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  • 251.
    Sundqvist, Bertil
    et al.
    Umeå University, Faculty of Science and Technology, Physics.
    Bäckström, Gunnar
    Umeå University, Faculty of Science and Technology, Physics.
    Thermal conductivity of gold and silver at high pressures1978In: Journal of Physics and Chemistry of Solids, ISSN 0022-3697, E-ISSN 1879-2553, Vol. 39, no 10, p. 1133-1137Article in journal (Refereed)
    Abstract [en]

    The thermal diffusivities of gold and silver have been measured under pressure up to 2.5 GPa at room temperature. From the measured data the pressure dependence of the thermal conductivity, λ, has been calculated. The values found for the pressure coefficient λ−1 δλ/δP were 3.9 × 10−2GPa−1 for gold and 4.0 × 10−2 GP silver at atmospheric pressure. The results are compared to theoretical predictions of the pressure dependence and also to previous experimental results for copper and aluminium. For the noble metals, small angle or “vertical” scattering of electrons is shown to have a stronger volume dependence than “horizontal” scattering.

  • 252.
    Sundqvist, Bertil
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Edlund, Ulf
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Jacobsson, Per
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Johnels, Dan
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Jun, Jan
    Launois, Pascale
    Moret, Roger
    Persson, Per-Axel
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Soldatov, Alexander
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Wågberg, Thomas
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Structural and physical properties of pressure polymerized C601998In: Carbon, vol. 36 issue 5-6: Proceedings of Symposium A: Fullerenes and Carbon Based Materials, of the Joint Meeting of the European Materials Research Society (E-MRS'97) and the International Conference on Advanced Materials (ICAM'97), Strasbourg 1997, Elsevier B.V. , 1998, p. 657-660Conference paper (Refereed)
    Abstract [en]

    We discuss the structural and dynamic properties of C60 polymerized under low-P, low-T conditions, and suggest that the disordered mixed orthorhombic-tetragonal-rhombohedral phases produced under these conditions arise from nucleation of molecular chains in random directions because of the quasi-free molecular rotation under standard reaction conditions in the fcc phase of C60. Polymerization in He gives results qualitatively different from those obtained in other media.

  • 253.
    Sundqvist, Bertil
    et al.
    Umeå University, Faculty of Science and Technology, Physics.
    Fischer, John E.
    Pressure-temperature phase boundaries in KC24: Evidence for a kinetically-hindered low-temperature staging transition1986In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 34, no 5, p. 3532-3535Article in journal (Refereed)
    Abstract [en]

    The pressure-temperature phase diagram of KC24 was mapped out using in-plane resistivity anomalies to identify phase boundaries. Surprisingly, the 300-K staging transitions at 3.4 and 6.4 kbar are found to connect to the 1-bar ordering-stacking transitions at Tu=123 K and Tl=96 K, respectively, whereas the loci of P, T anomalies cannot be equilibrium phase boundaries since the low-P, low-T transitions do not involve stage transformations. We suggest that this unusual behavior is due to kinetic hindering of the low-T staging transitions, predicted by simple equilibrium models and observed in the analogous Li compound. A possible origin of the slow staging kinetics at low T in KC24 is the pinning of discommensurations at Daumas-Herold boundaries.

  • 254.
    Sundqvist, Bertil
    et al.
    Umeå University, Faculty of Science and Technology, Physics.
    Fischer, John E.
    Pressure-temperature phase diagrams of stage-2-4 potassium-graphite intercalation compounds deduced from anomalies in the basal plane resistivity1987In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 35, no 15, p. 8231-8242Article in journal (Refereed)
    Abstract [en]

    The basal-plane resistivities ρ of stage-2–4 potassium-graphite intercalation compounds (K-GIC’s) have been measured as functions of temperature T and pressure p using a contactless method. The pressure range investigated was 0–1.4 GPa. For stage-2 K-GIC (KC24) measurements were made in the temperature range 90–300 K, while for the higher-stage materials the range was mainly limited to 245–300 K. In all cases ρ increases with p through the anomalous regime near the phase transitions, whereas dρ/dp is always negative in the stable high-p (high-stage) phases. Approximate p-T phase diagrams are deduced from anomalies in ρ corresponding to the staging and in-plane order-disorder transitions, respectively. In all cases the slopes dp/dT of the phase boundaries for the high-pressure staging transitions are such that the transitions extrapolate to positive T at atmospheric p, although no such transitions have been reported. The low-p staging-ordering phase boundary of KC24 is particularly complex, involving segments with both dp/dT→0 (125<200 K) and dp/dT→∞ (T≊125 K). The p-T diagrams are compared with recent structural experiments and models. We suggest that the complexity of the KC24 phase diagram is attributable to the weakly incommensurate in-plane structure at low p and T.

  • 255.
    Sundqvist, Bertil
    et al.
    Umeå University, Faculty of Science and Technology, Physics.
    Fransson, Åke
    Umeå University, Faculty of Science and Technology, Applied Physics and Electronics.
    Inaba, Akira
    Meingast, Christoph
    Nagel, Peter
    Pasler, Volker
    Renker, Burkhard
    Wågberg, Thomas
    Umeå University, Faculty of Science and Technology, Physics.
    Physical properties of two-dimensionally polymerized C601998In: Fullerenes: Recent Advances in the Chemistry and Physics of Fullerenes and Related Materials, vol. 6: Proceedings of the 193rd Meeting of the Electrochemical Society, Symposium Fullerenes: Chemistry, Physics, and New Directions XI, San Diego 1998, Pennington, NJ: The Electrochemical Society , 1998, p. 705-716Conference paper (Refereed)
    Abstract [en]

    Preliminary data are reported for the thermal expansion, compressibility, and specific heat of two-dimensionally polymerized C60 obtained by treating fullerene samples at temperatures above 800 K under a pressure of 2 GPa. The samples have also been characterized by Raman spectroscopy and inelastic neutron scattering. The measured data for the thermophysical properties are strongly modified by the creation of strong covalent intermolecular bonds and we show that the results are compatible with the predictions of simple theories.

