The serial sectioning technique was used to investigate Na self-diffusion in single crystals with various degrees of purity. Three materials were used: high-purity, somewhat less-pure and NaCl doped with 2.65 x 10-5Sr2+ ions per Na+ ion. The Na self-diffusion data for pure material in the intrinsic region were the same for high-purity and somewhat less-pure single crystals (table 127). The data for temperatures ranging from 600 to 726C could be described by:

D (cm2/s) = 29 exp[-1.97(eV)/kT]

The diffusivities which were obtained in the extrinsic region for undoped high-purity and somewhat less-pure crystals were compared (table 128). The data for high-purity single crystals at temperatures ranging from 390 to 550C could be described by:

D (cm2/s) = 1.6 x 10-3 exp[-1.245(eV)/kT]

The data for less-pure single crystals at temperatures ranging from 387 to 550C could be described by:

D (cm2/s) = 6.0 x 10-5 exp[-0.984(eV)/kT]

Diffusion data were also presented for the diffusion of Na in Sr-doped single crystals (table 129). The data for Sr-doped single crystals at temperatures ranging from 448 to 588C could be described by:

D (cm2/s) = 6.5 x 10-5 exp[-0.894(eV)/kT]

The data showed that the diffusivity in the extrinsic region increased with the impurity content, whereas the activation energies decrease with impurity concentration.

Influence of Purity on the Self-Diffusion of Sodium in NaCl Single Crystals. F.Bénière, F.Chemla: Comptes Rendus de l’Academie des Sciences, 1968, 266[10], 660-3

Table 128

Self-Diffusion of Na in Single Crystals of

Pure NaCl in the Extrinsic Region