The diffusion of Ba through activated BaO&sngbnd;SrO cathode coatings was studied as a function of temperature. Most of the radioactive tracer material diffused according to a dependence of log10D vs1/Tsimilar to that obtained by Redington for diffusion of Ba in single crystals of BaO. The activation energy was 4.1±0.6 ev above 1280°K and 0.40±0.07 ev below that temperature.