In this report, a diffusion analysis has been extended to a lattice containing two interstitial sites, and the results obtained are used to understand: (1) the formation of a nitrided/unnitrided N configuration for intermediate N content and (2) the abnormally small (apparent) diffusion frequency factor, both of which characterize the newly developed R2Fe17nitrides. It turns out that the diffusion mechanism for N atoms in the R2Fe17lattice is a chemical reaction diffusion rather than a free‐diffusion process. ©1995 American Institute of Physics.