up to 19 kbar1974Inngår i: Journal of Physics and Chemistry of Solids, ISSN 0022-3697, E-ISSN 1879-2553, Vol. 35, nr 3, s. 421-424Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The pressure dependency of the thermal conductivity of KCl has been measured at room temperature up to 19 kbar. The high pressure tool was of the “belt” type and a solid medium was used. The specimen was cylindrical and was heated along its axis. The conductivity was found to increase linearly at a rate of (3·3 ± 0·3) per cent/kbar.

  • 20.
    Alm, Ove
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Bäckström, Gunnar
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Thermal conductivity of NaCl up to 40 kbar and 240-400 K1975Inngår i: High Temperatures-High Pressures, ISSN 0018-1544, E-ISSN 1472-3441, Vol. 7, nr 2, s. 235-239Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The thermal conductivity, λ, of NaCl has been measured at pressures up to 40 kbar and temperatures between 240 K and 400 K in a solid medium in a 'belt' type of high-pressure apparatus. A steady state method with axial heating of a cylindrical specimen was employed. The increase of lambda with pressure was almost linear and the ratio of the thermal conductivity at 25 kbar to that at atmospheric pressure, λ(25)/λ(0), was found to be 1.72, and independent of temperature within the experimental error.

  • 21.
    Alm, Ove
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Bäckström, Gunnar
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Thermal conductivity of NaF at high pressures1979Inngår i: High Temperatures-High Pressures, ISSN 0018-1544, E-ISSN 1472-3441, Vol. 11, s. 339-341Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The thermal conductivity, λ, of NaF was measured over the pressure range 0-3 GPa at room temperature. An approximately linear variation of λ with P was observed in this range, and the ratio λ(P)/λ(0) was found to be 1.12 for P = 1 GPa.

  • 22.
    Al-Naseri, Haidar
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Brodin, Gert
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Linear pair-creation damping of high-frequency plasma oscillation2022Inngår i: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 29, nr 4, artikkel-id 042106Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We have studied the linear dispersion relation for Langmuir waves in plasmas of very high density, based on the Dirac-Heisenberg-Wigner formalism. The vacuum contribution to the physical observables leads to ultraviolet divergences, which are removed by a charge renormalization. The remaining vacuum contribution is small and is in agreement with previously derived expressions for the time-dependent vacuum polarization. The main new feature of the theory is a damping mechanism similar to Landau damping, but where the plasmon energy gives rise to creation of electron-positron pairs. The dependence of the damping rate (pair-creation rate) on the wavenumber, temperature, and density is analyzed. Finally, the analytical results of linearized theory are compared with numerical solutions.

  • 23.
    Andersson, Britt M.
    et al.
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Fysik.
    Easterling, Kenneth E.
    Guo, Shi-ju
    Sundqvist, Bertil
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Fysik.
    Electrical resistivity and critical temperature of Bi-based high-Tc superconductors to 1 GPa1990Inngår i: High Pressure Research, volumes 3 to 5: High Pressure Science and Technology: Proceedings of the 12. AIRAPT and 27. EHPRG Conference, University Paderborn 1989, London: Gordon and Breach , 1990, s. 120-122Konferansepaper (Fagfellevurdert)
    Abstract [en]

    We have measured the electrical resistance R of a sintered, two-phase, high-TC superconductor with the nominal composition BiSrCaCu2Ox, as a function of T and p. We find d(lnR)/dp ≃ -0.06 GPa-1 at 295 K, while dTC/dp is 2.5 K/GPa for the phase with Tc ≃ 76 and 2 K/GPa for that with TC ≃ 106 K.

  • 24.
    Andersson, Britt M.
    et al.
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Fysik.
    Easterling, Kenneth E.
    Loberg, Bengt
    Niska, John
    Sundqvist, Bertil
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Fysik.
    High-pressure properties of high-Tc superconductor samples produced by hot isostatic pressing1990Inngår i: High Pressure Research, volumes 3 to 5: High Pressure Science and Technology: Proceedings of the 12. AIRAPT and 27. EHPRG Conference, University Paderborn 1989, London: Gordon and Breach , 1990, s. 123-126Konferansepaper (Fagfellevurdert)
    Abstract [en]

    The electrical resistance of dense YBa2Cu3Ox and YBa2Cu4Oy produced by hot isostatic pressing has been measured vs. T and p. At 295 K we find d (ln R)/dp ≃ -0.12 and -0.09 GPa-1, respectively, with no systematic dependence on initial density. For 1-2-4, dTC/dp ≃ 5.1 K/GPa, which is ten times that of 1-2-3.