  • 256.
    Sundqvist, Bertil
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Iwasiewicz-Wabnig, Agnieszka
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Kováts, Éva
    Pekker, Sándor
    High pressure studies of the rotor-stator compound C60-cubane.2007In: Materials Research at High Pressure: Proceedings of Symposium PP at the 2006 MRS Fall Meeting, Boston, MA, USA; Materials Research Society Symposium Proceedings vol. 987E, Warrendale: Materials Research Society , 2007, p. 0987-PP03Conference paper (Refereed)
    Abstract [en]

    Insertion of cubane (C8H8) into the octahedral voids of the C60 lattice leads to the formation of an interesting rotor-stator compound which can be converted into a C60 co-polymer by heating. We have treated a number of C60C8H8 samples for up to 3 h each in the range 380-875 K under pressures up to 2 GPa. The resulting materials were investigated by Raman spectroscopy and X-ray diffraction. Depending on treatment conditions, at least five different structural phases can be found. In addition to the four structural phases observed at atmospheric pressure and different temperatures we find that a new polymeric state is created at pressures above 1 GPa, and we tentatively identify its structure as pseudo-orthorhombic. The cubic-orthorhombic phase transition line is found to have a slope of 295 K GPa-1, much larger than the slope of the fcc-sc line in pure C60.

  • 257.
    Sundqvist, Bertil
    et al.
    Umeå University, Faculty of Science and Technology, Physics.
    Jacobsson, Per
    Umeå University, Faculty of Science and Technology, Physics.
    Jun, Jan
    Launois, Pascale
    Moret, Roger
    Soldatov, Alexander
    Umeå University, Faculty of Science and Technology, Physics.
    Wågberg, Thomas
    Umeå University, Faculty of Science and Technology, Physics.
    Polymerization of C60 under hydrostatic and non-hydrostatic conditions1997In: Fullerenes: Recent Advances in the Chemistry and Physics of Fullerenes and Related Materials, vol. 5: Proceedings of the 192nd Meeting of the Electrochemical Society, Paris 1997; Symposium Fullerenes: Chemistry, Physics, and New Directions, Pennington, NJ: The Electrochemical Society , 1997, p. 439-449Conference paper (Refereed)
    Abstract [en]

    We have submitted both powder and single crystal C60 to pressures in the range 1 - 2 GPa at temperatures between 300 and 900 K in order to study pressure polymerization. Reaction conditions varied, from non-hydrostatic conditions with powder samples in steel capsules treated in solid pressure media, to hydrostatic experiments using silicone oils, N2 or He gas. The reacted samples were characterized by Raman spectroscopy and x-ray diffraction. Depending on experimental conditions, their structures varied from orthorhombic (single crystals) to more or less disordered face centered cubic lattices, and the observed Raman spectra could usually be correlated with the observed structures. The results are used to refine and update the pressure-temperature phase diagram of C60.

  • 258.
    Sundqvist, Bertil
    et al.
    Umeå University, Faculty of Science and Technology, Physics.
    Lundberg, Bo
    Umeå University, Faculty of Science and Technology, Physics.
    Contactless basal plane resistivity measurements under pressure and the pressure/temperature phase diagram of stage 2 SbCl5 intercalated graphite1986In: Journal of Physics C: Solid State Physics, ISSN 0022-3719, Vol. 19, no 35, p. 6915-6929Article in journal (Refereed)
    Abstract [en]

    The basal plane resistivity rho of stage 2 SbCl5 intercalated graphite has been measured as a function of temperature T and pressure p in the range 195-300K and 0-1.75 GPa, using a contactless method. rho is found to increase with increasing p. New evidence is found for the existence of the high-pressure (>1 GPa) phase suggested by Houser and co-workers (1984). The p/T phase boundaries for the low T(<230K) and intermediate p (>0.35 GPa) ordered phases are outlined. A re-analysis of previous results for stage 1 SbF5 intercalated graphite indicates a similar phase diagram for this material.

  • 259.
    Sundqvist, Bertil
    et al.
    Umeå University, Faculty of Science and Technology, Physics.
    Lundberg, Bo
    Umeå University, Faculty of Science and Technology, Physics.
    Contactless measurements of the basal plane resistivity of FeCl3 and SbF5 intercalated graphites under pressure1984In: Journal of Physics C: Solid State Physics, ISSN 0368-3516, Vol. 17, no 5, p. L133-L138Article in journal (Refereed)
    Abstract [en]

    The basal plane resistivities of stage 1 SbF5 and stage 2 FeCl3 graphite intercalation compounds have been measured for the first time at high pressure, using a recently developed contactless method. The resistivity is found to increase with increasing pressure in both materials. In the SbF5 intercalated material a phase transition was found at 1.2 GPa. This could be the first pressure-induced stage transformation observed in an acceptor intercalation compound.

  • 260.
    Sundqvist, Bertil
    et al.
    Umeå University, Faculty of Science and Technology, Physics.
    Lundberg, Bo
    Umeå University, Faculty of Science and Technology, Physics.
    Contactless methods for measuring electrical resistivity under pressure1984In: High Pressure in Science and Technology, Part III: General Topics: Proceedings of 9th AIRAPT International High Pressure Conference, Albany, NY, 1983. Materials Research Society Symposia Proceedings vol. 22., New York: North-Holland, Elsevier Science Publishing Co., Inc. , 1984, p. 281-284Conference paper (Refereed)
    Abstract [en]

    A new inductive contactless method to measure the electrical conductivity of metals under pressure is described. A ferromagnetic Metglas 2826 toroid core is used to minimize errors due to external magnetic fields. Experimental results for tin and brass are shown to agree very well with conventional four-terminal measurements.

  • 261.
    Sundqvist, Bertil
    et al.
    Umeå University, Faculty of Science and Technology, Physics.
    Lundberg, Bo
    Umeå University, Faculty of Science and Technology, Physics.
    Contactless resistivity measurements under high pressure1983In: Journal of Physics E: Scientific Instruments, ISSN 0022-3735, Vol. 16, no 5, p. 408-411Article in journal (Refereed)
    Abstract [en]

    For the first time, a contactless inductive method has been devised for measurements of the electrical conductivity of metallic materials under very high pressures (>1 GPa). A sample in the form of a thin disc is placed in a pick-up coil in a steady-state AC magnetic field. The output voltage from the coil is analysed with a lock-in amplifier to find the component due to eddy currents in the sample, from which the conductivity is calculated, using a semi-empirical expression. The influence of the steel pressure vessel is eliminated by making simultaneous measurements on a known reference material. Experimental results are shown for tin and sodium up to 1.3 GPa.

