Diffusion of Thallous Chloride in Single Crystals of KCl by a Novel Spectrophotometric Method

A novel attachment to the Beckman DU spectrophotometer is described, by means of which the diffusion profile of some heavy-metal ions in alkali halides may be recorded. The diffusion of Tl+ ions in KCl in the temperature range 270°-400°C was measured. It is concluded that the activation energy for the diffusion of Tl+ varies with temperature, parallel to that of the self-diffusion of K+ ions, calculated from conductivity measurements. The diffusion constants of the Tl+, at any temperature, are several orders higher, as the associated vacancies of the divalent impurities present are also involved in the diffusion process.