Hydrogen diffusion in crystalline SiO2

Dense Ceramic Membranes for Hydrogen Separation

“…Others have reported mixed proton transport in the same material [99], providing an illustration of the uncertainty of the relative roles of various oxidation states of hydrogen. If we move on to even more covalent oxides (still with large band gaps) such as SiO 2 , it appears that neutral species take over even more in permeation; both H and H 2 O are believed to diffuse in SiO 2 much as neutral entities [100,101].…”

Migration of Atomic and Molecular Hydrogen in SiO2: A Molecular Dynamics Study

“…The activation energies for a-quartz, ß-quartz, tridymite and cristobalite are 1.29, 0.62, 0.71, and 1.19 eV. As for the diffusivity prefactor, we obtained the following values: 417, 2.1 10" 2 , 2.0 10~3 and 7.3 10" 2 cm" 2 /s for el and ß-quartz, tridymite and cristobalite [14].…”

“…The interatomic potential by Vashishta et al has been successfully applied to some investigations on Si0 2 based materials [10,11]. Moreover it gives and accurate description of the Si0 2 vibrational properties thanks to the short-range three-body term [14]. This important feature assures a proper thermal bath for the diffusing particle, a requisite that must be satisfied to study a diffusion phenomena.…”

“…The model parameters -three for each pair (see Table 1) -have been fitted to a selected set of properties of the cor responding bonds [14]. In particular for the H-H interac tion the fitted parameters have been determined in order to [14].…”

“…The model parameters -three for each pair (see Table 1) -have been fitted to a selected set of properties of the cor responding bonds [14]. In particular for the H-H interac tion the fitted parameters have been determined in order to [14]. We have computed the energy bar rier for migration of H in a-quartz along the linear reac tion path linking two neighboring minima as extracted from our MD simulations, both with HF calculations and present model.…”