  • 25.
    Andersson, Britt M.
    et al.
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Fysik.
    Sundqvist, Bertil
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Fysik.
    Defects and the thermal conductivity of YBa2Cu3O7-d and YBa2Cu4O81993Inngår i: Journal of Alloys and Compounds, volume 195: Proceedings of Symposium A on High Tc Superconductors of the 1992 E-MRS Fall Conference, Strasbourg 1992, Elsevier Sequoia S.A. , 1993, s. 655-658Konferansepaper (Fagfellevurdert)
    Abstract [en]

    We present below the first measured data for the thermal diffusivity and the thermal conductivity, λ, of dense, sintered ceramic YBa2Cu4O8 (1-2-4) as a function of temperature T between 40 and 310 K. At 300 K, λ is 6.3 Wm−1K−1, increasing with decreasing T to about 9.5 Wm−1K−1 near Tc. This T dependence is much stronger than in YBa2Cu3O7−δ (1-2-3). Only a very small enhancement is observed in λ below Tc. As in 1-2-3, λ is mainly limited by phonon scattering by defects.

  • 26.
    Andersson, Britt M.
    et al.
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Fysik.
    Sundqvist, Bertil
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Fysik.
    Thermal conductivity and thermal diffusivity of dense, bulk YBa2Cu4O81994Inngår i: High Temperatures - High Pressures volume 26, issue 1: Proceedings of the 13th European Conference on Thermophysical Properties (13 ECTP), Lisboa 1993, London: Pion Press , 1994, s. 53-57Konferansepaper (Fagfellevurdert)
    Abstract [en]

    We have measured the thermal conductivity, lambda, and the thermal diffusivity, a, of dense bulk ceramic YBa2Cu4O8 (1-2-4) between 30 and 300 K. For this material lambda is about 10 W/Km near 100 K, comparable with the in-plane thermal conductivity for single crystals of the more common high-Tc material YBa2Cu3O7 (1-2-3). Also, lambda has a much stronger T dependence in 1-2-4 than in 1-2-3. We find that, for 1-2-4, lambda can be very well described by a semiclassical phonon theory, which includes phonon, electron, and boundary scattering. The difference between the present results and those for 1-2-3 can be explained mainly in terms of a smaller amount of point-defect scattering in 1-2-4 because of the stable oxygen stoichiometry of this material.

  • 27.
    Andersson, Britt M.
    et al.
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Fysik.
    Sundqvist, Bertil
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Fysik.
    Thermal conductivity of YBa2Cu4O8 dominated by phonon-phonon interactions1993Inngår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 48, nr 5, s. 3575-3578Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The thermal conductivity κ of dense sintered ceramic YBa2Cu4O8 in the range 30–310 K has been measured. At 100 K, κ is 10 W m-1 K-1, approaching the in-plane κ of single crystals of other high-Tc materials. κ decreases rapidly with increasing T to 7.4 W m-1 K-1 at 300 K. Fitting standard models for κ(T) to the data we find that κ is limited mainly by phonon-phonon interactions. Depending on the model used, the best fit is found for effective values of FTHETADebye between 155 and 185 K, characteristic for the acoustic phonon branches, indicating that such phonons carry most of the heat. Finally, we suggest a possible way to test the electron-phonon model for the electrical and thermal conductivities in high-Tc materials.

  • 28.
    Andersson, Britt M.
    et al.
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Fysik.
    Sundqvist, Bertil
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Fysik.
    Thermal conductivity of YBa2Cu4O8 under high pressure1993Inngår i: Physica. C, Superconductivity, ISSN 0921-4534, E-ISSN 1873-2143, Vol. 216, nr 1-2, s. 187-194Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The thermal diffusivity a of YBa2Cu4O8 (1-2-4) has been measured as a function of pressure p and temperature T over the range 85<T<310 K and up to 1 GPa (10 kbar). From the data obtained we have calculated the pressure dependence of the thermal conductivity κ as a function of T. κ increases slowly with increasing p above 150 K but decreases below this value. Most of the high-T increase with p is caused by an increase in the electronic thermal conductivity κe. For the phonon thermal conductivity, which dominates κ in 1-2-4, we find that charge transfer with p causes a strong increase in electron-phonon scattering with p, while the p dependence of the boundary scattering and phonon-phonon scattering is in reasonable agreement with the behaviour predicted by simple models.

