The Doorways for the Motion of Helium Atoms in the Structure of Crystalline and Amorphous Silicon Oxides Accordingto Molecular Dynamics Simulations.

Abstract

Investigation of the helium diffusion in crystalline modifications of quartz is of fundamental importance for solving environmental, geological, and geochronological problems. Study of helium diffusion in amorphous silica is of significance for designing new materials used in vacuum technology. The diffusion coefficients in α-quartz determined by different researchers differ by approximately ten orders of magnitude [1], and the diffusion mechanism is poorly understood. Conversely, for vitreous SiO₂, there has long been a great body of reliable and systematized data on the diffusion coefficients as functions of temperature [2]. Until recently, one of the obstacles to the description of thermal motion has been the absence of are liable model of the glass structure. For vitreous SiO₂, Shackelford [3] assumed the interstises are conected by channels that ensure free diffusion. Later, more rigorous analysis of the interstice distribution and their connectivity was performed in [4]. The molecular dynamics method has not hitherto been directly applied to solve these problems. The purpose of this work is to fill this gap.