engleski

Investigation of Mixed Glass Former Effect and Thermally Induced Crystallization in Li2O-P2O5-GeO2 Glasses

In order to improve the stability, safety and required performance of lithium-ion batteries many novel glass and glass-ceramic materials are being investigated for their potential use as a solid electrolytes [1, 2]. Ternary ion conducting 40Li2O–(60-x)P2O5–xGeO2, x=0–25 mol%, glasses have been chosen as a model glass system for the mixed glass former effect and crystallization investigations. Electrical properties of these glasses were studied by impedance spectroscopy (IS) to determine the influence of the structural changes induced by gradual substitution of one glass network former, P2O5, by other network former, GeO2, keeping Li+ ion content constant. Glass-ceramics have been prepared by controlled crystallization of these glasses at different temperatures selected according to the DTA curves. Changes that occurred in structure and electrical properties of glass-ceramics were analysed. In glasses, the dc conductivity increases for the three orders of magnitude with increasing germanium content. This conductivity enhancement was attributed to the facilitated mobility of Li+ ions due to the depolymerisation of phosphate chains and incorporation of germanium atoms into network, confirmed by Raman and MAS NMR. Heat-treated glasses have been characterized using XRD and MAS NMR. Microstructure study showed crystalline grains embedded into glass matrix. Grain size and degree of crystallinity varies with germanium content and crystallization temperatures. Heat-treated GeO2-free samples showed slightly higher dc conductivity values than the non-treated glasses. On the other hand, when germanium oxide was added into the system, the dc conductivities of heat-treated samples showed lower values if compared with values obtained for glasses. Decrease in dc conductivity is more pronounced for samples with high germanium content and higher degree of crystallinity. Correlated behaviour between conductivity and changes in microstructure indicates that in the heat-treated glasses a part of the Li+ ions enters randomly distributed crystalline grains, which are not enough connected to form easy conducting pathways.

Mixed glass former effect ; Crystallization ; Ion transport

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