Ma. Pariselle et al., Anomalous defect production in alkali iodides bombarded with high energy argon ions at temperatures between 20 and 300 K, RADIAT EFF, 151(1-4), 1999, pp. 1-12
KI, RbI and K0.8Rb0.2I have been bombarded with high-energy argon ions at t
emperatures 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 s
imilar to that for X-irradiation. The rate is low at 20 K, rises to a maxim
um at 200 K followed by a decrease at 300 K. Most unusual defect growth beh
aviour is observed for K0.8Rb0.2I. The measured F centre production is comp
letely suppressed at 20 K and is insignificant at 100 K. This effect appear
s only in part due to the formation of F+-I centre pairs. The F/V centre ra
tio is much smaller in K0.8Rb0.2I as compared with KI or RbI. The overall d
efect production rate in K0.8Rb0.2I is larger at 20 K than at 100 K. Studie
s of the halogen interstitial centres including annealing and subsequent Ra
man experiments show that in spite of differing production efficiencies at
low temperature in the pure and mixed crystals, their structures appear rel
atively similar. The results suggest a modified production mechanism in K0.
8Rb0.2I under heavy ion bombardment, a conclusion that is supported by comp
arative X-irradiation experiments at 100 and 200 K. The results are examine
d in relation to current ideas regarding defect production in alkali halide
s.