Detailed crystallographic analysis of the ice V to ice XIII hydrogen-ordering phase transition

Abstract

Ice V is a structurally highly complex material with 28 water molecules in its monoclinic unit cell. It is classified as a hydrogen-disordered phase of ice. Yet, some of its hydrogen-bonded water molecules display significant orientational order. Upon cooling pure ice V, additional orientational ordering cannot be achieved on the experimental time scale. Doping with hydrochloric acid has been shown to be most effective in enabling the phase transition of ice V to its hydrogen-ordered counterpart ice XIII. Here, we present a detailed crystallographic study of this phase transition investigating the effects of hydrochloric and hydrofluoric acid as well as lithium and potassium hydroxide doping. The magnitudes of the stepwise changes in the lattice constants during the phase transition are found to be more sensitive indicators for the extent of hydrogen order in ice XIII than the appearance of new Bragg peaks. Hydrofluoric acid and lithium hydroxide doping enable similar ordering processes as hydrochloric acid but with slower kinetics. The various possible space groups and ordered configurations of ice XIII are examined systematically, and the previously determined P21/a structure is confirmed. Interestingly, the partial hydrogen order already present in ice V is found to perpetuate into ice XIII, and these ordering processes are found to be independent of pressure. Overall, the hydrogen ordering goes along with a small increase in volume, which appears to be the origin of the slower hydrogen-ordering kinetics under pressure. Heating pressure-quenched samples at ambient pressure revealed low-temperature “transient ordering” features in both diffraction and calorimetry.

Is pressure the key to hydrogen ordering ice IV?

“…However, it has also been suggested that ice XIX is a new hydrogen-ordered phase of ice VI. 3,4 Calorimetric measurements of high-pressure HCldoped ice V/XIII has shown the emergence of a transient ordering regime 29 similar to what is observed for ice XIX/VI. Further experiments aiming at increasing the pressure on the ice V/XIII system could produce a deep glassy state of ice V, and yet another crystallographically unique phase of ice.…”

“…In previous work, LiOH-doped ice V was analysed and shown to successfully aid in the formation of ice XIII. 23,29 A 0.81 GPa, 0.0 1M LiOH-doped ice IV sample was therefore made and analysed as shown in thermogram 5 in Figure 3(a). But, similar to LiOH-doped ice VI, this dopant does not aid in hydrogen-ordering as this thermogram looks similar to the pure H2O ice IV thermogram.…”

“…These findings are also supported through the changes in lattice constants for the ice XIII to ice V phase transition. 29 Recently, the discovery of a low-temperature endotherm associated with HCl-doped ice VI was mentioned as being due to a more and/or differently ordered ice XV. 38 However, through extensive calorimetry, diffraction, and spectroscopic studies this notion has now been questioned and the new endotherm has been shown to be due to a deep glassy state of ice VI.…”

Thermodynamically Stable Intermediate in the Course of Hydrogen Ordering from Ice V to Ice XIII

“…In this study, we investigate the calorimetric behavior of the ice V–XIII pair as a model case to elucidate the hydrogen ordering process in ice. Here, ice V–XIII is selected for its three properties: (i) a completely ordered configuration can be defined for ice XIII, ,, (ii) the hydrogen order–disorder transition takes place reversibly at ambient pressure, ,, and (iii) the orientational glass-transition temperature is below the hydrogen order–disorder transition boundary, , which means that the water molecules have enough mobility to rearrange the configurations.…”

Slightly Hydrogen-Ordered State of Ice IV Evidenced by In Situ Neutron Diffraction

“…To enhance molecular reorientation and suppress orientational glass formation, it is effective to dope disordered phases with a small amount of acid or base. It is known that KOH doping effectively promotes the ice I h -to-XI disorder-to-order transformation , and HCl doping does the ice V-to-XIII, ,, VI-to-XV, ,,, and XII-to-XIV ,− transitions.…”