| 51. |
- Andersson, Ove
(författare)
-
Glass-liquid transition of water at high pressure
- 2011
-
Ingår i: Proceedings of the National Academy of Sciences of the United States of America. - : National Academy of Sciences. - 0027-8424 .- 1091-6490. ; 108:27, s. 11013-11016
-
Tidskriftsartikel (refereegranskat)abstract
- The knowledge of the existence of liquid water under extreme conditions and its concomitant properties are important in many fields of science. Glassy water has previously been prepared by hyperquenching micron-sized droplets of liquid water and vapor deposition on a cold substrate (ASW), and its transformation to an ultraviscous liquid form has been reported on heating. A densified amorphous solid form of water, high-density amorphous ice (HDA), has also been made by collapsing the structure of ice at pressures above 1 GPa and temperatures below approximately 140 K, but a corresponding liquid phase has not been detected. Here we report results of heat capacity C(p) and thermal conductivity, in situ, measurements, which are consistent with a reversible transition from annealed HDA to ultraviscous high-density liquid water at 1 GPa and 140 K. On heating of HDA, the Cp increases abruptly by (3.4 ± 0.2) J mol-1 K-1 before crystallization starts at (153 ± 1) K. This is larger than the Cp rise at the glass to liquid transition of annealed ASW at 1 atm, which suggests the existence of liquid water under these extreme conditions.
|
|
| 52. |
- Andersson, Ove, et al.
(författare)
-
Glass Transitions in Pressure-Collapsed Ice Clathrates and Implications for Cold Water
- 2012
-
Ingår i: The Journal of Physical Chemistry Letters. - Washington : American Chemical Society (ACS). - 1948-7185. ; 3:15, s. 1951-1955
-
Tidskriftsartikel (refereegranskat)abstract
- Ice is known to collapse to amorphous ice upon pressurization at low temperatures and shows the unusual feature of multiple distinct solid amorphous water states, which have inspired models of liquid water’s structure and unusual properties.Here, we use heat capacity Cp measurements to show that similarly collapsed ice clathrates display identical glass behavior as amorphous ice but that crystallization above the glass transition temperature Tg of ∼140 K at 1 GPa is inhibited. This effect of the homogeneously distributed “guest molecules” in water reveals a relatively strong reversible Cp increase above Tg but no further transition before crystallization at ∼190 K.This is consistent with a glass−liquid transition of water at Tg, which suggests a new path to study an ultraviscous liquid water network and evaluate water models
|
|
| 53. |
|
|
| 54. |
- Andersson, Ove, et al.
(författare)
-
Nature of the pressure-induced collapse of an ice clathrate by dielectric spectroscopy
- 2008
-
Ingår i: Journal of Chemical Physics. - : American Institute of Physics (AIP). - 0021-9606 .- 1089-7690. ; 129:23
-
Tidskriftsartikel (refereegranskat)abstract
- Collapse of an ice clathrate of type II structure containing tetrahydrofuran as guest molecules has been studied at different pressures by dielectric spectroscopy. The sample was pressurized to 1.3 GPa at 130 K and the resulting collapsed state was pressure cycled. The dielectric relaxation time increases at a progressively rapid rate during pressurizing and then decreases slowly on depressurizing, but the dielectric relaxation time does not reach the value of the original state. With increase in pressure, the limiting high frequency permittivity due to orientation of H2O molecules first increases by about 5% until 0.75 GPa and then decreases slightly until 1 GPa, and finally it increases until ~1.2 GPa. The decrease is attributed to the loss of contribution from the reorientational motion of tetrahydrofuran molecules and the increase to densification as the structure mechanically collapses completely in the 1–1.25 GPa range. The relaxation time of the collapsed state is comparable with that of the high-density amorph formed on pressure collapse of ice.
|
|
| 55. |
|
|
| 56. |
- Andersson, Ove, et al.
(författare)
-
Phase behavior and thermal conductivity of urea at pressures up to 1 GPa and at temperatures in the range 50–370 K
- 1994
-
Ingår i: International journal of thermophysics. - : Plenum Publishing. - 0195-928X .- 1572-9567. ; 15:3, s. 513-524
-
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.
|
|
| 57. |
- Andersson, Ove, et al.
