Anomalous defect production in alkali iodides bombarded with high energy argon ions at temperatures between 20 and 300 K

• Published in: Radiation effects and defects in solids 1999-11, Vol.151 (1-4), p.1-12
• Main Authors: Pariselle, M. A., Comins, J. D., Ramstein, B., Lefrant, S., Spiesser, M., Balanzat, E.
• Format: Article
• Language: English
• Subjects: Alkali halides; Defect production; Ion bombardment
• ISSN: 1042-0150; 1029-4953
• DOI: 10.1080/10420159908245930

KI, RbI and K 0.8 Rb 0.2 I have been bombarded with high-energy argon ions at temperatures between 20 and 300 K, followed by an in situ measurement of the optical absorption. In KI and RbI, the rate of F centre production in its broad features is typical of class I alkali halides and follows a pattern similar to that for X-irradiation. The rate is low at 20 K, rises to a maximum at 200 K followed by a decrease at 300 K. Most unusual defect growth behaviour is observed for K 0.8 Rb 0.2 I. The measured F centre production is completely suppressed at 20 K and is insignificant at 100 K. This effect appears only in part due to the formation of F + -I centre pairs. The F/V centre ratio is much smaller in K 0.8 Rb 0.2 I as compared with KI or RbI. The overall defect production rate in K 0.8 Rb 0.2 I is larger at 20 K than at 100 K. Studies of the halogen interstitial centres including annealing and subsequent Raman experiments show that in spite of differing production efficiencies at low temperature in the pure and mixed crystals, their structures appear relatively similar. The results suggest a modified production mechanism in K 0.8 Rb 0.2 I under heavy ion bombardment, a conclusion that is supported by comparative X-irradiation experiments at 100 and 200 K. The results are examined in relation to current ideas regarding defect production in alkali halides.