  • 262.
    Sundqvist, Bertil
    et al.
    Umeå University, Faculty of Science and Technology, Physics.
    Neve, Jesper
    Rapp, Östen
    Pressure dependence of the electron-phonon interaction and Fermi-surface properties of Al, Au, bcc Li, Pb, and Pd1985In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 32, no 4, p. 2200-2212Article in journal (Refereed)
    Abstract [en]

    The electrical resistance of Li, Pd, Au, and Pb is measured as a function of temperature and pressure in the region -20 °C to +30 °C and 0–1.3 GPa. Self-consistent linear muffin-tin orbital band-structure calculations of these elements and of Al are performed at normal and reduced volumes. Results are obtained for the density of states N(EF), the average Fermi ve- locity, the optical mass, the plasma frequency ω, and the volume dependence of these parameters. The pressure dependence of the electron-phonon interaction λ(p) is obtained from these measurements and the calculated ω(p). For the superconducting elements there is good agreement with the measured superconducting Tc(p). Results from our previous measurements and calculations on Al, V, Nb, and La and published results for ω(p) are included in this comparison. λ(p) increases with pressure for bcc Li and decreases for Pd and Au. Pressure is expected to suppress spin fluctuations much faster than λ(p) in Pd. The possibility of inducing superconductivity by pressure in Pd and bcc Li is discussed. The electronic Grüneisen parameter γe is obtained from λ(p) and the volume dependence of N(EF). Comparison with other results for γe generally shows good agreement.

  • 263.
    Sundqvist, Bertil
    et al.
    Umeå University, Faculty of Science and Technology, Physics.
    Nilsson, E.M. Charlotta
    Umeå University, Faculty of Science and Technology, Physics.
    Constant-pressure versus constant-volume resistivities of some high transition temperature superconductors1994In: Physica C, volume 235-240: Proceedings of the 4th International Conference on Materials and Mechanisms of Superconductivity: High-Temperature Superconductors (M2S HTSC IV), Grenoble 1994, part II, Elsevier Science B.V. , 1994, p. 1407-1408Conference paper (Refereed)
    Abstract [en]

    The resistivity varrho is always measured at constant p, while theory assumes constant V. For high temperature superconductors there are large differences between constant-p and constant-V resistivities. We have previously shown constant-V results for YBa2Cu3O7−δ and show here similar data for La2−xSrxCuO4. Constant-V data for varrho agree with the behaviour expected for a normal metal, with low-T linearity in T and saturation at high T. We speculate that similar effects will be observed in doped fullerenes (M3C60, M = Li, K, Rb, …).

  • 264.
    Sundqvist, Bertil
    et al.
    Umeå University, Faculty of Science and Technology, Physics.
    Nilsson, E.M. Charlotta
    Umeå University, Faculty of Science and Technology, Physics.
    In-plane electrical resistivity of La2-xSrxCuO4 at constant volume1995In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 51, no 9, p. 6111-6114Article in journal (Refereed)
    Abstract [en]

    Literature data for the in-plane electrical resistivity ρ of single-crystal La2-xSrxCuO4 with 0.07 ≤x≤0.34 have been corrected to constant crystal volume V using literature data for the pVT properties and for the resistivity vs pressure p. The original data at constant p show the usual anomalies observed for ceramic high-transition-temperature superconductors, such as linearity of ρ to extremely high T at optimum doping and an upwards curvature (ρ∝T1.5) for overdoped material. After correction, the data for ρ at constant volume are linear in T for overdoped material only. We show that phonons cannot be ruled out as the major carrier scattering agent.

  • 265.
    Sundqvist, Bertil
    et al.
    Umeå University, Faculty of Science and Technology, Physics.
    Persson, Niklas
    Umeå University, Faculty of Science and Technology, Physics.
    Dielectric properties of C60 under high pressure2002In: Journal of Physics: Condensed Matter vol. 14 issue no. 44: Proceedings of the Joint 18th Conference on High Pressure Science and Technology (AIRAPT 18) and the 11th High Pressure Conference of China (HPCC-11), Beijing 2001, Bristol: Institute of Physics , 2002, p. 10437-10440Conference paper (Refereed)
    Abstract [en]

    The dielectric properties of C60 have been measured as functions of temperature and hydrostatic pressure in the ranges 80–370 K and 0–0.8 GPa. The results show sharp anomalies at the rotational transition above 260 K and large relaxation peaks associated with the rotational 'glass transition'. From the measured frequencies of the loss peaks we calculate the energy barrier for molecular jumping between the 'pentagon' and 'hexagon' molecular orientations. The energy barrier increases by 13% GPa−1.

  • 266.
    Sundqvist, Bertil
    et al.
    Umeå University, Faculty of Science and Technology, Physics.
    Rapp, Östen
    Measurement of the pressure dependence of the electron-phonon interaction in aluminium1979In: Journal of Physics F: Metal Physics, ISSN 0305-4608, Vol. 9, no 9, p. L161-L166Article in journal (Refereed)
    Abstract [en]

    The authors report measurements of the electrical resistance of aluminium in the temperature range 30-40 degrees C and the pressure range 0.2-1.0 GPa. From these experiments the pressure dependence of the electron-photon interaction lambda is evaluated. With p in GPa the result is lambda (p)= lambda 0 exp(-0.0467p+4.7*10-4 p2). This expression for lambda describes accurately the observed pressure dependence of the superconducting Tc for pressures up to about 4 GPa.

  • 267.
    Sundqvist, Bertil
    et al.
    Umeå University, Faculty of Science and Technology, Physics.
    Sandberg, Olov
    Umeå University, Faculty of Science and Technology, Physics.
    Bäckström, Gunnar
    Umeå University, Faculty of Science and Technology, Physics.
    The thermal properties of an epoxy resin at high pressure and temperature1977In: Journal of Physics D: Applied Physics, ISSN 0022-3727, E-ISSN 1361-6463, Vol. 10, no 10, p. 1397-1403Article in journal (Refereed)
    Abstract [en]

    The thermal conductivity lambda , thermal diffusivity and heat capacity per unit volume has been measured for an epoxy resin, Araldite AW 106, with hardener HV 953 U. Measurements have been carried out at room temperature up to 2.5 GPa and between 300 and 430K at 0.11 and 0.27 GPa. The glass transition temperature and its pressure (P) dependence have been determined. The quantity delta lambda / delta P was found to change abruptly in the temperature region of the glass transition.

