The diffusion mechanism of N atoms in this lattice was studied by using X-ray diffraction, thermal conductivity and nuclear magnetic resonance methods. The results revealed that a small number of N atoms, which entered the lattice but did not occupy octahedral interstitial sites, was mobile at the nitrogenation temperature. Most of the N atoms, which entered the octahedral sites, were immobile. On the basis of the nitrogenation characteristics of such systems, a trapping diffusion model was proposed. A previously proposed free diffusion model was considered to be a high-temperature approximation to the trapping diffusion model. The results and theoretical analyses showed that N-lattice interactions, rather than N-N interactions, led to the formation of an observed nitrided-unnitrided configuration. They also caused a marked decrease in the apparent diffusion frequency factor and were responsible for the stability and irreversibility of N uptake. It was also shown how N-lattice interactions affected N uptake under various nitrogenation conditions.

Y.D.Zhang, J.I.Budnick, W.A.Hines, N.X.Shen, J.M.Gromek: Journal of Physics - Condensed Matter, 1997, 9[6], 1201-16