| 61. |
- Andersson, Ove
(författare)
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Simulation of a glass transition in a hot-wire experiment using time-dependent heat capacity
- 1997
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Ingår i: International journal of thermophysics. - : Plenum Publishing. - 0195-928X .- 1572-9567. ; 18:1, s. 195-208
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Tidskriftsartikel (refereegranskat)abstract
- The transient hot-wire method is used for simultaneous measurements of the thermal conductivity λ and the heat capacity per unit volume ρcp and yields a peak in λ and a dip in ρcp near a glass transition. Through simulations, it is shown that these anomalous results arise due to a time dependence in cp, which is described by a fractional exponential function: cp(t) = cp(liquid) + [cp(glass) - cp(liquid)] e(-(t/τ)β), where τ is the heat capacity relaxation time and β is a sample dependent parameter (0 < β ≤ 1). By a comparison with experimental data for cyclohexanol and glycerol, it is demonstrated that this model can be used to reproduce the peak and the dip as well as the temperature at which these occur. In addition, it is shown that the maximum in λ occurs at τ = 0.3 s, whereas τ of the minimum in ρcp is dependent on β and moves from 0.4 to 1 s for a change in β from 1 to 0.5. The difference in τ between the peak and the dip is in agreement with the experimental results. It is concluded that the anomalies reveal glass forming characteristics such as a rough classification in terms of strong and fragile glass formers.
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| 62. |
- Andersson, Ove, et al.
(författare)
-
Spontaneous transformation of water's high-density amorph and a two-stage crystallization to ice VI at 1 GPa : a dielectric study
- 2004
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 120:24, s. 11662-11671
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Tidskriftsartikel (refereegranskat)abstract
- Dielectric relaxation spectra of a metastable crystal phase formed on implosive and exothermic transformation of pressure-amorphized hexagonal ice have been measured in situ at 0.97 GPa pressure over a range of temperature. The metastable phase showed no relaxation peak at 130 K and 0.97 GPa. When heated at a fixed pressure of 0.97 GPa, it began to transform at ∼ 145 K exothermally to a phase whose relaxation rate and equilibrium dielectric permittivity increased. A second, but slower exothermic transformation also occurred at ∼ 175 K. After keeping at 213 K, the relaxation rate and equilibrium permittivity reached the known values of these two quantities for ice VI. Thus the metastable phase transformed to ice VI in two stages. It is conjectured that the intermediate phase in this transformation could be ice XII. The rate of transformation is not determined by the reorientational relaxation rate of water molecules in the ices
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| 63. |
- Andersson, Ove, et al.
(författare)
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Sub-Tg features of glasses formed by cooling glycerol under pressure – Additional incompatibility of vibrational with configurational states in the depressurized, high density glass
- 2016
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 145
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Tidskriftsartikel (refereegranskat)abstract
- The vibrational state of a glass is naturally incompatible with its configurational state, which makes the glass structurally unstable. When a glass is kept at constant temperature, both the vibrational and configurational states of a glass change with time until it becomes metastable (equilibrium) liquid and the two states become compatible. The process, known as structural relaxation, occurs at a progressively higher rate during heating, and the properties of a glass change accordingly. We add to this incompatibility by depressurizing a glass that had been formed by cooling a liquid under a high pressure, p, and then investigate the effects of the added incompatibility by studying thermal conductivity, κ, and the heat capacity per unit volume ρCp of the depressurized glass.We use glycerol for the purpose and study first the changes in the features of κ and of ρCp during glass formation oncooling under a set of different p. We then partially depressurize the glass and study the effect of the p-induced instability on the features of and Cp as the glass is isobarically heated to the liquid state.At a given low p, the glass configuration that was formed by cooling at high-p had a higher κ than the glass configuration that was formed by cooling at a low p. The difference is more when the glass is formed at a higher p and/or is depressurized to a lower p. On heating at a low p, its κ decreases before its glass-liquid transition range is reached. The effect is the opposite of the increase in observed on heating a glass at the same p under which it was formed. It is caused by thermally assisted loss of the added incompatibility of configurational and vibrational states of a high-p formed glass kept at low p. If a glass formed under a low-p is pressurized and then heated under high p, it would show the opposite effect, i.e., its κ would first increase to its high p value before its glass-to-liquid transition range.
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| 64. |
- Andersson, Ove, et al.
(författare)
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Thermal Conductivity and Heat Capacity of Dianin's Clathrates under Pressure
- 2001
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Ingår i: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1520-6106 .- 1520-5207. ; 106:1, s. 192-196
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Tidskriftsartikel (refereegranskat)abstract
- The thermal conductivities, λ, and heat capacities of polycrystalline Dianin’s compound and its CCl4 and ethanol clathrates have been investigated in the temperature range 40-300 K for pressures up to 1 GPa. All high-pressure results for λ show typical crystal-like behavior, whereas previous atmospheric pressure results for single crystals as well as recent results on polycrystalline samples show glasslike behavior. The change from glasslike to crystal-like dependence might be caused by a frequency shift of localized vibrations on pressurization, moving the localized vibrations outside the frequency range of the dominant heat carriers and reducing thermal resistance due to resonance scattering.
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| 65. |
- Andersson, Ove, et al.
