Lithium-Ion Mobility in Quaternary Boro–Germano–Phosphate Glasses

• Published in: The journal of physical chemistry. B 2016-04, Vol.120 (16), p.3978-3987
• Main Authors: Moguš-Milanković, Andrea, Sklepić, Kristina, Mošner, Petr, Koudelka, Ladislav, Kalenda, Petr
• Format: Article
• Language: English
• Subjects: Boron Compounds - chemistry; Electric Conductivity; Germanium - chemistry; Glass - chemistry; Ions - chemistry; Lithium - chemistry; Magnetic Resonance Spectroscopy; Phosphates - chemistry; Spectrum Analysis, Raman; Temperature; Transition Temperature
• ISSN: 1520-6106; 1520-5207
• DOI: 10.1021/acs.jpcb.6b01424

Effect of the structural changes, electrical conductivity, and dielectric properties on the addition of a third glass-former, GeO2, to the borophosphate glasses, 40Li2O–10B2O3–(50 – x)­P2O5–xGeO2, x = 0–25 mol %, has 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 compensate these delocalized charges connecting both phosphate and germanium units, which results in reduction of both bond effectiveness and binding energy of Li+ ions and therefore enables 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 the increase in conductivity indeed is controlled by the modification of structure as a function of GeO2 addition.