| Issue |
J. Phys. Colloques
Volume 48, Number C1, Mars 1987
VIIth Symposium on the Physics and Chemistry of Ice
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|---|---|---|
| Page(s) | C1-653 - C1-653 | |
| DOI | https://doi.org/10.1051/jphyscol:1987194 | |
J. Phys. Colloques 48 (1987) C1-653-C1-653
DOI: 10.1051/jphyscol:1987194
PRESSURE DEPENDENCE OF EQUILIBRIUM CONCENTRATIONS OF SELF-INTERSTITIALS IN ICE CRYSTALS
K. GOTO1, T. HONDOH1 et A. HIGASHI21 Department of Applied Physics, Faculty of Engineering, Hokkaïdo University, Sapporo 060, Japan
2 Division of Natural Sciences, International Christian University, Mitaka-shi, Tokyo 181, Japan
Abstract
From recent X-ray topographic studies on dislocation loops in ice single crystals formed by heat treatment, we have concluded that the predominant point defects in ice are self-interstitials, not vacancies, at least above -50°C. The formation energy and the formation entropy were found to be 0.4 eV and 4.9 k, respectively, from the temperature dependence of the equilibrium concentrations determined by measuring the number and sizes of dislocation loops formed by quenching. Such a low value of the formation energy suggestes that lattice distortion around a self-interstitial must be small. To reveal this distortion, i.e. to determine the formation volume of an interstitial, pressure dependence of the equilibrium concentrations were measured in the present study. The equilibrium concentration of self-interstitials under a high hydrostatic pressure must be larger than that under the atmospheric pressure because total volume of the crystal reduces by introduction of interstitials. Therefore, by rapid reduction of the hydrostatic pressure, self-interstitials must be supersaturated and segregate into dislocation loops as similar to those in quenched ice crystals. The difference of the equilibrium concentrations under high hydrostatic pressure and low one can be determined by measuring the number and sizes of the dislocation loops formed. In the present experiments, a single crystal of ice was put in a teflon pressure-cell filled with silicone oil and kerosene and hydrostatic pressure was changed from 0.1 to 190 MPa. For measuring the number and sizes of dislocation loops, limited projection X-ray topographs were taken after reduction of the pressure. The determined concentrations at 160 MPa (-20.6°C) and 190 MPa (-20.6°C) were 2.5 x 10-6 and 2.7 x 10-6, respectively. The formation volume determined from the above values of concentrations was approximately -2.5 x 10-29 m3 or -0.8 (Ω is the molecular volume of ice). This result indicates that only about 20% of lattice expansion is caused by introduction of an interstitial water molecule.