Unusual Grüneisen and Bridgman parameters of low-density amorphous ice and their implications on pressure induced amorphization

Thermal conductivity of normal and deuterated water, crystalline ice, and amorphous ices

The effect of deuteration on the thermal conductivity κ of water, crystalline ice, and amorphous ices was studied using the pressure induced amorphization of hexagonal ice, ice Ih, to obtain the deuterated, D₂O, forms of low-density amorphous (LDA), high-density amorphous (HDA), and very-high density amorphous (VHDA) ices. Upon deuteration, κ of ice Ih decreases between 3% and 4% in the 100-270 K range at ambient pressure, but the effect diminishes on densification at 130 K and vanishes just prior to amorphization near 0.8 GPa. The unusual negative value of the isothermal density ρ dependence of κ for ice Ih, g = (d ln κ/d ln ρ) _T = -4.4, is less so for deuterated ice: g = -3.8. In the case of the amorphous ices and liquid water, κ of water decreases by 3.5% upon deuteration at ambient conditions, whereas κ of HDA and VHDA ices instead increases by up to 5% for pressures up to 1.2 GPa at 130 K, despite HDA's and VHDA's structural similarities with water. The results are consistent with significant heat transport by librational modes in amorphous ices as well as water, and that deuteration increases phonon-phonon scattering in crystalline ice. Heat transport by librational modes is more pronounced in D₂O than in H₂O at low temperatures due to a deuteration-induced redshift of librational mode frequencies. Moreover, the results show that κ of deuterated LDA ice is 4% larger than that of normal LDA at 130 K, and both forms display an unusual temperature dependence of κ, which is reminiscent of that for crystals (κ ∼ T ^-1), and a unique negative pressure dependence of κ, which likely is linked to local-order structural similarities to ice Ih.

Structural relaxation and thermal conductivity of high-pressure formed, high-density di-n-butyl phthalate glass and pressure induced departures from equilibrium state

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.

Transient Pronounced Density Variation in Amorphous Ice Structures

The structural transformation of different high-density amorphous (HDA) ice modifications into the low-density amorphous (LDA) ice is studied by small-angle neutron scattering (SANS) techniques. All experiments have been performed at stationary conditions allowing to collect detailed information not only on the SANS formfactor but also on its time evolution and, hence, the kinetics governing the transformation process. A parametrization of the SANS formfactor by a superposition of the Debye-Bueche formfactor, characterizing a non-particulate two phase mixture, and a Porod-limit scattering formfactor is carried out successfully. The Porod-limit scattering indicates the presence of sharp interfaces and surfaces present in the sample material. Interpreting this signal as due to a grainy consistency of the amorphous samples grain sizes of the order of at least some micrometers can be approximated. The Debye-Bueche ansatz accounts for the formation of a transient pronounced signal on mesoscopic length scales. Its analysis results in an average domain size of 12–16 Å characterizing a hypothetical two phase mixture in its state of strongest intermixture, i.e., strongest heterogeneity. Interpretation of the Debye-Bueche formfactor by the Porod invariant results in a sample contrast that is by a factor of about 4 smaller than a hypothetical first-order transition between any modification of HDA and LDA. This statement is valid for an unstrained two-phase system separated by sharp interfaces. A detailed discussion is given which tries to set the present results into a more realistic context.