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| 2. |
- 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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| 3. |
- Johari, G.P., et al.
(författare)
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Effects of pressure-temperature protocols on the properties of crystals and ageing effects : an analogy with glasses
- 2022
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Ingår i: Philosophical Magazine. - : Taylor & Francis. - 1478-6435 .- 1478-6443. ; 102:4, s. 299-320
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Tidskriftsartikel (refereegranskat)abstract
- Properties of a crystal are used to determine the point defects concentration, n, the self diffusion coefficient, D and variation of n and D with tempertaure, T. Also, spontaneous change in the properties of a crystal’s non-equilibrium state is used to determine the decrease in n with time. Both n and D decrease with increase in the pressure, P, until the pressurising-rate dependent, kinetic-freezing pressure for defects disorder, PD-F, is reached. At P > PD-F, a crystal is in a non-equilibrium state. We consider such configurationally-frozen states of a crystal produced by using three unusual P-T protocols: (i) pressurising a crystal to P > PD-F, cooling to a low T and depressurising, (ii) pressurising to P < PD-F, cooling through the defects freezing temperature, TD-F, and depressurising, and (iii) cooling a crystal at 1 bar to T D-F pressurising and maintaining at high P. The non-equilibrium state of the crystal would have defect concentration that kinetically froze at P = PD-F or T = TD-F, but its volume and phonon properties would not correspond to the kinetically-frozen state at P = PD-F or at T = TD-F. On aging, their properties would change differently than those of a non-equilibrium state of a crystal produced by quenching at a fixed P. We relate n, D and the electrical resistivity to thermal conductivity, κ, by the Wiedemann-Franz equation, and discuss how κ would change on aging of a crystal. The above-given effects alter the properties of metallic and non-metallic, metastable materials during their commercial use.
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| 4. |
- Johari, G. P., et al.
(författare)
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Effects of stacking disorder on thermal conductivity of cubic ice
- 2015
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Ingår i: Journal of Chemical Physics. - : American Institute of Physics (AIP). - 0021-9606 .- 1089-7690. ; 143:5
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Tidskriftsartikel (refereegranskat)abstract
- Cubic ice is said to have stacking disorder when the H2O sequences in its structure (space group Fd (3) over barm) are interlaced with hexagonal ice (space group P6(3)/mmc) sequences, known as stacking faults. Diffraction methods have shown that the extent of this disorder varies in samples made by different methods, thermal history, and the temperature T, but other physical properties of cubic and hexagonal ices barely differ. We had found that at 160 K, the thermal conductivity, kappa, of cubic ice is similar to 20% less than that of hexagonal ice, and this difference varies for cubic ice samples prepared by different methods and/or subjected to different thermal history. After reviewing the methods of forming cubic ice, we report an investigation of the effects of stacking disorder and other features by using new data, and by analyzing our previous data on the dependence of kappa on T and on the pressure. We conclude that the lower kappa of cubic ice and its weaker T-dependence is due mainly to stacking disorder and small crystal sizes. On in situ heating at 20-50 MPa pressure, kappa increases and cubic ice irreversibly transforms more sharply to ice Ih, and at a higher T of similar to 220 K, than it does in ex situ studies. Cooling and heating between 115 and 130 K at 0.1 K min(-1) rate yield the same kappa value, indicating that the state of cubic ice in these conditions does not change with time and T. The increase in kappa of cubic ice observed on heat-annealing before its conversion to hexagonal ice is attributed to the loss of stacking faults and other types of disorders, and to grain growth. After discussing the consequences of our findings on other properties, we suggest that detailed studies of variation of a given property of cubic ice with the fraction of stacking faults in its structure may reveal more about the effect of this disorder. A similar disorder may occur in the mono-layers of H2O adsorbed on a substrate, in bulk materials comprised of two dimensional layers, in diamond and in Zirconium and in numerous other crystals.
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| 5. |
- Johari, G P, et al.
(författare)
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In situ transformation of amorphous ices at high pressures
- 2007
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Ingår i: Physical Review B. ; 76, s. 134103-1
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Tidskriftsartikel (refereegranskat)abstract
- By using thermal conductivity and its change with temperature and pressure as a criteria for in situ structural transformation of the crystalline and amorphous solid forms of water, we report two findings: (i) transformation of high-density amorph (HDA) directly to cubic ice on slow depressurization and (ii) slow transformation or dilation of metastable HDA at 130 K to a low-density amorph (LDA) even when the pressure was increased from 0.2 to 0.3 GPa, and then gradual reversion by collapse of the LDA to HDA on further pressurization to 0.5 GPa. We also discuss implications of these findings for the current understanding of the transformations of metastable ices under pressure, particularly of those studied in situ.
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| 6. |
- Johari, G. P., et al.
