The mobility of hydrogen in amorphous ceramics with the composition, Si13B13C60N13 (AM26C), was investigated To measure the diffusivities, deuterium was used as a tracer; which was introduced via isotope exchange from the gas phase at 700 to 1100C. Depth profiling was performed using secondary ion mass spectrometry. The profiles could be fitted to complementary error functions. The diffusivities obeyed:

D(m2/s) = 5 x 10-12exp[-0.8(eV)/kT]

These parameters were close to those reported for glassy carbon and thin amorphous C-B-N films. It was concluded that the amorphous C(BN)x phase was the transport path for hydrogen in AM26C ceramics. A direct interstitial diffusion mechanism could account for the activation enthalpy of 0.8eV. The low value of the pre-exponential factor was attributed to an entropy factor arising from the temperature dependence of the chemical potential of hydrogen.

Atomic Motion and Diffusion Mechanism of Hydrogen in Amorphous Ceramics of the System Si-B-C-N. W.Gruber, G.Borchardt, H.Schmidt: Defect and Diffusion Forum, 2007, 263, 63-8

Figure 29

Diffusivity of 15N in Si3BC4.3N2