Secondary ion mass spectrometry was used to profile the diffusion of O in polycrystalline -cristobalite and vitreous SiO2. It was found that the tracer concentration profiles in cristobalite were consistent with a model that was based upon 2 mechanisms. That is, bulk diffusion and short-circuit diffusion. The profiles of partially crystallized samples which contained vitreous SiO2 and -cristobalite were fitted by using the sum of 2 complementary error functions, and by taking account of interstitial network exchanges. The bulk O diffusivity, at temperatures ranging from 1240 to 1500C, was some 5 times higher in vitreous silica than in -cristobalite.

18O Diffusion through Amorphous SiO2 and Cristobalite. J.Rodríguez-Viejo, F.Sibieude, M.T.Clavaguera-Mora, C.Monty: Applied Physics Letters, 1993, 63[14], 1906-8