Ove Andersson

Glass–liquid transition of water at high pressure

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 Cp 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.

Water’s polyamorphic transitions and amorphization of ice under pressure

Transformations of waters high density amorph (HDA) to low density amorph (LDA) and of LDAs to cubic ice (Ic) have been studied by in situ thermal conductivity kappa measurements at high pressures. The HDA to LDA transformation is unobservable at p of 0.07 GPa, indicating that, for a fixed heating rate, an increase in pressure increases the temperature of HDA to LDA transformation and decreases that of LDA to ice Ic, causing thereby the two transformations to merge, and HDA appears to convert directly to ice Ic. Thus either LDA forms but converts extremely rapidly to ice Ic, or LDA does not form. At a fixed p and T, in the range of pressure amorphization of hexagonal ice, kappa continues to decrease with time. Therefore, the amorphization of ice Ih is kinetically controlled. When HDA at 1 GPa was heated from 130 to 157 K and densified to very HDA, its kappa increased by 3%. Our findings and a scrutiny of earlier reports show that a reversible transition between HDA and LDA does not occur at approximately 135 K and approximately 0.2 GPa. Since there is no unique HDA, it is difficult to justify the conjecture for a second critical point for water.

Thermal conductivity of crystalline and amorphous ices and its implications on amorphization and glassy water

The thermal conductivities kappa of the crystalline phases and amorphous solid states of water as well as clathrate hydrates are summarized and discussed. In particular, this review concerns the unusual temperature T and pressure p behaviors of kappa for some phases and states, which include glass-like K for crystalline clathrate hydrates and crystal-like kappa for low-density amorphous ice. The latter result implies that glassy water and low-density amorphous ice are different states. The results for the various phases and states are in most cases described well by the equations: kappa = D x T(-x) and 1n kappa = E + F x p, under isobaric and isothermal conditions, respectively. All phases that exhibit negative values for F are known to amorphize upon pressurization at low temperatures. Ice XI, which is obtained by annealing ice Ih below 70 K, exhibits positive F, which indicates that this phase does not amorphize like ice Ih upon pressurization.

Phase diagram, structure, and disorder in C60 below 300 K and 1 GPa

Earlier structural studies have shown that the pentagon-to-hexagon orientation ratio in the orientationally ordered simple cubic phase of C60 decreases under pressure. From anomalies observed in the compressibility and thermal conductivity of C60 under pressure we have deduced a pressure-temperature phase diagram for this substance in the range below 300 K and 1 GPa (10 kbar). We conclude that C60 forms a new, completely “hexagon” ordered structural phase above about 0.6 GPa at 150 K (1.2 GPa at 300 K), and that the glass transition shifts upwards in T under pressure by 54 K GPa−1. However, above 0.1 GPa, pentagon-to-hexagon orientation relaxation seems to occur on heating at an almost pressure independent temperature near 100 K.

A low-temperature high-pressure apparatus with a temperature control system

A low-temperature high-pressure apparatus was designed using commercial cryogenic equipment. Pressures up to 1 GPa and temperatures down to 40 K can be obtained in a volume of up to 30 cm3. The app ...

Thermal conductivity, heat capacity and phase diagram of cyclooctanol in liquid, solid and glassy crystal states under high pressure

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.

Thermal conductivity of crystalline and glassy crystal cyclohexanol under pressure

The thermal conductivity λ of phases liquid, I, II, III and the glassy crystal state of cyclohexanol has been measured using the transient hot-wire method at temperatures in the range 100–370K and at pressures up to 0·7 GPa. It was inferred from the observed temperature dependence of the thermal resistivity W (= λ-1) that molecular orientational disorder made a dominant contribution to the resistivity for the glassy crystal state under isobaric conditions. The same was found for plastic crystal phase I under isochoric conditions and also under isobaric conditions especially at the highest pressure. It was suggested that conformational disorder may make an important contribution to W for molecular crystal phases II and III.

Formation of molecular alloys by solid-state vitrification

Abstract Formation of a vitreous molecular alloy was observed when a mixture of deoxycholic acid (DCA) and tri- O -methyl-β-cyclodextrin (TMCD) crystals was subjected to mechanical milling at room temperature. Only a single glass transition temperature T g , varying with the composition, was observed by DSC. This means that the vitreous state exhibits a single relaxation process as a whole by forming a molecular alloy. The T g showed a maximum value at the equimolar composition, indicating a strong interaction between the two components. A study of the phase diagram clarified the existence of inter-molecular compounds between them. Thermal conductivity of the milled solid of equimolar mixture exhibited a temperature dependence characteristic of glassy materials. p -Terphenyl and tris(hydroxymethyl)aminomethane crystals could not be vitrified. When each of them was milled with DCA or TMCD, vitreous molecular alloys were obtained in a limited composition range. These alloys exhibited also a single T g and underwent a phase separation on devitrification. Formation of molecular alloys was discussed based on the nature of disorder of the system.

Low-temperature heat capacity of urea

The heat capacity of urea was measured with an adiabatic calorimeter in the temperature range 15–310 K. The data were extrapolated to 0 K by a model function to derive some standard thermodynamic functions including the enthalpy increments Δ0TH, the entropy increments Δ0TS, and the Giauque function (=Δ0TS−Δ0TH/T). A simple model for the reproduction of the experimental heat capacities of urea, based on the Debye and Einstein functions, is described. The Debye characteristic temperature determined in this way was compared with those calculated from properties other than the heat capacity. Any positive evidence of a suggested phase transition in urea around 190 K was not observed in the present heat capacity measurements. Possible existence of a phase with a Gibbs energy lower than that realized in the present investigation is discussed briefly.

Electric resistance of single-walled carbon nanotubes under hydrostatic pressure

The electric resistance of single-walled nanotube mats has been studied systematically under both ambient and high hydrostatic pressures up to 1.5 GPa. Both the temperature dependence of the resistance and the magnetoresistance indicate that electrical transport occurs by variable range hopping, apparently in 2D. We suggest that this unexpected dimensionality arises from a fractal network of tubes and bundles. Under hydrostatic pressure (HP) the resistance still shows 2D variable range hopping and decreases with increasing HP. An irreversible increase in localization length and DOS is induced below 0.5 GPa. The behavior is reversible and due to strong interaction of tubes from 0.5 GPa up to 1.05 GPa. These results indicate that 2D variable range hopping occurs within bundles.