engleski

Electrical Mobility of Lithium ions in Boro-germano-phosphate Glasses

Lithium ion mobility upon addition of germanium oxide in the two series of mixed glass former lithium phosphate and boro-phosphate glasses has been investigated. The electrical conductivity of the ternary mixed glass former 40Li2O-(60-x)P2O5-xGeO2 glasses as well as quaternary 40Li2O–10B2O3–(50-x)P2O5–xGeO2, glasses with 0 to 25 mol% GeO2 have been carried out over a wide range of temperatures (183 to 523 K) and frequencies (0.01 Hz to 1 MHz).1, 2 The observed changes in dc conductivity due to the addition of GeO2 at constant lithium ion concentration is attributed to the reorganization of the glass network. In this talk, both structure and electrical/dielectric properties of these glass systems and their dependence on GeO2 content will be reported. Structure of these glasses was studied by 31P and 11B MAS NMR spectroscopy and Raman spectroscopy. 31P MAS NMR and Raman spectra reflect the depolymerization of phosphate chains by the incorporation of GeOn polyhedra. In addition, 11B MAS NMR spectra in boro-phosphate glasses reveal the formation of mixed structural units B(OP)3(OGe) and further, a decomposition of the 11B MAS NMR spectra gives quantitative measure on the number of BO3 and B(OP)3(OGe) structural units.1 This structural analysis has been combined with impedance measurements and modeling to develop understanding of the role of GeO2 addition on the lithium ion mobility. The increase in dc conductivity with addition of GeO2 is attributed to the formation of ion conducting channels arising from the structural modification and formation of the P-O-Ge linkages, resulting in an easy migration of Li+ ions along these bonds. At higher GeO2 content, the glass network is found to be more densely packed which increases its anionic character, and hence results in a slight decrease in the mobility of Li+ ions. The MIGRATION concept was used to calculate the spatial extent of localized diffusion of Li+ ions around the network3, yielding a more complete picture about transport in these two glass systems.

Electrical transport ; Impedance spectroscopy ; MAS NMR ; Germanate glasses

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