Molecular diffusion of oxygen and water in crystalline and amorphous silica

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Abstract
The hydrolytic weakening of quartz requires diffusion of water to dislocation cores, while the oxidation of silicon requires diffusion of oxygen and/or water through amorphous silica (a-SiO2). Perfect α-quartz channels and larger dislocation channels are used to model the diffusion in α-quartz and a-SiO2 in conjunction with a classical interatomic potential for SiO2. Our results show that water and oxygen molecules are heavily compressed in perfect channels and much less so in the dislocation channel. The diffusion of these molecules through enlarged channels involves much lower activation energies and such channels will be preferred paths over the perfect channels.