| 41. |
- Andersson, Ove, et al.
(författare)
-
An ice phase of lowest thermal conductivity
- 2004
-
Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 120:20, s. 9612-9617
-
Tidskriftsartikel (refereegranskat)abstract
- On pressurizing at temperatures near 130 K, hexagonal and cubic ices transform implosively at 0.8–1 GPa. The phase produced on transformation has the lowest thermal conductivity among the known crystalline ices and its value decreases on increase in temperature. An ice phase of similar thermal conductivity is produced also when high-density amorphous ice kept at 1 GPa transforms on slow heating when the temperature reaches ∼155 K. These unusual formation conditions, the density and its distinguished thermal conductivity, all indicate that a distinct crystal phase of ice has been produced.
|
|
| 42. |
- Andersson, Ove, et al.
(författare)
-
Chirality and the thermophysical properties of molecular solid phases under pressure: (+)- and (±)-camphor
- 1990
-
Ingår i: Molecular Physics. - : Taylor & Francis Group. - 0026-8976 .- 1362-3028. ; 70:6, s. 1065-1083
-
Tidskriftsartikel (refereegranskat)abstract
- Thermal conductivity λ, heat capacity per unit volume pcP and P-T phase diagrams are investigated for both (+)- and (±)-camphor. The transient hotwire method is used at temperatures in the range 100–430 K and at pressures up to 1·75 GPa. We detect solid phases I-IV for (+)-camphor and I′-V′ for (±)-camphor. We conclude that λ is independent of enantiomeric composition for plastic-crystal phase pairs I-I′, II-II′ and IV-IV′. Phase V′ also appears to be a plastic-crystal phase. Non-plastic phases III and III′ show a variation of λ with T that differ considerably from that expected for a simple crystal, with the greatest such difference being observed for the racemic compound III′. An unannealed specimen of the racemic compound III′ is probably chirally disordered and shows a variation of λ with T for T < 130 K, which may indicate phonon-assisted fracton hopping.
|
|
| 43. |
- Andersson, Ove, et al.
(författare)
-
Collapse of an ice clathrate under pressure observed via thermal conductivity measurements
- 2008
-
Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 78, s. 174201-
-
Tidskriftsartikel (refereegranskat)abstract
- Irreversible transformation of the tetrahydrofuran ice clathrate at 130 K was studied by measuring thermal conductivity k with increase in pressure p. Initially, k increases slowly with p up to 0.75 GPa where it levels off, is roughly constant up to 0.95 GPa, then decreases up to 1.05 GPa. Pressure collapses the clathrate structure, plausibly beginning with lattice distortion, and k increases at 1.05 GPa in a sharp sigmoid-shape manner due to large densification until the transformation is complete at 1.25 GPa. This is the opposite of that found for ice whose k decreases first slowly with increase in p and then rapidly in an inverted sigmoidshape manner [O. Andersson and H. Suga, Phys. Rev. B 65, 140201 (2002)]. At 1.08 GPa and 131 K, k increases with time t (s) according to exp(t /2945), which is also the opposite of the collapse of ice [G. P. Johari and O. Andersson, Phys. Rev. B 70, 184108 (2004)]. The difference in its behavior is attributed to strong phonon scattering from the tetrahydrofuran guest molecules. k of the collapsed clathrate is 30% less than that for the collapsed ice, which is comparable with the 25% lesser k of the tetrahydrofuran-water solution from k of water at ambient pressure. On depressurizing at 130 K, k decreases progressively more rapidly and k of the collapsed state at 0.3 GPa is slightly lower than that of the as-made clathrate, showing that its original structure is not recovered.
|
|
| 44. |
|
|
| 45. |
|
|
| 46. |
- Andersson, Ove
(författare)
-
Dielectric relaxation of the amorphous ices
- 2008
-
Ingår i: Journal of Physics. - : Institute of Physics (IOP). - 0953-8984 .- 1361-648X. ; 20
-
Tidskriftsartikel (refereegranskat)abstract
- The dielectric properties of the low and high density amorphous ices are discussed in terms of those for supercooled water and crystalline ices, and also used to evaluate the transition behaviour upon pressure cycling at 130 K. The dielectric relaxation of the high density amorphous ice is described well by the symmetrical Cole–Cole function with an almost pressure independent relaxation time τ ∼ 2 s at 133 K and a relaxation time distribution factor of 0.7. At the high to low density amorphous ice transition, the dielectric relaxation time increases by about two orders of magnitude despite a ∼30% decrease in density, and τ of the low density amorphous ice is in the range 102–103 s at 130 K. The relaxation time behaviour of the high density amorphous ice is similar to that of supercooled liquid water, whereas τ of the low density amorphous ice appears to be prolonged by the ice rules, in correspondence to that of the crystalline ices.
|
|
| 47. |
|
|
| 48. |
- Andersson, Ove, et al.