  • 268.
    Sundqvist, Bertil
    et al.
    Umeå University, Faculty of Science and Technology, Physics.
    Soldatov, Alexander
    Umeå University, Faculty of Science and Technology, Physics.
    Andersson, Ove
    Umeå University, Faculty of Science and Technology, Physics.
    Lundin, Anders
    Umeå University, Faculty of Science and Technology, Physics.
    Persson, Per-Axel
    Umeå University, Faculty of Science and Technology, Physics.
    Orientational disorder and the p-T phase diagram of fullerenes1995In: Fullerenes: Recent Advances in the Chemistry and Physics of Fullerenes and Related Materials, volume 2: Proceedings of the 187th ECS Meeting, Symposium Fullerenes: Chemistry, Physics, and New Directions VII, Reno 1995, Pennington, NJ: The Electrochemical Society , 1995, p. 891-905Conference paper (Refereed)
    Abstract [en]

    The translational and orientational structures of fullerenes are very sensitive to pressure, p, because of the weak intermolecular potentials. We have recently carried out high-p studies of the thermal conductivity lambda and the bulk modulus B of C60 and C70, and we show here how the p-T phase diagrams of these materials can be mapped from data for B and lambda and a knowledge of the structures at zero pressure. We discuss how B and lambda are modified by translational, rotational and orientational disorder in the materials, mainly showing examples related to the orientational substructure and its evolution with T and p in C60. We also discuss briefly the structures and phase diagrams of C70 and C61H2, and we show preliminary experimental results suggesting that the structure of high-p, high-T treated C60 is probably not polymeric as recently suggested by several groups.

  • 269.
    Sundqvist, Bertil
    et al.
    Umeå University, Faculty of Science and Technology, Physics.
    Soldatov, Alexander
    Umeå University, Faculty of Science and Technology, Physics.
    Lundin, Anders
    Umeå University, Faculty of Science and Technology, Physics. Umeå University, Faculty of Science and Technology, Applied Physics and Electronics.
    Andersson, Ove
    Umeå University, Faculty of Science and Technology, Physics.
    Measurements of thermophysical properties as a tool to study the phase diagrams of fullerenes under pressure1997In: High Temperatures - High Pressures vol. 29, issue 1: Proceedings of the 14th European Conference on Thermophysical Properties (ECTP-14), Lyon 1996., London: Pion Press , 1997, p. 119-124Conference paper (Refereed)
    Abstract [en]

    The ways in which measurements of thermophysical properties such as the thermal conductivity and the bulk modulus can be used as tools to study the evolution of the translational, rotational, and orientational structure of fullerenes with temperature and pressure are discussed. Recent experimental data for C60 and C70 are discussed and explained in terms of models for their orientational and rotational structures. In particular, effects of molecular reorientation, orientational ordering, and the freezing in of abnormal orientational order in C60 under pressures up to 1 GPa at temperatures below 300 K, and polymerization of C60 at similar pressures above 450 K, are examined.

  • 270.
    Sundqvist, Bertil
    et al.
    Umeå University, Faculty of Science and Technology, Physics.
    Talyzin, Alexandr
    Umeå University, Faculty of Science and Technology, Physics.
    Andersson, Ove
    Umeå University, Faculty of Science and Technology, Physics.
    Complex hydrides studied by Raman spectroscopy and thermal conductivity measurements under high pressure2006In: Hydrogen Storage Technologies: Proceedings of Symposium Z at the 2006 MRS Fall Meeting, Boston, MA, USA; Materials Research Society Symposium Proceedings vol. 971E, Warrendale: Materials Research Society , 2006, p. 7-12Conference paper (Refereed)
    Abstract [en]

    The pressure-temperature phase diagrams of alkali metal alanates and borohydrides are of large current interest, and we have recently studied phase transformations under pressure in several of these materials. We here report Raman studies of KBH4 under pressure at room temperature, showing a phase transition near 6 GPa. Although no structural information is yet available, the similarity between KBH4 and NaBH4 suggests the new structure is orthorhombic. We also report studies on LiBH4 showing that the high pressure phase of this material is metastable to zero pressure below 200 K.

  • 271.
    Sundqvist, Bertil
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Tolpygo, V. K.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Electrical resistance of dysprosium under pressure2014In: / [ed] Buttler, W; Furlanetto, M; Evans, W, Institute of Physics Publishing (IOPP), 2014, Vol. 500, p. 182040-Conference paper (Refereed)
    Abstract [en]

    The electrical resistance of dysprosium metal has been measured as a function of hydrostatic pressure up to 1.2 GPa at temperatures from 300 K to 700 K, and at atmospheric pressure from 80 to 700 K. Our data at atmospheric pressure and at room temperature agree well with literature data. The total pressure coefficient of resistance at 300 K is found to be dlnR/dp = -2.98 x 10(-2) GPa(-1) and to decrease slightly with increasing temperature. The results are discussed in terms of simple free-electron type models.

  • 272.
    Sundqvist, Bertil
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Tolpygo, Vladimir Kirillovich
    Umeå University, Faculty of Science and Technology, Department of Physics. Honeywell Aerospace, Phoenix, AZ, 85034, USA.
    Saturation and pressure effects on the resistivity of titanium and two Ti-Al alloys2018In: Journal of Physics and Chemistry of Solids, ISSN 0022-3697, E-ISSN 1879-2553, Vol. 122, p. 41-50Article in journal (Refereed)
    Abstract [en]

    The electrical resistivities of a phase titanium and two Ti-Al alloys have been measured as functions of temperature, T, between 4 and 700 K and, in the range 175 to 700 K, as a function of pressure up to 1.2 GPa. All materials showed resistivity saturation effects at the highest temperatures. A “parallel resistivity” saturation model could be fitted to all data with excellent results if Mott-Fermi smearing, expected for a transition metal, was included by adding a term in T3 to the phonon-induced resistivity. However, in the standard saturation model the fitted resistivity parameters were not always realistic. A modified saturation model which partially retained Matthiessen’s rule could be fitted equally well and gave numerically acceptable results for both residual, electron-phonon and saturation resistivities. This new model also fitted the T dependence of the pressure coefficients with a single set of coefficients, each valid for all three materials. Although simple free-electron and Debye models could apparently explain the observed pressure dependence of the impurity and electron-phonon resistivities, a model taking band structure changes with pressure into account showed that the electron-phonon interaction factor of titanium is practically independent of pressure while the plasma frequency has a strong pressure dependence. This model gave reasonable numerical results for the pressure dependence of both the residual, electron-phonon and saturation resistivities and also agreed with experimental data for the superconducting critical temperature Tc under pressure for a titanium.

