Difference in Structure and Electronic Properties of Oxygen Vacancies in α-Quartz and α-Cristobalite Phases of SiO2

Abstract

(Formula presented.) -cristobalite ((Formula presented.) -C) is a polymorph of silica, mainly found in space exploration and geochemistry research. Due to similar densities, (Formula presented.) -C is often used as a proxy for amorphous SiO (Formula presented.), particularly in computer simulations of SiO (Formula presented.) surfaces and interfaces. However, little is known about the properties of (Formula presented.) -C and its basic oxygen defects. Using density functional theory (DFT) simulations we provide a comprehensive report on the properties of perfect structure and oxygen vacancies in (Formula presented.) -C. The calculated properties of (Formula presented.) -C are compared with those of the better-characterized (Formula presented.) -quartz ((Formula presented.) -Q). Our results demonstrated that the positively charged O vacancy in (Formula presented.) -C is most stable in the dimer configuration, in contrast to (Formula presented.) -Q, which favors the puckered configuration. A back-projected configuration was also predicted in both polymorphs. We calculated the optical transition energies and isotropic hyperfine constants for O vacancies in both (Formula presented.) -Q and (Formula presented.) -C, and compared our findings with the results of previous studies and experiments. This work, thus, offers one of the first in-depth investigations of the properties of oxygen vacancies in (Formula presented.) -C.