(författare)
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Instability and thermal conductivity of pressure-densified and elastically altered orientational glass of Buckminsterfullerene
- 2018
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Ingår i: Journal of Chemical Physics. - : American Institute of Physics (AIP). - 0021-9606 .- 1089-7690. ; 148:14
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Tidskriftsartikel (refereegranskat)abstract
- We report on the temperature, pressure and time (T, p and t)- dependent features of thermal conductivity, k, of partially ordered, non-equilibrium state of C60-OG, the orientational glass of Buckminsterfullerene (at T below the orientational freezing temperature Tog) made more unstable (i) by partially depressurizing its high-p formed state to elastically expand it, and (ii) by further pressurizing that state to elastically contract it. The sub-Tog effects observed on heating of C60-OG differ from those of glasses, because phonon propagation depends on the ratio of two well-defined orientational states of C60 molecules and the density of the solid. A broad peak-like feature appears at T near Tog in the k-T plots of C60-OG formed at 0.7 and heated at 0.2 GPa, which we attribute to partial overlap of the sub-Tog and Tog features. A sub-Tog local minimum appears in the k -T plots at T well below Tog of C60-OG formed at 0.1 GPa and heated at 0.5 GPa, and corresponds to the state of maximum disorder. Although Buckminsterfullerene is regarded as an orientationally-disordered crystal, variation of its properties with T and p is qualitatively different from other such crystals. We discuss the findings in terms of the nature of its disorder, sensitivity of its rotational dynamics to temperature and the absence of the Johari-Goldstein relaxation. All seem to affect the phenomenology of its glass-like transition.
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| 9. |
- Johari, G. P., et al.
(författare)
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Structural relaxation and thermal conductivity of high-pressure formed, high-density di-n-butyl phthalate glass and pressure induced departures from equilibrium state
- 2017
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Ingår i: Journal of Chemical Physics. - : American Institute of Physics (AIP). - 0021-9606 .- 1089-7690. ; 146:23
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Tidskriftsartikel (refereegranskat)abstract
- We report a study of structural relaxation of high-density glasses of di-n-butyl phthalate (DBP) by measuring thermal conductivity, κ, under conditions of pressure and temperature (p,T) designed to modify both the vibrational and configurational states of a glass. Various high-density glassy states of DBP were formed by (i) cooling the liquid under a fixed high p and partially depressurizing the glass, (ii) isothermal annealing of the depressurized glass, and (iii) pressurizing the glass formed by cooling the liquid under low p. At a given low p, κ of the glass formed by cooling under high p is higher than that of the glass formed by cooling under low p, and the difference increases as glass formation p is increased. κ of the glass formed under 1 GPa is ∼20% higher at ambient p than κ of the glass formed at ambient p. On heating at low p, κ decreases until the glass to liquid transition range is reached. This is the opposite of the increase in κ observed when a glass formed under a certain p is heated under the same p. At a given high p, κ of the low-density glass formed by cooling at low p is lower than that of the high-density glass formed by cooling at that high p. On heating at high p, κ increases until the glass to liquid transition range is reached. The effects observed are due to a thermally assisted approach toward equilibrium at p different from the glass formation p. In all cases, the density, enthalpy, and entropy would change until the glasses become metastable liquids at a fixed p, thus qualitatively relating κ to variation in these properties.
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| 10. |
- Johari, G.P., et al.
(författare)
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Vibrational and relaxational properties of crystalline and amorphous ices
- 2007
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Ingår i: Thermochimica Acta 461, issue 1-2. - : Elsevier BV. ; , s. 14-43
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Konferensbidrag (refereegranskat)abstract
- Pure water forms 15 crystalline ices at different temperatures and pressures, and its solutions containing small molecules form three crystallographically distinct clathrates. Its vapours deposited on a substrate at T< 100K produce a porous amorphous solid and pure water vitrifies (T-g = 136 K) when hyperquenched in micron-size droplets. At a temperature below 140 K, hexagonal and cubic ice collapse when pressure exceeds similar to 1 GPa to a similar to 30% denser amorphous solid, which on heating at ambient pressure transforms to an amorphous solid with density similar to that of hexagonal ice. In this essay, we describe (i) the thermal conductivity of the ices and clathrates and the thermal conductivity and heat capacity of water's amorphous solids, their thermodynamic paths and their transformations, and (ii) the dielectric relaxation time of ultraviscous water formed on heating the amorphous solids. We also describe the characteristics of pressure collapse and subsequent amorphization of hexagonal and cubic ices that occurs over a period of several days according to a stretched exponential kinetics and a pressure-, and temperature-dependent rate constant. This process is attributed to the production of lattice faults during deformation of the ice and the consequent distribution of the Born instability pressures. This ultimately produces a kinetically unstable high-energy amorphs in the same manner as random deformation of crystals produces kinetically unstable high-energy amorphs, with density and properties depending upon their temperature-pressure-time history. On heating at 1 GPa pressure, the pressure-amorphized solid relaxes to a lower energy state, becoming ultraviscous water at 140 K. But on heating at ambient pressure, it irreversibly transforms slowly to a low-density amorph that differs from glassy water and vapour-deposited amorphous solid.
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