  • 273.
    Sundqvist, Bertil
    et al.
    Umeå University, Faculty of Science and Technology, Physics.
    Wågberg, Thomas
    Umeå University, Faculty of Science and Technology, Physics.
    Persson, Per-Axel
    Umeå University, Faculty of Science and Technology, Physics.
    Jacobsson, Per
    Stafström, Sven
    Moret, Roger
    Launois, Pascale
    Structure and stability of pressure polymerized C602000In: Molecular Materials: Molecular Crystals and Liquid Crystals Section C, vol. 13: Proceedings of the 4th International Workshop on Fullerenes and Atomic Clusters (IWFAC'99), St. Petersburg 1999, Overseas Publishers Association N.V. , 2000, p. 117-122Conference paper (Refereed)
    Abstract [en]

    We discuss the bond energy of the orthorhombic C60 polymer and the structure of the two-dimensional C60 polymers. For the orthorhombic polymer, measurements of the dissociation energy by different methods give results that differ by a factor of two. We show that optical excitations lead to a temporary weakening of the intermolecular bonds and optical measurements thus show a low apparent bond energy. We have also polymerized a single crystal of C60 into two-dimensional phases. X-ray diffraction studies of this crystal have enabled us to determine the stacking sequences of both the tetragonal and the rhombohedral structures.

  • 274.
    Sundqvist, Bertil
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Wågberg, Thomas
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Yao, Mingguang
    Umeå University, Faculty of Science and Technology, Department of Physics.
    High pressure studies of alkali metal doped fullerides A4C602011In: Diamond and Related Materials, Volume 20, issue 4: Proceedings of New Diamond and Nanocarbon 2010 (NDNC2010), Elsevier , 2011, p. 600-603Conference paper (Refereed)
    Abstract [en]

    The electrical resistance R of K4C60 and Li4C60 has been measured between 100 and 300 K under pressures up to 1 and 2 GPa, respectively. For both materials, the temperature coefficient of R is negative at all pressures and temperatures in this range. The transport properties of Li4C60 at low pressure are compatible with a recent observation of high ionic conductivity, but surprisingly, this conductivity term increases strongly with increasing pressure, contradicting an intuitive model. For K4C60 we see no sign of a recently suggested structural phase transformation at low temperature, nor can we find any convincing evidence for a lattice disproportionation as recently observed for Rb4C60.

  • 275.
    Sundqvist, Bertil
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Yao, Mingguang
    Andersson, Ove
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Ionic conductivity in three crystalline phases of LiBH4 under pressure2013In: High Pressure Research, ISSN 0895-7959, E-ISSN 1477-2299, Vol. 33, no 1, p. 141-151Article in journal (Refereed)
    Abstract [en]

    The AC electrical conductivity of LiBH4 was investigated below 2GPa between 1Hz and 1.6MHz. The high-temperature phase has an ionic conductivity of up to 0.01Scm(1), while the low-temperature phases have conductivities two orders of magnitude lower. All phases show an Arrhenius behaviour with activation energies E-a between 0.5 and 0.7eV, in good agreement with earlier data except for phase III, which is found to have the highest activation energy of the phases studied. The high-temperature phase has a minimum in E-a near 1GPa, close to the triple point, correlated with a sudden change in activation volume. These features may indicate an isostructural phase transition. The conductivities of the ambient temperature phases increase temporarily by an order of magnitude after transitions between these phases, probably due to new diffusion channels via structural defects. The phase diagram agrees well with earlier results.

  • 276.
    Sundqvist, Bertil
    et al.
    Umeå University, Faculty of Science and Technology, Physics.
    Yao, Mingguang
    Umeå University, Faculty of Science and Technology, Physics.
    Wågberg, Thomas
    Umeå University, Faculty of Science and Technology, Physics.
    Electrical transport properties of A4C60 (A=Li,Na,Rb) under pressure2008In: High Pressure Research vol. 28 issue 4 December 2008: Proceedings of the 46th European High pressure Research Group Meeting (EHPRG 46), Valencia (Spain), September 2008, London: Taylor & Francis , 2008, p. 597-600Conference paper (Refereed)
    Abstract [en]

    In search of structural phase transformations, the electrical resistances of the alkali metal-intercalated fullerene compounds Li4C60, Na4C60, and Rb4C60 have been measured as functions of temperature and pressure. The compounds have different lattice structures, and in the first two, the fullerene molecules form two-dimensional covalently bonded polymer lattices. No phase changes could be identified over the ranges 100-400 K and 0-2 GPa. All materials are semiconducting under the conditions studied, and we see no strong dependence of the band gaps on pressure.

  • 277.
    Talyzin, Alexander V.
    et al.
    Umeå University, Faculty of Science and Technology, Physics.
    Tsybin, Yu. O.
    Schaub, T.M.
    Mauron, P.
    Shulga, Yu.M.
    Züttel, Andreas
    Sundqvist, Bertil
    Umeå University, Faculty of Science and Technology, Physics.
    Marshall, A.G.
    Composition of hydrofullerene mixtures produced by C60 reaction with hydrogen gas revealed by high-resolution mass spectrometry.2005In: Journal of Physical Chemistry B, ISSN 1520-6106, Vol. 109, no 26, p. 12742-12747Article in journal (Refereed)
    Abstract [en]

    Complex solid hydrofulleride mixtures were synthesized by prolonged hydrogenation of C60 at 120 bar hydrogen pressure, 673 K temperature, and different reaction periods. The high degree of hydrogenation was confirmed by infrared spectroscopy and X-ray diffraction. The identity of hydrogenation products was determined by high-resolution field desorption/ionization Fourier transform ion cyclotron resonance mass spectrometry. Despite partial gas-phase fragmentation of hydrofullerene ions during mass analysis, the data suggest that the synthesized mixtures consist of mostly C58-60Hx hydrofullerenes. Increasing the duration of hydrogenation results in synthesis of C59Hx and C58Hx as major products. Possible hydrofullerene fragmentation pathways during both material synthesis and mass spectrometric analysis are discussed. Gas-phase fragmentation in the mass spectrometer arises from hydrofullerene ions C60Hx+ with x > 40 and C59H44+ with drastically decreased molecular stability relative to the known C60H36.

  • 278.
    Talyzin, Alexandr
    et al.
    Umeå University, Faculty of Science and Technology, Physics.
    Andersson, Ove
    Umeå University, Faculty of Science and Technology, Physics.
    Sundqvist, Bertil
    Umeå University, Faculty of Science and Technology, Physics.
    Kurnosov, Alexander
    Dubrovinsky, Leonid
    High pressure phase transition in LiBH42007In: Journal of Solid State Chemistry, ISSN 0022-4596, Vol. 180, no 2, p. 510-7Article in journal (Refereed)
    Abstract [en]

    The high-pressure phase transition from ambient pressure alpha-LiBH4 to high-pressure beta-LiBH4 was observed by Raman spectroscopy and X-ray diffraction between 0.8 and 1.1 GPa. The phase boundary between these two phases was mapped over a large range of temperatures using thermal conductivity studies and differential thermal analysis. The structure of the high-pressure phase could not be identified due to small number of experimentally observed reflections, but it was shown that it is different from previously reported theoretical predictions.

