Interdiffusion of N and O was investigated by means of electron energy-loss spectroscopy and transmission electron microscopy. Diffusion couples, Al2O3/AlN, were prepared by oxidizing AlN ceramics, and were annealed at temperatures ranging from 1500 to 1900C (table 156). The couples were encapsulated in a Ta ampoule in order to ensure an inert atmosphere, and the O concentration profiles across the oxide/nitride interface were measured by means of electron energy-loss spectroscopy. It was found that O/N interdiffusion in AlN could be described by:

D (cm2/s) = 1.5 x 10-8exp[-240(kJ/mol)/RT]

The magnitude and temperature-dependence of the interdiffusion were comparable to those which had been reported for other non-oxide ceramic materials. Under normal AlN sintering conditions, the O/N interdiffusion was too slow to provide an effective means for O removal from AlN grains.

M.Sternitzke, G.Müller: Journal of the American Ceramic Society, 1994, 77[3], 737-42

Table 156

Diffusivity of O in AlN as a Function of Temperature