4.7 Article

Understanding the paradigm of vitrification-devitrification transitions in oxide network forming compounds using a revised positron lifetime analysis

Journal

JOURNAL OF NON-CRYSTALLINE SOLIDS
Volume 622, Issue -, Pages -

Publisher

ELSEVIER
DOI: 10.1016/j.jnoncrysol.2023.122646

Keywords

Positron annihilation; Lifetime; Devitrification; Glass; Volumetric nanostructurization

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This study investigates the vitrification and devitrification transitions in network oxide compounds using a revised positron annihilation lifetime analysis. It finds that volume-expanded vitrification and volume-contracted devitrification processes occur in SiO2-based network systems, while polymorphous transformations are unfavorable in B2O3-based systems. However, these transitions become possible in modified borates like lithium tetraborate Li2B4O7.
Vitrification and devitrification transitions in network oxide compounds such as silicates and borates keeping the same composition of crystalline and non-crystalline polymorphs are examined in terms of volumetric nanostructurization using a revised positron annihilation lifetime analysis. Assuming simple conversion between Psdecay and positron-trapping channels responsible for three-component lifetime spectra, probability of polymorphous crystalline-vitreous transformations is estimated by kappa parameter defined as relative changes in average lifetimes for direct (Ps-to-positron) and inverse (positron-to-Ps) trapping conversion. Both volume-expanded vitrification and volume-contracted devitrification processes are realized in SiO2-based network systems where disordered counterparts are fused quartz, amorphous films or cylindrical-porous glass (kappa < similar to 6%), while they are questionable in grown silica films (kappa similar to 8%). Polymorphous transformations are unfavorable in B2O3-based systems because of entropy gain rearranging superstructural grouping in their networks (kappa-28%). But in modified borates like lithium tetraborate Li2B4O7 where Ps- and positron-related traps are composed of Li vacancies, these transitions become possible (kappa similar to 3.2 %).

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