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Sökning: swepub > (1990-1994) > Sundqvist Bertil > Engelska > Andersson Britt M.

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1.
  • Andersson, Britt M., et al. (författare)
  • Thermal conductivity of polycrystalline YBa2Cu4O8
  • 1994
  • Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121. ; 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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2.
  • Andersson, Britt M., et al. (författare)
  • Defects and the thermal conductivity of YBa2Cu3O7-d and YBa2Cu4O8
  • 1993
  • Ingår 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.. - 0 444 81529 5 ; s. 655-658
  • Konferensbidrag (refereegranskat)abstract
    • 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.
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3.
  • Andersson, Britt M., et al. (författare)
  • Electrical resistivity and critical temperature of Bi-based high-Tc superconductors to 1 GPa
  • 1990
  • Ingår 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. - 2-88124-746-6 ; s. 120-122
  • Konferensbidrag (refereegranskat)abstract
    • 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.
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4.
  • 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 : LT-19 Part II: Contributed Papers, Proceedings of the 19th International Conference on Low Temperature Physics, Brighton 1990. - 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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5.
  • 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 : High Pressure Science and Technology: Proceedings of the 12. AIRAPT and 27. EHPRG Conference, University Paderborn 1989. - London : Gordon and Breach. - 2-88124-746-6 ; s. 123-126
  • 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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6.
  • 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 : Proceedings of the 13th European Conference on Thermophysical Properties (13 ECTP), Lisboa 1993. - 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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7.
  • 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. ; 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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8.
  • Andersson, Britt M., et al. (författare)
  • Thermal conductivity of YBa2Cu4O8 under high pressure
  • 1993
  • Ingår i: Physica. C, Superconductivity. - Elsevier B.V.. - 0921-4534. ; 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<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.
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9.
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10.
  • Sundqvist, Bertil, et al. (författare)
  • Resistivity of high-Tc superconductors: Linear in T at constant p, non-linear at constant V
  • 1990
  • Ingår i: Solid State Communications. - Elsevier Science Ltd. - 0038-1098. ; 76:8, s. 1019-1022
  • Tidskriftsartikel (refereegranskat)abstract
    • The observed constant-pressure resistivity varrhop of most high-Tc superconductors is linear in temperature T over large ranges. We show that this is not true for the constant-volume resistivity varrhov; for 1–2–3 YBCO the correction from varrhop to varrhov is -32% at 500 K relative to the low-T value. Since theory predicts varrhov rather than varrhop, the observed linearity of varrho probably cannot be used as a tool to choose between theories for high-Tc superconductivity.
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