Amorphous Ice Made by ''Melting'' at 77 K

AMORPHOUS ICE MADE BY ”MELTING” AT 77 K O. Mishima, L. Calvert, E. Whalley

To cite this version:

O. Mishima, L. Calvert, E. Whalley. AMORPHOUS ICE MADE BY ”MELTING” AT 77 K. Journal de Physique Colloques, 1984, 45 (C8), pp.C8-239-C8-242. 10.1051/jphyscol:1984846. jpa-00224347

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HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. JOURNAL DE PHYSIQUE Colloque C8, supplément au n°ll, Tome 45, novembre 1984 page C8-239

AMORPHOUS ICE MADE BY "MELTING" AT 77 K*

0. Mishima , L.D. Calvert and E. Whalley

Division of Chemistry, National Research Council, Ottawa K1A 0R9, Canada

Résumé - La glace I semble fondre lorsqu'elle est comprimée sous une pression de 10 kbars à 77 K; elle se transforme en une nouvelle forme de glace amorphe dont la masse volumique est" de 1,31 g cm-3 sous une pression de 10 kbars, et de 1,17 g cm-3 sous une pression de zéro.

Abstract - Ice I appears to melt when compressed to 10 kbar at 77 K to form a new kind of amorphous ice having a density of 1.31 g cm-3 at 10 kbar and 1.17 g cm-3 at zero pressure.

I - INTRODUCTION

Amorphous solids can be made by cooling the liquid below the glass transition, which has been used since before recorded history-' and by depositing the vapor onto a cold plate2. Several other methods have been used3-1* but these two are the principal methods that use thermodynamic or pseudo-thermodynamic transitions. This paper describes a new way, by "melting" a crystal by pressure below the glass transition of liquid.

If a crystal melts with a decrease of volume, then, by le Chatelier's principle its melting temperature falls as its pressure rises. The stable part of the melting line ends, of course, at a triple point, but, as the melting transition is first-order, the melting line cannot end abruptly except at zero temperature. When such a solid is compressed at low enough temperature to prevent transformation to another crystalline phase and to ensure that the melt is a glass, it must either transform to a glass or become a crystal that is greatly superheated into the liquid region, either of which would be very interesting.

The melting curve of ice I extrapolates to ~10 kbar at 77 K, as is shown in the phase diagram in Fig. 1. We have therefore squeezed ice Ih at 77 K and have recovered the product and examined it by determining its density, by thermal analysis, and by x-ray diffraction5.

II - EXPERIMENTAL METHODS AND RESULTS II.1 Compression measurements

About 1.2 cm3 of water in an indium cup was placed in a steel cylinder, mounted in a hydraulic press, and the cylinder cooled to liquid-nitrogen temperature. The sample was squeezed, and the displacement of the piston relative to the cylinder was measured to ±-2.5 um by a dial gauge. Independent experiments showed that the pressure in the sample was ~0.90 of nominal. The displacement of the piston during four independent compressions and decompressions is plotted in Fig. 2. The ice compresses elastically up to ~10 kbar, and then starts to transform to another phase. About 2/3 of the final volume change occurs in the first ~0.7 kbar. A similar sample of ice IX at the same temperature did not transform below 25 kbar, although it is always metastable relative

•N.R.C. No. 23717 +N.R.C. Research Associate 1983-85.

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1984846 JOURNAL DE PHYSIQUE

PRESSM I kkr Fig. 1 Phase diagram of ice in the pressure-temperature plane. The melting point ice Ih is extrapolated beyond the liquid-Ih-111 triple point as the dashed line.

nominal plkbor Fig. 2 Four independent compressions of ice Ih as a function of the nominal pressure to ice I1 and becomes also metastable relative to ice VI at -9.4 kbar and to ice VIII at -10 kbar.

