| 1. |
- Andersson, Britt M., et al.
(författare)
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Thermal conductivity of polycrystalline YBa2Cu4O8
- 1994
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 49:6, s. 4189-4198
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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)
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Thermal conductivity and thermal diffusivity of dense, bulk YBa2Cu4O8
- 1994
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Ingår i: High Temperatures - High Pressures volume 26, issue 1. - London : Pion Press. ; , s. 53-57
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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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| 3. |
- Lundin, Anders, et al.
(författare)
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A piston-and-cylinder device for compressibility studies on polymers and other "soft" materials
- 1994
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Ingår i: High Pressure Research volume 13, issue 1-3. - Yverdon : Gordon and Breach. ; , s. 141-145
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Konferensbidrag (refereegranskat)abstract
- We describe an all-steel piston-and-cylinder device for pVT studies on “soft” materials, including liquids, in the range 100-450 K and 0-1.5 GPa. The internal diameter is 15 mm with sample lengths between 10 and 50 mm. Piston displacements are measured to within 0.1 μm using differential transformer transducers. Pressure is calculated from force per unit area and the deformation of pistons and cylinder under pressure are taken into account. The inaccuracy in ΔV/V is less than 0.5%. Experimental data are shown for indium and urea.
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| 4. |
- Lundin, Anders, et al.
(författare)
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Compressibility of C60 between 150 and 335 K and up to 1 GPa
- 1994
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Ingår i: Europhysics letters. - : IOP Publishing. - 0295-5075 .- 1286-4854. ; 27:6, s. 463-466
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Tidskriftsartikel (refereegranskat)abstract
- The bulk modulus B of C60 has been measured in the range 150-335 K and up to 1 GPa, for the first time in the f.c.c. rotationally disordered phase, through the f.c.c. → s.c. transition, and in the s.c. phase. At 298 K we find B values of 8.8 (s.c.) and 6.8 GPa (f.c.c.), significantly lower than those found in previous studies. At the transition B decreases with decreasing V, which is probably an effect of orientational ordering on intermolecular interactions.
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| 5. |
- McRae, Edward, et al.
(författare)
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On the relevance of certain transport-structure correlations in SbCl5-intercalated graphite to our overall understanding of GIC c axis conductivity
- 1994
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Ingår i: Molecular Crystals and Liquid Crystals Section A, volumes 244-245. - Yverdon : Gordon and Breach. ; , s. 61--66
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Konferensbidrag (refereegranskat)abstract
- This paper presents some new data on the SbCl5-intercalated graphite family as concerns the relationships between c axis resistivity, ρc(T,p), and intercalate layer structure. Results on the influence of intercalate layer crystallization and the nature of the host graphite are discussed and compared with those on other GIC families. Certain data are examined in the light of available theories and such an analysis raises a number of questions.
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| 6. |
- Sundqvist, Bertil, et al.
(författare)
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Constant-pressure versus constant-volume resistivities of some high transition temperature superconductors
- 1994
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Ingår i: Physica C, volume 235-240. - : Elsevier Science B.V.. ; , s. 1407-1408
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Konferensbidrag (refereegranskat)abstract
- 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, …).
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| 7. |
- Sundqvist, Bertil, et al.
(författare)
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Structure, disorder, and phase diagram of C60 up to 1 GPa and below 300 K
- 1994
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Ingår i: High Pressure in Material Science and Geoscience. - Praha, Czech Republic : Prometheus. - 8085849933 ; , s. 109-112
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Konferensbidrag (refereegranskat)abstract
- We have measured the compressibility and the thermal conductivity of C60 in the range below 300 K and up to 1 GPa (10 kbar). From the data obtained we have deduced the p-T phase diagram of C60. Literature data show that the ratio of pentagon-to-hexagon oriented molecules in the orientationally ordered phase decreases with increasing pressure, and from our data we conclude that C60 forms a new, completely "hexagon oriented" phase above 0.6 GPa at 150 K, or 1.2 GPa at 300 K. The glass transition temperature (90 K at atmospheric pressure) is found to increase by 54 K/GPa.
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| 8. |
- Sundqvist, Bertil, et al.
(författare)
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Thermal conductivity of bulk YBa2Cu4O8 and the phonon transport model
- 1994
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Ingår i: Physica C, volume 235-240. - : Elsevier Science B.V.. ; , s. 1377-1378
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Konferensbidrag (refereegranskat)abstract
- We have measured the thermal conductivity varkappa of bulk YBa2Cu4O8 (1-2-4) between 30 and 310 K and at pressures p up to 1 GPa. At p = 0, varkappa = 10 Wm−1K−1 near 100 K, twice that of sintered YBa2Cu3O−δ (1-2-3). varkappa also decreases with increasing T more rapidly than in 1-2-3, to 7.4 Wm−1K−1 at 300 K. Under pressure, varkappa increases slowly with p above 150 K, but dvarkappa/dp decreases at lower T. Our results are in excellent agreement with a semi-classical model for phonon thermal conductivity, provided we assume significant charge transfer with pressure. The calculated phonon mean free path is much larger than the lattice spacing at all T.
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