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- Andersson, Ove, et al.
(författare)
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Phase behavior and thermal conductivity of urea at pressures up to 1 GPa and at temperatures in the range 50–370 K
- 1994
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Ingår i: International journal of thermophysics. - : Plenum Publishing. - 0195-928X .- 1572-9567. ; 15:3, s. 513-524
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Tidskriftsartikel (refereegranskat)abstract
- The thermal conductivity of the solid phases I and III of urea was measured at temperatures in the range 50-370 K for pressures up to 1 GPa. Phase III, previously detected only at pressures above 0.5 GPa, was observed here at low pressures (< 0.07 GPa) below about 230 K. Extrapolation of the I-III phase line indicates that phase III might be obtained at 218 K at atmospheric pressure and, consequently, that urea might exhibit two solid phases at atmospheric pressure. The temperature dependence of the thermal conductivity of both phase I and phase III could be described by the Debye model for thermal conductivity assuming phonon scattering by three phonon umklapp processes only. Despite a volume decrease at the I --> III transition, the thermal conductivity decreased by about 20%. Normally, thermal conductivity increases at a phase transition at which volume decreases. This rather unusual behavior of urea might be due to an increase in the nearest-neighbor distance at the I --> III transition.
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| 2. |
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| 3. |
- 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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