  • 29.
    Andersson, Britt M.
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Sundqvist, Bertil
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Thermal diffusivity and thermal conductivity of YBa2Cu3O7-d and YBa2Cu4O8 between 20 and 300 K1992Inngår i: Proceedings of the Joint Nordic Spring Meeting '92 / [ed] Per-Anker Lindgård, Roskilde: Risö National Laboratory/Grafisk Service, Risö , 1992, s. 251-Konferansepaper (Annet vitenskapelig)
  • 30.
    Andersson, Britt M.
    et al.
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Fysik.
    Sundqvist, Bertil
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Fysik.
    Niska, John
    Loberg, Bengt
    Thermal conductivity of polycrystalline YBa2Cu4O81994Inngår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 49, nr 6, s. 4189-4198Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We have measured the thermal conductivity κ and the thermal diffusivity a of a dense bulk ceramic polycrystalline sample of YBa2Cu4O8 (1:2:4) in the temperature range 30–300 K. We find κ≊10 W m-1 K-1 at 100 K, significantly higher than in ceramic YBa2Cu3O7-δ (1:2:3) and approaching the in-plane value for single-crystal 1:2:3, and decreasing to 7.6 W m-1 K-1 at 300 K. The data for this sample can be described by standard theories for phonon thermal conductivity of crystalline materials with boundary, phonon, and electron scattering. The higher κ in 1:2:4 as compared to 1:2:3 is, in this model, due to the smaller point defect scattering in the former. The fitted parameters for the three scattering mechanisms all agree with independent estimates based on simple models; inserting data for electric resistivity, grain size, carrier density, and lattice properties we can predict κ and its T dependence to within about 20%. We also discuss models for the phonon and electron thermal conductivities in some detail, including some second-order effects such as inelastic electron scattering and a T-dependent carrier density.

  • 31.
    Andersson, Britt M.
    et al.
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Fysik.
    Sundqvist, Bertil
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Fysik.
    Niska, John
    Loberg, Bengt
    Easterling, Kenneth
    Electrical transport in dense, bulk YBa2Cu4O8 produced by hot isostatic pressing1990Inngår i: Physica B Volumes 165 & 166, Part 2: LT-19 Part II: Contributed Papers, Proceedings of the 19th International Conference on Low Temperature Physics, Brighton 1990, Elsevier B.V. , 1990, s. 1699-1700Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Dense (98.5%) bulk sintered specimens of YBa2Cu4O8 have been produced by hot isostatic pressing. Data for the electrical resistivity π versus temperature T and pressure p in the range 70–300 K and 0–0.7 GPa are reported and discussed. The critical current density of the material studied exceeds 100 Acm−2 below 60 K.

  • 32.
    Andersson, Britt M.
    et al.
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Fysik.
    Sundqvist, Bertil
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Fysik.
    Niska, John
    Loberg, Bengt
    Easterling, Kenneth
    Electrical transport properties of dense bulk YBa2Cu4O8 produced by hot isostatic pressing1990Inngår i: Physica. C, Superconductivity, ISSN 0921-4534, E-ISSN 1873-2143, Vol. 170, nr 5-6, s. 521-531Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Highly dense sintered YBa2Cu4O8 has been produced by hot isostatic pressing (HIP). The electrical resistivity varrho of this material has been measured as a function of temperature T and pressure varrho in the range 40–650 K and 0–0.7 GPa. Both the temperature dependence and the pressure dependence of varrho are found to be well described by a model based on the standard Bloch-Grüneisen theory. It is pointed out that varrho is liner in T only under isobaric conditions, while varrho is strongly nonlinear in all high-Tc superconductors under isochoric (constant volume) conditions. The critical current density of the material is 900 A/cm2 at 4 K, while the resistivity is 630 μΩ cm at 294 K.

  • 33.
    Andersson, Göran
    et al.
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Fysik.
    Sundqvist, Bertil
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Fysik.
    Pressure dependence of the c-axis resistance of stage 2 SbCl5 intercalated graphite to 4 GPa1988Inngår i: Solid State Communications, ISSN 0038-1098, E-ISSN 1879-2766, Vol. 65, nr 7, s. 735-738Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The c-axis electrical resistance R has been measured under pressure up to 4 GPa (40 kbar) at room temperature for stage 2, HOPG-based SbCl5 intercalated graphite. In addition to the well known ordering transition at 0.3–0.5 GPa a second anomaly in R is observed above 1 GPa, corresponding to a further phase transition which is not completed until above 2.4 GPa. In all phases R depends more strongly on p for the intercalated material than for HOPG, and the total decrease in R is over 80% to 4 GPa.

