Journal
JOURNAL OF NON-CRYSTALLINE SOLIDS
Volume 528, Issue -, Pages -Publisher
ELSEVIER
DOI: 10.1016/j.jnoncrysol.2019.119760
Keywords
In-situ neutron total scattering; Structural change of fused silica; Short- and medium-range structure; First sharp diffraction peak; Rigid-unit mode
Funding
- National Science Foundation [1928538]
- Direct For Mathematical & Physical Scien [1928538] Funding Source: National Science Foundation
- Division Of Materials Research [1928538] Funding Source: National Science Foundation
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The common belief that glass structure is completely frozen-in at room temperature is challenged at both macroscopic and atomic scales. Here, we demonstrate an analytical method to elucidate the fine details of a continuous structural change of fused silica (FS) at temperatures below the glass-transition temperature using in-situ neutron total scattering. We find that the SiO4 tetrahedron expands through the entire temperature range with a local coefficient of thermal expansion of 9.1 x 10(-6) K-1, while the average medium-range distance, derived from the first sharp diffraction peak of the structure factor, expands at a rate of 21 x 10(-6) K-1. Such an expansion difference reflects glass-structure changes within the rigid-unit mode model, where each tetrahedron behaves as a rigid unit and the flexible rotations between rigid units lead to more than two times higher medium-range thermal expansion. We further demonstrate that such rotations change the shape of individual rings, leading to a measurable change in the first sharp diffraction peak (FSDP). This study paves the way to measure the structural changes of other silicate glasses, especially through the glass transition.
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