Immobilization diffusion in R2Fe17 nitrides

The diffusion of nitrogen in R2Fe17 intermetallics is investigated by an ap proach which reconciles the solid-solution and immobilization theories of n itrogen diffusion. It turns out that two-sublattice diffusions may yield sh arp concentration profiles but leave the phase structure of the nitride unc hanged. Beside the reaction time and a local relaxation time there exists a global relaxation time which governs the smoothing of concentration gradie nts. Due to the large number of unknown energy parameters involved it is di fficult to make quantitative predictions, but in general the diffusion beha vior depends on factors such as the use of N-2 or NH3 as a nitrogen source. (C) 1998 American Institute of Physics. [S0021-8979(98)42411-3].