Theory of amorphous SiO2andSiOx. I. Atomic structural models

Abstract

Based on existing periodic models for amorphous Si, a series of random-network models with periodic boundaries have been constructed for amorphous Si${\mathrm{O}}_2$ and $\mathrm{Si}{\mathrm{O}}_x$, with $x=1.5, 1.0, \mathrm{and} 0.5$. The network structures in which an O atom always bonds to two Si atoms in a bridging position and a Si atom is tetrahedrally linked to four O atoms (for $a$-Si${\mathrm{O}}_2$) or both O and Si atoms (for $\mathrm{Si}{\mathrm{O}}_x$), are computer relaxed using a Keating-type of elastic potential. The resulting models have no internal voids or dangling bonds and have densities similar to the experimental values. Results are presented for the total and partial radial distribution functions, as well as for bond-angle and bond-length distributions and statistics of bonding patterns. For $\mathrm{Si}{\mathrm{O}}_x$ with $x=1.0\mathrm{}$, models are constructed according to both the random-bond concept and the random-mixture concept. Detailed examination of these two types of models indicates the former should be slightly more favored although the radial distribution functions of the two are quite similar. This conclusion is opposite to that reached by Temkin. Utilization of these periodic models for the study of electronic structures in $a$-Si${\mathrm{O}}_2$ and $\mathrm{Si}{\mathrm{O}}_x$ is also discussed.