  • 34.
    Andersson, Göran
    et al.
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Fysik.
    Sundqvist, Bertil
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Fysik.
    Bäckström, Gunnar
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Fysik.
    A high-pressure cell for electrical resistance measurements at hydrostatic pressures up to 8 GPa: Results for Bi, Ba, Ni, and Si1989Inngår i: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 65, nr 10, s. 3943-3950Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A modified Bridgman anvil high-pressure device, capable of producing hydrostatic pressures up to 8 GPa (80 kbar), was designed and built. The size of the pressure chamber (10 mm in diameter) allows the use of large specimens and simple experimental procedures. Experimental results show that hydrostatic conditions are necessary if accurate quantitative information is desired about the electrical properties of materials under pressure. Accurate data on resistance (and resistivity) versus pressure at 294 K are given for Bi, Ba, Ni, and Si. The initial pressure coefficients of R were d(ln R)dP=0.13, −7.6×10−2, −2.0×10−2, and −0.26 GPa−1, respectively. Barium has a resistance minimum near 0.9 GPa. For Bi we observe sharp transitions at 2.55, 2.7, and 7.7 GPa, and for Ba at 5.55 GPa, but we cannot verify the existence of a transition in Ba near 7 GPa. Neither do we confirm the phase transformation in Ni recently reported to occur above 2.5 GPa. For Si, R(P) agrees very well with a theoretical function calculated from the change in band gap and electron mobility with pressure.

  • 35.
    Andersson, Göran
    et al.
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Fysik.
    Sundqvist, Bertil
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Fysik.
    Bäckström, Gunnar
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Fysik.
    Electrical resistivity measurements under hydrostatic conditions up to 10 GPa1984Inngår i: Journal de Physique Colloques vol. 45: Supplément C8, Physics and Physicochemistry of Highly Condensed Matter; Proceedings of the XXIInd Meeting of the EHPRG, Aussois, Sept. 1984, 1984, s. 379-382Konferansepaper (Fagfellevurdert)
    Abstract [en]

    A large scale Bridgman anvil system has been designed. Steel gaskets permit compression of a methanol-ethanol medium over a volume of 500-250 mm3. Up to 12 wires have been used to contact specimens. The system has so far served up to 7.5 GPa, with anvils made of ASP tool steel. The transition Bi III-V was found to occur at a lower pressure than the recommended average. The electrical resistance of copper was measured up to 6 GPa under hydrostatic conditions.

  • 36.
    Andersson, Odd E.
    et al.
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Fysik.
    Behrens, Peter
    Sundqvist, Bertil
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Fysik.
    C-axis resistance of HgCl2 intercalated graphite as a function of temperature and pressure1989Inngår i: Synthetic Metals volume 34: Proceedings of the Fifth International Symposium on Intercalated Graphite, Berlin (West) 1989, Lausanne: Elsevier Sequoia SA , 1989, s. 485-490Konferansepaper (Fagfellevurdert)
    Abstract [en]

    The c-axis resistance of stage 3 HgCl2 intercalated graphite has been measured as a function of temperature T and pressure p in the range 40 to 300 K and up to 1 GPa (10 kbar). The absolute resistivity and its T- and p- dependence are all in good agreement with data for other acceptor compounds. The measurements show that a previosly unknown phase transformation occurs above 0.4 GPa. Below 250 K the high pressure phase is metastable down to zero pressure, and an x-ray diffraction analysis of metastable material shows that no stage change occurs. The transition thus probably leads to a different in-plane structure characterized by a more densely packed intercalate layer.

  • 37.
    Andersson, Odd E.
    et al.
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Fysik.
    Lelaurain, Michelle
    Marêché, Jean-Francois
    McRae, Edward
    Sundqvist, Bertil
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Fysik.
    Pressure-induced modifications of structural and transport properties in SbCl5 intercalated graphite1992Inngår i: Materials Science Forum volumes 91-93, Part I: Intercalation Compounds ISIC-6: Proceedings of the Sixth International Symposium on Intercalation Compounds, Orléans 1991., Zürich: Trans Tech Publications , 1992, s. 301-306Konferansepaper (Fagfellevurdert)
    Abstract [en]

    The structure and the c-axis resistivity of SbCl5 intercalated graphite have been studied as functions of T and p, over the ranges 40 to 295 K and 0 to 0.7 GPa. Slow cooling or slow application of pressure p > 0.4 GPa lead to states of complete but different crystallization of the intercalate, but after rapid cooling or pressurization any crystallization is incomplete. The resistivity of the high pressure crystallized phase is about 50% lower than that of the low T, low p phase under identical p-T conditions. No significant difference is seen between the behaviour of HOPG-based and single crystal based materials.

