Structure and properties of potassium niobato-borophosphate glasses

Bulk glasses of the series (1 − x)[0.5K2O–0.1B2O3–0.4P2O5]–xNb2O5 with x = 0–45.7 mol% Nb2O5 were prepared by slow cooling in air and investigated by Raman, 31P, and 11B MAS NMR spectroscopy. The incorporation of Nb2O5 into the parent borophosphate glass results in a substantial increase in the glass transition temperature and chemical durability of glasses. Raman spectra showed that Nb atoms form distorted NbO6 octahedra, which are isolated at low Nb2O5 content, whereas at higher Nb2O5 content they form clusters. 11B NMR spectra of the glasses revealed the interaction between Nb2O5 and BO4 tetrahedral units, which results in a partial transformation of tetrahedral BO4 units to trigonal BO3 units and the formation of mixed B(OP)4−n(ONb)n units.