It was recalled that solid solutions of B in some face-centered cubic metals were of hybrid type. That is, the solute atoms were expected to be located at both interstitial and substitutional sites in the metal lattice. Recent particle-tracking auto-radiographic studies of B diffusion in Ni-based solutions revealed that the diffusivity could be described by a pre-exponential factor of 6.6 x 10-7m2/s and an activation energy of 0.99eV. The small activation energies which were found in such studies had led to the suggestion that the B atoms occupied interstitial sites in Ni. It was pointed out here that such deductions could not be made. This was because the kinetic behavior of hybrid solid solutions might be determined mainly by a small fraction of interstitial solutes, whereas most of the solute atoms were substitutional.

R.B.McLellan: Scripta Metallurgica et Materialia, 1995, 33[8], 1265-7