  • 38.
    Andersson, Odd E.
    et al.
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Fysik.
    Lelaurain, Michelle
    Marêché, Jean-Francois
    McRae, Edward
    Sundqvist, Bertil
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Fysik.
    Structure, c-axis resistivity, and p-T phase diagram of SbCl5 intercalated graphite1989Inngår i: Synthetic Metals volume 34: Proceedings of the Fifth International Symposium on Intercalated Graphite, Berlin (West) 1989, Lausanne: Elsevier Sequoia SA , 1989, s. 187-192Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Experimental data are reported for the c-axis resistivity varrhoc of stages n = 3,4,5 and 8 SbCl5 intercalated graphite as a function of T and p, in the range 40 – 300 K and 0-0.5 GPa (5 kbar). varrhoc varied in a systematic way with p, T, and n. Well ordered low-T phases were obtained for all stages; disordering at 200 – 235 K gave rise to well defined multiple anomalies in varrhoc. We also report x-ray diffraction data on the stage 2 compound: evidence was found for large variations in the in-plane structure even for nominally identical samples.

  • 39.
    Andersson, Odd E.
    et al.
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Fysik.
    Sundqvist, Bertil
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Fysik.
    McRae, Edward
    Lelaurain, Michelle
    Marêché, Jean-Francois
    A study of temperature and pressure induced structural and electronic changes in SbCl5 intercalated graphite: Part IV: Basal plane resistivity1995Inngår i: Journal of Materials Research, ISSN 0884-2914, E-ISSN 2044-5326, Vol. 10, nr 7, s. 1653-1660Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Using an inductive technique, we have measured the in-plane resistivity rhoa of stages 2, 4, 5, and 8 SbCl5-GIC's versus temperature T and pressure p in the ranges 130–300 K and 0–0.85 GPa. The room temperature values of rhoa range from 4.0 µOcm for the stages 5 sample to 7.7 µOcm for the stage 8 sample. At all pressures, rhoa shows a metallic temperature dependence rhoa ~ Ta, with 1 < a < 2, but in contrast to the c-axis resistivity rhoc, it depends only very weakly on pressure and/or intercalate structural order. We show that the behavior observed is consistent with a band conduction model.

  • 40.
    Andersson, Odd E.
    et al.
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Fysik.
    Sundqvist, Bertil
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Fysik.
    McRae, Edward
    Marêché, Jean-Francois
    Lelaurain, Michelle
    A study of temperature and pressure induced structural and electronic changes in SbCl5 intercalated graphite: Part II. Experimental data for c-axis resistivity1992Inngår i: Journal of Materials Research, ISSN 0884-2914, E-ISSN 2044-5326, Vol. 7, nr 11, s. 2989-3000Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We present experimental data for the c-axis resistivity ?c of stage s = 2, 3, 4, 5, and 8, SbCl5 intercalated graphite, over the temperature range 40 to 300 K and the pressure range 0 to 0.8 GPa (0–8 kbar). For most specimens studied, resistance anomalies are observed below 230 K at atmospheric pressure and at pressures up to 0.5 GPa at 293 K. These anomalies are explained in terms of structural changes from a disordered or partly crystallized in-plane intercalate structure at atmospheric pressure and T > 230 K to an almost completely crystallized structure below this temperature, or at elevated pressures, as discussed in a companion paper. In the crystallized phases ?c is approximately linear in T except for stage 8, for which a nonlinear behavior, with a negative temperature coefficient of resistivity below 200 K, is observed. The results are compared with previously available literature data, and the p-T phase diagram is briefly discussed.

  • 41.
    Andersson, Odd E.
    et al.
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Fysik.
    Sundqvist, Bertil
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Fysik.
    Polo, V.
    Vangelisti, René
    Marêché, Jean Francois
    McRae, Edward
    The c-axis resistivity for two HOPG-based, first stage CuAl2Cl8 and second stage CuCl2 - graphite intercalation compounds as a function of both pressure and temperature1996Inngår i: Journal of Physics and Chemistry of Solids, volume 57, issues 6-8: Proceedings of the 8th International Symposium on Intercalation Compounds (ISIC-8), Vancouver 1995, Elsevier Ltd. , 1996, s. 719-723Konferansepaper (Fagfellevurdert)
    Abstract [en]

    In this paper we present data for the c-axis resistivity of first stage CuAl2Cl8 GIC and second stage CuCl2 GIC as functions of pressure, p, (0.0 < p < 1.5 GPa) and of temperature, T, (4 < T < 300 K). We show evidence of a possible new high-pressure phase above 1.0 GPa for the CuAl2Cl8 GIC and we show that the CuCl2 GIC is very stable at all pressures and temperature investigated. We make a comparison with previous results on SbCl5 GICs and other chloride intercalation compounds and with theories treating the temperature and pressure coefficients of transport parameters in layered solids.