(författare)
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Thermal conductivity, heat capacity and phase diagram of cyclooctanol in liquid, solid and glassy crystal states under high pressure
- 1990
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Ingår i: Molecular Physics. - : Taylor & Francis Group. - 0026-8976 .- 1362-3028. ; 71:3, s. 523-539
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Tidskriftsartikel (refereegranskat)abstract
- Using the transient hot-wire method, thermal conductivity and heat capacity per unit volume are measured for solid and liquid phases and glassy crystal states of cyclooctanol, and information is provided on the phase diagram under high pressure. A new solid phase (III) is detected and characterized as a normal crystal phase, whereas all other solid phases (I, II, IV, V) are characterized as plastic crystal phases. We find evidence that the plastic crystal phases I, II and IV could each be the source for a distinct glassy crystal state. It is argued for phase II that its possession of both a low thermal conductivity and a low dielectric permittivity could be accounted for by assuming restricted reorientational motion of the molecules. The unusual (although small) decrease of thermal conductivity observed through the glassy to plastic crystal transitions may indicate that phonons can couple to reorientational motion in the plastic crystal phases I, II and IV.
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| 66. |
- Andersson, Ove, et al.
(författare)
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Thermal conductivity of amorphous ices
- 2002
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Ingår i: Physical Review B. - : American Physical Society. - 2469-9950 .- 2469-9969 .- 0163-1829 .- 1095-3795. ; 65:14
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Tidskriftsartikel (refereegranskat)abstract
- The thermal conductivities κ of high-density amorphous (HDA) ice and low-density amorphous (LDA) ice were measured under pressure. The results for HDA show typical glasslike behavior, i.e., positive dκ/dT, whereas LDA exhibits crystal-like behavior, indicating that phonon-phonon scattering is dominant. LDA appears to be unique among apparently topologically disordered glasses to exhibit such behavior. Moreover, the results imply that LDA and glassy water formed by rapid cooling are different states.
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| 67. |
- Andersson, Ove, et al.
(författare)
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Thermal conductivity of (+)- and (±)-camphor at pressures up to 0·5 GPa and temperatures down to 40 K
- 1992
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Ingår i: Molecular Physics. - : Taylor & Francis. - 0026-8976 .- 1362-3028. ; 76:2, s. 433-444
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Tidskriftsartikel (refereegranskat)abstract
- The transient hot-wire method was used to investigate the thermal conductivity of (+)- and (±)-camphor in the temperature range 40–300 K and for pressures up to 0·5 GPa. Results for the thermal conductivity of crystalline (+)- and (±)-camphor exhibited maximum values at temperatures of 60 and 70 K, respectively, independent of pressure. Above the maxima, the thermal conductivity λ exhibited a less pronounced temperature dependence than the variation λ ∼T-1 which is predicted theoretically for perfect crystals. We showed that the Debye theory can describe the thermal conductivity of molecular crystals like (+)- and (±)-camphor when structural disorder is assumed to provide a significant contribution to the phonon scattering process. We investigated two samples of (±)-camphor of estimated purity 99·3% and 97% and both samples exhibited the same thermal conductivity within experimental inaccuracy.
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| 68. |
- Andersson, Ove, et al.
(författare)
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Thermal conductivity of C60 at pressures up to 1 GPa and temperatures in the range 50-300 K
- 1996
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 54:5, s. 3093-3100
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Tidskriftsartikel (refereegranskat)abstract
- The thermal conductivity λ of C60 shows anomalies near 260 K and 90 K which are associated with the well-established phase transition and glass transition, respectively. Both transition temperatures increase with pressure, at the rates 120 K GPa-1 and 62 K GPa-1, respectively. With increasing temperature, λ of the simple cubic (sc) phase increased below 170 K (glasslike behavior) but decreased above. The glasslike behavior of λ is probably due to a substantial amount of lattice defects. Possible reasons for the change of sign of dλ/dT near 170 K are discussed. In the face centered cubic (fcc) phase (T≳260 K at atmospheric pressure) λ was almost independent of temperature, a behavior which is far from that of an ordered crystal (λ∝T-1 for T≳Debye temperature). This result can be attributed to the molecular orientational disorder of the fcc phase. The relaxation behavior associated with the glassy state and its unusually strong dependence on thermal history are discussed briefly, and data which support a previously reported relaxation model are presented. At room temperature, the density dependencies of λ, (∂ lnλ/∂ lnρ)T, were 5.5 and 9.5 for the fcc and sc phases, which are values typical for an orientationally disordered phase and a normal crystal phase, respectively.
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| 69. |
- Andersson, Ove, et al.
(författare)
-
Thermal conductivity of C60 under high pressure
- 1995
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Ingår i: Science and Technology of Fullerene Materials. - Pittsburgh, PA : Materials Research Society. - 155899260X ; , s. 549-554
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Konferensbidrag (refereegranskat)abstract
- We have measured the thermal conductivity lambda of highly pure polycrystalline C60 in the range 50 to 300 K under pressures up to 1 GPa. The results are discussed in terms of the lattice structure and dynamics. In particular, we discuss the phase diagram as delineated by anomalies observed in lambda and cp at the f.c.c.-to-s.c. transition at 260 K and the glass transition at Tg = 90 K, and also the effect on lambda of the orientational motion in the s.c. phase. The results are found to be compatible with a p/T phase diagram recently suggested by us.
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| 70. |
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