First-principles investigation of oxygen-excess defects in amorphous silica

Using ab initio calculations, we investigate the interactions among neutral excess oxygen atoms and amorphous silica (a-SiO2), along with hole trapping on neutral excess-oxygen defects. The calculations demonstrate that the interaction of excess oxygen with the a-SiO2 network results in two distinct defect structures referred to as the oxygen bridge-bonded (OBB) and peroxy linkage configurations. The OBB configuration may relax to a lower-energy structure after trapping a hole, representing a potential relaxation channel to the peroxy radical (POR) defect. The calculated hyperfine parameters are in excellent agreement with POR defect experiments and show that the oxygen atoms trapping the unpaired spin are bound to only one silicon atom. This implies that the OBB configuration is the major precursor of POR defects. (C) 2017 Author(s).