  • 42.
    Andersson, Ove
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Dielectric relaxation of the amorphous ices2008Inngår i: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 20, artikkel-id 244115Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The dielectric properties of the low and high density amorphous ices are discussed in terms of those for supercooled water and crystalline ices, and also used to evaluate the transition behaviour upon pressure cycling at 130 K. The dielectric relaxation of the high density amorphous ice is described well by the symmetrical Cole–Cole function with an almost pressure independent relaxation time τ ∼ 2 s at 133 K and a relaxation time distribution factor of 0.7. At the high to low density amorphous ice transition, the dielectric relaxation time increases by about two orders of magnitude despite a ∼30% decrease in density, and τ of the low density amorphous ice is in the range 102–103 s at 130 K. The relaxation time behaviour of the high density amorphous ice is similar to that of supercooled liquid water, whereas τ of the low density amorphous ice appears to be prolonged by the ice rules, in correspondence to that of the crystalline ices.

  • 43.
    Andersson, Ove
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Glass-liquid transition of water at high pressure2011Inngår i: Proceedings of the National Academy of Sciences of the United States of America, ISSN 0027-8424, E-ISSN 1091-6490, Vol. 108, nr 27, s. 11013-11016Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The knowledge of the existence of liquid water under extreme conditions and its concomitant properties are important in many fields of science. Glassy water has previously been prepared by hyperquenching micron-sized droplets of liquid water and vapor deposition on a cold substrate (ASW), and its transformation to an ultraviscous liquid form has been reported on heating. A densified amorphous solid form of water, high-density amorphous ice (HDA), has also been made by collapsing the structure of ice at pressures above 1 GPa and temperatures below approximately 140 K, but a corresponding liquid phase has not been detected. Here we report results of heat capacity C(p) and thermal conductivity, in situ, measurements, which are consistent with a reversible transition from annealed HDA to ultraviscous high-density liquid water at 1 GPa and 140 K. On heating of HDA, the Cp increases abruptly by (3.4 ± 0.2) J mol-1 K-1 before crystallization starts at (153 ± 1) K. This is larger than the Cp rise at the glass to liquid transition of annealed ASW at 1 atm, which suggests the existence of liquid water under these extreme conditions.

    Fulltekst (pdf)
    fulltext
  • 44.
    Andersson, Ove
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Simulation of a glass transition in a hot-wire experiment using time-dependent heat capacity1997Inngår i: International journal of thermophysics, ISSN 0195-928X, E-ISSN 1572-9567, Vol. 18, nr 1, s. 195-208Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The transient hot-wire method is used for simultaneous measurements of the thermal conductivity λ and the heat capacity per unit volume ρcp and yields a peak in λ and a dip in ρcp near a glass transition. Through simulations, it is shown that these anomalous results arise due to a time dependence in cp, which is described by a fractional exponential function: cp(t) = cp(liquid) + [cp(glass) - cp(liquid)] e(-(t/τ)β), where τ is the heat capacity relaxation time and β is a sample dependent parameter (0 < β ≤ 1). By a comparison with experimental data for cyclohexanol and glycerol, it is demonstrated that this model can be used to reproduce the peak and the dip as well as the temperature at which these occur. In addition, it is shown that the maximum in λ occurs at τ = 0.3 s, whereas τ of the minimum in ρcp is dependent on β and moves from 0.4 to 1 s for a change in β from 1 to 0.5. The difference in τ between the peak and the dip is in agreement with the experimental results. It is concluded that the anomalies reveal glass forming characteristics such as a rough classification in terms of strong and fragile glass formers.

  • 45.
    Andersson, Ove
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Thermal conductivity of normal and deuterated water, crystalline ice, and amorphous ices2018Inngår i: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 149, nr 12, artikkel-id 124506Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The effect of deuteration on the thermal conductivity kappa of water, crystalline ice, and amorphous ices was studied using the pressure induced amorphization of hexagonal ice, ice Ih, to obtain the deuterated, D2O, forms of low-density amorphous (LDA), high-density amorphous (HDA), and very-high density amorphous (VHDA) ices. Upon deuteration, kappa of ice Ih decreases between 3% and 4% in the 100-270 K range at ambient pressure, but the effect diminishes on densification at 130 K and vanishes just prior to amorphization near 0.8 GPa. The unusual negative value of the isothermal density rho dependence of kappa for ice Ih, g = (d ln kappa/d ln rho)(T) = -4.4, is less so for deuterated ice: g = -3.8. In the case of the amorphous ices and liquid water, kappa of water decreases by 3.5% upon deuteration at ambient conditions, whereas K of HDA and VHDA ices instead increases by up to 5% for pressures up to 1.2 GPa at 130 K, despite HDA's and VHDA's structural similarities with water. The results are consistent with significant heat transport by librational modes in amorphous ices as well as water, and that deuteration increases phonon-phonon scattering in crystalline ice. Heat transport by librational modes is more pronounced in D2O than in H2O at low temperatures due to a deuteration-induced red-shift of librational mode frequencies. Moreover, the results show that kappa of deuterated LDA ice is 4% larger than that of normal LDA at 130 K, and both forms display an unusual temperature dependence of kappa, which is reminiscent of that for crystals (kappa similar to T (-1)), and a unique negative pressure dependence of kappa, which likely is linked to local-order structural similarities to ice Ih. 

