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Mixed alkali effect in lithium-sodium phosphate glasses modified with tungsten oxide
Authors: Kalenda Petr | Koudelka Ladislav | Mošner Petr | Nikolic Juraj | Moguš-Milanković Andrea
Year: 2017
Type of publication: ostatní - přednáška nebo poster
Page from-to: nestránkováno
Titles:
Language Name Abstract Keywords
eng Mixed alkali effect in lithium-sodium phosphate glasses modified with tungsten oxide Lithium and sodium phosphates belong to materials studied as solid electrolytes for batteries. Their modification with other oxides can be due to the optimization of electrical properties or chemical durability thermal stability etc. This contribution is devoted to the study of lithium-sodium tungsten-phosphate glasses of the composition xLi2O-(40-x)Na2O-30P2O5-30WO3 with x = 0, 10, 20, 30 a 40 mol% Li2O. Basic parameters of the glasses were determined (density, molar volume, chemical durability) and their thermal behavior was studied by differential thermal analysis, dilatometry and hot-stage microscopy. Temperature dependence of glass transition temperature reveals a minimum at x = 20 mol% Li2O, characteristic for the mixed-alkali effect, whereas the thermal expansion coefficient decreases monotonously from 19.9 to 13.1 ppm/K. The replacement of sodium cations by lithium cations results in a lower ionicity of W-O bonds, which is reflected by the shift of band of W-O vibrations from 941 to 954 cm-1. Electrical and dielectric properties were measured within the range of 106 Hz to 0,01 Hz and the temperature range 303-513 K. From the obtained dependences of D.C. electrical conductivity on temperature, the activation energy was calculated using Arrhenius equation. Activation energy reaches a maximum at the glass with 20 mol% Li2O, whereas electrical conductivity reveals a minimum at the same composition. The observed nonmonotonous behavior of electrical conductivity and its activation energy is characteristic for the mixed-alkali effect observed previously also in other phosphate glasses.

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