| 1. |
- Celzard, Alain, et al.
(författare)
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Conduction mechanisms in some graphite-polymer composites: effects of temperature and pressure
- 1998
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Ingår i: Journal of Applied Physics. - : American Institute of Physics. - 0021-8979 .- 1089-7550. ; 83:3, s. 1410-1419
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Tidskriftsartikel (refereegranskat)abstract
- This article is devoted to the conduction mechanisms involved in some highly electrically anisotropic resin–graphite particle composites. These materials are known to show a percolation phenomenon as the filler content is varied; they are epoxy or polyurethane based, the conducting particles are oriented single-crystal platelets, and samples are in the form of thick films. Because of their strong anisotropy, two types of measurements were made, i.e., parallel to and perpendicular to the plane of the films. Study of the resistivity variations of samples containing various concentrations in conducting particles was carried out first as a function of temperature from 4.2 to 300 K at ambient pressure, and second as a function of hydrostatic pressure up to 1.2 GPa, at room temperature. As the temperature is varied, the changes in resistivity of all the samples studied (i.e., above percolation threshold) are weak; analysis leads to the conclusion that thermally activated tunneling plays a dominant role above but close to the percolation threshold phic. As a function of pressure, more samples were studied: when the filler content is above phic, resistivity changes are quantitatively in agreement with what is expected from both percolation theory and tunneling; below threshold, the observed behavior is partially attributable to an ionic conduction mechanism throughout the polymer.
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| 2. |
- Edman, Ludvig, et al.
(författare)
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Electrical resistivity of single crystal graphite under pressure: an anisotropic 3-D semimetal
- 1998
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - : American Physical Society. - 1098-0121 .- 1550-235X. ; 57:11, s. 6227-6230
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Tidskriftsartikel (refereegranskat)abstract
- The in-plane (ρa) and c-axis (ρc) resistivities of natural single-crystal graphite have been measured from 4 to 450 K at zero pressure and from 77 to 450 K under pressures up to 500 MPa. Data for ρc differ strongly from earlier results obtained on synthetic graphite in showing a strong T dependence of the pressure coefficient, while data for ρa agree well with those from previous studies. Our results can be analyzed quantitatively in a simple free-electron model, and we conclude that in contrast to quasi-two-dimensional synthetic graphite, natural single-crystal graphite is an anisotropic three-dimensional semimetal.
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| 3. |
- Sundqvist, Bertil
(författare)
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Comment on "Pressure and temperature diagram of polymerized fullerite"
- 1998
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - : American Physical Society. - 1098-0121 .- 1550-235X. ; 57:5, s. 3164-3165
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Tidskriftsartikel (refereegranskat)abstract
- Fullerenes such as C60 can be polymerized by treatment under high-pressure, high-temperature conditions. I point out that there is a strong correlation between the rotational state of the C60 molecules in the initial (pristine) material and the structure of the resulting polymer.
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| 4. |
- Sundqvist, Bertil
(författare)
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Improving thermal insulation in high pressure experiments
- 1998
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Ingår i: Review of Scientific Instruments. - : American Institute of Physics. - 0034-6748 .- 1089-7623. ; 69:9, s. 3433-3434
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Tidskriftsartikel (refereegranskat)abstract
- The use of internal ovens is common in high-temperature–high-pressure experiments. Improving the thermal insulation means better efficiency and lower thermal strain on pressure vessels and feedthroughs, but is difficult when using solid media. The addition of a layer of amorphous solid (glass) in the form of a mixed powder is reported to give a significant reduction (20%–50%) in the power dissipated in a high pressure oven.
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