  • 46.
    Andersson, Ove
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Brant Carvalho, Paulo H. B.
    Department of Materials and Environmental Chemistry, Stockholm University, Stockholm, Sweden.
    Häussermann, Ulrich
    Department of Materials and Environmental Chemistry, Stockholm University, Stockholm, Sweden.
    Hsu, Ying-Jui
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Evidence suggesting kinetic unfreezing of water mobility in two distinct processes in pressure-amorphized clathrate hydrates2022Inngår i: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 24, nr 34, s. 20064-20072Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Type II clathrate hydrates (CHs) with tetrahydrofuran (THF), cyclobutanone (CB) or 1,3-dioxolane (DXL) guest molecules collapse to an amorphous state near 1 GPa on pressurization below 140 K. On subsequent heating in the 0.2-0.7 GPa range, thermal conductivity and heat capacity results of the homogeneous amorphous solid show two glass transitions, first a thermally weak glass transition, GT1, near 130 K; thereafter a thermally strong glass transition, GT2, which implies a transformation to an ultraviscous liquid on heating. Here we compare the GTs of normal and deuterated samples and samples with different guest molecules. The results show that GT1 and GT2 are unaffected by deuteration of the THF guest and exchange of THF with CB or DXL, whereas the glass transition temperatures (Tgs) shift to higher temperatures on deuteration of water; Tg of GT2 increases by 2.5 K. These results imply that both GTs are associated with the water network. This is corroborated by the fact that GT2 is detected only in the state which is the amorphized CH's counterpart of expanded high density amorphous ice. The results suggest a rare transition sequence of an orientational glass transition followed by a glass to liquid transition, i.e., kinetic unfreezing of H2O reorientational and translational mobility in two distinct processes.

    Fulltekst (pdf)
    fulltext
  • 47.
    Andersson, Ove
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Carvalho, Paulo H. B. Brant
    Hsu, Ying-Jui
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Haussermann, Ulrich
    Transitions in pressure-amorphized clathrate hydrates akin to those of amorphous ices2019Inngår i: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 151, nr 1, artikkel-id 014502Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Type II clathrate hydrates (CHs) were studied by thermal and dielectric measurements. All CHs amorphize, or collapse, on pressurization to 1.3 GPa below 135 K. After heating to 160 K at 1 GPa, the stability of the amorphous states increases in a process similar to the gradual high density to very high density amorphous ice (HDA to VHDA) transition. On a subsequent pressure decrease, the amorphized CHs expand partly irreversibly similar to the gradual VHDA to expanded HDA ice transformation. After further heating at 1 GPa, weak transition features appear near the HDA to low density amorphous ice transition. The results suggest that CH nucleation sites vanish on heating to 160 K at 1 GPa and that a sluggish partial phase-separation process commences on further heating. The collapsed CHs show two glass transitions (GTs), GT1 and GT2. GT1 is weakly pressure-dependent, 12 K GPa(-1), with a relaxation time of 0.3 s at 140 K and 1 GPa; it is associated with a weak heat capacity increase of 3.7 J H2O-mol(-1) K-1 in a 18 K range and an activation energy of only 38 kJ mol(-1) at 1 GPa. The corresponding temperature of GT2 is 159 K at 0.4 GPa with a pressure dependence of 36 K GPa(-1); it shows 5.5 times larger heat capacity increase and 4 times higher activation energy than GT1. GT1 is observed also in HDA and VHDA, whereas GT2 occurs just above the crystallization temperature of expanded HDA and only within its similar to 0.2-0.7 GPa stable pressure range.

