Effect of germanium oxide on the structure and properties of lithium borophosphate glasses

Lithium borophosphate glasses with addition of germanium oxide were studied along the compositional series (100 − x)[0.5Li2O–0.1B2O3–0.4P2O5]–xGeO2, with x = 0–25 mol.%. Their properties (density, glass transition temperature, coefficient of thermal expansion, chemical durability) were measured and their structure was studied by 31P and 11B MAS NMR spectroscopy and Raman spectroscopy. The addition of GeO2 to the parent borophosphate glass results in an increase of their glass transition temperature, while their chemical durability only slightly decreases. 31P MAS NMR and Raman spectra reflect the depolymerization of phosphate chains by the incorporation of GeOn polyhedra. 11B MAS NMR spectra reveal the formation of mixed structural units B(OP)3(OGe) in the borophosphate glasses and the decomposition of 11B MAS NMR spectra brings quantitative data on the number of BO3 and B(OP)3(OGe) structural units. A small amount of BO3 trigonal units is formed in the glasses as well.