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

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) Li 2 O-0.125WO 3 -0.375 P 2 O 5 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) Li 2 O-0.125WO 3 -0.375 P 2 O 5 , 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.