  • 279.
    Talyzin, Alexandr
    et al.
    Umeå University, Faculty of Science and Technology, Physics.
    Dzwilewski, Andrzej
    Umeå University, Faculty of Science and Technology, Physics.
    Sundqvist, Bertil
    Umeå University, Faculty of Science and Technology, Physics.
    Tsybin, Y.
    Purcell, J.M.
    Marshall, A.G.
    Shulga, Y.
    McCammon, C.
    Dubrovinsky, Leonid
    Hydrogenation of C60 at 2 GPa Pressure and High Temperature.2006In: Chemical Physics, ISSN 0301-0104, Vol. 325, no 2-3, p. 445-451Article in journal (Refereed)
    Abstract [en]

    Hydrogenation of C60 at 2 GPa and 723–823 K was performed with thermal decomposition of LiAlH4 as a hydrogen source. Analysis

    of hydrogenation products showed that the method can produce not only C60H36, but also hydrofullerides C60Hx with 44 < x < 52.

    Unlike other hydrogenation methods in which pristine C60 reacts with hydrogen, the high pressure/high temperature conditions result

    first in C60 polymerization into a tetragonal phase which later reacts with hydrogen. It is suggested that hydrogen first attacks intermolecular

    carbon–carbon bonds, resulting in complete depolymerization of C60 at a later stage of the hydrogenation process. This model

    suggests the possibility to select starting points for hydrogenation by choosing specific polymeric structures of C60. Hydrogenated polymeric

    C60 was identified as an intermediate reaction product. Characterization of highly reduced material was performed by Raman and

    IR spectroscopy, X-ray diffraction, and atmospheric pressure photoionization Fourier transform ion cyclotron resonance mass

    spectrometry.

  • 280.
    Talyzin, Alexandr
    et al.
    Umeå University, Faculty of Science and Technology, Physics.
    Sundqvist, Bertil
    Umeå University, Faculty of Science and Technology, Physics.
    High pressure study of NaAlH4 by Raman spectroscopy up to 17 GPa2006In: High Pressure Research, ISSN 0895-7959, Vol. 26, no 3, p. 165-73Article in journal (Refereed)
    Abstract [en]

    A high-pressure Raman study was carried out on NaA1H(4) up to 17 GPa using the diamond anvil cell method. In the pressure region 2-5 GPa, several of the original modes split. Although this might be a sign of some structural change, the spectral changes do not allow us to claim the existence of a clear phase transition in this pressure range. The spectra revert to their ambient pressure forms on decreasing pressure below < 3.0-1.4 GPa. A phase transition to beta-NaA1H(4) was found at 14-16 GPa. This phase transition is also reversible with an unusually strong hysteresis: the beta-NaA1H(4) can be followed upon decompression down to 3.9 GPa. Analysis of Raman data shows that this phase transition is compatible with a theoretical prediction of a strong volume collapse.

  • 281.
    Talyzin, Alexandr
    et al.
    Umeå University, Faculty of Science and Technology, Physics.
    Sundqvist, Bertil
    Umeå University, Faculty of Science and Technology, Physics.
    Reversible phase transition in LiAlH4 under high pressure conditions.2004In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 70, no 18, p. 180101(R)-Article in journal (Refereed)
    Abstract [en]

    The structural stability of the hydrogen storage compound LiAlH4 was studied by Raman spectroscopy in the pressure interval 0–6 GPa. A slow phase transition from a-LiAlH4 to a b phase was observed to occur between 2.2 and 3.5 GPa. The phase transition is reversible and a reverse transformation to a-LiAlH4 was observed below 1.4 GPa. Analysis of Raman spectra from b-LiAlH4 shows that they cannot be explained by the theoretically predicted a-NaAlH4-type structure with I41 /a symmetry.

  • 282.
    Talyzin, Alexandr
    et al.
    Umeå University, Faculty of Science and Technology, Physics.
    Sundqvist, Bertil
    Umeå University, Faculty of Science and Technology, Physics.
    Araujo, C. Moysés
    Ahuja, Rajeev
    Raman spectroscopy and structural transformations in hydrides under pressure.2005In: Proceedings of the Joint 20th AIRAPT and 43rd EHPRG Conf. on High Pressure Science and Technology, Karlsruhe 2005, 2005, p. T5-P027Conference paper (Other academic)
    Abstract [en]

    We have investigated the structural stability of the hydrides LiAlH4, NaAlH4, and NaBH4 under high pressure at room temperature using Raman spectroscopy. For all compounds studied we observe reversible structural phase transformations under pressure. The Raman results are not always compatible with the structures predicted by earlier theoretical calculations for the high-pressure phases, and further theoretical studies of the stability of NaBH4 under pressure have been carried out.

  • 283.
    Talyzin, Alexandr
    et al.
    Umeå University, Faculty of Science and Technology, Physics.
    Sundqvist, Bertil
    Umeå University, Faculty of Science and Technology, Physics.
    Peera, Ashgar A.
    Imus, P.
    Billups, W. Edward
    Gentle fragmentation of C60 by strong hydrogenation: a route to synthesizing new materials2004In: Chemical Physics Letters, ISSN 0009-2614, E-ISSN 1873-4448, Vol. 400, no 1-3, p. 112-116Article in journal (Refereed)
    Abstract [en]

    A large number of small hydrogenated fullerenes and unusual polycyclic aromatic hydrocarbons were detected by mass-spectrometry in samples obtained by C60 reaction with hydrogen gas at 673 K. A synthesis of a large number of sequential breakdown products instead of fast formation of amorphous carbon was found due to immediate termination of dangling bonds by hydrogen atoms during the C60 fragmentation process. This opens a possibility to synthesize these unusual materials in bulk amounts. Investigation of breakdown products could also help to select building blocks for synthesis of cage structures by purely chemical methods.

