The diffusion of Ag and Pt in α-alumina crystals was investigated by using secondary ion mass spectrometry techniques at 800 to 1150C and 900 to 1200C. Previous radio-tracer measurements had yielded higher Ag diffusion coefficients than those found here. The discrepancy was attributed to resolution differences between the secondary ion mass spectrometry and radio-tracer techniques. The former permitted the deduction of bulk diffusion coefficients, while the latter yielded dislocation-related values. The Ag and Pt diffusion coefficients were 1 to 2 orders of magnitude higher than those of Cr and Al. It was suggested that such a difference could be related to the ability of low-valency cations to occupy interstitial sites; thus allowing a proportion of the noble elements to dissolve in the alumina by a self-compensating route. A diffusion mechanism was therefore proposed which involving the correlated jumps of interstitial and substitutional foreign atoms.

Silver and Platinum Diffusion in Alumina Single Crystals. E.G.Gontier-Moya, J.Bernardini, F.Moya: Acta Materialia, 2001, 49[4], 637-44

Table 41

Grain Boundary Diffusivity of O in AlN