Self‐diffusion of cesium‐134 and diffusion of rubidium‐86 in cesium iodide single crystals

The self‐diffusion of Cs‐134 and the diffusion of Rb‐86 in CsI single crystals were measured in the temperature range 404 to 603 °C using the tracer‐sectioning technique. The temperature dependencies of diffusion coefficients are D = (17.6 ) exp [−(35460 ± 140)/RT] cm2 s−1 for Cs‐134 and D = (27.3−2.7+3.0) exp [−(34540 ± 160)/RT] cm2 s−1 for Rb‐86. Comparison of present data with earlier results on diffusion parameters of Na‐22 in CsI single crystals shows that there is no dependence of the activation energy Q on characteristics of the homovalent impurities. On the other hand, the pre‐exponential factor D0 increases steadily with decreasing ion radius of the diffusing cations. The independence of Q on homovalent impurity characteristics is in qualitative agreement with known anomalous properties of cations with small ion radii in alkali halide crystals and with the expected temperature dependence of the correiation factor.