  • 284.
    Talyzin, Alexandr
    et al.
    Umeå University, Faculty of Science and Technology, Physics.
    Tsybin, Yu. O.
    Purcell, J.M.
    Schaub, T.M.
    Shulga, Yu.M.
    Noreus, Dag
    Sato, T.
    Dzwilewski, Andrzej
    Umeå University, Faculty of Science and Technology, Physics.
    Sundqvist, Bertil
    Umeå University, Faculty of Science and Technology, Physics.
    Marshall, A.G.
    Reaction of hydrogen gas with C60 at elevated pressure and temperature: Hydrogenation and cage fragmentation.2006In: Journal of Physical Chemistry A, ISSN 1089-5639, Vol. 110, no 27, p. 8528-34Article in journal (Refereed)
    Abstract [en]

    Products of the reaction of C60 with H2 gas have been monitored by high-resolution atmospheric pressure

    photoionization Fourier transform ion cyclotron resonance mass spectrometry (APPI FT-ICR MS), X-ray

    diffraction, and IR spectroscopy as a function of hydrogenation period. Samples were synthesized at 673 K

    and 120 bar hydrogen pressure for hydrogenation periods between 300 and 5000 min, resulting in the formation

    of hydrofullerene mixtures with hydrogen content ranging from 1.6 to 5.3 wt %. Highly reduced C60Hx (x >

    36-40) and products of their fragmentation were identified in these samples by APPI FT-ICR MS. A sharp

    change in structure was observed for samples with at least 5.0 wt % of hydrogen. Low-mass (300-500 Da)

    hydrogenation products not observed by prior field desorption (FD) FT-ICR MS were detected by APPI

    FT-ICR MS and their elemental compositions obtained for the first time. Synthetic and analytical fragmentation

    pathways are discussed.

  • 285.
    Talyzin, Alexandr
    et al.
    Umeå University, Faculty of Science and Technology, Physics.
    Tsybin, Yu.O.
    Peera, A.A.
    Schaub, T.M.
    Marshall, A.G.
    Sundqvist, Bertil
    Umeå University, Faculty of Science and Technology, Physics.
    Mauron, P.
    Züttel, A.
    Billups, W.E.
    Synthesis of C59Hx and C58Hx fullerenes stabilized by hydrogen2005In: Journal of Physical Chemistry B Letters, ISSN 1520-6106, Vol. 109, no 12, p. 5403-5Article in journal (Refereed)
    Abstract [en]

    Prolonged hydrogenation of C60 molecules by reaction with H2 at elevated temperature and pressure results

    in fragmentation and collapse of the fullerene cage structure. However, fragments can be preserved by

    immediate termination of dangling bonds by hydrogen. Here we demonstrate that not only fullerene fragments

    but also hydrogenated fragmented fullerenes (e.g., C58H40 and C59H40) can be synthesized in bulk amount by

    high-temperature hydrogenation of C60. We confirm successful synthesis of these species by matrix-assisted

    laser desorption ionization time-of-flight mass spectrometry and complete speciation of the resultant complex

    fullerene mixtures by high-resolution field desorption/ionization Fourier transform ion cyclotron resonance

    mass spectrometry.

  • 286.
    Talyzin, Alexandr V.
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Sundqvist, Bertil
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Szabó, Tamas
    Dmitriev, Vladimir
    Structural breathing of graphite oxide pressurized in basic and acidic solutions2011In: Journal of Physical Chemistry Letters, ISSN 1948-7185, E-ISSN 1948-7185, Vol. 2, no 4, p. 309-313Article in journal (Refereed)
    Abstract [en]

    Graphite oxide immersed in excess of basic or acidic water media was studied using synchrotron X-ray diffraction at high pressure using diamond anvil cells. The lattice spacing of graphite oxide in excess of NaOH solution increases by the enormous value of 85% at 1.6 GPa. In contrast, structure expansion of graphite oxide immersed in liquid water with added HCl is significantly less pronounced compared with compression in pure water. The point of media solidification correlated with a sharp decrease in graphite oxide layers separation because of partial withdrawal of water from the structure. Therefore, pressure-induced structural breathing of graphite oxide due to insertion/desertion of water into/from interlayer space is strongly enhanced in basic media and suppressed in acidic media. The magnitude of structural breathing also depends on relative amounts of graphite oxide powder and solution. Strongly diluted samples with low relative amount of graphite oxide powder in the suspension exhibited less pronounced high-pressure anomaly.

  • 287.
    Talyzin, Alexandr V.
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Sundqvist, Bertil
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Szabó, Tamás
    Dékány, Imre
    Dmitriev, Vladimir
    Pressure-induced insertion of liquid alcohols into graphite oxide structure2009In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 131, no 51, p. 18445-18449Article in journal (Refereed)
    Abstract [en]

    Graphite oxide (GO) immersed in an excess of methanol and ethanol media is found to undergo a phase transformation at about 0.2−0.8 GPa, with an expansion of the unit cell volume by 40%, due to pressure-induced insertion of solvent into interlayer space. The pressure at which the structural expansion occurs does not correlate with the solidification pressure of the alcohol, in contrast to the graphite oxide/water system. The expanded high-pressure phase of GO/ethanol could be quenched back to ambient pressure. Compression of graphite oxide with a 2:1 water/methanol medium revealed a complex anomaly with two steps attributed to insertion of methanol and water at different pressure points.

  • 288. Ullakko, Kari
    et al.
    Sundqvist, Bertil
    Umeå University, Faculty of Science and Technology, Physics.
    Pietikäinen, Juha
    Isothermal Martensite Transformation of Fe-Ni-C Alloys as a Function of Hydrostatic Pressure1990In: Materials Science Forum volumes 56-58: Martensitic Transformations: Proceedings of the 6th International Conference on Martensitic Transformations (ICOMAT 89), Sydney 1989, Zürich: Trans Tech Publiations , 1990, p. 197-200Conference paper (Refereed)
    Abstract [en]

    Isothermal martensite transformation as a function of hydrostatic pressure was studied in Fe-Ni-C alloys. It was observed that the transformation was much the same as it happens as a function of time. Any noticeable differences in the morphology between isothermal and athermal martensite were not seen.

