Sheets and wedges of Hf were annealed in N (1 to 30bar) at temperatures of between 1160 and 1800C. Diffusion couples were used to study phase equilibria in the Hf-N system and hence the diffusion of N in the various nitrides. It was found that the activation energy for N diffusion was equal to 2.7eV for all 3 nitrides: HfN, Hf3N2, Hf4N3. It was concluded that the identical diffusion mechanism (migration via octahedral N vacancies) operated in the 3 phases.

W.Lengauer, D.Rafaja, C.Zehetner, P.Ettmayer: Acta Materialia, 1996, 44[8], 3331-8