Ultra-slow relaxation in ice and related substances

Abstract

Introduction.A wide range of substances can be vitrified by cooling their liquids. At temperatures well below the fusion point, the relaxation time for viscous flow becomes so long that the liquid ultimately behaves like a solid. The glassy states of liquid are found to exhibit the glass transition T g and residual entropy S 0 as indicative of non-ergodicity of the frozen-in non-equilibrium system.1) The liquid undergoes a heat capacity discontinuity over a narrow temperature interval of T g , where the relaxation time for the structural change in a liquid becomes of the order of 1 ks that corresponds to the time scale for a single heat-capacity determination.Corresponding to the C p drop, the entropy of the liquid bends at T g and results in residual entropy S 0 that is a measure of the extent of frozen-in disorder. These quantities are highly time-dependent. If the liquid were cooled with an infinitely slow rate, the liquid follows the extrapolated curve of entropy of the undercooled liquid and finally intersects that of the corresponding crystal. Since any disordered system with less entropy than that of the crystal cannot be considered, the entropy of the equilibrium liquid must bend at this temperature in order to avoid the entropy crisis. The temperature is known as the Kauzmann temperature T K . Thus the seemingly second-order character of the glass transitions in real liquids is believed to be a kinetic manifestation of the underlying second-order phase transition in the "equilibrium" liquid. Essentially the same phenomena were found to occur also in some crystalline solids that have orienta- Abstract: Of prime interest in numerous studies on water, an important substance to all living systems, may be its physical, chemical, biological characteristics in our internal and external environments. One of the central problems underlying all these researches is a basic structural problem. An important question was why ordinary ice did not obey the third law of thermodynamics. The proton-disordered phase I h remains down to the lowest temperature without exhibiting any indication of phase transition. We found that the glass transition is not a characteristic property of liquid but of wide occurrence in condensed systems that failed to maintain thermal equilibrium during continuous cooling. Crystalline substance that exhibited freezing-in process on cooling was designated as "glassy crystals". In fact, ice I h exhibited a glass transition at around 110 K due to slowing down of reorientational motion of the water molecules. A particular kind of impurity was found to accelerate dramatically the motion, and to induce a long-awaited phase transition at 72 K. The transition removed a substantial fraction of the residual entropy of ice. The dopant acted as a kind of catalysis for releasing the immobilized non-equilibrium state to recover thermal equilibrium in the laboratory time. Structure and some properties of the ordered low temperature phase, designated as ice XI, are discussed. The same ordering processes observ...

Doping-enhanced dipolar dynamics in ice V as a precursor of hydrogen ordering in ice XIII

“…This figure contains data on KOH-doped ice I h /XI [64,65], KOD-doped ice I h /XI [16], RbOH-doped ice I h /XI [14], HCl-doped ice V/XIII from this paper, and HCl-doped ice XII/XIV [53]. The data on the potassium hydroxide doped clathrate hydrates refer to the guest molecules THF (tetrahydrofuran, doped with KOH [18,70] or KOD [20]), ACE (acetone, with KOH) [21], or TMO (trimethylene oxide, with KOH) [21]. The arrows indicate the phase transition temperatures.…”

“…Table I further summarizes parameters like activation energy E, phase transition temperature T c , and relaxation time τ , measured just above and below T c . The table also includes data on various KOH-doped clathrate hydrates, which at high temperatures crystallize in the cubic structure sII and which can display (at least partial) proton ordering at low temperatures when containing tetrahydrofuran (THF) [69][70][71][72], acetone (ACE), or trimethylene oxide (TMO) as guests [18][19][20][21][22]. These clathrates may currently be considered as closest reference systems for an empty structure sII clathrate hydrate, i.e., for ice XVI for which a hydrogen ordered companion phase was not observed experimentally so far [7].…”

“…For hexagonal ice (ice I h ) [11][12][13][14][15][16][17] and for related systems such as the sII clathrate hydrates [18][19][20][21][22], it has long been shown that alkali hydroxide doping can lead to a lowtemperature orientational ordering [23]. Despite occasional other suggestions [24], dopants such as alkali or hydrogen halides, earth alkali hydroxides, or ammonia are ineffective in catalyzing a hydrogen ordered low-temperature phase [11].…”

Heat capacities and thermodynamic functions of hexagonal ice from T=0.5K to T=38K

“…When the sample had almost reached its melting point and the non-equilibrium temperature rose relatively quickly (in 20 s) from T = 273.14 K to T = 273.16 K, the amount of heat applied to the sample was drastically reduced, and the sample was allowed to cool to T = 270 K over the next 24 h, thereby allowing it to fully re-crystallize. Taking the sample only to its melting point allowed some of the ice crystals to remain in equilibrium with the liquid and act as seed crystals, or sources of nucleation, for the bulk crystal as the sample was cooled to T = 270 K. Once T = 270 K was reached, the sample was cooled slowly over the next 36 hours to T = 80 K in order to keep the sample in equilibrium through the glass transition reported between T = 110 K [11][12][13][14] and T = 136 K [15][16][17][18]. Once the sample reached T = 80 K, it was cooled to lower temperatures with liquid helium.…”

Electronic and nuclear quantum effects on the ice XI/ice Ih phase transition

“…This phase transition has been subject of a large number of experimental [4][5][6][7][8] and theoretical studies [9][10][11][12][13][14][15][16][17][18][19][20][21] . However, open questions remain about the mechanisms behind the phase transition and the importance of nuclear quantum effects in the temperature of the transition 22 . Experimentally, it is difficult to observe the phase transition from ice Ih to ice XI.…”