Reconstruction and stability of β-cristobalite 001, 101, and 111 surfaces during dehydroxylation

Abstract

We analysed the dehydroxylation of 001, 101, and 111 β-cristobalite surfaces using the periodic density functional theory method and established the OH density stability diagrams of these surfaces as a function of temperature and water partial pressure. Our calculations suggest that important surface reconstructions, involving SiO₂ unit migrations, are required to reach the experimentally measured values for hydroxyl coverage. Our thermochemical data, i.e., 3.7–5.2 OH nm⁻² in standard conditions and 1.4–2.6 OH nm⁻² at P = 10⁻¹⁰ atm and T = 800 K, agree with the experimental values for amorphous silica and explain the trends observed, although some topological differences obviously exist between our periodic models and amorphous silica surfaces.