Isothermal diffusion of Ba2+ ions in NaCl crystals

Using carrier-free 133Ba the temperature dependence of the diffusion coefficient D of Ba2+ ions in NaCl crystals has been measured in the temperature range between 400 and 750°C. The obtained values of D ranged from 2 × 10−10 to 4 × 10−8 cm2/s and for a given temperature they were dependent on the purity of crystals. It is shown that in the whole temperature range the degree of association of Ba2+ ions with vacancies is close to unity (0.4 to 0.8) and that the diffusion process is limited by the jump frequency of the Ba2+ ion to the associated vacancy. The temperature dependence of this frequency may be represented by w2 = 1.6 × 1012 exp (−0.81 eV/kT) s−1.