Self-diffusion studies of Si in amorphous precursor-derived ceramics (Si3BC4.3N2 and Si2.6C4.1N2.3) were carried out in order to compare the atomic transport properties of B-containing and B-free material in the Si–(B)–C–N system. Ion-implanted stable 30Si isotopes were used as tracers, and secondary ion mass spectrometry was used for depth profiling. The experimentally determined diffusivities were lower by a factor of 10 for Si3BC4.3N2 than for Si2.6C4.1N3.3 within the entire temperature range investigated. This suggested that the mobility of the constituent elements played an important role in stabilization of the amorphous state of Si3BC4.3N2 at high temperatures. Both ceramics obeyed an Arrhenius behaviour:

Si3BC4.3N2:     D (m2/s) = 1.0 x 10-3 exp[-5.7(eV)/kT]

Si2.6C4.1N3.3:     D (m2/s) = 3.0 x 10-3 exp[-5.55(eV)/kT]

The results were consistent with a diffusion mechanism that was mediated by vacancy-like defects in the amorphous ceramics.

Comparison of 30Si Diffusion in Amorphous Si–C–N and Si–B–C–N Precursor-Derived Ceramics. H.Schmidt, G.Borchardt, S.Weber, H.Scherrer, H.Baumann, A.Müller, J.Bill: Journal of Non-Crystalline Solids, 2002, 298[2-3], 232-40