Diffusion and isotope effects in the diffusion of homovalent cations in cesium iodide

Preexponentials D₀ and activation energies Q for self-diffusion and diffusion of homovalent cations of small radius in single crystals of CsI measured by the tracer sectioning method are as follows: for ¹³⁷Cs, 19±{}1.5 cm² s^-1 and 35.59±{}0.18 kcal/mol; for ⁸⁶Rb, 30.7±{}3.0 cm² s^-1 and 35.13±{}0.22 kcal/mol; for ⁴²K, 47±{}6 cm² s^-1 and 35.30±{}0.30 kcal/mol; for ²²Na, 34.94±{}0.20 kcal/mol, respectively. The temperature dependence of the isotope effect for diffusion of ²²,24Na in CsI is described by a simple exponent: E=126 exp[-(13.3±{}1.5 kcal/mol)/RT]. Calculations based on these experimental results and the ``five-frequency model'' of diffusion are provided to obtain the main diffusion parameters for all homovalent cations in CsI. The diffusion behavior of these cations in CsI is in good agreement with the model of ``displaced homovalent cations of small radius.''