  • 289. Ulyanov, A. N.
    et al.
    Maksimov, Igor S.
    Umeå University, Faculty of Science and Technology, Physics.
    Nyeanchi, Emmanuel B.
    Umeå University, Faculty of Science and Technology, Physics.
    Medvedev, Yu. V.
    Yu, Seong-Cho
    Starostyuk, N.Yu.
    Sundqvist, Bertil
    Umeå University, Faculty of Science and Technology, Physics.
    Structure and pressure effects on the properties of La0.7Ca0.3-xSrxMnO3 manganites.2002In: Journal of Applied Physics vol. 91: Proceedings of the 46th Annual Conference on Magnetism and Magnetic Materials, Seattle 2001, American Institute of Physics , 2002, p. 7739-7741Conference paper (Refereed)
    Abstract [en]

    We report a study of the structure and pressure effects on magnetic and transport properties of a lanthanum manganite, La0.7Ca0.3–xSrxMnO3 (0<=x<=0.3, Deltax = 0.03). The pressure coefficient of the Curie temperature (Tc), dTc/dP, is shown to depend on x. The temperature Tc increases approximately linearly under applied pressure as dTc/dP[approximate]14 K/GPa in the orthorhombic (Pbnm) phase and as dTc/dP[approximate]7.5 K/GPa in the rhombohedral (R3-bar c). The value of dTc/dP shows a minimum ([approximate]3.5 K/GPa) and the temperature of the resistance maximum, Tp(x), shows a change of slope at x = 0.15, corresponding to a concentration structural phase transition. Differences between the values of dTc/dP and the slopes of Tp vs x in Pbnm and R3-bar c phases are explained by the different effect of external pressure on the Mn–O bond length and the Mn–O–Mn bond angle, and by the different internal pressure effect (depending on the value of x) in those phases, respectively.

  • 290. Ulyanov, A.N.
    et al.
    Maksimov, Igor S.
    Umeå University, Faculty of Science and Technology, Physics.
    Nyeanchi, Emmanuel B.
    Umeå University, Faculty of Science and Technology, Physics.
    Yu, Seong-Cho
    Medvedev, Yu.V.
    Starostyuk, N.Yu.
    Sundqvist, Bertil
    Umeå University, Faculty of Science and Technology, Physics.
    La0.7Ca0.3-xSrxMnO3 manganites: Effect of structure on the magnetic and transport properties.2002In: Journal of the Physical Society of Japan, ISSN 0031-9015, E-ISSN 1347-4073, Vol. 71, no 3, p. 927-929Article in journal (Refereed)
    Abstract [en]

    The effect of lattice structure on the magnetic and transport properties of La0.7Ca0.3-xSrxMnO3 (x= 0; 0.03; 0.06; ...; 0.3) lanthanum manganites have been studied. Curie temperature pressure coefficient, dTc/dP, showed the dependence on x value. Temperature Tc increased almost linearly under applied pressure as dTc/dP≈14 K/GPa and as dTc/dP≈7.5 K/GPa in the orthorhombic (Pbnm) and rhombohedral (R3c) phases, respectively. The value of dTc/dP(≈3.5 K/GPa) showed a minimum and a temperature of the resistance maximum, Tp(x), showed a change of slope at x=0.15, corresponding to the concentration structural phase transition. Differences between the values of dTc/dP and slopes of Tp versus x in Pbnm and R3c phases are explained by the different effect of external pressure on the Mn–O bond length and Mn–O–Mn bond angle, and by the different internal pressure effect in those phases, respectively

  • 291. Ulyanov, A.N.
    et al.
    Maksimov, Igor S.
    Nyeanchi, Emmanuel B.
    Umeå University, Faculty of Science and Technology, Physics.
    Yu, Seong-Cho
    Medvedev, Y.V.
    Starostyuk, N.Y.
    Sundqvist, Bertil
    Umeå University, Faculty of Science and Technology, Physics.
    Crystal symmetry and pressure effects on the properties of mixed-valence manganites2003In: Journal of Magnetism and Magnetic Materials vol. 258-259, Special Issue SI: Proceedings of the 2nd Moscow International Symposium on Magnetism, Amsterdam: Elsevier B.V. , 2003, p. 312-314Conference paper (Refereed)
    Abstract [en]

    A lattice structure effect on the magnetic and magnetotransport properties of La0.7Ca(0.3-x)SrxMnO3 lanthanum manganites have been studied. The Curie temperature pressure coefficient increased almost linearly under an applied pressure as dTc/dP=14K/GPa and as dTc/dP=7.5K/GPa in the orthorhombic and rhombohedral structures,respectively. This is caused by the different pressure effect on the Mn–O bond distances and on the Mn–O–Mn bond angles in those phases. The anomalous low value of dTc/dP(=3.5K/GPa) for La0.7Ca0.15Sr0.15MnO3 composition and a jump of the magnetoresistance maximum value at the concentrational Pbnm2R%3c phase transition were observed and discussed.

  • 292. Wang, Lin
    et al.
    Liu, Bingbing
    Liu, Dedi
    Hou, Yuanyuan
    Yao, Mingguang
    Zou, Guangtian
    Li, H.
    Luo, Z.J.
    Li, Y.C.
    Liu, J.
    Sundqvist, Bertil
    Umeå University, Faculty of Science and Technology, Department of Physics.
    High-pressure studies of Nano/sub-micrometer C70 rods2005In: High Energy Physics and Nuclear Physics B, ISSN 0254-3052, Vol. 29, no Supplement, p. 112-115Article in journal (Refereed)
    Abstract [en]

    We have successfully synthesized C-70 rods in nano/sub-micrometers scale by evaporating solvent method. The diameter of the as grown C-70 rods is similar to 500 nm, and the length is similar to 10 mu m. The EDXD pattern and Raman spectroscopy for as -grown sample indicate that the as grown C-70 rod is in hcp structure. The pressure-induced structural phase transition has been studied by using DAC combined with EDXD and Raman spectroscopy methods under quasi-hydrostatic pressure up to 26.1GPa. It is found that hcp structure transforms into amorphous phase for C-70 rods in the pressure range from 23.3 to 26.1GPa, which is higher than the transformation pressure for bulk C-70 crystals. The phase transition is irreversible and it is induced by the collapse of C-70 cage.

  • 293. Wang, Lin
    et al.
    Liu, Bingbing
    Liu, Dedi
    Yao, Mingguang
    Hou, Yuanyuan
    Yu, Shidan
    Cui, Tian
    Zou, Guangtian
    Iwasiewicz, Agnieszka
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Sundqvist, Bertil
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Synthesis of thin, rectangular C60 nanorods using m-xylene as shape controller2006In: Advanced Materials, ISSN 0935-9648, E-ISSN 1521-4095, Vol. 18, no 14, p. 1883-1888Article in journal (Refereed)
    Abstract [en]

    Thin, rectangular C60 nanorods in face-centered cubic structure are synthesized by using m-xylene as a shape controller. These unusual nanorods can easily grow on various substrates. The smallest nanorods have widths smaller than 30 nm. The nanorods are highly crystalline in single phase. A significant expansion of the lattice constant is also found in the C60 nanorods when their widths decrease below about 80 nm.

     

  • 294. Wang, Lin
    et al.