The serial sectioning technique, and carrier-free 133Ba, were used to study the diffusion of Ba2+ ions in single crystals which contained Ca as the predominant impurity. The resultant diffusivity values ranged from 2 x 10-10 to 4 x 10-8cm2/s and, for a given temperature, they depended upon the purity of the crystals. The temperature dependence of the diffusivity was described by:

D (cm2/s) = 4.2 x 10-4 pexp[-0.81(eV)/kT]

where p was completely determined by the temperature and by the concentration of aliovalent impurities in the crystal. It was shown that, over the entire temperature range, the degree of association of Ba2+ ions with vacancies was close to unity (0.4 to 0.8) and that the diffusion process was limited by the jump frequency of the Ba2+ ion to the associated vacancy.

Isothermal Diffusion of Ba2+ Ions in NaCl Crystals. J.Grno, V.Trnovcová: Physica Status Solidi A, 1973, 18[1], 303-12