  • 48.
    Andersson, Ove
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Chobal, Oleksandr
    Department of Solid State Electronics, Uzhhorod National University, Ukraine.
    Rizak, I
    Department of Integrated Technologies of Aviation Manufacture, National Aerospace University of “KhAI", Kharkov, Ukraine.
    Rizak, V
    Department of Solid State Electronics, Uzhhorod National University, Ukraine.
    Tricritical Lifshitz point in the temperature-pressure-composition diagram for (PbySn1-y)2 P2(SexS1-x)6 ferroelectrics2009Inngår i: Physical Review B Condensed Matter, ISSN 0163-1829, E-ISSN 1095-3795, Vol. 80, s. 174107-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The heat capacity of Sn2P2S6 ferroelectric crystals has been measured under quasihydrostatic pressures up to 0.7 GPa. The analysis of the heat-capacity and literature data for the birefringence shows that the tricritical point of Sn2P2S6 is in the 0.20–0.25 GPa range. Moreover, in the approximation of a linear change in the free-energy expansion coefficients, with respect to concentration and pressure, thermodynamic trajectories have been constructed for (PbySn1−y)2 P2(SexS1−x)6 solid solutions. We have thereby identified the region of the T-p-y-x diagram for (PbySn1−y)2 P2(SexS1−x)6 showing the tricritical Lifshitz point.

    Fulltekst (pdf)
    fulltext
  • 49.
    Andersson, Ove
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Filinchuk, Yaroslav
    Dmitriev, Vladimir
    Quwar, Issam
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Talyzin, Alexandr
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Sundqvist, Bertil
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Phase coexistence and hysteresis effects in the pressure-temperature phase diagram of NH3BH32011Inngår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 84, nr 2, s. 024115-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The potential hydrogen storage compound NH3BH3 has three known structural phases in the temperature and pressure ranges 110–300 K and 0–1.5 GPa, respectively. We report here the boundaries between, and the ranges of stability of, these phases. The phase boundaries were located by in situ measurements of the thermal conductivity, while the actual structures in selected areas were identified by in situ Raman spectroscopy and x-ray diffraction. Below 0.6 GPa, reversible transitions involving only small hysteresis effects occur between the room-temperature tetragonal plastic crystal I4mm phase and the low-temperature orthorhombic Pmn21 phase. Transformations of the I4mm phase into the high-pressure orthorhombic Cmc21 phase, occurring above 0.8 GPa, are associated with very large hysteresis effects, such that the reverse transition may occur at up to 0.5 GPa lower pressures. Below 230 K, a fraction of the Cmc21 phase is metastable to atmospheric pressure, suggesting the possibility that dense structural phases of NH3BH3, stable at room temperature, could possibly be created and stabilized by alloying or by other methods. Mixed orthorhombic Pmn21/Cmc21 phases were observed in an intermediate pressure-temperature range, but a fourth structural phase predicted by Filinchuk et al. [ Phys. Rev. B 79 214111 (2009)] was not observed in the pressure-temperature ranges of this experiment. The thermal conductivity of the plastic crystal I4mm phase is about 0.6 W m−1 K−1 and only weakly dependent on temperature, while the ordered orthorhombic phases have higher thermal conductivities limited by phonon-phonon scattering.

    Fulltekst (pdf)
    AnderssonPRB84_2011
  • 50.
    Andersson, Ove
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Häussermann, Ulrich
    A Second Glass Transition in Pressure Collapsed Type II Clathrate Hydrates2018Inngår i: Journal of Physical Chemistry B, ISSN 1520-6106, E-ISSN 1520-5207, Vol. 122, nr 15, s. 4376-4384Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Type II clathrate hydrates (CHs) M·17 H2O, with M = tetrahydrofuran (THF) or 1,3-dioxolane, are known to collapse, or amorphize, on pressurization to ∼1.3 GPa in the temperature range 77–140 K. On heating at 1 GPa, these pressure-amorphized CH states show a weak, stretched sigmoid-shaped, heat-capacity increase because of a glass transition. Here we use thermal conductivity and heat capacity measurements to show that also type II CH with M = cyclobutanone (CB) collapses on isothermal pressurization and undergoes a similar, weak, glass transition upon heating at 1 GPa. Furthermore, we reveal for both THF CH and CB CH a second, much more pronounced, glass transition at temperatures above the thermally weak glass transition on heating in the 0.2–0.7 GPa range. This result suggests the general occurrence of two glass transitions in water-rich (94 mol %) pressure-collapsed CHs. Because of a large increase in dielectric permittivity concurrently as the weak heat capacity increase, the first glass transition must be due to kinetic unfreezing of water molecules. The thermal features of the second glass transition, measured on isobaric temperature cycling, are typical of a glass–liquid–glass transition, which suggests that pressure-amorphized CHs transform reversibly to liquids.

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