(författare)
-
Effect of pressure on thermal conductivity and pressure collapse of ice in a polymer-hydrogel and kinetic unfreezing at 1 GPa
- 2011
-
Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 134:12, s. 124903-
-
Tidskriftsartikel (refereegranskat)abstract
- We report a study of aqueous solutions of poly(vinylalcohol) and its hydrogel by thermal conductivity,κ, and specific heat measurements. In particular, we investigate (i) the changes in the solution and the hydrogel at 0.1 MPa observed in the 350-90 K range and of the frozen hydrogel at 130 K observed in the range from 0.1 MPa to 1.3 GPa, and (ii) the nature of the pressure collapse of ice in the frozen hydrogel and kinetic unfreezing on heating of its high density water at 1 GPa. The water component of the polymer solution on cooling either first phase separates and then freezes to hexagonal ice or freezes without phase separation and the dispersed polymer chains freeze-concentrate in nanoscopic and microscopic regions of the grain boundaries and grain junctions of the ice crystals in the frozen state of water in the hydrogel. The change in κ with temperature at 1 bar is reversible with some hysteresis, but not reversible with pressure after compression to 0.8 GPa at 130 K. At high pressures the crystallized state collapses showing features of. and specific heat characteristic of formation of high density amorphous solid water. The pressure of structural collapse is 0.08 GPa higher than that of ice at 130 K. The slowly formed collapsed state shows kinetic unfreezing or glass-liquid transition temperature at 140 K for a time scale of 1 s. Comparison with the change in the properties observed for ice shows that κ decreases when the polymer is added.
|
|
| 49. |
- Andersson, Ove, et al.
(författare)
-
Effects of pressure and temperature on the thermal conductivity of Sn2P2S6
- 2011
-
Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 83:13
-
Tidskriftsartikel (refereegranskat)abstract
- The thermal conductivity kappa of the ferroelectric, paraelectric, and incommensurate phases of polycrystalline Sn2P2S6 has been measured in the 0.1-0.7 GPa range. The thermal conductivity kappa of the ferroelectric phase decreases with increasing pressure p. This unusual behavior, which is found in only a few other phases, is attributed to a negative Gruneisen parameter. The temperature T dependence of kappa for the ferroelectric phase (kappa similar to T-1) is well described by the Debye model for kappa, with three-phonon Umklapp scattering serving as the dominant scattering mechanism near and above the Debye temperature (similar to 100 K) up to a few tenths of degrees below the ferro- to paraelectric phase transition, where kappa(T) gradually changes and becomes temperature independent upon further heating. The thermal conductivity of the paraelectric and incommensurate phases was temperature independent and indistinguishable. Possible causes for the unusually weak T dependence at high temperatures and implications of the p dependence of kappa are discussed.
|
|
| 50. |
- Andersson, Ove, et al.
(författare)
-
Evidence suggesting kinetic unfreezing of water mobility in two distinct processes in pressure-amorphized clathrate hydrates
- 2022
-
Ingår i: Physical Chemistry, Chemical Physics - PCCP. - : Royal Society of Chemistry. - 1463-9076 .- 1463-9084. ; 24:34, s. 20064-20072
-
Tidskriftsartikel (refereegranskat)abstract
- Type II clathrate hydrates (CHs) with tetrahydrofuran (THF), cyclobutanone (CB) or 1,3-dioxolane (DXL) guest molecules collapse to an amorphous state near 1 GPa on pressurization below 140 K. On subsequent heating in the 0.2-0.7 GPa range, thermal conductivity and heat capacity results of the homogeneous amorphous solid show two glass transitions, first a thermally weak glass transition, GT1, near 130 K; thereafter a thermally strong glass transition, GT2, which implies a transformation to an ultraviscous liquid on heating. Here we compare the GTs of normal and deuterated samples and samples with different guest molecules. The results show that GT1 and GT2 are unaffected by deuteration of the THF guest and exchange of THF with CB or DXL, whereas the glass transition temperatures (Tgs) shift to higher temperatures on deuteration of water; Tg of GT2 increases by 2.5 K. These results imply that both GTs are associated with the water network. This is corroborated by the fact that GT2 is detected only in the state which is the amorphized CH's counterpart of expanded high density amorphous ice. The results suggest a rare transition sequence of an orientational glass transition followed by a glass to liquid transition, i.e., kinetic unfreezing of H2O reorientational and translational mobility in two distinct processes.
|
|
