The tracer diffusion of hydrogen was studied in precursor derived amorphous Si-C-N and Si-B-C-N ceramics using deuterium as a tracer and secondary ion mass spectrometry. As the amorphous ceramics were separated into carbon-rich phases (amorphous carbon and amorphous C[BN]x) and silicon-rich phases (amorphous Si3N4 and amorphous Si3+(1/4)xCxN4-x) the diffusivities of hydrogen in amorphous carbon, amorphous SiC and amorphous C-B-N films were also measured. The silicon-rich phases were identified as being diffusion paths for hydrogen in the precursor-derived ceramics. Diffusion of hydrogen in these materials was explained using a trap-limited diffusion mechanism, with a single trap level. Activation enthalpies of about 2eV were found for the precursor-derived ceramics, where the activation enthalpy was the sum of a migration enthalpy and a binding enthalpy. The low values for the pre-exponential factors, less than 10-7m2/s, could be explained by using an appropriate expression for the entropy factor.

Trap-Limited Diffusion of Hydrogen in Precursor Derived Amorphous Si-B-C-N-Ceramics. W.Gruber, G.Borchardt, H.Schmidt: Journal of Non-Crystalline Solids, 2007, 353[44-46], 4121-7