Structure changes in amorphous silica by neutron irradiation

Abstract

Wide angle, small angle, and very-small angle X-ray scatterings (WAXS, SAXS and VSAXS) as well as optical microscopy are observed for amorphous silica before and after neutron irradiation [3×10 10 n th/cm 2, (48±2)°C]. The results are analyzed by employing the continuous random network (CRN) model [Zachariasen, J. Am. Chem. Soc. 54 (1932) 3841] that is topologically equivalent to the dense random packing (DRP) model for metallic glass (hard spheres being replaced by deformable spheres containing Si 2O 4 structural units). The effects of irradiation, as deduced from the broadening of the innermost haloes in WAXS, are interpreted in terms of an enhancement of randomness in the packing of the spheres materializing the structural unit, and in the internal structures of the spheres. This involves the rearrangements of the OSiO network that results in the local invalidation of the CRN-DRP equivalence. Consequently, small (25 Å) and large ( 2×10 5 A ̊ ) structural inhomogeneities are produced that can effectively be disclosed by WAXS, SAXS, VSAXS, and optical microscopy. Arguments are advanced in which these structural changes are viewed as deviations from the DRP-equivalent CRN model in an analogous way as interpreting the radiation effects of amorphous Pd 80Si 20 (Doi et al., J. Non-Crystalline Solids 34 (1979) 405).