The diffusive behavior of 64Cu in single crystals was studied at 400 to 550C. The results depended upon the diffusion source and diffusion direction, and involved both fast and slow processes:

gas, parallel to c-axis, slow:     D (cm2/s) = 6.2 x 10-3 exp[-27.2(kcal/mol)/RT]

gas, perpendicular to c-axis, slow:     D (cm2/s) = 1.4 x 10-3 exp[-22.0(kcal/mol)/RT]

gas, parallel to c-axis, fast:     D (cm2/s) = 1.5 x 10-2 exp[-22.0(kcal/mol)/RT]

gas, perpendicular to c-axis, fast:     D (cm2/s) = 6.65 x 10-3 exp[-20.5(kcal/mol)/RT]

solid, perpendicular to c-axis, slow:     D (cm2/s) = 8.4 x 10-4 exp[-16.7(kcal/mol)/RT]

solid, perpendicular to c-axis, fast:     D (cm2/s) = 2.0 x 10-4 exp[-13.0(kcal/mol)/RT]

J.Zmija, M.Demianiuk: Acta Physica Polonica A, 1971, 39[5], 539-53