EELS STUDY OF OXYGEN DIFFUSION IN ALUMINUM NITRIDE

The oxygen/nitrogen interdiffusion in AlN ceramics was investigated by electron energy-loss spectroscopy (EELS) in combination with transmission electron microscopy (TEM). Al2O3/AlN diffusion couples were prepared by oxidation of an AlN ceramic. The samples were annealed for different times in the temperature range from 1500-degrees to 1900-degrees-C. The diffusion couples were encapsulated in a tantalum ampoule to guarantee an inert atmosphere. Oxygen concentration profiles across the oxide/nitride interface were measured by EELS. The oxygen/nitrogen interdiffusion coefficient in AlN is given by D = 1.5(+6.0)/-1.2 x 10(-8) exp[- 240 +/- 40 (kJ/mol)/(RT)] (cm/s). The magnitude and temperature dependence of the N/O interdiffusion is comparable to diffusion coefficients reported in the literature for other non-oxide ceramic materials. At standard AlN sintering conditions the O/N interdiffusion is so slow that it cannot provide an effective means for oxygen removal from the AlN grains.