Ionic and Electronic Conductivity of Sodium Iodide and Lithium Tungsten Phosphorus Oxide Glasses

^1,3 Moulay Ismail University Meknes, Faculty of Science and Technology Er-Rachidia, Chemistry department, Morocco
² Moulay Ismail University Meknes, National School of Arts and Crafts, Laboratory of Engineering Sciences and Professions, Meknes, Morocco
⁴ Mohamed 1st University Oujda, Multidisciplinary Faculty of Nador, Chemistry department, Nador, Morocco
⁵ Cadi Ayyad University, UCA, Faculty of Sciences Semlalia, LPCME, Morocco.

^* Corresponding author: This email address is being protected from spambots. You need JavaScript enabled to view it.

Abstract

Morocco exports phosphates and is exploring new applications for local phosphate mining resources, we have turned our attention to phosphate materials derived from the xNaI-(0.5-x)Li₂O-0.125WO₃-0.375P₂O₅ with (x=0, 0.1, 0.2, 0.25, 0.3, 0.4, 0,5). Phosphate glasses are less durable than silicate glasses; lithium replaces sodium, causing structural changes. This study focuses on the electrical conductivity of oxide glasses in the xNaI-(0.5-x)Li₂O-0.125WO₃-0.375P₂O₅, and in particular the effect of incorporating two modifiers or the effect of mixed alkalis. The results are noted as:(i)the mixed-alkali glasses (Li/Na) exhibit slower dissolution and higher chemical durability than single-alkali glasses, with the strongest durability enhancement around Na/(Na+Li) ≈ 0.5–0.6; (ii)The mixed-alkali effect (MAE) reduces alkali ion mobility, which suppresses proton exchange and slows dissolution; larger alkali ions contribute most to the MAE; (iii) Dissolution and conductivity are non-additive: glasses with only Li or Na are more conductive (Li > Na) and have lower activation energies, while MAE introduces a pronounced minimum in conductivity at certain compositions (near Na/(Na+Li) ≈ 0.6) and can raise the activation energy there; (iiii) In phosphate glasses, introducing alkalis lowers melting temperature but increases water sensitivity; MAE arises from redistribution/mobility changes of Li and Na ions within the phosphate network.