Authors: Shangcong Cheng.
The first sharp diffraction peak (FSDP) in diffraction data of silica glass is a prominent feature, occurring at the value of scattering vector Q = 15 nm-1. Although, it is widely accepted that FSDP correlates well with the medium- range structure of glass materials, the structural origin of FSDP has remained an outstanding issue. This work will first briefly review a newly proposed nanoflake model for the medium-range structure of silica glass. Then, based on the nanoflake model, it is suggested that the FSDP of silica glass is caused by a nano-layer structure formed by SiO4 tetrahedra. This layer structure is different from the (111) plane of β-cristobalite crystal with an oxygen atom layer in the middle connecting the top and bottom layers of SiO4 tetrahedra. This work also discusses the origin of the observed shoulder of FSDP at 7.5 nm-1. It is predicted that the intensity variation of both peaks at 15 nm-1 and 7.5 nm-1 reflects the rearrangements of silica glass network in the cooling process.
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