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  • 1.
    Andersson, Göran
    et al.
    Umeå University, Faculty of Science and Technology, Physics.
    Sundqvist, Bertil
    Umeå University, Faculty of Science and Technology, Physics.
    Bäckström, Gunnar
    Umeå University, Faculty of Science and Technology, Physics.
    A high-pressure cell for electrical resistance measurements at hydrostatic pressures up to 8 GPa: Results for Bi, Ba, Ni, and Si1989In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 65, no 10, p. 3943-3950Article in journal (Refereed)
    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.

  • 2.
    Andersson, Göran
    et al.
    Umeå University, Faculty of Science and Technology, Physics.
    Sundqvist, Bertil
    Umeå University, Faculty of Science and Technology, Physics.
    Bäckström, Gunnar
    Umeå University, Faculty of Science and Technology, Physics.
    Electrical resistivity measurements under hydrostatic conditions up to 10 GPa1984In: 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, p. 379-382Conference paper (Refereed)
    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.

  • 3.
    Andersson, Ove
    et al.
    Umeå University, Faculty of Science and Technology, Physics.
    Sundqvist, Bertil
    Umeå University, Faculty of Science and Technology, Physics.
    Bäckström, Gunnar
    Umeå University, Faculty of Science and Technology, Physics.
    A low-temperature high-pressure apparatus with a temperature control system1992In: High Pressure Research, ISSN 0895-7959, E-ISSN 1477-2299, Vol. 10, no 4, p. 599-606Article in journal (Refereed)
    Abstract [en]

    A low-temperature high-pressure apparatus was designed using commercial cryogenic equipment. Pressures up to 1 GPa and temperatures down to 40 K can be obtained in a volume of up to 30 cm3. The apparatus is of the piston-cylinder type with a piston diameter of 45 mm, and the pressure can be varied at all temperatures, An adaptive temperature control system keeps the temperature inside the pressure cylinder constant to within ±0.1 K.

  • 4.
    Ross, Russel George
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Andersson, Per
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Sundqvist, Bertil
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Bäckström, Gunnar
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Thermal conductivity of solids and liquids under pressure1984In: Reports on progress in physics (Print), ISSN 0034-4885, E-ISSN 1361-6633, Vol. 47, no 10, p. 1347-1402Article, review/survey (Other academic)
    Abstract [en]

    Thermal conductivity of solids and liquids under pressure is covered in this review. Experimental techniques are critically considered and compared, and an introduction to theory is provided. Results are presented and discussed for ionic crystals, normal molecular crystals, plastic crystal phases, clathrate hydrates, polymers and glass-formers, liquids, covalent and semiconducting crystals, rocks and metals. Special attention is given to isochoric conditions, change of crystal structure and molecular orientational disorder. Available reliable measurements at pressures up to a few GPa indicate the need for theoretical development, especially in connection with molecular crystals and ferromagnetic metals.

  • 5.
    Sundqvist, Bertil
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Bäckström, Gunnar
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Low noise and drift by parallel amplifiers1975In: Review of Scientific Instruments, ISSN 0034-6748, E-ISSN 1089-7623, Vol. 46, no 7, p. 928-929Article in journal (Refereed)
    Abstract [en]

    A low noise and low drift amplifier has been constructed using several monolithic operational amplifiers in parallel. It is shown that each amplifier may be connected by only three resistors. An input noise of 0.15 µV (p–p) in the band 0.1–10 Hz was obtained with six amplifiers, and the noise is expected to decrease as N−1/2 as the number of units is increased.

  • 6.
    Sundqvist, Bertil
    et al.
    Umeå University, Faculty of Science and Technology, Physics.
    Bäckström, Gunnar
    Umeå University, Faculty of Science and Technology, Physics.
    Pressure dependence of the thermal conductivity of aluminium1977In: Solid State Communications, ISSN 0038-1098, E-ISSN 1879-2766, Vol. 23, no 10, p. 773-775Article in journal (Refereed)
    Abstract [en]

    The thermal diffusivity, a, of aluminium has been measured at pressures up to 2.5 GPa at room temperature, and from these results the pressure dependence of the thermal conductivity, λ, has been calculated. Both quantities increase with pressure. The increase in a amounts to 4.6% to 1 GPa and 10.4% to 2.5 GPa. The initial pressure coefficient of the electronic thermal conductivity λe is found to be [λe]-1λe/P = 3.7 × 10-2GPa-1, which agrees very well with a recent theoretical calculation.

  • 7.
    Sundqvist, Bertil
    et al.
    Umeå University, Faculty of Science and Technology, Physics.
    Bäckström, Gunnar
    Umeå University, Faculty of Science and Technology, Physics.
    Thermal conduction of metals under pressure1976In: Review of Scientific Instruments, ISSN 0034-6748, E-ISSN 1089-7623, Vol. 47, no 2, p. 177-182Article in journal (Refereed)
    Abstract [en]

    It is shown that the original Ångström method of determining the thermal diffusivity of metals is not valid in the case of a specimen surrounded by a solid medium, and an appropriate modification is described. Several simplifications of this method are also presented and criteria for their validity given. An electronic system has been developed for automatic sampling and analysis of the temperature data. The new method has been applied to Cu under pressure, and the results show that the thermal conductivity rises by 6.4% up to 2.5 GPa (25 kilobar).

  • 8.
    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 copper under high pressure1977In: High Temperatures-High Pressures, ISSN 0018-1544, E-ISSN 1472-3441, Vol. 9, no 1, p. 41-48Article in journal (Refereed)
    Abstract [en]

    The thermal diffusivity, a, of copper has been measured at room temperature up to a pressure of 2.5 GPa (25 kbar) by means of a method recently developed. In this pressure range the diffusivity increases linearly with a slope of (1/a)da/dp = 2.7x10-2 GPa-1. As the density and specific heat of copper are known as functions of pressure, this result can be used to obtain the pressure dependence of the thermal conductivity, lambda, with the result (1/lambda)d(lambda)/dp = 3.1x10-2 GPa-1. This value is shown to agree well with theoretical calculations of this slope. However, a comparison between this result and the pressure dependence of the electrical conductivity shows deviations from the Wiedemann-Franz law.

  • 9.
    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.

  • 10.
    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.

  • 11.
    Zhu, Xiaomei
    et al.
    Umeå University, Faculty of Science and Technology, Physics.
    Brändström, Erik
    Umeå University, Faculty of Science and Technology, Physics.
    Sundqvist, Bertil
    Umeå University, Faculty of Science and Technology, Physics.
    Bäckström, Gunnar
    Umeå University, Faculty of Science and Technology, Physics.
    Measurement of the total transverse force on moving vortices in YBCO films1996In: Proceedings of 10th Anniversary HTS Workshop on Physics, Materials, and Applications, Houston 1996, Singapore: World Scientific , 1996, p. 417-418Conference paper (Refereed)
    Abstract [en]

    We have designed a mechanical experiment to measure the total transverse force on moving vortices in type II superconductors. The vortices are driven into motion by the vibration of a permanent magnet above a relatively large superconductor. The transverse force is measured by monitoring the motion of the superconducting film mounted on a quartz plate.

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