The compression of a volume of indium equal to the volume of indium and ice was measured to determine the compressions of ice I and the new phase. The density of the recovered phase was measured as 1.17 g cm-3 by weighing in liquid nitrogen, which agrees well with the density determined from the compression and decompression measurements. The specific volumes are plotted in Fig. 3, where the new phase is described as "amorphous" in anticipation of later conclusions. The change of specific volume at the transition is consistent with the transition being essentially the melting of ice to a high-density "liquid" or glass. In the extrapolation in Fig. 3, the effects of the glass transition were not allowed for, but should cause no major effect . 11.2 X-ray diffraction

Two specimens were analyzed by x-ray powder diffraction at -9.5 K using the techniques described in Ref. 6, and microphotometer traces of representative patterns of the 1.1 - ICE Ih AT I bar ; ION LIQUID- I ......

AMORPHOUS ICE ...... _...... -'- ...... D ...... \g pJ 9.8 kbor ...... L\OU

AT 10 kbar 0.7 I , I I I 50 I50 T/K 250 350

Fig. 3 The specific volume of ice and water under various conditions. The solid and dashed lines represent direct measurements and the dotted lines are reasonable extrapolations. Lines A and C represent the solid and the liquid respectively along the liquid-I line, and lines B and D represent the liquid at zero and 9.8 kbar respectively. The vertical bars represent the specific volumes of the phases as labelled.

Fig. 4 Representative diffraction patterns of an apparently homogeneous sample of the new phase at -95 K, taken after heating to the temperatures attached to the lines for -10 min.

second are reproduced in Fig. 4. Both specimens had a typically amorphous diffraction pattern with its main peak at 3.0 A and a secondary feature at 2.0 8. A number of spots due to untransformed ice Ih remained. The first specimen was a powder, and when it was heated to -130 and -170 K and cooled to 95 K it transformed to ice Ic, the Ih pattern remaining. After heating to -200 K and cooling, the ice Ic had rransformed to Ih and the original Ih spots had clearly grown.

The se'kond specimen was mostly a fragment -0.4 mm across and was heated successively to several temperatures for about 10 min each. The position of the first diffraction peak at -95 K moves to longer spacing approximately linearly in the temperature up to 155 K, when the sample resembles the phase obtained by condensing the vapor or quenching the-liquid. On further heating the sample to 175 K, the amorphous pattern disappeared and the ice Ih spots grew considerably, but no Ic pattern was produced. The direct transformation of amorphous to ice Ih instead of to ice Ic is new. JOURNAL DE PHYSIQUE

111 - DISCUSSION

Clearly, a new amorphous phase of ice of density -1.31 g cm-3 is produced by the transformation of ice Ih at 77 K and 10 kbar, near its extrapolated melting point. The density decreases reversibly on decreasing the pressure and reaches 1.17 g cm-3 at zero pressure, which is 26% denser than the films made by condensing the vapor in the range 82-110 K~. When heated it transforms irreversibly and gradually towards a phase that resembles the phase made by condensing the vapor. Amorphous ice having density in the range 1.31-0.93 g can now be made as required.

The ease of the transformation suggests that the crystal becomes unstable and transforms, perhaps at the surface, to a phase resembling the supercooled liquid. The supercooled liquid is too viscous for the transformation to be reversible on the laboratory time scale, and so is not at equilibrium melting, but may be considered as a new kind of transition - an easy transformation from a crystalline solid to a dense amorphous solid.

Amorphous solids can now be made in several ways, and at least four of them have been used to make amorphous phases of ice, namely, condensing the vapor at low temperature,*-'' quenching the liquid,l2 transforming the crystal at high pressure below the glass transition of the liquid, and warming the phase so produced. Phases having a wide range of properties can now be made, and a study of them should help to tell how molecules act on one another.

A possible nomenclature to distinguish the different methods of preparation is amorph-v, amorph-1, and amorph-c, for the phases made from the vapor, liquid, and crystal respectively, and amorph-c-h for the phases made by heating amorph-c.

Similar transformations may occur in all solids having negative volumes of melting if the temperature is low enough. Obvious examples are the structure-I1 clathrate hydrates, l3 ammonium fluoride I,l4 ammonium fluoride monohydrate, indium antimonide,l5 and germanium,16 which may transform to an amorph at -10, -20, -20, -50, and -170 kbar at 77 K if they do not transform to a dense crystal.

An obvious way to transform an unsymmetrical to a symmetrical hydrogen bond is to squeeze ice I to a few tens of kilobars. l7 Unfortunately, ice I transforms to the amorphous phase at much lower pressures.

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