An investigation was made, of the contribution which vacancies and vacancy pairs made to self-diffusion, by using ionic conductivity, tracer diffusion (serial sectioning) and drift mobility (applying an electric field during diffusion) methods. The results indicated that vacancy pairs contributed significantly to self-diffusion. The Na-diffusion data, for temperatures ranging from 640 to 790C, could be described by:

D (cm2/s) = 620 exp[-2.21(eV)/kT]

The corresponding data for single vacancies could be described by:

D (cm2/s) = 32 exp[-2.00(eV)/kT]

and those for vacancy pairs by:

D (cm2/s) = 1.1 x 105 exp[-2.75(eV)/kT]

Diffusion of Vacancies and Vacancy Pairs in NaCl. V.C.Nelson, R.J.Friauf: US Atomic Energy Commission Report COO-1197-30, 1968

Table 129

Self-Diffusion of Na in Single Crystals of

Sr-Doped NaCl in the Extrinsic Region