Rare Gas Mobility in Pure and Doped Potassium Bromide

The mobility of the inert gases argon and xenon in pure and doped single crystals of KBr was studied. The gases were introduced by ion bombardment. The recently established system of stages was used to interpret the results. Normal volume diffusion was found for xenon at low gas concentration, the activation enthalpy being 1.4 + 0.2 eV. This release was independent of doping, thus favoring a transport process for xenon independent of single vacancies. As most probable alternative, a mobility via small vacancy clusters, e. g. vacancy pairs was suggested. Trapping of xenon was found at higher xenon concentrations. This retarded release was shown to depend on doping and was more pronounced in crystals with an excess of cation vacancies. The diffusion of argon occurred with a similar activation enthalpy, but was most probably due to an interstitial motion.