engleski

Lithium-ion Mobility in Quaternary Boro-Germano-Phosphate Glasses

Effect on the structural changes, electrical conductivity and dielectric properties on the addition of a third glass former, GeO2, to the borophospahte glasses, 40Li2O–10B2O3–(50-x)P2O5–xGeO2, x = 0-25 mol%, have been studied. Introduction of GeO2 causes the structural modifications in the glass network which results in a continuous increase in electrical conductivity. Glasses with low GeO2 content, up to 10 mol%, show a rapid increase in dc conductivity as a result of the interlinkage of slightly depolymerized phosphate chains and negatively charged [GeO4]- units which enhances the migration of Li+ ions. The Li+ ions compensates these delocalized charges connecting both phosphate and germanium units as a result of which both bond effectiveness and binding energy of Li+ ions is reduced enabling their hop to the next charge compensating site. For higher GeO2 content the dc conductivity increases slightly, tending to approach a maximum in Li+ ion mobility caused by the incorporation of GeO2 units into phosphate network combined with conversion of GeO4 to GeO6 units. The strong cross-linkage of germanium and phosphate units creates heteroatomic P-O-Ge bonds responsible for more effectively trapped Li+ ions. A close correspondence between dielectric and conductivity parameters at high frequencies indicates that indeed the increase in conductivity is controlled by the modification of structure as a function of GeO2 addition.

Germanophosphate glasses ; Mixed glass formers ; Ionic conductivity ; Dielectric properties

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