Formation of a two-dimensional layered structure in silica under shear stresses: Anab initiostudy

Abstract

The behavior of ␣-cristobalite under pure shear stresses is studied using an ab initio technique. The application of shear stress on the a-b planes yields a two-dimensional layered monoclinic phase with C 2 space group via an orthorhombic phase having C222 1 symmetry. In the layered structure, each silicon atom is fourfold coordinated. On the other hand, shearing of a-c and b-c planes causes first a transformation into monoclinic phases within P2 1 symmetry and then structural failure. We also study the behavior of ␣-cristobalite under the simultaneous application of shear stress and hydrostatic pressure. We consider six different loading conditions and find that the shear stresses have no influence on the densification mechanism until a first-order phase transformation occurs. On the other hand, the shear stresses play a significant role during the first-order phase transformation and result in the Cmcm, anataselike, and stishovite structures in our simulations. The phase transformation from ␣-cristobalite to the Cmcm structure is due to the shear deformation on the a-b planes and proceeds via an orthorhombic intermediate phase having C222 1 symmetry.

Novel Two-Dimensional Silica Monolayers with Tetrahedral and Octahedral Configurations

“…It has the SiO 2 stoichiometry, and is weakly anchored on the metal surface due to vdW interactions. ,, Such ultrathin bilayers, which could possibly be peeled off from the substrate, are now being explored by experiments. ,− On the theoretical front, structural and electronic properties of α-silica with alternating sp 3 and sp 2 bonds have been reported recently . In spite of the extensive experimental efforts, freestanding and transferable monolayer silica has not yet been realized and the monolayer configuration beyond the tetrahedral building blocks has seldom been reported. − There also appears to be a lack of fundamental understanding about the stability, electronic structure, and suitability of silica monolayers as a noninteracting dielectric in vdW electronics.…”