(författare)
-
Phase coexistence and hysteresis effects in the pressure-temperature phase diagram of NH3BH3
- 2011
-
Ingår i: Physical Review B. Condensed Matter and Materials Physics. - : American Physical Society. - 1098-0121 .- 1550-235X. ; 84:2, s. 024115-
-
Tidskriftsartikel (refereegranskat)abstract
- The potential hydrogen storage compound NH3BH3 has three known structural phases in the temperature and pressure ranges 110–300 K and 0–1.5 GPa, respectively. We report here the boundaries between, and the ranges of stability of, these phases. The phase boundaries were located by in situ measurements of the thermal conductivity, while the actual structures in selected areas were identified by in situ Raman spectroscopy and x-ray diffraction. Below 0.6 GPa, reversible transitions involving only small hysteresis effects occur between the room-temperature tetragonal plastic crystal I4mm phase and the low-temperature orthorhombic Pmn21 phase. Transformations of the I4mm phase into the high-pressure orthorhombic Cmc21 phase, occurring above 0.8 GPa, are associated with very large hysteresis effects, such that the reverse transition may occur at up to 0.5 GPa lower pressures. Below 230 K, a fraction of the Cmc21 phase is metastable to atmospheric pressure, suggesting the possibility that dense structural phases of NH3BH3, stable at room temperature, could possibly be created and stabilized by alloying or by other methods. Mixed orthorhombic Pmn21/Cmc21 phases were observed in an intermediate pressure-temperature range, but a fourth structural phase predicted by Filinchuk et al. [ Phys. Rev. B 79 214111 (2009)] was not observed in the pressure-temperature ranges of this experiment. The thermal conductivity of the plastic crystal I4mm phase is about 0.6 W m−1 K−1 and only weakly dependent on temperature, while the ordered orthorhombic phases have higher thermal conductivities limited by phonon-phonon scattering.
|
|
| 58. |
- Andersson, Ove, et al.
(författare)
-
Pressure-induced collapse of ice clathrate and hexagonal ice mixtures formed by freezing
- 2009
-
Ingår i: Journal of Chemical Physics. - : American Institute of Physics Publishing LLC. - 0021-9606 .- 1089-7690. ; 131, s. 114503-114513
-
Tidskriftsartikel (refereegranskat)abstract
- We report thermal conductivity κ measurements of the pressure-induced collapse of two mixtures of ice and tetrahydrofuran (THF) clathrate hydrate formed by freezing aqueous solutions, THF·23 H2O and THF·20 H2O, one containing twice as much excess water than the other. On pressurizing, κ of the solid mixture first decreases at the onset pressure of 0.8 GPa, as occurs for collapse of pure ice, reaches a local minimum at a pressure of 1.0 GPa, and then increases as occurs for the collapse of the pure clathrate THF·17 H2O. This shows that in the apparently homogeneous mixture, the ice and the clathrate collapse as if the two were in a mechanically mixed state. The manner in which the clathrate aggregate can arrange in the solid indicates that ice occupies the interstitial space in the tightly packed aggregates and H2O molecules belonging to the lattice of one form hydrogen bond with that of the other, a feature that is preserved in their collapsed states. On decompression, the original clathrate is partially recovered in the THF·20 H2O mixture, but the collapsed ice does not transform to the low density amorph. We surmise that on irreversible transformation to the original clathrate, the aggregates expand. Any pressure thus exerted on the small domains of the collapsed ice with a hydrogen bonded interface with the clathrate aggregates could prevent it from transforming to the low density amorph. Measurements of κ are useful in investigating structural collapse of crystals when dilatometry is unable to do so, as κ seems to be more sensitive to pressure-induced changes than the volume.
|
|
| 59. |
|
|
| 60. |
- Andersson, Ove, et al.
(författare)
-
Reorientational relaxation in C60 following a pressure induced change in the pentagon/hexagon equilibrium ratio
- 1995
-
Ingår i: Physics Letters A. - : Elsevier Science B.V.. - 0375-9601 .- 1873-2429. ; 206:3-4, s. 260-264
-
Tidskriftsartikel (refereegranskat)abstract
- The orientational structure of C60 depends on pressure and temperature. Pressurization below the glass transition temperature Tg can freeze in non-equilibrium orientational structures. The relaxation of such structures on heating through Tg has been studied through thermal conductivity measurements and the effects observed are explained in a simple model.
|
|
