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Sökning: WFRF:(Sundqvist Bertil)

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11.
  • Andersson, Britt M., et al. (författare)
  • Electrical transport in dense, bulk YBa2Cu4O8 produced by hot isostatic pressing
  • 1990
  • Ingår i: Physica B Volumes 165 & 166, Part 2. - : Elsevier B.V.. ; , s. 1699-1700
  • Konferensbidrag (refereegranskat)abstract
    • 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.
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12.
  • Andersson, Britt M., et al. (författare)
  • Electrical transport properties of dense bulk YBa2Cu4O8 produced by hot isostatic pressing
  • 1990
  • Ingår i: Physica. C, Superconductivity. - 0921-4534 .- 1873-2143. ; 170:5-6, s. 521-531
  • Tidskriftsartikel (refereegranskat)abstract
    • 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.
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13.
  • Andersson, Britt M., et al. (författare)
  • High-pressure properties of high-Tc superconductor samples produced by hot isostatic pressing
  • 1990
  • Ingår i: High Pressure Research, volumes 3 to 5. - London : Gordon and Breach. - 2881247466 ; 3:1-6, s. 123-125
  • Konferensbidrag (refereegranskat)abstract
    • 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.
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14.
  • Andersson, Britt M., et al. (författare)
  • Thermal conductivity and thermal diffusivity of dense, bulk YBa2Cu4O8
  • 1994
  • Ingår i: High Temperatures - High Pressures volume 26, issue 1. - London : Pion Press. ; , s. 53-57
  • Konferensbidrag (refereegranskat)abstract
    • 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.
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15.
  • Andersson, Britt M., et al. (författare)
  • Thermal conductivity of polycrystalline YBa2Cu4O8
  • 1994
  • Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 49:6, s. 4189-4198
  • Tidskriftsartikel (refereegranskat)abstract
    • 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.
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16.
  • Andersson, Britt M., et al. (författare)
  • Thermal conductivity of YBa2Cu4O8 dominated by phonon-phonon interactions
  • 1993
  • Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 48:5, s. 3575-3578
  • Tidskriftsartikel (refereegranskat)abstract
    • 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.
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17.
  • Andersson, Britt M., et al. (författare)
  • Thermal conductivity of YBa2Cu4O8 under high pressure
  • 1993
  • Ingår i: Physica. C, Superconductivity. - : Elsevier B.V.. - 0921-4534 .- 1873-2143. ; 216:1-2, s. 187-194
  • Tidskriftsartikel (refereegranskat)abstract
    • 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
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18.
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19.
  • Andersson, Göran, et al. (författare)
  • A high-pressure cell for electrical resistance measurements at hydrostatic pressures up to 8 GPa : Results for Bi, Ba, Ni, and Si
  • 1989
  • Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 65:10, s. 3943-3950
  • Tidskriftsartikel (refereegranskat)abstract
    • 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.
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20.
  • Andersson, Göran, et al. (författare)
  • Electrical resistivity measurements under hydrostatic conditions up to 10 GPa
  • 1984
  • Ingår i: Journal de Physique Colloques vol. 45. - : EDP Sciences. - 0449-1947. ; , s. 379-382
  • Konferensbidrag (refereegranskat)abstract
    • 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.
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