In this study, the effect of GeO2on the thermal stability and proton mobility (μH) of proton-conducting phosphate glasses was experimentally investigated using 22HO1/2-3NaO1/2-(12 −x)LaO3/2-xGeO2-63PO5/2glasses. Increasing glass transition temperature (Tg) andμHatTgwere experimentally found out, when LaO3/2was substituted with GeO2, and this behavior coincides well with the prediction obtained from a linear regression model previously proposed. Based on the glass structure and nature of a P-O bond, both enhancedTgandμHatTgwere strongly related to the formation of heteroatomic P-O-Ge linkages. The Ge atoms are six-fold coordinated with O atoms, and they tightly bridge the (PO3−)nphosphate chains through the heteroatomic P-O-Ge linkages, resulting in rigid phosphate frameworks with higherTg. The formation of the heteroatomic P-O-Ge linkage results in increased covalency in the P-O bond. This increases the ionicity of the O-H bond owing to the balanced electron transfer to prevent excessive decrease in electron density on the O atom in the P-O-H bond. Thus,μHatTgincreases because the increasing ionicity weakens the O-H bond. Herein, the increasing covalency in the P-O bond is discussed according to the difference in the electronegativity and atomic orbitals that contribute to the bond with an O atom between La⋯O and Ge-O bonds.
ASJC Scopus subject areas
- Renewable Energy, Sustainability and the Environment
- Materials Science(all)