Absence of germanate anomaly in ternary lithium germanophosphate glasses: Modification behavior of mixed glass system of strong and fragile formers

Ternary lithium germanophosphate glasses have been synthesized over a wide range of compositions. Thermal and spectroscopic techniques (IR, Raman, and P-31 MAS NMR) have been used to investigate their properties and structure s. It is found that modification occurs almost exclusively on the P2O5 part of the structure and the GeO2 network appears unaffected. GeO6/2 octahedra are not formed in the glasses, except in one GeO2-rich and Li2O-poor compo sition. Thermodynamic arguments are given to rationalize this behavior. The unique behavior of the T,values and molar volumes have been discussed in t erms of a model, which considers modification occurring only on the P2O5 pa rt of the glass structure. F-1/2 fragilities of these glasses have been eva luated from DeltaT(g) and T-g values, and a relation between F-1/2 and the physical dimensionality has been proposed.