Vacancies in HF-doped and in Irradiated Ice by Positron Annihilation Techniques

• Published in: Journal of Glaciology
• Main Authors: Eldrup, M., Mogensen, O. E., Bilgram, J. H.
• Format: Article in Journal/Newspaper
• Language: English
• Published: Cambridge University Press (CUP) 1978
• Subjects: Earth-Surface Processes; Journal of Glaciology
• Online Access: http://dx.doi.org/10.1017/s0022143000033347; https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S0022143000033347

Abstract Positron annihilation techniques, which are specifically sensitive to vacancy-type defects have been used to study the effect on ice of irradiation and HF doping. Main conclusions are that immobile water-molecule vacancies can be created at low temperatures by either irradiation or HF doping. Upon heating, the vacancies become mobile at about 100 K. Some of them cluster into di- and multi-vacancies which grow in size with temperature up to at least 145 K. A vacancy migration energy of 0.34 ± 0.07 eV is deduced, about three times higher than previously assumed. Possible mechanisms for vacancy formation by HF doping are discussed. Out-diffusion of HF is followed at –26 ° C over several weeks. The diffusion constant derived agrees within uncertainty (a factor of two) with the large value obtained by Haltenorth and Klinger. In particular two results seem important for other parts of ice physics. One is that HF doping creates an appreciable increase in the vacancy concentration, the influence of which should be considered in models for other defects in ice. The other is that vacancies migrate at about 100 K, a fact which might be important for the interpretation of some of the many “anomalous” effects observed in ice at about that temperature.